Friction occurs when two surfaces come into contact, as when a wheel rests on a floor. Friction is the force that resists movement between the objects. Under theoretically perfect conditions, the ideal wheel environment would be a hard, smooth wheel rolling over a hard, smooth surface. In real life, perfect conditions never exist. In a typical work environment, using a hard wheel will often result in higher rolling resistance, as well as increased noise and vibration.
Both static and dynamic forces affect friction. The initial push force necessary to place an object in motion is the static force. Static force is generally greater than dynamic force which is the exertion necessary to keep the object moving. Wheel design must consider bother static and dynamic force.
In a wheel or caster system, there are three places where friction can affect force:
- at the point where the axle and wheel interface;
- if a swivel caster, in the swivel housing; and
- at the ground/wheel interface, particularly at any points where the wheel will slide or pivot on a surface.
The efficiency of a wheel or caster in reducing friction is dependent not only upon the appropriate design of the wheel itself, but also on the materials used in its construction and the placement of the wheels on the equipment to be moved.