Step 1 – Determine your product and mounting type.
Step 2 – Determine your Load Capacity. The load capacity is determined by the formula below, safety factor and unevenness.
- T = Required load capacity of one wheel or caster
- E = Deadweight of the transport unit
- Z = Maximum additional load
- n = number of wheels or casters used
- S = safety factor
The safety factor is influenced by the speed and the ratio between wheel diameter and height of the obstacles and consists of 4 categories:
- Indoor manual transport (height of the obstacles < 5 % of the wheel Ø): Safety factor: 1.0 to 1.5
- Outdoor manual transport (height of the obstacles > 5 % of the wheel Ø): Safety factor: 1.5 to 2.2
- Indoor power-driven transport (height of the obstacles < 5 % of the wheel Ø): Safety factor: 1.4 to 2.0
- Outdoor power-driven transport: Safety factor: 2.0 to 3.0
Step 3 – Select your Tread Material.
The hardness, shape, and tread material have a considerable influence on the operational comfort, smooth-rolling performance, and starting, rolling, and swivel resistance of the wheels or casters. Generally, a wheel tread or tire should be softer than the floor otherwise damage to the floor can occur.
The floor on which a wheel is running must be able to withstand the pressure, especially with high loads. Extra care should be taken with wood, tar, concrete, or electrically conductive floors.
Step 4 – Determine Maneuverability – Starting, rolling, and swivel resistance
The starting resistance is the force that must be overcome to accelerate a loaded wheel from static into dynamic conditions.
The rolling resistance is the force that has to be overcome to move a loaded wheel at a constant speed. It is caused by a permanent compression and rebound of the tread during the rolling process (hysteresis). With the hysteresis, energy losses occur due to the internal friction of the material.
Starting and rolling resistance factors:
- Wheel diameter
The swivel resistance is the force that has to be overcome to make a directional change with a swivel caster.
Swivel resistance factors:
- Contact surface (floor)
The maneuverability of the transport unit depends on the number, type and arrangement of the castors. These factors will also have an influence on the load capacity, mobility, guidance, turning circle and stability of the vehicle.
Step 5 – Select the Bearing Type
The wheel bearing is important for the rolling characteristics of a wheel and, consequently, for the mobility of the application equipment. It must meet the requirements concerning load capacity, duration of operation, environmental influences, starting and rolling resistance, and possible further requirement criteria.
The plain bore is a simple, cost-effective, and durable wheel bearing, corrosion-resistant, and maintenance-free under standard conditions. Plain bores are mainly used for light duty and transport equipment casters are suitable for low speeds and intermittent use. For wheels with tubular steel hubs, plain bore bushings made of nylon are used. At high speeds under high loads, overheating may occur. Cast iron wheels with plain bore must be regularly lubricated.
The roller bearing is a sturdy, robust, largely maintenance-free wheel bearing type that only requires a small mounting space. Roller bearings (also called needle bearings) have a small radial bearing play and have proven particularly successful with casters for transport equipment. Roller bearings consist of steel rollers fitted into a plastic or steel cage. These rollers roll between the axle tube and the wheel hub. As there is no sliding friction, only rolling friction during the rotation around the axle, the rolling resistance of the wheel is relatively low, even with higher loads. Roller bearings are lubricated with long-life grease and are maintenance-free under standard conditions. In addition to the standard version, roller bearings are also available in stainless steel.
A central ball bearing offers a very precise, light running performance and a good sealing. These bearings are mostly used for synthetic wheels with small loads and guide rollers. The wheel center is directly injected onto the central ball bearing. The central bearing is equipped with two sealing caps as standard. Ball bearings are lubricated with long-life grease and are maintenance-free under standard conditions.
Step 6 – Consider Your Application’s Environmental Influence
The chemical resistance of wheels or casters must be considered especially in cases where the components have direct contact with aggressive substances. Chemical resistance does not only depend on the type of aggressive substance but also the concentration and the duration of contact as well as other environmental conditions such as temperature and humidity.
Step 7 – Additional Options and Requirements
Do you require locking systems for rolling and/or swivel motions? Do you require a locking or guiding system for the swivel motion?
Locking systems can be used to block the rolling and / or swiveling movements of castors in the idle state
Do you require a brake system?
Drum brakes use a spring to keep the brake in the braked state. Directional reset devices align the position of a swivel castor in a given direction in the unloaded state.