JPH0116564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mandrel rolling mill, which is a continuous tube rolling machine that reduces the wall thickness of the tube material using grooved rolls while passing the mandrel through the tube material, and finishes the length of the tube material to a predetermined dimension. It is related to the device.

Conventionally, as a method for manufacturing small to medium diameter seamless pipes by rolling, there is a method in which a raw pipe is heated to a predetermined temperature in a heating furnace and then perforated with a piercer, and then rolled in a mandrel mill.

In this mandrel mill rolling, the raw tube and the mandrel are brought together to the exit side of the mandrel mill, the mandrel and the raw tube are separated, and the raw tube is charged into a reheating furnace and then cut to a predetermined size by a stretch reducer. It is finished and goes through a finishing process to become a product.

In rolling the pipe material using a mandrel mill, which is one step of this pipe manufacturing method, as shown in FIGS. 1a, b, and c, a mandrel 11 is passed through the pipe material 12 to be rolled (a),
From the time of rolling (b) to the end of rolling (c), the mandrel 11 reaches the exit side of the final stand of the mandrel mill together with the tube material 12 without any restraint. This is the so-called full-float mandrel mill rolling.

In addition, as shown in FIGS. 2a and 2b, the mandrel 11 is restrained by the restraint device 13 during rolling, and the tube material 12 is
There is a mandrel mill (hereinafter referred to as an MPM mill) equipped with a mandrel drive device 14 that controls the moving speed of the mandrel 11 in accordance with the rolling.

In the MPM mill, the mandrel 11 is kept at a predetermined speed while the tube material 12 is being rolled (a), and after the tube material 12 is rolled, the mandrel 11 is moved on the same pass line from the first stand 1 to
It is pulled back by the mandrel drive device 14 to the entry side of No. 1 (b), and the next rolling is carried out.

In this way, the current mandrel mill has 12 tubes.
There are two main types of rolling: full-float mandrel rolling, in which the mandrel 11 is kept free in the rolling direction, and MPM rolling, in which the mandrel 11 is controlled so that it moves at a predetermined speed in the rolling direction.

In full-float mandrel rolling, the speed of the mandrel 11 changes when the tube material is biting in and when the tube material falls out, and the relative speed with the tube material changes each time. Therefore, it is difficult to perform stable rolling, and thickening occurs at the leading and trailing ends of the tube material. Defects in thickness and shape are likely to occur.

On the other hand, keep the moving speed of the mandrel constant.
MPM rolling attempts to compensate for the above-mentioned drawbacks of full float mandrel rolling by controlling the moving speed of the mandrel 11, and furthermore, compared to full float mandrel rolling, the movement speed of the mandrel 11 after rolling is controlled. The process of separating the tube materials can be omitted, and the length of the mandrel 11 is shorter than in full-float mandrel rolling.
As soon as the rolling by the mandrel mill is completed, the mandrel 11 can be pulled back to the entry side and the next rolling can be carried out immediately, which is excellent in improving productivity.

However, compared to full float mandrel rolling,
In order to actively move the mandrel 11, a large-capacity drive equipment and an associated mechanical mechanism are required, making the rolling equipment relatively expensive.

In any of the above-mentioned rolling methods, a mandrel 11 is added as a rolling component to a rolling stand 1-1 to 1-n equipped with a pair of grooved rolls, and these grooved rolls 1-1 to 1-n are used to roll a tube material using a mandrel mill.
Pipe material 1 which is a material to be rolled between n and mandrel 11
2 is rolled asymmetrically.

However, theoretical analysis including the deformation mechanism within the roll bite has not yet been sufficiently conducted, and the current state of the art is that it is inferior to other forms of sheet rolling, long bar rolling, etc. in terms of production technology.

The reason for this is the mechanical specifications of the mandrel mill as a production facility, including the insufficient theoretical analysis.
In addition, the optimum method for determining the control method cannot be determined strictly, and in particular, the problem of lubrication, which is a difficult problem in plastic working, is important in the inner surface of the mandrel 11 and the tube material 12, which is the material to be rolled. It is something that occupies.

In the case of full-float mandrel rolling, regardless of the level of the friction coefficient between the inner surfaces of the mandrel 11 and the tube material 12, one must be concerned about the complexity and difficulty of the process of separating the tube material 12 and the mandrel 11 after rolling by the mandrel mill. In some cases, rolling is possible.

In addition, in MPM rolling in which one end of the mandrel 11 is fixed and its moving speed is controlled constant during rolling, if the inner surfaces of the mandrel 11 and the tube material 12 have poor lubrication and a high level of friction coefficient, the axial stress of the mandrel 11 and the rolling mill stand The force applied in the rolling direction also becomes excessive.

In addition, oil shortage due to operation of the mandrel 11, changes in lubrication performance due to rolling conditions and changes over time, wear of the mandrel 11, and not only rolling in the roll bite, but also the mandrel 11 and the pipe material 12 coming out of the roll bite. It is difficult to maintain a truly stable rolling state considering that they mutually influence each other due to frictional force in the rolling direction due to contact stress. , variations occur in the rolling torque, the load in the rolling direction generated on the mandrel 11, etc., and it is difficult to obtain a high-quality product with excellent wall thickness, dimensions, and shape.

This mandrel 11 and the pipe material 12 which is the material to be rolled
In mandrel mills, which are tube rolling machines, the problem of internal friction is particularly important compared to other rolling methods, and unless this point is taken into account, truly high-quality products cannot be obtained. do not have.

The present invention is aimed at reducing as much as possible the inconveniences during rolling caused by the friction that inevitably occurs between the tube material 12, which is the material to be rolled, and the mandrel 11 in a mandrel mill, and when actively operating the mandrel. To provide a mandrel rolling device that can obtain rolled products by a mandrel mill with excellent dimensions and shapes while avoiding the considerable cost of equipment and the complexity of operation.

FIG. 3 schematically shows the overall configuration of the present invention in which rolling is carried out across all stands of a mandrel mill.

The rolling load is detected by load cells 21-1 to 21-2.
1-n, and the rotation speeds of the grooved rolls 1-1 to 1-n are detected by motor rotation speed detectors 22-1 to 22-2.
Calculated by the calculator 23 from the output value of 2-n,
Motor 2 via speed control devices 24-1 to 24-n
The rotational speeds of 5-1 to 25-n are controlled to the value set by the tension setting device 26 for the tension or compression force during rolling of the tube material 12, which is the material to be rolled.

In Fig. 3, the mandrel 11, which is an important mechanical element of the mandrel mill, is the grooved roll 1-1 to 1-1.
The mandrel has a stepped shape in which the diameter of the part directly below the stand which is involved in rolling the tube material 12 is large, and the diameter of the part which is located in the middle of the stand and which is not directly involved in rolling is small.

In the case of the mandrel 11 shown in FIG. 3, the entrance end is in the shape of a flange as shown in 15, and while the tube material 12 is being rolled, it is completely fixed to the mandrel restraint device 13 and only slightly moves in the rolling direction. Nor. That is, it is a mandrel mill of a completely fixed mandrel type, which is a feature together with the fact that the mandrel 11 has a stepped shape.

The mandrel 11 equipped with this flange 15 is moved by a mandrel drive device 1 before and after rolling.
4 is used to move forward and backward. The mandrel drive device 14 is in charge of moving the mandrel 11 forward and backward only when the mandrel 11 is under no load, and only needs to be extremely small in capacity to simply move the weight of the mandrel 11.

The rolling method of the present invention in which the movement of the mandrel 11 in the rolling direction is completely blocked by the mandrel restraining device 13 during rolling will be hereinafter referred to as NFM (Non-Float Mandrel).
This is called mandrel rolling.

FIG. 4 is a diagram showing the state and load characteristics of the tube material 12 being rolled by the grooved roll 1-1 and the mandrel 11 of the first stand, with the rolling torque G on the vertical axis and the time t on the horizontal axis. .

After the start of rolling (time t ₀ ), the pipe material 12 is moved to the grooved roll 1
The required rolling torque when reaching the exit side l ₁ position (time t ₁ ) of −1 is G ₁ and the exit side l ₂ position (time t ₂ )
The figure shows that the required rolling torque is _G2 when . Even though only the first stand is rolling, the torque G changes as the rolling progresses (G ₀ →G ₁ →G ₂ ).

FIG. 4 shows an example where the speed of the tube material 12 is faster than the speed of the mandrel 11, and the required rolling torque increases with the passage of time. The reason for this is that the tube material 12 is rolled between the grooved roll 1 and the mandrel 11 in the roll bite, and even after the rolling is finished and exits the roll bite, a contact force is generated between the mandrel 11 and the tube material 12, and the tube material 12 and the mandrel This is because a frictional force corresponding to the level of friction between the tubes 11 acts on the rolled pipe material 12.

This frictional force is 2・μ ₁・P ₁・l, and the fourth
Acts in the direction shown. Here, μ ₁ is the friction coefficient between the pipe material 12 and the mandrel 11 after being rolled on the first stand, P ₁ is the contact force between the pipe material 12 and the mandrel 11 per unit length, and l is the friction coefficient from the roll bite exit side. It is distance.

μ ₁ is a value determined by the lubricant used and the lubrication method, and P ₁ is a value determined by the shape of the grooved roll 1 and the pipe material 12.
This value is determined by the material conditions, dimensions and shape, and rolling conditions (thickness reduction rate, etc.). Also, l increases with time.

In the mandrel mill, as long as the diameter of the mandrel 11 is uniform, the mandrel 11 and the tube material 12 come into contact after rolling to generate the frictional force τ, which increases with time t and changes the load characteristics such as the required rolling torque. This also affects the quality of the rolled product.

In addition, if the mandrel diameter on the exit side of the grooved roll is large due to wear of the mandrel 11, this frictional force τ becomes a considerably large value, and this mandrel 11
The value of τ itself is unstable because the wear is not necessarily uniform in the longitudinal direction.

That is, in a mandrel mill, mandrel 1
As long as it is assumed that the diameter dimension of 1 is uniform, rolling in a constant steady state will not be satisfied due to the influence of the frictional force outside the roll bite.

FIG. 5 corresponds to FIG. 4, but shows an example of mandrel mill rolling in which the diameter of the mandrel on the exit side of the roll bite is made slightly smaller so that the tube material 12 after rolling and the mandrel 11 do not come into contact with each other. in this case,
The rolling method is the NFM method described above.

Although the rolling torque is shown as an example of the load characteristic, it does not increase over time as shown in FIG. In other words, this shows that rolling in a constant steady state is possible.

By making the diameter of the part of the mandrel 11 directly involved in rolling in the roll bite slightly larger than the diameter of the part of the mandrel 11 that is not directly involved in rolling by reducing the wall thickness of the tube material 12 between the stands, it is possible to improve the conventional mandrel. To enable stable rolling by completely eliminating the frictional force between a tube material 12 and a mandrel 11 after rolling, which inevitably occurs in a mill.

Next, the operation of the mandrel 11 will be specifically described. FIG. 6 shows that the pipe material 12, which is the material to be rolled, is in the first
While being transported onto the entrance table of the stand,
At this time, the stepped mandrel 11 is being pulled back rearward by the mandrel drive device 14. FIG. 7 shows that the stepped mandrel 11 is connected to the mandrel drive device 14.
The figure shows the state just before the start of rolling, which has been set by operating the mandrel restraining device 13, the tube material 12, and the rolling mill stand.

A flange provided at the rear end of the mandrel 11 is fixed in contact with a mandrel restraint device 13 so that the mandrel 11 does not move in the rolling direction during rolling. Rolling is carried out across all the stands shown in FIG.

Figure 8 shows the state in which the pipe material 12 has passed through the final stand, and the mandrel 11 immediately after passing through the final stand.
is pulled back to the position shown in FIG. 6 by the mandrel drive device 14, and the pipe material 1, which is the next material to be rolled, is
2 is conveyed onto the entry table and subjected to repeated rolling.

As described above, the mandrel 11 is fixed to the mandrel restraint device 13 during rolling, and movement during rolling is completely prevented. The mandrel drive device 14 only moves the mandrel 11 forward and backward when the mandrel 11 is under no load, so it can be of an extremely small capacity. That is, it is possible to realize mandrel mill rolling of the tube material by the NFM method by fixing the mandrel 11 so that the movement of the mandrel 11 is blocked during rolling.

According to the present invention, as the mandrel 11, the diameter of the portion directly below the roll gap of each of the grooved rolls 1-1 to 1-n and involved in the rolling that actually reduces the wall thickness of the tube material 12 is set between the stands, and the grooved Roll 1-
By using a so-called stepped mandrel whose diameter is slightly larger than the diameter of the portion not subjected to rolling by 1 to 1-n, the separation between the rolled pipe material 12 and the mandrel 11, which inevitably occurs in conventional rolling with a mandrel mill, is improved. Stable rolling is possible with no frictional force.

This stepped mandrel may be made in one piece, or the part with a slightly larger diameter that is directly involved in rolling and the part that is not directly involved in rolling that is located between other stands are manufactured separately and connected during use to form the mandrel. It may also function as a. In this case, the length of the large-diameter portion directly below the rolls is only required to be slightly larger than the contact length during rolling, and the machining accuracy of the mandrel itself is much improved compared to machining a long object. Furthermore, it is also economically viable to use a high-grade material that has superior heat resistance, abrasion resistance, impact resistance, etc. than materials conventionally used only in this part.

On the other hand, in a portion with a slightly smaller diameter that is not directly involved in rolling, it is sufficient that the rolled tube material 12 does not come into contact with the mandrel 11, and machining accuracy is not required so much. Rolling with a mandrel mill using the NFM method requires a mandrel restraint device 14 that fixes the movement of the mandrel during rolling, but the mandrel drive device that operates the mandrel forward and backward movement can be used by simply moving the mandrel 11, which is low cost. All you need is capacity equipment.

This NFM rolling method is similar to conventional rolling methods such as
It is also easily applicable to full float mandrel mill equipment. By using a stepped mandrel and rolling by the NFM method,
The wear of the mandrel due to rolling is only in one place, and it is not uneven in the longitudinal direction as in the conventional method.
It also becomes possible to quantitatively understand the amount of wear with higher accuracy.

As explained above, according to the present invention, the friction force between the mandrel after rolling and the pipe material to be rolled, which inevitably occurs in conventional mandrel mills, is reduced to zero,
Stable rolling is possible. Moreover, mandrel operation can be realized with simple and inexpensive equipment. and,
Rolling using the NFM method can be easily applied by modifying an existing mandrel mill.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining a conventional full-float mandrel mill, Figure 2 is a diagram for explaining an MPM mandrel mill, and Figure 3 is a schematic diagram of NFM mandrel mill rolling using a stepped mandrel according to the present invention. , FIG. 4 is a diagram showing an example of the influence of the frictional force between the rolled tube material and the mandrel that inevitably occurs in a mandrel mill, and FIG. Figures 6, 7, and 8 show an example of eliminating the
The figure is a diagram for explaining the NFM mandrel rolling method according to the present invention. 1-1 to 1-n... Rolling roll, 11... Mandrel, 12... Rolled pipe material, 13... Mandrel restraining device, 14... Mandrel driving device, 15
...Flange, 25-1 to 25-n...Drive motor.

Claims (1)

[Claims] 1. In a mandrel rolling device that passes a mandrel through a pipe material and rolls the pipe material through a plurality of grooved roll rolling stands, the mandrel has a diameter larger in the area that receives direct rolling force near the center of the roll of each rolling stand, and the roll A mandrel restraining device that fixes the mandrel at the rolling position during rolling by providing a step with a smaller diameter in a range that is not directly subjected to rolling force at an intermediate position, and a mandrel restraining device that allows the mandrel to pass through the rolling position and the pipe material. A mandrel rolling device comprising a mandrel drive device that drives the mandrel back and forth between a return position and a return position.