Overburr mostly occurs on the parting and closing surface, that is, between the dynamic die and the static die, the sliding part of the slider, the gap of the insert, the porosity of the ejector rod, etc., flows into the molten material, forming excess flash burrs on the parts.

Such burrs play a leverage role in forming, which will further increase the burrs, resulting in a local depression of the mold, and the formation of the burrs into an increased vicious circle. Therefore, if a flash burr is found at the beginning, it is necessary to trim the mold as soon as possible.

Burrs are produced for the following reasons

1. Insufficient clamping force

Compared with the projected area of the molding parts, if the clamping force is small, there will be a gap between the dynamic and static molds due to the action of the injection pressure, which is bound to appear a flash burr. Especially when the side gate is placed on the hole near the center of the part, because the molding gate needs a large injection pressure, it is easy to appear burrs.

Reducing the injection pressure or increasing the locking force can eliminate this defect, if according to the specific situation to use a good flow of plastic using low pressure molding, sometimes it is very effective.

2. Mold local coordination is not strict

First of all, discuss the problem of dynamic and static mold closing is not strict, although the mold itself is tight, when the injection machine of the elbow type mold locking mechanism is formed, it is often due to the poor parallelism of the mold or the poor adjustment of the mold locking device. Produce phenomena such as unbalanced clamping on the left and right sides, that is, only &ndash on the left and right sides; The edge is locked, and the other — The edge is not tightly attached, and the pull rod (two or four pullers) must be adjusted at this time to make it balanced.

Secondly, there are also due to the mold itself poor matching caused by tight sticking. Especially when the center of the part has a forming hole, due to the supporting effect of this part, when the clamping force is not enough, it is also easy to appear burrs.

The other is the sliding core, because the moving core is an action mechanism, often produce burrs, so the sliding core is very important. Especially for the left and right parting of the Huff die, the side of the projected area is also affected by the molding pressure, if the design can not fully withstand this pressure often appear burrs. Regarding the gap of the insert and the pore of the ejector rod, it will not only produce the phenomenon of increasing the vicious circle of burrs, but also increase the ejector resistance.

3. Mold deflection caused by

If the mold original degree is insufficient, the injection pressure will produce deflection, then if there is a hole near the center, the hole surrounding will produce burrs; There is also the use of the center hole to open the side gate, the hole and the perimeter of the runner will also produce burrs. The burrs generated by this reason are caused by poor mold making, so they are more difficult to repair. Adopt reinforcing mold, can make the burr reduced.

4. The plastic fluidity is too good

is simply due to the plastic fluidity is too good, in theory is not the cause of burrs. However, when the plastic fluidity is too good, even the tiny gap plastic can also drill into, so it is very easy to appear burrs. To eliminate this burr, you can reduce the melting temperature or injection pressure, you can also reduce the mold temperature or injection speed,

5. Too much molten injection

This is not the direct cause of burrs. It is wrong to inject too much molten material in order to prevent shrinkage holes, and it should be taken to increase the injection time or pressure holding time to form (see shrinkage holes).

6. There are foreign bodies on the mold surface

There are foreign bodies on the mold closing surface, which will inevitably produce burrs. To solve this problem, it is obviously necessary to clean the surface of the mold and make the closing surface close.

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