Rubber Molding

The process of rubber molding has been in existence for decades. Machines and molds are used to form such items as gaskets, wiper blades, bumpers, tubing, and even diving suits. Uncured rubber or elastomer material is transformed by using intense heat and high pressure. The end result typically will have high-tensile strength with varying degrees of rigidity or flexibility.

The History of Rubber Molding

The first commercial rubber products were produced in a home oven in the late 1800s. Since that time, the process has changed little. Larger, more precise machinery is in use today with robotic, programmable, and manual operations. The process, regardless of method, requires vulcanization—the thermal reaction of heat and pressure to create a solid structure that will maintain its shape under many different conditions.

The Importance of Rubber Molding

Finished rubber goods are everywhere and all must undergo the molding process before becoming usable to the consumer or in industry. In today's marketplace, hybrid machining processes also include the bonding of rubber to metal or plastics as opposed to aftermarket coupling. This has greatly increased the range of goods available for scientific, medical, residential, and commercial applications.

Compression Molding

An industry standard, the compression molding process involves placing uncured rubber inside a mold, which is then closed. Over time, and with heat and pressure, the rubber cures, or vulcanizes. This process is usually recommended for larger parts in short runs. The two-part molds are inexpensive and there is little excess compound, which is an asset when using higher-priced material. A drawback is that trimming or smoothing of seams (known as “flash”) is often required. Labor is intensive to achieve the finished product. It is also difficult to produce a precise and consistent product.

Transfer Molding

In this process, the raw rubber is injected under pressure from a holding chamber into the mold through a small opening (called the “gate”). Both the gate point-of-contact and any “flash” will require trimming. This process is recommended for a wide range of parts, including metal-to-rubber bonds. It has a higher rate of consistency and requires less time for curing. Also, more complex parts can be produced. Molds and labor are both typically higher. There is greater waste as the compound left behind in the gate and holding chamber must be discarded or recycled.

Liquid Injection Molding

In this process, the rubber is mixed and then cut into strips that are fed through a screw-type injector directly into the mold. The injection unit heats and liquefies the raw rubber, which in turn eases the flow into the cavity. The efficiency of the stripping method eliminates the need to weigh out pre-formed rubber to fit a mold or holding pot.