5. CHOOSING THE RIGHT WHEEL
Any product that isn’t used under the conditions for which it was designed may not satisfy the user’s needs. It may also damage materials and cause injuries.
Here are some examples in which wheels and castors are used incorrectly:
- using a wheel not suitable for the floor will deteriorate the wheel covering and damage the floor;
- choosing a fixed castor under operating conditions for which a equipment must be very manoeuvrable will make it extremely difficult to move that equipment;
- applying a load that exceeds the wheel’s rated load capacity will lead to wheel malfunctions and premature deterioration.
Therefore, a technical analysis of the operating conditions must be performed. The most economical solution should be chosen only after the product has been technically evaluated. The purpose of performing a technical analysis on a equipment moving solution is to define the operating conditions and any external factors that may affect equipment use.
The following factors must be analysed in order to choose the right wheel:
- nature and condition of the ground (5.1)
- environment (5.2)
- magnitude and nature of the load (5.3)
- speed and means of traction (5.4)
- manoeuvrability (5.5)
- diagrams (5.6)
The process of choosing the right wheel to match the operating conditions can be divided into three steps:
- Step one: identifying the correct type of wheel based on the floor and the characteristics of the operating environment;
- Step two: calculating the dynamic capacity, static load and rolling resistance required by the specific application and, therefore, determining the wheel diameter;
- Step three: identifying the correct bracket and checking the dynamic capacity of the castor (wheel+bracket assembly).
If the evaluation of these various aspects generates different data with reference to the same wheel and/or castor characteristic, the final choice must be made based on the most conservative condition.
Static load [N]
Static load is the maximum load that a motionless (stationary) wheel can support without generating any permanent deformations that may reduce its operating efficiency. A wheel mounted on a equipment that is seldom moved, and therefore almost always remains in the same position, is defined as being subjected to a static load.
Dynamic carrying capacity
Dynamic carrying capacity of a wheel is defined as the value (expressed in N) of the maximum load that can be supported by that wheel in conformity with ISO 22883:2004 and UNI EN 12532:2001 that, for industrial wheels, require dynamic testing under the following conditions:
- constant speed of 1.1 m/s (4 km/h)
- overcoming 500 obstacles and 15,000 revolutions of the diameter;
- obstacles with width 100 mm and height 5% of the wheel diameter with an elastic rolling strip (hardness up to 90 Shore A) and 2.5% of the diameter for wheels with a rigid rolling strip (hardness greater than 90 Shore A);
- temperature 20 °C (tolerance ± 10 °C);
- non-continuous operation (3 minutes of operation and 1 minute stopped);
- smooth, hard and horizontal floor.
Rolling resistance is the value (expressed in N) of the maximum load that can be supported by each single wheel at a constant speed of 4 km/h with application of a tractive force or thrust equal to 50N (excluding the initial pickup). This value is obtained by applying a tractive force of 200N to a 4-wheeled equipment and measuring the magnitude of the maximum transportable load per wheel during normal moving conditions.
The applied tractive force of 200N complies with the international workplace standard for indoor moving and is universally recognised as the human fatigue limit that can be supported for extended periods of time.