Machine Requirements

Screw and cylinder:

• During metering, about 30-70 % of the maximum metering volume should be used
• Three-zone screw with a length of 18-22 D
• Zones: feed 50–60 %, compression 20–25 %, metering 20–25 %
• Flight depth ratio 2-2.5 : 1
• Ideal minimum flight depth: metering zone 2 mm, feed zone 4 mm
• We recommend screws made of corrosion-resistant and wear-resistant steels. For the injection cylinder, we recommend bimetallic equipment.

Design of a three-zone screw

Nozzle:

• In general, open nozzles are preferred. If shutoff nozzles are used, the heat caused by friction should kept as low as possible.
• Proper working heater bands are crucial in order to avoid freezing of the nozzle or the formation of a cold slug. Long equipment nozzles in combination with attached injection molding unit require a heating strip covering the entire nozzle body.
• The bore diameter should measure at least 4 mm
• In order to facilitate problem-free demolding of sprue gates, the exit diameter (d1) of the machine nozzle should be about 0.5-1 mm smaller than the bore diameter (d2) of the sprue bushing. Make sure that the radius of the machine nozzle is smaller than the sprue bushing radius (e.g. nozzle radius = 35 mm, sprue bushing radius = 40 mm).

Nonreturn valve:

• Make sure the nonreturn valve work properly; as a rule of thumb, the gap between nonreturn valve and cylinder should be < 0.02 mm.

Clamping force:

• Common cavity pressures (processing TROGAMID^®-Campus samples) stay within the range of 300-500 bar.
• It is recommended to calculate the clamping force utilizing injection molding process simulation. Runner and machine nozzle should be taken into account, in order to predict the injection pressure as accurate as possible. In general, pressure at end of filling or start of packing/ holding determines the clamping force.