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The measurement process was adjusted for Pr = 0.01, 0.02, and 0.03, irrespective of the initial waviness of the rolled product and its length.
Grip heads with smooth (unchanneled) jaws, which were set in wedge-operated clamps provided with needle rollers (the wedge surfaces were inclined at 9º ) were used at the points of clamping to prevent damage to the surface of the rolled product (this achieved a metal savings of from 1.5 to 7.5%). In this case, the rolled product was held in the grip heads(up to 10 sec) at the initial moment of tensioning to ensure its reliable containment; this made it possible to increase the coefficient of friction between the jaws and rolled product from 0.178 to 0.253 [4]. The increase in the frictional force is explained by the fact that mutual introduction of material, which is elastoplastic in nature, is observed under the high specific pressures generated at the points of contact between the rolled product and jaws.
A static friction force, which is governed by Coulomb's dry-friction law [5], acts on the contact boundary between the rolled product and jaws. In this case, the maximum static friction force depends on the force of the normal pressure and on the condition of the contacting surfaces. Proceeding from this, we used interchangeable uncut jaws with a smoothly machined contact surface heat-treated to an HRC of no more than 40. For the selected wedge angle and the presence of rolling friction between the wedges, the frictional force between the rolled product and jaws is sufficient to contain the strips without slipping at the points of grip for both a soft material (carbon steel) and a material with an increased surface hardness (for example, steels 12KhI8NIOT and 09G2S).
The tests indicated that smooth jaws with a wedge angle of 9ºand rolling supports can be used successfully to grip both carbon and corrosion-resistant steels, and，in this case, to provide for adequate reliability of fixture of the ends of the rolled product without their being damaged.
The force parameter of the production process employed to straighten strips by stretching (tensioning force) is defined by the equation P = Fσs, where F is the cross-sectional area of the strip being straightened [6], while the yield stress σs is defined by the equation σs = A(ε)n, where A and n are coefficients that can be determined from an experimental hardening curve, and ε is the degree of deformation.
Moreover, it is possible to derive group equations for inpidual groups of steels exhibiting a uniform variation in technical characteristics. Using the algebraic method of determining coefficients A and n, σs can therefore be determined with a sufficiently high accuracy from the following equations:
Σ=σ0.2+3.4
Σ=σ0.2+3.2
where σ0.2 is the yield point of the metal.
The degree of deformation ε, which is required for straightening strips by the method of stretching, is 1-3%; substituting an ε value equal to 3% in Eqs. (4) and (5), we therefore obtain equations for practical determination of σs:
Σ=σ0.2+6.56
Σ=σ0.2+8.03
for St0, St3, steels 0, 8, I0, 20, and 09G2s (4), and steels 12Kh18N10T, 12Kh18N10T, 08Kh18N10T, 12Kh18N9, and 36Kh18N25S2 (5), respectively. Nomo grams of allowable strip sections are calculated from these equations (see Figs. 2a and b).
The straightening-stretching machine (force of 1000 kN) has been introduced at the Chemical Machine-Building Plant in Ruza.
矫直机是对金属棒材、管材、线材等进行矫直的设备。矫直机通过矫直辊对棒材等进行挤压使其改变直线度。一般有两排矫直辊，数量不等。也有两辊矫直机，依靠两辊（中间内凹，双曲线辊）的角度变化对不同直径的材料进行矫直。主要类型有压力矫直机、平衡滚矫直机、鞋滚矫直机、旋转反弯矫直机等等。
这种矫直机的矫直过程是：辊子的位置与被矫直制品运动方向成某种角度，两个或三个大的是主动压力辊，由电动机带动作同方向旋转，另一边的若干个小辊是从动的压力辊，它们是靠着旋转着的圆棒或管材摩擦力使之旋转的。为了达到辊子对制品所要求的压缩，这些小辊可以同时或分别向前或向后调整位置，一般辊子的数目越多，矫直后制品精度越高。制品被辊子咬入之后，不断地作直线或旋转运动，因而使制品承受各方面的压缩、弯曲、压扁等变形，最后达到矫直的目的。