US3708285A

US3708285A - Apparatus for and method of de-waxing,presintering and sintering powdered metal compacts

Info

Publication number: US3708285A
Application number: US00106383A
Authority: US
Inventors: G Scheyer
Original assignee: Adamas Carbide Corp
Current assignee: Hertel Cutting Technologies Inc
Priority date: 1971-01-14
Filing date: 1971-01-14
Publication date: 1973-01-02
Anticipated expiration: 1990-01-02

Abstract

IN THIS APPARATUS A DE-WAXING OPERATION IS PERFORMED IN HYDROGEN, AND THE SAME VESSEL IS USED FOR VACUUM SINTERING WITHOUT MOVING OF THE PART TO BE HEAT TREATED, AND IN ONE CONTINUOUS OPERATION.

Description

Jan. 2, 1973 SCHEYER 3,708,285

APPARATUS FOR AND METHOD OF DE-WAXING, PRESINTERING AND SINTERING POWDERED METAL COMPACTS Original Filed July 25, 1969 3 Sheets-Sheet 1 60 FIG. I 69 DRAIN INVENTOR.

GERARD SCHEYER Jan. 2, 1973 G. SCHEYER 3,708,285

APPARATUS FOR AND METHOD OF DE-WAXING, PRESINTERING AND SINTERING POWDERED METAL COMPACTS Original Filed July 25, 1969 3 Sheets-Sheet z :IZ -l JI'; INVENTOR. GERARD SCHEYER 95 94 ATTGRNEX 3,708,285 PRESINTERING 3 Sheets-Sheet 3 G. SCHEYER POWDERED METAL COMPACTS Jan. 2, 1973 APPARATUS FOR AND METHOD OF DE-WAXING AND SINTERING Original Filed July 25, 1969 aten 3,7@8,Z85 Patented Jan. 2, 1973 3,708,285 APPARATUS FOR AND METHOD OF DE-WAXING, PRESINTERING AND SIN'I'ERING POWDERED METAL COMPACTS Gerard Scheyer, Morris Plains, N..I., assignor to Adamas Carbide Corporation, Kenilworth, NJ.

Original application July 25, 1969, Ser. No. 844,972. Divided and this application Jan. 14, 1971, Ser. No. 106,383

Int. Cl. 1322f 9/00; C22c 29/00 US. Cl. 75-221 11 Claims ABSTRACT OF THE DISCLOSURE In this apparatus a de-waxing operation is performed in hydrogen, and the same vessel is used for vacuum sintering without moving of the part to be heat treated, and in one continuous operation.

This application is a division of my copending application Ser. No. 844,972 filed July 25, 1969 now US. Pat. No. 3,654,374.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to apparatus for and process of heat treating metal powders such as tungsten carbide that have been compacted cold and which contain a paralfin lubricant or binder, so that the lubricants or binder, are volatilized and removed and sintered bring the compacts to final hardness.

(2) Description of the prior art Heretofore the time cycles involved were such that the compacts went through the preheat, heat and cool-down processes in one furnace, and at room temperature, were thereafter transferred into a sintering furnace for the sintering cycle.

SUMMARY OF THE INVENTION An object of this invention is to provide a highly improved apparatus of the character described in which the de-waxing in hydrogen and sintering in vacuum is combined in a single vessel without transfer of the compact from the vessel.

Another object of this invention is to provide a highly improved process of the character described comprising placing compacts in a pot which is placed inside of a chamber; feeding hydrogen to the pot and feeding argon to the chamber; applying heat to the chamber so that the Waxes in the compacts are volatilized and carried off through a removable graphite chimney communicating with the pot, the argon protecting the graphite components from oxidizing and excluding the air, then flushing out the hydrogen from the pot with argon, removing the chimney, placing a sight glass over the chimney opening, stopping all the gas flow and pumping out all gas from the chamber and pot to produce a vacuum and bringing up the heat to sinter the compacts in vacuum.

Yet another object of this invention is to provide in apparatus of the character described, a highly improved cooled port through which the graphite chimney passes, to keep the graphite cool and stop it from oxidizing, and under vacuum operation when the graphite chimney has been removed and a sight glass has been installed, to prevent clouding up of the sight glass by preventing condensible vapors to settle on the sight glass.

Still another object of this invention is to provide a relatively inexpensive apparatus of the character described which shall be economical to operate and which shall yet be practical and efficient to a high degree.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

The invention accordingly consists in the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter described, and of which the scope of invention will be indicated in the following claims. The invention also consists in steps of a process hereinafter described.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical axial cross-sectional view of apparatus embodying the invention and showing the position of the parts during the de-waxing operation;

FIG. 2 is a cross-sectional view taken on line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 1;

FIG. 4 is a vertical cross-sectional view of the upper portion of the apparatus shown in FIG. 1 with the graphite chimney removed, the sight glass mounted on the cooled port and the swinging graphite sight hole disc or plate moved to center sight hole with the hole in the lid of the inner part; and

FIG. 5 is a piping diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the drawing, designates apparatus embodying the invention. Said apparatus comprises an outer container 11 having an outer cylindrical wall 12 and a circular bottom wall 13 formed with a central hole 14. Within said container 11 is a circular inner bottom wall 15 spaced above wall 13. Mounted on wall 15 is an inner cylindrical wall 16. Between

walls

12, 16 and 13, 15 is a water jacket 17 closed at its upepr end by a ring 18. A water inlet pipe 19 leads to the upper end of the jacket 17.

Attached to the underside of bottom wall 13 is a pipe 20 extending downwardly and closed by a plug 21 having a central opening 22. Pipe 20 is provided with an outlet drain pipe 23.

Extending upwardly through center hole 22 of plug 21 is a stainless steel pipe 24 which passes through a central opening 25 in wall 15 and thereabove.

The pipe 24 extends below plug 21 and attached to its lower end is a T-fitting 26 having branches to which

pipes

27, 28 are attached. Pipe 24 is welded to wall 15 as at 29.

On top of wall 15 is a stool piece or base 30 having a central opening 31 through which pipe 24 passes upwardly. Said base 30 has an outer upwardly extending flange 32. On base 30 is a cylindrical tube 33. The upper end of pipe 24 is located below the level of the upper end of tube 33. A ceramic tube 34 fits onto pipe 24 and rests on the base 30. The upper end of tube 34 is located just below the upper end of tube 24. Between pipe 34 and tube 33 are vertical, circular graphite felt layers 35. The layers 35 extend to a height just above the upper end of ceramic pipe 34 and rest on base 30. Mounted on the upper ends of layers 33 are circular discs 36 of graphite felt. Said discs form multi-layers and are disposed below the upper end of tube 33, and are formed with a central hole 37. The pipe 24 reaches said central hole 37.

Mounted on top of tube 33 is a pot 40 having an outer cylindrical wall 41 and a bottom wall 42 grooved at the periphery of its underside, as at 42, to receive the upper end of tube 33. On top of pot 40 is a cover disc 43 formed with a central opening 44 at the center of an upwardly extending boss 45 formed with an outer downwardly divergent frusto-conical surface 46. The tube 33, pot 40 and lid 43 are of graphite.

Extending through

walls

12, 16 and the water jacket 17 is a horizontal pipe 50, the functions of which will be explained hereinafter. Also passing through

walls

12, 16 and the water jacket 17 are three, equiangularly spaced, horizontal radiating tubes 51, the purpose of which will be hereinafter explained.

On top of

walls

12, 16 is a top closure 52 for the container 11. Said closure 52 comprises a circular wall 53 mounted on ring 18 and formed with a central opening 54, and with an offset opening 55. Fitted onto wall 53 is a water jacket forming member 56 comprising a top wall 57 from which a cylindrical flange 58 extends downwardly contacting and attached to the periphery of wall 53, and attached at its lower end edge to the ring 18. Wall 57 has an opening 57a aligned with opening 55. Between

walls

53 and 57 is formed a water jacket 60. Extending from flange 58 is a water drain pipe 61. Top wall 57 has a central hole 62 aligned with opening 54. Extending through

openings

54, 62 is a short vertical pipe 63 extending from the underside of wall 53 to above wall 57. Pipe 63 is sealed to walls 5.3, 57.

At the upper end of pipe 63 is a pipe 64 having an inner diameter same as pipe 63, and an outer upwardly divergent frusto-conical surface 65.

At the upper end of pipe 64 is a flange 66 having a central hole 67 which may be of an inner diameter somewhat less than the inner diameter of

pipes

63, 64. Flange 66 has bolt holes 68.

Mounted on flange 66 is a cooled port 69 comprising a lower flange 70 having bolt holes 71 registering with bolt holes 68 to receive attaching bolts. Welded to the flange 70 are inner and outer

concentric tubes

73, 74, respectively forming a water jacket 75 therebetween. Welded to the upper end of said

tubes

73, 74 is an upper flange 76.

Extending from the lower end of tube 74 is a Water inlet pipe 78. Attached to the upper end of tube 74 is a nipple 79. Surrounding the outer tube 74 is a tube of rubber or other heat insulating material. Outlet nipple 79 is connected by pipe 81 to an inlet nipple 82 leading to water jacket 60.

Mounted on boss 46 of lid or cover 43 is a graphite chimney 85. The lower end of chimney 85 has an internal beveled surface 86 resting on conical surface 46. Said chimney 85 passes upwardly through

pipes

63, 64 and through the cooled port 69 and thereabove. A thermocouple 86a passes down through graphite pipe 85 and opening 44 into the pot 40. The opening 44 is of greater diameter than the thermo-couple 86a.

Disposed within the container 11 is an insulating chamber 90. Said chamber 90 comprises a cylindrical wall 91 surrounding the pot 40 and comprising an outer perforated stainless steel cage 92 with graphite felt layers 93 at its inside attached to said cage by moly clips 94 which pass through holes 95 in the cage 92. Any other suitable attaching means may be employed.

At the lower end of cage 92 and attached thereto, is a circular horizontal perforated stainless steel disc 96 formed with an opening 97 through which tube 33 passes and which is located above base 30. On disc 96 are flat layers 99 of graphite felt.

At the upper end of cage 92 is a perforated stainless steel disc 100 disposed above

pipes

50, 51 and located below wall 53 and formed with a central opening 101 through which graphite chimney 85 passes. Attached to the underside of disc 100 are layers 102 of graphite felt. These may be attached by moly clips or in any other suitable manner.

Extending through pipes 51 are electric heating elements 104. Said heating elements pass through openings 104a in chamber 90. Openings 104a are larger than the heating elements. Hung from these heating elements and located in the chamber, are heating units 105 such as made by C. I. Hayes Inc. of Cranston, R1. for electric heat treating vacuum furnaces. The units 105 comprise graphite cloth pieces 106 to the lower ends of which, arcuate weighted members 107 are attached.

Extending through

openings

55 and 57a of

walls

53, 57 of member 52, is a vertical tubular bearing 110. Extending through said bearing 110 is a vertical axle 111 of a crank member 112. At the upper end of axle 111 is a radial handle 113. Fixed to the lower end of axle 111 is a plate 114 of somewhat elliptical shape. In FIGS. 1 and 2, the plate 114 is offset from opening 54. Plate 114 comprises a top layer 114a of metal such as Inconel 600 and four layers 114b of graphite felt cemented to layer 114a and to each other by graphite cement. Plate 114 has a through hole 115 smaller than but centralized with respect to pipe 63 in the position of FIG. 4 (with the graphite chimney 85 and the thermo-couple 86a removed).

Piping for supplying gases to the furnace and for creating vacuum is illustrated in FIG. 5. As shown, pipe 24 is connected to

pipes

27, 28. Pipe 27 is connected through a hydrogen solenoid valve (to control flow of hydrogen to the pot 40), to pipe 121 in which is interposed a hydrogen flow meter 122 (to measure flow of hydrogen to pot 40). Pipe 122 passes to a hydrogen shut off valve 123 (to shut off flow of hydrogen to pot 40), to pipe 124 which leads to a hydrogen supply. Instead of pure hydrogen, dissociated ammonia may be used. The dissociated ammonia comprises about 75% hydrogen and about 25% nitrogen.

Pipe 27 is connected through an argon solenoid valve 125 (to control flow of argon to pot 40), to pipe 126 connected to an argon flow meter 127 (to measure flow of argon to pct 40), which in turn is connected to pipe 128. Pipe 128 connects to an argon shut off valve 129 (to shut 01f flow of argon to pot 40) which is connected to pipe 130 connected to pipe 131 leading to a supply of argon.

Pipe or port 50 is connected through pipe 132 to a helium cool down valve 135 which in turn is connected by pipe 136 to helium supply 137.

Pipe 50 is connected by pipe 138 to pipe 139 connected to an argon bleed valve 140, which in turn is connected through pipe 141 to the argon supply pipe 131. Pipe 139 is also connected to pipe 142 which connects to an argon solenoid valve 144. Valve 144 connects to pipe 145 which connects to argon valve 147. Valve 147 connects to pipe 148 which connects to an argon flow meter 149. Said meter 149 connects to pipe 150 which connects to

pipes

141, 131. An argon pressure switch 152 connects through pipe 153 to said pipe 150.

Pipe 138 connects to a pipe 154 which connects to a high vacuum valve 155. Valve 155 connects to pipe 156 which connects to a booster pump 157. Said booster pump connects through pipe 158 to a pipe 159. Pipe 159 connects to a foreline valve 160 which connects through pipe 161 to a pipe 162. Pipe 162 connects to a rough line valve 163 to a pipe 164 which connects to

pipes

138, 154.

Pipes

158, 159 connect through pipe 165 to a hold line valve 166. Said valve 166 is connected to pipe 167 which connects to solenoid valve 168. Said valve 168 is connected through pipe 169 to a holding pump 170.

Pipes 161, 162 are connected through pipe 171 to a mechanical pump 172.

The compacts or parts to be heat treated are placed on pans 181 which are stacked in spaced relation in the pot 40 by means of spacers 182. The pans 181 have center holes 183 which are aligned with hole 44.

The pans 181 with the parts 180 thereon may be stacked in pot 40 to the top.

At the beginning, the graphite chimney and thermocouple are in place as shown in FIG. 1. Hydrogen is flowed through pipe 27 to pipe 24, but supply of argon to pipe 24 is shut off. Argon is supplied to port or pipe 50 at the same time.

The metal powders (tungsten carbide) are compacted as usual, cold, in order to make a part out of them. As the press friction is very great, the metal contains a lubricant or binder such as paratfin.

Heretofore, a pre-sintering was performed in either a hydrogen furnace or a vacuum furnace. The sintering process was also performed in a hydrogen 'furnace' or a vacuum furnace. However, the part first went entirely through the pre-sintering cycle including pre-heat, heat, and cool down, and when it cooled to room temperature, it was transferred to a sintering furnace for the sintering cycle. It was difficult to get rid of all the waxes which were trapped.

In accordance with the present invention the de-waxing in hydrogen and sintering in vacuum is accomplished in the single vessel without transfer.

There is also on the market a furnace which heat treats compacts in a vessel with various chambers, done in a vacuum chamber, but the compact has to be moved from one area to another to perform the various functions.

In the present invention, an atmospheric de-waxing operation is performed in hydrogen, and the same vessel is used for vacuum sintering without moving the part to be heat treated and in one continuous operation.

The cycle of the operation of the apparatus described is as follows: The chamber 90 is filled with argon. The argon enters container 11 through pipe or port 50 and passes through openings 104a into chamber 90. The inner pot 40 is filled with hydrogen. As the temperature increases, the parts Will be de-waxed. The waxes will volatilize and pass up to the atmosphere through the graphite chimney 85. The argon protects the graphite components from oxidizing by excluding the air. The argon pressure is heavier than air and protects the elements.

The hydrogen burning at the top of the graphite chimney thereby burns the volatilized waxes. No air can mix so that the hydrogen burns and puts the Wax vapors into the atmosphere. The de-waxing is carried out at about 400 C. The hydrogen prevents oxidation of the compacts.

The liberated wax would break down if it contacted the heating elements. With the present apparatus this is avoided by keeping the waxes separate so that they cannot reach the heating elements.

When temperature has been reached where all waxes have been volatilized, the supply of hydrogen to the pot is shut off and argon is flowed into the pot. The flushed out hydrogen burns at the top.

Argon is now inside of the pot and outside of the pot, and the temperature is still at 400 C. When the hydrogen fiame goes out we know that argon is in the pot.

The graphite tube 85 and the thermo-couple 86a are now removed through the water cooled port 69, and a sight glass 190 will be placed over the port (FIG. 4), with an O-ring 191, placed between the sight glass and the upper surface of flange 76. Then all argon fiow will be stopped through

pipes

50 and 28.

The vacuum system will then be started and argon will be pumped out or exhausted from the chamber and pot. A vacuum suitable for sintering the compact will be achieved by means of the mechanical pump 172 and booster pump 157, the holding pump 170 being merely used to protect the booster pump.

The electric input to the heating elements is increased when the prescribed vacuum pressure has been achieved. At about 750 the compacts are presintered and at about 1450" C. the compacts are sintered. The presintering is accomplished as the temperature rises from the dewaxing temperature to the sintering temperature. There is no cool-down between presintering and sintering. It is not necessary because the parts are not handled between dewaxing and sintering.

The flow of cooling water in jacket 75 and the provision of the rubber heat insulating tube on the tube 74 keep the port 69 cool. The condensible gases flowing up are attracted to the inside surface of tube 73 and keeps the sight glass from clouding up.

Thus the cooled port has two functions.

(1) It keeps the graphite chimney cool and stops it *from' oxidizing (while the 'chimney is'in place); and" (2) Under vacuum operation, when the graphite chimney has been removed, and the sight glass has been installed, the sight glass is prevented from clouding up by preventing condensible vapors from settling on the sight glass and clouding it thereby preventing actual temperature reading.

The operator looking down through the sight glass and through opening 183 in pans 181 can observe the color to judge the temperature.

After sintering is completed, and the heating units turned off, the compacts may be cooled by supplying helium to the pipe 50 from the helium supply 137.

It will thus be seen that there is provided an article in which the several objects of this invention are achieved, and which is well adapted to meet the conditions of practical use.

As possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings, is to be interpreted as illustrative only.

I claim:

1. A process for treating powder metal compacts comprising placing the compacts in a pot open to the atmosphere and surrounded by a chamber, flowing a hydrogen comprising gas through the pot to the atmosphere, and an inert gas to the chamber, heating the pot and burning the hydrogen comprising gas to the atmosphere to dewax the compacts, then flushing out the hydrogen comprising gas from the pot to the atmosphere with an inert gas flowed into the pot, then pumping out the inert gases from the pot and from the chamber by creating vacuum therein, and increasing the heat in the chamber to sinter the compacts.

2. The process of claim 1, wherein the pot is closed to the atmosphere and opened to the chamber after the hydrogen is flushed out of the pot to the atmosphere.

3. A process for treating a powdered metal compact, said compact containing a volatilizable wax, which process comprises placing the compact into a pot having a passage to the air, supplying a flow of a non-oxidizing gas to the pot and out the passage to exclude air from the pot, heating the pot to a temperature to volatilize said wax from said compact and said gas causing the volatilized wax to fiow out through said passage and burn in the air, said gas continuing to exclude air from the pot to prevent oxidizing of the compact during dewaxing of the compact, creating a vacuum in the pot, and heating the pot to a temperature to sinter the compact in vacuum, without having to remove the compact from the pot.

4. The process of claim 3, wherein the temperature is raised to about 400 C. in the pot during de-waxing and is raised to about 1450 C. for the sintering operation.

5. The process of claim 3, wherein the gas is flushed out of the pot by shutting off supply thereof to the pot and then supplying an inert gas to the pot before creating vacuum to remove the inert gas from said pot.

6. The process of claim 3, then shutting off the heat,

ceasing creation of vacuum and cooling the pot by introducing helium into said pot.

7. The combination of claim wherein said inert gas comprises argon.

8. The process of claim 3, wherein said non-oxidizing gas is a gas comprising hydrogen.

9. The process of claim 8, wherein said gas comprising hydrogen is dissociated ammonia.

10. The process of claim 8, which further comprises burning the hydrogen in the air together with burning of said volatilized Waxes.

11. A process for heat treating powdered metal compacts comprising de-waxing the compacts in a vessel which opens to the atmosphere by flowing hydrogen comprising gas into the vessel and heating the vessel to burn the gas in the atmosphere, then flushing out the'hydrogen comprising gas from the vessel by shutting ofi flow of said hydrogen comprising gas to said vessel, and flowing an inert gas into said vessel, then removing said inert compacts in vacuum without removing the compacts from said vessel.

References Cited UNITED STATES PATENTS 2,363,575 11/1944 De Lamatter et a1. 75--204 X 2,205,386 6/1940 Balke et a1. 75-221 X 2,185,410 1/1940 Lederer 75221 X FOREIGN PATENTS 1,005,179 9/ 1965 Great Britain 75221 OTHER REFERENCES Schwarzkopf, P. et al., Cemented Carbides, MacMillan, 1960, pp. 38-9.

CARL D. QUARFORTH, Primary Examiner R. E. SCHAFER, Assistant Examiner US. Cl. X.R.