Bonding process for magnetic steel and steel sheet of loudspeaker

Abstract

The invention belongs to the field of loudspeaker manufacturing, and particularly relates to a bonding process for magnetic steel and a steel sheet of a loudspeaker. In a traditional process, during anaerobic adhesive bonding, glue on the outer side of a bonding surface is in contact with air, only 80% of the area is cured, and the baking effect is still limited after the anaerobic adhesive is baked in a 60-DEG C oven. Anaerobic adhesive needs to be cured in an oxygen-free environment, and the problem that the adhesive on the outer side makes contact with air cannot be solved through a traditional pressure maintaining technology. The process comprises the following steps: coating a steel sheet with glue, covering with magnetic steel, applying pressure of 60-80 N, maintaining the pressure and curing at 100 DEG C, uniformly placing a product on a turnover disc with gaps, placing the product in a vacuum box, exhausting air to form a negative pressure environment, reducing the oxygen concentration, and maintaining for 1 hour under vacuum negative pressure for secondary curing. According to the process, the glue on the outer side is fully cured through vacuum drying, the bonding area is enlarged, the average value of shearing force is greatly improved, the consistency is remarkably improved, the bonding strength is effectively enhanced, and the process is particularly suitable for products with small sizes and limited bonding surfaces and has popularization value.

Description

Technical Field

[0001] The invention belongs to the field of loudspeaker manufacturing, and in particular relates to a bonding process between a loudspeaker's magnetic steel and a steel sheet. Background Art

[0002] In the speaker production process, glue is usually used to bond the metal components, magnetic steel, and steel sheets. The type of glue used is anaerobic glue. The curing principle of anaerobic glue is that when stored in a conventional aerobic environment, oxygen will combine with the free radicals produced by the decomposition of the initiator in the glue, inhibiting the polymerization reaction and keeping the glue liquid. When the glue is coated on the metal surface and isolated from the air to form an oxygen-free environment, the trace oxygen dissolved in the glue will be consumed and can no longer inhibit the polymerization reaction. The free radicals decomposed by the initiator in the glue begin to initiate monomer polymerization, forming long-chain polymers and cross-linking and curing.

[0003] The existing traditional bonding process is to apply glue on the surface of the steel sheet, then cover the magnet on the glue, use pressure-maintaining equipment to apply 60-80 Newtons of pressure to the magnet and steel sheet, and accompany it with a high temperature of about 100°C to spread the anaerobic adhesive across the bonding surface, expel all air, and form an oxygen-free environment to allow the glue to solidify. The high temperature has the effect of accelerating the reaction time. The product after pressure-maintaining and solidification is then placed in a 60°C oven for baking to accelerate the complete curing time of the glue.

[0004] However, according to the curing principle of anaerobic adhesives, polymerization reaction and curing can only occur in an oxygen-free environment. In traditional methods, the glue on the outer side of the bonding surface is still in contact with the outside air. Even if it is placed in an oven for baking, the glue in contact with the air cannot react. The actual area of ​​the glue that effectively undergoes polymerization reaction and curing is only about 80%, resulting in unsatisfactory bonding strength.

[0005] Therefore, a new bonding process for loudspeaker magnets and steel sheets is urgently needed. Summary of the Invention

[0006] The present invention proposes a bonding process for the magnetic steel and steel sheet of a speaker. By introducing a process step of secondary curing in a vacuum box, the glue on the outer side of the bonding surface contacting the air is further cured, thereby expanding the bonding area and significantly improving the bonding strength.

[0007] The technical solution of the present invention is as follows: A process for bonding a loudspeaker magnetic steel and a steel sheet comprises the following steps: Step (1), coating the surface of the steel sheet with anaerobic adhesive, and covering the magnetic steel on the coated steel sheet; Step (2), applying a pressure of 60-80 N to the magnetic steel and the steel sheet, and curing them under pressure at a temperature of about 100°C; Step (3) places the product after pressure-maintaining and curing into a vacuum box, closes the sealing door, starts the vacuum pump to extract the air in the box to form a vacuum negative pressure environment, and maintains the product under the vacuum negative pressure environment for a preset time for secondary curing.

[0008] Furthermore, the negative pressure level of the vacuum negative pressure environment is selected according to the equipment capacity to reduce the oxygen concentration in the box.

[0009] Furthermore, the preset time is 1 hour.

[0010] Furthermore, in step (3), the products are evenly placed on the turntable with gaps left between the products.

[0011] Furthermore, the anaerobic adhesive is an anaerobic adhesive used for bonding metal parts, and its curing requires an oxygen-free environment.

[0012] Furthermore, the vacuum box is a vacuum drying box.

[0013] Furthermore, the vacuum drying oven only forms a negative pressure environment by vacuuming during the secondary curing process, without applying additional heating temperature.

[0014] Furthermore, after the secondary curing is completed, the product is taken out and transferred to the next process.

[0015] The beneficial effects of the present invention are: The present invention replaces the traditional oven baking process with a vacuum drying process, which can fully cure the glue and effectively expand the bonding area. According to the shear force test method for evaluating the bonding strength between magnetic steel and steel sheets in the industry, after adding the "vacuum box secondary curing" process, the distribution mean and consistency of the shear force are significantly improved compared with the traditional oven baking process, thereby significantly improving the structural bonding strength. This process has reference and promotion value in the bonding process of metal parts in the speaker field, especially in products with small size and limited bonding surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the conventional glue bonding structure of the present invention; Figure 2 This is a schematic diagram of the effective curing area structure of the conventional glue of the present invention; Figure 3 1 is a data comparison chart of the median bonding force between the improved bonding process of the present invention and the traditional bonding process.

[0017] In the picture: 1. Magnet; 2. Steel sheet; 3. Glue. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0019] Example 1 This embodiment provides a bonding process for a loudspeaker magnet and a steel sheet, comprising the following steps: Step (1), coating the surface of the steel sheet with anaerobic adhesive, and covering the magnetic steel on the coated steel sheet; Step (2), applying a pressure of 60-80 N to the magnetic steel and the steel sheet, and curing the steel sheet under pressure at a temperature of about 100°C; Step (3) is to place the product after pressure-maintaining curing into a vacuum box, close the sealing door, start the vacuum pump to extract the air in the box to form a vacuum negative pressure environment, and maintain the vacuum negative pressure environment for a preset time for secondary curing.

[0020] Among them, the negative pressure level of the vacuum negative pressure environment is selected according to the equipment capacity to reduce the oxygen concentration in the box, and the preset time is 1 hour.

[0021] In step (3), the products are evenly placed on the turntable with gaps between the products.

[0022] Anaerobic adhesive is an anaerobic adhesive used for bonding metal parts. Its curing requires an oxygen-free environment, and the vacuum box is a vacuum drying box.

[0023] During the secondary curing process, the vacuum drying oven only creates a negative pressure environment by vacuuming, without applying additional heating temperature. After the secondary curing is completed, the product is taken out and transferred to the next process.

[0024] In this embodiment, a "vacuum box secondary curing" process method is proposed. The present invention introduces the process step of vacuum box secondary curing to further cure the glue on the outside of the bonding surface that contacts the air, thereby expanding the bonding area and significantly improving the bonding strength.

[0025] Key points that require detailed explanation include: This embodiment proposes a bonding process for a loudspeaker magnet and a steel sheet, comprising the following steps: Step (1): Use anaerobic adhesive specially made for metal parts and form a continuous and uniform adhesive layer on the surface of the steel sheet using a dispensing machine. The thickness of the adhesive layer is controlled at 0.15-0.2mm. After the magnetic steel is precisely aligned, it is covered on the adhesive-coated steel sheet to ensure that the center deviation between the two does not exceed 0.05mm. Step (2): Use hydraulic pressure holding equipment to apply a constant pressure of 65 N to the magnet and the steel sheet, and simultaneously start the built-in heating module of the equipment to stabilize the ambient temperature of the workpiece at 102 ° C. During the pressure holding process, the pressure fluctuation is monitored in real time by the pressure sensor to ensure that the pressure deviation is within the range of ± 5 N. The pressure is maintained for 10 seconds until initial solidification. Step (3): Place the workpieces after pressure-maintaining and curing evenly on a turnover tray with a grid structure. The area occupied by a single workpiece is not less than 5 cm², and the distance between adjacent workpieces is kept above 1 cm to ensure the uniformity of air flow. Push the turnover tray into the vacuum drying oven, close the sealing door and start the rotary vane vacuum pump (pumping rate 80 L / min). Within 5 minutes, the negative pressure in the box reaches -0.075 MPa (corresponding to an oxygen partial pressure of about 15 kPa). Maintain this vacuum negative pressure environment for 1 hour. During this period, the pressure stability is monitored in real time by a vacuum gauge (accuracy ±0.001 MPa). The heating function of the drying oven is not enabled during the secondary curing process. The reaction is completed by relying on the natural temperature of the environment (25±2°C). After the curing is completed, the nitrogen purge system (pressure 0.1 MPa) is first used to slowly restore the normal pressure in the box, and then the workpiece is taken out and transferred to the next process. This embodiment creates a vacuum negative pressure environment so that the adhesive layer on the outer side of the bonding surface between the magnet and the steel sheet, which is originally in contact with the air, is placed in a low-oxygen atmosphere, prompting the anaerobic adhesive to continuously undergo a cross-linking reaction, effectively expanding the curing range of the adhesive layer and significantly improving the interface bonding reliability.

[0026] Among them, step (3) uses a vacuum drying oven with a double-chamber structure, the maximum vacuum degree of the front chamber can reach -0.092MPa, the workpiece placement density is controlled to no more than 2 workpieces per square decimeter of tray area, the spacing is expanded to 2cm, and the vacuum pump is upgraded to a Roots-rotary vane pump group (pumping rate 200L / min), which can achieve a negative pressure environment of -0.085MPa within 8 minutes. Under this working condition, secondary curing is carried out, and the curing depth of the edge of the adhesive layer is significantly increased compared with the conventional process. The industry standard shear force test method verifies that the failure mode of the bonding interface changes from cohesive failure of the adhesive layer to parent material failure, indicating that the bonding strength reaches the material's ultimate bearing capacity; The existing oven equipment was adaptively modified by removing the original heating system and installing a 304 stainless steel vacuum chamber (wall thickness 6mm). The chamber size is consistent with the original oven liner, integrating a vacuum sealing component (silicone rubber sealing ring, compression rate 25%) and a vacuum exhaust interface, matching a rotary vane vacuum pump, adding a PLC control module, integrating a vacuum degree PID adjustment function, and being able to set a multi-segment negative pressure curve from -0.06 to -0.09MPa. It is equipped with a touch screen human-machine interface, which displays parameters such as pressure and time in real time. The workpieces after pressure holding and curing are arranged in a single layer in the modified vacuum chamber, and the vacuum pump is started to the target negative pressure (such as -0.08MPa) and maintained for 1 hour to complete the secondary curing. The energy consumption of the modified equipment is reduced by 30% compared with the original oven, and no additional high-temperature heating is required, avoiding the problem of adhesive layer aging caused by local overheating in the traditional process.

[0027] In-depth explanation of the technical principles: Based on the oxygen inhibition curing characteristics of anaerobic adhesives, the present invention creatively introduces vacuum environment control technology. On the basis of conventional pressure-maintaining curing to form an internal oxygen-free reaction zone, an external low-oxygen atmosphere is constructed through a vacuum drying oven (the oxygen concentration is reduced to below 5%), and the gas partial pressure gradient is used to promote the rapid discharge of residual oxygen at the edge of the adhesive layer, breaking through the curing limitation of the adhesive layer on the outside of the interface due to contact with air in traditional processes. The vacuum environment also reduces the surface tension of the adhesive liquid, promotes its penetration into the metal micro-interface, and forms a denser cross-linked network structure. Scanning electron microscopy observation shows that the fracture surface of the adhesive layer using this process presents obvious toughness fracture characteristics, and the density of the fibrous drawing structure is significantly increased compared with the traditional process, which intuitively reflects the improvement of the cohesion of the adhesive layer.

[0028] The present invention solves the problem of curing of anaerobic adhesives at open interfaces through an innovative combination of environmental parameters, forming a collaborative process system of "pressure-driven initial curing-deep cross-linking in a vacuum environment". This process does not rely on specific brands of glue or special metal surface treatment, and is suitable for equipment modification and process upgrades of existing speaker production lines. It has significant technical advantages, especially for precision devices with narrow bonding surfaces such as micro speakers.

[0029] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A bonding process for a loudspeaker's magnetic steel and steel sheet, characterized in that: The following steps are involved: Step (1), coating the surface of the steel sheet with anaerobic adhesive, and covering the magnetic steel on the coated steel sheet; Step (2), applying a pressure of 60-80 N to the magnetic steel and the steel sheet, and curing them under pressure at a temperature of about 100°C; Step (3) places the product after pressure-maintaining and curing into a vacuum box, closes the sealing door, starts the vacuum pump to extract the air in the box to form a vacuum negative pressure environment, and maintains the product under the vacuum negative pressure environment for a preset time for secondary curing.

2. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 1, characterized in that: The negative pressure level of the vacuum negative pressure environment is selected according to the equipment capacity to reduce the oxygen concentration in the box.

3. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 1, characterized in that: The preset time is 1 hour.

4. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 1, characterized in that: In step (3), the products are evenly placed on the turntable with gaps left between the products.

5. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 1, characterized in that: The anaerobic adhesive is an anaerobic adhesive used for bonding metal parts, and its curing requires an oxygen-free environment.

6. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 1, characterized in that: The vacuum box is a vacuum drying box.

7. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 6, characterized in that: The vacuum drying oven only forms a negative pressure environment by vacuuming during the secondary curing process, without applying additional heating temperature.

8. The bonding process of the loudspeaker magnetic steel and steel sheet according to claim 1, characterized in that: After the secondary curing is completed, the product is taken out and transferred to the next process.

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