Silicone Rubber Compression Moulding for Bellows

Silicone Compression Moulding, also known as Rubber Compression Moulding, Compressin Mold, Compression Mold Tooling , etc. Silicone Rubber Compression Moulding is the process of placing a given amount of uncured solid silicone rubber material into a mold cavity, which is then closed and heated. When the parts have cured, they are removed from the mold. Silicone Compression moulding has been used to mold silicone rubber parts since the beginning of the rubber manufacturing industry. It is one of the oldest methods still used to mold silicone rubber parts.

Silicone Rubber Compression Moulding for Bellows Pros

• Cost Economic: Silicone Compression molding for bellows is cost economic, and the compression molding process of bellows is quite simple when compared to injection molding.

• Minimum Tolerance: With the development of economy, we can minimum the tolerance at 0.02-0.1mm by using good steel material, good located pins, and good mold-making equipment.

• Allows for Insert: Compression molding allows for insert, fabric and encapsulating molding for prototypes with simpler handling and faster process development

• Allows for Various Material: Rubber Bellows Material are carefully selected materials to provide the best protection for your equipment. Molded Rubber Bellows are available in a several rubber materials including natural rubber (NR), chloroprene rubber (CR), EPDM or silicone rubber (Si), and in a large variety of shapes and sizes to suit your specific needs. 

Silicone Rubber Compression Molding for Bellows Cons

• Due to the limitation of mold structure & compression molding way, it is hard to achieve non-flash effect by located pins & mold-making equipment.

• Material Wasted due to the flash

• It is hard to achieve automation unless the product structure is quite simple & production volume is large. When flash (the resin that escapes between two parts) occurs, it must be manually trimmed, thus slowing down productivity. Additionally, you’re unable to regrind this excess material, which creates more waste.

Silicone Rubber Compression Molding Design

Simple parts, even ones with mild undercuts, can typically be de-molded from a two plate compression mold thanks to the high elongation percentage of silicone rubber. Parts with complex geometries often require a pick-apart compression mold that can be made up of as few as three different plates or actions, but may have as many as eight or more different plates. The plates and cores are assembled together to contain and form the silicone to mold the part. This can cause de-molding to be significantly longer when compared to the liquid injection molding process, where an action(s) would be used to remove the part. The pick-apart mold must have all of the plates unbolted and disassembled so that the silicone part can be removed.

• Two Plate: for Simple part designs typically only require a two plate mold, which includes a cavity side and a core side. After the material is loaded, the mold plates are assembled and inserted into a compression molding press between the two platens. Next the press is clamped to a set pressure to produce high quality parts. Heat and pressure are applied for a given amount of time allowing the silicone to spread throughout the mold cavity and cure. Then pressure is released from the press, which then opens the mold when the molding process is OK, then remove the silicone parts by hand. This completes a normal compression molding cycle for a simple silicone part design.

• Three Plate: For part designs with hole or undercuts, it will require to add a middle plate, like silicone grommet, rubber grommet, etc. 2 plate mold tools consist of one parting plane and mold splits in two halves. Whereas three plate mold consist of two parting planes and mold splits in three sections as the followed picture shows: Being a tool of increased complexity, the three-plate mould is, therefore, more time-consuming and expensive to manufacture than its two-plate cousin.

Compression Molding Bellows Production Notes

Some problems which may appear during production Process:

1. Flashing is too big: to solve this problem, we need to pay attention to 3 points when production; the first one is mold-design, second one is workers' skill about removing flash, and the production technology is also very important, if molding pressure is not enough, will also make the flash hard to be removed. 

2. Mold misalignment & uneven wall: this problem mainly caused by mold tool, like mold-making precision, misalignment of upper mold and down mold, datum angle & the 4 located pins are not accurate enough.

3. Lip cracking: the situation is relative to raw materials hardness & durometer, products' structure, and die-cutting tool.

4. Lack of Material

Custom Rubber Bellows Shape

• Rubber Bellows Shapes

• Single & Multi Convoluted Bellows

• Tapered Bellows

• Straight & Axial Bellows

• Square Rubber Bellows

• Rectangular Rubber Bellows

• With or Without Flanged Bellows

• Overmolded or not with Metal or Plastic Hooks

Custom Rubber Bellows Application

                 Miniature Rubber Bellows                              Tapered Rubber Bellows

           Rubber Flange  Bellows                                          Square Rubber Bellows