Fig. 25.—Screw press.
The soap finally emerges through the nozzle (to which is attached a cutter of suitable shape and size according to the form it is intended the final tablet to take) as a long, polished, solid bar, which is cut with a knife or wire into lengths of 2 or 3 feet, and if of satisfactory appearance, is ready for cutting and stamping. The nozzle of the plodder is heated by means of a Bunsen burner to about 120° or 130° F. (49°-55° C.) to allow the soap to be easily forced out, and this also imparts a good gloss and finish to the ejected bar—if the nozzle is too hot, however, the soap will be blistered, whereas insufficient heat will result in streaky soap of a poor and dull appearance.
(iv.) Cutting and Stamping.—In cutting the soap into sections for stamping, the cutter should shape it somewhat similar to the required finished tablet.
Many manufacturers cut the soap into sections having concave ends, and in stamping, the corners are forced into the concavity, with the result that unsightly markings are produced at each end of the tablet. It is preferable to have a cutter with convex ends, and if the stamping is to be done in a pin mould the shape should be a trifle larger than the exact size of the desired tablet.
Fig. 26—Pin mould.
The stamping may be performed by a hand stamper (Fig. 24), a screw press (Fig. 25), or by a steam stamper. The screw press works very satisfactorily for toilet soaps.
There are two kinds of moulds in use for milled soaps:—
(a) Pin Moulds in which tablets of one size and shape only can be produced (Fig. 25). The edges of the mould meet very exactly, the upper part of the die carries two pins attached to the shoulder, and these are received into two holes in the shoulder of the bottom plate. The superfluous soap is forced out as the dies meet.