Rolling method for boards with different longitudinal thicknesses

Abstract

Disclosed is a rolling method for a board having various longitudinal thicknesses, comprising the following steps: 1) setting a number N of uniform-thickness segments of a sample, thicknesses h.sub.1, h.sub.2, . . . , h.sub.N of the uniform-thickness segments, lengths L.sub.1, L.sub.2, . . . , L.sub.N of the uniform-thickness segments, and lengths T.sub.1, T.sub.2, . . . , T.sub.N1 of transitional segments between the uniform-thickness segments, the N uniform-thickness segments having N1 transitional segments therebetween, and both the thickness and length having a unit of mm; 2) selecting a raw material; 3) setting a rolling force, a roll gap and a rolling period of time for each segment; 4) preparing rolling; 5) conducting rolling; 6) optimizing rolling parameters, measuring thicknesses and lengths of the uniform-thickness segments and lengths of the transitional segments after the rolling member is rolled; comparing the measured thicknesses of the uniform-thickness segments with the set thicknesses for the sample, so as to correct the rolling force P.sub.i and roll gap G.sub.i set for each segment in step 3); comparing the measured lengths with the positions marked in step 4), so as to correct the rolling period of time set for each segment in step 3); repeating steps 4) and 5) using raw materials of the same size, and making correction again, wherein a rolled member meeting the requirements of the sample can be made after 2-3 times of trial rolling. This method avoids preparation of a raw material in the form of a roll, avoids study on a complex controlling method for various-thickness rolling of the roll, and saves the raw material and test time.

Claims

1. A rolling method for manufacture of a board having various longitudinal thicknesses, comprising the following steps: 1) setting a number N of uniform-thickness segments for a sample, thicknesses h.sub.1, h.sub.2, . . . , h.sub.N of the uniform-thickness segments, lengths L.sub.1, L.sub.2, . . . , L.sub.N of the uniform-thickness segments, and lengths T.sub.1, T.sub.2, . . . , T.sub.N1 of transitional segments between the uniform-thickness segments, wherein the N segments have N1 transitional segments there between, and both the thickness and length have a unit of mm; 2) selecting a raw material having the following properties thickness: H max(h.sub.1, h.sub.2, . . . , h.sub.N), unit: mm; length: $L=\frac{\underset{i=1}{\overset{N}{.Math.}}\left(L_i{h}_i\right)+\underset{i=1}{\overset{N-1}{.Math.}}\frac{T_i\left(h_i+h_{i+1}\right)}{2}}{H},\mathrm{unit}\text{:}\mathrm{mm};$ the raw material needed thus has a length of L0+L unit: mm; wherein L0 is a sum of a clamp length and an allowance of a roller entrance; 3) setting a rolling force, a roll gap and a rolling period of time for each segment i) calculation of the rolling force
P.sub.i=f(H, h.sub.i, b, R, , t.sub.f, t.sub.b, T, {dot over ()}, .sub.s0)(1) wherein P.sub.ithe rolling force set for the i.sup.th uniform-thickness segment, kN; H, h.sub.ithickness of a rolling member at an entrance and thickness of the rolling member at an exit of the i.sup.th uniform-thickness segment, mm; bwidth of the rolling member, mm; Rradius of a working roller, mm; .sub.s0initial yield stress of a strip, kN/mm.sup.2; friction coefficient between the working roller and the rolling member, 0.02-0.12; t.sub.b, t.sub.fback tension and front tension applied by the clamp to the rolling member, MPa; Trolling temperature, C.; {dot over ()}deformation rate, s.sup.1, calculated using Ekelend formula:
{dot over ()}=f(V.sub.r, R, H, h.sub.i, b, C.sub.H, P.sub.i) V.sub.rstand velocity, m/min; C.sub.HYoung's modulus of the rolling member, MPa; ii) calculation of the roll gap according to the spring equation of a rolling mill: $\begin{array}{cc}{G}_i=h_i-\frac{P_i}{M}& \left(2\right)\end{array}$ wherein G.sub.ithe roll gap set for the i.sup.th uniform-thickness segment, mm; P.sub.ithe rolling force set for the i.sup.th uniform-thickness segment, kN; Mstiffness of the stand, kN/mm, which is an intrinsic parameter of a stand and is measured before rolling begins; iii) calculation of the rolling period of time:
t.sub.2i1=L.sub.i/V.sub.r or t.sub.2i=T.sub.i/V.sub.r (3) wherein L.sub.i, T.sub.ilength of the i.sup.th uniform-thickness segment and length of the i.sup.th transitional segment, mm; V.sub.rrolling velocity, mm/s; 4) preparing rolling marking start and end points of the uniform-thickness segments and the transitional segments on the raw material based on the constant volume principle in view of a required sample shape with width spread ignored, wherein the lengths of the uniform-thickness segments and the transitional segments are calculated as follows: $L_{\mathrm{i\_}0}=\frac{L_i{h}_i}{H},\mathrm{mm};$ $T_{\mathrm{i\_}0}=\frac{T_i\left(h_i+h_{i+1}\right)}{2H},\mathrm{mm};$ 5) rolling conducting rolling using the set values calculated according to step 3); 6) optimizing rolling parameters measuring thicknesses and lengths of the uniform-thickness segments and lengths of the transitional segments after the rolling member is rolled; comparing the measured thicknesses of the uniform-thickness segments with the set thicknesses for the sample, so as to correct the rolling force P.sub.i and roll gap G.sub.i set for each segment in step 3); comparing the measured lengths with the positions marked in step 4), so as to correct the rolling period of time set for each segment in step 3); repeating steps 4) and 5) using raw materials of the same size, and making correction again, wherein a rolled member meeting the requirements of the sample can be made after 2-3 times of trial rolling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of flexible rolling.

(2) FIG. 2 is a schematic view of a thickness profile of a board having a periodically varying longitudinal thickness according to the disclosure.

(3) FIG. 3 is a schematic view showing manufacture of a non-uniform-thickness board on a single rolling mill.

(4) FIG. 4 is a schematic view of a shape of a non-uniform-thickness sample.

DETAILED DESCRIPTION OF THE INVENTION

(5) The disclosure will be further illustrated with reference to the following Examples and accompanying drawings.

(6) As shown by FIG. 3, a common single rolling mill is used to conduct non-uniform-thickness rolling according to the disclosure, so as to manufacture, for example, a non-uniform-thickness board shown in FIG. 4, wherein 10 represents rolling mill, 20 represents clamp, and 30 represents board. Specifically, the manufacture is conducted according to the following steps: 1) setting a number N=5 of uniform-thickness segments for a sample, thicknesses h.sub.1, h.sub.2, h.sub.3, h.sub.4, h.sub.5 of the uniform-thickness segments, lengths L.sub.1, L.sub.2, L.sub.3, L.sub.4, L.sub.5 of the uniform-thickness segments, and lengths T.sub.1, T.sub.2, T.sub.3, T.sub.4 of transitional segments between the uniform-thickness segments, wherein the 5 segments have 4 transitional segments therebetween, and both the thickness and length have a unit of mm; 2) selecting a raw material having thickness: H max(h.sub.1, h.sub.2, h.sub.3, h.sub.4, h.sub.5), unit: mm;

(7) length: the length of the clamp and the entrance balance of the roller should be taken into consideration; the length of this part is assumed to be L0; the extension of the board should also be taken into consideration; based on the constant volume principle and ignoring width spread, the length of this part can be calculated using the following formula:

(8) $L=\frac{\underset{i=1}{\overset{5}{.Math.}}\left(L_i{h}_i\right)+\underset{i=1}{\overset{4}{.Math.}}\frac{T_i\left(h_i+h_{i+1}\right)}{2}}{H}\left(\mathrm{mm}\right)$
hence, the length of the raw material needed is L0+L (mm). 3) determining set values: for the shape shown by FIG. 4, setting is conducted as follows (see formulae (1), (2), (3) for the methods for setting roll gap, rolling force and rolling period of time)

(9) TABLE-US-00001 Setting Setting rolling Setting rolling period of No. Longitudinal Position roll gap force time 0 0 G.sub.1 P.sub.1 0 1 L.sub.1 G.sub.1 P.sub.1 t.sub.1 2 L.sub.1 + T.sub.1 G.sub.2 P.sub.2 t.sub.2 3 L.sub.1 + T.sub.1 + L.sub.2 G.sub.2 P.sub.2 t.sub.3 4 L.sub.1 + T.sub.1 + L.sub.2 + T.sub.2 G.sub.3 P.sub.3 t.sub.4 5 L.sub.1 + T.sub.1 + L.sub.2 + T.sub.2 + L.sub.3 G.sub.3 P.sub.3 t.sub.5 6 L.sub.1 + T.sub.1 + L.sub.2 + T.sub.2 + L.sub.3 + T.sub.3 G.sub.4 P.sub.4 t.sub.6 7 L.sub.1 + T.sub.1 + L.sub.2 + T.sub.2 + L.sub.3 + T.sub.3 + G.sub.4 P.sub.4 t.sub.7 L.sub.4 8 L.sub.1 + T.sub.1 + L.sub.2 + T.sub.2 + L.sub.3 + T.sub.3 + G.sub.5 P.sub.5 t.sub.8 L.sub.4 + T.sub.5 9 L.sub.1 + T.sub.1 + L.sub.2 + T.sub.2 + L.sub.3 + T.sub.3 + G.sub.5 P.sub.5 t.sub.9 L.sub.4 + T.sub.5 + L.sub.5

(10) The thickness of a uniform-thickness segment of the rolling member is determined by a roll gap G.sub.i or a rolling force P.sub.i, and the lengths of a uniform-thickness segment and a transitional segment are determined by a rolling period of time t.sub.i. The actual rolling effect is related with the rolling velocity. Hence, the rolling velocity should be set first for the rolling, so that the rolling can be conducted at a constant velocity V.sub.r.

(11) The maximum loaded pressing velocity of the rolling mill is V.sub.p. Hence,

(12) $h_i=\frac{V_p{T}_i}{V_r}\left(h_i=h_{i+1}-h_i\right)\left(i=1,2,\mathrm{.Math.},5\right);$

(13) The rolling velocity must meet the following relationship:

(14) $V_r\frac{V_p{T}_i}{h_i}\left(\mathrm{mm}\text{/}s\right)\left(i=1,2,\mathrm{.Math.},5\right);$ 4) preparing rolling

(15) Adjustment of the controlling values: as described above, the set values for controlling the rolling include roll gaps, rolling forces and rolling periods of time for the uniform-thickness segments. In real rolling, the shape of the rolling member is usually different from the set shape due to variation of the board strength, fluctuation of the rolling velocity of the board and other factors. Therefore, the set values need to be adjusted in light of the shape of the rolling member after rolling. A simple method is as follows:

(16) Making marks on the original board: in view of the required shape after rolling, points 0 . . . 9 are marked on the original board correspondingly based on the constant volume principle with width spread ignored, wherein the lengths of the uniform-thickness segments and the transitional segments can be calculated respectively as follows:

(17) $L_{\mathrm{i\_}0}=\frac{L_i{h}_i}{H}\left(i=1\mathrm{.Math.}5\right)$$T_{\mathrm{i\_}0}=\frac{T_i\left(h_i+h_{i+1}\right)}{2H}\left(i=1\mathrm{.Math.}4\right)$ 5) rolling

(18) Setting is conducted according to step 3) and rolling is conducted; 6) optimizing rolling parameters

(19) Measuring thicknesses and lengths of the uniform-thickness segments and lengths of the transitional segments after the rolling member is rolled; comparing the measured thicknesses of the uniform-thickness segments with the set thicknesses for the sample, so as to correct the rolling force P.sub.i and roll gap G.sub.i set for each segment in step 3); comparing the measured lengths with the positions marked in step 4), so as to correct the rolling period of time set for each segment in step 3); repeating steps 4) and 5) using raw materials of the same size, and making correction again, wherein a rolled member meeting the requirements of the sample can be made after 2-3 times of trial rolling.

(20) The method of the disclosure can be carried out on a single reciprocating rolling mill only with the need of some modification to the control system. The method can be popularized in the research area of various-thickness boards. As vehicle lightening gains increasing attention, this technology will have a prospect as wide as that of VRB.

(21) In addition, the method of the disclosure can also be applied to manufacture of another lightweight materialmagnesium alloy. Temperature and rolling speed are very crucial factors for rolling magnesium alloy boards. Use of this technology on a single warm rolling mill allows various percentages of reduction of the boards when completely identical boundary conditions are ensured. This is of great significance for study on properties of magnesium alloy boards.