Solution for Bubble Generation in Rotational Molded Products
During the production of rotational molding products, the materials in the mold gradually melt, flow, and adhere to the inner surface of the hot mold as the mold rotates during the heating process. The air inside the mold expands due to the volume of heating, and the air pressure increases, gradually flowing to the outside of the mold through the exhaust hole until the air pressure inside and outside the mold reaches equilibrium, and vice versa. At the same time, maintain a certain pressure in the mold cavity. In the process of resin melting and densification, the gas trapped between the powder particles is pressed to the Free surface of the plastic melt, but because of the surface tension of the melt, the gas is not enough to be separated from the melt. Melt the surface and easily form bubbles, resulting in the formation of products. In severe cases, bubbles on the inner surface and gas entanglement on the outer surface can form larger pores. "If the melt has good fluidity, the heating speed of the mold will be very slow, and the vent hole of the mold is unobstructed, so the gas in the melt can escape smoothly. On the contrary, the gas in the melt tends to be trapped to form Product defect. When the mold is not tightly closed, during the mold heating process, part of the gas in the cavity will flow to the outside of the mold through the gap of the mold clamping part, so that the product can enter the mold Corresponding part, gas 7 liters or bubbles; During the cooling process of the mold, if the mold is not tightly closed, there will be a pressure difference between the inside and outside of the mold, and air will enter the mold through the gap in the clamping part (parting surface) of the mold. This gap generates product holes on the outside and the formation of holes is also related to the shape of powder particles. When the tail of polyethylene (PE) powder particles is slender or hairlike, they will pile up and form a bridge, which can better maintain air, especially at the corners of rotational molded products. Powder bypass can lead to the formation of large voids.
Solution
Adjust the length of the Submarine snorkel or the same wire coil to the appropriate distance in the mold. Ventilation pipes usually use fine metal fluoride plastic pipes, whose diameter is determined by product size and material properties. (Usually, the diameter of thin-walled products is set to 10-12 millimeters per cubic meter). The length of the tube should ensure that the end of the product extends to the center or appropriate position of the mold cavity according to the depth of the product cavity. In order to avoid resin powder overflowing from the exhaust port when the mold rotates, the exhaust pipe should be filled with Glass wool, steel wool, graphite powder, etc.