Choosing the Proper Caster
The following are main factors to consider when choosing a caster:
Load Capacity
The most important factor to determine is whether the caster can work normally and influence the service life of the caster. Take a cart with four casters for example: It is an ideal state that each caster rolls on the ground and the weight is distributed evenly. Nevertheless, because of an uneven floor surface (ex. door thresholds) perhaps only three of four casters touch the ground. Or, perhaps the load is uneven causing the four casters to receive weight unequally. Therefore, the safety coeffecient must be taken into consideration when calculating the load capacity.
Take a cart with four casters as an example. Consider this formula:
T = (E+Z)/3
If the number of wheels exceeds four, consider this formula:
| T = (E+Z)/n x s |
T = Load capacity
E = Weight of the cart
Z = Weight of goods
n = Number of wheels
s = Safety coeffecient (Generally take 1.3 to 2.0) |
Environmental Conditions
The Fork
The service life and performance of a caster depend on the materials and environment in which it is used. If the steel, which is the most frequently used for bracket, does not have an anti-corrosion layer, it possesses almost no resistance to a moist environment. The steel will rust and weaken. There are three kinds of anti-corrosion layers:
Lacquer Allows various color options. However, if the paint is chipped, protection is lost.
Zinc Allows small area damage. Zinc decays first because of electricity chemistry process. Zinc white rust has the tendency to cover with the naked steel, thus stopping the rust corroding to the inside of the steel.
Chromate Greater anti-corrosion and anti-moisture than zinc plating. Outstanding performance. Able to bear machinery damage due to its hard surface.
The Wheel
All-plastic wheels have greater ability of anti-corrosion and anti-moisture than wheels with assembled steel parts.
The Bearing
No bearing or Delrin bearing has greater ability of anti-abrasion than steel bearings.
Temperature Resistance
This generally involves only the wheel, especially the tread. Surrounding temperature and heat produced by rolling friction must be considered. Rolling friction is determined by the material, shape, load capactiy of the tread AND the course, length, and state of the ground. If the wheel or core of the wheel is plastic, influence of temperature such as load capacity and stationary in cold or hot conditions are important when choosing the material and bearings.
Chemical Resistance
Chemical resistance of the wheel should be considered, especially when corrosive substance contacts directly with the tread or the whole wheel.
Start and Rolling Resistance
A force must overcome a resistance to get the casters started or moving. The level of this resistance depends on various factors: load, temperature, wheel material, type and size of the bearings and of course the ground on which the caster runs. Therefore, when choosing the right caster, it is important to adjust all these factors carefully.
Relation between wheel diameter and start resistance
- At the chart to the right, we see the starting resistance reduces while the wheel diameter increases. In other words, a larger diameter wheel is easier to move.
Relation between tread material and rolling resistance
- At the chart to the right, we see the softer material must overcome greater resistance as the load increases. Therefore, we should match the soft material with light loads, and hard material with heavy loads.
We have just briefly introduced the methods of choosing the proper caster above. There is introduction of different materials and brackets in this catalogue. If you continue having difficulty making a decision, please feel free to contact us, we will be pleased to help you find the optimum combination for your application.
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