Web-Glazing.—Glazing Calender.—When paper has to be glazed in the web, it is passed between a series of rolls, which are constructed upon several different systems. In one form of this machine the rolls are alternately of finely polished iron, and compressed paper, or cotton, the iron rolls being bored hollow to admit of their being connected to steam pipes, for heating them when necessary. In this machine there are eight rolls, the centre pair being both paper rolls, which have an effect equivalent to reversing the paper, by which both sides are made alike. Another form of glazing calender, of American origin, but which has been improved upon by our own engineers, consists of a stack of rolls made from chilled iron, the surfaces of which are ground and finished with exquisite precision upon a system adopted in America. A representation of this calender as manufactured by Messrs. Bentley and Jackson is given in Fig. 37. Such rolls as require heating are bored through, and their ends fitted with brass junctions and cocks, to regulate the admission of steam. The standards are of cast iron, planed and fitted with phosphor bronze bearings; the bearings to carry the top roll of the stack are furnished with wrought-iron screws and hand wheels, and wrought-iron lifting links can be attached to raise one or more of the rolls, according to the finish required on the paper. Compound levers are also supplied, to regulate and adjust the pressure on the ends of the rolls.
Fig. 38.
Damping Rolls.—An important improvement in connection with the calendering of paper was introduced by Messrs. G. and W. Bertram a few years since, by which a higher finish is given to the paper than had previously been attainable. This consists of a damping apparatus A (Fig. 38) which is placed between the last drying cylinders B of the machine and the glazing calenders C. The damping-rolls consist of two brass or copper rolls, about 14 inches in diameter, through which a constant stream of cold water is passed, while a line of steam jets, issued from finely-perforated pipes, plays over the face of the rolls. The cold water within the rolls condenses the steam, thereby imparting a uniform moisture to the under surface of the paper, which enables it to take a better surface when passing through the glazing rolls. The steam-pipes can be regulated so as to give any amount of dampness required by adjusting the steam cocks accordingly. By reference to the engraving, it will be observed from the disposition of the rolls that the web of paper is reversed, thus equalising the moisture on both sides, by which the paper-maker is enabled to produce an evenly-finished paper.
Fig. 39.
The chilled-iron glazing-rolls, as originally introduced, were fitted up in stacks of seven, and sometimes as many as nine rolls, but it was found in practice that so large a number of rolls gave unsatisfactory results; the heavy pressure, acting on the paper immediately after leaving the drying cylinders, had the effect of "crushing" the paper, giving it a thin feel. It is now considered preferable to use calenders having not more than four, or at most five rolls. An arrangement of this description, manufactured by Bertrams, is represented in Fig. 39. The system recommended by Mr. Dunbar is to employ three sets of rolls, disposed as follows:—"First, a set of three rolls; second, a set to consist of four rolls, and a stack of five to give the finishing or dry surface. With this arrangement of calenders, and the assistance of the damping apparatus, any desired surface can be got by varying and regulating the drying of the paper, which any careful machine-man can do with ordinary attention."
Finishing.—To give a still higher finish to the paper, it is subjected to what is termed "friction-glazing," which consists in passing it through a stack of rolls, formed alternately of small iron rolls and larger paper ones, the iron rolls revolving at a much higher speed than the paper-rolls. The effect of this final glazing operation gives the paper a very fine surface.
Plate-Glazing.—Donkin's Glazing Press.—This term, which is also called "super-calendering," is applied to a method of glazing hand-made paper, and is also adopted for the better qualities of machine-made paper. It consists in placing sheets of paper between highly polished plates of either copper or zinc, the latter being more generally used. The metal plates, with the sheets of paper placed alternately between them, are made up into packs or "handfuls" (the operation being usually performed by women), and these are passed between two powerful rolls, giving a pressure of from twenty to thirty tons, and each pack, consisting of about forty plates and as many sheets, is passed through the rolls several times, the pressure being regulated by means of screws or levers and weights acting on the ends of the top roll. A machine for glazing paper in packs, manufactured by Messrs. Bryan Donkin and Co., is shown in Fig. 40. Some descriptions of paper, as "antique" and "old style," for example, are surfaced with good cardboard instead of copper or zinc plates. As soon as the handful has passed through the rollers, the motion of the machine is reversed, by which means the pack is made to pass forwards and backwards repeatedly, according to the extent of gloss or smoothness required.
