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2. Molding Conditions

Content Introduction Molding Conditions Use of Regrind Mold Design
  Mold Shrinkage and Dimensional Accuracy Safety Precautions Molding Defects Countermeasures


2.1Pre-drying

Although DURAFIDE® absorbs little moisture, pre-drying at 140°C for 3 hours or 120°C for 5 hours is recommended in order to improve appearance of molded products and to prevent drooling.

Meanwhile, depending on the grade, pre-drying at 105°C for 5 hours is recommended to avoid bridging at the time of drying.

For carbon fiber filled grades (2130A1, 7140A4 etc.), pre-drying is particularly important, because moisture absorption is high due to carbon fibers.

And for natural color grades, it is important to keep the same drying conditions to obtain more stable hues.

 

 

2.2 Injection Molding Machines

In order to avoid discoloration by retention in the cylinder, it is necessary to select an injection molding machine whose shot capacity is balanced with shot weight.

An open nozzle is commonly used, but in order to avoid drooling of molten material, a shut-off valve is occasionally favorable. And steel with abrasion resistance and corrosion resistance is recommended for barrel and screw. There is a possibility that serious corrosion wear may occur in standard barrels and screws, so it is recommended to consult sufficiently with the molding-machine maker before use.

 

 

2.3 Molding Conditions

The range of molding conditions applicable for DURAFIDE is shown in Fig. 2-1. To decrease flash, a slightly higher cylinder temperature and slightly lower injection pressure will give better results.

So long as the appearance of molded products is satisfactory, a lower injection speed may reduce effects upon flashing. Typical molding conditions applicable for 1140A1 are shown in Table 2-1.

 

Fig. 2-1 Range of Molding Conditions

 

Table 2-1 Typical Injection Molding Conditions of DURAFIDE® 1140A1
Item
Conditions
Pre-drying
140°C × 3hrs
Cylinder temperature No.1 (hopper side)
290 - 300°C
No.2
300°C
No.3
310°C
No.4 (nozzle side)
310°C
Nozzle temperature
310 - 320°C
Mold temperature
150°C
Injection pressure
40 - 70MPa

 

 

2.4 Setting Molding Conditions

(1) Cylinder Temperature

If the cylinder temperature underneath the hopper is too low, abrasion of the cylinder and screw is prone to increase.

If there is no flowability problem, a slightly lower cylinder temperature may decrease discoloration by retention in the cylinder. Especially, a temperature between 300°C and 320°C is recommended for molded products other than in black color.

 

(2) Mold Temperature

Mold temperature greatly affects characteristics of molded products.

Considering the appearance of molded products, dimensional stability in service at high temperature, heat resistance and creep resistance, it is advisable to avoid mold temperatures below 120°C and to adopt a mold temperature of over 130°C.

 

(3) Injection Pressure

Normally, an injection pressure of 30 to 100MPa is suitable and in order to decrease flash, low pressure molding is recommended.

 

(4) Injection Speed

Fast injection is necessary to obtain satisfactory surface appearance of molded products. However, this tends to result in warpage and burns of molded products. It is, therefore, meaningless to use excessively high-speed injection so long as the surface appearance is satisfactory.

 

(5) Back Pressure

A back pressure of 2 to 5MPa is recommended in order to stabilize metering. If metering is unstable, a slightly higher back pressure of between 8 to 10MPa should be applied.

 

(6) Screw Speed

Normally, a screw speed of 40 to 100rpm is appropriate. A rotational speed over 200rpm is not recommended as it may cause breakage of glass fibers and heat generation in melt.

 

(7) Retention in Cylinder

DURAFIDE has no great increase in viscosity even when it is retained in the cylinder for a long time. This means that the use of a hot runner molding system is effective.

 

 

2.5 Purging after Molding

Purging is usually done first with GF-filled polycarbonate while retaining the cylinder temperature at molding, then with polyethylene. After that, it is recommended to repeat purging with the GF filled polycarbonate and polyethylene alternately. It is more effective if the new purging material is fed after completely purging out material fed before. Instead of GF filled polycarbonate, it is also possible to use a commercially available acrylic type purging material.

Details of starting and stopping the molding machine, and changing the molding material are given below.

 

(1) Stopping the Molding Machine

After purging the DURAFIDE remaining in the cylinder and maintaining the molding temperature of DURAFIDE, the cylinder should be purged with a resin which is the same molding temperature as DURAFIDE and has good thermal stability. (Commercially available high-density polyethylene and acrylic types are recommended.) If DURAFIDE is to be subsequently molded, the cylinder can be purged with DURAFIDE.

 

(2) Starting the Molding Machine

In starting up a machine containing another resin that is stable within the DURAFIDE molding temperature range, the cylinder temperature can be raised to this level and purging can be done with DURAFIDE.

When the resin remaining in the cylinder has a different molding temperature range, the following steps should be carried out:

- Set the cylinder temperature at the molding temperature of the remaining resin.

- Purge the cylinder with purging material that has good thermal stability and can be used in the molding temperature ranges of both DURAFIDE and the remaining resin (for example, high-density polyethylene or polycarbonates, as appropriate, are recommended).

- After that, set the cylinder temperature at the DURAFIDE molding range and purge the cylinder again.

In general, when DURAFIDE is the resin remaining in the cylinder, it is possible to raise the cylinder temperature to the DURAFIDE molding range and to purge with DURAFIDE.

 

(3) Changing the Molding Material

When the resin has the same molding temperature range as DURAFIDE, purge the cylinder at the molding temperature, following the same procedures used in starting and stopping the molding machine.

When the resin cannot be replaced under the same molding condition, it is recommended to purge the cylinder with a resin that can be used at the molding temperatures of both DURAFIDE and the replacement, and has good thermal stability (e.g., high-density polyethylene).

 

(4) Other

If DURAFIDE of natural color remains in the cylinder for a long time, discoloration may occur. In such case, thorough purging is required.

 

 


Content Introduction Molding Conditions Use of Regrind Mold Design
  Mold Shrinkage and Dimensional Accuracy Safety Precautions Molding Defects Countermeasures