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Selection Criteria

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It is normally observed that 80 % of the castor failures are due to improper selection of castor wheels, hence, while selecting any wheel or castor for any purpose or application, one should keep following points in his mind.

Load Carrying Capacity

  • Uneven Loading of Castors :- The operator may put heavier boxes on the one side of the platform of the trolley. As a result, one or two castors may be subjected to higher loads as compared to other castors. One must consider what is the maximum load any one castor is subjected to.
  • Unevenness of Flooring :- On uneven flooring, only three wheels out of four wheels fitted to trolley touch the ground & takes the load. Thus each wheel gets overloaded by 33 %. This overload is generally never considered.
  • Shock Loads :- Even if the flooring is good, generally, there are number of joints. While rolling over the joint, there is a jerk which creates shock load. Many a times trolley is lifted by a mechanical means, carried to some other destination and then placed on the floor. While placing trolley on the floor, there is always a jerk, small or big depending upon the carefulness of the operator. This creates a shock load.
  • Speed of the Trolley :- The castors are designed to work for manually pushed or pulled trolleys having speed below 6 km/hr. The load carrying capacity reduces in proportion of the speed.

To take care of overload for above mentioned reasons, a thumb rule is to consider the load carrying capacity of a castor at 50 % to 60 % of the nominal capacity.

Pushing / Pulling Efforts

  • Diameter of the Wheel :- As the diameter of wheel increases, the pushing / pulling efforts are reduced proportionately. Try to use higher diameter wheels as far as possible.
  • Type of Wheel :- Floor conditions & bearing in the wheel remaining the same, pushing / pulling efforts depends very much on the material of the wheel. Rubber being soft, rubber wheels get compressed under load & due to high coefficient of friction needs more pulling / pushing efforts. As against this, cast iron being very hard & low coefficient of friction, pushing / pulling efforts are minimum n cast of cast iron wheel.
  • Type of Bearing used in wheel :- If we consider the pushing / pulling efforts required are moderate for wheels with PLB & SIB, pushing / pulling efforts are less for wheels with NRB & minimum for wheels with BB. However periodic cleaning & greasing of bearings must be ensured.

Floor Surface

Pushing / Pulling efforts, noise level & life of wheel depend upon roughness of the surface on which wheels roll. Rubber, PU wheels & light duty castors may be avoided on rough surface if slightly higher noise level is permitted. It is advisable to use UHMW-PE or Cast Iron wheels & medium duty or heavy duty castors on rough surface depending upon the load. Rubber, PU or PP wheels & light duty castors may be used on smooth surface & light loads.

Noise Level

Rubber & PU wheels are soft & have low noise level. PP, NYL & UHMW-PE wheels have comparatively higher noise level. CI wheels have very high noise level. If very low noise level is essential, you may check for Rubber or PU wheels with higher diameter.

Atmospheric Conditions

In chemical or pharmaceutical industries, castor wheels are subjected to use in highly corrosive atmosphere. In food industries, the atmosphere is highly humid. In such industries, polymer wheels with stainless steel brackets are suggested to use. In order to reduce cost of the castor, today many industries are using mild steel brackets with hard nickel chrome plating as a substitute for stainless steel brackets.

Pushing / Pulling by power driven vehicle

All wheels & castors are designed for manual pulling or pushing at a speed not exceeding 6 Km/Hr. Therefore, pushing / pulling of trolleys or trolley mounted equipments by power driven vehicle must be avoided. The driver does not get any feel even if the wheel or bracket get jammed. As a result, a jammed wheel or castor is dragged over the road and gets completely damaged. Therefore, life of wheel or castor cannot be predicted in such a situation.

However, if pushing / pulling of trolleys or trolley mounted equipments by power driven vehicle is unavoidable, UHMW-PE or CI wheels with heavy duty brackets are suggested. Much higher factor of safety must be considered.

Comparision Of Wheels & Their Properties

Type of Wheel Load Bearing Capacity Resistance to wear Shock Absorption Capacity Road Grip Resistance to chemicals Noise Level Comparative Life Safe Working Temp
SRT Fair Fair Good Good Poor Low 1 P 500 C
BRT Good Good Excellent Excellent Poor Low 3 P 500 C
PU-PP Good Better Excellent Excellent Better Low 3 P 500 C
PU-CI Good Better Excellent Excellent Better Low 5 P 500 C
PP Good Fair Fair Fair Excellent Medium 3 P 500 C
NYL Better Better Fair Fair Excellent Medium 8 P 900 C
UHMW Better Better Fair Fair Excellent Medium 10 P 700 C
FBR Better Good Fair Fair Better Medium 8 P 1700 C
CI Excellent Excellent Nil Fair Poor High 20 P 2500 C