Despite years of reliable service the 170m elevator installed at the Himachal Pradesh plant of Ambuja Cement in India finally succumbed to the stress of continuous operation, writes N. Muthuswami, AUMUND Group.
The elevator, installed in one of the largest and most modern cement works in India, worked 24/7, raising raw meal to the pre- heater tower at a continuous rate of 650tph (tonnes per hour).
Whilst the machine remained in service, a detailed inspection revealed a replacement belt would soon be required and the company decided to invite bids for the supply and supervision of installation of the necessary components on a scheduled preventative maintenance basis. At 170 metres centre distance, this is the highest belt bucket elevator installed in the world today and as such only a very few companies had the expertise to deliver a competent replacement service.
Originally, the machine was fitted with a steel cord belt of width 1,450mm and tension rating of 3,500N/mm. After passing the application data through their sophisticated computerized selection programme,AUMUND decided to offer an alternative based on its own design concept resulting in a belt width of 1,050mm and with a bucket size of 1,000mm at 430mm pitch.
The AUMUND belt concept is very different in that continuous close pitch longitudinal ropes are employed, without rope free bucket mounting spaces, with additional wire ropes running laterally across the width of the belt adding considerable lateral stiffness without significantly changing the belt longitudinal flexibility. This cross-stabilized construction gives improved stability to the belt with improved bucket fixing, the Achilles Heel of every bucket elevator and probably the most common cause of elevator failure, plus improved directional stability, and better tracking.
Using continuous wire ropes at close pitch both longitudinally and horizontally without rope free spaces gives maximum strength and stability but does require the bucket fixing is punched through the belt, steel ropes and all... Of course this is taken into account with the tension calculation and the ruptured ropes are ignored in the full belt width tension rating.
To make the necessary belt punching, AUMUND has developed a special punching machine design which gives clean fixing holes accurately aligned relative to the belt edge and at precisely the correct pitch. The belt is held in a cassette and advanced automatically under the punching frame using a precision encoder to measure the pitch. The belts are prepared at the AUMUND works in Germany and shipped to site at the exact required dimensions including a prepared joint and the required clamping strips.
In addition to the new belt the elevator will be fitted with new drive pulley including friction linings and rubber bucket mounting strips all to be supplied locally. The casings, inlet and outlet plus the complete drive unit will remain unchanged.
This is an excellent example of the AUMUND rebuild and refurbishment service offered across the equipment range including belt and chain elevators, pan and bucket conveyors plus plate feeders. A refurbished machine can be supplied with all new moving parts by AUMUND retaining often only the structural elements resulting in a substantially new machine with typically a 30% cost reduction compared to outright replacement. With minimum changes to the structural parts and chute works installation time is significantly reduced and machines may generally be upgraded to the AUMUND standard during a scheduled outage. Of course once upgraded in this way the client can expect the usual AUMUND dependability and access to service support and genuine AUMUND spare parts. Not only can existing life expired machines be upgraded in this way often at the same time AUMUND can wring additional performance opening the possibility of plant capacity improvement with minimum new investment.