JPS5848242B2 - Continuous rolling method for pipes - Google Patents

Description

[Detailed description of the invention] This invention relates to a method for manufacturing seamless pipes.

In the production of seamless metal pipes, for example, seamless steel pipes, a billet with a square or round cross section is perforated into a relatively thick tubular material called a shell, and then a mandrel mill or semi-floating mandrel mill is used. Perform intermediate rolling to reduce wall thickness and outer diameter. and stretch it in the length direction.

The shells to be subjected to these intermediate rolling processes are all hollow cylindrical shapes with both ends open, and the intermediate rolling is carried out by inserting a mandrel into the inner hole.

However, in such a shell with both ends open, air flows through the tube during rolling or transportation, and significant secondary scale is generated inside the tube, which impairs the inner surface quality of the tube.
Or it may be the cause of the mandrel's burning failure.

Furthermore, even in the subsequent reducing mill, the secondary scale formed on the inner surface causes wrinkles on the inner surface, impairing the quality of the tube.

Although the present invention uses a bottomed cylindrical blank tube, this has only been used in the conventional push bench method.

The push bench method involves inserting a longer mandrel into a round simple tube with a bottom, pushing the bottom of the tube with one end of the mandrel, and punching between roller rows or die rows.
The rollers are not driven.

The mandrel must be made longer than the pipe after it has been formed, and it is not possible to mass-produce long pipes.

With a mandrel, the front end of the tube is always faster than the mandrel during rolling, so even if one end of the mandrel is inserted to the bottom of the tube and rolling is started, the front end of the tube will advance much further than the front end of the mandrel at the exit of the rolling mill, reducing the overall length. cannot be rolled to uniform dimensions across the entire surface.

There have been no reports of attempts using bottomed tubes in semi-floating mandrel mills.

The present invention prevents the occurrence of secondary scale by providing an intermediate rolling mill with a circular simple tube with a bottom closed at one end, thereby producing a tube with excellent inner surface quality, and improving the life of the mandrel of the rolling mill. The purpose of this is to prevent poor biting in each stand of the intermediate rolling mill.

The tubular material used in the present invention is not limited to the manufacturing method of the tubular material, but a bloom having a square or round cross section is formed with one end closed using a press roll punching machine or a press punching machine. Are there any relatively thick-walled cylindrical tubes with holes in them? is then rolled using an elongator to a cross-sectional size suitable for the next step, but the shape with one end closed is maintained.

The intermediate rolling mill of the present invention, which uses such a tubular material, is a so-called semi-floating mandrel that is classified in the same manner as the rolling mill described in Japanese Patent Publication No. 42-24987, and the rolling mill is a rolling mill that uses two or more rolling mills. Approximately elliptical calibers bored in the rolls are arranged in series with their phases shifted by 90 degrees, and the rolls on each stand are driven by a motor whose speed can be controlled, and a mandrel is installed on the entry side lot line to adjust the circumferential speed of the roll caliber. A mandrel moving device must be provided to move the mandrel at the desired speed relative to the mandrel.

Figure 1 shows that 1 is the first rolling roll and 2 is the second rolling roll according to the present invention.
The phase of the caliber is shifted by 90 degrees in the circumferential direction between the rolling rolls.

3 is a third rolling roll, and the phase of the caliber is shifted by 90 degrees with respect to the second rolling roll.

That is, it is arranged in the same phase as the first rolling roll.

Furthermore, when additional rolling mills are subsequently installed, the arrangement is repeated in the same manner.

In the present invention, two or more rolling rolls can be appropriately selected and arranged depending on the relationship between the dimensions of the tubular material and the rolled product.

Reference numeral 4 denotes a mandrel, which has a part that performs tube rolling in cooperation with the rolling rolls 1 and 2.3, and this part has a cylindrical shape.

Rolling row. It is preferable that approximately elliptical calibers are bored in the wheels 1, 2.3, and the ellipticity approaches 1.0 as rolling progresses.

An IJ roll 5 is disposed on the exit side of the final stand to remove the rolled tube from the mandrel.

The rolling equipment used in the present invention is generally constructed as described above, and the rolling method of the present invention will be further described below.

The material to be subjected to the rolling process of the present invention is a tubular material perforated by any means for tube rolling. Must be.

Such bottomed cylindrical blank tubes are manufactured using, for example, a press roll perforator or an Erhardt press, but they can also be manufactured using an inclined roll perforator such as a Mannesmann perforator, which generally performs through perforation, to support the mandrel in the latter stage of the perforation. By releasing , a cylindrical tube with a bottom can be obtained.

FIG. 2 shows the positional relationship between the tube and the mandrel from the start of rolling of the tube to the end of rolling in the present invention.

The arrangement direction of the rolls is as shown in FIG. 1, but the direction is changed for simplicity.

In Fig. 2a, the thrust block 6 is advanced in the rolling direction as shown by the arrow, the mandrel 4 is inserted into the bottomed cylindrical pipe P prepared at the rolling inlet, and only the mandrel is advanced, so that the front end of the mandrel 4' pushes the bottom y of the bottomed cylindrical blank tube P, and as the mandrel moves forward, it is first fed into the I-th rolling roll set 1, 1' and the front end is bitten.

Subsequently, in FIG. 2b, the tube bottom y and the mandrel front end 4' are made to pass through the roll axis 1', and this part is made to reach the roll axis z of the next pair of rolls 2,2.

During this period, the relative relationship between the advancing speed of the mandrel and the inner circumferential speed of the Caliher of the rolling roll of the first stand is a speed at which the tube does not advance with respect to the mandrel, and can be empirically determined by the following equation.

The equal sign in the lower limit of equation (1) applies when the speed of the tube of the rolling roll and the speed of the mandrel are equal, and if VM is smaller than this value, the front end of the tube will separate before the mandrel.

The constant on the right side of equation (1) is determined by skewering a mandrel into a shell with both ends open and observing the discharge velocity of the front end of the tube from the roll and the discharge velocity of the mandrel so that the two coincide.

(When working with KVM/VR near the lower limit of the Y formula determined, due to industrial variations, the bottom y of the tube and the front end 4 of the mandrel may become slightly separated when passing through the rolling rolls. This will not be a problem as long as it is within the planned cut-off length of the pipe end.

The upper limit of equation (1) indicates that the tube comes out at a speed 1.2 times faster than the speed of the flange of the roll, and the tube advances relative to the caliber over the entire contact surface with the roll caliber. It is shown that.

Although such advancement of the tube over the entire contact surface looks unnatural, it is not impossible, and the friction hill may disappear and the pushing force of the mandrel may actually decrease.

(1) Shikimata & Mound Iy formula also applies to everything after the second stand.

That is, as shown in Fig. 2C, until the front end 4' of the mandrel and the bottom y of the bottomed cylindrical tube pass through the roll axis 3' of the final stand, the relationship of formula (1) or one-piece formula is maintained in each stand. power should be maintained.

Connect the roll axis 3' of the final stand to the mandrel front end 4.
' and the bottom y of the bottomed cylindrical tube pass, a new speed relationship is established between the roll circumferential speed of each stand and the forward speed of the mandrel.

That is, the circumferential speed of the rolls in each stand is modified so that the constant flow rate law holds, and the forward speed of the mandrel is reduced to a speed at which the mandrel can continue to advance until the trailing end of the tube passes through the final stand.

This causes the V to move forward away from the mandrel tip 4' as shown in FIG. 2d.

To make sure that the constant flow rate holds between each stand, do the following.

The roll standard diameter that expresses the roll circumferential speed can be set to any value t between the roll caliber bottom diameter and the roll flange diameter, but for simplicity, if it is expressed in terms of the roll caliber bottom diameter, VIA1-V2A2-・・・・・・・・・・=VnAn・
・・・・・・・・・・・・ (2) AIA2An v1=v2−=・・・・・・・・・=Vn−・・・・・・
...<2YA. A. A
O V, /E1=V2/E2=--=V1/El ++・
...(2y where vi l V2...vn is the circumferential speed of the roll standard diameter part of the stand 1, 2...n, respectively, Ao is the cross-sectional area of the tube before rolling, AI r
A2...An is 1, 2...n, respectively
Cross-sectional area of the pipe after stand rolling, El + E2...
...En is the cumulative growth rate after 1, 2...n stands, respectively.

Figures 3 to 9 show the time course of the roll circumferential speed, mandrel speed, and tube speed of the continuous rolling mill, and the VRI s
VR2 + VR3 are roll caliber bottom peripheral speeds of 1 and 2.3 stands, respectively, VM is mandrel forward speed, V
PT and vPB are the forward speeds of the front and rear ends of the tube, respectively, and tl+j2+j3 are the forward speeds of the front end of the tube of 1 and 1, respectively.
2. Time to be bitten by 3 stands, jl'+ j2
'+t3' has the rear end of the tube 1, 2, respectively. It's time to go through the 3rd stand.

Figure 3 shows a typical mandrel mill's roll peripheral speed VR, mandrel forward speed vM, and forward speed VP of the front and rear ends of the tube.
T, VPB is shown.

The mandrel movement is not externally constrained and vM is between VPT and VPB.

FIG. 4 shows the case of a typical semi-floating mandrel mill, where the mandrel forward speed vM is kept at a constant value lower than vP and VPB, and VM is controlled by the thrust floc.

FIG. 5 shows a typical push bench in which the rolls are not driven and may be replaced by dies.

VM is always equal to VPT. FIG. 6 shows one of the embodiments of the present invention, in which VRl1, VR2, VR3 are constant and t3
Until then, VM and vPT are equal, but immediately after t3, vM is set to a small constant value.

In this case, VM/VR may exceed the upper limit of the IY formula.

FIG. 7 shows one of the embodiments of the present invention, and up to t3, V
M and VPT are kept constant, and VM/V at each stand.
R is kept at a constant value within the IY formula, and after t3, VM is kept at a small constant value.

In this case, VM/VR until t3 is higher than in the case of Fig. 6.
can be maintained at an optimum level, and the pushing force of the mandrel is not strained.

FIG. 8 shows one embodiment of the present invention, in which VR1, VR
2, instead of keeping VR3 constant, vM and VF until t3
The speed is increased while keeping r the same.

In this case as well, VM/VR can be maintained optimally compared to FIG. 6, and the pushing force of the mandrel does not become unreasonable.

After t3, VM is set to a small constant value.

FIG. 9 shows one of the embodiments of the present invention, and FIGS.
This is a combination of the cases shown in the figure.

For the case of FIG. 7 or FIG. 8, vM and “Rl t
This is the most preferable example since the amount of change in VR2 rVR3 is small.

At each stand, VM/vR is always kept at a constant value within the formula (lY), and after t3, vM changes to a small constant value.

Although the above description has been made regarding the case where there are three rolling stands, the same applies to all cases where there are two or more rolling stands.

By the method described above, rolling is completed to the rear end of the tube, and the second
As shown in Figure e, the tube P is removed from the mandrel 4 by the stripper rolls 5, 5, and at the same time the mandrel 4 is moved back to the rolling standby position shown in Figure 2a.

In the present invention, the bottom portion of the tube is bitten into the first stand,
A pushing force is applied to the mandrel 4 until it has passed through the final stand, so during this time the mandrel 4 and the bottomed cylindrical tube P
Pinch rolls 7K are used to compress these and keep them in place so that they do not bend.

The pinch roll 7 can take a mandrel position, a shell position, and a retracted position when passing the thrust block.

By the method described above, a simple circular tube with a bottom can be rolled to have uniform dimensions over its entire length.

The key point of the present invention is to roll a bottomed cylindrical tube with the bottomed part as the front end, prevent secondary scale from occurring on the inner surface of the tube before, during and after rolling, and produce a tube with excellent inner surface quality. It is possible to manufacture the rolling mill, improve the life of the mandrel of the rolling mill, and furthermore prevent bad biting in each stand of the intermediate rolling mill.

In addition, the reason why secondary scale can be prevented from forming on the inner surface of the tube is that because a simple circular tube with a bottom is used, air does not flow through the tube during transportation, waiting for rolling, rolling, etc. , air only slightly convects from the open end of the tube.

In this case, if a small amount of the oxygen-consuming moisturizing agent commonly used in the previous step remains, the inside of the tube is filled with non-oxidizing gas and overflows from the open end, preventing internal oxidation.

In the continuous rolling method of the present invention, an oxygen-consuming lubricant such as petroleum or graphite is mixed as a mandrel lubricant.

Therefore, even when reheating and reducing rolling are performed in the next step, secondary scale is not generated on the inner surface of the tube.

Therefore, it is possible to reduce the inner surface flaws that tend to occur on the inner surface of the tube when extremely large elongation is applied in a reducing mill.

Is the cause of the inner surface pock after reduction rolling due to scale intrusion in the previous process or the reduction rolling process? Involvement of the internal scale is the main cause.

In a mandrel mill, the biting at the front end of the tube causes momentary stagnation, which disturbs the constant flow rate law and tends to result in unstable rolling.

In a seflotating mandrel mill, the advancement speed of the mandrel is significantly slower than the advancement speed of the tube, resulting in poor engagement.

In the present invention, since the mandrel is pushed until all the stands are completely engaged, it is clear that no defective engagement occurs.

As described above, the present invention obtains the above-mentioned effects by using a method of continuously rolling a bottomed cylindrical blank tube to a uniform dimension over its entire length, and by using the bottomed cylindrical blank tube.

Furthermore, for the semi-floating mandrel mill method shown in Figure 4, rolling can be started at the same time the front end of the mandrel enters the first stand, so unlike the conventional method, rolling can be started until the front end of the mandrel is placed on standby in the final stand. This saves time and improves efficiency.

[Brief explanation of the drawing]

Figure 1 is a schematic layout diagram of the main parts such as the rolling roll and mandrel of the present invention, Figure 2 is an explanatory diagram of the positional relationship of the rolling roll, mandrel, round simple tube with a bottom, etc. of the present invention, and Figure 3 is a diagram of the conventional method. Figure 4 is an illustration of the speed relationship of a conventional semi-floating mandrel mill, Figure 5 is an illustration of the speed relationship of a conventional push bench,
FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are all explanatory diagrams of speed relationships of the present invention. 1, 2.3... Roll, 4... Mandrel,
5... Stripper roll, 6... Thrust block, 7... Pinch roll, P... Cylindrical tube with bottom, y
...The bottom of a cylindrical tube with a bottom.

Claims (1)

[Claims] 1. When continuously rolling a bottomed tube with one end closed, insert the mandrel to the bottom of the bottomed tube, and roll the mandrel toward a row of roll calibers arranged in series so that the tube does not move forward with respect to the mandrel. The relationship between the insertion speed and the circumferential speed vR of the vM caliber is set as vM≧VR, and the tip of the mandrel is passed between the roll axes of the final stand, and then the caliber circumferential speed of all stands is large relative to the speed of the mandrel. A continuous rolling method for tubes characterized by rolling the tube while separating the bottom of the tube from the tip of the mandrel.