RU2533471C1 - Method of operating cast iron working rolls - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed process comprises removal of roll from mill stand, temperature measurement, grinding with shaping in smooth concaved generatrix with allowance for thermal correction to preset concavity to said generatrix, feed of lubricant-coolant to rolls and fitting of rolls in the stand. Thermal correction before grinding is specified by mathematical relationship that sets the number of finishing stand whereat said roll is used. Note here that specific lubricant-coolant flow rate is set equal to 1-8 l/min.

EFFECT: higher efficiency and quality.

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Description

The invention relates to rolling production and can be used in the operation of cast-iron work rolls with a diameter of 750-950 mm in continuous finishing groups of stands of quarto sheet hot rolling.

A known method of operating S-shaped work rolls of sheet stands of quarto hot rolling, including dumping them from the stand, measuring the surface temperature along the length of the roll barrel at least at three points, grinding the barrel on a smooth concave generatrix taking into account the correction determined by the temperature measurement [ one].

There is also known a method of operating the cast iron workers of a sheet rolling mill of a quarto hot rolling, including dumping them from the mill, cooling, rough grinding, fine grinding according to a smooth concave generatrix taking into account thermal correction, with the supply of cutting fluid to the rolls, and subsequent filling into the crate [2 ].

The disadvantages of the known methods are that they are not suitable for preparing rolls with a conditionally cylindrical barrel shape. In addition, only measuring the temperature on the surface of the barrel does not allow to accurately determine the current value of the thermal convexity of the roll, which changes during grinding. This reduces the quality of the strips, leads to an increase in their non-flatness and distortion in the shape of the cross section.

The closest analogue to the present invention is a method for preparing work rolls of a broadband hot rolling mill, including rolling them out of the cage, measuring the temperature along the roll barrel, grinding with profiling along a smooth concave generatrix taking into account the thermal correction for the design profile, with a lubricating-cooling feed to the rolls liquid, and subsequent filling in the crate, and the value of the thermal correction is set according to mathematical dependencies taking into account the weighted average rolling width and the time between lkoy grinding and [3].

The disadvantages of this method are as follows. The cooling of cast-iron work rolls with a diameter of 750-900 mm of a sheet rolling mill quarto before grinding begins within 10-18 hours. For this reason, for the uninterrupted preparation of polished work rolls in operation, it is necessary to have a 3–4-fold margin at the same time. This leads to a “freeze” of the funds spent on their acquisition, which results in an increase in the cost of production of sheet metal. In addition, not taking into account the constant change in temperature of the work rolls during the grinding process leads to a violation of the optimal shape of the concave forming barrel. As a result, the cross-sectional profile of the strips is distorted, non-flatness appears, and their quality deteriorates.

The technical problem solved by the invention is to reduce the number of work rolls in operation, while improving the quality of the hot rolled strips.

To solve the technical problem in the known method of operating the work rolls of the finishing group of sheet rolling stands of quarto hot rolling, including rolling the roll out of the stand, measuring the temperature along the roll barrel, grinding with profiling along a smooth concave generatrix taking into account the thermal correction to a given value of the concavity of the generatrix line, s supply to the rolls of cutting fluid, and subsequent filling in the crate, according to the invention, the thermal correction is set by the ratio:

δ = (k ₁ · 947.2 · Δt-k ₂ · 4.486 · Δt ² -k ₃ · 876.4) · 10 ^-5 (mm),

where k ₁ = 1.0-1.4 (mm / ° C); k ₂ = 1.0-1.4 (mm / ° C ² ); k ₃ = 1.0-1.4 (mm) are the coefficients depending on the stand number of the finishing group in which the work roll is installed;

$$\Delta t=t_c-\frac{t_{\mathrm{one}}+t_2}{2}$$

t _c - surface temperature in the middle of the roll barrel, ° C,

t ₁ and t ₂ - surface temperature at the end sections of the roll barrel, ° C,

wherein the specific flow rate of the cutting fluid is set to 1-8 l / min.

The invention consists in the following. 1.5-2 times reduction in the number of cast iron work rolls involved in the production process can be achieved by grinding them in the hot state. Moreover, to determine the temperature correction, it is not the temperature value itself that matters, but the temperature difference on the edge of the barrel and in its middle, which characterizes the magnitude of the thermal convexity of the generatrix line.

The initial thermal profile of the work roll before grinding substantially depends on the serial number of the stand of the finishing group in which it was operated. In addition, in the grinding process, carried out with the supply of cutting fluid, there is a continuous change in the temperature field of the roll, due to its heating from friction with an abrasive wheel and cooling when pouring cutting fluid. It turned out to be possible to take into account all the factors affecting the profile of the work roll during grinding in the heated state with sufficient accuracy for practical use by experimental studies of the influence of the above parameters on the actual shape of the generatrix line after cooling the roll to room temperature.

Based on experimental studies of the parameters of the state and grinding of hot cast iron work rolls with a diameter of 750-950 mm dumped from various stands of the finish group (stand number of the finish group, pause time before grinding, initial temperature distribution over the barrel surface, generalized grinding mode with lubricant-cooling supply liquid, its specific consumption), the value of the thermal correction was determined experimentally, the value of which is determined by the empirical equation:

δ = (k ₁ · 947.2 · Δt-k ₂ · 4.486 · Δt ² -k ₃ · 876.4) · 10 ^-5 .

Moreover, as shown by experiments, for the penultimate and last stands of the finishing group, empirical coefficients k ₁ ; k ₂ ; k ₃ take a minimum value of k ₁ = 1.0 (mm / ° C); k ₂ = 1.0 (mm / ° C ² ); k ₃ = 1.0 (mm), and for the first and second stands - the maximum value of k ₁ = 1.4 (mm / ° C); k ₂ = 1.4 (mm / ° C); k ₃ = 1.4 (mm). For intermediate stands of the finishing group, k ₁ = 1.2 (mm / ° C); k ₂ = 1.2 (mm / ° C ² ); k ₃ = 1.2 (mm).

It was experimentally established that when the specific flow rate of the cutting fluid is less than 1 l / min when grinding a hot cast iron roll, defects in the form of burns are formed on its barrel, accompanied by local softening and destruction of the barrel surface. Grinding rolls with burns, which increases their consumption. An increase in specific consumption of more than 8 l / min leads to additional local cooling and distortion of the shape of the forming barrel. This increases the flatness of the hot rolled strips.

Method implementation examples

1. On a continuous broadband hot rolling mill 2000 to ensure high flatness of the strips with minimal transverse thickness variation in the last, 7th stand of the finishing group, cast iron work rolls with a diameter of D _n = 800 mm are used, which are cold, i.e. at a temperature of + 20 ° C, they are profiled along an optimized smooth concave generatrix line in the form of a parabola branch with a concavity amplitude δ _s = 0.50 mm.

On the work roll dumped out of the 7th stand, the barrel surface temperature is measured at three points: on the left edge of the barrel t ₁ = 61 ° C; in the middle part t _c = 80 ° C; on the right edge of the barrel t ₂ = 59 ° C.

According to the measurement results, the temperature difference is calculated:

$$\Delta t=t_c-\frac{t_{\mathrm{one}}+t_2}{2}=80-\frac{59+61}{2}=\mathrm{twenty}\left({}^{\circ }C\right).$$

Given the fact that for the cast iron work rolls of the last stand of the finishing group, empirical coefficients k ₁ = 1.0 (mm / ° C); k ₂ = 1.0 (mm / ° C); k ₃ = 1.0 (mm), calculate the thermal correction:

δ = (1 · 947.2 · Δt-1 · 4.486 · Δt ² -1 · 876.4) · 10 ^-5 = (1 · 947.2 · 20-1 · 4.486 · 20 ² -1 · 876.4 ) · 10 ⁵ = 0.16 (mm).

The hot work roll, rolled out of the cage, without cooling to room temperature, is installed on a roll-grinding machine and it is roughened (peeled) and finely ground (profiled) by a rotating abrasive wheel. In the grinding process, a cutting fluid is supplied to the cutting zone with a specific flow rate q = 4.5 l / min, which is used as a 0.5-1.7% solution of soda ash in water. The profiling of the barrel of the non-cooling roll is performed according to the smooth concave generatrix in the form of a parabola branch with the concavity amplitude δ _g , taking into account the thermal correction δ, taking into account the increase in concavity to its optimal preset value δ _s as the roll cools:

δ _g = δ _s −δ = 0.50-0.16 = 0.34 (mm).

After complete cooling of the work roll, a control measurement of the maximum concavity is performed, which, as a result of thermal contraction, decreases to a predetermined value δ _s = 0.50 mm.

The polished roll is heaped up together with the same work roll in the 12th mill stand and hot rolling of strips of carbon steel from 1.0 to 12.0 mm thick is carried out.

In the industrial implementation of the proposed method in the experiments, the specific consumption of the cutting fluid supplied to the cutting zone during grinding was varied and its effectiveness was evaluated. The results are presented in the table. From the data presented in the table, it follows that with a specific consumption of cutting fluid q = 1-8 l / min, the best indicators of roll resistance and the quality of hot-rolled strips are achieved.

Table No. q, l / min The presence of burn barrels Flatness of strips, mm / m one 0.9 there is 6-15 2 1,0 no 5 3 4,5 no four four 8.0 no 5 5 9.0 no 7-17

2. A worn-out cast-iron work roll is thrown out of the 1st stand of the finishing continuous group and temperature is measured at three points on its barrel: on the left edge t ₁ = 69 ° C, in the middle part t _c = 90 ° C and on the right edge t ₂ = 71 ° C. Then calculate the average temperature difference at the edges of the barrel and in the middle:

. $$\Delta t=t_c-\frac{t_{\mathrm{one}}+t_2}{2}=90-\frac{69+71}{2}=\mathrm{twenty}\left({}^{\circ }C\right)$$

.

To grind a hot roll according to the proposed formula, the thermal correction δ is calculated, taking into account that for the first stands of the finishing group, the empirical coefficients k ₁ = 1.4 (mm / ° C); k ₂ = 1.4 (mm / ° C ² ); k ₃ = 1.4 (mm):

δ = k * (947.2 * Δt-4.486 * Δt ² -876.4) * 10 ^-5 =

= 1.4 · (947.2 · 20-4.486 · 20 ² -876.4) · 10 ^-5 = 0.23 mm.

The non-cooling work roll, which has been thrown out of the cage, is installed on a roll-grinding machine and is roughened (peeled) and finished grinded (profiled) by a rotating abrasive wheel with a supply of cutting fluid with its specific flow rate q = 6.0 l / min.

To obtain rolled strips with high flatness, the cast iron work roll of the 1st stand of the finishing group at room temperature + 20 ° C should have an optimal profile in the form of a smooth concave generatrix line (parabola) with a concavity amplitude δ _s = 0.60 mm.

The profiling of the barrel of the non-cooling working roll is made taking into account the thermal correction δ along the smooth concave generatrix in the form of a parabola branch with the concavity amplitude δ _g , taking into account the increase in concavity to its optimal value 53 as the roll cools:

δ _g = δ _s −δ = 0.60-0.23 = 0.37 (mm).

After grinding is completed, the work roll is again dumped into the 1st stand of a continuous finishing group and the strips are hot rolled. Due to the fact that the work roll as a result of grinding acquires optimal profiling, the rolled strips have minimal non-flatness.

The technical and economic advantages of the proposed method consist in the fact that measuring the actual temperature of the roll barrel at three points before grinding and calculating the heat correction to a given value of the concavity of the generatrix line according to the proposed empirical formula allows grinding of cast iron work rolls of a continuous finishing group of stands in a hot state, not waiting for them to cool to room temperature. Due to this, the total working fleet of mill rolls 2000, which are simultaneously in operation, can be reduced by 15-20%. This saves the “frozen” working capital of the enterprise and provides an increase in the profitability of the production of hot-rolled sheet steel by ~ 3%.

Literature

1. Patent of the Russian Federation No. 2301123, IPC B21B 28/00, 2007;

2. L.I. Borovik, A.I. Dobronravov. Technology of preparation for operation of rolls of sheet mills. M., Metallurgy, 1984, p.40-44, 86-87;

3. Auth. testimonial. USSR No. 1600881, IPC B21B 28/02, 1990

Claims (1)

A method of grinding cast iron work rolls of the finishing group of sheet rolling stands of quarto hot rolling during operation, including measuring the temperature along the length of the roll barrel between roll rolls from the stand and filling in the stand and grinding with profiling along a smooth concave generatrix taking into account the thermal correction to a given value of the concavity of the generatrix line , with the supply of cutting fluid to the rolls, characterized in that the thermal correction before grinding is set depending on the stand number in the group according to the ratio
δ = (k ₁ · 947.2 · Δt-k ₂ · 4.486 · Δt ² -k ₃ · 876.4) · 10 ^-5 , mm;
where k ₁ = 1.0-1.4, mm / ° C; k ₂ = 1.0-1.4, mm / ° C ² ; k ₃ = 1.0-1.4, mm - coefficients depending on the stand number of the finishing group in which the work roll is installed, the minimum values of which correspond to the last, maximum values - to the first stands of the group,
$$\Delta t=t_c-\frac{t_{\mathrm{one}}+t_2}{2}$$

t _c - surface temperature in the middle of the roll barrel, ° C,
t ₁ and t ₂ - surface temperature at the end sections of the roll barrel, ° C, while the specific flow rate of the cutting fluid is set to 1-8 l / min.