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Plate Rolling Techniques

Plate Rolling

Plate Rolling Process, Basics of Sheet Metal Rolling, Plate Rolling Formula,2 Tips and 11 Key Points for Plate Rolling

Metal sheet and plate rolling play an essential part in metal fabrication, it comes down to understanding the properties of the material and how pressure from the plate rolls can affect those properties.

PRS 3 Roll Steel Plate Rolling Machine
PRA 3 Roll Steel Plate Rolling Machine
PR4 4 Roll Steel Plate Rolling Machine

What is Plate/Sheet Rolling?

plate rolling machine
Plate Rolling Machine

Metal sheet and plate rolling(sheet rolling) is typically the 2nd step in the tank or ductwork fabrication process after the flat sheet or plate is typically cut to size on a CNC laser or plasma cutting table, the metal plate rolling process is used for steel and aluminum plate into full cylinders, cylinder segments, full cones, and cone segments for future fabrication at your facility. Plate rolling can help form tanks, metal ductwork, pipe, cones, and more.

Plate rolling machines typically use a series of hardened precision rolls utilizing either hydraulic or mechanical power.

Steel plate rolling machines work with a wide range of materials in sheet metal and heavy plate rolling services. Plate rolling machines can roll plates in most metal materials and grades. For sheet metal, a plate roller can roll aluminum, stainless steel, galvanized steel, mild steel, painted, and polished materials. While there are countless applications for rolled plate and rolled sheet metal, encounter certain applications more than others. The heavy plate rolling services are most often used to create components for metal duct work, circular tank walls, machine housings, piping, stacks, molds, and bridges.

Read More: Plate Rolling Machine, Sheet Metal, Steel Plate Bending Roll

Plate rolling process

In the plate rolling process, a flat plate of metal is formed into a specific curve or radius. The plate is placed between rollers, which turn in opposite directions, and which have a gap smaller than the thickness of the metal plate. As the plate moves between the rollers it is compressed or made thinner. As the work is performed, the plate is eventually molded into a full cylinder, cylinder segment, full cone, and cone segment that can then be used as part of a fabrication project.

Plate Rolling Formula

plate rolling formula
Plate Rolling Formula
Image Source:CAPACITY CALCULATOR - BARNSHAWS

The plate rolling process entails two groups of important variables. The first group hinges on the machine, such as the number of rolls, their diameter, position, and how they move. All these depend on the machine being used. The second variable group deals with the workpiece involved, such as the maximum plate width (W), maximum plate thickness (Th), and the minimum workpiece diameter (Ø), as well as the type of metal and its yield strength (YS). These variables can be plugged into an equation: W x Th2 x YS/g = K, where K is the constant and g is a parameter that takes into account the workpiece diameter and the machine geometry.

Applying such equations requires detailed application information, of course, but the important takeaway here is the factor Th2. Note that the sheet thickness value is squared, implying that a small change in thickness can have a dramatic effect on roll parameters.

Works Cited: Plate rolling rolls on

4 REASONS PRE-BENDING IS CRUCIAL IN THE PLATE ROLLING PROCESS

  1. Eliminates Waste: The pre-bending process helps minimize waste by creating an optimum geometrical formation so that both ends of the material can get in touch after rolling as perfectly as possible. Practicing the pre-bending process while having experience and being a skilled plate rolling machine operator plays a very critical role in eliminating waste.
  2. Eliminates the Need for Extra Trimming: The resources used on extra material trimming in plate rolling are nothing to be ignored for any efficiently and effectively functioning fabrication shops or operations. The need for extra trimming can easily be avoided through pre-bending by forming an optimum alignment of both ends of plate metal after rolling the material.
  3. Saves Time: Especially for high-volume production shops, wasting a minute out of the production time means wasting money and it can add up really fast over time. Since pre-bending helps an operator to form the desired shapes faster, the operating time per plate metal on a plate bending machine diminishes, which means rolling more parts with less time.
  4. Smooth Bending Surface and Uniform Curvature / Thickness: The pre-bending process is one of the most important practices in plate rolling when it comes to being able to get the results that were initially intended to get, which is simply rolling the material correctly. Properly rolled material will inevitably result in a smooth material surface and uniformity in material curvature and thickness.

Click for the chart of tensile strengths for aluminum and stainless steel to compare with mild steel

Other 3-types of the metal plate bending process

  • Air Bending – this process works by pressing a punch onto the workpiece and forcing it down into a bottom V-shaped die. This die is mounted onto the press. The punch creates the bend so that the space between the side wall of the V and the punch is larger than the thickness of the workpiece. As this process requires less bend force, it tends to use smaller tools than other techniques. Air bending is extremely flexible, allowing a number of different materials and thicknesses to be bent in variable angles. This process also requires fewer tool changes than other methods, meaning higher productivity.
  • Bottoming – in this technique, sheet metal is forced against the V opening within the bottom tool. A set amount of space is left between the bottom of the V opening and the workpiece. This method offers more precision and less spring back, but a different tool set will be required for every different material, bend angle, and thickness.
  • Coining – in the coining process the top tool forces the material down into the bottom die with 5-30 times the amount of power of air bending. This causes perpetual deformation through the workpiece and there is very little spring back if any at all. This method offers high levels of accuracy.

Read More: Bending basics: 12 types of metal bending processes

2 Tips for plate rolling

Tips 1#: The Math Behind Plate Rolling

The plate rolling process entails two groups of important variables. The first group hinges on the machine, such as the number of rolls, their diameter, position, and how they move. All these depend on the machine being used. The second variable group deals with the workpiece involved, such as the maximum plate width (W), maximum plate thickness (Th), and minimum workpiece diameter (Ø), as well as the type of metal and its yield strength (YS). These variables can be plugged into an equation: W x Th2 x YS/g = K, where K is the constant and g is a parameter that takes into account the workpiece diameter and the machine geometry.

Applying such equations requires detailed application information, of course, but the important takeaway here is the factor Th2. Note that the sheet thickness value is squared, implying that a small change in thickness can have a dramatic effect on roll parameters.

Tips 2#: MINIMUM BENDING RADIUS

The minimum diameter is the smallest diameter you desire to roll your material into because it is a great driving factor for the size of the machine that will be appropriate for your workshop’s certain needs.

There’s a rule of thumb to determine a steel’s minimum bend radius: Divide 50 by the material’s tensile reduction percentage as specified by your supplier. This value will vary by grade.

If the steel has a tensile reduction value of 10 percent, divide 50 by that value: 50/10 = 5. Next, subtract 1 from that answer: 5 – 1 = 4. Now, multiply that answer by the plate thickness. If the material is 0.5 in. thick: 4 × 0.5 = 2. So in this case, the minimum inside bend radius is 2 times the material thickness.

Click for a Bend Radius Chart for aluminum and stainless steel for recommended minimum bend radii.

11 Key Points for the Plate Rolling Process

Points 1#: Operating Parameters

That means that even a small increase in thickness can make a difference in the way the rolls will perform.

Begin with selecting the correct bending rolls to roll the part on. Modern plate rolling machines are usually cambered (crowned) at 50% of the full-rated value of the machine. Therefore, a 2-inch machine is cambered to roll a 1-inch plate. All plate bending machines are really designed to function best when used to half their working value.

Problems arise when the upper limits of any plate bending machine are approached, be it roll former or press brake. That means that even a small increase in thickness can make a difference in the way the rolls will perform.

Points 2#: Right-size Roller

Almost all plate rolling machines achieve precise measurements working at 50% of the full rated value of the roll.

  1. You can roll a sheet or plate at 1 1/2 times the upper roll of the 3-roll or 4-roll plate bending machine’s diameter. If the top roll has a 10-inch-diameter, the minimum best practice “rollable” inside diameter will be 15 inches.
  2. Plate Rolling Machines that incorporate planetary guides keep roughly 50% more area under bend pressure at any one time. This design can achieve ratios of one-to-one with the upper roll diameter.

Points 3#: Pre-Bending

In the initial-pinch 3-roll plate bending machine, the pinch rolls provide the “grabbing” force, while the bending roll’s position determines the forming geometry.

The plate rolling machine needs to grab the material during rolling. That’s why, in any rolling operation, there is a narrow unbent flat section on the plate’s leading and trailing edges. An operation known as pre-bending reduces the length of these unbent flat sections. These flat sections should be no more than two to three times the material thickness of most rollers. Pre-bending the plate’s leading and trailing edges before performing the final rolling can remove these flats.

The per-bending process involves pinching the plate material firmly between two of the rolls and then using the side or lateral roll to force the material into an initial bend before rolling commences. This process must be repeated on each end of the plate being rolled to avoid large flattened sections at the mating ends of the cylinder.

Using most double-pinch and four-roll systems it’s possible to pre-bend the leading plate edge without removing the sheet or plate from the roller before performing the final rolling.

Pre-Bend capacity is always less than that of the rated bending capacity so it is important to ensure the rolling system you are looking at can properly pre-bend the material you are working with.

Read More: Pre-bending

Points 4#: Consistency

Consistent roll bending involves controlling the forming roll pressure and location. Softer materials require less pressure than harder materials. The yield strength of soft material will cause it to start forming sooner than a high-yield strength material will. That being said, different types of materials with identical thicknesses and rolled to identical diameters have will dramatically different positions of the rolls.

Every time the “forming roll” is raised, lowered, or moved in, or out, the roll changes. The more you raise, lower, or move the rolls the more pressure you add or remove from the process.

A point of note, the closer the “forming roll” gets to the pinch rolls, the greater the required pressure but also the closer to the edge the radius will get.

Points 5#: Springback

As in any forming operation, rolling, too, has to deal with spring back, a property of the material in rolling sheet metal that may require an overlap, sometimes by inches. But, just like spring-back on a press brake, when you release the part from the pressure it will spring back. If rolled to the correct diameter, a closed and appropriate gap will be the result.

Points 6#: Anti-Deflection

One common anti-deflection method is for the rolls to have slightly larger diameters in the middle of the rolls than at the ends.

The roller is rigid near the ends and deflects in the center. The roller can remain cylindrical but is no longer straight, this deflection is a normal part of machine operation.

The rollers deflect in the same way the ram of the press brake does under load; it “opens” or “flexes” in the center, deflection, which has the effect of lessening the pressure from the forming roll on the bend at the center. So, many plate rollers employ some form of anti-deflection device or crowning system.

A roller supported from one only side is considered a cantilevered roller which will deflect in increasing amounts the further away from the supported end the workpiece gets. A roller supported from both ends will have maximum deflection at the center of the roller.

Points 7#: Crowning

If there is not enough crowning the effect will be a “barreling”. This is where the ends of the cylinder hold a tighter diameter than the center. Too much crowning will produce the opposite effect, the cylinder will have an hourglass shape.
There are two possibilities for the barreling effect: there isn’t enough crowning in the center of the “forming roll” or the “pinch rolls” are not set correctly.

Read More: Best Buyer’s Guide for 3 Roll Plate Bending Machine

Points 8#: Roll Distortions

High-yield strength materials can handle more pressure. But soft, low-yield strength metals such as H-series aluminum, increasing the pinching pressure can distort the material. The material can thin and distort under excess roll pressure so some caution is required.

  1. Every change in crowning pressure changes the amount of deflection in the center of the roll. A slight barrel shape confirms the center of the roll is deflecting away from parallel.
  2. There may also be thinning or distorting of the edge of the workpiece. If this is the case, try decreasing the pinch roll pressure slightly. Allow the middle of the roll to deflect just enough that the rolling surfaces return to the parallel line of pressure that should be present across the width of the workpiece during rolling. This will not eliminate the barreling effect; in fact, it will most likely make the barreling worse. With inefficient machine crowning shimming may also be required.
  3. If you have excessive crowning a slight hourglass shape is a result. The line of pressure across the roll now looks like a frown. The frown turns into a straight line of pressure when the crowning is reduced.

Points 9#: Shimming for Crown

At some point, you may need to shim a workpiece to create a
crown. Placed in the center of the workpiece and in the center of the roller, the shims themselves can be pieces of cardboard, plastic, or even light gauge sheet metal, etc. This is a manual way to add crowning effectively. Just as shimming press brake dies start with a wide shim and gradually build to a center.

It is not a good practice, nor will you have good results if you try to place a thick narrow shim dead center.

It is also possible to shim along the edges of the workpiece to compensate for any excessive crowning and hourglassing that may be present.

Read More: 1/4″ Plate Roller  3/8″ Plate Roller

Points 10#: Additional support systems

Bend past 180° and gravity will pull the sheet inward.

In thin-gauge rolling, you also have to worry about how the rolled cylinder will behave as it climbs up and over the centerline of the roll. Thick plates have the structural mass to maintain their shape throughout the rolling process. Thin sheet metal can bow under its own weight changing the radius and distorting the part. Gravity can change the point of the bend! At first, it forces the material away from the “pinch rolls” and then toward the “forming roll”.

For large or tight-tolerance work an additional overhead support system will be required; and if the material is structurally weak, the sides of the roll may need to be supported and guided through the rolling process as well.

Points 11#: Plate Rolling Capacities

The narrower the width of the plate entering the machine, the thicker the plate that can be rolled. For example, the plate bending machine can roll a 2″ thick, 12′ wide steel plate, or it can roll a 12″ thick, 3′ wide steel plate. The bending rolls can also roll thick material to very tight diameters—for example, 2″ thick, 10″ wide material can be rolled to a 19″ diameter.

The type and grade of the material determine both the largest dimensions that can be rolled and the minimum radii that can be rolled. For harder materials, maximum heavy plate rolling dimensions become smaller and minimum radii become larger.

Read More: Best Buyer’s Guide for 4 Roll Plate Bending Machine

roll forming process
roll forming

About Steel Plate Roll forming

Steel plate rolling involves passing a piece of steel plate through one or more pairs of rollers in order to reduce the overall thickness of the material. This process also ensures that the workpiece thickness is unchanging throughout. This procedure is categorized according to the temperature of the steel plate being rolled. If the temperature is above the recrystallization point the process is called hot rolling and if below it is called cold rolling.

Hot Rolling

Hot rolling processes have more weight than any other manufacturing process available. Finished products are usually of very high quality but can be left covered in mill scale due to the high temperatures during processing. This oxide is removed via pickling to leave behind a smooth surface. This method is usually employed to produce sheet metal or other materials, including:

  • Automotive parts (frames, wheels, water heaters, etc.)
  • Agricultural equipment
  • Compressor shells
  • Metal buildings
  • Guard rails

Cold Rolling

Cold rolling increases a material’s strength, improves the surface finish, and maintains tighter tolerances. However, cold rolling cannot reduce the thickness of material as well as hot rolling can, especially in a single pass. Cold rolled sheets and strips come in various conditions:

  • Full-hard
  • Half-hard
  • Quarter-hard
  • Skin-rolled

Full-hard cold rolling reduces a material’s thickness by up to 50%. Each respective condition then reduces thickness as we go down the list, finishing with skin-rolling that reduces thickness by no more than 1%. This last condition is used more commonly to provide a uniform finish. Common applications of cold rolling include smaller parts such as:

  • Metal furniture
  • Motorcycle parts
  • Lighting fixtures
  • Hinges

Works Cited