Tho linoleum, as it leaves tho scratcher, is in a condition somewhat resembling damp earth. While warm it is soft and plastic, and, if pressed into a mould while in this condition, it retains tho shape of the mould on cooling. When cold, however, it cannot be moulded, and, if subjected to pressure, regains its original shape as soon as the pressure is removed. Care must be taken not to allow tho warm material to accumulate after it has left tho scratcher, as it is very liable to heat spontaneously, and either char in the centre of the heap or oven burst into flame.
The next operation is to apply the prepared linoleum to the canvas, which is similar in texture to that used for oilcloth, and is made of jute. The width should be about 78 in., for although the finished linoleum is only 6 ft. wide, yet a margin must be allowed, so that the edges of the fabric may be cut accurately when finished. To prevent stoppage of the rolling-machine, a sufficient number of lengths of canvas for one day's work are sewn together by means of a sewing-machine.
The working parts of the machine used for rolling the liuoleum on to the canvas are shown in section in Fig. 712. Tho granulated linoleum, as it leaves the scratcher, is placed in the hopper a. The bottom of the hopper is formed by an endless web of fine wino gauze b, similar to that used in paper-making. A rotary motion, communicated to the web by the roller c, carries it slowly forward through the steam-chest e. In the pipes of the steam-chest circulates steam at a pressure of about 30 lb. a sq. in. The quantity of linoleum carried forward by the wire gauze can be regulated by a slide on the lower side of the hopper a. The rollers c d must be kept perfectly parallel, or the wire gauze would gradually work towards one side of the machine, and become damaged. From the carrying-wire, the linoleum falls between the rollers h i. These are steam-heated to a temperature of at least 121° F.), and their bearings are so mounted that tho distance between the face of the rollers can be accurately adjusted. The best material for those rollers is chilled cast iron ; if their faces were too soft, any nails which might enter the machine among the granulated linoleum would cause an indentation in them, and a corresponding projection on the face of the finished fabric. Such indentations cannot altogether be avoided ; they are removed by drilling a hole of the requisite diameter in the face of the roller. Into this an accurately fitting plug of cast iron is hammered, the top of which is then filed off level with the roller. Another disadvantage of ordinary
cast iron is that its surface soon becomes corroded by the acrylic acid of the oxidized oil, and, owing to its coarsely crystalline structure, it becomes so deeply pitted as to necessitate re-polishing. Chilled cast iron, on the other hand, offers more resistance to corrosion, and its texture being finely granular, the face of the linoleum pressed against it does not become rough.
The canvas passes from f, upon which it has been wound after sewing, over, the top of the roller h. The object of the small guide-roller g is to bring the canvas, ae soon as possible, into contact with the heated roller, in order to drive off any moisture which it might contain, and which would prevent the adhesion of the linoleum. The necessary tension is given to the canvas by a brake fixed upon f, and regulated by a weight or spring. When the canvas arrives between h and i, it meets the heated linoleum, which is pressed into it with great force. The thickness of the linoleum film is regulated by the space between the rollers. Passing round the heated roller i, the face of the fabric acquires an additional smoothness, and is then cooled' as quickly as possible by passing between the polished rollers k 1. These should be well supplied with cold water, especially in summer, as the face of the cloth becomes spongy if not cooled quickly. A slight pressure is applied between 1 and k, but not sufficient to retard the passage of the cloth, or it would buckle up between k and i. Steel wires are suspended at each side between h and i, to cut off any portion of the linoleum which may project beyond the canvas. The revolving wooden roller m takes up the linoleum after it has passed through the cold rollers, another being substituted for it as soon as it is full. As the canvas is generally made in pieces of about 100 yds., this is a convenient length for each roll of linoleum as removed from the machine, especially as it permits the canvas to be separated at the joint made by the sewing-machine. At this stage the face of the linoleum may be regarded as finished, with the exception of seasoning and, if required, printing. The back of the fabric, however, is plain canvas, which is exceedingly liable to absorb moisture, and to shrink in consequence. This must be prevented by filling its pores with a protective solution technically known as " backing." The usual backing, and that which gives the best results in practice, is a mixture of size and pigment, which is laid on warm.