Cast Polyurethane Tyred Wheels
Types of commonly used cast polyurethanes are:
- TDI - toluene diisocyanate
- MDI - methylene diphenyl diisocyanate
- NDI - naphthalene diisocyanate
Cast Polyurethane is a good choice as a tyring material for the benefits it brings to heavy load applications.
When floor preservation is a key consideration polyurethane tyred wheels are generally the best solution for heavy loads.
Soft polyurethanes are suitable for uneven running surfaces and offer greater grip than a standard hardness polyurethane.
Standard Hardnesses
92 - 95 Shore A
75 - 85 Shore A (Soft & high grip)
Potential Polyurethane Shore A Hardness range
50 - 98 Shore A
Hardness Selection
When selecting a suitable hardness of cast Polyurethane, several factors should be taken into consideration from the specific application.
Load Capacity
The hardest Shore A Polyurethane range (92 - 98 Shore A) has the highest load potential. When selecting softer Shore A Polyurethane, the load is reduced when compared to higher Shore A Polyurethane products with the same dimensions.
Running Surface
For smooth floors, for example concrete or resin floors, a harder Polyurethane is generally the solution. Uneven or soft running surfaces, including thresholds, benefit from softer Polyurethane use.
Grip
For drive wheels all hardness can be used. The best grip is given by a softer Shore A Polyurethane material.
Protection
Softer Polyurethanes have better protection due to improved elastic properties.
Running Speed
When an application exceeds speeds of 4 - 6 Km/h, derating of a MDI and TDI polyurethanes need to be considered. NDI Polyurethanes tend to be a good choice at higher speeds due to their resilient properties.
For wheel & castor applications, two German derived DIN EN standards are often used in the UK and Europe. These are used to derive a load capacity for a particular product.
- DIN EN 12532 - Castors and wheels for applications up to 1.1 m/s (4 km/h).
- DIN EN 12533 - Heavy-duty wheels and castors with speeds between 1.1 or 4.4 m/s and (4 or 16 Km/h).
Towing
All polyurethanes can potentially be used.
Speed, running surface conditions, environment, use and rest time will need to be considered when choosing the correct solution.
Drive Wheel Mounting Systems
A number of options are possible depending on the drive mechanism used.
Keyway
A keyway slot is machined into the axle and bore of the wheel, and a specially hardened key steel is used to link the two parts to create a live axle.
Taper Lock Bush
A split bush system that tightens through the use of bolts on a smooth axle.
Also known as Fenner Taper Lock Bush.
Sprocket
Used with a chain drive, a sprocket is machined into a wheel.
Spline
Hub with PCD.
Single Flanged Wheel - Polyurethane
Can be made from a machined steel, cast iron or synthetic centre with a bonded cast Polyurethane tread.
This solution has advantages for noise reduction and grip when used as a drive wheel.
A flat running bar is recommended. This product can be used on rail, but due to the convex profile of some rails the performance and load can be affected.
The flange often has an angle of 3 - 5 degrees to prevent binding on the edge of the running rail.
The set-up is similar to that for steel single flanged wheels. A fitting dimension with a tolerance of 1 - 2mm between the edge of the flange and head of the rail is advised. Care should be taken to measure the widest point of the rail centres to ensure the correct set-up.
It is possible to manufacture a double flanged Polyurethane tyred wheel through the use of bolt-on flanges.
Options with different hardness Polyurethanes are possible. Please see below for further information.
Please refer to Polyurethanes for performance and specification detail.
Rebonding - Refurbishment
Recycling and refurbishing products is often a more cost effective solution than buying new.
Many wheel types benefit from a refurbishment process. Common wheels that benefit from this include; fork lift drive wheels, Special hub wheels, large diameter and unusual size wheels.
Refurbishment can be especially cost effective on Polyurethane tyred wheels. Opportunities to change the performance characteristics are also possible.
Refurbishment can also be carried out to damaged bores and drive wheel systems. In addition to direct bonding of new Polyurethane material, options including Polyurethane & Rubber press on bands offer alternative solutions.
Due to the recycling aspect of wheel refurbishment, benefits to the environment are achieved. These can be considered for environmental requirements.