The process of choosing the right wheel to match the operating conditions can be divided into three steps:
a. identifying the correct type of wheel based on the floor and the characteristics of the operating environment;
b. calculating the dynamic capacity, static load and smoothness required by the specific application and, therefore, determining the wheel diameter;
c. identifying the correct castor and checking the dynamic capacity of the wheel and castor assembly.
A technical analysis of the operating conditions is therefore essential for choosing the right wheel.
In particular, the following factors must be carefully considered in the choosing of the wheel:
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NATURE AND CONDITION OF THE GROUND
The nature and condition of the ground and the presence of any obstacles will have an influence on choosing the right wheel. They are also important factors affecting the performance of the moving trolley as well as the efficiency and the duration of the wheels and castors.
The main flloor-wheel covering combinations are the following:
| Tiles |
elastic rubber or pneumatic |
| Asphalt |
elastic rubber or pneumatic |
| Cement-resin |
polyurethane or rubber |
| Dirt floor |
elastic rubber or pneumatic |
| floor with gratings |
elastic rubber or pneumatic |
| floor with chips, obstacles or other materials |
elastic rubber or pneumatic |
ENVIRONMENT
To choose the right wheel, it's also important to determine if the wheel materials are compatible with the chemical-environmental conditions, the temperature and the humidity in addition to the inductive electrostatic phenomena that may affect wheel operation.
Chemical-environmental conditions
Because there are so many different types of aggressive chemical agents in work environments, it's difficult to provide a complete and exhaustive description. The main chemical substances that a wheel may come in contact with include:
- weak acids (e.g. boric acid, sulphurous acid);
- strong acids (e.g. hydrochloric acid, nitric acid);
- weak bases (e.g. alkaline solutions);
- strong bases (soda, caustic soda);
- chlorinated and aromatic solvents (e.g. acetone, turpentine);
- hydrocarbons (e.g. petrol, oil, diesel oil, mineral oils);
- alcohol (e.g. ethyl alcohol);
- fresh water;
- salt water;
- saturated steam.
Tellure Rôta presents a table showing the compatibility of the materials used to build Tellure Rôta wheels in different operating environments.
Table of chemical aggressives
Temperature
If operating temperatures in an application differ from the standard range of values indicated by the manufacturer, check the resistance of the wheel materials. This not only applies to the rolling strip and the centre, but also to the type of lubricant used (it may be necessary to contact the manufacturer).
Tellure Rôta presents a table showing, for every TR series, the load capacity reduction as a function of temperature.
Table of temperature
MAGNITUDE AND NATURE OF THE LOAD
The magnitude of the load is the value (expressed in Kg) obtained by adding the weight to be transported to the trolley weight (tare).
The nature of the load, either a liquid or a solid, has a significant effect on the wheel load capacity calculation.
The formula to determine the load capacity for each wheel is:
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where:
Q = load capacity for each wheel
Pu = weight to transport
Pc = trolley tare (trolley weight)
n = number of wheels in contact with the ground.
Solid load:
For a solid load, n=3 for a four-wheeled trolley (where three out of four wheels are considered to be in contact with the ground at all times).
Liquid load:
For a liquid load n=2 for a four-wheeled trolley (where two out of four wheels are considered to be in contact with the ground at all times).
SPEED AND MEANS OF TRACTION
Trolley speed is an important factor when choosing a wheel.
In fact, if the speed is zero, and thus the use is mainly static, it is enough to compare the load capacity for each wheel with the static load indicated in the manufacturers' catalogues.
If the speed is other than 0, then the means of traction must be taken into consideration.
Manual moving
For manual moving, the speed is generally less than or equal to 4 km/h.
Choosing a wheel that allows only one operator to move a load should be based on a wheel smoothness value determined by the following formula:
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where:
S = smoothness
Pu = weight to transport
Pc = trolley tare (trolley weight)
n = number of trolley wheels (maximum 4)
Mechanical moving with towing devices
For towed mechanical moving, the wheel should be chosen based on the trolley's operating speed.
The wheel rated dynamic load capacity normally refers to a speed of no more than 4 km/h (1.1 m/s).
If the speed is higher than 4 km/h, a correction factor must be applied to the load capacity value since the materials forming the wheel undergo chemical-physical changes during which their performances decrease with an increase in operating speed.
Tellure Rôta presents a table showing the indicative percentages of load capacity reduction with an increase in speed for different types of Tellure Rôta wheels.
Table of operating speed
On-board mechanical movement
For trolleys with an on-board drive (trolleys with drive wheels - self-propelled trolleys), the wheels are subjected to particular stress and strain.
Since many factors have to be evaluated, it is recommended to contact the manufacturer to choose the wheels and castors to apply to self-propelled trolleys.
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