Hydraulic Bending Rolls

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Sheet metal and plate bending rolls come in various sizes and designs; some electrical, some human-powered, and some using hydraulic power.

A hydraulic bending roll passes the sheet metal or plate through a series of rollers to bend and shape it into a cylinder or curved shape. Typically using three rollers, these machines are commonly used for a gradual, long bend like what would be seen in the plates of steel that make up a huge oil tank, or for producing lengths of pipe in an oil pipeline. A common design is the pyramid-style roll bender, which usually has one moving roll (generally the topmost roll). Another common bending roll is the initial pinch type. Initial pinch bending rolls feature two rolls (usually the bottom rolls) that are adjustable, along with a fixed top roll. The biggest advantage of these machines is that they can roll a perfect circle. It is not possible to make a perfect circle with a pyramid-type bending roll. Four-roll machines have the advantages of initial-pinch and double-pinch rolls - they make it even easier to get a perfect circle bend. Some bending rolls can be ordered with extra-large ...
... openings between upper and lower rolls. An extra-large opening boosts the machines capacity for bending thick, short (in width) plates or structural shapes.

The larger four-roll machines can handle capacities from 5 to 13 in length, and material that ranges from 14 gauge to 2" in thickness. Bending thickness can be increased slightly when working with a narrower piece. Other features often include a cone bending attachments, digital electronic readouts to indicate the positions of the adjustable rolls, automatic lubrication and controls for the various functions (and the readouts) in a movable control console. High-production four-roll machines might also feature overhead and side support, hydraulic feed and ejection devices for finished parts. Later-model four-roll machines have lateral rolls whose position can be adjusted through hydraulic cylinders to achieve a precise bending radius. The rotation system for rolls is usually comprised of two hydraulic motors and two planetary gearboxes which are fitted directly onto the rolls. Newer machines can also be ordered with graphical CNC controls for precision and ease of operation.

Cylinder shapes can be achieved with little (if any) gap in the middle of the seam if the rolls are equipped with "crowning" of the rolls. Crowning is where the middle of the rolls are made slightly larger in diameter. This compensates for any deflection that can occur when bending thicker metal close to the rated capacity of the machine. If the roll is not equipped with crowning, a gap can be fixed with a ratchet strap, clamps, come-along or vise grips with a chain attachment. If the crowning isnt sufficient or the machine is not equipped with this feature, a piece of shim stock can be taped to the bending roll to compensate for the deflection.

A cone or funnel shape can be achieved by pre-cutting a flat metal blank with the proper inner and outer radius needed for the cone shape. The inner radius is held against a cone rolling attachment, and should go through the machine slower than the outer radius. The position of the bending roll can then be adjusted independently (on the drive side) to match the desired taper of the cone.

Of course, any powered roll machine can be extremely dangerous to use if caution is not taken. They can easily crush fingers and hands, and safety guards such or devices such as Light Curtains are essential for safe operation. A well-trained operator is equally important.