The majority of design engineers have little experience with rubber and aren’t sure how to select the rubber best suited for their applications, especially since there are so many options. This is why many designers turn to companies that specialize in rubber compounding for guidance. Many people consider rubber compounding both an art and a science because the base polymer is highly customizable. Here is a simple, high-level overview of compounding:
There are 5 main ingredients in a rubber compound formula and each are measured in parts per hundred (phr):
- Processing Aid
- Curing System
To start a rubber compound, you must select an elastomer. When selecting an elastomer, it’s important to know what substances the finished rubber component may come into contact with (e.g., oils, ozone, etc.) because some elastomers have properties better suited for certain applications than others. It is also important to understand the overall intended application and desired physical properties. For example, if you need a rubber component that has excellent recovery, you might select a natural or synthetic polyisoprene as your base elastomer.
Next, fillers need to be chosen and, again, this will vary depending on what the desired properties of the finished rubber component are. The most common fillers are carbon black, amorphous silica and clay. So, if a designer identified that their end product needed to have high abrasion resistance, there would be specific fillers added into the formula to help achieve that property. It’s also important to note that there is no rubber compound formula that will give you all of the ‘ideal’ properties at the same time. One property will have to be compromised in order for another to be made prominent.