Due to the poor distribution of pigment or filler, the color change of plastic or pigment is uneven on the surface of plastic parts. The causes of uneven color are different with different phenomena. The uneven distribution of pigment is mainly near the feed inlet. If the color of the whole part is uneven, it is caused by poor thermal stability of plastic. If the color of the welding part is uneven, it is related to the nature of pigment.
Especially in small batch production, due to the color matching between toner and color masterbatch, the color is uneven and the fee is seriously charged.
If it is mass production, if the granular material is used, there will be no color difference problem.
The size change of plastic parts is unstable mainly due to poor die strength, poor precision, unstable operation of injection machine and unstable forming conditions.
The main reason is that when the parts are taken manually, the forming cycle of each mold is inconsistent, resulting in unstable product size.
Residual gas in the plastic part due to excessive inflation or poor exhaust in the melt, and presents small volume or clusters of holes (note that it should be different from vacuum bubbles).
The main reason is that during mass production, the exhaust slot is blocked by material powder, resulting in insufficient exhaust, and bubbles or charring will occur inside or in part of the product.
Due to poor clamping, too large gap, too good plastic fluidity and too much feeding, the plastic parts extrude excess sheets along the edge.
Due to the low material temperature and the incompatibility between resin and attachments during the separation and confluence of molten materials, the fusion of molten materials is poor and obvious fine joint seams are generated along the surface or inside of plastic parts.
Because the melt does not flow neatly along the die surface to fill the cavity, but flows in a semi solidified wave shape on the cavity surface or the melt has stagnation.
Due to the strong filling effect and poor mold demoulding performance, it is difficult to demould the plastic parts, or the plastic parts are deformed and cracked after demoulding, or the residual direction of the plastic parts does not meet the design requirements.
Due to the mixing of different materials or low mold temperature, the shear effect of molten material flowing along the mold surface is too large, resulting in thin layer peeling and decline of physical properties.
Sometimes, if the nozzle material is added too much, it will also cause delamination and peeling, because the material has no physical properties.
Due to mechanical resistance in the gate sleeve, insufficient cooling or pull rod failure, the gate is stuck in the gate sleeve.
Because the cooling is not reached, the gate sticking die is caused.
Or the pulling force of the rear die of the rubber mouth is not enough.
Due to the poor contact between the melt and the mold surface, there are small pits on the surface of the plastic part, resulting in random radiation of light or plastic decomposition, foreign matters and impurities, or the mold surface is not bright, resulting in poor or uneven transparency of the transparent plastic.
Due to moisture or inflation in the material, too much volatile matter, excessive shear effect on the molten material, poor tightness between the molten material and the mold surface, or rapid cooling, mixing with different materials or decomposition and deterioration, silver white shiny needle stripes or mica flake spots appear on the surface of the plastic part along the material flow direction.
Internal stress caused by residual stress, shear stress, cooling stress and uneven shrinkage during forming; Due to poor demoulding, insufficient cooling, insufficient strength of plastic parts, mold deformation and other reasons, the plastic parts have the phenomena of shape distortion, uneven warpage or eccentric hole, uneven wall thickness and so on.
Due to excessive internal stress of plastic parts, poor demoulding, uneven cooling, poor plastic performance or poor design of plastic parts and other disadvantages (such as deformation), there are fine cracks on the surface of plastic parts and near the feed inlet, or cracks or no cracks under the action of load and solvent.
As the plastic decomposes or the combustible volatiles and air in the material decompose and burn under high temperature and high pressure, the combustibles are injected into the plastic cavity with the molten material, showing black spots and black stripes on the surface of the plastic part, or carbon burns along the surface of the plastic part.
It is mainly due to insufficient material supply, poor melt filling flow, excessive inflation and poor exhaust, resulting in dissatisfaction with the filling cavity, incomplete shape of plastic parts or dissatisfaction with the filling of individual cavities in case of multiple cavities.
It is mainly due to insufficient cooling time, or too fast ejection speed and unbalanced ejection force, resulting in thimble marks on the product surface.
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