What are the different types of castors?

You can excuse yourself if you’re not familiar with all things castors. There is a lot to know, after all. Here we’ll give you important terminology to get you started but first, a few basics about castors.

No matter what the type, any castor has two main parts:

• Rig – also known as the fork, yoke or housing. This is every piece of the castor except for the wheel.

• Wheel – that round device bears the weight of your product. It has to easily move the product by turning around an axle passed through the centre of the structure.

Castor types

That brings us to the castor types. These terms describe the structure and functionality of the castor:

• Swivel – a castor that can rotate 360° and roll in any direction. The swivel lead

• Rigid – a castor that only moves in a straight line. These tend to be stronger than swivel castors due to their construction.

Swivel lead

Let’s say you’re engineering a heavy-duty industrial application that requires castors. You must consider the appropriate swivel lead in order to achieve the performance you’re after. The swivel lead of a castor is the distance from the vertical centreline of the castor swivel section to the vertical centreline of the wheel. This is sometimes called ‘swivel offset’ or ‘swivel radius’.

If you lengthen the swivel lead, your product is easier to turn, as you’re reducing the force needed to begin motion. This, in turn, reduces the fatigue on operators of your application. Keep in mind, however, increasing the swivel lead on an industrial castor also results in a larger turning radius and reduces the ability to make a true 90° turn.

Swivel radius

This is another handy term to know. Swivel radius is a circular measurement used to determine castor clearance. It’s the distance from the centre of the swivel mechanism, to the furthest point on the castor. This point may be the wheel or a brake that you added. It’s important to know the swivel radius; if it’s too big, the castors may not be able to swivel the full 360°. Measure before the castors are fastened to the product it’s bearing.

Brake castors

These can be swivel or rigid castors. They simply have a brake as an added accessory to the wheel or as part of the rig.

• Side Brake: There are different types of these, but none can completely stop a swivel castor, as they lock only the wheels. Your application can still move around because of the swivelling action.

• Total Lock Brake: If you want to stop all movement, then you want a ‘total lock brake’, which locks the wheel and swivelling action.

Mounting methods

You can mount castors to almost anything. The question is how to do it. Here are some of your options:

• Bolt-hole Castors (Also called Hollow Kingpins or Stemless Castors)
These fit directly into a socket. Alternatively, you can fit bolt-hole castors through a hole and capped with a nut threaded onto the stem.

• Mounting Plate
Ideal when mounting to flat services. The castors – either swivel or rigid – are already attached to a plate. Plates spread the load over a wide area, which is why this is the main mounting type for large castors.

You’ll also hear about the Bolt-hole Pattern. This is the measurement between mounting holes on the top plate, including length and width dimensions.

• Stem
Stem castors have either a threaded or nonthreaded rod. You can screw threaded studs into a t-nut while unthreaded studs are inserted into a pilot hole or caster socket and held in place with a ring or grip neck holds.

Raceway

This is the area of the rig where ball bearings, or rollers, rotate and causes the castor to swivel. Terms associated with the raceway are:

• Kingpin: the bolt or rivet used to hold swivel raceways together are called the kingpin. Kingpins are usually the weakest point of a castor and should never be used for towing applications. Over time, the kingpin tends to stretch, loosening the ball bearings. The ball bearings are harder than the steel of the raceway, which results in “brinelling” within the top plate. This causes the rig to stop swivelling.

Advantages to these castors include the ability to tighten the kingpin to achieve varying levels of swivel resistance. You can also prolong the life of the castor as the swivel area wears by adjusting the kingpin nut.

• Kingpinless: as the name clearly says, this is a castor without a kingpin. A kingpinless castor’s top plate and inner raceway are of one-piece construction. These castors are much stronger than castors with kingpins, which is why they’re often used in demanding shock-load applications.

Features to look for in castors

When you look at your castor options, some features will matter more than others, depending on your application. Here’s a glance at what you’re likely to come across:

RoHS Compliant - castors which meet the Restriction of Hazardous Substances directive for manufacturing without the use of hazardous materials.

NSF Listed – castors approved by NSF International for use in the foodservice industry. It’s important to note that castors with threaded guards are never NSF approved.

Low Profile - castors with a small overall mount height. This usually applies to applications that need to move but do not need much floor clearance. Examples of applications include business machines, photocopiers and refrigerators.

Maintenance Free - castors designed with precision bearings that and don’t require lubrication during castor life. However, maintenance-free castors should still be checked for signs of wear.

Floor Protective - castors whose wheels are made of material proven to minimise the chance of damage to floors. These wheels are less likely to leave scuff marks and may even reject metal shavings and floor debris. Rubber is a good example of a floor-protective material.

Ergonomic – these castors are designed to make movement easier and reduce work strain.

Donut Tread – a rounded wheel tread, making the wheel easier to move. A donut tread – as opposed to a flat tread – is an example of what can made a castor ergonomic.

Dual Wheel – a wide castor fork, or rig, contains two wheels on the central axle. This provides higher-load ratings and better stability than single wheel castors.

Twin Wheel – not to be confused with dual wheel. These are usually nylon or thermoplastic castors with two wheels attached to the outside of the central castor body. Like dual wheels, twin wheel castors provide stability and easy turning.

Thread Guarding – this is the plastic or metal disc which covers the wheel hub, bearing, and exposed axles. It prevent debris from engaging with the wheel or axle.

Spring-Loaded – castors with springs to provide sock absorption during loading and movement.

High Temp – castors rated to stand up to high temperatures. Use these for applications involving autoclaves, ovens or any situation involving high temperatures.

Never Flat – these castors use Semi-Pneumatic wheels so that they’ll never go flat.

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Questions?

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