Due to declining factory orders and rising labor and energy costs, businesses that fabricate with plate metal are seeing their profit margins dwindle.
To remain competitive, manufacturers must continue to invest in new production equipment, whether to replace obsolete equipment or to capitalize on new business opportunities.
Manufacturers must conduct thorough assessments prior to adding new plate rolling equipment. While debt capital is still available to purchase new machinery, repaying the loan will not generate a satisfactory rate of return unless the equipment adds value to the production. Unfortunately, many buyers end up purchasing equipment that is incapable of meeting production volumes and tolerances simply because they are unaware of all available options and considerations.
To assist manufacturers in optimizing plate rolling operations, five critical factors to consider when selecting a plate bending machine are listed.
1. Take into account the rolling properties of the material to be rolled.
While the drawings specify rolling a plate to the same dimensions, a tougher material will require a much higher-rated rolling machine. Without such considerations, defects will occur, and the manufacturer will accumulate an excessive amount of scrap.
Today’s steel is significantly stronger and requires a greater degree of strength to bend. Numerous varieties of steel exist as a result of the American Society of Mechanical Engineers’ detailed classifications: A36, A516 grade 70, Hardox 400/500 series, and AR 200/300 series, to name a few. And each of these steels requires a different amount of pressure to roll.
The temper and yield strength of a metal must be matched to the customer’s application in order to accurately determine the plate roller’s specifications. This is especially critical given the dramatic changes in steel characteristics over the last couple of decades. The term “mild steel” no longer exists.
2. Consult an equipment dealer willing to discuss your unique plate-rolling requirements.
Customers must be aware of the appropriate questions to ask in order to receive the appropriate responses. Each manufacturer faces unique challenges, and an astute sales representative can determine precisely which equipment will work best for their process through systematic querying.
Additionally, manufacturers must carefully consider whether to roll conical or parabolic shapes in order to reach a broader market. Hydraulically operated four-roll machines are ideal for this type of work because they eliminate surface scarring and thus reduce the need for grinding the lamination (bullnosing) on a cone’s minor diameter edge.
Accurate conical rolling is further enhanced by torsion bar parallelism, as opposed to electronic or proportional value systems, which merely maintain theoretical balance. The machine’s finite parallelism enables it to be adjusted to its maximum conical tilt and back to parallel in less than five seconds.
Customers must discuss issues such as inside diameters, material types, tolerances, and the finished product’s desired shape. For instance, certain products, such as those used in the pressure vessel industry, require no more than 1% out-of-round diameters or they are considered defective. By employing an insufficiently powerful plate roller, excessive barrel effect can render such a product ineffective and quickly erode any potential profit margin.
Matching plate-rolling equipment to a manufacturer’s specific requirements requires attention to detail. It is critical that the dealer you work with is willing to meet with you and discuss your business’s unique needs. Numerous issues must be addressed, many of which a purchasing manager may not anticipate initially.
3. Maintain the machine’s optimal operating parameters.
It is recommended that manufacturers identify the material and thickness that account for the majority of their work. Then (a company) can deliver a machine that cambers to that specification, saving valuable production time and reducing scrap.
Cambering on high-quality rolling machines is typically set at 50% of the machine’s full-rated value. As a result, a one-inch machine is cambered to roll a half-inch plate with a near-perfect edge.
Ignoring this critical point may result in an out-of-spec product that the customer will reject. The most common cause of problems is when rollers attempt to exceed the limits of their plate roll. When 5/8-inch plate is rolled through a machine rated for 1-inch, a small amount of barrel effect is almost certain to occur. This may or may not be a tolerable error margin.
However, when the plate thickness of a machine approaches the upper limit of its rating, severe defects can occur. It will be unsellable unless corrected with a shim. On the other hand, when very thin material is rolled through a machine designed for extremely thick plate, the finished product may be tighter in the center than at the ends. Once again, tedious shimming is required to compensate for this “hourglass” effect.
4. Consider bending diameters carefully
The smaller the diameter, the greater the amount of bend pressure required. When thick material must be rolled into small inside diameters (ID), the diameter of the top roll and the machine layout can mean the difference between a product whose cylindrical edges meet and one that does not.
As a general rule, most machines can roll plate at 1 1/2 times the diameter of the upper roll. Thus, given a top roll with a diameter of ten inches, inside diameters as small as fifteen inches can be obtained. However, new machines equipped with planetary guides are capable of bending approximately 50% more area of the plate during the rolling operation, resulting in ratios of 1.1 times the upper roll diameter. This results in a 30% advantage for small diameters.
At 50% of the full rated value, all machines achieve precise measurements. As a result, with a 1.1 roll geometry, a 3/8-inch machine equipped with a 10-inch top roller can consistently roll 3/16-inch plate to 11-inch ID without experiencing barrel defects.
5. Include both horizontal and vertical supports to avoid unintentional bends.
Adequate support requires both side and vertical roller supports, as specified by the plate-rolling machine’s manufacturer. Once employed, plate rolling becomes a one-man operation rather than a two-man operation. This results in the release of valuable manpower that can be redirected to other tasks.
When the inside diameter of a cylinder exceeds 200 times the thickness of the material, the material’s weight becomes sufficient to bend the cylinder as it exits the top roll and moves away from the machine. Without adequate support, undesirable radii result.
This issue is easily resolved by purchasing a machine that includes both side and vertical roller supports.
Certain manufacturers attempt to cut costs by using “improvised” support such as a forklift or overhead crane. This shortcut, however, requires the use of equipment that could be better utilized elsewhere. Due to its inability to adequately support the material, it is still possible for unforeseen bends to occur.