In the manufacturing of plastic parts using injection moulding process, a myriad of parameters must be established and controlled. The parameters include temperature, time and pressure. While all the parameters are vital to the production of high-quality plastic moulded parts, the pressure is the most different attribute during the injection moulding process. Therefore, it is necessary to understand everything to do with injection moulding pressure. Unfortunately, most small-scale plastic products manufacturers get into the industry knowing only one type of pressure, that is, injection pressure. This article highlights the different kinds of pressures that are associated with plastic moulding.
Holding Pressure -- Once molten plastic is injected into a mould, it is vital to fill the mould, and this is achieved by dropping the machine that holds the pressure which exists inside of the dies. The holding pressure helps to pack the plastic molecules tightly in such a way that every cavity within the mould is filled. The machine is supposed to hold the pressure until the injection gate freezes, and in most instances, this usually takes about four seconds. Once this time lapses, holding pressure no longer has any effect on the plastic molecules. Therefore, it is crucial for the holding pressure to be released in good time. If you release the pressure earlier than necessary, then you will end up with semi-molten plastic that will be sucked out of the cavity. Consequently, it will lead to uneven cooling and low-quality plastic products.
Clamp Pressure -- When injecting molten plastic into a mould, it is necessary to keep one end of the mould closed so that it doesn't give way to the injection pressure. It is achieved by clamp pressure, and, as the name suggests, the pressure helps to clamp the moulds tightly together. However, the amount of clamp pressure required depends on the flow difficulty level of the plastic. For instance, if you are dealing with a plastic material that flows smoothly, then the injection pressure required is low. Consequently, you need less clamp pressure to keep the mould tightly closed. On the other hand, if the molten plastic has a stiffer flow, then a higher clamp pressure is necessary to accommodate a higher injection pressure.
Back Pressure -- It is the pressure that is created as the screw returns after injecting molten plastic into a mould cavity. Once plastic pellets are placed on the front end of the screw, and the screw is turned backward, a build-up of pressure occurs on the front part. Back pressure ensures excellent colour and additive, blending thus producing plastic parts with vivid colours. It also helps to remove small amounts of trapped air inside the molten plastic before the air reaches the mould and compromise the plastic part's quality.
Talk with a plastic moulding manufacture facility about the plastic items you need.