Feed Screws for Injection Molding and Extrusion
You know you are going with the best when you buy an injection molding screw or extrusion screw from Thermoplastic Industrial Replacement (TIR). Information on our wide range of premium designs and material options may be found on this page.
An optimal injection molding or extrusion process depends on the injection molding screw or extruder screw design, and the quality of manufacturing the screw. It cannot be overstated that the injection molding screw design and quality is critical to your success. Our designers, engineers and machinists understand what it takes to design and manufacture extrusion and injection molding screws that perform best for our customers. TIR manufactures barrier screws, mixing screws, general purpose screws, volume reduction screws, and more. TIR's quality standards exceed those of the SPI.
Injection molding screws and extrusion screws from TIR are built for consistent end-product quality, along with high performance and wear resistance.
Capabilities
New Feed Screws
- Injection and Extrusion feedscrews made new to OEM specifications
- Any make or model feed screw with 4140 HT Steel, 4340 HT, CPM-9V, Stainless, CPM-10v, Nitrided Nitralloy, Inconel, Colmonoy 83, Colmonoy 56 or nitrided flights
- Tool Steel feed screws
OEM Feed Screw Rebuilding Materials
- Colmonoy #83: Tungsten carbide hard-surfacing for greater wear resistance
- Colmonoy #56: For standard processing
- Industrial Hard Chrome: to protect the root diameter and sides of the feedscrew flight from normal wear and corrosive conditions
- Encapsulation of the root diameter and sides of the feedscrew flight with N-50 or tungsten carbide for high wear processing
Feed Screw Types
Tapered and Parallel Extruders
- Tapered and Parallel Screw: Gradually tapering screw toot (the channel depth gradually changes) in the compression zone. The feed zone and the metering zone are parallel and of constant depth. Unlike the double parallel screw the velocity of the un-melted portion of the melting material bed is maintained and there is less risk of polymer stagnation.
- Double Parallel Screw: Features a "step" that is, a rapid decrease in channel depth (over one screw turn or less), between the parallel feed and metering sections. In the "stepped" screw (a double parallel screw or nylon screw), it is claimed that the rapid decrease in channel depth acts as a barrier to forward flow of un-melted granules and therefore fixes the melting point at the step.
- Screw with Tapered Root Diameter over Full Length: A tapered screw may be selected from heat sensitive materials (UPVC). This screw which has a gradually tapering screw root, that is, the channel depth gradually changes -- usually the diameter of the screw root increases steadily from the hopper end to the die end of the extruder so as to gradually compress the material.
- Dedicated Screw: A screw that is designed to suit one type of material, for instance, nylon (PA 66) or polyvinyl chloride (PVC). A general-purpose (GP) screw is designed to suit as wide a range of plastics as possible and is not the ideal answer for the processing of any specific material, For example, a screw designed for a semi-crystalline, thermoplastics material, such as PA 66, must provide a greater heat input than one designed for an amorphous, thermoplastic material. If a machine will be dedicated to one plastic for a long time, then it is worthwhile considering the purchase of a specially designed, or dedicated, screw. (ref. The Dynisco Extrusion Processors Handbook Written by John Goff & Tony Whelan).
Barrier Design Feed Screw
- This type of screw contains a barrier to hold back un-melted material. The flights of a conventional screw are often filled with a mixture of solid and molten plastic. It is difficult for the screw to grip the solid resin since it floats or "swims" in a pool of melt. Barrier design screws are used to improve the ability of the machine to produce melt, and to give more uniform melt. The barrier screw has two separate flights that are separated by the flight land. These two separate flights may only run for part of the screw length. For example, it may run for 13 diameters (13 D), in place of the compression zone, on a 24 D screw. As the resin melts it is transferred from one flight to the other over the narrow land. Thus the screw separates the melt pool and solid bed. This produces improved output per rpm and a lowering of melt temperature. (ref. The Dynisco Extrusion Processors Handbook Written by John Goff & Tony Whelan).
Zero Compression Feed Screw
- A large amount of heat will be generated, when a conventional screw is used to extrude a plastic material, because of the compression ratio on the screw. To avoid this heat generation, machines are now built which have screws where the depth of the screw flight is the same along its entire length (zero compression)(Figure 19). Such screws give very little mixing, but this can be improved by the use of mixing sections located near the screw tip. Such zero compression screws are commonly used with barrels that have longitudinal grooves in the feed section. These grooved barrel assemblies are now considered essential for the processing of high molecular weight PE, and PP, at high throughput rates. These assemblies give consistent outputs even if the diehead resistance alters due to the use of parison programming in blow molding operations. For blow molding machines, such barrels are available in diameters of up to 90 mm (3.5") with L/Ds of 20/1 or greater. (ref. The Dynisco Extrusion Processors Handbook Written by John Goff & Tony Whelan).
Typical TIR Mixer Options:
- Dulmage Mixer: This is a high shear dispersive mixer used primarily for creating a good homogenous melt and color dispersion when processing unfilled nylon.
- Barrier Screw: This provides improved melt quality and increases throughput rates an average of 10%-20% for a wide range of materials.
- Spiral and Straight Maddock Mixers: Dispersive type mixers for good homogenous melt for any non-shear sensitive materials.
- Spiral Maddock Mixer: Dispersive type mixer for good homogenous melt for any non-shear sensitive materials such as Olefins.
- Saxton Mixer: General purpose distribution mixer provides good melt quality and color mix for most materials.
- Pin Row Mixer: General purpose distribution mixer provides good melt quality and color mix for most materials.
The Feed Screw Manufacturing Process:
The screw rotates inside the extrusion barrel and pushes the plastic materials from the hopper into the die where it is pressed into the desired product. As the screw rotators, the material slips on the screw and adheres to the inside of the barrel, producing a purely axial movement of the polymer. If the material is sticking to the screw and slips on the barrel, there is no output; the material and the screw rotate together. Some screws are designed to improve mixing, whereas others are designed for a particular material or process. Using a lathe operation, the bar of steel is turning down to a precise bar. The bars come irregular and are turned to a particular size. One turned, it goes into a milling machine where it is put through a process called channeling, where a deep channel is laid down the outside diameter in a spiral way. The hard-facing (carbide) alloys are then applied to the channels and they become the top of the flights on the screw. The screw needs protection from the hostile environment of the extruder. Then it goes into the welder where it is welded and put in a tank of vermiculite that slow cools the screw. The screw remains in the tank for 2-3 days due to the rate of cooling the welds have is different from the base steel. Once the hard facing is welded, the steel needs cut away to be sized properly. For precision, they are placed in OD grinders. Then it comes out of the CNC machine and goes to a belt polishing station staring with a heavy grit and moving to a finer grit in the process to remove imperfections. Plastics adhere to rough surfaces and impede the process without a very fine polish. Some screws are chrome plated, then it is buffed and polished. Finally the drive end is applied to the screw, allowing it to fit in the machine it will be going into.
Feed Screws We Service
Single / Twin
Give us a call at 1-800-922-7735 and we can work with you on solutions that will meet your needs. TIR can design a new feedscrew to help eliminate your problems!
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