The successful and efficient manufacture of pipe or pipe requires optimization of 10,000 details, including equipment maintenance.Given the myriad of moving parts in every mill type and every piece of peripheral equipment, adhering to a manufacturer’s recommended preventive maintenance schedule 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 or pipe mill operations.Read the second part.
Manufacturing tubular products can be laborious, even under the best of circumstances.Factories are complex, require a lot of regular maintenance, and depending on what they produce, competition is fierce.Many metal pipe producers are under tremendous pressure to maximize uptime to maximize revenue, with little valuable time for routine maintenance.
There isn’t a best-case scenario for the industry these days.Materials are expensive and partial deliveries are not uncommon.Now more than ever, pipe producers need to maximize uptime and reduce scrap, and receiving partial deliveries means reducing uptime.Shorter runs mean more frequent changeovers, which is not an efficient use of time or labor.
“Production time is at a premium right now,” said Mark Prasek, North American Tubing Sales Manager at EFD Induction.
Conversations with industry experts on tips and strategies for getting the most out of your plant revealed some recurring themes:
Running a plant at maximum efficiency means optimizing dozens of factors, most of which interact with others, so optimizing plant operations isn’t necessarily easy.The Holy Word of former The Tube & Pipe Journal columnist Bud Graham offers some perspective: “A tube mill is a tool holder.” Remembering this quote helps keep things simple.Understanding what each tool does, how it works, and how each tool interacts with other tools is about a third of the battle.Keeping everything maintained and aligned is another third of it.The final third involves operator training programs, troubleshooting strategies, and specific operating procedures unique to each pipe or pipe producer.
The primary consideration for running a mill efficiently is mill independent.is the raw material.Getting maximum output from the mill means getting maximum output from each coil fed to the mill.It starts with a buying decision.
coil length.Nelson Abbey, director of Fives Bronx Inc. Abbey Products, said: “Tube mills thrive when the coils are the longest. Machining shorter coils means machining more coil ends. Each coil end requires a butt weld Every butt weld produces scrap.
The difficulty here is that coils that are as long as possible can be sold at a premium.Shorter coils may be available at better prices.Purchasing agents may want to save some money, but this is inconsistent with the point of view of the manufacturing floor personnel.Almost everyone who runs a factory would agree that the price difference would have to be significant to make up for the production losses associated with additional factory shutdowns.
Another consideration, Abbey said, is the capacity of the decoiler and any other constraints on the entry end of the mill.It may be necessary to invest in higher capacity entry equipment to handle larger, heavier coils to take advantage of the benefits of purchasing larger coils.
The slitter is also a factor, whether the slitting is done in-house or outsourced.Slitters have the largest weight and diameter they can handle, so getting the best match between coils and slitters is critical to maximizing throughput.
In summary, it is an interaction between four factors: the size and weight of the coil, the necessary width of the slitter, the capacity of the slitter, and the capacity of the inlet equipment.
Coil width and condition.On the shop floor, it goes without saying that the coils have to have the right width and the right gauge to make a product, but mistakes happen from time to time.Mill operators can often compensate for strip widths that are slightly too small or too large, but this is only a matter of degree.Careful attention to the width of the slit muls is critical.
The edge condition of the strip is also the most important issue.Consistent edge presentation, without burrs or any other inconsistencies, is critical to maintaining consistent welds along strip lengths, says Michael Strand, president of T&H Lemont.Initial coiling, slitting and rewinding also come into play.Coils that have not been carefully handled can bend, which is problematic.The forming process developed by the roll die engineers starts with flat strip rather than curved strip.
Tool Notes.”Good mold design maximizes throughput,” said Stan Green, general manager of SST Forming Roll Inc.He points out that there is no single strategy for tube forming, and therefore no single strategy for mold design.Roll tool suppliers vary in how they process tubes and therefore their products.Yields also vary.
“The radius of the roll surface is constantly changing, so the rotational speed of the tool changes across the tool surface,” he said.Of course, the tube goes through the mill at only one speed.Therefore, design affects yield.Poor design wastes material when the tool is new, and it only gets worse as the tool wears out, he added.
For companies that don’t stick to the training and maintenance route, developing a strategy to optimize plant efficiency starts with the basics.
“Regardless of the style of the factory and the products it makes, all factories have two things in common—the operators and the operating procedures,” Abbey said.Running a factory as consistently as possible is a matter of providing standardized training and following written procedures, he said.Inconsistencies in training can lead to differences in setup and troubleshooting.
To get the most out of a plant, from operator to operator, shift to shift, each operator must use consistent setup and troubleshooting procedures.Any procedural differences are usually a matter of misunderstandings, bad habits, shortcuts, and workarounds.These always make it difficult to run the plant efficiently.These problems may be homegrown or introduced when trained operators are hired from competitors, but the source makes no difference.Consistency is key, including operators who bring experience.
“It takes years to train a tube mill operator, and you really can’t rely on a one-size-fits-all plan,” Strand said.”Every company needs a training program that fits its factory and its own operations.”
“The three keys to efficient operations are machine maintenance, consumables maintenance and calibration,” said Dan Ventura, president of Ventura & Associates.“A machine has a lot of moving parts – whether it’s the mill itself or peripherals on the inlet or outlet end, or the beating table, or what have you – and routine maintenance is important to keep the machine in top condition.”
Strand agrees.”Using a preventive maintenance inspection program is where it all starts,” he said.”It offers the best opportunity to run a factory profitably. If a pipe producer only responds to emergencies, it is out of control. It is at the mercy of the next crisis.”
“Every piece of equipment on the mill has to be aligned,” Ventura said.”Otherwise, the factory will fight itself.”
“In many cases, when rolls exceed their useful life, they work harden and eventually crack,” Ventura said.
“If the rolls are not kept in good condition with regular maintenance, then they need emergency maintenance,” says Ventura.If the tools were neglected, repairing them would require removing two to three times the amount of material they would otherwise have to remove, he said.It also takes longer and costs more.
Investing in backup tools can help prevent emergencies, Strand noted.If the tool is frequently used for long-term operation, more spare parts will be required than the tool used infrequently for short-term operation.The tool function also affects the reserve level.Fins can come off the fin tool and weld rolls can be affected by the heat of the weld box, issues that do not plague forming and sizing rolls.
“Regular maintenance is good for equipment, and proper alignment is good for the products it makes,” he said.If these are ignored, factory employees spend more and more time trying to make up for it.This time can be used to make good, best-selling products.These two factors are so important and often overlooked or overlooked that, in Ventura’s view, they offer the best opportunity to get the most out of the plant, maximize yield and reduce scrap.
Ventura equates mill and consumable maintenance with car maintenance.No one’s going to drive a car for tens of thousands of miles between oil changes with bare tires.This will lead to expensive solutions or destruction, even for poorly maintained plants.
Regular inspection of the tool after each run is also necessary, he said.Inspection tools may reveal problems such as fine line cracks.Such damage is discovered as soon as the tool is removed from the mill, rather than immediately before the tool is installed for the next run, giving the most time to manufacture a replacement tool.
“Some companies are working through scheduled closures,” Green said.He knew it would be difficult to comply with a scheduled shutdown in this situation, but he pointed out that it was very dangerous.Shipping and freight companies are so overcrowded or understaffed, or both, that deliveries aren’t on time these days.
“If something breaks at the factory and you have to order a replacement, what are you going to do to get it delivered?” he asked.Of course, air freight is always an option, but it can spiral the cost of shipping.
The maintenance of rolling mills and rolls is not just about following a maintenance schedule, but coordinating the maintenance schedule with the production schedule.
In all three areas – operations, troubleshooting and maintenance, breadth and depth of experience matters.Warren Wheatman, vice president of T&H Lemont’s Die Business Unit, said companies that only have one or two mills to produce their own tubes often have fewer people dedicated to mill and die maintenance.Even though the maintenance staff are knowledgeable, small departments have less experience than larger maintenance departments, putting the smaller staff at a disadvantage.If the company does not have an engineering department, the maintenance department has to do the troubleshooting and repairs itself.
Strand added that training for operations and maintenance departments is now more important than ever.The wave of retirements associated with aging baby boomers means the tribal knowledge that once rocked companies is drying up.While many tube producers can still rely on equipment supplier consultation and advice, even this expertise is not as abundant as it once was and is shrinking.
The welding process is just as important as any other process that occurs when manufacturing a pipe or pipe, and the role of a 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 the main driver right now.”
He said many were behind eight goals because the raw material came late.”Usually when the material finally comes out, the welder goes down,” he said.A surprising number of tube producers are even using machines based on vacuum tube technology, which means they are using machines that are at least 30 years old for care.Service knowledge for such machines is not extensive, and replacement tubes themselves are difficult to find.
The challenge for pipe producers who are still using them is how they age.They do not fail catastrophically, but degrade slowly.One solution is to use less welding heat and run the mill at a slower speed to compensate, which can easily avoid the capital outlay of investing in a new machine.This creates a false sense that everything is fine.
Investing in a new induction welding power source can significantly reduce the plant’s electricity usage, Prasek said.Some states—especially those with large populations and stressed grids—offer generous tax rebates on purchases of energy-efficient equipment.A second motivation for investing in new products is the potential for new production possibilities, he added.
“Typically, a new welding unit is much more efficient than an older one, and it can save thousands of dollars by providing more welding capacity without upgrading electrical service,” Prasek said.
The alignment of the induction coil and the resistor is also important.John Holderman, general manager of EHE Consumables, says a properly selected and installed induction coil has an optimal position relative to the welding roll, and it needs to maintain proper and consistent clearance around the tube.If set incorrectly, the coil will fail prematurely.
The job of the blocker is simple – it blocks the flow of electrical current, directing it to the edge of the strip – and as with everything else on the mill, positioning is critical, he says.The correct location is at the apex of the weld, but that’s not the only consideration.Installation is critical.If it’s fastened to a mandrel that isn’t rigid enough to support it, the position of the blocker may change, it actually drags the ID along the bottom of the tube.
Taking advantage of trends in welding consumable design, the split coil concept can have a significant impact on mill uptime.
“Large diameter mills have long used split coil designs,” Haldeman said.”Replacing a single piece of induction coil requires cutting the pipe, replacing the coil and re-threading it,” he said.The split coil design comes in two parts, saving all your time and effort.
“They’ve been used in large rolling mills, but it took some fancy engineering to apply this principle to small coils,” he said.Even less work for the manufacturer.”Small two-piece coils have specialized hardware and cleverly designed clamps,” he said.
With regard to the cooling process of the blocker, pipe producers have two traditional options: a central cooling system in the factory or a separate dedicated water system, which can be expensive.
“It’s best to cool the resistor with clean coolant,” Holderman said.For this reason, a small investment in a dedicated choke filter system for mill coolant can greatly increase choke life.
The mill coolant is often used on the choke, but the mill coolant collects metal fines.Despite every effort to trap fines in a central filter or capture them with a central magnet system, some people pass and find their way to the obstacle.This is not the place for metal powders.
“They heat up in the induction field and burn themselves into the resistor housing and ferrite, which causes premature failure and then shuts down to replace the resistor,” Holderman said.”They also build up on the induction coils and eventually cause damage from arcing there as well.”