Recent harsh and extended winters have seen the demand for rock salt increase, which has resulted in increased production from the country’s mines. Efficient and reliable equipment is essential if the roads are to be kept clear of snow and ice each winter. One mine in Cheshire reviewed the condition of the existing main hoist and concluded it should be replaced with a more efficient drive system from Brevini Power Transmissions.
With the original hoist equipment, driven by a helical gearbox, installed in 1973, concerns were raised over the reliability and safety of this plant. The main contractor responsible for the scheme who was to replace the drive system, approached Brevini Power Transmission, a long term supplier of drive solutions, to advise on the project. Initial site investigations showed the full extent of the complications that would have to be overcome in order to ensure a successful conclusion.
The original hoist lifted a nine tonne skip over a distance of 155 meters in just over 1 minute. To capitalise on the work which would be carried out it was decided that the new equipment should offer improved capacity, as well as efficiency and reliability, so the site would benefit from improved productivity once the project was complete. The new motor power was specified at 780kW at a speed of 590rpm with the required output speed of 21rpm. The duty cycle would see the skip accelerate for 10 seconds, travel at nominal speed for 25 seconds before decelerating for 10 seconds and unloading. This must be repeated for 24 hours per day, six days per week - a very demanding schedule and one with little margin for unplanned maintenance or repair work.
With the specifications laid out, Brevini was set the challenge of designing the new gearbox, while the engineers from the main contractor planned how the exchange would be carried out. The new drive had to be designed in such a way that it would fit into the footprint of the original helical gearbox and not interfere with the existing machinery which was to be retained. This included the original tacho drive system, which provides real time data on the position and speed of travel of the hoist. The whole project to remove and install the new gearbox would all have to be completed inside a very tight timeframe.
The layout of the original drive train included the gearbox and coupling as well as a long driveshaft which would have to be cut and then machined to match the new drive coupling supplied by Brevini. Clearly, once the shaft had been cut there would be no turning back and the new drive system would have to be successfully installed and commissioned to meet the client’s production requirements. The engineers at Brevini based the gearbox design one of the largest models of the PIV Posired 2 range, the PD85 gearbox which was modified to ensure that it fitted in to the space available when the original drive was removed. Weighing in at around 13 tonnes, the operation of replacement would require careful planning and coordination by all the engineers involved.
The output shaft of the PD85, measuring 370mm, was designed for a shrink fit to the drive coupling which was also supplied by Brevini. The final connection to the driveshaft of the hoist would require on site machining before the whole installation could be commissioned.
Dave Brown, sales manager for Brevini U.K., comments: “This was a project with a number of challenges for us, not least the tight timeframe for delivery. We have delivered a bespoke solution to meet the exacting requirements of the client by using our expertise in the field of heavy duty drive applications. More and more of our retrofit work for similar applications is being won on the basis that we will provide a customer-specific solution, rather than something off the shelf, but without the traditional downsides of cost and long lead times.”
The new hoist drive was successfully commissioned on time and the rock salt production continued to plan. Not only does the new drive system provide reliable and efficient service it has also considerably reduced the noise and vibration levels within the shaft and increased the mine's output capacity. The new gearbox has also reduced the maintenance requirements on the hoist system allowing the engineers to concentrate on other areas of the mine. The Posired 2 range of gearboxes is a series of universal modular drives with a wide range of accessories and options. It is available in 25 different sizes with nominal output torques up to 1,000 KNm. This versatility and ease of use makes the Posired 2 range well suited to a wide variety of applications and are able to satisfy the majority of clients' needs.