US2991520A

US2991520A - Cored passageway formation

Info

Publication number: US2991520A
Application number: US558987A
Authority: US
Inventors: Robert F Dalton
Original assignee: Howard Foundry Co
Current assignee: Howard Foundry Co
Priority date: 1956-01-13
Filing date: 1956-01-13
Publication date: 1961-07-11
Anticipated expiration: 1978-07-11

Description

July 11, 1961 R. F. DALTON CORED PASSAGEWAY FORMATION 3 Sheets-Sheet 1 Filed Jan. 13. 1956 R. F. DALTON CORED PASSAGEWAY FORMATION July 11, 1961 3 Sheets-Sheet 2 Filed Jan. 15. 1956 INVENTOR. fiberzfflaforz,

July 11, 1961 R. F. DALTON CORED PASSAGEWAY FORMATION 5 Sheets-Sheet 3 Filed Jan. 13. 1956 PERCENT HKOHOFLUOR/C #670 M/ M/XTl/HE United States Patent 2,991,520 CORED PASSAGEWAY FORMATION Robert F. Dalton, Chicago, Ill., assiguor to Howard Foundry Company, Chicago, 111., a corporation of Illinois Filed Jan. '13, 19 56, Ser. No. 558,987 12 Claims. (Cl. 22-131) The present invention relates generally to the formation of cored passageways in metal castings, and is directed particularly to overcoming the difliculties normally present in the formation of small bore passageways having one or more curves. An important innovation of the invention is the provision and use of a flexible gas-permeable refractory sleeve as the primary member of a core element.

Generally, there are two known methods of producing bores or passageways in castings. One of these methods involves machine operations, such as drilling, after a casting has been made. The operation of drilling holes or passageways is inherently limited. The drilled passageways must always be straight or composed of two or more straight sections. This method of forming passageways is not only an extra operation, thus involving extra expense, but involves the risk of spoiling a certain percentage of castings due to the drifting of the drill to an extent that the passageways do not run true. Even if drilled passageways meet but are not precisely connected, turbulent flow may result because of the imperfect junction. This may result in an insufficient flow of fluid or foaming of the liquid with its attendant disadvantages.

The other common method of forming passageways in castings is to cast them to shape with suitable cores of refractory material as a part of the mold in which the metal is cast. Examples of castings formed in this manner in the foundry industry are water cooled motor blocks and water cooled cylinder heads used in the automotive industry. Here the cored passageways are formed by casting the metal around a core composed of a refractory aggregate such as foundry sand bonded with an organic binder such as core oil or resin. As a result of the casting operation the core disintegrates and collapses and the refractory aggregate may be shaken out from the rough casting.

This latter method involves certain disadvantages and practical limitations. The cores must be capable of venting the core gas generated during the metal pouring operation so that the gas may escape from the mold without requiring its passage through the metal itself. The formation of gas pockets within the casting results in the manufacture of an inferior casting which, in many cases, is completely non-useable. In the instance where a refractory aggregate such as sand is used, the core gas escapes through the interstices of the aggregate in a desirable manner.

An additional disadvantage accompanying the use of refractory aggregate cores is the practical limit experienced in the forming of passageways of small diameter. As the cores become smaller in diameter they become more fragile to manual handling and metal pouring, and since the cross sectional area of the core becomes smaller, the problem of venting the core gas becomes greater. Therefore, this method is impractical in the forming of small diameters such as A inch to 5 inch or less due to the lack of a suitable material from which the core may be made.

Efforts have been made to devise other methods of forming cored passageways, one being the use of cast-in stainless steel tubes. Thes tubes must be accurately preformed to the desired longitudinal shape and dimensions,

accurately placed and supported in the mold, and molten amount of skill to produce.

metal cast directly around the tubes. The tube assemblies where several passageways are involved are expensive to manufacture as they require a considerable They have the further disadvantage of often having imperfect interiors due to imperfect joints, weld spatter and flowing weld material. Thus it is necessary to test these tubes for pressure drop before placing them in the mold to be sure that the in terior is sufliciently clear for its intended use. It furthermore is necessary to examine the exterior of the tube thoroughly to make sure that the surface is clean and free of any foreign materials which will form gas pockets or otherwise prevent the molten metal from accurately surrounding the tubing. Still further, the cast-in metallic tube of the type described increases the weight of the casting which is often a real objection, particularly in the aircraft industry.

The disadvantages and inadequacies of these prior art passageway forming methods have become increasingly serious as modern casting operations have become more complicated entailing the increased use of many small bore passageways of complex shapes. While there are some refractory materials such as glass, quartz, carbon and plaster which are available for molding into cores capable of producing intricately formed passageways, the use of these materials has been found limited in application due to the difficulties accompanying the molding of the materials into the desired shape, the formation of scrap castings due to the use of non-permeable core materials, as well as the difficulties accompanying the removal of the cores from the formed casting.

It is an object of the present invention to overcome the aforementioned difiiculties as well as generally improve the art of forming cored passageways in metal castings by the provision and use of a new type of core element which may be readily formed in many desirable shapes and sizes, which is inexpensive to form, which is capable of supplying to the finished casting an accurately placed cored passageway, which is capable of efliciently venting any gas that may be generated on the surface of the core, and which may be readily removed from the casting to thereby produce a casting that is radiographically and metallurgically sound in the area surrounding the cored passageway.

Another object is to provide a method of forming castings having cored passageways therein, which method makes use of the improved core element to thereby substantially simplify casting procedures.

Certain other objects of the invention will in part be obvious and in part appear hereinafter.

It is intended by the present invention to make use of a core element in foundry castings which includes a flexible gas-permeable refractory sleeve. Preferably the sleeve is formed from braided, woven or suitably matted glass fibers or asbestos but it is intended to include within the scope of the present invention the use of any flexible refractory material which is capable of being braided, woven or matted in such a manner as to 'form a gaspermeable sleeve. Such sleeves are normally collapsible and therefore must be made sufficient-ly rigid to be capable of retaining their shape while positioned in the mold during the casting operation. There are several different procedures available which are capable of supplying the sleeve with the requisite rigidity. One of such procedures includes the interweaving of thin metallic strips or threads with the glass fiber in the formation of the sleeve to provide the sleeve with increased rigidity while at the same time retaining the requisite permeability and flexibility of the sleeve. This procedure is particularly adapted for use in the formation of sleeves having small outside diameters such as on the order of inch to M inch or even less.

from a metal having a melting point lower than that of the metal of the casting. Under these circumstances the casting is cooled sufficiently-to solidify the cast metal immediately outside and in contact with the refractory, permeabl'e sleeve while the 'over-all'temperature is maintained at a degree sufficient to retain the core supporting wire in a molten state. The wirestrand may then be poured from the passageway of the casting followed by subsequent manual removal of the sleeve.

A preferred procedure of internally supporting the sleeve sufiiciently to impart adequate rigidity to the sleeve to withstand the weight ofthe metal being cast includes the use of tubes formed from a metal which is soluble in solvents which do not attack the metal of the casting. These metal tubes are available in a wide range of sizes and, as a result, are capable of a wide variety of applications. Obviously, tubes of a'wide range of diameters and various cross sectional configurations may be used according to this invention 'In the use of joined segments of tubing as an internal support of a flexible refractorysleeve of the type described, it is unnecessary that the tube segments be perfectly joined as'the continuous outer surface of the flexible sleeve insures theformation of a smooth passageway as well as accurate joints. As previously described, the exacting skill normally required in the formation of cast-in tubes 'is not necessary as the flexible sleeve is, capable of counterbalancing imperfections at the joints of the supporting tube. All that is required of a supporting tube is that it be capable of imparting to the sleeve the requisite rigidity necessary to withstand casting conditions while presenting a sufliciently accurate exterior to prevent raised or depressed points in the sleeve. The supporting tubeis inserted within a finished'sleeve or the sleeve material,'such as glass fiber strands, may be actually braided over the tube to thereby form a much smoother surface resulting in a'smoother coredhole in thec'astiug.

Ductile tubing, such as certain grades of copper and soft steeltubing,may be used in a continuous form under circumstances normally making its use undesirable. For example, if a bare copper tube is cast in aluminum, a scrap casting will result as the aluminum will dissolve the copper until all of the latter is used up. Due to'the presence of the sleeve the use of ductile copper tubing is greatly expanded. Obviously, duc'tile'tubing is a preferred source of tubing as it can be readily pre-shaped to conform with the shape of passageway desired. The copper, due to the presence of the sleeve which acts as a barrier, is prevented from being dissolved by themetal of the casting.

An important advantage of utilizing a tube as an internal support 'of the sleeve is to provide an internal passageway within the core element for the introduction of a solvent capable of dissolving the metallic tubing while at the same time being ineifective with respect to the metal of the casting. Following the removal of the dissolved metal tubing from within the sleeve, the latter may be manually withdrawn from the passageway of the casting.

A further advantage residing in the use of a hollow metallic tube is that the tube may be perforated, as by drilling, at regular intervals for the purpose of helping to remove any gas formed on the surface of the glass fiber sleeve when the molten metal is' poured. Due to the permeability of the sleeve the gas can escape through the sleeveand the drilled holes into the tube and through the tube out of the casting.

The general method of forming cored passageways will now be more completely described in connection with the drawings, wherein:

FIG. 1 is a perspective view of a wooden form with a length of ductile metallic tubing formed in position thereon;

FIG. 2 is a perspective view of the core element including the outer gas-permeable refractory sleeve positioned about the internally supporting metallic tube, which core element is ready for placement in a mold;

FIG. 3 is an enlarged cross section of the core element of FIG. 2;

FIG. 4 is a perspective view of the completed mold illustrating the position of the core element of FIG. Zin

the mold as indicated by the dotted lines;

FIG. 5 is an enlarged fragmentary perspective view of a manner in which the metallic tubing may be removed from the sleeve within the finished casting;

FIG. 6 is an enlarged fragmentary cross-sectional view of the casting illustrating the partial removal of the metallic tube from the core;

FIG. 7 is a view similar to FIG. 6 illustrating the total removal of the metallic tube from the core;

FIG. 8 is an enlarged perspective view of the casting illustrating the removal of the sleeve from the cored passageway of the casting;

FIG. 9 is an enlarged partial cross-sectional view of the'cored passageway in the casting following removal of the core element; and

FIG. 10 is a graph setting forth a curve representing the solubility of magnesium in mixtures of nitric and hydrofluoric acids.

Referring to FIG. 1, a wooden form 10 is shown as containing a-number of curvilinear sections, such as 11 and 12, which cooperate to serve as a pattern for the preshaping of the core element. To provide the casting with a small diameter multi-curved internal passageway, it'has been found desirable to utilize a core element 13 as shown in FIGS. 2 and 3. The particular core element 13 illustrated is formed from an outer flexible gas-permeable sleeve "14 of woven glass fibers internallysupported by a copper tube 15. Certain grades of copper tubing, being ductile, may be bent to conform with the shape of the passageway desired in the casting. An-example of this procedure is illustrated in FIG. 1 wherein the copper tube 15 is shown as positioned on the wooden form 10 and pre-shaped to its contour.

Following the pre-shaping of the copper tubing 15 the glass fiber sleeve 14 is positioned about the tubing and the core element is ready for insertion within the mold. FIG. 4 illustrates a known manner of obtaining a metal casting of intricate shape. A pattern is used in the conventional manner to form the mold cavity ingreen or dry sand or other siliceous materials. The core element 13 is positioned within a cope 16 and drag 17 as illus trated by the dotted lines. The mold is provided with a gate 18 and sprue passageways 19 through which the molten metal is introduced into the mold. The cope16 further includes a riser 20 which provides for a reservoir of metal to counteract shrinkage of the casting in the known manner. The ends of the core element 13 as designated by the numeral 21 extend outwardly of the mold cavity into core prints in the sand. In this manner the core 13 is supported by its ends 21 in a suspended manner within the mold cavity to properly position the passageway to be formed in the casting. Gas trapped about the core element 13 by the incoming molten metal is allowed to permeate through the sleeve 14 and ultimately escape out of the mold cavity. This feature is of particular importance in the present invention as without the Provision of means for allowing the trapped gas to escape-from the mold cavity, gas pockets would be formed in the casting about the internal passagewaytherein and the casting would be imperfect probably to the extent that itwould be completely non-useable.

'In FIG. 5 a finished castingZZ is shown as still coutaining the core element 13 within the internal passageway formed thereby. The first step in removing the core element 13 from the passageway involves the connection of an inlet or solvent line 23 to one end of the passageway of the casting 22 and an outlet line 24 to the other end of the pasageway of the casting 22. The outlet line 24 may be connected to a source of vacuum if necessary or a stainless steel lined centrifugal pump may be used and a solvent which is capable of dissolving the copper tube 15 while at the same time being ineffective or passive with respect to the metal of the casting 22 is introduced into the line 23 and flows through the interior of the copper tube 15 throughout the entire length of the core element 13. An example of a solvent suitable for use in dissolving copper tubing from a core element used in a magnesium casting is 33% nitric acid combined with 67% hydrofluoric acid. This mixture of acids is capable of efficiently removing the copper and the glass fiber sleeve from the casting without aflecting the magnesium of the casting. In the instance where the casting is formed from aluminum, it has been found that nitric acid alone may be used to remove the copper without destroying the sleeve. In line with the last mentioned circumstances, FIG. 6 illustrates partial solvent removal of the tube 15 indicating its initial inside diameter by the dotted line 25. Ultimately, only the sleeve 14 remains within the passageway of the casting 22 as illustrated in FIG. 7. The sleeve 14 is then manually withdrawn from the casting 22, as illustrated in FIG. 8, and the desired intricate passageway 26 remains within the casting 22.

FIG. 9 illustrates the type of passageway 26 formed as a result of the above described operations and it can be seen that the pasageway 26 is substantially smooth and perfectly formed, By following this procedure, the passageway 26, even though intricate throughout its length, is, in cross section, uniform in shape and dimensions. It is unnecessary to resort to subsequent machining operations to insure the obtaining of a passageway consistent with respect to a desired diameter throughout the entire length thereof. Furthermore, due to the refractory and permeable nature of the sleeve 14, gas trapped within the mold by the casting operation is allowed to escape from the passageway and no undesirable gas pockets are present to deform the passageway during the formation thereof. Obviously, the tube 15 may be of any desired crosssectional shape to form square, rectangular, oblate, elliptical, etc. passageways. The tube may vary in its crosssectional shape throughout its length. The sleeve 14 is adapted to conform to the shape of the tube 15 and will normally increase the outer diameter of the tube 15 approximately 0.02 of an inch.

It will be seen that the core element 14 is inexpensively and simply formed. There are no disadvantages present resulting from having imperfect interiors in the passageway of the casting due to imperfect joints existing in the core element, weld spatter or flowing weld material. Glass fiber has the ability to allow the molten metal to lie against it in such a manner as to result in the formation of a substantially smooth interior in the passageway. The surface of the cast hole may be made smoother by rubbing the surface of the sleeve 14 with a filler such as a dry plumbago or titanium dioxide. This will fill in the interstices of the refractory material and aid in the formation of a smoother wall. The sleevei easily removed manually from the passageway, as demonstrated in FIG. 8, regardless of the complexity of the passageway because of its strength, flexibility and pliability. Efficient and intact sleeve withdrawal is obtained by reason of the directing of the sleeve in the mold for full circumferential outer surface contact with the casting metal and for coinciding longitudinal center line positioning in the passageway formed thereby in the casting.

In the instance where a ductile copper tube is utilized in internally supporting the core element, the glass fiber sleeve guards against a mixing of the copper in the molten metal of the casting such as would occur in the instance where an unprotected coppercore is used in an aluminum alloy casting, In preventing mixing of the copper, the copper tube may be completely removed from the casting and the metal surrounding the passageway formed in the casting does not have its properties changed as a result of an increase in copper concentration. From this it can be readily seen that by reason of the "sleeve, copper tubing can be put to a wide variety of uses in the casting art. This latter feature is of importance due to the desirable property of ductility existing in certain grades of copper.

While the foregoing explanation made in conjunction with FIGS. 1-9 has dealt primarily with the use of a sleeve formed from glass fibers and internally supported by ductile copper tubing, it should be understood that it is well within the scope of the present invention to make use of other suitable materials capable of bringing about the advantages previously discussed. The basic concept of the present invention is to make use-of material'which is capable of being braided or woven to form a flexible gas-permeable refractory sleeve for use in the same manner as described in connection with the glass fiber sleeve. In the event that metallic material is utilized in forming such a sleeve any strips or wires of a metal not soluble in the molten metal of the casting or in the particular acid used to remove the internal supporting tubing therefrom may be used. By referring to the materialas being refractory material, it is meant that such material is capable of withstanding the temperatures used in the casting operation without being affected thereby.

As a further illustration of the type of material highly adaptable for use in the forming of a flexible gas-permeable sleeve, it'has been found that braided or woven wire strands of stainless steel produce a sleeve particularly adapted for use in the formation of a passageway in a magnesium alloy casting. The diameter of the Wires used in forming a stainless steel sleeve will normally fall within the area of 0.0036 of an inch. Stainless steel is not soluble in molten magnesium and, as a result, a casting having a variance in metallic composition in the vicinity of its cored passageway will not result from the use of a stainless steel sleeve.

Still referring to the use of a stainless steel sleeve-in the formation of a cored passageway in a magnesium alloy casting, additional advantages are present. For example, once the casting has been formed and it is desired to remove the tubing internally supporting the sleeve prior to the removal of the sleeve, the acid used would preferably be a suitable mixture of nitric and hydrofluoric acids. The hydrofluoric acid is present in the mixture to passivate the mixture with respect to the magnesium alloy so that the latter will not be damaged by acid action. The acid mixture, being passive with respect to the magnesium casting and the sleeve, will dissolve the sleeve-supporting tubing, such as copper tubing, following which the unaffected sleeve may be manually removed and a clean bore is left in the casting.

It is generally considered desirable to make use of a material in forming the sleeve which will not be afiected by the acid or acid mixtures used in removing the sup porting tubing. In the casting of magnesium, it is essential that the nitric acid used in removing the copper tubing be passivated by the presence of suflicient amounts of hydrofluoric acid thereby alleviating acid action with respect to the magnesium of the casting. When a glass fiber sleeve is used under these circumstances, the hydrofluoric acid present in the mixture attacks the glass fibers and the sleeve is at least partially destroyed to an extent that its continuity is interrupted and its strength is materially reduced thereby eliminating the possibility of manually withdrawing the sleeve from the cored passageway of the casting. While a substantially clear bore may still be obtained it is nevertheless necessary to resort to other techniques in removing the damaged glass fiber sleeve from the cored passageway. Such techniques, for example, include the use of air blasts or wet sand blasting which, of course, involves the cost of making available additional equipment for use in the foundry.

Toovercome this last mentioned problem, the sleeve maybe-formed from a material'which is capable of withstanding hydrofluoric acid action and retaining its continuity and strength. Such material, under the specific conditions set forth above, is stainless steel and a sleeve of woven stainless steel wires will perform in the manner desired during the casting operation and in addition be unaffected by the action of the hydrofluoric acid contained in the acid mixture. As a result, the stainless steel sleeve may be manuallywithdrawn fiom the cored passageway without the necessity of using air blasts or other specialized procedures. Since the stainless steel sleeving is between the ductile iron or copper tube and the cast metal, the manual removal of the sleeve is excellent evidence of the cleanliness of the cored passageway.

In FIG. 10 a graph is presented which illustrates the variation in solubility of a magnesium alloy in a mixture of nitric and hydrofluoric acids, which mixture varies with respect to the hydrofluoric content. The curve presented in FIG. 10 was derived from determining the percent weight loss of magnesium with varying percentages of hydrofluoric acid in the mixture of acids. An immersion time of 1 hour was used in each instance and the alloy tested was typical of available magnesium alloys, all of which have a magnesium content of at least 90%, the particular alloy tested having the following composition:

The nitric acid commercial-source used was a 70% grade while the hydrofluoric acidwas a 50% grade. The curve presented in FIG. 10' is a semi-logarithmic curve, the ordinate representing the percent loss of magnesium being plotted on a logarithm scale and the abscissa representing the concentration of hydrofluoric acid being plotted on an arithmetic scale.

In considering the curve presented in FIG. 10, it will be noted that as the percent concentration of hydrofluoric acid increases in the mixture, the percent loss of magnesium decreases. In foundry operation it is of course desirable to maintain the loss of magnesium at a minimum while at the same time maintain the concentration of nitric acid in the acid mixture at a level sufficient to properly dissolve the supporting tube of the core element. A mixture of equal quantities by volume of these acids has been'found adequate for use in foundry production and in referring to the graph of FIG. 10 it will be noted that under such circumstances the percent weight loss of magnesium will be maintained at well below 0.1%. At the same time it has been found that 50% nitric acid is capable of dissolving the supporting tube of the core element within a reasonable time.

Whereas the element copper is soluble in molten magnesium alloys, a sleeve composed of sutficiently fine and closely woven stainless steel wires placed about the copper tube prevents the solution of the latter in the mag nesium alloy. While copper has been referred to almost exclusively because of the ductile nature of certain grades of copper, it should be understood that any suitable supporting tubing capable of carrying out the principles of the present invention may be used. For example, tubing formed from soft steel exhibits ductile properties which allow such tubing to be readily used in forming intricate passageways in castings ofthe type above discussed. Soft steelof the type designated as SAE 1015 has been found to be highly adaptable for use. The soft steel will be dissolved by the nitric acid of the acid mixture and will not be affected by thewmolteumagnesium inthe. event that contact should be made therebetween. -It should :be further understood that the .glass fibers maybe iinterwoven with steel wires to form a sleeve for use in a magnesium-casting. Due to the presence of hydrofluoric acid-in the acid mixture someof the glass'fibers may -be dissolved thereby; however, the presence of the-steelwires being unaffected by the hydrofluoricacid will provide the sleeve with adequate strength and continuity to allow subsequent-manual withdrawal of the-sleeve from the cored passageway in the casting.

The following examples are illustrative-of-metho'ds of forming cored passageways in castings which incorporate the principles of the present invention. However, it should be understood that these examples, being illustrative, are notintended to be construed as limiting the scope of the present invention.

Example I A Wooden form was constructed to conform with a desired shape of a metal casting to which was to be supplied an intricate internal passageway. A soft copper tube of inch outside diameter was pre-shaped by pressing the latter against the wooden form to conform with the desired intricate longitudinally extending shape of the contemplated passageway. The pre-formcd copper tube was then sheaved'with a sleeve of woven glass fiber of the type sometimes used as wire insulation on electric motors. The assembled core element was then placed in a pro-shaped cavity of a sand mold and molten aluminum alloy, No. 355 of the Aluminum Company of America, was poured into the mold cavity at a temperature of 1380 F. The mold was allowed to cool and the casting was shaken out after which the heads, risers and gates were removed following normal foundry cleaning room methods. The casting passageway was further enlarged at its extremities with a drill of /2 inch diameter to an extent of approximately /2 inch in depth. Into these enlarged holes rubber tubing was placed. One tube was attached to a glass funnel and the other tube to a water aspirator with a suitable overflow bottle. 1500 cc. of concentrated nitricacid was passed through the cored passageway. This acid dissolved the copper tube, and the solution was drawn into the water aspirator. The pasageway was then washed through with water following which approximately 25 cc. of fresh, copper free, nitric acid was passed through the passageway and tested for copper content with sodium sulfide. The test was negative indicating that all copper had been removed from the core element. The passageway was again washed with water and 300 cc. of carbon tetrachloride was passed therethrough. The casting was disconnected from the washing arrangement and the passageway blown dry with compressed air. The latter action partially pushed the glass fiber sleeve out of the small cored passageway whereupon it was easily fully removed by pulling. The glass fiber sleeve was intact despite the previous operations perforrned'in casting the metal and removing the inner copper core.

Example II A wooden form was constructed to conform with a desired shape of a metal casting to which was to be supplied an intricate internal passageway. A ductile soft steel tube formed from SAE 1015 steel of approximately & inch outside diameter was pro-shaped by pressing it against the wooden form to conform with-the desired intricate longitudinally extending shape of the contemplated passageway. The pro-formed steel tube was then sheaved with a sleeve of woven stainless steel wires, each having a diameter .of approximately 0.0036 of :an inch. The assembled .core element was then placedinia .pre shaped cavity of a sand mold and molten magnesium alloy identified as ZRE 1 supplied by Magnesium Elek- 9 tron Limited of London, England, and having a general composition as follows:

The stainless steel used in forming the sleeve had an approximate composition as follows:

percent Chrome 18 Nickel 8 Maximum carbon .05 Iron Remainder The molten magnesium alloy was poured into the mold cavity at a temperature of around 1400" F. The mold was allowed to cool and the casting was shaken out after which the heads, risers and gates were removed following normal foundry cleaning room methods. The casting passageway was further enlarged at its extremities with a drill of /2 inch diameter to an extent of approximately 12 inch in depth. Into these enlarged holes plastic tubing was placed. One tube was attached to a plastic funnel and the other tube to a polyethylene bucket. One gallon of a mixture of 5 0% by volume of 70% grade hydrofluoric acid and 50% by volume of 38 Baum (69- 71% grade) nitric acid was passed through the cored passageway. This acid mixture dissolved the steel tube and the resulting solution was drawn into the bucket. The passageway was then washed through with water and dried following which the stainless steel sleeve was manually withdrawn therefrom. It was found that the sleeve was intact and was readily and completely removed from the cored passageway.

The copper tube used in the aluminum casting is interchangeable with a soft steel tube. The stainless steel sleeve may be used with either aluminum or magnesium alloys. A glass fiber sleeve is preferred for use with aluminum while a stainless steel sleeve is preferred for use with magnesium alloys to eliminate partial destruction by the action of hydrofluoric-nitric acid mixtures.

While certain acid solvents have been specifically referred to, it should be understood that any suitable solvent may be used in carrying out the method of the present invention. The solvents used will depend upon the type of material forming the sleeve and the supporting tube. A further consideration in determimng the proper solvent for use resides in the type of metal used in the casting. The principal function of the solvent is to remove the supporting tube from the core element and in doing so this solvent should preferably be ineffective against the metal of the casting.

If desired, m'pples surrounding a portion of the core ends 21 may be formed integral with the ends of the castings. In this manner flexible, acid resistant tubing, such as rubber or Tygon, which is a compounded halide polymer, condensation resin and diene derivative, made by US. Stoneware C0., of Akron, Ohio, may be suitably attached to the nipples without the necessity of widening the ends of the passageway.

In order to obtain the best results in the shortest time it has been found that the dissolving of the sleeve-supporting tubing should preferably be carried out at a temperature within the range of 70 to 140 F. Within this range the acid apparently is most effective and the dissolving action is obtained in the shortest possible time. It should be understood, however, that this range is considered merely to be preferable and should not be construed as a limiting factor in carrying out the various procedures of the present invention.

While specific reference has been made to the formation of curved passageways of an intricate nature, it should be understood that the core element including the sleeve and supporting tubing may be readily used inforniing straight line bores in castings. The core element of the present invention, of course, eliminates the many difficulties accompanying the formation of curvilinear passageways in castings. However, the core element is also very useful in the formation of straight line passageways. When the core element is used in the latter situation it is possible to manually remove the supporting tube from within the sleeve following which the sleeve will collapse inwardly and may be readily removed manually from the bore. It is generally considered in ,conventional foundry practices that in the forming of straight bores in castings, a tube of a length of no greater than five times its diameter may be used without a resultant scoring of the inner surface of the passageway caused by the removal of tubes of a greater length. By making use of a sleeve element the supporting tube may be of any length desired as it will not come into contact with the surface of the casting defining the bore. In this connection, tubes of A; inch diameter and 20 inches long have been successfully used without scoring.

This application is a continuation-in-part of my copending application, Serial No. 538,091, filed October 3, 1955, now abandoned.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A passageway forming core element for use in making foundry castings, said element including a flexible gas-permeable refractory woven stainless steel sleeve internally supported by copper tubing which is soluble in solvents ineffective with respect to the metal of said castrugs.

2. The method of forming a cored passageway of substantially controlled dimensions in a metallic casting which comprises: inserting within a mold a flexible gas-permeable sleeve formed from woven strands of refractory material and internally supported by metallic tubing, pouring said mold, dissolving said tubing with a solvent ineffective with respect to the material of said sleeve and the metal of said casting, and thereafter manually withdrawing said sleeve from said casting.

3. The method of forming a cored passageway of substantially controlled dimensions in a metallic casting which comprises: inserting within a mold a flexible gaspermeable sleeve formed from woven strands of refractory material and internally supported by a metallic memher having a melting point less than the metal of said casting, pouring said mold to surround said sleeve with molten metal, cooling said metal to a temperature above the melting point of said member, flowing the molten metal of said member out of the interior of said sleeve, and thereafter manually withdrawing said sleeve from said casting.

4. The method of forming a cored passageway of substantially controlled dimensions in a magnesium casting which comprises: inserting within a mold a flexible gaspermeable sleeve of woven stainless steel strands internally supported by soft steel tubing, pouring said mold to surround said sleeve with molten magnesium, cooling said magnesium, dissolving said tubing with an acid mixture of approximately 50% nitric and 50% hydrofluoric, and thereafter manually withdrawing said sleeve from said casting.

5. The method of forming a cored passageway of substantially controlled dimensions in an aluminum casting which comprises: inserting within a mold a flexible gaspermeable sleeve of Woven glass fibers internally supported by copper tubing, pouring said mold to surround said sleeve with molten aluminum, cooling said aluminum, dissolving said tubing with nitric acid, and thereafter manually withdrawing said sleeve from said casting.

"a ac 52b 6. The method of forming -a cored-passageway'of' substantially controlled dimensions in a metallic casting which comprises: inserting-within a mold -a gas permeable sleeve of inter-twinedstainless steel strands internally supported by copper tubing, pouring said mold to surround said sleeve with molten metal, cooling said metal, dissolving said tubing with a mixture of nitric acid and hydrofluoric acid which is passive-with respect to' the metal of said casting and thereafter -manually withdrawing said'sleeve from' said casting.

'7. A mold foruse in the formation of a metallic casting, said mold including a-mold cavity 'provided with means for receiving metallic material thereinto, and a'core element supported in said cavity to'be surrounded by metallic material, said core element consisting of a flexible andgas-permeable, sleeve formed'from woven-strands of refractory material, and reinforcing means received in said sleeve to support the same against radial collapse, said sleeve being directed in said .mold for full circumferential outer surface contact with said metallic material and for coinciding longitudinal center line positioning in a passageway formed thereby in a casting to permit intact manual withdrawal thereof'from said passageway.

8. The method of forming a cored passageway of substantially controlled dimensions-in a metallic casing which comprises: inserting within a mold a flexible gas-permeable sleeve internally supported by a metallic member, said sleeve being formed from woven strands of refractory material, pouring said mold, removing said metallic member from the interior of said sleeve, and thereafter manually withdrawing said sleeve fromsaid casting.

9. A passageway forming core element for use in making foundry castings, said element including a flexible gas-permeable sleeve formedfrom woven strands of 12 refractory material, said sleeve being internally supported by a metallic member.

10. A passageway forming core element for nsedn making foundry castings, said element including a flexgas-permeable sleeve formed from woven strands of ,re-

fractory asbestos, said sleeve being internally supported by ameta llic'member.

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