1. Introduction to Roll Forming
1.1 What Is Roll Forming?
Roll forming is cost-effective compared to other sheet metal forming processes for uniform profiles. During the last ten years, the process has developed into forming profiles with varying cross-sections and is thereby becoming more flexible. The rolls' motion can now be controlled concerning many axes enabling a considerable variation in the profiles and the formed sheet, the so-called 3D roll forming, or flexible roll forming technology. The roll forming process also has advantages compared to conventional forming for high-strength materials. Furthermore, computer tools supporting the design of the process have also been developed during the last ten years. This is quite important when designing the forming of complex profiles.
2. What Is Roll Forming Mill?
2.1 Genel Information About Roll Forming Mills
The heart of the roll forming line is the mill. The mill provides the power and support to the tooling that forms the metal. The complete roll forming line is aligned with the shaft shoulders of the roll forming mill. The mill design variations are unlimited, but mills can be classified as cantilevered, duplex, through-shaft duplex, standard (conventional), or rafted (plated). Those not fitting into any of these categories may be considered as “special mills.”
2.2 What Are The Roll Forming Mill Types?
2.2.1 Cantilevered Roll Forming Mills
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, unsophisticated machines and require a little adjustment. The cantilevered mills have become more popular and have been used to form many simple, narrow sections.
2.2.2 Duplex Roll Forming Mills
Two cantilevered mills facing each other are called a duplex mill. Duplex mills have one joint base and drive. They can form both edges of narrow or wide products leaving the center flat. The minimum strip widths depend on how close the opposing rolls can be pushed together, and the maximum widths usually depend on how far the two mills can be moved from each other. The width of the formed products can be changed quickly by adjusting one or both sides of the duplex mill in or out.
2.2.3 Through-Shaft Duplex Roll Forming Mills
The through-shaft duplex mill is a combination of the duplex and conventional (standard) mills.
2.2.4 Standard (Conventional) Roll Forming Mills
The standard (conventional) mills' shafts are supported at both ends. This design enables the 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.
2.2.5 Double-High Roll Forming Mills
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 (Figure 2.19). 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 is formed. If the coil is fed into the upper level rolls, then another profile is formed.
2.2.6 Rafted (Plated, Cassetted) Roll Forming Mills
The development of rafted mills was a significant breakthrough in reducing roll change time from 8 hr or more on a large panel mill (or 4 hr on a smaller mill) to between 30 and 45 min and as low as 5 min. The mill has a bed on which the drive is located, and the interchangeable plates are placed. The plates are holding four to eight or more stands. The number of stands on a plate is usually restricted by the lifting capacity (crane) at the user’s plant.
2.2.7 Side-by-Side Roll Forming Mills
Tool changeover time can further be reduced by mounting more than one set of tooling on the mill shafts. The most straightforward arrangement for the narrow sections is to install two sets of rolls on standard shafts.
2.2.8 Portable and Truck-Mounted Roll Forming Mills
Installers of construction products occasionally find it necessary and often more economical to form the job site's products.
2.3 What Are The Roll Forming Mill Components?
2.3.1 Mill Bed
The mill base, sometimes called “bed,” supports the stands, shafts, rolls, drive train, and the components needed to form the sections. The essential requirements for the base are:
- Rigidity
- Smooth, leveled top surface
- A keyway used for aligning the stands
- Drainage for coolant and lubrication liquids
2.3.2 Mill Stands
In most cases, the drive-side stands are exposed to considerable forces and bending moments. The operator-side (outboard) stands are exposed to lesser forces. They usually support the shafts through needle bearings and long bearing sleeves. As a result, no forces are acting on the stand in the axial direction of the shaft.
2.3.3 Mill Shafts
The construction of the cantilevered shafts and the operator side of the two-end-supported shafts are similar.
2.3.4 Powertrain
Roll forming lines are usually powered by electrical motors. In a very few cases, mills are driven by hydraulic motors. Hydraulic pumps driven by electrical motors power most hydraulic motors. Occasionally, the pump is driven by diesel engine, as truck-mounted lines work at remote job sites.
2.3.5 Chain Drives
Driving each top and bottom shaft with a continuous chain usually provides very little shaft adjustability, and the speed can be restricted.
2.3.6 Gear Drives
One possibility is to drive the shafts with a spur-gear train. The problem with this gear arrangement is again the adjustability of the top shafts. Moving the top shafts up a small amount causes only the tip of the gears touching each other. This “out-of-pitch diameter” engagement does not provide.
2.3.7 Side-Roll Groups
Side-roll stands, however, are an integral part of the equipment and tooling. Side rolls have several advantages. The shafts can be oriented at any angle instead of just being horizontal, as in the main passes. This flexibility allows locating the side rolls at optimum angles. A smooth drive and can easily chip or break the teeth of the gears.
2.3.8 Lubrication System
Lubricants are used to reduce friction between the formed parts and the rolls, to eliminate the pick-up of zinc, aluminum, or other metals by the rolls, and to avoid scratching or marring the product surface. When thick materials are formed, lubricants are also used as a coolant to dissipate the heat created by the forming.
