Industrial Plastic: Strengths And Limitations

One of the key questions we ask customers is “what is the application?” This question isn’t asked in order to steal your idea but to ensure that the plastic you’re looking for is optimal, or even workable in that application! Industrial plastics are excellent mechanical materials overall; however, like anything they do have both strengths and limitations. This article will review the core line of industrial plastics we carry, give the strengths, the limitations, and common applications/places where the plastic is wrongfully specified.

UHMW Polyethylene

Strengths: Well balanced properties, economical, and readily available.

Weaknesses: Poor dimensional stability

Specification errors: high load bushings, unrealistic tolerances, not compensating for thermal expansion.

 

Nylon

Strengths: High load bearing strength, diverse formulations, suits a wide variety of applications.

Weaknesses: Absorbs water, poor impact and cold-temperature properties.

Specification errors: Impact parts, marine applications (without accounting for swell), using nylon bushings in high RPM applications.

 

Acetal

Strengths: High load bearing strength, replaces nylon in “wet” applications, machines to excellent tolerances.

Weaknesses: Impact, temperature (especially steam) resistance.

Specification errors: Using black (copolymer) acetal in food processing applications. It is not food-safe, unlike the blue and white.

 

Tuffkast

Strengths: Excellent impact, cold weather, bearing, and moisture-resistance properties.

Weaknesses: High cost, elevated temperatures.

Specification errors: Typically in applications that generate high internal heat, such as a hammer cushion for pile drivers. Tuffkast is also softer than nylon, which can lead to increased wear in certain applications.

 

Polycarbonate

Strengths: Extremely high impact strength.

Weaknesses: Very prone to scratching.

Specification errors: As glass/sight part without upgrading to a anti-scratch version of the plastic.

 

Acrylic

Strengths: Scratch resistant, economical, stronger than glass, fairly resistant to weathering.

Weaknesses: Difficult to fabricate, prone to cracking.

Specification errors: Using in “Do-it-yourself” projects without proper knowledge of fabrication procedures.

 

Polyurethane

Strengths: Impact resistance, rebound, good bearing strength (bearing grades only).

Weaknesses: Water saturation degrades the plastic (especially softer grades), vibration degrades the plastic’s composition.

Specification errors: Vibration or moisture applications.

 

Rubber

Strengths: Lots of choice between properties, cost, wide application variety.

Weaknesses: Polyurethane is superior in many applications, grades must be selected carefully.

Specification errors: Choosing an ineffective grade of rubber for an application to save on cost, assuming the lower grade will still function.

For more information about which plastic is best for your application, please contact us.

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3 Critical Issues You Need To Know About These Popular Plastics

Many industrial plastics can “overlap” in applications where sometimes the optimal choice is only marginally better than several others. Many plastics may work in an application, such as nylon and acetal for sheaves, but certain issues in the operational environment may mean you need to stay away from a certain plastic! Three of the most popular plastics we carry are UHMW polyethylene, cast nylon, and PTFE. But each of the following has a critical issue you need to know about that often discredits the material in certain applications.

UHMW – Impingement

UHMW is a great wear material at an affordable cost…Usually. The one place where it isn’t good at all is with impinging wear, that is wear from a mating partner (could be anything from grains, to rocks, to another sliding component). Impingement is when something hits that UHMW on an angle. With UHMW anything that is remotely abrasive needs to hit it on a 90 degree angle. If the angle is any sharper you risk very quick deterioration of the UHMW plastic. It simply does not hold up to impingement. Often polyurethane, which has excellent impingement resistance, is a substitute and one can be creative, for example only using polyurethane in the impact zone and use UHMW for the rest of the application.

Nylon – Cold Temperatures

Many people know that nylon is affected by moisture swell, what fewer people know is that it gets brittle in cold temperatures, about 10 Fahrenheit or -12 Celsius. This can come as a shock, as nylon is known as a high-load plastic able to handle 4,000 PSI in bearing applications. It is not intuitive to think that cold temperatures would greatly affect the nylon but it is true. Fortunately, replacements are available, specifically Redco Tuffkast is often best to replace nylon. Tuffkast solves not only cold weather issues with nylon but also absorbs much less moisture, so Tuffkast’s properties help in that case as well.

PTFE – Wear

It is often that customers request PTFE for a wear or lining application, even including heavy applications such as dump truck liners! We do try to warn them that PTFE has very poor wearing ability. It is a soft, almost waxy material, that while it is available in sheet form (and seems solid enough) it really cannot hold up to aggressive wear. Bronze filled PTFE is available which increases the wear capabilities; however, by that point there is often a less expensive, more available plastic, that can be suggested as a replacement. PTFE should be avoided in high wear applications wherever possible.

Hopefully you are surprised by at least one of those points, in the hopes that it will assist your material choice in your next application.

To discuss the optimal plastic for your application, get in touch with us today.

Product Spotlight: Redco Acetal

In the world of thermoplastics acetal (polyoxymethylene or POM) sometimes gets overlooked in applications as customers consider more well-known plastics such as UHMW, nylon, or PTFE. However, acetal offers excellent versatility, overall properties – all while being the most machinable thermoplastic. Unlike many other plastics, acetal is quite hard with a dense weight that reminds one more of a metal than a plastic.

Given this property, acetal can be used to replace precision machined acetal parts that were formally metal. Examples are gears, valves, and parts like the bolt in paintball markers. Acetal is often used as a nylon replacement in marine applications. This is because it can take similar load yet will not absorb water like the nylon will. But there is often no reason why you could not have specified acetal as a nylon replacement in the first place.

Where acetal really excels; however, is dimensional stability. It is one of, if not, the most dimensionally stable plastic. What this means is it can be machined to tighter tolerances than other plastics and will hold those tolerances better. In addition, it has excellent resistance to creep at normal operating temperature. If dimensional stability in an application is of top priority than acetal should be near the top of your list!

As with any plastic, acetal does have some concerns. They are attacked by strong acids and oxidizing agents so keep that in mind. Acetal comes in two common grades the homopolymer and copolymer, with the copolymer being better in hot air or water environments. Acetal is available in FDA approved grades, including metal and x-ray detectable grades. Acetal should not; however, be used with chlorine washdowns or cleaners. In that case PET should be selected as a substitute.

For answers to your questions about Redco Acetal please contact us.

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PET – The “Forgotten” Plastic

In the world of mechanical/industrial grade plastics PET-P commonly known simply as “PET” is the underappreciated soldier. PET performs every day in harsh environments: farming machinery, food processing, and medical industries in particular. It’s constantly dirtied, steamed, soaked and coated with all sorts of substances every day – but it doesn’t get any respect!

PET (polyethylene terephthalate) is a crystalline, high-molecular weight plastic that is notable for its balanced properties. It is most similar to acetal and is an excellent substitute for it in many applications. In particular vs. acetal, PET can handle a higher operating temperature – 230 degrees Fahrenheit constant – and is not affected by chlorine cleaners or wash downs (unlike acetal). In addtion, PET is very dimensionally stable – a significant advantage it holds over more popular plastics such as UHMW and nylon.

Another important note is that PET is FDA approved for direct food contact. It serves as a “bridge” between plastics with a lower temperature threshold such as UHMW and acetal and more expensive heat-tolerant plastics such as your virgin and filled PTFEs.

Redwood Plastics can quote PET parts complete or material alone; however, none of our branches stock PET so please be very specific about your requirements as minimums may apply.

If you have interest in this product or other Redwood Plastics products contact us today.

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Food-Safe Plastic Bushings

Bushings are used in all types of manufacturing industries and food processing is no exception. Metal bearings such as roller bearings and bronze bearings are widely used but, as in other industries, plastic bushings tend to perform significantly better than metal, permitting less maintenance, increased production, and reduced downtime. Yes, the upfront cost of a plastic bushing is usually more than a metal one. But ask yourself how quickly you would expect a bushing that is a few dollars more to pay itself off with more production and less maintenance work? Plastic bushings are suitable especially when you need:

  • Increased bearing life
  • Less or no greasing
  • Self-lubrication properties
  • Better wear and lower coefficient of friction than metals

There are several food-safe (FDA) compliant plastics for this application. One of the very best is Rulon 641: a white, food-grade bearing material with phenomenal load and wear characteristics. Rulon 641 can handle a pressure velocity (PV) value up to 10,000 and is suitable for pairing with mild, 303 or 316 steel. Another bushing material that performs very well in food processing applications is Redco acetal. Acetal is a very hard plastic, but also very machinable to tight tolerances and the homopolymer (white) version of the product is FDA compliant. As is the new blue acetal now showing up more in applications, as the blue has a color different than most foods and that visibility is desirable to many customers in the food processing industry.

Several other plastics can be used as bearings in certain applications: white-natural UHMW polyethylene and certain food-safe grades of nylon or polyurethane as well. However, acetal and the Rulons will often be choices where you cannot go wrong. The first step in us assisting you with your food-safe bushing is to fill out our bushing design form. You can then upload it to our RFQ form and email us here.

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New FDA Food Safety Rules

The U.S. FDA is putting the finishing touches on some major rule changes and the rest of the world needs to take note (read more here). Why? Because these rules do not only affect domestic food but imports as well which must now be held to the same FDA standards. The emphasis of the new rules will be on prevention instead of reaction. Functionally, this means companies will be required to have a written, preventative food-safety plan that addresses food quality concerns. How do these rules relate to plastics? One word: contamination.

The threat of contamination is behind the development and recent proliferation of blue FDA approved plastics as well as X-ray and metal detectable acetals and UHMW-PE. These plastics could, and should, play a key role in preventative food safety moving forward. The plastics can be caught by detection machines if they ever break into the food and the blue plastic can be easily spotted by workers on the processing line. There is no excuse why these plastics cannot be implemented: they are FDA approved, have obvious advantages over traditional natural grades of plastic, and are available in several grades – even a FDA approved dryslide (extra low coefficient of friction) specialty grade! Like it or not, these new FDA rules are coming and formulating your preventative food safety plan should involve Redco foodsafe plastics.

For answers to your questions on our line of food-safe acetals and UHMW-PE please contact us today.

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Plastic Bushing Solutions

Industrial plastics serve as an excellent bushing/bearing material in everything from needle bearings to large marine bushing applications. Since many industrial plastics are suitable for different bushing applications its best to know the advantages, and potential drawbacks, of each material. The following is not meant to be an extensive guide to selecting a bushing material, just a primer to the different options:

UHMW polyethylene:

UHMW-PE can serve as an excellent low-load bushing, 500-800 PSI is at the top of its limitations. UHMW has the benefit of being economical, self-lubricating and readily available. Customers tend to be very familiar with this particular plastic and trust it. Areas for concern with UHMW are its relative low-load, and high thermal expansion.

Nylon 6:

Cast nylon (nylon 6) is a widely used bushing material and can handle up to 4,000 PSI. Cast nylon is available in several grades including heat stabilized, Moly-filled and oil-filled. The primary area of concern with nylon is its moisture saturation: 4% in a water saturated environment. Impact and cold environments are also a concern for nylon. Nylon bushings can either be made with much more generous allowances in aqueous environments, or acetal may be a substitute.

Acetal:

Acetal is one of, if not, the best plastic to machine due to its hardness and ability to machine to tight tolerances. Acetal is often a good substitute for nylon in marine environments.

Industrial laminates:

Often just called “Micarta” or “phenolic” by customers, industrial laminates excel in high-load, low RPM applications. Certain industrial laminate bearings can handle in excess of 24,000 PSI. You do need to be aware that these bushings should be lubricated and that certain rotational speeds will not work. If you need to know the specifics, just ask.

Redco 750 and 750 XL

Polyurethane bushings are often an excellent choice. They handle abrasion, impact, and can be molded (perhaps with some machining to finish them). Polyurethane can handle up to 2,500 psi. Cold temperatures may be a concern, and tooling costs are often involved with urethane parts, but the end result are effective bushings that can be produced with low-lead times and in quantity.

For answers to your questions on our bushing or bearing material, contact us today.

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