US2828532A - Method for constructing parallel slot gas burner - Google Patents

Description

R. R. TAYLOR April 1, 1958 METHOD FOR CONSTRUCTING PARALLEL SLOT GAS BURNER 2 Sheets-Sheet 1 Original Filed Dec. 20, 1954 INVENTOR.

m N MWW a v! N T A A m R April 1, 1958 R. R. TAYLOR METHOD FOR CONSTRUCTING PARALLEL SLOT GAS BURNER Original Filed Dec. 20, 1954 2 Sheets-Sheet 2 INVENTOR.

ROLAND R- TAYLOR WM ATTORNEY United States Patent METHOD FOR CONSTRUCTING PARALLEL SLOT GAS BURN ER Roland R. Taylor, South San Francisco, Calif., assignor to Fraser & Johnston Co., San Francisco, Calif., a corporation of California Original application December 20, 1954, Serial No. 476,338. Divided and this application February 11, 1957, Serial No. 642,923

3 Claims. (Cl. 29-157) This invention relates to a method for making an improved gas burner. This application is a division of application Serial Number 476,338, filed December 20, 1954.

It has been a problem in gas furnaces to obtain enough port area in a small space for the large quantities of gas necessary to produce the required amount of heat. The conventional approach was to employ a cast-iron burner unit in which was drilled a large number of round holes. The size of any one hole is limited by the gas pressure being used and by the burning rate of the fuel, because fuels which burn very quickly tend to flashback inside the burner when the opening is large. It has been found that for most natural, liquefied petroleum, and manufac tured gases the burner holes must be relatively smallabout 0.120 inch in diameter or less-if flashback is to be avoided. It takes many such holes to give any significant port area. Thus when a burner is drilled with a No. 32 drill, each hole is about 0.01057 square inch in area. This is about as large a hole as is normally practical, and it takes about 100 of these holes to make one square inch of port area. One square inch is not sufficient for most burners; so normally there had to be about one hundred holes to each 15,000 B. t. u. input. In order for a burner to accommodate an input of 150,000 B. t. u., there would have to be 1000 of these drilled ports. This type of construction was objectionable for several reasons. In the first place, such burners took up too much room and resulted in large furnaces. In the second place, the manufacturing costs were high. The holes could not normally be drilled by gang drill, because the rough cast material tended to break drill points very frequently; the time it took to replace drill points made it more feasible to drill each hole individually, and this increased the labor cost of manufacturing the burner.

It has long been known that, theoretically, improved results can be obtained by cutting a narrow slot instead of drilling holes. Such a slot was normally cut in a cast iron burner by a metal saw, a bridge being used at spaced locations to maintain the proper slot width and to keep the cast-iron burner housing from closing in at the slot. A single slot of an inch wide and 16 inches long, will provide a full inch of port area or as much as 100 holes of approximately of an inch in diameter, which cannot be gotten into a line less than 20 inches long. But the manufacturing cost of these slots in cast iron is very high, and an excessively long burner unit is required, because it is not feasible to drill parallel slots; the reason for this is that a center portion in between parallel slots would be free floating and would tend to close one slot and open the other, thereby causing flashback in one slot.

For these reasons, the problem of obtaining correct port area has for a long time remained unsolved. However, attempts were made to solve the problem by using sheet steel instead of cast iron and by forming several parallel slots instead of having only a single slot. The

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problem with sheet steel has been to obtain correct spacing without causing other problems and to arrive at a practical and economically feasible method of doing this.

As already stated, it is important to keep the width of each slot constant at a rather critical amount. When the slot has been too wide (that is more than about ,4 of an inch) flashback has occurred, and this has sometimes resulted in serious explosions. On the other hand, the slot should not be too narrow, for there is a definite relatien between the total slot area and the amount of gas the burner will effectively burn. For example, with natural gas, gas can be effectively burned at about the rate of 15,000 B. t. u. per square inch of port area. Best operation is obtained when each of the parallel slots is exactly the same width over its entire length.

In attempting to solve this problem the prior art has tried various types of spacing members, each of which had its disadvantages. For example, corrugated spacing members have been widely used, but they impeded tr e tlow of gas and resulted in an uneven distribution of gas that significantly reduced the amount of gas that could be burned per total slot area, since these corrugated members extended the entire length of the slot. Nowhere near the theoretical value was obtained, even after accounting for the undesirable fact that the corrugated spaced members themselves consumed a substantial area. The slot thickness is not truly constant where corrugated spacers are used but varies at every point, causing further unevenness of flow. In fact, the effective slot area proved to be less than half of the theoretical value. For these reasons, most manufacturers who attempted this solution have now returned to drilling holes in cast-iron burners.

Other types of spacing members have been tried, but these spacers have generally occupied the whole width of the slot for their length, and therefore have greatly reduced the slot area per length of slot. Also these spacing members have had to be secured in place, and their installation has been a problem and an expense.

Still other attempts to provide constant spacing have involved a large amount of die work and welding, and yet these structures have not proven satisfactory. All the prior art attempts also had the disadvantage that they required excessive amounts of metal to insure proper spacing, and this, too, added further to the expense as well as to the weight of the finished burner.

The present invention solves this problem in an efiicicnt and inexpensive manner. it provides slots of constant width with superior performance characteristics, produces the assembly without adding any significant amount of additional metal, and the structure operates with negligible interference with the flow of gas.

These important results are accomplished partly by employing screw threads in a novel manner both to hold in place metal members defining the slot and to space them apart. The spacing may be determined by temporary spacer jigs in the factory, which are withdrawn after the burner is assembled; so there is no need to introduce any permanent spacing members besides the screws themselves.

Thus the present invention obtains a maximum port area from a plurality of narrow slots. The importance of the present invention lies partly in its ability to provide exact spacing so that narrow slots can be used without causing additional problems and partly in its ability to obtain the maximum port area with any given width of slot, because of the fact that there is very little interference with the slot area.

The present invention also solves the lint problem. Chicago, in particular, has stringent laws against burners which become clogged with lint and the other materials that float around in furnace rooms. Heretofore, these materials got inside the burner along with the air taken in to support combustion of the gas, and they clogged the narrow slots in sheet-metal burners. Members using corrugated spacers were particularly susceptible to lint-clogging because their many edges caught the floating particles, and the particles would build up until they partially choked the burner ports. When the ports are thus choked, the fiow of air-gas mixture is reduced and the static pressure within the burner is increased. With increased static pressure the air aspiration is reduced, and a yellow sooting flame results, clogging fun nace and flue passages. At times the internal static pres sure will get high enough to cause the gas to seep from the mixer of the burner, causing a tire outside the firebox.

In the present invention the lint problem has been solved by a combination providing the sheet steel burner walls with a smooth bend where the lint cannot lodge and providing the metal spacers with coined edges too smooth to catch lint. The importance of this construction is exemplified by the fact that until the burner described herein was submitted to tests, Chicago had disapproved every slot burner made from sheet steel; yet this new burner passed the test with flying colors.

Another important feature of the present invention is its adaptability to many different types of gases. Since gases differ in specific gravity, calorific value and in many other particulars, heretofore a burner which would give satisfactory results with all natural gases would not work satisfactorily with liquefied petroleum gases such as butane and propane.

The present invention makes it possible to use exactly the same burner with both natural and liquefied petroleum gases, simply by changing the size of the orifice where the gas enters the hollow burner. The burner itself can easily be modified in manufacture, without making any fundamental change of design, to accommodate manufactured gases. This is done simply by using thicker spacing members, to make fewer or smaller spaces between the same housing members. In fact, many manufactured gases can be accommodated by the identical burner that is used for natural gas by simply changing the orifice size. In tests on particularly diflicult types of manufactured gases made at Portland, Oregon one of the burners described herein satisfactorily handled inputs of 20,000 B. t. u. up to and including 45,000 B. t. u. without any change being made in the burner. With this new burner, a narrow enough slot can be maintained accurately and any desired number of slots may be provided.

The present invention also solves important problems concerning the manufacture of the burner. It does this by making it possible to use a small number of standard sheet steel parts and by simplifying their assembly. The burners side walls can comprise one or two die pressed pieces, while the spacer elements themselves can be provided by a series of identical strips. The present method makes possible rapid and inexpensive assembly of these parts. Burners made according to this invention cost about two-sevenths as much as cast iron slotted or drilled burnerswhich themselves were cheaper to manufacture than any usable sheet steel burners heretofore on the market.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment thereof.

In the drawings:

Fig. 1 is a view in elevation of a gas burner unit made by a method embodying the principles of the invention. This particular burner unit is an end burner having crossover ports extending out from one side only, but it is to be understood that the invention applies where there are no cross-over ports at all and also where there are crossover ports on both sides of the burner.

Fig. 2 is an enlarged top plan view of the burner unit or in) of Fig. 1, the view being broken in the middle and at one end to conserve space.

Fig. 3 is a view in section, taken along the line 3-3 of Fig. 2 and showing the slot construction of the main burner.

Fig. 4 is a further enlarged view of the upper portion of Fig. 3.

Fig. 5 is a view on the same scale as Fig. 3, taken along the line 5-5 of Fig. 2 and showing the slot coni struction of the cross-over burner.

Fig. 6 is a view similar to Fig. 2 of a modified form of burner manufactured from the same burner housing blanks and differing only in the spacer, used to reduce port area.

Fig. 7 is a view in front elevation showing a burner unit like that of Fig. 1 being assembled in a jig, accord ing to the method of the present invention.

Fig. 8 is a view in section taken along the line 88 in Fig. 7.

Fig. 9 shows the relation between one side piece of a burner housing, one spacing member, and one side plate of the jig of Figs. 7 and 8.

The burner unit 10 may be employed as part of a gas furnace, the burner unit alone being shown herein because the invention does not concern the structure of other parts of the furnace. As Figs. 1 to 4 show, the hollow burner unit 10 has a gas inlet 11, a generally tubular passage 12, and slots 13, 14, 15, 16 and 17 from which the gas issues, the slots being formed by the upper side walls 18 and 19 of the metal housing member 20 (which comprises side pieces 21 and 22) and by a series of generally rectangular metal strips 23, 24, 25 and 26. The side members 18 and 19 are preferably integral with the pieces 21, 22, a smooth corner 27 being formed by bending, so that it is free from burrs or other lint-catching obstructions. Similarly, the edges 28 of the strips 23, 24, 25, 26 are all coined by tumbling, so that they will be smooth.

The cross-over burner 30 includes a housing 31 formed from wall members 32, 33 and providing a tubular passage 34. A center strip 37 held between the upper ends 35, 36 of the walls 32 and 33 divides the space between the two end members 35, 36 into the two slots, 38, 39. 'i his cross-over burner 30 serves to carry the flame from one burner unit 10 to a succeeding adjacent burner unit so that only one unit of the furnace need be ignited in order to light the whole furnace. It will be understood that the cross-over burner 30 could have more than two slots and that the main burner could also have more or fewer single slots.

The novel method of this invention make it possible to produce the burner 10 at a fraction of the cost which former methods took. For example, a sheet steel burner formerly produced at one factory cost $3.50 per unit. The present invention is now being used at this factory to produce even better burners of the same capacity and otherwise substantially identical or better performance for $1.00 each.

In the method of this invention, the burner housing side walls 21 and 22 and the spacer strips 23, 24, 25, and 26 are placed in a jig 40 which properly positions the strips 23, 24, 25 and 26 at the correct spacing from each other, from the burner side walls 18 and 19, and longitudinally. To make this possible the side housing members 18 and 19 and the spacer strips 23, 24, 25, and 26 are pre-punched to provide a series of holes 41 in the housing members 18 and 19 and a corresponding series of holes 42 in the strips 23, 24, 25 and 26. These holes 41 and 42 may be gang-punched, since they are in sheet steel, and all holes in each housing member or strip can be punched in one punch press operation. Both the spacer strips 23, 24, 25, 26 and housing members 18, 19 are punched with the same die, so that alignment will be perfect. This makes it possible to get accurate assembly of the burner unit 10.

The jig 40 includes a series of spacer-setting plates 43, each provided with a series of notches 44 on their upper edges 45 corresponding in location to the holes 41 and 42 of the strips and housing members. The plates 43 are the thickness of the slots 13, 14, 15, 16 and 17 and separate the strips 23, 24, 25, 26 from each other and from the burner housing side portions 18 and 19 a distance exactly desired.

The jig 40 also includes a series of generally rectangular support plates 46, whose widths correspond to the burner housing portions 18, 19 and strip portions 23, 24, 25, 26 which they support. (Thus in the modification shown in Fig. 6, some of the plates 43 are removed from the jig and a single wide plate 46 (not shown) is used instead of the thinner plates 46 shown in Fig. 8.) The support plates 46 align the strips 23, 24, 25, 26 and burner housing elements 18, 19 to the correct vertical position and retain them there, and also aid in correctly spacing apart the plates 43. Both the plates 43 and 46 are provided with holes 47 through which are passed bolts 48, that secure the plates 43 and 46 together loosely and to heavy end jig members 49, which have notches 44 like the plates 43.

The housing members 21 and 22 have their portions 18 and 19 inserted in the jig, as shown in Figs. 7 and 8, and the strips 23, 24, 25, 26 are likewise inserted while the jig 40 is loose. Then they are aligned by inserting a metal rod (not shown) through one or two of the aligned series of holes 41 and 42, passing through both housing members 18, 19 and all strips 23, 24, 25, and 26.

Once accurate alignment is obtained, a cam 50 adjacent one jig end member 49 is turned by its handle 51 and serves to tighten the members 49, 43, and 46 together, against the nut 52 on the bolt 48, the members 49, 43, and 46 being slidable along the base 53. This action holds all the burner slot elements tightly in place, as shown in Figs. 7 and 8.

The next step is to tap the openings 41 and 42 and insert screws 54 which retain the burner elements 18, 19, 23, 24, 25 and 26 permanently in place. This step may be done in a single operation by using self-tapping screws 54, or the holes 41, 42 may be threaded in one operation and the screws 54 threaded in place afterwards. The notches 44 give access to the holes 41, 42 and prevent drilling of the jig members 43 and 49.

Once the screws 54 are in place, the burner housing is complete, so far as its slot portion is concerned. The cam 59 may be turned to loosen the jig 40, and the burner unit it) taken out. Preferably this is done by an ejector 55 having two end blocks 56 that raise the slotforming portions 18, 19, 23, 24, 25, 26 of the burner housing 20 vertically out of the jig 40, this vertical movement serving to prevent any twisting of these members. From then on the threaded screws 54 both hold the metal strips 23, 24, 25, 26 in place, keep them aligned with the burner housing slot side members 18 and 19, and keep them spaced apart at precisely the correct distance. The screws 54 may have Phillips heads or any other type of head.

It will be seen that the screws 54 take up a relatively small amount of the slot area, and being round offer a negligible resistance to the flow of fluid around them. The effect is very nearly that of a spaced slot with no interference at all. The spacing is positive, and once the screws 54 are in place the spacing cannot be changed without removing the screws; so there is no chance of variation from the predetermined spacing which was selected at the time of assembly.

The burner housing 20 is completed by welding the seams 57, 58 together. Instead of doing this, the members 21, 22 may be made from a single piece, but the two-piece welded construction is far preferable, since it saves money on the forming operation.

The cross-over member 30 is assembled by the same method and is welded to the housing 20.

The burner housing 60 shown in Fig. 6 is like the housing 20, except that there are only two parallel slots 61 62, provided by a single wide spacer 63 held by the screws 54 in proper spaced relation between the burner slot sides 18 and 19 of the same housing blanks 21 and 22. This illustrates how adaptable this new burner is.

The exactly spaced slots are in all cases extremely practical, and the screws 54 maintain the exact spacing at all times. The coined edges 28 and smooth corners 2-7 will not catch lint, so very efiicient operation becomes possible. Wide variations in fiuid flow may be handled by any one slot arrangement, while new slot arrangements are inexpensively arranged in the factory.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

l. A method for manufacturing a gas burner having parallel slots from sheet metal housing sides, sheet metal strips, and screws, comprising the steps of providing holes in said strips and sides, aligning said housing sides and said strips with corresponding holes aligned and with spacer means between them providing the correct slot width, threading said holes; inserting screws through said holes in threaded engagement with said sides and strips while they are so aligned and spaced, and withdrawing the spacer means from between them so that said screws hold them spaced apart.

2. A method for manufacturing a gas burner unit having parallel-slot ports from a pair of sheet metal housing sides, sheet metal strips and screws, comprising the steps of pro-punching said housing sides and strips at predetermined locations capable of alignment with each other; disposing each of said sides and strips generally parallel to each other while separating them from each other by spacers whose thickness represents the correct port spacing; inserting a tool through the corresponding punched holes through said sides and strips to accurately align them; clamping said side, strips, and spacers together while maintaining said alignment to hold said sides and strips the exact distance apart for correct port spacing; threading said punched holes and inserting said screws into said holes while retaining said alignment; welding a seam of said housing sides together to make a unitary housing, and then unclamping said housing and withdrawing it from said spacers, said screws then maintaining the correct spacing distance.

3. A method for manufacturing a gas burner unit having parallel slots from sheet metal housing members, sheet metal strips, and screws, comprising: providing holes through said housing members and strips at predetermined locations capable of alignment with each other; positioning said housing members and said strips parallel to each other while spaced apart from each other by spacing means, said holes being aligned with each other; threading said holes and inserting screws through said holes into threaded engagement with said housing members and strips; and then withdrawing said spacing means, leaving the screws spacing apart said strips and housing members.

References Cited in the file of this patent UNITED STATES PATENTS 1,723,311 Stine Aug. 6, 1929

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