Mining the Volcano

Thirty kilometres east of Montreal, in a huge quarry carved out of the north side of Mont St-Hilaire, lumbering haul trucks and a cat’s cradle of conveyors feed five hungry rock crushers. Demand for the Poudrette Quarry’s annual 600,000 to 800,000 tonnes of product is enormous, so its two plants run around the clock.

“To start and stop the plants is very, very expensive,” explains Alexandre Poudrette, production manager and a third-generation Poudrette to run the quarry, which his grandfather opened in 1954. It takes from one to one-and-a-half hours to go from a cold start to full production of consistent-quality product. For the maintenance crew then, says Poudrette, “the biggest challenge is to maximize and optimize production time.”

There are only 18 hours of downtime a week–once a day for three hours, four days a week. This time can be used for repairs, but it is principally for intensive preventive maintenance inspections. “For example,” says Poudrette, “we do visual inspections, check oil levels, inspect the crusher liners in the crusher head assemblies and inspect the screens.

“There are certain pieces we inspect every day, like the interiors of the crushers,” he explains. “The crushers and the screens are the heart of the plant.” Four times a year the major pieces in the crushers are disassembled for inspection. Three times a year there is a 10-hour shutdown to change the worn parts in them. “In August we changed the crusher liners in five hours. That was exceptional,” he vaunts.

“I have a very good maintenance team. My maintenance supervisor has 53 years of experience,” Poudrette says. There are 10 people in the maintenance department–three mechanics, six general maintenance workers and a maintenance supervisor.

During the coldest and snowiest two-and-a-half to three months of the winter, from about January to March, production stops. Then, two maintenance workers toil full-time carrying out maintenance projects on the equipment, readying it for the next 9- to 10-month production cycle.

In two years, Poudrette wants to reduce the weekly downtime to just 10 hours. He plans to achieve this by installing more equipment, which will permit him to maintain production by strategically shutting down the plant system by system, instead of the current practice of stopping the whole plant.

Poudrette has already shaved downtime by replacing some of the steel screens, which grade the rock, with thick rubber screens. Their up-front cost, at $2,200 apiece, is about 10 times that of steel. “But,” he explains, “I have to replace a whole set of steel screens every month. The rubber screens cost a bit less per year in all, but there is a great reduction in downtime. We save a minimum of six hours of maintenance a week.”

The quarry produces gravel for applications such as asphalt, concrete and re-mix. Its finest grade product is 130,000 to 150,000 tonnes a year of washed shingle gravel, which has a diameter ranging from just 0.5 millimetres to 1.7 millimetres.

Mont St-Hilaire is an extinct volcano. The rock is exceptionally hard and abrasive nepheline syenite, which is extremely hard on all of the steel wear surfaces. It requires constant diligence by the maintenance crew to keep the equipment in good repair. The air in the immediate area of the tightly clustered systems in the crushing facilities is thick with brown-grey rock dust, which collects everywhere in fine drifts.

The crushing facility, which has a 400-tonne an hour capacity, has a total of five crushers–a jaw crusher in the primary crusher area and four omnicone crushers for the finer work. Some 50 motors, ranging from 5 to 250 hp, run the crushers and 30 conveyors.

The jaw crusher plates have to be replaced after every 150,000 tonnes of production. The cones in the secondary and tertiary omnicone crushers are changed after every 250,000 tonnes of production. The major pieces in the crushers are disassembled four times a year for inspection.

The maintenance garage has a minimum of equipment, such as steel saws, vices, a press, welding gear and repair tools. They stock one each of the seven motor types the plants use, plus conveyor bearings and small crusher parts like seals and bolts.

Every two years Poudrette brings in AVA Specialists Inc. from nearby Boucherville, Que., to do a vibration analysis on the eight crusher screens. The screen bearings are replaced every 20,000 hours. Outside contractors also do vibration analyses and amperage checks on the motors. Electrical work and oil analyses are contracted out. “I call subcontractors for special technical support–for example, Nordberg, the fabricators of the crushers.” Bearing replacements are also done off-site.

The annual maintenance budget is $1.5 million. “I’m not sure if we can reduce the maintenance budget, because we run 24/7,” says Poudrette. The goal is to keep the equipment in absolutely top shape because, he explains, “An hour of production is worth far more than the cost of pieces.”

The quarry has pen and paper maintenance scheduling, and just started keeping fully detailed maintenance records this year. Soon, though, the maintenance department will begin the transition to a computerized maintenance program called Amelie.

Amelie is a small-business maintenance software package created by AVA Specialists. It was designed to fill a niche for an inexpensive, but sufficiently comprehensive and flexible, maintenance package suitable for small companies.

Poudrette has already installed Amelie on the company computer and soon he will be hiring someone who will be responsible for entering the maintenance parts and the scheduling data. He expects the program will make controlling things easier and improve the efficiency of the machines. “Then,” he explains, “we will really understand what is going on in the plant and know the state of the parts.”

Contributing editor Carroll McCormick is based in Montreal.