February 1, 2008
A new screen and cone crusher help a Georgia quarry achieve flexibility to meet high customer demand.
Although it may seem a little ironic, the biggest challenge faced by the Lafarge Friendship Quarry in recent months has been keeping stone on the ground.
Between the quarry’s ability to produce various sizes of crushed stone and the needs of a burgeoning Atlanta market, stone is moving out of the quarry so quickly Plant Manager Don Richards hasn’t had a chance to build up any inventory — producing just enough rock to meet the needs of a wide range of customers.
The Friendship Quarry, located in Buford, Ga., consists of more than 450 permitted acres, which yields more than 2 million tons of crushed granite each year. From rip rap to sand, the aggregates operation provides crushed rock to a number of industries, residential, and commercial builders and the Georgia Department of Transportation.
“I’d like to have about twice as much stone on the ground as I do right now, but our operation runs year round,” Richards says. “Our plan is to slowly build inventory during the winter months, but for right now, we are basically running an on-demand operation.” He credits a new plant built in March 2007 and outfitted with a Metso Minerals Model IS453 (8- by 24-foot triple-deck screen) inclined vibrating screen and HP400 cone crusher for adding the flexibility and production capability to make it possible.
Leave no stone uncrushed
With the demand for stone escalating, Richards says the operation reached a point where it was running its secondary line longer hours just to meet the demands of customers.
The operation consists of two, 12-hour shifts operated by an eight-person crew. Generally, the first shift is considered the production shift when most of the crushing occurs. Although production can continue into the second shift, the main purpose of the “off shift” is to perform scheduled maintenance.
“What it came down to is that we needed to manage our inventory better,” Richards says. “We had excess amounts of larger stone that we couldn’t reduce to the smaller sizes such as clear stone or sand. We did not have the ability to re-crush stone without running our primary or secondary plant overtime and cutting into the time we have set aside for maintenance.”
Don Richards, plant manager of Lafarge’s Buford, Ga.-based Friendship Quarry, says the new Metso HP400 at his operation is able to handle increased throughput and to quickly generate the wide range of product gradation needed at the plant.
The challenge of the project was to increase production to meet demand, while at the same time, to ease the burden on the existing operation by reducing the overtime on re-crush circuits. Richards knew the equipment used in the new plant needed to be highly flexible as well. That’s when he looked to his long-time distributor, Nor-X, and Metso Minerals to provide the necessary equipment to make it happen.
Conventional yet versatile
For this particular application, Richards specified Metso’s Model IS453 (8- by 24-foot triple-deck screen) inclined vibrating screen with MV vibrator and an HP 400 cone crusher.
Richards was already familiar with the capabilities of Metso’s IS screens. The aggregates operation has used two of them on its production lines since 2003. After consulting with other Lafarge quarries, and even some local competitors about cone crushers, Richards was confident IS screens combined with the HP 400 was the way to go for its new line.
“There isn’t a better screen for the price, and with two IS screens already in place, it made perfect sense to install another one just like it,” Richards says. “Metso has been known for rock crushing for many, many years. Again, it came down to flexibility, the HP400 is a quality product that can handle increased throughput and generate the wide range of product gradation we were looking for — quickly.”
The large, conventional-sized inclined screens are designed to accept a wide range of deck media — a requirement of the Friendship Quarry. The adjustable speed and stroke enable the end-user to fine tune the IS to reach its peak productivity.
“The IS screens may not be custom-built for our application, but the design is flexible enough to handle all of our rock,” Richards says. “If there’s a screen out there that matches 95 percent of your needs, you don’t need a special design — especially if you have excellent distributor support and a company such as Metso willing to help you tweak it so the equipment will completely meet your needs.”
Richards says the company was able to stroke up to about 900 rpms from 700 to 800 rpms to use the screens to their fullest capacity. “We’ve cut plant run time by about 4 hours every day, or basically 20 hours a week,” he says. “My guys are now able to use that time for plant maintenance, which is very important to our operation for safety and productivity.”
Grease and go
Richards said ease of maintenance is a critical benefit of Metso’s IS screens, specifically the bearing packages of the MV “ Modular” vibrator and its lubrication method.
The IS screen’s bearings are grease lubricated as opposed to using a closed-loop, oil-based lubrication system. The grease lubrication design enables Richards’ crewmembers to lubricate the bearings on a weekly basis and be assured that the bearings have been purged. Many screens that use an oil-based lubrication system run a high risk of contamination. When using a closed-loop system, the catch is that the contaminant will be carried to other bearings in the system. This will cause multiple bearing failures and subsequent replacements.
The IS screens have standalone, modular, bearing cartridges on either side, connected with a drive shaft. As a result, if there is a bearing failure on one side of the screen, it won’t contaminate the other bearings.
Lafarge’s Friendship Quarry has used two IS screens on its production lines since 2003.
This capability also increases the ability to service the screen. In the event a bearing does need replacement, the cartridge “pops” out, and the operator can make a quick replacement in less than an hour. A complete teardown of the screen is unnecessary, which reduces downtime.
Although automatic greasing units are available, Richards likes the fact that employees are physically going into the system and performing the lubrication themselves. Many times, problems get overlooked using screens with an oil lubrication system.
“With an oil-lubricated machine, the perception is that as long as it’s not leaking, you don’t need to worry, but you still have to check the oil level, and the potential for contamination is always a concern,” Richards says. “My guys are going to perform their visual inspections every night and when they open the machine up, they’re going to grease the bearings. The Metso screens are very easy to maintain. As long as you grease the bearings, they’ll run for a very long time with very little effort.”
Richards is quick to point out that since the first Metso IS screens were installed in 2003, they haven’t needed to replace any bearings. He says it’s a testament to the design and heavy-duty features of the IS screens, but more importantly, the effectiveness of the Lafarge Friendship Quarry’s comprehensive maintenance program.
The heavy-duty design enables the IS screens to hold up and perform even with the most demanding production schedules, Richards notes. Unlike most vibrating screens, the IS screen design is aided by computer engineering programs. This ensures that the IS screen has a good balance of structural strength, bearing life, and performance. The IS screen frame also is huck bolted. Traditional nuts and bolts can vibrate loose during operation. Huck bolts provide firm connections even under high G-force. Additionally, the screens have very thick side plates and use bolted reinforcement plates, which add strength in the most critical areas. The IS design also includes reinforcement cross members which provide additional strength.
“We designed the plant to achieve a certain amount of flexibility in our operation, and both Nor-X and Metso were instrumental in deciding what we should do and what products would work best within the application,” Richards points out. “The IS screens and the HP400 cone crusher have delivered.”
Article and photos provided by Metso Minerals.