Feed screws for Extrusion and Injection Molding

For 27+ years TIR has been at the forefront in extrusion and injection feedscrew manufacturing, rebuilding and design.  Information on our wide range of premium designs and material options may be found on this page.

An optimal extrusion or injection molding process relies on the appropriate design for the polymer, as well as the quality of manufacture. It cannot be overstated that optimal design and the quality of manufacture are two of the most important factors when considering your feedscrew vendor. 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 injection screws, and more. Extrusion and injection molding feedscrews from TIR are manufactured for consistent end-product quality, along with high performance and wear resistance.

TIR's quality standards meet or exceed SPI guidelines.

Capabilities

Feed screw: New, Rebuild and Design

• Extrusion and injection feedscrews made new to OEM specifications
• Optimal feed screw design
• Any diameter and length
• Any make or model

New Feed screw Base Materials and Alloys

• Base Materials Made From: 4140 HT Steel, 4340 HT, Tool steel CPM-9V and CPM-10v, Stainless Steel, Nitrided Nitralloy and Inconel‍
• Colmonoy #56: A hard surface weld for the majority of standard processes
• ‍Colmonoy #83: Tungsten carbide hard-surfacing for greater wear resistance
• Colmonoy #57: Nickle-based Hard-Surfacing Agent
• Colmonoy #88: Nickle-based Hard-Surfacing Agent favored for abrasive wear
• Stellite Alloys
• 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 Rebuild Alloys

• Colmonoy #56: A hard surface weld for the majority of standard processes
• Colmonoy #83: Tungsten carbide hard-surfacing for greater wear resistance
• Colmonoy #57: Nickle-based Hard-Surfacing Agent
• Colmonoy #88: Nickle-based Hard-Surfacing Agent favored for abrasive wear
• Stellite Alloys
• Industrial Hard Chrome: Used 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

Design

• Custom designed feedscrews for your process
• Contact TIR

Feed Screw Types

Single Feed Screw

• The “general-purpose (GP) screw” can trace its design back to the 1960s. The idea was to have one screw design capable of handling a range of polymers (except for rigid PVC). Back then, the number of polymers was limited compared with today and the competition for production efficiency was not as great. So the concept made some sense. With the development of more advanced extrusion screw-design technology and new types of polymers, this concept had largely disappeared. Most processors today understand the need to have specific screw designs for each polymer to maximize output and melt quality. There is no such thing as a “true” GP screw, due to the myriad individual polymer characteristics involved for efficient processing. In the design of a high-productivity screw, the following list reveals some but not all the data considered: Viscosity at various shear rates and temperatures; Glass-transition temperature; Specific heat and heat of fusion; Melting point and processing temperature; Solid, bulk and melt density; Feeding characteristics. (ref. www.ptonline.com General - Purpose Screws on the Comeback? Written by Jim Frankland)
• So-called general-purpose screws are primarily used in injection molding, which makes sense because there are backpressure adjustments for melt quality in this process, and plasticating rate does not determine the cycle time. But such screws have little value in extrusion, which is totally dependent on the screw design for both melt quality and output. If there really were a good “general-purpose” extrusion design there would be no further need for screw designers. (ref. www.ptonline.com `General Purpose' = No Purpose Written by Jim Frankland)
• Almost all processes using a single screw require some degree of mixing, whether it’s just to homogenize regrind with virgin resin or to mix in some color concentrate. Although there have been many presentations on mixing by experts over the years, processors often find it complicated to apply this information to their own requirements. Many processors also confuse poor melting with poor mixing. Most polymers and additives cannot be effectively mixed until everything that can be melted is melted. As a result, melting and mixing often must be dealt with in the same screw design, although the solutions are often not the same. (ref. www.ptonline.com; Single-Screw Mixing Written by Jim Frankland)

Barrier Design Feed Screw

• These types of screws offer more melt uniformity. Barrier screws have a number of advantages, but the most important is the ability of the designer to pinpoint the location where melting is to be completed. In conventional screws, the typical melting pattern occurs in the compression section. The channel depth is gradually reduced in this region, forcing unmelted polymer outward, where it is subjected to high shear forces that cause it to melt. (ref. www.ptonline.com; The Melting Precision of Barrier Screws Written by Jim Frankland) 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)
• A properly designed barrier screw allows for complete elimination of unmelt while not restricting output. The unmelted polymer can be contained in the solids channel until it is melted, with the melted polymer contained in a second melt channel. This allows for the completion of melting to be “designed in.” Additionally, the thermal history of the entire melt is more uniform since it was all melted the same way. And since the melting was completed well before the screw discharge, the melt is thermally homogeneous to encourage uniform die flow. This design also eliminates the need for a mixer in most cases. (ref. www.ptonline.com; The Melting Precision of Barrier Screws Written by Jim Frankland)

Mixing Feed Screw

• Almost all processes using a single screw require some degree of mixing, whether it’s just to homogenize regrind with virgin resin or to mix in some color concentrate. Although there have been many presentations on mixing by experts over the years, processors often find it complicated to apply this information to their own requirements. Many processors also confuse poor melting with poor mixing. Most polymers and additives cannot be effectively mixed until everything that can be melted is melted. As a result, melting and mixing often must be dealt with in the same screw design, although the solutions are often not the same. (ref. www.ptonline.com; Single-Screw Mixing Written by Jim Frankland)
• There are three kinds of mixing: dispersive, distributive, and extensional. Extensional mixing occurs predominantly in the twin screw extrusion process. Dispersive mixing is similar to using two materials to be mixed on two plates and rotating one plate. The shear stress developed in the polymer between the plates would be proportional to the distance between the plates and the speed at which the plate was rotated. Distributive mixing would be similar to putting the two materials in a bowl and mixing with a spoon. The number and path of the spoon strokes would be proportional to the degree of mixing. Screws inherently provide both dispersive and distributive mixing. Generally, the shallower the screw the more dispersive mixing occurs, and the more disruptions in the flow path the more distributive mixing occurs. dispersive mixing occurs as the polymer and additives pass through the narrow gap between the screw flight and barrel, where the shear stress is very high. Distributive mixing occurs as the polymer leaking over the flights is continuously blended into the polymer in the adjacent channels dispersive mixing occurs as the polymer and additives pass through the narrow gap between the screw flight and barrel, where the shear stress is very high. Distributive mixing occurs as the polymer leaking over the flights is continuously blended into the polymer in the adjacent channel dispersive mixing occurs as the polymer and additives pass through the narrow gap between the screw flight and barrel, where the shear stress is very high. Distributive mixing occurs as the polymer leaking over the flights is continuously blended into the polymer in the adjacent channels. Worn screws would be an easy solution to many mixing problems, but the downside is you get decreased output from them. As the polymer leakage over the flights increases with increasing barrel/screw clearance, both dispersive and distributive mixing increase significantly. The above mentioned information is for illustration of the principles and are not necessarily the only recommended designs. (ref. www.ptonline.com; Single-Screw Mixing Written by Jim Frankland)‍
• Egan Mixer: A mixer combining strong dispersive and distributive characteristics. A reduced diameter provides multiple high-shear regions as well as leakage flow and many reorientations for high levels of both dispersive and distributive mixing. All of the flights are undercut so there is a lot more dispersive and distributive mixing than with the Maddock mixing section.‍
• Maddock Mixer: A very popular example of a mixer that is primarily dispersive, with lesser distributive characteristics. Dispersive type mixers for good homogenous melt for any non-shear sensitive materials. In the Maddock mixer, melt passes over a very narrow clearance where it experiences high shear for a high degree of dispersive mixing. Melt is divided several times and reoriented to provide some distributive mixing.‍
• Saxton Mixer: A mixer that is mostly distributive with minor dispersive characteristics. General purpose distribution mixer provides good melt quality and color mix for most materials. In the Saxton mixer, melt is divided many times and recombined with numerous reorientations to provide mostly distributive mixing.‍
• Pin Row Mixer: General purpose distribution mixer provides good melt quality and color mix for most materials. ‍
• 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: (See above section) This provides improved melt quality and increases throughput rates an average of 10%-20% for a wide range of materials. A properly designed barrier screw allows for complete elimination of unmelt while not restricting output. The unmelted polymer can be contained in the solids channel until it is melted, with the melted polymer contained in a second melt channel. This allows for the completion of melting to be “designed in.” (ref. www.ptonline.com; Single-Screw Mixing Written by Jim Frankland)

No one mixer fits all situations, so it is important to determine exactly what your overall process requirements are before selecting a mixer or even a combination of mixers. See the below section for mixer types. TIR manufactures and rebuilds a multitude of both simple and very complex mixing sections for extrusion and injection  feed screws, selected for your material and application. Please contact us for analysis and advice on mixing section materials and design for your application.

Compression Feed Screw

• This is a very rare screw, but used when 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)

Tapered and Parallel Feed Screw

• Tapered and Parallel Feed Screw: Gradually tapering screw root (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 Feed 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.
• Feed 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 Feed 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)

Feed Screw Design

• “Universal” extrusion screws: “What’s the hold-up? Why can’t there be one Feed screw design to run all polymers?” To many people “plastics” are all the same. But, in fact, different plastic types can have very different processing properties. A single screw preforms three basic functions: solids conveying, melting and metering or pumping. Each of these functions is controlled by the individual properties of the specific polymer, namely their thermal, viscoelastic, solid and melt density, and frictional properties. These properties can be so diverse that it’s highly unlikely that a universal screw would be able to process them all efficiently. That’s not to say that some polymers cannot be processed at all on a particular screw, but not at their optimum efficiency. (ref. www.ptonline.com Why Are There No `Universal' Screws for All Polymers? Written by Jim Frankland)

• Properly engineered flight profiles on your extruder screw or injection molding screw not only optimizes processing, but can reduce the effects of wear on screw/barrel components. We are continually researching new screw and barrel materials that would best fit our customer’s needs in providing high wear resistance against abrasive, corrosive and adhesive wear. Optimizing performance improves processing and will extending the life of the screw and the barrel. Improved output, better mixing, and critical melt quality can all be achieved through proper screw design. Crystaline and amorphous material process differently so the designs are different for each. Different barrier screw designs and various mixers are available from TIR and are selected to achieve desired outcomes. TIR engineers work with our customers to provide the best possible design based on customer requirements, including documented inspections, complete upsize, downsize and thermoset conversions.

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, rebuild and manufacture a feed screw from 19mm to 20in diameter and up to 40' in length specific to your process and manufacturing goals.