JPH0366463A - Method for measuring solid and viscous frictional forces between mold and cast billet in continuous casting and continuous casting method - Google Patents

Abstract

PURPOSE:To predict the surface quality of a cast billet with high precision by using the frictional force between a mold and the cast billet which are obtained from the wave form of the exciting force of the mold. CONSTITUTION:The frictional force R between the mold and the cast billet of continuous casting is obtained from the wave form of the exciting force of the mold, divided into a solid frictional force Rs and a viscous frictional force RL and obtained by formulas. In the formulas, Rms ; Rs between mold and lubricating agent, x ; speed of mold, Vp ; travel speed of solid phase of lubricating agent between mold and cast billet, Rxx ; Rs between lubricating agent and cast billet, Vr ; travel speed of cast billet, RmL ; RL between mold and lubricating agent, RsL ; RL between lubricating agent and cast billet are defined. Consequently, the surface quality of the cast billet can be predicted with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION However, [Industrial Application Field] The present invention relates to a method for measuring the frictional force between a mold and a slab in continuous steel casting equipment, and a continuous casting method using the measuring method.

[Conventional technology 1] In continuous steel casting, it is necessary to reduce and stabilize the frictional force generated between the mold and the slab in order to improve the surface quality of the slab and improve the stability of casting. It was wanted. Therefore, when selecting the lubricant called mold powder that is optimal for the casting conditions (casting speed, 14 types, casting temperature, etc.).

This method of measuring frictional force played a very important role.

Now, the conventional method of measuring frictional force is to measure the excitation force of the mold with a load cell, and then subtract the inertial force of the mold, the equivalent spring force of the mold vibration system, the viscous force, and the mechanical friction force of the vibration system. It is common to find the frictional force R between the mold and the slab using the following formula (1). Mass C: Viscosity coefficient of the mold vibration system: Equivalent spring constant fO of the mold vibration system: Mechanical frictional force 'i of the mold vibration system: Large mold acceleration: Mold speed X: Mold displacement.

The frictional force R between the mold and the slab oscillates with a certain periodicity as the mold vibrates, but evaluating only this amplitude as a representative value of the frictional force makes it difficult to accurately evaluate and select a lubricant. It was difficult to carry out the process in a consistent manner and to determine how to deal with the surface quality of the slab.

Therefore, we evaluate the frictional force R between the mold and slab by dividing it into viscous friction force and solid friction force, and dividing these into positive period (slab moving speed VR > mold speed large) and negative period (VR ≦ large). The method of
This method was proposed in Publication No.-18553.

However, when separating the frictional force R between the mold and the slab into the viscous frictional force RL and the solid frictional forces R and S, conventional methods ignore the moving speed of the thin solidified layer of lubricant that exists between the slab and the mold. Since the frictional force R between the mold and the slab is simply expressed by the following equation (2), there is a problem in that the viscous frictional force RL and the solid frictional force RS cannot be accurately evaluated.

R=RL+RS=Rfff)C-VR)Here, R
L: viscous friction coefficient R″S=solid friction coefficient.

In other words, when selecting and evaluating lubricants and evaluating slab surface quality based on the values of viscous frictional force R1 and solid frictional force RS, there is a risk of not being able to make the correct judgment and making the wrong judgment. There is a point.

[Problem to be solved by the invention]

The present invention enables highly reliable selection and evaluation of lubricants and evaluation of slab surface quality by separating the content of the frictional force R between the mold and the slab, that is, the viscous friction force and the solid friction force, with more precision. The purpose is to That is, regarding quality control of slabs, it is thought that the quality of lubrication between the mold and slab depends on the inflow state of molten powder during the negative period. Therefore, during operation, especially in the negative period, the viscous friction force R2
By continuously monitoring the value, it is possible to detect fluctuations in the lubricant inflow state, and by visually inspecting the corresponding part of the slab that corresponds to the detected fluctuation, the surface quality of the slab can be guaranteed. be able to.

Furthermore, it can be applied to predicting slab breakout.

That is, it is considered that the solid friction force RS reflects the mechanical contact state between the mold and the slab. Therefore, a breakout can be predicted by detecting the restraint between the mold and slab at the early stage of the restraint breakout, especially through the solid friction force in the positive period.

As can be seen from the above explanation, if the frictional force exerted on slab defects is divided into two parts and one is not divided accurately, the correlation with each slab defect will vary greatly, reducing the number of slab defects. Otherwise, the above correlation will be misunderstood.

[Means to solve the problem J During casting, i! It is known that mold powder as a lubricant is consumed in an amount of about 0.3 to 0.0, skg/m'.

The mold is cooled to a surface temperature of 200 to 500°C, the solidification temperature of the lubricant is estimated to be approximately 700 to 1200°C, and the surface temperature of the slab inside the mold is estimated to be approximately 1100 to 1400°C. It is thought that the lubricant inside the mold is solid on the mold side and liquid on the casting side.

The total thickness of this lubricant is estimated to be 0.3 to 2 mm from the thickness of the mold powder piece taken at the lower end of the mold, of which 0.1 to 0.3 mm is in the liquid phase and the majority is in the solid phase. It is said that. Nevertheless, conventionally, when separating the frictional force R into the viscous frictional force RL and the solid frictional force RS, analysis and calculations have been performed while ignoring the moving speed of the lubricant existing between the mold and the slab.

The present inventors have clarified the behavior shown in FIG. 3 as a result of various experiments and analyses. The step-like change in the frictional force R between the mold and slab that was actually obtained (the broken line in Figure 3) does not occur at the time of large VR=0, as has been conventionally said. This is a behavior that cannot be explained by equation (2) above.

Therefore, the friction force R is calculated by introducing the moving speed of the lubricant as follows (3)
) It has been found that the waveform behavior of the frictional force H between the mold and the slab actually obtained by equation (1) can be approximately explained.

+RSL (VP-VR) where, Vp: Movement speed of the solidified phase of the lubricant between the mold and the slab R''■L: Coefficient of viscous friction between the mold and the lubricant Rms:
Solid friction coefficient between mold and lubricant RS1: Viscous friction coefficient between lubricant and slab R: bs: Solid friction coefficient between lubricant and slab.

In equation (3) above, the first term on the right side is the frictional force due to the viscosity between the mold and the lubricant, the second term is the solid frictional force between the mold and the lubricant, and the third term is between the lubricant and the slab. The fourth term means the solid friction force between the lubricant and the slab, and the sum of these is expressed as the frictional force R between the mold and the slab. Therefore, the sum of the first and third terms in equation (3) above is the viscous friction force R
L, the sum of the second and fourth terms becomes the solid friction force RS.

Here, it has been found that VP can be determined by defining it as follows.

In other words, the step-like change point of the frictional force R between the mold and the slab, as shown in (b) in Figure 3, obtained by using equation (1), is from the mold of the solidified phase of the lubricant fixed to the mold. means the point of movement due to slip.

This method assumes that the mold speed at this time is equal to the lubricant moving speed Vp, and that Vp when no slip occurs is equal to the mold speed. The slip point is determined by time differentiation of the frictional force R between the mold and the slab, as shown in FIG. 3(a). If Vp per -cycle is determined in this way, it will be as shown in FIG. 3(d).

When the frictional force R between the mold and the slab is qualitatively determined from the VP thus determined based on the above equation (3), the result is as shown in FIG. 4(g). In other words, as mentioned above, x-VR≠
This can fully explain the step change in the frictional force R between the mold and the slab when the frictional force R is 0.

Therefore, since R, x, VR, and vp are given in equation (3), the four unknowns are RL, Rms, RSt, and RSs.

The method for finding these four unknowns is as follows.

■ Since large-VP and Vp-VR are functions of time, they are divided into positive periods and negative periods excluding the data of Heaven = Vp and Vp = = Vp, and N (4 or more) time series (3
), the coefficients R■L, R'' can be calculated by multiple regression.
(2) The sum of L and solid friction coefficient (Rms+R S) is obtained.

■ When heaven = VP, the 1.2th term on the right side of equation (3) is zero, so equation (3) can be expressed as ... (4) In other words, in the area where x = Vp By creating equation (4) for M (2 or more) time series divided into positive periods and negative periods, RSL and RSs can be found by multiple regression.

(2) Similarly, when VP=VR, the frictional force R between the mold and the slab is expressed by the following equation (5).

VP: From the two large -Vp values that become VR (5)
If two equations are created, RL and Rr can be obtained by simultaneous equations.
Find nS. In addition, Rff15 is calculated using the RSs of the positive period and the negative period obtained in the above (■), and the sum of the solid friction forces obtained in the above (RSs + Rmsl to R
It can also be determined by subtracting Ss.

RL, Rms, RiL obtained from the above,
By substituting RS5, x, Vp, and V* into the above equation (3), it becomes possible to separate the frictional force into four frictional forces that constitute one period of change in the frictional force H between the mold and the slab.

As described above, according to the present invention, the friction force in each region of the positive period and the negative period can be detected separately. Therefore, sufficient measures can be taken to predict breakout and determine whether or not the lubricant is appropriate. Therefore, the present invention can be effectively applied to the following various cases.

That is, regarding slab quality control, it is thought that the quality of lubrication between the mold and slab depends on the inflow state of molten lubricant during the negative period. Therefore, if the present invention is used to continuously monitor the viscous friction force RL value during operation, especially during the negative period, it is possible to detect fluctuations in the lubricant inflow state, and to take appropriate measures in response to the detected fluctuations. The surface quality of the slab can be guaranteed by visually inspecting the relevant part of the slab.

Furthermore, the present invention can be applied to predicting slab breakout. That is, it is considered that the solid friction force RS reflects the mechanical contact state between the mold and the slab. Therefore, breakout can be predicted by detecting the restraint between the mold and slab at the initial stage of restraint breakout, particularly through the solid friction force in the positive phase region.

Furthermore, the present invention can be applied to equipment monitoring and diagnosis. That is, by tracking the viscous frictional force and the solid frictional force separately in the positive period and the negative period continuously and over a long period of time, it is possible to predict the deterioration of mechanical hardness and use it as a means for monitoring and diagnosing equipment.

Furthermore, the present invention can be applied to determine the suitability of a lubricant. That is, since the correspondence between the friction force and the surface properties of the slab is used to determine the suitability of a lubricant that affects the surface properties of the slab, the friction force value can be used.

By computing the above procedure online, the frictional force R between the mold and the slab is converted into the solid frictional force RS.
The amplitude of RS (ΔRS) and the amplitude of RL (ΔRL) within the cycle, the maximum values of ΔR1, and ΔRS in the positive period and negative period, ΔRL, ΔRL, and ΔRSΔRS are characterized. If used as a value, it becomes possible to predict the surface quality of slabs and optimize lubricants with higher accuracy than before.

FIG. 2 shows the calculation processing flow of ΔRS and ΔRL.

After noise is filtered from the measured values of Fm, Fm, and VR, the frictional force R between the mold and the slab is calculated. At this time, heaven was given by integrating the father in advance, and M,
C, and i' are given values determined from data when the mold is in idle operation (only vibration is performed without casting, so R=O). Vp is determined from the change in R between the mold and the slab over one cycle, separated into R2g:RS and RL, and finally P PΔRS, ΔR
L, ΔRS, ΔRS, ΔRL, and RL are found. By monitoring changes in these characteristic values over time, the critical values at the time of occurrence of defects 1 on the surface of the slab, such as bumps, vertical cracks, depressions, etc., can be determined in advance, and this can be used to predict the occurrence of defects. Further, by selecting a lubricant such that these characteristic values are lower than these critical values, optimization of the lubricant becomes possible.

(Example) A 5US430 slab with a cross section of 200 x 1030 was cast using a continuous caster for steel having a mold vibration mechanism shown in Fig. 1.
Casting was performed at a casting speed (VR) of 0.8 m/min.

In FIG. 1, the molten metal poured into the mold is continuously cast as a slab 2 while being drawn out at a moving speed VR. Frictional force R is generated between the mold l and the slab 2. The mold l is supported by a spring 9 and is vibrated by a motor 3. The motor 3 vibrates the vibrating beam 4 in the direction of the arrow 5, and the vibrating lever 6 supported on the fulcrum 7 vibrates the mold l in the direction of displacement lO. Load cell 8 detects mold vibration resistance force.

The mold amplitude at this time is 8 mm, and the vibration frequency is 44 to 67 cycles/min. The lubricant is Powder A, which is used in the process.
Two types of powder were used: and Powder B, which was used experimentally.

The vibration drag force Fm of the mold is determined by the load cell 8 as shown in Figure 1.
It was measured with Prior to measuring the friction force, the total mass M of the vibration system was 25.3 tons, and the viscosity coefficient C was determined from the measurement of Fm during idle operation.
was determined to be 0, and the equivalent spring constant was determined to be 1.74 ton/cm, and using these values, the frictional force R between the mold and the slab was determined from equation (1) using the calculation flow shown in FIG. This mold/
Estimating Vp from the time differential value of R between slabs, ΔRL/ΔR
I asked for

FIG. 5 shows the relationship between ΔRL/ΔR and casting speed. For comparison, the value of ΔRL/ΔR obtained by separating the same data into RL and RS using the conventional method (1) is also shown. As can be seen from this figure, Powder B has a larger ratio of viscous frictional force than Powder A, and also has a smaller absolute value, so it was judged to be advantageous for the surface quality of the slab. However, the results of the conventional method showed no difference in powder.

The actual number of grooves (number/rf) on the surface of the slab is shown in Table 1.

Since there is less powder B in Table 1, the determination according to the present invention is more sensitive and reliable than the determination according to the conventional method, and the variation (standard deviation σ) is also smaller.

From the above, it can be seen that the friction force measurement between the mold and the slab according to the present invention can predict the surface quality of the slab with high accuracy.

[Effects of the Invention J] According to the present invention, (1) Since the surface quality of the slab can be predicted with high accuracy, surface care judgment can be made without manual intervention, resulting in highly efficient work.

(2) Since the surface quality can be predicted with high reliability, partial casting work is possible and yield increases.

The following effects can be expected.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an embodiment showing the framework of the mold vibration mechanism, Fig. 2 is an example of a calculation/analysis flowchart for carrying out the present invention, and Fig. 3 is a diagram showing the lubricant from the frictional force between the mold and the slab. 4 is a schematic diagram for estimating the moving speed of the solidified phase, FIG. 4 is a chart qualitatively showing the frictional force behavior based on the present invention, and FIG.
Figure 6 shows the viscous frictional force ΔRc, /
It is a graph showing a comparison of ΔR and ΔRL.

Claims (1)

[Claims] 1. A method for measuring the frictional force between a mold and a slab in continuous casting, comprising: determining the frictional force R between the mold and the slab from an excitation force waveform of the mold;
A method for measuring solid frictional force and viscous frictional force between a mold and a slab in continuous casting, characterized in that the frictional force R is divided into a solid frictional force R_S and a viscous frictional force R_L, and each is determined by the following equation. R=R_S+R_L R_S=R_■_S・(■−V_P)/｜■−V_P|
+R_■_S・(V_P-V_R)/｜V_P-V_R
｜ R_L=R_■_L・(■−V_P)+R＿■＿L・(
V_P-V_R) However, R_■_S: Solid friction coefficient between the mold and lubricant ■: Mold speed V_P: Movement speed of the solidified phase of the lubricant between the mold and slab. R_■_S: Solid friction coefficient between lubricant and slab V_R: Slab moving speed R_■_L: Viscous friction coefficient between mold and lubricant R_■_L
: Coefficient of viscous friction between lubricant and slab 2 Solid friction force R_S between mold slabs obtained using the measurement method according to claim 1
1. A continuous casting method characterized by detecting a restraint breakout from a change in , and adjusting operating conditions based on the detection. 3. The inflow state of the lubricant is detected from the change in the viscous frictional force R_L between the mold slabs obtained using the measuring method according to claim 1, and the operating conditions are adjusted based on the detection. Continuous casting method.