A method for preparing a multilayer metal composite pipe includes steps of: internally and externally grinding blank pipes; cleaning oil stains; assembling a multilayer metal pipe; drawing to reduce a diameter; performing high-speed friction welding at the pipe ends; performing heat treatment; performing four-roller cross-rolling; straightening; performing two-roller cold-rolling; performing cold-drawing to reduce the diameter; performing cold-expansion to reduce the diameter; performing precise cold-rolling; degreasing; brightening; performing surface grinding; cleaning dust; detecting multilayer metal interface bonding; detecting flaws; testing metal structure performance; and sizing and packaging. By cycling the cold-drawing, the cold-expansion, and the precision cold-rolling, key indicators such as product dimensional accuracy, surface quality, material properties, and crystal grain size can be collaboratively controlled, so as to achieve higher accuracy, better performance, and more outstanding extreme specifications. The present invention solves the problem of inconsistent extension due to differences in metal properties.

A method for preparing a multilayer metal composite pipe includes steps of: internally and externally grinding blank pipes; cleaning oil stains; assembling a multilayer metal pipe; drawing to reduce a diameter; performing high-speed friction welding at the pipe ends; performing heat treatment; performing four-roller cross-rolling; straightening; performing two-roller cold-rolling; performing cold-drawing to reduce the diameter; performing cold-expansion to reduce the diameter; performing precise cold-rolling; degreasing; brightening; performing surface grinding; cleaning dust; detecting multilayer metal interface bonding; detecting flaws; testing metal structure performance; and sizing and packaging. By cycling the cold-drawing, the cold-expansion, and the precision cold-rolling, key indicators such as product dimensional accuracy, surface quality, material properties, and crystal grain size can be collaboratively controlled, so as to achieve higher accuracy, better performance, and more outstanding extreme specifications. The present invention solves the problem of inconsistent extension due to differences in metal properties.

In order to improve the quality of pipe-like work pieces, a rolling mill has at least two successive consecutive rolling stages that have mandrel rods. A threading line for the mandrel rod of the second rolling stage can lie on an extraction line for the mandrel rod of the first rolling stage. The same advantage can be achieved in a rolling method for the production of pipe-like work pieces, comprising at least two successive consecutive rolling stages, wherein the two rolling stages perform the rolling with the use of mandrel rods. The work piece is brought from the mandrel rod of the first rolling stage onto the mandrel rod of the second rolling stage, without entirely emptying an interior of the work piece and/or without changing the direction of movement of the work piece or braking the work piece in the meantime and accelerating it once again.

In order to improve the quality of pipe-like work pieces, a rolling mill has at least two successive consecutive rolling stages that have mandrel rods. A threading line for the mandrel rod of the second rolling stage can lie on an extraction line for the mandrel rod of the first rolling stage. The same advantage can be achieved in a rolling method for the production of pipe-like work pieces, comprising at least two successive consecutive rolling stages, wherein the two rolling stages perform the rolling with the use of mandrel rods. The work piece is brought from the mandrel rod of the first rolling stage onto the mandrel rod of the second rolling stage, without entirely emptying an interior of the work piece and/or without changing the direction of movement of the work piece or braking the work piece in the meantime and accelerating it once again.

The invention relates to a method for producing seamless pipes of heated massive metal blocks, by means of a mandrel (4), which is fastened on a rolling rod (5), in the case of which a coating material is applied onto the inner side of the hollow block (3) during the forming process by means of the influence of the rolling rod (5) from the massive metal block to a hollow block (3), which is created during the forming.

It is an objective to provide a plug capable of enhancing a usage count of the plug, which is for use in a piercing machine for piercing-rolling a billet, and a regenerating method of the plug. The plug (10) is for use in a piercing machine (30) for piercing-rolling a billet (36). The plug (10) includes a body (18), a columnar portion (20), and a sprayed film (16). The body (18) has a maximum diameter at its rear end. The columnar portion (20) has the same diameter as the diameter of the rear end of the body (18), and extends from the rear end of the body (18). The sprayed film (16) is formed on a surface of the body (18) and on a surface of the columnar portion (20).

It is an objective to provide a plug capable of enhancing a usage count of the plug, which is for use in a piercing machine for piercing-rolling a billet, and a regenerating method of the plug. The plug (10) is for use in a piercing machine (30) for piercing-rolling a billet (36). The plug (10) includes a body (18), a columnar portion (20), and a sprayed film (16). The body (18) has a maximum diameter at its rear end. The columnar portion (20) has the same diameter as the diameter of the rear end of the body (18), and extends from the rear end of the body (18). The sprayed film (16) is formed on a surface of the body (18) and on a surface of the columnar portion (20).

A piercer plug with increased life and a method of manufacturing it are provided. The piercer plug 1 includes a tip portion 2 and a trunk portion 3 made of the same material as the tip portion 2 and continuous to the tip portion 2. The trunk portion 3 includes a cylindrical portion 5 having a hole used for attaching a bar. The tip portion 2 is harder than the cylindrical portion 5.

A piercer plug with increased life and a method of manufacturing it are provided. The piercer plug 1 includes a tip portion 2 and a trunk portion 3 made of the same material as the tip portion 2 and continuous to the tip portion 2. The trunk portion 3 includes a cylindrical portion 5 having a hole used for attaching a bar. The tip portion 2 is harder than the cylindrical portion 5.

A rolling mill for rolling hollow or, in all cases, concave rod-shaped bodies, in particular tubes, in particular seamless tubes, said rolling mill comprising a rolling section (10) with a plurality of mill stands and/or rolling dies (11) arranged in succession to define a rolling axis Y, said rolling mill further comprising moving means for moving a mandrel (20) and a tubular blank (21) fitted onto an end portion (22) of said mandrel (20) along said rolling axis and through said mill stands or rolling dies (11) in succession; wherein said moving means are structured so as to move said mandrel (20) and said blank (21) along said rolling axis Y and through said mill stands or rolling dies (11) in succession by applying a traction on said mandrel.