JPH04722B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining when to replace a mandrel in a tube rolling mill that reduces the wall thickness of a raw tube using grooved rolls while the mandrel is passed through the tube.

Conventionally, the method of manufacturing tubes by rolling involves rolling a blank tube pierced with a piercer or the like to a predetermined outer diameter and wall thickness using a mandrel mill, plug mill, etc., and there are various rolling methods.

In recent years, mandrel mills have been adopted from the viewpoint of productivity such as rolling efficiency, yield advantages, and difficulty in automation, as well as from the viewpoint of quality such as the quality of the inner surface of the tube material, accuracy of wall thickness distribution, and the occurrence of scratches. It's starting to look like this.

FFM is also applied to the rolling method using this mandrel mill.
(Full Float madrel mill), SFM (Semi-
Restrained floating mandrel mill), RRM
(Fully−Restrained＆Retracted mandrel mill)
Methods such as these are being implemented. The above-mentioned mandrel mill methods are classified mainly based on the difference in the operation of the mandrel, but the method still involves rolling the raw pipe passed through the mandrel between a grooved roll and a mandrel.

FIGS. 1 and 2 are schematic diagrams before and during rolling with a mandrel mill. The figure shows a configuration using RRM. In FIGS. 1 and 2, reference numeral 1 designates a mandrel propulsion block, to which a mandrel bar 2 is connected, and to this mandrel bar 2, a mandrel 3 is further connected.

4 is a propulsion device for the mandrel propulsion block 1, and 5 is a drive motor for the propulsion device 4. The mandrel propulsion block 1 slides on a track, which is not shown in the figure. 6 is a mandrel drive control beam, which is connected to the mandrel propulsion block 1 during rolling, as shown in FIG.

The mandrel drive control beam 6 is controlled by a mandrel drive control device 7 and a mandrel drive motor 8 which is a drive source. A gear mechanism or a hydraulic mechanism is generally used for the mandrel drive control device 7. The drive rod 9 is controlled by the mandrel drive control device 7.
is drive-controlled, the mandrel drive control beam 6 connected to this drive rod 9, the mandrel propulsion block 1 connected to the mandrel drive control beam 6, and the mandrel 3 integral with this mandrel propulsion block 1. The drive will be controlled.

When the raw tube 10 pierced by a piercer or the like comes onto the entrance table, the mandrel propulsion block 1 moves forward, and the mandrel 3 moves the raw tube 10 and the grooved rolls r ₁ , r ₂ . . . r incorporated into the rolling stand. It penetrates between _o-1 and r _o , and at the same time mandrel propulsion block 1
and the mandrel drive control beam 6 are connected.

While the raw pipe 10 is being rolled by the grooved rolls r ₁ to r _o, the mandrel 3 is controlled by the mandrel drive control device 7.
Movement and speed will be controlled. 14-
(1), 14-(2),...14-(n-1), 14-
(n) are motors for driving the grooved rolls r ₁ , r _{2 .} . . r _o-1 , r _o, respectively.

In Figures 1 and 2, the grooved rolls r ₁ , r ₂
...r _o-1 and r _o are drawn in a line as shown in the figure for convenience, but in reality, it is common for the roll axis of each stand to be arranged at an intersection angle of 90° with the adjacent stud. be. In actual work, it is extremely important to control the tension or compression force acting on the tube material passed through each stand and rolled to an appropriate value in accordance with the rolling conditions.

Inappropriate tension or compressive force acting on the tube material between the stands not only changes the diameter and wall thickness of the tube material, resulting in uneven dimensions in the rolled product, but also
This causes serious defects such as protrusion and scratches. Further, if the mandrel is not replaced at an appropriate time, there is a problem that the inner columnar shape of the product tube material will not be good.

However, in tube rolling mills such as mandrel mills that are equipped with a mandrel and grooved rolls, and rolling is performed between the mandrels and grooved rolls, the mandrels are not replaced at an appropriate time. is the current situation.

The present invention enables quantitative determination of the coefficient of friction between the inner surface of the pipe material and the surface of the mandrel such as a mandrel, and enables mandrel replacement to obtain a product with good inner surface properties of the pipe material without making a mistake in the timing of replacing the mandrel. It provides a method for determining the timing.

First, a basic model in which a tube material is rolled between a mandrel and a grooved roll will be described. Third
The figure shows pipe material 1 between grooved roll r _i and mandrel 3.
1 is a schematic diagram showing rolling. Although the tube material before rolling is referred to as the raw tube 10, during rolling it is all referred to as the tube material 11.

In Figure 3, mandrel 3 has rear tension.
T _B,i is working, and the forward tension of the mandrel T _B,i+1
= 0, or the rear tension T _n,i of the tube material and the front tension T _n,i+1 of the tube material are both in the state of T _n,i =T _n,i+1 =0. The longitudinal tension may be a compressive force.

Such a state corresponds to RRM or SFM of the above-mentioned mandrel mill rolling methods, and corresponds to a case where rolling is performed only on the first stand or the last stand.

In Figure 3, the rolling load is P _i,0 and the rolling torque is G _i,0
Further, the coefficient of friction between the inner surfaces of the mandrel 3 and the tube material 11 is assumed to be μ _i . The rolling torque G _i,0 is expressed by equation (1).

G _i,0 = T _B,i・_i +2a _i・P _i,0 ...(1) In equation (1), _i is the shape and dimensions of the grooved roll and the dimensions and shape of the pipe material before and after rolling. It is the average roll radius determined by the diameter of the mandrel, and a _i is generally 2a _i = G _i,0 / in rolling plate material or long steel.
It corresponds to the physical quantity expressed as P _i,0 .

Since the mandrel 3 and the tube material 11 always have a relative velocity, μ _i is a coefficient of kinetic friction, and there is a relationship expressed by the following equation (2).

T _B,i = μ _i・P _i,0 ...(2) From equations (1) and (2), we obtain the following equation.

G _i,0 = (μ _{i i} + 2a _i ) P _i,0 ...(3) That is, equation (3) is the relation between rolling load and rolling torque when there is no tension when rolling pipe material using a mandrel. . However, in a continuous rolling mill, tension or compression forces act on the rolled material on the front and rear surfaces of the stand.

FIG. 4 is a schematic diagram during continuous three-stand rolling. As mentioned above, the roll axes of adjacent stands are arranged at a 90° intersecting angle with each other.
It is shown as shown for convenience. In Figure 4,
The rolling torque G _i of the i-stand is expressed by the following equation (4).

G _i = T _B,i・_i −T _B,i+1・_i+1 +2a _i P _i +ΔG _i,b −ΔG _i,f ……(4) Here, from the balance of the force in the rolling direction, the following There is a relationship expressed by equation (5).

T _B,i = μ _i・P _i T _B,i+1 = μ _i+1・P _i+1 ...(5) Therefore, equation (4) becomes the following equation.

G _i = (μ _i・_i・P _i −μ _i+1・_i+1・P _i+1 ) +2a _i・P _i +ΔG _i,b −ΔG _i,f ……(6) Equation (4), In addition, in equation (6), ΔG _i,b is i
Viewed from the stand, this is the torque change from the no-tension state due to the generation of rear tension T _n,i (hereinafter referred to as rear torque), and ΔG _i,f is the front tension applied to the pipe material 11.
This is the torque change from the time of no tension due to the occurrence of T _n,i+1 (hereinafter referred to as forward torque). From equation (6), ΔG _i,f becomes equation (7).

ΔG _i,f = (μ _i・_i・P _i −μ _i+1・_i+1・P _i+1 )+2a _i P
_i −G _i +ΔG _i,b ...(7) In order to make the forward tension of i-stand zero, the correction amount for the roll rotation speed of i-stand is to add the proportional-integral control gain g _i of i-stand to the forward tension torque. It is given by the following equation.

ΔN _i =g _i ·ΔG _i,f (8) N _i indicates the motor rotation speed of the i-stand. Further, when controlling the tension applied to the front tube material of the i-stand to T _n,i+1, ΔN _i becomes the following equation.

ΔN _i = g _i (ΔG _i,f −ΔG _i,T ) ...(9) In equation (9), ΔG _i,T is the forward target tension torque corresponding to the target tension T _n,i+1. Yes, and is expressed by the following equation (10).

ΔG _i,T = 1/η _i・_i・T _n,i+1・(1+f _i ) ...(10) η _i is the reduction ratio (gear ratio) of the i stand, f _i is the advance rate of the i stand It is. At this time, the rear tension torque ΔG _i+1,b acting on the i+1 stand is expressed by the following equation since the rolling force required for rolling the same tube material can be considered constant.

ΔG _i+1,b = −N _i /N _i+1 ΔG _i,f ……(11) Equations (1) to (11) above are used to control tension when continuously rolling pipe material with a mandrel and grooved roll. This is an analytical model that introduces the tension acting on the mandrel and the friction coefficient between the mandrel and the tube material, and takes into account the tension applied to the tube material itself and the torque arm of the tube material rolling.

FIG. 5 shows a conceptual diagram in which, for example, a load detector 12 is installed in order to know the tension T _B acting on the mandrel. 5a and 5b show an example in which a load detector 12 is installed on the mandrel propulsion block 1 to detect the tension T _B applied to the mandrel bar 2 connected to the mandrel.

In addition, as shown in FIG.
This is to detect T _B.

It is also easy to modify an existing mandrel mill and install a load detector to detect the tension in the mandrel.

Alternatively, if the mandrel drive torque G _B of the mandrel drive motor 8 shown in Figs. 1 and 2 is known, the tension T _B applied to the mandrel 3 can be calculated as follows (12).
It can also be determined by the formula.

G _B ω _B = T _B V _B + α _B ... (12) ω _B is the angular velocity of the mandrel drive motor 8,
V _B is the speed of movement of the mandrel, and α _B is a constant determined by the use of the mandrel drive control device 7.
The mandrel motion speed V _B is a rigid body that does not undergo plastic deformation, and can be easily determined from ω _B and the reduction ratio of the mandrel drive control device.

The rolling load P _i can be detected by a load cell installed in the rolling mill, and the rolling torque G _i is generally calculated using the following equation (14) when a torque converter is not installed.

G _i = βV-I・R/N _i I-γdN _i /dt-δ ...(14) In equation (14), V is the motor voltage, I is the motor current,
R is the armature resistance, N _i is the motor rotation speed, β, γ,
δ is a constant, the first term on the right side is motor torque, the second term is acceleration/deceleration torque, and the third term is loss torque.

Thus, by knowing the tension, rolling load, and rolling torque that act on the mandrel during rolling, the friction coefficient between the inner surface of the pipe material and the mandrel during rolling can be determined, and the mandrel can be replaced based on the change in the determined friction coefficient over time. It is possible to determine the timing.

Hereinafter, a case of tensionless control (zero tension acting on the pipe material) of pipe material rolling will be specifically described as an example. FIG. 6 is a conceptual diagram showing a state in which rolling is performed only in the first stand in an n-stand mandrel mill, and the mandrel 3 penetrates through the n-stands,
And the direction of movement is backward (upstream). This corresponds to the RRM described above.

There is no tension (compression force) acting on the pipe material 11, and the rolling load is P _1,0 , the rolling torque is G _1,0 ,
Let the tension of the mandrel be T _B,1 . For the rolling load and rolling torque, 1 means the first stand, and 0 means no tension.

When tension exists, it is indicated as P _1,1 and G _1,1 .
Also, the precision 1 of the mandrel tension T _B,1
indicates that rolling is performed only on the first stand.
When T _B,i is used, it indicates the mandrel tension when rolling is performed from the first stand to the i-th stand. The same applies to the following symbols.

In Figure 6, there are relationships (15) and (16).

G _1,0 = μ ₁・P _1,0・₁ +2a ₁・P _1,0 ……(15) T _B,1 = μ ₁・P _1,0 ……(16) Equation (15) and (16) ) μ ₁ and a ₁ are calculated from the formula.
Next, FIG. 7 is a conceptual diagram in which the pipe material 11 is rolled between the first stand and the second stand, and a tension T _n,1 is generated in the pipe material between the first stand and the second stand. . The rolling torque G ₁ of the first stand is G ₁ = (μ ₁・P ₁ − _{μ 2}・P ₂ ) ₁ +2a ₁ P ₁ −ΔG _i,f Therefore, ΔG _1,f = (μ ₁・P ₁ − μ ₂・P ₂ ) ₁ +2a ₁ P ₁ −G ₁
...(17) Also, T _B,2 = μ ₁・P ₁ + μ ₂・P ₂ ...(18) From equation (18), μ ₂ is calculated, and from equation (17), ΔG _1,f
is calculated.

The speed correction amount of the first stand is ΔN ₁ = g ₁・ΔG _1,f ...(19) At this time, the rear tension torque of the second stand is ΔG _2,b
is ΔG _2,b = −N ₁ /N ₂ ΔG _1,f Therefore, G _2,0 = G ₂ + ΔG _2,b ... (20) The control is completed before the pipe material 11 is caught in the third stand. If so, the second stand is also in a tension-free state, and the detected rolling load P ₂ and rolling torque G ₂ at this time are
is, of course, the relationship expressed by equation (21).

P _2,0 = P ₂ , G _2,0 = G ₂ ...(21) At this time, since the relationship is as shown in equation (22) below,
Calculate a ₂ using equation (22).

G _2,0 =μ ₂ P _{2 2} +2a ₂ P _2,0 (22) Fig. 8 shows a conceptual diagram when the pipe material 11 is inserted up to the third stand. With the start of rolling in the third stand, some tension T _n,1 , T _{n, 2} occurs, and a corresponding tension torque is generated. 1st
The front tension torque ΔG _1,f of the stand is ΔG _1,f = (μ ₁・P ₁ −μ ₂・P ₂ ) ₁ +2a ₁・P ₁ −G ₁ ……(23) The rear tension torque ΔG of the second stand _2,b is ΔG _2,b = −N ₁ /N ₂ · ΔG _1,f ... (24) Therefore, the forward tension torque of the second stand ΔG _2,f
is, ΔG _2,f = (μ ₂・P ₂ − μ ₃・P ₃ ) ₂ + 2a ₂ P ₂ −G ₂ + ΔG _2,b ……(25) μ ₃ in formula (25) is calculated by the following formula. do.

T _B,3 = μ ₁・P ₁ + μ ₂・P ₂ + μ ₃・P ₃ ...(26) ΔG _2,f expressed by equation (25) can be calculated, and therefore the speed correction amount ΔN of the second stand ₂ is, ΔN ₂ = g ₂ · ΔG _2,f ... (27) The speed correction amount ΔN ₁ of the first stand at this time is, ΔN ₁ = g ₁ ΔG _1,f + ΔN ₂ /N ₂ N ₁ ... (28) becomes. The rear tension torque ΔG _3,b of the third stand is ΔG _3,b = −N ₂ /N ₃ ΔG _2,f ... (29) Therefore, the non-tension torque G _3,0 of the third stand is, G _3,0 = G ₃ + ΔG _3,b ... (30) If the control is completed before the pipe material 11 bites into the fourth stand, the third stand will also be in a tension-free state, and the detected rolling load at this time will be If P ₃ is the rolling torque and G ₃ is the rolling torque, then P _3,0 = P ₃ , G _3,0 = G ₃ ...(31) G _3,0 = μ ₃ P _{3,0 3} +2a ₃ P _{3, 0} ...(32). Calculate a ₃ using formula (32).

It is possible to calculate the friction coefficient μ _i for all stands by performing calculations in the same manner. When the tension of the pipe material rolled between the mandrel and the grooved roll is controlled to be constant, the friction coefficient μ _i can be determined in the same way using the basic model based on equation (9).

According to the present invention, the friction coefficient μ _i between the mandrel surface and the pipe inner surface can be determined by direct calculation from the mandrel tension value, rolling load, and rolling torque. Mandrels wear out under harsh rolling conditions, and their surface roughness also increases. If this wear on the surface of the mandrel or the increase in surface roughness exceeds a limit, it will have a great negative effect on the inner surface properties of the tube material. Therefore, the mandrel is empirically replaced at a certain time, for example, based on the number of rolled pipes or the number of rolled tonnages.

According to the present invention, it is possible to quantitatively understand the change over time in the coefficient of friction between the mandrel and the inner surface of the pipe material. For example, as shown in Fig. 9, it is possible to know when to remove the mandrel by setting the upper limit of the coefficient of friction μ _i . It becomes like this. In Figure 9, the horizontal axis is time,
The vertical axis is the friction coefficient, and the shaded area is the upper limit range of the friction coefficient μ _i indicating the time to replace the mandrel. By quantitatively understanding changes in the coefficient of friction over time, it will be possible to make concrete improvements to mandrel lubrication systems and lubricants.

As described above, according to the present invention, the coefficient of friction between the inner surface of the pipe material and the surface of the mandrel such as a mandrel can be quantitatively determined, and products with good inner surface properties of the pipe material can be obtained without making a mistake in the timing of replacing the mandrel. Obtainable.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing the outline of a mandrel mill, Figures 3 and 4 are block diagrams to explain the basic tension control model, and Figure 5 is a block diagram showing the tension acting on the mandrel during rolling. FIGS. 6 to 8 are explanatory diagrams of a method for concretely implementing tension control along the rolling process starting from the first stand biting, and FIGS.
The figure is a diagram for explaining the change over time in the coefficient of friction between the mandrel surface and the contents of the tube material, and the timing for replacing the mandrel.

Claims (1)

[Scope of Claims] 1. A rolling stand having a mandrel and a plurality of pairs of grooved rolls into which a rolled pipe material penetrated by the mandrel is inserted, and the pipe material is rolled by the grooved rolls and the mandrel. In a tube rolling mill that performs rolling, the tension applied to the mandrel, the rolling load,
From the rolling torque, calculate the friction coefficient between the inner surface of the pipe material during rolling and the surface of the mandrel using a predetermined calculation formula,
A method for determining when to replace the mandrel based on changes in the coefficient of friction over time.