What is the molding process of the injection molding screw barrel?

1. Injection temperature

The injection molding screw barrel must be made after considering the shape, size, mold structure, product performance, requirements and other aspects of the product. Generally, the temperature used in molding is between 270 and 320℃. If the material temperature is too high, such as exceeding 340℃, PC will decompose, the color of the product will become darker, and defects such as silver wire, dark stripes, black spots, and bubbles will appear on the surface. At the same time, the physical and mechanical properties will also decrease significantly.

2. Injection pressure

It has a certain influence on the physical and mechanical properties, internal stress, and molding shrinkage of the injection molding screw barrel. It has a great influence on the appearance and demolding of the product. Too low or too high injection pressure will cause certain defects in the product. Generally, the injection pressure is controlled between 80 and 120MPa. For thin-walled, long-flow, complex-shaped, and small-gate products, in order to overcome the resistance of melt flow and fill the mold cavity in time, a higher injection pressure (120-14 5MPa). Thus, a complete product with smooth surface is obtained.

3. Holding pressure and holding time

The size of the holding pressure and the length of the holding time have a great influence on the internal stress of the injection molding screw barrel. If the holding pressure is too small, the shrinkage compensation effect is small, and vacuum bubbles or shrinkage on the surface are prone to occur. If the holding pressure is too large, it is easy to produce large internal stress around the gate. In actual processing, high material temperature and low holding pressure are often used to solve the problem. The choice of holding time should depend on the thickness of the product, the size of the gate, the mold temperature, etc. Generally, small and thin products do not need a long holding time. On the contrary, large and thick products should have a longer holding time. The length of the holding time can be determined by the gate sealing time test.

4. Injection speed

It has no obvious effect on the performance of the injection molding screw barrel. Except for thin-walled, small gate, deep hole, and long process products, medium or slow processing is generally adopted. Multi-stage injection is best, and slow-fast-slow multi-stage injection is generally adopted.

5. Mold temperature

Generally, it can be controlled at 80-100℃. For products with complex shapes, thinner shapes, and higher requirements, it can also be increased to 100-120℃, but it cannot exceed the mold thermal deformation temperature.

6. Screw speed and back pressure

Due to the high melt viscosity of the injection molding screw barrel, the screw speed should not be too high, which is beneficial to plasticization, exhaust, maintenance of the molding machine, and prevent excessive screw load. It is generally appropriate to control it at 30-60r/min, and the back pressure should be controlled between 10-15% of the injection pressure.

7. Requirements for the molding machine for producing injection molding screw barrels

The maximum injection volume of the product should not exceed 70-80% of the nominal injection volume. The injection molding screw barrel uses a single-start thread with equal pitch and a gradual compression screw with a check ring. The length-to-diameter ratio of the screw is L/D of 15-20, and the geometric compression ratio is C/R.