US3537295A

US3537295A - Method and apparatus for testing foundry mold materials

Info

Publication number: US3537295A
Application number: US653468A
Authority: US
Inventors: Julius Heimgartner
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1966-07-20
Filing date: 1967-07-14
Publication date: 1970-11-03
Anticipated expiration: 1987-11-03
Also published as: NL131169C; DE1573829A1; NL6612764A; DE1573829B2; CH460388A; GB1191699A

Description

9 J. HEIMGARTNER I 3,537,295

METHOD AND APPARATUS FOR TESTING FOUNDRY MOLD MATERIALS Filed July 14, 1967 I 2 Sheets-Sheet 1 Y 6 'X I] J I 4 -5 a 14 Inventor: Juuus HE/MGARTNEF? r ,0 'r RNE VS Nov. 3, 1970 V J. HE IMGARTNER I 3,537,295

I METHOD AND APPARATUS FOR TESTING FOUNDRY MOLD MATERIALS Filed July 14. 1967 2 Sheets-Sheet z lnvenlurf Jumua HE/MGARTNER 5V 2 g at ,47'7'0 NEVS United States Patent 3,537,295 METHOD AND APPARATUS FOR TESTING FOUNDRY MOLD MATERIALS Julius Heimgartner, Sulz-Attikon, Switzerland, assignor to Sulzer Brothers, Ltd., Winterthur, Switzerland, a

corporation of Switzerland Filed July 14, 1967, Ser. No. 653,468 Claims priority, application Switzerland, July 20, 1966,

Int. Cl. G01n 25/00 US. Cl. 73-15.4 7 Claims ABSTRACT OF THE DISCLOSURE The mold materials to be tested form at least a part of the surface of the mold cavity into which casting melts of a certain temperature are poured. The mold is rotated so as to stress the mold materials to be tested at certain specific surface pressure whereby the characteristics of the mold materials are tested.

This invention relates to a method and apparatus for testing founry mold materials. More particularly, this invention relates to a method of and apparatus for testing mold materials wherein the mold materials to be tested form at least a part of the surface of a mold cavity.

Mold materials such as sand, blacking, molding compounds, ceramic substances and steel, which are used as materials for the manufacture of casting molds tend to sinter or to react chemically under the effect of the metallostatic pressures and elevated temperatures of the melts placed in the mold cavities. The result of this is that liquid metal is caused to penertate into the hollow pores between the individual grains of the mold material. The surface of the casting is thus undesirably modified. This phenomenon is referred to as sintering or metal penetration. Since sintering of the mold surface depends not only on pressure and temperature, but also on the properties of the melt and other effects which cannot be easily determined, it is necessary for the durability of mold materials to be investigated by experimental means with a certain melt at various pressures and temperatures.

Heretofore, a plurality of methods have been known for testing the operational characteristics of mold materials. However, these methods have been costly and timeconsuming and have been unsuitable for the performance of systematic batch investigations. Such a method, for example, consists in the incorporation of a relatively small test mold into to mold of a large casting with the test mold connected via ducts to the mold cavity of the casting. When the principal casting is teemed, the test mold is simultaneously filled and the appropriate metallostatic pressures and high temperatures are reached. This method yields results approximating actual operational conditions but such tests require a long time, since it is necessary to wait until the principal casting is solidified, struck and fettled, before the test mold can be investigated.

In another method a test mold is made whose ingate is closed immediately after casting and the liquid metal is placed under a certain pressure by means of a compressed gas. This method is also awkward and provides information only of a certain pressure, namely that applied with a compressed gas.

Furthermore, test cores are frequently cast into thick cast blocks to simulate very high thermal stresses, particularly if the test specimens are constructed as thin finger cores. This method is suitable for the relative evaluation of a mold material because it indicates whether one mold material is better than another but only rarely supplies data which can be applied to other cases.

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Furthermore, various kinds of mold material test apparatus are known by means of which specimens can be investigated at elevated temperatures as regards their mechanical strength and decomposition characteristics, their expansion or gas development. However, the test results thus obtained do not provide suflicient criteria for evaluating the test material in practical operation.

In most foundries, it has therefore been necessary to subject mold materials to tests on the casting itself. Such tests endanger teeming which may result in Waste or involve substantial effort for finishing operations. The normal production run is thus obstructed. Furthermore, it is often difiicult to find the test specimens or to identify them.

Accordingly, it is an object of the invention to utilize laboratory batch tests on mold materials at various pressures.

It is another object of the invention to reduce the amount of material and time needed for testing mold materials.

It is another object of the invention to substantially satisfy the conditions of practical operation in batch testing mold materials.

It is another object of the invention to produce high metallostatic pressures as they are found in actual operational condition in relatively small test rigs.

Briefly, the invention provides a method of testing mold materials wherein a cavity mold is set into rotation during casting and subsequent solidifying of a liquid melt. The cavity mold is rotated at a speed to produce in a single cavity mold different specific surface pressure of specific magnitude with a continuous pressure gradient.

Since the liquid melt assumes the rotational velocity of the rotating mold, specific surface pressures of different magnitude are obtained at different distances from the center of rotation. Also, any variation of the rotational speed enables the magnitude of the surface pressures to be varied within wide limits. Furthermore, the absolute values of each surface pressures can be calculated in a simple manner.

If the critical surface pressure for a single mold material is to be determined, it will be advantageous if the cavity mold is constructed of the material to be tested. After rotation at a suitably selected angular velocity with a melt within the mold, zones which do not withstand the applied streeses will be produced outside of a circle having a certain radius, while the mold material surface within the circle will be sound. Measuring the radius of the circle and a knowledge of the agular velocity enables the critical pressure p to be calculated in a simple manner.

For investigating different mold materials under the effect of the same casting material at a certain temperature, it is advantageous for the mold materials to be tested 'by inserting them as specimens into the cavity mold. Furthermore, it is advantageous if the cavity mold is filled from its periphery.

In order to obtain uniform loading, in particular heating up, at all positions of the mold material to be investigated or for all indivdual specimens, it is necessary for each position of the cavity to be flooded by the same amount of fluid material. This can be achieved by constructing the cavity mold in the form of a rotational hyperboloid which is filled from its periphery. Since the ordinate branch'of the hyperboloid, which approaches asymtotically to the center of rotation, must be broken off at a certain height, uniform flooding in the manner described heretofore is achieved only approximately. Without any substantial additional effort and without any major increase in the size of the cavity mold, this defect can however be compensated by placing upon the hyper- FIG. 2;

boloid the separated volume thereof in the form of a correcting cylinder of the same volumetric capacity.

If the effect of different temperatures under otherwise identical conditions is to be determined, the temperatures of the same melt may be varied before casting into several identical hollow molds.

These and other objects and advantages of the invention will become more apparent form the following detailed description and appended claims taken in conjunction with:

FIG. 1 illustrates a vertical sectional view taken on the axis of rotation of a test rig wherein the cavity mold is made of the mold material to be tested;

FIG. 2 illustrates a view similar to FIG. 1 01f a test rig wherein different mold materials are positioned for simultaneous testing;

FIG. 3 illustrates a view taken of line III-III of FIG. 4 illustrates a modified test rig wherein the surface of a mold cavity can be flooded at all positions by the same volume of liquid casting metal;

FIG. 5 illustrates a view similar to FIG. 1 of a test rig wherein different mold materials can be tested simultaneously; and

FIG. 6 illustrates a view taken on line VI-VI of FIG. 5.

Referring to FIG. 1, a mold 1 which is constructed of the mold material to be tested has a central cavity 2 into which molten casting metal is poured after being raised to a desired temperature. The cavity 2 communicates with the exterior of the mold 1 through an opening 3 through which the molten metal is poured into the cavity 2. Alternatively, the cavity can be filled fromthe periphery as hereinafter described. The mold 1 is supported on a casting table 4 having a vertical axis of rotation 5. The casting table 4 is rotated by means of a drive (not shown) at certain known angular velocities.

After the molten metal has been poured into the cavity 2 of the rotating mold 1 and casting table 4, rotation of the mold 1 is continued until the metal has solidified therein. The surface of the cavity which is to be tested is thus subjected to a combined pressure which is created by the static pressure due to the weight of the casting metal and the component of pressure produced by the centrifugal force acting on the cavity surfaces. The centrifugal action resulting from rotation causes the pressure in the cavity 2 to increase as the distance r from the axis of rotation increases. The'rotational speed of the casting table, and thus the centrifugal action on the cavity surface, can be varied so as to cover a wide range of different specific surface pressures.

With the above arrangement, the pressure for a particular mold material to which the material can be stressed at a particular temperature by a particular casting material without the quality of the mold surface being impaired can be determined.

In order to test the mold material, the mold 1 is opened after cooling and distance r from the axis of rotation of the casting at which destruction'of the' cavity surface begins is measured. The zone merging from the sound casting surface to the poor casting surface of the cavity is determined by simple observation or by roughness measurements, for example, by means of apparatus commonly employed for texture determination.

The specific surface pressure P at each position of the cavity mold comprises, as already mentioned, two components and can be determined by the following expression:

In this expression and is that proportion of the pressure which occurs due to the centrifugal effect as the result of rotation of the surface pressure ZwZ P=p( Referring to FIGS. 2 and 3, the mold 1 is constructed of a known mold material for testingof several mold materials. For example, the mold 1 can be constructed in a manner as above from sand for a once only use or as a two-part permanent mold which can be used repeatedly. The mold materials to be tested are formed as small, preferably cylindrical, specimens 8 and are inserted into the cavity 2' of the mold 1 at difierent distances from the axis of rotation 5'. As each specimen 8 is at a different radial distance from the axis of rotation, the material of each is stressed at a different pressure from the other. After insertion of the specimens 8, a molten casting metal is poured into the rotating mold 1' in the manner described above. After cooling and opening of the mold, the strength of the materials tested is once again determined either by the optical impression created by the surface of the specimen casting or by means of texture measurement.

In positioning the specimens 8 in the cavity 2', the specimens 8 are inserted in a manner as either to partially project from the surface, as shown at the left hand side of FIG. 2, or to be flush with the surface, as shown at the right-hand side of FIG. 2. Since the basic components of the mold 1 are generally produced for economic reasons of a material of lesser grade, such as sand, which cannot withstand the applied pressures when individual specimens are investigated, the insertion of the extending specimens 8 facilitates the tracing of the specimen positions to be investigated in the mold-1'. Furthermore, the surfaces of the extending specimens 8 are subjected to increased thermal stresses because the heat dissipation from the extending part is rendered more diflicult. Thus, where desired, in order to obtain a uniform stressing over the entire surface of the cavity 2', especially with regard to the thermal stress, each position of the surface is flooded by the same quantity of hot molten casting material, for example, as hereinafter described.

It is noted that uniform flooding on a hollow mold or, generally speaking of any vessel, is present at the moment when the identical quantity of liquid flows within a given time over each area unit of the wetted part of the vessel. Uniform flooding can be achieved upon compliance with the following conditions:

(a) the mold rotates during the pouring-in operation, filling in the process from the outside to the inside;

(b) the pouring-in takes place from the periphery;

(c) the hollow space of the mold is designed as a hyperboloid of rotation.

Referring to FIG. 4, a mold 1" is constructed with a cavity 2" in the shape of a rotational hyperboloid so as to facilitate a uniform flooding of the cavity surface. As above, the mold 1" is either made of the material to be tested, as shown at the left hand side of FIG. 4, or small specimens 8 are inserted into the mold cavity, as shown at the right-hand side of FIG. 4. A duct 10 which has an upper end in the shape of a funnel 9 extends through the mold 1 to an annular duct 11 which concentrically surrounds the mold cavity. The annular duct 11 communicates through other annular openings 14 with the external wall of the mold cavity 2" so as to permit a peripheral filling of the cavity. In filling the mold'cavity,

a molten casting metal is porued into the funnel 9 and transmitted into the mold cavity from the periphery of the cavity so as to ensure uniform flooding of the surface of the cavity 2". A duct (not shown) is also provided in the mold so that during filling of the mold cavity the entrapped air in the mold is allowed to escape. This arrangement can also be used in the other described molds to facilitate peripheral filling of the respective mold cavities.

Since the ordinate branch of the hyperboloid cavity is broken off at level H, a certain error in the uniform flooding of the cavity surface results. However, this error can be estimated by calculating the separated residual volume of the hyperboloid. Also, if stringent requirements are made on the accuracy of uniform flooding the error can be compensated for by a correcting volume 13 which is cylindrical in its simplest form and which has a magni tude corresponding to the separated residual volume of the hyperboloid.

For example, in producing the mold 1", the correcting volume cylinder 13 is placed at the ordinate branch of the hyperboloid as indicated on the left-hand side of FIG. 4. It is understood that this correcting volume cylinder 13 is arranged symmetrically to the axis of rotation with FIG. 4 illustrating the two uses in which the correcting volume is taken into consideration (left-hand side as viewed) or is disregarded (right-hand side) i.e. the resultant error is neglected. In this manner, all those portions of the cavity surface disposed outside a circle having a radius r are uniformly flooded. In this arrangement, the specific surface pressure is also calculated in accordance with the above expression, the height h being merely replaced by the height H The drive for the mold 1" and the testing of the mold materials to be investigated are performed in the manner described above and like reference characters have been used to indicate like parts. It is, of course, possible in this arrangement to inset individual specimens 8 into the surface of the cavity 2" formed by the generating curve y. This procedure merely modifies the calculation of the pressure component G of the specific surface pressure P.

Referring to FIGS. 5 and 6, in the event that a relatively small amount of liquid casting metal is available for test purposes, a relatively large number of specimens 8 can be investigated in an overall mold 1 of relatively small size.

It is noted that the molds as in FIGS. 1, 5 and 6, when constructed of sand, are inserted into a mold box 12 which is constructed of metal or other suitable material in order to provide the molds with additional stability.

It is also noted that the molds constructed as two-part permanent molds as in FIGS. 2, 3 and 4 are made of ceramic compounds, graphite or steel.

Finally it is noted that the rotational speeds reached in rotation are so selected that the pressure loading of the surface of the respective cavities approximately correspond or exceed the pressure prevaling on the cavity surface of the mold in static casting under practical conditions. Generally, the rotational speeds employed are in a range of 50 to 200 revolutions per minute provided the dimensions of the test apparatus and the quantities of melt required for the tests do not become excessive.

What is claimed is:

1. In a method of testing foundry mold materials under high pressure wherein the mold materials to be tested from at least a portion of the surface of a mold cavity in a rotatable mold, the steps of rotating the mold and cavity about an axis of rotation passing therethrough, and casting and cooling a molten metal in the rotating cavity under a generated specific surface pressure having a continuous pressure gradient across the surface of the cavity whereby the surface of the test casting can be tested by measuring visually or by roughness measurement the distance from the axis of rotation of the casting at which destruction of the mold material begins and by determining the angular velocity of the mold so as to determine the pressure thereby to which the mold material can be loaded without impairing the quality of the casting.

2. A method as set forth in claim 1 which further comprises the step of initially inserting the mold materials to be tested into the mold cavity in the form of individual specimens.

3. A method as set forth in claim 1 wherein the molten metal is poured into the mold cavity from the periphery of the mold cavity.

4. A method as set forth in claim 1 wherein the mold cavity is designed as a hyperboloid of rotation and the molten metal is poured from the periphery of the cavity so that the molten metal is flooded uniformly over the surfaces of the cavity during casting and cooling thereof.

5. A method as set forth in claim 1 wherein the molten metal is poured into the mold cavity at different temperatures in successive tests whereby the effect of different casting metal temperatures is investigated in each test.

6. An apparatus for testing foundry mold materials comprising:

a mold having a cavity disposed therein and an opening communicating with the exterior periphery of said mold, said cavity being in the shape of a rotational hyperboloid and a rotatable casting table supporting said mold thereon and having an axis of rotation passing centrally through said cavity in said mold whereby rotation of said mold and pouring of a molten metal into said cavity achieves a uniform flooding and heating of the mold material in said cavity to be tested.

7. An apparatus as set forth in claim 6 wherein the ordinate branch of said cavity is broken off at a predetermined level and wherein a hollow correcting volume cylinder is formed in said mold above said cavity of a volume equal to the volume of the broken off ordinate branch of said cavity.

References Cited UNITED STATES PATENTS 2,452,613 11/1948 Taylor 61; al 73-15 2,521,206 9/1950 Dietert et al. 73-15.6 2,638,646 5/1953 Rubissow 164150 3,159,018 12/1964 Patterson et al. 73-15.6 3,369,388 2/1968 Vepson 73-15 FOREIGN PATENTS 153,542 3/1964 Russia.

JAMES J. GILL, Primary Examiner H. GOLDSTEIN, Assistant Examiner U.S. Cl. X.R.