- Email: [email protected]
Injection Molding Process Parameters
Chapter 27
Injection Molding Process Parameters In this chapter, we will present the main injection-molding parameters for a number of thermoplastics. When setting an injection-molding machine with a new resin, you should always use the recommended process data from the raw material producer if available. If you do not have them, look on the producer’s website or search for them on the Internet. NOTE: The values shown in Table 27.1 are typical for an unmodified standard grade of the polymer in question and serve only as a rough guide. Contact your plastic raw material supplier for accurate information about your specific grade! The Melt temperature is one of the most important parameters. When processing semi-crystalline plastics, you should always consider the risk that you may get unmelted granules in the melt. To eliminate this risk, you should use the cylinder temperature profile that depends on the capacity utilization of the cylinder (see Section 26.8). You should also be aware that additives such as flame retardants or impact modifiers often require a lower temperature than the standard grade. Glass fiber reinforced grades should have, as a rule, the same temperature settings as unreinforced grades. The Mold temperature is also one of the most important parameters for achieving the best quality. For semi-crystalline plastics you need a certain temperature to ensure that the material’s crystal structure will be correct and thus provide the best strength and dimensional stability (less post-shrinkage). See Section 26.9. Drying is needed for plastics that are either hygroscopic (absorb moisture) or sensitive for hydrolysis (degraded chemically by moisture). See more in Section 26.7. We recommend that molders use dehumidifying (dry air) dryers in their production. Therefore we publish both the temperature and drying time needed to be below the maximum allowed moisture content for the material, provided that the dry air dryer is working with a sufficiently low dew point. Note also that if you dry the material longer than the indicated time in the table you should reduce the temperature 10–20 °C because some materials can oxidize or degrade thermally. Material where “Does not normally need to be dried” is given in the table may still need to be dried if condensation will occur on the surface of the granules. If this is the case, a drying temperature of 80 °C and a drying time of 1–2 hours usually works well. The reason that the maximum Peripheral speed is published in the tables is that many molders in good faith are dosing up the next shot with too high of a screw speed and thus unnecessarily degrading the polymer chains in the cylinder by high shear and friction, resulting in poorer quality. In Section 26.13 (Figure 26.40) you will find a formula where you can calculate the maximum allowed peripheral speed to maximum allowed rotation speed depending on the screw diameter. If you cannot find the recommended maximum peripheral speed for your resin, you should take into account that high-viscosity grades sometimes require 30% lower
297
Chapter 27 — Injection Molding Process Parameters rotation speed compared to a less viscous standard grade. For example, impact-modified acetal with a melt index of 1–2 g/10 min has a recommended maximum peripheral speed of 0.2 m/s, compared to 0.3 m/s for a standard grade with melt index of 5–10 g/10 min. For glass fiber reinforced grades you will usually find the recommended maximum peripheral speed to be 30–50% of the speed for the unreinforced grade. Also, impact modified, flame retardant grades used to be more sensitive to shear than standard grades. Having sufficiently high Hold pressure is especially important for semi-crystalline plastics. Usually it is recommended to have as high a pressure as possible without getting flashes in the parting line or having ejection problems. We provide hold pressures because many molders sometimes in good faith set far too low a hold pressure, resulting in poorer quality. Other important parameters such as hold pressure time, hold pressure switch, back pressure, injection speed, and decompression are more dependent on the part design and machine conditions. We therefore cannot give any general values of these parameters, but refer you instead to Chapter 26. Table 27.1 Typical processing data for unmodified standard grades of common thermoplastics.
Semi-crystalline commodities Material
Type
Melt temperature Nominal
Unit Polyethylene
PEHD
Range
Mold temp.
Drying Temp. Time
Max moisture
Dew point
%
°C
°C
°C
°C
°C
200
200–280
25–60
Does not normally need to be dried
Hours
Hold pressure
Max peripheral speed
MPa
m/s
25–35
1.3
Polyethylene
PELD
200
180–240
20–60
Does not normally need to be dried
25–35
0.9
Polyethylene
PELLD
200
180–240
20–60
Does not normally need to be dried
25–35
0.9
Polyethylene
PEMD
200
200–260
25–60
Does not normally need to be dried
25–35
1.1
Polypropylene
PP
240
220–280
20–60
Does not normally need to be dried
35–45
1.1
Mold temp.
Drying Temp. Time
Max moisture
Dew point
Hold pressure
Max peripheral speed
%
°C
Amorphous commodities Material
Type
Melt temperature Nominal
Unit Polystyrene
PS
HIPS
PS/SB
SAN
Range
°C
°C
°C
°C
230
210–280
10–70
Does not normally need to be dried
Hours
MPa
m/s
45–50
0.9
230
220–270
30–70
Does not normally need to be dried
45–50
0.6
240
220–290
40–80
Does not normally need to be dried
45–50
0.6
ABS
240
220–280
40–80
80
3
0.1
− 18
45–50
0.5
ASA
250
220–280
40–80
90
3–4
0.1
− 18
40–45
0.5
PVC
Soft
170
160–220
30–50
Does not normally need to be dried
40–45
0.5
PVC
Hard
190
180–215
30–60
Does not normally need to be dried
50–55
0.2
230
190–260
30–80
8
60–80
0.6
PMMA
298
4
0.05
−18
27 Injection Molding Process Parameters
Semi-crystalline engineering polymers Material
Type
Unit
Melt temperature Nominal
Range
Mold temp.
Drying
°C
°C
°C
°C
Temp. Time
Max moisture
Dew point
%
°C
Hours
Hold pressure
Max peripheral speed
MPa
m/s
Acetal
POM Homo
215
210–220
90–120
Does not normally need to be dried*
60–80
0.3
Acetal
POM Copo
205
200–220
60–120
Does not normally need to be dried*
60–80
0.4
Polyamide 6
PA6
270
260–280
50–90
80
55–60
0.8
2–4
0.2
− 18
Polyamide 66
PA66
290
280–300
50–90
80
2–4
0.2
− 18
55–60
0.8
Polyester
PBT
250
240–260
30–130
120
2–4
0.04
− 29
50–55
0.4
Polyester
PET+ GF
285
280–300
80–120
120
4
0.02
− 40
50–55
0.2
Mold temp.
Drying
Hold pressure
Max peripheral speed
Amorphous engineering polymers Material
Type
Melt temperature Nominal
Unit Polycarbonate
PC
Range
Temp. Time
Max moisture
Dew point
°C
°C
°C
°C
Hours
%
°C
MPa
m/s
290
280–330
80–120
120
2–4
0.02
− 29
60–80
0.4
Polycarbonate
PC/ABS
250
230–280
70–100
110
2–4
0.02
− 29
40–45
0.3
Polycarbonate
PC/PBT
260
255–270
40–80
120
2–4
0.02
− 29
60–80
0.4
Polycarbonate
PC/ASA
Mod. PPO
250
240–280
40–80
110
4
0.1
− 18
40–45
0.3
290
280–310
80–120
110
3–4
0.01
− 29
35–70
0.3
Mold temp.
Drying
Hold pressure
Max peripheral speed
Semi-crystalline advanced thermoplastics Material
Type
Melt temperature Nominal
Unit Fluoroplastic Aromatic polyamide
FEP/ PFA
Range
Temp. Time
Max moisture
Dew point
%
°C
°C
°C
°C
°C
350
300–380
150
Does not normally need to be dried**
Hours
MPa
m/s
Low***
****
PA6T/66 325
320–330
85–105
100
6–8
0.1
− 18
35–140
0.2
PA6T/XT 325
320–330
140–160
100
6–8
0.1
− 18
35–140
0.2
LCP
355
350–360
60–120
150
3
0.01
− 29
20–60
Max
PPS
330
300–345
70–180
150
3–6
0.04
− 29
45–50
0.2
PEEK
370
360–430
160–200
160
2–3
0.1
− 18
50–65
0.2
299
Chapter 27 — Injection Molding Process Parameters
Amorphous advanced thermoplastics Material
Type
Unit
Melt temperature Nominal
Range
Mold temp.
°C
°C
°C
Drying Temp.
Time
Max Dew moisture point
°C
Hours
%
°C
Hold pressure
Max peripheral speed
MPa
m/s
Polyetherimide PEI
380
370–400
140–180
150
4–6
0.02
− 29
70–75
0.5
Polysulfone
340
330–360
120–160
150
4
0.02
− 29
50–70
0.4
PSU
PPSU
370
350–390
140–180
150
4
0.02
− 29
50–70
0.4
PES
360
340–390
140–180
140
4
0.02
− 29
60–80
0.2
* If the granules have been exposed to moisture or condensation you should dry approximately 2 hours at 100 °C ** If the granules have been exposed to moisture or condensation you should dry 3–4 hours at 150 °C *** Hold pressure should be as low as possible **** Stainless special screws are required
300
Injection Molding Process Parameters In this chapter, we will present the main injection-molding parameters for a number of thermoplastics. When setting an injection-molding machine with a new resin, you should always use the recommended process data from the raw material producer if available. If you do not have them, look on the producer’s website or search for them on the Internet. NOTE: The values shown in Table 27.1 are typical for an unmodified standard grade of the polymer in question and serve only as a rough guide. Contact your plastic raw material supplier for accurate information about your specific grade! The Melt temperature is one of the most important parameters. When processing semi-crystalline plastics, you should always consider the risk that you may get unmelted granules in the melt. To eliminate this risk, you should use the cylinder temperature profile that depends on the capacity utilization of the cylinder (see Section 26.8). You should also be aware that additives such as flame retardants or impact modifiers often require a lower temperature than the standard grade. Glass fiber reinforced grades should have, as a rule, the same temperature settings as unreinforced grades. The Mold temperature is also one of the most important parameters for achieving the best quality. For semi-crystalline plastics you need a certain temperature to ensure that the material’s crystal structure will be correct and thus provide the best strength and dimensional stability (less post-shrinkage). See Section 26.9. Drying is needed for plastics that are either hygroscopic (absorb moisture) or sensitive for hydrolysis (degraded chemically by moisture). See more in Section 26.7. We recommend that molders use dehumidifying (dry air) dryers in their production. Therefore we publish both the temperature and drying time needed to be below the maximum allowed moisture content for the material, provided that the dry air dryer is working with a sufficiently low dew point. Note also that if you dry the material longer than the indicated time in the table you should reduce the temperature 10–20 °C because some materials can oxidize or degrade thermally. Material where “Does not normally need to be dried” is given in the table may still need to be dried if condensation will occur on the surface of the granules. If this is the case, a drying temperature of 80 °C and a drying time of 1–2 hours usually works well. The reason that the maximum Peripheral speed is published in the tables is that many molders in good faith are dosing up the next shot with too high of a screw speed and thus unnecessarily degrading the polymer chains in the cylinder by high shear and friction, resulting in poorer quality. In Section 26.13 (Figure 26.40) you will find a formula where you can calculate the maximum allowed peripheral speed to maximum allowed rotation speed depending on the screw diameter. If you cannot find the recommended maximum peripheral speed for your resin, you should take into account that high-viscosity grades sometimes require 30% lower
297
Chapter 27 — Injection Molding Process Parameters rotation speed compared to a less viscous standard grade. For example, impact-modified acetal with a melt index of 1–2 g/10 min has a recommended maximum peripheral speed of 0.2 m/s, compared to 0.3 m/s for a standard grade with melt index of 5–10 g/10 min. For glass fiber reinforced grades you will usually find the recommended maximum peripheral speed to be 30–50% of the speed for the unreinforced grade. Also, impact modified, flame retardant grades used to be more sensitive to shear than standard grades. Having sufficiently high Hold pressure is especially important for semi-crystalline plastics. Usually it is recommended to have as high a pressure as possible without getting flashes in the parting line or having ejection problems. We provide hold pressures because many molders sometimes in good faith set far too low a hold pressure, resulting in poorer quality. Other important parameters such as hold pressure time, hold pressure switch, back pressure, injection speed, and decompression are more dependent on the part design and machine conditions. We therefore cannot give any general values of these parameters, but refer you instead to Chapter 26. Table 27.1 Typical processing data for unmodified standard grades of common thermoplastics.
Semi-crystalline commodities Material
Type
Melt temperature Nominal
Unit Polyethylene
PEHD
Range
Mold temp.
Drying Temp. Time
Max moisture
Dew point
%
°C
°C
°C
°C
°C
200
200–280
25–60
Does not normally need to be dried
Hours
Hold pressure
Max peripheral speed
MPa
m/s
25–35
1.3
Polyethylene
PELD
200
180–240
20–60
Does not normally need to be dried
25–35
0.9
Polyethylene
PELLD
200
180–240
20–60
Does not normally need to be dried
25–35
0.9
Polyethylene
PEMD
200
200–260
25–60
Does not normally need to be dried
25–35
1.1
Polypropylene
PP
240
220–280
20–60
Does not normally need to be dried
35–45
1.1
Mold temp.
Drying Temp. Time
Max moisture
Dew point
Hold pressure
Max peripheral speed
%
°C
Amorphous commodities Material
Type
Melt temperature Nominal
Unit Polystyrene
PS
HIPS
PS/SB
SAN
Range
°C
°C
°C
°C
230
210–280
10–70
Does not normally need to be dried
Hours
MPa
m/s
45–50
0.9
230
220–270
30–70
Does not normally need to be dried
45–50
0.6
240
220–290
40–80
Does not normally need to be dried
45–50
0.6
ABS
240
220–280
40–80
80
3
0.1
− 18
45–50
0.5
ASA
250
220–280
40–80
90
3–4
0.1
− 18
40–45
0.5
PVC
Soft
170
160–220
30–50
Does not normally need to be dried
40–45
0.5
PVC
Hard
190
180–215
30–60
Does not normally need to be dried
50–55
0.2
230
190–260
30–80
8
60–80
0.6
PMMA
298
4
0.05
−18
27 Injection Molding Process Parameters
Semi-crystalline engineering polymers Material
Type
Unit
Melt temperature Nominal
Range
Mold temp.
Drying
°C
°C
°C
°C
Temp. Time
Max moisture
Dew point
%
°C
Hours
Hold pressure
Max peripheral speed
MPa
m/s
Acetal
POM Homo
215
210–220
90–120
Does not normally need to be dried*
60–80
0.3
Acetal
POM Copo
205
200–220
60–120
Does not normally need to be dried*
60–80
0.4
Polyamide 6
PA6
270
260–280
50–90
80
55–60
0.8
2–4
0.2
− 18
Polyamide 66
PA66
290
280–300
50–90
80
2–4
0.2
− 18
55–60
0.8
Polyester
PBT
250
240–260
30–130
120
2–4
0.04
− 29
50–55
0.4
Polyester
PET+ GF
285
280–300
80–120
120
4
0.02
− 40
50–55
0.2
Mold temp.
Drying
Hold pressure
Max peripheral speed
Amorphous engineering polymers Material
Type
Melt temperature Nominal
Unit Polycarbonate
PC
Range
Temp. Time
Max moisture
Dew point
°C
°C
°C
°C
Hours
%
°C
MPa
m/s
290
280–330
80–120
120
2–4
0.02
− 29
60–80
0.4
Polycarbonate
PC/ABS
250
230–280
70–100
110
2–4
0.02
− 29
40–45
0.3
Polycarbonate
PC/PBT
260
255–270
40–80
120
2–4
0.02
− 29
60–80
0.4
Polycarbonate
PC/ASA
Mod. PPO
250
240–280
40–80
110
4
0.1
− 18
40–45
0.3
290
280–310
80–120
110
3–4
0.01
− 29
35–70
0.3
Mold temp.
Drying
Hold pressure
Max peripheral speed
Semi-crystalline advanced thermoplastics Material
Type
Melt temperature Nominal
Unit Fluoroplastic Aromatic polyamide
FEP/ PFA
Range
Temp. Time
Max moisture
Dew point
%
°C
°C
°C
°C
°C
350
300–380
150
Does not normally need to be dried**
Hours
MPa
m/s
Low***
****
PA6T/66 325
320–330
85–105
100
6–8
0.1
− 18
35–140
0.2
PA6T/XT 325
320–330
140–160
100
6–8
0.1
− 18
35–140
0.2
LCP
355
350–360
60–120
150
3
0.01
− 29
20–60
Max
PPS
330
300–345
70–180
150
3–6
0.04
− 29
45–50
0.2
PEEK
370
360–430
160–200
160
2–3
0.1
− 18
50–65
0.2
299
Chapter 27 — Injection Molding Process Parameters
Amorphous advanced thermoplastics Material
Type
Unit
Melt temperature Nominal
Range
Mold temp.
°C
°C
°C
Drying Temp.
Time
Max Dew moisture point
°C
Hours
%
°C
Hold pressure
Max peripheral speed
MPa
m/s
Polyetherimide PEI
380
370–400
140–180
150
4–6
0.02
− 29
70–75
0.5
Polysulfone
340
330–360
120–160
150
4
0.02
− 29
50–70
0.4
PSU
PPSU
370
350–390
140–180
150
4
0.02
− 29
50–70
0.4
PES
360
340–390
140–180
140
4
0.02
− 29
60–80
0.2
* If the granules have been exposed to moisture or condensation you should dry approximately 2 hours at 100 °C ** If the granules have been exposed to moisture or condensation you should dry 3–4 hours at 150 °C *** Hold pressure should be as low as possible **** Stainless special screws are required
300