Evaluating requirements before you buy
April 10, 2003
Horizontal payoff of coiled materials on pallet uncoilers can help reduce downtime for coil changeover, increase coil handling efficiency, and improve operator safety.
You can increase your chances for success by taking the time early in your evaluation to understand and identify operational considerations in pallet uncoiler machine selection. To make the job run smoothly, you need to align the machine's capacities with the job's requirements. Applying time and effort at the beginning of the project will help you achieve a smooth installation of new equipment and a trouble-free start-up of the production line.
Before specifying equipment, take a look at the application. What coils do you have? What will the material demand be? What improvement goals do you plan to achieve? As you develop this information, share it with everyone involved in the operation and the decision chain so that they all have the same understanding and expectations. Make sure everyone agrees these are the criteria on which the equipment purchase should be based.
Establishing these criteria also will be important as you deal with competing machine vendors. Each request for proposal will originate from a common standard, and you will have more confidence that the machinery proposals you receive will have equalized machine capacities. Apples-to-apples comparison will be important to the quality of your vendor selection.
Coil load is a good place to start your research. Coils have mass and dimension. Specifying the gross weight and the outside and inside diameters of the coil load usually are easy enough; you know what you're currently buying.
However, this may be a good time to look into the future. Coil loads generally are increasing in weight and size. Looking ahead at this point may indicate that a larger table size and higher weight capacity than are needed right now might be a smarter purchase. Larger coil ODs or more coils on the pallet can increase your run-time efficiency and also might lower the unit cost of material.
The weight of the coil load determines how strong structural support must be and how much power is needed for the turntable drive. You must identify the intended weights to ensure you specify a machine that can support the load mass under rotation. The motor and drivetrain for the uncoiler also need to be sized to the requirements of accelerating, uncoiling, and stopping the mass of the load.
Pallet decoilers generally require the strip to change from a vertical plane exiting the uncoiler to a horizontal plane entering the production line.
The coil OD must fit safely and securely on the uncoiler rotating table. In many cases, a coil with a larger OD may ride on a smaller-diameter turntable. Generally, coil diameter should not exceed turntable diameter by more than 15 percent. As rotation speeds increase, take more care and concern with overhanging loads.
The uncoiler turntable should be big enough so that the pallet and coils will ride on it in a stable manner. Make sure that the coil OD and pallet corners will have clearance to rotate without interfering with parts of the uncoiler machine, building structures, other machinery, or personnel passageways. Also make sure that the pallet stringers will sit securely on the table surface.
Strip dimension is an important factor in specifying your new uncoiler requirements. The width and thickness of the material will impact the size of the strip guides, determine the back tension range of the feed control mechanism, and may require additional loop support devices.
Thicker materials require equipment designed to control the clockspring expansion without interfering with coil rotation.
Pallet decoilers generally require the strip to transition from a vertical plane exiting the uncoiler to a horizontal plane entering the production line (see Figure 1). The flexibility of the strip in this transition generally depends on its thickness and width. Clearly identifying these dimensions will enable you to evaluate accurately the prospective machine's ability to guide and control the strip.
These dimensions also will determine the loop length and floor space requirements. Thicker and wider materials will require more loop length to make the twist transition and consequently will take up more floor space.
Standard horizontal pallet decoiling works well for strip materials up to 0.065 inch thick. Thicker coiled materials tend to clockspring, continually opening and expanding in OD. This can result in coil instability on the pallet, causing rotation problems. Thicker coils also require additional equipment designed to control the expansion without interfering with coil rotation and payoff (see Figure 2).
Pallet uncoilers most often are loaded by forklift truck, but overhead travel cranes and fixed gantry cranes also are used.
The loading method may be an evolving factor in your project. If you are handling one coil at a time now and transitioning to pallet handling, or if you have been exclusively using vertical dereelers, now is the time to look at the loading systems before specifying uncoiler equipment. Pallet uncoilers most often are loaded by forklift truck, but overhead travel cranes and fixed gantry cranes also are used (see Figure 3).
No matter which loading operation you select, be sure to notify your prospective machine vendors. Make sure that no parts or structures of the uncoiling equipment will obstruct your loading method and that there will be plenty of floor space around the installation to accommodate the loading equipment.
Once the uncoiler is installed, its strip feeding orientation might force you to change your loading approach or access. The pass line of the coil strip might block access. Being familiar with the space in which the equipment will be working will help you sidestep potential problems.
The full pallet of coils is loaded directly on the turntable, thus freeing up some floor space in the area.
One consideration for floor space requirements is coil pallet storage. With earlier methods of coil handling, it was common to maintain a pallet of coils on the floor adjacent to the feed line area. With pallet decoiling, this "at-hand" storage is no longer necessary. The full pallet of coils is loaded directly on the turntable, thus freeing up some floor space in the area (see Figure 4). New coils can come directly from the coil storage room in full-pallet load units.
You must clearly identify the material demand rate to ensure that you choose an uncoiler that can pay off at the rates required for the job. The demand may be stated as feed length per cycle and cycle count per minute. Be sure to look at the uncoiler's maximum stroke feed length, acceleration rate, and stopping parameter.
Coil ID is a critical point to identify, because this portion of the coil requires maximum rotation from the uncoiler. If a job requires a feed rate of 100 feet per minute (FPM), a new coil with a 40-in. OD will rotate at 10 revolutions per minute (RPM) to meet the demand rate. As the coil unwinds and gets smaller, the uncoiler rotation rate needs to increase to keep up with demand rate. Each smaller coil wrap provides fewer feet of strip per rotation.
At the coil's center, assuming a 16-in. ID, the rotation rate is 24 RPM to maintain the same 100-FPM demand. The pallet uncoiler has to be controlled in a manner that allows it to increase rotation automatically as it accommodates the decreasing size of the coil.
In some cases, coils with very small IDs can be a problem for a pallet uncoiler. Turntable RPM requirements quickly increase when the specified ID of a coil is smaller. For example, for the same 100-FPM job, the 24 RPM required for a 16-in. ID increases to 31 RPM for a 12-in. ID and 64 RPM for a 6-in. ID. The difference between 24 and 64 RPM requires a considerable upgrade in uncoiler drive strength and control parameters.
Attending to the details of your application will simplify your transition to pallet uncoiling. Understanding coil sizes and weights, the dimension of the strip, the loading arrangements, and the speed demands of the job will help you eliminate unpleasant surprises. Your company and the equipment vendors providing quotes will be able to make their decisions based on a common set of specifications and requirements. Getting it right in the beginning will help produce a positive outcome for your project.
Tim Malarky is director of marketing with Norwalk Innovation Inc., 7 Progress Drive, Shelton, CT 06484, 203-929-2221 or 800-688-2645, fax 203-944-0753, email@example.com, www.norwalkinnovation.com. Norwalk Innovation Inc. is a manufacturer of uncoiling systems.