The Causes and Solutions of Mold Fouling
The Causes and Solutions of Mold Fouling
1. Causes of mold fouling
Mold fouling occurs during injection molding of almost all thermoplastics. When the functional requirements of the product must be mixed with related additives (such as modifiers, fire retardants, etc.), these additives are likely to remain on the surface of the mold cavity during the molding process, leading to the formation of mold scale.
There are other reasons for the formation of mold scale. The common ones are as follows:
- Thermal decomposition products of plastic resins
- Extreme shear force of the injection molding machine screw during injection molding
- Inappropriate gas-exhaust
2. Solutions of mold fouling
The cause of the mold fouling is complicated. It is more easy for us to strengthen the maintenance than find out its cause.
Mold deposits on the mold surface are easier to remove at the initial stage. Therefore, mold cavities and gas-exhaust channels must be cleaned and maintained regularly (for example, after each batch of molding production). If the mold is not maintained for a long time, it is very difficult and time-consuming to remove the mold deposits after the mold has formed a thick layer.
The sprays used for the maintenance of injection molds mainly include: release agent, anti-rust agent, thimble oil, glue stain remover, mold cleaning agent, etc.
The chemical composition of mold deposits is very complex. So we must try the new methods and try to remove it, such as general solvents and various special solvents, oven sprays, and caffeinated lemonade. Another peculiar way is to use rubber for cleaning model tracks.
When using hot runner molding and heat-sensitive raw materials, the melt residence time will be longer. Thereby increasing the risk of raw materials decomposing and forming mold scale. Then, we must clean the screw of the injection molding machine.
Larger runners and gates are used when forming shear-sensitive materials. Multi-point gates can reduce the runner distance, lower the injection speed, and reduce the risk of mold fouling.
Efficient mold air-exhaust can reduce the possibility of mold fouling. Set appropriate mold exhaust during the mold design stage. An automatic exhaust system or the exhaust methods that can easily remove mold deposits will be the best choices. The improvement of the exhaust system can reduce the mold deposits on the mold.
Cover the surface of the mold cavity with a special non-stick coating to prevent the formation of mold deposits. Tests should be conducted to evaluate the effect of the coating. Titanium nitride treatment on the inner surface of the mold can avoid the formation of mold scale on the mold.
