Don’t Get Flattened by the Wrong Plate Roll
Don’t Get Flattened by the Wrong Plate Roll
Six Questions that Can Help You Select the Right Equipment
By Kyle Jorgenson
President of JMT
Adapted from an article Kyle wrote for The Fabricator magazine, October 2013 issue.
Plate rolling is not like working a press brake, where there is a single bend and one direction of inertia. A plate roll involves multiple forces and directions of inertia as the forming takes place. If operators don’t understand this science and the process dynamics, they are forced to use “proprietary radius finders,” also commonly known as hammers, chains, cranes, forklifts, come-alongs, oxyacetylene torches, and jacks of all types.
Aside from a skilled operator, the machine you choose is equally imperative for effective plate rolling. Answering the following questions will help you find the best machine for your plate rolling projects.
What Type of Material Am I Rolling?
Yield, tensile strength, width, thickness, and diameter (or radius) of the part all have to be considered. These properties, more than anything else, determine the proper plate roll sizing. For example, a higher yield or tighter diameter will require more pressure to form.
Also, minimum and maximum width is important. Even something as straightforward as material thickness can vary, yet still fall into accepted plate and sheet mill tolerances. For instance, a 0.25-in. plate can sometimes vary in thickness from 0.23 to 0.262 in.
On the application side, you need to know the minimum and maximum diameter of the cylinders to be formed and if cones or special shapes will be made. All of this information is integral in finding the correct type and size of plate roll. The end goal is to achieve parallel surfaces while producing the diameter you need.
Do I Understand the Importance of Crowning?
Keep in mind that most metal fabricators are going to require a plate roll to work with many materials, which will affect the machine’s rolls in different ways. To accommodate this variety, most manufacturers’ rolls are machined with optimal crowning.
With insufficient crowning you won’t get a satisfactory roll form and wind up with either a barrel effect (the part has a greater diameter in the middle than at the ends) or an hourglass effect (the material is tighter in the middle than on the ends).
A roll operator needs to learn and practice the techniques that can combat crowning deformations, such as increasing or decreasing the initial crowning in the center, reducing or increasing pinch pressure, adding shims to either the middle or the outer surfaces of the rolls, changing the rolling speed, changing the number of passes to roll the part and so forth.
What Type of Machine Fits My Production Needs?
Certain types of plate rolling machines are easier to operate than others. Also, cone rolling or rolling of a special shape, such as elliptical, can be accomplished with greater accuracy on certain types of machine.
4-ROLL PLATE ROLLS produce the fastest and most accurate bends. The plate is held securely in place between the top and bottom rolls, while the side rolls move vertically to create the bend. The bottom roll moves up to hold the plate surface securely against the top roll while the side roll is raised to form an accurate prebend, minimizing the flat zone on the plate edge. Plate feeding can take place on either side of a four-roll machine. If fed from only one side, they can even be placed up against a wall to save floor space. The so-called “back” side roll (at the far side of the feeding point) also functions as a backgauge to square the plate for proper alignment. This eliminates the need for someone to assist the operator. The plate is kept square without slipping during both prebending and rolling because of the constant secure clamping of the top and bottom rolls. Four-roll machines do not require the operator to remove, flip, and then try to square the plate a second time after prebending, as is the case with three-roll, initial-pinch machines. To perform cone-rolling on a four-roll machine, the side rolls can be tilted to establish the cone angle, and the bottom roll also can be tilted to clamp and drive the major end of the cone.
3-ROLL VARIABLE-GEOMETRY PLATE ROLLS can roll the widest range of material types and thickness in relation to the size of the top roll. They are suitable for medium and thick plate bending. Unlike traditional three-roll cylinder machines, the lower rolls on three-roll, variable geometry machines move horizontally right to left, and the upper roll moves up and down. As on four-roll machines, material loads parallel to the floor, so the machine pit can be constructed to working level. By design, the upper roll can be used as a traditional press. Side rolls can move close under the top roll, so that thinner plate bending can be done on smaller diameters. Also, top and side rolls have tilt capability for cone bending.
3-ROLL DOUBLE-PINCH PLATE ROLLS are economical plate rolls that are relatively easy to operate. The side rolls are positioned to the right and left of the top roll and are on the same axis. The axis of each roll helps make the bend. The “back” side roll (at the far side of the feeding point) also functions as a backgauge to square the plate for proper alignment. This eliminates the need for someone to assist the operator. Three-roll, double-pinch machines do not require the operator to remove, flip, and then try to square the plate a second time after prebending, as is the case with three-roll, initial-pinch machines. For cone rolling on a three-roll, double-pinch machine, the side rolls can be tilted to establish the cone angle.
Do I Require a Mar-free Finish on the Rolled Parts?
If you require a mar-free finish, you need polished, precision-ground rollers. They are easy to clean and won’t pick up mill scale as much as traditional rollers.
With these specialty rollers, however, comes a need for vigilance. You have to be careful with what you send through the rollers, because even though they are hardened, they still can be damaged. (You have to be especially vigilant when rolling narrow pieces, because all the pressure of the machine can be focused on a very small area.)
If you need to have rollers made out of specialty alloys, you won’t suffer sticker shock. The cost of the rollers typically isn’t exorbitant, but of course, the application ultimately might justify the cost.
What Part Handling Options Do I Need for My Rolling Applications?
A plate rolling application could require NC or CNC side and overhead supports, motorized loading tables, plate alignment systems, infeed conveyors, or part ejectors. These are important safety and productivity tools that should not be forgotten when choosing a new plate rolling machine.
Some of these options might be only a small percentage of the purchase price, but could have extremely fast return on investment.
Will I Be Doing Any Welding in the Plate Roller?
Welding around expensive controls found on a new plate rolling machine could lead to extensive electrical damage from the welding power source. It could fry the system.
You need to take special care to make sure the welding ground is on the part, not on the machine. It never starts out like that, but before a shop realizes it, a welder is on top of the plate roller trying to join up the two ends. It’s convenient, but if it’s done improperly and without the correct protection on the machine, controls and electrical systems can be damaged.
If you even think that this is a possibility, you need to have an upgraded, shielded electronic system to protect the plate rollers’ electronics. It’s better to be safe than sorry.
Plate rolling is an art when compared to some other fabricating processes, but having the right equipment and accessories for the job can help even a new operator turn out quality rolled parts after a few days of training. You shouldn’t be intimidated with the thought of rolling; it just might be a new forming option to offer your customers.
Has this list of questions raised even more questions for you? Please don’t hesitate to contact our Plate Roll Experts here at JMT for even your tiniest concerns.
(For the complete article, please see The Fabricator, October 2013, pages 170-172.)