RU2281846C1 - Method for restoring cast iron rolling rolls with damaged journals - Google Patents

Abstract

FIELD: metallurgy, namely processes for restoring cast iron working rolls with journals damaged at operation.

SUBSTANCE: method comprises steps of mechanically removing damaged layer; multi-layer electric arc surfacing of rotated roll in place of removed layer while feeding steel wire electrode to welding zone for further cooling surfaced journal; surfacing three or four layers with use of wire electrode of austenite steel at peripheral velocity of roll 25 - 30m/h, electric current density 40 - 60 A/mm² and electric arc voltage 30 -40 V; sustaining temperature of journal in first (three or four) layers no more than 300°C and in next layers no more than 450°C.

EFFECT: possibility for complete restoration of geometry size and working properties of damaged shafts at keeping their strength and hardness.

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Description

The invention relates to the field of metallurgy, and more particularly to rolling production, and can be used to restore cast iron work rolls with necks damaged during operation.

During operation of the rolling rolls, the neck of the rolls is damaged due to the destruction of the bearings. Rolls with damaged necks are not suitable for further operation, although the working layer of their barrels has not yet been developed.

A known method of repair of steel rolling rolls, including mechanical removal of the damaged section of the barrel by performing in place of the defect ring grooves with regulated sizes, depending on the depth and width of the defect. Then the roll is heated and electric arc welding is performed at the place of the annular groove. After surfacing, heat treatment of the roll is carried out [1].

The disadvantage of this method is that heating the barrel roll leads to a decrease in the hardness of its working layer. This reduces the resistance of the roll, and in some cases is unacceptable. The known method is not suitable for the restoration of the necks of cast-iron rolls.

There is also known a method of restoring rolling rolls, including mechanical removal of barrel defects, preliminary and concomitant heating of the roll, electric arc surfacing with subsequent thermal and mechanical processing of the barrel [2].

This method is not suitable for the restoration of cast-iron rolls with damaged necks, because heating the roll leads to a decrease in the hardness of the barrel and a decrease in its durability.

The closest in technical essence and the achieved results to the proposed invention is a method for the restoration of steel rolling rolls with damaged necks, according to which, after mechanical removal of the damaged layer, the neck of the roll is heated to surfacing to a temperature of 380 ... 440 ° C at a speed of 50 ... 80 ° C / h, multilayer surfacing is carried out with a steel electrode at a speed of 20 ... 40 m / h at an electric current density of 25 ... 35 A / mm ² , heat treatment is carried out by heating to a temperature of 430 ... 470 ° C and holding at this tamper ature for 0.5 ... 1.5 hours [3] - prototype.

The disadvantages of this method are that it is designed to restore steel rolls, so the surfacing modes do not provide satisfactory weldability with cast iron. In addition, the thermal effect in the processes of heating for surfacing, surfacing and subsequent heat treatment leads to a decrease in the hardness and strength of the deposited metal on the neck of the roll. As a result, the roll resistance decreases.

The technical problem solved by the invention is to increase the durability of cast iron rolls.

This problem is solved by the fact that in the known method of repairing rolls with damaged necks, including mechanical removal of the damaged layer, multilayer arc welding of the rotatable roll at the place of removal with the supply of a steel wire electrode to the welding zone and subsequent spontaneous cooling of the weld neck, according to the first three four layers of surfacing are made with a wire electrode of austenitic steel with a peripheral roll speed of 25 ... 30 m / h, electric density current 40 ... 60 A / mm ² and arc voltage 30 ... 34 V, the remaining layers are fused with a pearlite class wire electrode with a peripheral roll speed of 30 ... 40 m / h, electric current density 60 ... 80 A / mm ² and a voltage on the arc of 30 ... 34 V, and the neck temperature is maintained on the first three or four layers no higher than 300 ° C, and on the subsequent layers no higher than 450 ° C.

The invention consists in the following. The destruction of the bearing support of the rolling roll during the rolling process is accompanied by heating of the neck and welding of an inner cage to it, damage to the surface of the cast-iron neck by fragments of a destroyed bearing. A roll with a damaged neck is not suitable for further use. Attempts to restore rolls with damaged necks by known methods led to the fact that, due to the low weldability of cast iron, detachment of the deposited metal occurred, and the thermal effect during heating, arc welding and heat treatment of the neck had a negative effect on the hardness and strength of the deposited layer of the neck of the rolling roll. This led to a decrease in the roll resistance, and in some cases, the reconstructed rolls were completely unsuitable for further operation.

When implementing the proposed method, the ratio of the indicated parameters of surfacing and the use of an austenitic-grade steel electrode leads to the formation of a plastic and strong metal in the transition layer, which does not form cracks in the main (neck) and deposited metal. Before surfacing from the roll neck by machining on a lathe, remove the damaged layer with a depth of 10 ... 15 mm, because at this depth, cast iron neck defects from bearing failure are guaranteed to be absent. Then, a transition layer of metal is applied to the neck of the roll with an annular groove by arc welding using an austenitic class steel electrode, which has good alloying with both cast iron and pearlite class steel, after which surfacing is carried out according to the proposed regime with an pearlite class electrode until restoration of the nominal size the cervix.

Surfacing at a peripheral roll rotation speed of 25 ... 30 m / h, electric current density of 40 ... 60 A / mm ² and arc voltage of 30 ... 34 V on the first three to four layers allow to regulate the penetration in the cast-iron neck and mixing the base metal with an austenitic-grade steel electrode. This leads to fixing the chemical composition of the transition layer and obtaining the optimal transition layer in terms of mechanical properties and weldability. Surfacing of the remaining layers with pearlite-grade steel wire with a peripheral roll speed of 30 ... 40 m / h, an electric current density of 60 ... 80 A / mm ² and an arc voltage of 30 ... 34 V make it possible to form the required working layer of the neck under the bearing and restore mechanical strength.

During the experiments, it was found that the temperature of the neck in the process of surfacing the first three to four layers must be maintained no higher than 300 ° C due to phase transformations in the deposited layer. Due to this, the weldability of the deposited layer with cast iron is improved, the formation of cracks in cast iron is eliminated. In the subsequent surfacing of the remaining layers with a pearlite-grade steel wire, its good fusion with a transition layer is achieved. Thus, on the first 3-4 layers of surfacing, a viscous transition layer is formed from an austenitic steel-cast iron mixture, and on the next layers - a high-strength layer, due to which the strength of the damaged roll neck is fully restored.

Thus, the proposed technology provides a complete restoration of the geometric dimensions and service properties of the damaged neck of the roll without reducing hardness and strength.

It was experimentally established that a decrease in the peripheral speed of roll rotation of less than 25 m / h leads to a lengthening of the process and overheating of the roll neck above the permissible temperature. With an increase in the rotation speed of more than 30 m / h, the number of discontinuities in the metal increases, which affects the quality of surfacing.

When the electric current density is less than 40 A / mm ² due to insufficient penetration, the surfacing quality deteriorates. An increase in the electric current density of more than 60 A / mm ² leads to overheating of the neck, in particular the underlying layer, which is unacceptable.

A decrease in arc voltage below 30 V leads to instability of the welding arc, and an increase in voltage of 34 V entails overheating of the roll neck.

An increase in temperature above 300 ° C leads to a deterioration in the weldability of cast iron and an increase in defects in the deposited layer.

The use of austenitic class steel wire is due to the fact that upon mixing of the roll material (cast iron) and the surfacing wire during the surfacing process, a transition layer is formed with high ductility and viscosity. Due to this, cracks do not occur in cast iron and deposited layer. An increase in the number of first layers deposited using an austenitic wire of more than four leads to an increase in the transition layer and a decrease in the strength of the roll neck. A decrease in the number of first layers of less than three leads to cracks during subsequent surfacing with a pearlite steel electrode.

It has been experimentally established that when surfacing with a pearlite class wire electrode, a decrease in the peripheral speed of roll rotation of less than 30 m / h leads to a lengthening of the process and overheating of the roll neck above the permissible temperature. With an increase in the rotation speed of more than 40 m / h, the number of discontinuities in the metal increases, which affects the quality of surfacing.

When the electric current density is less than 60 A / mm ² due to insufficient penetration, the quality of surfacing is deteriorated. An increase in the electric current density of more than 80 A / mm ² leads to overheating of the neck, in particular the underlying layer, which is unacceptable.

A decrease in arc voltage below 30 V leads to instability of the welding arc, and an increase in voltage above 34 V leads to overheating of the roll neck.

The use of a pearlite class steel wire is due to the fact that upon mixing the transition layer material (cast iron + austenitic wire material) and the pearlite class surfacing wire during surfacing, a working layer is formed with high hardness and wear resistance.

An increase in temperature above 450 ° C leads to a deterioration in weldability and an increase in defects in the layer deposited with pearlite-grade steel.

Method implementation examples

A work roll made of cast iron grade LPHN _D -71 of a continuous broadband hot rolling mill 1700, with a neck damaged due to the destruction of the bearing support, is mounted on a lathe. Using the cutter, a mechanical removal of the damaged layer is carried out with the formation of an annular groove 350 wide and 15 mm deep on the roll neck. Then the roll is installed on the surfacing machine, the roll is brought into rotation with a _peripheral speed of V _ok1 = 27 m / h. Surfacing of the first 4 layers is carried out under an AN-60 grade flux layer with an austenitic steel electrode wire 4.0 mm in diameter. The density of the electric current during surfacing J ₁ = 50 A / mm, with a voltage on the arc U ₁ = 32 V. During the surfacing process, the temperature of the neck is maintained equal to T ₁ = 200 ° C due to its cooling in pauses of surfacing.

Surfacing of the remaining layers is carried out under an AN-60 grade flux layer with a pearlite-grade steel electrode wire of 4.0 mm diameter with a speed of V _ok2 = 35 m / h. The density of the electric current during surfacing J ₂ = 70 A / mm ² , with a voltage on the arc U ₂ = 32 V. During the surfacing process, the temperature of the neck is maintained equal to T ₂ = 400 ° C due to its cooling in pauses of surfacing.

Surfacing is carried out until the neck is restored to its nominal size with machining allowance. After surfacing, the roll spontaneously cools to ambient temperature.

The indicated technological conditions ensure the production of a defect-free weld neck of the reconstructed roll. After surfacing is completed, the roll is installed on a roll grinding machine and the weld neck is ground to a nominal diameter.

The recovered cast iron roll is assembled with bearings and pillows, dumped into the finishing stand of a continuous broadband mill 1700 and hot rolling of steel strips is carried out.

Implementation options of the proposed method and the resistance index of work rolls (specific consumption of reconditioned rolls per ton of rolled metal) are given in the table.

As follows from the data given in the table, when implementing the proposed method (options 2-4), an increase in the durability of restored cast-iron rolling rolls with damaged necks is achieved (the specific consumption of rolls is minimal). In the case of transcendental values of the declared parameters (options 1 and 5), the resistance of the restored rolls decreases. Also lower durability are cast iron rolling rolls with damaged necks restored by the prototype method (option 6).

Table
Surfacing modes and specific consumption of rolls No. Surfacing modes of the first layers Surfacing modes of subsequent layers p / p V _ok1 , m / h U ₁ , B J ₁ , A / mm ² T ₁ , ° C N layers V _ok2 , m / h U ₂ , B J ₂ , A / mm ² T ₂ ° C The lot. roll consumption, kg / t one. 24 29th 39 150 2 29th 29th 59 250 1.4 2. 25 thirty 40 180 3 thirty thirty 60 380 1,1 3. 27 32 fifty 200 four 35 32 70 400 0.8 four. thirty 34 60 300 four 40 34 80 450 1,2 5. 31 35 61 350 5 41 35 81 460 1,5 6. thirty not regl. thirty 400 to fill up. thirty not regl. thirty 400 2,8

The technical and economic advantages of the proposed method consist in the fact that the regulated parameters of electric arc surfacing during the restoration of cast iron rolls with damaged necks provide both high quality surfacing and eliminate negative thermal effects on the roll barrel, while maintaining its high hardness and strength. This is achieved by increasing the resistance of the restored rolls.

The prototype method is adopted as the base object. The application of the proposed method will improve the profitability of the recovery of cast-iron rolling rolls with damaged necks by 20-30%.

Literature used in the preparation of the description of the invention

1. Auth. testimonial. USSR No. 1683834, IPC B 21 V 28/02, 1991

2. Auth. testimonial. USSR No. 1579679, IPC В 23 К 9/04, 1990

3. RF patent No. 2139156, IPC B 21 V 28/02, B 23 P 6/00, 1999

Claims (1)

A method for recovering cast iron rolling rolls with damaged necks, including mechanical removal of the damaged layer, multilayer arc welding of the rotatable roll at the place of removal with the supply of a steel wire electrode to the welding zone and subsequent spontaneous cooling of the weld neck, characterized in that the first three or four layers of surfacing are made by wire electrode of the austenitic steel at a peripheral speed of rotation of the roll 25 ... 30 m / h, the electric current density of 40 ... 60 A / mm ² and the voltage on the row e 30 ... 34 V, and the remaining layers of the deposited wire electrode pearlitic a peripheral speed of rotation of the roll 30 ... 40 m / h, the electric current density of 60 ... 80 A / mm ² and the voltage on the arc 30 ... 34 V, and the neck temperature is maintained on the first three or four layers no higher than 300 ° C, and on subsequent layers no higher than 450 ° C.