Pinions instead of belts

NorStone AS, a subsidiary of HeidelbergCement AG, is Norway’s largest producer of gravel products. The company supplies aggregates for concrete and asphalt, pipe cover gravel for coastal regions, and other special products. Each year NorStone’s production facilities at Tau in south-west Norway produce over 6.6 million tonnes of gravel products of various types and quality classes. The demand is large, and even with its present annual production capacity of 2.3 million tonnes of material the Tau plant can scarcely meet the demand. This makes it especially important to ensure that the plant is operational as much as possible and to minimise unplanned downtime.

“We have found that service and spare parts for geared motors are now available to us very quickly. We hold some parts in stock ourselves, and for all of the rest we have complete trust in NORD Drivesystems as a supplier,” explained Ivar Ullestad, Maintenance Manager at Tau, as the reason for going back to the former solution. “This allows the known advantages of drive solutions with geared motors to be fully exploited. In particular, direct drive leads to higher reliability, which means less downtime and therefore less lost production time. Another important aspect is that less maintenance is necessary. In addition to reducing maintenance costs, this increases safety in the plant,” added Ullestad.

Working conditions are a significant factor in such considerations. “You have to bear in mind that we work outdoors all year round. Most of the locations for the conveyor belt drives are open and unprotected. Due to the harsh weather conditions in the west of Norway, with wind, rain and sleet, as well as the dusty and rather unpleasant environment at the site, we try to minimise repair and maintenance times for our maintenance staff.”

The Tau plant runs seven days a week, 24 hours a day in shift operation. The 168 production hours include 16 hours of scheduled maintenance. The plant is only shut down for the winter break. During this break, annual maintenance inspection and overhaul tasks are performed in two to three weeks. The direct drives have contributed to a distinct increase in reliability, amounting to approximately 4.5% in the last three years. “We are very satisfied with this trend. With the change from shaft and belt drives to direct drive with geared motors, in the first place we eliminate the aspect of belt wear which is considerable. Furthermore, no water or dust can enter the drive mechanism. This means that the decision in favour of compact, robust geared motor units yields clear advantages and has therefore proven to be an intelligent move,” summarised Per Thu, Production Manager of the NorStone plant.

The direct drives brought more than just higher reliability and reduced financial and labour expenditure for maintenance activities. The relative investment costs for purchasing new gear units also proved to be lower. Replacing a complete package, consisting of a shaft-type gear unit along with belt pulleys, belts, a shed, belt cover and motor turned out to be more costly than purchasing a comparable geared motor. As a series of periodic gear unit replacements was already planned, a comprehensive switch from shaft and belt drive to direct drive was a logical choice for Ullestad. He is currently working to standardise drive components. “With a staged cutback in drive systems for the conveyor belts, we are standardising aspects such as motor size, shaft size and drum diameter in order to limit diversity and thereby simplify maintenance, stock management and service. We are also developing backup solutions which, among other things, involves keeping components in stock ourselves.”