When it comes to metal fabrication equipment, you may have heard of an angle roll bending machine. Some may refer to it as a section bending machine, but its purpose is still the same – form raw pieces of metal into desired shapes and sizes.
If you have ever seen an angle roll bending machine, you would agree that most are constructed in a vertical steel frame. It is common that the bending portion of the machine is located on one side, with the power and drive of the machine on the opposite side.
This writing is intended to educate and help the purchaser of Angle Bending Machines to ask the right questions when considering a purchase.
Small units are powered by an electric motor with a reducer. The power transmission is accomplished by gear trains and or chains / sprockets combinations. These are units used in small job shops and rod iron fabricating establishments. The new generation of the section bending machines is powered by hydraulic systems. These are used for bending from the smallest bars to very large wide flanged structural beams.
The large hydraulic units have a double pump hydraulic system, with one providing the flow for the rotation of the rolls and the other for the extension and retraction of hydraulic cylinders attached to arms carrying the bending rolls.
Some designs use one main hydraulic motor, usually mounted to an epicyclical in-line reduction gear, which imparts rotation to all three rolls. Another variation is each roll having its individual hydraulic motor/ reduction box combination directly driving it.
The Bending Process:
There are some terms used in the industry describing the capacities of Section Bending Machines and the process used, which the purchaser should become familiar with.
Square and rectangular rods, round rods, square and rectangular tubing, round tubing, standard pipe, equal leg and unequal leg angles, “C” and “MC” channel, “S” and “WF” beams, “T” bars …these are sections which can be rolled on section bending machines.
“Leg out” means the leg of a section, like in angles will stick outward from the ring formed in a radial direction. “Leg in” means the leg of a section, like in angles will stick inward from the ring formed in a radial direction toward the center of the ring. “Leg out” is also known as “Easy way” and “Leg in “Hard way” There are exceptions to this terminology when it comes to channels, whereby one can bend a channel leg in, leg out and the hard way when bent on its side.
Bending of round sections, pipes and round tubing require special tooling other than what is usually provided standard with section bending machines. In special cases with square and rectangular tubing where the wall thickness is low…the manufacturer should be consulted as to whether special all section enveloping tooling is required to avoid the section from collapsing under the bending forces.
Bending Channels, S beams and WF beams the hard way, present a special challenge because the force of bending would sometimes collapse the web connecting the flanges. Most manufacturers of heavy section bending machines offer what is called a “Traction Tool”, which holds the section back and supports the web so as to avoid collapse.
Each section has what is known as a “Section Modulus”. This value is a measure of the resistance a section displays to bending. It is the quotient of the sections Moment of Inertia about the axis passing through its center of gravity, which coincides with the neutral axis of the section and the furthest distance on the section from that neutral axis. In symmetric sections bending about the neutral axis both ways will give the same section modulus, however in non symmetric sections, the section moduli are different for calculations of leg in and leg out bending.
Depending on the design of the machine, each machine will have a certain capacity of bending. Thus the pressure exerted on the machine members will dictate the limit, before rendering the deflections the members sustain unacceptable or the wear and tear caused on the machine would be excessive. This limit is what is specified as W or S (Section Modulus Capacity) in in3 or cm3.
In general catalogs and brochures describing section bending machines would give the maximum section sizes a machine can bend of each type of structural or bar section. With a minimum diameter the machine can bend them to. By rule of thumb and practice it has been established that the minimum diameter of bars, tubes and pipes is ten times the height of the leg or the dimension taken in the radial direction. For the rest of the sections it is approximately 11 to 12 times the height of the section or the leg.
When a section dimension and thickness is not mentioned on the capacity charts, the user either needs to calculate the section modulus of the section and if this is less than the Section modulus capacity of the machine, he/ she will be in the safe zone and no damage will come to the machine. If in doubt it would behoove the user to contact the manufacturer for professional advice.
Section bending machines have become sophisticated and are using NC and CNC to bend complicated forms. These controls have canned programs for standard sections and they use teach mode where by the operator can produce the part manually and the machine keeps track of all the steps he/ she uses to accomplish the job. Then the program is memorized and archived for continuous use.
The new controls can even collect their own section characteristic data, by bending a piece of the section at different settings. The radius produced at a certain setting is input into the program and by taking three readings, the program surmises the reaction of the section to bending forces; then uses the information when the program parameters are entered and the part is run…at first trial the machine would produce a near perfect part. With small adjustments, what used to take hours of testing, experimenting and developing is cut down drastically.
Controllers have large memory capacity and many job programs are stored and recalled easily. Most units have RS232 communication capability and lately USB ports have been appearing on most of them. There are many operating systems used on these controllers…some are still using DOS, some use Windows and even Linux, while some have proprietary operating systems.
With each passing day, technology is improving, and this is no different for angle roll bending machines. Computers and engineers are largely responsible for section bending machine construction, and this allows for more precise equipment. Some inexperienced shoppers may jump at a machine with greater horsepower or even one that weighs more. Do not be fooled; instead consider these things when buying: reliability and durability of materials used in the machine’s construction, solid design, and of course ease of maintenance.