Method for making mandrels of pilger rolling mills

FIELD: rolled tube production, namely processes for making mandrels of pilger mills for rolling of hot rolled tubes with mean and large diameters.

SUBSTANCE: method of making mandrels of pilger mills for rolling of hot rolled tubes with mean and large diameters in range 273-550 mm comprises steps of casting steel ingots; forging cylindrical solid or hollow blanks; subjecting blanks to rough working, to heat treatment and working them for final size; hardening blank surface by means of roller; maintaining mandrels until formation of lattice of thermal erosion cracking. Before heat treatment constant- thickness heat- and wear-resistant layer is welded on outer surface of carbonaceous mandrel blank along 2/3 of its working length of mandrel from its joint part while taking into account allowance for mechanical working. Thickness of said layer is decreased towards end of mandrel by 3-4 times. During process of operation mandrel is reground. Then heat- and wear-resistant constant-thickness layer is welded on outer surface of mandrel along 2/3 of its working length from joint part. Thickness of said layer is decreased towards end of mandrel by 3-4 times. Regrinding and layer surfacing steps are performed multiply. Invention allows to use carbon steel instead of alloyed steel at making mandrels, provides increased by 3.5 - 4 times strength of mandrels.

EFFECT: lowered cost of mandrels and therefore reduced cost of conversion of hot rolled tubes in tube rolling aggregates with pilger mills.

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The invention relates to pipe production, namely the method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameters (273-550 mm).

A known method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameters, including the casting of ingots of steel grade LED1 (50HN) with the chemical composition according to GOST 4543-71, forging them into a cylindrical billet (forgings) with ukonom 2,25-2,5, rough machining with allowance on a diameter of 10-15 mm, taking into account leashes forgings during heat treatment, heat treatment domowych blanks, machining of dies to finish size with subsequent hardening by rolling surface of the roller and exploitation to education grid razgonnyj cracks, waves or longitudinal cracks (Faganello and other Hot rolling pipe. - M.: metallurgy, 1962, s-356; Report on the topic 22-V-13-541-73: "Development of technology for manufacture of mandrels increased wear resistance and their introduction into production at the Chelyabinsk pipe rolling plant", Dnepropetrovsk, 1975; TA 158-148-98 "Technological process of machining the guides and work roll piercing mill, mandrels and piligrimage rolls in workshop No. 1").

The disadvantage of this method is that Dorn fail, for "the wave" (bumps), surface rashanim ring t is Eminem and coarse longitudinal cracks, as well as uneven abrasion of their length (the loss of the geometric dimensions). As a rule, during rolling of pipe diameter and 426 377 mm on the mandrels of steel grade LED1 main defect is the "wave" (bumps). "Wave" on the surface of the mandrels occurs at a distance of 1500-2000 mm from domowego castle. "Wave" is a plastic deformation of the surface layers of metal mandrels, which is caused by heating their surfaces to a temperature above 650°and caused by prolonged contact of the cartridge-tubes and mandrels or rolling of two or more sockets on the same mandrel without cooling. When rolling pipe size 426×9×32000-35000 mm, the contact time of the mandrel with the sleeve-tube is from 5.0 to 6.0 minutes. During this time the mandrel in the area of 2000-4000 mm from the castle part is heated from 600 to 650°C. the Highest temperature of the mandrel is in the area from 2000 to 3000 mm from domowego castle, i.e. the Central part. The resistance of the mandrels on the "wave" is in direct dependence on the instructions for their operation. Ring cracks are associated with poor machining, the presence of hubs voltage (undercuts and grooves from the incisors). Coarse longitudinal crack depth of 1/3 to 3/4 of the radius of the mandrels are a consequence of the low values of plastic properties and impact toughness of the steel at cyclic temperatures.

Known also with the persons making mandrels piligrimage mills of steel grade DM2 (HF), with the following content elements: carbon - 0.24 to 0.32 per cent, manganese - 0,3-0,6%, silicon 0.15 to 0.40 per cent, chromium - 1,6-1,9%, molybdenum - 0.6-0.9 percent), vanadium - 0,15-0,25%, Nickel up to 0.5%. Dorn made of this steel is more durable. The resistance of their 1.2-1.3 times higher than that of steel LED1 (Report on: 23-V-13-81/19-72/ P2-app "Finding steels with improved thermal stability and development of composite structures vilgerdarson". The Ural research Institute for the pipe industry. Ufa aviation Institute, Chelyabinsk pipe-rolling plant, Chelyabinsk, 1972

However, the known method also has disadvantages. Dorn with a carbon content of 0.24 to 0.32 per cent fail mainly because of the appearance on their surface razgonnyj cracks and uneven wear along the length (the loss of the geometric dimensions). Asgarnia cracks occur due to thermal and structural stresses in the surface layer Dorin, which are heated by contact with hot shells-pipes to a temperature of Ac1-AC3 (650°C and above). Education grid razgonnyj cracks are the result of irreversible structural changes (shear deformation within the grains, grinding grains, the formation of voids, the deformation at the grain boundaries and the formation of submicroscopic tearing and damage of the surface layer). Termostato damage to the surface is the cause of the first foci of destruction, iniziare what were the further development of cracks. With increasing number of cycles of heating and cooling increases the number and size of cracks, the cracks are connected and intertwined, forming a so-called "grid". Education grid razgonnyj cracks on the surface of the mandrels accelerates wear and loose metal particles. In the cracks of the intense oxidation of the metal and the processes of their wedging. A decisive influence on the life of the mandrels has the intensity of development of the grid razgonnyj cracks in larger, which is a criterion for rejection of the mandrels.

The closest technical solution is the method of manufacture and operation of the mandrels (pots) piligrimage mills for rolling hot-rolled pipes of large and medium diameters, including the production of conical electroslag ingot of steel DM2-III and subsequent forging of a cylindrical billet having a castle and a working part, and forging its working parts are carried out with a linear increase okovki in the direction of the locking parts when the ratio of the maximum okovki to a minimum of 1.26-1,56 (RF Patent No. 2055660 from 10.03.96,, bull. No. 7).

However, the known method also has disadvantages. The resistance of the mandrels increased 1.2-1.3 times compared to the existing, but Dorn also fail, for longitudinal cracks and the grid razgonnyj cracks, and the costs in the cost of pipe the leaves from 2.5 to 3.0%.

The technical result of the proposed method is to reduce the cost of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameter by reducing consumption surfacing wear-resistant heat-resistant wire SVHG and replacement steel HIP on carbon steel for the manufacture of domowych blanks.

The technical result is achieved by the fact that in the known method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameters, including the casting of ingots of steel the forging of a cylindrical solid or hollow workpieces, rough machining, heat treatment and machining of dies to finish size with subsequent hardening the surface of the roller and exploitation to education grid razgonnyj cracks, before the heat treatment on the outer surface of the carbon pipes blanks for two-thirds of the working length of the mandrel from the castle part, subject to the allowance under mechanical processing is applied by way of welding heat-resistant wear-resistant layer of constant thickness, which reduces to the end Dorn 3-4 times, and during operation are grinding mandrel and is applied to the outer surface of two-thirds of the working length of the mandrel from the castle part of the heat-resistant layer is constant the second thickness, which reduces to the end of the mandrel 3-4 times, while the grinding and applying a layer produced repeatedly.

Dorn in the process are subjected to repeated cyclic heating and cooling. In addition to thermal impact of the mandrel exposed to the pressure rolls piligrimage mill and longitudinal stretching caused by the friction forces of the deformable metal during rolling and extract the mandrels of the pipe feeding apparatus. Because of the variability of the deformation zone, for one revolution of the rolls, the pressure on the mandrel and the effect of friction forces are constantly changing. The complexity of the operating conditions of the mandrels is long finding them in contact with the heated plastically deformable metal, the lack of cooling in the deformation process, large temperature changes of the working surface of the mandrels during one cycle of operation (cooling to a temperature of 180-200°With the bath water and grease, heat in the rolling process and work within 3.5-6.0 minutes at a temperature of 500-650°). Joint action of high temperatures and pressures lead to the rapid release of the mandrels of the system, mainly on the grid razgonnyj cracks. Asgarnia cracks on the surface of the mandrels begin to appear through 0,80-0,85 from the average of their resistance, which then begin to progress, grow, both qualitatively and quantitatively, i.e. in breadth and depth. In this m the ment of the mandrel is forcibly withdrawn from service and permacoat to remove the deposited heat-resistant layer. After regrinding to the outer surface of two-thirds of the working side of the mandrel from the locking parts put heat-resistant layer with accounting allowance under machining, constant thickness, which reduces to the end of the mandrel 3-4 times, produce heat treatment, machining to finish size with subsequent hardening by rolling the roller and return the mandrel in the production cycle. Dorn after regrinding and application of new heat-resistant layer operate until (inception) grid razgonnyj cracks. The cycle is repeated, that is, they withdraw from the process, permacoat to remove the heat-resistant layer, put a new heat-resistant wear-resistant layer, produce heat treatment, machining and subsequent hardening of the roller. Thus, the mandrel operate to failure for reasons not related to rzhanymi cracks (failure of the mandrel, the wear of the castle and so on).

Comparative analysis of the proposed solutions with the prototype shows that the inventive method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameter differs from the known fact that before the heat treatment on the outer surface of the carbon pipes blanks for two third servant is whose length of the mandrel from the locking parts, taking into account an allowance under mechanical processing is applied by way of welding heat-resistant wear-resistant layer of constant thickness, which reduces to the end of the mandrel in 3-4 times, and during operation are grinding mandrel and is applied to the outer surface of two-thirds of the working length of the mandrel from the castle part of the heat-resistant layer of constant thickness, which reduces to the end of the mandrel 3-4 times, while the grinding and applying a layer produced repeatedly. Thus, the claimed method meets the criteria of the invention of "Novelty". Comparison of the proposed method not only prototype, but also with other technical solutions in this field of technology is not allowed to reveal in them the features distinguishing the claimed solution to the prototype that allows to conclude that the criterion of "Substantial differences".

The method was tested on pipe installation piligrimage mills 8-16" JSC "Chelyabinsk tube rolling plant". The production was set two new mandrel diameter 309/310 and 409/410 mm, made by the existing and proposed technologies. Data on the resistance of the mandrels piligrimage mills TPA 8-16" "CHTPZ"made by the existing and proposed technologies listed in the table. The average resistance of the mandrels with a diameter of 309/310 mm, manufactured and operated by an existing method, status is made by 800 tonnes of pipe size h mm, and the mandrels with a diameter of 409/410 mm - 1100 tonnes of pipe size h mm Surfacing experienced mandrels were made with wire, steel grades SWONG. From the table it is seen that the mandrel diameter 309/310 mm, manufactured by an existing method, was laminated 865 tonnes of pipe size 325×9 mm, and the mandrel 409/410 mm - 1185 tons of pipe size 426×9 mm mandrel made on existing technology, out of order on the grid razgonnyj cracks. On the new mandrel diameter 309/310 mm, manufactured by the proposed method with the surfacing of heat resistant wear-resistant layer of constant thickness at 2/3 the length of the mandrel from the locking parts, which decreases 3-4 times to the end of the mandrel (up to 3.0 mm), four times and overlaying laminated 3605 tonnes of pipe size 325×9 mm Resistance Dorn produced by the proposed method increased by more than 4.0 times. After the fourth repoint Dorn was sent to repair the castle. After welding and milling cheeks castle, as well as reshaping and fifth overlaying the mandrel will be sent to the mills for further use. Dorn before each welding was ground to 2/3 the length of the mandrel from the locking parts up to a diameter 290±1 mm, which by the end of the mandrel gradually increased up to a diameter 298-300 mm pilot mandrel diameter 409/410 mm after five deposits and four of re resistance Dorn was 4455 tonnes of pipe size 426×9 mm, i.e. firmness is th Dorn increased 3,76 times. Dorn before each welding was ground to 2/3 the length of the mandrel from the locking parts up to a diameter of 390±1 mm, which by the end of the mandrel gradually increased up to a diameter 400-402 mm

Thus, the mandrel diameter 309/310 mm, manufactured and operated by an existing method, laminated 865 tonnes of pipe size 325×9 mm (Dorn went out on a grid razgonnyj cracks). On the mandrel, made by the proposed method with a constant thickness of the deposited layer PA 2/3 the length of the mandrel, after the first installation and the four and re-welding of heat-resistant wear-resistant layer, laminated 3605 tonnes of pipe size 325×9 mm Resistance Dorn grew 4.16 times. The mandrel diameter 409/410 mm, manufactured and operated by an existing method, laminated 1185 tons of pipe size 426×9 mm mandrel out of order on the grid razgonnyj cracks. The mandrel diameter 409/410 mm, produced according to the proposed method, the resistance for five surfacings and four times, was 4455 tonnes of pipe size 426×9 mm, i.e. the resistance increased 3,76 times. Dorn will be used in the work after repair (welding and milling domowego castle), and the fifth and subsequent re-profiling and cladding on the working surface of a heat-resistant layer.

The application of the proposed method of manufacture of mandrels piligrimage mills for rolling hot-rolled tubes b is logo and medium diameters will give the opportunity to use as the basis of solid and hollow domowych billet carbon steel, to increase their resistance, compared with the existing method, on average 3.5-4.0 times, to reduce the cost of dies, and therefore, reduce the cost of the process of hot-rolled pipes on TPA with piligrimage mills.

The method of manufacture of mandrels piligrimage mill for rolling hot-rolled pipes of large and medium diameters, including the casting of ingots of steel, the forging of a cylindrical solid or hollow workpieces, rough machining, heat treatment and machining of dies to finish size with subsequent hardening the surface of the roller and exploitation to education grid razgonnyj cracks, characterized in that before the heat treatment on the outer surface of the carbon pipes blanks for two-thirds of the working length of the mandrel from the castle part, subject to the allowance under mechanical processing is applied by way of welding heat-resistant wear-resistant layer of constant thickness, which reduces to the end of the mandrel in three four times, and during operation are grinding mandrel and is applied to the outer surface of two-thirds of the working length of the mandrel from the castle part of the heat-resistant layer of constant thickness, which reduces to the end of the mandrel in three or four times, while the grinding and applying a layer of produce mnogo atno.



 

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EFFECT: steel with improved mechanical characteristics.

11 cl, 2 tbl, 1 ex

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FIELD: rolled tube production, namely methods for making and using technological tools, possibly at making mandrels of pilger mills for rolling hot rolled tubes with large and mean diameters.

SUBSTANCE: method for making mandrels of pilger mills for rolling hot rolled tube with diameters 273-550 mm comprises steps of casting steel ingots; forging cylindrical or hollow blanks; rough working and heat treatment of them; mechanically working mandrels for final size and strengthening them due to rolling out by means of roller; exploiting mandrel until formation of lattice of thermal-erosion cracking. Mandrel blanks are made of carbon steel. On outer surface of blanks heat- and wear-resistant layer is surfaced. After occurrence of thermal-erosion cracking mandrels are reground; heat- and wear- resistant layer is surfaced. Blanks are worked for final size and strengthened due to rolling out by rollers. Thickness of surfaced heat- and wear-resistant layer is determined according to expression Δ = A (1 + K* D/S), where A - minimum thickness of surfaced layer after finishing equal to 10 mm; D - maximum diameter of tube rolled on mandrel, mm; S - minimum thickness of wall of tubes rolled on mandrel, mm; K - coefficient taking into account geometry size of tubes. Heat- and wear-resistant layer is multiply surfaced on mandrel blanks. Invention provides possibility for using mandrel blanks of carbon steel instead of alloy steel.

EFFECT: lowered consumption of mandrels, reduced cost of conversion of hot rolled tubes in tube rolling aggregates with pilger mills.

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