#### Understanding Wheel Capacity

When you calculate the required capacity of your wheels, there are two areas you will need to consider:  Total capacity and roll-ability.

• Total Capacity:  When using wheels by themselves, (without the swivel or rigid horn), or when replacing a wheel in a caster horn you must always remember to figure out your total capacity needs.  Generally, a wheel by itself will have a greater load capacity then a wheel in a swivel or rigid horn.  To figure your total capacity you can once again take your total weight and divide by the number of wheels you intend on using.  While there is factory safety factors built into wheel capacity’s, it is still important not to overload your wheels for safety reasons.

• Rollability:  When you begin approaching the maximum load capacity of a wheel, the ease of rolling your load may drastically reduce. The wheel compound you choose will affect the roll-ability.  If you are using a wheel with a harder compound, the roll-ability will probably not reduce much.  However if you are using a softer compound, as you reach the load capacity of your cart or piece of equipment, it will become very hard to maneuver.

#### How to Measure Wheels

Wheel measurement is fairly straight-forward and includes both wheel diameter and wheel width.

• Wheel Diameter – You can determine the diameter of your wheel by measuring across the face of the wheel.  Wheel sizes available are from 2? to 20?, giving you many options.  When trying to determine what diameter wheel to use, remember that the bigger the wheel, the easier it rolls.  However, a larger diameter wheel will probably cost more than a smaller diameter wheel of the same material, and may place your cart too high off the ground.

• Wheel Hub Length and Type – The hub length is measured thru the center of the wheel, the hub is the portion of the wheel that fits between the arms of the caster rig. There are two hub styles: Centered and offset. In a centered hub wheel, the hub sticks out an equal amount on both sides of the wheel, where in a offset hub wheel, the hub sticks out further on one side than the other.

#### How to Select Bearings

• Plain Bearing – In a plain bearing, the hub material is actually the bearing. The wheel rotates on a steel axle and is the most economical bearing application.

• Roller Bearing – Normally this is a two-piece bearing, consisting of a roller assembly and a hardened outer race. The split-sleeve bearing consists of an outer raceway of hardened spring steel with a hardened roller and cage assembly. A full caged bearing assembly consists of a fully encased outer raceway with a hardened roller and cage assembly. All roller bearings operate in conjunction with a hardened shaft called a spanner.

• Ball Bearing – This is a unique stamped construction that has a one-piece outer raceway, which is cold-rolled and formed to a close tolerance ball groove. The inner raceway is machined and hardened. The bearing is shielded and grease packed. These bearings will react to thrust loading and considerable radial load.

• Delrin Bearing – Delrin is a registered trademark of Dupont; this is an acetal resin molded into a flange type bearing. The bearing is press fitted into the hub of the wheel and is rotated around a hardened spanner. This bearing has high mechanical strength, high impact, low static, and dynamic coefficients of friction, with a wide use temperature range (-40 degrees to +230 degrees F).

• Precision Bearing – This type of sealed precision bearing consists of a hardened outer raceway and inner raceway, separated by a concentric ring of hardened steel balls. This bearing is used in pairs and is usually press fitted into a deep pocket of a wheel that has high load and high speed capabilities. This type of bearing is primarily used to carry radial loads only.

• Bearing Spanner – The spanner is used when you need to make a reduction from the inside diameter of the wheel bearing to accommodate your axle size. Typically, a spanner is used to reduce from a ¾ inch bearing I.D. to a ½ inch, or 5/8 inch axle size. You can also use a spanner to reduce from a ½ inch bearing I.D. to a 3/8 inch axle size.

Wheel tread material (or compound) can be a large and rather complex issue. Multiple options are available. First you must determine your load capacity, then the type of floor you will be rolling on.  The environment you are working in can have an affect on your choice as well.  If there is high heat, greasy floors, caustic materials, etc., there are special compounds for many special applications.

First, a quick note on hub material:

• Hub Material – The hub on a caster wheel is much like the wheel on your vehicle, where as the tread is like the tire. Caster wheel hubs are made from many different materials. The 3 most common are Steel, aluminum, and poly. Steel will normally always give you the highest capacity, but hub material is normally more of a preference than anything.

The following compounds are listed generally from softest to hardest.

• Pneumatic – This wheel provides a cushioned ride for delicate instruments and breakable items. the tube-type, pressurized tire combines shock absorption with quiet operation and easy rolling. Standard with ball bearings.

• Dyna-Tred TPR – Thermoplastic rubber resists chemicals, caustics, oils, acids, and wear. Rugged polypropylene hub won’t dent, mar, fade or stain. Tread and hub are double bonded and mechanically interlocked to eliminate tread separation. Gives dollies, carts and trucks a soft and cushioned non-marking ride. Temperature operating range is -40 degrees F to +180 degrees F. Durometer is 70A.

• Soft Rubber – This composition rubber wheel combines a soft rubber tread with a hard rubber core for quiet movement, a cushioned ride, and maximum floor protection. Temperature operating range is -40 degrees F to +158 degrees F. Durometer is 75A.

• Mold-on Rubber – Cushioned rubber tread permanently vulcanized to a semi-steel core is recommended for quiet movement with heavy loads. Molded core provides added strength with a reinforced, double-thick hub. Vulcanized rubber-tread wheels are standard with roller bearings. Temperature operating range is -40 degrees F to +159 degrees F. Durometer rating is 75A.

• Polypropylene – This polypropylene wheel has a light weight, low cost, high impact strength. It resists water and chemical absorption, even stands up to repeated steam cleaning. Non-marking tread provides excellent floor protection. Polypropylene makes the strongest, longest lasting, and most economical wheel in many caster applications. It’s available with plain or roller bearings. Temperature operating range is -20 degrees F to +180 degrees F. Durometer is 60D.

• Dyna-Tred PU Wheels – Polyurethane tread for high load capacity and extended wear. Protects floors and resists chemicals, caustics, acids, and oils. Rugged polypropylene hub will not dent, mar, fade, or stain. Tread and hub are mechanically interlocked to eliminate tread separations. Temperature operating range is -40 degrees F to +180 degrees F. Durometer is 90A.

• Mold-on Polyurethane – Polyurethane tread permanently attached to a metal core delivers a cushioned ride, excellent mobility, and extended life under extremely heavy loads.  Duro-Tred wheels protect floors and loads better and will wear four to ten times longer than other wheel materials. Standard with roller bearings. Temperature operating range is -40 degrees F to +180 degrees F. Durometer rating is 95A in standard.

• Thermoplastic – Reinforced Thermoplastic material and specific processing create this high performance, durable, and cost effective wheel. The RT series of wheels, designed for use in the Faultless brand 1400 and 400 Series Casters, are ideally suited for food processing, tool storage, sanitary maintenance, and applications requiring easy mobility under heavy loads. They are extremely resistant to water, chemical absorption, and steam cleaning. Standard wheel operating temperature range is -20 degrees F to +250 degrees F and the High Temperature version range is -20 degrees F to +480 degrees F. Durometer is 65D.

• Hard Rubber – Hard-rubber molded composition all through, this wheel is impervious to oils, greases, and gasoline. It combines many desirable characteristics: high-loading rating, good mobility, high-impact resistance, and good floor protection. Temperature operating range is -40 degrees F to +158 degrees F. Durometer is 75D.

• Phenolic – Phenolic compound reinforced with macerated fabric makes a high-strength, high-impact wheel resistant to oil, gasoline, even dilute acids. Compression-molded under extreme pressure, these wheels gain a dense uniform consistency. Phenolic wheels are non-marking, non-conductive, and spark-proof. They are available with plain or roller bearings. Will not warp or swell in a temperature operating range of -40 degrees F to +300 degrees F. durometer is 75D.

• Sintered Iron – Powdered iron, compacted and sintered to cast-iron strength, makes a concentric and smooth tread that runs quietly and protects floors. Standard with plain bearings. Temperature operating range is -40 degrees F to +500 degrees F.

• Semi-Steel – Cast iron toughened with steel, this wheel has extremely high load ratings and exceptionally long wear life. It’s recommended for rough wood and concrete floors – a good choice for moving heavy loads in manufacturing and warehousing. Long-life features include a heavy tread and plain or roller bearings. Ideal in extreme operating temperature ranges of -40 degrees F to +800 degrees F with optional high temperature grease.

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