What You Need to Know About the Cold Pot Molding Process

Injection Compression Press

Cold pot molding (sometimes called Injection Transfer) is a variation of the transfer molding process with a significant difference focusing on reducing rubber material waste. Unlike a traditional “hot pot” transfer mold in which the rubber material in the pot is vulcanized and discarded, the rubber material in the cold pot remains uncured.

With many unique benefits, this process produces highly accurate and successful rubber parts without extra waste. Here’s a closer look at what you need to know about cold pot molding:

Understanding the Cold Pot Process

 Cold pot molding utilizes a pot and plunger similar to a traditional hot pot transfer mold. However, in cold pot molding, the cold pot and plunger components are insulated from the heated mold and are water-jacketed to keep the rubber material at a controlled temperature– warm enough to allow the rubber to flow easily but cool enough to not vulcanize or cure.

The rubber material stays in an unvulcanized state inside the cold pot until the press is clamped.  The clamping action forces the material through a thin sheet of polyester fabric and then through the sprues directly beneath it. These sprues transfer the rubber material to the heated mold cavities where the rubber vulcanizes to the desired shape. Once the vulcanization process is complete, the press is opened, molded parts and sprues are removed and the cycle is repeated. 

Sustainability in Cold Pot Molding

The only rubber material wasted in the cold pot process can be found at the transfer sprue transition area between the insulated pot and the heated mold.  These vulcanized sprues attach to the polyester fabric weave during the clamping cycle. When the fabric is pulled away, it removes the sprues from the mold, leaving a clear transfer path for the next cycle. The fabric and sprues are then discarded.

The following images show the waste of a traditional hot pot transfer pad (approximately 15” diameter and .080 to .100” thick) compared to the waste of a cold pot consisting of a polyester fabric sheet with the attached sprues.

Hot Pot Waste:

Cold Pot Sprue1

Cold Pot Waste:

Cold Pot Sprue2

Key Benefits

Cold pot molding significantly reduces rubber material waste, making it an ideal process for complex parts using high-cost rubber compounds. The process also provides excellent flash control and accuracy during the molding process. 

Sustainability is a major benefit, which sets it apart from traditional transfer molding. Since less cured rubber materials are wasted, less products are sent to a landfill. Not only is cold pot molding an excellent method in creating accurate parts, it’s also better for the environment. 

Disadvantages to Watch out for

While there are many unique benefits of cold pot molding, there are also some disadvantages to be aware of. In this process, higher costs are associated with the molds as more complex and additional components are added. It also requires a special molding press to complete the process, which can be pricey to obtain. However, because this process promotes sustainability and reliable parts, purchasing this specific equipment may be the right choice for many manufacturers. 

Molding With Apple Rubber

Apple Rubber produces many different complex custom molded shapes with these configurations.  Typically, cold pot molding is ideal for lip or wiper seals and u-cups since they hold low flash on edges, making them sharp. We also can produce high-volume grommets with complex shapes quickly and efficiently. 



Complex Shapes:

complex shapes