A. What causes casters to fail prematurely?

Casters are usually the last things anyone worries about until they fail. When they do fail its generally due one or more of the following causes:

1. Capacity Mismatch: If you are using a caster that us under rated for the load capacity of the application, you will have much higher kingpin failure rates. If you are not sure the maximum load that a caster with need to hold it is better to over estimate on the caster capacity than it is to go with a lighter duty series because of cost. (See Critical Measurements - Load Capacity)
   
   
2. Wheel Material Mismatch: Kingpins are the weakest points on the caster but the wheel material can also cause premature failure if you do not pay attention to the environment the caster is used in. Any wheel that is made of two different materials must be bonded together somehow. The two most common ways are:

   a. Chemical Bond: A chemical bond is when the tread of a wheel is bonded to the core of the wheel by means of an adhesive or bonding agent. Bonds of this type are susceptible to de-bonding when the wheel is subjected to heat buildup from continuous use applications. Because the two materials expand at different rates when heat is applied to the wheel, the bond is broken and the wheel tread will come off the core. Also, because this is a chemical bond, some other chemicals that come in contact with the wheel will break down the bond agent and cause de-bonding as well. Examples of wheels with this type of bond are:

   • (PCI) Polyurethane Tread bonded to a Cast Iron core.
   • (RCI) Rubber Tread bonded to a Cast Iron Core.
   • (PAL) Light Duty Polyurethane Tread bonded to an Aluminum Core.
     
     

   b. Mechanical Bond: A bond that uses a bonding agent and physical interlocking of the tread with the wheel. Cores of a wheel will have a set of protrusions that extend out from the core, which allows the wheel material to be molded around them, thereby mechanically interlocking the tread to the core. This is the strongest way to bond the tread with the core. Heat build up is less of a factor. The two materials are less likely to separate from each other because they are physically intertwined.

   • (PPBG) Light Duty Polyurethane Tread on Polyolefin Core.
   • (PAL) Heavy Duty Polyurethane on Aluminum Wheels.
   • (XLG) Heavy Duty Polyurethane Tread on Polyolefin Core.

    

   c. Lack of Regular Maintenance: All casters can be maintained in one way or another.

   • Bearings should be greased regularly. Most axles and swivel raceways can have Zerk fittings on them to assist in greasing those parts.
   • Casters can get very dirty with items they roll over. Floors that have debris on them will cause wheel bearings or raceways to stop turning. These parts should be cleaned and removed from the moving parts, (i.e.: Threads, Dirt, Dust, Food, etc.)

3. Harsh Environmental Applications: Environments must be considered when you are trying to use a caster that's going to last. Harsh environments will degrade caster performance and will cause premature failure if you overlook where it is being used. Some common harsh environments are:

a. High Heat: Applications where temperatures are higher than 150 Degrees can cause the grease to run out or burn out of the bearings. High temperature grease will help in these applications but do not come standard in most casters and costs more. Heat can be either a dry or wet heat and must be considered when choosing the right caster. Both the fork and the wheel will have to be considered because some wheels are better for dry heats then wet heats. Same for the fork. Here are materials we recommend for each heat type:

• Wet heat: use stainless steel metal parts and water resistant High temp wheels like High Temp Glass Filled Nylon (HTGFN). Seals on the raceway will help keep grease in. High temp Phenolic is NOT good in wet heat applications.
• Dry heat: Stainless or Zinc Plated forks will be ok and you can use High Temp Phenolic or HTGFN in Dry heats. Other than the wheel, you must use all metal components for spanners, retainer washers, Lock nuts etc.
• Corrosive Environments: Environments where the casters are exposed to corrosive liquids such a salt spray, break fluid, solvents, oil, gasoline, urea etc, will breakdown the wheel material, tread bonding agents, and/or corrode the steel on the forks and in the bearings. Use stainless steel metal parts and Polyolefin wheels, which can withstand all of the mentioned chemicals.

4. Abuse: Applications that are inherently tough on casters are considered abusive. That does not mean that you can't find a caster that will take the abuse. In most cases you just have to go to a series of caster that will be able to handle the load and the abuse at the same time. Even if the caster capacity is much higher than the cart requires you will save money in the long run by paying more now for a caster that will last.