US3807943A

US3807943A - Muffle furnace for treatment of articles on conveyor

Info

Publication number: US3807943A
Application number: US00238355A
Authority: US
Inventors: R Mckinstry
Original assignee: Anchor Hocking LLC
Current assignee: Anchor Hocking LLC
Priority date: 1970-08-10
Filing date: 1972-03-27
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30

Abstract

A furnace for treatment at elevated temperature of articles moving on a conveyor. The conveyor travels through a horizontal open-ended tunnel which is centered axially within a surrounding hollow combustion enclosure. The enclosure includes an inner wall that is spaced from the tunnel so that a generally annular combustion space or zone is presented between the enclosure inner wall and the tunnel. Burning gases are injected tangentially into the combustion zone and establish a swirling movement of the burning gas around the outside of the tunnel. The articles may be contacted with a treating vapor while in the tunnel.

Description

United States Patent. [191- McKinstry 1 MUFFLE FURNACE FOR TREATMENT OF ARTICLES ON CONVEYOR [75] Inventor: Richard G. McKinstry, Lancaster,

Ohio

[73] Assignee: Anchor Hocking Corporation,

Lancaster, Ohio 22 Filed: Mar. 27, 1972 21 Appl. No.: 238,355

Related US. Application Data [63] Continuation-impart of Ser. No. 62,489, Aug. 10,

1970, Pat. No. 3,659,551.

[52] US. Cl. 432/135, 432/209, 432/146 [51] Int. Cl. F27b 9/00 [58] Field of Search 432/11, 18, 31, 53, 90,

[5 6] References Cited UNITED STATES PATENTS [451 Apr. 30, 1974 1,875,365 9/1932 Begeman 432/153 3,129,084 /1964 Labino 432/210 2,671,654 3/1954 Hombruch et a1. 432/153 1,415,011 5/1922 Benjamin 432/178 2,171,340 8/1939 Mark1ey.... 432/31 3,291,465 12/1966 Wilde 432/1 1 3,154,133 10/1964 Launder 432/209 1,884,748 10/1932 Koch et a1. 432/242 3,558,112 1/1971 Gaede 432/242 3,410,547 1 H1968 Bielefeldt 432/242 Primary Examiner.1ohn J. Camby Assistant Examiner-l-lenry C. Yuen Attorney, Agent, or FirmWood, Herron & Evans 1 A furnace for treatment at elevated temperature of articles moving on a conveyor. The conveyor travels through a horizontal open-ended tunnel which is centered axially within a surrounding hollow combustion enclosure. The enclosure includes an inner wall that is spaced from the tunnel so that a generally annular combustion space or zone is presented between the enclosure inner wall and the tunnel. Burning gases are injected tangentially into the combustion zone and establish a swirling movement of the burning gas around the outside of the tunnel. The articles may be contacted with a treating vapor while in the tunnel.

18 Claims ,7 Drawing Figures MUFFLE FURNACE FOR TREATMENT OF ARTICLES ON CONVEYOR -This application is a continuation-in-part of my copending application Ser. No. 62,489, titled Glass Treating Tunnel, filed Aug. 10, 1970, now U. S. Pat. No. 3,659,551, issued May 2, 1971.

The present invention relates to furnaces for elevated temperature treatment of articles moving on a conveyor. More particularly, it is directed to a gas fired furnace wherein the articles may be contacted with a special treating vapor while they are passing through a tunnel or muffle by which the vapor is isolated from the gas flame and the products of combustion.

Various manufacturing processes include a step wherein articles are exposed to and treated by a hot vapor of some type. For example, in the manufacture of glass articles such as lightweight bottles for carbonated beverages, the bottles may advantageously be subjected to a vapor treatment at elevated temperature, in order to improve the strength and abrasion resistance of the bottles. A cuprous halogen vapor can be used in that process, such as cuprous chloride (Cu Cl The vapor is maintained at a temperature of the order of about 1,000F. for an exposure or treating period that typically is of several minutes duration. Examples of such processes are set forth in F. J. Shonebarger U. S. Pat. No. 3,489,546, titled Strengthening of Oxidized Soda-Lime Glass Articles, issued Jan. 13, 1970, and No. 3,502,454, titled Strengthening and Coloring of Articles Made of Reduced Soda-Lime Glass Compositions, issued Mar. 24, 1970.

The present furnace is useful in such cuprous halogen vapor treatment of glass containers, and it is explained hereinafter primarily in relation to such processes. However, it should be understood that the furnace is suitable for use in carrying out other high temperature treatments of articles moving on a conveyor such as decorating or annealing, with or without the presence of a special vapor.

As set forth in the Shonebarger patents referred to above, when the vapor contacts the glass surface an ion exchange reaction takes place whereby the sodium ion content of the glass surface is partly replaced by copper ions. This modifies the composition of the glass in a .thin surface zone on the article. The resulting modified glass is believed to have a lower coefficient of expansion than the remainder of the article, and on cooling it forms a compression layer which improves the strength of the article.

To carry out such vapor treatments on a production basis, it is desirable to treat the bottles while they are moving on a conveyor line; that is, a continuous treatment rather than a batch treatment. Advantageously, this is done while the bottles are moving on the take-offconveyor on which they are placed directly from the forming machine.

Previously identified US. Pat. No. 3,659,551 is directed to one type of furnace that is useful for carrying out processes such as the cuprous halogen vapor treatment. An electrically heated furnace is described there, in which the heater elements are situated within the vapor contacting zoneythe vapor is not isolated from the heat source.

It has been found over a period of time that the euprous halogen vapor in such an electrical furnace will gradually attack and corrode the furnace structure, cs-

pecially the electrical heater elements. This can seriously reduce their operating life which is, of course, detrimental to process economics.

A further concern is the fact that the presence of water vapor in the vapor containing zone can be detrimental. lf gas is used as the heat source, the water vapor resulting from combustion of the gas will react with the cuprous vapor; this leads to an unduly rapid rate of consumption of the cuprous vapor source. A copper oxide deposit can also form. This detracts from efficient practice of that process in an open gas flame environment.

The present invention concerns a continuous, gas fired muffle furnace in which the flame and products of combustion are isolated from the articles being treated. The articles move through the furnace on a traveling conveyor that runs through a tubular or tunnel like muffle, which is heated by flame contacting only its exterior surface. Articles on the conveyor inside the tunnel are thereby isolated from the flame.

The cuprous halogen vapor treating process is sensitive to temperature, temperature control being important for article to article uniformity and quality control. Small temperature variations can cause visible differences in the color of certain types of containers. Also, the nature of the compression band formed on the surface of the articles by the treatment is dependent upon the time-temperature cycle, a shorter, hotter cycle tending to produce a more sharply defined band, and, hence, a greater compressive strength with resultant higher article strength. Relatively longer and cooler exposures tend to establish wider compression bands, with a smaller strength improvement, in addition to reducing process throughput.

Moreover, it is important that the temperature be uniform from top to bottom of the article. The tall and narrow shape of the bottles themselves makes them especially susceptible to tunnel temperature variation in the vertical direction. This is difficult to achieve in a long horizontal continuous furnace, wherein the ends of the muffle must be open to accommodate the travel of the conveyor through them. A full range of glass containers will require a tunnel height of about 15 inches. It has been found that unless special provision is made to establish vertical temperature uniformity, heat applied to the outside of the muffle will tend to establish vertical convection currents in the muffle such that the top part of the muffle (and hence the upper portions of the bottles) will be heated more than the bottom part, such that undesirably non-uniform treatment results.

It has been a major objective of the present invention to provide a continuous horizontal muffle furnace which is exteriorly heated by a flame pattern that will establish a high degree of temperature uniformity, as measured in the vertical direction at any given station inside the muffle.

[n the cuprous halogen vapor treatment of bottles and in other heat treating processes, controlled temperature bariation along the direction of travel is necessary. A proper thermal cycle or time-temperature schedule as the ware moves along the conveyor is needed to produce ware of constant quality, and to produce the desired strengthening in minimum time. To achieve this, it is important that the temperature of the ware (which at each moment should be uniform across its entire vertical height) change according to a predetermined schedule as the conveyor travels through the muffle. In particular, for cuprous halogen vapor treatment processing of containers, the temperature should rise above the annealing point of the article, to a level as hot as possible but not, of course, so high as to cause undesirable deformation or sag; the temperature should remain at that level during the vapor treatment, then cool.

It has been a major objective of the present invention to provide a furnace whereby the temperature of articles moving on a conveyor inside the muffle will follow a desired schedule or profile as they move in the horizontal direction, but such that at any given point on the conveyor the articles have a nearly flat vertical temperature profile.

In the preferred embodiment, the furnace of this invention contemplates a combustion enclosure within which a hollow, generally circular cross-sectioned combustion zone is defined. An elongated open ended tunnel or muffle runs through the combustion zone, aligned substantially along the axis thereof, and is supported on stilts" or open stands in the combustion zone so that all sides of the tunnel are exposed to and acted upon by flame within the combustion zone. The tunnel includes means for supporting and guiding a conveyor, which travels through it from end to end.

The combustion zone and the tunnel within it are heated by a plurality of gas burners which inject gas flames into the combustion zone only. The burners enter the zone through an inside wall of the combustion enclosure, and they are directed so that flame will circulate circumferentially around the tunnel in the zone; that is to say, the burner flames are injected tangentially into the space between the tunnel and the inner wall of the combustion enclosure.

The burners are preferably of the excess air type and have a high output volume of gases. These gases are curled or wrapped circumferentially around the tunnel to completely envelop it. The burners are placed at angularly spaced positions around the tunnel, one burner entering the combustion zone above the tunnel on one side thereof, a next burner entering the combustion zone on the other side and below the tunnel. Thus the output gases from each burner reinforce one another in traveling less than the full circumference of the tunnel. The burners are preferably spaced axially from one another. The output gases travel to an exhaust or outlet stack, which extends from the combustion zone through the wall of the furnace, and which is spaced longitudinally of the tunnel from the burners. The motion of the gas around the tunnel describes a horizontal spiral or helix as it travels to the exhaust.

The ends of each combustion zone are closed by bulkheads, and there may be a plurality of combustion sections along the tunnel such that the temperature in each section can be controlled essentially independently of the temperature in adjacent sections. The output of each of the burners can be regulated to give a desired longitudinal temperature profile.

Where, as in the cuprous halogen treating process, a special vapor phase is to be maintained inside of the tunnel it is preferred to use air doors to minimize escape of the treating vapor and to minimize heat transfer through the ends of the tunnel. I have found that air doors that direct a sheet of air transversely across the tunnel from top to bottom thereof, without any opposed outlet, are especially effective for this purpose.

It is recognized that continuous muffle furnaces are known in the broad sense, one such furnace (for the manufacture of coke) being shown and described in U. S. Pat. No. 1,730,570. There, the muffle extends vertically, and the conveyor is an auger. Schmidt U.S. Pat. No. 3,459,414 shows apparatus for convective heat treatment of a metal billet wherein the billet is seated in a vertical chamber with a top outlet, and gas jets are directed angularly into an annular space around the billet. There is no muffle or conveyor, and the hot gases rise to the top of the furnace. Plotkowiak U.S. Pat. No. 3,470,624 is similar, in that a cylindrical billet of metal is seated in the center of a vertical chamber. Cooling gas is directed tangentially into an annular space around it, which is swept out to a top outlet. No muffle or conveyor is shown. The prior art constructions do not provide the horizontal helix or swirl of hot gas around the outside of an open ended muffle, as this invention provides.

The invention can best be further described by reference to the accompanying drawings, in which:

FIG. 1 is a side elevation, somewhat diagrammatic in nature, of a furnace in accordance with the invention, in a preferred form for the cuprous halogen vapor treatment of glass bottles;

FIG. 2 is an enlarged axial section of a portion of the tunnel of the furnace of FIG. 1, showing the inlet air door;

FIG. 3 is an axial section of another portion of the tunnel of the furnace of FIG. 1, showing the air doordrift controller in the vapor treatment section of the tunnel;

FIG. 4 is an axial section of another portion of the vapor treatment section of the tunnel showing the cross-chute for boats that will contain the cuprous halogen source;

FIG. 5 is a transverse section taken on line 5-5 of FIG. 2, the same configuration also appearing on line 5-5 of FIG. 3;

FIG. 6 is an enlarged transverse sectional view taken on line 66 of FIG. I; and

FIG. 7 is an enlarged transverse sectional view taken on line 77 of FIG. 1.

The specific furnace illustrated in the drawings and described below is especially useful for the cuprous halogen vapor process, but the invention is not limited to such use.

The furnace of the illustrated embodiment includes four longitudinal sections, each of which is made separately for end to end assembly in situ. The first three of the four sections are heating sections; the fourth section is a cooling section and has no gas burners in it. All are traversed by a horizontal conveyor 10 which runs longitudinally through the furnace from end to end thereof. The conveyor travels on a horizontal run between end rolls (not shown), and returns on a run beneath the furnace. In FIG. 1, the direction of conveyor travel is from left to right, as designated by the arrow at 15.

The four sections of the furnace are designated as 11 through 14. The first section 11 constitutes a temperature equalizing section wherein articles traveling on the conveyor are heated and brought to uniformly elevated temperature; the next section 12 comprises the vapor treatment section, in which the articles are contacted with the treating vapor. The third section 13 is an annealing section, in which the articlesout of substantial contact with the treating vaporgo through a controlled gradual temperature reduction. The fourth section, designated at 14, is merely a final cooling section and has no burners in it.

In each of the sections 11-14, the conveyor runs through a surrounding tunnel or muffle, designated at 20. As best shown in FIG. 6, tunnel is a duct or tube which may be rectangular in cross-sectional shape. It rests on support means in the form of longitudinally spaced stands or brackets 21. The brackets 21 position tunnel 20 so that it is essentially centered in the hollow, surrounding combustion enclosure designated generally at 22. The combustion enclosure 22 has an inner wall surface 23 which surrounds but is spaced radially from the tunnel 20 so that an open, generally annular combustion zone 25 is defined around tunnel 20, between the tunnel and wall 23.

More specifically, the furnace enclosure 22 includes an outer liner or shell 26 of sheet metal. This shell 26 supports and protects flat insulating elements which are mounted to it by bolts or studs 28. The insulation is suitably in two layers, a thicker outer insulation layer 29 comprising batts of refractory fibers, and a thinner layer comprising compressed, mechanically rigid and durable slabs of a refractory insulating material. For the cuprous halogen process, the insulation should be capable of withstanding temperatures up to about 2000F. Fiberfax" insulation, manufactured by Babcock and Wilcox Corporation, is available commercially in the forms described and is suitable. v

The bolts 28 project inwardly from shell 26 and pass through both layers of insulation 29 and 30, both layers being held in place by fastenings 31. The standards 21 projectupwardly from shell 26 through apertures in the insulation.

It can be seen in FIG. 6 that the inner layer of insulation 30 defines an internal space around tunnel 20 that is square or rectangular in section. In order to promote a more uniform circular or swirling movement of flame around the tunnel 20 (as subsequently described), the longitudinal edges at which the vertical and horizontal surfaces of the insulation layer 30 meet, are rounded by curved fllet segments 32. The filets are mounted and supported on the bolts 28. Thus, the inner wall 23 of combustion zone 25 is comprised by the filet sections 32 and portions of the surfaces of the inner insulation layer 30. Together, these define the approximately circular sectioned surface or wall 23 around combustion zone 25.

From a theoretical standpoint, it would be desirable that tunnel 20 also have a circular cross-section, similar to wall 23, for the most uniform swirling flow of gas around it. However, in order to withstand the corrosive action of certain treating vapors, including cuprous chloride, it is desirable to use stainless steel as the tunnel material. Circular tubes of stainless steel of the necessary diameters are not readily available and would be expensive to fabricate. It is convenient and less expensive to produce the tunnel 20 from flat plate or sheet stainless material by forming it as a rectangular box with welds at the long edges. In use, this has been found not to limit unduly the swirl of the burning gas around it. For resisting attack of CuCl vapor in section 12, No. 601 lnconel stainless works well as the tunnel material. In the other sections, and for the stands, No. 316 stainless is satisfactory since they are not exposed to the concentrated vapor.

The conveyor 10 travels through the tunnel over its base or bottom, and is supported on and guided therein by longitudinally extending angles or brackets designed at 33. These prevent wear between the tunnel surface and the belt.

The tunnel is preferably not fastened rigidly to the stands 21, but sits between guide edges 34, 34 presented at the tops of each stand. Relative longitudinal movement (as much as 2-4 inches for a 21 foot long tunnel) between the tunnel and the stands will occur by .reason of thermal expansion of the tunnel as it is heated, in relation to the shell 26 to which the stands 21 are mounted, and this is accommodated by the slidable supports described.

The combustion zone 25 is heated by burning of natural gas or the like within it. Each section 11-13 is a separate furnace, and each is heated by a plurality of gas burners, each designated at 37.

In the illustrated embodiment, the combustion zone of the temperature equalizing section 11 is heated by two burners, the vapor treatment section 12 is heated by three burners, and the annealing section 13 has four burners, some of which may not be needed, depending upon the annealing schedule. The number of burners in any particular section is not critical to the invention, and will depend upon the nature of the heat treatment to be used and the type and rate of articles being treated.

Each gas burner 37 can be of a type which is known per se; preferably it is of the so-called excess air type. Excess air burners operate with the forceful injection of a large excess of air directly into the gas to be burned. This excess air is usually within the range of 2-10 times the quantity of air necessary for stoichoimetric combustion of the gas flow. In the illustrated embodiment a 300-400 percent excess is used. The flame has a high forward velocity, and a much more uniform temperature than an ordinary gas flame. Such burners are commercially available; as an example of one suitable type, the burners in the furnace illustrated are Series 4423 XS Air Gas Burners, made by North American Mfg. Co., Cleveland, Ohio.

As shown in FIGS. l and 6, the burners 37 of each section are spaced from one another in the longitudinal direction, and they enter the combustion chamber 25 alternately above and below tunnel 20, and from opposite sides. In other words, the burners are staggered and opposed, being above the muffle on one side, and below it on the other. The burners enter the combustion zone tangentially, through ports 37 in the wall 23. Ideally, the burners are; p ositioned so that if the axis of the burner were extended to a point half way across the combustion zone, it would roughly perpendicularly bisect a radial line 40 drawn from the tunnel 20 to wall 23 (see FIG. 6). Thus, in operation each burner directs the flame across the top or bottom of the tunnel circumferentially around the combustion zone. The circular slope of inner wall 23 deflects the flame around the tunnel, so that a swirling motion of flame and hot air is established around the outside of the tunnel, see FIG. 6. The heating flame virtually surrounds the exterior surface of the tunnel, passing between the brackets 21 which support it from below, and around the four sides of the tunnel. This produces extremely even temperatures across any given sectional area of the tunnel. Data shows that the temperature at the top of a bottle (shown in phantom at 24 in FIG. 6) in the tunnel is within of the temperature at the bottom of the bottle.

Each sction 11-13 has an exhaust stack or outlet 38 which is adjacent an end of the section. The stack extends from the combustion zone 25 through the insulation layers 29 and 30, and through the shell 26. The stack is equipped with a damper and a furnace pressure gage, not shown.

Control thermocouples are located inside the tunnel in each section, and each section has its own automatic temperature control which may be of conventional type.

The burning gas and excess air swirls as a helix from the burners to the stack 38 adjacent the end of the section. This gas bathes the tunnel and extends entirely around it, by reason of the vortex established by the tangential injection and the spiral gas flow to the stack.

The tunnel isolates the products of gas combustion outside it in the combustion zone, from the treating vapor and the articles in the tunnel, so that no reaction between them takes place; likewise, the burners in the combustion zone are isolated from the treating vapor, so that corrosive attack of the burners or wall 23 by the treating vapor does not occur. Heat is conducted evenly through the tunnel wall from all sides (including the top and bottom); the swirling gas movement irons out" hot spots.

In the furnace illustrated, changes in the longitudinal temperature profile are needed. Where this is a consideration, it is desirable to block axial flow of combustion gases in zone 25, from one section to another. This is accomplished by provision of bulkheads or partitions of the type designated at 40. These are positioned at the joints or flanges 41 at which the sections are connected end to end. As shown in FIG. 7, the bulkheads 40 are metal sheet or plate partitions which at their outer edges are clamped between the mating flanges 41 and which extend radially inward across the combustion zone 25, toward tunnel 20. The bulkheads must not however be connected rigidly to the tunnel; their inner edges 42 are just slightly spaced from the tunnel wall. The bulkheads 40 are partly segmented by radially extending slots or slits 43. Thus, inner portions of bulkheads 40 within the combustion zone 25 and adjacent the tunnel can expand without buckling under the heat of combustion, relative to the cooler outer portion at the flanges 41 adjacent shell 22. The slots 43 are closed or very narrow at operating temperature. Axial shifting of the tunnel due to longitudinal expansion relative to the bulkheads is also accommodated, since they are not connected.

The bulkheads impede longitudinal flow of flame and combustion products from section to section, and if all three sections 11-13 are maintained at about the same furnace pressure, temperatures in each section along the length of the tunnel can be controlled independently.

By way of illustration of the controllability of temperature, in the particular furnace illustrated, the belt travels at a rate of 22 inches per minute. The ware entering equalizing zone 11 has a temperature of about 250-375F. Travel time in the first zone is 2.2 minutes. The oven temperature (as measured by a traveling thermocouple) increases in the first minute of travel to about ll20F., then more slowly to about l260F. in the next minute, then holds at about l260 for the remainder of the first zone. (Note the stack 38 is located in the direction of conveyor travel from the burners in this zone). This is the peak temperature in the particular furnace illustrated. At this point, the temperature in zone 25 outside the muffle is about l280F. Travel time in the treating zone 12 is 2.4 minutes, during which the temperature drops approximately lineally from l260 to ll. In the annealing zone 13, temperature is reduced from II70 to l0l0F. in three minutes, then more rapidly to 700 in the next l.0 minutes of travel. (For this rate of drop, operation of only two of the four burners is necessary.) In the unheated cooling zone 14, temperature drops to about 280 in 3.3 minutes. A time or position versus temperature trace displays virtually no bump as the ware traverses the burners. The oven temperatures are adjusted so that actual ware temperature never quite reaches its softening point.

Tunnel 20 is open ended, that is, it has no door or closure at either end. In order to minimize the flow of cooler outside air into the tunnel, and at the same time to prevent the loss of heat and/or treating vapor through the open ends of the tunnel, air doors are mounted at various stations along the tunnel. Specifically, an inlet air door is positioned at the entrance to the tunnel in section 11, and an outlet air door is provided in section 13. Additional air doors of a somewhat different type are provided at spaced positions in the vapor treatment section. 12.

The entrance and exit air doors are designated at 45 and 46, and may be similar to one another. The doors within the vapor treatment section are designated at 47 and 48, and are similar to one another but they are angulated to direct flows toward one another, as will be described. In each case, the tunnels use dry air (-F. dew point) in order to avoid the introduction of moisture into the tunnel. The entrance and exit

air doors

45 and 46 each direct a thin sheet of air, moving at relatively low velocity (e.g.l0O-300 fpm) transversely or perpendicularly into the tunnel from the top thereof. No special air door exhaust duct is provided for either door, and the flow they inject tends to pressurize" the inside of the tunnel and thereby to pump heated gases back into the furnace and to prevent entrance of cool outside air. It has been found unnecessary to collect or recirculate the atmosphere.

Each

tunnel door

45 and 46 includes a nozzle 50, generally rectangular in cross-section (see FIGS. 2 and 5), which extends transversely across the tunnel, preferably at the top thereof. The nozzle is not full width, and as shown in FIG. 5, extends across the central only of the width of the tunnel. The short or less-thanfull width of the nozzle 50, in relation to the tunnel width, avoids long air flow along the sidewall. This minimizes air current drag on the tunnel sidewalls and also promotes flow with minimal swirl and cross-mixing in the tunnel. The edges of the air flow from

nozzles

50, 54 are approximated by the dotted lines in FIG. 5.

Each nozzle is fed through a large rectangular plenum chamber 51, which in turn is fed by a flow straightener section 52. The latter comprises a bundle of tubes of relatively small diameter; in the illustrated embodiment there are 37 such tubes, each having an external diameter of inch, 3 541 inches long and tack welded together to form the bundle. Air is supplied to this source from a dry (80F.D.P.) compressed air line located outside of the furnace, through a long line 53 (see FIG. 6). The line 53 passes through inner wall 23, and has a relatively long travel around the combustion zone 25, so that air passing through line 53 is heated to a furnace temperature in its travel to the plenum chamber 51. Flow straightener 52, in combination with the plenum 51, promotes temperature uniformity with minimal turbulance of the air entering the tunnel. This insures more laminar flow, with a minimum of mixing with atmospheric air. In this connection, it has been found that the low air velocities mentioned are far more desirable for this purpose than higher velocities.

Air doors

45 and 46 have nozzles 50 which are directed perpendicularly to the conveyor, as shown in FIG. 2. In contrast, the

air doors

47 and 48, where the tunnel enters and leaves the vapor treatment section 12, have nozzles 54 which are directed angularly toward one another, see FIGS. 2 and 3. This angle, designated at 55, in FIG. 3, is preferably 20 to 30 with respect to a line perpendicular to the belt. In other respects, these doors 47 and 48.and their air supplying ducts are similar to the

doors

45 and 46.

The angulated nozzles of

doors

47 and 48 accomplish several things:

l. The treating vapor is pumped toward the center of the treatment section 12, so that escape of vapor to the equalizing section 11 or the annealing section 13 is reduced; 7

2. They create a stirring action such that temperature and vapor concentrating uniformity are promoted, and thereby eliminate a need for circulating fans;

3. These curtains control drift through the tunnel. More specifically, concerning this latter effect, the length of the furnace may be such that a pressure differential will exist between its two ends, and there may be a gentle flow of air from one end through the tunnel to the other end. This most frequently occurs on days when it is very windy outside the plant. Drift is not merely the result of conveyor movement, and in fact can move in the opposite direction to the conveyor. If not counteracted, such drift can result in undesirable loss of heat and/or vapor. If drift occurs, it can be counteracted by increasing the air flow through one of the

air doors

47 or 48, and/or reducing that in the other 48 or 47. Alternatively or in addition, the furnace may also be provided with a drift control tube of the type described in my previously identified application.

The means for generating a treating vapor do no comprise a part of the invention, and will depend on the particular type of treatment in which the tunnel is to be used. Where the tunnel is to be used for a cuprous chloride vapor treatment, suitable vapor generating means are described in my previously identified US. Pat. No. 3,659,551.

To introduce a vapor (if used) into the treatment section, a cross tube 60 extends through and across the furnace at the middle of the vapor treatment section 12, directly beneath tunnel 20. It communicates with the interior of the tunnel through an opening 56. Refractory boats containing a supply of granular cuprous chloride or other treating material are introduced, through a suitable closure at one end of this tube 60, and are pushed in a line through the tube. The temperature of the boats increases as they pass through the combustion zone 25, sufficiently that copper chloride vapor is generated, which rises into the treating tunnel as the boats pass beneath opening 56. After depletion of their supply of cuprous chloride, the boats are withdrawn from the other side of the furnace. The entrances and exits to tube 60 are preferably cooled to permit handling of the boats at the loading and discharging ends thereof.

The furnace pictured and described is dimensioned for a single line of articles. Where the number of articles to be treated is much greater, the capacity of the furnace can be increased by use of a wider tunnel, carrying a belt with multiple lines of articles, or by use of a plurality of tunnels mounted at laterally spaced positions across a wide combustion zone. To accommodate thermal expansion of a wide tunnel and to support its roof under the effect of the high temperatures used in the glass treating example, it is desirable in the latter case to hang the tunnel roof from the shell. For this purpose it is contemplated that stainless steel rods would extend upward from the outside of the muffle roof, through the combustion zone to cross beams to the top outside of the furnace.

The invention also contemplated a new method of heat treating glass articles, by placing them generally in line on a conveyor, continuously moving the conveyor with the articles on it through the open ended muffle while heating the muffle, or at least the mid portion of it, with hot gasses that are applied tangentially to its exterior surface and caused to flow in the longitudinal direction as a helix around the outside surface of the muffle.

While I have described a particular type of furnace in accordance with my invention, for use in the cuprous halogen treatment of glass articles, those skilled in the art will appreciate that other embodiments of the invention may be used in accordance with the scope of the claims which follow:

I claim:

1. A furnace for elevated temperature treatment of articles carried therethrough on a conveyor, compriss structure defining an elongated tunnel having a horizontal axis and open at each end,

a conveyor through the tunnel from end to end thereof for carrying articles to be treated,

a combustion enclosure. surrounding said tunnel over at least a part of the length of the latter, said enclosure having an inner surface which is spaced radially from the tunnel so that a hollow annular combustion zone is defined between the said surface and the tunnel,

structure at each end of the combustion zone closing the space between the tunnel and said surface,

a plurality of gas burners entering said zone through the said surface of said enclosure and aimed to inject burning gas into the zone in a direction generally tangential to the tunnel, said burners being of the excess air type for producing a flame having a high forward velocity,

said burners positioned in cooperating arrangement so that the gases injected into said zone by the said burners circulate about the said axis of said tunnel and completely encircle said tunnel on all sides thereof,

said means supporting the tunnel centrally within the combustion zone, the said means supporting said tunnel so that said burning gas may circulate past the said means and encircle the circumference of the tunnel.

2. The furnace of claim 1 which further includes an outlet stack for said combustion zone, said outlet being spaced axially from said gas burners so that there is a helical flow of gas in said zone around the tunnel, from the burners to the outlet stack.

3. The furnace of claim 1 wherein the conveyor is a continuously movable belt.

4. The furnace of claim 1 which further includes means for injecting air into the tunnel, said air being heated to substantially the temperature of the combustion zone.

5. The furnace of claim 1 wherein an air door is provided adjacent each end of the tunnel which blows air transversely into the tunnel from the top thereof.

6. The furnace of claim 5 which further includes passages for supplying air to the respective air doors, which passages extend through the combustion zone so that air in the passages will be heated in passing therethrough.

7. The furnace of claim 1 wherein the surface of said enclosure is essentially circular in cross section, and the tunnel extends along the horizontal axis of said surface.

8. The furnace of claim 1 wherein the tunnel is supported on standards extending from the enclosure toward the center of the combustion zone, so that an open annular space extends entirely around the horizontal axis of the tunnel.

9. The furnace of claim I wherein the gas burners enter the combustion zone at longitudinally spaced positions, alternately above and below the tunnel, from opposite sides of the tunnel.

10. The furnace of claim 1 wherein the tunnel is rectangular in section.

11. The furnace of claim 1 wherein the combustion zone is divided longitudinally by bulkheads into separate sections, the bulkheads extending toward but not to the tunnel from said surface to impede longitudinal gas flow therepast.

12. The furnace of claim 11 wherein the bulkheads include radial slots to accommodate differential thermal expansion thereof.

13. A furnace for vapor treatment at elevated temperature of articles carried therethrough on a conveyor, comprising,

structure defining an elongated tunnel having a horizontal axis and open at each end, said tunnel comprising a metal tube having guide means along the bottom part thereof for supporting and guiding a conveyor,

said conveyor comprising an endless belt running through the tunnel from end to end thereof for carryingarticles to be treated,

an insulating enclosure surrounding but spaced from said tunnel on all sides thereof, said enclosure having an inner surface which is generally circular in cross-section so that a hollow annular combustion zone is defined between the said surface of the enclosure and the tunnel,

support means supporting the tunnel so that it is centered within the combustion zone,

gas burners opening to the combustion zone through the said inner surface, the burners being excess air burners which in use project a flame of burning gas into the annular combustion zone in a direction essentially parallel to the inner surface,

a gas outlet spaced longitudinally from said burners and opening through the enclosure from the combustion zone,

the gas burners being staggered angularly and longitudinally from one another such that the gases projected into the combustion zone by said burners cooperate to form a helical swirl wrapping around said tunnel on all sides thereof,

the said helical swirl moving longitudinally from said burners to said outlet,

said support means so supporting said tunnel within said combustion zone that said burning gas may circulate circumferentially around the said tunnel past said support means.

14. The furnace of claim 13 wherein said tunnel is fabricated as a rectangularly sectioned tube.

15. The furnace of claim 13 wherein said enclosure is fabricated with flat insulation blocks, and has curved sheet metal filets that run along the corners between horizontal and vertical insulation blocks to impart a rounded cross-sectional shape to said combustion zone.

16. The furnace of claim 13 wherein said combustion zone is divided longitudinally into separate sections by bulkheads,

each section comprising a furnace of the type described for independent temperature control.

17. The furnace of claim 13 which further includes a passage extending through the combustion zone and opening into the tunnel for injecting air thereinto which has been heated by combustion zone.

18. The furnace of claim 17 which includes a pair of air doors entering said tunnel at spaced longitudinal positions, each said door having a nozzle angulated toward the other for directing air toward the other.

Claims

1. A furnace for elevated temperature treatment of articles carried therethrough on a conveyor, comprising, structure defining an elongated tunnel having a horizontal axis and open at each end, a conveyor through the tunnel from end to end thereof for carrying articles to be treated, a combustion enclosure surrounding said tunnel over at least a part of the length of the latter, said enclosure having an inner surface which is spaced radially from the tunnel so that a hollow annular combustion zone is defined between the said surface and the tunnel, structure at each end of the combustion zone closing the space between the tunnel and said surface, a plurality of gas burners entering said zone through the said surface of said enclosure and aimed to inject burning gas into the zone in a direction generally tangential to the tunnel, said burners being of the excess air tYpe for producing a flame having a high forward velocity, said burners positioned in cooperating arrangement so that the gases injected into said zone by the said burners circulate about the said axis of said tunnel and completely encircle said tunnel on all sides thereof, said means supporting the tunnel centrally within the combustion zone, the said means supporting said tunnel so that said burning gas may circulate past the said means and encircle the circumference of the tunnel.

3. The furnace of claim 1 wherein the conveyor is a continuously movable belt.

9. The furnace of claim 1 wherein the gas burners enter the combustion zone at longitudinally spaced positions, alternately above and below the tunnel, from opposite sides of the tunnel.

10. The furnace of claim 1 wherein the tunnel is rectangular in section.

13. A furnace for vapor treatment at elevated temperature of articles carried therethrough on a conveyor, comprising, structure defining an elongated tunnel having a horizontal axis and open at each end, said tunnel comprising a metal tube having guide means along the bottom part thereof for supporting and guiding a conveyor, said conveyor comprising an endless belt running through the tunnel from end to end thereof for carrying articles to be treated, an insulating enclosure surrounding but spaced from said tunnel on all sides thereof, said enclosure having an inner surface which is generally circular in cross-section so that a hollow annular combustion zone is defined between the said surface of the enclosure and the tunnel, support means supporting the tunnel so that it is centered within the combustion zone, gas burners opening to the combustion zone through the said inner surface, the burners being excess air burners which in use project a flame of burning gas into the annular combustion zone in a direction essentially parallel to the inner surface, a gas outlet spaced longitudinally from said burners and opening through the enclosure from the combustion zone, the gas burners being staggered angularly and longitudinally from one another such that the gases projected into the combustion zone by said burners cooperate to form a helical swirl wrapping around said tunnel on all sides thereof, the said helical swirl moving longitudinally from said burners to said outlet, said support means so supporting said tunnel within said combustion zone that said burning gas may circulate circumferentially around the said tunnel past said support means.

16. The furnace of claim 13 wherein said combustion zone is divided longitudinally into separate sections by bulkheads, each section comprising a furnace of the type described for independent temperature control.