JPH08300020A - Method for controlling flow rate of viscous liquid dispersed with lubricant for hot rolling of stainless steel - Google Patents

Abstract

PURPOSE: To enable flow rate control without installation of a flowmeter by driving a pump by a variable revolution motor, measuring the pressure of a lubricant dispersed viscous liquid delivered from the pump, and controlling the number of revolution of the motor so that the measurement of the pressure may maintain within a set range. CONSTITUTION: A duct 5 communicating with a nozzle 1 is equipped with a transfer pump 6 and in the downstream side a plunger pump 7, so that a jetting pressure is imparted by these pumps to the lubricant dispersed viscous liquid jetted from the nozzle 1. The transfer pump 6 and the plunger pump 7 are both such as their discharge is variable by the revolution control of the driving motors 8, 9. An output meter 10 is installed in the discharging side of the duct of the transfer pump 7 while a pressure gauge 11 is installed also in the discharging side of the duct of the plunger pump 7. A detected value from the pressure gauge 11 is equivalent to a discharge pressure from the nozzle 1. Control by feeding back is such that if this measured pressure exceeds a set upper limit value a, the number of revolution is lowered for the motor 9, and that if it goes below a set lower limit value b, the number of revolution is raised.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the flow rate of a lubricant-dispersed viscous liquid when jetting the lubricant-dispersed viscous liquid to a work roll in order to prevent seizure during hot rolling of stainless steel.

[0002]

2. Description of the Related Art Since stainless steel products are required to have a clean surface, it is necessary to prevent the occurrence of surface defects in the steel plate manufacturing process. However, when hot-rolling stainless steel with a hot rolling equipment such as a tandem mill, flaws often occurred on the surface of the steel sheet due to seizure of the stainless steel on the rolling rolls.

Defects on the surface of rolled products caused by seizure have become a serious problem especially in hot rolling of stainless steel. Generally, stainless steel has a Cr content of 1
3% by weight or more, which forms a stable protective film of chromium oxide on the surface of the steel, and exhibits excellent corrosion resistance and oxidation resistance by passivating the surface. However, this surface oxide film is significantly thinner than that of ordinary carbon steel and has a high resistance to hot deformation. Therefore, during hot rolling of stainless steel, seizure with the roll is likely to occur, and this seizure may cause surface defects. Seen as a problem.

Generally, seizure on the roll is said to be caused by direct contact (metal touch) between the metal surface of the material to be rolled and the metal surface of the hot rolling roll.
In stainless steel containing 13% by weight or more of Cr, it is difficult to form an oxide film, the formation rate is extremely slow even if it is formed, and as mentioned above, it is extremely thin and easy to crack. There are many opportunities for touching, which often causes burn-in.

If the surface of the stainless steel hot-rolled sheet is flawed due to the seizure, even a slight flaw is not suitable for mirror finishing applications. As a result, the use of the obtained stainless steel sheet is restricted. In addition, stainless steel plates with surface flaws require additional surface care such as polishing. Furthermore, if the degree of flaws is significant, it cannot be used as a product and is scrapped. Thus, the flaws on the surface of the steel sheet reduce the yield and increase the manufacturing cost.

From the above, in order to suppress the occurrence of surface defects during hot rolling of stainless steel as much as possible, reduction of load on the rolling rolls, selection of rolling conditions, selection of roll material, improvement of lubricant, etc. Various countermeasures have been tried. For example, as a lubricant, various methods have been proposed to prevent seizure by supplying animal fats and oils, vegetable fats and oils, mineral lubricants, synthetic lubricants and the like to the surface of a rolling roll.

On the other hand, Japanese Patent Laid-Open No. 64-83 by the same applicant
In Japanese Patent Publication No. 309, iron oxide powder is added to a viscous aqueous solution.
Disclosed is a lubricant for hot rolling of stainless steel dispersed in an amount of ˜30 wt%. Further, in Japanese Patent Application No. 6-79534 by the same application, an apparent viscosity of a viscous aqueous solution in which an acrylic acid polymer containing 10 to 40% by weight of iron hydroxide having an average particle size of 0.1 to 1 μm is dissolved is 1000.
A lubricant for hot rolling of ~ 50000 cp stainless steel is proposed.

[0008]

A lubricant prepared by dispersing the above iron oxide powder or iron hydroxide powder in a viscous aqueous solution (abbreviated as "lubricant-dispersed viscous liquid") is used for stainless steel which is hard to form an oxide film. On the other hand, it is based on the idea of supplying an oxide film equivalent to an oxide film from the outside during hot rolling, which makes it possible to prevent the aforementioned seizure. However, when actually trying to continuously supply the lubricant of this viscous dispersion to the rolling rolls in good condition, the following problems were encountered.

Regarding the rolling oil used for normal hot rolling, the flow rate is controlled so that the measured flow rate becomes a set flow rate, and the amount used is controlled. Similarly, when the above-mentioned lubricant-dispersed viscous liquid is sprayed onto a rolling roll, it is necessary to know how much is sprayed in order to control the flow rate, but the lubricant is iron oxide or Since iron hydroxide is dispersed in a viscous liquid in an amount of 1 to 30% by weight, an oval type flow meter for liquid flow rate measurement is worn so much that a measurement error becomes large, so that it cannot be used for flow rate measurement. Alternatively, even if an ultrasonic flow meter is used, it cannot be used because the reliability of the measurement of pulsating fluid is poor. Therefore, it is not possible to measure the flow rate as in the case of rolling oil and control the flow rate so that the value falls within the set range.

The present invention is intended to solve the problem of flow rate control based on the properties peculiar to the lubricant-dispersed viscous liquid.

[0011]

According to the present invention, a lubricant-dispersed viscous liquid in a storage tank is pumped by a pump to an injection nozzle, and the lubricant is applied to the surface of a work roll during hot rolling of stainless steel from this nozzle. When injecting the dispersed viscous liquid, the pump is driven by a rotation speed variable motor, the pressure of the lubricant dispersed viscous liquid discharged from the pump is measured, and the pressure of the motor is adjusted so that the measured pressure value falls within a set range. Provided is a method for controlling a flow rate of a lubricant-dispersed viscous liquid for hot rolling of stainless steel, which is characterized by controlling a rotation speed.

Further, according to the present invention, the lubricant-dispersed viscous liquid in the storage tank is pumped by a pump to an injection nozzle, and the lubricant-dispersed viscous liquid is injected from this nozzle onto the work roll surface during hot rolling of stainless steel. In this case, the pump is driven by a rotation speed variable motor, the pressure of the lubricant-dispersed viscous liquid discharged from this pump is measured, and the rotation speed of the motor is controlled so that this pressure measurement value falls within a set range. Predicting nozzle wear, nozzle clogging, or leakage from the piping system from changes in the rotational speed of the motor and pressure measurement values, and issuing an alarm when these predicted values exceed set values. A method for controlling the flow rate of a lubricant-dispersed viscous liquid for hot rolling of stainless steel is provided.

In performing such control, the initial flow rate and the flow rate increase / decrease rate or the flow rate increase / decrease amount of the pump are initially set, the injection pressure is set after the initial setting, and the injection pressure set value is set. And the actual pressure are compared and determined, when the pressure set value and the actual pressure are not equal, the rotational speed of the drive motor of the pump is controlled, and the actual flow rate is calculated from the rotational speed of the pump. The control flow includes a step of determining that the actual flow rate is within the upper and lower limit values of the set flow rate, and a step of issuing an alarm when the actual flow rate is outside the upper and lower limit values.

[0014]

According to the present invention, the flow rate of the lubricant-dispersed viscous liquid injected from the nozzle can be controlled within a set range without using a flow meter. The extent of the phenomenon such as nozzle wear, nozzle clogging, or leakage from the piping system that is encountered when using the lubricant-dispersed viscous liquid can be predicted, and the flow rate can be maintained appropriately. However, operational troubles can be avoided.

[0015]

EXAMPLE FIG. 1 shows an example of the equipment configuration in the case of injecting a lubricant-dispersed viscous liquid from a nozzle 1 onto a work roll for hot rolling. The lubricant-dispersed viscous liquid is stored in the main tank 2 and the auxiliary tank 3, and is supplied to the nozzle 1 through the switching valve 4 and the conduit 5. This lubricant-dispersed viscous liquid is a mixture of 20% by weight of iron hydroxide having an average particle size of 0.2 μm in water and a cross-linking acrylic polymer, which is a thickener, added to the viscous liquid. The state is maintained. Nozzles 1 are installed on each of the upper and lower work rolls of the rolling stand (4 on a certain stand), and the lubricant dispersion viscous liquid is evenly distributed over the rolling width of the work rolls rotating from these nozzles. Spaced for supply.

A transfer pump 6 and a plunger pump 7 are provided downstream of the transfer pump 6 in the conduit 5 leading to the nozzle 1. The injection pressure of the lubricant-dispersed viscous liquid injected from the nozzle 1 by these pumps is Granted. As the transfer pump 6 and the plunger pump 7, those having a variable discharge amount by controlling the rotational speeds of the drive motors 8 and 9 are used.

An inverter frequency control method is used for controlling the rotation speed of the drive motor, and the rotation speed control is executed by an operation signal from a control panel (not shown). Further, a pressure gauge 10 is installed on the discharge side pipeline of the transfer pump 6, and a pressure gauge 11 is also installed on the discharge side pipeline of the plunger pump 7. The detection value of the pressure gauge 11 is the nozzle 1
Corresponds to the discharge pressure from.

As described above, in the case of the lubricant-dispersed viscous liquid, it is not possible to directly measure the flow rate flowing in the conduit 5 by the flow meter. Therefore, based on the assumption that the pressure value measured by the pressure gauge 11 has a correlation with the flow rate, the rotation speed control of the motor 9 is performed so that this pressure value becomes substantially constant. That is, as shown in FIG. 2, feedback control is performed in which the rotational speed of the motor 9 is reduced when the measured pressure exceeds the upper limit set value a and is increased when the measured pressure falls below the lower limit set value b.

However, it has been found that the injection amount fluctuates despite the pressure being controlled to be substantially constant. One of the causes is wear of the nozzle 1. The nozzle used had an elliptical bore diameter of 0.5-0.6 mm on the minor axis side and 1.0 mm on the major axis side, but the wear was very large at the orifice part of the nozzle, and the pressure caused by this wear. Even if is constant, the flow rate changes. The degree of this nozzle wear varies depending on the concentration of the lubricant used and the injection conditions, but when viewed as the wear rate, it reaches 1.6 to 2.0 times the diameter of a new nozzle in a short time, and the flow rate is It will increase significantly.

The second reason is leakage of the lubricant-dispersed viscous liquid from the pipe and nozzle clogging. Even if such a phenomenon occurs, within the discharge capacity range of the pump, the rotation speed control is controlled so as to maintain a predetermined pressure, but even in this case, the pressure is apparently constant. Even if there is, the flow rate will change.

This relationship is shown in FIG. In a normal state, the relationship between the pressure and the flow rate should show a correlation as shown by the solid line A. However, if the nozzle is worn or leaks from the pipe, the flow rate increases as indicated by the dashed line B, and if the nozzle is clogged, the flow rate decreases as indicated by the broken line C.

Therefore, the pressure of the lubricant-dispersed viscous liquid discharged from the pump is measured and the measured value is set for the system in which the wear of the nozzle, the leakage from the pipe, and the nozzle clogging do not substantially occur. A predetermined flow rate can be maintained by controlling the pump discharge pressure, that is, the rotation speed of the pump motor so that the range is achieved.

However, due to the nature of the lubricant-dispersed viscous liquid, in reality leakage from the pipe can be prevented, and wear and clogging of the nozzle can be reduced as much as possible, but it is difficult to eliminate them. Is.

Therefore, for a system in which the flow rate changes even if the pressure is constant, it is necessary to control the flow rate change prediction. In order to do this, the present invention employs a method of predicting a change in flow rate from a change in the rotational speed of the pump motor.

Now, let the discharge amount of the plunger pump 9 be Q
If i (liter / min), this Qi is calculated by the equation (1). Qi = Ni × q = (fi / F) × R × q (1) where Ni: pump rotation speed (rpm) q: discharge amount per pump rotation (liter / min) fi: VVVF frequency (Hz) R: Rated pump speed (rpm) F: Commercial frequency (Hz)

In the equation (1), the rotational speed Ni of the pump is (fi / F) × R. The meaning of this equation is that the motor for driving the pump does not perform inverter (VVVF) frequency control. For example, the number of revolutions of the motor itself can be recognized by the sequencer so that Ni can be obtained. In addition, Ni itself is P which is provided on the shaft of the pump
It can be grasped from the output of LG (pulse generator). The discharge amount per revolution of the pump q (liter /
min) can be calculated if the fluid can be identified. Normal F
(Commercial frequency) is 60 (Hz). Therefore,
The discharge amount Qi of the pump 9 can be calculated by the equation (1) from the situation where the rotation speed control of the pump motor is being performed.

On the other hand, if the nozzle to be used can be specified, the flow rate Q (liter / min) flowing out from the nozzle can be obtained from the wear coefficient of the nozzle and Bernoulli's theorem by using the discharge pressure and the equation (2). Q = A × k (P / P ₀ ) ^0.5 (2) where A: nozzle flow rate (liter / min) at P ₀ (initial nozzle) k: nozzle wear coefficient P: discharge pressure (kgf / cm ² ) P ₀ : reference pressure (kgf / cm ² ).

The measured value required to calculate the equation (2) is P (discharge pressure), which is measured by the pressure gauge 11.

The normal flow rate at which the nozzle is not worn is Q
_When it is set to ₀ , the upper limit value and the lower limit value of this flow rate Q ₀ are preset, and this range is preset as a normal range. This can be performed as follows.

First, the relationship between the pressure and the flow rate in the initial state is obtained. When the nozzle is new (k ₀ ), k ₀ = 1.0. Therefore, the discharge pressure P of the pump at this time is obtained. Is changed to, for example, 10, 20, 30 to 80, and each flow rate Q corresponding to the pressure is obtained from the equation (2), and Qi is obtained from the actual pump rotation speed at that time by the equation (1). .

At that time, since the flow rate characteristic of the nozzle is generally calculated on the basis of the flow rate at the reference pressure based on water, since the lubricant dispersed viscous liquid used in the present invention has a high viscosity, the flow rate characteristic Correction is necessary. For this purpose, the flow rate ratio Qi / Q obtained from the pressure may be obtained. Let η as the flow coefficient as in Eq. (3). η = Qi / Q (3)

Therefore, the reference set flow rate Q ₀ is obtained by the equation (4). Q ₀ = A × k ₀ (P / P ₀ ) ^0.5 × η (4)

Further, the maximum value and the minimum value of the flow rate from the nozzle are set, and the above-mentioned upper limit value and lower limit value are set by the equations (5) and (6). Qmax = A × kmax × (P / P ₀ ) ^0.5 × η · · (5) Qmin = A × kmin (P / P ₀ ) ^0.5 × η · · (6)

FIG. 4 shows Q ₀ , Qma thus obtained.
An example of setting x and Qmin is shown by the relationship between the discharge pressure and the discharge flow rate.

Thus, according to the present invention, Q ₀ , Qma
By setting x and Qmin in advance, the measured value of the discharge pressure of the pump 7 and the rotational speed of the pump 9 are monitored, and these values are set to Qmax.
Feedback control is performed so as not to deviate from the setting range between Qmin and Qmin. An example of the control flow is shown in FIG. Then, as shown in the figure, when Qmax is exceeded, nozzle wear or piping leak is output as an alarm, and Qmi
If it is out of n, the nozzle is clogged.

FIG. 6 shows the result when this control was actually carried out. The lubricant-dispersed viscous liquid used was prepared by mixing 20% by weight of iron hydroxide having an average particle diameter of 0.2 μm with water and adding a thickener for a cross-linked acrylic polymer. The system of the device is as described in FIG.

In FIG. 6, the set flow rate Q ₀ is the flow rate when the nozzle is new and has no wear. The hatching area is set as the normal area so that even if the nozzle wears during operation, it will not interfere with normal operation, and the nozzle wear rate is 1.
If it exceeds 6 times (160%), it will be replaced with a new nozzle. The upper limit is set to 200% of the set value, and the lower limit is set to 50% of the set value assuming the nozzle is clogged.
From the wear record of the nozzle from the cycle process of regular repair of the rolling mill, the normal range is 100 to 160% of the set value.
And then sprayed.

The rated speed of the drive motor 9 is 60
The commercial frequency of (Hz) is 1800 (rpm), and the discharge amount of the plunger pump 7 has a characteristic of 188.5 × 10 ^-3 (liter / rev), but the pump is rotated through the speed reducer. Therefore, substitute the reduction ratio of 3.08,
The q of the equation (1) was obtained. Then, the upper limit is set by the equation (5), and the lower limit is set by the equation (6) by the relationship between the discharge pressure and the discharge amount.

The ▲ and ● marks in FIG. 6 indicate the normal range, while the ■ mark shows an example in the case where the hose connecting the nozzle and the pipe breaks and leaks. It is beyond the bounds.

[0040]

As described above, according to the present invention,
Flow control when pumping the lubricant-dispersed viscous liquid to the nozzle can be realized without installing a flow meter. As a result, the problem of measurement error over time that is encountered when using a flow meter is eliminated, and accurate flow control is always possible. Further, it is possible to predict the degree of phenomena such as nozzle wear, nozzle clogging, and leakage from the piping system, and it is possible to prevent problems due to these phenomena. Further, according to the control method of the present invention, even if the shape of the nozzle or the characteristics of the lubricant-dispersed viscous liquid is different, control can be performed accordingly.

Therefore, the problem of roll seizure that occurs during hot rolling of stainless steel has been solved in actual operation, and it has become possible to stably produce a stainless steel sheet having good surface properties.

[Brief description of drawings]

FIG. 1 is an equipment layout diagram showing an example of a lubricant dispersion viscous liquid supply facility to which the flow rate control of the present invention is applied.

FIG. 2 is a pressure change diagram when the pump discharge pressure is controlled to fall within a set range.

FIG. 3 is a diagram showing changes in the actual flow rate when controlling the pump discharge pressure to a predetermined value.

FIG. 4 is a diagram showing the relationship between pump discharge pressure and discharge flow rate.

FIG. 5 is a diagram showing a relationship between pump discharge pressure and discharge flow rate in the embodiment.

FIG. 6 is a flow chart of control of the present invention.

[Explanation of symbols]

 1 Injection Nozzle 2 Main Tank for Lubricant Dispersion Viscous Liquid 3 Auxiliary Tank for Lubricant Dispersion Viscosity Liquid 4 Switching Valve 5 Piping 6 Transfer Pump 7 Plunger Pump 8 Transfer Pump Motor 9 Rotation Speed Variable Motor 10 Pressure Gauge 11 Pressure Gauge

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F04B 49/08 311 8315-4E B21B 37/00 137Z

Claims (5)

[Claims] 1. A lubricant-dispersed viscous liquid in a storage tank is pumped to a jet nozzle by a pump, and the lubricant-dispersed viscous liquid is jetted from this nozzle onto the surface of a work roll during hot rolling of stainless steel. The pump is driven by a variable rotation speed motor, the pressure of the lubricant-dispersed viscous liquid discharged from the pump is measured, and the rotation speed of the motor is controlled so that the measured pressure value falls within a set range. Flow control method for lubricant-dispersed viscous liquid for hot rolling of stainless steel. 2. A lubricant-dispersed viscous liquid in a storage tank is pumped to a jet nozzle by a pump, and when the lubricant-dispersed viscous liquid is jetted onto the surface of a work roll during hot rolling of stainless steel, The pump is driven by a variable rotation speed motor, the pressure of the lubricant-dispersed viscous liquid discharged from this pump is measured, and the rotation speed of the motor is controlled so that this pressure measurement value falls within a set range. The amount of wear of the nozzle is predicted from the change in the number and the pressure measurement value, and an alarm is issued when the predicted amount of wear exceeds a set value. Flow control method. 3. A lubricant-dispersed viscous liquid in a storage tank is pumped to a jet nozzle by a pump, and the lubricant-dispersed viscous liquid is jetted from this nozzle onto a work roll surface during hot rolling of stainless steel. The pump is driven by a variable rotation speed motor, the pressure of the lubricant-dispersed viscous liquid discharged from this pump is measured, and the rotation speed of the motor is controlled so that this pressure measurement value falls within a set range. The degree of nozzle clogging is predicted from the change in the number and the pressure measurement value, and an alarm is issued when the predicted nozzle clogging amount exceeds the set value. A lubricant dispersion viscous liquid for hot rolling of stainless steel. Flow control method. 4. The lubricant-dispersed viscous liquid in a storage tank is pumped to a jet nozzle by a pump, and the lubricant-dispersed viscous liquid is jetted from this nozzle onto the surface of a work roll during hot rolling of stainless steel. The pump is driven by a variable rotation speed motor, the pressure of the lubricant-dispersed viscous liquid discharged from this pump is measured, and the rotation speed of the motor is controlled so that this pressure measurement value falls within a set range. Number of changes in pressure and measured pressure value predicts leakage of the lubricant-dispersed viscous liquid between the pump and nozzle, and issues an alarm when the predicted amount of leakage exceeds a set value. Flow control method of lubricant-dispersed viscous liquid for hot rolling. 5. A step of initially setting an initial flow rate and a flow rate increase / decrease rate or a flow rate increase / decrease amount of a pump, a step of setting an injection pressure after the initial setting, and a step of comparing and determining an injection pressure set value and an actual pressure. , When the pressure setting value and the actual pressure are unequal, the step of controlling the rotational speed of the drive motor of the pump, the step of calculating the actual flow rate from the rotational speed of the pump, and the upper and lower limit values of the set flow rate 5. The method according to claim 2, 3 or 4, further comprising a step of determining that the actual flow rate is within the range and a step of issuing an alarm when the actual flow rate is outside the range of the upper limit value and the lower limit value.
The method for controlling the flow rate of a lubricant-dispersed viscous liquid for hot rolling of stainless steel according to 1.