Short mouldings The causes of short mouldings are many and varied and are sometimes difficult to diagnose. It is，for example, perfectly easy to flash a mould and still obtain a short moulding. On the basis that the same property，too low…
Flow marks Material entering a mould always follows an almost identical path with successive mouldings. From a sprue gate into a flat plate it forms a spreading disc pattern. From a side gate of proper design into a flat plate,…
Flash The escape of a thin web of material at parting lines,around ejector pins or at other parts of the mould，can be caused in several ways. It could be the material，the machine, the mould, or the process that is at…
Cracking or Crazing This fault occurs only when there is residual stress in a moulding which may be affected by an aggressive environment. The term ‘aggressive，may be considered a misnomer for such environments as a low concentration of ozone in…
Burn marks What is Burn Marks If an area of a moulding becomes the oxidized, discolored, or blackened, the first thing to do is to examine the venting of the mould. Air trapped in the mould is heated to a…
Undercuts An undercut is a part of the mould where the molten plastic flows behind a retaining section thereby preventing the hardened plastic moulding from being easily ejected. Undercuts, in general, require moulds with moving parts to allow the product…
Internal stress and warping When thick sections are moulded，rapid changes in temperature can cause thermally induced stresses due to differential expansion. If surface layers cool faster than the interior through poor conduction, the contraction of the surface will be greater…
Sinking The moulding of thermoplastics in thick sections presents other shrinkage problems, especially where mould shrinkage is high (e.g. highly crystalline materials). In a thick section of an injection moulded product，for example, the outside layers in contact with the cold…
Effects and Influence of Mould Design upon Maintenance It is an unquestioned truism that mould maintenance, in reality, originates in the design department when the core features of the mould mechanism are worked out.Moreover, they, in turn, are reflected in the manner…
The correct kind of maintenance for plastic moulds is one which certainly involves much more than is embraced in the all-too-customary practice of a merely perfunctory examination of the tool upon its removal from the production stage, with the almost…