Injection molding pipe fittings often encounter the phenomenon that the mold cannot be filled in the process of processing. When the injection molding machine just started working, because the mold temperature was too low, the heat loss of the molten PVC material was large, which was prone to early solidification, and the resistance of the mold cavity was large, and the material could not fill the cavity. This phenomenon is normal and temporary. It will disappear automatically after continuous injection of digital molds. If the mold cannot be filled up all the time, consider the following conditions and make appropriate adjustments:

Bubbles on the pipe

Heat bubbles are generated due to high heating temperature. Too high process temperature will cause bubbles in the volatiles in the raw materials, and will also partially decompose the PVC material to produce bubbles, which are commonly known as hot bubbles. Appropriately adjust the injection speed

The injection speed is too fast. Because the molding process of PVC-U injection molded products should adopt lower injection speed and higher injection pressure. The injection speed can be adjusted appropriately.

If the gate is too small or the flow channel section is too small, the material flow resistance is too large. The gate and runner section can be enlarged to reduce melt flow resistance.

The content of moisture or other volatile matter in the raw materials is too high or the raw materials have been stored for too long, and the moisture in the air is absorbed. Strictly control the content of volatiles in the raw materials when purchasing raw materials, and the raw and auxiliary materials should not be stored for too long during periods or regions with high humidity in the air.

Poor product gloss

The surface gloss of PVC injection molded products is largely related to the fluidity of PVC materials. Therefore, improving the fluidity of materials is an important measure to improve products. Because the temperature of the molten material is low and the fluidity of the material is poor, the heating temperature of the material can be appropriately increased, especially the temperature at the nozzle.

The formula is unreasonable, so that the plasticization of the material is not in place or the filler is too much, the formula should be adjusted, and the plasticization quality and fluidity of the material should be improved through the reasonable combination of processing aids, and the amount of fillers should be controlled.

Insufficient mold cooling, improve mold cooling effect. If the gate size is too small or the runner cross-section is too small, the resistance is too large. You can increase the runner cross-section appropriately, increase the gate, and reduce the resistance.

The content of moisture or other volatiles in the raw materials is too high. The raw materials can be fully dried, or the moisture or volatiles can be removed through the material. If the exhaust is poor, an exhaust groove can be added or the gate position can be changed.

There are obvious weld lines

The temperature of the melted material is low, and the heating temperature of the barrel can be appropriately increased, especially the nozzle temperature should be increased. If the injection pressure or injection speed is low, the injection pressure or injection speed can be appropriately increased.

If the mold temperature is low, the mold temperature can be appropriately increased. If the gate is too small or the cross section of the runner is too small, you can increase the runner or enlarge the gate appropriately.

Poor mold exhaust, improve mold exhaust performance, add exhaust grooves. The volume of the cold slug well is too small, so the volume of the cold slug well can be increased appropriately.

The amount of lubricant and stabilizer in the formula is too much, and their amount can be adjusted. The cavity setting is unreasonable and its layout can be adjusted.

Severe sink marks

Gaoan’s injection pressure is low, so the injection pressure can be increased appropriately. The set pressure holding time is not enough, you can increase the pressure holding time appropriately.

The set cooling time is not enough, you can increase the cooling time appropriately. If the amount of sol is insufficient, increase the amount of sol appropriately.

The water transportation of the mold is uneven, and the cooling circuit can be adjusted to make all parts of the mold cool evenly. The structural size of the mold gating system is too small, and the gate can be enlarged or the main, branch, and runner cross-sectional dimensions can be enlarged.

Difficult to demold

Difficulty in demolding is caused by the mold and improper process, but in most cases it is caused by the improper demolding mechanism of the mold. There is a material hook mechanism in the demolding mechanism, which is responsible for hooking out the cold material at the main, runner and gate: the ejection mechanism uses the ejector rod or the top plate to eject the product from the movable mold. If the demolding angle is not enough, demolding will be difficult. There must be sufficient pneumatic pressure during pneumatic ejection and demolding. , Otherwise there will be difficulties in demolding. In addition, the core pulling device of the parting surface, the thread core pulling device, etc. are all important parts in the demolding structure, and improper design will cause the difficulty of demolding. Therefore, in the mold design, the demolding mechanism is also a part that must be paid attention to. In terms of process control, too high temperature, too much feed, too high injection pressure, and too long cooling time will cause demoulding difficulties.

In summary, various quality problems will occur in the processing of PVC-U injection molded products, but the reasons for these problems are in equipment, molds, formulas, and processes. As long as there are complete equipment and molds, reasonable formulas and processes, problems can be avoided. But in actual production, these problems often appear, or appear without knowing the reasons and solutions, depending on the accumulation of experience. Rich operating experience is also one of the conditions to ensure the perfect product.