39 The Centrifugal Sand Mixing Machine consists of a rapidly revolving table, having on its upper surface a number of prongs arranged concentrically. The sand is fed into the hopper at the top of the machine, from which it falls upon the revolving table and is thrown by centrifugal force from prong to prong and out against the inside of the cover or hood. It emerges from beneath the hood in a fine shower, free from lumps and thoroughly mixed.

40 The table, spindle, spindle pulley, and bearings are enclosed in the housing or base upon which the machine stands, so as to protect effectually these parts from sand and dust.

41 A removable door is placed at the front of the housing to afford access to the spindle and bearings for cleaning or lubrication. The hopper can be lifted off for convenience of cleaning the prongs or removing stones, nails, etc., which do not pass between them.

42 The high rate of speed at which the table revolves, from 800 to 1200 revolutions per minute, causes the sand to be tossed with much force from prong to prong, thus breaking up agglomerated lumps of gravel or clay, insuring not only complete disintegration but a degree of mixing not attainable by any other method. Every

portion of sand is thoroughly "combed out," and analytical tests have shown the uniformity of mixture of heterogeneous compounds after passing twice through this little machine.

43 Fig. 4 shows a machine arranged to be driven by belt over the

MOTOR

carrier pulleys at the back of the housing to the pulley on the table spindle.

44 Fig. 5 shows a machine driven by an electric motor enclosed within the housing where it is thoroughly protected from sand, dirt, etc.

DISCUSSION

MR. E. H. MUMFORD As we all know, the mere handling of molding sand has a strange effect upon it. There are two classes of treatment, which, while not affecting its porosity, will vastly increase its strength. One is putting it through a reciprocating riddle, turning it over with a shovel, or otherwise throwing it about. The alternative treatment. is rubbing the alumina in the sand into the silica.

2

In one of the classes of treatment involving the use of the scraper conveyor there enters another curious effect. In the scraper conveyor, turning the sand over always in one direction, there is a tendency to roll the particles of alumina up into balls, much as a snow ball is rolled along, gathering more snow; but under this treatment it has been common experience that more or less damage is done, as the speed of the conveyor is greater or less, the tendency being to cause the alumina to gather apart from the rest of the sand and the silica particles to be wiped clean of their coating of alumina, the result being that while you have all the constituents of a good strong sand, it has lost its bond and is practically worthless for many kinds of molding. 3 There is no question but that the Sellers centrifugal mixer is better than any other method of impacting or turning over and throwing together.

4 The experiments of Mr. Ronceray, which would doubtless prove of interest to members of the Society, consist of putting into an ordinary heap of sand a certain percentage of pure white silica sand, making the heap so rotten that it would not mold anything, and then rolling or rubbing that mass of sand on a plate with a hand roller. He takes six samples and gives each two minutes rubbing. After rubbing thus, the color of the first sample is gray; the next sample is less gray, and, finally, when you get to the sixth sample, it is practically the same color as the original heap. Every single crystal of silica has been coated with the dark alumina of the foundry sand. So, after twelve minutes rubbing by hand with an iron roller on an iron plate, the last sample is even darker and stronger than the original heap from which it was taken.

5 In our molding machine demonstration plant in Philadelphia. we use ordinary heap sand for our demonstrations, and, as it never feels the heat of molten iron, it has been almost impossible to keep this sand weak enough to be a fair sample of molding sand. We have to keep adding silica sand to it.

MR. H. M. LANE Mr. Mumford has brought out a point in regard to rubbing the alumina into the sharp silica to make the sand stronger which reminds me of a recent experience in a foundry in Ohio.

2 The foundryman was using a sharp, bank sand, mixed with a small amount that contained a little natural bond and a certain amount of core binder-a dry binder in this case- and had been discarding 50 per cent of the core sand and using about 15 to 20 per cent of the natural bond to make the mixture strong enough. He designed and put in a mill, which is essentially a clay grinding mill,

and grinds his core material, using 90 per cent of the old core sand. He finds that in the large cores the binder in the interior of the cores has not been so badly burned out but that it still retains a great deal of bonding quality, so that he now uses only half of the binder. He has thrown out all of the expensive imported sand and uses the local bank sand. He formerly had a power riddle and four men working all day to supply his foundry with core sand. Today he has a night force to haul the sand out, as formerly, but he has two men working less than half a day to supply the entire foundry with core sand. He formerly had to wheel the burnt core sand some 450 feet away from the foundry and dump it over the bank. Now he wheels it through a partition into the next room.

3 Counting the saving in time and labor and the saving in using a cheaper grade of sand, he figures that he has made over $2000 a year. In other words, he will pay for his mill in eight or ten months.

4 The foundry referred to is that of the Falls River and Machine Company, at Cuyahoga Falls, Ohio, and the mill was designed by Geo. H. Wadsworth.

5 In regard to the Worthington practice of grinding the bond in thoroughly, they found that they got the bond on the corners of the sand, if I may so express it, thus giving a very porous core, while if they mixed it by hand they got a much denser core. In other words, the venting of pockets and chambers gives less trouble than formerly because less compound was used and the pores were not being stopped up. They have been able to cast a great many very thin jackets in this way without any trouble at all even though vent passages were cut.

MR. E. H. MUMFORD At a large foundry making steam pumps all the sand used in the smallest port cores is run through a mill, and with very good result. Nothing but raw linseed oil is used as a binder. The ratio of sand to binder is from 60 to 90 to 1. This very large ratio of sand to binder is entirely due to the rubbing in of the binder upon the small crystals of silica.

No. 1171

POWER SERVICE IN THE FOUNDRY

BY A. D. WILLIAMS, JR., PITTSBURG, PA.

Non-Member

In view of the progress that has been made in other mechanical lines, it is remarkable that the foundry of today remains much as it was in the past. Since it plays a most important part in the industrial economy of all metal manufacturing plants, either directly or indirectly, it merits better treatment than it has received.

2 Some years ago the chemists turned their attention to the foundry and the results are seen in the replacement of empirical by scientific methods of mixing and melting and in the heat treatment of castings. The concrete results of their experiments are apparent in a reduction of the percentage of castings lost and the production of castings better suited to the purpose for which they were made.

3 The mechanical end of the foundry offers an interesting field for the engineer, not only in the designing of the castings, but in the invention of ways and means suited to their production. To a degree this work has been started, but has been confined to the production of molding machines and appliances, and the greatest progress has been made in those foundries which are devoted entirely to special lines of work, in which large quantities of castings of the same or similar characteristics are turned out. In the foundry whose output comprises a large variety of castings ranging from bench work to heavy housings and bed plates, the methods in use today differ but slightly from those of twenty years ago, the improved facilities consisting mainly in the provision of a better crane service for handling the work.

4 The principal reason why power is not used to a larger degree. in foundry work arises from the fact that few foundries are so designed.

Presented at the New York Meeting (December 1907) of The American Society of Mechanical Engineers and forming part of Volume 29 of the Transac