Sage-Tips

How do you adjust back pressure injection molding?

The back pressure is generated by the metering section of the mixing screw. It is possible to control the hydraulic back pressure during the injection molding process. The back pressure settings typically start at fifty PSI and increase in ten PSI increments.

How do you set a mold safety?

Start with a low pressure that will not close the mold and increase it until you get clamp pressure. This should show the minimum pressure needed to trigger clamp-up. If the mold will not close after a period of running, remember that tools warm up and grow, so recheck your trigger position and adjust as necessary.

How do you reduce injection pressure?

Select a different material with a lower viscosity, which requires less injection pressure to fill the mold. Increase the melt temperature to reduce the viscosity. This reduces the injection pressure required to fill the mold.

What does back pressure do in injection molding?

Within the injection molding machine, the screw is circulated around the barrel at the back, with a hydraulic motor placed at the back. The back pressure prevents the linear motion of the plastic particles inside the barrel. The amount of back pressure applied should not be very high or low.

What causes short shots in injection molding?

A short shot occurs when the flow of molten material doesn’t completely fill the cavities in a mold. The result is that the molded component is incomplete after cooling. Short shot might appear as incomplete compartments in plastic shelves of a display or missing prongs on a plastic fork, for example.

How do you set holding pressure in injection molding?

Hold pressure and speed are usually 50\% – 65\% of the top injection pressure and speed. That is to say, the holding pressure is approx. 0.6 – 0.8MPa lower than the injection pressure that feeds plastic into the mold cavity.

How important is back pressure?

However, a little back pressure is a good thing. In fact, it helps. The right size pipe is large enough to breathe well but small enough to create a high exhaust flow. Steps in the exhaust system also create negative pressure waves that travel back to the cylinder and help empty the cylinder of those gases.

Should I slow down my machine when mold is low pressure?

If you need to slow your machine down to ensure low pressure is working, do so. Set mold protection to be on during the entire mold-closing cycle if you have a machine that can monitor the entire stroke and will stop and alarm is anything is out of a normal band.

How often should mold protection be done by the machine controller?

Each mold has its own particular requirements, and machine controllers handle mold protection in a number of ways. But it should be done daily if not once per shift.

What tonnage of clamp force does my mold need?

Find the correct tonnage of clamp force this mold requires and set it appropriately; do not assume that full clamp force is needed. Too much clamp force—especially on small molds—damages both the mold and machine. According to SPE/SPI guidelines, the mold should occupy at least 70\% of the distance between the tiebars.

What should I do if the mold does not close?

Start with a low pressure that will not close the mold and increase it until you get clamp pressure. This should show the minimum pressure needed to trigger clamp-up. If the mold will not close after a period of running, remember that tools warm up and grow, so recheck your trigger position and adjust as necessary.