Avonmore Electrical received a call from a long-standing customer in a bit of a panic, a foot-mounted gearbox and stand-alone motor where installed for over 35 years on the main de-barker infeed conveyor. This was installed in the early 80’s and had worked continuously feeding the plant since then. The original manufacturer was no longer trading and the gearbox and motor details pointed to ASEA who were no longer trading (they are now the A in ABB), this unit looked like it was manufactured through a third party with no details coming forward.
One of our Engineers attended site and took some dimensions, through measuring the Drive drum and working out the linear speed we were able to determine the required output speed and calculate the transmission ratio of the gearbox, The customer advised the conveyor was just short of 100 metres long and inclined @ 15°, there was heavy shock loading, anything up to 20 stop/starts per hour and the conveyor would be required to start under full load of 40,000 kg’s. Avonmore Electrical work closely with some of the leading gearbox manufacturers in the world and this was going to be a very special unit to fit the specification. We first calculated the generated output torque from the old unit, utilising the information provided from the customer we were able to estimate the torque needed to drive the conveyor (there was also a secondary 1” triplex drive providing additional torque through another reduction). Our base torque value came in at 21,000 Nm. We now needed to calculate service factors. Due to the heavy shock loading and the stop/starts, a high service factor was desired. The nature of the wood processing industry means this is a must and we settled on a service factor of 3.0 or above.
The motor chosen was an ABB 90kW 4 pole with IE3 efficiency, there was no need for increased capacity on the motor bearings as thedirect coupled drive meant there was no exteranl axial forces on the motor.
The specification agreed was as follows:
- ROSSI R3I 360 UP2A
- Reduction Ratio 38.4:1
- Rated Input Power PN1 288 kW
- Output Torque M2 22,185 Nm (Based on fitted 90kW Motor)
- Backstop CCW Direction
- 180mm Solid Low Speed Shaft
- ABB 90kW Foot Mounted TEFC Electric Motor.
The decision to fit a backstop was an added safety precaution to ensure the inclined conveyor does not back drive in the event of a power failure, the gearbox was modified in ROSSI and fitted with spherical roller bearings to cope with the extreme forces exerted on the output shaft, the triplex chain drive means there is some high axial forces on the low-speed shaft bearings and also the stop/starts’ with conveyor starting fully loaded means the need for increasing the capacity of the bearings was a must.
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