JPH03170604A - Manufacture of clad tube using powder - Google Patents

Abstract

PURPOSE:To easily manufacture a sound clad tube without any porosity at a low cost by executing hot extruding work to a hollow billet enclosing metal powder after packing the metal powder to the specific packing density between an outer pipe and an inner pipe assembled to be concentric. CONSTITUTION:A metallic cylinder composed of the outer pipe 1 made of a carbon steel, etc., and the inner pipe 2 made of mild steel, etc., is assembled concentrically. The metal powder 3 of satellite alloy, 'Hastelloy alloy(R)', etc., is packed into between double tubes constituted like this and a cover 4 is fixed. Then, vibration packing is executed and packing density of metal powder 3 is made to >=55% of the theoretical density. After that, evacuation is executed from degassing hole 5 arranged to the cover 4 while heating the above billet and the billet is sealed. Further, the above hollow billet is heat to the prescribed temp. and the hot extruding work is executed. Then, it is desirable to execute the hot extruding work under the condition that the cross sectional area of the metal powder packed part in the cross section at the right angle to the extruding direction is made to 10-60% of the total cross sectional area. In this way, the sound clad tube of difficult-to-work without any thickness deviation, can be easily obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a clad pipe in which different materials are combined to impart different characteristics to the inner and outer surfaces of the pipe.

[Conventional technology]

Double pipes whose inner surfaces are clad with wear-resistant alloys or corrosion-resistant alloys are used for cylinders for injection molding machines that require inner wear resistance, and for chemical plant piping that requires inner corrosion resistance. .

Such internally clad pipes are manufactured by hot extruding billets made by filling the gap between double pipes with metal powder. However, if the density of the metal powder part in the billet to be hot extruded is not set to at least 80% of its theoretical density, the powder part will not be sufficiently heated during the heating stage of the billet for hot extrusion. Cracks become more likely to occur during hot extrusion, or the hot extruded cladding layer cannot form a healthy structure free of volocity (the presence of which deteriorates wear resistance and corrosion resistance). Therefore, for example, in JP-A No. 62-44504, this billet is pre-pressurized by cold isostatic pressing.
Alternatively, a method is used in which the billet is hot extruded after pre-pressing with hot isostatic pressing to further increase the density of the powder.

[Problem that the invention seeks to solve]

However, when pre-pressing as described above is carried out, the billet is deformed, and furthermore, if the metal wall of the billet is thin, wrinkles and cracks occur, making hot extrusion impossible.

Furthermore, various solutions to this problem have been considered, but the shape of the billet becomes complicated, and after the preliminary pressurization,
In some cases, machining may be required again. Therefore, the cost of manufacturing clad pipes by hot extrusion using metal powder, including the cost of pre-pressing, is extremely high.

The present invention was devised in view of the above-mentioned problems of the prior art, and does not require pre-pressing by cold or hot isostatic pressing as described above, and directly hot-presses billets filled with metal powder. The purpose of the present invention is to provide a method by which inner clad pipes made of difficult-to-process alloys such as Stellite alloy with excellent abrasion resistance and Hastelloy alloy with excellent corrosion resistance can be manufactured more easily and at lower cost by extrusion. It is something.

[Means for solving problems]

Therefore, as a way to obtain a clad tube by directly hot extruding without pre-pressurizing, in the present invention, metal powder is inserted between the double tubes constructed by assembling metal cylinders concentrically. When filling, we investigated whether or not the vibration filling method, which is currently used as a powder filling method, could be adopted. That is, when billets are produced by filling a double tube with metal powder using the vibratory filling method, each filling density is made different, and these billets are directly hot extruded to form a sound cladding layer without porosity. We investigated and researched the conditions for obtaining . As a result, by directly hot extruding a billet with a metal powder packing density of 55% or more of the theoretical density, we can produce inner clad pipes with excellent wear resistance and corrosion resistance, which have a sound cladding layer without voluminousness, at a low cost. It was discovered that it can be manufactured using Furthermore, in the process of these investigations and researches, it was found that in the shape of a billet filled with metal powder, the thickness and shape of the cladding layer were made uniform by increasing the amount of metal relative to the total cross-sectional area of the billet at right angles to the hot extrusion direction. We have also found that this can be achieved by making the cross-sectional area of the powder-filled part between 10% and 60%. [Function] When hot extrusion is performed directly after metal powder has been filled by the vibratory filling method, the heated billet is loaded into the container of the hot extruder, and is then filled with metal powder by the mandrel bar and extrusion stem. During the absetting process, in which the cladding pipe is extruded from between the die and the mandrel bar under pressure, the metal powder is densified under high pressure as the outer and inner pipes of the billet deform. become. That is, in the conventional manufacturing process, the powder is solidified by hot isostatic pressing or cold isostatic pressing, but in the present invention, this is done in the absetting process. If the vibration packing density of the metal powder into the billet is 55% or more, the porosity of the metal powder will almost completely disappear during this process, and the densification will be completed at the stage of passing through the die part. be judged. Under normal hot extrusion conditions for clad pipes, the extrusion ratio is in the range of 5 to 15, but even if the extrusion ratio is increased, the metal powder filling density of the billet is 5 to 15.
If it is lower than 5%, it is estimated that densification will not proceed sufficiently even in the above-mentioned absetting and extrusion processes, and as a result, volocity will remain in the cladding layer after extrusion.

On the other hand, the thickness and shape of the hot extruded cladding layer vary greatly depending on the cross-sectional area of the metal powder portion relative to the total cross-sectional area of the billet. If this area ratio is less than 10%, the deflection will be significantly large.

If it exceeds 60%, the thickness of the cladding layer at the tip of the hot extruded material will increase abnormally, the uniform thickness in the longitudinal direction of the tube will be significantly reduced, and a part of the cladding layer will overlap with the outer tube material. It may break through and cause scratches on the outer surface, reducing the yield of the pipe. [Examples] Specific examples of the present invention will be described below.

As shown in Fig. 1, carbon steel (SCM 440) is used as the outer tube material (1), mild steel is used as the inner tube material (2), and stellite alloy (1%C-30%Cr-4.5%W-Co ) of Ar
Atomized powder (350 μm or less) and Hastelloy alloy (
tS%Cr-16%M-3.5%W-7%Fe-Ni)
After vibrating and filling the same powder (3) into the double tube, the deaeration hole (4)
A billet was produced by welding the attached mild steel lid (5) (
The billet has an outer diameter of 80 mm, an inner diameter of 30 nm, and a length of 250 nm.
Two types were manufactured: one with an outer diameter of 210 m, an inner diameter of 50 m, and a length of 500 m).

Further, while drawing a vacuum through the deaeration hole (4),
After heating at 600°C for several hours, it was sealed. Then, this billet is heated to a temperature of 1150 to 1200°C for 3 to 4 hours,
Then, hot extrusion was carried out at an extrusion ratio of 5 to 16 to produce a clad pipe as a test material.

The packing density of each billet was varied by changing the filling weight and vibration intensity.

The table below shows the density (%) and powder filling area ratio (%) relative to the theoretical density of the powder part after vibration filling of the prototype clad pipe.
, the hot extrusion conditions and the presence or absence of porosity in the crund layer of the manufactured tube are shown. As is clear from the table, when the density of the powder after vibration filling is 55% or more, no volocity is detected in the cladding layer of the extruded material, regardless of the alloy or extrusion conditions, and the cladding layer of the extruded material is healthy. It is clear that extrusion is achieved.

Further, FIG. 2 shows the results of hot extrusion of billets in which the ratio of the powder-filled portion to the total cross-sectional area of the billet was varied from 5% to 80%. If the value is less than 10%, a large thickness deviation has occurred in the cladding layer. Moreover, when it exceeds 60%, the thickness of the unsteady parts at the top and bottom of the cladding layer increases abnormally, and a phenomenon in which a part of the unsteady part breaks through the outer pipe (carbon steel) is observed, and as a result, the outer pipe (carbon steel) 1) A large scratch occurred on the surface over the entire length.

〔Effect of the invention〕

As described in detail above, according to the present invention, stellite alloys, which are difficult to process, can be produced by direct hot extrusion without pre-pressing using conventional cold isostatic pressing or hot isostatic pressing. It is possible to manufacture at low cost a double-walled pipe or the like whose inner surface is clad with Hastelloy alloy, and a great effect can be expected in the use of metal pipes or the like that require wear resistance or corrosion resistance.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a powder-filled billet, and FIG. 2 is a graph showing the influence of the powder-filled area ratio on the total cross-sectional area of the billet on the extrusion characteristics of the clad pipe. In the figure, (1) is the outer tube, (2) is the inner tube, (3) is the powder, and (4
) indicates the lid, and (5) indicates the deaeration hole. Fig. 1 Fig. 2 Fig. 0 20 40 60 80 100 Powder section ink (%)

Claims (2)

[Claims] (1) In a method for manufacturing a clad pipe, in which metal powder is filled between a double tube formed by assembling metal cylinders concentrically, and then hot extrusion is performed on a hollow billet that is sealed. , the metal powder is filled between the double tubes by vibration filling, and the packing density is 55% of the theoretical density of the metal powder.
A method for manufacturing a clad pipe using powder, characterized by the above steps. (2) In the method for manufacturing a clad pipe described in the preceding paragraph, hot extrusion is performed so that the cross-sectional area of the metal powder filled portion is 10% or more and 60% or less of the total cross-sectional area of the billet in a cross section perpendicular to the hot extrusion direction. A method for manufacturing a clad pipe using the powder according to claim 1.