How to do the defect problem of the injection molding product bulging?

In the injection molding process, how should the delay valve and speed match? Let's take a look at this case today. This product is a car rear bumper, it has a lot of gate, using delayed sequence valve to shoot glue, this product has nine gates, from the middle one, and then to the two sides of the row of 4, this product is prone to a lot of problems, such as tiger skin grain, flow pattern, air pattern, size problem, today those questions do not talk about, we only talk about one drum problem.

After this product will spray paint, but after painting will find a problem is the drum bag, the surface is like the field ridge drum bag, and then we found out that this is the reason?

This is a drum bag at the junction of two different streams of material, so you might ask, if it's a delay room, how can there be a connection line?

Yes, the delay valve is not connected to the line, the middle valve is opened first, the second valve is opened later, when the material of the first valve comes here, the second valve needle is passed, the second valve needle is opened again, and then, the third is the fourth.

The position of the drum occurs in the edge area, that is to say, after the last valve needle is opened, and the material in front will form a joint line in the center, not on the surface, but on the combination line of the heart, this combination line will have a drum on the surface, so what about this drum?
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This method is not the same as the adjustment of other conventional products. We use a pure injection molding process.

Specifically, to solve the drum problem, the core of its solution is to reduce the speed of the glue. For the vicinity of drum defects, we should reduce the speed of glue injection, specifically, the whole product, if there is a drum bag, is in the second half.

In the first half, it is not easy to have drum defects, and our speed is also higher. Generally speaking, like this product PP material, the wall thickness is about 2.7 to 3.0 degrees, then our mold temperature is about 20 to 30 degrees, the material temperature is 230 degrees, that is, the shooting speed is in the first 70 percent, from here to here 70 percent, our shooting speed is controlled at 30 percent ≤ 40 percent.

When it comes to the place where bulging is easy to appear in the second half, the shooting speed will be controlled between 5% and 10%. If the drum is more severe, the speed should be lower, say, 5%. If the drum is not strong, the shooting speed can be higher, for example, that is, 10% of the shooting speed, so that the defect of the drum can be alleviated with the low shooting speed.