The introduction of exotic materials such as Kevlar has reduced stretch and increased power transmission capabilities. Many companies produce quality vee-belts, but the selection to match required functional specifications can often be misleading or misunderstood.
The most basic of all requirements remains the one the quarrying industry has dealt with for the past 50 years and more – that is, maintaining belt tension to the belt manufacturer’s specifications.
Leverlink, which has designed motor bases for more than two decades, was approached by a client that had a slurry pump that was taking up to 26 man hours to remove old belts and fit new ones. In addition, the service life of the vee-belts was considered by the client to be insufficient.
Leverlink was asked to make recommendations to dramatically improve the labour cost of the vee-belt change-out, and to provide better service life of the vee-belts.
The slurry pump was mounted conventionally on four M52 jacking bolts (see Figure 1). The height of the jacking bolts was slightly above shoulder height, making the job risk-intensive when adjusting with a large spanner and extension to raise or lower the electric motor.
Recognised risks were slips, trips, falls and strain injuries. In addition, the difficulty of facing pulleys and ensuring drive and driven shafts were parallel increased the time of the job dramatically. Furthermore, the guard covering the vee-belts, drive and driven pulleys required a crane to remove it.
Leverlink evaluated the problem and the costs involved, and recommended replacement of the conventional M52 jacking bolt method with a Verti-Lift rubber torsional spring motor base (Figure 2). Leverlink has manufactured this design for more than 20 years and it has been proven in the harshest of environmental conditions.
{{image2-a:r-w:200}}The benefits of the rubber torsional spring motor base were as follows:
- A single adjusting screw, which is enclosed and lubricated.
- The parallelogram operating system of the motor base ensures the drive and driven shafts remain parallel at all times.
- The parallel system also ensures the drive and driven pulleys remained faced.
- To raise and lower the electric motor now requires the rotation of only a single adjusting screw.
- The rubber torsional spring stores energy to accommodate stretch and maintain the correct belt tension as per the manufacturer’s specifications for extended periods of time.
The rubber torsional springs are sized to lift the mass of the motor and supply sufficient force to tension the specified number of vee-belts. In doing this, energy is stored in the rubber torsional springs to allow for vee-belt stretch take-up.
The vee-belt tension should be checked on a regular basis. This can be done in a few minutes through a window in the guard, remembering that maintaining the correct tension according to the belt manufacturer’s specifications is critical to the vee-belt’s service life.
The service life of the drive and driven pulleys will also be extended due to non-slippage of the vee-belts in the pulley grooves. The guard was upgraded to 316 stainless steel (which can be painted to client safety colours) in a lightweight design that could be removed by one man (Figure 3).
A window at mid-belt span length was included to enable checking of the vee-belt tension. This takes no more than five minutes, and it can be re-tensioned if required. The guard does not have to be removed.
After 20 years of carrying out this type of conversion, the results were fairly predictable for Leverlink, as was the satisfaction of the customer.
Installation of the lightweight 316 stainless steel guard allowed removal and replacement in less than 20 minutes. The rubber torsional spring motor base, with its stored energy principle, more than doubled the vee-belt and pulley life.
Simply minimising the vee-belt drive slippage did all this. In fact, the whole dynamic of the job had changed.
A belt change-out now takes two man hours instead of 26, and the number of change-outs per year has halved. The payback period was less than one year.
Source: Leverlink