Rubber Extrusions

Since the 19th century, natural and synthetic rubber products have come to be employed in countless industrial, commercial, and consumer contexts. Although different rubber processing methods exist, extruded rubber remains a popular choice for many manufacturers because of its strength, uniformity and customizability. Rubber extruders can form extruded shapes of any size; the modularity of this manufacturing method opened the door to a long list of industrial products that are now indispensable. Weatherstripping, rubber trim and extruded rubber seals have become essential for effective climate and moisture control. Rubber sheeting enjoys an almost universal presence in the entrance to many homes and businesses as textured floor matting. Rubber bumpers, bushings, grommets and connectors all contribute to effective, efficient and safe workplaces, vehicles and homes. For every other context in which a rubber product is needed, rubber extruders can produce custom rubber profiles to meet unusual or unique needs.

Extruded rubber performs under most conceivable circumstances; from space shuttles to submarines and from cars to bicycles, rubber extrusions connect tubing, insulate electronics and erase mistakes on paper. In homes, rubber trim can be found lining baseboards, protecting paint and wallpaper from damage. Rubber mats can be placed under rugs to protect hard floor surfaces and prevent injury from slipping. Rubber grommets line the openings in sheet-metal power strips, protecting the cords from wear and the consumer from the risk of shock. Rubber sealants keep bathroom fixtures watertight and kitchens water-efficient. Weatherstripping has become increasingly important for commercial and residential builders with an interest in maintaining energy-efficiency. In industrial contexts, rubber rods, rollers and sheets absorb vibration and noise from machinery with moving parts. Rubber bushings make vehicle suspension systems effective, and rubber bumpers protect freight trucks and loading docks. A rubber extruder's production is limited only by its designer's creativity; as long as an extruder has a hopper, conveyance channel, a die and the raw material, it can make almost any shape.

During the rubber extrusion process, raw rubber material (or stock) is processed through a screw extruding machine. A rubber extruder is made up of two main parts: a heated shearing screw conveyor and a die through which the plasticized and pressurized rubber is squeezed. A shearing screw conveyor is as its name suggests: a conveyor and a screw. The screw is positioned parallel to the conveyor. As the screw turns, it pushes the plastic material while it becomes heated in the conveyor channel. A die is not at all like its ambiguous name suggests; it is the tool that will give the rubber its shape. In advance of the actual extrusion process, an engineer will design a die, either according to the specifications of his project or those of his customers (as is the case when custom extruded profiles are made), and install it in the extruder. The stock is deposited in a hopper, which is a container suspended above the conveyor. When the process begins, gravity sends the stock through the bottom of the hopper onto the conveyor (pre-heating of the stock is optional, depending on the precision of the die and the desired qualities of strength). It is softened through heating and shearing, and pressurized by the rotation of the screw. The pressure pushes the rubber through the die, which is located at the end of the extruder. The rubber then emerges from the extruder in a profile that matches the shape of die shape.

The qualities of the finished product will depend on the extrusion process and on the qualities of the raw rubber stock. Rubber exists in many forms, each with its own set of unique properties. Natural rubber, also called "gum rubber," has excellent abrasion and acid resistance, while synthetic rubbers such as silicone and viton have excellent heat resistance, chemical resistance and weathering. Silicone extrusions are particularly attractive to customers in the healthcare and food service industry because of their heat-resistance and chemical inertness. Neoprene also features good heat-resistance, nitrile rubber is resistant to oils and butyl has low air permeability and performs as an excellent sealant for that reason. Properties like tensile strength, hardness, aging, flexibility, permeability and speed of recovery from deflection will vary in different materials. Rubber extrusions often compete with plastic extrusions for some sealing and gasketing applications. Rubber extrusions are usually slightly more expensive than plastic extrusions, but rubber's qualities of resilience, flexibility and impermeability make rubber extrusions the obvious choice for most sealing applications.


 

Image Provided by Timco Rubber Products, Inc.	Image Provided by Fairchild Industries

Rubber Extrusion Types

• Co-extrusion is a variation of the basic extrusion process, where two separate extruders connect to a single die and two or more separate batches of rubber material are mixed by separate screws, and then fed into the die at the same time. This allows for the convergence of rubber materials that contain different properties like color and consistency.
  
• Cold feed extrusion involves performing the extrusion process without pre-heating. This is best suited to produce profiles, hoses, cable and sheaths.
• Extruded rubber seals are products that are used to seal or fill gaps, insulate surfaces or spaces from water or atmospheric conditions and protect surfaces from corrosion.
• Extruded rubber is rubber that has been melted and forced into a die.
• Hot feed extrusion involves pre-heating the rubber material before performing the extrusion process.
  
• Pin barrel extruders have a special design with many pins protruding from the cylinder wall toward the screw's center that enhance the mixing and dispersing of the rubber as it is kneaded between the screws and the cylinder. This method can be applied to many rubber compound formulations for diverse applications.
  
• Rubber bumper products serve as shock absorbers in consumer and commercial contexts. They also absorb vibration and noise caused by moving parts in industrial machinery.
• Rubber bushings are placed between moving parts to absorb vibration; they have uses in vehicle suspension systems, manufacturing machinery and more.
• Rubber connectors are extruded rubber products that join the ends of tubes or pipes together.
• Rubber extruders are machines that mold raw rubber material into usable products with heat, pressure and a die.
• Rubber grommet products are rubber rings inserted into an opening in sheet metal to protect cords or electrical wires from abrasion.
• Rubber profiles are extruded rubber products in any shape or form.
• Rubber sheet products are used for a variety of purposes including matting, lining, floor covering and stair treads.
• Rubber trim is a long, thin piece of extruded rubber that can be used in many applications. 
• Silicone extrusions are extruded rubber products that are processed from raw silica stock.
• Vented extruders have screws of an original and unique design. This type is easy to maintain and occupies very little floor space.
• Weatherstripping is used to insulate a building to make heating and cooling more efficient.

Rubber Extrusion Terms

Accelerator - A substance that quickens the pace of vulcanization and lowers the operating temperature required during the process.
 
Adhesion - Term for the bond between a rubber surface and a non-rubber surface.

Air Curing - Vulcanizing a rubber product in the air instead of in a press or steam vulcanizer.
 
Atmospheric Cracking - Crevices that form on rubber surfaces due to exposure to environmental conditions, such as temperature extremes and precipitation.
 
Atmospheric Pressure - The amount of force the atmosphere exerts upon the earth's surface, measuring 14.7 psi at sea level.
 
Chalking - The development of a powdery residue on a rubber surface as a result of surface breakdown.
 
Checking - Small cracks on the surface of rubber, usually from environmental damage.
 
Compression Set - A measurement of a rubber material's return to its initial shape after deformation.
 
Creep - Deformation on a rubber surface due to the application of stress.
 
Die Swell - The incidence of swelling that occurs after the extruded profile comes out of the die. The rubber product's properties determine the amount of swelling that will occur.
 
Drift - A change in a rubber material's hardness over time.
 
Durometer - An apparatus used for measuring the hardness of rubber.
 
Dusting - Applying powder to rubber to prevent adhesion to something else.
 
Elasticity - A characteristic of rubber, describing its tendency to return to its initial shape after warping.
 
Elastomer - A material capable of returning to its initial length after being stretched at room temperature to twice its original length.
 
Elongation - An increase in length after the application of stress. This occurs during stretching.
 
Flex Test - A laboratory test that measures a rubber material's resistance to bending deformation.

Friction - The resistance to motion when different surfaces are in contact.
 
Hysteresis - Energy loss in the form of heat that results from the deformation of elastomeric material, caused by the application of stress.
 
Mastication - The softening of raw rubber by mechanical and atmospheric forces.
 
Memory - The extent of a rubber material's ability to resume its original shape after deformation.
 
Modulus - The amount of stress required to create a certain amount of elongation.
 
Optimum Cure - The point during vulcanization at which rubber material attains the intended properties.
 
Plasticity - The degree to which rubber will retain deformation.
 
Psi - Pounds per square inch. This measurement indicates pressure level.
 
Resilience - The comparison of the amount of energy needed to create an elastic deformation, and the amount of energy needed to recover from such a deformation.
 
Tensile Strength - The maximum amount of stress that may be applied to rubber before breaking occurs.
 
Vulcanization - The process of increasing the strength and elasticity of rubber materials through the application of heat and pressure.