The filter nozzle catches the metal particles in the melt inside the nozzle, before they reach the mold.
Where does the metal come from?
Plastic raw material can contain metal particles or metal dust. Their sources are mostly regrind, particles left over from the production of the raw material, and worn parts of the machine.
Metal separation systems and hopper magnets largely prevent metal from entering the plasticizing unit. However, depending on the metal concentration in the raw material or coming from the regrind, they cannot stop it from getting in entirely.
Why is it critical for the hot runner?
Most molds today have hot runners, and the runner diameters are very small. A small metal particle of 1-5 mm can clog the runner and stop or disrupt production. The filter nozzle is the last protection before the mold for metal that has got into the line.
How does it work?
A filter insert with a hole diameter of 1 mm or 3 mm is placed inside the nozzle. As the melt passes through the holes of the insert, the metal particles are held in the filter. Because the perforated structure divides the melt and brings it back together, it also contributes to material mixing.
Pressure loss and maintenance
When the filter is first fitted, the injection pressure loss is up to 3% with the 1 mm filter and up to 1% with the 3 mm filter. As the filter holds metal, this figure rises. When the pressure loss limit you have set is reached, the tip of the nozzle is removed and the filter is cleaned or replaced. Because a spare inner filter can be kept, maintenance does not stop production for long.
Choosing the hole diameter is a balance: 1 mm holds smaller particles but the initial pressure loss is higher; with 3 mm the pressure loss is lower.
