Rubber moulding is a process used to create rubber products using elastomers or untreated rubber.Both these materials are taken from their natural sources and then the process begins. Elastomer is widely used because it has elastic properties that allow it to return to its original shape when pressure is applied. Rubber moulding requires a block of rubber to be pressed into a mould cavity and then it is exposed to heat. Though there are variations in different rubber moulding methods, the pressure and heat applications are constants.
There are three main types of rubber mouldings such as compression, injection and transfer. Read this blog-post by our experts learn some interesting details.
Rubber Mouldings – The Three Types of Processes
- Compression Moulding
This is the simplest form of rubber moulding. A sheet of rubber is placed inside a mould cavity and is squeezed between the top and bottom plates. The manufacturers ensure that the uncured rubber weighs more than the finished product so that the air is driven out from the mould cavity during its closure. If its weight is the same or less than the finished product, then air-traps and voids will appear in the final product. After the mould cavity is pressed, the excess rubber will flow into the overflow which can be accumulated and used afterwards in another round. In the end,the rubber will be cured using heat to produce the end product based on its specifications.
Note- Manufacturers may use more than two mould plates based on the configuration and complexity of the raw material to achieve the desired finished product.
- Injection Moulding
This process is different from the previous method as the rubber is heated first by the mould and the friction of the runner, sprue, screw and gate. The runner is the distribution system within a mould connecting the sprue, the initial entry point of the rubber into the mould to the gate, the entry point of rubber into the mould cavity. The screw is the rotating component of an injection press. All these parts of the injection press work at the same time to produce a concrete end product.
This process requires higher consistency rubber-like Silicone, also known as ‘gum stock’. It is supplied to the injection moulding machine and nozzle constantly for continuous production. This is supplied to the injection barrel through a pressurized device called a ‘stuffing box’. The injection press closes the heated mould and pressure is applied to keep it close during the curing and injection cycle. Then, the screw injects the rubber through the nozzle into the mould. The silicone travels to the mould through a system of runners and sprues, enters the mould cavities through a gate or gates to finally take shape and complete its curing cycle.
- Transfer Moulding
This method is similar to injection moulding because the rubber enters the cavity after the mould is closed. In this process, the uncured rubber is not placed directly in the mould, unlike compression moulding. Instead, it is kept in a transfer pot that is located above the mould cavity. The rubber is pushed into the cavity by a piston through a sprue, runner and gate system of the press. The uncured rubber is then cured using both heat and pressure. The rubber that results from this method is less expensive than what is produced from compression moulds.
Each one of these processes has its own advantages and disadvantages when it comes to the final finished product. Hence, manufacturers like us choose a suitable process based on a product’s specifications.