Rubber Molding: 101

Rubber Molding: 101

April 21, 2022


Application and Design

Understanding the purpose of a seal or part is critical to getting it right the first time.  Seals have specific application requirements including the conditions like the temperature, pressure, and fluid compatibility.  It also includes things like size, part retention, sliding friction, seal cycling, and low closure force demands. 

Sealing Devices has solutions for each of these needs.  Whether it is a highly engineered press in seal or metal inserted over molded seals, we have many options.  We can produce everything from basic grommets to highly engineered press in place seals.  Sealing Devices can mold most elastomers to handle various fluids.  We can offer differing durometers for low closure force seals or high-pressure seals.  Understanding the design needs, allows us to help design in all the requirements.

Process Types

Sealing Devices has a dedicated team specifically for rubber molding.  They understand all the advantages of each type of molding process. 

  • Compression molding offers the easiest solution for prototyping and the lowest material waste.
  • Transfer Molding holds better tolerances and reduced parting lines.
  • Injection Molding is better for high production quantities and can dial in the amount of injection load better than other types.
  • Insert Molding is another offering where rubber is integrally molded directly to metal or other substrates. This often provides hard mounting locations and integrated compression stops to create a better seal.

Marrying the molding type with the design that meets all the function requirements gives us a solution that optimized the best product and the best process.  Long term, it provides process stability which results in cost and delivery dependability.

Mold Features

Every Mold has features to make the specific part needed.  Understanding the Seal and the manufacturing process allows us to incorporate these features in locations that are not critical to the seal or function of the part.  Here are common features and terms to understand for molds and molding processes:

Cavity: A machined pocket in a metal plate that fills with compound to form the outer geometry of the rubber part.

Compound: The raw material which includes raw rubber and fillers based on the desire material properties which is used to fill the cavity of the mold.

Core: A portion of a mold that presses into a cavity and the materials flows around to create inner part geometry.  Core pins are commonly used to make holes in a part as one example.

Cycle Time: The time to process one complete molding cycle from the start of one part to the start of the next part.

Flash: Commonly at a parting line, excessive unnecessary material that unintentionally flows between the two halves of the mold and attaches to the molded part.  Where excess flash exists, secondary operations are required for removal.

Gate Marks: Location where rubber is forced or injected into a tiny hole in the cavity.  The material is then broken or torn to remove the part from the mold.

Parting Line: Location on the part where the two halves of mold come together.  Some parts allow a rib of material when the two halves do not mate perfectly.

Platen Size: The size of the plate in the press which is the maximum size of the mold it can run.

Undercuts: Section of a mold that cannot be removed during mold separation without part deflection.  These should be avoided as they cause complex processing and increased cycle time.

 

Sealing Devices will do what we can to avoid placing mold features like parting lines and gate marks in critical sealing locations to provide optimal part design.  We review the clamping forces, platen sizes and clearance window to make sure we can process the part.  We review part undercuts and areas where mold inserts are necessary so we can optimize the best cost.

Having the knowledge of both Sealing and Molding, gives Sealing Devices an advantage that competitors that only focus on sealing or only focus on molding to not have. One of the greatest benefits Sealing Devices offers is our experience and knowledge in both Sealing and Rubber Molding.  Our engineers and technicians consider the importance of both the functional design requirements of the seal along with the ability to improve part manufacturability in the rubber molding process.  This experience gives us the capability to bring a functional product to your customer, while offering a solution that lasts down the road without major design changes.