Website Maintenance on August 2
Our website will be unavailable from 9:30 until 13:30 on August 2 (Japan time) due to system maintenance. We apologize for any inconvenience and thank you for your understanding.

 Home  > Technical Support > Molding Technology > Molding Technology for DURACON® POM

Molding Conditions / Molding Cycle

Contents Introduction Safety Molding Machines Molding Conditions Recycling
Molding Characteristics Product Design Mold Design Countermeasures for Defects

Standard Conditions  Predrying  Condition Setting  Molding Cycle  Countermeasures for MD

List of DURACON® POM grades This page's PDF(0.97MB)

4. Molding Conditions

4.8 Molding Cycle

4.8.1 Injection and Pressure Retention Time

The molding cycle is generally set such that the sum of injection time and retention time is slightly longer than the gate seal time. As shown in Fig. 4-5, the gate seal time is the shortest time within which material equal to the weight of the molding is injected. If the sum of injection time and retention time is shorter than the gate seal time, the following problems may occur:

  • Mold shrinkage increases. (Fig. 4-6)
  • Dimensional accuracy decreases. (Fig. 4-7)
  • Voids and sink marks are generated.
  • Deformation increases. (Fig. 4-8)
  • Impact strength decreases. (Fig. 4-9)

 


Fig. 4-5 Weight of molding and gate seal time
Molding conditions:
 Cylinder temperature: 190°C
 Injection pressure: 75MPa
 Injection speed: 17mm/s

Mold:
 120×120×3mm flat plate
 (side gate 4w×2t)

Fig. 4-6 Mold shrinkage and gate seal time
Molding conditions:
 Cylinder temperature: 190°C
 Injection pressure: 75MPa
 Injection speed: 17mm/s

Mold:
 120×120×3mm flat plate
 (side gate 4w×2t)

Fig. 4-7 Dimensional variation and gate seal time
Test piece:
 ASTM tensile test piece
 (thickness: 3.2mm)

Measured section:
 Longitudinal direction
 (213mm)

 

The gate seal time must be measured on actual moldings, as it varies with the relation between the capacity of the molding machine and the material weight per shot, the gate size, the molding wall thickness at gate section, and molding conditions. Refer to the data for test pieces shown in Table 4-1 and Table 4-2.

 

Table 4-1 Gate seal time (side gate)

Mold temp. (°C) Wall thick. (mm) Gate size (w × t) Gate seal time (sec.)
M90-44 GH-25
40 1 2 x 1 4 -
2 2 x 1 9 6
4 x 2 9 6
3 2 x 1 11 10
4 x 2 17 10
6 x 3 20 11
4 2 x 1 14 11
4 x 2 20 15
6 x 3 26 16
60 1 2 x 1 4 -
2 2 x 1 10 6
4 x 2 10 7
3 2 x 1 14 10
4 x 2 19 12
6 x 3 21 12
4 2 x 1 15 13
4 x 2 22 17
6 x 3 31 18
80 1 2 x 1 5 3
2 2 x 1 11 7
4 x 2 12 7
3 2 x 1 17 14
4 x 2 22 14
6 x 3 24 15
4 2 x 1 18 16
4 x 2 27 20
6 x 3 34 21

  GH-25: Glass fiber 25% reinforced grade, Test piece: 80×80mm flat plate

 

Table 4-2 Gate seal time (pin gate)

Mold temp. (°C) Wall thick. (mm) Gate size
(Ø)
Gate seal time (sec.)
M90-44 GH-25
40 1 0.5 3.4 2.8
1.0 3.4 2.8
2 1.0 8.6 6.2
1.5 9.0 6.4
3 1.5 13.8 10.6
2.0 15.8 11.2
60 1 0.5 3.8 2.8
1.0 3.8 2.8
2 1.0 9.8 7.0
1.5 10.6 7.8
3 1.5 16.6 12.8
2.0 18.2 12.8
80 1 0.5 4.2 3.4
1.0 4.2 3.4
2 1.0 11.8 7.8
1.5 12.6 9.0
3 1.5 19.2 15.8
2.0 20.6 16.8

  GH-25: Glass fiber 25% reinforced grade, Test piece: 50×50mm flat plate

 


Fig. 4-8 Warpage and gate seal time
Test piece:
 120mm diameter disk
 Thickness 2mm
 (1.5mm dia. pin gate)

Fig. 4-9 Impact strength and gate seal time
Molding conditions:
 Cylinder temperature: 180°C
 Mold temperature: 80°C
 Injection pressure: 100MPa
 Injection speed: 50mm/s

Mold:
 Tensile impact test piece
 (2.5mm dia. pin gate)

 

4.8.2 Cooling Time

Fig. 4-10 shows approximate times to knock out DURACON® POM M90-44 molded products as obtained by actual measurement and calculation. In general, holding pressure time should be a little longer than gate sealing time as mentioned before. Cooling time is determined by plasticating time plus product knockout time (holding pressure and cooling time). Moreover, a longer cooling time may be necessary when the product wall is thick, the molded products have a heat-accumulating thin and long core, or deformation is a problem.


Fig. 4-10 Minimum times for knockout of moldings
Test piece:
 80×80mm flat plate, 1-8mm thick

Side gate:
 2w×1t (case of thick 1-4mm)
 4w×2t (case of thick 5-8mm)

Calculation method:
The minimum time for knockout is calculated from the estimated ratio in normal moldings, which is based on the ratio of solidified layer capable of being knocked out in an 80×80mm flat plate.

 


Standard Conditions  Predrying  Condition Setting  Molding Cycle  Countermeasures for MD

Contents Introduction Safety Molding Machines Molding Conditions Recycling
Molding Characteristics Product Design Mold Design Countermeasures for Defects