18 project updates
REPLACING AN OBSOLETE GEARBOX AND MOTOR DRIVE A 35-YEAR-OLD FOOT-MOUNTED gearbox and stand-alone motor had been working continuously to power the infeed conveyor of a de-barking process. The original manufacturer was no longer trading, and the gearbox and motor details pointed to ASEA, who was also no longer trading (they are now the A in ABB). Having decided that the gearbox and motor had finally reached the end of their useful lives, the company called on Avonmore Electrical for help and advice. An Avonmore engineer attended the site and took some dimensions. By measuring the drive drum and working out the linear speed, it was possible to determine the required output speed and calculate the gearbox’s transmission ratio. The customer advised the conveyor was just short of 100m in
length with a 15° incline and was subject to heavy shock loading, anything up to 20 stop/starts per hour and the conveyor needed to be able to start under a full load of 40,000kg. Avonmore Electrical calculated the generated output torque from the old unit. Utilising the information provided by the customer, it was possible to estimate the torque needed to drive the conveyor – there was also a secondary 1in triplex drive providing additional torque through another reduction. The base torque value came in at 21,000Nm. The next step was to calculate service factors. Due to the heavy shock loading and the stop/starts, a high service factor would be desirable due to the wood processing industry’s nature – a service factor of 3.0 or above was therefore decided upon. The motor chosen was an ABB 90kW
4-pole with IE3 efficiency. There was no need for increased capacity on the motor bearings as the direct-coupled drive meant there were no external axial forces on the motor. A backstop was also added as a safety precaution to ensure the inclined conveyor does not back drive in the event of a power failure. The gearbox was modified to meet the application requirements and fitted with spherical roller bearings to cope with the extreme forces exerted on the output shaft. The triplex chain drive means there are some high axial forces on the low-speed shaft bearings and also the stop/starts, with the conveyor starting fully loaded meaning the need for increasing the capacity of the bearings was a must. www.avonmore-electrical.com
OVERHAUL OF TWO 90KW CENTRIFUGAL FANS JJ LOUGHRAN WAS ASKED BY A LOCAL POWER station to assess two 90Kw centrifugal fans. The company’s electrical engineering team attended the site and checked the motors’ insulation resistance, and found that the values recorded were below nominal levels, which would not allow the motors to operate safely. The extract fans could not be repaired on site, so an engineering team was immediately dispatched to mechanically disconnect both fans from the ductwork, crane them out of position and send them to JJ Loughran’s engineering workshop for an overhaul. Due to the power station’s critical nature, initial inspection and removal were carried out on the same day. Once in the workshop, the motors were dismantled into individual parts, and each unit was electrically inspected. The mechanical dimensions on the front and back end caps were checked to ensure the values were within machine tolerances. All individual parts were cleaned, rotors and extract fan blades were dynamically balanced, and the bearings were replaced. The motors were then reassembled and tested before the units were delivered back to the site and were mechanically and electrically reinstalled, run and tested. JJ Loughran made a recommendation that 230VAC heaters be fitted into the motor windings. Because the fans do not run constantly, these heaters would be energised when the motor is not in use, ensuring dampness or condensation buildup does not occur within the stators. www.jjloughran.com Quarter 2 2021
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