A plastic extrusion is a profile with a given cross section shape (two given dimensions, height and width) that can be cut to any length. The plastic can be either a thermoplastic (heat does alter its characteristics) or a thermoset (heat does not alter its characteristics). Thermoplastics can be regrounded and used again. Thermosets cannot be easily reused. Polyvinylchloride (PVC), Polystyrene, ABS and Polyethylene are all examples of a thermoplastic. Urethane, Epoxy, Alkyd and Melamine are examples of thermosets.

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What is the difference between extrusion and injection molding? 

Extrusion is a process where molten plastic is pushed through a two-dimensional die opening. After the molten plastic exits the die opening, it passes through a series of sizers or forms that hold the shape of the part as it cools. A puller or conveyor grips the cooled extrudate and moves it through the sizing equipment. The extrusion process is capable of producing two dimensional profiles or shapes that are continuous in length, yet can be either coiled or cut to length at the end of the process.

Injection molding is a process where molten plastic is injected into one or more cavities in a three-dimensional mold. This mold opens and closes as parts are formed and purged from the mold cavity. Unlike extrusion, this process is capable of producing three-dimensional shapes.  

The major difference between extrusion and injection molding are:

• Tool Costs – Extrusion tooling costs are much lower than injection molding.
• Lead Times – Tooling lead times of extrusion tools can be shorter than those of injection molds.
• Dimensional Tolerances - Dimensional tolerances of extruded parts are greater than those of injection molded parts. Generally, dimensional tolerances of extruded parts are in the 2% to 5% range. Because injection molded parts are formed in a static cavity, this process is capable of holding much tighter tolerances.  

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What is extrusion tooling?

Extrusion tooling consists of a die, downstream sizers and calibrators. The die itself is designed much like a funnel. The molten plastic enters the die at an enlarged opening that gradually narrows as the plastic nears the exit point of the die. The exit point of the die approximates the shape of the finished product. Once the plastic has exited the die it passes through a series of sizers that hold the suspended plastic in shape until it has had time to cool. Water baths, blown air, internally cooled sizers and vacuum sizers are often employed to form extruded parts during this cooling process.

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How expensive is extrusion tooling?

The cost of extrusion dies and downstream sizing can vary depending on the material, the profile configuration, the production volume and the tolerances specified. Tooling (die and downstream) for a complex, multi hollow shape with close tolerances is much more expensive than tooling for a simple shape.

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Why do I have to buy tooling?

Unless you are buying a profile from an extruder that runs stock shapes, you will have to buy tooling. The vast majority of custom extruders do not pass the full cost of the tooling and development charges onto the customer initially. The exception to this would be if it was a one-time production run. Most extruders make an investment in the tooling (by sharing in the development costs) to foster a long term relationship with the customer.

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Do you build the tooling?

The extruder is responsible for the building the tooling. Most extruders have in-house tool building facilities where they build all or part of their tooling. Some extruders may farm out part or all of the tooling to an outside source. This depends on the complexity of the tooling, the extruders tooling backlog or if it otherwise exceeds the extruder’s in house capabilities. It is extremely important that the customer is satisfied with the samples and communicates with the extruder on any exception prior to the running full production.

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Why does it take so long to build tooling?

The tooling lead time can vary considerably depending on the material, profile configuration, tolerances specified and the extruder’s tooling backlog. Not only does the tooling have to be built, but the die also has to be developed (or trailed). A die is designed in theory and based on the extruder’s experience. After the die is built it is setup on the machine and sampled. It is extremely rare that a die will produce an acceptable part the first time it is sampled. This means a die must be removed from the machine and modified to adjust the flow of plastic to form a part within acceptable tolerances. This modification process may have to be repeated many times.

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What determines the price of an extrusion?

This question does not have a simple answer. Below is a list of some of the factors affecting extrusion pricing:

• A. Material cost – the price of the raw material used in the extrusion process.
• B. Cost of the extrusion tooling – the development cost of the tooling is spread over the production run or future production runs.
• C. Shape and size of the profile – simple shape vs a complex multi hollow.
• D. Ease of extrudability – type of material, setup time, tolerances to be held, etc.
• E. Quantity ordered - affects material cost (if it is a "made to order" material from the extruder's supplier) and amortization (spreading) of the setup costs.
• F. Special fabrication - is there secondary fabrication tooling involved?
• G. Special color. 

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How do I know what material I need?

Material selection is a difficult, yet vital element of the design process. Designers may choose from an enormous variety of materials each with its own range of specific grades and formulations to satisfy most any property requirements. The first step is to conduct a detailed function analysis. In short, specifically define exactly how you expect the finished profile to perform. In doing so, it is equally important to determine what characteristics you do not want the profile to have. The more complete and accurate your requirements are defined, the better your material choice will serve its purpose. Begin by answering these questions:

• Load – what type of load will the part see?
• Temperature – what maximum and minimum temperatures will be seen?
• Appearance – is colour important? Should it be transparent or opaque?
• Chemicals – will the part be exposed to any chemicals? What specific types?
• Environment – will the part be used indoors or outdoors? Is electrical conductivity an issue?

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What about regulatory requirements – UL, NSF, SUDA, and FDA, CSA, JIT, etc. ?

Now that you have determined the characteristics your profile should possess, match them with the material, which offers those same physical properties. Thermoplastic materials are divided into two categories: general purpose plastics and engineered plastics.

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How do I know if my design will work?

While a good knowledgeable extruder can help out in the material and design recommendation, they cannot guarantee your design will always work. If you have a profile that needs testing it is often recommended to build prototype tooling first. Not all extruders will build prototype tooling. A lot depends on the customer, the profile and the future potential of the project. Most extruders, at best, break-even on prototype tooling unless they are a company that specializes (and charges) in that area. Still, prototype tooling can be built cheaper that production tooling. You have to realize that you will not get the quality (as close of a tolerance) that production tooling offers.

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What is a minimum production run?

There is no concrete answer. Only the following information. It can take several hours to set up an extrusion line and get the profile into a production mode. This time varies depending on the size and complexity of the profile and the amount of downstream tooling involved. An extruder must amortize (or spread) this setup cost over the amount of production requested. As a result the larger or longer the production run, the lower the price per piece or foot (all things being equal). Also, if your profile requires a non-standard material or colour there may be minimum purchase requirements from the supplier. This would result in higher costs and probably longer lead times for orders.

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How long are the extrusions?

Since the extrusion process lends itself to running a continuous length part, the answer is any length that is practical. One of the greatest benefits of an extrusion is the various length possibilities. Many customers used the same part in various lengths. By ordering various lengths the customer can save time, money and inventory problems. With today’s sophisticated saws and cutters, parts can be economically cut to any desired length.

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What about colour?

One of the greatest things about certain plastics is that they lend themselves to colour-matching. While PVC, ABX and Styrene are excellent materials for matching almost any colour. Materials such as Noryl and other engineering materials are very limited in colour matching abilities. Working with a knowledgeable extruder will enable you to make a material and colour selection that will fit your needs.

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What about fabrication of the plastic profile?

A number of secondary fabrication processes are capable of being performed on extruded products. They include:

• Close tolerance cutting
• Notching
• Stamping
• Routing
• Punching
• Tape applications
• Lamination
• Heat sealing
• Embossing

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Material Listings

Vinyl (PVC) – PVC’s tremendous versatility, blending capabilities and cost efficiency makes it one of the most widely used plastics available. It is excellent for complex, intricate designs and often replaces steel, aluminum, wood and glass.

• Vinyl has very good colorability, abrasion resistance, good chemical resistance, and excellent extrudability.
• It is available in flexible and rigid: outdoor and indoor grades; as well as a variety of specially modified grades. Flexible PVC is mainly used for sealing applications as in weather stripping in dual-extrusions for cushioning and impact absorption. Rigid PVC ranges from normal to high impact grades. Exterior grades have exceptional weatherability. Common uses include pipes, home siding and windows. Interior grades lack the weatherability of the exterior grades. Uses include tubing, commercial refrigeration, electrical race-ways, furniture and others.

Polystyrene – Styrene’s colour versatility and extrudability make it very attractive for high volume applications. This work horse is used heavily for advertising, packaging and indoor building products. It is appropriate for any application requiring colourability, extrudability or cost-efficiency.

• Unmodified styrene is a “crystal” water clear colour; however it is a very low impact, brittle material.
• Modified grades are available which offer high-impact resistance and good electrical properties. It has extensive advertising applications due to its exceptional colourability in any shade.

Polypropylene – combines many features to make it a very versatile thermoplastic. It is also the lightest weight plastic of the general purpose group.

• Polypropylene offers excellent colourability and moderate strength. In addition it has a good balance between thermal resistance, electrical conductivity and chemical resistance.
• The natural resins are milky white and semi-translucent.
• Some polyproylenes are UL listed and approved by the FDA for use in food and drug containers.
• Modifications offer high molecular weight, increased toughness, and heat stabilization to withstand high temperatures for prolonged periods for time.
• Common extrusion uses include: wire and cable coatings and hinge applications.

Acrylic – is a widely used plastic known for its clarity, strength and versatility. Acrylic offers superb optical quality, surface hardness, mechanical stability and excellent weatherability over may years of exposure.

• Acrylics are mar resistant and chemical resistant, easy to clean and among the most scratch-resistant plastics available.
• Common uses include: sky lights, safety glass I public buildings and outdoor signs.
• Modifications are available which greatly increase the impact resistance.
• Other modifications include a molecularly oriented formula which increases crack resistance.

Polyethylene – is the largest volume thermoplastic polymer used today due to its availability in a wide range of grades that have an equally wide range of properties with excellent processing features.

• Polyethylene’s all have excellent chemical resistance, excellent electrical properties, low friction coefficients and near zero moisture absorption. Polyethylenes are categorized according to density: low through high. Low density offers good toughness, flexibility and relatively low heat resistance.
• In film form it has good clarity and good resistance to chemical attack unless exposed to higher temperatures. High density has considerably higher rigidity and tensile strength than low density polyethylene.
• In exchange for stiffer material properties it sacrifices some degree of impact strength , yet it remains superior to most other thermoplastics in this area. Extra High Molecular Weight is the most common modification. It has excellent stress-cracking resistance, good rigidity and excellent impact strength even at low temperatures.
• Common extrusion uses include water and gas distribution pipe, wire insulation and sheet film.

ABS – is the last general – purpose plastic. It combines the best characteristics of each of its three chemical components. Acrylontrile gives ABS good chemical resistance and high heat stability. Butadiene provides impact strength and toughness. Styrene lends its rigidity, high gloss, colourability and processing ease.

• Combined, this polymer is one of the most widely used plastics available at very economical rates.
• Unmodified, the resin is translucent to opaque. Transparent grades are also available.  
• Although unmodified ABS has limited weatherability, a modified grade which includes UV stabilizers offers exceptional weather resistance and strength with prolonged exposure to sunlight and radiation.
• Another modification provides higher impact resistance which gives this superior impact strength, even at low temperatures.
• Other available modifications include extreme chemical resistance and increased abuse resistance.
• Common uses include: pipe, refrigeration linings, bathtubs, coolers, hard sided luggage and truck bed liners. Engineered Plastics Engineered plastics are a higher grade of thermoplastic materials which have been specifically designed for certain industries but which have applications in others as well.

Polycarbonate (Lexan) – is one of the toughest, most versatile engineered thermoplastics.

• Lexan is characterized by high molecular weight, with high impact strength over a wide range of temperatures, and an excellent combination of toughness, transparency and dimensional stability.
• The naturally water clear and transparent resin possesses good insulating and electrical industries.
• Extrusions include door thresholds, automotive bright trim, shelf rails, fluorescent lighting luminaries and safety glass I gas stations, banks and other public buildings to protect against vandals.

Modified Phenylene oxide (Noryl) – offers various grades of flame and UV-light resistance for use in business and computer equipment.

• Noryl is characterized by excellent impact resistance, high temperature applications for UL approval, high mechanical strength, toughness and low water absorption.

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