Rubber Molding

About Rubber Molding and Rubber Molding Services Including: EPDM, Foam Rubber, Liquid Silicone Rubber, Natural Rubber, Neoprene, Rubber Baseboard, Rubber Diaphragms, Rubber Grommets, Rubber Seals, Rubber Washers, Rubber Sheets & Silicone Rubber.

Rubber molding is the process of forming rubber materials into various shapes and parts through the use of both heat and pressure. Rubber molding is advantageous compared to rubber extrusion because rubber molding is able to form tighter tolerances and more complex shapes. As a result, rubber molded parts are often preferred for sealing, shock absorption and flow control applications. With a wide variety of rubber materials used in molding process, diverse industries utilize rubber molded products, including: automotive and transportation, in order to protect motorized, moving or noisy equipment from vibrating against other hard surfaces by acting as a cushion against potentially damaging shocks; industrial manufacturing, which uses rubber grommets, rubber washers, rubber diaphragms and other types of rubber seals to seal tubing for fluid transfer systems; sports and recreation, in which rubber sheets are used in protective equipment and padding for floors, walls and rails; and construction and architecture, for protective applications such as rubber baseboard, which is used to protect the joint created by a wall and the floor from hazards such as furniture, human contact and machinery. Some of the most common types of rubber materials used for molding processes include synthetic rubbers such as styrene, viton, EPDM, neoprene and silicone rubber, natural rubber, as well as various rubber states including liquids, such as liquid silicone rubber, and foam rubber.

One of the most common usages of rubber molded parts is for sealing applications. As a result, there are a variety of different molded rubber parts that work as seals, including washers, grommets and diaphragms. At their most basic, rubber seals are used to join two components in order to prevent leaks and to aid in compression. Thus rubber grommets, for instance, work in this capacity and yet they also function to reinforce a hole in one of the components, such as the end of a tube, or to shield another part from the sharp edges created by the hole. Rubber washers add another dimension, by primarily being used to support the weight of a threaded fastener, but also are also used in taps or valves to control the flow of liquids or gases. Lastly, rubber diaphragms are used as a barrier between two chambers and serve to transmit pressure between systems without exchanging media. Another common usage of molded rubber products is for protection, such as with rubber sheets and rubber baseboards. Used for a wide variety of applications, rubber sheets can also be extruded, but molding provides a better fit to the exact specifications. Rubber baseboards can also be extruded, but molding allows for a wider range of decorative options. When it comes to the material, natural rubber is used much less commonly than synthetic rubber materials. Extremely popular silicone rubber is most commonly molded in liquid form; neoprene, foam rubber and EPDM are also heated so that they are molded in a liquid state, or at least semi-solid state that increases malleability.

There are three main rubber molding processes: injection molding, compression molding and transfer molding. All of these molding processes incorporate the use of both heat and pressure in order to mold the raw rubber materials into a finished part. The injection molding process, while commonly used for plastics, is also a major force in the rubber molding industry. In order to begin injection molding rubber materials, first the raw rubber materials must be heated to a liquid state. Next, the heated rubber material is forced into the open cavity of a mold, which is then clamped shut. The rubber material is then cooled as water or other fluids circulate through the cooling system of the mold and extract the heat. The rubber is held in the mold under high pressure until the part solidifies; upon solidification, the part is ejected from the mold. The beginning of the compression molding process is very similar to injection molding; the raw rubber material is first preheated and then placed into an open, heated mold cavity. Once in the mold, the process begins to differ from injection molding in that the cavity is then closed by way of a top force, typically referred to as a plug member, and pressure is applied. The applied pressure forces the liquid rubber material into contact with every area of the mold cavity, maintaining both heat and pressure until the rubber has fully set. A combination of compression and injection molding, transfer molding is typically an automated process. In transfer molding, the raw rubber materials are first pre-heated in a separate chamber referred to as a pot, and then transferred to the mold cavity through a small hole, also known as a gate. Once in the mold cavity, extreme pressure is applied to the rubber until it is cured, after which it will be ejected from the mold.

There are a few rubber molding processes outside of the major three; including, blow molding and liquid injection molding (LIM), a process that is specific to liquid silicone rubber. Blow molding rubber is a similar process to injection molding rubber; however, blow molding uses expandable tubes and compressed air flow. To begin, in a hollow tube is placed between the two halves of a blow mold. The blow mold then closes, pinching off the bottom half of the tube, and air is injected into the top, forcing the raw rubber material outwards to the walls of the blow mold like balloon, which creates a hollow part. In the LIM process, two components of liquid silicone rubber are pumped through pipes and tubing in order to reach the vulcanization equipment, one of which contains the platinum-based catalyst. The two components are mixed in the static mixer into one very homogeneous material and then transferred to the cooled metering section of the machine. From the cooled metering section, the liquid silicone rubber compound is pushed through cooled sprue and runner systems into the heated cavity where vulcanization occurs. After vulcanization, the liquid silicon rubber is poured into an open mold, which contains a hollow cavity of the desired shape. The liquid silicone rubber is then allowed to solidify in the mold and is injected upon setting.

Rubber Molding and Rubber Molding Services Image Provided by Jet Rubber Company	Rubber Molding and Rubber Molding Services Image Provided by Timco Rubber Products, Inc.

Rubber Molding and Rubber Molding Services Images Provided by Fairchild Industries

Rubber Molding and Rubber Molding Services Image Provided by Rader Products, LLC

---

Rubber Molding Types

• Blow molding is a less-common process of placing a hollow tube between the two halves of a blow mold. The blow mold then closes, pinching off the bottom half of the tube, and air is injected into the top, forcing the material outwards to the walls of the blow mold.
  
• Compression molding is a process that compresses the rubber material in a mold under heat and pressure to achieve the desired shape.
• EPDM, or Ethylene-Propylene-Diene Monomer, an elastomer, is a type of synthetic rubber.
• Foam rubber is rubber that was manufactured with the addition of a foaming agent in order to create a flexible, air-filled substance.
• Injection molding involves melting rubber in an injection unit and then injecting it into the mold where it stays until after cooling when the finished product is ready.
• Liquid silicone rubber is the liquid form of a synthetic, two-component, elastomeric polymer that is made from silicone elastomers.
• Molded rubber is formed through pressing melted rubber into dies.
• Natural rubber is an elastic hydrocarbon polymer that was originally developed from a milky substance, known as latex, which can be found in the sap of some plants. 
• Neoprene is a brand name for a type of synthetic rubber that is also known as polychloroprene.
• Rubber baseboard is a molded rubber product used to cover the joint that is formed when a wall meets the floor.
• Rubber diaphragms are flexible seals that are resistant to a variety of media at different pressures.
• Rubber grommets are rubber rings inserted into a hole in sheet metal to protect cords or electrical wires from the abrasion.
• Rubber seals are used to prevent leakage at joints.
• Rubber sheets are flat pieces of rubber used for a variety of purposes.
• Rubber tubing refers to long, hollow cylinders used to transport liquids and gases.
• Rubber washers are primarily used to support the weight of a threaded fastener, but also are also used in taps or valves to control the flow of liquids or gases.
• Silicone rubber is a synthetic, two-component, elastomeric polymer that is made from silicone elastomers that can be cured at room temperature into a solid elastomer for use in molding; however, it is usually molded from a liquid form.
• Transfer molding involves building a "piston and cylinder"-like device in the mold and squirting the rubber into it through small holes. The mold is then closed and under hydraulic pressure the rubber or plastic is forced through a small hole into the cavity where it cures.

---

Rubber Molding Terms

Abrasion Resistance - A rubber compound's capability to withstand mechanically caused deterioration.
 
Accelerated Life Test - A test made to replicate in a short period of time the breakdown resulting from normal working conditions.
 
Accelerator - A substance that increases the speed of vulcanization when used in small quantities in conjunction with vulcanizing agents.
 
Activator - A compound used to increase the effectiveness of an accelerator, small amounts at a time.
 
Adhesion - Tendency of rubber to cling or bond to any surface it contacts.
 
Aftercure - The continuance of vulcanization, even after the energy source has been taken away.
 
Air Checks - Depressions and marks on the surface of rubber, caused by air trapped during the molding process.
 
Autoclave - Uses steam under pressure to vulcanize rubber products.
 
Backrind - A defect in the molding process, where the rubber near the parting line sinks below the surface and the parting line ends up ragged and torn.
 
Batch - The result of a mixing operation.
 
Blank - Rubber compound that fills a mold.
 
Bloom - A discoloration of rubber, caused by a liquid or solid migrating towards the surface.
 
Breakout Friction - The necessary force to start the sliding between a rubber seal and its mating surface.
 
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 - The permanent deformation of rubber after removing the compression.
 
Conducting Rubber - Rubber that is able to conduct electricity.
 
Crosslink - A chemical bond between polymer chains.
 
Cure Date - The date of completion of the molding process for a rubber product.
 
Deflashing - Any of a variety of processes for waste edge removal from molded rubber parts.
 
Dispersion - The application of force used to evenly disperse various compounds through rubber.
 
Durometer - An instrument that measures the hardness of rubber.
 
Dusting - Applying powder to rubber to prevent adhesion to something else.
 
Dynamic Seal - A seal necessary for the prevention of leaks beyond parts that are in relative motion.
 
Elasticity - A characteristic of rubber, describing its tendency to return to its initial shape after warping.
 
Elongation - Extension of rubber when exposed to stress.
 
Extruder - A machine that forces rubber through a hole that shapes it into the finished product.
 
Fatigue Breakdown - The wearing out of elastomers after repeated deformations.
 
Flexural Strength - The flexing capability of a material with no permanent deformation or breakage.
 
Flow - Capability of uncured rubber to move in the mold and runner system in the molding procedure.
 
High Consistency Rubber (HCR) - Rubber processed on a rubber mill that has a much greater viscosity than liquid silicone rubber.
 
Hysteresis - The process of mechanical energy changing to heat in rubber under strain.
 
Insert - A material that rubber is chemically or physically bonded to during the molding process.
 
Logy - Slow recovery rate of rubber after stress.
 
Mastication - The softening of raw rubber by mechanical and atmospheric forces.
 
Monomers - A chemical compound that is able to endure polymerization.
 
Non-Fill - A defect that occurs when the rubber does not completely fill out the mold.
 
Parting Line - A line on the surface of rubber resulting from where the two halves of the mold met.
 
Peptizer - A material that is used to quicken the softening of rubber compounds under heat or mechanical action.
 
Pigment - An insoluble compound that gives rubber its color.
 
Plasticity - The degree to which rubber will retain deformation.
 
Polymerization - Chemical reaction in which one or more simple materials are transformed into complex materials that have different properties from the originals.
 
Reinforcing Agent - A substance that is added to rubber to increase its resistance to the harms of the vulcanization process.
 
Scorch - The result when rubber vulcanizes too quickly.
 
Spew - Extra material that leaks from the mold as it closes.
 
Splice - The term for the uniting of two parts of vulcanized rubber to make a whole.
 
Vulcanization - A thermo-setting reaction that involves the use of pressure and heat, and results in highly increased elasticity and strength of materials like rubber.