The Engineer’s 7-minute Guide to Rubber Molded Parts

A seal is either used to prevent two elements from coming apart or to prevent anything passing between them. Sealing can prevent water damage, water leakage, corrosion, deterioration from weather, and also provides an airtight barrier that can prevent the loss of air or heat. Seals are most often used any time you need to keep environmental conditions from two or more spaces from mixing.

Because of its resiliency, rubber is ideal for shock absorption in equipment that moves around a lot or that creates substantial vibration or noise. We have a great deal of experience solving for Noise, Vibration, and Harshness (HVH). Many of RPM’s vibration control products are specifically designed for applications that include electrical motors, diesel engines, fans and blowers, material handling equipment, compressors, measuring instruments, punch presses, lathes, and a variety of other industrial equipment.

This is the standard process for most rubber components on the market today. Molding produces rubber parts by pressing a block of rubber into a metal cavity. The rubber inside of the cavity is then exposed to heat, activating a chemical reaction. The three most common methods of molding are rubber injection molding, compression molding, and transfer molding.

Extrusion is much different than molding. Extruded parts are forced through a cross-section die while under pressure. Because these parts are often made with soft, unvulcanized rubber compounds, the resulting extruded rubber product is in a soft, pliable state. Finished extruded products typically need to be vulcanized, or hardened, before you can use them. Depending on the elastomer or application, we employ a number of different curing methods to make sure the extrusion will perform as intended.

For products that require the stability of metal but the flexibility of rubber, rubber-to-metal bonding is an excellent solution. This process involves a mold as well, but the mold has metal inserts that the rubber is bonded to during the molding process. A heat-activated adhesive is sprayed onto the metal parts before they are put into the mold. The resulting bond is often stronger than the elastomer itself! 

Standard parts tend to be the first choice for OEM designers and engineers. However, they may not always be the best fit for your design.

Many of our customers already have a design for their product drafted and ready to go. The problem is that - due to the complexity - it’s not always possible to use standard parts without compromising other aspects of a design. What if you could have exactly what you wanted without a significant increase in price? It’s possible with a custom solution.

You’re in the middle of a redesign. Feedback from your customers reveals more rattling than expected and sensors that keep breaking, all of which you need to fix, and fast.

Whether you used a rubber part in the previous design or not, consider using it now. Rubber components are best-in-class solutions for:

• Noise Dampening
• Vibration Isolation
• Sealing

Retrofitting a part into a design in production isn’t always as straightforward as during prototyping or New Product Introduction (NPI), but it can be done successfully. Here at RPM, our engineers work directly with you to review your specifications, requirements, and if we don’t have a standard rubber part to help solve the challenge, we build you one.

This is where the real fun begins. From autonomous off-road vehicles to the cutting-edge medical equipment, rubber molded parts allow you the freedom to design at will. Due to its elasticity, rubber can take virtually every shape. With wide ranges of durometer, compression sets, and heat aging - you have a material that will allow you to seal, dampen, or isolate notice, particulars, and motion.

Here at RPM, we’ve built a team of experts not just in the materials of rubber, but in the processes in which it becomes your part. We offer extrusion, injection molding, and rubber-to-metal bonding.

If you’re working on a design right now and are unsure of the best way to solve your noise, vibration, or sealing challenge, reach out to our team right away. We’re here to help.

99% of natural rubber is produced from a softwood tree native to Brazil. Most know this tree as “the rubber tree.” Latex, a milky liquid, is produced from the tree through a process known as “rubber tapping.” A spout is tapped into the tree trunk, and latex slowly seeps out into a bucket. This latex goes through a refinement process to remove the isoprene polymers that make up natural rubber. Then, this isoprene is typically vulcanized - heated in the presence of sulfur to improve its resilience, elasticity, and durability.

Natural rubber’s benefits include…

• A high resiliency rate - It’s able to return to its original state quickly. It can also withstand cutting, chipping, or tearing better than synthetic rubber.
• A high tensile strength - It stays strong when stretched out.
• Adhesiveness - It’s an excellent elastomer that’s able to bond to metal using our specially designed adhesives.

However, the pros come with some cons, as natural rubber doesn’t hold up as well as synthetic when exposed to light, UV rays, and heat. It’s also more difficult to produce than synthetic rubber. For these reasons, natural rubber is best used to solve vibration-related problems.

Synthetic rubber is an elastomer that has been artificially produced. It’s made in chemical plants by turning monomers into polymers. Monomers are byproducts of petroleum (gasoline) in the production process, meaning that most synthetic rubber is made through gas and oil production.

From a material standpoint, synthetic rubber is easier and more economical to produce. It’s also more malleable and shapeable, meaning you can use it for more applications. There are many different varieties of synthetic rubber. Each variety has its pros and cons. Below are the most popular ones that we typically use at RPM.

A recent trend that we’ve noticed has been the use of a 3D printer for prototyping rubber components. While we are big fans of innovation and often help our customers innovate their designs through custom molded rubber products, there are few things you should consider before deciding to use 3-D printing as your only prototyping.

The biggest factor is that while rapid, 3-D printing hasn’t yet evolved to include the elastomers that would make up your final part. A critical component of prototyping is to ensure that your part will function and fit as expected. You can ensure that you’ll end up with the best rubber molded parts by prototyping with the material you intend to use in the final production.

Unlike metals, molded rubber components offer a wide range of tolerances. Below are the most common known properties of rubber that have allowed it to become one of the most versatile materials in manufacturing:

• Durometer: Depending on the compound of the rubber used, you’ll have options for the durometer of your final part.
• Elasticity: Useful when being applied to an area of motion, the elasticity of rubber provides flexibility in your protection.
• Compression Set: Most applications of rubber parts must be able to withstand compression to some degree, selecting the right rubber allows you to spec that into your design.
• Heat Aging: If your final product will be exposed to varying temperatures, rubber’s heat aging properties allow for expansion and contraction, keeping your design’s integrity intact.

For more information, the ASTM has a complete resource section on the standards for rubber elastomers.