One Huge Improvement

Switching from a wheel-mounted to a tracked crushing and screening system revolutionizes operations for The Dutra Group

For the past 12 years The Dutra Group of Richmond, California, had been using a portable, wheel-mounted, electric-powered crushing, screening and conveying system which they transported about four times a year between their 300-acre basalt quarry at San Rafael and their concrete recycling yards at Richmond, as well as two former sites. All are located in the San Francisco bay area and range from 15 to 35 miles apart.

When sufficient material stockpiles were built up at the quarry, the equipment was moved to one of the recycling yards to crush between 60,000 and 80,000 tons of rubble; then on to another yard or back to the quarry. Each move required four or more men and 11 truck loads, including towing two crushers and a screen, and took 11 days to complete.

In February 2010 Dutra switched to a diesel-powered, track-mounted Powerscreen crushing and screening system that requires only two men, four trucks and two days for each move. In addition, the company says the new system has substantially increased material production at all sites and has dramatically reduced costs overall.

‘The old system was too complicated and cumbersome, and was costing us too much in lost production time, maintenance time and expense, and moving costs,’ said quarry manager Jon Guglielmini. ‘Each move cost about $25,000 one way, or $100,000 for four annual moves. In addition, we lost a total of 44 production days for four moves. With the new Powerscreen system, each move costs about $10,000, or $40,000 for four moves, and we lose only eight production days in total.

‘Sometimes we want to move the crushing and screening system from place to place within the quarry, to follow the face or put the equipment down in the pit. Moving the old wheeled system took two days. Moving the new tracked system takes two men about 3h.’

The Dutra Group’s old system included a jaw crusher, apron feeder, cone crusher, a side conveyor, a return conveyor to the cone, a screen-feed conveyor, a screening plant, two 60ft land conveyors, a 125ft radial stacker, several chutes and a generator.

The new Powerscreen system comprises an 1180 Premiertrak jaw crusher, two 1300 Maxtrak Automax cone crushers, a Chieftain 2100X double-deck dry screen, a Chieftain 2100X triple-deck dry screen, and a tracked conveyor.

At the quarry, the jaw feeds the primary cone directly (all-in-feed), with no need for an intermediate screening plant. Material then goes to the two-deck screen, with oversize going on to the secondary cone under the reject side to be re-crushed and returned to the two-deck screen. The remainder goes to the three-deck screen for distribution to four stockpiles: 3/4in, 1/2in, 3/8in and quarry dust (3/16in).

‘The old wheel-mounted system was much too labour intensive and time-consuming to set up and tear down,’ said Mr Guglielmini. ‘It was electric powered, so we had wires and connections to deal with and a generator to transport. We had to jack up the jaw 7ft to get the apron feeder under it. We had to jack up the cone about 3ft. Everything was mounted on blocks and hydraulic jacks. We had to build ramps. If you tried to tow the equipment, the wheels sank into soft or muddy ground. It was all a problem – an expensive one.

‘We have none of that with the new system. Tracks don’t get mired in mud. We just drive the equipment into place and start the engines. The most we might have to do sometimes is build a 1ft high ramp to the jaw plant. When we move the system, the tear-down and clean-up are quick and simple; we drive the equipment on to lowboy trucks, and off we go.’

According to Mr Guglielmini, the new system is also much more versatile. ‘At the rock quarry we use all six pieces of equipment, but we only need four at the recycling yard: the jaw, the cone, the 2100 double-deck, and a stacker conveyor. At the yard we produce 3/4in base material and 3/4in drain, which is clean. We also make manufactured sand using the jaw, cone and screen in closed circuit.

‘We feed 3/4in clean material directly into the cone from the jaw. I have never before seen a cone that can handle fines going into it without plugging up. With the 1300 cone we can recycle in the morning and make sand in the afternoon with just a screen change, but no liner change,’ said Mr Guglielmini.

‘When we first started investigating tracked equipment, Paul Campbell, owner of Powerscreen of California, the state-wide dealer for Powerscreen and Pegson, told us the Pegson 1300 cone could make sand from 3/4in material. I was very sceptical but Paul volunteered to bring in the jaw, cone and screen plants for a test in closed circuit, and he was absolutely right.

‘We put the whole system through every kind of gruelling test we could think of, and it came through with flying colours. We actually tried to prove the equipment couldn’t perform as claimed, but we couldn’t do it. The 1300 cone can actually make sand from 3/4in, 1/2in and 3/8in clean material.

‘The new tracked system is also much more efficient. This equipment likes to be fed constantly, and when we do we can get production of up to 360 tons/h in the quarry. Our daily goal is at least 3,000 tons, and we normally achieve 3,200 with the new system. With our old system, we might have achieved 3,000 tons three times in 12 years.’

Dutra also had a lot of unplanned downtime for repairs with the old system. A major problem was with mesh and rebar clogging and tearing up the conveyors and chutes. In addition, the old system had eight wear points where material drops from one piece of equipment to another, whereas the new system has only four.

The new tracked system runs like a dream, according to Mr Guglielmini. ‘The manufacturer’s maintenance recommendations are followed and the equipment is checked periodically for wear. This has resulted in very dependable service from all the new equipment, whereas the old wheel-mounted system took three times as much maintenance time and work,’ he said.

However, making the decision to purchase a tracked system was only the beginning. Mr Guglielmini still had to convince his corporate management that the payback would be worth the cost of purchasing the six new pieces of equipment. ‘To make that recommendation, I had to stick my neck out pretty far,’ he said. ‘But I was convinced that tracked equipment was the way to go.

‘Before going to management, we considered a number of factors: purchase cost, equipment efficiency, fuel consumption, equipment durability, parts, and anticipated maintenance downtime. In other words, what is it going to cost to buy the equipment, to operate and maintain it annually over a period of years, and what will it be worth in resale value down the road? Powerscreen of California was a big help in determining these things.

‘Having examined each piece of equipment for construction design and quality, we then went to management with all the facts, figures, features and benefits of the tracked equipment. It really was a major change in philosophy for our company, but we decided to go ahead with the purchase, and it turned out to be a very smart decision. Management is happy with the outcome. It’s all just one huge improvement.’