RU2237563C1 - Process for restoring rolling rolls - Google Patents

Abstract

FIELD: rolling equipment, namely restoration of cast iron rolling rolls with journals damaged at operation.

SUBSTANCE: process comprises steps of mechanically taking off damaged layer and performing electric arc surfacing in place of taking off material at feeding electrode to welding zone; further cooling surfaced journal. Surfacing is realized at rate 40 - 50 m/h at density of electric current 35 -45 A/sq. mm. Temperature of journal is kept during surfacing no more than 400 C. Then journal is cooled until temperature of environment at mean rate 5 - 20 C/s.

EFFECT: possibility for providing high strength of cast iron rolls due to increased hardness and strength of surfaced layer.

1 tbl, 1 ex

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 dimensions, 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 result to the present invention is a method for the restoration of steel rolling rolls with damaged necks, according to which, after mechanical removal of the damaged layer of the neck, the rolls are heated for surfacing to a temperature of 380-400 ° C at a speed of 50-80 ° C / h, 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 temperature for 0.5-1.5 h [3].

The disadvantages of this method are that it is designed to restore steel rolls. In addition, the thermal effect in the processes of heating for surfacing, surfacing and subsequent heat treatment leads to a decrease in hardness and strength of the deposited metal on the neck of the roll, which leads to a decrease in the resistance of the rolls.

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 for the restoration of rolling rolls, including mechanical removal of the damaged layer of the neck, arc welding at the place of removal with the electrode feeding into the welding zone and subsequent cooling of the weld neck, according to the proposal, when restoring cast iron rolls, surfacing is performed at a speed of 40-50 m / h at a current density of 35-45 a / mm ^2, wherein during welding the neck temperature is maintained not higher than 400 ° C, and subsequent cooling leads to ambient temperature with average speed 5-20 ° C / h.

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, the deposited metal exfoliated, and the thermal effect during heating, electric arc surfacing and heat treatment of the neck negatively affected 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 turned out to be completely unsuitable for further operation.

When implementing the proposed method, first, the damaged layer with a depth of 8-12 mm is removed from the roll neck by machining on a lathe, because at this depth, cast iron neck defects from bearing failure are guaranteed to be absent. Then, layers of metal are applied to the neck of the roll with an annular groove by steel-arc welding using a steel electrode until the nominal size of the neck is restored to the mode: surfacing speed is 40-50 m / h, electric current density is 35-45 A / mm ² , and the temperature of the neck is maintained no higher than 400 ° FROM. Due to this, the weldability of the deposited layer with cast iron is improved, the formation of cracks in cast iron is excluded, the strength and hardness of the deposited layer is increased.

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 surfacing speed of less than 40 m / h leads to a lengthening of the process and overheating of the roll neck above the permissible temperature. With an increase in the surfacing speed of more than 50 m / h, the number of discontinuities in the metal increases, which affects the quality of surfacing.

When the electric current density is less than 35 A / mm ² due to insufficient penetration, the surfacing quality deteriorates. An increase in the electric current density of more than 45 A / mm ² leads to overheating of the neck, especially the underlying layer, which is unacceptable.

An increase in temperature above 400 ° C leads to a deterioration in the weldability of cast iron and a decrease in the hardness and strength of the deposited layer.

With a decrease in the average cooling rate of less than 5 ° C / h, the production recovery process is lengthened, and the roll resistance does not increase. An increase in the average cooling rate above 20 ° C / h causes the formation of cracks in cast iron, which impairs the resistance of the roll.

Method implementation examples

A work roll made of cast iron of the LPHNd-71 brand of a continuous broadband hot rolling mill 2000, 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 400 wide and 10 mm deep on the roll neck. Then the roll is installed on the surfacing machine, the roll is brought into rotation. Surfacing is carried out under an AN-60 grade flux layer with a 4.0 mm diameter steel electrode wire. The surfacing speed is V _sv = 45 m / h, the electric current density during surfacing is J = 40 A / mm. In the process of surfacing, the temperature of the neck is maintained equal to T = 200 ° 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 is cooled to ambient temperature with an average rate of V _cool = 12 ° C / h.

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 2000, and the steel strips are hot rolled.

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).

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 the negative thermal effect on the deposited layer of the roll neck, 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%.

Sources of information

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

2. Autosvid. 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 of restoring rolling rolls, including mechanical removal of the damaged layer of the neck, electric arc surfacing at the location of removal with the electrode being fed into the welding zone and subsequent cooling of the weld neck, characterized in that during the restoration of cast iron rolls, surfacing is performed at a speed of 40-50 m / h at an electric density current 35-45 A / mm ² , and in the process of surfacing the neck temperature is maintained no higher than 400 ° C, and subsequent cooling is carried out to ambient temperature with an average speed of 5-20 ° C / s.