Hot or combination hot and cold

84.55 - Metal-rolling mills and rolls therefor. 8455.10 - Tube mills - Other rolling mills : 8455.21 - - Hot or combination hot and cold 8455.22 - - Cold 8455.30 - Rolls for rolling mills 8455.90 - Other parts (I) ROLLING MILLS Rolling mills are metal working machines consisting essentially of a system of rollers between which the metal is passed; the metal is rolled out or shaped by the pressure exerted by the rollers, and at the same time the rolling modifies the structure of the metal and improves its quality. In some cases, in addition to their normal functions, rolling mills ma be used to produce a pattern on the metal surface, or to roll together two or more sheets of di erent metals to produce a laminated product. & Similar machines for rolling materials other than metal, e-g., calenders, are excluded (headin 84.20). Other roller machrnes (e.g., for gumming metal foil on to a paper support) (heading 84.20), %ending, foldin ,straightening or flattening machines (heading 84.62) are not regarded as rolling mills in the sense descriged above and are therefore also excluded froom this heading. Rolling mills are of various types according to the particular rolling operations for which they are designed, viz. : (A) Rolling out to reduce the thickness with a correspondin increase in length (e.g., in the rolling of ingots into blooms, billets or slabs; rolling of sla s into sheet, strip, etc.). % (B) Rolling of blooms, billets, etc., to form a particular cross-section (e.g., in the production of bars, rods, angles, shapes, sections, girders, railway rails). (C) Rolling tubes. (D) Rolling of wheel 'blanks or wheel rim blanks (e.g., to shape the flanges of railway wheels). Most rolling mills are designed for the operations indicated at (A) or (B) above. The essential element of these is known as a " stand ', and consists of two, three or four rolls mounted horizontally one above the other in heavy metal housings, the metal being assed through an adjustable ga between the rollers. In three high and double two high stan s, the metal, after being passed etween two of the rollers, is then passed though two others; some stands have two or more additional rolls which act as support to give additxonal power and steadiness to the working rollers. % B Most mills consist of a number of such stands arranged either side by side, or slightly staggered, or tandem fashion (for example, continuous rolling mills for sheets); the speeds and gaps of the rollers are adjusted to produce a progressive and gradual rolling down of the metal. Certain rolling mills may have side rollers for working on the edges of the material, or for producing particular sections (e.g., girders). For flat products rollers are plain (exce t that certain finishin cases e.g., for &e operations under rollers may produce a of the ro Is, but the working rollers have above) the rolling is channels cut in their surface so that a gap (or pass) of a particular shape is formed between the two rollers. The metal as it passes throu h is formed to the shape of the gap, and assing through a succession of such gaps, gradua ly varying in shape, the metal is thus worke to the desired cross-section. (~5 \ B i Rolling mills of the kinds referred to above vary considerably in size, from small machines for rolling precious metals up to very heavy rolling mills for steel. Most of the rolling mills referred to above are for hot rolling, but certain finishing mills (particularly for sheet or strip) roll the metal cold. Among the rolling mills of the type referred to at (C) and @) above are : (1) Mannesmann or similar machines for piercing billets; these have large inclined rollers which rotate the heated billet and force it over a piercing mandrel, thus forming the rough tube. (2) Mills for rollin out the pierced billets to reduce the thickness of the walls, increase the length and pro uce a satisfactory surface to the walls. The walls of the tube are worked between a mandrel or plug on the inside, and either rollers with a circular pass or conical rollers on the outside. In certain cases rollers with eccentrically cut channels to give a variable pass are used (step rolling). (3) Finishing mills for tubes, to f i s h or reduce the thickness of the walls, or to reduce the diameter, or roduce a perfect circular cross-section. These may operate with or without an internal m A 1 . (4) Radial mills for rolling the walls of large diameter cast steel tubes. The tube rotates between a number of rollers operating on the outside and correspondmg rollers on the inside. (5) Wheel or disc rolling mills. These usually consist of sets of conical or cylindrical rollers variously arranged, between which the roughly formed wheel revolves; the various parts of the wheel (e.g., flanges of railway wheels) are worked to the r uired shape by the pressure of the rollers. Similar machines are used for shaping flanged tyres or railway wheels, and for certain railway rails. '7 equipment such tanks, stri coilers, or Rsttening (11) ROLLS AND OTHER PARTS Sub'ect to the general provisions re arding the classification of parts (see the General Exp anatory Note to Section XVI), the eading covers parts of rolling mills. Amon the parts covered by this heading are the rolls of rolling mills. These vary considerably in ength and diameter, those for steel ranging a proximately from 30 to 520 cm in len and from 18 to 137 cm in diameter. They are ma e of cast iron, or of cast or forged stee , usually special1 hardened on the surface and carefully rnachlned to exact dimensions; they ma be plain, or witx grooves of various shapes to form the necessary passes. Each roll ends in necL, often specially shaped for mounting in the housings of the rolling mill. Outside the roll necks, wobbler-ends are cut to which the driving force is applied. t I f' P f