Wire Rod Mills

High Speed Wire Rod Rolling Systems-Block Mills
The wire rod block has a group and not individual drive for all stands, the shaping in the different passes is done with a calculated tension between the stands in the block in other words the shaping is not tension free like in the intermediate mill. The tension between the stands depends first from constant parameters like the shape of the groove, working roll diameter in the groove, roll diameter relations between the stands, calculated cross section reduction but also from variable parameters like bar temperature, spread of material in the groove depending from type of material and temperature of the material. The different types of material can have different deformation resistance and consequently different roll forces. With higher roll forces the groove open according the mill modulus. All that means that geometrical tolerances like diameter and roundness of the finished rod is not better than the tolerances of the intermediate mill train rolled entry section into the block due to the non uniform tension in the bar created by difference spread in the groove caused by different cross sections of the entering bar, due to different bar temperature, material properties regarding spreading and elongation. The round bar coming from the last stand of the intermediate mill train is cropped on a rotating start – stop- crank shear generally at top end and at tail end so far as necessary depending from the steel grade and pass design in the intermediate mill. In case of a cobble in the block this shear cuts the bar in scrap pieces of about 500 mm length easy to handle and to charge it into the melting furnace either into the converter as cooling scrap or into the EAF as base metal. This avoid that the total bar or rest of the bar runs into the block and more material is in the block as necessary. This shopping starts together with the snap shear directly in front of the wire rod block which can make only one cut. In the block the shaping from pre - finished bar to finished rod is done according the PPRM roll pass schedule.