In the secondary encapsulation process, how to ensure that the bonding strength meets the requirements of the power tool housing from a process perspective?

In the secondary encapsulation process of the power tool housing, the selection of materials and the adjustment of formulas are the key links to ensure the bonding strength. For TPE materials, their compatibility with the reinforced nylon substrate can be improved by modification. For example, the introduction of specific grafts or elastomers in the TPE formula can increase the polarity of TPE and make it better integrated with the nylon substrate. At the same time, adding an appropriate amount of compatibilizer can further improve the interface compatibility between the two and reduce the generation of interface defects.

In addition, the hardness selection of TPE soft glue is also very important. The appropriate hardness range can better adapt to the encapsulation requirements and ensure close fit with the nylon substrate during the encapsulation process, thereby improving the bonding strength. In addition, the use of primers is also an effective means to improve the bonding strength. Primers can form a strong bonding layer between the nylon substrate and the TPE soft glue through mechanisms such as molecular penetration, chemical bonding and interface optimization. Before applying the primer, the surface of the nylon substrate needs to be thoroughly cleaned to remove oil and mold release agent residues to ensure that the primer can fully play its role. When applying the primer, the coating thickness needs to be controlled and it needs to be completely dried by a suitable drying method to prepare for the subsequent TPE injection molding.

The reasonable setting of process parameters plays a decisive role in ensuring the bonding strength. In terms of temperature control, appropriately increasing the injection temperature of TPE can enhance its fluidity, so that it can be fully melted and evenly coated on the surface of nylon parts during the injection process. This not only ensures that TPE is in full contact with the nylon substrate, but also reduces the problem of weak encapsulation caused by insufficient temperature. At the same time, the setting of injection speed and pressure should also be cautious.

Reasonable injection speed and pressure can ensure that TPE flows smoothly in the mold and avoid material decomposition or product defects. If the injection speed is too fast or the pressure is too high, the material may decompose under high temperature and high pressure, resulting in defects such as bubbles and cracks, thereby affecting the bonding strength. Therefore, during the production process, it is necessary to continuously adjust and optimize the process parameters according to the actual situation to achieve the best bonding effect.

In terms of runner design, the flow characteristics of TPE should be fully considered, and the runner structure of the mold should be improved to ensure that TPE can flow evenly in the mold. Increasing the number of glue inlets and adopting a multi-point glue feeding method can make TPE fill various parts of the mold more quickly and evenly, thereby improving the firmness of the glue coating. In addition, the design of the clamping force and the exhaust groove should not be ignored. Increasing the clamping force in the glue coating area can effectively prevent the mold from loosening during the injection molding process and ensure that the TPE and the nylon substrate are tightly combined under high pressure. A reasonable exhaust groove design can avoid the occurrence of air entrapment and prevent interface defects caused by air entrapment, thereby ensuring the bonding strength.