Reducing coil changeover time and mill downtime - Focusing on coil entry equipment for greater productivity
By Jeff K. Carson
Many tube and pipe producers overlook the important role that coil changeover time plays in making a profit. Producers who ignore the role of coil entry equipment lose production time because of lengthy coil changeover times and unnecessary mill downtime. Five main tips can help you reduce lost time and achieve higher productivity.
Purchase Larger Coils
As line speeds have increased over the years, so have coil weights and outside diameters (OD). Many will remember when the standard coil had a 48-in. OD, which quickly was replaced by the popular 60-in.-OD size. About 18 years ago, the 72-in.OD coil was introduced to the tube and pipe industry, resulting in much longer run times.
Today some tube mill operators and roll formers use 80-in.-OD equipment on all lines. They recognize the payback from the larger coils. Although the payback varies and depends on the thickness of the metal, mill operators and roll formers using 80-in.-OD equipment report an average of 18 percent fewer coil changeovers per shift.
Using larger coils means two things. First, tube mills and roll forming lines require larger-capacity uncoilers. Second, uncoiler passlines have increased along with the OD of the full backing plates.
Use Powered Traversing Sub-bases.
A company that consumes large quantities of narrow coils can tap into the benefits of using a powered traversing sub-base on the uncoiler.
These sub-bases allow multiple coils to be loaded onto each mandrel of the uncoiler. This allows the operator to load each side of the uncoiler with two, three, or even four coils. With the powered sub-base, each new coil can be jogged easily into alignment with the mill. After emptying the outside coil, the mill operator slides the uncoiler over until the next full coil is in line with the mill. This process is more efficient than replenishing individual coils because forklift or crane operators can restock up to four coils at once.
Employ Double-ended Uncoilers.
Unlike a single-ended uncoiler, a double-ended uncoiler never has to run empty. While one side of a double-ended uncoiler is feeding the coil into the tube mill, operators can remove the spent coil from the other side and replace it with a fresh coil. Many uncoiler manufacturers have optimized this 180-degree swing with hydraulically powered rotation and either shock absorbers for the landing or a two-speed motor for a soft, cushioned swing. Additional features once thought to be luxuries now are becoming standard items. These features include hydraulic mandrel expansion, flip-down coil retainers, outboard coil retainers, snubber cylinders, powered hold-down arms, automatic proportional valve drag systems, and peeler tables. Many of these features make the uncoiler faster and more efficient. Several of them are safety features, serving to protect operators.
Use Single-point Operator Controls.
Line operators are the best sources of information on eliminating downtime and waste on the production floor. Many have found that having one pendant control is not much good if it disappears to the other side of the uncoiler as it rotates. This causes operators to have to walk around the entire unit to reclaim the controls. Having two pendants—one for each side—ensures that a pendant is always where the operator needs it. After a double-ended uncoiler rotates, a pendant control for the new side is accessible to the operator, and it is capable of controlling all the functions of the machine.
This is important because the majority of coil entry machines require two people to operate the controls during a coil changeover. One operator holds the jog-forward pendant as the strip feeds forward while a second operator stands at the control panel to run the snubber or the hold-down arm. Single-point operator controls reduce the number of uncoiler personnel needed for a coil changeover by 50 percent.
Incorporate Accumulators and End Shear Welding Machines.
Creating a strip without an end is the ultimate goal of every mill. A strip accumulator and an end shear welding machine are the indispensable tools for achieving this goal. Operators feed strip at an accelerated rate and store the slack in the accumulator. The extra material in the accumulator allows enough time for the shear welding machine to join the tail end of the current coil to the leading end of the next coil. Rather than rethreading the tube mill after a coil runs empty, using an accumulator and end welding machine facilitates feeding a continuous strip into the mill. These two pieces of equipment also are suitable for roll forming lines. The alternative—allowing a strip to end—requires rethreading an entire system, including the flattener, loop control No. 1, servo feeder, prepunch die or press, loop control No. 2, roll former entry guide and roll tooling, and the cutoff press and die.
Complementary Equipment for Optimal Operations.
Materials, machines, and components that complement each other and your operations can help reduce coil changeover time and mill downtime. Selecting the right coil entry equipment or upgrading from yesterday’s technology can optimize productivity and profitability for your company.
Jeff K. Carson is vice president of sales, Samco Machinery Ltd., 315 Nantucket Blvd., Toronto, ON M1P 2P2, phone 416-285-0619, fax 416285-1353, e-mail jcarson@samco -machinery.com, Web site www. samco-machinery.com. Samco manufactures roll forming equipment and tooling and coil entry equipment for the tube mill and roll forming industries.
Reprinted with permission from the January/February 2002 issue of TPJ–The Tube & Pipe Journal®, copyright 2002 by The Croydon Group, Ltd., Rockford, Illinois, www.thefabricator.com.
TPJ January/February 2002