All plastic injection moulding presses are classified based on the tonnage, or more specifically, the clamping pressure or force they can exert. At Skar, we have more than 30 injection presses which can exert a range of pressures of between 25 and 450 tons.
A machine rated for 25 tons can exert 25 tons of clamping force on the mould during the injection process and so on.
It is important that the right press is selected because the wrong choice could impact on the quality of the item being made. An incorrect force can also cause flashing where excess material appears on the edge of the item being formed.
Factors that will affect the clamp force required include the size of the part being formed and the type of polymer being used.
The viscosity of the polymer will have an impact. The thicker the material the greater the injection pressure that will be required, and so the greater the clamp force needed to keep the mould closed.
Every plastic compound has a Melt Flow Index (MFI), which is a measure of the ease of flow of its melt. Each thermoplastic polymer will react differently to pressure depending on its MFI. The higher the MFI, the higher the pressure needed.
The size of the part is also key. Typically, the clamp force that is required can be calculated by taking the area in square inches of the item to be manufactured and multiplying it by a factor of between two and eight depending on the flow of the material being used.
For further enquiries or more detailed information please call us on 01473 828000 or email us at sales@skar.co.uk