April 1, 2008
by Jim Breen
Thanks to ongoing advances in the aggregates industry, the focus in Europe is increasingly switching from stationary to mobile crushing and screening machines. This trend is strongly evident in Ireland, where mobile plant plays a key role in the aggregates sector.
Roadstone, a subsidiary of CRH, is just one of the many Irish companies that has recognized the benefits that accrue from “added mobility.”
The origins of Roadstone go back to the early 1930s. Initially called Roche Brothers, and later The Castle Sand Co., the business developed steadily during the 1940s. In 1949, Tom Roche launched Roadstone Limited on the Irish Stock Exchange.
Today, Roadstone employs about 1,500 people at more than 50 locations around Ireland. It manufactures and supplies aggregate, asphalt, and ready-mixed concrete. Its growing range of concrete and masonry products includes paving, roof tiles, and clay bricks.
Roadstone’s Two-Mile-Ditch Quarry, located close to Galway City on the west coast of Ireland, churns out a very diverse mix of products, including aggregates, gravel, asphalt, lime, concrete blocks, and associated masonry products.
Until 2001, the quarry had relied mainly on a stationary plant for its primary crushing operation. But then the company invested in a new mobile crusher (Kleemann MR 172), associated primary screen (Kleemann MS 18), secondary plant (Kleemann MF 14), and aggregates screen (Kleemann MS 20 P4).
This was just one of a batch of mobile crushers that Roadstone had purchased around that time. A year earlier, an MR 152 had been delivered to the company’s processing facility in Roscommon. Another MR 172, just like the unit in Galway, had been acquired for the company’s Mayo quarry. Moreover, plans were afoot to install further Kleemann mobile crushers in other locations such as southeast Ireland.
Maurice McLucas, location manager of Two-Mile-Ditch Quarry, says he chose Kleemann crushers for his operation because of his familiarity with the company’s products after working with a subcontractor that had been using them. “The [Kleemann] machines proved reliable and performed consistently when it came to size reduction,” McLucas points out.
McLucas also cites numerous reasons as to why his aggregates operation was interested in switching from a stationary to a mobile crusher. Prior to the changeover, McLucas says, 50-ton dump trucks were typically needed to haul the extracted material back to the stationary plant. This alone was a major cost factor. “By switching to a mobile crusher that can work at the rock face, we’ve reduced the amount of internal haulage that we have to undertake,” he says. “After each blast, we no longer have to load, haul, and reload all of the extracted rock. Now, we just load it directly into the crusher, which can be positioned exactly where we want it.”
Although much of the crushed material still has to be trucked back to the operation’s onsite processing plants (such as block-making facilities), the tonnage typically amounts to 35 to 45 percent of the total extracted material. But one or two dump trucks are sufficient now, whereas previously, at least three were needed, McLucas says.
An added bonus is that road-going trucks can travel right up to the rock face, where they can be loaded with “filling,” he notes. “Much of this is sold without any further processing, so it’s getting to the end-user with little or no re-handling,” McLucas says. “This all helps to cut costs.”
Harry Byrne, the company’s regional operations manager, notes that changing to a mobile crusher has not only helped cut costs, but it has enabled the operation to specify a machine that has allowed it to meet production targets without using subcontractors.
Harry Byrne, Roadstone’s operations manager for the western region, is an advocate of mobile crushing technology, which Two-Mile-Ditch Quarry uses. Switching to a mobile crusher allows at-the-face work instead of requiring several 50-ton dump trucks to transport the material.
“Before we changed over, we could crush about 500,000 tons per year with our own static plant,” he explains. Subcontractors’ machines were hired in to bulk up production. Now, we’re extracting our production target of nearly 1 millions tons per annum using just one machine, the MR 172.”
Admittedly, on paper the MR 172 is a higher-capacity unit than the stationary unit it replaced — so it should deliver more, Byrne points out. “Nevertheless, the extra throughput is not just down to the size of the machine,” he says. “The whole system is better balanced now, and we have more control of our stockpiles.”
Impact versus jaw
Byrne says his operation chose an impact crusher rather than a jaw-type machine because the area in which the quarry is located is predominantly limestone — much less abrasive rock. An impact crusher is better suited to this softer-type material, he says.
The Kleemann 172 can average 450 tons per hour. Two-Mile-Ditch Quarry now crushes about 4,000 tons per day.
“We typically crush more than 4,000 tons per day,” Byrne adds. “That’s on a nine-hour shift. We generally average about 450 tons per hour. And because the capacity of the primary crusher determines the performance of the entire quarry, the MR 172 plays a critical role.”
To simplify logistics and service backup, Roadstone opted for matching Kleemann screening equipment when installing the crusher. This enables Roadstone to crush at the face as well as carry out secondary processing there.
Internal haulage and re-handling are kept to a minimum because so much processing takes place at the blast site. In some cases, ready-for-sale products are being taken directly from a machine that works at the rock face, meaning it doesn’t have to be reloaded elsewhere on the site.
“Our Kleemann MR 172 is set up to crush down to six inches or smaller,” Byrne says. “The crusher’s own pre-screener removes blast fines in either 3-inch to zero or 1-3/4-inches to zero sizes. This is sold off-site or taken for further processing, depending on demand.”
The screener, which works in tandem with the MR 172 impact crusher, takes the 6-inch to zero rock and splits it up into three different sizes. These include 1-1/2 inch to-zero (state-spec road base), 3-inch clean stone, and larger 6-inch clean stone.
Because so much processing takes place at the blast site, internal haulage and re-handling are kept to a minimum, Byrne says. “For example, in some cases we’re taking ready-for-sale products from a machine that works at the rock face,” he says. “That means it doesn’t have to be re-loaded elsewhere on site.”
Jim Breen is a freelance writer based in Ireland and wrote this article on behalf of Kleemann/McHale. Breen writes for several machinery and equipment publications in the agricultural, forestry, and plant/construction sectors.