The shafts of the cantilevered mills are supported at one end only; hence, they are sometimes called “overhanging” or stub-type mills. Cantilevered mills, producing lock-forms at the edge of sheets, have been popular with sheet metal workers for a long time. They are low-cost, nonsophisticated machines, and require little adjustment. The cantilevered mills become more popular and have been used to form many simple, narrow sections. To utilize the mill for two sections, the opposite side of the “cantilevered” shaft ends can be tooled to form another section.
The advantages of the cantilevered mills are:
* Relatively low cost
* Capability to form the edge of sheets of any width
The disadvantages of the cantilevered mills are:
* Singular adjusting screw makes it difficult to set the required roll gap.
* Double-adjusting screws makes it very difficult to adjust the shafts up or down, while keeping the top shaft parallel to the bottom shaft.
* The deflection of the two opposing shafts under the same load is approximately four times the deflection of the same shaft supported at both ends. Owing to the larger deflection of the cantilevered shaft, the shaft length (and the maximum formed width) is limited. The first two shortcomings can be eliminated by using double-adjusting screws connected with gears (one shaft-height adjusting screw rotates the other one). The deflection can be reduced by using larger shaft diameter shafts or by applying a connector (yoke) between the top and bottom shafts at the operator side. This connecting unit can be applied to form narrow sections only. Using cantilevered mills, the maximum width of the formed part of the product seldom exceeds 4 in. (100 mm). To facilitate fast profile changes, rafted (plated) cantilevered mills have been developed. The plate, supporting the stands, shafts, and tools, can be lifted off and exchanged with another one within a few minutes.
( Roll Forming Handbook,George T. Halmos; Page: 2-1)
Standard (Conventional) Mills (21 Nisan 2011 22:45)
The shafts of the standard (conventional) mills are supported at both ends. This design enables building and use of the mills for materials with any width and thickness. Therefore, standard mills are the most popular machines used to roll form metals. In most cases, the drive-side (inboard) stand holds the shafts in position and accommodates the drive. The operator-side (outboard) stand supports the other end of the shafts. This stand is removable to facilitate roll changes. Both the operator- and drive-side stands are fastened to a common base. The drive-side stands are fixed at one location. The operator-side stands are in most mills also fixed at one position. In other types of mills, the operator-side stands can be placed into different locations along the shafts to accommodate wider and thinner material, or narrower but thicker material.
( Roll Forming Handbook,George T. Halmos; Page: 2-9)
Double-High Mills (21 Nisan 2011 22:45)
To satisfy the demand for roll forming two profiles in a limited plant area with quick profile changeover, the “double-high” mills have been developed. The double-high mills have alternating short and tall stands. Rolls for one profile are installed in the short stands, and rolls for another profile are mounted on the tall stands. The lines have one uncoiler and one cutoff press. If the material is fed into the lower-level rolls, then one profile (e.g., farm sidings) is formed. If the coil is fed into the upper level rolls, then another profile (e.g., farm roofing) is formed. To accommodate the profiles exiting at two different levels, the cutoff die also has two levels. The handling equipment for finished products beyond the cutoff die must be adjustable up and down to suit the two product exit heights. Double-high mills save space, and the changeover time between two products is relatively short. However, because of the crowded condition, it is difficult to install side-roll stands, to make adjustment, or to check the forming conditions.
( Roll Forming Handbook,George T. Halmos; Page: 2-10)
Pull-Through Mills (21 Nisan 2011 22:49)
Roll forming mills can have nondriven forming rolls. Most side-roll stands and often the top shafts are not driven. On rare occasions, none of the shafts/rolls is driven. In the latter cases, the strip is pulled through the mill by other means while the idle (nondriven) rolls are doing the forming. When forming thin material (e.g., 0.003 to 0.020 in. or 0.075 to 0.5 mm) in small mills, the strip can be pulled through by a “caterpillar” belt, winder drum, curving head, or by other means. If a thin material is joined to a thicker roll-formed section in their full lengths, then the mill, which forms the thick material, can pull the thin material through a separate nondriven mill. This method is sometimes used in ceiling gridlines to join the prepainted “cap” to the galvanized structural part. Pull-through roll forming has limited applications but it has other great potentials. It can provide straight sections with better cross-sectional tolerances than other methods Thicker materials, such as 0.060 to 0.100 in. (1.5 to 2.5 mm), require more pulling force. Pairs of driving rolls located between each idle forming roll passes can produce structural “U,” “C,” “Z,” and other sections. Profiles within the limits can be changed quickly by exchanging the idle profile forming rolls only.
( Roll Forming Handbook,George T. Halmos; Page: 2-15)
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