If Your Mill Isn’t Firing on All Cylinders, It’s Time for a Tune-up
A good preventive maintenance program can help to keep your mill in top condition, but even so, an annual checkup with an alignment is a good idea.
Making welded tube or pipe for a living is anything but easy. Attracting, training, and keeping mill operators is a chore; raw material prices are unpredictable; and ever-smaller orders and just-in-time deliveries can create all sorts of logistical headaches. When profit margins are slim, production schedules are full, and you’re short-handed, just getting through a day, a week, or a month can be an ordeal. Probably the last thing on your mind is scheduling a service call, but indeed mill services are necessary from time to time to remain competitive and profitable.
That being said, an annual service visit with an alignment isn’t the only maintenance needed to keep a mill running efficiently. A regular preventive maintenance schedule—one that has specific tasks scheduled weekly, biweekly, and monthly—is necessary to keep your mill in top condition so it can run at peak efficiency with minimum downtime and scrap rates. An annual service visit and alignment also can help to diagnose small problems—which often become invisible—before they become big and expensive problems.
Keeping the mill in the best possible shape for a year is the best way to get the most out of the mill and the most out of the annual service from the mill vendor.
Experience, Judgment, and Routine Maintenance
Regular preventive maintenance practices—good ones—are necessary for keeping the mill in the best condition possible. Poor maintenance practices lead to more frequent service calls from a qualified mill service provider, more extensive service calls, longer downtime, and higher repair costs. Bear in mind that the best tools for routine mill maintenance aren’t tools you can buy. They’re tools that take time to develop: experience and judgment.
Years ago, many mill supervisors had years of experience with tube mills because often they had spent years as operators. This means that they had worked their way up from the beginning and spent a lot of time in informal apprenticeships, usually working with direct supervision to learn how to run the mill. They then spent a couple of years honing that knowledge and experience by optimizing the shop’s practices to make the mill run as efficiently as possible. In doing so, they developed enough understanding to work independently and eventually trained other mill operators. Often it amounted to a decade of experience before progressing to become a supervisor or a mill manager.
This system worked well during a time when most people spent an entire career working for a single employer and the company structure was a proprietorship. When the employees spent their entire working lives under one roof and the ownership was a family with a long tradition of tube or pipe production, everyone had a lot of skin in the game. In the shops where the operators, supervisors, and managers meshed well, the resulting chemistry helped to maximize the facility’s productivity.
Some mills are still run like that, but many aren’t. Fewer people seek manufacturing careers these days, and those who do rarely stick with one employer, so experience doesn’t accumulate like it used to. Furthermore, many tube and pipe producers now are owned by corporations, and the owners don’t always know the dividends paid by investing in maintenance for the equipment and training for the staff.
This doesn’t mean that such mills can’t develop good maintenance practices or won’t perform preventive maintenance on a routine schedule, but both of these are less likely when experience and budgets are limited or constrained by short-term business decisions.
Sensing the Symptoms
Many of us rely on our tube or pipe mills the way we rely on our cars. We drive our cars almost daily, we pay close attention to them, and to make them last, we refer to the manufacturer’s recommended maintenance schedule. Many of us look at the tire treads as a matter of habit, check the oil and radiator coolant frequently, and occasionally verify that the headlights and turn signals are working.
Regular mill maintenance is much more involved and takes much more time, but it isn’t difficult. It’s just a matter of knowing what to do and doing it on a schedule. If you were to dig through the documentation that came with your mill, you’d probably find a preventive maintenance checklist and schedule. If you don’t have one, contact the mill builder to get one. If the mill builder is no longer in business, ask around—one of the other mill builders will likely welcome the chance to offer its expertise in maintenance, repair, and operations.
Keep in mind that scheduled maintenance is just one facet of the productive chemistry associated with a solid mill management program. Knowing how the mill should operate—how it looks and how it sounds—likewise is important. An experienced and knowledgeable operator, supervisor, or maintenance technician notices when something doesn’t seem right. When the material is hard to thread or it bangs into every stand along the way, it’s time for a closer look by the resident maintenance group and the resident mill expert, or it’s time for an external mill service consultation. Here are other indicators to consider, and if you know what to look for, you know when service is due:
- Can you shake hands with a shaft? If you grab a roll shaft, try to move it back and forth or up and down using a shaking motion, and it moves, the bearings are probably shot.
- Do roll stand shafts or bearings break without warning? They’re forged, they’re tempered, and they’re tough enough to withstand normal mill stresses. If you’re breaking shafts or bearings, you’ve got a big problem.
- Is the scrap rate going up? Is the uptime going down?
- Is the process marking the tubing?
- Are the edges buckling? Is the seam “breathing” differently from the way it used to?
- Do you have to run your mill slower to make good tube or pipe?
- Do you find yourself making adjustment after adjustment (while scrap is piling up) just to get the mill dialed in, or to keep it dialed in?
In short, if you have a new problem, something may be amiss. In many cases, the operators know the mill well enough to remedy small problems, but work-arounds aren’t solutions. Mill servicing and alignments are necessary for keeping downtime and scrap to a minimum and productivity to a maximum.
Making the Call
Mill preventative maintenance isn’t like dropping your car off at the shop with a list of complaints. To keep the downtime to a minimum during a mill service visit, a little preparation goes a long way:
- Strip the mill. Remove the steel and remove the tooling.
- Clean everything. When everything is clean, take a thorough look. The mill service technician isn’t likely to be too forgiving—he wants to work in a clean environment.
- Put away tools and supplies. Operators usually keep tools handy, but putting them away makes room for the service team’s tools and gives them some space to work.
- Take a close look at the walkways and access points. You can’t get rid of garbage cans, tool boxes, fire extinguishers, supply carts, and all the other items that are necessary in a typical industrial environment, but if they’re in the way, consider moving them. When a service technician is on-site, you want him to have an easy time working on and around the mill, upstream and downstream, front and back.
Keep in mind that mill service alignment doesn’t start at the first forming stand and end at the last sizing stand. It includes the entry and exit portions of the mill, also. Get the entire mill ready, from end to end.
The mill might not look like a piece of precision equipment, but the mill technician is going to treat it as such. Gone are the days of aligning the tooling with a length of piano wire. Nearly all tube fabricators have tighter tolerances these days than they did in previous decades, so servicing and aligning a mill to today’s standards requires expensive precision equipment and fixtures. The technician’s work probably won’t be as intricate as that of a watch maker, but it will be akin to that of a custom car restorer.
Unless scheduling or budgetary constraints get in the way, the mill service personnel will prefer to stick around after the alignment while you mount the tooling, thread the mill, and begin welding the product.
Many mill operators are accustomed to using a variety of tools to help the strip along, but this isn’t how tube or pipe producing systems are designed to run. The test of a well-executed mill alignment—along with properly maintained tooling—is in how smoothly the leading edge of the strip moves through the mill on its own, progressing from one pass to the next, threading itself without assistance. Many operators these days rarely see this and have forgotten the material should self-thread through most of the system.
Maximizing Your Investment
In a typical tube or pipe production facility, the investments are everywhere. The property, building, mills, tooling, inventory, and operator training are the main ones, and each contributes to the overall capability to turn coiled steel into a saleable product. After investing hundreds of thousands of dollars, or perhaps millions of dollars, into such a facility, it makes sense to maximize all the investments by taking good care of the moneymaker.
The mill processes thousands of dollars’ worth of raw material every hour. Maximizing its productivity means maximizing its throughput, getting the most out of the mill that you can, every minute of every hour, every hour of every shift, and you can’t do that on a mill that isn’t running at 100 percent of its capability. A good maintenance program, including regular mill checkups from a mill service provider, is a proven strategy to get the most return from your many investments. Setups will go smoother, production will run more efficiently, and the company will maximize its profitability.
Mill Service and Alignment Can’t Cure Every Ailment
Mill service and alignments usually are necessary for problems that started small and built up slowly over time. When you have a sudden problem, you might need mill service, but it’s possible you don’t.
New applications. After using a mill that has served you well for decades making products from common carbon steel, you mistakenly believed the same mill could make new products at higher speeds from a thicker material or a different grade material—one that is higher in minimum yield strength or one that has a different surface finish requirement. In a nutshell, you are asking the mill to make a product outside of its capacity, but it simply can’t produce in the new combination of speed, size, thickness, yield strength, or surface finish. You need a major mill upgrade and likely a roll design upgrade rather than an alignment.
Newly ground tooling. You figured you could save a little money by having a local machine shop regrind your worn tooling. Not knowing the critical dimensions, the local guys changed the root diameters or eliminated critical multiradius dimensions. You don’t need mill service; you need new tooling. You also need a better roll management program and a relationship with a competent roll designer and builder.
New shafts. Rather than getting shafts from the mill supplier, you took a different route, buying them from a supplier that doesn’t specialize in weld mills. If the chamfers are incorrect or in the wrong locations, the design tolerances ignored, and the shafts not heat-treated properly (or not at all), they will compromise your mill alignment and thus compromise your uptime, scrap rate, and overall productivity. It’s best to work with service providers who understand the demands of a weld mill.
Keep in mind that you might need a mill alignment because your mill—whether new or used—was never aligned properly when it was installed. If it was a new mill and the installers assumed that the mill was precisely aligned at the factory, and that the alignment wasn’t disturbed during shipping and installation, they might not have aligned it at all. Whether it was new or used, if they aligned it without consulting the mill builder, they might have done so improperly, referencing various incorrect machined surfaces on the mill bases or ancillary process systems, such as the uncoiler and the cutoff system. If they failed to align the mill at the center of the tube- or pipe-making process, which is necessary before grouting the mill bases into position, it’s not aligned.