Filling of PVC injection vinyl figure

The filling of the PVC injection vinyl figure is the first step in the entire PVC injection cycle. The time starts from the start of PVC injection after the mold is closed until the mold cavity is filled to about 95%. In theory, the shorter the filling time of PVC injection vinyl figure, the higher the molding efficiency, but in practice, the molding time or PVC injection speed is subject to many constraints.

High-speed filling of PVC injection vinyl figure. The shear rate is relatively high during high-speed filling, and the viscosity of the plastic decreases due to the effect of shear thinning, which can reduce the overall flow resistance; the local viscous heating effect will also make the thickness of the solidified layer thinner. Therefore, in the flow control stage, the filling behavior often depends on the volume to be filled. That is, in the flow control stage, because of the high-speed filling, the shear-thinning effect of the melt is often great, and the cooling effect of the thin wall is not very obvious, so the effect of the speed prevails..

Low-speed filling of PVC injection vinyl figure. When filling at low speed, the shear rate is lower, the local viscosity is higher, and the flow resistance is higher. Because the hot plastic has a slower replenishment rate and a slower flow, the heat conduction effect is more obvious, and the heat is quickly taken away by the cold mold wall. Coupled with a smaller amount of viscous heating, the thickness of the cured layer is thicker, which can further increase the flow resistance at the thinner part of the wall.

The melt of two strands

Because of the flow of the fountain, the plastic polymer chains in front of the flow wave are aligned to the almost parallel flow wavefront. Therefore, when two strands of plastisol meet, the polymer chains on the contact surface are parallel to each other; in addition, the properties of the two melts are different (the residence time in the mold cavity is different, and the temperature and pressure are different). The structural strength is poor on the microscopic level. Place the parts at an appropriate angle under light and observe with the naked eye, you can find that there are obvious joint lines, which is the formation mechanism of weld marks. The weld mark not only affects the appearance of the plastic part but also easily causes stress concentration due to the looseness of the microstructure, which reduces the strength of the part and breaks.

PVC doll vinyl figure generally has better weld line strength in the high-temperature area, because the polymer chains are more mobile and can penetrate each other under high-temperature conditions. In addition, the temperature of the two strands of melt in the high-temperature area is closed, The thermal properties of the melt are almost the same, which increases the strength of the welded area; on the contrary, in the low-temperature area, the welded strength is poor

When some PVC doll manufacturers produce injection molded products, it often happens that air is trapped inside PVC injection molded vinyl figures, forming small volumes or series of small holes. This problem has little effect, but it will always come true. It's a headache.

Then the main reasons why PVC injection vinyl figures produce bubbles are:

The exhaust system of the production equipment is poor, and there will be bubbles if there is no gas that can be discharged in time.

Excessive injection speed of auxiliary materials during the production process will also produce bubbles.

l  If the cooling time of the plastic parts is not controlled properly during the production process, the local temperature will be uneven, and air bubbles will also be generated.

l  If too much or too little material is added during the production process, bubbles will also be generated.

l  During the production process, if the holding pressure of the equipment is too low or the holding time is too short, bubbles will also be generated.

l  The raw material is damp, causing the water content to be too high. The water molecules or other low-molecular volatiles in the production process cannot be discharged in time, and bubbles will also be generated.

l  The plastic raw materials will also produce bubbles after a long time in the barrel.

l  If the melt temperature of the PVC injection doll is too high, bubbles will also be generated.

The solution for PVC injection vinyl figure to produce bubbles:

l  If there are no bubbles, it is necessary to increase the mold temperature and reduce the time and cycle of PVC injection molding;

l  If you want to design plastic parts without bubbles, you can't leave a part with too large thickness disparity;

l  If you want to have no bubbles, you need to use good raw materials, ensure the particle size of the raw materials, and not make the diameter difference too large;

l  If there are no bubbles, you need to wait for the raw materials to dry before production, and control the water content;

l  If there are no bubbles, check the exhaust system to ensure that there are no blocked channels;

l  In order to have no bubbles, you need to pay attention to the parameters of the pressure holding.

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