When starting to ram a flask, see that the sands to be used are well cut through and properly tempered. Select a flask large enough to hold the pattern and have at least 2 inches clear of the flask all around for bench work, and 4 to 8 inches on floor molds, depending upon the weight of the work to be cast. See that the flask is strong enough to carry the sand without racking and that the pins fit. Have the necessary tools at hand, such as sieve, rammer, slicks, etc.
Fig. 32. Cold-Shuts.
Examine the pattern to be molded to see how it is drafted and note especially how the parting line runs. That part of the mold forming the surface between the parts of the flask is called the joint, and where it touches the pattern this joint must be made to correspond with the parting line.
The joint of a mold may be a plane or flat surface, or it may be an irregular one. When the joint is a flat surface it is formed entirely by the mold board except with work bedded in the floor; there it is struck off level with a straightedge. When it is irregular the drag joint must be coped out for every mold needed, that is, shaped freehand by the molder before making up the cope; or, by another method, the shape of the cope joint is built up first in a match frame with the cope part of the pattern bedded into it, and upon this form the drag may be packed repeatedly, receiving each time the desired joint surface without further work on the molder's part.
Our first problems in molding illustrate these three methods of making the joint. It is aimed to give the directions for making up molds in as concise a form as possible. The student should refer frequently to the preceding sections and familiarize himself with the reasons underlying each operation.
In the small faceplate shown in Fig. 33, all of the parting line aaa will touch the mold board, so the joint will be flat. The draft is all in one direction from the cope side c, therefore all of the pattern will be in the drag. Use a snap flask for this piece.
Place a smooth mold board upon the bench or brackets. Place the drag with sockets down upon this. Set the pattern a little to one side of the center to allow for the runner. Sift sand over this about 1 1/2 inches deep. Tuck the sand firmly around the pattern and the edges of the flask as indicated by the arrows in Fig. 34, using the fingers of both hands and being careful not to shift the sand away from the pattern at one point when tucking at another.
Fig. 33. Faceplate.
Fill the drag level full with well-cut sand. With the peen end of the rammer slanted in the direction of the blows, ram first around the sides of the flask to ensure the sand hanging in well, as at 1 and 2 in Fig. 35. Next carefully direct the rammer around the pattern, as at 3, 4, and 5. Do not strike closer than 1 inch to the pattern with the end of the rammer.
Shifting the rammer to a vertical position, ram back and forth across the flask in both directions, being especially careful not to strike the pattern nor to ram too hard immediately over it. The student must judge by feeling when this course is properly rammed. Now fill the drag heaping full of sand. Use the butt end of the rammer around the edges of the flask first, then work in toward the middle until the sand is packed smooth over the top. With a straightedge strike off the surplus sand to a level with the bottom of flask. Take a handful of sand and throw an even layer about 1/4 inch deep over the bottom of the mold. On this loose sand press the bottom board, rubbing it slightly back and forth to make it set well. With a hand at each end, grip the board firmly to the drag and roll it over. Remove the mold board and slick over the joint surface with the trowel. Dust parting sand over this joint (burnt core sand is good on this work), but blow it carefully off of the exposed part of the pattern.
Set the wooden runner or gate plug about 2 inches from the pattern, as shown in Fig. 23, page 24. In snap work the runner should come as near the middle of the mold as possible, to lessen the danger of breaking the sides, and to allow the weight to be placed squarely on top of the mold.
Set the cope on the drag and see that the hinges come at the same corner.
Sift on a layer of sand about 1 1/2 inches deep. Tuck firmly with the fingers about the lower end of the runner and around the edges of the flask. Fill the cope and proceed with the ramming the same as for the drag.
Fig. 34. Molding Sand with Fingers.
Fig. 35. Molding Sand with Rammer.
Strike off the surplus sand, swinging the striking stick around the runner so as to leave a fair flat surface of sand. Partially shape a pouring basin as illustrated in Fig.23, with a gate cutter, before removing the runner. Draw the runner and finish the basin with a gate cutter and gently smooth it up with the fingers. Carefully moisten the edges with a swab and blow it out clean with the hand bellows.
Lift the cope and repair any imperfections on the mold surface with the trowel or slicks. See that the sand is firm around the lower end of the runner. Blow through the runner and all over the joint to remove all loose parting sand. Slick over the sand which forms the top surface of the gate, between the runner and the mold.
Having finished the cope, moisten the sand about the edges of the pattern with a swab. Drive a draw spike into the center of the pattern and with a mallet or light iron rod, rap the draw spike slightly front and back and crosswise. Continuing a gentle tapping of the spike, pull the pattern from the sand. If any slight break occurs, repair it with bench lifter or other convenient slick. Cut the gate and smooth it down gently with the finger; blow the mold out clean with the bellows. No facing is needed if the castings are to be pickled. The mold should now be closed and the snap flask removed.