Flasks may be of three or more parts. Deep molds are rammed up in courses and harder in the lower portions to resist the head of metal. No soft spots, causing swells, or hard spots, causing scabs, must be made near the pattern. For heavy work about one inch of sand mixed with seal coal (ground bituminous coal) is riddled on all surfaces of the pattetn to make a smooth casting.
When possible a pattern is made in two parts, divided at the parting line, allowing the drag part to be laid on a flat board. When an odd job is made without a mold-board a cope is on a bottom board and rammed with sand and struck off. The pattern is roughly bedded in this sand.
Parting sand is thrown over the surface and the drag is rammed up. Then the mold is rolled over, the cope is taken off and the sand shaken out. The drag is then finished and the cope put on and the mold is finished.
Where there are deep places in the pattern the molder tucks sand around large nails with the heads down near the pattern, or sticks called soldiers, or gaggers, L pieces of rod or of cast iron, the toe being near the pattern and the long end along the side of the bars. These must be tucked with the fingers and pened thoroughly. The molder then finishes the cope, venting thor oughly, especially around the sprues.
by Bedding In.—In the foundry floor are pits with molding sand level with the floor. A hole is dug in this sand to take the pattern, around which the sand is packed. To allow for the escape of gas gener ated by a large quantity of iron, the hole is dug deeper than required for the pattern and a bed of very fine cinders is packed and connected by a pipe with the surface of the floor. The cin der bed is covered with sand. If the pattern is not deep or for open sand molds, the sand is leveled off even with the floor. Sand is packed in four small piles at the corners of the bed and two straight edges are leveled on these piles. Sand is tucked solid about these straight edges. Sand is then shoveled inside and out side and rammed hard outside the straight edges. The sand between is struck off.
After the molder has riddled sand quarters of an inch thick over the whole face he places two strips about eight inches long and one-quarter to one-half inch thick on the ends of the straight edges. With a third
i straight edge on these strips he with his helper presses down first one end of the straight e e and then the other, moving across the bed, ma ing all of an even hardness. He strikes off and vents all over the surface down to the cinder bed. Then with a fine sieve, a little facing sand is riddled over the whole surface and it is smoothed with a troweL Strips of wood equal to the thickness of the casting are laid on the bed to represent the outside of the casting and the outside of the mold, and the gates are built up with sand. If pins or lugs are required on the lower surface, a pattern for them is pressed into the sand at the required points. A casting more than three inches thick is made with a cope.
Bedding In with a Cope.— If the upper surface of a casting is to be perfectly flat the cope with sprue holes may be rammed on any flat surface and can be set on the mold already bedded in the floor.
If a pattern with an uneven top surface has been bedded in the floor a cope is set in place and stakes are driven about it in the floor to insure its location, and the cope is then rammed. To raise 'the cope, flat boards are laid on the sand and with crowbars the corners are started, then it is lifted with the crane.
The cope is replaced and held down with iron weights so that the head of metal cannot raise it. Very large and complicated molds can be made in green sand. The mold may be formed by templets and by parts of patterns.
Sand may be built out from the sides by in serting anchors, or separate cores may be used. Such molds are faced by painting on lead fac ing with a camel's hair brush or by rubbing facing on with the hand.
Dry Sand Molds.— These are made from sand richer in loam than that used for green sand molds. They are made in iron flasks with iron bottom boards. The molding is substan tially the same as green sand except that all joints are beveled back from the mold so that when the cope is put on the edges will not crush. This causes a fin on the casting which is chipped off. The cope and drag are placed in an oven and thoroughly dried. Dry sand cast ings are more sound than if made in green sand.