Polyurethane Problems

A customer recently approached us with a pressing problem.  They were burning through wheels, left and right.  Nuts and bolts were being buried in the tread.  The cart took six 10” x 4” polyurethane on iron wheels, to service a 42,000 lb load. Polyurethane is supposed to roll over obstructions without picking up the debris.

What was discovered to be the problem was the grade of polyurethane being used.  A low grade polyurethane, despite its durometer, can become impregnated with obstructions.  In order to solve the problem the wheels were replaced with an ultra high performance polyurethane. 

Under normal circumstances, the standard wheels would have done just fine, but under such heavy load (7,000 lbs per wheel) the lower grade polyurethane simply couldn’t hold up.

Rolling right along

For as much importance that is stressed on the choice of wheel materials, sometimes, bearing selection doesn't get a fair shake. The right bearing can be the difference between a successful solution, and a problem in the making. When selecting a caster, consider the following when selecting the bearing for the application:

• How much does the cart and load, combined, weigh?
• For lighter applications, you can use Delrin, Roller, or Plain bearings
• For heavier applications, use Roller or Precision Ball Bearings.
• In what manner will the equipment be moved?
• If it's a push pull application, consider Delrin, Roller or Precision Ball Bearing
• If it will be towed all the time, use a Tapered Bearing.
• If it's a combination of the two, use a Precision Ball Bearing.
• Will it be exposed to considerable amounts of moisture, like a wash-down application?
• If so, use a Delrin or Stainless Steel Precision Ball Bearing.
• If not, any bearing will do.

Take a look at these questions, by answering them, you should be able to get a good idea of what kind of bearing you're application requires. Beyond these, consider any ergonomic or environmental requirements.

If you need some more information, please contact us for help!

A thorn in the lion's paw

The other day, I heard one of our inside salesmen on the phone with a customer. Apparently the customer was commenting on how often their cast iron wheels would seemingly "lock-up". The salesman handled the call correctly, and here's how:

Cast Iron wheels are very hard, as that's the nature of cast iron. This presents a problem, however, as the wheels are susceptible to being stopped by floor debris. Since the wheel is hard and the floor, assuming it's concrete, is hard as well, neither will give. Thus the object, say a small nut, is stuck between the floor and the wheel. The wheel will no longer spin freely and the cart becomes hard to push, due to the increased friction. If the obstructing object is big enough, and the speed fast enough, the wheel can even crack.

So, how do you get around it? Well, assuming that your floors often have obstructions strewn about, there are some pretty simple solutions. Using a polyurethane or rubber treaded wheel will help alleviate this problem. Poly and rubber will give to the obstruction, allowing the wheel to keep on turning. The other option, if capacity is the largest concern, is going to Vulkollan, a special polyurethane designed for heavy and abusive loads.

It helps to keep this in mind, hard floors want soft wheels and soft floors want hard wheels.

Check out the caster selection at our website.

And just what is Phenolic anyways?

We hear this a lot. It's an odd material, looks like plastic, has the strength of cast iron and the absorbency of a nice cotton towel.

You read that right, a cotton towel. A phenolic wheel, or phenolic anything for that matter, is made pretty simply: take shredded denim, add phenolic resin, press and cure. This creates a few problems, most notably the cotton towel thing. Cotton is hydrophyllic, meaning, in a literal sense, it loves water. Phenolic is hard and brittle, just like cast iron. So when the wheel rolls across the ground, it cracks a little bit. Expose it to moisture and it will suck up water through the cracks.

This is especially problematic for operations where hygienic conditions are a must, like food production. Phenolic wheels, when they absorb the water, also absorb all the floating microbes. The cotton on the inside becomes a breeding ground for bacteria. So now, as the wheel passes across an unprotected floor, the bacteria come back out, and thus contamination.

So, the question is, how do you get around phenolic? It's cheap, it's relatively durable, and carries a heavy load. There is no easy answer.

We still sell a lot of phenolic wheels, but the numbers are fading away. Materials like Nylon and Polypropylene can carry almost as big of a load and do not have the problems with moisture. In heavier duty applications, more focus has been given to longevity than to acquisition cost, so polyurethane tread wheels (iron or aluminum core) have been slowly replacing them in some applications.

To consider your alternatives, click here for medium duty or click here for heavy duty casters.