Machine Selection

When determining the size of equipment to be used for molding an Asahi Kasei Plastics material, total shot weight and total projected area are the two basic factors to be considered.

Optimum results are obtained when the total shot weight (all cavities plus runners and sprue) is equal to 25% to 80% of the maximum shot capacity of the machine. A very small shot in a large barrel machine will create unnecessarily long residence time which could cause material degradation.

Once the total projected area of the complete shot (all cavity and runner areas subjected to injection pressure) has been determined, 2.5 to 5 tons of clamp force should be provided for each square inch of projected area to avoid flashing of the part. Wall thickness, flow length and molding conditions will determine the actual tonnage required. Highly filled materials with long flow lengths should be molded with at least 4 to 5 tons per square inch of projected area. For unfilled materials with heavy sections and short flow lengths, 2.5 tons per square inch are usually sufficient.

Screw Design

Injection molding machine screw profiles for our compounds generally correspond to those of their unfilled counterparts.

Relatively shallow flighted screws are recommended for lubricated crystalline materials such as PTFE lubricated nylon and Acetal to promote uniform plastication.

A wide range of our materials can be satisfactorily processed using general purpose crystalline and amorphous screw configurations. The slightly lower performance of the general purpose screw should be weighted against the cost and inflexibility of maintaining several specifically tailored screws.

Screw and Barrel Wear Considerations

The effect of the reinforcement on screw and barrel wear can vary widely. The rate of wear varies with the hardness geometry and level of reinforcement. Relatively soft non-fibrous filler materials such as talc and calcium carbonate have a minimal effect on wear rate.

Conversely, hard fibrous filler materials such as glass and mineral fibers will increase the wear rate of unprotected screws and barrels in extended use situations.

The base thermoplastic will also influence the rate of screw and barrel wear. Thermoplastics with high melt viscosities (stiff melt flows) tend to increase wear by increasing the scouring action of the melt on the screw and barrel surfaces.

Note: By encapsulating the filler material in the compound, Asahi Kasei Plastics materials offer greater protection to the screw and barrel. Screw and barrel wear in the feed and transition sections are significantly lower with precompounded thermoplastics than with reinforced dry blends.

Screw and Barrel Coatings

For moderate use of polymers filled with talc or calcium carbonate or the occasional molding of glass fiber-filled products, chrome plated screws and nitrided barrels will provide good component life.

For continuous use of talc or calcium carbonate products or for moderate molding of glass fiber-filled thermoplastics, bimetallic barrels and hard faced screw flight tips are recommended.

The selection of proper screw and barrel treatments is extremely complex. Several wear reducing products are available for each. These products vary widely in their cost application, lead time requirements and effectiveness. To further complicate the issue screw flight tip coatings vary in their compatibility with barrel lining materials. The coating requirements for each molding situation must be evaluated individually.

Our Technical Service Personnel are available to assist you with the determination of proper screw and barrel treatments for your applications.

Because we cannot anticipate or control the different conditions under which this information and our products may be used, we do not guarantee the applicability or accuracy of this information or the suitability of our products in any given situation. The information and products referenced herein are intended for use by persons having technical skill and understanding, at their own discretion and risk. We cannot anticipate or control conditions of information and product usage. Users of our products should make their own tests to determine the suitability of each product for their particular purpose. WE MAKE NO REPRESENTATIONS OR WARRANTIES OF ANY KIND, INCLUDING ANY EXPRESS OR IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. Also, statements concerning the possible use for our products are not intended to be nor are they recommendations to use our products in the infringement of any patent.