Method for producing seamless pipes

Abstract

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.

Claims

1. A method of making seamless pipe comprising the steps of: piercing a massive heated metal block with a mandrel fixed to a rolling rod to form in the block a throughgoing hole having an inner surface; and during the piercing and prior to formation of scale on the inner surface, feeding a scale-inhibiting coating material to the inner surface of the hollow block through the mandrel so as to coat the surface and prevent the formation of scale, the scale-inhibiting coating material being a mixture with water of sodium tripolyphosphate and sodium N-metaphosphate free from borate together with graphite.

2. The method defined in claim 1, further comprising the step after piercing the block of: separating the inner surface of the block from the mandrel; and commencing application of the scale-inhibiting coating material to the inner surface of the hollow block immediately after the separation of the inner surface of the hollow block from the mandrel.

3. The method defined in claim 1, wherein the scale-inhibiting coating material is applied to the inner surface of the hollow block through openings in the mandrel or in the rolling rod.

4. The method defined in claim 1, wherein the scale-inhibiting coating material is composed so as to form an air-impermeable cover layer on the inner surface of the hollow block.

5. A The method of defined in claims 1, wherein the cover layer on the inner surface of the hollow block has a thickness of less than 100 μm on average.

6. The method defined in claim 1, further comprising the step of: feeding inert gas through the rod and/or the mandrel into the hollow block during piercing.

7. The method defined in claim 1, wherein the scale-inhibiting coating material is a powder, the method further comprising the step of: conveying the powder to the inner surface of the hollow block as a powder solution or mixture with water.

8. The method defined in claim 7, wherein the water is 60-90% by volume of the mixture or solution.

9. The method defined in claim 1, further comprising the step of: supplying the liquid scale-inhibiting coating material at a pressure of 3 to 40 bar.

10. A method of making seamless pipe comprising the steps of: piercing a massive heated metal block with a mandrel fixed to a rolling rod to form in the block a throughgoing hole having an inner surface; during the piercing and prior to formation of scale on the inner surface, feeding a powdered scale-inhibiting coating material to the inner surface of the hollow block through the mandrel so as to coat the surface and prevent the formation of scale; conveying the powdered scale-inhibiting coating to the inner surface of the hollow block with a carrier gas; and pressurizing the carrier gas to a pressure of less than 20 bar.

11. The method defined in claim 10, wherein a particle size of at least 90% of the powdered scale-inhibiting coating material is less than 840 μm.

12. A method of making seamless pipe comprising the steps of: piercing a massive heated metal block with a mandrel fixed to a rolling rod to form in the block a throughgoing hole having an inner surface; making a mixture with water of a) borax and sodium tripolyphosphate together with soap and mica, or b) borax and sodium sulfates together with graphite; and during the piercing and prior to formation of scale on the inner surface, feeding the mixture to the inner surface of the hollow block through the mandrel so as to coat the surface and prevent the formation of scale.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be defined in detail below with reference to the drawing whose sole figure is a schematic view of a device for the supply of nitrogen through the rolling rod and for the supply of coating material through the rolling rod. The coating material is applied by a PLC-controlled application system using an adjustable metering device.

DETAILED DESCRIPTION OF THE INVENTION

(2) The drawing schematically shows a piercing mill in which a block 3 is driven between an upper roller 1 set at an angle, and a lower roller 2 set at an angle against a mandrel 4 fixed to a rolling rod 5 so as to be capable of being detached. The forming of a solid metal block 3 into a hollow block 3a takes place hereby viewed from left to right in the figure, wherein the hollow block shell 3a separates from the mandrel 4 in the forming process and forms an air gap between the rolling rod 5 and the inner surface 6 of the hollow block 3a.

(3) According to the invention, coating material is fed from a coating material supply 9 via a metering device 10 and a supply line 8 for the coating material through the rolling rod 5 and the mandrel 4, if necessary, to the inner surface 6 of the hollow block 3a so as to effect a complete sealing of the inner surface 6 of the hollow block 3a in this manner. The powdery coating material is applied onto the inner face 6 of the hollow block 3a together with nitrogen in a controlled manner at a pressure of 1-5 bar through the supply line 8 and the rolling rod 5. The atmospheric oxygen is already replace almost completely by the nitrogen in the hollow block 3 by the excess of nitrogen that does not react with the red-hot metal of the hollow block 3 and that has been introduced through the rolling rod 5 and contacted with the inner face 6 of the hollow block 3a. If necessary, additional nitrogen can be added into the interior of the hollow block 3 via further unillustrated supply lines.