What is the cause of poor mold release when injection molding products are sticky?
1. The surface of the mold cavity is rough. If there are surface defects such as chisel lines, nicks, scars, and depressions in the mold cavity and runner, the plastic parts will easily adhere to the mold, resulting in difficulty in demolding. Therefore, the surface finish of the cavity and the runner should be improved as much as possible, and the inner surface of the cavity should preferably be chrome-plated. When polishing, the action direction of the polishing tool should be consistent with the filling direction of the molten material.
2. The mold is worn and scratched or the gap at the insert is too large. When the molten material produces flash in the scratched part of the mold or in the gap of the insert, it will also cause difficulty in demolding. In this regard, the damaged part should be repaired and the gap of the insert should be reduced.
Third, the mold rigidity is insufficient. If the mold cannot be opened at the beginning of injection, it indicates that the mold is deformed under the action of injection pressure due to insufficient rigidity. If the deformation exceeds the elastic limit, the mold cannot return to its original shape and cannot be used further. Even if the deformation does not exceed the elastic limit of the mold, the molten material is cooled and solidified under high conditions in the mold cavity, and the injection pressure is removed. After the mold recovers its deformation, the plastic part is clamped by the elastic force, and the mold still cannot be opened.
Therefore, when designing the mold, sufficient rigidity and strength must be designed. When trying the mold, it is best to install a dial indicator on the mold to check whether the mold cavity and the mold base are deformed during the mold filling process. The initial injection pressure during the mold test should not be too high, and the deformation of the mold should be observed at the same time. , while slowly increasing the injection pressure to control the deformation within a certain range.
When the rebound force is too large to cause the clamping failure, it is not enough to only increase the mold opening force. The mold should be disassembled and decomposed immediately, and the plastic parts should be heated and softened and taken out. For molds with insufficient rigidity, a frame can be placed on the outside of the mold to improve rigidity.
Fourth, the drafting slope is insufficient or dynamic, and the parallelism between the fixed templates is poor. When designing and making molds, a sufficient demoulding slope should be ensured, otherwise the plastic parts will be difficult to demould, and when forcibly ejected, the plastic parts will often be warped, and the ejection part will be white or cracked. The movement of the mold and the fixed platen should be relatively parallel, otherwise the cavity will be offset, resulting in poor demoulding.
5. The design of the gating system is unreasonable. If the runner is too long or too small, the strength of the connection between the main runner and the sub-runner is insufficient, the main runner has no cold slug cavity, the gate balance is poor, the diameter of the main runner and the diameter of the nozzle hole are not properly matched, or the sprue sleeve and nozzle If the spherical surface does not match, it will lead to mold sticking and poor mold release. Therefore, the length of the runner should be appropriately shortened and its cross-sectional area should be increased to improve the strength of the connection between the main runner and the branch runner, and a cold slug hole should be set on the main runner.
When determining the gate position, the filling rate of each cavity in the multi-cavity mold can be balanced and the pressure in the cavity can be reduced by adding auxiliary gates and other methods. In general, the diameter of the small end of the sprue should be 0.5~1mm larger than the diameter of the nozzle, and the concave radius of the sprue sleeve should be 1~2mm larger than the spherical radius of the nozzle.