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Best practices for roll form tooling maintenance

Establish a roll tooling regrind schedule, stick to it, and maximize investment

Best practices for roll tooling maintenance

Tube and pipe producers often struggle to plan cost-effective roll tool regrind schedules. Many push the tooling a little longer than they should and then are surprised when regrinding is needed urgently.

On any tube or pipe mill, roll tooling is a critical investment. The tooling set is highly engineered tool steel, precision machined and designed to work with a specific mill to produce large volumes of precision pipe or tube products.

The word investment implies a cost and a value. The cost is the price paid for the tooling set, but its value is mill uptime. The true value, realized when a precisely engineered product is made, is measured in thousands (or millions) of linear feet or in tonnage. So taking proper care of this tooling investment contributes to the company’s financial bottom line.

A key concern is regrinding the tooling when necessary. Note that the term regrinding is a traditional word for an antiquated process. Although the term still prevails, the process has advanced remarkably over the decades. Roll tooling today is reconditioned by precision machining of the critical worn surfaces.

Regrind Signs

Mill roll tooling is designed and built to last, but nothing lasts forever. Knowing when to send mill tooling out for service is important. Good recordkeeping generally is the best way to determine a tooling set’s reconditioning trigger point.

One of the best practices is to evaluate setups based on time and material. From one setup to the next setup, the time needed to change over tooling and get the mill running at designed production speeds should be consistent. The same is true for the amount of material used (scrapped) to fine-tune the setup to make sellable pipe or tube, running at the optimum speed. The resources used for a setup, time and material, should be consistent and predictable from one setup to the next.

Another best practice is to clean the rolls and inspect them every time they are removed from the mill. Use profile gauges to measure the amount of wear on the working surfaces (see Figure 1).

Progressive wear is expected; unusual wear can indicate a mill maintenance issue that should be addressed sooner rather than later. The checkup should include measuring and recording the wear on the roll faces, spacers, and bores. Furthermore, a visual check for sharp corner radii, rim to contour, can indicate unusual wear based on setup or alignment issues. Also look for stress cracking in the contour, especially on weld rolls. These should also be noted and evaluated.

As the roll tooling wears, the standard setup times may change proportionally. When the setup personnel need more and more time and generate more and more scrap to fine-tune the setup, a likely culprit is excessively worn tooling. Another overlooked culprit may be the mill progressively losing its mechanical alignment and contributing to premature tooling wear. Taking a few extra minutes or using a few extra feet of raw material once in a while is not a concern, but setups that need ever-increasing amounts of time and scrap consistently are problematic and a warning flag.

Recording the number of linear feet or the tonnage produced by the tooling set is the final piece of data. The combination of tool use, setup times, and setup scrap can help you determine when to recondition the tooling and when to align the mill.

Waste Not, Want Not

If you establish that one roll tooling set can make 2 million feet of product per regrind and consider five regrinds to be the maximum life of the tooling set, you’ll get 12 million ft. of tube throughout that tooling set’s service life. If you regrind the roll tooling set prematurely, say every 1.5 million ft., the tooling service provider will machine less material each time, and the tooling will still probably make about 12 million linear ft. of product. However, while the tooling will be capable of making good product throughout its service life, seven regrinds rather than five increases the overall tooling maintenance cost.

Best practices for roll tooling maintenance

Figure 1 Making regular visual inspections, checking critical dimensions, and recording the information in a comprehensive log are the three key elements to maximizing your roll tooling investment.

Alternatively, if you try to make the roll tooling set last longer than the optimum reconditioning interval, for example 3.5 million ft., you’ll lose out in two ways. First, after making 2 million ft. or so of product, your mill operators will waste increasing amounts of time on setup and scrap more material trying to compensate for excessively worn tooling. Another casualty is the operating speed. The operators will have to decrease the mill speed to compensate for the excessive wear, reducing the mill’s output per hour. Finally, the tooling provider will have to machine a lot more material off during the regrind process. This is more costly and more time-consuming, and it takes a lot out of the tooling set’s service life. In this example, you might get only 8 or 10 million ft. of pipe or tube product (instead of the ideal amount, 12 million ft.) before the tooling is no longer viable, cutting the service life drastically, straining budgets for unplanned tooling replacements, and compromising order deliveries.

In establishing the reconditioning schedule, a little skepticism from the tube or pipe producer—especially in the accounting department—is understandable, but any reputable tooling provider isn’t interested in making money on unnecessary regrinds. A good tooling provider is a business partner; its main interest is in helping its customers run their businesses successfully. When tube and pipe producers do well, their vendors do well. Reconditioning roll tooling isn’t a goal; it’s an inevitability which should be managed.

Dealing with a Dynamic Environment

Most tube or pipe producers don’t work in static, predictable environments. Things change. Some changes are mundane, and some are substantial:

  1. A fin blade or a weld roll breaks, and replacing it chews up a bit of your tooling budget, reducing the spares you planned to keep in inventory. No big deal.

  2. When doing a tooling setup, an operator discovers a forming or sizing roll that was broken or damaged and put back into inventory. It happens all the time, but it shouldn’t be treated as a run-of-the-mill occurrence. You need a replacement, fast.

  3. One of your salesmen starts asking questions about running high-strength material. Your mill was built decades ago to run conventional materials; some of the latest materials didn’t even exist when your mill was built. This is no time for snap decisions. The engineering and production staffs need to consider whether the current roll design is adequate and, just as importantly, whether the mill is adequate.

The first and second scenarios are somewhat common occurrences; the third signals a sea change in the way your mill operates—and your business, too. Because the last one affects the interactions among the mill, the tooling, and the material, it also affects the maintenance programs of the tooling and the mill.

Broken Fin Blades or Weld Rolls. If the broken fin blade or weld roll in scenario 1 was discovered during a run, you might be able to get a spare out of your inventory and finish the run. If not, you may be forced to end the run early and order more spares to replenish your inventory before the next scheduled run.

Damaged Forming or Sizing Rolls. After finding out who put a damaged tool back into inventory, and having a little chat about responsibility, you might need to contact your tooling vendor. Bear in mind that a problem with a driven roll may be addressed differently from a problem with an idle roll. Any changes to driven rolls may require rework of all the driven rolls to maintain the intended forming progression. For idle rolls, a less intrusive approach may be more cost-effective and still get the job done.

When you receive the reground roll tooling or replacement tooling, you will get a report that denotes the critical dimensions with notes about the current state of the tooling (see Figure 2). Using these notes in conjunction with the original setup charts is essential to compensate for changes in dimension

Best practices for roll tooling maintenance

Figure 2

You’ll likely receive a set of bearing block shims each time you receive reground tooling. It is not unheard of for these shims to be misplaced or simply not used in the next setup, which contributes to long setup times, generating more scrap, and running at lower-than-ideal speeds. Keep the shims and use them as they were intended to be used.

Teaching an Old Mill New Tricks. Be extremely cautious in making any plans to make tubing from advanced, high-strength steel or any other material that wasn’t considered when the mill was designed and built. Even if you’re changing to another common steel grade, changing to a different thickness, strength property, or any other critical characteristic can wreak a little havoc if those changes don’t comply with the design latitude of the roll tooling or mill.

This is becoming more common, most likely the result of the increasing availability of higher-tensile-strength alloys; misplaced optimism about the design windows of tooling and mill; or organizational changes that bring in new operators who are short on experience regarding tooling and mill limitations.

A very common issue is that these new, high-tensile-strength products aren’t suitable for a conventional mill and conventional tooling. The material is too hard, exceeding the mill’s drive capacity, and the reduced material thickness isn’t suitable for the tooling design. These issues can be addressed through consultation with the tooling vendor and the mill builder.

Mill Mods. The primary component among the mill, tooling, and material is the driven roll stand. Its job is to drive each roll in proper alignment and in coordination with adjacent driven stands, forming the material progressively through the mill according to the material’s mechanical properties and the laws of physics.

Any mill modifications, however slight, may affect the way the strip moves through the mill—and it’s likely your mill is different today from when it was first built, installed, and commissioned. Discussing any and all mill modifications with your roll tooling provider is critical in getting your tooling redesigned or reground properly to work with your mill.

More Science, Less Speculation

Experienced mill operators aren’t easy to find, and nobody in this industry doubts the value of 10 or 15 years of experience running a mill. Many of the managers and executives involved in tube and pipe production once were mill operators themselves, so often the knowledge gathered on the shop floor runs throughout the entire organization, at least informally.

A drawback in some experience-based operations is that some mill operators and managers rely exclusively on their knowledge and experience, which isn’t consistent from one shift to the next or even one operator to the next. In some operations, setup is referred to as the black art, and it isn’t uncommon for a tooling setup to vary from one shift to the next for the same product made on the same mill. This doesn’t apply merely to an initial setup; in extreme cases, one shift makes new mill settings in the middle of a product run—one that was running just fine on the previous shift.

Too often mill operators perform setups by relying on the tribal knowledge they acquire from their colleagues and on their own accumulated experience rather than technical knowledge available from the equipment and tooling vendors. Some have very little knowledge and learn by making one mistake after another, forgoing the benefit of the knowledge that is readily available from their roll tooling or mill supply vendor.

To bring consistency to setup practices, which reduces setup time, simplifies troubleshooting, and gets the most out of the mwill and the tooling, mill operators are generally better off if they rely on the science and the design behind the forming process. This suggests that both experienced and inexperienced shops need to formalize the knowledge related to their mill alignment, tooling changeovers, tooling setups, and quality assurance procedures.

Using a prescribed, formalized setup as a starting point is a very good foundation. Tribal knowledge can help the operator deal with slight variations in the raw material’s hardness or dimensions, make slight adjustments as the tooling wears, and troubleshoot other problems that pop up, but that should be the extent of it. Using a single benchmark for every setup helps to ensure consistency in the setups, stability in the processes, and integrity in the final product.

Monitor your setup times, keep track of setup scrap, and use trigger points to stop the upward creep of setup time and scrap generation. These steps can make the difference between an excellent operation and a not-so-excellent one.

John Hillis is president of T & H Lemont, 5118 Dansher Road, Countryside, IL 60525, 708-482-1800, jhillis@thlemont.com, thlemont.com.

About the Author

John Hillis

President and CEO

708-482-1800