Dave Lippert, Contributing Writer
The most obvious thing is wheel capacity—how much weight can the wheel carry? The common math looks something like this: take the total weight and divide by the number of wheels, typically four.
Unfortunately, this math assumes equal weight distribution all the time, and life doesn’t work that way. Loads can be concentrated at one end or on one side, and during motion it is possible for one wheel to become partially or completely unloaded. Better math looks like this: total weight divided by three (or fewer than the total number.)
Next, affecting the load on each wheel is what happens when a load is dropped onto the wheel, or the wheel encounters shock-loading while rolling over concrete floor joints, door sills and the like. These impacts can cause shock loads of three times the stationary load. Wonder why some wheels break during use? This may be the reason.
Wheel diameter plays a bigger role than most realize. When a smaller wheel will do for achieving the needed load capacity, it may be inadequate ergonomically. Larger diameter wheels are easier to push (much easier), and they also roll over those floor joints and door sills more easily. What is extra strain and the increased likelihood of a back or shoulder injury worth?
Another criteria is floor condition. Is there debris? What about metal chips? Dirt and dust? Assuming some or all of this is unavoidable, it matters to the wheels. Some tread materials are available that minimize the collection of metal shavings. Larger diameter wheels roll over debris more easily than smaller wheels. Bearing seals protect the wheel bearings from dirt and dust.
Industrial wheels are used primarily indoors. However, some venture into the great outdoors. If this is the case, there are additional considerations. Some polyurethane treads are susceptible to deterioration when exposed to lots of sunlight. Moisture can lead to rust, reducing the bearing performance. The pavement conditions (or maybe it is gravel) are normally not as smooth or firm as the typical concrete indoors. The flatness of the ground or outdoor pavement is rarely close to that of indoor floors, which means the load distribution will change rapidly and frequently over the wheels. Occasionally, there is even an extreme condition, such as a rail crossing.
What about noise? Many don’t consider wheels to be a noise contributor, but hard plastic, nylon or metal wheels will be noisy, particularly under light loads. Harder wheels are normally easier to push (ergonomic heroes), but can be very noisy (ergonomic goats.) The industrial wheel industry offers a myriad of wheel and tread materials, making selection potentially difficult for the novice. Information on the manufacturers’ websites can be extremely helpful, as can a call or chat with factory salespeople.
Chemicals are frequently the enemy of certain wheel materials. Water may be the most common, but there can be detergents, fuels, oils, coolants and an endless list of chemicals specific to a production facility. How prevalent is/are the chemicals? Are the wheels subjected to washdown applications; do they run through puddles; or is chemical exposure occasional and minimal? Wheel selection can be tricky when chemicals abound, but it is critical to desired wheel performance.
Excessive heat, such as that found in ovens and autoclaves, can be the cause of many wheel failures. Knowing the peak temperature and the duration will aid good wheel selection. While the obvious consideration may be the wheel and tread material, the bearing and lubrication are also keys. Factory consultation is better than relying only on a few published numbers on a website.
Which do you prefer to wear out first—the wheel or the floor? Some wheels such as forged steel are virtually indestructible. But, over time, these wheels will wear out concrete floors. One solution is to run them predominantly on steel plates or tracks. Some nylon wheels have high capacities and other durability characteristics, yet they’re easier on concrete floors. In the end, it is a tradeoff that should be decided in advance of purchasing wheels.
Maintenance really matters. Many industrial wheels now come with sealed precision ball bearings, which require no lubrication maintenance. If there is a lubrication fitting, it is there for a reason. Periodic lubrication will keep wheels rolling easily. Along with lubrication, maintenance means checking wheels for condition, including broken sections, tread deterioration, debris embedded in treads or tread separation.
Something often overlooked, particularly on taller loads, is stability. Wheel placement is a vital consideration, and missing this can lead to serious consequences. As the center of gravity of the entire wheeled system is higher, the wheels should be positioned further out, making a wider and longer base. There is no right answer here, but consider the floor conditions; pavement slopes and irregularities; forces applied to move the item; wheel diameters; and probably more application-dependent conditions. Considering all of the above can help contribute to a safe design.
Finally, think value—not only price. The cost of frequent maintenance and downtime for wheel replacement can be significantly more than the initial cost of a better wheel. What might look good on the purchase order may not look as good on the bottom line, after dragging down operations by causing delays, late orders and other production problems.
Does wheel selection suddenly seem pretty complicated? It is more involved than most realize. Good manufacturer websites can be very helpful in this regard, as can contact experienced sales personnel. WMHS
Dave Lippert is President of Hamilton Caster.