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.

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Nylon For Specialty Applications

Nylon is a family of plastics with several different additives that make them suitable for applications where natural-grade nylon isn’t optimal or won’t be successful. There are three grades of nylon specifically that should be highlighted for their properties in applications with unique demands.

Firstly Redco SL which offers a low coefficient of friction with excellent wear resistance. It was developed for applications where external lubrication is either very difficult or impossible. Redco SL performs better than other nylons and many plastic where the part is rarely accessed for maintenance.

Secondly, Redco glass-filled nylon serves very well for prototypes. The glass filling results in a very dimensionally stable part which can be held to tighter tolerances. This part also has the lowest “cold flow” of any nylon. If you’re looking for a “proof of concept” part than Redco glass filled nylon is an excellent choice.

Lastly, Redco blue is a grade of nylon for high-heat applications, able to withstand up to 250 degrees Fahrenheit ongoing in application. This alone isn’t especially unique, as several plastics such as PTFE handle temperatures just as high. However, Redco blue nylon is the best “bang for your buck” for a heat-tolerant plastic. The alternatives such as the aforementioned PTFE, PEEK, ULTEM, etc. are all much more expensive. If you’re having trouble finding a heat-tolerant plastic and you know your application is 250 degrees F or less, then Redco blue may be an excellent choice for your application.

To see if the Redco nylon products listed above or another plastic is optimal for your application, please contact 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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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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Product Spotlight: Bushings and Bearings

Important note: Redwood Plastics does not stock many bushings or bearings. Customers view our bushing and bearing section and believe we have many off-the-shelf solutions and this is not true. What we can do, is take your available information on your application and try to come up with the best solution out of the many bearing-grade plastics we have available. Most commonly, these are the materials chosen:

Nylon: Handling 4000PSI and available in several grades with various fillers and performance enhancers, nylon is probably our most used bearing material. Nylon can be used in very large or small bushings, since nylon is available in cast or extruded forms. The extruded nylon can be made into very small bushings and larger bushings can be cast to net size and machined to completion.

Tuffkast: Nylon has drawbacks: water absorption, cold weather performance and impact. Tuffkast is a co-polymer that can provide the bearing properties of nylon with the impact resistance of polyurethane. The only reason it isn’t used more is that it’s still earning name recognition.

Polyurethane: Polyurethane is available in Redco 750 and 750 SXL bearing grades. The nice thing about urethane is if you need a mass-produced bushing because we can supply a precision-molded product, machining them to finish if necessary. Polyurethane has great impact resistance and can handle loads up to 2500PSI.

Phenolic/Composites: Composite bushings allow for the highest loads a plastic bushing can take. They perform extremely well high-load, low RPM applications. A benefit of composite bushings is that the material (or a liner on the inner diameter) is designed to create a lubricating film on the shaft, meaning no greasing in some applications. Some of these bearings can be purchased (though are not stocked) in finished sizes common throughout various industries.

Turnaround time for finished bushings varies, but is usually a few weeks. We can always supply just the bearing grade material to you in almost all cases to improve delivery or reduce costs if you want to machine them yourself. If interested in a finished bushing or bearing, unless you know exactly what you’re looking for, the first step is to complete our bearing design worksheet, available by clicking these links for a simple sleeve bushing or a flanged bushing. That can be emailed to sales@redwoodplastics.com and will be reviewed by the appropriate contact for quotation.

For more information on our bushing and bearing solutions, visit our website’s dedicated page here.

 

Redco Kiln Wheel Bushings

Redco Kiln Wheel bushings are an essential component to sawmills that have large dry kilns. These plastic bushings enable the carts to run freely through the mills and we supply the bushings in three grades:

Redco Blue kiln wheel bushings:

Standard Redco blue nylon kiln wheel bushings are a cost-effective and proven solution as a kiln wheel bushing. The nylon used in these bushings is head stabilized to handle long drying periods in the kiln. These bushings should not be used in sawmills where they will be exposed to very cold temperatures for a sustained period as nylon becomes brittle below -12 Celsius.

Redco Hi-Temp Yellow kiln wheel bushings:

A premium kiln wheel bushing we’ve been developing on at one of our western American branches the last couple of years. The yellow bushings in testing outlast and outwore the blue nylon bushings significantly and use a proprietary material we’ve developed to replace Redco blue kiln wheel bushings at a modest cost premium. The yellow bushings have more than paid for themselves in increased lifespan and, yes, they make the carts run smoother as well. These bushings are a direct substitution for Redco blue nylon kiln wheel bushings but are still not the correct choice in very cold weather environments and do not have increased load capacity over the regular blue.

Redco Phenolic kiln wheel bushings:

Phenolic kiln wheel bushings are used in high load (36,000lbs+) applications or where extreme cold is involved. Due to the properties of phenolic material (a fairly high coefficient of friction), it is recommended to put a grease groove in the bushing.

To work with a Redwood representative on your next kiln wheel bushing order please contact us.

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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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