JP2005179146A - Squeeze roll for producing electric resistance welded pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a squeeze roll for producing an electric resistance welded pipe, the squeeze roll being prevented from being broken by thermal shock when it is used by improving thermal shock resistance and strength of a silicon nitride-based ceramic. <P>SOLUTION: The squeeze roll for producing the electric resistance welded pipe is used for producing the electric resistance welded pipe, wherein at least a part brought into contact with a base material for the electric resistance welded pipe is formed from a sintered compact containing silicon nitride as a main component, and the sintered compact has a thermal conductivity at normal temperature of ≥50 W/(m×K). Further, the sintered compact containing silicon nitride as the main component contains aluminum in an amount of ≤0.2 wt.% and oxygen in an amount of ≤5.0 wt.%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ceramic squeeze roll used for manufacturing an electric resistance welded tube.

  ERW pipes used for hot water supply pipes, water supply pipes, heat exchangers for air conditioning equipment and refrigeration equipment, etc. are rolled into a tubular shape while running a strip-like material made of copper, brass, aluminum, stainless steel, etc. It is formed and welded by a welding means comprising a high frequency dielectric welder, a high frequency resistance welder or the like, and continuously welded while feeding both end edges of the material. At the time of welding, both ends of the material rounded in a C shape are heated by a high frequency dielectric welding machine including a work coil such as an induction heating coil or a ferrite core, and Joule heat is generated intensively at both ends. The raw material is rolled into a C-shape, and both end edges heated when passing between a pair of left and right squeeze rolls are pressed and abutted to be welded to form a tube.

  The squeeze roll for manufacturing ERW pipes has a thread-wound shape with a constricted central part, and the roll surface that is the contact surface with the pipe material has an arc shape corresponding to the cross-sectional outline of the pipe after molding. It is formed on a curved surface. Since the squeeze roll comes into contact with and slides on a material heated to a high temperature in a high stress state, the squeeze roll is required to have sufficient strength to withstand the stress during sliding as well as wear resistance. In addition, since it is placed immediately after high-frequency welding, it tends to become high temperature due to heat conduction from the high-temperature welding bead and induction heating, and sufficient thermal shock resistance is also required.

  In Patent Document 1, in a ceramic squeeze roll having a forming surface that forms an arc having a predetermined radius in a cross section including a rotation axis, the edge portion including one edge of the forming surface in the cross section is in the edge direction. Describes a squeeze roll characterized in that it is formed in an outwardly spreading shape. Moreover, silicon nitride, alumina, silicon carbide and the like are listed as ceramics constituting the squeeze roll.

  In Patent Document 2, a squeeze roll is composed of a ceramic sintered material containing 40 to 70 wt% titanium nitride and 20 to 60 wt% silicon nitride in total and having a bending strength of 1000 MPa or more. It is described.

JP-A-8-103815 Japanese Patent Laid-Open No. 10-194838

  The wear resistance is improved by forming the squeeze roll with a silicon nitride ceramic sintered body. However, the conventional silicon nitride ceramics are not particularly satisfactory in terms of thermal shock resistance and strength, and may be destroyed by thermal shock during use.

  Accordingly, an object of the present invention is to provide a squeeze roll for manufacturing an electric resistance welded tube that can improve the thermal shock resistance and strength of silicon nitride ceramics and can be prevented from being broken by thermal shock during use.

  The squeeze roll for manufacturing an electric resistance welded tube according to the present invention comprises at least a part of the sintered body mainly composed of silicon nitride which is in contact with the electric resistance welded tube material, and the sintered body has a thermal conductivity of 50 W / ( m · K) or more.

  In the present invention, the sintered body containing silicon nitride as a main component has an aluminum content of 0.2% by weight or less and an oxygen content of 5.0% by weight or less. In addition, the sintered body mainly composed of silicon nitride has a relative density of 98% or more and a four-point bending strength at room temperature of 700 MPa or more. In addition, an R portion or a chamfered portion is provided on a shoulder portion of the caliber that comes into contact with the electric sewing tube material of the squeeze roll.

  The present invention increases the thermal conductivity of the material forming the squeeze roll itself, so that the heat generated by the temperature rise and cooling reaches the inside through the surface of the roll quickly in the manufacturing process of the ERW pipe, and the thermal shock resistance is improved. Rise. The conventional silicon nitride ceramic sintered body has a thermal conductivity at room temperature of about 30 W / (m · K) at most, but the silicon nitride ceramic sintered body in the present invention exists as an impurity in the sintered body. By reducing the content of aluminum and oxygen, preferably the content of aluminum in the sintered body is 0.2% by weight or less and the content of oxygen is 5.0% by weight or less at room temperature. The thermal conductivity can be 50 W / (m · K) or more. The thermal conductivity at normal temperature is more preferably 60 W / (m · K) or more.

  Different types of ions present as impurities in the silicon nitride-based sintered body, particularly aluminum and oxygen, become phonon scattering sources and reduce the thermal conductivity. The silicon nitride-based sintered body is composed of a silicon nitride particle phase and a surrounding grain boundary phase, and aluminum and oxygen are contained in each of these two phases. Since aluminum is close to the ionic radius of silicon, which is a constituent element of silicon nitride, it easily dissolves in silicon nitride particles. Due to the solid solution of aluminum, the thermal conductivity of the silicon nitride particles themselves is lowered, and as a result, the thermal conductivity of the sintered body is significantly lowered.

  Further, since an oxide is mainly added as a sintering aid, most of oxygen exists as a grain boundary phase component. In order to achieve high thermal conductivity of the sintered body, it is important to reduce the amount of the grain boundary phase having a lower thermal conductivity than the silicon nitride particles of the main phase. Therefore, when the total area ratio of the silicon nitride particles and the grain boundary phase constituting the silicon nitride ceramic sintered body is 100% on the surface of the silicon nitride ceramic sintered body, the silicon nitride particles have an area ratio of 70. It is desirable to occupy ~ 99.9%.

  Furthermore, it is desirable that the silicon nitride ceramic sintered body has a relative density of 98% or more and a four-point bending strength at room temperature of 700 MPa or more so that it can sufficiently withstand mechanical stress and impact. Further, when the shoulder portion of the caliber that comes into contact with the electric squeeze tube material of the squeeze roll is a corner portion, the surface of the material to be molded may be wrinkled. In order to prevent this, it is desirable to provide a rounded portion or chamfered portion on the shoulder portion of the caliber that comes into contact with the ERW material. Preferably, an R portion of 0.3 mm or more or a chamfered portion of 0.3 mm or more is formed.

  FIG. 1 shows an example of an electric resistance tube manufacturing process using the squeeze roll for manufacturing an electric resistance tube according to the present invention. In FIG. 1, the electric sewing tube material 3 proceeds in the direction of the arrow and is heated by the dielectric coil 5 in the middle. Thereafter, the electric sewing tube material 3 is press-formed into a steel tube by a pair of squeeze rolls 1 for manufacturing the electric sewing tube. The squeeze roll 1 has a thread-wound shape with a constricted central portion, and the roll surface 2 which is a contact surface with the ERW tube material 3 has an arcuate curved surface whose cross-sectional shape corresponds to the cross-sectional outer shape of the tube after molding. (So-called caliber) is formed. The end portion of this caliber, that is, the rounded portion R or chamfered portion of the shoulder portion 6 is formed. By using such a squeeze roll, the final electric welded tube molded body 4 is manufactured.

  The squeeze roll for producing an electric resistance welded tube of the present invention was produced as follows. First, a silicon nitride powder having an average particle size of 0.5 μm, 3.0 wt% magnesium oxide powder having an average particle size of 0.2 μm, and yttrium oxide powder having an average particle size of 2.0 μm as a sintering aid are used. 0% by weight was added, an appropriate amount of a dispersant was added, and the mixture was pulverized and mixed in ethanol. Subsequently, after spray drying, the mixture was granulated through a sieve, filled in a rubber mold, and subjected to cold isostatic pressing (CIP) with hydrostatic pressure to produce a molded body. This formed body was fired for a predetermined time in an inert gas atmosphere at 1700 to 1900 ° C. to obtain a squeeze roll for manufacturing an electric resistance welded tube made of a silicon nitride ceramic sintered body.

  Further, from the silicon nitride ceramic sintered body of the present invention, a test piece for measuring thermal conductivity and density having a diameter of 10 mm × thickness of 3 mm and a four-point bending test piece having a length of 3 mm × width of 4 mm × length of 40 mm are collected. did. The density was determined from the Archimedes method based on JIS R2205. The relative density was obtained by dividing the measured density by the theoretical density calculated by calculating the measured density by the Archimedes method based on JIS R2205. The thermal conductivity was calculated by measuring the specific heat and thermal diffusivity at room temperature in accordance with the laser flash method JIS R1611. The 4-point bending strength was measured according to JIS R1601 at room temperature.

  Further, the area% of the silicon nitride particles was obtained by individually taking out the silicon nitride particles by eluting the grain boundary glass phase with hydrofluoric acid from the sintered body and observing it with an SEM. The aluminum content in the silicon nitride-based sintered body was measured by an induction plasma emission analysis method (abbreviated as ICP method), and the oxygen content was measured by an infrared absorption method.

  The silicon nitride-based sintered body forming the squeeze roll for manufacturing the electric resistance welded tube of the present invention has a relative density of 99%, a thermal conductivity of 68 W / (m · K) at room temperature, and a 4-point bending strength at room temperature of 900 MPa. there were. Further, when the total area ratio of the silicon nitride particles and the grain boundary phase constituting the silicon nitride ceramic sintered body was 100%, the silicon nitride particles were 95% in area ratio. Further, the aluminum content in the silicon nitride sintered body was 0.02% by weight, and the oxygen content was 0.5% by weight.

  Using the squeeze roll for manufacturing the electric resistance welded tube of the present invention, it was tested in an actual electric resistance welded tube manufacturing process line that receives a thermal shock due to temperature rise and cooling. As a result, the wear resistance was good, the strength was sufficient, and the thermal conductivity was 50 W / (m · K) or higher, so that no phenomenon of breaking the roll due to thermal shock during use was observed.

  According to the squeeze roll for producing an electric resistance welded tube of the present invention, the squeeze roll is made of a silicon nitride material having high thermal conductivity, so that the squeeze roll is hardly broken and has a long service life and a high quality electric resistance welded tube. Can be produced stably.

It is a figure which shows an example of the electric sewing pipe manufacturing process using the squeeze roll for electric sewing pipe manufacture of this invention.

Explanation of symbols

1 squeeze roll, 2 roll surface, 3 ERW material, 4 ERW molded body,
5 Dielectric coil, 6 shoulder

Claims (4)

A squeeze roll used for manufacturing an electric resistance welded tube, wherein at least a part of the squeeze roll that comes into contact with the electric resistance welded tube material is a sintered body mainly composed of silicon nitride, and the sintered body has a thermal conductivity at room temperature. A squeeze roll for manufacturing an electric resistance welded tube characterized by being 50 W / (m · K) or more. 2. The battery according to claim 1, wherein the sintered body containing silicon nitride as a main component has an aluminum content of 0.2 wt% or less and an oxygen content of 5.0 wt% or less. Squeeze roll for sewing tube manufacturing. The sintered body mainly comprising silicon nitride has a relative density of 98% or more, and a four-point bending strength at room temperature of 700 MPa or more. For squeeze rolls. The squeeze roll for manufacturing an electric resistance tube according to any one of claims 1 to 3, wherein an R portion or a chamfered portion is provided on a shoulder portion of the caliber which comes into contact with the electric resistance tube material of the squeeze roll.