Molding problems manifest themselves in many ways, from visual defects like burn marks, to physical problems such as delamination. This category of defects covers that broad group not caused primarily by cooling or flow problems.
Air traps occur when converging flow fronts surround and trap a bubble of air.
A brittle molded part has a tendency to break or crack.
Burn marks are small, dark or black spots on the part's surface.
Cracking can cause part failure, a short part life and be visually unacceptable.
Delamination, sometimes referred to as lamination or layering, is a defect in which the surface of a molded part can be peeled off layer by layer.
Dimensional variation is characterized by the molded part dimension varying from batch to batch, or from shot to shot while the machine settings remain the same.
Discoloration is a color defect characterized by a molded part's color having changed from the original material color.
In most cases, excessive part weight is an undesirable molding characteristic.
Fish eyes are a surface defect that results from unmelted material being pushed with the melt stream into the cavity and appearing on the surface of a molded part.
Flashing occurs when a thin layer of material is forced out of the mold cavity at the parting line or ejector pins location.
A flow mark or halo, is a surface defect in which circular ripples or wavelets appear near the gate.
Jetting occurs when polymer melt is pushed at a high velocity through restrictive areas, such as the nozzle, runners, or gates; or into open, thicker areas, without forming contact with the mold wall.
A short shot is the incomplete filling of a mold cavity which results in the production of an incomplete part.
Sink marks and voids both result from localized shrinkage of the material at thick sections without sufficient compensation.
A weld or meld line on plastic parts can cause structural problems and/or be visibly unacceptable.