About Rubber Molding and Rubber Molding Services Including: EPDM, Liquid Silicone Rubber, Natural Rubber, Rubber Diaphragms, Rubber Grommets, Rubber Seals, Rubber Washers, Rubber Sheets & Silicone Rubber.
Rubber molding and molded rubber products provide solutions for a range of sealing, shock absorption and flow control applications. Unlike
extruded rubber products, molded rubber parts can be molded with tight tolerances into fairly complex shapes, such as
rubber seals,
rubber grommets,
rubber diaphragms and rubber bellows. Rubber pads,
rubber sheets and rubber bumpers are very common molded rubber products used to protect and pad equipment, doors and rails;
rubber washers and rubber diaphragms are essential in sealing and controlling differential pressure in automotive and flow control applications. Vibration isolators, also known as shock mounts or vibration mounts, are used extensively in the automotive and transportation industries, among other equipment industries, to protect motorized, moving or noisy equipment from vibrating against other hard surfaces by acting as a cushion against potentially damaging shocks. Automotive, appliance control, lawn and garden, sporting goods, medical, electrical, government, recreational industries and many others rely on molded rubber products for critical sealing, flow control and shock absorption applications.
Molded rubber products are made from a wide variety of natural and synthetic uncured elastomers. An elastomer is any material with sufficient resilience or memory for returning to its original shape in response to pressure or distortions. Commonly used elastomers include
natural rubber, ethylene propylene (EPDM), viton, latex rubber,
silicone rubber, nitrile, styrene butadiene rubber (SBR), butyl and neoprene. Latex rubber is usually derived from natural rubber, or "gum rubber", and is highly flexible, tensile and relatively cost effective. Silicone can be molded as both a liquid or solid, and
liquid silicone rubber products are often injection molded and highly prized for their tight tolerances, fast production rate and high temperature resistance. SBR and nitrile are used for their petroleum hydrocarbon resistance, and EPDM for its ability to remain unaffected by ozone, sunlight and weathering. Butyl is water, alkali, steam and oxygenated solvent resistant. Rubber and elastomers can be derived from natural sources to produce latex and polyisoprene, although most modern rubbers are synthetic, produced through highly controlled chemical processes.
While there are variations in specific rubber molding methods, all rubber molding services use heat and pressure to form molded rubber products. The three most common methods in the rubber molding process are compression molding, injection molding and transfer molding. Each of these rubber molding methods is different, but all involve pouring liquid rubber material into a mold where the rubber molecules form cross-links by heat and/or pressure curing. Compression molding squeezes raw rubber material which has been placed within a heated mold cavity until excess material comes out as flash or sprue, at which time the mold is removed to set in open air. Transfer molding is similar to compression molding, except that the mixed resin is first placed in a heated transfer chamber until it is liquefied, then it is pressed into the heated mold by a plunger until a flash forms; rubber transfer molding is unique in its ability to mold other materials, such as strengthening fabric, within a rubber part. Injection molding is the latest advancement in rubber molding, producing high tolerance, highly repeatable parts with short production times.
Different molding processes carry different advantages and disadvantages. One disadvantage of compression and transfer molding is shrinkage, in which the rubber product reduces in size in the mold after cooling to room temperature. The amount of shrinkage is determined before production and accounted for appropriately in the size of the rubber mold. Another disadvantage of both compression and transfer molding is the trimming and finishing which is required to remove the excess rubber around the seams of the mold. Distortion after molding is a concern with all molded rubber parts, because rubber materials are flexible and become amorphous under raises in temperature. For this reason, rubber parts must be allowed to fully set after molding and must be properly cured; molded rubber parts going in to applications which demand high chemical resistance and/or heat resistance are usually vulcanized, a process which treats parts with high heat and sulfur curatives in order to link polymer molecules together, solidifying the rubber part.
Rubber Molding Types
- 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.
- is a process that compresses the rubber material in a mold under heat and pressure to achieve the desired shape.
- , or Ethylene-Propylene-Diene Monomer, an elastomer, is a type of synthetic rubber.
- 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.
- 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.
- Rubber diaphragms are flexible seals that are resistant to a variety of media at different pressures.
- are rubber rings inserted into a hole in sheet metal to protect cords or electrical wires from the abrasion.
- are used to prevent leakage at joints.
- are flat pieces of rubber used for a variety of purposes.
- refers to long, hollow cylinders used to transport liquids and 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.
- 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
- A rubber compound's
capability to withstand mechanically caused deterioration.
- A test made to replicate in a short period
of time the breakdown resulting from normal working conditions.
- A substance that increases the speed of vulcanization
when used in small quantities in conjunction with vulcanizing agents.
- A compound used to increase the effectiveness of an
accelerator, small amounts at a time.
- Tendency of rubber to cling or bond to any surface it
contacts.
- The continuance of vulcanization, even after the energy
source has been taken away.
- Depressions and marks on the surface of rubber, caused
by air trapped during the molding process.
- Uses steam under pressure to vulcanize rubber products.
- 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.
- The result of a mixing operation.
- Rubber compound that fills a mold.
- A discoloration of rubber, caused by a liquid or solid
migrating towards the surface.
- The necessary force to start the sliding between
a rubber seal and its mating surface.
- The development of a powdery residue on a rubber surface
as a result of surface breakdown.
- Small cracks on the surface of rubber, usually from
environmental damage.
- The permanent deformation of rubber after removing
the compression.
- Rubber that is able to conduct electricity.
- A chemical bond between polymer chains.
- The date of completion of the molding process for a
rubber product.
- Any of a variety of processes for waste edge removal
from molded rubber parts.
- The application of force used to evenly disperse various
compounds through rubber.
- An instrument that measures the hardness of rubber.
- Applying powder to rubber to prevent adhesion to something
else.
- A seal necessary for the prevention of leaks beyond
parts that are in relative motion.
- A characteristic of rubber, describing its tendency
to return to its initial shape after warping.
- Extension of rubber when exposed to stress.
- A machine that forces rubber through a hole that shapes
it into the finished product.
- The wearing out of elastomers after repeated
deformations.
- The flexing capability of a material with no
permanent deformation or breakage.
- Capability of uncured rubber to move in the mold and runner
system in the molding procedure.
- Rubber processed on a rubber mill
that has a much greater viscosity than liquid silicone rubber.
- The process of mechanical energy changing to heat
in rubber under strain.
- A material that rubber is chemically or physically bonded
to during the molding process.
- Slow recovery rate of rubber after stress.
- The softening of raw rubber by mechanical and atmospheric
forces.
- A chemical compound that is able to endure polymerization.
- A defect that occurs when the rubber does not completely
fill out the mold.
- A line on the surface of rubber resulting from where
the two halves of the mold met.
- A material that is used to quicken the softening of
rubber compounds under heat or mechanical action.
- An insoluble compound that gives rubber its color.
- The degree to which rubber will retain deformation.
- Chemical reaction in which one or more simple
materials are transformed into complex materials that have different
properties from the originals.
- A substance that is added to rubber to increase
its resistance to the harms of the vulcanization process.
- The result when rubber vulcanizes too quickly.
- Extra material that leaks from the mold as it closes.
- The term for the uniting of two parts of vulcanized rubber
to make a whole.
- A thermo-setting
reaction that involves the use of pressure and heat, and results in highly
increased elasticity and
strength of materials like rubber.