Having been sufficiently softened by re-beating, each cake of cement is cut by a strong lever knife into four nr six pieces, which are then ready for the first mixing-machine. This consists of three steam-heated rollers, about 9 in. in diameter, of which the two upper ones are placed level with each other, while the third ocoupies a central position beneath them. The bearings of each roller can be adjusted by screws, so as to regulate the feed of cork and cement. Above the upper two rollers, is fixed a hopper, large enough to contain a sack of cork. For this quantity of cork, one cake of cement is fed in at one side between the lower and the two upper rollers. It passes out on the other side, in the shape of thin shreds mixed with the cork. No unproteoted lights should be allowed in this department, on account of the danger of explosion from the large pro portion of cork-dust floating in the air. When lights are requited, they should be placed in lanterns, communicating directly with the external atmosphere, and having no connection with the room in which this mixing•machine is located. The mixture of cement and cork-dust has also the dangerous property of igniting spontaneously if left in a heap in a warm place. As the vicinity of the steam-heated rollers generally elevates the temperature considerably, it is well not to mix at once more than one sackful of cork with a corresponding quantity of cement. When this batch has been removed, another is commenced, and so on. On leaving the first machine, the mixed cork and cement are either raised by an elevator, or carried in sacks, to the second machine, in which they are more thoroughly mixed, and incorporated with the colouring matter. This machine consists of a horizontal drum, in which a spindle, furnished with beaters, works at a speed of about 200 rev. a minute. On the upper side of the drum, a hopper is fixed, in such a way that it can be closed by an iron slide, fitted into a short shoot connecting it with the drum. The capacity of the interior is such that it will contain at least one sack of cork with the necessary cement and colouring matter. It is fixed immediately above the next machine, the communication being regulated by means of a slide. The colouring matter is put into the hopper together with the mixed cork and cement, as they leave the preceding machine. The quantity of colouring matter to be added must depend, not only upon the tint which is to be given to the finished linoleum, but also upon the quality of the pigment itself. It is customary at present to make the body of linoleum of two colours—brown and red. For the brown, yellow ochre and barytes are used ; for the red, oxide of iron, and vegetable black. Many other colours may be produced by altering the colour of the pigments ; but the brown hue of the cement and cork precludes white or any delicate tint. As a guide, the following mixture for red linoleum may be cited :—Pulverized cork, 56 lb.; linoleum cement, 46 lb. ; red oxide of iron, 17 lb.; vegetable black, 13 oz.; litharge, 8 oz.
The small addition of ground litharge, per cent., although general, appears to be merely a matter of routine, as excellent linoleum can be made without it. It hastens the drying of the linoleum, but renders it more brittle, and, for sanitary reasons, the less lead put into an article intended for use in dwellings, the better.
The various materials, having been beaten about in the drum for 2-3 minutes, are transferred to the next•machine, by simply opening the slide which had hitherto supported them. The ment of this, the most important of the machines, is shown in Figs. 710 and 711. With the exception that the lower part is steam-jacketed, it resembles a sausage-machine of great strength. In Fig. 711, a indicates the hopper, through which the material falls from the preceding machine. On entering, the material is seized by
revolving knives or cutters b, which carry it tween the fixed knives a. The edges of the knives b are shaped like chisels, the bevelled edge being turned towards the outlet of the machine d (Fig. 710), in which direction, therefore, the material is gradually propelled. The fixed knives c (Fig. 711) are inserted before bolting on the back-plates e. Between each couple of fixed knives, iron distance-pieces are inserted, the thickness of which is the same as that of the revolving cutters—I in. All the cutters are made of wrought, or malleable cast iron. The knives b are also separated by washers, equal in thickness to the fixed cutters. The screws f (Fig. 710) prevent the fixed knives from changing their position. The revolving cutters are kept in their places by a large nut g, screwed upon the steel shaft h. This shaft, as will be seen from the section (Fig. 711), is octagonal, the openings in both washers and revolving cutters being of a corresponding shape. The cutters and distance-pieces must be carefully planed and adjusted, to prevent them from catching each other, which would cause serious damage to the machine. In order to prevent the shaft h from shifting, it is fixed between steel pins k 1, the chief thrust being upon 1. Both these pins are adjustable by screws. The motive power is derived from the pulley m. A movable pulley is necessary here, so that the machine may be stopped at once, in case a bolt or other hard substance enters it. As shown in Fig. 710, the case, which is of cast iron, is con structed in two halves, united by bolts. The lower half, which is steam jacketed, is fixed, while the upper half can be lifted off after the removal of the bolts. Steam is only admitted for a short time at the commencement of work ; it is then turned off, as the beat produced by the friction in the machine, and by the rapid oxidation of the material, is quite sufficient to soften the latter.
It may oven happen in summer that tho heat from these sources will char and destroy the linoleum, in which case, cold water should be run through the hollow bottom of the machine, tho steam pipes being snpplied with a branch leading from a cistern. In passing through this machine, the linoleum mixture becomes very compact, and is so thoroughly mixed that the particles of cork and cement can hardly be distinguished by the naked eye. It issues from the machine below and around the nut g (Fig. 710), and falls into baskets, in which it is removed to the next machine.
This consists of a pair of ordinary mixing-rollers, as used in the manufacture of indiarubber. One of the rollers is steam-heated, while the other is kept cool by a current of cold water running through it. The linoleum adheres to the face of the cold roller, and is removed from it by a steel scraper or "doctor," which is pressed against the face of the roller by a weighted lever. Tho material leaves this machine in the form of thin sheets, in which any particles of wood or other impurities can be easily detected. The sheeted linoleum is then placed in the hopper of the next machine, which is termed a "scratcher." This resembles the preceding one, with the exception of the " doctor," which is replaced by a rapidly revolving cylinder, studded with numerous points, which work upon the surface of the linoleum adhering to the cold roller, and remove it in the shape of small pellets. The method of covering the scratching-oylinder is to insert wire nails into thick strips of indiarubber, these strips being then wound around the wooden cylinder, and secured by screws. The elasticity secured in this way prevents injury to the "scratcher," in case any hard substance should he introduced.