Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/754

682  1em (Author:Thomas Galloway—Author:Wesley Stoker Barker Woolhouse)

 

 CALENDER, a mechanical engine employed for dressing nnd finishing cloths and various descriptions of fabrics, preparatory to sending them into the market. It is also used by calico-printers to prepare the surface of their cloths for the operations of printing. The first object of calendering is to produce in the cloth as perfect extension and smoothness of surface as can be attained, so that no wrinkle or doubled folding may remain in it. The second end attained by the calendering of cloth is the compression of the yarn or threads of which the texture is composed, which iu some degree divests them of their cylindrical shape, and reduces them to a degree of flatness, which, by bringing them more closely into contact with each other, gives to the fabric a greater appearance of closeness and strength than it would otherwise possess. The opera tion of the calender also improves the superficial appearance, by flattening down all knots, lumps, and other imperfec tions, from which no material from which cloth is fabricated can ever be entirely freed during the previous processes of spinning and weaving. And, thirdly, in certain fabrics it is desirable that cloth should receive, by means of friction, an additional lustre or polish, which is distinguished by the appellation of glazing. For the accomplishment of these objects the agencies on which the calenclerer has to rely are moisture, heat, pressure, and friction, and these he variously combines to produce many different effects. The term calender, which really means only the chief mechanical engine employed, gives the general name to the finishing establishments where all the varied operations of cloth-lapping are carried on ; and it is as usual to say that goods are packed as that goods are dressed at a calender. The common domestic smoothing-iron may be regarded as a form of calendering utensil ; as is also the old-fashioned domestic mangle, which consists of a cylinder applied to a plane, upon which it is rolled backward and forward, until some degree of smoothness is produced by this reciprocating motion. . A form of mangle, consisting of an enormously heavy cylinder, which is worked forwards and backwards over a plane surface, is still used in calendering establish ments for the finishing of very heavy linens and similar goods. The smoothing calender completes the substitution of cylindrical for plane surfaces, all the parts which operate upon the cloth being of that form. This ingenious engine, which was introduced into Britain from Flanders and Holland during the persecution of the Huguenots, has, since its introduction and adoption, undergone no very material or important alteration or improvement in point of theoretical principle; nor, until the extension of the cotton manufacture had introduced a general spirit of mechanical improvement, were any great advances made in the practical applications of it. Calenders are constructed with from two to five rollers or cylinders, technically termed &quot; bowls,&quot; three or five- bowl calenders being most frequently employed. The materials of which these cylinders are made are wood, compressed paper, and metal, such as chilled cast-iron, brass, or copper. They are variously arranged in, relation to each other, and as mechanical arrangements are re quired 1st, for varying pressure ; 2d, for apptying heat within a metal bowl from steam, hot iron, or burn ing gas ; and 3d, for varying the rate of motion of a pair of the bowls so as to produce friction the gearing of a calender is somewhat complex. Commonly a three-bowl calender has an upper and under cylinder of paper, the central one being of metal, and in such an implement either two pieces may pass through at the same time, or one piece may receive two pressures. An ordinary five-bowl calender has the first, third, and fifth cylinders of paper, the inter mediate being of metal, and here four successive pressures may be given. Fig. 1, PJate XXXII., is an elevation of a five-roller calender for finishing cloth. A, A are two paper rollers, of 20 inches diameter each. B, B are two cast-iron cylinders, externally turned imtil perfectly smooth; their diameter is 8 inches, allowing the substance of iron to be 2 inches, and leaving a perforation of 4 inches diameter. C is a paper roller of 14 inches diameter; D, D is the framing of cast-iron for containing the bushes in which the journals of the rollers revolve ; E, E are tivo levers by which the rollers are firmly pressed together while the cloth is passing through. Fig. 2 is an end view of the same calender, with the wheels for glazing cloth. The wheel on the upper cylinder is 10 inches diameter, the wheel on the under cylinder is 13 inches diameter ; they are connected by the wheel F, which communicates the speed of the upper cylinder, so that the wheel on the under cylinder being nearly one-third of an inch more in diameter, the difference of their motions retards the centre paper roller, by which means the upper cylinder passes over the cloth one-third faster than the cloth passes through the calender, and polishes it in con sequence. The construction of paper or pasteboard rollers for calenders is a process of great interest and importance. The frequent heating and cooling to which the apparatus is subject necessarily produces w r arping and splitting in wooden bowls, which are thereby rendered useless, but the substitution of paper afforded a radical cure for these defects as well as a collateral advantage arising from its being susceptible of a much higher degree of superficial polish, which is always transferred to the cloth. In the construction of paper cylinders an axis or journal of malleable iron and two circular plates of cast-iron of the same diameter as the cylinder to be made are, in the first place, provided. A plate is secured on one end of the journal. The entire space between the two iron plates is then to be filled with circular pieces of paper or pasteboard, exceeding by about 1 inch in diameter the iron plates, and having each a correspondent perforation, through which the iron journal passes. A cylinder is thus formed, the substance of which is of paper locked together by plates of iron at the extremities, and susceptible of immense? compression which it receives in a hydraulic press. After undergoing this preparation, the cylinder is exposed to strong heat in a confined apartment in which the paper contracts and becomes loose. It is again put into the press, more sheets of paper are added, and this process goes on till the cylinder has gradually acquired the requisite compression. It is then re-exposed to the ordinary tem perature of the atmosphere, and by its re-expansion pre sents a body almost remarkably compact, its specific gravity in this state being greater than even that of silver. 