Understanding Industrial Caster Capacity

When you calculate the required capacity of your casters, there are two areas you will need to consider: Safety and rollability.

  • Safety: When installing casters, safety should always be of utmost importance. An overloaded caster can fail and cause the load to become unstable.  This can result in damage to the load if it overturns and injury to people.  Make sure you do not load your casters beyond their rated capacity.

  • Roll-ability: When you begin approaching the maximum load capacity of a caster, the ease of rolling your load may drastically reduce. The wheel compound you choose will affect the roll-ability.  If your 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.

To calculate caster capacity, take the total weight of your load divided by the number of casters you will use to carry the load.  It’s that simple!  Make sure you include the weight of any cart you are using.

Example – A cart with 4 casters:

  • Load weight = 1,500 lbs

  • Cart weight  =  100 lbs

  • Total weight = 1,600 lbs

  • 1,600 lbs / 4 casters = 400 lbs per caster

How to Measure Industrial Casters

Whether you are replacing a caster or installing new casters, considering the overall height of the caster is important, as the height of the caster will affect the height of the chair, cart or whatever it is ultimately attached to.  Overall height is the combined measurement of the wheel itself and the frame it is mounted in. Plate casters can be measured from where the wheel touches the ground to the surface of the plate. Stem casters should be measured from the ground point to the base of the stem (the stem is inserted into a mounting, and therefore does not affect the height of what it is attached to). If you are replacing casters, you will probably want to match the height of what you already have.

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 Width – Wheel width is measured across the tread of the wheel.  Generally, the wider the wheel, the more stable it becomes.  Your load capacity also increases as your tread width widens.  If you are concerned about damaging your floor because of the weight of your cart, a wider wheel will generally spread the load out.  This has the effect of lightening the load that your floor feels.

  • 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.

When to Use Brakes and How to Select Them

Though it would seem the decision to add brakes to a caster would be fairly simple, there are actually a couple of things to consider. You can add a brake to a swivel caster, but not to a rigid caster. Also, there are different brake styles available. The two different styles are specific to a particular caster type and cannot be interchanged.

The side brake locks only the wheel, but the swivel action of the caster is not locked. While effectively braking the cart, the cart can still move around a few inches because of the swivel action of the caster. The “total lock” brake locks both the wheel and the swivel action.

Brakes are designed to be engaged and disengaged with your foot. You can use your hands, but it is inconvenient to bend over and safety is a concern because there are places your hand can be pinched.

If you only want to keep your cart from rolling away, brakes on two of the casters may be all you need. If you need to keep your cart completely still, you should use total lock casters, which lock both the wheel and the swivel action. These can be used on a cart with four swivels, or with two swivels and two rigid casters.

  • Side Brake – The traditional style side brake has a lever on the side of the wheel that must be activated to apply the wheel brake. Within the side brake family, there are two different styles. Each style accomplishes the same thing, they both lock the wheel only, and not the swivel. The first style is the rollock brake. This brake uses an arm that is activated by the foot lever which makes face contact with the wheel and effectively stops it from rolling. The second style is the side friction brake. This brake used the foot lever to compress the axle hub together onto the wheel keeping it from rolling.

  • Total Lock Brake – While other brakes lock the wheel only, this brake locks not only the wheel, but also keeps the swivel from turning. These are a great choice when safety is important, such as on a piece of power equipment, as it helps to keep the equipment completely still.

How to Select Bearings

While bearing style is sometimes only a personal preference, there are times that choosing the correct bearing for your particular application is important. Many casters do not give you a choice of bearing, so you may need to choose a different caster if bearing choice is important.

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.

Choosing a Tread Material

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.

  • 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.

  • 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.

  • 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. Black/Gray wheel is for mid- to light-duty use and Blue/Gray is for heavy-duty use.

  • 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.

Choosing an Attachment Style: Plates vs. Stems

  • Plate – If your mounting options are flexible and you need to keep your expenses down, plate casters, which are available in swivel and rigid, are generally more economical than stem casters. With many different plate sizes available, plate casters may also give you a more stable mounting base.  Plate casters are usually mounted with 4 bolts, but they can be welded on.

  • Stem – Where space is limited, like on a bench or table leg for instance, a stem caster may be your best option. There are two different types of stem casters: Grip ring and threaded. When measuring a stem caster attachment, always measure the diameter first, and then the length. Example: 3/8 x 1-1/2 = 3/8 inch diameter stem that is 1-1/2 inches in length.

  • Grip Ring – A grip ring stem caster has a friction or compression ring in the stem and is generally used with a socket of some type.

  • Threaded – A threaded stem caster has threads on the stem and is intended to go through your material and secured with a nut on the other side.

When making the decision to use stem casters, always remember this one important issue: Stem casters are available in swivel only. There are not stem casters available for rigid applications.

Choosing a Caster Type: Rigid vs. Swivel

  • Swivel casters turn 360 degrees and provide you with instant response to directional change.

  • Rigid casters do not turn and are intended for straight back and forth movement.

Rigid casters used in conjunction with swivel casters can provide great mobility. When building a cart, the question you must ask is: “Am I using this cart in tight area’s where quick turning response is a must, or will I be going long distances where steering control is a must?”

  • 4 Swivels – In tight areas where there is not much room to maneuver, four swivel casters might be your best option. This will provide you with instant directional change, making parking easy in limited spaces.  However, using all swivel casters can be harder to control if you are trying to go in a straight line.

  • 2 Swivel, 2 Rigid – If your cart will be used for long distance runs, to gain more control, you probably want to use two swivel casters and two rigid casters. If you place the swivels on one end of your cart and rigids on the other end, it gives your cart easy steering over long distances, and the ability to keep your cart going in a straight line.




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