VIKING POLYMERS, LLC

109 Ragsdale Road Post Office Box 577 Jamestown, NC 27282

Tel: (336) 454-1174 Fax: (336) 887-4567

Injection Molding Processing General Guide – Rigid Compounds

Introduction

Viking Polymers injection molding compounds have been designed with the injection molder in mind for

ease in processing. Molding characteristics have been optimized while achieving the necessary material

properties (properties vary depending upon the product).

Warning

Never mix Viking Polymers injection molding compound with acetal (POM) or acetal copolymers. Mixing

the two materials, even in trace amounts, will cause degradation to occur at processing temperatures.

Thoroughly purge the machine between running these materials (see purging).

Material

In general terms, Viking Polymers compounds are amorphous thermoplastics. More specifically, they are

acrylic/PVC alloys or PVC compounds. Unlike crystalline polymers like polystyrene, acrylic,

polycarbonate, etc. Viking rigid compounds do not melt, they soften when heated.

Choosing Equipment

Clamp Force Requirements: 3-3.5 tons/sq.in. (422-492 kg/sq.cm.)

Shot Size: The machine should be properly sized for the job. At least 75% of the rated shot size should

be utilized. This is done to reduce the residence time of the material in the barrel which will reduce the

amount of thermal degradation of the material.

Shot size rating is based on polystyrene. Since the specific gravity of Viking Polymers injection molding

compound is much higher than that of polystyrene, the shot size must be converted using the following

formula:

Viking Polymers injection molding compound shot size = Rated shot size x 1.35

To estimate the residence time of the material in terms of cycles use the following formula:

Residence Time (cycles) = 2(Rated Shot Size x 1.35)/Actual Shot Size Used

(The average barrel holds about two shots)

Resident time should be limited to 2.7 cycles.

Materials of Construction: Molds should be constructed from 420 stainless steel for corrosion resistance.

Chrome plating of the mold cavity will further add to the corrosion resistance to the tool, but is not

necessary.

Screw Type: Screws with a compression ratio range of 2.0-2.6 can be used.

Screw Tip: Viking Polymers injection molding compounds should be processed with a ring check valve.

However, smear tips are also acceptable.

Material Preparation

Drying: Drying is not typically necessary. However, if the material is old or has been stored in moist

conditions, drying may be required. In this case, dry the material at 130ºF (54ºC) for 2 hours.

Coloring: Precolored material is recommended. It can be difficult to achieve a homogeneous color mix by

using a color concentrate. Custom colored material can be provided which will insure a properly colored

part, and will not require the use of a concentrate.

Start-Up Conditions

The following conditions are recommended as a guideline for start up. Some adjustments may be

necessary depending upon the specific part being molded or the machine being used. Processing should

be optimized for the specific situation after the initial start-up.

Barrel Zone 1: 315ºF (157ºC)

Barrel Zone 2: 340ºF (171ºC)

Barrel Zone 3: 365ºF (185ºC)

Nozzle: 370ºF (188ºC)

Melt Temperature: 385 - 405ºF (196 - 207ºC)

Mold Temperature: 90 - 140ºF (32 - 60ºC)

Screw Speed: The screw speed should be set so that the screw reaches the back position less than 5

seconds before the mold opens. This will reduce the residence time in the barrel.

Back Pressure: 100 - 400 psi (350 - 1375 kPa). This will insure a homogeneous melt. However, excessive

back pressure can lead to degradation.

Injection Pressure: 1200 psi (8275 kPa)

Second Stage Pressure: 800 psi (6190 kPa)

Hold Pressure: 600 psi (4100 kPa)

Cushion: Using the smallest cushion possible is recommended (< _ inch (5mm)).

Residence Time: Material should not be allowed to sit stagnant in the machine for longer than 10 minutes

without cycling.

Regrind Usage

Regrind can be used up to a level of 20% repeatedly with no significant loss in properties. Regrind can be

used up to 100%, but there is a finite number of cycles that this can be repeated before degradation

harms the product quality. The regrind should be well mixed with virgin material to ensure a

homogeneous mixture.

Annealing

Annealing of parts to relieve stress should be performed at 120ºF (49ºC) for 4 hours.

Shut-Down

Purge: After molding it is necessary to thoroughly purge the barrel to eliminate the chance of corrosion.

This should be done after each run, even if the machine is only going to sit over night. Materials such as

PMMA, ABS, or a commercially available purging compound should be used. The barrel should be

purged for 5 to 10 cycles to insure proper cleaning.

Neutralize Mold: After molding it is necessary to neutralize and protect the mold to prevent corrosion. This

should be done after each run, even if the tool is only going to sit over night. A two step mold treatment in

which step one neutralizes the mold and step two prevents rust from occurring is recommended. Use of a

mold cleaner is recommended before using the tooling again.

These suggestions and data are based on information that we believe to be reliable and accurate at the

time of publication. They are offered in good faith, but without guarantee, as the conditions and methods

of use of our products are beyond our control. We recommend that the prospective end user determine

the suitability of our materials and suggestions before adopting them on a commercial scale.