What does an operation do when its profits are buried in millions of tonnes of sand and its equipment needs to be portable enough to move on a moment’s notice? Figuring that out is a daily task at Lonesome Prairie Sand & Gravel, a 35-year-old aggregates company in Canada.
The mountains of sand are especially troublesome for the company’s operation in Big Boy quarry, Wakaw, Sask. Profits are a challenge because though crews sift through more than a million tonnes of material every year, only about 180,000 to 270,000 tonnes is sellable aggregates. In most circumstances, the quarry would also sell the sand, but because Big Boy is too far from large sand-buying markets, they are only able to sell about 45,000 tonnes a year, severely limiting profitability.
Haver & Boecker’s F-Class vibrating screen features four-bearing technology, which minimizes structural vibrations. (Credit: Haver & Boecker)
The site is in western Canada, where pits are generally non-sustainable and gravel is becoming harder and harder to find, meaning most aggregates operations must use portable equipment so they can quickly move to the next job. A single Lonesome Prairie crew could operate in as many as 15 to 20 pits per year, so it’s important that they’re able to move everything in as little time as possible.
Lonesome Prairie had been using two portable vibrating screens in the Wakaw location, but the equipment wasn’t holding up to conditions. The machines regularly bogged down, leading to sand going through the crushers and contaminating the sellable material, resulting in wasted product and lost profit. In order to maximize yields, the operation used screen media with opening sizes as large as 7, 8 and 9 mm and overloaded the screens with as much as 4,500 tonnes of material a day. The larger opening sizes meant smaller rock – about 5% to 8% of the sellable rock – was falling through with the sand the operation considers waste material. The issue cost Lonesome Prairie about $200 an hour in production losses.
Production rates and lost revenue were only compounded by high maintenance costs. The sand caused the vibrating screens to wear quickly and require nearly continuous replacement of screen media. Crews needed to change screen media every two weeks, resulting in two to three hours of downtime and 900 to 1,400 tonnes of lost production for each change-out.
“The many issues were frustrating for our crew and our customers,” said Henry Derksen, Lonesome Prairie Sand & Gravel operations manager. “Contamination meant our material wasn’t as clean as it should be and we were concerned the issues would drive away our buyers.” Lonesome Prairie management approached Hikon Industries. They explained what they were looking for: a user-friendly, portable vibrating screen that would meet production requirements and be manufactured out of as many modular components as possible to allow for inexpensive repair.
Lonesome Prairie provided their desired tonnage rate, gradation samples and other specifications, and Hikon started looking for a vibrating screen to match. They talked to several manufacturers, including Haver & Boecker. They were also aware of the company’s Tyler F-Class vibrating screen, which features an advanced double- eccentric shaft design, supported by four high-performance, double-spherical roller bearings. The technology minimizes structural vibrations and delivers a consistent stroke, virtually eliminating surging, blinding, pegging and material contamination.
Hikon and Haver & Boecker agreed to work together and started to design a Tyler F-Class portable plant.
Hikon custom-built the chassis around the 1,825 by 6,100-mm, three-deck F-Class. Haver & Boecker engineers factored in the desired tonnage and the material that Lonesome Prairie processes to determine what the machine’s stroke should be, the speed and general mounting guidelines. Hikon took feedback from the aggregates company, including adding a specially sized jaw crusher on the chassis. Lonesome Prairie also asked that the bottom deck of the vibrating screen be end-tensioned. In the company’s operation, the design results in longer lasting screen media and 30% more productivity than side-tensioned machines. Haver & Boecker customized the machine for Lonesome Prairie’s specific needs. When the engineering design was in place, both manufacturers got to work.
The finished plant included a hydraulic system to lift and position the vibrating screen at the optimal angle. Crews use the hydraulic system to set up the portable vibrating screen in less than 30 minutes, with the entire plant – including conveyors and other peripheral equipment – taking about half a day. The same task can take around two weeks for fixed equipment – a length of time Derksen said could mean a loss of about $300,000 in production during the busy season for a 24/7 operation.
The F-Class portable plant arrived at Big Boy quarry in April 2016, and Lonesome Prairie began testing immediately. They were skeptical of the results the manufacturers had promised, thinking it was too good to be true. Doubts vanished when they found the single vibrating screen increased aggregates production by about 25%. The improved screening action allowed the operation to maintain needed production rates while using screen media with an open area of about 4 mm, preventing waste of the smaller sellable material the company lost while using larger open area screens.
“Price can be a problem in western Canada because our competitive market often calls for cheaper equipment that fit the budget. But despite the higher price tag, I have no doubts we’re improving profits with this machine,” Derksen said. “We couldn’t believe our eyes; bad weather didn’t even faze it. People don’t believe us when we tell them our costs are so far down and we’re getting more productivity out of than the 1,825 by 6,100-mm and 1,825 by 4,875-mm units we were using before.”
Derksen said the two prior units together produced about 360 t/h. The F-Class virtually eliminated blinding and maintained consistent g-force during surging. This boosted material processing to 450 t/h, including about 270 to 320 t/h of sand with the rest being clean, sellable material.
This article was provided by Haver & Boecker.