Manufacturing method of fire detector shell, shell and fire detector

Abstract

The invention relates to the technical field of fire fighting equipment, in particular to a manufacturing method of a fire detector shell, the shell and a fire detector, and aims to solve the problems that in the prior art, the insulating property is remarkably reduced in a high-temperature environment, the insulating resistance value of a conventional insulating material is sharply reduced at 150-200 DEG C, and the insulating property is poor. And the normal work of the detector circuit is severely influenced. The performance of the base material and the coating is optimized through a specific formula and manufacturing steps, splicing treatment is strengthened, the problems that high-temperature insulation is reduced, flame retardance is uneven and splicing is weak are solved, and the method has the advantages that the insulation performance in the high-temperature environment is improved, it is ensured that flame retardance is evenly distributed, and sealing protection at the splicing position is enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fire-fighting equipment, in particular to a manufacturing method of a fire detector shell, a shell and a fire detector. BACKGROUND

[0002] As the core component of modern building fire-fighting systems, the shell performance of the fire detector directly affects the reliability and service life of the detector. The commonly used insulating high-temperature resistant plastic shell on the market has many technical defects in actual application: Firstly, the insulation performance significantly decreases at high temperatures, and the insulation resistance value of conventional insulating materials sharply decreases at 150-200℃, which seriously affects the normal operation of the detector circuit; There is a local failure problem in the flame retardant performance, and due to uneven dispersion of the flame retardant, the flame retardant grade of the weak part of the shell is obviously lower than that of other areas, which is easy to form a burning breakthrough in a fire; The upper and lower shells are not well protected at the splicing part, and the traditional splicing method lacks effective sealing and strengthening measures, so that this area becomes a weak link of the overall protection.

[0003] These problems not only reduce the reliability of the fire detector, but also may cause false alarms or missed alarms, which brings serious hidden dangers to fire safety. SUMMARY

[0004] (I) Technical problems to be solved The purpose of the present application is to provide a manufacturing method of a fire detector shell, a shell and a fire detector, which has the advantages of improving the insulation performance at high temperatures, ensuring uniform distribution of the flame retardant performance, and enhancing the sealing protection of the splicing part.

[0005] (II) Technical solutions The present application provides a manufacturing method of a fire detector shell, and the technical solution is as follows: The composition of the shell includes, by mass fraction: Modified base material formula: polyphenylene sulfide 60-70 parts, decabromodiphenyl ethane 12-18 parts, antimony trioxide 4-6 parts, mica powder 10-14 parts, antioxidant 1-2 parts, lubricant 1-2 parts; Ceramic coating formula: methyl vinyl silicone rubber 45-55 parts, ceramic powder 30-40 parts, aluminum hydroxide 6-10 parts, silane coupling agent 1-3 parts, vulcanizing agent 2-4 parts, colorant 1-3 parts; The manufacturing method includes the following steps: S1, modified base material preparation: after drying the polyphenylene sulfide particles at 120±10℃ for 3-5h, mix the particles with the formula amount of decabromodiphenyl ethane, antimony trioxide, mica powder, antioxidant and lubricant, and granulate by double screw extrusion to prepare modified polyphenylene sulfide particles; S2. Injection molding of upper and lower shells: Modified polyphenylene sulfide granules are injected into the mold, and after injection molding, pressure holding, cooling, demolding and stress release post-treatment, the upper shell and lower shell are obtained. S3. Ceramic coating treatment on the shell surface: After pretreatment of the surfaces of the upper and lower shells, a coating slurry prepared from methyl vinyl silicone rubber, ceramic powder, aluminum hydroxide, silane coupling agent, vulcanizing agent and colorant is applied and cured to form a surface functional layer. S4. Integrated splicing of upper and lower shells: Flame-retardant sealant is applied to the splicing surface of the lower shell, and after being aligned with the upper shell, the splicing is completed by hot pressing and mechanical fixing. S5. Finished Product Performance Testing: The insulation, flame retardant, and sealing performance of the assembled shell are tested.

[0006] Furthermore, this application also proposes that, in step S1, the process parameters for twin-screw extrusion granulation include: a feeding section temperature of 160-180℃, a compression section temperature of 260-280℃, a melting section temperature of 290-300℃, and a die head section temperature of 280-290℃; a screw speed of 180-220 r / min; a vacuum degree of -0.07 to -0.09 MPa; and a particle size of 2-3 mm after granulation.

[0007] Furthermore, this application also proposes that in step S2, the mold adopts a dynamic mixing gate design, and the cavity surface is nitrided. Injection molding process parameters include: barrel temperature of 275-295℃, first-stage injection pressure of 75-85 MPa, second-stage injection pressure of 45-55 MPa, holding time of 10-20 s, and cooling time of 20-30 s.

[0008] Furthermore, this application also proposes that, in step S3, the surface pretreatment includes: sandblasting the splicing surfaces and screw hole areas of the housing, and plasma cleaning the remaining surfaces of the housing. The ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 2.5-3.5:2.

[0009] Furthermore, this application also proposes that the coating is applied using an electrostatic spraying process, with a wet film thickness of 70-90 μm; The curing process includes three stages of heating: the first stage is 75-85℃ and held for 8-12 min, the second stage is 115-125℃ and held for 15-25 min, and the third stage is 175-185℃ and held for 10-20 min.

[0010] Furthermore, this application also proposes that in step S4, the flame-retardant sealant is a silicone rubber sealant with a hardness of Shore A 35-45 and a coating thickness of 0.8-1.2 mm. The hot pressing process parameters are: upper mold temperature 115-125℃, lower mold temperature 75-85℃, pressure 0.4-0.6 MPa, and holding time 8-12 s.

[0011] Furthermore, this application also proposes that, in step S4, the mechanical fixing is as follows: ceramicized silicone rubber sealing rings are installed at the screw holes of the upper and lower housings, and high-temperature resistant insulating screws are used for locking and fixing, with a screw tightening torque of 0.7-0.9 N·m.

[0012] Furthermore, this application also proposes a fire detector housing, comprising an upper housing and a lower housing, wherein the base material is a composite material composed of the above-mentioned modified base material formulation, the surface has a functional layer composed of the above-mentioned ceramic coating formulation, and the joints are sealed and bonded by flame-retardant sealant and hot pressing process.

[0013] Furthermore, this application also proposes a fire detector, including the aforementioned fire detector housing and a detection circuit installed within the housing.

[0014] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the performance of the substrate and coating through specific formulations and manufacturing steps, and strengthens the splicing process, solving the problems of decreased insulation at high temperatures, uneven flame retardancy, and weak splicing. It has the advantages of improving insulation performance under high temperature environments, ensuring uniform distribution of flame retardant performance, and enhancing the sealing and protection of splicing joints. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic diagram illustrating the overall steps of manufacturing a fire detector housing; Figure 2 This is a schematic diagram of the exploded structure of a fire detector housing. Figure 3 This is a schematic diagram of the overall structure of a fire detector.

[0017] 1. Housing; 11. Upper housing; 12. Lower housing; 2. Mounting base. Detailed Implementation

[0018] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0019] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] Traditional fire detector housings suffer from insulation degradation under high temperatures, leading to internal short circuits. Uneven dispersion of flame retardants during injection molding reduces the flame retardancy rating at housing edges and abrupt changes in wall thickness, causing localized failures and compromising housing integrity. Furthermore, the joint between the upper and lower housings is poorly protected, relying solely on simple fixing, allowing high-temperature gases to easily penetrate. The discontinuity between the insulation and flame retardant layers in this area also constitutes a weakness in overall protection.

[0021] In response, this application proposes a method for manufacturing a fire detector housing. The housing is composed of a modified substrate formula and a ceramic coating formula by weight. The manufacturing method includes steps such as modified substrate preparation, injection molding of upper and lower housings, ceramic coating treatment of the housing surface, integrated splicing of upper and lower housings, and finished product performance testing. It aims to solve the problems of insulation performance degradation, local failure of flame retardant performance, and weak protection at splicing points in fire detector housings under high temperature environments in the prior art.

[0022] For ease of understanding, the following explains some key terms in this embodiment: Modified substrate formulation: refers to the composition of composite materials used to form the main body of the fire detector housing. It optimizes the performance of the base polymer by introducing a variety of additives to improve the material's high temperature resistance, insulation and flame retardancy.

[0023] Polyphenylene sulfide (PPS): A high-performance thermoplastic engineering plastic with excellent heat resistance, chemical stability and mechanical strength, providing structural support and basic temperature resistance as a shell substrate.

[0024] Decabromodiphenyl ethane: A highly efficient brominated flame retardant that achieves flame retardancy by releasing bromine free radicals during combustion, thereby interrupting the combustion chain reaction.

[0025] Antimony trioxide: As a flame retardant enhancer, it works synergistically with bromine-based flame retardants to promote char layer formation and further improve the flame retardant performance of materials.

[0026] Mica powder: a flaky inorganic filler that can form a physical barrier in a polymer matrix, improving the insulation properties and dimensional stability of the material, and enhancing its heat resistance.

[0027] Ceramic coating formulation: refers to the composition of coating materials applied to the surface of the housing that can form a dense ceramic layer under high temperature, aiming to provide additional insulation, flame retardancy and thermal protection functions.

[0028] Methyl vinyl silicone rubber: an elastomer with good heat resistance, flexibility and electrical insulation properties. As the main base material for ceramic coatings, it ensures good adhesion between the coating and the substrate and maintains integrity at high temperatures.

[0029] Ceramic powder: refers to inorganic powder that serves as a skeleton component in ceramic coatings. It reacts with the silicone rubber matrix at high temperatures or sintersects itself to form a ceramic layer with high strength and insulation.

[0030] Aluminum hydroxide: an inorganic flame retardant and filler that absorbs a large amount of heat and releases water vapor when heated and decomposes, thus cooling, diluting flammable gases and promoting carbonization.

[0031] Twin-screw extrusion granulation: a process that uses a twin-screw extruder to melt mix, shear, plasticize and granulate polymers and their additives, aiming to achieve highly uniform dispersion of components.

[0032] Injection molding: a molding method in which molten plastic is injected into a mold cavity and then cooled and solidified to obtain a product of the desired shape. It is suitable for mass production of complex-shaped shells.

[0033] Post-stress relief treatment: refers to heat treatment or other treatments performed on the product after injection molding to eliminate or reduce residual stress inside the product and prevent deformation or cracking during use.

[0034] Surface pretreatment: refers to the cleaning, activation, or roughening of the substrate surface before coating, in order to improve the wettability and adhesion between the coating and the substrate.

[0035] Flame-retardant sealant: An adhesive that combines flame-retardant and sealing properties, used to fill and seal gaps in housing joints, preventing the penetration of flames and high-temperature gases, and maintaining the insulation and flame-retardant continuity of the joints.

[0036] Hot pressing: a process that uses heat and pressure to tightly bond two or more components together, used here to promote the curing of flame-retardant sealant and a tight bond with the splicing surfaces of the housing.

[0037] This application provides a method for manufacturing a fire detector housing, wherein the housing comprises, by weight, a modified substrate formulation and a ceramic coating formulation.

[0038] The modified substrate formulation includes 60-70 parts polyphenylene sulfide, 12-18 parts decabromodiphenyl ethane, 4-6 parts antimony trioxide, 10-14 parts mica powder, 1-2 parts antioxidant, and 1-2 parts lubricant. Polyphenylene sulfide, as the matrix material, can be selected from products with different molecular weights or degrees of polymerization. Other bromine-based or phosphorus-based flame retardants can be selected and used in combination with antimony trioxide. Other flake or fibrous inorganic fillers can be used as insulation reinforcements. Antioxidants and lubricants can be selected from conventional plastic processing aids.

[0039] Furthermore, the ceramic coating formulation includes 45-55 parts methyl vinyl silicone rubber, 30-40 parts ceramic powder, 6-10 parts aluminum hydroxide, 1-3 parts silane coupling agent, 2-4 parts vulcanizing agent, and 1-3 parts colorant. Methyl vinyl silicone rubber can be replaced with other types of silicone rubber, such as vinyl silicone rubber. The ceramic powder can be a single component, such as alumina powder or silica powder. Alumina hydroxide can be replaced with other inorganic flame retardants. The silane coupling agent can be a coupling agent with a different structure. The vulcanizing agent and colorant can be conventional commercially available products.

[0040] The manufacturing method includes the following steps: Step S1, Preparation of Modified Substrate. After drying polyphenylene sulfide (PPS) granules at 120±10℃ for 3-5 hours, they are mixed with the prescribed amounts of decabromodiphenyl ethane, antimony trioxide, mica powder, antioxidant, and lubricant. The mixture is then granulated via twin-screw extrusion to obtain modified PPS granules. The drying temperature and time of the PPS granules can be adjusted according to the initial moisture content of the material and equipment conditions; for example, the drying time can be extended at a lower temperature. Pre-mixing can be performed using a high-speed mixer. In addition to a twin-screw extruder, a single-screw extruder can also be used for granulation, or a Banbury mixer can be used for mixing followed by pelletizing.

[0041] Step S2: Injection molding of the upper and lower shells. Modified polyphenylene sulfide granules are injected into the mold. After injection molding, pressure holding, cooling, demolding, and stress relief post-treatment, the upper and lower shells are obtained. Injection molding can be performed using a conventional injection molding machine. A standard gate can be used in the mold design. The pressure holding, cooling, and demolding times can be adjusted according to the shell dimensions and material properties. Annealing can be used for stress relief post-treatment.

[0042] Step S3: Ceramic coating treatment of the shell surface. After pretreatment of the surfaces of the upper and lower shells, a coating slurry prepared from methyl vinyl silicone rubber, ceramic powder, aluminum hydroxide, silane coupling agent, vulcanizing agent, and colorant is applied and cured to form a functional surface layer. Surface pretreatment can be performed by mechanical polishing, solvent wiping, or chemical cleaning. Coating can be done by conventional methods such as brushing, dipping, or spraying. Curing can be carried out in an oven at a constant temperature and time.

[0043] Step S4: Integrated splicing of the upper and lower shells. Apply flame-retardant sealant to the splicing surface of the lower shell, align it with the upper shell, and then complete the splicing through hot pressing and mechanical fixing. The flame-retardant sealant can be a commercially available adhesive with flame-retardant properties. Application can be done manually or with a dispensing machine. Hot pressing can be performed using a flatbed heating device. Mechanical fixing can be achieved using screws, rivets, or clips.

[0044] Step S5, Finished Product Performance Testing. The assembled shell is tested for insulation performance, flame retardancy, and sealing performance. Insulation performance can be tested using an insulation resistance tester. Flame retardancy testing can be performed according to UL94 standard. Sealing performance testing can be performed using an airtightness test or a watertightness test.

[0045] Therefore, this application improves the high-temperature resistance and insulation performance of the housing body by employing a specific modified substrate formulation, and enhances the dispersion uniformity of the flame retardant, thereby effectively mitigating the problems of insulation performance degradation and localized flame retardant failure of the fire detector housing at high temperatures. Simultaneously, the surface ceramic coating provides the housing with additional thermal protection and insulation barriers. Furthermore, by applying flame-retardant sealant to the joints and combining hot pressing with mechanical fixing, the sealing, insulation, and flame-retardant continuity of the joint area are enhanced, solving the problem of weak joints and ensuring higher reliability of the fire detector housing in fire environments.

[0046] In some embodiments described above in this application, twin-screw extrusion granulation is proposed for preparing modified substrates. However, in this process, the uncertainty of process parameters may lead to uneven dispersion of flame retardants, thereby causing local failure of flame retardant performance.

[0047] In this regard, this application further proposes that the process parameters for the twin-screw extrusion granulation in step S1 include: a feeding section temperature of 160-180℃, a compression section temperature of 260-280℃, a melting section temperature of 290-300℃, and a die head section temperature of 280-290℃; a screw speed of 180-220 r / min; a vacuum degree of -0.07 to -0.09 MPa; and a particle size of 2-3 mm after granulation.

[0048] The process parameters of twin-screw extrusion granulation have a decisive influence on the properties of polymer-modified materials. This process uses the rotation and shearing action of the screw to fully mix, melt, and plasticize the polymer with various additives, and finally extrude them into granules. In addition to parameters such as temperature, rotation speed, and vacuum degree, screw configuration, feeding method, and die design are also key factors affecting the granulation effect.

[0049] The feeding section temperature is primarily used to preheat and initially soften the material entering the extruder. This temperature range (160-180°C) aims to prevent polyphenylene sulfide (PPS) particles from prematurely melting and agglomerating, thus preventing unmelted particles from encapsulating the flame retardant and hindering dispersion. This ensures the material enters the subsequent compression section in a semi-softened state, laying the foundation for thorough mixing. In other embodiments, preheating of the feeding section can also be achieved through external heating devices or premixing equipment to achieve similar material pretreatment effects.

[0050] The compression section is the region where the material begins to melt and is subjected to shear force. This temperature range (260-280℃) perfectly matches the initial melting temperature of polyphenylene sulfide (PPS). At this point, the melt viscosity is moderate, which allows the screw shear force to break up flame retardants such as decabromodiphenyl ethane and antimony trioxide from their agglomerated state, while preventing the decomposition of flame retardants due to excessively high temperatures, thus promoting their initial dispersion in the polymer melt. In addition to temperature control, the screw compression ratio and the design of the shear elements also significantly affect the melting and mixing effect of the material.

[0051] The melting zone is a critical area for ensuring complete melting and achieving a high level of mixing. Within this temperature range (290-300°C), the polymer melt viscosity further decreases, facilitating the uniform distribution of dispersed flame retardant particles and mica powder at the molecular or microscale within the polyphenylene sulfide matrix. This is particularly beneficial for flake-like mica powder, as the melt flowability at this temperature ensures its uniform alignment along the melt flow direction, forming a continuous insulating barrier. In addition to precise temperature control, increasing the length of the melting zone or employing more efficient mixing elements (such as kneading blocks) can further enhance mixing uniformity.

[0052] The die head section temperature control measures the final temperature of the extrudate before it leaves the die. This temperature range (280-290°C) is slightly lower than that of the melt section, designed to ensure stable extrudate formability, prevent material degradation or flame retardant accumulation on the extrudate surface due to excessively high temperatures, and avoid extrusion difficulties or product surface defects due to excessively low temperatures. Die head temperature control can also be achieved through a die head heating / cooling system or by adjusting the die head flow channel design.

[0053] Screw speed directly affects the shear strength and residence time of the material within the extruder. This speed range (180-220 r / min) is designed to provide sufficient shear force to break up flame retardant agglomerates and promote uniform mixing, while avoiding excessive shear heat from excessive speed that could lead to material degradation or flame retardant failure. Besides adjusting the speed, changing the screw geometry (such as screw clearance and thread depth) or using different types of mixing elements can also adjust the shear force.

[0054] Vacuum is used to effectively remove moisture, volatile substances, and air bubbles from materials during extrusion. This vacuum range (-0.07 to -0.09 MPa) helps improve material density and prevents air bubbles from forming cavities in the melt. These cavities can cause breakage in the flame retardant after cooling and solidification, and when the shell is exposed to fire, the flame can easily spread along the cavities, leading to localized flame retardant failure. Besides vacuum devolatilization, pre-drying the material or degassing before extrusion are also methods for removing volatiles.

[0055] The uniformity of particle size after granulation is crucial for subsequent injection molding. This particle size range (2-3 mm) is designed to ensure that the modified particles melt uniformly in the injection molding machine barrel, avoiding the formation of flame-retardant dead zones due to incomplete melting of some particles caused by uneven particle size, thereby ensuring the consistency of flame retardant distribution in all areas of the injection-molded shell. In addition to controlling the granulation process, subsequent screening or grading can also be used to obtain a narrower particle size distribution.

[0056] By using the above technical solutions, the various process parameters of twin-screw extrusion granulation can be precisely controlled, which can effectively solve the problem of uneven dispersion of flame retardants in modified substrates.

[0057] Specifically, the gradient temperature control of the feeding section, compression section, melting section and die head section, together with the optimization of screw speed, ensures that the polyphenylene sulfide particles melt gradually at a suitable temperature and generate sufficient shear force to fully disperse the flame retardant agglomerates such as decabromodiphenyl ethane and antimony trioxide. At the same time, it promotes the uniform arrangement of flaky mica powder along the melt flow direction, thereby achieving a microscopic uniform distribution of flame retardants and insulating fillers in the entire substrate.

[0058] By precisely controlling the vacuum level, volatiles and bubbles in the melt can be effectively removed, preventing the formation of flame-retardant breakpoints or insulation defects within the material. Strictly limiting the particle size after granulation further ensures the melt consistency of the modified substrate and the uniform distribution of the flame retardant during subsequent injection molding. This allows the final fire detector housing to achieve the expected flame-retardant rating and insulation performance in all areas, including corners and areas of abrupt wall thickness changes. This significantly improves the overall protective capability and reliability of the housing in a fire environment, effectively avoiding the problems of localized flame-retardant performance failure and insulation performance degradation in traditional processes.

[0059] In some of the solutions described above in this application, injection molding is proposed to manufacture the housing of a fire detector. However, in this process, improper mold design and inaccurate process parameters may lead to uneven melt flow and insufficient distribution of flame retardant at the corners and abrupt changes in wall thickness of the housing, resulting in local failure of flame retardant performance.

[0060] In this regard, this application further proposes that in step S2, the mold adopts a dynamic mixing gate design and the cavity surface is nitrided; the injection molding process parameters include: barrel temperature of 275-295℃, first-stage injection pressure of 75-85MPa, second-stage injection pressure of 45-55MPa, holding time of 10-20 s, and cooling time of 20-30 s.

[0061] Specifically, the mold employs a dynamic mixing gate design, the core of which lies in the micro-stirring structure, such as a spiral guide channel, installed inside the gate. When the modified polyphenylene sulfide melt enters the gate from the barrel, these stirring structures can perform secondary shearing and mixing on the melt, effectively dispersing flame retardant particles that may re-agglomerate in the melt, ensuring that the flame retardant is uniformly dispersed before entering the mold cavity. Furthermore, this gate design can optimize the melt flow direction, allowing it to fill the corners and abrupt changes in wall thickness of the shell more smoothly, avoiding the "dead zones" easily formed by traditional gates. Another approach is to design the gate as a flow channel with a special geometry, such as a multi-stage contraction-expansion or curved flow channel, to induce turbulence or laminar shearing in the melt, thereby achieving a mixing effect.

[0062] The cavity surface is nitrided, for example through gas nitriding or plasma nitriding, to form a nitrided layer with high hardness and low friction coefficient. This not only improves the hardness and wear resistance of the mold, but more importantly, it significantly reduces the friction coefficient between the melt and the cavity wall, thereby reducing melt retention on the cavity wall. By ensuring that the melt fills the entire cavity at a stable flow rate, the risk of flame retardant migration into the melt interior due to melt retention, forming a "surface flame retardant-depleted zone," is effectively avoided. Another approach is to use surface strengthening techniques such as ion nitriding or salt bath nitriding to achieve similar surface hardness and low friction characteristics.

[0063] The setting of the injection molding process parameters works in conjunction with the mold design. Specifically, the barrel temperature is controlled at 275-295℃ to ensure that the polyphenylene sulfide substrate is fully melted without thermal degradation, while maintaining the melt viscosity within a suitable range of 1000-1500 Pa·s to match the shear efficiency of the dynamic mixing gate and ensure the effective dispersion of the flame retardant.

[0064] The primary injection pressure is set at 75-85 MPa to achieve high-pressure, rapid filling of the mold. This high pressure enables the melt to quickly overcome the significant flow resistance at the corners and abrupt changes in wall thickness within the mold cavity, ensuring these areas are fully filled and reducing temperature loss during melt flow. This prevents the flame retardant from failing to reach the mold due to excessively rapid cooling.

[0065] The secondary injection pressure is set at 45-55 MPa to apply appropriate pressure during the holding phase. This pressure range can compensate for the volume deficiency caused by cooling contraction at abrupt changes in wall thickness while avoiding excessive compression that could lead to material deformation or flame retardant migration, thereby maintaining the uniformity of flame retardant concentration in all areas of the casing.

[0066] The holding time is set to 10-20 seconds to provide sufficient time to compensate for material shrinkage, especially for thicker areas, to ensure that these areas have sufficient melt replenishment and avoid insufficient replenishment leading to low flame retardant content, thereby maintaining the stability of the shell shape.

[0067] Cooling time is controlled at 20-30 seconds to ensure that all areas of the shell, including corners and abrupt changes in wall thickness, can cure simultaneously and fully. This helps avoid deformation or structural defects caused by premature demolding and ensures a stable distribution of flame retardant in the cured material.

[0068] Through the above technical solution, this application precisely solves the technical problem of insufficient flame retardant distribution caused by poor melt flow at corners and abrupt changes in wall thickness during the injection molding process of fire detector housings by combining "mold structure optimization and injection parameter gradient control". The dynamic mixing gate design ensures uniform dispersion of flame retardant before the melt enters the mold cavity and guides the melt to smoothly fill complex structural areas.

[0069] Nitriding of the cavity surface reduces friction between the melt and the mold, minimizes melt retention, and prevents the formation of flame retardant-deficient zones. Simultaneously, precise control of the barrel temperature, primary injection pressure, secondary injection pressure, holding time, and cooling time optimizes melt flow, filling efficiency, shrinkage compensation, and the curing process, ensuring uniform distribution and stable presence of the flame retardant in all areas of the housing (including corners and around screw holes). This synergistic effect significantly improves the consistency and reliability of the overall flame retardant performance of the fire detector housing, effectively avoiding the risk of "localized failure" of flame retardant performance in traditional solutions, thereby guaranteeing the structural integrity and functional safety of the fire detector in fire environments.

[0070] In some of the embodiments described above in this application, surface pretreatment is proposed to ensure good adhesion of the ceramic coating. However, in the process of its implementation, insufficient surface treatment of splicing surfaces and screw hole areas may lead to insufficient coating adhesion, becoming weak points in protection. In addition, the composition of ceramic powder is not specifically limited, which may affect the insulation and flame retardant effect of the coating.

[0071] In this regard, this application further proposes that in step S3, the surface pretreatment includes: sandblasting the splicing surface and screw hole area of ​​the shell, and plasma cleaning the remaining surface of the shell; the ceramic powder is a mixture of kaolin and quartz powder with a mass ratio of 2.5-3.5:2.

[0072] The splicing surfaces and screw holes of the housing are sandblasted, using high-speed jets of abrasive particles to physically impact and grind these areas. This treatment effectively removes residual mold release agents, oil, oxide layers, and other contaminants, significantly increasing surface roughness and creating a microscopic uneven structure. These uneven structures provide more mechanical anchoring points for subsequent coating slurries, thereby greatly improving the adhesion between the coating and the substrate and preventing coating peeling under high temperatures or mechanical stress.

[0073] Sandblasting can be achieved in various ways. For example, dry sandblasting can be used, where compressed air drives abrasives such as quartz sand, alumina, or silicon carbide to impact the target surface. The particle size of the abrasive, the blasting pressure, and the blasting angle can be adjusted according to the desired roughness. Wet sandblasting can also be used, where the abrasive is mixed with water to form a slurry for blasting. This method can reduce dust pollution and produce a more uniform and fine roughness on the surface.

[0074] Plasma cleaning is performed on the remaining surfaces of the casing. The purpose is to utilize the active particles in the plasma (such as ions, free radicals, and electrons) to chemically and physically act on the material surface. Plasma can efficiently remove organic contaminants, grease, and particles from the surface, while simultaneously activating the surface and introducing polar functional groups, thereby increasing surface energy and hydrophilicity. This results in better wetting and spreading properties of the coating slurry in these areas, ensuring a uniform and dense coating coverage and avoiding defects such as sagging or missed areas, thus guaranteeing the continuity of the overall coating's insulation and flame-retardant properties.

[0075] Plasma cleaning can be performed using low-pressure plasma cleaning, where the part to be treated is placed in a vacuum chamber and an inert gas (such as argon) or a reactive gas (such as oxygen or air) is introduced, and plasma is generated through radio frequency or microwave discharge; or it can be performed using atmospheric pressure plasma cleaning, where a plasma jet is generated through high-voltage discharge under atmospheric pressure to perform local or continuous treatment on the material surface, which is suitable for production line integration.

[0076] The ceramic powder is a mixture of kaolin and quartz powder. Kaolin is a layered silicate mineral that can undergo dehydration and phase transformation at high temperatures to form refractory phases such as mullite, giving the coating good ceramicization ability and a certain degree of toughness, which helps to prevent the coating from cracking at high temperatures.

[0077] Quartz powder, primarily composed of silicon dioxide, possesses a high melting point and high hardness. In coatings, it serves as a high-temperature resistant skeleton material, significantly improving the coating's thermal stability and mechanical strength, and enhancing its high-temperature insulation properties. Besides kaolin and quartz powder, ceramic powder can also be a combination of other high-temperature resistant inorganic materials. For example, a mixture of aluminosilicate fibers and alumina powder can be used, with the aluminosilicate fibers providing reinforcement and the alumina powder providing high-temperature stability; alternatively, a mixture of silicon nitride powder and silicon carbide powder can be used, with silicon nitride exhibiting excellent thermal shock resistance and high-temperature strength, while silicon carbide provides high hardness and wear resistance.

[0078] The mass ratio of kaolin to quartz powder is 2.5-3.5:2. This precise mass ratio is optimized to achieve a synergistic effect between kaolin and quartz powder, balancing the toughness and high-temperature stability of the coating. Kaolin provides ceramicization conversion capability and a certain degree of toughness, while quartz powder provides a high-temperature framework and structural stability.

[0079] By controlling the ratio within the range of 2.5-3.5:2, it can be ensured that the coating can form a dense ceramic structure at high temperatures, maintaining excellent insulation and flame retardant properties, while avoiding brittleness or softening problems caused by excessive amounts of a single component. This mass ratio can be achieved by accurately weighing the two powders and then mechanically mixing or mixing them into a slurry. For example, a high-speed stirrer or ball mill can be used to thoroughly mix the two powders evenly, ensuring consistent distribution in the coating. Alternatively, it can be achieved by pre-fabricating composite powders, i.e., co-precipitating or co-grinding kaolin and quartz powder in a specific ratio during the powder production stage to form a composite ceramic powder with a uniform component distribution.

[0080] Through the above technical solution, this application effectively solves the problems of poor coating adhesion and unstable overall performance by adopting differentiated surface pretreatment methods for different parts of the fire detector housing and optimizing the composition ratio of ceramic powder.

[0081] Specifically, sandblasting the splicing surfaces and screw holes significantly increases the surface roughness of these complex structural areas, forming a strong mechanical bond. This greatly improves coating adhesion and effectively prevents the coating from peeling off from these weak points under high temperatures during a fire, ensuring the reliability of localized protection. Simultaneously, plasma cleaning of the remaining surfaces of the casing efficiently removes contaminants and activates the surface, ensuring uniform coating spread and good wetting in planar areas, maintaining the continuity of overall insulation and flame-retardant properties.

[0082] Using kaolin and quartz powder at a specific mass ratio of 2.5-3.5:2 as ceramic powder, the optimal balance between coating toughness and high-temperature resistance is achieved by leveraging the ceramicization transformation capability of kaolin and the high-temperature skeletal effect of quartz powder. This ensures that the coating maintains its intact structure, excellent insulation properties, and stable flame retardant rating even under extreme high-temperature environments. This combination of differentiated pretreatment and precise ceramic powder formulation fundamentally enhances the overall protective capability and reliability of the fire detector housing under fire conditions.

[0083] In some of the solutions described above in this application, a coating and curing process is proposed to form a surface functional layer to improve the insulation and flame retardant properties of the housing. However, in this process, the coating may be uneven in thickness or have insufficient adhesion due to improper process. If a single temperature is used in the curing process, it may cause internal stress or insufficient cross-linking, thereby affecting the continuity and stability of the surface functional layer and ultimately weakening the protective effect of the housing in high-temperature environments.

[0084] In this regard, this application further proposes that the coating is applied using an electrostatic spraying process with a wet film thickness of 70-90 μm; the curing process includes a three-stage heating process: the first stage is 75-85℃ and held for 8-12 min, the second stage is 115-125℃ and held for 15-25 min, and the third stage is 175-185℃ and held for 10-20 min.

[0085] Specifically, electrostatic spraying is a coating method that uses a high-voltage electrostatic field to charge paint particles, which then adhere to the surface of the object under the influence of the electric field. This process effectively improves paint utilization, reduces waste, and helps achieve uniform coating coverage. Implementation methods include, but are not limited to: using a manual electrostatic spray gun, with manual control of the spray path and speed, suitable for small batches or complex-shaped housings; or using an automated electrostatic spraying production line, with precise spraying via robotic arms or robots, suitable for mass production and ensuring coating consistency. During implementation, parameters such as spraying voltage, atomizing air pressure, distance between the nozzle and the housing surface, and paint viscosity can be adjusted to optimize the effects of paint particle charging, atomization, and uniform adsorption.

[0086] Wet film thickness refers to the thickness of a coating in its liquid state before it is fully dried and cured. Precise control of wet film thickness is crucial for ensuring the performance of the cured dry film. It must be thick enough to provide an effective insulation and flame-retardant barrier, while avoiding excessive thickness that could lead to cracking or peeling during drying, or insufficient thickness that would result in inadequate protection. This wet film thickness can be achieved in several ways, such as by adjusting operating parameters of the electrostatic spraying equipment, such as the feed rate, spraying speed, and number of sprays; or by using an online wet film thickness gauge for real-time monitoring and feedback to ensure the wet film thickness remains within the target range.

[0087] The curing process employs a three-stage heating method, which divides the coating curing process into three distinct temperature stages. This segmented heating strategy aims to precisely control the physicochemical changes within the coating to optimize its performance. This can be achieved, but is not limited to: using a segmented oven or tunnel furnace, achieving three-stage heating by setting different temperatures and conveyor speeds in different zones; or using a single oven with precise temperature control, where the internal temperature is programmed to change over time to achieve segmented heating.

[0088] The first stage involves heating the coating at 75-85°C for 8-12 minutes. This gentle heating promotes the slow evaporation of low-boiling-point solvents in the coating, effectively reducing the bubbles and internal defects that may result from rapid solvent escape.

[0089] Simultaneously, this temperature range also helps activate the hydrolysis reaction of the silane coupling agent in the coating formulation, enabling it to form preliminary chemical bonds with the surface of the shell substrate, laying the foundation for good adhesion of the subsequent coating. The second stage is at 115-125℃ and held for 15-25 minutes, mainly targeting the vulcanizing agent in the coating, decomposing it within this temperature range and initiating the crosslinking reaction of the methyl vinyl silicone rubber. The precise temperature and time control in this stage aims to ensure that the silicone rubber molecular chains are fully crosslinked, thereby significantly enhancing the coating's toughness, strength, and adhesion to the substrate, avoiding performance defects caused by insufficient or excessive crosslinking.

[0090] The third stage, held at 175-185℃ for 10-20 minutes, aims to promote the chemical bonding between the ceramic powder and the silicone rubber matrix, forming a dense "ceramicized precursor structure." During this high-temperature stage, the chemical reactions within the coating are further deepened, allowing the ceramic components to bind more tightly to the silicone rubber network. This improves the coating's heat resistance and chemical stability, ensuring it maintains structural integrity and functionality even under extreme high-temperature environments.

[0091] By employing electrostatic spraying, the coating particles can be uniformly adsorbed onto the shell surface using an electric field, effectively avoiding localized accumulation or omissions that may occur with traditional coating methods, and significantly improving the uniformity of coating coverage. Simultaneously, precisely controlling the wet film thickness within the range of 70-90 μm ensures sufficient thickness to provide an effective insulation and flame-retardant barrier, while preventing cracking or peeling during drying due to excessive thickness, thus maintaining the integrity of the coating. The curing process utilizes a three-stage heating strategy, working synergistically with the pre-treated shell surface to further optimize coating performance. Specifically, the first stage promotes the slow evaporation of low-boiling-point solvents through gentle heating, effectively reducing the generation of bubbles and internal defects, and activating the hydrolysis reaction of the silane coupling agent, laying the foundation for good adhesion between the coating and the substrate.

[0092] The second stage accelerates the decomposition of the vulcanizing agent, triggering full cross-linking of the methyl vinyl silicone rubber, which significantly enhances the toughness, strength, and adhesion of the coating to the substrate, avoiding performance defects caused by insufficient cross-linking.

[0093] The third stage promotes the chemical bonding between the ceramic powder and the silicone rubber matrix, forming a dense ceramicized precursor structure. This improves the heat resistance and chemical stability of the coating, ensuring that the functional layer maintains structural integrity and consistent performance even under high fire temperatures. The synergistic effect of the above technical solutions enables the surface functional layer to form a continuous, stable, and highly adhesive protective layer on the fire detector housing, effectively solving the problems of uneven coating thickness, insufficient adhesion, curing stress cracking, and unstable high-temperature performance.

[0094] This significantly improves the insulation and flame-retardant properties of the housing in high-temperature environments, ensures the safety of the detector's internal circuitry, and maintains the structural integrity of the housing. This effectively addresses the technical challenges of fire detector housings, such as insulation degradation at high temperatures, "partial failure" of flame-retardant properties, and weak protection at joints.

[0095] In some of the solutions described above in this application, flame-retardant sealant is applied to the joint of the housing and then hot-pressed to enhance the sealing and flame-retardant properties. However, if the hardness or thickness of the sealant is inappropriate or the hot-pressing process parameters are not precise, the joint may not be properly sealed, the flame-retardant effect may be insufficient, and it may be impossible to effectively prevent the penetration of high-temperature gas and ensure the continuity of insulation.

[0096] In this regard, this application further proposes that in step S4, the flame-retardant sealant is a silicone rubber sealant with a hardness of Shore A 35-45 and a coating thickness of 0.8-1.2 mm; the hot pressing process parameters are: upper mold temperature 115-125℃, lower mold temperature 75-85℃, pressure 0.4-0.6 MPa, and holding time 8-12 s.

[0097] Specifically, the flame-retardant sealant is a silicone rubber sealant. Silicone rubber sealant is a sealing material with silicone rubber as its main component, characterized by excellent high and low temperature resistance, weather resistance, electrical insulation, flame retardancy, and elasticity. In the splicing application of fire detector housings, silicone rubber sealant can effectively fill splicing gaps, provide reliable sealing, and maintain the overall flame-retardant performance of the housing. Besides silicone rubber sealant, fluorosilicone rubber sealant can also be selected according to specific needs, as it performs better in terms of oil and solvent resistance; or special polyurethane sealant can be selected, which typically has higher mechanical strength and abrasion resistance.

[0098] The flame-retardant sealant has a hardness of Shore A 35-45. Shore A hardness is an indicator of the softness or hardness of an elastic material. Limiting the hardness of the flame-retardant sealant to this range ensures that it possesses sufficient flexibility to fully fill the microscopic gaps at the joint surface while maintaining the necessary structural stability to prevent excessive deformation or failure under pressure or high temperature. In addition to Shore A 35-45, sealants with Shore A 25-35 can be selected for greater flexibility, or sealants with Shore A 45-55 can be selected for higher load-bearing capacity and extrusion resistance, depending on the specific morphology of the joint surface and the required compression.

[0099] The coating thickness of the flame-retardant sealant is 0.8-1.2 mm. Coating thickness refers to the thickness of the sealant layer applied to the splicing surfaces of the housing. Precise control of this thickness is crucial to ensuring a final sealing effect; too thin a layer may result in an incomplete seal, creating a gas permeation channel; while too thick a layer may lead to material waste, sealant overflow, and even affect the subsequent housing assembly accuracy. In addition to 0.8-1.2 mm, a thickness of 0.6-1.0 mm can be selected to accommodate narrower or shallower gaps, or a thickness of 1.0-1.5 mm can be selected to accommodate wider or deeper gaps, depending on the width and depth of the splicing joint and the sealant's compression ratio.

[0100] The hot-pressing process parameters include an upper mold temperature of 115-125℃ and a lower mold temperature of 75-85℃. The hot-pressing process applies specific temperatures and pressures to promote the full flow, curing, and tight bonding of the flame-retardant sealant to the joint surface and the shell surface. Setting different temperatures for the upper and lower molds aims to create a temperature gradient, optimizing the flow and curing process of the sealant while simultaneously protecting different parts of the shell. In addition to this temperature gradient design, a scheme can be adopted where the upper and lower mold temperatures are the same (e.g., both set to 100-110℃), or a segmented heating method can be used, i.e., preheating to a lower temperature and then rapidly increasing to the curing temperature, to shorten the overall curing time.

[0101] The pressure applied during the hot pressing process is 0.4-0.6 MPa. This pressure ensures a tight fit between the upper and lower shells and allows the flame-retardant sealant to fully fill the joint gaps, expelling any micro-air bubbles that may be present, thus forming a dense, defect-free sealing layer. In addition to 0.4-0.6 MPa, a pressure of 0.3-0.5 MPa can be selected to suit softer shell materials or low-viscosity sealants, or a pressure of 0.5-0.7 MPa can be selected to suit harder shell materials or high-viscosity sealants, depending on the strength of the shell material, the viscosity of the sealant, and the required compression.

[0102] The holding time for the hot pressing process is 8-12 seconds. Holding time refers to the time during which the sealant maintains its state after the application of temperature and pressure. Within this time period, the flame-retardant sealant can complete sufficient flow, curing, and cross-linking reactions, ensuring the formation of a stable physical and chemical structure in the sealing layer, thereby achieving a durable and reliable sealing effect. In addition to 8-12 seconds, a holding time of 6-10 seconds can be selected to suit fast-curing sealants or high-temperature environments, or a holding time of 10-15 seconds can be selected to suit slow-curing sealants or low-temperature environments, depending on the sealant's curing rate, hot pressing temperature, and required production efficiency.

[0103] By synergistically optimizing the type, hardness, coating thickness, and hot-pressing process parameters of the flame-retardant sealant, the problem of weak protection at the joints of fire detector housings can be effectively solved. Specifically, selecting silicone rubber sealant and limiting its hardness to Shore A 35-45 not only ensures the sealant's flexibility when filling microscopic gaps, but more importantly, it matches the thermal expansion coefficient of the modified polyphenylene sulfide housing substrate. This prevents delamination gaps between the sealant and the housing due to differences in thermal expansion and contraction during high fire temperatures or ambient temperature fluctuations, effectively maintaining the sealing integrity of the joints.

[0104] Meanwhile, this hardness range ensures that the sealant fully fills the gaps during hot pressing and prevents overflow due to excessive pressure during subsequent mechanical fixing, thus maintaining assembly accuracy. The 0.8-1.2 mm coating thickness, combined with the sealing groove structure of the housing splicing surface, ensures that the effective sealing thickness of the sealant after hot pressing is sufficient to completely cover the sealing groove, effectively blocking the penetration of high-temperature gases and avoiding overflow or clogging of screw holes due to excessive thickness. During the hot pressing process, the upper mold temperature of 115-125℃ activates the vulcanizing agent in the silicone rubber sealant, promoting chemical bonding with the ceramic coating on the housing surface and significantly enhancing adhesion. The lower mold temperature of 75-85℃, lower than the upper mold, effectively protects the ceramic coating at the bottom of the lower housing from high temperatures and creates a "hot on top, cool on bottom" temperature gradient, guiding the sealant to flow evenly downwards, ensuring complete filling of the sealing groove and avoiding the uneven sealant distribution problem in traditional hot pressing methods.

[0105] The application of pressure (0.4-0.6 MPa) ensures a tight fit between the upper and lower housings, fully compresses the sealant, eliminates microscopic gaps, and prevents irreversible deformation of the modified polyphenylene sulfide (PPS) housing. A holding time of 8-12 seconds allows sufficient time for the sealant to complete its vulcanization reaction, achieving initial curing and preventing displacement during subsequent mechanical fixing. It also avoids over-vulcanization that could lead to sealant brittleness and compromise long-term aging resistance. These synergistic effects ensure that the insulation resistance and flame retardant rating at the joint remain consistent with the housing body, significantly improving the overall reliability of the fire detector housing in extreme environments.

[0106] In some of the solutions mentioned above in this application, flame-retardant sealant and hot pressing process are proposed to achieve sealing and bonding of the upper and lower shells. However, in this process, the mechanical fixing part may lack a special sealing reinforcement structure, resulting in poor sealing or insecure fixing of the screw hole area at the splice, which can easily lead to gas infiltration or discontinuity of the insulating flame-retardant layer under high temperature environment.

[0107] In this regard, this application further proposes that in step S4, the mechanical fixing is as follows: ceramicized silicone rubber sealing rings are installed at the screw holes of the upper and lower housings, and high-temperature resistant insulating screws are used for locking and fixing, wherein the locking torque of the screws is 0.7-0.9 N·m.

[0108] Among them, ceramicized silicone rubber sealing rings are a specially formulated elastomer that possesses the flexibility and sealing properties of silicone rubber at room temperature, effectively filling the gap between screw holes and screws and preventing gas penetration. When exposed to high-temperature environments such as fires, the sealing ring can undergo a phase transformation, converting into a dense inorganic ceramic layer, thus maintaining its structural integrity and sealing function even under extreme temperatures.

[0109] The unique feature of this material is its ability to form a continuous insulating barrier at high temperatures, preventing flames or hot gases from passing through the screw hole area. Besides silicone rubber substrates, other elastomer materials with similar ceramic-like properties can also be used, such as certain specially modified fluorosilicone rubbers or vinyl silicone rubbers, to meet different application requirements and performance specifications.

[0110] High-temperature resistant insulating screws are screws made of materials with excellent heat resistance and electrical insulation properties. These screws maintain their mechanical strength and dimensional stability in high-temperature environments while providing reliable electrical insulation to prevent short circuits caused by the screws conducting electricity.

[0111] Commonly used high-temperature resistant insulation materials include high-performance engineering plastics, such as polyamide-imide, polyetheretherketone, or polyimide. These materials not only possess high strength and abrasion resistance but also do not easily soften, melt, or decompose at high temperatures. Alternatively, ceramic screws or composite material screws can be used to meet even higher temperature resistance and insulation requirements.

[0112] Tightening torque refers to the rotational torque applied when tightening a screw, and its precise control is crucial for ensuring the reliability of the connection and the sealing effect. Controlling the screw tightening torque within a specific range of 0.7-0.9 N·m aims to achieve the optimal compression state of the ceramicized silicone rubber seal ring. This ensures that the seal ring deforms sufficiently to fill the gap and form an effective seal, while preventing damage to the seal ring or the housing material due to overtightening.

[0113] This torque range is typically determined through experimental verification and structural mechanics analysis to balance sealing performance, structural integrity, and assembly efficiency. In practice, precise control of the tightening torque can be achieved using power tools with preset torque, manual torque wrenches, or torque control systems on automated assembly lines.

[0114] Through the above technical solution, this application effectively solves the problem of weak protection in the screw hole area at the splicing of the upper and lower shells of the fire detector. Specifically, ceramicized silicone rubber sealing rings are installed at the screw holes of the upper and lower shells. At room temperature, these sealing rings, relying on their elastic properties, can effectively fill the tiny gaps between the screw holes and screws, thereby blocking the penetration of gas or moisture. During a fire, when the ambient temperature rises above 400℃, the sealing ring can simultaneously transform into a dense inorganic ceramic layer. This ceramic layer seamlessly connects with the ceramicized coating on the shell surface and the mica powder insulation barrier in the modified substrate, forming a continuous and stable "substrate-coating-sealing ring" insulation system.

[0115] This not only avoids the insulation breakage in the screw hole area caused by the melting and failure of traditional ordinary silicone rubber sealing rings at high temperatures, but also ensures that the insulation resistance of the screw hole area remains above 10¹¹Ω even at temperatures above 200℃, thus guaranteeing the insulation safety of the detector's internal circuitry and preventing false short-circuit alarms. Simultaneously, this ceramic layer effectively prevents flames from directly contacting the screw, enhancing the flame-retardant properties of the screw hole area.

[0116] Furthermore, high-temperature resistant insulating screws are used for locking and securing the screws. These screws are typically made of high-performance engineering plastics such as polyamide-imide, whose coefficient of thermal expansion is close to that of the modified polyphenylene sulfide shell. This effectively avoids screw loosening caused by differences in thermal expansion and contraction at high temperatures, ensuring the long-term stability of the mechanical fixation. The screw material itself has excellent insulation properties, eliminating the risk of electrical conductivity that metal screws may pose at high temperatures, further enhancing overall electrical safety.

[0117] The tightening torque of the screws is precisely controlled within 0.7-0.9 N·m. This optimized range ensures that the compression ratio of the ceramicized silicone rubber seal is maintained within the optimal sealing range of 35%-40%. This guarantees a tight seal in the screw hole area while preventing the seal from cracking or the housing material from being damaged due to over-tightening, thus ensuring the assembly qualification rate and the structural integrity of the housing.

[0118] In summary, this application constructs a comprehensive protection system targeting the screw hole, a critical weak point, through "specialized protective structure design for the screw hole area + synergistic matching of materials and torque". This ensures that the flame retardant rating and insulation performance of the screw hole area are consistent with the housing body, completely eliminating the protection shortcomings of screw holes in traditional solutions and significantly improving the overall protective integrity and reliability of the fire detector housing in extreme fire environments.

[0119] Traditional fire detector housings suffer from insulation degradation under high temperatures, leading to internal short circuits. Uneven dispersion of flame retardants during injection molding reduces the flame retardancy rating at housing edges and abrupt changes in wall thickness, causing localized failures and compromising housing integrity. Furthermore, the joint between the upper and lower housings is poorly protected, relying solely on simple fixing, allowing high-temperature gases to easily penetrate. The discontinuity between the insulation and flame retardant layers in this area also constitutes a weakness in overall protection.

[0120] Example 1

[0121] like Figure 1 As shown, the formulation ratio of the fire detector housing in this disclosure (parts by mass, total of 100 parts each): Modified substrate formulation: 65 parts polyphenylene sulfide, 15 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 1.5 parts antioxidant, and 1.5 parts lubricant; Ceramic coating formulation: 50 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 8 parts aluminum hydroxide, 2 parts silane coupling agent, 3 parts vulcanizing agent, and 2 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0122] Process flow: S1. Preparation of Modified Substrate: Polyphenylene sulfide (PPS) granules were placed in a hot air dryer and dried at 120℃ and 1.5 m / s for 4 hours, ensuring the granule moisture content did not exceed 0.05%. The dried PPS granules, along with the prescribed amounts of decabromodiphenyl ethane, antimony trioxide, mica powder, antioxidant, and lubricant, were added to a high-speed mixer and premixed at 800 rpm and 80℃ for 15 minutes. The premixed material was then fed into a Φ35... A twin-screw extruder with a diameter of mm was used. The temperatures of each section of the extruder were set as follows: feeding section 170℃, compression section 270℃, melting section 295℃, and die head section 285℃. The screw speed was 200 rpm, and the vacuum degree was -0.08 MPa. The extruded material was cooled in a 25℃ cooling water bath and then cut into modified polyphenylene sulfide granules with a particle size of 2.5 mm by a pelletizer with a speed of 300 rpm. After granulation, the granules were placed in an oven and dried at 110℃ for 2 hours.

[0123] S2. Injection Molding of Upper and Lower Shells: A 120-ton horizontal injection molding machine is used. The mold is designed with a dynamic mixing gate and a spiral stirring structure in the main runner. The mold cavity surface is nitrided to achieve a hardness of HV800. The upper mold temperature is controlled at 130℃ and the lower mold temperature at 125℃. The injection molding machine barrel temperature is set as follows: front section 285℃, middle section 295℃, rear section 275℃, and nozzle 290℃. The injection parameters are set as follows: first-stage injection pressure 80MPa, injection speed 60mm / s, second-stage injection pressure 50MPa, injection speed 30mm / s, holding time 15s, cooling time 25s, and mold opening stroke 80mm. After demolding, the shell is placed in an 80℃ oven for 30 minutes for stress release treatment. Then, the splicing positioning lines are marked by a 20W laser marking machine with a speed of 500mm / s.

[0124] S3. Ceramic Coating Treatment of Shell Surface: In the surface pretreatment stage, the splicing surfaces and screw holes of the shell are sandblasted with 80-mesh quartz sand at a pressure of 0.3 MPa, and the surface roughness reaches Ra1.2 μm after treatment. The remaining surfaces of the shell are plasma cleaned with a mixture of argon and oxygen at a ratio of 3:1, with a plasma cleaning power of 300W and a treatment time of 60s. When preparing the coating slurry, all raw materials are mixed according to the formula ratio and placed in a planetary mixer. The mixture is stirred for 30 minutes at a speed of 1500 rpm and a vacuum of -0.09 MPa. The slurry is coated using an electrostatic spraying process with a spraying voltage of 60kV, an atomizing gas pressure of 0.4 MPa, a nozzle distance of 200 mm from the shell surface, and a wet film thickness of 80 μm. After coating, the shell is placed in a tunnel oven for three-stage curing: the first stage is 80℃ for 10 minutes, the second stage is 120℃ for 20 minutes, and the third stage is 180℃ for 15 minutes. After curing, the shell is allowed to cool naturally to room temperature.

[0125] S4. Integrated splicing of upper and lower shells: Apply silicone rubber sealant to the sealing groove on the splicing surface of the lower shell. The sealing groove is 2mm wide and 1mm deep. Use a dispensing machine with a needle inner diameter of 0.8mm and a dispensing speed of 5mm / s to apply the sealant, controlling the thickness of the sealant layer to 1.0mm. Align the upper and lower shells according to the positioning lines and place them in a hot press. Set the upper mold temperature to 120℃, the lower mold temperature to 80℃, and the pressure to 0.5MPa, and hold the pressure for 10s. Use an automatic screwdriver to screw in polyamide-imide insulating screws. Set the screwdriver torque to 0.8N·M, and simultaneously insert a 1mm thick ceramicized silicone rubber sealing ring into the screw hole. Finally, place the spliced ​​shell into an oven and keep it at 100℃ for 30 minutes to allow the sealant to fully cure.

[0126] S5. Finished Product Performance Testing: Insulation resistance test: According to GB / T1410-2006 standard, the insulation resistance at 25℃ is 1.2×10⁻⁶. 14 Ω, the insulation resistance at 200℃ is 8.5×10¹¹Ω; Flame retardant performance testing: Any part of the shell tested according to UL94 standard reached V-0 level, the burning time did not exceed 5 seconds, and there were no molten drips; Sealing test: The housing was filled with 0.2 MPa compressed air, and then immersed in water for 5 minutes. If no bubbles were generated, the airtightness was 1.2 × 10⁻⁶. -6 Pa・m 3 / s.

[0127] S6. Texture processing (optional): A wiring window with a specification of 20×15mm is stamped in the middle of the conductive plate; radial grooves are processed in the contact area of ​​the wire clamp frame, with a groove depth of 40μm and an extension angle of 70°; cross grid patterns are processed near the through holes, with a grid specification of 0.3×0.3mm and a protrusion height of 25μm.

[0128] Example 2

[0129] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 68 parts polyphenylene sulfide, 12 parts decabromodiphenyl ethane, 4 parts antimony trioxide, 14 parts mica powder, 1 part antioxidant, and 1 part lubricant. Ceramic coating formulation: 50 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 8 parts aluminum hydroxide, 2 parts silane coupling agent, 3 parts vulcanizing agent, and 2 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0130] Process Flow The difference from Example 1 is as follows: S1. Preparation of modified substrate: The drying temperature of polyphenylene sulfide particles was adjusted to 110℃ and the drying time was extended to 5h; the temperature of the feeding section of the twin-screw extruder was set to 160℃ and the screw speed was adjusted to 180 rpm. S2. Injection molding of upper and lower shells: The temperature of the rear section of the injection molding machine barrel is reduced to 270℃, and the cooling time is extended to 28s; S6 texture processing is not performed; S5. Finished Product Performance Testing: Insulation resistance is 9.8×10¹³Ω at 25℃ and 7.2×10¹¹Ω at 200℃; flame retardancy rating reaches UL94V-0; airtightness is 1.5×10¹³Ω. -6 Pa・m 3 / s; Due to the increased proportion of polyphenylene sulfide, the density of the substrate is enhanced, and the air tightness is slightly better than that of Example 1.

[0131] Example 3

[0132] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 65 parts polyphenylene sulfide, 15 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 1.5 parts antioxidant, and 1.5 parts lubricant; Ceramic coating formulation: 53.5 parts methyl vinyl silicone rubber, 31.5 parts ceramic powder, 8 parts aluminum hydroxide, 2 parts silane coupling agent, 3 parts vulcanizing agent, and 2.5 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 2.5:2, i.e., 17.5 parts kaolin and 14 parts quartz powder.

[0133] Process Flow The difference from Example 1 is as follows: S3. Ceramic coating treatment on shell surface: The wet film thickness of electrostatic spraying is reduced to 75μm, and the dry film thickness after drying is 60μm; the curing parameters are adjusted to the following: first stage 85℃ for 12min, second stage 125℃ for 25min, and third stage 185℃ for 20min. The S6 texture processing is retained, and the depth of the radial grooves is adjusted to 35μm; S5. Finished Product Performance Testing: The insulation resistance at 200℃ is 6.8×10¹¹Ω. Due to the reduced proportion of ceramic powder, the high-temperature insulation performance is slightly lower than that of Example 1. After ceramic treatment at 800℃, the coating showed no cracks, and the airtightness was 1.3×10¹¹Ω. -6 Pa・m 3 / s.

[0134] Example 4

[0135] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 66 parts polyphenylene sulfide, 14 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 2 parts antioxidant, and 1 part lubricant. Ceramic coating formulation: 50 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 8 parts aluminum hydroxide, 2 parts silane coupling agent, 3 parts vulcanizing agent, and 2 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0136] Process Flow The difference from Example 1 is as follows: S4. Integrated splicing of upper and lower shells: hot pressing pressure increased to 0.6MPa, pressure holding time extended to 12s; sealant coating thickness increased to 1.2mm; S6 texture processing is not performed; S5. Finished product performance testing: The tensile strength at the joint is 18 MPa, higher than the 16 MPa in Example 1; the airtightness is 8.5 × 10⁻⁻⁻⁶. 7 Pa・m 3 / s, due to the high-pressure hot pressing, the seal is tighter, and the airtightness is the best among all embodiments; the insulation resistance at 25°C is 1.0×10. 14 Ω.

[0137] Example 5

[0138] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 64 parts polyphenylene sulfide, 16 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 1.5 parts antioxidant, and 1.5 parts lubricant; Ceramic coating formulation: 48 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 10 parts aluminum hydroxide, 1 part silane coupling agent, 3 parts vulcanizing agent, and 3 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0139] Process Flow The difference from Example 1 is as follows: S3. Ceramic coating treatment on the shell surface: The thickness of the wet film after electrostatic spraying is increased to 90μm, and the thickness of the dry film after drying is 72μm; the plasma cleaning time is extended to 80s. The S6 texture processing is retained, and the height of the cross-grid pattern protrusion is increased to 30μm; S5. Finished product performance testing: The burning time in the flame retardant test does not exceed 3s, and is shorter than 5s in Example 1. Due to the increase of aluminum hydroxide content to 10 parts, the heat absorption and flame retardant effect is better; the insulation resistance at 200℃ is 9.1×10¹¹Ω; the coating adhesion is 5.0MPa. Due to the increase in coating thickness, the adhesion is higher than that in Example 1.

[0140] Example 6

[0141] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 60 parts polyphenylene sulfide, 18 parts decabromodiphenyl ethane, 6 parts antimony trioxide, 14 parts mica powder, 1 part antioxidant, and 1 part lubricant. Ceramic coating formulation: 51 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 7 parts aluminum hydroxide, 2 parts silane coupling agent, 3 parts vulcanizing agent, and 2 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0142] Process Flow The difference from Example 1 is as follows: S2. Injection molding of upper and lower shells: Cooling time is extended to 30s, and demolding adopts a full gas-assisted process with a gas-assisted pressure of 0.3MPa; S4. Integrated splicing of upper and lower shells: screw tightening torque reduced to 0.7 N·m; S6 texture processing is not performed; S5. Finished product performance testing: The shell warpage does not exceed 0.05mm, which is less than 0.1mm lower than that of Example 1, due to the reduction in molding deformation caused by extending the cooling time; the insulation resistance is 7.8×10¹¹Ω at 200℃, and the flame retardant rating reaches UL94V-0 level.

[0143] Example 7

[0144] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 67 parts polyphenylene sulfide, 13 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 1.5 parts antioxidant, and 1.5 parts lubricant; Ceramic coating formulation: 50 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 8 parts aluminum hydroxide, 2 parts silane coupling agent, 4 parts vulcanizing agent, and 1 part colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0145] Process Flow The difference from Example 1 is as follows: S3. Ceramic coating treatment on shell surface: The vulcanizing agent is added last in the raw material mixing stage to avoid premature cross-linking, and the mixing time is shortened to 25 minutes. S4. Integrated splicing of upper and lower shells: The thickness of the sealant coating is reduced to 0.8mm, and the temperature of the hot-pressing upper mold is reduced to 115℃; The S6 texture processing is retained, and the radial groove extension angle is adjusted to 80°. S5. Finished Product Performance Testing: The coating adhesion was 5.2 MPa. Due to the increase of the vulcanizing agent to 4 parts, the coating cross-linking was more complete, and the adhesion was higher than in Example 1. The insulation resistance at 200℃ was 8.8 × 10¹¹ Ω, and the airtightness was 1.4 × 10¹¹ Ω. -6 Pa・m 3 / s.

[0146] Example 8

[0147] The formulation ratio of the fire detector housing in this disclosure (parts by mass, total 100 parts): Modified substrate formulation: 67 parts polyphenylene sulfide, 13 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 1.2 parts antioxidant, and 1.8 parts lubricant; Ceramic coating formulation: 49 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 9 parts aluminum hydroxide, 3 parts silane coupling agent, 2 parts vulcanizing agent, and 2 parts colorant; wherein the ceramic powder is a mixture of kaolin and quartz powder in a mass ratio of 3:2, i.e., 21 parts kaolin and 14 parts quartz powder.

[0148] Process Flow The difference from Example 1 is as follows: S1. Preparation of modified substrate: The screw speed of the twin-screw extruder was increased to 220 rpm, and the vacuum degree was reduced to -0.09 MPa; the mixing time of the high-speed mixer was extended to 20 min; S2. Injection molding of upper and lower shells: The first-stage injection speed is reduced to 50 mm per second, and the second-stage injection speed is increased to 35 mm per second; S6 texture processing is not performed; S5. Finished product performance testing: The impact strength of the modified substrate is 12kJ / m. 3 10 kJ / higher than in Example 1 3 The increased screw speed results in more uniform mixing of raw materials; the airtightness is 9.2 × 10⁻⁶. -7 Pa・m 3 / s; the insulation resistance at 25℃ is 9.5×10¹³Ω.

[0149] Example Insulation resistance at 25°C (Ω) Insulation resistance at 200°C (Ω) Flame retardant rating (UL94) Seam air tightness (Pa m 3 / s) Coating adhesion (MPa) Core alignment direction 1 1.2 x 10 4 ]]> 8.5×10¹¹ V-0 1.2 x 10 -6 ]]> 4.8 Base complete process 2 9.8×10¹³ 7.2×10¹¹ V-0 1.5 x 10 -6 ]]> 4.6 Pps content + drying process 3 1.1 x 10 4 ]]> 6.8×10¹¹ V-0 1.3 x 10 -6 ]]> 4.5 Ceramic powder ratio + curing parameters 4 1.0 x 10 4 ]]> 8.2×10¹¹ V-0 8.5 x 10 -7 ]]> 4.7 Hot press pressure + lubricant content 5 1.3 x 10 4 ]]> 9.1×10¹¹ V-0 1.0 x 10 -6 ]]> 5.0 Aluminum hydroxide content + coating thickness 6 8.5×10¹³ 7.8×10¹¹ V-0 1.1 x 10 -6 ]]> 4.4 Cooling time + locking torque 7 1.0 x 10 4 ]]> 8.8×10¹¹ V-0 1.4 x 10 -6 ]]> 5.2 Vulcanizing agent content + sealant thickness 8 9.5×10¹³ 8.0×10¹¹ V-0 9.2 x 10 -7 ]]> 4.9 Screw rotation speed + additive ratio All embodiments in the table above meet the requirements for fire detector housings, namely, an insulation resistance of not less than 8.5 × 10¹³ Ω at 25°C and not less than 6.8 × 10¹¹ Ω at 200°C. In Embodiment 5, the insulation barrier is enhanced due to the increased aluminum hydroxide content (10 parts), resulting in optimal insulation resistance at 200°C. In Embodiment 6, the insulation performance is relatively lower due to the reduced polyphenylene sulfide content (60 parts), decreasing the proportion of the substrate.

[0150] All embodiments achieved a UL94V-0 flame retardant rating. Embodiment 5 had the highest aluminum hydroxide content, reaching 10 parts, resulting in a more significant heat absorption effect and the shortest burning time, not exceeding 3 seconds. This demonstrates the combined effect of aluminum hydroxide's heat absorption and flame retardancy, along with the synergistic flame retardant effect of bromine-antimony.

[0151] Examples 4 and 8 exhibited the best airtightness, both not exceeding 9.5 × 10⁻⁶. -7 Pa・m 3 / s. In Example 4, the hot pressing pressure was increased to 0.6MPa, and in Example 8, the screw speed was increased to 220 rpm, making the substrate more compact. The airtightness of both processes was improved by more than 100 times compared to the traditional process, which can effectively prevent high-temperature gas from penetrating into the shell.

[0152] Examples 7 and 5 showed the highest coating adhesion, at 5.2 MPa and 5.0 MPa, respectively. Example 7, with its increased vulcanizing agent content of 4 parts, exhibited more complete coating cross-linking; Example 5, with its increased coating thickness, had a larger bonding area with the shell. Both examples effectively prevented protective failure caused by coating detachment under high-temperature conditions.

[0153] The above eight embodiments not only jointly demonstrate the stability and reliability of the basic process system of modified PPS substrate + ceramic coating + integrated splicing, but also mutually confirm the reasonable range of each key parameter and the law of performance influence through single parameter fine-tuning and multi-dimensional performance verification. The results of different embodiments are consistent in the same performance dimension, such as meeting the V-0 standard and the insulation resistance meeting the requirements. The trends in different adjustment directions are complementary. For example, the PPS content and the increase or decrease of the coating thickness do not affect the basic standard, but only optimize specific performance. This forms a complete chain of evidence, which not only verifies the universality of the process, but also provides a basis for parameter optimization in different application scenarios. For example, the hot pressing parameters of Embodiment 4 are selected for high air tightness requirements, and the cooling parameters of Embodiment 6 are selected for high molding accuracy requirements.

[0154] Example 9

[0155] In this regard, such as Figure 2 As shown, this application proposes a fire detector housing 1, manufactured using the aforementioned method. The housing 1 includes an upper housing 11 and a lower housing 12. Its substrate is a composite material composed of a modified substrate formulation, and its surface has a functional layer composed of a ceramicized coating formulation. The joints are sealed and bonded using flame-retardant sealant and a hot-pressing process. The core innovation of this embodiment lies in the deep synergistic combination of the modified substrate formulation, the ceramicized coating formulation, the flame-retardant sealant, and the hot-pressing process, constructing a three-dimensional protection system of "substrate body protection - surface strengthening - joint sealing." This solves the comprehensive problems of insulation performance degradation at high temperatures, localized failure of flame-retardant performance, and weak protection at joints, achieving consistent protection across the entire area and high-temperature stability.

[0156] Specifically, the substrate of shell 1 is a composite material formulated with a modified substrate composition. This composite material is prepared by mixing 60-70 parts of polyphenylene sulfide, 12-18 parts of decabromodiphenyl ethane, 4-6 parts of antimony trioxide, 10-14 parts of mica powder, 1-2 parts of antioxidant, and 1-2 parts of lubricant by weight. Polyphenylene sulfide serves as the matrix material, providing high-temperature resistant skeletal support. Decabromodiphenyl ethane and antimony trioxide work synergistically to achieve highly efficient flame retardancy, while mica powder forms a continuous insulating barrier within the substrate. Due to the use of a twin-screw extrusion granulation process to ensure uniform dispersion of the components, the insulation resistance of the substrate remains stably above 10¹¹Ω at a high temperature of 200℃, and the overall flame retardancy rating reaches UL94 V-0. This fundamentally avoids the localized failure problems around corners and screw holes caused by uneven dispersion of flame retardants in traditional shell 1.

[0157] Furthermore, the surface of the housing 1 is coated with a functional layer composed of a ceramicized coating formulation. This functional layer is formulated by weight of 45-55 parts methyl vinyl silicone rubber, 30-40 parts ceramic powder, 6-10 parts aluminum hydroxide, 1-3 parts silane coupling agent, 2-4 parts vulcanizing agent, and 1-3 parts colorant. Surface pretreatment employs plasma or sandblasting processes to enhance adhesion, and the coating undergoes a three-stage curing process to form a chemical bond with the substrate. When the fire temperature exceeds 400°C, the methyl vinyl silicone rubber reacts with the ceramic powder to form a dense inorganic ceramic layer with an insulation resistance of not less than 10¹²Ω. This layer not only covers minor defects on the substrate surface (such as injection molding bubbles) but also provides an additional high-temperature insulation barrier, effectively compensating for the inadequacy of protection provided by a single substrate.

[0158] Furthermore, the joints of the upper and lower shells 11 and 12 are sealed and bonded using flame-retardant sealant and a hot-pressing process. The flame-retardant sealant is a silicone rubber-based material with a Shore A hardness of 35-45, whose coefficient of thermal expansion matches that of the substrate. Gradient hot-pressing parameters are set at the joint surface to ensure uniform filling. The joint area also integrates a ceramicized silicone rubber sealing ring, which is ceramicized synchronously with the surface functional layer.

[0159] Example 10 Traditional fire detector housings suffer from insulation degradation, partial failure of flame retardant properties, and weak protection at joints under high-temperature environments, leading to short circuits, false alarms, or functional failures in the internal circuitry. To address this, [further solutions are needed]. Figure 2-Figure 3 As shown, this application proposes a fire detector, including the fire detector housing 1, the mounting base 2, and the detection circuit installed in the housing 1. The mounting base 2 is located at the bottom of the housing 1 and is used to install the fire detector on the corresponding panel. That is, the mounting base 2 is fixed first by fasteners, and then the fire detector is installed on the mounting base 2 for overall fixation.

[0160] Specifically, the fire detector housing 1 is made using a modified substrate formulation and a ceramic coating formulation. The modified substrate formulation includes components such as polyphenylene sulfide, decabromodiphenyl ethane, antimony trioxide, and mica powder. The upper housing 11 and lower housing 12 are produced by twin-screw extrusion granulation and injection molding processes, ensuring that the flame retardant is uniformly dispersed in the melt, so that all areas of the housing 1 (including the corners and around the screw holes) meet the V-0 flame retardant standard, avoiding localized failure.

[0161] After pretreatment, the surface of housing 1 is coated with a ceramicized coating. This coating consists of methyl vinyl silicone rubber, ceramic powder, and aluminum hydroxide, which transforms into a dense inorganic ceramic layer under high temperature, forming a double-layer insulation system that effectively maintains insulation performance under high-temperature conditions. Flame-retardant sealant is applied to the joints of the upper and lower housings 11 and 12, and the joints are then fixed by hot pressing and mechanical means to achieve a tight seal, ensuring the continuity of the insulation and flame-retardant layers and preventing the infiltration of high-temperature gases.

[0162] Furthermore, the detection circuit is fixed to the inner wall of the housing 1 by an insulating bracket made of polyamide-imide. The coefficient of thermal expansion of this insulating bracket matches that of the substrate of the housing 1, preventing circuit displacement due to thermal deformation at high temperatures.

[0163] Meanwhile, a ceramicized silicone rubber gasket, made of the same material as the sealing ring at the joint, is placed between the bracket and the housing 1, forming a multi-layer insulation structure of housing-gasket-bracket-circuit, enhancing the overall insulation continuity. This design ensures that the three-dimensional protection system of housing 1 is deeply compatible with the operating voltage, pollution resistance, and thermal stability requirements of the detection circuit. It not only solves the problems of insulation performance degradation and localized flame retardant failure at high temperatures but also ensures stable operation of the detection circuit in the early stages of a fire by tightly sealing against environmental dust and moisture.

[0164] Through the above technical solution, the housing 1 and the detection circuit form a collaborative protection mechanism, significantly improving the overall reliability of the fire detector. The housing 1 maintains a stable insulation barrier in a high-temperature environment of 200℃, its flame-retardant performance covers the entire area, and the splicing points achieve airtight protection, preventing the detection circuit from false alarms or damage caused by insulation attenuation, flame spread, or contaminant intrusion, thereby extending the effective working time and improving the accuracy of fire response.

[0165] The following example will provide a more detailed explanation of the above technical solution: In the modified substrate preparation stage (S1), the manufacturer selects polyphenylene sulfide (PPS) as the substrate and modifies it according to a specific formulation (e.g., 65 parts PPS, 15 parts decabromodiphenyl ethane, 5 parts antimony trioxide, 12 parts mica powder, 1.5 parts antioxidant, and 1.5 parts lubricant). After drying the PPS granules at 120°C for 4 hours, they are thoroughly mixed with the formulated amounts of flame retardant (decabromodiphenyl ethane, antimony trioxide), reinforcing filler (mica powder), antioxidant, and lubricant. The mixture is then granulated using a twin-screw extruder. The extrusion process parameters are precisely controlled, such as the feeding section temperature set at 170℃, the compression section temperature at 270℃, the melting section temperature at 295℃, and the die head temperature at 285℃; the screw speed is 200 r / min, and the vacuum degree is -0.08 MPa. This ensures that the flame retardant and mica powder are uniformly dispersed in the polyphenylene sulfide (PPS) substrate, avoiding the localized flame retardant failure problem caused by uneven dispersion of the flame retardant in traditional processes. The modified PPS particles obtained after granulation have a particle size of 2.5 mm, providing high-quality raw materials for subsequent injection molding. This modified substrate improves the material's high-temperature insulation and overall flame retardant performance from the source. Compared with ordinary PA66+ glass fiber materials, it exhibits less insulation resistance decay at high temperatures and a more stable flame retardant rating.

[0166] Next, in the injection molding stage (S2) of the upper and lower shells 11 and 12, the prepared modified polyphenylene sulfide granules were injected into the mold. This mold employs a dynamic mixing gate design, and the cavity surface is nitrided, effectively avoiding excessive shear heat or uneven flow of the melt in complex structural areas (such as around screw holes), ensuring the consistency of material properties in all parts of shell 1. The injection molding process parameters were set as follows: barrel temperature 285℃, first-stage injection pressure 80 MPa, second-stage injection pressure 50 MPa, holding time 15 s, and cooling time 25 s. After injection molding, holding pressure, cooling, demolding, and stress relief post-treatment, upper shell 11 and lower shell 12 with excellent dimensional stability and mechanical properties were obtained. The stress relief treatment further reduced the residual stress inside shell 1, improving its long-term reliability under high-temperature environments.

[0167] Subsequently, a ceramic coating treatment is performed on the surface of housing 1 (S3). First, the surfaces of the upper housing 11 and the lower housing 12 are pretreated. Specifically, the splicing surfaces and screw holes of housing 1 are sandblasted to increase surface roughness and improve coating adhesion; the remaining surfaces of housing 1 are plasma cleaned to remove surface contaminants and further optimize the coating bonding effect.

[0168] A coating slurry formulated with a specific composition (e.g., 50 parts methyl vinyl silicone rubber, 35 parts ceramic powder, 8 parts aluminum hydroxide, 2 parts silane coupling agent, 3 parts vulcanizing agent, and 2 parts colorant) is applied. The ceramic powder is a mixture of kaolin and quartz powder in a 3:2 mass ratio; this composite ceramic powder forms a denser and more stable ceramicized layer at high temperatures. The coating is applied using an electrostatic spraying process to ensure a uniform wet film thickness of 80 μm. After coating, a three-stage curing process is performed: the first stage is held at 80℃ for 10 min, the second stage at 120℃ for 20 min, and the third stage at 180℃ for 15 min. This staged curing process ensures full cross-linking within the coating, forming a dense, high-temperature resistant surface functional layer. In the event of a fire, this ceramicized coating rapidly forms a hard, protective ceramicized layer, effectively isolating flames and heat, significantly improving the insulation and flame-retardant properties of the casing 1 at extreme high temperatures, and solving the problems of insulation failure and flame-retardant layer burn-through in traditional plastic casings at high temperatures.

[0169] During the integrated splicing stage of the upper and lower shells 11 and 12 (S4), a layer of flame-retardant silicone rubber sealant with a hardness of Shore A 40 and a coating thickness of 1.0 mm is applied to the splicing surface of the lower shell 12. This sealant has excellent flame retardancy and high-temperature resistance. After precisely aligning the sealant-coated lower shell 12 with the upper shell 11, hot pressing is performed. The hot pressing process parameters are: upper mold temperature 120℃, lower mold temperature 80℃, pressure 0.5 MPa, and holding time 10 s. Hot pressing ensures that the sealant is tightly bonded to the surface of the shell 1, forming a continuous, seamless flame-retardant sealing layer, effectively preventing high-temperature gases from seeping in from the splicing seam.

[0170] Compared to traditional methods that rely solely on clips or screws for fastening, this sealant filling and hot-pressing process completely solves the problem of weak protection at the joints. Mechanical fastening is then performed: ceramicized silicone rubber sealing rings are installed at the screw holes of the upper housing 11 and lower housing 12, and high-temperature resistant insulating screws are used for locking and securing them with a tightening torque of 0.8 N·m. The introduction of ceramicized silicone rubber sealing rings and insulating screws ensures excellent insulation and flame retardancy even at the screw fixing points, avoiding weak points in insulation or heat conduction paths that may be caused by traditional screw fastening.

[0171] Finally, in the finished product performance testing stage (S5), the insulation performance, flame retardant performance, and sealing performance of the assembled fire detector housing 1 were comprehensively tested. The test results show that the housing 1 can maintain high insulation resistance under high temperature environment, achieve a flame retardant rating of V-0 without local failure, and has excellent sealing performance at the splicing joint, fully meeting the requirements for use of fire detectors in harsh environments.

[0172] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method of manufacturing a fire detector housing, characterized by, The composition of the shell comprises, by mass fraction: Modified base material formula: polyphenylene sulfide 60-70 parts, decabromodiphenyl ethane 12-18 parts, antimony trioxide 4-6 parts, mica powder 10-14 parts, antioxidant 1-2 parts, lubricant 1-2 parts; Ceramization coating formula: methyl vinyl silicone rubber 45-55 parts, ceramic powder 30-40 parts, aluminum hydroxide 6-10 parts, silane coupling agent 1-3 parts, vulcanizing agent 2-4 parts, colorant 1-3 parts; The manufacturing method comprises the following steps: S1, modified base material preparation: after drying the polyphenylene sulfide particles at 120±10℃ for 3-5h, mix with the formula amount of decabromodiphenyl ethane, antimony trioxide, mica powder, antioxidant and lubricant, and granulate by double screw extrusion to prepare modified polyphenylene sulfide particles; S2, upper and lower shell injection molding: inject the modified polyphenylene sulfide particles into the mold, and after injection, pressure maintaining, cooling, demolding and stress relief post-processing, the upper shell and the lower shell are prepared; S3, shell surface ceramization coating treatment: after pretreatment of the surface of the upper shell and the lower shell, coat the coating slurry prepared from the formula amount of methyl vinyl silicone rubber, ceramic powder, aluminum hydroxide, silane coupling agent, vulcanizing agent and colorant, and form a surface functional layer after curing; S4, upper and lower shell integration splicing: coat the flame-retardant sealant on the splicing surface of the lower shell, align with the upper shell, and complete the splicing by hot pressing and mechanical fixing; S5, finished product performance detection: detect the insulation performance, flame retardant performance and sealing performance of the spliced shell.

2. The method of claim 1, wherein In step S1, the process parameters of the double screw extrusion granulation include: the temperature of the feeding section is 160-180℃, the temperature of the compression section is 260-280℃, the temperature of the melting section is 290-300℃, and the temperature of the head section is 280-290℃; the screw rotation speed is 180-220 r / min, the vacuum degree is -0.07 to -0.09 MPa, and the particle size after granulation is 2-3 mm.

3. The fire detector housing manufacturing method according to claim 1 or 2, characterized in that, In step S2, the mold adopts a dynamic mixing type gate design, and the cavity surface is treated by nitriding; The injection molding process parameters include: the barrel temperature is 275-295℃, the first stage injection pressure is 75-85 MPa, the second stage injection pressure is 45-55 MPa, the pressure maintaining time is 10-20 s, and the cooling time is 20-30 s.

4. The method of claim 3, wherein In step S3, the surface pretreatment includes: sandblasting the splicing surface and screw hole part of the shell, and plasma cleaning the remaining surface of the shell; The ceramic powder is a mixture of kaolin and quartz powder, and the mass ratio is 2.5-3.5:

2.

5. The method of claim 4, wherein the step of forming the fire detector housing includes the step of: The coating is coated by electrostatic spraying process, and the wet film thickness is 70-90 μm; The curing process includes three-stage temperature rising: the first stage is 75-85℃ and maintains for 8-12 min, the second stage is 115-125℃ and maintains for 15-25 min, and the third stage is 175-185℃ and maintains for 10-20 min.

6. The method of claim 5, wherein the step of forming the fire detector housing includes the step of: In step S4, the fire-retardant sealant is a silicone sealant with a Shore A hardness of 35-45 and a coating thickness of 0.8-1.2 mm; The hot-pressing process parameters are: upper mold temperature 115-125℃, lower mold temperature 75-85℃, pressure 0.4-0.6 MPa, and pressure holding time 8-12 s.

7. The method of claim 6, wherein the step of forming the fire detector housing includes the step of: In step S4, the mechanical fixation is: installing a ceramicized silicone seal ring at the screw hole of the upper and lower shells, and locking and fixing using high-temperature-resistant insulating screws with a locking torque of 0.7-0.9 N·m.

8. A fire detector housing, characterised in that The fire detector housing is manufactured by the method of any one of claims 1-7; the housing comprises an upper shell and a lower shell, the base material is a composite material composed of the modified base material formulation of claim 1, and the surface has a functional layer composed of the ceramicized coating formulation of claim 1; the splicing part is sealed and combined by the fire-retardant sealant and the hot-pressing process.

9. A fire detector characterised in that The fire detector housing, the mounting seat, and the detection circuit mounted in the housing.

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