US3523570A - Method of press forming thin-walled cast iron parts - Google Patents

Description

United States Patent [72] Inventors Daniel Edward Groteke 1,942,578 1/1934 Stockfleth 29/149. Jeffersonville, 1nd. 1,998,516 4/1935 Monzer 1 249/176X James Alexander Stavrolakis, Louisville, 2,28 5 ,81 l 6/ l 942 Gay 164/77 Ky. 2,379,401 6/1945 Poulter 164/63 [21] Appl. No. 604,773 2,923,040 2/1960 Goodwin et a1 164/63 [22] Filed: Dec. 27,1966 2,991,518 7/1961 Schaefer 164/63 [45] Patented Aug. 11, 1970 2,371,703 3/1968 De Wilde... l64/98X continuation-in-part of Ser. No. 379,919, 1,473,246 1 1/1923 Montupet... 164/256 Filed July 2, 1964, now Pat. No. 3,318,370. 2,448,632 9/1948 Smith l64/254X [73] Assignee American Standard Inc. 3,287,769 1 1/1966 Hess et a1 l64/256X a Corp. ol'Delaware 2,847,739 8/1958 Sylvester.

[54] METHOD OF PRESS FORMING THIN- FOREIGN PATENTS WALLED CAST IRON PARTS g 11 clmmslwl'awmg 175,353 711953 Austria. 164/306 52 US. Cl 164/119, 3 4/1963 p 1154/3106 164/66, 136, 120, 320, 126, 306, 477,384 7/1915 France. 164/309 338349/781 161157 Primary Examiner .1. Spencer Overholser [51] Int. Cl B22d 27/14 Ass/Sm", Examiner v Rising [50] Field of Search 164/1 19; A;mmey she|d0n Parker and Tennes L Erstad 164/Slush Castmg D1gest; l64/306,285 U. S. Foreign; 164/77, 309; 164/119, 309 Foriegn; [64/136, 0-] ,300,000; 164/61, 62, 63, 65; 164/120 54/284 285 4 l64/RAM Digest 3 ABSTRACT: A process for press casting thin-walled articles is 321 64/1 13 u S5164 19; 164/255 disclosed in which the metal to be cast is maintained under a 258; 249/78 114,82 6157; 29/528 US; first pressureand in a molten state. The pressure is then in- 164/77; 64/254 253 661 320! creased to a second pressure allowing the molten metal to flow 338; 34/310, 308 through a confined path into a mold and allowed to solidify while maintainin a re ion of metal within said confined path [.56] References and in a molten state? The pressure is then decreased causing the UNITED STATES PATENTS molten metal to separate from the solidified metal to yielda cast metal article. Y

fllllllll 1 l ELECTRIC ELECTRIC RESISTANCE l RESISTANCE HEATERS HEAT ERS j MOLTEN IRON 1N AN INDUCTION FURNACE FIG.2

Sheet FURNACE IRON IN AN INDUCTION MOLTEN Patented Aug. 11, 1970 INDUCTION Sheet Patentd Aug. '11, 1970 I N AN FURNACE MOLTEN l RON Sheet of 4 FIG. 4

Patented Aug. 11, 19 70 METHOD OF PRESS FORMING THIN-WALLED CAST IRON PARTS This application is a continuation-inpart of U.S. Application 379,919 filed July 2, l964 now US. Patent No. 3,318,370 issued May 9, 1967.

This invention relates to a process for press forming thinwalled articles and more particularly to an automatic process of press forming thin-walled cast iron articles.

It is well known that the difficulty of obtaining acceptable castings increases as the cross-sectional area of the casting decreases. The occurrence of holes such as caused by misruns, slag, and sand, in thin-walled castings is frequent and serious, particularly when such castings are to be enameled, as in the case of sinks, bathtubs and the like.

The main object of this invention is to provide an automated process for formation of light, strong, uniform thin-walled fixtures which process produces castings requiring a minimum of secondary operations prior to enameling and with little or no scrap loss.

Various techniques have been suggested and tried in order to obtain satisfactory thin-walled castings. United States Patent 1,952,201 to F lammany et al., shows a process in which liquid metal is forced, by gas pressure from a retort to a mold. It has been found that this type of process can be modified in a manner such that the process can readily be automated, and can produce an article having a hole therein and which requires only a small amount of working in order to yield a finished article.

In accordance with the present invention, thin-walled, castiron articles are formed by first maintaining molten-metal under a pressure, and then increasing the pressure to a second pressure, thus causing the molten-metal to flow upwardly through a confined path, into a mold. Advantageously a quantity of molten-metal which exceeds the quantity of metal in the press-formed article, is forced in the female section of the mold and then the male section is lowered into the female section to form a mold cavity which will be heretofore referred to as mating-spaced contact. Thus, the molten-metal completely fills the mold cavity between the male and female sections.

Advantageously a first annular region of metal within the confined path is maintained in a molten state while a second annular region adjoining and above the first region cools as solidified.

Then the pressure is then decreased from the second pressure to the first pressure, thereby causing the liquid-level of the molten-metal to drop below the level of the second annular region of solidified metal and thus yielding an article having a formed opening.

These and other related objects, features and advantages of the present invention will be more fully understood as the description of the invention proceeds, particularly when taken together with the accompanying drawings in which;

FIGURE 1 is a vertical sectional elevation of an apparatus for carrying out the present invention, and shows a first stage of operation;

FIGURE 2 shows the apparatus of FIGURE l at a second stage;

FIGURE 3 shows a third stage of operation; and

FIGURE 4 shows a fourth stage of operation.

As a preferred embodiment of the invention there has been selected apparatus suitable for the casting of bathtubs or sinks. It should be understood, however, that the present invention is in no way limited to the casting, of such shapes.

Referring now to FIGURE 1 of the drawing, the apparatus of the invention comprises a male die 3 (cope) which is maneuvered, as for example, by means of a piston, such that at the start of any given cycle it is in open position and a female vdie (drag) mounted above a pressurized melting furnace 14 connected therewith by a snorkel tube 6 preferably made of a refractory alloy or compound. Furnace 14 has a gas-tight lid 19. An auxiliary heat source 7 surrounds the upper part of tube 6. This tube can be cooled if needed by passing water which enters a cooling coil at 8 and exits at 10. The diameter of snorkel tube 6 is such as to enable it to receive the core projection 11 on male die 3.

Provision is made to cool both the male and female dies by passing air, steam, or water through passages 13.

An inert gas which is non-oxidizing under the ambient conditions is maintained over the molten metal in the furnace. Suitable inert gases for the purposes of this invention include nitrogen, argon, helium, chlorine or carbon dioxide. Any means well known in the art can be used to convey the selected gas to the furnace.

At the start of any given forming cycle, the gas pressure (Pl) over the metal in the furnace is higher than the outside atmospheric pressure. This value is sufficient to keep a column of molten metal in the snorkel tube 6 above the heat source. The pressure then is increased to a value high enough to force metal up into the female die in an amount sufficient to give a full casting with minimal excess. This amount is denoted in the drawing by fill line 1 while the necessary pressure may be denoted by P2. The level of the fill metal and the volume of the overflow trap are balanced to insure that all overflow metal, after forming, is still connected to the casting by a parting line flash which is sheared from the finished casting in a secondary trimming operation. The level of the metal in the mold is controlled by the duration and value of the fill pressure. The desired height of the metal is a function of the volume of the overflow trap which is controlled by the design and size of the part being press formed.

While this prefill operation takes place by increasing the gas pressure, the male die may either be in position 2, which it has reached upon completion of the previous cycle (FIGURE 1), at a point just above the metal fill line or in the position shown in FIGURES 2, 3 and 4. However, if the latter position is used, the insulating value of the coating on the dies must be high enough to permit filling the casting before solidification occurs. To form the casting, the male die (cope) 3 is slowly brought into the female mold (drag) 2 as shown in FIGURE 2 to the extent that the central core projection 11 penetrates the central opening 16 in the female mold and displaces the molten metal to the shape defined by the dies when closed. solidification of the molten cast iron is controlled by means of the heating means 7, so that below line 30, the cast iron is in a molten state, and above line 30, it is in a solid state. The position of line 30 is critical to the extent that it must be above the lower surface 32 of the projection 11. The heating source must be located proximate the region of the liquidlevcl line 30, the exact position depending upon variables such as the heat output of the heating source 7, the heat capacity of the snorkel tube 6, particularly in its upper section 42, the degree to which the metal is being cooled, as well as the heat capacity of the metal. Obviously, it is critical that the heat source 7 is capable of preventing solidification from taking place below surface 32, and while permitting solidification to take place far enough below the top of opening 16 to yield an article having the desired dimensions.

As shown in FIGURE 3, the male core projection 11, in combination with the female cavity, or opening 16, forms an annular or toroidal region 33 in the solidified metal and a similar region 34 in the molten metal. The annular region in most applications would have concentric inner and outer peripheries. However, it is possible to employ any desiredconfiguration, or combination of configurations, as for example a square outer periphery (interior of the female mold) and a circular inner periphery (exterior of the male core projection).

As soon as solidification is complete, the pressure is restored to P1, to permit the level of the molten metal to fall to the level shown in FIGURE 4, and denoted by reference character 12 before opening the mold. The life of the snorkel tube is thus extended by minimizing thermal shock.

When the metal level has returned to the level indicated by 12, the male die is quickly retracted to position shown in FIGURE 1. The press-formed casting will then either remain in the female die or will adhere to the male die. This position can be controlled by regulating cycle timing, die temperatures, or the surface finish of the dies. For example, lengthening the time a mold remains closed lowers the temperature of the press-formed part and increases its shrinkage. The cast section then locks onto the cope side of the die assembly. The preferred method is to open the mold when the casting is between l750and 1500F. The casting remains in the drag side of the mold and is easily removed without any danger of cracking. Cycle time is a function of metal volume poured, cooling used, die temperatures, die draft angles, surface finish of the molds, etc.

The finished casting can be removed by ejection off the male die with ejection pins, by picking up the casting from the female mold with a conventional vacuum holder, or by the use of an expanding clamp on the inside surfaces of the cast part. Preferably the casting should be retracted from the mold before it has cooled below black heat.

All the die surfaces which are wet by the molten metal should be coated with either lampblack, or, preferably by a multilayer coating disclosed in United States Patent No. 3,266,107. The coating described in said patent consists of a base coating of a high conductivity, high ductility material used in the base layer, an inert refractory metal oxide and a plasma-sprayed overlayer of refractory oxide.

The apparatus of the invention may be automated by the use of an hydraulic system disclosed in Patent Application No. 379,919.

In successful demonstrations of the practice of the invention, the dies of the machine shown in FIG. I were maintained at a temperature of 700 to 800 F. and the metal pouring temperature between 2400 and 2750 F. However, this invention should not be considered as being restricted to these temperatures because the range is subject to die temperatures, coating thickness, wall thickness of casting, etc. The casting metal had the following composition: 3.70% total carbon, 2.40% silicon, 0.90% manganese, 0.08% sulpher, .50% phosphorous, balance iron. Castings were made with individual thicknesses of 0.020 to 0.125 inch. The surface appearance of all the cast shapes were excellent.

Having thus described and explained this invention and its mode of operation, it will be understood that numerous variations in the form and arrangement of parts shown and described may be made without departing from the nature and scope of the invention.

We claim:

1. The process of press-forming thin walled, cast-iron articles, comprising:

a) Maintaining molten cast iron in a confined path under a first pressure which is above atmospheric pressure;

b) increasing said pressure to a second pressure and causing molten cast iron to flow upwardly through said confined path into a mold comprising a male and female section;

causing said molten cast iron within the cavity between the male and female sections of said mold to solidify;

simultaneously with step c, maintaining a first annular region of metal within said confined path in a molten state and causing a second annular region adjoining and above said first region to cool and solidify; and

decreasing said pressure from said second pressure to said first pressure, thereby causing the liquid-level of said molten cast iron to drop below the level of said second annular region of solidified metal and yielding an article having a formed opening.

2. The process of press-forming thin-walled, cast-iron articles, comprising sequentially:

a) maintaining molten-metal in a melting furnace under a first pressure;

b) increasing said pressure to a second pressure and causing molten-metal to flow out of said furnace through a confined path, into the female section of a mold, the quantity of molten-metal which fills said mold exceeding the quantity of metal in the press-formed article;

c) lowering the male section of said mold into matingspaced contact with said female section, whereby molten-metal completely fills the mold cavity between said male and female sections.

3. The process of press-forming thin-walled, cast-iron articles, comprising (a) maintaining molten-metal under a first pressure;

(b) increasing said pressure to a second pressure and causing molten-metal to flow upwardly through a confined path, into the female section of a mold, the quantity of molten-metal which fills said mold exceeding the quantity of metal in the press-formed articles;

(c) lowering the male section of said mold into said female section to form a mold cavity between said male and female sections, whereby molten-metal completely fills said mold cavity;

(d) simultaneously with step c, maintaining a first annular region of metal within said confined path in a molten state and causing a second annular region adjoining and above said first region to cool and solidify; and

(e) decreasing said pressure from said second pressure to said first pressure, thereby causing the liquid-level of said molten-metal to drop below the level of said second annular region of solidified metal and yielding an article having a formed opening.

4. The process of Claim 3, wherein;

in step (d), said first and said second annular regions are formed by a section of said male mold projecting through a cavity in said female mold, and into said confined path;

5. The process of Claim 1, wherein;

in step (d), said first and said second annular regions are formed by a section of said male mold projecting through a cavity in said female mold, and into said confined path.

6. The process of Claim 4, wherein;

a coolant is circulated in contact with said male and female molds to cause solidification of molten-metal therein, while said molten-metal in said first annular region is heated in order to maintain said molten metal in the molten state.

7. The process of Claim 5, wherein; a coolant is circulated in contact with said male and female molds to cause solidification of molten-metal therein, while said molten-metal in said first annular region is heated in order to maintain said molten metal in the molten state.

8. The process of Claim 1, wherein; said female mold is heat-insulated and preheated to a temperature from about 400 to 1200 degrees F, prior to step (b).

9. The process of Claim 2, wherein, said female mold section is heat-insulated and preheated to a temperature from about 400 to 1200 degrees F prior to step (b).

10. The process of Claim 8, wherein;

said male mold section is heated prior to step (b), to a temperature from about 400 to 1200 degrees F, and said male mold section is separated from said female mold section after step (c) but while the solidified metal is at red heat.

11. The process of Claim 9, wherein;

said male mold section is heated prior to step (b), to a temperature from about 400 to 1200 degrees F, and said male mold section is separated from said female mold section after step (e) but while the solidified metal is at red heat.

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