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Everyday information the injection moulder requires from Invotec Solutions.
The below article can be used for machine setters and machine operators of injection moulding machines.
Discover our full range of plasticising components or for the injection moulder.
View our other articles form our setter and operators guide for injection moulders. Taken from our moulders catalogue (Toolbox Edition)
How To Calculate The Injection/Plasticising Rate.
EXAMPLE: POLYCARBONATE
(Injection rates using two different polymers i.e PC and PP on the same moulding machine)
Calculate injection rate values given the following data
- Screw diameter = 35mm
- Material being processed = Polycarbonate (PC)
- Maximum available injection velocity = 220mm/sec
- Maximum screw stroke = 240mm
- Maximum shot volume = 231cm3
- Injection speed selected = 80mm/sec
- Final screw stop position (including decompression distance) = 147mm
- Changeover position = 10mm
- Actual screw stroke used: Final screw stop position – changeover position / 147 – 10 = 137mm
Conversion into actual shot volume used = 131.8cm3
Maximum available shot weight in PC: Maximum shot volume available x Melt Density of PC
Therefore: Maximum available shot volume x (Room Density of PC x 0.85)
= 231 x (1.21 x 0.85)
= 231 x 1.029
= 237.70g of PC
Actual shot weight used for PC = Actual screw stroke volume x Melt Density of PC = 131.8 x 1.029 = 135.62 g
Predicted injection time = 137/80 = 1.56 seconds
Injection rate in PC in cm3/sec
= Actual shot volume used / injection time
= 131.8cm3 / 1.56 = 84.49cm3/sec
Actual injection rate in grammes/sec
= Actual shot weight used / injection time
= 135.62g/1.56 = 86.94g/sec
EXAMPLE POLYPROPYLENE
(Injection rates using two different polymers i.e PC and PP on the same moulding machine)
Calculate injection rate values given the following data
- Screw diameter = 35mm
- Material being processed = Polypropylene (PP)
- Maximum available injection velocity = 220mm/sec
- Maximum screw stroke = 240mm
- Maximum shot volume = 231cm3
- Injection speed selected = 80mm/sec
- Final screw stop position (including decompression distance) = 147mm
- Changeover position = 10mm
- Actual screw stroke used = Final screw stop position – changeover position = 147 – 10 = 137mm
Conversion into actual shot volume used = 131.8cm3
Maximum available shot weight in PP = Maximum shot volume available x Melt Density of PP
Therefore: Maximum available shot volume x (Room Density of PP x 0.85)
= 231 x (0.90 x 0.85)
= 231 x 0.765
= 176.72g of PP
Actual shot weight used for PP = Actual screw stroke volume x Melt Density of PP = 131.8 x 0.765 = 100.83g
Predicted injection time = 137/80 = 1.56 seconds
Injection rate in PP in cm3/sec
= Actual shot volume used / injection time
= 131.8cm3 / 1.56 = 84.49cm3/sec
Actual injection rate in grammes/sec
= Actual shot weight used / injection time
= 100.83g/1.56 = 64.63g/sec
EXAMPLE POLYACETAL (POM) which is a high density material
Calculate injection rate values given the following data
- Screw diameter = 40mm
- Material being processed = Polyacetal (POM)
- Maximum available injection velocity = 180mm/sec
- Maximum screw stroke = 260mm
- Maximum shot volume = 326.77cm3
- Injection speed selected = 50mm/sec
- Final screw stop position (including decompression distance) = 106mm
- Changeover position = 10mm
- Actual screw stroke used = Final screw stop position – changeover position = 106 – 10 = 96mm
Conversion into actual shot volume used = 120.65cm3
Maximum available shot weight in POM = Maximum shot volume available x Melt Density of POM
Therefore: Maximum available shot volume x (Room Density of POM x 0.85)
= 326.77 x (1.40 x 0.85)
= 236.77 x 1.19
= 388.86g of POM
Actual shot weight used for POM = Actual screw stroke volume x Melt Density of POM = 120.65 x 1.19 = 143.57g
Predicted injection time = 96/50 = 1.92 seconds
Injection rate in POM in cm3/sec
= Actual shot volume used / injection time
= 120.65 cm3 /1.92 = 62.84cm3/sec
Actual injection rate in grammes/sec
= Actual shot weight used / injection time
= 143.57g/1.92 = 74.78g/sec