Cover Story: How to push and pull with ease
Industrial casters and wheels generally make the job of moving equipment easier, but trouble can arise with either the caster or the wheel. The following tips explain how to get the best solution.When...
December 1, 2002 | By MRO Magazine
Industrial casters and wheels generally make the job of moving equipment easier, but trouble can arise with either the caster or the wheel. The following tips explain how to get the best solution.
When it comes to industrial casters and wheels, the best maintenance practice is preventive maintenance, and even better than that is to ensure that the right caster has been selected for the job in the first place.
Choose the right caster that contains the right wheel that’s made from the right material, and you’ll have a device that will last for years and give trouble-free service. Go wrong on any one of those three variables and you’ll be forever changing casters or wheels, because, generally speaking, there’s not much you can do to fix them.
It’s when you have a mismatch to the task at hand that casters generally fail or perform poorly, causing higher operating costs, downtime and ergonomics issues. Even where the caster is the right one for the job, such factors as a hostile environment or lots of debris or rough handling can affect performance and longevity.
In such circumstances, the best strategy is to clean the place up and try to educate people, like the lift truck operators who insist on lowering their forks at breakneck speed when dropping off loaded carts or things like scrap bins. If that doesn’t work, shock-absorbing casters might do the trick. Or even change the wheel material to something like Neoprene D, to cushion most of the shock and vibration.
There are solutions. You just have to find them.
The first indication that there’s trouble with a caster usually comes with squeaks or push-resistance. The dang thing just won’t turn properly, or the cart behaves like a bad supermarket buggy. This can happen pretty quickly when wheel or caster bearings become dirty or contaminated with debris, or the lubricant breaks down and is not refreshed through maintenance. The solution here is quite simple: use sealed precision bearings in the wheel whenever possible. They cost a little more but are virtually maintenance free. Sealed swivel assemblies will solve one of the biggest headaches of all, which is friction in the swivel housing.
Sometimes problems arise from rust or corrosion of the outer part of the caster, or because water enters the seal during a wash cycle. This can be prevented with special finishes and specialized seals, assuring years of fluidity of movement and no operating noise.
Flat spots on the wheel can cause severe resistance to rolling, leading to ergonomics issues and eventual failure. Technically known as “compression sets,” flat spots make a good argument for never leaving a loaded cart stationary for extended periods, for that’s when the wheel material is apt to deform. It’s much the same reason why sports car fans don’t over-winter their vehicle without placing it on blocks or adding air to the tires.
Flat spots may also develop when a non-swivel wheel is forced to slide across the floor perpendicular to the rolling direction. Fortunately, most flat-spot problems can be avoided by using such advanced wheel materials as neoprene, though if a seized-up wheel is pushed for any duration, a flat spot may still occur, whatever the material.
The environment can also play a role in causing flat spots. One example is a food plant installation that saw cartloads of processed product being pushed into a blast freezer. The carts went in fine, pushed by a single person, but had to be dragged out by several people because the wheels wouldn’t turn properly. For years it was assumed that the wheels had frozen and that it was a problem you had to live with. But then some astute maintenance person realized that it was due to a frozen flat spot.
The wheels in use at the plant were of urethane, a fine material for most applications but obviously not for heavy loads in freezers. The solution was to switch to solid elastomer wheels. Yes, they cost a little more but they retain their elasticity under virtually all conditions. Now, only one person need push the cart out, and his biggest concern is not backstrain but frostbite!
Just remember that to repair or replace a caster without addressing the root cause will not provide a long-term solution. If you do have a problem, a simple examination should help reveal what is going wrong and how to prevent a recurrence.
A program of preventive maintenance involving basic lubrication where necessary and clearing debris from the wheels will also pay handsome dividends. If you are faced with recurring problems, bear in mind that caster technology is constantly evolving and that new types of casters and wheel material can often solve what were once persistent problems.
Wheel material, in fact, can have an impact on all the reasons why casters perform inadequately. For example, a pliant or soft wheel may flatten under the weight of a load, gripping the floor and making swiveling/pivoting more difficult, leading to premature failure or ergonomic issues. On the other hand, if the floor is uneven or there’s lots of debris, the soft wheel will deform and absorb the barrier, lowering push resistance.
Another consideration is debris getting embedded in the surface of the wheel, resulting in increased rolling resistance, vibration and noise. A hard material may overcome the problem but may not roll well in areas with severe debris. A softer wheel might work, providing it has the elasticity to “bounce back” and resist debris. Periodic examinations will reveal whether or not your caster wheels are becoming encrusted or are subject to severe cuts or “chunking,” which is when bits of wheel material are chewed up and missing.
Even if you can’t clean up the environment, you still have options. Again, neoprene is an excellent choice for replacement wheels, and urethane generally works well too. Solid elastomer will roll comparatively well on a rough floor, though it may pick up debris and is best suited to a smooth clean floor. In a tough application, you may need to replace solid elastomer wheels at regular intervals.
Sometimes the problem is as simple as having the wrong-size wheel. A larger-diameter wheel grips the floor better and generally results in easier rolling. A possible drawback is when it comes to pivoting, since the larger-wheel’s superior grip will tend to require extra push force.
You can address the matter of pivoting in several ways, including the use of casters designed with an extended offset, which makes positioning easier and promotes good ergonomic practices. The longer lever arm allows for easier pivoting than if the wheel is located close to the housing. As well, extended offset designs track better, eliminating chatter and vibration while reducing noise.
Offset or not, the single-wheel caster still pivots on the wheel surface, which can cause maintenance issues. If there’s a lot of premature wear or there are manoeuvrability issues, you might consider the twin-wheel caster. The wheels rotate in opposite directions during pivoting, so the issue of gripping the floor never arises. So, if people are complaining that swiveling is difficult, suggest a switch to twin-wheel casters.
Certain operating environments require specialized casters and wheel materials. For example, static electricity can be an important factor to contend with in flammable areas, medical facilities and electronics plants. Clean rooms and the presence of certain chemicals may also affect caster selection.
In summary, you have lots of options when it comes to wheel or caster repair and replacement, though the choice of wheel size and material is often a compromise. As a general rule, bigger is better, and softer, resilient neoprene will give highly satisfactory results — unless the weight is heavy, when you may need to turn to solid elastomer — unless there’s a lot of debris when urethane may get the nod! And if, despite your best efforts, you just can’t find an acceptable solution, an experienced caster expert should be able to help.
This article was provided by Rob E. Hilborn, president of Darcor Ltd. of Toronto. For
information on the ergonomics of casters, get your free copy of The Ergonomics of Manual Material Handling, the industry white paper produced by Darcor and Ergoweb. Log on to www.ergocasters.com.