Simple Solutions That Work! Issue 11

36 Contact: JERRY SENK [email protected] sand against the pattern face. Then to jolt and squeeze simul- taneously to compact the top of the mold preferably against a compensating squeeze surface to sufficiently support the mold face. Some type of pre-jolt is necessary to evenly compact the sand where is is most important to form a rigid mold, at the pat- tern face and joint line. Since these types of high pres- sure automatic production sys- tems require the foundry to use flasks, there are costs and main- tenance to consider. Flasks for high pressure automatic molding are expensive, as are pallets/mold cars. Flasks require maintenance cleaning and routine planned pin and bushing replacement. Howev- er, they should last at least ten to fifteen years, so cost is expensed over a long period. These systems require handling equipment through the various stages of mold and casting pro- duction. The most important job they do is to ensure parting line accura-cy. They support the mold through its various stages of movement and assist in resisting the metal head pres-sure, allow- ing a softer mold to be made than is necessary for a flaskless one. Because the green strength require-ment is less, so is the clay content. This reduces the cost of sand preparation and increases mould permeability. They also allow at least 8O% of the mould area to be used, where only 6O% can be used effectively without flasks. The higher capital cost of a high pressure IN-LINE, CROSS-LOOP or PALLET INDEX system does to some extent limit their market, however with life spans over 25 years, this investment needs to be weighed against the demand and productivity capacity these sys- tems create. The heart of the high speed systems and the part which keeps it producing moulds in ex- cess of 300 per hour, is the mold- ing machine. Being high pressure jolt squeeze units, powered hy- draulically, they can be costly, but from experience and knowledge built up over many years, certain criteria are necessary to include in a four post molding machine to produce molds of consistent high quality. a. Rigid structure to withstand the forces developed by the machine. b. Sand hopper to evenly distrib- ute the correct amount of sand into the flask. c. Aerator to fluff the sand as it falls into the flask. d. Upset frame to give a head of sand above the flask for squeezing. e. Pre-jolt action to compact the sand before squeezing. f. Option of simultaneous jolting with squeezing to improve effective squeeze forces. A high pressure molding machine will possess all of these features. Referring back to investigation of the effects of jolting and squeez- ing, the jolt was found to be very important whereas squeeze assist- ed in improving mold rigidity, but also decreased the production cy- cle as the pressure increased. This has led to the development of a range of systems that can utilize one molding machine rather than having to use two machines, with the utilization of a pattern shuttle to make the cope and the other to make the drag. As most four post molding ma- chines incorporate a pattern shut- tle for rapid change of pattern, this unit can be used also for pro- ducing cope and drag half molds alternatively, making it possible to have only one molding machine in the system. This immediately cuts the pro-duction capacity in half, but also reduces the capital cost significantly. It is possible to achieve up to 100/120 molds per hour using a single machine within an IN-LINE arrangement. Referring back to information that the jolt is more important than the squeeze for hard rigid molds, it was thought possi- ble to obtain this , with a flat squeeze head, leading to the design of a four post machine without the expensive squeeze feature. CONCLUSION It is fairly reasonable to forecast that green sand will continue to be the most important medium for making molds, well into the foreseeable future. The demand for castings in the developed countries will decrease further, and alternative methods and materials will be adopted. The foundries which survive the market changes that will take place during this transition will have to mechanize more effec- tively and economically as basic labor, will either be too expen- sive or unobtainable. References 1. John H. Price-Davies, Foundry Trade Journal, 1980 2. K.E.L. Nicholas & W.R. Roberts, British Foundryman, 1963 3. W. Wiebelhau, SCRATA Conference Proceedings, 1973 4. H. R. Golka, Production of High Density Moulds by Jolt & Squeeze 5. J.W. Nimmo, Inverness, Illinois