Machinery's Handbook, 31st Edition
Pipe and Tube Bending 1461 or bending machines with fully automatic control, however, all functions are available automatically. These bending machines can be supplemented with automatic feeding and unloading systems for the production of large series without any problems. Compression Bending.— Compression bending is a process whereby pipe or tube is bent to a reasonably tight radius, usually without the use of mandrel or precision tooling. It is accomplished by clamping the tube/pipe behind the rear tangent point and then by a wiper shoe on a rotary arm rolling or compressing the material around and onto a bending die (Fig. 70).
Clamp
Clamp
Workpiece
F
F F
Wiper shoe
v
Wiper shoe
F
Tangent Fixed bending die
a) Starting Position
b) Ending Position
Fig. 70. Compression Bending Roll Bending.— Roll bending is used for bending tube/pipe to a large radius (i.e., to a large circumference). Pipe and tube roll benders comprise three rolls on separate shafts; the tube or pipe is rolled through the rolls while the top roller exerts downward pressure on the top roll to deform the tube or pipe (Fig. 71). Roll pipe and tube benders are available in 2- or 3-driven roll machines, with either manual or hydraulic adjustment of the top roll. This tube/pipe bending process is ideal for forming helical pipe coils for heat transfer applications, as well as for making long sweeping sections such as those used in steel con struction-curved trusses and roof components for structures requiring large open spaces. Pipe cross sections are defined very little when such sweeping sections are formed. The oldest method of bending a tube/pipe consists of first packing it with loose particles (usually sand) and then bending it into a suitable tool. The filler functions to prevent the tube from buckling inward. After the tube has been bent, the sand is shaken out. Workpiece
Adjustable roll
F
Workpiece
Driven rolls
a) Starting Position
b) Ending Position
Fig. 71. Roll Bending Use of Filling Material in Bending.— A simple method of preventing distortion consists of using filling material inside the pipe, supporting the walls to prevent flattening at the bend. Dry sand is often used. Materials such as resin, tar, or lead are also sometimes employed. The pipe is first filled with the molten resin, lead, or low-melting-point alloy, and then after bending, the pipe is heated to melt and remove the filling material. Resin has often been used for bending small brass and copper pipes, and lead or other alloys for
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online