The idea of this case study is to explain the meaning on each bearing and to show how the use of a ball bearing can be beneficial for the user. James Glover the sales Director at AUT explains the comparsions below.
Here are six main criteria for comparison between the two wheels:
Start Up Coefficient
Dynamic Carrying Capacity
Static Carrying Capacity
Rolling resistance is defined as the value (expressed in daN) of the maximum load that can be supported, by each single wheel, at a constant speed of 4km/h with application of a tractive force or thrust equal to 5 daN (excluding the initial pick up/ start-up coefficient)
Essentially rolling resistance should provide a simple insight into how much force it requires, for the user, to maintain a speed of 4km/h under given loads. The reason we believe this to be of importance is it tells us how hard the user is working. What you can determine is that across all different loadings, the input required from a user is lower using a ball bearing centre versus a roller bearing.
We can look at this is two ways, when comparing a ball bearing centre over a roller bearing.
Users can move equivalent loads for less effort
Users can move higher loads for the same effort required
Start-up coefficient is defined as ‘The force required, by an individual or machine, to create movement of a trolley, under a pre-determined load, whilst maintaining all external factors; such as floor type’
Essentially it’s the amount of effort required to take something from stationary to moving. Under very light loads 5-20Kg the ball bearing has a very small impact. However as the load increases, to around 60kg, the ball bearing starts to make a huge difference.
What we can conclude form this is, an operator moving trolleys, all day, doing large volumes of repetitions, will save a huge amount of effort, thus reducing the risk of RSI and other health and safety issues. As there are so many variables in real world examples it is simply impossible to give exact numbers.
We can say for sure that the following statement is true:
The heavier the load and the more frequent the repetition of usage, the higher the saving, on user input, when using a ball bearing over a roller bearing.
Dynamic Carrying Capacity, Static Carrying Capacity and Material Specification
The above three criteria, while critical for health and safety purposes, will all be consistent between ball bearing or roller bearing centres. The bearing type does not determine any of these factors. Your current castor carrying capacity of 125kg is actually determined by the lowest capacity component, which in this case is the bracket.
Once the testing has been complete between the existing wheel and the new wheel, we do expect to see some differences in the carrying capacities. This is due to the fact we expect the testing to reveal that the existing wheel is not 100% nylon added to that it is slightly smaller (on the tread) than the proposed new wheel. These two variances will effect carrying capacities but the bearing type would not.