US1893061A

US1893061A - Forehearth for molten glass

Info

Publication number: US1893061A
Application number: US393680A
Authority: US
Inventors: Karl E Peiler
Original assignee: Hartford Empire Co
Current assignee: Hartford Empire Co
Priority date: 1929-09-19
Filing date: 1929-09-19
Publication date: 1933-01-03
Anticipated expiration: 1950-01-03

Description

Jan. 3, 1933. K. E. PEigER FOREHEARTH FOR MOLTEN GLASS Filed Sept. 19, 1929 8 sheets-shea 1 Jama 3 1933. K. E. PEaLER FOREHEARTH FOR MOLTEN GLASS Filed Sept. 19, 1929 8 Sheets-Sheet 2 l /la Jan. 3, 1933.

K. E. PEILER 1,893,061

FOREHEARTH FOR MOLTEN GLASS Filed Sept. 19, 1929 8 Sheets-Sheet 3 WZ'Z n ess.

Jan. 3, 1933. K. E. PEILER FOREHEARTH FOR MOLTEN GLASS 1929 8 Sheets-Sheet 4 Filed Sept Z/mm WM I Jan 3y 1933 K. E. PEiLER 39893,@62

FOREHEARTH FOR MOLTEN GLASS Filed Sept, 19, 1929 8 Sheets-Sheet 5 8 Sheets-Sheet 6 K. E. PEILER FOREHEARTH FOR MOLTEN GLASS Filed Sept. 19, 1929 Jan. 3, 1933.

8 sheets-sheet 7 ZZe, 16445104/ V7) [fi 77E Pe K. E. PEiLER 'FOREHEARTH FOR MOLTEN GLASS Filed sept. 19, 1929 Jan. 3, 1933.

Jan. 3, 1933.

K. E. PEzLER 1,893,061

FOREHEARTH FOR MOLTEN GLASS Filed Sept. 19, 1929 8 Sheets-Sheet 8 /f'l/Ql i Y/Ziz a' e2@ in Wiz@ s /faHZZT Pfz'ie;

f e5 Lf? i tra, a, ieee E. EEHIER, OF WEST HARTFORD, CONNEGTCUT, ASSIGNOR T0 HARTFORD-MEME COMPANY F HARTFORD, (ZNNEGTKCUT, il QEPORTON Olq1 DELAWARE lFGBmE-ETH FR MGMT@ GLASS application neu september ie, reas. serial no. scacco.

rlhis invention relates to improvements in orehearths lor receiving molten glass from a melting furnace and tor conducting such vglass to a `leed spout, basin, or other supply chamber from which glass is to be ted, gath- V ered, drawn or otherwise removed.

lit is usual in taking glass from a melting furnace or tanlr to provide a orehearth or extension, having a channel along which molten glass 'ows :trom the furnace or tank to a place at which glass is to be `ed in mold chargess gathered by suction in a gathering receptacle, or otherwise removed. Glass dov/ing along a channel oit a :torehearth or extension tends to lag or dow more slowly and to become relatively cool at the sides ot the channel While hotter glass will flow at a relatively high velocity along the longitudinal median portion ci@ the channel, thus producing the condition known as channeling. rlhis condition is objectionable in that the glass entering the chamber or place oi? delivery or removal ot glass at the outer end ot the orehearth or eirtension is notuniiorrn in viscosity, tempera-- ture and condition. ln some instances, the relatively cool and stagnant glass at the sides ot the *forehearth channel may become cordy or partially devitriiied and portions thereof may be entrained `Witli the relatively hot and more swiftly ilovving glass at 'the longitudinal :media-n portion el the torehearth and may seriously interfere with the feeding or removal ot glass at the delivery end of the torehearth.

lt has been proposed prior to the present invention to eliiect cooling of the glass at the longitudinal median portion of the forehearth channel with a view to reducing the temperature and velocity ot ovv ot such glass to coincide more nearly `with the temperature and velocity of flow of glass at the side portions of the orehearth channel. Patent No. l,656,869, granted to ine January l?, 1928, illustrates and discloses means for and methods orn cooling the glass at the longitudinal median portion ot the tank by providing an opening or openings in the top ot the -torehearth above thelongitudinal median portion thereof and regulating the effective size and character of such' opening or openings to etlect regulable accelerated cooling of the glass at the middle or" the 'forehearth channel. 'lhe construction and methods of such patent obviate many of the 'objectionable teatures' of orehearths provided prior thereto. However, the opening or openings at the top of the orehearth tend to influence draft and ring conditions Within the orehearth and, in some circumstances, it may be desirable to obviate such influence on draft and ring conditions.

lt also has been proposed to etllect local cooling of part of the glass in a 'orehearth by passing a cooling medium through a member adjacent to such glass. ln some instances, the member through which the cooling medium is to be passed is a refractory Wall of the glass conducting channel. Such local cooling, it etiective to lower the tem.

perature and reduce the velocity or ovv oi" any portion of glass in the forehearth, probably also would tend to lower the temperature and rate ot' iloW of the remaining glass in the torehearth and thus might prevent the delivery at the outer end of the orehearth of glass at a desirablyhigh temperature. Moreover, such local cooling of relatively hot glass in the iiorehearth Would not obviate the objectionable features which result jfrom the presence of the cooler and more slowly moving or stagnant glass at the sides o the torehearth.

An object ot the present invention is to provide for the conditioning of glass during its passage along the flow channel of a forehearth or lilre extension Arorn a melting 'furnace or other source of supply oi molten glass to a leed spout, gathering basin or other place of delivery ot glass at the outer end of the torehearth so that the glass passing to such place of delivery will be or uniform temperature, viscosity and condition throughout and ci proper temperature5 viscosity and condition tor use in the manner desired.

further object of the invention is to produce an even tloW ofi the glass in the channel o a forehearth throughout the cross section oix such glass by causing a relatively greater radiation or heat from the glass at the longitudinal median portion ofi torelll@ hearth without causing any interference with or influence on the draft and firing conditions within the forehearth and by distributing the temperature within the space above the glass in the forehearth so that the heating of the glass in the side portions of the channel of the forehearth will be intensified as required to produce a. condition of uniform viscosit and temperature throughout the' cross section of the glass in the channel.

A further object of the invention is the provision of improved means for and improved method of cooling glass in the longitudinal median portion of a forehearth by radiation alone while preventing drafts or iow of cold air at the cooling place. v

y A further object of the invention -is to provide improved means for causing independently regulable flow of heating media longitudinally of the forehearth above the glass in the side portions ofthe glass fiow channel.

l above the glass in the furnace is practically prevented by closing communication between the space above the glass in the forehearth and the space above the glass in the furnace. Conditioning and control of theA temperature and viscosity of the glass in the forehearth are effected by regulating` the temperature and' draft conditions in the forehearth to control the distribution transversely of the forehearth of the currents of heating media `which move longitudinally of the forehearth above the glass therein, as by causing the heated gases to pass lon itudinally of the forehearth mainly or entirely at the side portions thereof, and by causing relatively greater radia, tion of heat from the glass at the longitudinal medium portion -ofV the forehearth without opening the space above such glass to the atmosphere and-therefore without influencing or altering' draft or firingl conditions in the forehearth.

A desirable arrangement for effecting conditioning of glass in the forehearth and distribution of heat therein comprises a source of heat, such as a burner, located so as to discharge a heating blast downwardly and forwardly into the outer end portion of the forehearth and means, such as stacks having dampers therein, in communication with the rear .or inner portion-.of the space above the glass in the forehearth at opposite sides of the longitudinal median line thereof for in.

ducing drafts rearwardly igthe forehearth above the.k glassanfthe .side portions of the glass conducting 1 channel of the forehearth whereby the heating of the glass in the side portions o'f the forehearth will be relatively great. VIn conjunction with this local heating of the glass in the side portions of the forehearth, the invention` provides for regulably ycontrolled relatively great radiation of heat y 'the front orl outer end portion of the forehearth and the velocity and heating characteristics of the heating media passing. rearwardly above the glass in the side portions of the forehearth may be regulated by regulating the intensity` and volume of flame from the burner and/or regulating the draft inducing action of the stacksat the rear of the forehearth. j

In the drawings:

Figure 1 is a. `generallyA longitudnal vertical sec-tion through'a forehearth embodying the invention and shown appurtenant to a portion of al glass melting tank, the section line on which the view is taken extending centrally of 4the forehearth from the outer end of the forehearth for part of the length thereof and then. being offset laterally to extend nearerito one side ofthe forehearth for the remainder ofthe length of the latter;

Fig. 2is a transverse vertical section to the forehearth, substantially along the line 2--2 of Fig. 1;

Fig. 3 is a .fragmentary vertical section through. a portion of the top of the forehearth embodying the invention, showing -a removable refractory block in position to reduce or prevent heat radiation from a portion of the heat rad'ating metallic cover section of the top of the forehearth; p

Fig. 4 is a view similar to Fig. 3 but showing a modified form of top structure of a forehearth embodying the invention and illustrating'a method of preventing radiation of heat through part or all of the metallic cover plate of the top by placing a removable refractory block or blocks beneath part or, all of such metallic cover plate.

Fi g. 5`is a fragmentary longitudinal vertical section through a vmodified forehearth structure, generally similar tothat shown in Fig. 1 but provided at its outer end with a gathering basinand means for regulating the draft conditions therover; y

' Fig. 6 is a view similar .to Fig. 1 but showing a forehearth having a basin for a gathering pool at its outer/end and provided with a modified formof heat radiation controlling 'neeaeei top structure and with a modified construction for controlling the transverse distribution of heat within the space above the glass in the forchearth;

Fig. 7 is a transverse section through the forehearth structure of Fig. 6, taken substantially along the line 7 7 of Fig. 6; Y

Fig. 8 is a fragmentary longitudinal vertical section through a forehearth generally similarto that shown in Fig. 6 but provided at its outer end with a spout for the feeding of glassY through a submerged outlet;

Fig. 9 is aview generally similar to Fig. 1 but showing another form of forehearth structure embodying the invention;

Fig. 10 is a transverse section through the forehearth structure of Fig. 9, the view being taken substantially along the line 10-16 of Fig. 9;

Fig. 11 is a fragmentary longitudinal vertical section through still another form of forehearth embodying the invention;

Fig. 12 is a transverse vertical section 'along the line 12-12 of Fig. .11;

Fig. 13 is a view similar to Fig. 11, showing still another form offorehearth structure for carrying out the invention;

Fig. 14 is a fragmentary plan view, partly in section, showing a portion of the forev` hearth vstructure of Fig. 13'; and

Fig. 15 is a transverse vertical section substantially along the line 15-15 of Fig. 13.

rlhe forehearth structure shown in Figs. 1 and 2 comprises a metallic frame work 1 connected with the frame structure of a melting tank 2, Fig. 1, so as to permit independent expansion and contraction of the walls of the forehearth and of the 'melting furnace. The glass conducting channel of the forehearth is supported by the metallic frame structure and comprises a refractory bottom, side and top walls respectively indicated generally at 3,- 4 and 5. The walls of the forehearth channel are Aspaced from the metallic frame work structure by suitable refractory spacingmembers, such as indicated at 6 and adjusting mechanism, such as those indicated at 7, whereby the forehearth channel will be supported bv the metallic casing and may be adjusted relatively thereto according to particular requirements or conditions and as required to receive molten glass 8 from the furnace outlet 9 to the best advantage. rll`he refractory glass conducting walls of the forehearth channel may be insulated, as by insulation such as indicated at 10, at the bottom, sides and for part of the top thereof to prevent orminimize radiation of heat from the glass through such portions of the fore- 601 hearth. A suitabl insulated refractory feed spout 11 is provi ed at the outer end of the glass conducting channel, Fig. 1.k rlhis lfeed spout is shown as having a discharge outlet 12 in its base, below the glass level, through 65 which molten glass may be discharged under the control of the glass feeding mechanism generally indicated at 13.

A refractory separator block 14 extends transversely of the glass `conducting channel adjacent to the furnace outlet and dips into the glass so as to prevent communication between the space above the glass in thefurnace 'and the space above the glass in the forehearth.

The structure shown is suitable for the feeding of glass in mold charges and as described so far is generally similar in' con'- struction to that of the forehearth structure of the well-known Hartford single feeder, a disclosure of which may be found in my copending application, Serial No. 683,57 6, filed December 31, 1923.

A pair of stacks 15 communicate with the space above the glass at the inner or rear portion of the forehearth at opposite sides of the longitudinal median line of the forehearth channel. Each of these stacks is provided with a damper 16 and with suitable mechanism 17 for adjusting the damper to vary the effective draft outlet of the stack.

The space above the glass adjacent to the feed spout 11 is enlarged upwardly to provide a firing chamber 18. rlhe walls of the firing chamber 18 are formed of suitable refractory material and. so far as practicable, preferably are provided on their outer surfaces with heat insulating material. The rear wall of such firing chamber preferably is inclined forwardly and upwardly and constitutes a burner block. indicated at 19, provided with an inwardly enlarging opening 2() through which flame from a burner 21 may be projected forwardly and downwardly in the firing chamber. rlhe top wall of the ring chamber preferably is inclined downwardly and forwardly, as indicated at 22, so that the flame and heat from the burner 21 will be deflected downwardly and forwardly into the feed spout and against the glass therein. the inner walls of the feed spout being formed to cause a return or rearward movement of the heated gases close to the glass in the forehearth channel.

With this arrangement, the llame and heat from the burner not only will locally heat the glass passing into the feed spout and in the latter but will be constrained to pass rear-` wardly along the surface of the glass in opposte side portions of the forehearth ch annel to the stacks 15 and thence through the latter to the atmosphere. The effective heating action and velocity of movement of the heated gases above the glass in4 the side portions of the forehearth channel may be regulated by adjusting the dampers 16, by controlling the volume and character of flame from the burner 21, or by a combination of these adjustments. As a result of the passage of the heated gases above the glass in the side portions of the forehearth channel, the glass which otherwise would tend to become colder and-more viscous and to How more slowly than the glass at the longitudinal median portion of the forehearth channel is heated more intensely than the middle glass, thus tending to cause more uniform velocity of flow and temperature and viscosity conditions in the glass throughout the cross section of the glass conducting channel.

In addition to the control of the distribution of heat transversely of the forehearth, a further control of the temperature and viscosity conditions throughout the cross section of the forehearth is effected by means which will now be described. The longitudinal median portion of the refractory top 5 of the glass conducting channel of theforehearth is cut away, as indicated at 23, to provide an opening of predetermined length and width above the glass 'at the longitudinal median line of the forehearth. A metallic cover plate 24 is arranged tocover the opening123. The cover plate 24 preferably is an arched member, as shown, having supporting flanges at.

its marginal edges insulated from the refractory top wall of the' forehearth' by suitable heat insulating material, such as indicated -at,25. This metallic cover plate 24 should have high heat resisting qualities. A

metal known commercially as Q-alloy has been found to be satisfactory for the purpose. The insulation on the refractory top of the glass conducting channel of the forehearth may extend flush with the crown of the cover member 24, las shown in Figs. 1 and 2.

- A cooling pipe 26 for blowing air or other i cooling media on' the metallic member 24 may be disposed above the latter and may be provided with longitudinally spaced downwardly turned discharge nozzles 27, each provided with an independently controllable valve 28,' whereby the member 24 may be locally cooled to dilferent extents at different places along its length.

The operation of the embodiment of the invention just described may be substantially as follows:

Molten glass from the tank 2 will flow through the tank outlet 9 beneath the refractory separator or gate member 14 into the flow channel of the forehearth. Tendency of the glass in the side portions of the flow channel to lag behind the glass in the longitudinal median portion of the flow channel and to become cooler and more viscous may be minimizedor practically prevented by reason of the relatively intense and greater local heating ofthe glass in the side portions of the orehearth by the heated gases which are conducted in clearly defined channels from the firing` chamber 18 rearwardly along the side walls of the forehearth .channel to the stacks 15.` At the same time, the temperature of the glass at thek longitudinal median portion of the forehearth channel may be reduced by -claimed in my copending reason of the relatively greater radiation heat through the metallic heat radiating plate section of the glass at the forward end ofthe channel may be obtained. The glass supplied to the feed spout 11 therefore will be homogeneous and of uniform and desirable telnperature, viscosity and condition.

It may be desirable at times to shut oil' the relatively greater radiation of heat fron the longitudinal median portion of the forehearth through the metallic plate 24 or through a portion thereof. This may be done by placingl a refractory block 29 on lthe me' tallic member 24 or on any portion of the latter, as shown in Fig. 3. If desired, the inetallic coolino' member may extend above the heat insulation on the refractory top 5a of the forehearth channel, as illustrated in F ig. 4,-in which the metallic cooling member 1s designated generally at A24a'. 1n such construction, the metallic cover member may include hinged side sections 30, each of which may be swung outwardly and upwardly to permit a refractory cover block 31 to bev essential respects with the construction of Fig. 1 as hereinbefore described except that the feed spout 11 and associate feeding mechanism 13 o f the construction of Fig. 1 are replaced in the construction of Fig. 5 by a basin 38 for holding'a pool of moten glass from which glass maybe removed by suction molds or`other gathering receptacles. The iring'space of the construction shown in Fig. 5 is indicated'at 18a and the front wall thereof may comprise a vertically adjustable refractory baille 39 which depends close to the glass and is adjustable to Vary the exchange of heat permitted between the space in the firing chamber and the space above the glass in the gathering basin. Suitable glass circulating means, not shown, may be provided for use in connection with the glass gathering pool in the basin 38. The basin construction of the form o f forehearth shown in Fig. 5 comprises features which are disclosed and. prior application, Serial No. 387 ,285, filed August 21` 1929, and which therefore need not Y as they are not being claimed in this application. The same reference: characters have been usel to designate like parts of the conbe described herein structions of Figs. 1 and 5 and the operation of the construction shown in Fig. 5 will be y understood fromthe hereinbefore given statement of the operation of the construction of Fig. 1 supplemented by the brief description above given of the construction of Fig. 5.

In the construction shown in Figs. 6 and 7, the refractory top 56 of the forehearth channel comprises blocks which extend transversely across such channel and have central por-` tions thereof depending downwardly to provide a longitudmal baille 32. The ytop 5a is formed with a series of longitudinally spaced openings 33, each of which may be formed in one of the component blocks of the top 5a. Each opening 33 extends downwardly through the baffle portion 32 of the refractory top of the channel and is covered at its upper end by a metallic heat radiating cover member 34. An individual blow nozzle 35, provided with a regulating valve 36, may be provided above each of the cove-r plates 34 for projecting a regulable volume of air or other cooling media against the plate 34. The baffie 32 depends close enough to the glass level practically to prevent passage of any appreciable volume of heated gases along the lonitudinal median portion of the glass in the orehearth and the side Walls of the baille 32 cooperate with the adjacent portions of the side walls 4a of the glass conducting channel of the forehearth and of the refractory top 5a to define passages, indicated at 37, above the side portions of the forehearth channel through which heated gases and products of combustion pass from the firing chamber 18a, at the front of the' forehearth rearwardly to the stacks 15a. Each of the stacks 15a is provided with a damper'l and with damper adjusting mechanism 17. The particular forehearth structure shown in Fig. 6 has thefront or outer end portion thereof formed as P a basin 38, as in Fig. 5, for holding a pool4 of molten glass from which glass may be re i moved by suction in molds or other gathering receptacles.- In order to controldraft and temperature conditions over the glass in the gathering basin, the front or outer wall of the firing chamber 18a may comprise the vertically adjustable refractory baile 39 which depends close to the glass butcan be adjusted with respect to the glass level to vary the exchange of heat between the space in the firing chamber and the space above the glass in the gathering basin.

The glass conducting channelof'the rfoehearth construction of Fig. 6 may correspond in all other essential respects with the construction shown in Fig. 1 and heretofore de- Y scribed. Consequently parts of-the construction of Fig. 6 which are identical or not essentially different from corresponding parts of Fig.r 1 will not be described but are designated by the same reference characters as The construction shown in Fig. 8 diers 'from that shown in Fig. 6 in that a feed spout 11a and glass feeding mechanism 13 are provided, as in Fig. 1, at the outer end of the forehearth in lieu of the gathering basin 38 of F ig. 6. Otherwise, the construction shown in Fig. 8 conforms in all essential respects with the construction shown in Fig. 6.

ln Figs. 9 and 10, the refractory top of the glass conducting channel is desi nated 56 and may be said to be of the canti ever type of construction. rlfhis top wall comprises longitudinal series of cantilever blocks having their outer portions supported on the side Walls 46 of the forehearth channel structure and on portions of the side members of the metallic casing, as best seen in F ig. 10, such blocks being clamped securely in place by the metallic side frame members 40, the metallic top plate 41 and `the adjustable connections 42 between the metallic top and side frame members. The cantilever blocks of the refractory top of the glass conducting channel have portions spaced apart above the longitudnal median portion of the forehearth channel to provide the opening 236. A metallic cover plate 246 covers the openin 236 and may be retained in place by thec amp members 43. The cantilever blocks have cutaway portions at their bottoms to provide the central baille .326 and the side passa es 44 for conducting heated gases from t eA firing chamber 186 ,to the stacks 156. Acooling pipe 266 having the separate nozzles 276 ar-r spaced portions of the metallic plate lmay be provided for locally applying cooling air or other cooling mediato the lates 246, if desired. Each of the nozzles 2 6 may be rovided with a separate re ulating valve 286. The remaining parts oft e construction shown in Figs. 9 and 10 are substantially identical with .corresponding parts of the construction shown in Fi 1 and have beenl designated by the same re erence characters.

In Figs. 11 and 12, the refractory top of the forehearth channel is designated generally at 5c and is of the arched type of construction.' The component blocks of this arched refractory top member of the forehearth channel are supported on the refractory side walls 4c of the channel structure, as best seen in Fig. 12, and include crown or key blocks haying depending lower portions formed to provide a baille 320 above the longitudinal median portion of the forehearth channel for part of the length of the latter and the side passages 370 for the v-assage of heated gases 1':

ins

QF lard tion shown in the baile 320, and is covered at its upper end by a heat radiating metallic plate 34e. Anv individual blow nozzle '-350 provided with a separate valve 36e may be provided. above each of the plates 340 for discharging air or cooling media thereon. The remaining parts of the forehearth structure of Figs. 1.1 and 12 are not-essentially different from like parts of the constructiongof Fig. 1 and have been designated by the same' reference characters.

The forehearth co struction of Figs. 13 to 15 inclusive has are actory top designated 5d, comprising refractory blocks so formed and so disposed as t provide longitudinally spaced vertical openings 33d above the longitudinal median portion of the glass in the forehearth and the muffled longitudinally ex tending side passages 37 for conducting heated gases from thel front firing chamber 18d to the lowerends of the stacks 15d. As clearly shown in Fig. 15, the, blocks of 'the refractory top 15d have their lower surfaces close to the glass level,and the heating of the glass in the side portions of the glass conducting channel is effected by radiant heat imparted from the gases passing through flues or muilled passages 37d through the bot-- toms of such passages to the glass therebeneath. Each of the openings 33d is covered at its upper end by a metallic heat radiating plate 34d. Such o enings may be square in cross-sectional con guration as shown in Fig. 14. A separate blow nozzle 35d, controlled by a valve 36d, may be provided above each of the metallic plates 34d, for discharging` air or other cooling medium thereagainst when desired.

The remainin portions of the construc- Figs. 13`to 15, inclusive, are designated by the same reference characters as generally corresponding parts of they c'onstruction'shown in Fig. 1.

In'the use of each of the specifically different constructions hereinbefore described and illustrated in the respective views of the drawings, conditioning of the glass in the forehearth may be regularly controlled by the conjoint action of the means which controls the distribution of temperature and draft .conditions within the forehearth and the means which permits relatively greater radiation of'heat from the glass at the longitudinal medianv portion of the forehearth so that the glass passing to a feed spout, glass athering basin or other supply-chamber at e outer end o the forehearth will be uniform in temperature, viscosity and condition and will be of desired predetermined regulable condition, temperature and viscosit for use as' required for a particular service. The regulation and control of the temperature and condition of the glass within the fore# hearth may be entirely independent of draft and temperature conditions within the space above tbe glass in-the furnace and is effected 'of said channel.

furnace of a Vforehearth having a channel along which nace, means or introducin a heating medium into the s ace above tle lass adjacent to the outer en of the channe and separate v draft inducing means respectively communif lass may iow from said fur-,

eating at opposite sides of the longitudinal median line of the forehearth with the space above the glass adjacent to the inner end of said channel for causing the path of movement of heat from the outer end of the channel .to-be mainl above the side portions of the glass insai channel.

2. Thel combination with a glass melting furnace of a forehearth havin .an enclosed channel along whiclrmolten g ass may flow from the furnace, means for introducing a heating mediuminto the space above the glass adjacent to the outer end of said channel, and a pair of stacks respectively lcommunicating at opposite sides of the longitudinal median line of the channel with the'space above the glass adjacent to the inner end of the channel for causing the heated gases at the outer end of the channel to pass longitudinally of the channel abovethe glass in the side portions 3. The combination with a glass melting furnace of a forehearth pro'ecting therefrom and havin a flow channel or receivin molten glass rom the furnace, said fore earth having a firing chamber above the glass adjacent to the outer end ofthe channel and having separate draft inducing means respectively in communication at o posite sides of the longitudinal median line o the channel with the space above the glass adjacent to Athe inner end of the channel, and means for projectin a heating mixture in combustion downwar l'y .and forwardly in said firing chamber abovethe longitudinal median line ofsaid channel. y

l 4.1The combination with a glass melting furnace of a forehearth proj ectin therefrom and having a channel along whi glass may flow from the furnace, means for separating the space above the glass in the forehearth from the ace above the glass in theA furnace, means for introducing a heating medium into ass in said channel adthe space above the jacent to one end of tie latter to cause heating of the glass in the forehearth independently of heat from the furnace, means, including separate draft Ainducing means, respectively communicating with the space above the glass in the channel at opposite sides of the longitudinal median line thereof, for causin the heated gases in the forehearth to trave lon-l rasee-,oei

greater radiation of heat `from glass atthev longitudinal median portion of said channel than from the glass in the side portions ot said channel.

5. 'lhe combination with a glass melting furnace of a orehearthprojecting therefrom and having a channel along which glass may flow from the furnace, means for introducing a heating medium into the space above the glass adjacent to the outer end of the channel, a cover structure :for said channel having an imperforate lmetallic portion located' above the glass in the longitudinal median portion of said channel to cause a relatively greater radiation of heat from part of the lass at the longitudinal median portion'ot t e channel than from the glass in the side portions of the channel, saidmetallic portion having its outer surface exposed at the top of said cover structure, means tor causing heated gases-Withintheforehearth to travel longitudinally ot the channel mainly above the glass in the side portions or' said channel and means for insulating the glass conducting channel of the Jorehearth at the bottom and sides thereof.

6.' 'lhe combination with a glass melting furnace of a orehea'rth having a refractory channel along `which glass may now from the orehearth, means. separating the space above the glass in the orehearth from the space above the glass in the furnace, means Jfor introducing a'heatin'V medium into the space above the glass in t e Jorehearth, means for controlling the distribution of flow of heated gases Within thel oreheartli to cause said eli) heated ases to travel mainly above the glass in the side portions of said channel, and impertcraf metallic means above part oi the glass at the longitudinal medianl portion of said channel for causing a relatively greater radiation or heat' from the glass at the longitudinal median portion ot the channel than from the glass in the side portions of the dow channel, said impertorate metallic means having its inner surface exposed to heat from the underlying glass and its outer surface exposed at the outer side of the orehearth.

7. The combination with a glass melting turnace of a orehearth having a refractory channel along which glass may flow from the furnace, means' separating t ie space above the glass in the forehearth from the space above the glass in the furnace, means tor introducing a heating medium into the space above the glass in the orehearth, means tor controlling the distribution ot iloW of heated gases Within the orehearth to cause said heated gases to travel mainly above the glass in the side portions of said channel, imperiorate metallic means above part ot the glass at the longitudinal median portion of said channel for causing a relatively greater radiation ci heat from the glass at the longitudinal median portion o the channel than trom' the glass in the side portions or said channel, said impertorate metallic means being in direct heat communicating' relation with bot-h the space Within the orehearth and the atmosphere outside or the orehearth, and means lfor locally cooling said imperiorate heat radiating means. l

8.".lhe combination-With a glass melting 'furnace of a orehearth having a refractory channel along which glass may ow from the orehearth, means separating the space above the glass in the orehearth from the space above the glass in the furnace, means Sor introducing a heating medium into the space above the glass in the orehearth, meansfor controlling the distribution ot. new of' heated gases Within the torehearthto cause said heated gases to travel mainly above the glass in the side portions ci said channel,

imperiorate metallic means above part of the y glass at the longitudinal median portion o' said'channel ior causing a relatively greater radiation of heat from the glass at the lon gitudinal median portion ot the channel than :trom the glass in the side portions ot the channel, and means tor locally cooling said imperforate heat radiating means, said coo-ling means being adjustable to vary the cooling ot said imperiiorate metallic means inde# pendently at a plurality of ditierent Aplaces above the longitudinal median line ci the lorehearth 9. 'lhe combination vvitha glass melting furnace oi" a orehearth projecting therefrom and having a channel along'vvhich' glass'may flow trom the furnace, said channelha-ving refractory bottom, side and top Walls, said refractory top Wall being spaced from the I` glass in the channel, refractory means scparating the space above the glass in the channel 'from the space above the glass in the turnace, said refractory top vvall having a vertical opening iormed therein above the longitudinal median line of the channel, ametallic member completelyclosing the upper vend ot' said opening 'to cause a relatively greater radiation oit heat from the glass belovv said metallic member than'trom the glass in the side portions ot said channel, means for introducing va heating medium into the space above the glass adjacent to one end of said channel, and means for controlling the distribution ot llow of heated gases above the glass in the channel to cause said heated gases to travel longitudinally of the Jforehearth mainly above the glass in the side portions ot said channel and laterally of the space beneath said metallic heat radiating member.

l0. rl`he combination with a glass melting furnace o a forehearth projecting therefrom and having a channel along which glass may iiovv from the furnace, said channel having refractory bottom, side and top Walls, said 'ies l refractory to wall being spaced from the glass in the c annel, refractory means separating the space above the glass in the channel from the space above the glass in the furnace, said refractory top wall having a vertical opening formed therein 'above the longitudi-4 nal median line of the channel, a -metallic member completely closing the upper end of said opening inv the refractoryvtop Wall of the lchannel to cause a relatively greater radiationifofjheat from the glass below said me- -tallic member than from 'the glass in the side portions of said channel, means for introducing a heating mediuminto the space above the glass adjacent to one end of said channel, and means for controlling the distribution of flow. of heated gases above'the glass in the channel to cause said heated gases to travel longitudinally of the forehearth mainly above the glass in the side portions of said4 channel andv laterally of the space beneath said metallic heat radiating member, said heat radiating member being formed'to per-v mit removable refractory blocks to be placed in position to shut olf said relatively great radiation of `heatthrough aregulable portion or all of said opening in the refractory top member.

11. The combination with a glass melting furnace of a forehearth'projecting therefrom and having anenclosed channel along which glass may owfrom the furnace, said forehearth being formed to provide side passages above the glass in the side portions of said .35 channel for conducting heated gases lo ngi-,l

tudinally of the forehearth, means separating the space above the glass in the forehearth from the space above the glass in thefurnace, ymeans for introducinga heating medium into 40 the space above the glass in the channel adjacent to one end of each of said side passages, and separate means in communication with the space above the glass in the channel at the opposite end of each of said side passages for causing a draft in each side passage, whereby the heated' gases in said channel will travel mainly through said side passages, and imperforate means located above the space' between said side passages for causinoa rela- 5. tively greater radiation of heat from the glass at thelongitudinal median portion of the.

channel than from the glass below said side passages. v

12, The combination with a glass meltingv 55 furnace of a forehearth projecting therefrom and havin a channel along which molten glass may ow from the furnace, said channel having refractory bottom, side and top walls, the refractory top wall of the channel having w a vertical opening therein above the longitudinal median line ofthe glass in the channel, andl an imperforate metallic closure for the upper end of said opening for causing a relatively greater radiation of heat from glass at the longitudinal median portion of the channel than from the glass in theside portions of said channel.

1 3. The combination with a glass melting furnace of a forehearth projectin therefrom and having a channel along whic glass may flow from the furnace, said channel having a top structure formed with a relativelyv thin mperforate portion above the `glass in-the longitudinal median portion. of the channel to cause a relativeily greater radiation of heat from the longitudinal median portion of the glass in the channel than from the glass in the side portions of said channel, the inner and outer surfaces of saidimperforate portionLof the top structure respectively being exposed to heat from the underlying glassand to a cooling medium above the forehearth.

14. The combination with a glass meltingl said furnace, means for introducing a mix` ture, in combustion into a firing space above the glass in the. channel adjacent toone end of the latter, .and separate independently regulable draft inducing means communicating at opposite sides of the longitudinal median line of the channel top for causing independently regulable flow of heated gases from said firing space longitudinally of the channel above the glass in the side portions of said channel.

15. The combination with a glass melting furnace of a forehea'rth having a channel along which glass may flow from said fur nace, a cover Ienclosing said channel, said cover having a longitudinally-extending chamber with a bottom opening communicating with the space above the longitudinal median portion of the glass in the channel, and means for absorbing heat from said chamber while the top 'of said chamber is closed to the atmos here.

16. The combination with a glass melting furnace of a forehearth having a channel along which glass may flow from said furnace, a cover enclosing said channel, chamber means disposed in said cover for providing a heat column` above the median portion of the glass in the channel higher ythan the heat column above the side portions of said channel and means for. absorbing heat from said chamber while'the top of said chamber is .closed to the atmosphere;