How to determine proper shot size and plasticizing capacity based on part weight and screw diameter when purchasing an injection molding machine?
• Total part weight incl. runner should be 25%-75% of theoretical shot size; below 25% risks degradation, above 75% starves plasticizing.
• Screw diameter sets theoretical shot size; usable shot = 0.8 × screw cross-section × max stroke.
• Plasticizing capacity must be ≥ total part weight ÷ cooling time in g/s, or cycle time extends.
• Verify screw L/D ratio 20:1-24:1; 20:1 for PP/ABS, 22:1+ for PC/POM.
• Request screw curve charts to confirm injection pressure and rate match part wall thickness.
• Screw diameter sets theoretical shot size; usable shot = 0.8 × screw cross-section × max stroke.
• Plasticizing capacity must be ≥ total part weight ÷ cooling time in g/s, or cycle time extends.
• Verify screw L/D ratio 20:1-24:1; 20:1 for PP/ABS, 22:1+ for PC/POM.
• Request screw curve charts to confirm injection pressure and rate match part wall thickness.