Rubber molding is a staple method used in the rubber industry to give rubber shape. In rubber molding, heat and pressure are applied to mold the rubber accurately into a desired shape. In recent times, 3D printing has also gained popularity as a manufacturing method, but it is still not as widely applied as rubber molding and has its limitations.
In this blog, we will examine in detail the various rubber molding methods used to design and manufacture rubber seals and how they differ from each other by the best China rubber seal manufacturer.
Rubber molding is a manufacturing method for creating a unique shape from raw material rubber according to specific dimensions and creating a final rubber component that is a part of complex machinery. In industry, three different types of rubber molding methods are used in making seals, which are
◉ Compression molding
◉ Transfer Molding
◉ Injection molding
The main principle of rubber molding remains the same in all three methods. All methods require the rubber to be heated and stuffed into a mold die where it takes the desired shape. During the molding process, the rubber is vulcanized. The vulcanization of rubber gives the rubber elastic qualities, allowing it to retain its molded shape even after stretching.
This molding technique involves filling the mold cavity with raw or unvulcanized rubber for vulcanization or curing. Harvey Firestone invented compression molding in the 1890s, making it the oldest of the molding methods.
◉ Raw rubber is mixed in batches of fixed mass.
◉ The raw rubber material is shaped as a finished product called a preform.
◉ Preforms are inserted into an open mold consisting of two identical halves.
◉ The mold is closed by closing the two halves.
◉ The rubber takes the mold shape and is vulcanized in this step by applying heat and pressure.
◉ Lastly, rubber is taken out of the mold by hand to reveal the final product.
◉ The manufacturing apparatus and tools are inexpensive.
◉ The processing time is brief.
◉ Compression molding does not lead to a high wastage of raw material.
◉ The technique is suitable for processing stiff rubber materials.
◉ Taking out the mold by hand slows down the lead time and pace of manufacturing.
◉ Performing rubber is an extra step that adds to process time, thus lowering manufacturing efficiency.
Compression molding is a molding technique suitable for prototyping and small-scale production. Hence, it is not the preferred technique for mass-producing molded seals and is only used for manufacturing a prototype design.
In transfer molding, a preform is put into the molding chamber. Then, the raw rubber is put into a cavity for curing. Similar to compression molding, this method consists of putting the ‘preform’ rubber material in the mold, except that the tooling methods are more sophisticated and the molds have a more intricate shape.
◉ Raw rubber is mixed in fixed-mass batches
◉ The perform is put into a pot placed in a molding chamber
◉ The preformed material is pumped into the part cavity by a plunger.
◉ The rubber takes the mold shape and is vulcanized through heat and pressure.
◉ The finished shape is taken out of the mold.
◉ Lead time is short as multiple cavities are used simultaneously.
◉ It requires a few forms that can fill hundreds of molding cavities.
◉ Dimensional tolerance is more precise
◉ Rubber components with custom colors are more easily produced.
◉ Higher precision in shapes.
◉ This technique leads to a lot of raw material waste.
◉ The main cause is that the remainder of the rubber is left in the pot after transfer and has to be discarded or recycled.
◉ Tooling costs more.
This molding method is preferable for creating parts with accurate dimensions for low-volume manufacturing. There is a greater diversity of finished products, and transfer molding is well-suited for bonding rubber to delicate metal parts, making rubber seals with composite materials, etc.
This is widely considered the most efficient way of rubber molding and consists of injecting molten polymer material under high temperature and pressure conditions into a closed mold cavity. This method was invented more recently in the 1960s
◉ Raw rubber is mixed in fixed mass batches.
◉ After mixing, the raw material is cut into strips of uniform dimensions, typically 1.25 inches wide and 0.375 inches thick.
◉ The strip is placed onto a screw on the injection molding machines. The screw refills the barrel with the required quantity of material.
◉ After filling, the mold is closed shut.
◉ The material in the barrel is injected into the mold cavity.
◉ Rubber is cured by subjecting it to heat and pressure.
◉ The finished product is demolded.
◉ High production rates
◉ It may be carried out using different rubber materials such as silicone, neoprene, nitrile, and EPDM
◉ Minimal waste
◉ Cycle and production time are other critical factors that are fast.
◉ Preforms are entirely eliminated from the process; therefore, the time and labor required to produce them are eliminated.
◉ Total eradication of the option for the operator to preforms.
◉ The injection screw heats the material before injecting it into the cavity, this reduces the viscosity of the material, and thus, it is injected into the cavity.
◉ Possible shortening of the cure time because the rubber is pre-heated.
◉ Chances of a shorter curing time due to heat that is introduced when the screw is being charged
◉ Setup is expensive, and changeover is costly
◉ Cannot adapt to low-volume production
Do not use rubber injection molding for prototyping because this will require the use of a mold, which has cost implications. Nevertheless, it suits large-scale rubber-finished products such as electronic parts, seals, gaskets, and consumer goods. Products made using injection molding are widely used in the aerospace, medical, and automobile industries.
When it comes to high-quality seals, durability is everything. Renjie offers rubber molded seal designs manufactured from cutting-edge molding techniques and premium raw materials, providing superb sealing in extreme temperatures and pressures. As a specialized China rubber seal supplier, we use advanced molding techniques to offer customized designs that fit any industry’s requirements. So, if you require top-quality seals, contact us to source the best quality.
In conclusion, rubber seals can be manufactured through three main molding methods. The most common processes are compression molding, transfer molding, and injection molding. All the methods have their benefits and should be used under some conditions. Compression molding is one of the most widely used methods for forming large-volume rubber seals. The transfer molding has added advantages in better defining the seal shape or contour. Last, injection molding is ideal for creating sophisticated seals with strict tolerance requirements. By understanding the above essential molding methods of rubber seals, one can decide which method to use depending on the seal application and size, etc.
