Our capabilities include:
Injection Molding • Transfer Molding • Compression Molding • Rubber Metal Bonding • Extrusion
RPM Engineering Corp. specializes in rubber manufacturing for several diverse industries, including the automotive industry.
RMP is ISO 9002; QS 9000 and PPAP III certified and is capable of meeting difficult project specifications.
Injection molding rubber was originally an extension from the plastics industry in the early to mid-1960s. After overcoming the initial issues of temperature (plastics is cooled when molding and rubber is heated) and pressure (rubber injection molding requires significantly more pressure per square inch of cavity surface), the process has become the most efficient way to mold rubber in most cases. Injection and injection-transfer molding start with more efficient material preparation. The material is mixed, typically in large batches, and then stripped immediately after being mixed, into continuous strips. This strip is fed into a screw which charges a barrel as needed with a pre-defined amount of material. When the mold is closed, the material in the barrel is injected into the mold cavities and cured.
Compression molding involves taking rubber compound or mixed raw material and making "pre-forms" that are in the shape of the end product. These shapes are then loaded, typically by hand, into an open mold. The mold is closed forcing the material to fill the mold cavity. After the rubber is cured then it is removed from the mold.
This is an automated operation that combines elements from both the compression molding and the injection molding processes. This combination has the good surface finish, dimensional stability, and mechanical properties obtained in compression molding and the high automation capability and low cost of injection molding. Transfer molding is a process where the amount of molding material is measured and inserted before the molding takes place. There is a secondary raw material step to prepare it into "pre-forms". These “pre-forms” are preheated and loaded into a chamber known as the pot. A plunger is then used to force the material from the pot through channels known as a sprue and runner system into the mold cavities. The mold remains closed as the material is inserted and is opened to release the part from the sprue and runner once the rubber cures. A plunger is raised up and the "transfer pad" material may be removed and thrown away. The transfer mold is opened and the part can be removed. The flash and the gate may need to be trimmed. The molds in both compression and transfer molding remain closed until the curing reaction within the material is complete. These types of molding are ideal for high production runs as they have short production cycles. Transfer molding, unlike compression molding, uses a closed mold so smaller tolerances and more intricate parts can be achieved.
Extrusion is a process used to create objects of a fixed, cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections and work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms finished parts with an excellent surface finish. The extrusion process can be done with the material hot or cold.
Rubber and Metal Bonding
Bonding rubber to metal to produce metal and rubber products involves gluing rubber to metal by way of various adhesives. A mold is also used to give the rubber a certain shape when the rubber is bonded to the metal. While steel was originally the most common metal to use, today aluminum bonding is popular because it saves on both cost and weight without compromising the product's quality or seal strength. Metal bonding is used to fabricate products for many different applications within the automotive, aerospace, construction, plumbing, electric, industrial machinery, vibration absorber and medical industries, as well as rubber roller manufacturers. Silicon bonding is mostly used to make surgical instrument handles as well as other products including rubber lined rollers, engine mounts, gaskets, reinforced tires, bearings, rubber lined tanks/pipes, conveyor belts, electrical cables and plugs. In the rubber metal bonding process there are three main components: the rubber material, the bonding agents and the metal substrate. Any type of rubber can be used, providing that the material can flow into the mold without developing a significant level of cross-linking and that the substances making up the rubber material will not bleed rapidly to the surface of the uncured stock. The bonding agents consist of solutions based on solvent or water, with a primer coat based on phenolic-style resins and a topcoat of polymers and other materials.