This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The method of preparing a mould is as follows The sand having been prepared, the moulder frees the patterns from all glue and adhering foreign particles. He then selects the most appropriate "flasks," which are frames, or boxes without top or bottom, made of wood, for containing and holding the sand. The models are then examined to ascertain the most appropriate way of inserting them into the sand. The bottom flask is then placed upon a board, face downwards. A small portion of strong facing-sand is rubbed through a sieve, the remainder shovelled in and driven moderately hard into the flask. The surface is then struck off level with a straight metal bar or scraper, a little loose sand sprinkled on the surface, upon which another board is placed and rubbed down close. The 2 boards and the flask between them are then turned over together; the top board is removed, and fine brick-dust is dusted over the clean surface of moist sand from a linen bag. The excess of brick-dust is removed with a pair of hand-bellows, and the bottom half of the mould is then ready for receiving the patterns. The models are next arranged upon the face of the sand, so as to leave space enough between them to prevent the parts breaking into each other, and for the passages by which the metal is to be introduced and the air allowed to escape.
Those patterns which are cylindrical, or thick, are partly sunk into the sand by scraping out hollow recesses, and driving the models in with a mallet, and the general surface of the sand repaired with a knife, trowel, or piece of sheet-steel. The level of the sand should coincide with that of the greatest diameter or section of the model.
After the 6and is made good to the edges of the patterns, brick-dust is again shaken over it, the patterns also receiving a portion. The upper part of the flask is then fitted to the lower by pins of iron fitting in metal eyes; and a little strong sand is sifted in. It is then filled up with the ordinary sand, which is rammed down and struck off flush with the edge of the flask. The dry powder serves to keep the 2 halves from sticking together.
In order to open the mould for the extraction of the patterns, a board is placed on the top of the flask and struck smartly at different places with a mallet. The upper part of the flask is then gently lifted perpendicularly and inverted on its board. Should it happen that any considerable portion of the mould is broken down in one piece, the cavity is moistened and the mould is again carefully closed and lightly struck. On the second lifting, the defect will usually be remedied. All breaks in the sand are carefully repaired before the extraction of the patterns.
To remove the models, they are driven slightly sidewise with taps of a mallet, so as to loosen them by enlarging the space around them. The patterns are then lifted out, and any sand which may have been torn down must be carefully replaced, or fresh sand is used for the repairing. Should the flask only contain one or two objects, the ingate or runner is now scooped out of the sand, so as to lead from the pouring-hole to the object. Where several objects are in the same flask, a large central channel, with branches, is made. The entrance of the pouring-hole is smoothed and compressed, and all the loose sand blown out of the mould with hand-bellows.
The faces of both halves of the mould are next dusted with meal-dust or waste flour, put together, and the boards replaced - one just flush with the side of the flask in which the pouring-hole is situated, and the other (on the side from which the metal is to be poured) is put about 2 in. below, and secured by hand-screws. The mould is then held mouth downwards, that any sand loosened in the screwing down may fall out. It is now ready to be filled.
Where the bottom half of the flask requires to be much cut away for imbedding the patterns, it is usual, when the second half is completed, to destroy the first or "false" side, which has been hastily made, and to repeat it by inverting the upper flask and proceeding as before.
When many copies of the same patterns are required, an "odd side" is prepared - that is, a flask is chosen which has one upper and two lower portions. One of the latter is carefully arranged, with all the patterns barely half-way imbedded in the sand, so that when the top is filled, and both are turned over, all of the patterns are left in the new side. A second lower portion is then made for receiving the metal while the first one is kept for rearranging the patterns. By this plan, the trouble of arranging the patterns for every separate mould is avoided, as the patterns are simply replaced in the odd side and the routine of forming the two working-sides is repeated. (W. II. Cooper.)