US3731650A

US3731650A - Gas distributor for casting mold manufacture

Info

Publication number: US3731650A
Application number: US00195284A
Authority: US
Inventors: W Schweikert; J Mosier
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1971-11-03
Filing date: 1971-11-03
Publication date: 1973-05-08
Anticipated expiration: 1990-05-08

Abstract

A gas distributor for use in a mold cup and main sprue of a casting mold to be coated internally with a pyrolytic coating includes a gas receiving and distributing nozzle and a main sprue conduit. The nozzle delivers gas to the cup through a plurality of discharge holes and the conduit delivers gas to the base of the main sprue. Hole outlets deliver such gas angularly along the cup toward the main sprue to avoid turbulent flow.

Description

United States Patent 1191 11 1 3,731,650

Schweikert et al. 1 May 8, 1973 54 GAS DISTRIBUTOR FOR CASTING 1,356,715 10/1920 l-lachmann ..1 18/48 x MOLD MANUFACTURE 2,586,348 2/1952 Kuebler ..118/48 lnveaiais'ywimar '11. schwe'iiea; "3611'; s.

Me o 9 Gin/@93 6 Qh Q Assignee: General Electric Company, Cincinnati, Ohio Filed: Nov. 3, 1971 Appl. No.: 195,284

u.s. c1 ..118/48, 239/543 111:. c1 ..C23 l 3 0 FieldofSearch T1 18/47-49.5; 117/106- 107.2; 239/539, 543

References Cited UNITED STATES PATENTS 3/1920 Hachmann ..l l8/48 X Primary Examiner-Morris Kaplan Attorney-Derek P. Lawrence et a1.

[57 ABSTRACT A gas distributor for use in a mold cup and main sprue of a casting mold to be coated internally with a pyrolytic coating includes a gas receiving and distributing nozzle and a main sprue conduit. The nozzle delivers gas to the cup through a plurality of discharge holes and the conduit delivers gas to the base of the main sprue. Hole outlets deliver such gas angularly along the cup toward the main sprue to avoid turbulent flow.

1 Claim, 1 Drawing Figure PAIENIEBH 3,731,650

INVENTORSJ 6'41 FZWV ,WILBUR H. SCHWEIKERT JOMN S. MOSIER ,4 770EMEY- GAS DISTRIBUTOR FOR CASTING MOLD MANUFACTURE BACKGROUND OF THE INVENTION The high chemical reactivity between molten metals found in Group IV b of the Periodic Table of Elements with refractory material generally used in precision casting molds has resulted in the use of such materials as graphite as a mold material or as a barrier material within the mold. One method for making a mold suitable for use in casting of titanium articles involves the deposition of a pyrolytic coating, one example of which is graphite, on the inner walls of such a mold. Such pyrolytic graphite coating method and the resulting mold is described in U.S. Pat. No. 3,284,862 Schweikert, issued Nov. 15, 1966 and assigned to the assignee of the present invention.

One problem which has been recognized in the manufacture of such a mold is the proper introduction and application of a gas from which the pyrolytic coating is produced. Such gas is first introduced on walls of the pouring cup and main sprue which first receive molten metal and on which a heavier coating generally is necessary because of washing by the molten metal. In one example, under certain conditions, it was found that either blistering of pyrolytic graphite occurred in such areas or pyrolytic graphite was not properly formed due to turbulent gas flow or regions of gas stag nation.

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide, for use in the apparatus for providing a pyrolytic coating on internal walls of a casting mold, a gas distributor for the mold cup and main sprue to avoid turbulent flow and gas stagnation in those areas during generation of the pyrolytic coating.

Another object is to provide apparatus including such a distributor to hold both the distributor and the mold during processing.

These and other objects and advantages will be more clearly understood from the following detailed description, the examples and the drawing, all of which are meant to be representative of rather than limiting on the scope of the present invention.

Briefly, the present invention, in one form, provides, in apparatus for providing a pyrolytic coating on internal walls of the casting mold, a gas distributor for use in a mold cup and main sprue connected with the cup. The gas distributor comprises a gas receiving and distributing nozzle and a main sprue conduit. The gas receiving and distributing nozzle includes a gas inlet and a conduit port which communicates with a conduit inlet. Also included is a nozzle wall, the outer surface of which is shaped generally to conform with the shape of the cup and which converges toward the main sprue conduit. Through the nozzle wall are a plurality of gas discharge holes the outlets of which direct the gas angularly along the cup in the direction of the main sprue in order to avoid turbulent flow and gas stagnation.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a sectional, partially diagrammatic view of the gas distributor of the present invention positioned within a casting mold for provision of a pyrolytic coating on the internal walls of the mold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Precision casting molds of refractory materials have long been produced by the well known investment casting technique sometimes referred to as the lost wax process. For the manufacture of precision cast parts, such as those made of Ti or its alloys, it has been recognized that the interposition of certain pyrolytic coatings between the refractory material and the metal to be cast into the mold avoids reaction between the mold and the metal. In addition, use of a pyrolytic coating reduces contamination of the metal with coating material.

In practical casting manufacture, such precision casting molds are made to produce a plurality of articles in a single mold. Such a mold includes a pouring cup into which molten metal is first poured. The molten metal then passes into a main sprue or passageway from which it is passed into various other secondary passages which feed molten metal to that portion of the mold which is to produce the article. Thus, it is important that the pouring cup and main sprue be able to withstand washing of the molten metal in order to avoid reaction with the refractory material of which the mold walls are made.

It has been found that the present invention, positioned in the drawing in use in the generation of a pyrolytic coating on the walls of a precision casting ceramic mold, avoids the problems of coating blistering and powdering such as sooting in the case of pyrolytic graphite. In the drawing, the gas distributor of the present invention includes a gas receiving and distributing nozzle shown generally at 10 and preferably of graphite and a main sprue conduit shown generally at 12 and preferably of ceramic material such as dense aluminum oxide. The gas receiving and distributing nozzle has a gas inlet 14 and a conduit port 16 communicating with conduit inlet 18. The gas receiving and distributing nozzle 10 also includes a nozzle wall 20 having an outer surface 22 shaped generally to conform with the shape of mold pouring cup 24 and converging generally toward conduit port 16. A plurality of gas discharge holes 28 extend through nozzle wall 20. Each discharge hole has a hole outlet 30 which directs gas entering nozzle 10 through gas inlet 14 angularly toward the main sprue conduit 12 and along the cup in the direction of the main sprue 26.

The main sprue conduit 12 communicates with the gas receiving and distributing nozzle 10 at the distributing nozzle 's conduit port 16 and the main sprue conduit inlet 18. Gas received by the main sprue conduit is discharged through conduit outlet 32 generally toward main sprue base 34, thus avoiding gas stagnation in that region.

Gas discharged from the gas distributor of the present invention through gas discharge hole outlets 30 is directed in substantially laminar flow by outlets 30 along with surface of mold pouring cup 24 toward and into the interior of main sprue 26, toward main sprue base 34. In the area of the main sprue base, it mingles with gas discharged from conduit outlet 32 for distribution into other portions of the mold upon the walls of which the pyrolytic coating is to be deposited. For example, gas passes through secondary channels 36 into article mold cavity 38 in which the precision cast article is to be produced. The gas then is discharged through mold vents 40.

During processing of the mold to deposit a pyrolytic coating on its inner walls, the mold is placed in an ordinary heating enclosure (not shown), which can discharge gas emitted from mold vents 40. One such enclosure is shown in the above identified U.S. Pat. No. 3,284,862 as a graphite susceptor enclosing the mold. Surrounding the susceptor is an induction coil which, together with the susceptor, serves as a means to heat the mold and the gas through radiation. A graphite cover and a graphite base, shown partially in the drawing at 41, can be used to complete the enclosure.

Although the entire heated enclosure is not shown because of the variety of ways in which such heating can be accomplished, the drawing does show a graphite mold and nozzle holder 42 which rests within such'enclosure on base 41 and which is adapted to carry both the casting mold as well as the gas distributor of the present invention. Mold pouring cup lip 44 is located within holder first recess 46 to block gas discharged from outlets 30 from flowing around lip 44 and away from main sprue 26. In addition, nozzle wall rim portion 48 of nozzle wall 20 is located within holder second recess 50 to position outer surface 22 of nozzle wall 20 in proper spaced relationship with pouring cup 24. If desired, a sealing material 52, commonly used in the art, can be located in recess 46 and beneath holder 42 for additional sealing. Holder 42 includes a holder gas inlet 54 which cooperates with nozzle gas inlet 14 and base gas inlet 56 to allow passage of gas from a source, (not shown), into nozzle 10.

In one example, a ceramic shell mold having porous walls was made from commercially available materials by the lost wax process. After dewaxing, the mold was mounted on holder 42 on which had been mounted the gas distributor of the present invention, as shown in the drawing. The assembly thus provided was placed in a vacuum furnace apparatus, of the type described above, where it was heated in the range of l900 2200 F. During that time, acetylene gas was introduced through

inlets

54 and 56 into gas inlet 14 of mold through vents 40. The result was a continuous pyrolytic graphite coating on the internal walls of the mold without blistering or sooting on such critical surfaces as those of the pouring cup 24 and the main sprue base 34.

Thus, the present invention, which provides gas in laminar flow along critical internal wall surfaces of a mold on which a pyrolytic coating is to be'deposited, avoids blistering and sooting through controlled gas flow and elimination of gas stagnation. Although the present invention has been described in connection with specific examples and embodiments, it will be understood by those skilled in the art, the modifications such as in conditions, materials, configurations, etc. and other variations which can be made within the scope of the present invention.

What is claimed is:

1. In apparatus for providing a pyrolytic coating on internal walls of a casting mold through use of a gas, a gas distributor for use in a mold cup and main sprue connected with the cup, the gas distributor comprising:

a gas receiving and distributin nozzle- D a mam sprue conduit open a a conduit mlet and a conduct outlet;

the gas receiving and distributing nozzle including:

a. a gas inlet;

b. a conduit port communicating with the conduit inlet;

c. a nozzle wall having an outer surface shaped generally to conform with the shape of the cup and converging toward the conduit port; and

d. a plurality of gas discharge holes through the nozzle wall, each having a hole outlet which directs the gas angularly toward the main sprue conduit whereby gas is passed along the cup in the direction of the main sprue; and

a mold and nozzle holder including:

a. a holder first recess shaped to receive a mold pouring cup lip;

b. a holder second recess located radially inward from the holder first recess and shaped to receive the nozzle wall rim portion; and

c. the holder having a holder. gas inlet radially inward from the holder second recess.

4 18 I I it

Claims

1. In apparatus for providing a pyrolytic coating on internal walls of a casting mold through use of a gas, a gas distributor for use in a mold cup and main sprue connected with the cup, the gas distributor comprising: a gas receiving and distributing nozzle; a main sprue conduit open at a conduit inlet and a conduct outlet; the gas receiving and distributing nozzle including: a. a gas inlet; b. a conduit port communicating with the conduit inlet; c. a nozzle wall having an outer surface shaped generally to conform with the shape of the cup and converging toward the conduit port; and d. a plurality of gas discharge holes through the nozzle wall, each having a hole outlet which directs the gas angularly toward the main sprue conduit whereby gas is passed along the cup in the direction of the main sprue; and a mold and nozzle holder including: a. a holder first recess shaped to receive a mold pouring cup lip; b. a holder second recess located radially inward from the holder first recess and shaped to receive the nozzle wall rim portion; and c. the holder having a holder gas inlet radially inward from the holder second recess.