An introduction to the dishing and flanging process
There are hundreds of manufacturers of tanks, silos, pressure vessels, truck tanks, and metal rolls components all over the world. Most of these companies need to produce or source dished ends of various types, sizes, and specifications to complete their products.
However, there are only a few dished end manufacturers that can supply this kind of product, a significant reason dished end production has become a very profitable business and a craft that companies are carrying on and conserving generation after generation.
Tanks, pressure vessels, silos, truck tanks, and more all require dished ends. Fabricators make these ends using various processes. One popular method is dishing and flanging. The dishing and flanging occurs in two sequential operations that each require specific machinery: the dishing of the blank and the forming of the
plate edge.
The Dishing Process
Once the plate has been cut to size in a circular shape (using a circular shear, laser, plasma, or other method), the resulting dish is formed under a press that, with multiple hits distributed over the entire surface, will crown the plate.
To make different types of dished ends and different diameters, a dishing press must be equipped with a set of dies shaped with different radii. The dishing process is rather slow. It generally requires several hours depending on the plate dimensions and the material. This procedure can be automated with the use of a numerically controlled manipulator. It is possible to find presses with CNCs that can handle more than 10 axes and run automatically for hours like the presses series designed and manufactured by Faccin and Boldrini.
The Dishing of Polycentric Ends
A particular kind of dished end is widely used by the manufacturers of truck tanks: the polycentric dished end. These dished ends, often made of aluminium or stainless steel, are normally prepared with thin plates up to a maximum of 6 mm. This thickness allows the forming of polycentric-dished ends using a technique called hydroforming.
Faccin provides under its PPH series hydroforming presses that use high-pressure water against the sheet to form the dished end, which will take the shape of the holding die.
A hydroforming press, together with a precise CNC measuring laser for dished-end depth control and an efficient plate handling system, is the most productive technique for manufacturing oval and polycentric-dished ends for truck tanks.
The Flanging Process
The operation that follows dishing is the forming of the edge, which will allow the dished end to be welded to the tank body to support the pressure inside. During the flanging operation, the plate edge is formed with a flanging roll moving against and with the radius of the shaping roll. The two rolls turn and bend the material at the desired radius. This operation may cause lamination of the plate. The best-quality machines, like the BF series from Faccin and Ribo series from Boldrini, should be powerful enough to do the flanging in a minimum number of passes, causing a minimum thinning of the dished end.
A good flanging machine also should feature controls that always allow for the best contact of the rolls with the plate. This includes the ability to tilt the flanging and shaping rolls. The electric and hydraulic units make the difference between a good-quality and a low-quality flanging machine. The hydraulic unit must allow the movements to be proportional and simultaneous; it is of major importance, for example, to have simultaneous, fast movement of the carriage that holds the dished end to the rest of the axis.
Dishing and flanging machines are machines with many important technical aspects that should be properly evaluated. Selecting the right machine can make the difference between a successful and unsuccessful business.
Andrea Comparin
Sales Manager
For more information,
www.faccin.com & www.boldrini.com
