« ПретходнаНастави »
so that no straining will occur. A little patience will make a good squeezer hand who can pour his work and save it, while the lack of patience will produce a sloppy operator whose scrap pile will always be a source of trouble and money loss.
Proper Care of Machines The operator must be instructed to take proper care of his machine. Each night after the day's work has been put up, the squeezer should be cleaned, all sand brushed off and the machine oiled. This takes only a very few minutes and pays well. Squeezers soon become hard to operate unless cared for each day. Firms using large numbers of machines are coming to see the value of their proper daily care and are insisting on this being given. Remember the foundry is a hard place for machinery and the only way to get good service is to use proper care each day.
Foreman's Oversight It is up to the foreman to see that the sand is in proper temper and condition. A weak heap of sand is no economy; better far to add some new sand than compel the operator to work a sand heap that is too far gone to work well. The foreman should also see that the proper flask is provided and that the proper adjustments are made. It is unwise to allow the operator to judge these things.
Examples of Gain The gain that can be made with a hand squeezer over bench molding runs all the way from 25% to 200%, depending on the pattern and flask equipment and other facilities. As a general thing the harder the pattern is to mold by hand the greater the gain will be.
In addition to the economies in the foundry, machine molded castings will show great savings in the grinding room and machine shop.
Hard Sand Matches The hard sand match is considered by foundrymen to be the best match that can be made. If it is carefully made it will produce many thousands of molds. To make a hard sand match, bed the pattern or gate of patterns in the drag in the usual way. Be sure the parting line is correct in all places. Oil the pattern well to prevent it sticking. Riddle enough dry, well burned parting sand through a No. 30 riddle, to make the match. This parting sand should be composed of very fine particles but should not be dust. Now mix thoroughly through
this sand about a tablespoonful of litharge. After the litharge is evenly mixed through the sand, temper the sand with boiled oil to about the temper of molding sand. Protect all corners and places that will be exposed to greater wear by placing screws head down into the corners and exposed places. Nail heads or strips of metal can be used. These should be carefully placed against the pattern as the pattern lies in the drag. Place a wooden frame on the drag made of sufficient depth to cover the exposed pattern. Riddle carefully sufficient oil sand on to the pattern to hold the nails and screws in place. Tuck carefully with the fingers around the pattern so as to pack the sand next to the pattern and particularly all corners and pockets. Fill the frame with the sand and ram snug and even a little harder than if you were making a mold. Strike off the frame and screw the bottom board on to the frame. Roll over the match and drag and remove the drag flask. Carefully remove the molding sand with bellows taking care not to disturb the oil sand. Smooth off the face of the match with a trowel and rap the pattern sufficient to give a little clearance.
Place the match some place where it will not be disturbed and where it will keep warm but not get too hot and leave for 12 hours. It should now be quite hard and the pattern can be again rapped and removed. If thoroughly dry the face of the match should be shellacked. When dry it is ready for use.
The hard sand match is worn out by the molder being careless in placing the pattern in the match. If he is careful to
drop it squarely in place the edges last a long time, but if he places it on the face of the match and slides it into place the edges are quickly worn off unless fully protected. A good way to prevent the quick wearing of the match is to drill two holes through the runner and insert pieces of brass rod to nearly fit the holes. These pieces of rod should be inserted in the holes in the runner when the match is made so they will be imbedded in the match. When the molder puts the patterns in the match it will be necessary to engage these pins and the pattern drops into the match without touching the edges.
Directions for Making Squeezer Plates Fig. 18 shows a match plate in the process of being made. This is a very simple operation when once understood. Any good molder can make a match plate. You will see that the patterns to be plated are made in the center of a mold sufficiently large to allow for 6" of sand on each side of the proposed plate. After the mold has been made, the skeleton frame marked “D” is placed around the patterns, then the strips marked “BB” which are the same in thickness as the frame “D”, and usually 14" thick, are put in place. The intervening space is filled with sand, rammed carefully, and struck off true. The frame “D” and patterns are drawn, leaving the strips “BB” in place; the mold closed and poured from one sprue only, the other sprue acting as a riser. If the mold has been carefully made with fine sand, very little finishing will be found necessary. You will see that the whole operation of putting patterns on a plate, no matter how irregular the parting line may be, is simply to make a mold in a larger flask, then separate the joint between the two parts of the mold, the thickness the plate is required. The cope half of the pattern will be reproduced on one side of the plate, and the drag half on the other.