Spread Characteristics and Its Mathematical Models in Rod Rolling

Abstract

In order to develop a simple general formula for calculating the spread in rod rolling, the hot rolling of steel by square-oval, round-oval, square-diamond, and diamond-diamond passes has experimentally been studied. The profile of stress-free side surface of rolled rods and the various geometrical factors related with spread ratio have been investigated.
The profile of stress-free side surface differs for the four types of passes; in the square-oval pass, it is assumed to be a straight line; in the round-oval pass, two circular arcs with a radius larger than that of initial rods; in the square-diamond pass, the angle of side surface is similar before and after rolling; in the diamond-diamond pass, its angle after rolling is slightly smaller than before rolling. The calculated and measured values of the maximum projected width of contact are compared and a close agreement is obtained between them.
For all of these four passes, the spread ratio can be expressed by a single formula as follows:
Spread ratio=B₁-B₀/B₀=αLd_m/B₀+0.5·H₀·F_H/F₀
where B₀, B₁ : Width of material before and after rolling
H₀ : Height of material before rolling
Ld_m : Mean projected arc of contact
F_H/F₀ : Fractional reduction of area before rolling
α : Coefficient (=0.83).
This is a general, simple and sufficient accurate formula.