The general rule to select a suitable load capacity for castors is to take the load of your application for example trolleys and divide by three. The trolley weight and the weight of the load must be combined.
The reason for this is to ensure a safety margin. Should there be any thresholds or obstacles on the running surface, the load will triangulate – spread the load over three castors.
For example, If you have a trolley with a total load of 3000 Kg then a castor with a load capacity of 1000 Kg is the minimum you should select. Thos assumes that you will be using the castors at their full capacity. It is prudent to have a castor with a higher loads to extend the life of the castor and to ensure the application is fully covered. A load capacity of 1200 Kg would be a better choice in this case.
Consideration should also be given to the load distribution on the trolley. An example of this would a boat trolley. The load is offset by approx. 2/3 to the rear where the bulk of the boat including an engine is situated.
For example, a boat & trolley combined weigh 3000 Kg. With a 2/3 offset load, the castors selected should be at least 1333Kg each. To work out the load we need to add 1/3 to the total load stated originally, so 3000 Kg becomes 4000 Kg. Divided by 3 for safety gives a load requirement per castor of 1333 Kg. This does not allow for any additional safety, so the recommendation would be for a 1500 Kg load capacity castor.
What are the best castors for my floor
For smooth concrete floors free of obstructions and thresholds a hard wheel can be used. For example, Nylon standard Polyurethane (92 – 95 Shore A), soft polyurethane (75-85 Shore A) black rubber, thermoplastic rubber or non-marking rubber can be used.
The harder wheels Nylon, standard Polyurethane and steel are able to roll over obstacles not greater than 2% of the wheel diameter: 100mm wheel – obstacle height of 2mm.
If your floor is uneven and has larger obstacles to traverse, then a softer tread would be a better solution. Black rubber, non-marking rubber, or soft polyurethane (75-80n Shore A) are recommended to be used on uneven running surfaces. These softer treads can overcome obstacles which are 5% of the wheel diameter.
For example, 100mm wheel can traverse obstacles and thresholds of 5mm.
How difficult will my application be to push
Different tread materials are the biggest single influence on how much force is required to push a trolley.
In addition the starting force, to get the trolley moving, is higher than the force required to keep the trolley moving.
Assuming the running surface is a smooth concrete floor
Standard Polyurethane 92 – 95 Shore A
Staring force; 5% - 7% of the total load
Force to keep moving; 2 – 3% of the total load
Soft polyurethane 75 – 80 Shore A
Starting force; 2% – 2.5% of the total load
Force to keep moving; 1% - 1.5% of the total load
Nylon
Including Nylon 6, Nylon 66 & cast nylon
Starting force; 1.6% 2% of the total load
Force to keep moving; 0.8% - 1% of the total load
Rubber
Black and non-marking
75 – 80 Shore A
Starting force; 5% – 7% of the total load
Force to keep moving; 3 – 5 % of the total load
Steel or cast iron
Starting force; 2 – 3 % of the total load
Force to keep moving 0.8% - 1% of the total load
Is my floor suitable for heavy load castors
Floor pressure is worked out as a Nmm2 figure. Basically how much weight is put on a 1mm square area of the floor by the wheel.
Generally most factories with a smooth concrete floor have a floor rating between 15 Nmm2 and 22 Nmm2. To check your floor rating check with the people who installed the floors, or your landlord should have the information available.
Hard wheels with no tread compression, for example Nylon, Cast Iron and steel have a high Nmm2 value as only a small part of the tread is in contact with the floor. This could be 1mm wide by the tread width of the wheel. 100mm diameter x 50mm tread width gives a Nmm2 contact area of approx. 5mm. If the total load per castor is 500 Kg then a floor pressure of 100 Kg per Nmm2 is regenerated. This would be a trolley with a total load of 1500 Kg.
The Nmm2 figures are a static load rating, so if you are moving the load then the floor pressure is reduced depending on how quickly the application is moving.
If you have high load trolleys which are stored in one position then rolling the trolleys on to a small steel plate would increase the Nmm2 floor area protecting the floor.
What are the risks of using high loads on hard wheels
Generally companies find that hard wheels with a high load on hard nylon or cast iron wheels might break down the surface of the concrete floor.
If the floor construction has cavities under the floor these can be exploited by the high Nmm2 floor pressure causing the floor to collapse in that location.
How do I prevent floor failure from castor use
The first point is to find out what your floor is rated at and how it was constructed.
If there are concerns assuming you do not want to change your castor wheel type, is to artificially reduce the Nmm2 floor pressure. This can be achieved by using a rail solution, this can be traditional rail, box sections, steel plate etc.
If you are prepared to change the wheels then the traditional solution is polyurethane.
Polyurethane tread wheels have a Nmm2 figure of 8 – 15 depending on the hardness of the polyurethane tread. Therefore a polyurethane tread wheel is the most often recommended solution for high loads on a smooth concrete factory floor.
If your load is fairly light and the running surface is suitable then a rubber tread wheel would be a good choice. These wheels are more cost effective than a polyurethane tread wheel but not as cost effective as a nylon wheel.
Do I need swivel braked or fixed castors
Swivel castors give the greatest movement and the trolley can be moved in any direction.
Fixed castor are used on conjunction with swivel castors to have better directional control over a trolley. This is especially useful when crossing across a slope to stop the trolley from wanting to follow the slope.
Braked castors are a good choice if the trolley needs to be immobilised when not being used. The word brake is used, but it is not possible to use the mechanism to slow down a trolley and should only be used when the trolley is stationary.
Standard braked swivel castors have a trailing brake, that means if you are pushing the trolley the brake will be accessible, if you are pulling then the brake lever will be under the trolley.
A combination of fixed castors on the front of the trolley and swivel braked castors at the back will give the best solution if a trolley needs to be braked on a slope, this gives the best overall control of your trolley.
How do I fit my castors
Most castors are offered with a flat rectangular or square plate. This plate has 4 bolt holes often slotted to make it easier to fit. The best way of fitting is the bolts going down through the top plate and secured with a washer and nut. A Nylock style nut (a nut with a nylon section to lock the nut in place) is ideal to compensate for vibration which may loosen the nut over time.
Some castors are “single bolt hole fix” These are ideal for fitting inside a tube with an expander, or if there is not enough room to fit a plate fix castor and the load is fairly low.
What are the different tread materials and wheel type including centres
A cast Polyurethane tread is ideal for floor protection with higher loads, and are non-marking.
These are offered with Aluminium, cast iron or steel centres depending on the load and environmental conditions where the application is being used.
Injection moulded Polyurethane wheels allow for a good wear rate, ease of movement, floor protection, reduced noise against a nylon wheel, and are cost effective when compared to a cast polyurethane tread wheel.
These wheels are ideal for lower load applications.
Rubber tread wheels
These wheels are designed for low noise, floor protection, uneven surfaces, vibration protection and are a cost-effective solution.
The standard black rubber can mark floors, so a grey or blue non-marking rubber can be used to ensure the floor surface does not get marked.
The rubber is kept on the centre by capturing, like a car tyre, or direct bond to a synthetic or metal centre.
Both polyurethane and rubber have different capabilities to chemical exposure, washdowns and where the trolleys are kept outside. Chemical resistance charts are available to check on most suppliers’ websites, if you have any doubt the best option is to contact the supplier who you decide to use to confirm the correct tread material is used.
What is the difference between a wheel with a tread – Cast Polyurethane or Rubber and a hard nylon wheel
Polyurethane & rubber wheels have a higher rolling resistance so require more force to push the application.
Polyurethane & Rubber tread wheels can be used for towing and are not likely to slip and slide on a floor.
Nylon has a much lower rolling resistance so easier to push. Nylon is hard and are not recommended for towing applications, but are ideal for hand pushed trolleys.
Load capacities on a nylon wheel can be very high, especially if a cast nylon wheel is used. Nylon wheels are generally more cost effective than a wheel with a tread on. However other factors about your specific application may need to be taken in to account.
What are the best Industrial Castors for heavy use
The best castors are the ones that meet your application requirements, including environmental factors.
It is better to opt for a technically correct solution rather than being driven by price alone.
Once the wheel type has been determined, the frame is the next aspect to check. Frames are available for heavy industrial use and include pressed steel, semi-fabricated or fully fabricated.
Options for single and twin wheel castors are available depending on your requirement.
It is best to contact your supplier to discuss what combinations are most appropriate, and available from your chosen supplier.
Can I get high temperature castors for a bakery
Yes, there are several solutions available.
Bakeries generally use Phenolic resin which can stand high temperatures. Alternatively a silicone rubber captured tread wheel offers lower noise and better grip than Phenolic resin wheels.
If the application is not a food or pharmaceutical application, for example autoclaves, then a cast iron wheel can be used giving a very high temperature ceiling.
It is possible to use a stainless steel wheel, generally you would have to request this from your supplier as a special solution.
Care must be taken to ensure the bore is suitable, for example phenolic wheels and silicone rubber wheels have a plain bore through the wheel and would run on a steel reducer bush coated in Teflon. High temperature bearings are available, these are higher in cost than a standard bearing and should be specified according to your application.
High temperature swivel and fixed frames are available in stainless steel for high risk applications. The swivel castors either have a ball taken out of the swivel head to allow for expansion and self-cleaning. High temperature greases and pastes are available to ensure the swivel function is function at higher temperatures.
For very high temperatures a cast iron or steel frame can be used.
How do I measure my existing castor to get a direct equivalent
The critical dimensions required are:
Wheel diameter
Wheel tread width
Overall height
Fixing plate size
Bolt hole centres
Fixing bolt size.
Castors are an interchangeable part so there should be a direct equivalent available.
If you are considering changing your castors to improve performance, or perhaps your application has changed, determine what the critical elements are, for example the overall height, wheel diameter, tread type.
What are jacking castors and levelling castors
Jacking castors are used in several types of applications, for example:
Matching work heights for assembly lines, for example wings for aircraft, mating heavy parts, for example propellors or flanges on large pipe.
Lifting a longer trolley to clear a ramp and preventing the trolley from grounding out on the apex of the ramp when moving between areas.
Lifting a trolley which normally sits on fixed legs to move to a new location.
Levelling castors are used to ensure a level surface for an application when working.
Summary: The information given above is a starting point to help determine the correct castor combination for your application. It is always worth discussing your requirements with a specialist to ensure the correct solution is being offered.