US2041721A - Method of making foundry sand - Google Patents

Description

May26, 1936. c. L. NORTON METHOD OF MAKING FOUNDRY SAND Filed NOV. 19, 1934 Patented May 26, 1936 UNITED STATES PATENT OFFICE A* METHOD OF MAKING FOUNDRY SAND Application November 19, 1934, Serial No; 753,643

3 Claims.

My present invention relates to sand such as is used inthe preparation of molds and the like by means of which castings are made 4from `molten materials. Such sand may conveniently 5 be called foundry sand. Heretofore, it has been commercially customary to make molds of natural sand with or without certain additional agents such as clay. Natural sand is composed of an aggregation of small crystalline particles of silica, i. e. silicon dioxide or quartz, usually with small amounts of clay.

When such sand is used for molds for metal casting, the sudden rise in temperature which occurs when the molten metal is run into the mold causes the silica to b e cracked and broken into a considerable number of tiny fragments or dust, due to the tendencyor silica to alterl its crystalline form at different temperatures and because of its large rate of expansion. Accordingly natural sand deteriorates with use rapidly and becomes powdery and a mold made from old sand is less porous, so that it is necessary to discard the sand or submit it to a sifting or like process to remove the powdery portion. Where suitable natural sand is available, fresh sand can be added, but where it is not available it has been necessary to reclaim the old sand or bring fresh sand from a. considerable distance. Even when the sand is reclaimed it becomes worthless after a certain limited time.

Deterioration of sand under heat produces a powder so fine that it is readily carried into the air and enters the lungs of workmen causing an occupational disease known as silicosis. Silicosis at the present time is a serious menace to life and health of workmen in large foundries and claims for injury from silicosis cause large expense to foundrymen.

My present invention therefore has for its object an artificial foundry sand which is less subject to deterioration from use thereby increasing the length of life of the sand and reducing the 'menace to the'health and life of workmen using can be used repeatedly and therefore but a relatively small amount is required.

The artificial foundry sand embodying my invention is free from uncombined silica which is the chief ingredient in natural sand, and therefore does not produce the noxious .silica dust which when taken into the lungs is particularly harmful.

The accompanying drawing is a diagrammatic Y view showing apparatus by which the invention may be practiced and illustrating the several steps in the method.

In practicing my invention I employ silicate T of aluminum and preferably kaolin, for instance, washed Georgia white kaolin. This is placed in a rotary kiln and progressively heated therein to the point where incipient fusion begins, that is, Ato the point at which the kaolin begins to soften somewhat and the particles adhere together. At this temperature the silicate of aluminum is converted into a mass of crystals of mullite stuck together with small quantities of alumina-silica glass. If a rotary kiln is used, it is desirable to keep the temperature below that at which balling takes placein the kiln since if large masses of fused particles or partly fused particles ystick together in the kiln it becomesunmanageable or only manageable with difculty. For the kaolin mentioned above a temperature from about 2900* F. to 3100 F. is preferably employed. In practice a convenientmethod of determining the best temperature is to heat the kiln until the tendency to "balling begins to appear, whereupon the temperature is reduced just enough so that ,balling no longer takes place, after which that temperature is maintained. It is found that the length of time to which raw material is subjected to theheat is an important factor, higher temperatures being required for shorter heating times and lower temperatures being possible with longer heating times. It will also be understood that the temperature varies to some extent with the particular aluminum silicate employed and to some extent with the purity of the materials.v

It is not necessary that the raw materials shall be absolutely free from uncombined silica, since under the treatment above described the small quantities of uncombined silica combine with the aluminum silicate in the formation of mullite and silica-alumina glass.

After the heating is complete, the material is removed from the kiln `and allowed to cool. It is then in lumps and large grains and groups of grains something like popcorn in appearance. It

is then run through crushing rolls and sifted or graded to the size required.

In practice the foundry sand embodying my invention is used in the same way as natural sand except that in making the mold, a small quantity (from 5 to 15%) of unburned kaolin or high grade clay should be added so that it can be molded. To obtain the best results, care should be taken to avoid the presence of free silica in any substantial amount.

The sand embodying my invention made as described may be used repeatedly without substantial deterioration. For instance, the sand embodying my invention can be used ten times as long as high grade natural sand.

' I am aware that it has been proposed to ernploy broken re brick as an ingredient for foundry sand, any fused portions of the brick or slag adhering thereto being removed, but such material has been made solely from re brick burned at temperatures much below those necessary to produce incipient fusion, as here described, of the materials employed and consequently the material has not been rendered capable of withstanding the temperature and conditions to which it is to be subjected in foundry processes.

The sand embodying my invention also has the additional advantage that the particles have sharp keen edges which are retained under pouring conditions and can be rammed into a mold of good mechanical strength which maintains its shape during pouring. Accordingly sharp clean castings are produced. There is a noticeable freedom from washing in the molds.

I claim:

1. 'Ihe method of making foundry sand which comprises passing aluminum silicate continuously through a. kiln, progressively heating it therein to the temperature of incipient fusion, withdrawing it from the kiln, cooling and coinminuting it.

2. The method of making foundry molds which comprises charging aluminum silicate continuously into a rotary kiln, heating it progressively therein to the temperature of incipient fusion, withdrawing it from the kiln, cooling and comminuting it, mixing it with unburned kaolin which is substantially free from uncombined silica and forming a mold therefrom.

3. The method of making foundry sand which comprises passing kaolin continuously thrmgh a kiln, progressively heating it therein to a temperature of approximately 2900 F. to 3100" F., withdrawing it from the kiln, cooling and comminuting it.

CHARLES L. NORTON.

Images