Selecting the correct plate bending machine is a minefield. As you know, no machine can roll right up to the edge of the plate. The leftover straight section at the beginning and end of the plate is often called the green. The green presents a challenge, and in the machinery world, it is what separates the cheaters and the champions.
It usually is preferable to have the shortest green possible. To achieve this short green, you need a structurally stable machine, powerful hydraulics and good geometric design!
Reputable manufacturers will quote a pre-bend and rolling capacity.
Pre-bend capacity is what the machine is capable of before rolling. Pre bending capacity is a function of hydraulic power and mechanical strength.
Rolling capacity is what you can achieve with multiple passes and is variable depending on the length and radius to be rolled and the tensile strength. Tip, check the fine print and make sure the tensile strength the plate roll manufacturers base their capacities on is reasonable compared to what you use day to day.
There are many different styles and geometries of machines available, and each has its advantages. Three Roll Single Initial Pinch, Three Roll Double Initial Pinch, Four Roll Double Pinch, Three Roll Pyramid, Variable Geometry Rolls. There are also two roll machines for high-speed applications and vertically configured rolls that are an option for a long heavy plate. Plus there are many appropriate options to consider, such as cone bending attachments and top and side supports.
Unfortunately, there are many ways that manufacturers of Plate Bending Rolls can compromise the design and construction to get the price down, and they may not be forthcoming with those design choices. Being aware in advance might be the difference between the rolls being a worthwhile investment or a complete waste of money.
We would rather lose the deal than sell the incorrect machine for the job.