Dies are tools that are specially designed to form a raw material into a new shape. The material is then completely cooled and hardened.
Most raw industrial materials that can be liquefied can also be extruded, and this is true for natural and synthetic rubber. A rubber extrusion can take the shape of a variety of industrial products ranging from weatherstripping and trim products to small grommets and large bumpers. Because demand for rubber extrusions varies from one industry to another, a rubber extruder employed by a company that services the heating and cooling industry will be configured differently from machinery that services the automotive industry.
Despite these differences, all extruders are similar in their design and process to a certain point. Rubber extruders, like all extrusion machinery, begin with a collection of raw material (stock) that is loaded into the machinery. The stock may or may not be preheated and is then passed through a conveyor channel. The stock is then plasticized and pressurized.
There is some variation of method and machinery design at this point in the extrusion process; plastic and rubber extrusion machines use a screw system to pressurize and move stock through the machine while extruders of other materials may use a ram. At this point, the stock is in a moldable state and can be passed through the die. Within the rubber extrusion industry, the dieing process varies from one factory floor to another. A die can be configured to make extrusions of any shape or size.
Some companies specialize in custom extrusions, so even within one factory with multiple extrusion lines, each piece of extrusion machinery could be equipped with a different die. In all extruders, though, the pressure created in the screw or ram cylinder forces the stock through the die where it takes its new shape. When it emerges from the die, it is cooled with air or water. The newly extruded rubber product can be shipped as is, or it can move on to further processing. It can be sheared down or cut to size, and it can be vulcanized, in which case the product would be cured with sulfur or another chemical that adds strength and durability to the product.