World Executives Digest| An Essential Guide to Silicone Mold Designing and Building |Silicone molding is the most well-known among the molding processes. It’s used in packaging, medical, electronics, and in the atomotive industries. The wide hardness range of silicone makes it perfect for injection molding. These industries have seen exponential growth in the use of silicone molding in the last few years including over-molding and the use of multi-materials.
This article will discuss why silicone is a preferred material in molding and the intricacies of silicone mold designing and building.
Why is Silicone a Popular Material?
Silicone is a material with many applications. It has many endearing properties that can benefit the finished product in mind.
The benefits of silicone include the following:
- It is an inert, tasteless, odorless, and stain-resistant material that is ideal for food and medical applications
- It has the thermal-resistance property
- High-resistance to oxidation and weathering
- Durable and highly flexible
- Can be combined with other materials to enhance properties
- Light stable and colorfast when mix with FL-color pastes
- Has great electrical qualities
Silicone is synthetic polymers that have an alternating Si-O backbone. When a catalyst is added, the silicone molecules will cross-link. An example of this is the platinum crystal silicones.
The difference between the silicone molding and thermoplastics is on its processing. In thermoplastics, the resin is heated in the barrel and injected into the cold mold. In silicone molding, the liquid needs to be cold down to 5 to 25 degrees and is injected into a heated mold.
Designing and Building the Silicone Mold
The design and production of the silicone mold are also different from tooling and thermoplastic as well. Although they have different tooling design, the shared commonality in optimizing the processing elements like pressure, time, and temperature.
The viscosity of silicone is the same as that of peanut butter. But once this material is injected into the valves and gets in contact with the heated surfaces of the mold, it’s viscosity will change into that of water.
One of the most difficult parts in designing the mold is creating the runnerless molding system or the cold deck. The role of the cold deck is to have the same distribution of the material in each of the cavities using the same hydraulic pressure and temperature profile. The design uses titanium spacers and insulation boards placed between the heated and cold plates. This is to compensate for the difference in temperature from the heated mold plates to the cooled plates.
Another design modification is the specially designed nozzles. It maintains the temperature differential between the two sections. The tip of this nozzle is made with non-heat conducting alloy. Its role is to maintain the diameters at the gate area.
The material flows equally through the gates and minimizes the heat transfer from the hot surfaces in the area. This helps eliminate the cross-linking of the silicone material. Choosing the gate valve as a runner system eliminates scrap runners or secondary trimmings.
The development of silicone has greatly helped the molding process to accommodate multi-materials in its applications. It has made the process has been the driving force behind the innovations in electronics, automotive, medical parts, and soft-touch applications.