Archive for October, 2015

NSK Rescues Building Insulation Line

Friday, October 30th, 2015

Band saw manufacturer, Prosaw, found their bearings to be regularly failing on automated saws that had been supplied to a prominent manufacturer of building insulation. Both companies needed a solution to this problem, and fast.

In comes NSK. A large number of NSK bearings are used as replacements which deliver big savings and high quality products. NSK offers a service via NSK authorized distributors to help identify and deliver cost savings.

With their Added Value Programme (AID), NSK engineers help customers improve efficiency and reduce breakdowns. This can involve a comprehensive review and analysis of a company’s operation before making recommendations for improvement.

What Was the Diagnosis?

The bearings used on the followers that keep the saw blade in position were in some cases only lasting a matter of hours before they seized. This was odd since the maintenance team was fitting good quality bearings from well recognized manufacturers.

The problem is that to the casual eye, cheap bearings look the same as quality branded bearings. NSK takes on the task of explaining to maintenance workers that there are differences in everything from the dimensional accuracy of the raceways and rolling elements, to the hardness, and the purity of steel that is used.

The result of these differences can be like night and day when it comes to bearing life. That is why exchanging these for a good quality bearing can make all the difference in performance and operating life.

The bearings in this case, appeared to be of good quality, and had been used in prior work at Prosaw. Upon looking further, this was a case of bearing contamination.

How To Solve The Problem

Combating contamination in bearings is one of the single most effective ways to extend bearing life and consequentially to reduce the maintenance requirement of the machinery they are fitted to.

The insulation material produced fine abrasive particles when cut with the saw blades. These particles made their way through the bearing seals, into the lubricant, and into the bearings, wearing them out incredibly quickly.

NSK tested this theory and the results concluded that the bearings were failing due to particulate ingress.

From that point out, NSK recommended using the NSK Deep Groove Ball Bearings with high performance DDU sealing arrangement, made for use in dusty environments.

The DDU design keeps particulates at bay and effectively protects the bearing grease in a dusty environment. And the results were spectacular. The bearings on the saws now last several weeks, rather than only a few hours.

This solution came about from Prosaw’s want to provide excellent service, and calling in an expert component supplier.

Bearing Protection Best Practices

Friday, October 23rd, 2015

A lot can go wrong when dealing with bearings. With so many variables, it’s hard to think that even taking precautionary measures up front will save headaches down the line.

Nevertheless, it’s important to take those measures to protect bearings and ensure the longest life possible.

Today, we’ll go over some basic best practices for bearing protection, specifically suited to contaminated conditions where dust and moisture are prevalent.

It is difficult for bearings to operate in dusty or wet environments. In such conditions, the protection of bearings against contamination is paramount.

Proper Assembly

This will be the most important sentence of this post: If contamination occurs when the housing and bearing are joined, external protection won’t be sufficient to stop premature bearing failure.

This is the first and most vital checkpoint for making sure the bearings do not become contaminated early on.

When assembling the bearings into housings, take the following measures:

  1. Clear and wipe clean the work station.
  2. Wash your hands thoroughly.
  3. Ensure the air is as dust-free as possible.
  4. Use fresh, clean grease.
  5. Clean the components and remove all old grease, or buildup.

Housings and Seals

Although the bearing is contained within a housing, dust and moisture can enter via the shaft entry. There must be a reliable shaft seal to protect against bearing contamination inside the housing unit.

For dusty conditions, a labyrinth or contact type seal is best. Lip seals may have come with the equipment, and may work, but they wear down over time and will crack and deform, allowing dust or water to enter the bearing. Although this best practice is rarely followed, lip seals should be routinely replaced with better seal types.

If possible, use an automatic lubricator to keep the seals working their best. A small, consistent amount will force dust and moisture away from the bearing.

Note that a labyrinth seal requires the shaft to run straight and true. And, the gaps between the two parts in a labyrinth seal must be sealed to keep out contaminants.

Breathers

Breathers release hot air from the confined space and allow air to return when the space is cool. Enclosed bearings get hot during operation, and cool when not being used.

If the air that’s drawn back into the space is contaminated with dust or moisture, the bearing will become contaminated.

A poorly screened or filtered breather will allow for bearing contamination and cause premature failure.

Replace the inadequate breather with a low-micron air filter that will remove dust particles to micron and bigger.

Additionally, be sure the breather is protected from water spray and damp conditions.

These protective measures will lengthen your bearings’ lifespan. Remember most importantly, that if the bearing is contaminated when put into the housing, it won’t easily become uncontaminated.

Guide to Bearing Coatings

Friday, October 16th, 2015

Recent advances in material science have allowed the bearing to last longer, and perform better than ever before.

Previously, certain environments would cause irreparable damage to bearings in a very short time frame. With advancements in materials and coatings, bearings are now able to operate even where the environment is highly demanding.

Specialized coatings and bearing materials can be credited for this advancement. Coatings provide added performance and protection, often providing solutions to issues at a reasonable cost.

This is a guide to certain coatings and the applications they are best used for.

Coating Types and Uses

Black Iron Oxide – beneficial in wind power and rail appications, specificially for cylindrical roller bearings. Purpose is to improve running-in behavior, and oil film retention.

Ceramic Coating of Aluminum Oxide –  useful in electric and traction motors, or axle boxes. Specifically used on deep groove ball bearings, cylindrical roller bearings, and tapered roller bearings. Purpose is to improve current insulation.

Nickel Plating – food industry applications, specifically pillow blocks and track rollers. Advantage is corrosion protection.

Physical Vapor Deposition (PVD) – useful in various applications, including paper processing, rolling mills, wind, mining, and outdoor equipment. Purpose is to protect bearings from wear and friction, specifically deep groove ball bearings, and track rollers.

Thin Dense Chrome (TDC) – beneficial for applications involving an exposure to seawater, or vibrating screen bearings. Protects the bearing from corrosion and fretting corrosion, specifically spherical roller bearings and spindle bearings.

Polytetrafluorethylene (PTFR) – useful in ship engine applications, suction rolls, and bearings for cement mills. Protects from wear, and frictional behavior, specifically spherical plain bearings and spherical roller bearings.

Zinc with Metal Alloy – beneficial in various applications, including paper processing, rolling mills, outdoor equipment, and automotive applications. For the purpose of protecting bearings from corrosion, specifically insert bearings, and tapered roller bearings.

Manganese Phosphate (MnP) – useful in mixer gears, for help with sliding and running-in behavior, and to prevent wear and friction. Spherical roller bearings that have steel cages, and adaptor sleeves benefit form this coating.

There are many new advancements in bearing materials and coatings coming out rapidly in this industry. This is a short list of some common bearing coatings. The goal is always the same – improved bearing life and increased production time.

Black Oxidized Bearings for Wind Applications

Friday, October 9th, 2015

Wind turbines are subjected to a wide range of temperatures, wind speeds, and loads over their lifetime. These operating conditions often result in premature bearing damage and failure.

Black oxidized bearings have come forth as a solution to improve the operational reliability of bearings used in wind turbine applications.

The benefit of black oxidation in reducing the risk of premature failures has been proven by extensive field experience.

Gearbox manufacturers and wind turbine OEMs have reported a significant improvement in reduction of bearing failure rates with the use of black oxidized bearings.

The Process

A chemical reaction at the surface layer of the bearing steel is responsible for coating the bearing in black oxide.

Specifically, the bearing is immersed in an alkaline aqueous salt solution at a temperature between 130-150 degrees Celsius. The oxide layer is then produced from the reaction between the iron of the ferrous alloy and the reagents.

Typically, around 15 different immersion steps are followed for the oxidation process. Once finished, the bearing has a dark black surface layer.

The Benefits

Lab investigations, bearing tests, and field experience have shown demonstrated benefits of black oxidized bearings.

In the severe operating conditions of wind turbines, black oxidized bearings cope with both insufficient lubrication and surface damage significantly better than untreated bearings.

Black oxidized bearings reduce bearing surface distress and prolong bearing life, improving the overall safety margin. In use, there is a noticeable reduced friction after running-in.

The black oxide protects against tribochemical attack, reduces the permeation of hydrogen, and increases resistance to moisture damage. Lubricant adhesion is also improved, compared with the use of non-coated surfaces.

You can replace conventional bearings with black oxidized bearings during maintenance routines so that over time, the benefits of black oxidation can be applied to all bearing types used in a wind turbine gearbox system.

For optimal performance, the inner and outer rings, as well as the rolling elements ought to be black oxidized.

Bearing Questions and Answers

Friday, October 2nd, 2015

In the bearings applications we discuss on this blog, few are clean and sparkly, and make storage, installation, lubrication, and maintenance easy as pie. In other words, we all have questions about how to properly care for the bearings we use, that are beyond the manual. Today, we’re going through some frequently asked questions and offering some bite-sized answers for you.

Q & A

Q: If you have a new bearing that has been used, but is pretty dirty, what can you do to use it again?
A: Hand wash, and try not to spin it. Never wash double shield bearings, only wipe them off then apply lubricant before wrapping and storing.

Q: Besides storing bearings on the shelf, what’s the “correct” way to store them?
A: Keep bearings in a clean, dry location, and watch temperature changes as drastic changes can harm the bearing if any moisture is present. Handle bearings as little as possible, as your fingerprints can promote rusting. Take care not to drop or handle them roughly, they are precision components. Another best practice is to store them by keeping the oldest at the front, and always using the oldest bearing first.

Q: I understand lubrication is essential, but what is its main role?
A: Lubricant is used to establish and maintain a micro-thick separating film between rotating and static parts, so that the bearing can perform well, have long life, and keep from being damaged.

Q: Is getting the correct type of lubricant really important?
A: Yes, improper lubrication is responsible for approximately 43% of bearing failure – that’s a lot! Application specific grease or oil is important, as is lubricating frequency, quantity, and viscosity. Be sure to re-lube at proper intervals, and beware lubricant contamination. And, take note that over-lubrication of bearings used in high heat applications can be just as harmful as insufficient lubrication.

Q: Can seals be used in place of shields on a ball bearing?
A: Not if you want to avoid problems. A shield provides a clearance between the inner and outer race, whereas a seal is attached to the inner race and could cause problems rubbing on the inner race, depending on the speed, heat, and starting torque of the machine.

Q: How can I determine if a bearing is failing?
A: Three main indicators – excessive noise, heat, and/or vibration. If these are present more than expected, you can be pretty certain that a bearings is failing.

Q: Are there any common improper methods of mounting or installation?
A: A couple main ones here. One is contaminating the bearing during installation. The other is applying force on the incorrect ring, as it should only be applied to the press fitted ring.

Q: If my work space is dirty, how can I take care to install a new bearing without messing it up from the git-go? 
A: It’s understandable, after you’ve taken the time and care to properly store your bearings, that you would want to be sure to install them in a clean environment. But, that’s tricky. Clean the work bench area and the tools you will use on the new bearing, and keep away any linty cloths. Keep the bearing on its original wrapper or some clean paper when working on it. Don’t let the bearing sit on a dirty surface, even for a short time, or you’ll risk contamination and early failure. And, remember bearings shouldn’t be washed, except for oil mist or circulating oil system.

Q: Will a stainless steel bearing protect against rust?
A: Not to the extent you might think. Stainless steel is not rust proof. It is corrosion resistant and will rust in corrosive environments over time, but at a much slower rate than chrome alloy steel.

Q: What is a good waterproof seal?
A: Bearing seals are designed to retain the lubrication inside the bearing, and most are considered water-repellent, but they won’t prevent water from entering the bearing if it is submerged. If the bearing must operate while submerged in a liquid, use a ceramic hybrid or full ceramic bearing.

Q: What does “radial play” mean?
A: Radial Play refers to the fit or clearance of the balls within the bearing. The normal range is from C2 to C5, with C2 being the tightest fit (not much room for expansion of the balls or misalignment) and C5 being the loosest (allowance for some expansion as the bearing heats up or misalignment of the application).

Q: Can I flush out a lubricant and use another?
A: You would need a prescribed flushing agent, and a properly environmentally controlled environment in a controlled area. The bearing would have to be thoroughly dried post flush, and lubricated with the correct amount and type of grease. Short answer is yes, with some extra effort.

Remember, if you do the best you can, all these efforts will prolong bearing life and improve machine performance.