US2895191A

US2895191A - Method of and apparatus for precision coring in the casting of metallic articles

Info

Publication number: US2895191A
Application number: US521236A
Authority: US
Inventors: George R Sandenburgh; Marshall D King
Original assignee: Hills Maccanna Co
Current assignee: Hills Maccanna Co
Priority date: 1955-07-11
Filing date: 1955-07-11
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21

Description

G. R. SANDENBURGH ETAL 2 July 21 METHOD OF AND APPARATUS FOR PRECISION CORING IN THE CASTING OF METALLIC ARTICLES Filed July ll, 1955 METHOD F AND APPARATUS FOR PRECISIQN CORING IN THE CASTING 0F METALLIC AR- TICLES George R. Sandenburgh, Evanston, and Marshall D. King, Wood Dale, Ill.; said Sandenburgh assiguor to H1lls McCanna Company, Chicago, lll., a corporation of Illinois Application July 11, 1955, Serial No. 521,236

3 Claims. (Cl. 22-131) The `invention relates to a method of forming cored passageways in castings of aluminum or magnesium alloys and has reference in particular to the formation of cored passageways of complex and unusual shape and wherein a high degree of accuracy is obtained in the castings as to the internal diameter, conguration and location of the resulting passageways.

The invention has for its principal object to provide a method of coring intricate and complex passageways in aluminum or magnesium alloy castings which is characterized by a high degree of dimensional accuracy, wherein thermal expansion due to the heating of the core prior to pouring the casting or due Ato the high temperature of the molten metal during the pouring operation need not be considered in iiguring the core dimensions since the passageways cored by the present method will not deviate from the specified dimensions on the drawings of the article to be cast by more than permitted foundry tolerances, and wherein actual drawing dimensions can therefore be used exclusively in determining the size, conguration and location for the core material.

There are certain problems inherent in the use of sand cores which limit their use in the production of passageways of small diameter in castings of light alloys such as aluminum or magnesium. When molten metal is introduced into the casting cavity so as to contact with sand cores, gases are formed by Volatilization of the chemical inhibitors and core binders. These gases can not be allowed to bubble through the molten metal, on the contrary, the `gases must be permitted to escape through the core interior and out to the atmosphere. Sand cores have natural permeability but in long, thin or intricate cores it is necessary to form an interior cavity `called a vent for the escape of these gases. The interior cavity in the core naturally decreases it strength and thus increases the chances of the core breaking. In thin, intricate cores having unsupported lengths of more than a few inches, it is common practice to insert a steel wire for support. However, these wires introduce inaccuracies into the core during casing, due to the differential in thermal expansion between sand and the steel wires. The same is apt to cause warpage of the core, especially in intricate shapes.

Because of the above difficulties in the use of sand cores for intricate and small interior passageways in cast metal articles, -it has become standard practice to cast solid sections and drill or otherwise machine the desired passageways in the castings. Drilling is not entirely satisfactory since it has limitations and in addition the procedure is Very costly.

The above difficulties have been successfully solved by the techniques of the present invention which contemplate the use of preformed hollow glass tubing as core material. In particular the invention contemplates the use of. borosilicate glass tubing for producing smooth-surfaced passageways in castings of aluminum or magnesium alloys. Borosilicate glass, commercially known as Pyrex vnited States Patent 0 2,895,191 Patented July 21, 1959 ICC glass, has a number of characteristics particularly adapting it for use as coring material in the production of passageways -in light alloy castings. In the first place, borosilicate glass is a commercially available product, relatively inexpensive, and which can be purchased in a variety of shapes and sizes. Secondly, the accurate retention of the core dimensons when borosilicate glass is used is the result of its high resistance to thermal shock and poor heat transfer characteristics of the glass, plus the fact that the glass is put in compression from instantaneous solidiication, and contraction of the immediately formed metal layer surrounding and in contact with `the glass wall exterior, and also combined with the thermal gradient and resultant stress within the wall of the tube tending to cause compression.

During the time cycle of the pouring and solidication of the metal around the tube, the glass will soften and reach a plastic state from heat, which, plastic state then temporarily accommodates stress and alignment requirements with the hot solidifying metal mass, so that, upon total solidication, the glass core will still maintain itself in a solid, physical, unbroken state to achieve its inherent functions of forming a passageway and still main- Itain its precision of placement.

In View of the foregoing, another object of the invention resides in the use of borosilicate glass as coring material in the formation of intricate passageways in aluminum or magnesium castings. Said glass is capable of withstanding the pouring temperatures for alloys of aluminum and magnesium, and thus cores formed of said material will retain their predetermined shape during the pouring operation. Also the said glass as coring material is highly satisfactory in retaining its position, alignment and dimensional accuracy during pouring, notwithstanding some softening of the glass and movement thereof during cooling and shrinking of the casting.

Another object of the invention is to produce intricate passageways in aluminum and magnesium castings using borosilicate glass as the coring material, wherein lit is accordingly possible to dimension the cores by using the actual dimensions `therefor appearing on the drawings of the article -to be cast, and lwherein the same shrinkage allowances can be employed for both the pattern and the core.

With these and various other objects in view, the invention may consist of certain novel features of construction and operaiton as will be more fully described and particularly pointed out in the specification, drawings and claims appended thereto.

In Ithe drawings which illustrate an embodiment of the invention and wherein like reference characters are used to designate like parts- Figure l is an elevational View of the completed casting having internal passageways formed therein as indicated by dotted lines;

Figure 2 is a sectional view taken along line 2--2 of Figure l to more particularly illustrate the size, coniguration and location of the cored passageways in the completed casting;

Figure 3 is an end elevational view of the pattern required for producing the casting as shown in Figure l;

Figure 4 is a top plan view of the pattern as shown in Figure 3;

Figure 5 is an end elevational View of the `borosilicate glass core used in the production of the intricate passageways;

Figure 6 is a top plan View of the glass core shown in Figure 5;

Figure 7 is a top plan view of the mold used in casting the article shown in Figure l; and

Figure 8 is a transverse sectional view taken along line 8-8 of Figure 7.

Referring to the drawings and particularly Fgures 1 and 2, the casting selected for illustrating the invention is generally indicated'by the numeral 10, the same being formed of` a light metal such as a magnesium. alloy. The' casting 10 is substantially rectangular in shape and the same is characterized by having a plurality of passageways formed therein of an intricate and complex configuration. The passageways terminate in the four outlets such as 11, 12, 13 and 14, in the top surface 15 of the casting, and said outlets communicate with the interior connecting passageway generally indicated by numeral 16, and including the sloping passageways 17 and 18 and a connecting passageway 19.

Figures -3 and 4 disclose a pattern 20 designed for use in producing the said casting 10. The pattern 2t) essentially consists of a body portion 2.1 having the same rectangular shape as that of the casting. To provide the. core prints in the mold, the top surface 22 of the pattern is provided with the tubular projections identified by

numerals

23, 24, 25 and 26 and which correspond in shape and in location to the

outlet passageways

11, 12, 13 and 14.

Figures and 6 disclose the core which is located within the'mold cavity for producing the passageways. In accordance with the invention the core is formed of borosilicate glass, and said core, generally indicated by numeral 30, has the shape and configuration desired of the passageways for the completed casting. Accordingly, four projections such as 31, 32, 33 and 34 are provided which correspond in shape and in position to the outlet passageways 11 to 14 inclusive. As best shown in Figure 6, the said four glass projections are joined by a body portion 35 which includes the

sloping portions

36 and 37 and the connecting portion 38. The core 3) consists of a borosilicate glass tube. In any event, it will be understood that the core is of the appropriate size and shape and has the proper configuration for producing the desired passageways in the completed casting. The glass core can be formed by heat or by conventional glass blowing, or molding operations, and for more intricate and complex passageways Various sections of said coring material, or an assembly of blown glass sections, can be set in the mold cavity for subsequent pouring operations.

Due to the beneficial combination existing between the borosilicate glass cores and the casting metal of either aluminum or magnesium alloy the dimensions for both the pattern and the core can be taken directlyI from the drawings of the part to be cast. The pattern dimensions as well as the core dimensions would, howver, be expanded by a factor to compensate for the thermal. contraction which occurs between the solidification temperature of the casting material and the room temperature thereof. However, it is not necessary to consider the thermal expansion due to heating of the core prior to pouring the casting, or due to the temperature ofthe molten metal employed in the pouring operation since the passageways produced by the borosilicate material will not deviate from. the drawing dimensions by more than specified foundry tolerances. As regards the core 30, as shown in Figures 5 and 6, the same was produced using the actual dimensions as they appeared on a drawing of the part. Of course, the dimensions were expanded by the same shrinkage allowances as were used in the construction of the pattern. The core was then checked dimensionally prior to pouring of the casting and the resulting casting was subsequently sectioned and the passageway laid out. A comparison of the two sets of dimensions disclosed that the cored passageway `was within thirty-thousandths of the core dimensions. Whereas, aluminum and magnesium alloys constitute the preferred metals for the present glass coring technique, nevertheless the same is not necessarily limited to such alloys but can also be used in connection with other alloys having melting points below the softening point of the glass core whereby the core will not become distorted during the casting operation.

In Figures 7 and 8 the numeral 40 indicates a standard flask which is filled with sand 41. The preformed glass core assembly 3) is properly set within the mold cavity 42 with the glass ends or projections such as 31 to 34 inclusive being rmly held in proper position in the core prints 43 to 46, respectively. The mold cavity 42 is provided with a plurality of pouring gates and risers 47 and which are suitably connected by the ruimer 48.

In practice the molten alloy is poured into the prepared mold until the mold cavity is lled and whereby the molten metal completely surrounds the core material. The metal solidiiies in place and the glass core, which now forms the liner, or is actually the hole former in the solidied metal, remains intact without fracture or appreciable distortion or melting of the glass. The casting 10 is next removed from the mold and the projections, due to the pouring gates and risers, which are attached thereto, are removed and the rough casting is now ready for removal of the core material.

For this operation the casting `and core assembly may be submerged in a reagent selected for corroding the glass but which will not have any appreciable corrosion effect on the metal of the casting. Hydrotluoric acid or aqueous solutions of iluophosphoric acid with or without inhibitors such as arsenic oxide may be used. The reagent is permitted to selectively corrode the glass so that after a period of time the coring material will be completely removed, leaving precise and accurately formed passageways in the metal of the casting. When glass tubing is employed as the coring material, the corroding reagent may be caused to ow through the tubing and thus it is not necessary for the entire casting to be submerged in the reagent. When using the glass coring techniques as described for producing passageways in castings of magnesium and aluminum the gates and risers should be so located asto prevent any possibility of partial melting and/ or distortion of the glass core assemblies. In general, the gates and the risers should be located at a distance as far as possible from the glass cores.

Itis thus possible with the method of the present invention to use actual drawing dimensions exclusively in determining the configurations of the core and its location within the mold, and it is only necessary that they be expanded by the same shrinkage allowances as used inthe construction of the pattern. In addition to light alloy castings of aluminum and magnesium, other metals having pouring temperatures as high as l700 Fahr. may be cast in accordance with the invention. Of course, in such cases it is necessary to select glass composition for the coring material such as will withstand the pouring temperature of the metal being cast. Also the glass coring material should retain its predetermined design shape and it should be possible to corrode the coring material by a selective reagent without appreciable corrosion of the metal of the casting. Borosilicate glass having a typical composition such as SO2-80%; B2O3-l4%; Na2O-4%; Al2O3-2% is preferred in the glass cores since in addition to the above properties it is characterized by a relatively low coefficient of thermal expansion and a high resistance tothermal shock. Accordingly, the precisionl which is obtained in the core position and alignment and the high degree of dimensional accuracy, as regards the cored passageways, is directly due to these characteristics' in the glass coring material as they are exhibited when in combination with light weight metals such as alloys of aluminum and magnesium.

The invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings, as various other forms of the device will of course be apparent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. In a device for producing aluminum or magnesium alloy castings of the type having passageways formed therein, the combination with a pattern of the article to be cast the dimensions of which exceed those of the article by the normal shrinkage allowances, of a conventional rnold having a rnold cavity therein formed by said pattern, a core Within the mold cavity for forming the passageways within the cast article, said core comprising an assembly of tubular elements of borosilicate glass and said core having a position within the mold cavity for the proper location of the passageways, the dimensions Afor the size, shape and conguration of the core and the dimensions for the proper positioning of the core within the mold comprising the actual dimensions for the particular article to be cast expanded by the same shrinkage allowances as employed for the pattern.

2. In a device for producing aluminum or magnesium castings of the type having passageways therein, in combination, a conventional mold having a mold cavity therein, and said mold having openings leading to the mold cavity providing a pouring gate and a riser respectively, a core of borosilicate glass positioned within the mold cavity, said glass core having a size, shape and configuration corresponding to those of the desired passageways and said core having a position within the mold cavity for the proper location of ythe passageways, the dimensions of the core and the dimensions for the proper positioning of the core within the mold comprising the actual dimensions for the particular article to be cast corrected only to compensate for the natural contraction of the casting, the said pouring gate and riser openings being located a predetermined distance from the glass core to produce a casting to specied quality requirements.

3. A method of producing a cast metallic article characterized by having intricate and complex passageways therein, the steps which include preparing a mold by using a pattern of the article to be cast, the dimensions of which exceed those of the article by the normal shrinkage allowances, shaping a tube of borosilicate glass to form a core having the size, shape and congurations as desired for the passageways, positioning said core within the mold in the proper location as required for the passageways, the dimensions for the size, shape and configuration of the core and the dimensions for the proper positioning of the core within the mold comprising the actual dimensions for the particular article to be cast expanded by the same shrinkage allowances as employed for the pattern, pouring molten metal in the mold and permitting the metal to solidify, said metal being selected from the group consisting of aluminum and magnesium, removing the casting from the mold, and inally removing the glass core from the casting by flowing a chemical reagent through the same capable of corroding the glass core but which is unreactive to the metal of the casting.

References Cited in the ile of this patent UNITED STATES PATENTS 2,205,327 Williams June 18, 1940 l2,504,879 Brazil Dec. 15, 1942 2,362,875 Zahn Nov. 14, 1944 2,373,405 LOWit Apr. 10, 1945 2,494,403 NeS et al. Ian. l0, 1950 2,679,669 Kempa .Tune 1, 1954 OTHER REFERENCES Iron Age, April 12, 1951, pages 107 to 109.

Claims

1. IN A DEVICE FOR PRODUCING ALUMINUM OR MAGNESIUM ALLOY CASTING OF THE TYPE HAVING PASSAGEWAY FORMED THEREIN, THE COMBINATION WITH A PATTERN OF THE ARTICLE TO BE CAST THE DIMENSIONS OF WHICH EXCEED THOSE OF THE ARTICLE BY THE NORMAL SHRINKAGE ALLOWANCES, OF A CONVENTIONAL MOLD HAVING A MOLD CAVITY THEREIN FORMED BY SAID PATTERN, A CORE WITHIN THE MOLD CAVITY FOR FORMING THE PASSAGEWAY WITHIN THE CAST ARTICLE, SAID CORE COMPRISING AN ESSEMBLY OF TUBULAR ELEMENTS OF BOROSILICATE GLASS AND SAID CORE HAVING A POSITION WITHIN THE MOLD CAVITY FOR THE PROPER LOCATION OF THE PASSAGEWAYS, THE DIMENSIONS FOR THE SIZE, SHAPE AND CONFIGURATION OF THE CORE AND THE DIMENSIONS FOR THE PROPER POSITIONING OF THE CORE WITHIN MOLD COMPRISING THE ACTURAL DIMENSIONS FOR THE PARTICULAR ARTICLE TO BE CAST EXPANDED BY THE SAME SHRINKAGE ALLOWANCES AS EMPLOYED FOR THE PATTERN.