JPH01152219A - Heat treating method for preventing bending of cast iron tube - Google Patents

Abstract

PURPOSE:To execute heat treatment while preventing bending of a cast iron tube by supporting the cast iron tube having more than recrystallization temp. with plural points of parallel rollers and cooling at less than the recrystallization temp. under rotating/supporting condition. CONSTITUTION:Plural lines of the rotating roller line 4A-4D composing of the plural rotating rollers 6 as parallel setting at the prescribed interval are arranged on a supporting frame 3 and rotating-driven with a rotated driving device 5 containing a motor 9, etc. The ductile tube 1 having the temp. more than the recrystallization temp. just after centrifugal casting and heating in an annealing furnace is carried on the rotated supporting device 2 and supported while rotating the tube 1 with the above roller 6 brought into contact with three or more points on the straight line as parallel with the tube axis. Under this condition, the ductile tube 6 is air-cooled or forcedly cooled to make lower temp. than the recrystallization temp. By this method, the development of the bending of the ductile tube 6 under the heat treatment is prevented and also by straightening the deformation already developed, the high quality cast iron tube can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for heat treating cast iron pipes to prevent bending.

BACKGROUND OF THE INVENTION Normally, ductile pipes are centrifugally cast and then annealed to form ferrite. Conventionally, this annealing involves heating the ductile tube/pipe in a heating furnace to a predetermined temperature (recrystallization temperature) or higher, pulling the heated ductile tube out of the heating furnace, placing it on a table, and then cooling it naturally or by water cooling. This was a method of cooling.

Problems to be Solved by the Invention According to the conventional heat treatment method described above, the hearth of the annealing furnace may be poorly maintained, or the ductile tube may be cooled while being supported stationary on a pedestal, resulting in problems due to its own weight or uneven cooling. As a result, bending occurs, which requires straightening using a hydraulic straightening machine after cooling is completed, which poses a problem in that the work is extremely time-consuming. Furthermore, since straightening is performed after cooling is completed, it is not possible to completely remove bends and scratches, which causes quality deterioration.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for heat treating cast iron pipes that can solve the above problems.

Means for Solving the Problems In order to solve the above-mentioned problems, the heat treatment method for 915 iron pipes of the present invention provides that, when annealing the cast iron pipes, the pipe axis of the cast iron pipes is heated at a temperature equal to or higher than the recrystallization temperature immediately after heating. Supported in a rotating state by rollers that touch at three or more points on a straight line parallel to the
This is a method of cooling to a temperature lower than the recrystallization temperature in this rotationally supported state.

Effect: According to the heat treatment method described above, the cast iron pipe is cooled while being rotated once by a loaf that touches the pipe at three or more points on a straight line parallel to the pipe axis. can be straightened.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

First, the ductile pipe (
The rotation support device 2 for a cast iron pipe) 1 will be explained. This rotation support device 2 includes a pedestal 3 and a plurality of rows of rotating rollers 4A, 4B, 4C, 4 arranged on the pedestal 3 in a plurality of rows, for example, four rows.
D, and a predetermined rotating roller row 4A among this rotating roller row.
, 4C, and a rotation drive device 5 for rotating them. In addition, each of the above rotating rows 9 rows 4A, 4B, 4C,
4D is constructed by arranging a plurality of rollers 6, for example, 5 times each, at predetermined intervals corresponding to the length of the ductile pipe 1, and the above-mentioned rotary drive device.
Reference numeral 15 denotes a rotating shaft 7 disposed below the rotating roller row of the pedestal 3, and a rotating shaft 7 and a predetermined rotating roller row 4A, 4C.
It is composed of a Nuproket 9, 10 and a chain 11 that interlock and connect the support shaft 8 of the rotary loaf 6, and an electric motor (not shown) that rotates the rotary shaft 7.

Therefore, each rotating roller row 4A:4B, 4B:4C,
If three ductile tubes 1 are ahaed between 4C and 4B and the electric wander is driven, each ductile tube 1 will be rotated in a predetermined direction at a predetermined speed.

Next, a heat treatment method (annealing) of the ductile pipe 1 will be explained.

After heating the centrifugally produced ductile tube 1 to a predetermined temperature in a heating furnace, it is transferred onto a rotating support device 2 and supported between rotating roller rows 4A:4B, 4B:4C, 4C:4B.

The temperature of the ductile tube 1 at this time is the recrystallization temperature (550
℃), for example, about 650°C. Then, the rotary drive device 5 cools the rotary roller 6 in a predetermined direction, that is, the ductile tube 1, to a lower temperature than the recrystallization temperature while rotating the ductile tube 1 i times in a predetermined direction.

Cooling is basically air cooling (cooling rate: 60°C/min)
, target diameter 751XM to 100ff), but forced cooling may be used.

That is, air cooling may be performed using a blower or the like, or two fluids of air and water may be sprayed in the form of a mist (particularly on the inner surface of the tube). Promptly cooling to a temperature lower than 550°C by uniform forced cooling is effective in improving productivity. In this way, cooling while rotating can prevent bending and wrinkles, and even if the tube has creep deformation due to its own weight or deformation due to uneven cooling, that is, bending and wrinkles, the rotation of the tube can prevent the occurrence of bending. In addition, the curvature is corrected by coming into contact with a rotating roller.

In the above embodiment, the ductile tube is cooled by one rotary support device, but if the cycle time of the heating furnace is short, multiple rotary support devices may be provided to sequentially transport the ductile tube. , it may be cooled to a predetermined temperature.

Furthermore, in the above embodiment, a plurality of rotary loaves are arranged at predetermined intervals for each row of rotary rollers, but a long one-piece loaf may also be used.

Effects of the Invention According to the heat treatment method of the present invention described above, since the cast iron pipe heated to a temperature higher than the recrystallization temperature is cooled to a temperature lower than the recrystallization temperature while being passed through the mouth, creep deformation due to its own weight or deformation due to uneven cooling occurs. That is, even if a bend occurs, the straightness is naturally corrected by 1/C, and therefore the conventional correction work using hydraulic pressure is not necessary. Furthermore, since straightening is performed from around the recrystallization temperature, almost no bending remains after cooling is completed, and quality can be improved.

[Brief explanation of the drawing]

The drawing is a side view of a ductile pipe rotation support device used in an embodiment of the present invention. l...Ductile pipe, 2...Rotation support device, 4A,
4B. 4C, 4D... Rotating roller row, 5... Rotating drive device, 6... Rotating loaf. Agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. When annealing a cast iron pipe, the cast iron pipe is supported in a rotating state by rollers that touch at three or more points on a straight line parallel to the pipe axis at a temperature higher than the recrystallization temperature immediately after heating, and this rotational support A heat treatment method for preventing bending of cast iron pipes, characterized by cooling the pipes to a temperature lower than the recrystallization temperature.