US1250881A - Connection of the ends of tubes and tube-sheets. - Google Patents

Description

A. R. HODGS.

CONNECTION OF THE ENDS or TUBES AND TUBE SHEETS.

APPLICATION FILED FEB. 23. IQII- Patented Dec. 18, 1917.

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En srarus FFTCE.

ALLAN IE. HODGES, 0F MEMPHIS, TENNESSEE, ASSIGNOR OF ONE-HALF TO CYRUS A, 'MCALLISTER, OF MEMPHIS, TENNESSEE.

CONNECTION OF THE ENDS OE TUBES AND TUBE-SHEETS.

Specification of Letters Patent.

Patented Deeo 18, 191% Application filed February 23, 1917. Serial No. 150,516.

To all whom it may concern Be it known that I, ALLAN R. Honors, a citizen of the United States, residing at Memphis, in the county of Shelby and State of Tennessee, have invented new and useful Improvements in Connections of the Ends of Tubes and Tube-Sheets, of which the following is a specification.

This invention relates to improvements in the connection of the endsof boiler tubes in their supporting sheets, the improvements being of special advantage as applied to the back tube sheet of locomotive boilers wherein said sheet forms the front Wall of the firebox.

In the accompanying drawings Figure 1 is a sectional view illustrating the usual method of and means for securing boiler tube ends;

Fig. 2 is a sectional view and Fig. 3 an elevation illustrating steps of the method involved in the present invention;

Fig. 4 is a sectional view illustrating a further step in the present method; and

Fig. 5 is a sectional view illustrating the structure involved in the completed connection,

It is indispensable to'the safety and satisfactory operation of locomotive boilers that the joint between the tube ends and their supporting sheets be steam-tight and of such character that its integrity will not be seriously impaired by the strains developed in said sheets in consequence of expansion and contraction. For these purposes, the method and structure shown in Fig. l, is and for many years past, has been universally employed. This well known joint involves the A arrangement of a copper ferrule A between the end of the tube B and the sheet 0 in which said tube end is fitted. The method of jointure involves the expansion of the tube to secure the packing and sealing effect of the ferrule, the formation in the tube adjacent the inner face of the sheet of a circumscribing retaining corrugation D and the swaging of the tube extremity to provide a circumscribing terminal bead E which lies against and is, in some cases, welded to the outer face of the sheet. As applied to the back tube sheet, the usual method and means of jointure above described is a source of continual trouble. The expansion of a large number of tube ends into the sheet puts the sheet under compression and develops continually present compressive stresses which, in connection with the variations of temperature, produce destructive physical reactions. The back tube sheet in boilers of the usual construction is also subject to severe stresses transmitted to it by the tubes from the front tube sheet and is constantly 1sitraiined and frequently and seriously buc- In order to counteract the destructive effects of the stresses and strains to which the tube sheet and therewith the connections between it and the tube ends are subjected, it is necessary to reexpand and sometimes reroll the tube ends after each run of the locomotive or, under the most favorable conditions, at very close intervals. And each reexpansion of the tube ends increases the compression to which the sheet structure is subject and, hence, increases the normal compressive stresses developed. ,This greatly shortens the life of the tube sheet, imposes the necessity for the most careful inspection, and entails, in the aggregate, a very burdensome expense of time and labor.

It is, of course, desirable that the back tube sheet should be made as thin as possible in order that it may have more efficient heat-conducting property; but the common method of securing the tube ends imposes a limitation on the minimum thickness of the back tube sheet since the sheet must be suffieiently thick to provide ade uate bearings for the ferrules A; to have su cient strength to withstand the stresses to which it is subjected, these including the normal severe compressive stresses which are developed by the rolling andexpansion of the tube ends; and to allow for wear adjacent the tube holes as a consequence of'repeated renewals of the tubes and re-Working of the tubes while in service.

The present invention overcomes the above stated objections; and its principal objects are to provide an easily and inexpensively practiced method of securing the tube ends in the tube sheet producing a structure involving the connection of said ends in said sheet whereby the tube sheet sheets will not be impaired by the stresses and strains to which the said tube sheet and the said connections are subject; whereby the connections between the tube ends and the sheets, when once made, will require no renewal or repair during the life of the tubes; and whereby the necessary renewals of the tubes may be made with the same facility as their original installation.

Referring to Figs. 2-5 in which similar characters of reference designate similar parts throughout:

The tube sheet 1 is preferably of materially less thickness than the tube sheet C shown in Fig. l and representing the existing construction of back tube sheet. This reduction of the thickness of the tube sheet is made possible only by the present invention; and it greatly facilitates the practice of the invention. The tube sheet C in Fig. l, in accordance with the standard requirement, has a thickness of one-half, and in some instances five-eighths, of an inch. The tube sheet 1 of Figs. 25 has a thickness of three-eighths of an inch and has much greater heat-conductivity than the tube sheet C.

The joint between the end of the tube 2 and the sheet 1 involves a zone of welding metal 3 which hasa homogeneous union with said tube and sheet and is formed by any method of welding suitable for the purposes in view may be employed, 0. 9., the oxy-acetylene or the electric welding method.

In the practice of the invention, 1 form the tube sheet, which is preferably of the thinness described, with a conical opening 4 between its fiat faces and whose minimum diameter adjacent the inner face of the sheet is sufficiently greater than the external diameter of the tube 2 to provide an appreciable clearance 5 concentric to the tube. As applied to the connection of boiler tubes this clearance is preferably of about the same width as the thickness of the tube, in practice, about an eighth of an inch. The end of the tube which is inserted through the opening a is projected for about an eighth of an inch beyond the outer face of the sheet, as clearly shown in Fig. 2. Frior to welding, the tube end is centered with relation to and supported in the opening l by a suitable implement, conveniently a wedge N, which is inserted through the clearance 5 at the lowest point thereof, and which holds the tube end in concentric relation to said clearance.

The inclined face of the opening 4: and the external face of the tube end within said opening provide relatively extensive and ac cessible welding surfaces which become sub ject to the welding heat and quickly and uniformly fuse with the metal 3 which is introduced between said surfaces in the course of the Welding operation and, of' course, is of approximately the same molecular structure as the tube sheet and tubes.

After the tube end has been centered with relation to the opening t, as shown in Figs. 2 and 3, the welding operation is commenced preferably at the upper side of said opening and tube end; and when a comparatively small portion of the welding metal has been introduced between thetube sheet and the tube end and has become fused to the welcling surfaces, as shown in Fig. t, the wedge lV may be safely removed, the tube in such case having its further support during the rest of the welding operation by means of the small portion of welding metal referred to. Thereafter, the welding operation is continued throughout the extent of the tube and throughout the extent of the opening 5 until the metal 3 completely fills the space between the inclined face of the opening l and the adjacent portion of the external face of the tube.

In the course of the Welding operation, some of the metal at the extreme end of the tube will be lost; and it is in view of this that the tube is'caused to project to some extent beyond the tube sheet, preferably to an eighth of an inch, as above explained. The loss of the metal of the tube occurs in this projecting portion of the tube end and involves about half of the said projecting portion whereby when the welding operation is completed, the end edge of the tube will lie in a plane preferably very slightly beyond the plane of the outer face of the tube sheet, as shown in Fig. 5, in which figure the dot-and-dash line X indicates the original plane of the end face of the tube end as when the method was in the stage shown in Fig. 2. By proceeding in the manner described, it follows that the loss of the metal from the end of the tube does not entail any reduction of the extent of the welding surfaces and of the band 3, nor any impairment of the continuity of the welded joint between the tube sheet and the tube end.

It has been established by actual practice under the severe conditions of normal and continued use that the joint produced by the method herein described, and as shown in Fig. 5, possesses great strength and lasting qualities, is not sensitive to the destructive effects of the stresses of expansion and contraction and imposes no detrimental efiects on the tube sheet.

As previously stated, the present invention makes possible the use of a relatively thin tube sheet; but apart from this, the use of a relatively thin tube sheet greatly facilitates the practice of the method which the invention involves. Thus, if the present method be applied to a tube sheet of the ordinary half-inch thickness, it is necessary,

as demonstrated by my experiments, to make special provision for the cooling of the tubes during the welding operation, as by the use of air blasts directedthrough the tubes, heat-absorbing plugs inserted in the tube ends being wholly unsatisfactory; and

this introduces an undesirable element of complexity and expense into the practice of the method. As applied to a relatively thin tube sheet, specifically, a tube sheet threeeighths of an inch thick, the provision of special means for cooling the tube during the welding operation is, and has been established to be, wholly unnecessary.

While, as will appear from the foregoing description, the invention is of special advantage as applied to the connection of boiler tube ends in their supporting sheets, it will be understood that it is also of advantage as applied to analogous situations wherein tube ends are to be connected to' their supporting sheets.

I claim as my invention 1. A method of connecting the ends of tubes to their supporting sheets which consists in forming a conical opening between the fiat faces of the sheet whose minimum diameter is substantially greater than the external diameter of the tube to be secured, thereby to provide an appreciable clearance concentric to the tube, in centering the tube in said opening and in welding the tube to the sheet by wholly filling the space between said tube and the wall of said opening-and between the flat faces of said sheet with metal which becomes homogeneously fused to the sheet and to the tube, thereby to establish a homogeneous connection between the sheet and the portion of the tube inserted therein.

2. A method of connecting the ends of tubes to their supporting sheets which consists in forming a conical opening between the flat faces of the sheet Whose minimum diameter is substantially greater than the external diameter of the tube to be secured, thereby to provide a clearance concentric to the tube, in centering the tube in said opening with the edge face of the tube located slightly beyond the outer face of the sheet and in welding the tube to the sheet by wholly filling the space between said tube and the wall of said opening and between the flat faces of said sheet with metal which Jecomes homogeneously fused to the sheet and to the tube, thereby to establish a homogeneous connection between the sheet and the portion of the tube inserted therein, the portion of the tube beyond the outer face of the sheet being reduced in the course of the welding operation to a plane Very slightly )eyond the outer face of the sheet.

In testimony whereof I have hereunto set my hand in presence of two subscribing witiesses.

ALLAN R. HODGES. Witnesses:

JOHN S. POWERS, JOHN L. FLETCHER.

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