Is there always a problem with silicone encapsulation? First, avoid these pitfalls

Silicone encapsulation - wrapping a layer of silicone on top of a metal or plastic frame - may not sound complicated, but those who have done it know that it is a process that is prone to tipping over.

Lack of glue, overflow of glue, delamination, bubbles... There are various problems, and the root cause is often not in the silicone itself, but in the process details that are not noticed. The following pitfalls are the most commonly encountered in rubber projects.

Pit 1: The surface of the embedded part is not treated properly

The first step in gluing is not to inject glue into the mold, but to treat the surface of the embedded parts (metal or plastic parts).

Silicone needs to be "glued" to the insert, not by glue, but by chemical bonding. The prerequisite for this bonding is that the surface of the insert is sufficiently clean and has a suitable roughness. Many factories directly inject glue into the embedded parts, resulting in them being torn off as soon as they are packaged.

The correct approach is to first clean and remove oil stains from the embedded parts, and then perform surface treatment (spraying primer or plasma treatment). The treated embedded parts should be used up within the specified time. If left for a long time, the surface activity will decrease and the bonding effect will also be compromised.

Pit 2: The mold design ignores the exhaust

When liquid silicone is injection molded, the adhesive material is liquid and air is pushed out during the process of entering the mold. If the exhaust design of the mold is not in place, air will be trapped in the corners, and after molding, it will become bubbles or lack of glue.

The position and size of the exhaust groove depend on the structure of the product. Sharp edges, deep grooves, and thin-walled areas are all places that are prone to trapping air. If these are not considered during mold design, it is difficult to save them later by adjusting parameters.

Pit 3: Unstable positioning of embedded parts

In the rubber mold, the embedded parts should be placed firmly. If there is a deviation in the position of the embedded part in the mold, the resulting product will either have asymmetric encapsulation, or the embedded part will be offset or even exposed.

Small inserts rely on positioning columns on the mold, while large inserts may require magnets or mechanical clamping. The positioning method should be selected according to the shape and weight of the embedded parts, not all embedded parts can be solved by a single column.

Pit 4: The mismatch between molding temperature and time

The vulcanization temperature of liquid silicone is generally between 160-190 ℃, and the time depends on the product wall thickness. The temperature is low, the vulcanization is insufficient, the product is soft, and the adhesion is poor; The temperature is too high, and if the insert is made of plastic, it may deform or even melt.

Metal inserts are fine, but special attention should be paid to plastic inserts - the selected plastic skeleton material must be able to withstand the vulcanization temperature of silicone. PA (nylon), PBT and other high-temperature resistant engineering plastics are usually not a problem, while ordinary ABS may not be.

Pit 5: Lack of process control during mass production

The sample was made very well, but it overturned as soon as it was released in bulk. This situation is too common.

The reason is often that during the sample stage, manual insertion and inspection of each component are carried out one by one. However, as the speed increases during the batch stage, surface treatment of the components is reduced, the placement position is not confirmed, and the primer is still in use after expiration

Batch production requires writing SOPs for each stage, with operators following the steps and clear standards and frequencies for quality inspection. This is not tedious, it's about saving one's life.

In conclusion

90% of the problems with silicone encapsulation overturning occur during the "preparation stage" rather than the "injection stage". Embedding treatment, mold exhaust, positioning method, temperature coordination - these should be carefully considered and determined before opening the mold.

If you are planning a rubber wrapping project, confirming these details with the OEM in advance can save a lot of rework and scrap in the later stage. The money that should be spent on the design phase is much more cost-effective than spending it on the trial production phase.