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Tips for maximizing the efficiency of pipes and pipe rolling mills (Part 1)

Successfully (efficiently) manufacturing pipe requires 10,000 details to be optimized, including equipment maintenance. Considering the countless moving parts in every mill type and every peripheral equipment, adhering to the preventive maintenance plan recommended by the manufacturer is no easy task. Photo: T & H Lemont Inc.
Editor’s note: This is the first part of a two-part series on optimizing tube mill operations. The second issue will be released in October.
Even in the best case, manufacturing tubular products is laborious. Factories are complex, they require a lot of regular maintenance, and depending on the products they produce, competition is fierce. Many metal pipe manufacturers are under relentless pressure to maximize uptime to maximize revenue, leaving little precious time for routine maintenance.
Today, the industry does not have the best situation. Material costs are high, and partial deliveries are not uncommon. Pipe manufacturers now need more than ever to maximize uptime and reduce waste, and receiving partial deliveries means shortening uptime. Shorter runs mean more frequent conversions, which is not an efficient use of time or labor.
“Right now, production time is very precious,” said Mark Prasek, EFD Induction’s North American pipe sales manager.
Conversations with industry experts on making the most of the factory’s skills and strategies revealed some recurring themes:
Operating the rolling mill at maximum efficiency means optimizing dozens of factors, most of which interact with other factors, so optimizing the operation of the rolling mill is not necessarily easy. The philosopher of the former columnist Bud Graham of The Tube & Pipe Journal provides some insights: “The tube grinder is a tool rack.” Remembering this sentence helps keep things simple. Understanding what each tool does, how it works, and how each tool interacts with other tools is about one-third of the battle. Keep everything maintained and aligned is one-third of it. The last third involves operator training programs, troubleshooting strategies, and specific operating procedures unique to each pipe manufacturer.
The primary consideration for effective operation of a mill has nothing to do with the mill at all. This is the raw material. Obtaining the maximum output from the rolling mill means obtaining the maximum output from each coil that feeds the rolling mill. This starts with the purchase decision.
Coil length. Nelson Abbey, director of Abbey Products at Fives Bronx Inc, said: “When the coil reaches its longest length, the tube mill flourishes.” Handling shorter coils means handling more coil ends. Each coil end requires butt welds, and each butt weld produces waste.
The difficulty here is that the longest possible coil may be sold at a higher price; shorter coils may be offered at a better price. The purchasing agent may want to save some money, but this is inconsistent with the views of the manufacturing shop personnel. Almost everyone who runs the factory will agree that the price difference must be large to make up for the production losses associated with additional factory shutdowns.
Abbey says another consideration is the capacity of the uncoiler and any other restrictions on the entry side of the rolling mill. It may be necessary to invest in larger capacity inlet equipment to handle larger and heavier coils in order to take advantage of the benefits of buying larger coils.
The slitting machine is also a factor, whether it is slitting internally or the service is outsourced. Slitting machines have the maximum weight and diameter they can handle, so achieving the best match between the coil and the slitting machine is essential to maximize output.
In short, this is the interaction between four factors: the size and weight of the coil, the necessary width of the slitting machine, the capacity of the slitting machine and the capacity of the inlet equipment.
Coil width and condition. In the workshop, it goes without saying that the coil must have the correct width and the correct specifications to make the product, but errors will occur. Rolling mill operators can usually compensate for strip widths that are slightly too small or too large, but this is only a matter of degree. It is important to pay careful attention to the width of the slit mults.
The edge condition of the strip is also the most important issue. Michael Strand, president of T&H Lemont, said that consistent edge presentation, without burrs or any other inconsistencies, is essential for maintaining a consistent weld along the strip length. Initial coiling, slitting uncoiling and recoiling also work. A coil that is not handled carefully will bend, which is problematic. The forming process developed by rolling tool engineers starts with flat strips rather than curved strips.
Tool considerations. “Good mold design can maximize output,” said Stan Green, general manager of SST Forming Roll Inc. He pointed out that there is no single pipe forming strategy, and therefore no single mold design strategy. Rolling tool suppliers are different, and their methods of processing tubes are different, so their products are also different. Yields also vary.
“The surface of the roller has a constantly changing radius, so the rotational speed of the tool changes on the surface of the tool,” he said. Of course, the tube passes through the mill at only one speed. Therefore, the design affects the output. He added that when the tools are new, poor design wastes material, and as the tools wear out, the situation only gets worse.
For companies that do not have strict requirements in terms of training and maintenance, formulating strategies to optimize plant efficiency starts from the basics.
“Regardless of the style of the rolling mill and the products it produces, all rolling mills have two things in common-the operator and the operating procedures,” Abby said. He said that running the factory as consistently as possible is a matter of providing standardized training and following written procedures. Inconsistencies in training can lead to differences in setup and troubleshooting.
In order to maximize the use of the rolling mill, from operator to operator and shift, each operator must use consistent settings and troubleshooting procedures. Any procedural difference is usually a matter of misunderstandings, bad habits, shortcuts, and solutions. These always make it difficult to run the factory efficiently. These may be local issues, or they may have been introduced when a well-trained operator is hired from a competitor, but there is no difference in origin. Consistency is the key, including operators who bring experience.
“It takes years to train tube mill operators, and you really can’t rely on a universal, one-size-fits-all program,” Strand said. “Every company needs a training program that suits its own factories and operations.”
“The three keys to efficient operation are machine maintenance, consumable maintenance and calibration,” said Dan Ventura, president of Ventura & Associates. “This machine has many moving parts—whether it’s the rolling mill itself or the peripheral equipment at the inlet or outlet, or the jumping table, or what you have—daily maintenance is important to keep it in top condition.”
Strand agreed. “Using a preventive maintenance inspection plan is the beginning of everything,” he said. “It provides the best opportunity to run a factory. If the pipe manufacturer only responds to emergencies, it is out of control. It is at the mercy of the next crisis.”
“Every piece of equipment on the rolling mill must be aligned,” Ventura said. “Otherwise, the factory will fight on its own.”
“In many cases, when the rolls exceed their useful life, they will harden and eventually break,” Ventura said.
“If the rolls are not kept in good condition through regular maintenance, then they need emergency maintenance the day,” Ventura said. He said that if the tools were ignored, repairing them would require removing two to three times the amount of material that would otherwise have to be removed. It will also take longer and cost more.
Strand noted that investing in backup tools can help prevent emergencies. If tools are frequently used for long-term operations, more spare parts are required than tools rarely used for short-term operations. Tool functionality also affects the level of backup. The fin will be broken from the fin forming mold, and the welding roller will yield due to the heat of the welding box. These problems will not bother the forming roller and the sizing roller.
“Regular maintenance is good for the equipment, and correct alignment is good for the products it produces,” he said. If these are ignored, factory employees will spend more and more time trying to make up for it. This time can be used to make high-quality, marketable products. These two factors are very important, but are often overlooked or overlooked. In Ventura’s view, they provide the best opportunity to make the most of the rolling mill, maximize production and minimize waste.
Ventura equates the maintenance of mills and consumables with car maintenance. No one will drive tens of thousands of miles between oil changes and make tires bald. This will lead to costly solutions or destruction, even for poorly maintained factories.
He said that it is also necessary to check the tools regularly after each run. Inspection tools may reveal problems, such as fine lines and cracks. This type of damage is found immediately after removing the tool from the mill, rather than immediately before installing it for the next run, which provides the most time for tool replacement.
“Some companies are shutting down as planned,” Green said. He understands that it is difficult to comply with the planned shutdown during such a period, but he pointed out that it is extremely dangerous. Transportation and trucking companies are overloaded or understaffed, or both, to the extent that deliveries are not timely now.
“If something in the factory is broken and you have to order a substitute, what can you do to get it delivered?” he asked. Of course, air transportation is always an option, but it will spiral up transportation costs.
Rolling mill and roll maintenance is not just a matter of following the maintenance plan, but a matter of coordinating the maintenance plan with the production plan.
The breadth and depth of experience in the three areas of operation, troubleshooting, and maintenance are important. Warren Wheatman, vice president of T&H Lemont’s tool business unit, said that companies that have only one or two factories to make pipes for their own use usually have very few personnel dedicated to plant and tool maintenance. Even if the maintenance personnel are knowledgeable, the experience base of the small department is shallower than that of the large maintenance department, which puts smaller employees at a disadvantage. If the company does not have an engineering department, the maintenance department must carry out troubleshooting and repairs by itself.
Strand added that training for operations and maintenance departments is now more important than ever. The wave of retirements associated with the aging baby boom generation means that many of the tribal knowledge that has caused companies to go through hardships is being exhausted. Although many pipe manufacturers can still rely on the advice and advice of equipment suppliers, even this expertise is not as rich as before, and it is still shrinking.
The welding process is as important as any other process that occurs in the manufacture of pipes or pipes, and the role of the welding machine cannot be overestimated.
Induction welding. “Today, about two-thirds of our orders are for retrofits,” Prasek said. “They usually replace old, problematic welders. Throughput is currently the main driving force.”
He said that many people are behind the eight goals because the raw materials came late. “Usually when the material finally appears, the welder falls,” he said. A surprising number of tube manufacturers even use machines based on vacuum tube technology, which means they are using machines that are at least 30 years old. The service knowledge of such machines is not rich, and the replacement tube itself is also difficult to find.
The challenge faced by pipe manufacturers who are still using them is their degree of aging. They will not fail catastrophically, but will slowly degrade. A workaround is to use less welding heat and run the mill at a slower speed to compensate, which can easily avoid the capital expenditure of investing in new machines. This creates a false feeling that everything is fine.
Prasek said that investing in a new induction welding power source can significantly improve the power consumption of the factory. Some states—especially those with large populations and high grid pressure—provide generous tax rebates after purchasing energy-efficient equipment. He added that the second motivation for investing in new products is the potential for new production possibilities.
“Usually, the new welding device is much more efficient than the old welding device, it can provide more welding capacity without upgrading the power service, thereby saving thousands of dollars,” Prasek said.
The alignment of the induction coil and the resistor is also critical. John Holderman, general manager of EHE consumables, said that the correctly selected and installed induction coil has the best position relative to the welding roller, and it is necessary to maintain a proper and consistent gap around the tube. If it is not set properly, the coil will fail prematurely.
He said that the job of a retarder is simple-it stops the flow of current and directs it to the edge of the strip-and like everything else on a rolling mill, positioning is critical. The correct position is at the apex of the weld, but this is not the only consideration. Installation is critical. If you fix it on a mandrel that is not rigid enough to support it, the position of the resistor may change and it will actually drag the ID along the bottom of the tube.
Taking advantage of the design trend of welding consumables, the concept of separate coils can have a significant impact on the uptime of rolling mills.
“Large-diameter rolling mills have long used a sub-coil design,” Holderman said. “Replacement of a one-piece induction coil requires cutting the pipe, replacing the coil, and reinstalling the rolling mill,” he said. The split coil design is divided into two parts, which can save all time and energy.
“As necessary, they have been used in large rolling mills, but applying this principle to small coils requires some strange engineering,” he said. The manufacturer just needs less work. “The small two-piece coil has specialized hardware and cleverly designed clips,” he said.
Regarding the cooling process of the impedance device, the pipe manufacturer has two traditional choices: the factory’s central cooling system or a separate dedicated water system, which can be expensive.
“It is best to cool the resistor with clean coolant,” Holderman said. For this reason, a small investment in a special choke filter system for mill coolant can greatly extend the life of the choke.
The cooling liquid of the mill is usually used for the impedance device, but the cooling liquid of the mill collects fine metal powder. Despite every effort to capture the fine powder in a central filter or use a central magnet system to capture them, some have passed and found their way to the retarder. This is not the place for fine metal powder.
“They are heated in the induction field and burned into the resistor housing and ferrite, which can lead to premature failure, and then shut down and replace the resistor,” Holderman said. “They will also accumulate on the induction coil, and eventually will be damaged by the arc there.”


Post time: Oct-15-2021
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