CS247175B2 - Method of ribs forming on tubes - Google Patents

Abstract

A method of drawing ribs on tubes in characterized by that into the material of the tube from which the rib is drawn initial compressive stresses are introduced of the quantity preferably <MATH> where Fo denotes the area of the cross-section of the tube before drawing, Fr denotes the area of the cross-section of the core of the tube after drawing the rib, and Re is the plasticity limit. Next, ribs are drawn by driven tools with rolling-form-disks by the known method.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method for forming ribs on tubes, in particular ribs of low pitch on tubes of difficult-to-form materials.

Until now, the production of ribs on tubes by forming, also called rolling, has been carried out in heads, generally comprising three symmetrically arranged rollers composed of multiple rollers. The axis of each roll forms a constant angle with the rolling axis, which is the axis of the tube.

The value of this angle results from the geometric dependence of the helical contour of the ribs formed on the pipe. The rollers are driven by a rotational movement, so that upon introduction of the tube into their zone of operation, the rollers transmitting the rotary movement to the tube face the rib.

The shaping of the ribs on the tube is the result of a corresponding state of stress in the tube material causing plastic deformation in the material's zone of operation. The tube material deforms in the tool operating range in the axial and radial directions. The radial strain is manifested in the form of an increase in the diameter of the ribs and the axial strain is manifested in the form of an extension of the pipe.

The elongation of the tube during the forming of the ribs is a disadvantageous phenomenon because the size of the elongation is randomly variable for each section of the tube. This forces technological additions and therefore leads to waste.

The axial deformations of the pipe are caused by the corresponding axial stresses which the tool exerts in the area of its operation. Due to these stresses, the tool is subjected to very high axial loads. These loads cause the wheels of the tool to bend. As a result, the rib spacing is not uniform and is always greater than the spacing of the discs. A major problem with the rib forming methods used hitherto is the low tool life of the tool whose wheels are destroyed by the fatigue-inducing bending loads.

Polish Patent Specification No. 113419 discloses the construction of a tool using an additional disk that reinforces the tool and increases its durability. However, such a solution does not require an extension of the tube and it is difficult to form ribs of very small pitch on tubes of materials of high deformation resistance, since the increase in the load in the axial direction of the tool is considerably greater than the possibility of increasing the rigidity of the tool.

U.S. Pat. No. 3,876,593 discloses a method of manufacturing double-layer finned tubes using blocking the possibility of elongating the tube on which the ribs are formed. This blocking consists in clamping the end of the outer tube on the inner tube and then starting the forming process from the second, free end of the tube.

When forming the ribs in this way, different axial stresses can be observed along the length of the pipe. In the first phase, when the rib forming starts from the free end of the tube, the axial stresses in the undeformed portion of the tube continuously increase until a certain state of stress equilibrium is reached in the outer tube material.

At the same time, as a result of increasing axial stresses in the outer tube from the value of 0 at the beginning to the value corresponding to the equilibrium state, the rib diameter increases from a certain initial value to the desired value.

Pipe axes with different rib diameters usually do not meet the dimensional tolerance requirements and are waste material. A disadvantageous phenomenon of the first forming phase is also the excessive bending load of the tool wheels.

The principle of the method of forming the ribs on the tubes according to the invention is that the material of the tube from which the ribs are formed is given an initial compressive stress of (0.2).

0,7)

Fo - Fr

Fo = Re where Fo denotes the cross-sectional area of the tube before forming Fr denotes the cross-sectional area of the core of the tube after forming the rib and Re is the yield strength and then, while maintaining the initial compressive stress in the tube material,

By introducing an initial state of compressive stress into the material of the deformed tube, the tool is relieved from the stresses in the direction of the axis that bend the roll disks, practically in the first phase of contact of the tool with the material. Another effect of introducing an initial state of compressive stress is to remove the axial extension of the tube. Under these conditions, the work of the tool is limited to imparting plastic deformation to the pipe in the radial direction.

By manufacturing the finned tubes in the manner described, tubes of the same shape are obtained over their entire length while maintaining a high service life of the tools. With a tool free of harmful bending stress, ribs of very low pitch and high height can be formed from a material having a high yield point.

The method according to the invention for forming ribs on tubes is described in more detail with reference to the drawings in which Fig. 1 shows a tube clamped by a screw and a pressure stress diagram of this tube. and Fig. 4 is a cross-section of the tube after the rib forming.

The tube 2 was clamped by the screw 2 prior to the forming of the ribs, thereby causing a starting pressure stress of a certain value. The value of this voltage is preferably

Fo

Claims (1)

where Fo is the cross-sectional area of the pipe before drawing, Fr is the cross-sectional area of the pipe core 2 P ° rib forming 4 and Re is the yield strength of the pipe material. After initial clamping the tube _1 screw ^{2, the} tube is introduced into the zone of the action of driven tools 5 * provided with rolling wheels 2 · ^p s forming the ribs 4 axial stresses on the blade 2 does not act, which enables obtaining very small pitches of ribs, and the material is subjected to plastic strains only in the radial direction. OBJECT OF THE INVENTION Method of forming ribs on tubes rotatably driven, characterized in that the material The tube from which the ribs are formed is given an initial axial compressive stress of (0.2-0.7) ^Fo ~ ^Fr. Re, Fo where Fo denotes the cross-sectional area of the pipe prior to forming, Fr denotes the cross-sectional area of the pipe after the rib forming and Re is the yield strength, and then, while maintaining the initial no compressive stress in the pipe material, faces the rib zone.