Although there are many styles of molding machines on the market, these may be classified under four general types as follows: stripping-plate machines; squeezers; roll overs; and jar or jolt-ramming machines. The benefits derived from the use of these machines are manifold.
If no consideration were taken of the increase in production possible by their use, the improvement in the quality of castings alone would oftentimes warrant their installation, as the decrease in cost of machining castings produced by this method pays good dividends on the investment. The use of unskilled workmen on these machines is no small item in their favor.
The stripping-plate machine is best adapted to that class of work which offers difficulties in drawing the pattern from the sand.
Fig. 89 shows a pattern for a cast gear mounted on the stripping-plate machine. It is obvious that it would require a considerable degree of skill to produce this class of work by the hand-molding method. The pedestal base of the machine has a flat top. The stripping plate is supported above this by a rigid open framework. Working in guides carried on the sides of this framework is the drawing frame, made to rise or descend by a strong crank and connecting rod. On top of this drawing frame and parallel to the stripping plate is screwed the plate to which the pattern is fastened. The stripping plate is cast with an opening which leaves about 1 inch clear all around the pattern. When both pattern and stripping plate are properly set in place, this space is filled with babbitt metal, this being an easy way to secure a nice fit.
In many cases there may be an interior body of sand to be supported when the pattern is drawn. To accomplish this stools are used. A leg screwed into the stool plate supports the stool at the exact level of the stripping plate. The stool plate is fastened to the flat top of the machine inside of the box-like framework which supports the stripping plate, as seen in Fig. 90.
A flask is inverted on the machine, rammed, vented, and struck off. Movement of the crank lever at the side draws the pattern; and the mold then is removed and set on a level sand floor, thus doing away with bottom boards. A second stripping plate and pattern is used for ramming the cope boxes, Pulleys are manufactured on molding machines of this type, as shown by the equipment illustrated in Fig. 91. The rim patterns have the form of long hollow cylinders and can readily be set for any desired width of face. The hub carrying the core print separates from the spokes, lifts off in the mold, and is drawn by hand. The arm patterns are so flat and smoothly rounded that the mold is easily lifted off of them with little fear of breaking the sand. The cope and drag molds are both alike for a pulley mold.
Fig. 93. Match Plate Courtesy of Tabor Manufacturing Company, Philadelphia, Pennsylvania.
Fig. 92 shows a type of machine known as the hand squeezer, which only packs the sand. Here the patterns are carried on two sides of a plate set between the cope and drag, as in Fig. 93. Both boxes are filled with sifted sand and set on the machine. The boards are made to follow inside of the flask. The molder's weight on the lever compresses the sand.
The sprue is cut by a thin hollow steel tube called a sprue-cutter, which is pressed through the cope sand by the molder before separating the flask. In separating the mold the cope is first lifted from the drag, and the plate is gently rapped and lifted from the drag. To make a clean lift when parts of the patterns project in the cope, a second molder raps with an iron bar between the battens of the bottom board while the cope is being drawn off.
Such machines are used chiefly on thin work which vents and solidifies very rapidly - for the outer surfaces of the drag and cope are apt to he rammed so hard that they might choke the vent on heavier castings.
A somewhat different style of hand squeezer is shown in Fig. 94, which shows both cope and drag pattern plates attached to a portable table. Beginning the operation, the table holding the plates is turned face up with the two halves of the flask in position as shown in Fig. 95. After the sand is thrown in the flask and the surplus scraped off, the bottom boards are placed in position and held by four clumps. Next, the table is rolled over as in Fig. 96. The ramming or squeezing operation is accomplished by pulling down the long lever at the left of the machine, as shown in Fig. 97. At this point the clamps holding the cope and the bottom are automatically released.
Fig. 98 illustrates the method of drawing the patterns. The lexer is slowly lifted with the left hand, while the operator raps the vibrating pin with a mallet held in the right hand. When the long lever is returned to its upright position, the two halves of the mold rest on the sliding platform. This is drawn forward in the position shown in Fig. 99. The mold is then closed, the flask removed, and the completed mold carried to its position on the floor for pouring. Snap flasks are best adapted for this style of machine.
The roll-over machine which is illustrated by Fig. 100, has the pattern mounted on a wooden match plate as shown at A, which when in position to receive flask is resting on pins at BB. The mold is rammed by hand in the usual manner, the bottom board being clamped on by a special device to the frame C. The mold is next rolled over and rests at A. The pattern is withdrawn by the use of the foot pedal E, the operator meantime rapping the match plate with a wooden maul. This type of machine is best adapted to side floor work, the grate bar here shown being a good sample.