Rolling machine for metal sheet with four rollers usually has two fixed rollers, while the upper vertical rollers are positioned accordingly in order to complete the desired bending. By changing the relative position and rotating movement of the working roller,.
While bending, the work piece positioned between the lower and upper rollers. After placing the sheet between the rollers, the upper roller lowered to secure the work piece, and at the same time it has achieved sufficient pressure on the sheet, generating plastic bending.
When rotating the roller there is a friction between the sheet metal and the roller. So the sheet moves along its longitudinal direction. At the same time, the upper roller adds pressure to the work piece.
Rollers 2 and 3 move in the same direction and at the same speed. Because of the friction between the sheet metal and the rollers, the work piece moves in advance.
By adjusting the position of the upper roller, the desired bending angle can achieved. If the work piece does not achieve the proper curvature after the first bending. It can adjust and start the process in the opposite direction until the desired shape achieved.
How the roller machine rolling for metal sheet ?
After bending due to the position of the rollers on the work piece inevitably remains a flat part at the ends of the sheet. This flat part is approximately half the length of the gap between the centers of the lower rollers. Although the appearance of a straight part considered to be a flaw of symmetrical roller with 4 rollers. their simple structure, comfortable use and low price still make them the most wanted model of roll sheet metal bendind machines. In addition, there are methods which we can use in order to easily eliminate this problem. You can find some of them below:
Pre-bending with plate roller
This pre-bending involves bending the edges of the work piece on a press brake before the roll bending process.
When the roller crosses the lower limit of the upper roller (the roller deformation zone) in one turn and the pressure exceeds the bending limit, plastic deformation occurs and the sheet folded to its desired dimensions by its entire length. By adjusting the relative position between the lower and upper rolls. The sheet can fold to a diameter that is not less than the diameter of the upper roller. Here you can see the principle of the symmetrical circular bending machine with 3 rollers:
Adding a “base” for the work piece during the pre-bending
This method involves the installation of a “base” together with a workpiece designed for bending . And performing the edge pre-bending process on the circular bending machine itself.
The application of this method should take into account the possibilities of the circular bending machine . and calculate the strength of the applied force on the “base” and the workpiece.
Leaving allowance at the ends
If you add appropriate allowanceat plate ends before the bending. after the bending, cut off those parts into a desired bending shape.
Regarding the asymmetrical models of roll bending machines with 3 rollers. The position of the rollers adapted to eliminate the flat edges of the sheet, in which case the lower rollers can also mounted vertically. Thus, in a model with an asymmetric position of the rollers, the lower rotating roller lifted up to the middle of the gap between the two rollers, while the other positioned in the appropriate position so that the starting part of the sheet folded to form a circle. The flat edge eliminated on both sides by turning the rollers in half of the bending process by folding the back of the sheet. Additionally, the work piece can also turned around after completion of one bending cycle and then the back part will become the front and both flat edges will eliminate.
Rolling machine for metal sheet with 4 rolls
The principle of operation of the roll machine with 4 rolls is similar to the machine with 3 rollers. with the main difference being that the additional roller iused for better input of the material and execution of the process of pre-bending. During bending, the upper and lower rollers are static, the material firmly positioned between them, and the side rollers move and bend the material. In order to eliminate the flat edges of the material, the lower roller moves upward to hold the material firmly. And the side roller moves and occupies the position for pre-bendind.
Unlike a roll bending machine with 3 rollers, where during the pre-bending it assumed that the material lowered when entering the machine, in the roll machine with 4 rollers, the material positioned horizontally, allowing the use of motorized horizontal material holders when inserting materials in certain models. In addition, the input of materials carried out on both sides. So the machine placed next to the wall and save space.
The side rollers positioned to the left and to the right of the bottom roller, and have their own axes. The independent axis of each roller allows perfect bending. The “rear” side roller (located on the other side of the material insertion) also has a rear end stop function and aligns the material.
This feature allows the operator to work without the assistance of other people. Bending in the shape of the coupe is also possible on the machine with 4 rollers. The side rollers can be positioned in the corner for making the coupling. and the bottom roller can be lifted to hold and position the material.
How to bend the metal sheet with rolling machine
Machines with 4 rollers are faster and easier to operate, and can be managed by a less experienced operator. Ideal for folding materials up to 100mm thickness. However, an experienced operator can perform the same functions on a 3-roller machine. which generally has lower cost and is more commonly found in production facilities.
The advantage of a roll machine with 4 rollers has a unique complete bending process. The machine accepts the material in one stroke, performs the pre-bending and continues to bend the sheet. This system does not require an operator to remove, turn and then straighten the material after pre-bending. As is the case with 3-rollers bending machines. The material remaining in the machine makes the machine with 4 rollers up to 50% more efficient compared to 3-roller modelS. and allows the material to bend at the desired diameter immediately after pre-bending. The bending of the flat edge starts after bending the material in one direction.