Most of the burrs occur on the parting surface , that is , between the movable die and the static die , the sliding matching part of the sliding block , the gap of the insert , the hole of the ejector rod , and the like are flowed into the melt , and redundant flash burrs are formed on the workpiece .
Such flying edge burrs, in the forming of leverage, will further increase the flying burr, resulting in the mold part of the depression, forming when the flying edge burr into a vicious circle. If a flash burr is found at first, the mold must be trimmed as soon as possible.
There are several reasons for the formation of burrs.
1.Insufficient locking force
Compared with the projection area of the molded article , if the mold clamping force is small , a gap appears between the static mold due to the action of the injection pressure , so that the burr of the flash edge will occur .Especially the hole in the side gate near the central portions of parts, because the gate needs pressure injection molding, so prone to burr.
This defect can be eliminated by lowering the injection pressure or increasing the locking force, and it can sometimes be very effective to use low-pressure moulding for highly liquid plastics, depending on the circumstances.
2. The local fit of die is not strict.
First of all, the problem of dynamic and static die closure is discussed. Although the die itself is tight, when the injection machine with elbow bar locking mechanism is used, it is often due to the poor parallelism of the die or the bad adjustment of the mould locking device. A phenomenon such as the imbalance of the left and right side of the locking die is produced, that is, the left and right sides are only locked on one side and the other side is not tightly pasted. At this time, the pull rod (two or four skewers) must be adjusted to balance the development.
Secondly, it is also due to the poor matching of the die itself, especially when there are forming holes in the center of the parts, because of the supporting effect of this part, burrs are easy to appear when the locking force is not sufficient.
The other is the sliding core, because the moving core is the action mechanism, often produce burr, so the cooperation of the sliding core is very important, especially for the left and right parting of the Haff mold, its side projection area is also affected by molding pressure. Burrs often occur if the design cannot fully withstand this pressure. The gap between the inserts and the penstock pores will not only increase the burr vicious circle, but also increase the ejection resistance.
3. Die flexure
If the mold is not original enough, the injection pressure will cause flexure. If there is a hole near the center, the burr will occur around the hole. There is also burr around the hole and the sprue when using the center hole side gate. The burr caused by this reason is caused by bad mold making, so it is more difficult to repair. The burr can be reduced by reinforcing the mould.
4. Plastic fluidity is too good
Simply because the plastic is too fluidity is not the reason for the burr in theory. However, when the plastic is too fluidity, even the tiny slot plastic can get in. So it is easy to burr. To eliminate the burr, you can reduce the melting material temperature or injection pressure, but also reduce the mold temperature or injection speed.
5. Excessive injection of molten materials
This is not the direct cause of burr. In order to prevent shrinkage cavity from injecting too much molten material, it is wrong. We should increase injection time or holding time to form (reference shrinkage cavity).
6. Foreign body on mould surface
There is a foreign body on the die surface of the mould, which is bound to produce burrs. To solve this problem, it is obvious that Yu Jing should clean the surface of the mould, so that the surface of the die can be tightly pasted.