GB1581649A - Sealing apparatus and process - Google Patents

Description

(54) SEALING APPARATUS AND PROCESS (71) I, THOMAS MARSDEN SMITH, a citizen of the United States of America, of PO Box C 94, 114 Villinger Avenue, Cinnaminson, State of New Jersey, 08077, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following state ment The present invention relates to the sealing of heat exchange tubes to a tube sheet, and to apparatus suitable for use in that connection.

Among the objects of the present invention is the provision of novel methods and apparatus for effecting such sealing.

The foregoing as well as additional objects of the present invention will be more fully understood from the following description of several of its exemplifications, reference being made to the accompanying drawings wherein: Fig. 1 is a somewhat diagrammatic vertical sectional view of one set-up for practicing the present invention; and Fig. 2 is a similar view of a modified setup pursuant to the present invention.

Industry has need for relatively small allmetal heat exchangers, as for use in cooling oil that lubricates an internal combustion engine. Such a heat exchanger can have as many as several hundred heat exchange tubes connected between two sheets in a leakproof manner. Leak-proof connections for this purpose are generally made by a fusible metal sealant whose melting takes place at a temperature well above the maximum operating temperature of the heat exchanger.

While tin-lead solders can be used as sealants for operating temperatures near the normal boiling point of water when no great mechanical stresses are encountered, brazing alloys including the so-called silver solders are used for higher operating temperatures or higher stresses. Such leak-proof brazing of a quntity of relatively small tubes in a tube sheet has been an awkward industrial operation that takes substantial time to assure the heating of all joints to the desired sealing temperature, and generally requires patching to seal leaks resulting from uneven heating during the original sealing.

According to the preent invention there is provided apparatus for simultaneously sealing a plurality of metal tubes in holes provided in a metal sheet which apparatus comprises a generally downward directed gas-fired radiant heater, means below the radiant heater for supporting the plurality of tubes in position in the holes in the sheet with the sheet in a generally horizontal position, and means for causing hot gaseous burner combustion products to flow down into the tubes in the assembly, to cause the sheet and the upper ends of the tubes to be rapidly and substantially uniformly heated to a temperature high enough to melt a layer of fusible metallic sealant carried on the top surface of the sheet and thus seal the tubes to the sheet.

The invention also provides a process for simultaneously sealing a plurality of metal tubes in holes provided in a metal sheet, which process comprises supporting the plurality of tubes in position in the holes in the sheet with the sheet in a generally horizontal position and carrying on its upper surface a quantity of a fusible metal sealant, applying heat to the sheet from a gas-fired radiant heater positioned above it, and causing the hot burner combustion gases to flow down into the tubes in the assembly to rapidly and substantially uniformly fuse the metal sealant and thus seal the tubes in the sheet.

The heat for the fusion is desirably applied by a ceramic fiber burner such as described and claimed in Patent Application No 14634/77 (Serial No 1581648), to which the reader is directed. Those burners generally have a ceramic fiber mat made of the ceramic fibers described in U.S. Patent 3,449,137, with the mat formation as described in U.S.

Patent 3,787,194.

The most efficient heating results of the present invention are obtained when the burner that supplied the heat envelopes the top and sides of the sheet in the tube-andsheet assembly. Such an enveloping burner is desirably divided into sections that can be operated independently to first heat the margin of the sheet in the sheet-and-tube assembly, and then heat the center. A particularly effective burner construction for this purpose uses a single porous ceramic fiber mat in the general shape of a hat with a shallow plenum divided by a wall into two parts, air or other incombustible gas being fed through one part when that part is not being operated while the other part is being operated. The porous margin of the mat can be sealed by a high-temperature-resistant impregnant like aqueous sodium silicate, and the sealed margin clamped in place. Sheets of soft material like aluminium foil can be interposed between the sealed margin and the clamping members.

Turning now to the drawings, the apparatus of Fig. 1 includes a table 10 movable up and down as indicated by the two-headed arrow 12, and a radiant heater 50 positioned above the table. The table carries on its upper surface a block 14 having a number of vertical passageways 16 corresponding to the number of tubes 18 to be assembled into a heat exchanger, and located in a corresponding pattern. The upper ends of the passageways 16 are enlarged as at 20 to receive and position the lowest portion of each tube.

The lower ends of the passageways 16 open at the bottom of block 14 over a suction opening 22 in table 10.

A blower 24 is shown as carried by table 10 and as provided with a suction tube 26 connected as by flexible duct 28 to a mounting ring 30 secured around opening 22. A butterfly valve 32 can be fitted to the suction tube 26 to enable controlling of-the suction applied to the bottom of block 14 when the blower 24 is operated. Also the suction tube 26 can be spaced as by webs 27 within a wider intake mouth 29, so that when the blower operates it sucks air in around the suction tube 26 as it sucks through tube 26.

Block 14 also carries a set of supports 34 encircling the tubes 18 and holding a tube sheet 36 in position at or near the tops of tubes 18. Supports 34 can be removably fitted in sockets 40 in block 14, and can have their lower portion cut away as at 42 to allow for the positioning of another tube sheet 37 on block 14.

Heater 50 has a porous ceramic fiber mat 52 on the general shape of a hat with a horizontal flange 54 by which it is mounted in place behind a face plate 56. The crown section of the hat shape consists of a cylindrical portion 58 a few inches in height and a hemispherical portion 60, and a relatively shallow plenum space 62 is provided around the crown by a housing 64 to which the face plate 56 is removably secured.

The plenum space is divided by a partition 66 that extends around the inside of the housing, into a lower generally annular plenum portion 68, and an upper hemispherical shell-like portion 70. Separate inlet nipples 71, 72 are provided on the housing for separately supplying combustion mixture to the separate plenum portions. In the illustrated embodiment the housing 64 is made of a lower cylindrical section 74 and an upper hemispherical section 76.

Outwardly projecting flanges 78, 80 on these housing sections where they meet, serve as attachment structure for holding the entire housing together and also holding partition 66 in place. To this end a number of threaded flange bolts 82 project through aligned sets of openings in flanges 78, 80 and in partition 66, and nuts 84 threaded on these bolts secure these members together. The bolts 82 are distributed around the housing, and they also project downwardly for enough to provide securing means for the face plate 56 which is also provided with mounting openings aligned with the bolts. An extra set of nuts 86 threaded on the bolts secures the face plate in place.

The burner is constructed by first assembling the housing portions 66, 74, 76, then forcing the pre-formed and prepared mat in the assembly so that it firmly engages the inner lip of partition 66, and then securing the face plate. The partition lip can be turned up as shown at 67, to make a better seal against the mat.

An internally directed flange 88 at the lower end of lower housing section 74 is used to provide a ledge against which the mat flange 54 is held to help seal the edges of the mat against gas leakage. A cylindrical flange 90 is also shown as integral with and projecting up from the top of the face plate, to encircle the mat edges and closely fit around the lower edge of the housing. This helps hold the mat in position and strengthen the face plate. A central hole 92 in the face plate slightly larger than the mouth of the mat 52 permits the top of the tube-andsheet assembly to be brought into the burner a short distance above the mouth of the mat, as well as the movement of gases out from and into the work space 94 enveloped by the mat.

The burner is operated with gaseous combustion mixtures, and it is accordingly helpful to seal all locations through which such a mixture can leak out from the burner.

Thus the joint between the housing members 64 and 66 as well as between 66 and 74, can be sealed by gasketing or as shown by painting these junctures with a liquid silicone that cures to a solid sealant. Also the margin of the mat flange 54 is shown as encircled by a sheet of aluminium foil 93 carefully folded around the upper, lower and edge faces 94, 95, 96, and sealed against ledge 88 by a sealant such as a self-curing liquid silicone rubber.

It is also helpful to fill the pores of the mat in the outer section of mat flange 54, as by impregnating that section with aqueous sodium silicate that dries in place or liquid silicone rubber that cures in place, as indicated at 97. Another desirable feature is to water cool the outer margin of the face plate, as by brazing water-cooling coils 98 to its lower surface.

In n operation the apparatus of Fig. 1 has its table first fitted with the tubes and tube sheets as shown, although there will usually be many more tubes than indicated in the figure, and a quantity of powdered or granular fusible sealing material 99 spread over the upper sheet 36. The blower 24 is started and the table is raised to the position illustrated so that the upper sheet 36 has its upper surface and side edges enveloped by the burner. Both sections of the burner are then started, followed by opening of suction control valve 32. When the tubes 18 are copper or brass with a wall thickness of about 30 mils, and the upper sheet 36 is of copper, brass or steel with a width of 8 inches and a wall thickness of about 90 mils, and the burner is burning about 130,000 B.T.U. per hour of combustion mixture, a copperphosphorus or silver-copper-flux sealing braze will in less than about 1/2 minute be melted and will flow into and seal each tube to the sheet with a text-book seal, regardless of how many tubes there are. Care should be used when applying the fusible sealing material so that excess material does not plug any tubes, which would impede the flow of hot gas through the tube resulting in uneven heating.

To avoid overheating, the burner is shut off as soon as the sealing is completed, although the suction can be continued.

Prolonging the suction helps cool down the heated assembly and thus further reduces surface oxidation.

If the suction is not used during the heating the heat-up of the sheet is not uniform and much more heat-up time is needed before all parts of the sheet are hot enough to melt the sealing material. By that time the outer portions of the sheet are greatly overheated and if not badly damaged can also become sealed to the supports 34 even if the upper ends of the supports are about 3/8 inch thick steel. On the other hand when the burnt combustion gases are sucked down the tubes at a speed as low as about 1/2 linear foot per second the heat-up becomes so uniform that the sealing of all the tubes is completed long before the upper ends of supports 34 get hot enough to seal. The portions of the sheet 36 touched by the supports 34 will not heat-up very rapidly, with or without theforegoing gas flow, and this will also tend to make the immediately adjacent portions of the sheet a little slow in heating-up so that for best results it is desirable to have the tubes at least about 3/8 of an inch away from all supports. Those supports can also carry special fittings that make their upper ends more massive for even greater thermal inertia, but the 3/8 inch spacing of the tubes from their tops is still enough. Where there is considerable hardware around the margin of the tube sheet it is helpful to start the lower section 58 of the burner 50 before starting the upper section 60, and to start the upper section a few seconds later after the margin of the sheet has absorbed sufficient heat to be well on its way to sealing temperature. To guard against misoperation air without fuel is blown through the upper portion 60 of the mat while the lower portion is burning and the upper portion is not burning. This practically equalizes the pressures on both sides of partition 66 and thus minimizes flow of combustible mixture to undesired locations where it can be unintentionally ignited.

Filling the mat pores at 97 also avoids localized collection of stagnant combustible mixture.

There is no practical upper limit to the speed with which the hot combustion gases are forced down the tubes. There is for example no need for gas-tight connections between the tubes and passageways 16; indeed as shown by the open gap between suction tube 26 and suction intake 29, it is helpful to have air leaks that draw unheated air into the blower along with the hot combustion gases and thus help guard against overheating of the blower.

The tubes 18 are themselves not very wide, generally less than a half inch in inside diameter, so that it is difficult to effect extremely rapid gas movement through them.

Speeds of 20 feet per second are suitable.

The seals made in a fraction of a minute pursuant to the present invention are found to have far fewer flaws than seals made in two-and-a-half minutes without the use of the gas movement down the tubes. Moreover because of the much greater uniformity of the heat-up according to the present invention the melting and flow of the sealing material is also more uniform so that less sealing material is needed. As compared to the quantities of sealing material ordinarily used in the prior art, about half as much is needed for use with the present invention. Thus for joints in which the tubes have an outside diameter about 2 mils smaller than the diameters of the holes in the sheet, only about one gram of sealing material are needed for every square inch of sheet surface in accordance with the present invention.

Fig. 2 shows a modified sealing arrangement of the present invention. Here a burner 150 having a generally flat burner face 152 is used. This extends the heat-up time somewhat as compared to the construction of Fig. 1, and as a result wide assemblies may take as much as 50% more time to seal.

However the sealing time is still far less than obtainable from the prior art.

The burner 150 of Fig. 2 can be constructed in the manner described in the application No 14634/77 (Serial No 1581648) preferably along the lines of its Fig. 5 where the ceramic fiber mat has its margin merely fitted to a frame having an inert gas blow-through arrangement in which the inert gas thus blown through the margins of the mat acts as to seal those margins against combustible mixture leakage. No other margin sealing is then needed.

In the Fig. 2 arrangement tubes 118 are sealed to a sheet 136 while the tube-and-sheet assembly is held within a tubular casing 119 which eventually forms the shell of the heat exchanger. In about a half minute such an assembly can be sealed following which the assembly is inverted so that the opposite end is similarly sealed, and the sheets are then later brazed or welded to the shell margins.

Where the shell is steel of low wall thickness it can be sealed against the sheets at the same time as the tubes are sealed, preferably using the enveloping burner arrangement of Fig. 1.

While suction provides a convenient technique for moving the hot burnt combustion gases through the tubes, they can also be forced through from above. Thus the burner of Fig. 2 can have its frame provided with a depending cylindrical extension that encircles the shell 119 and has an asbestos lining pad that closely engages the shell. Operating the burner in such an arrangement causes the hot burnt combustion gases to be discharged downwardly through tubes 118 since they have essentially no other way to escape.

For the purposes of the present invention, brazing is considered a sealing operation in which metal having a melting point at least as high as about 450"F and generally a copper alloy such as an alloy of 45% silver with 55% copper by weight, is the sealant. Brazing temperatures can go as high as 1300"F or even higher. Flux such as borax is frequently used with the brazing metal to protect it and the parts being joined against excessive oxidation and to promote wetting of the parts by the melted braze. Some brazing metals are copper phosphorus alloys or other alloys that can be used without a flux.

The heater in the sealing apparatus of the present invention can be operated continuously while sealing a succession of assemblies, but is preferably operated only for short intervals while the sealing metal is being melted and flows into place. Thus the heater can be completely shut off between sealing sequences, and ceramic fiber burners are particularly helpful in such intermittent operations inasmuch as they heat up and cool down in only a few seconds. For such intermittent operations it is also helpful to have the burner plenum of relatively small volume, preferably not over about 1 1/2 inches deep. In this way combustion gas can be intermittently fed to the plenum and rapidly reach the exit surface of the fiber mat where it is burned, so that the timing of the burner action is simplified.

An igniter such as a pilot light assembly or an electric spark ignitor can be fitted near the margin of the burner to assure that it lights up each time a combustion gas feed is initiated. A settable automatic switching sequencer can be used to time the gas feed to the different burner portions as well as the suction blower.

Instead of, or in addition to, moving the table up and down to bring the work to the burner, the burner can be moved toward and away from the table. In the construction of Fig. 2 no vertical movement is needed by the table or the burner.

An auxiliary heater can also be provided around and above the lower tube sheet 37 in the construction of Fig. 1, and operated to seal the lower tube ends into that sheet while the tube-and-sheet assembly is held in the illustrated position. Thus a layer of sealing mixture can be applied to the upper surface of the lower sheet and the auxiliary heater started even before the burner 50 is lit inasmuch as the heat-up of the lower sheet takes longer than that of the upper sheet.

Where the margin of a ceramic fiber mat has its pores well sealed, as by the silicone or sodium silicate or other alkali metal silicate impregnant, the mat margin can be damped in place without wrapping the aluminium foil 93 around those edges. The aluminium foil or other gasketing can still be inserted between the mat margin and the plenum margin, or the silicone or alkali metal silicate can also be used to seal the mat edge to the plenum.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

WHAT I CLAIM IS: 1. Apparatus for simultaneously sealing a plurality of metal tubes in holes provided in a metal sheet which apparatus comprises a generally downwardly directed gas-fired raiant heater, means below the radiant heater for supporting the plurality of tubes in position in the holes in the sheet with the sheet in a generally horizontal position, and means for casuing hot gaseous burner combustion products to flow down into the tubes in the assembly, to cause the sheet and the upper ends of the tubes to be rapidly and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. Fig. 1, and as a result wide assemblies may take as much as 50% more time to seal. However the sealing time is still far less than obtainable from the prior art. The burner 150 of Fig. 2 can be constructed in the manner described in the application No 14634/77 (Serial No 1581648) preferably along the lines of its Fig. 5 where the ceramic fiber mat has its margin merely fitted to a frame having an inert gas blow-through arrangement in which the inert gas thus blown through the margins of the mat acts as to seal those margins against combustible mixture leakage. No other margin sealing is then needed. In the Fig. 2 arrangement tubes 118 are sealed to a sheet 136 while the tube-and-sheet assembly is held within a tubular casing 119 which eventually forms the shell of the heat exchanger. In about a half minute such an assembly can be sealed following which the assembly is inverted so that the opposite end is similarly sealed, and the sheets are then later brazed or welded to the shell margins. Where the shell is steel of low wall thickness it can be sealed against the sheets at the same time as the tubes are sealed, preferably using the enveloping burner arrangement of Fig. 1. While suction provides a convenient technique for moving the hot burnt combustion gases through the tubes, they can also be forced through from above. Thus the burner of Fig. 2 can have its frame provided with a depending cylindrical extension that encircles the shell 119 and has an asbestos lining pad that closely engages the shell. Operating the burner in such an arrangement causes the hot burnt combustion gases to be discharged downwardly through tubes 118 since they have essentially no other way to escape. For the purposes of the present invention, brazing is considered a sealing operation in which metal having a melting point at least as high as about 450"F and generally a copper alloy such as an alloy of 45% silver with 55% copper by weight, is the sealant. Brazing temperatures can go as high as 1300"F or even higher. Flux such as borax is frequently used with the brazing metal to protect it and the parts being joined against excessive oxidation and to promote wetting of the parts by the melted braze. Some brazing metals are copper phosphorus alloys or other alloys that can be used without a flux. The heater in the sealing apparatus of the present invention can be operated continuously while sealing a succession of assemblies, but is preferably operated only for short intervals while the sealing metal is being melted and flows into place. Thus the heater can be completely shut off between sealing sequences, and ceramic fiber burners are particularly helpful in such intermittent operations inasmuch as they heat up and cool down in only a few seconds. For such intermittent operations it is also helpful to have the burner plenum of relatively small volume, preferably not over about 1 1/2 inches deep. In this way combustion gas can be intermittently fed to the plenum and rapidly reach the exit surface of the fiber mat where it is burned, so that the timing of the burner action is simplified. An igniter such as a pilot light assembly or an electric spark ignitor can be fitted near the margin of the burner to assure that it lights up each time a combustion gas feed is initiated. A settable automatic switching sequencer can be used to time the gas feed to the different burner portions as well as the suction blower. Instead of, or in addition to, moving the table up and down to bring the work to the burner, the burner can be moved toward and away from the table. In the construction of Fig. 2 no vertical movement is needed by the table or the burner. An auxiliary heater can also be provided around and above the lower tube sheet 37 in the construction of Fig. 1, and operated to seal the lower tube ends into that sheet while the tube-and-sheet assembly is held in the illustrated position. Thus a layer of sealing mixture can be applied to the upper surface of the lower sheet and the auxiliary heater started even before the burner 50 is lit inasmuch as the heat-up of the lower sheet takes longer than that of the upper sheet. Where the margin of a ceramic fiber mat has its pores well sealed, as by the silicone or sodium silicate or other alkali metal silicate impregnant, the mat margin can be damped in place without wrapping the aluminium foil 93 around those edges. The aluminium foil or other gasketing can still be inserted between the mat margin and the plenum margin, or the silicone or alkali metal silicate can also be used to seal the mat edge to the plenum. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. WHAT I CLAIM IS:

1. Apparatus for simultaneously sealing a plurality of metal tubes in holes provided in a metal sheet which apparatus comprises a generally downwardly directed gas-fired raiant heater, means below the radiant heater for supporting the plurality of tubes in position in the holes in the sheet with the sheet in a generally horizontal position, and means for casuing hot gaseous burner combustion products to flow down into the tubes in the assembly, to cause the sheet and the upper ends of the tubes to be rapidly and

substantially uniformly heated to a temperature high enough to melt a layer of fusible metallic sealant carried on the top surface of the sheet and thus seal the tubes to the sheet.

2. Apparatus as claimed in claim 1, wherein the radiant heater has aconcave radiation surface arranged such that when the apparatus is in use, it envelopes the portions of the tubes projecting through the upper surface of the sheet.

3. Apparatus as claimed in claim 2 in which the concave radiation surface has two zones, one directing radiation primarily inwardly from the sides of the sheet-andtube assembly and the other directing radiation primarily downwardly.

4. Apparatus as claimed in any one of claims 1 to 3, wherein the radiant heater is a ceramic fiber burner.

5. Apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

6. A process for simultaneously sealing a plurality of metal tubes in holes provided in a metal sheet, which process comprises, supporting the plurality of tubes in position in the holes in the sheet with the sheet in a generally horizontal position and carrying on its upper surface a quantity of a fusible metal sealant, applying heat to the sheet from a gas-fired radiant heater positioned above it, and causing the hot burner combustion gases to flow down into the tubes in the assembly to rapidly and substantially uniformly fuse the metal sealant and thus seal the tubes in the sheet.

7. A process as claimed in claim 6, when carried out using apparatus as defined in any one of claims 1 to 5.

8. A process as claimed in claim 6 or claim 7, wherein the fusible metal sealant is a brazing metal.

9. A process as claimed in any one of claims 5 to 7, wherein the sealing is effected in not more than half a minute.

10. A process as claimed in any one of claims 6 to 9, wherein the radiant heater is arranged to radiate heat downwardly on the tube-and-sheet assembly and to also radiate heat inwardly toward the assembly from around it.

11. A process for simultaneously brazing a plurality of metal tubes in holes provided in a metal sheet, substantially as hereinbefore described with reference to the accompanying drawings.

12. An assembly comprising a plurality of metal tubes sealed in a metal sheet, when produced by a process as claimed in any one of claims 6 to 11.