April 11, 2006
Modern flying shear tube cutoff systems comprise state-of-the-art mainframes, tools, and controllers. This article, Part I of a two-part series, discusses the different types of mainframes, their capabilities, and construction. It describes and includes images of the construction process from start to finish.
The current generation of flying shear tube cutoff systems is even better-suited for the application than previous versions. With mainframes made from high-strength steel; tools made of lightweight, high-strength materials; and controls that use up-to-date programmable logic controllers with software developed over years of experience, today's machines process a wider range of tube and pipe specifications, including diameters from 0.250 in. to 6.625in., wall thicknesses from 0.020 in. to 0.250 in., speeds from 50 feet per minute (FPM) to 1,250 FPM, and lengths from 1 ft. to 90 ft. or more.
This article, Part I of a three-part series, covers the flying cutoff system mainframe.
Vertically disposed mainframes, such as the one shown in Figure 1, are applied to round tube with a limited range of shapes. These machines use dimple-free tooling to cut the round tube. Shapes, which typically are presented to the cutoff with the diagonal corners located at or near the vertical plane, are cut with single-cut tools that provide minimum end-cut distortion.
Reclined mainframes, like the unit shown in Figure 2, are used in tube mills that produce mostly shapes. Shapes presented to this machine with flats parallel to the floor are cut with single-cut tools. Because the machine is reclined at 45 degrees to the floor, the shear blade passes through the shape at or near the diagonal corners of the various shapes for minimum end-cut distortion. Rounds are cut with dimple-free tools that yield minimum-distortion cut ends.
The overall mainframe length varies with the tube cut time and speed specifications. The tube cut time varies depending on the diameter and wall thickness (D/T) ratio and material specifications.
In one example, tube cut time usually is fixed at approximately 0.2 second when D/T ratios are 10-to-1 or greater and the material is limited to mild steel. A fixed 0.2-second cut time has no effect on the overall mainframe length for a given speed specification.
Alloy steel, stainless steel, and mild steel tubing with D/T ratios of 6-to-1 or greater require very slow shear blade speeds that result in tube cut times as low as 1.0 second. Such long cut times have a significant effect on the overall mainframe length for a given speed specification. In this case, a variable-speed drive controls blade speed (tube cut time); the operator is given three speed settings. This variable-speed feature provides the opportunity to maintain maximum yield for a range of materials and D/T ratios. It provides the additional benefits of improved tool life and end-cut quality associated with optimized blade speeds.
Mainframe Construction, View 1
Mainframe Construction, View 2
The mainframe starts out as a welded construction fabrication as shown in Figures 3and 4. At the weld fabrication operation, multipass, heavy-duty submerged-arc welds are applied to all joints of the mainframe assembly.
Large bosses are welded in place as required to suit critically located main drive gear bearings, crankshaft bearings, and ram drive components (see Figure 5). These bosses, together with the overall heavy-duty mainframe design, are essential for long-term performance and system reliability.
The weld fabrication operation usually takes about 80 labor-hours. When all of the weld fabrication is completed, the finished mainframe is heat-treated, sandblasted, and primed as shown in Figure 6.
Beginning Final Assembly
Following weld fabricating, the mainframe then is machined to close tolerances using a boring mill (see Figure 7). This operation usually takes approximately 100 labor-hours with the mainframe repositioned on the floor-mounted boring mill table at least six times.
Fitting, Testing Components, View 1
Fitting, Testing Components, View 2
The mainframe and its components are staged at the final assembly floor upon completion. At this point all components are inspected against detailed drawings. When each part meets final inspection criteria, final assembly begins (Figure 8). Here all mainframe components, including the main drive, gears, crankshaft, ram, and rails, are fitted and tested before the accelerator and tooling are installed (see Figure 9 and Figure 10).
After all of the mainframe components are fitted (Figure 11), the mainframe is subjected to a manual operation test before the tools, accelerator, and controls are added.
Parts II and II will cover up-to-date tools, die set accelerators, and controls.