Custom Rubber Manufacturing

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Minor Rubber has been providing Custom Molded, Extruded, and Fabricated solutions for more than 70 years to the Electronics, Transportation, Defense (DOD), Medical, Agriculture, Aircraft/Aerospace industries, as well as many others. Our experience in molding and extruding help us meet the most demanding requirements of our customers. Whether your requirements for custom rubber products are large or small, complex or simple, our team can assist in finding a solution that satisfies your needs. Our facilities are located in the United States and Asia, allowing us to offer you versatility in providing solutions that are cost effective as well as of superior quality. From prototyping, to small or large volume production needs, Minor Rubber offers a one-stop solution to all of your rubber requirements.

Molding

Minor Rubber produces custom molded parts from a variety of different materials, hardness’s, and colors to suit a customer’s specific application. In addition to our commercial grade materials, we specialize in compounds that meet or exceed the requirements of Military (MILSPEC), ASTM, SAE, ANSI, and FDA specifications. When necessary, we are able to develop a compound that is geared towards a customer’s specific application. To see a list of available compounds please go to our resource page.

Minor’s capabilities in the area of molding include compression, transfer, and injection. Each of these methods has advantages and disadvantages over the others. Below you will find a brief overview of each of these methods.

Compression Molding:

Compression molding is the most fundamental method for molding, its origins date back as early as the 1820’s. It is implemented by placing a piece of uncured rubber, of a predetermined weight and size, into the cavities of an open mold. The mold is then closed, as far as possible, and placed into a hydraulic molding press. Pressure from the press causes the uncured rubber to form into the shape of each cavity, and heat from the platens of the press causes a chemical reaction, known as cross linking, causing the rubber in the cavity to “cure”.

Our molding press capabilities for our compression line range from 12” x 12” on the low end, up to and including 85” x 108” on the high end, with various press sizes in between.

Advantages of compression molding

• Inexpensive tooling
• Less compound waste
• Good choice for large parts
• Good for low production quantities
• Good for high durometer parts

Disadvantages of Compression molding

• Longer loading and process time
• Labor intensive finishing
• Heavier flash resulting in possible quality / tolerance issues

 
Transfer Molding:

Transfer molding is an extension of compression molding, but utilizing methods similar to injection molding. It is utilized in applications involving higher production quantities than would be normal for compression molding. The major difference between compression and transfer is that the uncured rubber is placed in a “pot / ram” combination built into the top of the mold, and utilizing the closure of the molding press to force the uncured rubber through small holes (sprues) into the cavity(s). The balance of the process is the same as is found in compression molding.
Our molding press capabilities for transfer molding are the same as for the compression line. Please see compression molding above for press capabilities.

Advantages of Transfer molding

• Shorter production cycle then the compression method
• Compound preparation and tool loading time is reduced; individual cavities do not have to be loaded with uncured rubber
•  Product finishing time is reduced. Since the mold is closed before introduction of the uncured rubber, the part when removed from the mold will exhibit less flash
•  Transfer molds can be run in a conventional compression type molding press; no special equipment necessary.

Disadvantages of Transfer molding

• Tooling is more expensive than a compression mold
• More material waste due to excess left in the “pot” and the runner system.

Injection Molding:

Injection molding is accomplished in a molding press specifically designed for that purpose. The mold is closed and locked into place by the operation of the press itself. Uncured rubber is pre-heated in an injection chamber prior to being injected into the mold itself, which “plasticizes” it allowing it to flow more readily through the injection system and into the cavities. This, along with the clamping and injection force provided by the press, allows curing temperatures to be elevated, shortening the curing cycle. Our injection press capabilities range from 24” x 24” up to 48” x 72”, with tonnage (clamping force) of 100 to 500 tons. The clamping force of an injection press is what keeps the mold tightly closed during the injection and molding cycle.

Advantages of Injection molding

• Shorter production cycle than the other two methods due to higher clamping/injection pressure and curing temperature
• Higher production rate per hour than other methods results in lower unit cost
• High clamping pressure on mold results in parts having very little or no flash compared to other methods
• Parts may not need any additional finishing processes

Disadvantages of Injection molding

• Requires large production runs to be efficient.
• Tooling cost considerably higher than other methods
• Not all compounds, or durometers, are suitable for this process

Extruding:

Our 90,000 sq ft extruding facility located in the U.S.A. is capable of producing custom profiles, tubing, cut washers and gaskets, as well as vulcanized spliced gaskets, gaskets with injection molded corners and seals in an infinite variety of shapes and sizes. Extrusions can be supplied in long lengths on reels, in coils, or as cut lengths. Many profiles can be fabricated to have holes, notches, or special cut outs in them to suit a specific application. Sizes of extruded shapes we produce vary based on the configuration of the extruded profile. Tubing and Cord sizes range from 1/32” I.D. up to 7” O.D., and wall thicknesses as thin as .040”.

Profile shapes, on the other hand, can range from .125” square up to and including 8” square. Wall thicknesses on extruded profiles, like tubing, can be as thin as .040”, but will depend on the shape of the cross section. Thin wall tubing and profiles have a tendency to collapse during the curing process. To overcome this, we have the capability to mandrel cure tubing, as well as some profile shapes, or provide special curing forms to help a particular profile hold its shape during the curing process.

There is an additional cost associated with either of these processes, as they are somewhat labor intensive, but the final result is well worth the effort in those applications where the normal extrusion and curing process just won’t suffice. We also offer various means of curing our extruded tubing and profiles in order to provide you with options to suit a particular application. Below are the methods we employ, as well the maximum length of the finished product based on each of the curing processes described. Be aware that each of these processes has certain restrictions, which are based on the material and the quantity being produced; contact our sales group for additional information.

Microwave Curing:	Length available – Continuous
Steam Curing (autoclave):	Length available – 50ft to 100 ft depending on the size of cross section
Salt Bath Curing:	Length available - Continuous
HAV (hot air vulcanizing):	Length available - Continuous (silicone only)

All of our extruded profiles and tubing can be produced in a wide variety of materials, colors and hardness’s. Please see our resource page for a list of available materials.