JPS6215283B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cold continuous rolling mill. Reducing the rolling load generated when rolling a metal plate has many advantages, such as downsizing the rolling mill, reducing roll wear, facilitating rolling of high-strength materials, and improving the shape of the plate. In order to achieve the above objective, conventionally a continuous rolling mill is used in which multiple 4-high rolling mills are arranged in which the upper and lower work rolls have the same diameter and speed, and by reducing the rolling reduction rate per machine, the rolling load However, although continuous rolling mills have high productivity, equipment costs are high, and when working with hard materials such as high-strength steel or thin work-hardened materials such as low carbon steel, the roll of the work roll is Although the rolling load increases due to flattening, the reduction of the material does not progress; the so-called rolling limit is easily reached, and rolling becomes difficult. Furthermore, multi-roll mills with small-diameter work rolls are used to roll hard materials such as high-strength steel, but the rolling speed is low, resulting in low productivity, and the large number of rolls increases roll costs. On the other hand, in recent years, rolling methods have been developed to reduce the rolling load.
The RD rolling method (Rolling Drawing method) was developed.
In this RD rolling method, as shown in Fig. 1, the rotational speeds of adjacent rolls a and b are set to different speeds V ₀ and V ₁ , and the thickness of the metal sheet S on the entry side is h ₀ and the thickness on the exit side is sawo h ₁
This is a different speed rolling method in which the relationship h ₀ /h ₁ =V ₁ /V ₀ is maintained, and the difference between the front tension t _f and the rear tension t _b of the roll gap is used for rolling. A large reduction can be achieved with rolling load. This variable speed rolling method was applied to a continuous rolling mill, and in order to eliminate the drawbacks of a continuous rolling mill using a multi-roll rolling mill having work rolls of equal diameter and constant speed, continuous rolling as shown in Figures 2 and 3 was carried out. Although a continuous rolling mill has recently been developed, the continuous rolling mill has the following drawbacks. (i) The threading process for winding the plate is troublesome, it is difficult to cool the rolls, and it is not suitable for high-speed rolling, resulting in poor productivity. (ii) Because it is rolling at different speeds, it is necessary to make the front tension t _f of the roll gap larger than the rear tension t _b , but the tension value increases as it approaches the exit side of the rolling mill, and rolling becomes impossible due to plate breakage. There is a risk that this will occur. (iii) When rolling high-strength materials, it is preferable to use small-diameter rolls, but if small-diameter rolls are used in the rolling mills shown in Figures 2 and 3, the deflection deformation of the rolls will increase, resulting in The shape becomes worse. Note that a, b, c, d, e, in Figures 2 and 3
a', b', c', d', and e' are rolls, and s is a metal plate. The present invention was made for the purpose of eliminating the above-mentioned drawbacks of conventional continuous rolling mills. The rolling mill is a constant speed rolling mill in which the circumferential speed ratio of the upper and lower work rolls is approximately 1, and the ratio of the inlet side plate thickness and the outlet side plate thickness of the rolling mill is approximately equal to the circumferential speed ratio of the upper and lower work rolls, and the forward tension is A different speed rolling mill that rolls so that the tension is greater than the rear tension is installed at least 1 on the upstream side of the constant velocity rolling mill in which the circumferential speed ratio of the upper and lower work rolls is approximately 1, including the most downstream constant velocity rolling mill. It is characterized by the provision of a stand. Next, the basic basis on which the present invention was made will be explained. If all the stands of a plurality of rolling mills can be made into different speed rolling mills, the effects of different speed rolling can be utilized to the fullest compared to normal rolling. However, when considering one different speed rolling mill, the difference between the rear tension t _b of the roll gap, the front tension t _f , the deformation resistance of the material k, the thickness h ₀ on the entry side, and the thickness h ₁ on the exit side. In order to achieve different speed rolling, the relationship t _f −t _b = _klo (h ₀ /h ₁ )...(i) must be maintained. However, in formula (i), l _o is a natural logarithm. Therefore, the tension between the rolling mills in which n stands of straight path type different speed rolling mills are consecutively arranged becomes higher as the stage progresses. If the value of each variable at No. stand is expressed in a sci-fi, equation (i) must hold true at each stand, so t _f , ₁ − t _b , ₁ = k _{1 lo} (h ₀ , ₁ / h ₁ , ₁ ) …(ii) 〓 t _f , _i −t _b , _i = k _{i lo} (h ₀ , _i /h ₁ , _i ) …(iii) t _f , _i+1 − t _b , _{i +1} = k _i+1 l _o (h ₀ , _i+1 /h ₁ , _i+1 ) …(iv) 〓 t _f , _o −t _b , _o = k _o l _o (h ₀ , _o /h ₁ , _o ) …(v). However, the forward tension t of the i-th stand
Since _f , _i is equal to the rear tension t _bi+1 of the i+1-th stand, t _f , _i = t _b , _i+1 (i=1 to n-1)...(vi). After all, if stands 1 to n are all different speed rolling mills that perform RD rolling, then by adding up the sides of equations (ii) to (v), respectively, and using the relationship of equation (iv), we get: So, if k _i is constant and K, then is obtained. In such rolling, the exit tension t _f , _o of the final stand (nth stand) needs to be t _f , _o < k (in actual rolling, t _f , _o < 0.3k) due to plate cutting. (though it is often considered this way in theory), l _o (h ₀ , ₁ / h ₁ , _o ) < 1, and therefore h
₀ , ₁ /h ₁ , _o <2.718. Therefore, the total elongation is approximately 272% (total reduction rate 63.2%)
Must be kept below. For example, 6 in Figure 4
Assuming that all stands are different speed rolling mills and the rolling reduction ratio of each stand is equal,
Elongation of board per stand ε(=h ₀ , _i /h ₁ ,
_i ) becomes ε=1.18 from ε ⁶ =2.72, and when expressed in terms of rolling reduction ratio, it becomes (1-1/ε)×100=15.4%. It can be seen that the rolling reduction rate of 15% per stand is about half that of a normal conventional rolling mill, and the effect of different speed rolling cannot be exhibited at all. Therefore, it can be seen that it is not practical to consecutively arrange different speed rolling mills due to constraints caused by tension. The above consideration was derived from research on different speed rolling by the inventor of the present application, and based on this consideration, at least one different speed rolling mill is installed upstream of a constant speed rolling mill placed in a tandem rolling mill. He came up with the idea of using a rolling mill. A normal constant speed rolling mill does not require a tension relationship like equation (i) like a different speed rolling mill, so if a normal rolling mill is inserted between different speed rolling mills, the different speed rolling mills before and after will affect each other. This means that the tension can be set without applying any pressure. In other words, if a normal rolling mill is installed between different speed rolling mills, the tension relationship between the different speed rolling mills (the later the stand is, the higher the tension needs to be) can be broken, and the effects of the different speed rolling mills can be fully utilized. able to demonstrate. The present invention has been made based on this idea. FIG. 4 shows a six-stand tandem rolling mill, and in the figure, 1 is an upper work roll, 2 is a lower work roll, 3 is an upper backing roll, 4 is a lower backing roll, and s is a metal plate. At least one stand among each stand No. 1 to No. 6 shall be a different speed rolling mill using the RD rolling method,
It is arbitrary which stand is used as the rolling mill for the RD rolling method, and the combinations shown in Table 1 are possible. In short, a different speed rolling mill may be installed upstream of a normal constant speed rolling mill. As explained in Fig. 1, the different speed rolling method is performed so that the ratio of the inlet side plate thickness and the outlet side plate thickness is approximately equal to the circumferential speed ratio of the upper and lower work rolls 1 and 2, and the front tension is larger than the rear tension. It is rolled.

【table】

[Table] In Table 1, RD is a different speed rolling mill using the RD rolling method, and NR is an upper work roll 1 and a lower work roll 2.
This is a normal rolling mill with constant diameter and constant speed (normal type uniform speed rolling mill). In the continuous rolling mill described above, the relationship h ₀ /h ₁ =V ₁ /V ₀ holds true as in the case of FIG. 1, and the exit tension t _f and the entry tension t _b of the roll gap are different speed rolling mills. Rolling is performed using the tension difference between the two, and rolling is performed using normal reduction in a normal constant velocity rolling mill. Next, the effect of rolling with the above-mentioned continuous rolling mill will be explained in detail. Now, regarding the case where the work roll diameter is 500mm and the rolled material at the entrance of No.i stand is a work-hardened steel plate of 1.15mm, compared to the case where both No.i and No.i + 1 stands are constant speed rolling mills, No.i is Different speed rolling mill mentioned above, No.i+1
investigated how much the total rolling reduction of No.i and No.i+1 stands could be improved when using a constant velocity rolling mill. However, the rolling force per unit plate width is 0.5ton/mm
Compare by level. (b) When both stands are regular constant velocity rolling mills (NR). Tension (Kg/mm ² ) is t _b , _i = 10, t _f , _i = t _b , _i+
1 = 25, t _f , _i+1 = 20, the rolling force is
When maintaining the pressure at 0.5 ton/mm, the rolling reduction rate of the No.i stand is 15%, the rolling reduction rate of the No.i+1 stand is 23%, and the total rolling reduction rate of both stands is 34.6%. (b) When the upstream stand is a variable speed rolling mill (RD) and the downstream stand is a regular constant speed rolling mill. Tension (Kg/mm ² ) is t _b , _i = 10, t _f , _i = t _b , _i+
1 = 40, t _f , _i+1 = 5. In different speed rolling, the reduction ratio can be obtained by increasing the forward tension, so t _f , _i
=40. t _f , _i+5 = 5 is No.i+1
Before (t _f , _i+1 ) after (t _b , _i+1 =
t _f , _i ) This is to make the average value of the tension the same as in (a). When the rolling force is set to 0.5ton/mm,
The rolling reduction ratio of the No.i stand is 35%, the rolling reduction ratio of the No.i+1 stand is 28%, and the total rolling reduction ratio of both stands is 53.2%. (c) When both stands are regular constant speed rolling mills and the tension conditions are the same as (b). The tension is t _f , _i-1 = 10, t _f , _i = t _b , _i+1 = 40,
When t _f , _i+1 = 5, the rolling reduction ratio of each stand is No.i stand 20%, No.i+1 stand 23
%, totaling 38.4%. Table 2 summarizes the above results.

[Table] Therefore, by arranging a different speed rolling mill in the No.i stand, the total rolling reduction ratio of the No.i and No.i+1 stands can be increased by 19 to 15%. The above-mentioned increase in total rolling reduction is due to the different speed rolling effect of No.i and No.i+1 stands, but RD rolling with a high reduction ratio requires a high forward tension, which is due to the difference between different speed rolling and constant speed rolling. This becomes possible only by combining rolling. Also, when installing a different speed rolling mill on the No. i stand and making the rolling reduction of the i-th stand as large as possible,
The forward tension t _f , _i =t _b , _i+1 of the i-th stand needs to be set large based on the relationship expressed by equation (i). Therefore, in different speed rolling using the RD rolling method, it is necessary to set the forward tension higher than the value used in normal constant speed rolling, but with the RD rolling method, rolling is possible even with a higher forward tension for the following reasons. It is. (a) The higher the rolling load in the stand, the worse the flatness of the plate leaving the No.i stand becomes, and it becomes difficult to control it with shape control means such as work roll bending. Also, if the shape of the board is bad, problems such as the board being squeezed in the next stand, No. i + 1 stand, are likely to occur. In this example, the No.i stand performs different speed rolling using the RD rolling method, and compared to constant speed rolling, the rolling force can be kept low even under high rolling pressure, so the ability of the shape control means can be fully demonstrated, and therefore, the ability of the shape control means can be fully utilized. Even if the rolling stock rises, there is no need to worry about the plate breaking or being squeezed by the normal rolling mill in the next stand. (b) Since No. i + 1 is rolled at a constant speed, even if the No. 1 stand exit tension t _f , _i is somewhat high, the exit tension t _f , _{i + 1} of No. It is possible to set the tension to a value that does not cause any risk of breakage, etc., and there is no need to set the tension as high as between the later stands, which is the case when different speed rolling mills are used consecutively.
The effect of increasing the tension between No.i+1 stands does not affect the tension between other stands. The continuous rolling mills shown in the combinations in Table 1 have the following effects depending on the installation position of the different speed rolling mills. (I) When No. 1 stand is used as a different speed rolling mill. If the No. 1 stand is used as a different speed rolling mill, the rolling load on the No. 1 stand will decrease due to different speed rolling, but the rolling load on the No. 1 stand will be reduced to the same value as in the case of a regular constant speed rolling mill. If you allow it,
In the continuous rolling mill of the present invention, the plate thickness at the entry side of the No. 1 stand can be made larger than in the case of a conventional constant speed continuous rolling mill, and the finished plate thickness of the hot strip can be made thicker. Saves energy and costs in hot rolling and pickling processes. In addition, if the plate speed at the exit side of this continuous rolling mill is constant, that is, if the production volume is constant, if the plate thickness at the entrance side of No. 1 stand can be made thicker, the speed of the unwinding reel can be lowered, and furthermore, fully continuous tandem rolling can be achieved. When this continuous rolling mill is installed in a machine, the capacity of the loop device that loops and accumulates metal sheets, which is required between the continuous rolling machine and the metal plate welding machine that sequentially welds rolling coils on the inlet side of the continuous rolling machine, increases. can reduce
Equipment costs and exclusive area can be reduced. Furthermore, regarding the quality of the product, the No. 1 stand will put a large pressure on the product, while the No. 2
It is possible to reduce the distribution of rolling reduction after the stand, and the rolling load on the subsequent stand can be reduced. Therefore, the amount of elastic deformation of the roll system in each of the subsequent stands is reduced, and the plate crown and plate shape of the product can be improved. () When the intermediate stand is used as a different speed rolling mill. Since the rolling reduction ratio can be increased, the number of stands can be reduced. Further, when the number of stands is the same, the rolling load per rolling mill can be reduced, and the shape of the plate can be improved. Among the above-mentioned effects of the continuous rolling mill of the present invention, a specific example of the reduction in the number of stands is as follows. In other words, if one or more different speed rolling mills are installed in a regular tandem rolling mill in place of the regular rolling mill,
Since the rolling reduction ratio of a different speed rolling mill can be large, even if the number of stands is reduced, the rolling load on each stand can be kept to the same level as a normal tandem rolling mill.
For example, in a continuous rolling mill with the arrangement shown in Fig. 4, low carbon steel is rolled from a raw pressure of 2.3 mm at the input side to a thickness of 0.21 mm at the outlet side.
Roll to mm on the following pass schedule. 2.3mm→1.8mm→1.16mm→0.8mm→0.5mm→0.3mm→
0.21mm In contrast, No. 1 stand, No. 4 stand are different speed rolling machines, No. 2 stand, No. 3 stand, No. 5
The rolling mill of combination No. 7 in Table 1, which uses regular stands, can roll at a schedule of 2.3 mm → 1.4 mm → 0.8 mm → 0.58 mm → 0.3 mm → 0.21 mm, so it is faster than a 6-stand regular rolling mill. can also be reduced by one stand. FIG. 5 shows an example of a two-stand tandem rolling mill, in which the No. 1 stand is a variable speed rolling mill using the RD rolling method, and the No. 2 stand is a normal type constant speed rolling mill. In this case as well, h ₀ /h ₁ =V ₁ /V at the entrance and exit sides of the different speed rolling mill, as in the case of Fig. 4.
₀ is established, and rolling is performed using the tension difference between the exit tension t _f and the entry tension t _b of the roll gap, and rolling is performed by normal reduction in a normal constant velocity rolling mill.
When rolling is performed in this way, "(I) When the No. 1 stand is used as a different speed rolling mill" in the embodiment shown in FIG.
The effect of The continuous rolling mill of the present invention is not limited to the above-mentioned embodiments, and any stand other than the most downstream stand may be used as a different speed rolling mill, and other modifications may be made within the scope of the invention. Of course, various changes can be made. According to the continuous rolling mill of the present invention, the most downstream rolling mill is a constant velocity rolling mill in which the circumferential speed ratio of the upper and lower work rolls is approximately 1, and the ratio of the inlet side plate thickness to the outlet side plate thickness of the rolling mill is the same as that of the upper and lower work rolls. At least one different speed rolling mill that rolls so that the front tension is approximately equal to the circumferential speed ratio of the work rolls and larger than the rear tension is installed on the upstream side of the constant velocity rolling mill, including the most downstream uniform velocity rolling mill. Because of this, various excellent effects such as those described below can be achieved. () Since the total rolling reduction ratio can be increased, the finished thickness of the hot strip can be made thicker.
Therefore, energy and cost savings can be achieved in hot rolling and pickling steps. () Since the rolling load of the stand on the downstream side of the variable speed rolling mill is lowered, the amount of elastic deformation of the roll system can be reduced, and the plate crown of the rolled material can be reduced.
The plate shape is improved and a product with good flatness can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the RD rolling method, Figs. 2 and 3 are explanatory diagrams of an example of a continuous rolling mill using the RD rolling method, and Fig. 4 is an explanatory diagram of an embodiment of the continuous rolling mill of the present invention. 5 are explanatory diagrams of other embodiments of the continuous rolling mill of the present invention. 1 is the upper work roll, 2 is the lower work roll, 3
4 indicates the upper backing roll, 4 indicates the lower backing roll, and s indicates the metal plate.

Claims (1)

[Claims] 1. In a continuous rolling mill in which a plurality of rolling mills are arranged continuously for rolling, at least the most downstream rolling mill is a constant velocity rolling mill in which the circumferential speed ratio of the upper and lower work rolls is approximately 1, and A variable speed rolling mill that rolls so that the ratio of the plate thickness on the inlet side and the plate thickness on the outlet side of the machine is approximately equal to the circumferential speed ratio of the upper and lower work rolls, and the front tension is greater than the rear tension, is used in the uniform speed rolling mill on the most downstream side. A continuous rolling mill characterized in that at least one continuous rolling mill is provided upstream of a constant velocity rolling mill in which the circumferential speed ratio of the upper and lower work rolls including the mill is approximately 1.