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CAT® 990 Wheel Loaders Keep Wood Moving at High Volume Paper Mill
New machines keep wood chips feeding consistently and reliably to digesters of pulp mill.
Date Posted: 5/1/2011
On an average day, 450 log trucks rumble in and out of the woodyard at a paper mill in southeast United States. On a really good day, 600 trucks, each carrying 30 tons of pine or hardwood, queue up to be unloaded by one of two CAT® 990H wheel loaders or a 40-ton P&H portal crane.
The CAT wheel loaders were purchased in January 2010 to replace two log stackers. “The log stackers are good machines built well for unloading log trucks,” explains the mill’s woodyard superintendent. “It was more a reliability issue; they just would not hold up in our environment. The 990s were a Godsend. It was a nightmare when our old log stackers were our only machines.”
The woodyard superintendent is responsible for overseeing all activity in the yard from unloading log trucks to ensuring there are enough wood chips to keep the pulp mill well-fed 24/7. Basically, he’s got to keep the wood moving. “My biggest challenge now is making sure we have enough wood chips to feed the digesters of the pulp mill. We have to run very consistently, very reliably to keep the mill running,” he says.
Early in 2009 the biggest challenge was at the beginning of the process — getting log trucks unloaded quickly and consistently. “We would have problems with the log stackers. They would be down and trucks would back up for a half a mile out on the highway. We’d actually end up cutting trucks off for the day because we couldn’t get them unloaded because nothing was running,” he recalls.
Mill management decided to buy two new pieces of equipment. The main requirements for the new machines were: enough capacity to unload a log truck in one pass, stability to lift a full load off the ground without tipping and, of course, reliability. Bottom line, it was all about getting trucks unloaded and out of the woodyard in a timely manner.
Show and Tell
The team charged with determining what machine to buy included the mill manager, the procurement manager, the woodyard superintendent and a woodyard senior operator. They evaluated several makes and models of wheel loaders and log stackers. Besides the CAT 990, they also considered the smaller CAT 988 wheel loader. They still had a 1984 CAT 988B that had already gone through one rebuild and, at 100,000+ hours, now was used as back-up.
After doing their homework, they told their CAT dealer rep, Mike Farris with Thompson Machinery in Tupelo, Miss., that they wanted to go look. So Farris arranged for a one-day whirlwind tour on the company jet to several locations in Georgia and South Carolina to see both the 990 and 988 working in mills doing the same work they needed them to do — unloading 30-ton trucks and reclaiming wood off the ground.
The evaluation team concluded that the 988 could do the job unloading 60,000 lb. truckloads in one pass, but it would be working at close to its maximum tipping capacity of about 65,000 lbs. They were concerned that the machine wouldn’t survive its full life cycle working at the maximum every minute of every day. On the other hand, with a tipping capacity of about 90,000 lbs., the 990 could unload 60,000 lb. truckloads, with another 30,000 lbs. of available capacity to spare.
One mill they visited in South Carolina had two 990s. “The company shared its maintenance records that showed one of the wheel loaders had 30,000 hours and basically no down time other than a hose or two. That’s what the company was looking for — a machine they did not have to work on,” Farris says.
The senior operator was able to ride along with the 990 operator in the jump seat. “I could tell what the machine was capable of doing, just riding with him,” he says. “I didn’t actually unload a truck or handle any wood, but I did operate the machine just to get the feel of it and the functions.”
He asked himself if he would want to run the 990 on a daily basis. “Comparing it to all the machines I’ve experienced in my years at the mill, I thought this was going be a real nice machine — a lot easier to operate, a lot more comfortable,” he says. “The cab was roomy and all the controls were user friendly and handy.”
He especially liked the joystick operation compared to the steering wheel in the old 988 back in the woodyard. “The joystick just seems to give you more room in front. You don’t have that big steering wheel right there in front of you. And I feel like I have a little more control, too.”
According to Farris, by the end of the day, the mill team had pretty much made up their minds that the 990 was the machine size they were looking for.
The plant has two wood lines that convey the logs into the mill for debarking and chipping. One line runs 24/7 producing 400 tons of wood chips per hour. The other wood line runs only as needed. When just one wood line is running, the woodyard superintendent has just one 990 on the ground. “Just because of the size of the 990, we can only have one feeding the wood line at a time,” he says. “This also gives us time for maintenance on the other machine.”
The 990 on duty works with the P&H crane to unload trucks and feed the wood line. On a typical day, the activity in the yard looks like a tightly choreographed dance between the 990 and the crane. In one big bite, the 990 unloads the first truck in line, backs away and drives off to dump the load on the in-feed deck. The log truck circles around to leave the woodyard, while the crane reaches down to grab the load off the next truck in line. By the time the 990 is back for another truckload, the crane is dropping its load on the in-feed deck.
“We need two pieces of equipment to feed the log line because it eats wood so fast,” explains the superintendent. “The crane also gives us increased capacity for storage. Probably 70 percent of our wood is held under the crane because we can stack it 60 feet high. That’s where most of our storage capacity is right there.”
A majority of the log trucks come during the day and most of their loads are run straight into the mill. During the night after the trucks are gone, the 990s are used to “reclaim” stored wood stacked on the ground and run it to the in-feed deck.
Reliability and Speed
The 990s are living up to the woodyard superintendent’s expectations for reliability. “I know the operator can get on that thing, crank it up, and it’s going to run. I can just tell you that the reliability of it is a lot better,” he says.
Hydraulic rather than electric power is a big factor. “The log stackers are all electric. They have a lot of switches and relays that would fail on a regular basis, and the motors would not hold up,” he explains. “The CAT machines are all hydraulic and they’re just built for this type of environment. We have a real bumpy lay down yard. They can take the bumping, and the hydraulics aren’t going to fail like the electrical components would in the log stackers.”
The mill ran a stacking trial soon after the 990 was first delivered. About 200 trucks were unloaded in six hours. “I wish I’d had this machine when I was out here, because I was nowhere near as tired as what I was a few years ago whenever I rode the other machine for a whole shift unloading trucks. I want to go back to this job now,” laughs the operator.
He also mentions the speed. “I know the 990 is faster because the guys can get the wood off the truck and to the deck faster than the guy that’s running the deck can get it moved into the mill,” he says. “With our old machines, you could just about keep up with the deck operator, but now sometimes the 990 operator finds he’s having to wait on him.”
The 990 is huge — it’s like sitting in a house — so operator visibility is a big issue. The operator has to be able to see his fork tips so he can slide them in under a truckload without damaging the truck. This was a problem with the older equipment. The old stackers would run plumb up against the frame of the trailer and damage the tires.
The 990 comes standard with a rear view camera and the mill added a front view camera. “I really pushed for the front camera, but I find myself looking at the tips themselves more than watching the camera when I unload. But the front camera is real handy at times when you’re picking up off the ground,” the operator says.
For the first 2,000 hours, the mill had a service contract with Thompson Machinery. “The Thompson service guys came out here and our guys helped them, so they could get familiar with maintaining the machines. Now we do it ourselves,” says the woodyard superintendent.
The superintendent and the CAT trainer, who came in from Arizona to train operators, created a list of about 30 items the operators need to check every day to make sure the machine stays reliable. “For example, they look at the U joints and the tires and they make sure everything is okay before they ever crank it up,” he says. “I have an oiler assigned to the machines and he greases them first thing every morning.”
The mill follows the book on all recommended servicing and the company also takes advantage of CAT’s S·O·SSM fluid analysis. “We’ve bought bottles from them and we’re still sending those samples off for testing. It’s a good way to diagnose problems before they become major ones.”
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