US2504143A - Process and apparatus for testing gas evolution characteristics of molding sand - Google Patents

Description

Apnl 18, 1950 w. H. MOORE 2,504,143

PROCESS AND APPARATUS FOR TESTING GAS EVOLUTION CHARACTERISTICS OF MOLDING SAND Filed NOV. 19, 1947 3 Sheets-Sheet l IN VEN TOR.

April 18, 1950 w. H. MOORE 2,504,143

PROCESS AND APPARATUS FOR TESTING GAS EVOLUTION CHARACTERISTICS OF MOLDING SAND Filed NOV. 19, 1947 3 Sheets-Sheet 2 emaREsE l I I I I I I I I I l I I I l l I I 4 IO 20 a0 40 5o (,0 70 e0 90 we no I I mo we no I80 H0 645 Fldh lb CUB/c cam/ways F64? mm O l 20 3O 40 50 8O I00 //0 I20 I30 I40 I50 60 I70 I60 1 0 5/95 Hon/w CUB/C cam/wraps P61? sfco/vo f u/MIIW Aprll 18, 1950 w. H. MOORE 2,504,143

PROCESS AND APPARATUS FOR TESTING GAS EVOLUTION CHARACTERISTICS OF MOLDING SAND Filed Nov. 19, 1947 5 Sheets-Sheet 3 Patented Apr. 18, 1950 PROCESS AND APPARATUS FOR- TESTING GAS EVOLUTION CHARACTERISTICS OF MOLDING SAND William H. Moore, Cleveland Heights, Ohio, assignor to Meehanite Metal Corporation, a corporation of Tennessee Application November 19, 1947, Serial N0. 788,837

7 Claims.

This invention relates to the determination of molding sand characteristics in general, and more particularly relates to the determination of gas pressure-time relationship within the sand body of a mold for casting metal.

An object of this invention is to correlate the gas evolution from foundry sand, with the permeability of the sand as actually packed in a flask, to determine the back-pressure of gas to be expected at any given moment during the casting interval.

Another object of this invention is to correlate the ferro-static pressure of metal in a sand mold with the ability of the sand to dissipate its own gas, and thereby determine the peak rate of gas evolution permissible from the sand.

Still another object of this invention is to provide means for determining the intensity of gas back-pressure during a period of exposure of sand to high temperature, and to thereby determine the ferro-static pressure required to balance the highest gas back-pressure.

Yet another object of this invention is to determine at what period of the casting interval the highest rate of gas evolution takes place, and correlate the amount of gas and the rate of gas evolution with the solidification rate of the particular body of metal being cast in a mold made of the sand packed to a particular degree.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing, in which:

Figure 1 is a front elevational view of a furnace, a cabinet, an orifice, and a pressure-time recording device;

Figure 2 is an enlarged and broken view of the sample chamber within the furnace;

' Figure 3 is a. sectional view of a small orifice escape;

Figure 4 is a sectional view of a sand orifice escape;

Figure 5 is a calibration curve showing the relationship between orifice back pressure and gas flow;

Figure 6 is a calibration curve showing the pressure developed in diameter 2" long specimens at different rates of gas flow;

Figure '7 is an illustration of a representative and typical curve actually produced by this apparatus, and

Figure 8 is another representative curve actually produced by this apparatus.

The problem of gas from cores and molds has always been regarded as something that exists but which is not sufllciently tangible to put down on paper in a way that will clearly show when and why blowholes, misruns, and cope draws, due to a condition in our sand may be expected.

Technical literature and advertisements set forth many pieces of apparatus to test the static gas pressure produced by a sample of sand. Total volume of gases evolved from sand samples has been a test used for many years by the foundry technicians and practical foundrymen. However, these tests do not provide the criteria of casting failures, because such tests do not determine at what period of the casting interval the highest rate of gas evolution takes place, nor do these tests correlate the amount of gas and the rate of gas evolution with the solidification rate of the paricular metals being cast in the mold made with the particular sand packed to a given degree.

It is well known that different binders give off varying amounts of gaseous materials when the sand containing them is subjected to heat, and the amount of gas in ccs./gram can be quite easily measured in a simple laboratory test. In this test, a weighed sample of sand is placed in a combustion boat and ignited at 1800- F. for 10 minutes, the products of combustion being led off and measured by volume.

A few typical results of this type of test is in- The exact amount of gas will of course depend on the degree to which the sample has been baked and the temperature at which it has been baked. In general, the higher the baking temperature, and the longer the baking time, the less the gas obtained from the mix.

values range from a low of 4.00 cos/gram for Quandt oil to 6.10 cos/gram for Hyten No. 4 with most of the commercial oils falling somewhere between these limits. Underbaked oil sands are liable to give of! excessive quantities of gas. The amount of gas is of course proportional to the amount of binder in the sand.

Therefore a relatively simple means is available for comparing one type of binder with the next but it is not so simple to correlate this information with any tendency for the materials to give trouble in casting attributable to the amount of gas they produce.

After the total evolution of gas from a particular sand under the particular condition of casting has been determined, the next most important phase confronting the foundrymen is the mold or core permeability. The permeability of a sand is a relative measure of the ability of the sand to carry gas. For example, with a sample of rammed sand, 200 cubic centimeters of air can be passed through the sample at a gram pressure in a certain period of time. Measuring this time and substituting in the permeability formula gives us the permeability number.

If now we force the air through the specimen at a faster rate, a resistance pressure can be expected to build up in the sand sample. Two factors are important; the amount of gas generated within a sand, and the ability of the sand to carry away this gas. Where the gas generated is high and the sand permeability is low, quite a high resistance pressure within the sand body can be expected to build up. Where the gas generated is zero. a zero permeability should be required in the sand. This statement is absolutely correct if the effect of voids in the sand on sand expansion and other heat phenomena is disregarded.

For many years total volume of gas evolved and the gas pressure produced by the sand have been used by foundries to help reduce the amount of defective castings produced. It was originally thought that a volume of gas, or gas pressure produced, were the factors producing gas defects in the casting. Undoubtedly, the amount of the gas and the pressure of the gas have much to do with the casting failures, but in spite of careful selection of sand for specific gas volume and pressure characteristics, a certain percentage of defective castings continued to be produced.

The development of the invention described herein was begun when the thought appeared that perhaps the time element of gas evolutions was all-important, rather than total volume of gas produced or pressure available from a sample in an absolutely enclosed chamber. For example. it makes no difference how much gas is evolved or how high the pressure of the gas may go after the metal of the casting has completely solidified. It thus appears that the total volume and pressure data has actually been a step toward a less troublesome path, but the vital factor of the time relationship of the gas evolved in comparison to metal solidification rates has been overlooked.

' density, and materials are used in the sand as binders which will give off a high gas evolution immediately upon being heated, then it will be seen that the gas pressure will build up to a high degree and will probably reach a pressure great enough to overcome the ferro-static pressure of the molten metal. Once the gas pressure reaches the ferro-static pressure of the molten metal, defects are formed by the air pushing through the metal. Furthermore, gas pockets sometimes form and force the molten metal away from the walls of the mold, and the resulting casting is not filled out properly.

This invention therefore involves the process of determining the back-pressure which will be produced by a given sample of core or molding sand and at what period of the heating cycle the highest pressure will be produced. Therefore, the principal determination to be made is the rate of gas evolution at any given moment during the casting and hardening period. 'That is, the magnitude of the evolution in relation to time after exposure of the sand to heat. The volume of gas evolved is the result of the moisture content of the sand, as well as the intrinsic gas evolution characteristics from the particular materials employed. Furthermore, the volume of gas produced during the first few minutes that the sand is exposed to high temperatures will vary considerably with the type of material employed. That is, the rate of gas evolution will vary considerably. For example, one particular sand sample may evolve only a relatively small total volume of gas, but this total volume may be evolved principally within the first 15 to 30 seconds of contact with the molten metal. On the other hand, another sample of sand may evolve a quite large total volume of gas, but the rate of gas evolution may be quite low at first and increase as the time of contact goes on.

Thus, in the first example, the back-pressure for a sand of any given density will be quite high during the initial contact period, and will thereafter taper off, whereas the back-pressure in sand 'of the same density in the second example will be relatively low during the initial period and will increase with time. However, it may be quite possible that the casting is sufficiently solidified Consequently, the apparatus and the process de- Y scribed hereinafter was developed and has provedto be the biggest advance in the technical knowledge of the effect, of gas evolution on castings that has been set forth to date.

It does not matter how much gas is produced to resist the increased gas pressure after a short period of time, and therefore the increase of back-pressure with time will be unimportant.

It does not matter how much gas is produced during casting if there is sufllcient time for the gas to travel through the sand without building up a resistance pressure in the sand body.

The entire procedure employed in testing the sand by this invention, is based on a duplication of conditions as practical as possible. Basically, the apparatus employed is simply a standard orifice leading from an enclosed heated chamber in which a sample of sand is placed, the rate of gas flow being measured by taking readings of the back-pressure caused by inserting the orifice in the stream of gas.

The drawings illustrate a practical arrangement of the various parts of apparatus finally developed after several preliminary experiments in order to test the rate of gas evolutions. The drawings do not show the actual commercial form of the furnace, because the furnace of another piece of testing equipment is actually 5 employed, and the two instruments assembled in one cabinet. However, to illustrate the furnace actually used would only detract from the explanation of this invention, and therefore a more or less diagrammatic showing of the furnace is all that is included in the drawing.

In Figure l of the drawings, an electrically heated furnace I is illustrated having a pipe ll leading to a time-pressure recorder IS. The time-pressure recorder I3 is employed for simplicity of recording the results obtained, and is of standard design available commercially. Any pressure in the pipe II will cause the stylus arm 22 to swing towards the circumference of a revolving chart 23. The chart 23 is rotated about its center at any desirable rate. In the ordinary sand test, it has been found that one revolution of the chart 2: in 5 minutes will produce an easily readable chart.

An orifice fitting I2 is placed in the pipe H at any convenient place, and I have illustrated it as being placed to extend through a table top of a suitable cabinet I9. Thus, the cabinet table top will serve as a convenient work place to hold a plurality of samples and charts.

The orifice placed in the fitting l2 may be either of a single hole orifice type I4, or a sand orifice type l5 as illustrated in Figures 3 and 4. However, a universal orifice comprising a controllable needle valve or diaphragm valve which can be adjusted to suit the degree of gas being evolved from the material under test, may be preferable for most routine work. Gas produced in the pipe II will escape from the pipe ll through the orifice in the holder i2 to atmosphere, but, the freedom of escape will be restricted by the orifice placed in the holder l2.

Therefore, a back-pressure will be produced in r the pipe H, and this back-pressure will cause the stylus arm 22 to swing to the left and record a path on the revolving chart 23. Thus, the intensity and duration of the gas evolution at any particular time of the evolution may immediately be ascertained from the chart 23 after the test has been finished.

In the apparatus illustrated in the drawings, I have provided the pipe I I with a sample chamber portion IS. A spring 18 is positioned in the pipe l6 as illustrated in the Figure 2, and a sample 25 of the sand to be tested may be placed in a sample chamber portion IS in contact with the spring It. A second spring l8 and a cap I! is then slipped on the other end of the sample chamber portion Hi to hold the sample 25 in a fixed position and to exclude the passage of gas from the pipe II at any place other than the orifice holder l2. Of course, the structure of the furnace and means to hold the sample are illustrated in one convenient form, and may be altered in any suitable manner to carry out the desired function.

The operation of this apparatus is quite simple. The operator simply adjusts the control 2| to the temperature which he desires to test the sample 25. After the furnace III has reached the desired temperature the sample 25 is placed in the sample chamber portion l6 and the cap l'lquickly tightened in place. Very soon after the cap I! is in place, the sample 25 will begin to give off gas. The gas will immediately build a pressure in the pipe H greater than atmospheric pressure, and therefore, the gas will begin to move through the orifice in the fitting l2. Of course, the pipe Ii will contain some atmospheric gases but it will readily be seen that the iii presence of other gases in the pipe H will make little difference in the final results, because the gases evolved will displace the gases previously present, and at theend of the test, will remain in place of the gases displaced. The orifice in the orifice fitting l2, as previously explained, will restrict the flow of gas therethrough and consequently will build up a back-pressure in the pipe H. The intensity and duration of this backpressure is then recorded on the revolving chart 23 over a period of timeat least equivalent to the time required for molten metal to initially solidify in a mold which is intended to be made of the sand being tested.

In the test of molding sand characteristics by this improved method, the gases evolved from the sample are restricted, but only to a small degree. The orifice employed is selected to accommodate the amount of gas to be given ofi', and therefore the gasback-pressure within the system does not exceed substantially two inches of water pressure at any time. The advantage is. that the natural gas production of a sand sample is not artificially disrupted by subjecting the sample to an ever increasing pressure. It is well known that a normal reaction can be materially disturbed by a change of pressure.

It is to be understood, that the type of furnace 10, the type of orifice in orifice fitting I2, and the type of pressure gauging and recording are all optional, and the drawings are intended to illustrate that combination which has been selected for this disclosure. For example, instead of the revolving chart 23 and the stylus arm 22, a suitable manometer filled with colored water and having an adjacent scale may be employed to measure the back-pressure, and these measurements recorded by hand. Obviously, the automatic recording illustrated is much preferred.

This apparatus, while determining peak pressures and extend of peak pressure periods, will also record the total volume of gas evolved. The apparatus is first calibrated by passing known amounts of air through the orifice and measuring the back-pressure produced. The calibration curve obtained with a 0.5 mm. orifice is shown in Figure 5 and enables the operator to determine the gas velocity through the orifice by reading the chart produced. In other words, the area under the line produced on Chart 23 is representative of the total volume of gas evolved. A representative and typical curve produced on the chart 23 is illustrated in the enlarged showing of Figure 7.

Several sands containing binders were tested for total volume of gas evolved by this method, and in general the results confirmed the laboratory tests measuring the total volume of gas evolved. Considerable difilculty was experienced. however, with pitch and pitch compounds in that they tended to clog up the single orifice with tar, thus making an accurate reading almost impossible.

After several almost hopeless attempts to prevent the single orifice from clogging, the thought occurred that rather than provide a single orifice of relatively large size, an orifice having a multiplicity of minute orifices could be substituted for a single orifice. Accordingly, the sand orifice was constructed. The sand orifice, instead of nearly solving the problem of providing an orifice, gave a result that revealed still another characteristic of foundry sand, namely the ability of a sand to dissipate and carry its own gas under actual foundry conditions.

It is generally known by foundrymen, that the sand body of a mold heats only a short distance below the surface actually in contact with the molten metal. Therefore the main body of the sand remains cold. But the cold'body of sand is the portion which will actually be required to conduct away the gas evolved. Therefore, by using the sand orifice IS, the operator can test the ability of the main body of the sand to carry away the gas. This ls not the usual permeability test and result obtained by passing a known amount of air through the sand under a known pressure head. Air will not clog sand, but the:

smoke and gas given off by foundry sands will clog cold sand. The result of this test will reveal the ability of the cold portion of the mold sand body to conduct the gases away that are produced by the heated portion. If the sand orifice becomes clogged by the gases produced by the heated sample, the ability of the sand to conduct the gases to atmosphere will be changed to a value different than would be indicated by a permeability test, but the change is representative of the eflect to be expected in actual practice.

In actual practice, the sand orifice l5 comprises a inch pipe two inches long rammed with a sample of sand. This sample therefore, is the same as any one of the sand samples used in finding the gas velocity developed during casting. That is, it is of exactly the same dimensions as the sample normally employed for testing. Known amounts of air were passed through the apparatus with the sand orifice ii in place, and the resistance offered by the sand orifice to the air fiow was measured by taking pressure readings on the time-pressure recorder ll.

The results of calibrating several samples of sand provided for use as the sand orifice ii are shown in Figure 6. In general this chart indicates that with gas fiows below ten cubic centimeters per second, the difierence in resistance pressure with varying permeabilities is not marked. As the rate of gas fiow increases, however, the lower permeability sand will build up quite an ap-' preciable resistance pressure. Therefore. if pressures are to be kept down with the mold, an open sand should be used when a high gas velocity is to be expected during casting. Therefore, while serving as an orifice to prevent clogging, the sand orifice I5 may be used to calibrate the permeability of a particular sand which is to be used for a mold. Thus, it will be seen the apparatus and method hereiri set forth not only provides an indication oi th relationship of peak gas evolution with time, but also provides information as to back-pressure expected from a given sand. From this data the operator may at once determine whether the gas evolved will come at a time when the metal is molten or solidified. If he determines that the peak gas evolution will come at a time when the metal is molten, then he can determine what back-pressure to expect because of the permeability of the particular sand employed. Also, having thus determined the back-pressure to be expected in the mold, or the core, the operator can determine whether or not the ferro-static pressure within the mold will be suflicient to hold the gas within the sand. If, for example, the risers were too short and the ferro-static pressure consequently low, it may be possible for the gas pressure produced within a core, or within the sand body of the mold, to exceed the ferro-static pressure and blow through the body of molten metal. Of course, while the metal is fluid it may be the opinion of some operators that bubbling of the gas through the metal will cause no appreciable harm. However, it is the better consensus of opinion that even bubbling through molten metal is to be avoided if possible. Certainly such blowthrough is to be avoided when the metal reaches the mushy stage of solidification. Furthermore, the gas may become entrapped in a portion of the mold cavity where it cannot readily escape by bubbling through the metal. Thus. the mold is not properly filled out and a defective casting results. Accordingly, having the information at hand from the apparatus and method of this invention the operator may increase the height of the risers to increase the ferro-static pressure to a value greater than the gas pressure to be expected. Or, a sand having a larger per-- meability number may be employed, and therefore, the gas may be conducted away with less back-pressure resulting.

The Figures 7 and 8 are two results of typical sand tests by this improved method and apparatus. For the sake of illustration, assume that a certain casting is to be made, and it is established that the casting will initially solidify in about 50 or 60 seconds. Before that time gas may pass through the molten metal without harm, and after that time the metal will be hard, and it will not matter how high the pressure goes. Assume further, that either Bentonite-Glutrin sand, or Oil sand is suitable for making the particular mold. which one should be used? Maximum pressure tests would indicate that either sand would be satisfactory, because both sands give the same maximum pressure. On the charts of Figures 7 and 8, the highest pressure indicated is 140 units. Furthermore, .total volume tests would not indicate whether the greatest gas flow would be before, during, or after the solidification range of 50 to 60 seconds after pouring, or whether the sand would clog and build up a high back-pressure.

However, by comparison of the charts in Figures 7 and 8, the operator can at once determine that the Bentonite-Glutrin sand is the correct sand to select, because that sand gives a large gas pressure within a couple of seconds after heatin and the peak prevails for only about 25 seconds. The Oil sand, on the other hand, steadily increases in gas production and pressure from the beginning and persists for about seconds. Therefore, the Oil sand would produce a high gas pressure during the critical solidification period, and is to be avoided.

Although the invention has been described in its preferred form with a certain degree of particularly, it is understood that the present disclosure of the preferred form has been mad only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

I claim as the invention:

1. Apparatus to test the gas evolution characteristics of foundry molding sand, comprising a closable sample chamber, means to heat said chamber to a high intensity heat comparable to the heat intensity from molten metal to be molded in a mold made of said sand, said sample chamber having outlet orifice means adapted to restrict gas exhaust from said chamber to atmosphere, and means to determine the gas pressure within said sample chamber, the gas evolution characteristics of the sand being determinable by the magnitude 1 of the gas back-pressure produced in the chamber in relation to time after exposure of the specimen to said source of heat.

2. Apparatus to test the gas evolution characteristics of foundry molding sand, comprising a pressure container system including a closable sample chamber, means to heat said chamber to a high intensity heat comparable to the heat intensity from molten metal to be molded in a mold made of the sand, said pressure container system having outlet orifice means adapted to restrict gas exhaust from said system to atmosphere, and pressure recording means including pressure-responsive means operable by gas pressure within said system, stylus arm means movable by said pressure-responsive means, a chart mounted for rotation about its center in position to be marked by said stylus arm means, means to rotate said chart at a pre-determined rotational speed, whereby said stylus arm and chart will trace a timepressure diagram on the chart, the gas evolution characteristics of the sand being determined by the magnitude of the ga back-pressure indicated by the diagram on the chart in relation to time after exposure of the specimen to said source of heat.

3. Apparatus to determine the total volume of gas evolved from a sample of foundry molding sand in a pre-selected period of time after the exposure of the sample to heat, comprising a closable sample chamber, means to heat said chamber to a high heat intensity, said sample chamber having outlet orifice means of predetermined size adapted to restrict gas exhaust from said chamber to atmosphere, and means to determine the gas pressure within said sample chamber, the total volume of gas evolved being determinable by the gas back-pressure in said chamber in said pre-selected period of time.

4. Testing apparatus, comprising a chamber having a closable opening therein and an orifice outlet to atmosphere, means to heat said'chamber, and means to determine the gas pressure within said chamber, samples of foundry sand being insertable in said chamber to determined the magnitude of gas evolution from the sand in relation to time after exposure of the sample to heat, as well as the total volume of gas evolved.

5. The process to determined the gas backpressure within a sand body upon exposure of the sand body to high heat, comprising the steps of providing a specimen the sand to be tested, in-

i0 serting the specimen in a closed chamber havin an orifice'outlet, applying heat to said chamber of an intensity comparable to the heat from molten metal to be molded in a mold made of said sand, and measuring the back-pressure variations produced by gas evolved from said specimen within said chamber escaping through said orifice over a period of time equivalent to the time required to pour said molten metal in said mold and for the metal to harden.

6. Apparatus to test the gas evolution characteristics of a foundry molding sand and the ability of the sand to dissipate its own evolved gas when used in actual foundry practice, comprising a closable sample chamber, means to heat said chamber to a high intensity heat comparable to the heat intensity from molten metal to be molded in a mold made of said sand, said orifice means including a sample of the sand to be tested rammed to a density comparable to the density of the sand rammed in a flask to make the mold. means to exhaust gas from said chamber to atmosphere through said said orifice means, and

means to determine the gas pressure within said sample chamber.

'7. The process to test the gas evolution characteristics of a foundry molding sand and the ability of the sand to dissipate its own evolved gas in a mold in actual foundry practice, comprising the steps of providing a sample of the sand, subjecting the sample to a high intensity heat in a closed chamber having an outlet, providing a sand orifice of the sand, th sand orifice being rammed to a density comparable to the density of the sand as it is rammed in a flask to make the mold, placin said sand orifices in said outlet to restrict the flow of gases from said chamber to atmosphere, and measuring the gas pressure within said chamber.

- WILLIAM H. MOORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,352,836 Hertel July 4, 1944 2,371,508. Dietert Mar. 13, 1945 2,4143% Dietert et al. Jan. 14, 1947 Certificate of Correction Patent No. 2,504,143 April 18, 1950 WILLIAM H. MOORE I It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 9, lines 44 and 48, for the word determined reed determine; column 10, lines 18 and 23, for said orifice read send orifice;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 18th day of July, A. D. 1950.,

JOE E. DANIELS,

Assistant Gommim'oner of Patents.

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