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Why are there bubbles in the production of polyurethane integral skin foam products?

In the production process of PU integral skin foam, there are some problems such as: pinholes, air bubbles, dry scars, less material, uneven surface, poor fracture, color difference, soft, hard, release agent and paint are not sprayed well, etc. The occurrence of the phenomenon, let’s talk about the problem and generation of bubbles today.


1. Mold: When the temperature of the mold is not high enough, it does not reach the temperature required for product production. Open the mold at a normal production speed, and bubbles may occur. In reality, there are three different materials: steel mold, aluminum mold, and resin mold. Molds, copper molds, and FRP molds have faded out of sight in recent years.
1) Some production units use electric ovens for heating.
2) Some are heated with water.
3) more with gas heating. Relatively speaking:
A. The cost of electric heating is relatively high. It is suitable for continuous production and large-scale production, and requires higher proficiency in operation.
B. water heating, simple, convenient and easy to control.
C. Gas heating is not advisable. Fireworks are prohibited in the original production site, which is unsafe, dangerous and difficult to control.
Steel molds and aluminum molds must be prepared for heating during production. Some are grooved on the surface, and then buried in aluminum tubes to transfer heat through the aluminum tubes. Some drill holes directly on the mold. I think it is best to drill directly. Convenient, heating is the most direct. If the temperature of the mold is low, air bubbles will be produced, and the curing time is not enough. If the temperature of the mold is too high, the product will be more bloated, and it will be easy to crack when the mold is opened. Different mold line production, such as the steel mold requirement is 45 degrees, maybe the resin mold requirement is only 40 degrees, the water intake of the ball valve of the water pipe can be properly adjusted to achieve the effect of temperature control. In general, mold heating has relatively little effect on the formation of self-skin bubbles.

2.The exhaust of the mold: some molds need exhaust to reduce the formation of air bubbles.
A. The perforation of 1.0-1.5 mm directly on the surface of the mold is better, if it is too large, the scar will be too large after the product is cut.
B. The peripheral exhaust of the mold is called grooving. You can use a blade, a saw blade, or a grinder, no matter which method is used, but it should be noted that when the grooving time is closer to the position of the parting line, it is necessary to shallow. If the parting line is too deep, it is directly related to the appearance of the product, and the scar after cutting the edge will be too large. The position of the vent hole and the vent slot is generally to place the mold at the normal foaming angle, and confirm the best position of the vent hole and vent slot according to the product. The principle is to open as few vent holes and vent slots as possible. . When the product with high requirements cannot have vent holes and vent grooves, after shaking the mold, place the foaming angle and loosen the mold button. When the original foam reaches the edge of the mold, quickly button the mold. reach the effect.

3. When the foaming position of the mold is not suitable, air bubbles can also be generated:
Some molds are flat, some are angled, and some molds need to be shaken 360 degrees. Personally, I think that the surface of the product is strictly flat and the back is not strict. You can shake the mold back and forth and put it in the best position. If the surface of the product is not strict The same strict requirements as the back side should be considered at this time, 360-degree shaking of the mold is to shake the material to the back of the product to reduce the generation of air bubbles.

Post time: Aug-05-2022