Usually, when we choose the right plate rolling machine that suits us, we need to answer some questions from the seller. The most important question is how much roll bending capacity do you need?
We need to know five parameters of the metal plate to roll bent to determine the roll bending capacity of the bending rolls:
- Maximum roll bending thickness
- Pre-bending thickness
- Maximum plate width
- Minimum bend diameter at maximum thickness
- Yield strength of the plate
Maximum bending width
Maximum bending width of plate bending machine: refers to the bending width under the maximum bending thickness.
The overall rolling capacity of bending rolls is determined by the physical length of the rolls which unlike other specifications cannot be “cheated” when purchasing a plate roll make sure you are sizing the roll length for the maximum width of the material you will be rolling understanding that the longer the rolls the larger the roll diameter has to be in order to maintain strength under rolling pressure. The adverse reflection of that is the larger the diameter you will need to be rolling.
Maximum roll bending thickness
The plate rolling capacity is determined by several factors. The thickness can roll is tied directly to the width of the plate bending. As the plate becomes smaller in width, the bending rolls can bend thicker material.
Minimum bend diameter at maximum thickness
How do determine the minimum bend diameter?
Although it is the upper roll of the plate rolling machine that determines the minimum bending radius.
But we can also know the minimum bending radius corresponding to our thickest sheet before communicating with the supplier of the plate rolling machine.
There’s a rule of thumb to determine a steel’s minimum bend radius, and this generally works for aluminum too: 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.
A plate rolling machine needs something to grab if it is expected to form the material into a cylindrical shape. As a result, any plate rolling operation typically leaves an unbent flat end section.
How to minimize the unbent flat end section?
The unbent flat end section can be bent prior to rolling, this process is called “pre-bending.” Pre-bending can be done in a 3-roll or 4-roll plate bending machine, how thick a plate you can pre-bend is controlled by the maximum pressure that can be applied by the top roll of the machine.
More specifically, the capacity of a plate rolling machine is defined by the maximum thickness and the minimum radius combinations that can be pre-bent for a given plate of maximum width. Pre-bending saves time. You do not have to cut then roll, cut then roll, etc. Pre-bending also eliminates flat spots and material waste.
When performing steel plate rolling of higher strength steels, you will have two main considerations:
- The tonnage/capacity of the machine
- The spring back of the material after pressure is released
The yield strength is the strength of the material you are rolling, or better put, the strength of resistance to bending that the material has. The harder the material the higher the yield strength and the larger/stronger the plate roll must be to roll the material. Yield points vary greatly from Aluminum to Stainless and other materials in between.
The tonnage is fairly linear in proportion with the yield strength. So if the yield strength doubles, so does the tonnage required to bend it. Most plate rolling machines are rated using a “standard” of mild steel A36 or 1018 with yield strength around 36,000 psi.
The spring back of the material is a more complicated formula, but in general:
- The higher the yield strength, the more that the material springs back
- The larger the forming radius, the more the spring back angle
Sources: “Plate Rolling 101 – Sizing the Right Plate Roll for Your Application”, Southern Fabricating Machinery Sales, Inc., Visited 13 Aug, https://www.southernfabsales.com/blog/plate-rolling-101-sizing