Plate Roller Buying Guide
What is a plate rolling machine?
A plate rolling machine is a machine that will roll different kinds of metal sheet into a round or conical shape.
Plate rolls are the ideal machine for metal sheet pre-bending and rolling.
Plate rollers are used to manufacture rounded parts for oil and gas rigs, tunnel supports, boiler equipment, pressure vessels, and heat exchangers among many other things.
A plate bending roll creates a mechanical advantage by pressing a metal sheet between a top roll and two side rolls. The mechanical advantage allows the machine to press the sheet firmly against the rolls, bending it into a conical or spherical shape. Throughout the process, a pinch roll is typically used to hold the metal plate in the correct position.
Plate rolling machines are extremely powerful and able to bend metal sheets of varying thicknesses (typically between 1/16 to 4 inches). Plate rolls come in 3-roll or 4-roll models.
4-roll models could be CNC automated and specifically designed for large-scale, high-volume plate bending needs.
Whilst four roll machines produce fast, accurate bends, three roll machines are ideal for fabricators working with a wide range of material thicknesses and types.
How to choose a right plate roller?
Rolling is similar to forming sheet metal with press brake; it can be a "black art" or maybe magic, but in reality it is neither.
Part of taking roll forming out of the realm of "black magic" is selecting the right sized roller for the job. A good "rule of thumb" for three and four roll machines is that you can roll sheet or plate at 1.5 times the upper roll diameter.
If the top roll has a 10-inch-diameter, the minimum best practice "rollable" inside diameter will be 15 inches.
To determine the proper plate roll sizing, it is critical that yield, tensile strength, width, thickness, and diameter (or radius) of the part are all considered because for example, a higher yield or tighter diameter will require more pressure to form.Minimum and maximum width is also important because even something as straightforward as material thickness can vary, yet still fall into accepted plate and sheet mill tolerances.
On the application side, you will need to know the minimum and maximum diameter of the cylinders to be formed.
You’ll also need to know if you will be making cones or special shapes as this will determine the correct type and size of plate roll.
Almost all machines achieve precise measurements working at 50% of the full rated value of the roll.
One of the key decision-making factors you should consider is not only what type of plate bender will meet your current needs, but which could also satisfy future business needs.
4 roller plate bending machines
Four-roller machines have a top roll, the pinching roll, and two side rolls. These plate rolling machines produce the fastest and most accurate bends.
The flat metal plate is placed in the machine on either side and "pre-bent" on the same side. The side rolls do the work of bending. The pinching roll holds the plate.
Plate held securely in place between the top and bottom rolls, while the side rolls move vertically to create the bend. Bottom roll moves up to hold the plate surface securely against the top roll while the side roll is raised to form an accurate pre-bend, 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 be placed up against a wall to save floor space.
Side rolls positioned to the right and left of the bottom roll and on their own axes. The independent axis of each roll helps make a perfect bend. The back-side roll (at the far side of the feeding point) also functions as a back-gauge to square the plate for proper alignment which eliminates the need for someone to assist the operator.
Plate is kept square without slipping during both pre-bending and rolling because of the constant secure clamping of 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 pre-bending, (this is not possible in three-roll, initial-pinch machines.)
A cylinder can be rolled to the required diameter immediately following pre-bending because the material can be kept in the machine.
Bending the back edge takes place after the cylinder is rolled allowing for a one-direction, single-pass operation.
For 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.
4 roll benders make it possible to create rectangular, elliptical and square-shaped output by carefully bending the metal in specific areas as it passes through the machine.
3 roller double-pinch plate rolling machines
Three-roll, double-pinch machines are available in light to very heavy capacities and do not require the operator to remove, flip, and then try to square the plate a second time after pre-bending, as is the case with three-roll, initial-pinch machines. Cylinders can be rolled to the required diameter immediately following pre-bending because the material can be kept in the machine (this is not possible in three-roll, initial-pinch machines)
Side rolls 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 also functions as a back-gauge to square the plate for proper alignment which eliminates the need for someone to assist the operator.
For cone rolling on a three-roll, double-pinch machine, the side rolls can be tilted to establish the cone angle.
Pre-bending on a three-roll plate rolling machine requires that plates be tilted down as they are being fed whereas on a four-roll machine plates are loaded horizontally at the feed level which allows the use of horizontal motorized roller tables to help feed the plate.
3 roller initial-pinch plate bending machines
single-pinch bending machine requires inserting the sheet metal twice to pre-bend both ends. However, there are also double-pinch models available to make pre-bending processes on both ends easier, faster, and more precise.
Single initial-pinch plate rolls are generally only suitable for light-capacity applications. They can be electromechanical or hydraulic and work by pinching the flat sheet between two vertically opposed rolls while the third bending roll moves upward to contact then bend the sheet. These tend to be older machines which in most applications require removal and reinsertion of the sheet to prebend both ends so although cost-effective they are more labor-intensive in a production setting than their modern counterparts.
3 roller variable geometry plate bending machine
The widest range of material types and thickness in relation to the size of the top roll can be rolled on three-roll, variable-geometry machines. They are suitable for medium and thick plate bending.
The three-roll variable pitch works by having all three rolls able to move and tilt. The top roll moves in the vertical plane and the side rolls move on the horizontal plane. When rolling, the top roll presses the metal plate between the two side rolls. The advantage of having the variable three roll is the ability to roll many thicknesses and diameters of cylinders.Three-roller machines have one pressing top roll and two pressing side rolls.
For example; The side-rolls are what produce the mechanical advantage. With the side rolls all the way open, one has the maximum mechanical advantage. With the side rolls all the way in, you have the least mechanical advantage. So, a machine has a capability of rolling 2-inch-thick material with the maximum mechanical advantage, but a job is only 1/2 inch thick. Reduce the mechanical advantage and one has a machine that can roll from 1/2 to 2 inches thick.
The independent axis of each roll helps make a perfect bend. The back-side roll (at the far side of the feeding point) also functions as a back-gauge to square the plate for proper alignment which eliminates the need for someone to assist the operator.
Static pre-bending and Dynamic bending
There are two types of plate bending processes. Static pre-bending is where the metal sheet is held stationary while a roll runs upward along the sheet, bending the leading edge. Dynamic bending, on the other hand, is where the plate or sheet is in motion while running through the machine. The motion of the sheet allows the machine to work more efficiently, thus increasing the sheet bending thickness.
The plate roller can also be used to create a cone shaped piece of metal. In order to do that the metal plate must be cut to the proper size before it is bent. A sheet metal cone can be formed by pre-cutting a flat metal blank with the correct inner and outer radius to form the cone shape wanted. The blank is fed on one side so that the inner radius can be held against a cone rolling attachment. The inner radius is fed through the roller at a slower rate than the outer radius. This process can be a little more difficult and needs to be very exact so cones take a lot of time to fabricate.
Both the three-roll and the four-roll machines are capable of inclining the forming rolls in a positive attitude, and both should have a hardened contrast die to control and slow down the speed of the small diameter.
Guiding the small diameter and inclining the rolls are necessary to roll a cone. In this case you are creating an unnatural situation for the rolling process. Because on a three-roll double pinch machine all three-rolls are driven, it makes it difficult for the contrast die to retard the rotation on the small diameter while making the large diameter move faster.
A four-roll machine which has inclinable forming rolls and a hardened contrast die, will roll cones better than a three-roll.
Plate rollers can be powered and controlled in multiple ways. Older plate mills are driven by electric motors and newer ones are directed by programs which are loaded into the CNC controller.
DRO: machine comes with Three digital readouts for easy roll positioning as standard accessory. you can set travel limit for each roll on DRO to avoid material over bending by mistake.
NC teach-in controller: In teach-in mode, operator’s all movements are recorded in the controller. In automatic mode all recorded movements are repeated. NC control system has the capacity to save numerous programs. Edit mode allows creating programs manually by inputting rolls position values.
programmable roll bender can improve your capabilities in repeat operations
CNC controller: starting from a menu of standard shapes (cylindrical, oval, polycentric, bucket etc.) and simply entering the shell data (radius, thickness, width, type of material) the control creates the drawing of the workpieces automatically and the complete bending program with all the necessary bending steps. If necessary, the program which theoretically calculated by the controller can be easily optimized by the operator.
Handling and automation options:
Your plate rolling application could require side and overhead supports, automated loading tables and in-feed conveyors, or automatic part ejectors. Don’t forget these important productivity tools when choosing a new plate rolling machine!
overhead supports can prevent light materials from collapsing when rolled to large diameters. A side support can also assist in preventing light materials from recurving toward the floor if the radius is very large.
Steel plate rolls–whether they have two or three bottom rolls–all have a top roll. The top roll can be sized to roll plate into cylinders or cylinder segments to radii close to the diameter of the top roll. However, relatively small top rolls can deflect in the center under the pressure of curving steel plate. Alternately, larger-diameter top rolls deflect less but limit the machine to rolling only larger diameters.
Benders and rollers, those who specialize in curving steel plate among other steel products, are asked to roll a variety of plate widths, lengths and thicknesses. Some of the possibilities will cause deflection of the top roll in the rolling process. The result will be the plate cylinder with a barrel form and ends that are not parallel.
With plate rolls that have a long top roll with a small diameter, you will see more deflection. Imagine standing on the middle of a wood beam supported at two ends. As the length on the wood beam gets longer, the deflection where you are standing would sag downwards more. The same concept is applied to steel plate rolling.
To compensate for this deflection in a plate roll, the top roll is “crowned.” A “crown” is the barrel shape of the top roll that is needed to obtain a uniform distribution of the pressure required for the rolling of steel plate. A plate roll has supports at each end and the top roll deflects in the middle when the plate is in motion. This affects the parallelism on the edges of the rolled part.
Insufficient crowning will create an unsatisfactory roll form with barrel effect (where the part has a greater diameter in the middle than at the ends) and hourglass effect (the material is tighter in the middle than on the ends) both possible deformations that can be caused.
Most metal fabricators need a plate roll to work with numerous materials which will affect the plate rolling machine’s rolls in different ways. As a result, rolls are machined with optimal crowning which is typically 75% of nominal capacity if yield, width, diameter, pinch pressure, and speed are equal.
The range of a roll (thickness/width/diameter) depends on the tolerance, with accepted variance of your parts. Options can be installed on the plate rolling machine to adjust for different tolerances and specific crowning can be applied to reach the desired range of material characteristics and part tolerances.
The harder materials and laser/plasma cutting techniques used today require hard outer roll surfaces on rolling equipment. A hardness rating from 50 to 55 Rockwell C scale will have a reasonable penetration depth and provide long-lasting protection against roll surface wear. A hardness rating exceeding 60 will have a shallow penetration and will likely result in cracking or crazing of the roll surface
Although traditional rollers produce quality, accurate products, they are by no mean polished. If you need a finish free of marks then you’ll have to invest in precision ground rollers which produce a polished finish, but can be more easily damaged. in order to roll aluminum composite, you can choose segmented rolls coated by plastic to avoid scratches on workpiece.
Most new plate rolling machines are equipped with safety devices such as emergency-stop buttons; safety trip wires; 12-VAC, low-voltage control circuitry; and detached operator control consoles. It is however still your responsibility as the owner to ensure the installation and proper use of these operation safety guards or devices.
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