First, let us get to clearly know the process of rubber molding. This is a process that can produce a product that is usable. Normally, we find that the rubber products are made of rubber which is uncured or elastomers. An elastomer is any sort of material which has enough memory or resilience so that it can return to its original shape with distortions or pressure. These elastomers and rubber are derived from the natural sources even though they are synthetic produced through processes which are chemical in nature. This material rubber works ideally when you require a material to first expand and also return to its original shape.
How does rubber molding work
With rubber molding you get molded parts of rubber that are created by a block of rubber being pressed into a metal cavity that is used for rubber molding. A chemical reaction is activated by exposing the rubber to heat. You might find variations in different methods, but all manufacturers of rubber tend to use the pressure and heat method for the formation of rubber molded products. You find three most common methods used for rubber molding and these are compression molding, transfer molding and rubber injection molding.
The working of Compression Molding
The compression molding works out to be the simplest form of molding. These compression molds vary in shape, size and complexity and these also contain single cavity or probably even more. This process is simple because all that you need to do is place the uncured rubber preform, shaping it to an approximate configuration and size of the finished part which you desire, in the mold cavity before the closure of the mold. During this process the rubber is squeezed, or compressed between the bottom and the top plates. It needs to be made sure that the uncured preform weighs more than the finished product so that the air is driven out of the mold cavity during the closure of the mold. In case of the preform weighing less or even same you find air traps, voids or even non-fills might appear on the finished product. The excess rubber then flows into the flash groove or the overflow. There might be a requirement of almost four mold plates depending on the complexity and the part configuration. The final step is the rubber being vulcanized or cured using pressure and heat. You get the rubber product in accordance to your specifications.
Knowing how Injection molding works
In the Injection Molding you have the rubber being supplied to the injection machines nozzle and barrel assembly continuously. Here you use the rubber of high consistency that is known as ‘gum stock’. Using a device which is pressurized, ‘a stuffing box’ you supply the gum stock to the injection barrel. The heated mold is closed by the injection press with pressure being applied so that the mold remains closed during the curing and injection cycles. Then you have the screw injecting the rubber into the mold through the nozzle. The silicone rubber enters the mold cavities through a gate after travelling through a system of sprues and runners. It packs and fills the cavities to the desired shape. This Silicone Rubber is heated with the friction of the Runner, Screw, Gate and Sprue besides the heat. After completing the cure cycle the Silicone Rubber is removed.
The Transfer molding method
This transfer molding might also vary in complexity, shape and size and contains cavities which can be more than one. In this process the rubber is placed in a Transfer pot which is above the cavity area. It is pushed into the cavity area by the use of a Piston through a Gate, Sprue and Runner system. The rubber is cured using the pressure and heat system. This transfer molding works similar to the Injection Molding system as the rubber enters the cavity only after the mold is closed. A rubber product which is made using the transfer molding works out less expensive than any rubber part which is made using the compression molding system.
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