A transfer molding mold and a transfer molding method for overmolding an insert

Abstract

The application discloses a transfer injection molding die and a transfer injection molding method for over-molding inserts, and belongs to the technical field of dies. In order to solve the problem that inserts are prone to displacement and the product defect rate is high when molding high-viscosity ceramicized silicone rubber by using the existing die pressing process, the application provides a transfer injection molding die which comprises a die body capable of closing a cavity and a material conveying system. The core lies in that an insert fixing part is arranged in the cavity and is used for positioning and fixing the insert before injecting glue; after the cavity is closed, the material conveying system injects glue into the cavity. The application also provides a transfer injection molding method which adopts the sequence of first fixing the insert, then closing the die, and then injecting the glue by using multi-stage pressure, and cooperates with a specific size of exhaust structure to adapt to high-viscosity glue. The application decouples the fixing of the insert and the glue filling process, fundamentally avoids the displacement and damage of the insert, significantly reduces defects such as bubbles and glue defects, improves the product quality and production efficiency, and is suitable for large-scale production of fireproof isolation structural parts.

Description

Technical Field

[0001] This invention relates to the field of mold technology, and specifically to a transfer molding mold for overmolding inserts and a transfer molding method. Background Technology

[0002] Fireproof and insulating structural components require extremely high levels of insulation, flame retardancy, and fire resistance. High-viscosity ceramicized silicone rubber is an ideal material for manufacturing such components due to its excellent flexibility and electrical insulation at room temperature, and its ability to transform into a hard ceramic body under high-temperature flame ablation. To achieve the ceramicization effect, a large amount of functional fillers (such as magnesium hydroxide and low-melting-point glass powder) needs to be added to this material, resulting in extremely high viscosity and poor flowability, posing a severe challenge to molding processes and mold design.

[0003] Currently, the industry generally uses the traditional two-plate mold compression molding process to form this type of coating. The typical process is as follows: the mixed high-temperature vulcanized silicone rubber is made into a blank, which is manually wrapped around the insert. Then the component is placed into the open cavity of the two-plate mold, and then the mold is closed and heated and pressurized for vulcanization.

[0004] However, this traditional process has several inherent drawbacks: First, during mold closing, the mold pressure directly acts on the rubber compound and inserts. The impact of the rubber flow and the mold closing pressure can easily cause insert displacement or even cracking, resulting in uneven coating thickness and localized performance failure. Second, the parting surface of the two-plate mold is prone to generating a large amount of flash. High-viscosity ceramicized silicone rubber has high hardness after curing, making flash trimming difficult and significantly increasing post-processing costs. Third, high-viscosity rubber has poor flowability and poor venting during molding, making the product prone to defects such as air bubbles and insufficient glue, seriously affecting the yield rate. Fourth, the consistency of manually wrapping the preform is poor, making it difficult to ensure uniform coating thickness and affecting product performance stability.

[0005] The root cause of the above problems lies in the fact that the molding principle of the two-plate mold, which involves "feeding material first, closing the mold, and applying pressure upon mold closing," cannot independently control the three key aspects of insert positioning, cavity sealing, and material filling, making it difficult to meet the requirements of high-viscosity and high-precision coating molding. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a transfer molding die and transfer molding method for overmolded inserts, aiming to achieve precise fixation of the inserts during the molding process, avoid displacement during mold closing and glue injection, eliminate defects such as air bubbles and insufficient glue, and improve product quality and production efficiency.

[0007] Technical solution To achieve the above objectives, the present invention provides a transfer molding die for overmolding inserts, comprising: A mold body that defines a closable cavity; and A material conveying system is used to convey the adhesive material outside the mold body into the mold cavity after the cavity is closed; An insert fixing part is provided inside the cavity. The insert fixing part is used to position and fix the insert before the adhesive is conveyed into the cavity. The cavity is provided with an exhaust structure, the geometry of which is adapted to allow gas to escape while preventing high-viscosity adhesive from flowing out of the cavity.

[0008] Furthermore, the insert fixing part is disposed in the lower mold assembly of the mold body, and is used to position and fix the insert before mold closing.

[0009] Optionally, the insert fixing part includes at least one of a positioning pin, a slot, and / or a negative pressure adsorption mechanism.

[0010] Furthermore, the depth of the exhaust structure is adapted to allow gas to escape while blocking the outflow of high-viscosity ceramicized silicone rubber with a viscosity greater than a certain threshold.

[0011] Preferably, the depth of the exhaust structure is 0.05 mm to 0.08 mm.

[0012] In one embodiment, the material conveying system includes: The feeding chamber is located in the upper mold assembly; A plunger that mates with the feeding chamber; and A flow channel system connecting the feeding chamber and the cavity.

[0013] Preferably, the flow channel system adopts an H-type or X-type balanced layout.

[0014] Furthermore, the cavity is also provided with an overflow groove at the end of the material flow.

[0015] Optionally, the mold is a three-plate transfer mold.

[0016] The present invention also provides a fireproof isolation structure manufactured using the above-mentioned transfer molding mold.

[0017] Another aspect of the present invention provides a transfer molding method for encapsulating an insert with high-viscosity ceramicized silicone rubber, comprising the following steps: The insert is placed in a cavity of a mold and positioned and fixed thereon. Before injecting a piece of adhesive into the cavity, the mold is closed to form a sealed cavity; The adhesive is injected into the sealed cavity using a multi-stage pressure injection method, wherein the injection pressure is changed during the filling process.

[0018] Furthermore, the multi-stage pressure injection method includes: first performing low-pressure filling with a first pressure, and then performing high-pressure filling with a second pressure higher than the first pressure.

[0019] Preferably, the first pressure is 5~8 MPa and the second pressure is 15~30 MPa.

[0020] In one embodiment, before injecting the adhesive into the cavity, the step further includes preheating the high-viscosity ceramicized silicone rubber to 90-95°C.

[0021] Furthermore, after the injection step, a step of holding pressure and vulcanizing at a mold temperature of 165~180℃ for 5~10 minutes is also included.

[0022] Optionally, the method employs the aforementioned transfer molding die.

[0023] Beneficial effects Compared with the prior art, the present invention has the following advantages: Significantly improves product quality and yield. By adopting the process sequence of "first positioning and fixing, then closing the cavity, and then injecting the adhesive," the direct effect of mold closing pressure on the insert and the impact of adhesive flow on the insert are fundamentally avoided, effectively preventing insert displacement, eccentricity, or even breakage, and ensuring the uniformity of the coating thickness.

[0024] Effectively eliminates molding defects. The specially designed venting structure and overflow groove work together, combined with the multi-stage pressure injection method, to fully expel gas from the cavity and collect cold material at the leading edge, significantly reducing defects such as bubbles and insufficient glue, making the interior of the product denser.

[0025] It significantly improves production efficiency and reduces costs. The vulcanization cycle of the injection molding process is shorter than that of the traditional molding process, and there is very little overflow at the parting line, resulting in a significant reduction in flash. Post-processing steps are simplified, and labor costs are reduced.

[0026] Enhanced overall product performance. The uniform, defect-free coating layer bonds tightly with the inserts, resulting in fireproof and insulating structural components with stable and reliable insulation, voltage resistance, flame retardancy, fire resistance, and mechanical properties, thereby improving product safety and service life. Attached Figure Description

[0027] Figure 1 This is an exploded structural diagram of one embodiment of the transfer molding die of the present invention, showing a three-plate structure; Figure 2 for Figure 1 A partial schematic diagram of the upper and lower mold components in the mold shown illustrates the positioning of the insert within the cavity; Figure 3 for Figure 1The diagram shows a cross-sectional flow chart of the mold in the closed state, illustrating the material filling path. Figure 4 This is a process flow diagram of one embodiment of the transfer molding method of the present invention.

[0028] The meanings of the labels in the figures are as follows: 10: Upper mold assembly; 11: Upper template; 12: Feeding chamber; 13: Plunger; 20: Runner plate; 21: Runner system; 22: Gate; 30: Lower mold assembly; 31: Lower mold plate; 32: Cavity; 33: Insert fixing part; 331: Locating pin; 34: Venting structure; 35: Overflow groove; 40: Insert; 50: Rubber compound. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] In existing technologies, when using a two-plate mold compression molding process to coat inserts to manufacture fireproof isolation structural components, the high-viscosity adhesive flows under the mold closing pressure due to the "material first, mold closing later, and pressure applied immediately upon mold closing" method. This can easily impact the insert, causing displacement or cracking, resulting in uneven coating thickness in the finished product. Simultaneously, the high-viscosity adhesive has poor flowability and poor venting, easily generating air bubbles and insufficient adhesive, and causing severe overflow at the parting line. This invention fundamentally solves these problems by decoupling the three key actions of "insert fixing," "cavity closing," and "insert filling."

[0031] Reference Figures 1 to 3 This invention provides a transfer molding die for overmolding inserts. The die includes a die body that can close to form a cavity 32, and a material conveying system. Unlike existing molding dies where the material is placed inside the cavity before mold closing, the material conveying system of this invention conveys the material 50 outside the die body into the cavity 32 after it has closed. This separates the flow and filling of the material from the mold closing action, preventing the closing pressure from directly acting on the material and reducing the impact on the insert 40.

[0032] like Figure 2As shown, an insert fixing part 33 is provided inside the cavity 32. This insert fixing part 33 is used to pre-position and fix the insert 40 before the adhesive 50 is conveyed into the cavity 32. This ensures that the insert 40 maintains a precise position throughout the subsequent adhesive injection process, avoiding displacement or skewing due to the impact of the adhesive flow, and ensuring that the final fireproof isolation structural component has a uniform thickness and accurate dimensions.

[0033] like Figure 2 As shown, in this embodiment, the insert fixing part 33 is disposed within the lower mold assembly 30 of the mold body. During production, the insert 40 is first placed in the cavity 32 of the open lower mold assembly 30, and positioned and fixed by the insert fixing part 33. Subsequently, the upper mold assembly 10 moves downward and closes with the lower mold assembly 30. This design ensures that the placement and fixing of the insert are completed before mold closing, making operation convenient and positioning reliable, and ensuring that the insert is not disturbed by external forces during mold closing.

[0034] To achieve more precise and secure fixing of the insert 40, the insert fixing part 33 can adopt various structural forms. For example... Figure 2 As shown, the insert fixing part 33 may include at least one of a positioning pin 331, a slot, and / or a negative pressure adsorption mechanism. For example, a positioning pin 331 that mates with a pre-drilled hole or edge on the insert 40 may be used for mechanical positioning; or a slot formed on the surface of the cavity 32 may be used to constrain the edge of the insert 40; or a negative pressure adsorption hole may be provided at the bottom of the cavity 32 to adsorb the insert 40 onto the cavity surface using vacuum suction. The above structures may be used alone or in combination to adapt to inserts 40 of different shapes and materials.

[0035] This invention is particularly suitable for molding high-viscosity ceramicized silicone rubber. This type of rubber compound has high viscosity and poor flowability, placing stringent requirements on the venting structure. Therefore, the geometry of the venting structure 34 is specifically adapted to allow gas to escape while effectively preventing the outflow of high-viscosity ceramicized silicone rubber with a viscosity exceeding a certain threshold. Optimized, the depth of the venting structure 34 is preferably between 0.05 mm and 0.08 mm. If the depth is less than 0.05 mm, volatiles in the rubber compound or a small amount of rubber at the leading edge can easily clog it, leading to venting failure; if the depth is greater than 0.08 mm, under high pressure, the rubber compound may be squeezed into the venting structure, forming flash that is difficult to trim. Therefore, this size range represents the optimal balance between efficient venting and prevention of overflow.

[0036] Reference Figure 1 and Figure 3The material conveying system is described in detail below. In this embodiment, the material conveying system includes a feeding chamber 12 located in the upper mold assembly 10, a plunger 13 that moves in conjunction with the feeding chamber 12, and a flow channel system 21 connecting the feeding chamber 12 and the cavity 32. During operation, the pre-formed rubber block is placed in the feeding chamber 12; after the mold closes, an external press drives the plunger 13 downward, squeezing the rubber 50 and injecting it into the sealed cavity 32 through the flow channel system 21 and the gate 22.

[0037] To ensure that the material fills each cavity evenly and synchronously (when the mold is a multi-cavity mold), the runner system 21 preferably adopts an H-type or X-type balanced layout. This layout makes the runner length and turning angle from the main runner to each cavity basically the same, ensuring that the injection pressure and filling time of each cavity are the same, and avoiding underfilling or overflow in some cavities due to uneven filling.

[0038] like Figure 3 As shown, an overflow groove 35 is also provided at the end of the rubber flow in the cavity 32. The overflow groove 35 is used to collect the cold material and any gas that may be trapped at the front of the rubber flow, preventing them from entering the product area and causing defects; at the same time, it provides a buffer space for the cavity, which helps to maintain pressure stability during the holding pressure stage, making the product more compact.

[0039] like Figure 1 As shown, the mold in this embodiment is preferably a three-plate transfer mold, which includes an upper mold assembly 10 (including an upper template 11), a runner plate 20, and a lower mold assembly 30 (including a lower template 31). The runner system 21 is mainly disposed on the runner plate 20. The three-plate structure divides the mold opening action into two steps: the first step is to open between the runner plate 20 and the lower mold assembly 30 to remove the product; the second step is to open between the runner plate 20 and the upper mold assembly 10 to remove the runner solidified material. This structure has clear functional divisions and is suitable for realizing the transfer molding process of the present invention.

[0040] Thanks to the aforementioned structural optimizations and process improvements, this invention enables the stable manufacture of high-quality fire-resistant isolation structural components. These components feature precisely positioned inserts, uniform coating thickness, and are free from internal defects such as air bubbles or insufficient adhesive. They also exhibit minimal burrs, significantly improving the reliability and consistency of their insulation, flame-retardant, and fire-resistant properties.

[0041] The following reference Figure 4 The transfer molding method provided by this invention will be described in detail. This method is particularly suitable for using high-viscosity ceramicized silicone rubber to coat inserts 40.

[0042] like Figure 4 As shown, the transfer molding method of the present invention includes the following steps.

[0043] Step S100: Place the insert 40 into the cavity 32 of the mold and position and fix it. Specifically, the insert 40 is precisely fixed in the preset position of the cavity 32 by the insert fixing part 33 (such as positioning pin 331, slot and / or negative pressure adsorption mechanism).

[0044] Step S200: Before injecting the adhesive 50 into the cavity 32, close the mold to form a sealed cavity 32. This step ensures that the insert 40 is not disturbed by external forces during the mold closing process and that the cavity is completely sealed.

[0045] Step S300: The adhesive 50 is injected into the sealed cavity 32 using a multi-stage pressure injection method. The multi-stage pressure injection method changes the injection pressure during filling. Specifically, step S300 further includes: Step S310: First, perform low-pressure filling with the first pressure. During this stage, the adhesive 50 flows around the insert 40 at a slower speed and with less impact force to avoid the insert 40 from tilting or vibrating due to the impact of the adhesive, thus playing a buffering and protective role.

[0046] Step S320: High-pressure filling is then performed using a second pressure higher than the first pressure. After the adhesive 50 flows smoothly through the insert 40 area, the pressure is switched to high pressure to ensure that the high-viscosity adhesive quickly fills the rest of the cavity, improving production efficiency.

[0047] After optimization, the first pressure is preferably 5~8 MPa, and the second pressure is preferably 15~30 MPa. The low pressure of 5~8 MPa is sufficient to drive the rubber material to flow slowly and form the initial coating of the insert without generating excessive impact; the high pressure of 15~30 MPa is sufficient to overcome the flow resistance of high viscosity ceramicized silicone rubber, ensuring that the cavity is completely filled and a dense structure is obtained.

[0048] Before injecting the rubber compound 50 into the cavity 32, the process includes preheating the high-viscosity ceramicized silicone rubber to 90-95°C. Preheating significantly reduces the viscosity of the rubber compound, improves its flowability, reduces injection pressure, lowers equipment load, and prevents underfilling due to excessively cold rubber compound.

[0049] Following the injection step, a further step (step S400) is performed by holding the mold at a temperature of 165~180℃ for 5~10 minutes to vulcanize. This temperature range is the optimal vulcanization temperature range for high-viscosity ceramicized silicone rubber, ensuring that the vulcanization reaction proceeds quickly and completely. This time is significantly shortened compared to traditional compression molding processes because pressure transfer is more uniform and efficient, and heat transfer is also faster in injection molding.

[0050] Finally, in step S500, the mold is opened and the product is ejected.

[0051] Obviously, the transfer molding method disclosed in this invention is preferably implemented using the aforementioned transfer molding mold. The structural features of the mold and the process steps of the method complement each other, jointly achieving precise control over the molding process of high-viscosity ceramicized silicone rubber-coated inserts, thereby obtaining high-quality fireproof and insulating structural components.

[0052] To illustrate the invention more clearly, a basic embodiment is described below. A transfer molding die is provided, comprising a die body consisting of an upper die assembly and a lower die assembly, which, when closed, form a cavity 32. The die also includes a material conveying system, comprising a feeding chamber 12, a plunger 13, and a single flow channel connecting the feeding chamber 12 and the cavity 32. The inner wall of the cavity 32 has a positioning step serving as an insert fixing part 33. An venting gap is provided at the end of the material flow in the cavity 32 as a venting structure 34. When using this basic die, the insert 40 is first placed into the cavity 32 of the lower die and fixed by the insert fixing part 33; then the upper and lower dies are closed to form a sealed cavity; then pre-formed material 50 is placed into the feeding chamber 12, and pressure is applied by the plunger 13 to push the material through the single flow channel into the cavity 32, covering the insert 40; during the filling process, air in the cavity is discharged from the venting structure 34. Although this embodiment has a simple structure, it fully embodies the core idea of ​​the present invention of "fixing first, closing later, and then injecting glue", which can significantly improve the problem of insert displacement compared with traditional molding process.

[0053] The following describes a complete and preferred embodiment for manufacturing fireproof isolation structural components, using specific parameters. This embodiment employs a three-plate transfer mold. The mold cavity steel is selected from S136 corrosion-resistant mirror steel, and the mold cavity surface is mirror-polished with a roughness Ra≤0.1 μm to reduce the flow resistance of the adhesive. The lower mold assembly 30 has an insert fixing part 33 composed of a positioning pin 331 and a negative pressure adsorption mechanism within its cavity 32, used for double fixing of the insert 40. The upper mold assembly 10 has a feeding chamber 12 and a plunger 13.

[0054] The runner system 21 adopts an H-shaped balanced layout, with a runner diameter of 8 mm and a total length controlled within 120 mm to prevent the rubber compound from staying in the runner for too long and thus premature vulcanization. Venting structures 34 with a depth of 0.06 mm and a width of 3 mm are provided at the highest point of the cavity 32 and at the end of the rubber compound flow. An overflow groove 35 with a volume of approximately 18% of the cavity volume is also provided at the end of the cavity 32. The mold temperature is controlled by a temperature controller in zones, and the mold temperature is stabilized at 175±3℃.

[0055] The process flow using the above-mentioned preferred mold is as follows: First, the insert 40 is roughened by surface sandblasting and coated with KH-560 silane coupling agent to enhance the interfacial bonding force with silicone rubber. Second, the high-viscosity ceramicized silicone rubber is preheated and softened at 92°C and cut into pre-formed blocks that match the feeding chamber 12. The processed insert 40 is placed into the lower mold cavity 32, negative pressure adsorption is activated, and it is precisely positioned by the positioning pin 331.

[0056] The mold is then closed, and the insert 40 is completely constrained by the inner wall of the cavity 32 and the insert fixing part 33. The preheated rubber block is placed into the feeding chamber 12. The injection molding machine is started, and the plunger 13 descends, using multi-stage pressure injection: the first stage uses low-pressure buffer filling at 7 MPa and a filling speed of 25 mm / s to ensure that the rubber material smoothly covers the insert 40; when the sensor detects that the rubber material has flowed through the insert area, it switches to the second stage and performs main filling at 18 MPa, with a total injection time of approximately 7 seconds.

[0057] After filling, the mold is held at 175℃ for 6 minutes for vulcanization, which is 50% shorter than the 12 minutes of the traditional molding process. After vulcanization, the mold is opened, and the finished product is ejected using an ejection mechanism and a vacuum-assisted demolding system. Finally, the gate and runner residue are removed, and the product is placed in an oven for a second vulcanization (200℃, 4 hours) to eliminate vulcanization byproducts and improve the final performance.

[0058] Fireproof insulation structural components produced using the above-mentioned molds and processes exhibit excellent performance after testing. Compared to a comparative example using traditional compression molding (using the same rubber compound and a traditional two-plate mold for one-time pressure vulcanization), the comparative example shows a material shortage rate as high as 15%, a bubble defect rate exceeding 10%, and insert misalignment between 0.3 mm and 0.5 mm. However, using the solution of this invention, the insert breakage rate is reduced from 5%~8% to below 0.5%, the bubble / material shortage defect rate is reduced from 12% to below 1%, the coating thickness tolerance is improved from ±0.3 mm to ±0.1 mm, the flash is reduced by more than 90%, and production efficiency is increased by 30%~50%. The finished product's normal volume resistivity is ≥1×10¹. 5 The flame retardant performance reaches UL94 V-0 level (Ω·cm), and a dense ceramic layer is formed after ablation at 800℃ for 15 minutes, with a quality retention rate of ≥50%. These data fully demonstrate the significant advantages of this invention in improving product quality, production efficiency, and reducing costs.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A transfer molding die for overmolding inserts, characterized in that, include: A mold body with a defined closable cavity; as well as A material conveying system is used to convey the adhesive material outside the mold body into the mold cavity after the cavity is closed; An insert fixing part is provided inside the cavity. The insert fixing part is used to position and fix the insert before the adhesive is conveyed into the cavity. The cavity is provided with an exhaust structure, the geometry of which is adapted to allow gas to escape while preventing high-viscosity adhesive from flowing out of the cavity.

2. The transfer molding die according to claim 1, characterized in that, The insert fixing part is disposed in the lower mold assembly of the mold body and is used to position and fix the insert before mold closing; the insert fixing part includes at least one of positioning pin, slot and / or negative pressure adsorption mechanism.

3. The transfer molding die according to claim 1, characterized in that, The depth of the venting structure is adapted to allow gas to escape while preventing high-viscosity ceramicized silicone rubber with a viscosity greater than a certain threshold from flowing out of the cavity; the depth of the venting structure is 0.05 mm to 0.08 mm.

4. The transfer molding die according to claim 1, characterized in that, The material conveying system includes: a feeding chamber located in the upper mold assembly; a plunger that cooperates with the feeding chamber; and a flow channel system connecting the feeding chamber and the cavity; the flow channel system adopts an H-type or X-type balanced layout.

5. The transfer molding die according to claim 1, characterized in that, The cavity is also provided with an overflow groove at the end of the material flow; the mold is a three-plate transfer mold.

6. A fireproof isolation structural component, characterized in that, It is manufactured using any one of the transfer molding dies according to claims 1 to 5.

7. A transfer molding method for encapsulating an insert with high-viscosity ceramicized silicone rubber, characterized in that, Includes the following steps: The insert is placed in a cavity of a mold and positioned and fixed thereon. Before injecting a piece of adhesive into the cavity, the mold is closed to form a sealed cavity; The adhesive is injected into the sealed cavity using a multi-stage pressure injection method, wherein the injection pressure is changed during the filling process.

8. The method according to claim 7, characterized in that, The multi-stage pressure injection method includes: first, low-pressure filling with a first pressure, and then high-pressure filling with a second pressure higher than the first pressure; the first pressure is 5~8 MPa, and the second pressure is 15~30 MPa.

9. The method according to claim 7, characterized in that, Before injecting the rubber compound into the cavity, the process includes a step of preheating the high-viscosity ceramicized silicone rubber to 90-95°C; after the injection step, the process includes a step of holding the mold at a temperature of 165-180°C for 5-10 minutes to cure under pressure.

10. The method according to claim 7, characterized in that, The method employs the transfer molding mold as described in any one of claims 1 to 5.

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