US3252694A

US3252694A - Metal treating system

Info

Publication number: US3252694A
Application number: US279053A
Authority: US
Inventors: Ii Raymond L Davis
Original assignee: Leeds and Northrup Co
Current assignee: Leeds and Northrup Co
Priority date: 1963-05-09
Filing date: 1963-05-09
Publication date: 1966-05-24
Anticipated expiration: 1983-05-24
Also published as: GB1069531A

Description

May 24, 1966 R. DAVIS 11 METAL TREATING SYSTEM 2 Sheets-Sheet 1 Filed May 9, 1963 -F ilter May 24, 1966 R. L. DAVIS ll METAL TREATING SYSTEM 2 Sheets-Sheet 2 Filed May 9, 1965 FI/SI United States Patent 3,252,694 METAL TREATING SYSTEM Raymond L. Davis 111, Newtown Square, Pa., assignor to Leeds and Northrup Company, Philadelphia, Pa., a corporation of Pennsyivania Filed May 9, 1963, Ser. No. 279,053 13 Claims. (Cl. 2665) This invention relates to metal treating systems of the type in which metal work is disposed Within a work chamber of a furnace and is subjected to an elevated temperature with an atmosphere within the work chamber of desired character.

The present invention is applicable to metal treating furnaces of many kinds and in particular to those in which it is desired to control the carbon content of the work and to those where heat treating and annealing is desired in the presence of a carburizing atmosphere which assures the maintenance of the carbon content of the work at a predetermined value. With furnaces having work chambers of relatively large size, a number of problems arise, particularly in the need of a large volume of gas required for purging the Work chamber from undesirable gases and contaminants which may be present. These contaminants frequently take the form of foreign material which may have adhered to the work and which are eliminated as the temperature of the work chamber rises to the range of heat treatment or carburizing.

In order to purge the furnace of undesirable gases and contaminants, it is desirable to utilize a purge gas, i.e., a gas which will not react adversely with the work and which will not be detrimental to the finish or carbon content of the work and one which will not deposit soot.

In accordance with one form of the present invention there is provided a carburizing atmosphere generator of small size and which includes a catalyst which promotes oxidation of hydrocarbons and other carbonaceous com bustible gases. To this atmosphere generator there is supplied a mixture of air and a carburizing agent. The generator preferably is relatively long with a lower portion including a catalyst bed disposed within the work chamber and a portion of the generator extending outwardly of the Work chamber. In this manner there is provided a generally rising temperature gradient from the outer inlet to the generator to the outlet disposed downstream from the catalyst bed. In this manner the mixture of air and carburizing agent is elevated in temperature before arrival at the catalyst bed. During the early stages of elevation in temperature, aldehydes are produced from the hydrocarbons and these are further oxidized in a preferred reaction sequence by the catalyst which promotes oxidation of carbonaceous compounds. The resultant purge gas supplied in relatively large volume is effective in displacing from the work chamber undesirable gases and contaminants and in so doing fills the work chamber with protective gas.

Further, in accordance with the present invention, the protective gas which fills the work chamber is thereafter utilized in combination with the carburizing agent and in place of previously supplied air to produce the carburizing atmosphere within the work chamber.

For further objects and advantages of the invention and for details of an automatic system which carries out the foregoing steps, as well as providing additional features of novelty, reference is to be had to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 diagrammatically illustrates the invention as applied to a metal treating furnace;

FIG. 2 is a sectional view of the atmosphere generator of FIG. 1; and

3,252,694 Patented May 24, 1966 FIG. 3 is an elevation partly in section of a modified catalyst bed including heat insulation surrounding it.

Referring now to FIG. 1 the invention in a preferred form has been illustrated as applied to a furnace 10 having a work chamber 11 within which work is to be disposed for treatment and also having a vestibule 12 which may not always be present depending upon particular applications of the invention. Where the vestibule 12 is utilized, it will be preferred to have both a door 13 for the vestibule, as well as a door 14 for the work chamber 11. Though metal treating furnaces are available in a number of different designs, it will in general be desirable to provide a circulating fan 15 for the work chamber. This fan may be driven by any suitable means, such as a motor 16.

The furnace, in particular the work chamber 11, is provided with any suitable heating means, generally electrical heating resistors, not shown. Before loading the furnace with work, which normally rests on rails or other means within the furnace such as baskets disposed in spaced relation with the fan 15, the work chamber 11 is brought up to a relatively high temperature, as for example about 1200 F. to 1500" F. The preheating or elevation of temperature within the work chamber in the absence of the work is for protective purposes, both to guard against an explosive atmosphere within the work chamber and to assure a minimum time requirement in developing in the work chamber of a protective atmosphere.

Assuming now that the door 14 to the work chamber 11 is in its illustrated closed position, that the vestibule 12 is loaded with work, preparatory to transfer into work chamber 11, and that the work chamber 11 is being heated to elevate its temperature; as the temperature of the work chamber 11 rises, the output of a thermocouple 17 having its hot junction within the work chamber 11 rises and by means of any suitable measuring equipment such for example as a recorder 18, the temperature will be continuously indicated. When the temperature of work chamber 11 arrives within an initial selected range, say 1200 F., the recorder 18 operates through a mechanical connection 19 to close contacts 20. A line switch 21 will have theretofore been closed and hence as the chamber 11 arrives at the temperature of 1200 F. the contacts 20 will connect the line L to a supply line or conductor 22, a second supply line on conductor 23 likewise being connected to the other side L of the line.

As soon as

conductors

22 and 23 are energized it will be seen that a motor 24 is energized to drive a gas compressor 25 of the constant delivery type. Simultaneously, a relay 26 is energized through a circuit extending from line 22 by Way of conductor 27, a switch 28 shown in its lowermost position with the door 14 closed, a switch 29 operated by the door 13 to, and illustrated in, its upper position with the door 13 open, a conductor 30 and thence through the operating coil of relay 26 to the other control conductor 23. The relay 26 immediately opens its contacts 26a and closes its

contacts

26b, 26c and 26d. By reason of the closing of the contacts 260, the

operating coils

35a, 36a, 37a and 38a, respectively provided for control valves 35-38, are energized.

The energization of coil 35a opens the valve 35 for supply of a carburizing agent from a supply line 39 by way of valve 35 and a flow indicator or meter 40 to the valve 38. This valve 38, by the energization of its coil 38a, will have been rotated through in the direction of the arrow, thus to connect the outlet from the flow meter 40 to a line leading to a throttle valve 41 and thence through a check-valve 42 and a throttle valve 43 to the inlet of the gas compressor 25. A second throttle valve 44, located in a bypass around the compressor, is utilized to regulate the output of the compressor in terms of quantity of gases delivered per unit length of time.

By reason of the energization of coil 36a the valve 36 will be rotated through 90 in the direction of the arrow, thus to connect a line 45 to a throttling valve 46 connected in a supply line 47 open to atmosphere. The air drawn through line 47 flows through a filter 48, a flow indicator 49 and by way of a throttle valve 50 to the inlet of the compressor 25. It is in this manner that the carburizing agent and air are both supplied to the gas compressor 25. In that compressor they are thoroughly mixed together and flow as a stream to the valve 37. This valve, rotated through 90 by reason of the energization of its operating coil 37a, connects the output from the compressor 25 directly to a flow connection 51 to an atmosphere generator 52.

The details of the generator 52 are more fully illustrated in FIG. 2 and the generator will be described with considerable particularity in connection therewith. For present purposes, it is sufiicient to say that the atmosphere generator 52 has at its lower end a catalyst bed 53. This catalyst bed suitably supported within the generator 52 comprises a material which promotes oxidation of carbonaceous compounds. In the preferred form of the invention, the catalyst comprises a fine mesh screen of nickel, preferably spirally wound in a tight coil though quite porous in respect to flow of gases therethrough. It is here emphasized that fine wires of nickel as in the fine mesh screen provide an oxidation-promoting catalyst of high efficiency.

Heretofore, there has been difficulty in supporting a fine mesh wire screen for high temperature operation. However, in accordance with the present invention, a fine mesh screen of nickel has been entirely satisfactory and by reason of a number of features embodied in the present invention. Thus, for example, the diameter of the tube 52 is relatively small, the depth or height of the bed of the catalyst 53 is limited. By reason of these two considerations, the fine mesh nickel material is self supporting at high temperature and provides a relatively long life for the catalytic bed. The tube 52 is relatively long and provides a heated portion above the catalytic bed 53 and a portion extending outwardly of the wall of the furnace. In short, there is a rising temperature gradient from the outer inlet to which flow connection 51 extends towards the outlet located downstream of the catalyst "bed 53.

Remembering that the operating temperature range of the Work chamber 11 is above 1200 F., normally 1500" F. to 1700 F., it will be understood that the mixture of carburizing agent and air entering the generator 52 as a stream will be rapidly elevated in temperature. The rate of flow of this stream and the transfer of heat to the generator 52 are regulated so that as the gases enter into the warmer zones within the generator 52 aldehydes are produced before arrival at the catalyst bed. The aldehydes represent compounds resulting from the initial oxidation of the hydrocarbons. They are formed as their temperatures rises to about 1000 F. by reason of their reaction with the oxygen of the air in mixture therewith. The mixture of the air, the carburizing agent and the aldehydes then pass through that part of the generator 52 disposed within the work chamber 11. Accordingly, the mixture is rapidly elevated in temperature and immediately passes through catalyst bed 53. Oxidation reactions take place both in the region of rapid heating of the mixture, in the catalyst bed, and the reactions continue after discharge of the mixture into the furnace.

Preferably, there will be utilized a rich mixture of carburizing agent or fuel gas and air. Where the fuel gas supply by way of line 39 is natural gas, the ratio may be as high as 1 or even 1.2 to 1. The gas mixture, as it leaves the catalyst bed and enters the chamber 11, will have a composition which may be generally stated as comprising 39% nitrogen, 39% hydrogen, 19% carbon monoxide, 1% water vapor, about /2 carbon dioxide and from 1% to 2% of methane (CH Since the gas mixture entering the gas generator 52 comprises air in mixture with natural gas (largely including CH it will be seen that only a small percentage of the methane in the original mixture has escaped oxidation reactions in the gas generator. These oxidation reactions are exothermic. The heat release within the gas generator 52 and particularly in the region of the catalyst bed is quite high, to a degree which elevates the temperature of the gas generator 52 within the work chamber 11 well above (several hundred degrees) the ambient atmosphere assumed to be at least 1200 F. To preserve and enhance this high temperature operation of the catalyst bed, heat insulation may be provided in the region of the catalyst bed to prevent loss of heat to the furnace atmosphere. For example, in FIG. 3, the catalyst bed 53 has been shown as being enclosed by heat insulation 530, which may be provided by winding about the nickel mesh screen a plurality of turns of woven ceramic fibre available on the market under the trademark Fiberfrax. This heat-insulated catalyst bed is then inserted into the end of tube in place of the bed there illustrated.

The foregoing mixture of gases discharged from the gas generator 52 into the work chamber 11 is combustible and at the temperature of that chamber burns with a hot flame. It burns by reason of the presence in the furnace of oxygen and in burning combustion products are formed including carbon dioxide and water vapor. These products of combustion are very undesirable in the work chamber 11. The water vapor and the carbon dioxide react to produce undesired oxidation of the work and additionally are strong decarburizing agents. Since the work chamber 11 has not yet been loaded with work, however, their initial formation has no adverse effects.

Since the door 14 of the work chamber is closed, the available oxygen within the work chamber is limited even though there may always be limited ingress of air due to leakage. Accordingly, as the oxygen within the chamber 11 is depleted by the initial burning of the mixture of gases discharged from generator 52, carbon monoxide and hydrogen begin to show their presence in the furnace gases. As the free oxygen is further depleted, the concentration of the carbon monoxide and of the hydrogen rises and methane appears in the atmosphere of the work chamber. By reason of the rising concentration of the foregoing gases the percentage of gases comprising the carbon dioxide and water vapor decreases and that percentage continues to decrease by reason of the outward flow of gases from the chamber 11 by way of the outlet passage 54. In this connection, as soon as the methane appears in the atmosphere, it reacts with carbon dioxide, the water vapor, and any remaining oxygen, since in respect to them, methane is a reducing agent.

The foregoing reactions continue until equilibrium has been established within the work chamber 11. At that time the gases issuing through the passageway 54 largely comprise nitrogen, methane, carbon monoxide and hydrogen. In this connection, it is to be understood that as the burning of the gases from the generator 52 ceases, by reason of the depletion of the available oxygen as described above, the reactions of the gases discharged from the generator 52 continue to take place within the work chamber 11. This fact greatly contributes to the efiiciency of the operation as a whole, since the gas generator 52 is not of itself relied upon for the completion of all of the desired reactions for the production within the chamber 11 of the desired atmosphere. Thus, the rate of flow of the mixture to the generator 52 may be quite high relative to its physical volume as compared with the physical volume of gas producers heretofore utilized for like purposes.

With the desired atmosphere established within work chamber 11, work may now be introduced therein. It will be remembered that this work, though not shown, has already been described as being within vestibule 12.

Accordingly, the vestibule door 13 will now be closed. Though the closing of door 13 energizes the operating coil of a timer 55, no immediate change in operations takes place and none will take place for the reasons set forth below.

Normally, the gases leaving passageway 54 are ignited and burn as a flame. This is a customary safety operation to prevent accumulation of an explosive mixture in or around the vestibule. Accordingly, as the closing of the door 13 eliminates the supply of oxygen to vestibule 12, the oxygen within the atmosphere of vestibule 12 is rapidly exhausted. This results in a major change in operation, namely the transfer from the supply line 63 of atmospheric air to the atmosphere of vestibule 12, now approaching the same character of atmosphere as produced within chamber 11. In this connection, it is emphasized that the showing of the vestibule door 13 and the supply pipe 63 is diagrammatic. The pipe 63 will normally extend through a side wall of the vestibule 12 and in spaced relation with the supporting structure for the work. The pipe 63 has been shown in the drawing in the region of the door better to illustrate the gas flow from vestibule 12.

After the vestibule 12 has been purged of its atmosphereic air, the door 14 is raised. The operating coil of timer 55 is de-energized by the resultant operation of switch 28 to reset the timer to its initial position. By conventional work-moving means, not shown, the work is now transferred from vestibule 12 to work chamber 11 and the door 14 is closed. With both doors closed, the operating coil of timer 55 is again energized and after a predetermined time interval the timer operates to initiate further changes in operation soon to be described.

The entry of the work into the chamber 11, because at approximately room temperature, causes a reduction in temperature of the chamber 11. The extent of the temperature decrease will depend upon the mass of the work introduced into the work chamber. Though the temperature of chamber 11 be reduced, the protective atmosphere is maintained by reason of the continued flow into the furnace of the mixture of gases from the gas generator 52. Though the reduction in temperature of chamber 11 may permit the formation of some carbon dioxide and water vapor over and beyond that encountered at the higher temperatures, the quantity formed will be of such low order as not adversely to affect the work. The temperature rise will be relatively rapid to the range within which the carbon dioxide and water vapor are present only in the low order of percentages which are not deemed deleterious to the operation as a whole. In this connection, the oxidizing reactions to be guarded against take place at a lower rate at reduced temperatures and for the reactions to take place, larger concentrations are required than at the higher temperatures.

It will be remembered that with both

doors

13 and 14 closed, the operating coil of the timer 55 was energized. The time interval before operation of the timer contacts will correspond with that needed to established within the work chamber 11 the reducing atmosphere above described at some length. The timer will ordinarily be of the type including a timing motor and clutch coil for the operation of its several contacts. For convenience and ease of explanation, the timer 55 has been shown as including a dash pot 56, with holdingcontacts 55c, to provide a predetermined time interval after energization of the operating coil before the opening of timer contacts 55a and 55b and the closure of contacts 550.

The completion of the purging operation produces within the furnace an atmosphere in which the hydrocarbons have largely been oxidized, and the carbon dioxide and water vapor reduced to levels not deleterious to the carburizing action. The furnace gas at this time and during its subsequent operation is ideally suited for enrichment and for carrying into the furnace the desired amounts of carburizing agent. Since the carrier gas is exposed and re-exposed to furnace catalysis, it becomes well equilibrated, that is, it attains high quality relative to, or for, carburizing and hence serves as a quality carrier gas satisfying all requirements for carburizing and hardening. The foregoing features, combined with a miniaturized gas generator, have reduced cost and increased reliability in operation, besides providing a system readily applicable to heat-treating furnaces of many kinds.

When the timer operates, the opening of the contacts a de-energizes the coil of relay 26 to restore its contacts to their illustrated positions. The opening of contacts 26c de-energizes the

coils

36a, 37a and 38a and results in the return of the corresponding

valves

36, 37 and 38 to their illustrated positions. The opening of contacts 26b and the closing of contacts 26a transfers the control of valve 35 to a control relay 6!), the operation of which will now be explained.

The control relay has been illustrated with its contacts closed. These contacts will remain closed until there will have been, developed in the work chamber 11 a carbon potential of predetermined and selected magnitude. During the purging operations and prior to the development of such carburizing atmosphere, these contacts will remain closed. Thus, with the contacts 261) and 26c of control relay 26 closed, it will be seen that the energizing circuit for the coil 35a of control valve 35 extends from the line 22 by way of contacts 26b, the contacts of an intermittently operated switch 57, and thence by way of contacts 260 to the other supply line 23.

The intermittently operated switch 57 is actuated by cam 58 driven by a motor 59, the energizing circuit of which is completed by way of contacts 260. The motor 59, through cam 58, opens the contacts 57 during a small fraction of each minute. Thus, the switch 57 when in its open position de-energizes the coil 35a to close valve 35 for some 5 to 10 seconds of each minute. This intermittent operation shuts off the carburizing agent from supply line 39 during these short periods of time. Accordingly, there is produced intermittent flow through the catalyst 53 of gas which is first rich in carbon and then for a relatively short interval there is produced flow of gas which is lean in carbon. In this manner, if there be any sooting or carbon deposit on the catalyst bed 53, the passage of the hot gases lean in carbon serves to remove such soot and carbon from the catalyst bed to keep it clean and active.

It is to be observed that the closing of timer contacts 550 completes a holding circuit for its operating coil. Accordingly, the timer will remain in its energized position until subsequent interruption of its holding circuit as by the opening of the vestibule door 13 to return the switch 29 to its uppermost, illustrated position. It will be remembered that the circuit for the timer is completed by way of switch 28 as well as switch 29. Hence, whenever the work chamber door 14 is opened, the timer will likewise be de-energized preparatory to its participation in a second cycle of operations. Thus, the raising of either of

doors

13 or 14 again results in energization of relay 26 to initiate further purging and carrier gas generation operations.

With the timer 55 energized and the remaining parts in their illustrated positions, it will be seen that the carburizing agent supplied by way of line 39 and valve 35 now flows by way of the flow meter 40 and a throttling valve 62, set for a materially lower rate of flow of carburizing agent than through the throttling valve 41 utilized during the purging operation. The carburizing agent flowing at this lower rate is again introduced into the gas compressor 25.

It is emphasized again that an important feature of the present invention is the transfer operation which takes place upon operation of valve 36 to its illustrated posiatmosphere. Thus, upon operation of the valve 36 the suction side of the compressor 25 is connected directly to an exhaust pipe 63 which leads to a moisture separator 64, the gas outlet from which is connected directly to a filter 65. The moisture separator 64 by removing water vapor contributes to the lessening of its concentration in the chamber 11. This in turn promotes the formation of more water vapor within the chamber 11 by reducing the CO to CO and oxidizing hydrogen. By providing an efiicient moisture separator, as by including refrigeration, there is formed a system of removing from chamber 11 CO and water vapor to an extent their concentrations in chamber 11 remain at low values.

The filter 65 may be of the type which removes only coarse particles from the stream. Though the gas stream from the work chamber and vestibule may be relatively free of foreign matter, nevertheless, it is deemed best to provide first a coarse filter 65, followed by a fine filter 48 which removes from the gas stream all finely divided particles which may be present therein. Thus the carrier gas from the work chamber 11 mixes with the carburizing agent as the two streams enter the gas compressor 25. In the compressor, additional and thorough mixing takes place, this mixing operation continuing as the stream moves through the passageway including valve 37, now by reason of the position of the valve, extending to a distributing pipe 66. The carrier gas and carburizing agent now develop in the work chamber 11 a carburizing atmosphere.

As the carbon potential of the atmosphere within the work chamber 11 rises, a carbon-sensitive element 70 disposed Within the furnace changes its output in proportion to the change in carbon potential. These changes are measured by means of a recorder 71 having a set-point knob for producing an output on a control line 72 at the time the carbon potential arrives at or slightly exceeds the set-point. Thus, assuming that the desired carbon potential has been reached within the work chamber 11, it will be seen that a circuit will be completed from a positive source of supply 73 which includes the operating coil of control relay 60, the circuit being traced by way of conductor 72 to the negative side of the source of supply 73. Thus, under the control of the carbon sensing element 70 and the recorder 71, the control relay 60 operates to energize and de-energize the coil 35a. In this manner the valve 35 is opened and closed for onperiods and off-periods which in respect to flow of car burizing agent will maintain at the set-point the carbon potential within the work chamber 11.

For details of the construction and operation of the sensitive element 70, and the associated measuring circuits embodied in the recorder 71, reference is to be had to Besselman et al. patent, 2,541,857, dated February 13, 1951. Reference may also be had to applicants Patent No. 3,084,999, and his pending application Serial No. 41,966, filed July 11, 1960 for Measurement and Control of Constituent Potentials, now Patent No. 3,128,323, for further examples of systems for control of relay 60.

Those skilled in the art will understand the desirable rates of flow for the purging of a heat treating furnace. However, it will be helpful to state that for a furnace approximating 18" x 24 x 15" a high rate, of the order of l to 2 cubic feet per minute, will be adequate if continued for a period of to minutes to produce within the furnace or heat treating chamber an atmosphere suitable for the initiation of carburizing or for controlled atmosphere treating. It is to be understood that operating conditions giver for an embodiment of the invention are to be taken as illustrative. They will vary materially depending upon the mass of the load, the extent of temperature reduction and other variables normally encountered in the operation of the furnace. They will vary with furnace size as well. For the above furnace, the catalyst bed 53 for the generator 52 will be adequate for flow of about 50 cubic feet per hour of air with a carburizing agent which can range from 25 to 60 cubic feet per hour of natural gas, the particular ratio being determined by particular operating conditions. For a clean furnace, one free from materials which tend to inhibit the carburizing action, the carburizing agent may be on the low side of the suggested range. The carburizing agent itself may be any one, or any mixture, of propane, butane, natural gas or manufactured gas.

Before describing in detail the gas generator 52, it is to be remembered that the catalyst bed 53 efficiently promotes the above-described reactions which bring the atmosphere to the desired character. By reason of the gradual depletion of oxygen within the work chamber 11, the removal of Water vapor, as by the separator 64. and by reason of the presence within most metal-treating furnaces of nickel-alloy parts, as the Nichrome heaters and ferrous Work, there will be promoted reactions which develop the same desirable furnace atmosphere. The ceramic furnace lining also contributes to the catalysis promoting the formation of CO and H from the reaction with methane (CH of CO and water vapor. More particularly, it will now be .assumed that all of the parts are in their illustrated positions as shown in FIG. 1. As the mixture of carburizing agent and air from the vestibule 12 are by the compressor 25 delivered to pipe 66, the temperature of the mixture will rise, and in the pipe 66 or in chamber 11 there will be formed CO and Water vapor. By reason of the continued depletion of oxygen in chamber 11, the reactions which take place are controlled to produce the higher concentrations of carbon monoxide and hydrogen. After the closing of the door 13 of the vestibule, the action of the moisture separator 64 then becomes more efiiective in reducing in chamber 11 the moisture content and further promotes the reduction in that chamber of carbon dioxide. Thus, for some application, the foregoing features of the present invention may be utilized without the inclusion in the system of generator 52. Where the generator 52 is included, and notwithstanding the intermittent operation of valve 35 as controlled by the intermittently operated switch 57, some sooting may occur in the catalyst bed 53. Should this sooting be in amount impeding flow through the bed, there will be a pressure rise of the stream in the pipe 51 and upon the outlet of compressor 25. As the outlet pressure of the compressor rises, more gas is bypassed from its outlet by way of the

throttle valves

44 and 43 to the inlet of the compressor 25. This automatically decreases the flow of gas by way of check valve 42, since back pressure on the pipe connected to the discharge side of that valve also rises. It will be seen from the foregoing that there has been provided automatic flow regulation of the carburizing agent. As resistance to flow through bed 53 rises, the supply of carburizing agent is decreased. As the supply of that agent is decreased, the gases delivered to the bed 53 by compressor 25 have a lesser carbon content. Because it is less, sooting ceases and the lean gaseous mixture passing through the bed 53 then picks up carbon from the bed 53. This automatic cleansing feature greatly aids in maintaining a relatively clean catalyst for high efiiciency operation. It further maintains high porosity of the bed, needed for the relatively high flow rates.

Referring now to FIG. 2, it will be seen that the catalyst bed 53, formed of a roll of nickel mesh wire, is supported in an outer tube 80. This spirally wound roll of fine-mesh nickel wire is inserted endwise from the bottom of the tube 80. A perforated plate 81 is removable by withdrawal of a cotter pin or locking wire 82 extending through openings located diametrically across the end of tube 80. A second perforated plate 83 is disposed just above the fine-mesh nickel screen and is held in place by any suitable means such as pins 84. In a typical embodiment of the invention, the catalyst bed formed by the spirally wound nickel screen ranged from four to six inches in length. The length of tube extending within the furnace below the furnace wall 85 will be of the order of ten inches. The tube 80 is suited to high temperature operation. It may be of Inconel, Nichrome or chrome iron.

The atmosphere generator 52 is supported from the furnace wall by any suitable means such as flange 86 having bolt holes for the fastening bolts. The flange is secured at an angle to pipe 87 to space the outlet end of pipe 80 from the space to be occupied by the'work. The flange 86 is welded to the outer pipe 87 of adequate supporting length. The upper end of the pipe 87 is welded to a fitting 88 of a union which, in conjunction with the threaded member 89 serves to secure thereto a mating element 90 which carries a series of set screws 91 which may be screwed into engagement with the tube 80 to predetermine its position within the furnace. Thus, the length of tube 80 above the element 90 may be of sufficient length to permit the generator 52 to be utilized with furnaces of many different designs and of varying wall thickness. The tube 80, which may be thirty inches long, is closed at its upper end by a cap 92 having a nipple 93 for attachment by coupling 94 of the passageway or flow line 51 from the gas compressor 25 of FIG. 1.

The diameter of the tube 80 in the embodiment just described may be of the order of one to two inches. With such a small internal diameter, the fine nickel screen, from three to ten inches in height, will nevertheless be effective though its operating temperature may approach its melting or fusion temperature. In accordance with the present invention, the catalyst bed consisting of nickel wire has proved highly satisfactory and has permitted the high throughputs needed for the generation of the purging atmosphere which is thereafter used as the source of supply of the carrier gas subsequently utilized in the generation of the carburizing atmosphere within the work chamber. The ease of renewing the catalyst bed and its relatively low cost for the quantity of gases which may be treated before requiring renewal represent added advantages.

What is claimed is:

l. A metal treating system comprising a furnace having a work chamber within which work may be disposed for treatment,

a gas compressor having an inlet and an outlet,

an atmosphere generator extending into said work chamber and in heat-exchange relation therewith, said generator having within the end portion disposed within said chamber a catalyst bed,

said generator extending outwardly of said chamber to provide a rising temperature gradient from an outer generator inlet to a generator outlet, said generator outlet being disposed downstream from said catalyst bed,

a flow connection between said outlet of said compressor and said generator inlet,

a flow connection for supplying air to said inlet of said compressor,

means including said compressor for supplying to said generator a carburizing agent thoroughly mixed with air for elevation in temperature within said generator for production of aldehydes prior to arrival at said catalyst bed, the catalyst of said bed having a composition which promotes oxidation of hydrocarbons for producing within said chamber a protective atmosphere, and

means for withdrawing gases from said work chamber for How to said inlet of said compressor in place of air theretofore supplied thereto for mixture with said carburizing agent to produce a carburizing atmos phere for said chamber.

2. The system of claim 1 in which there are provided means operable concurrently with the supply of said gases from said work chamber to said compressor for bypass- Hi ing said generator and for supplying said carburizing atmosphere directly to said work chamber.

3. The system of claim 1 in which said catalyst bed comprises open mesh nickel wire.

4. The system of claim 3 in which the generator has a cross-sectional area less than about four square inches with a catalyst bed less than about ten inches in height.

5. The system of claim 1 in which means are provided for the supply of said carburizing agent at a high rate during generation of said protective atmosphere within said work chamber and at a lower rate during development of said carburizing atmosphere within said chamber.

6. The system of claim 1 in which means are provided for intermittent supply of said carburizing agent during generation of said protective atmosphere within said work chamber thereby to provide intermittent flow through said catalyst bed of gases rich in carbon and of gases of decarburizing character to provide intermittent regeneration of the catalyst bed to prevent accumulation of carbon therein, the time of flow of said decarburizing gases being of short duration compared with the time of flow of said gases rich in carbon.

7. The system of claim 1 in which said furnace includes a vestibule, said work chamber and said vestibule each being provided with a door through which work may be placed in and withdrawn from said work chamber,

a passageway extending through the door of said work chamber for flow therethrough of gases from said work chamber, and

means operable with one of said doors closed concurrently with the closing of the other of said doors for initiating a timing period for generation of said protective atmosphere Within said work chamber.

8. A metal treating system comprising a furnace having a work chamber within which work may be disposed for treatment,

an atmosphere generator extending into said work chamber and in heat exchange relation therewith,

said generator having within the end portion disposed within said chamber a catalyst bed of composition for promotion of oxidation of hydrocarbons,

means for supplying to said generator a carburizing agent thoroughly mixed with air for said oxidation reactions of said hydrocarbons for producing within said chamber a protective atmosphere, and

means operable after production throughout said furnace of said atmosphere for discontinuing flow of said mixture of carburizing agent and air to said chamber and for thereafter supplying to said work chamber a mixture comprising carrier gas withdrawn from said work chamber and said carburizing agent.

9. The combination with a metal treating system including a furnace having a work chamber, of an atmosphere generator extending into said work chamber and including therein a catalyst bed,

means including a gas compressor of the constant delivery type for delivery to said generator of a stream of gases, said compressor having a bypass connection between inlet and outlet thereof and including in said bypass connection flow restrictions,

means including a flow connection extending intermediate said flow restrictions for delivery through the flow restriction leading to the inlet of said compressor of a carburizing agent, and

a second flow connection including a flow restriction for delivery to said inlet of atmospheric air, a rise in resistance to flow through said catalyst bed by reason of sooting thereof producing a rise in pressure at the outlet of said compressor and at the flow connection intermediate said flow restrictions for material reduction in flow of said carburizing agent relative to the flow of atmospheric air, thereby to produce in said catalyst bed gases leaner in carbon content and gases which decrease in carbon content as the resistance to flow through the catalyst bed increases, the

1 1 leaner character of the gases then flowing through said bed decreasing the carbon content in the bed to decrease the resistance to flow therethrough. 10. A metal treating system comprising a furnace havlyst bed for minimizing loss to the furnace atmosphere of heat from the region of said catalyst bed during occurrence of exothermic reactions in the region of said bed, said catalyst bed as a whole being disposed at the end ing a work chamber within which work may be disposed 5 portion of said generator within said work chamber, thus for treatment, to provide a part of said unobstructed space therein within an atmosphere generator extending into said work said furnace chamber.

chamber and in heat-exchange relation therewith, 13. In a metal treating system having a furnace includsaid generator having within the end portion disposed ing a work chamber within which work may be disposed within said chamber a catalyst bed, for treatment,

said generator extending outwardly of said chamber to an atmosphere generator extending into said work champrovide a rise in temperature gradient from an outer ber in heat-exchange relation with the furnace atmosinlet thereof to an outlet thereof, phere and including a catalyst bed through which said last-named outlet being disposed downstream from there may be supplied to said chamber an atmosphere said catalyst bed and said generator in the region including as one component a carburizing agent supupstream from said catalyst bed having an unobplied to said generator, the combination of, structed flow path to said catalyst bed, means for automatically decreasing the supply of the a gas compressor of the constant delivery type having carburizing agent upon increase in the How resistance an inlet and an outlet, said outlet being in communithrough said catalyst bed comprising, cation with said outer inlet of said generator, a gas compressor of the constant delivery type,

a bypass flow connection extending from the outlet to a bypass flow connection extending from said outlet to the inlet of said compressor, said inlet of said compressor,

a flow connection for a carburizing agent between a a flow connection for a carburizing agent between a source of supply and said bypass connection, source of supply and said bypass connection,

a restriction between said last-named flow connection a restriction between said last-named fiow connection and the inlet of said compressor, and the inlet to said compressor,

a flow connection for supply of air directly to the inlet a fiow connection for selectively supplying air and of said air compressor, carrier gas to the inlet of said compressor, and said air compressor thoroughly mixing together air supmeans providing a flow connection between said outlet plied directly to its inlet and said carburizing agent of said compressor and said atmosphere generator supplied to its inlet by way of said flow restriction, for flow into said atmosphere generator and thence a flow restriction in said flow connection for said carinto said furnace of said mixture after passage burizing agent to said bypass connection, through said catalyst bed, any increase in resistance said mixture of air and carburizing agent during passage to flow through said atmosphere generator producing through said atmosphere generator being preheated a rise in back pressure applied to said flow connection with formation of aldehydes in said mixture prior to through which said carburizing agent is supplied to its arrival at said catalyst bed, said bypass connection, thereby decreasing its rate of said catalyst bed having a composition which promotes flow in proportion to said increased resistance to flow oxidation of hydrocarbons for producing within said through said generator. chamber a protective atmosphere, and flow control means for withdrawing gases from said References Cited y the EXamiIlel work chamber for flow to the inlet of said compres- UNITED STATES PATENTS sor in place of air theretofore supplied thereto for mixture with said carburizing agent to produce a g 3;: i2 carburizing atmosphere for said chamber, any in- 2275106 3/1942 Harsc 266 X crease in resistance to flow through said atmosphere 2424248 7/1947 3 55 Z X generator producing a rise in back pressure appli 2459618 1/1949 Cam I 2 to said flow connection through which said earburiz 2546013 3/1951 Peckeet "i5 281 X ing agent is supplied to said bypass connection, there- 2550126 4/1951 S g 288 by decreasing its rate of flow in proportion to sa d 2630315 3/1953 2 '5, g 5 increased resistance to flow through saidgenerator. 147 6/1956 i fii gf 11. The metal treating system of claim 10 in whi said 2,873,173 2/1959 Neumeyer catalyst bed consists of nickel wire in the form of a spirally-wound nickel screen.

12. The metal treating system of claim 10 in which heat insulation is provided throughout the region of said cata- JOHN F. CAMPBELL, Primary Examiner.

MORRIS O. WOLK, Examiner.

Claims

1. A METAL TREATING SYSTEM COMPRISING A FURNACE HAVING A WORK CHAMBER WITHIN WHICH WORK MAY BE DISPOSED FOR TREATMENT, A GAS COMPRESSOR HAVING AN INLET AND AN OUTLET, AN ATMOSPHERE GENERATOR EXTENDING INTO SAID WORK CHAMBER AND IN HEAT-EXCHANGE RELATION THEREWITH, SAID GENERATOR HAVING WITHIN THE END PORTION DISPOSED WITHIN SAID CHAMBER A CATALYST BED, SAID GENERATOR EXTENDING OUTWARDLY OF SAID CHAMBER TO PROVIDE A RISING TEMPERATURE GRADIENT FROM AN OUTER GENERATOR INLET TO A GENERATOR OUTLET, SAID GENERATOR OUTLET BEING DISPOSED DOWNSTREAM FROM SAID CATALYST BED, A FLOW CONNECTION BELOW SAID OUTLET OF SAID COMPRESSOR AND SAID GENERATOR INLET, A FLOW CONNECTION FOR SUPPLYING AIR TO SAID INLET OF SAID COMPRESSOR, MEANS INCLUDING SAID COMPRESSOR FOR SUPPLYING TO SAID GENERATOR TO CARBURIZING AGENT THOROUGHLY MIXED WITH AIR FOR ELEVATION IN TEMPERATURE WITHIN SAID GENERATOR FOR PRODUCTION OF ALDEHYDES PRIOR TO ARRIVAL AT SAID CATALYST BED, THE CATALYST OF SAID BED HAVING A COMPOSITION WHICH PROMOTES OXIDATION OF HYDROCARBONS FOR PRODUCING WITHIN SAID CHAMBER A PROTECTIVE ATMOSPHERE, AND MEANS FOR WITHDRAWING GASES FROM SAID WORK CHAMBER FOR FLOW TO SAID INLET OF SAID COMPRESSOR IN PLACE OF AIR THERETOFORE SUPPLIED THERETO FOR MIXTURE WITH SAID CARBURIZING AGENT TO PRODUCE A CARBURIZING ATMOSPHERE FOR SAID CHAMBER.