KR20000039134A - Method for measuring forces applied to hydraulically driven cast mold - Google Patents

Abstract

PURPOSE: A method for measuring forces applied to hydraulically driven cast mold is provided to accurately measure the forces regardless of the cast condition by analyzing dynamic mechanism and a frequency. CONSTITUTION: In a method for measuring forces applied to hydraulically driven cast mold, upper and lower pressures(HU,HD) of a cylinder are measured using a pressure sensor, then a vibration displacement(S) of the mold is measured using a displacement sensor. Next, the upper and lower pressure and the vibration displacement are converted into a digital signal for a predetermined duration through an A/D converter. The digital upper and lower pressure signals and the digital displacement signal are input to a separator and a pressure difference and a vibration frequency are calculated. A mold driving force is calculated using the pressure difference and the frequency. A friction force is measured by filtering the pressure difference and the frequency.

Description

Method of measuring the forces acting on the mold of hydraulically driven machine

The present invention relates to a method of continuous casting using a hydraulic driven player, and more particularly, to a method for measuring the forces acting on the mold when continuous casting using a hydraulic driven player.

Normally, in continuous casting using a resonant mold, as shown in FIG. 1, the molten steel 12 received in the tundish 11 is injected into the mold 1 through the immersion nozzle 13. When the mold 1 vibrates up and down by the hydraulic piston 9 provided in the lower part of 1), the molten steel comes into contact with the wall surface of the mold 1 and cools down to the bottom of the mold.

In the lower part of the mold, the roll 14 guides the slabs 15, and water is sprayed between each roll to cool the slabs secondarily.

As such, the process of making casts by mold vibration in molten steel is called continuous casting.

In FIG. 1, reference numeral 2 denotes a leaf spring, and 10 denotes a hydraulic cylinder.

As described above, when continuously casting using a hydraulic-driven player, various forces act on the mold.

The forces include the force by weight of the mold, the mold driving force, and the frictional force acting between the mold and the solid shell of the cast.

Among the forces, frictional force has a great influence on the quality of the cast in the continuous casting process.

In addition, the phenomenon caused by the lubrication imbalance between the cast and the mold may be a sticky breakout (sticker breakout), etc. If this cast out phenomenon occurs it may lead to an operation stop.

In other words, the above-mentioned sticky cast elution is a phenomenon in which the molten steel leaks due to the peeling of the skin of the cast steel by the adhesion of the cast steel to the wall surface of the mold.

Therefore, by measuring the frictional force, it is possible to predict the current operating operation state, the surface quality of the cast steel, the breakout of the cast steel, and the like.

The frictional force acting between the mold and the cast steel is affected by the composition of the steel and the properties of the mold flux, the taper of the mold, the heat transfer state of the molten steel, and the like.

Conventional methods for measuring the frictional force acting between the mold and the cast piece exploit the fact that the strain is proportional to the strain force by finding a point where the strain is large when the mold is in operation.

In the conventional method, since the friction force acting between the mold and the slab cannot be directly measured by the deformation force, continuous casting operation is performed by injecting the deformation force and molten steel into the mold when the casting machine is operated without the liquid steel in the mold. The frictional force was used as the difference in the deformable force acting when

However, since the conventional method is not a method of directly using the friction force, there is a problem that the friction force cannot be accurately measured under different casting conditions such as casting speed, casting vibration frequency, and width of cast steel.

The present inventors have developed a device for measuring the frictional force between the mold and the slab of the hydraulically driven resonant mold that can solve the problems of the conventional method, which has been patented as Korean Patent Application No. 97-64793.

The frictional force measuring device presented in the above-mentioned Korean patent application is configured to measure the frictional force by dynamic equations using the weight of the mold, vibration displacement of the mold, elastic modulus of the leaf spring, and up and down hydraulic force of the hydraulic cylinder.

However, the weight of the mold used in the actual industry is the actual weight, and the weight of all the molds cannot be exactly matched. The elastic modulus of the leaf spring is invariable because the spring itself deteriorates under continuous operation. It decreases over time.

Therefore, in order to accurately measure the friction force using the friction force measuring apparatus, there is a problem in that the weight of the mold is accurately measured before the continuous casting operation is started, and the elastic modulus of the leaf spring is continuously changed over time.

MEANS TO SOLVE THE PROBLEM The present inventor conducted research and experiment in order to solve the above-mentioned all the problems of the prior art, and based on the result, this invention proposes this invention. This invention uses a hydraulically driven resonance mold for continuous casting. By using the dynamic mechanism and frequency analysis in this method, the aim is to more accurately measure the physical forces acting between the mold and the cast without the use of variables related to the mechanical specifications of the mold.

1 is a block diagram showing a typical player

2 is a block diagram showing an example of a player for implementing the present invention

3 is a circuit diagram showing an example of a separator;

4 is an example of a frequency analysis result for the hydraulic force

Explanation of symbols on the main parts of the drawings

1.Mould 4 ... Pressure sensor 5 ... Displacement sensor 6 ... Separator 7 ... Computer

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention provides a mold for forming a cast piece having a predetermined shape, a plurality of hydraulic cylinders having a piston for vibrating the mold up and down, a plurality of pressure sensors provided at regular intervals in the upper and lower portions of each hydraulic cylinder to measure the hydraulic pressure, A hydraulic pressure sensor including a displacement measuring sensor installed at one end of the piston to measure vibration displacement of the mold, and an A / D converter converting analog values measured from the pressure sensor and the displacement measuring sensor into digital signals, respectively. In the method of continuous casting using a driven continuous casting machine,

And a separator configured to receive the digital signal of the pressure sensor and the digital signal of the displacement measuring sensor and separate each force acting on the mold;

Measuring the upper pressure (HU) and the lower pressure (HD) of the cylinder from the pressure sensor, and measuring the vibration displacement (S) of the mold by the displacement sensor;

Converting the upper pressure HU, lower pressure HD, and vibration displacement S of the mold into a digital signal through an A / D converter for a predetermined time (sampling period);

Inputting an upper pressure (HU) signal and a lower pressure (HD) signal of the hydraulic cylinder converted as described above to a separator and subtracting it as shown in Equation (1) to obtain a hydraulic vehicle (H);

H = HD-HU

Inputting the mold vibration displacement (S) signal during the time T converted as described above to a separator and frequency analysis to obtain the vibration frequency (ω) of the mold;

Calculating a force M due to the weight of the mold by averaging the hydraulic difference H obtained during T time as in the following equation (2);

M = average {H}

Measuring a mold driving force by extracting signals appearing between bandwidths dω which are sufficiently small with respect to the hydraulic pressure H through a band-pass filter (BPF);

Measurement of the forces acting on the mold of the hydraulically driven player comprising the step of extracting a signal of frequency 2ω or more with respect to the hydraulic vehicle (H) through a high-pass filter (HPF, High-pass filter) It is about a method.

Hereinafter, the measuring method of the present invention will be described with reference to the drawings.

FIG. 2 shows a plurality of hydraulic cylinders 10 and hydraulic cylinders 10 each including a mold 1 for forming a cast piece having a constant shape, a hydraulic piston 9 for vibrating the mold 1 up and down. Pressure sensor 4 is provided at the upper and lower portions at regular intervals to measure the hydraulic pressure, displacement measuring sensor 5 installed at one end of the hydraulic piston 9 to measure the vibration displacement of the mold (1), and the pressure sensor (4) and a separator (100) is added to a conventional hydraulically driven continuous casting machine including an A / D converter (8) for converting the analog values measured from the displacement measuring sensor (5) into digital signals, respectively. The continuous casting machine is provided with.

The mold 1 is supported by a support frame 2 by a leaf spring 3.

The separator 100 is configured to separate the respective forces acting on the mold by receiving the digital signal of the pressure sensor provided in the hydraulic cylinder 10 and the digital signal of the displacement sensor 5 for measuring the vibration displacement of the mold. The separator 100 is connected to a computer 7 that receives and processes digital signal data.

An example of the separator 100 is shown in FIG. 3.

In order to measure the forces acting on the mold according to the present invention, first, the upper pressure (HU) and the lower pressure (HD) of the cylinder are measured from the pressure sensor (4), and the vibration displacement of the mold in the displacement sensor (5). (S) should be measured.

Next, the upper pressure HU, the lower pressure HD, and the vibration displacement S of the mold are converted into digital signals through the A / D converter 8 for a predetermined time (sampling period), and the separator 100 ).

The upper pressure HU and lower pressure HD signals are subtracted from the subtractor 101 of the separator 100 as in Equation (1) to obtain a hydraulic pressure H.

The mold vibration displacement S during the time T converted as described above is frequency-analyzed by the frequency analyzer 102 of the separator 100 to obtain the vibration frequency ω of the mold.

The hydraulic pressure H obtained during the T time as described above is averaged as in the following formula (2) in the average machine 103 to obtain the force M due to the weight of the mold.

(Equation 2)

M = average {H}

The mold driving force (O) is measured by extracting signals appearing between a sufficiently small bandwidth dω with respect to the hydraulic pressure H through the band-pass filter (BPF) 104.

The frequency multiplier 105 doubles the frequency omega and extracts a signal having a frequency of 2 omega or more with respect to the hydraulic pressure H through a high pass filter (HPF) 106 to obtain a frictional force F. Measure

Referring to the theoretical basis of the method for measuring the forces acting on the mold according to the present invention.

In the case of continuous casting using the hydraulically driven machine configured as described above, the resonant mold is controlled to perform sinusoidal vibration by the following equation (3).

_{s (t) = s o ·} sinωt

In the above equation ω = 2πｆ, ｆ is the vibration frequency and s _o is the amplitude of vibration.

When the mold vibrates, the speed [v (t)] and acceleration [a (t)] of the mold are as shown in the following formulas (4) and (5), respectively.

v (t) = s' (t) = s _o ωcosωt

a (t) = s '' (t) = -s o ω 2 · sinωt = -ω 2 · s (t)

The force acting on the mold by the leaf spring 2 connected to the mold 1 is expressed by the following equation (6).

F _s (t) = K s (t)

Where K is the elastic modulus of the leaf spring (2).

The force due to the mass of the mold and the vibration acceleration is shown in the following equation (7).

F _a (t) = m a (t)

Where m is the mass of the template (1).

The vibration velocity of the mold is related to the damping factor and the frictional force acting between the mold and the slab.

The force acting on the speed is shown in the following equation (8).

F _v (t) = Dv (t) + F _r (t) sign (v _c -v (t))

Where D is attenuation constant, F _r (t) is a frictional force, and sign () is a sign function that maps 1 if the value in parentheses is positive and -1 if it is negative.

Indeed, since the mold is continuously subjected to the excitation force, the force due to the damping constant D can be neglected and F _v (t) can be regarded as the frictional force acting between the mold and the slab.

The excitation force F _e (t) for driving the mold is the sum of the forces exerted on the mold, the force that the leaf spring acts on the mold F _s (t), the inertia force of the mold F _a ( t), the frictional force F _v (t) between the mold and the slab, and the force of the earth's gravity on the mass of the mold.

F _e (t) = F _v (t) + F _s (t) + F _a (t) + mg

= F _v (t) + {F _s (t) + F _a (t)} + mg

= F _v (t) + (K-mω ² ) s (t) + mg

= F _v (t) + F _o (t) + mg

Where g is gravity acceleration and F _o (t) is a mold driving force, which is the same as the following formulas (10) and (11).

g = 9.8 m / s ²

F _o (t) = (K-mω ² ) s (t)

With respect to the input s (t), the output F _e (t) is the pressure applied to the hydraulic cylinder and is the hydraulic difference in the upper and lower cylinders around the piston 9, and the hydraulic sensor 4 is installed in the upper and lower cylinders 10. Can be obtained by calculating the difference between the signal values of the up and down sensors.

s (t) is the vibration displacement of the mold that changes with time t, and the displacement value is obtained using the displacement measuring sensor 5.

When molten steel does not exist in the mold in the equation of the above-mentioned vibration force F _e (t), the friction force F _v (t) does not work (F _v (t) = 0).

When a frictional force does not act, it is as following formula (12).

F _e (t) = (K-mω ² ) s (t) + mg

The equation above when there is no filler inside the mold is a linear system.

Therefore, for sinusoidal input s (t) having an oscillation amplitude of s _o and an oscillation frequency of ω, the output F _e (t) appears in the form of a sine wave of the same frequency.

In other words, if the hydraulic force F _e (t) is subjected to frequency analysis (FFT) when no friction force is applied, the mold driving force F _o (t) appears in the frequency domain at the same frequency ω as the vibration signal s (t). Weight mg by weight is expressed as DC component.

Thus, frequency analysis of the hydraulic force F _e (t) in the presence of frictional force results in a mold drive force F _o (t) at the frequency ω and a frictional force F _v (t) due to the multiples of ω.

An example of frequency analysis of the hydraulic force F _e (t) is shown in FIG. 4.

At this time, the actual vibration frequency ω of the mold is 4.8 Hz.

The actual vibration frequency ω of the mold is calculated from the mold vibration displacement signal s (t).

In the frequency range for the hydraulic force F _e (t), the signals due to the DC component by the weight of the mold, the driving force to drive the mold at the vibration frequency ω, and the frictional force at the multiples of ω appear.

Therefore, signal processing operations are performed on the mold vibration displacement signal s (t) and the hydraulic force signal F _e (t) to separate the force, the mold driving force, and the frictional force by the weight acting on the mold.

As described above, the present invention can take measures such as the operation of injecting a mold flux to increase the lubrication action between the mold and the slab when the frictional force is large while measuring the frictional force during casting. Sticky cast rupture rapidly increases the friction between the mold and the castings in a short time, so if the friction is greater than normal by monitoring the friction, take measures such as increasing the injection of the mold flux or reducing the casting speed beforehand. There is an effect that can be prevented.

Claims (1)

A plurality of hydraulic cylinders having a mold for forming a cast piece having a predetermined shape, a plurality of hydraulic cylinders having pistons for vibrating the mold up and down, a plurality of pressure sensors provided at regular intervals at upper and lower portions of each hydraulic cylinder, and for measuring hydraulic pressure, Hydraulic-driven continuous comprising a displacement measuring sensor installed at one end and measuring vibration displacement of the mold, and an A / D converter converting analog values measured from the pressure sensor and the displacement measuring sensor into digital signals, respectively. In the method of continuous casting using a casting machine, And a separator configured to receive the digital signal of the pressure sensor and the digital signal of the displacement measuring sensor and separate each force acting on the mold; Measuring the upper pressure (HU) and the lower pressure (HD) of the cylinder from the pressure sensor, and measuring the vibration displacement S of the mold by the displacement sensor; Converting the upper pressure HU, lower pressure HD, and vibration displacement S of the mold into a digital signal through an A / D converter for a predetermined time (sampling period); Inputting an upper pressure (HU) signal and a lower pressure (HD) signal of the hydraulic cylinder converted as described above to a separator and subtracting it as shown in Equation (1) to obtain a hydraulic vehicle (H); (Equation 1) H = HD-HU Inputting the mold vibration displacement (S) signal during the time T converted as described above to the separator and frequency analysis to obtain the vibration frequency ω of the mold; Calculating a force M due to the weight of the mold by averaging the hydraulic difference H obtained during T time as in the following equation (2); (Equation 2) M = average {H} Measuring a mold driving force by extracting signals appearing between bandwidths dω which are sufficiently small with respect to the frequency difference ω through the band pass filter (BPF); Measurement of the forces acting on the mold of the hydraulically driven player comprising the step of extracting a signal of frequency 2ω or more with respect to the hydraulic vehicle (H) through a high-pass filter (HPF, High-pass filter) Way