US2458189A

US2458189A - Method of expanding tubing by freezing liquid therein

Info

Publication number: US2458189A
Application number: US605698A
Authority: US
Inventors: David E Morgan
Original assignee: Warren Webster & Co
Current assignee: Warren Webster & Co
Priority date: 1945-07-18
Filing date: 1945-07-18
Publication date: 1949-01-04
Anticipated expiration: 1966-01-04

Description

Jan. 4, 1949. D. E. MORGAN METHOD OF EXPANDING TUBING BY FREEZING LIQUID THEREIN 2 Sheets-Sheet 1 Filed July 18, 1945 INVENTOR 'flaq zdfl/i/alyaiz ATTORNEYS Jan. 4, 1949. MORGAN 2,458,189

METHOD OF EXPANDING TUBING BY FREEZING LIQUID THEREIN Filed July 18, 1945 2 Sheets-Sheet 2 wi i Q Q;

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I;\ C INVENTOR MAETMVM v ATTORNEYS flava'dlzdfozya Patented Jan. 4, 1949 METHOD OF EXPANDING TUBING BY FREEZING LIQUID THEBEIN David E. Morgan, Philadelphia, Pa., assignor to Warren Webster & Company, Camden, N. J., a corporation of New Jersey Application July 18', 1945, Serial No. 605,898

4 Claims.

This invention relates to methods for utilizing the expansion forces occurring upon the solidifying of liquid or molten materials upon lowering the temperature thereof, for the purpose of expanding or altering the shape of tubular containers and the like.

The various features of the invention are adapted to a number of different purposes. For example, in the manufacture of finned tubing such as is used for radiation purposes or otherwise, it is a difficult problem to firmly and permanently secure the fins in place on the tubing and in a manner to insure such uniformly good contact between the fins and tubing as will make possible the efficient transfer of heat. The methods heretofore available for this purpose have, so far as is known, involved serious difficulties. For example, one method has been to apply the fins one after another with a forced fit, on to the tubing. This has the difilculty of involving successive operations individual to each fin, and also as a succession of the fins are forced along the free end of the tube, the tubing becomes smaller and smaller so that the product is not uniform from end to end.

Other methods have involved placing the fins on the tubing and then drawing or projecting an expanding device through the tubing so that the tube walls are expanded into contact with the fins. These operations are relatively expensive and involve various mechanical difficulties, and are also generally impossible of application to tubing after it has been bent or substantially curved.

In accordance with the present invention, the succession of the fins may be first placed along the tubing in the desired spaced relation and then the tubing is filled with water or other liquid or molten material which will expand on solidifying. Then under controlled conditions, the assembly is subjected to temperatures low enough to cause freezing or solidifying of the contents, with the result that the tubing is expanded into firm contact with the inner edges of all of the fins.

While of course it has long been recognized that pipes or containers, upon the freezing of liquid therein, will become expanded, insofar as is known, no methods have been available for so controlling such expansion that the results could be put to the practical uses accomplished by the present invention.

As will be hereinafter further explained, the invention, in addition to its application to the securing of fins to tubing, may also be simul-- 2 taneously or separately utilized for reshaping the tubing, for example, to form a series of annular corrugations in the walls thereof. I have discovered further that the metal tubing when subjected to controlled expansion according to the invention may also be hardened thereby, to varying degrees as desired. Also the invention is well adapted to the controlled expansion of tubing in order to permanently secure the tubing within surrounding parts other than fins, such for example, as continuous sheaths or surrounding pieces of tubing which are formed either of the same or other metals or materials, within which the inner tube is primarily expanded.

Various further and more specific objects, features and advantages of the invention will appear from the detailed description given below taken in connection with the accompanying drawings which form a part of this specification and illustrate by way of example. preferred forms of the invention. The invention consists in such novel combinations of parts, methods and method steps as may be shown and described in connection with the apparatus herein disclosed.

In the drawings, v

Fig. 1 is an elevational view, partially broken away and partially in section, illustrating one embodiment of the invention;

Figs. 2 and 3 are elevational views respectively, showing two other embodiments of the invention;

Fig. 4 diagrammatically indicates one method according to which the freezing and subsequent thawing steps may be carried out in accordance with the invention;

Fig. 5 is an enlarged detailed view showing portions of a tube structure with surrounding fins secured thereon in accordance with the invention;

Fig. 6 illustrates a section of bent tubing with fins placed thereon in accordance with the invention;

Fig. 7 illustrates one form of radiator structure which may be made according to the invention;

Fig. 8 diagrammatically indicates the manner in which tubing may be expanded to form annular corrugations thereon in accordance with the invention;

Fig. 9 illustrates a section of tubing which has been expanded to fit within an outer length of tubing according to the invention; and

Figs. 10-12, inclusive, are sectional views of alternative arrangements of apparatus for carrying out the invention.

The proper control of the expansion effects upon the freezing of the liquid within the container, involves a number of factors which have to be carefully taken into consideration in order to obtain practical, accurate and uniform results. First it should be noted that the volume of the liquid to be frozen should be securely confined, since the liquid upon freezing, expands into regions of least resistance. Thus, in the case of normally open ended tubes, it is necessary while performing the method, to provide some means to firmly plug the ends of the tubes after same have been filled with the medium to be frozen. This in some cases, may be accomplished by threading the ends of the tube and applying ordinary pipe caps or the like. However, if the tube is of such dimensions as would require use of such a cap or the like embodying a considerable mass of metal, it has been found that the freezing willoccur first within the middle portions of the tubes and that excessive bulging will occur at the ends when freezing finally takes place there with consequent unsatisfactory and non-uniform expansion effects.

To overcome this diiiiculty, one form of end closure arrangement which has been found to give satisfactory results is illustrated in Fig. 1. Here the tubing which is to be expanded is indicated at l l surrounded by a plurality of radiating fins I2 which have been placed on the tube at the desired positions at which it is intended to have the same secured by reason of the expansion of the tube l I.

The tube II, for example, may be formed of copper and the fins l2 may be formed, for example, of copper or aluminum and may be either of a, rectangular, square or circular shape, and formed with a central aperture in which the tube, II is received. If desired, the inner edges of the fins around the aperture may be flanged as at 13, these flanges being preferably of suitable width tobprovide spacing means for the fins along the tu e.

As shown in Fig. 1, the end edges of the tube may be first flared outwardly somewhat as indicated at M, and after the tube has been filled with the medium which is to be frozen, such as water, a tapered plug as at l5 may be inserted and forced into the flared tube end. This plug may be formed, for example, of synthetic resin material such as a phenol formaldehyde condensation product. The tube end may then be surrounded by a hollow split, externally tapered, synthetic resin ring formed for example at two parts,

l6 and Mia, separable along a plane I! which.

preferably passes through the axis of the tube.

As indicated, the upper surfaces l8 of this twopart split ring may engage at their inner edges agz inst the flared tube portion l4, and the split ring may-be surrounded by an internally tapered rigid steel ring as at I9 recessed at its lower edge as at 20, to receive inwardly directed portions 2| and 22 of a rigid steel clamping member 23. The

upper portion of the clamping member 23 as shown, may extend diametrically across the assembly and may be threaded to receive a clamp ing screw 24, the lower end of which bears against the plug I 5. Upon tightening the screw 24, it

will be apparent that the plug I5 will be forced firmly into position to close the end of the tube,

since the clamping member grips the steel ring l9, which in turn bears internally against the split insulation ring Iii-Ilia and the latter presses up against the flared tube end It, With this arrangement, it will be apparent that through the use of a plug and split ring of synthetic material which is a good heat insulator, the WW 4 walls are kept out of contact with any metal parts of good heat conductivity or of substantial mass. If the necessarily relatively massive parts of the clamping or plugging means are not thus made of insulation material or insulated from the tube walls, then upon subjecting the assembly to freezing temperatures, the expansion effects will as above stated, not be uniform. The reasons for this are believed to be as follows. Heat will be readily dissipated through the exposed thin walls of the middle portions of the tube, with consequent rapid freezing action within these portions. At the same time, before the end portions of the assembly are cooled t freezing temperature, considerable heat would have to be conducted from the metal masses of the clamping parts or plug. into and through the walls of the end of the tube and along the tube into the more exposed cooler Thus, freezing is middle portions of the tube. delayed at the e." 6. portions until after such portions have been subjected to high internal pressures for some time, due to the expansion of the freezing medium at the middle portions. Hence, by the time freezing occurs in the end portions, they will have become excessively bulged. For this and possibly other reasons, it has been found highly desirable for satisfactory results to use some form of end closure means which will avoid any substantial masses of metal in contact with the end of the tube.

With the arrangement shown in Fig. 1, it has been found that the freezing action occurs substantially concurrently throughout the length of the tube including the end portions, and therefore, the expansion effects are substantially the same adjacent the end portions as at the middle portions of the tube.

- It will be understood that the opposite end of the tube ll may also be closed by an arrangement similar to that shown in Fig. 1.

In order to control the expansion within carefully predetermined limits, it is necessary to use a predetermined volume of the medium to be frozen, such volume being determined upon takinginto account the percentage by which the particular freezing medium used will expand upon lowering the temperature and solidifying it,

For example, if the medium used is water, its volume will expand by approximately 8.55% upon passing from the fluid to the solid state, and the linear coefiicient of expansion of ice is 0.0000507 per C., which factor may also in some cases, have to be taken into consideration, especially if low quick freezing temperatures are used. It will be apparent that if for example, the internal diameter of the tube is relatively large and if the walls are thin, they may not be able to withstand the 8.55% expansion, if the tubing is entirely filled with water. Even if the walls are able to withstand such expansion, the percentage of expansion may be greater than desired.

Thus, in order to control the amount of expansion within the desired limits, either some fluid medium has to be selected which will have the desired degree of expansion, taking into consideration the dimensions of the container, or preferably one may introduce a solid object into the container so that if for example, water is used as a freezing medium, its volume will be limited to a predetermined amount just suflicient to accomor other fluid within the tube to the amount necessary to secure the desired expansion effect.

Assuming for practical purposes that such rod is of the same length as the tube, the rod diameter may be determined by the following formula:

2 2 1 C where D equals the diameter of the rod, D1 is the initial internal tube diameter, D: is the final internal diameter, and C (in case water is used) equals 0.0855. For example, if the initial internal diameter of the tube is 4 inches and it is desired to expand such diameter to 4.05 inches, then it may be calculated according to the above formula, that the diameter of the rod should be 0.94 inch. It will be understood that if liquids other than water are used, the value of C in the above formula would be changed, depending upon the percentage by which the medium expands upon passing from the fluid to a solid state.

It has been found when using a rod as at 25 in Fig. 1, that it is important to retain such rod throughout its length substantially in its central position as shown. bend into proximity of the tube walls, the rate of freezing at these areas as compared with other regions within the tube will be varied, and the resulting expansion effects will be non-uniform longitudinally of the tube and around the tube. A convenient method of holding the rod in the desired axial position is to use one or more guide discs thereon as at 26, formed for example, of thermoplastic or other heat insulating material and having central apertures for receiving the rod. If special shapes are desired with nonsymmetrical or irregular expansion around the walls of the tube, a rod as indicated in dotted lines at 25 may be inserted and held in a desired non-axial or curved position by using guide discs with off-center apertures.

During the freezing action, the tubes will of course expand in length as well as in diameter, but if the expansion is controlled as above described, the expansion in length is ordinarily negligible for tubing such as used for radiation purposes and the like.

It has been found that with copper tubes, at least of dimensions customarily used for radiation purposes, it is essential that the tubing first be annealed before being expanded in accordance with this invention, since if tubing of hard copper is used, the expansion effect will almost invariably cause rupture. It has been further found that upon expanding the tubing by the method of this invention, the initial annealed tubing becomes to a considerable degree hard ened as a result of the expanding action. In some cases this hardening action is desirable in that it renders the tube more rigid so that in case fins are to be secured in place by the method, they will be less apt to become loosened in view of the finally hardened and rigid character of the tubing. In cases where it is desired to avoid a hardened final product, it of course may be annealed again after expanding.

Fig. 2 illustrates another arrangement for closing the ends of the tube. In this case, cap members as at of suitable thermoplastic or other heat insulating material, may be provided for each end of the tube and these may be clamped and held in place by a through bolt 3|, extending axially throughout the tube. Such bolt may preferably be of a diameter calculated in accordance with the same principles as above explained If any portions of the rodin connection with the rod 25 of Fig. 1. Accordingiy, the same bolt or rod may serve a dual purpose of securing the caps in place and of limiting the volume of the freezing medium to a desired predetermined amount.

From the standpoint of facilitating rapid production however, the arrangement of Fig. 1 is generally preferable over that of Fig. 2.

Fig. 3 illustrates another alternative arrangement for sealing the ends of the tubes, this ar-.

rangement as shown being adapted for providing closure means for an assembly of a plurality of the tubes as at II, II. In this case, each end of each tube may be provided with an insulation closure cap as at 35. These caps may be held in place by bars or plates of plastic insulation material as at 36, the latter'in turn being clamped between rigid end plates 37, by the action of through bolts as at 38. It will be understood that rods such as at 25 of Fig. 1, with accompanying. retaining meanssuch as discs 26, may also be used within the tubes of Fig. 3.

Fig. 4 illustrates somewhat diagrammatically the manner in which assemblies such as at Figs. 1-3 may, after preparation be supported upon a conveyor belt 40 and carried into, through and out of a suitable freezing bath as at 4|, thence into, through and out of a thawing bath as at 42. The speed of the conveyor belt, the dimensions of the freezing tank and the temperature of the refrigerant therein may of course be suitably adjusted depending upon the time required for the particular tube and closure assemblies being treated, to become cooled to freezing temperature. Also the dimensions and temperature of the thawing bath may be varied, depending upon the time re,- quired for the assemblies to become warmed to a temperature sufiicient to thaw the freezing medium within the tubes. If desired, the thawing bath may contain or be accompanied by a heating coil as at 43. Also this bath may incorporate any suitable cleaning fluid for eifectively cleaning the exterior surfaces of the tube and fins as the assemblies pass through. After the assemblies have been withdrawn from the thawing bath, theend closures may .be removed to permit discharge of the freezing medium.

In most cases, it appears advisable to use a freezing bath of relatively low temperature so as to cause rapid and more uniform freezing throughout the volume of liquid within the tubes, a temperature of 20 F. being satisfactory.

If the walls of the tubing are relatively thin and if the fins l2 are provided with flanges [3 which are relatively thin, as will usually be the case, then the expansion of the tubing according to this invention, will result in the formation of slight annular corrugations as shown in the enlarged view of Fig. 5. That is, along circumferential lines of the tubing which are engaged by the surrounding main body portions of the fins, the tubing will be restrained somewhat against expansion as compared with the surface portions which are surrounded only by the relatively yieldable flanges l3. Accordingly, a slight outward bulging or corrugation will form beneath each of the flanges l3, and this bulge will be of a shape such as to tend to firmly lock the fin'and its flange in position on the tube. This offers a substahtial advantage, particularly where the finned tubing is to be used for radiation purposes and where the temperature of the tube may vary within considerable limits from time to'time, thereby causing contraction and expansion dimculties 7- which would tend toloosen the fins in the absence of such locking eflect.

The corrugations also aid in preventing difllculties due to elongation of the finned tubing by reason of thermal expansion when the tubing is used in radiator structures. Thatls, the corrugations tend to impart a certain degree of longitudinal flexibility, and at the same time reduce thermal expansion longitudinally. Furthermore, the corrugation of fins formed exceptionally thin flexible material. For example, fins of thin aluminum may be applied to copper tubes with a considerable saving as compared with what has been obtainable with prior art structures of equivalent radiation capacity.

With the prior art mechanical methods for applying and securing the fins as-herein above referred to, it is necessary that the tubing remain, substantially straight, at least until after the fins are secured in place and thereafter it is substantially impossible to bend the assembly to form loops or turns in the tubing without loosening or effl'ect facilitates the firm securing medium and equipped with. end closure means as displacing the fins. On the other hand, with the present invention as indicated in Fig. 6, the tubing may be initially bent to conform to various desired curved shapes, such as a grid shape, Then the fins may be slipped on to the desired positions and thereafter firmly secured in place by the freezing and expansion method of this invention. If desired, long grids of radiation structure, may be made of the form indicated in Fig. 6 and kept in stock. Then these may be cut into sections of any desired heating capacity as needed, as by cutting the tube along a line such as indicated by the dot-dash line 45.

This embodiment of the invention makes it possible to provide finned U tubes with any desired number of "turns without resorting to sol- :lered or braised connections as has heretofore been the necessary practice for finned U tubes.

With the tube bent as in Fig. 6, in order to obtain the desired predetermined degree of expansion, one may either select a kind of freezing liquid which for the volume present, will give the desired expansion, or a rod as at in Fig. 1, may be inserted and left within the assembly permanently, if desired. Also a removable rod of flexible plastic material might be used.

As shown in Fig. 7, a plurality of the tubes as at Ila to lie, inclusive, may all be treated as a group, according to the invention, for the application of fins as at l2a which extend continuously from tube to tube. After the tubes have been expanded to firmly secure these fins thereon in accordance with the principles above described,.the 'assembly oftubes may be provided with headers as at 50, 5| into which the tubes may be brazed or otherwise sealed. Such an assembly may be made with any number of tubes to secure a radiator of desired capacity. When smaller radiators are called for, the assembly may be cut, as for example, along the dash line indicated at 52, thereby cutting through the headers as well as the fins.

The embodiment. of Fig. '7 makes possible a desired configurations on tubing which isnot to. Y be. provided with fins. For. example, as shown of Figs. 1-3, may be inserted within an aperture of a die member 56, this member having an ini ternal aperture formed with corrugations or other desired configurations so that when the tube is expanded therein, its wall surfaces will be correspondingly corrugated or'shaped. The die may of course be formed of parts separable as along a center line 51, to enable removal of the expanded tube.

Sheet metal bellows or similar devices, may be made in accordance with this embodiment of the invention by first expanding an annealed tube within a die as at Fig. 8, then annealing the tube,

and again expanding the same within a die hav-' ing deeper corrugations, and repeating this process until the desired form is completed.

Certain features of the invention may also be utilized for the purpose of expanding tubing or the like into firm contact with various other types of surrounding structuresjsuch as flanges, conduit joint parts, or for the expansion for example of tubes into sealing relationship with headers as in boilers. For example, as indicated the freezing method may be appliedto the tube 60 in substantially the same manner as indicated in connection with Fig. 1. This method has an r important advantage over other methods for encasing a tube within an outer shell in that all of the outside wall surfaces of the inner tube will be pressed into substantially uniform contact with the internal wall surfaces of the outer tube, despite any variations or irregularities which may exist in the surfaces, such for example, as irregularities indicated at 62. In view of this fact, the possibility of occurrence of small air pockets between the tubes will-be eliminated.

While with the invention as above described in connection with Figs. 1 to 4, the refrigerant for causing freezing is applied to the exterior of the tubes, it' is also possible to apply the refrigerant internallyof the tubes as for example, with apparatus such as indicated in Fig. 10. Here a tube 10 which is to be expanded and which may have With this arrangement, it will be apparent that the body of freezing medium as at 18 located be-' tween the interior walls of tube 10 and the rigid container 14 may be cooled to freezing temperature internally. This arrangement may have advantages as in cases where it is undesirable or inconvenient toapply a freezing bath to the external surfaces of the tube or container which is to be expanded.

In case it is desired to expand different portions along the length of a tube,'for example, to

various different degrees. this may be accomfrozen, has contained therein a rod as at ill, the

diameter of which varies from place to place. For example, if at the lefthand end of the tube 80 as shown in Fig. 11, it is desired to cause very little expansion, the rod is made relatively large,

' as at 8la within this portion of the tube. As

indicated, the rod may be tapered and/or varied in diameter according to steps, so as to leave more space for liquid in other parts of the tubing where greater expansion is desired.

In some cases it may be found desirable to expand a tube or other part to a greater degree than would be accomplished by freezing the amount of liquid contained within the tube itself.

In this case the tube or other cavity to be ex-.

panded may be connected with an external reservoir of the liquid to be frozen. One simple method for accomplishing this is somewhat diagrammatically indicated in Fig. 12, wherein a tubular part as at B4 is shown clamped within a split die member as at 85, having a cavity as at 86 for liquid in addition to the space within the member 84. When this assembly is suitably sealed and clamped with the parts in the position shown and with the space within the member 84 as well as the cavity 86 filled with liquid, it will 'be apparent upon freezing such liquid'that portions of the member 84 will be expanded into the cavity 81 to a greater extent than would be possible by merely freezing the contents of member 84 alone.

While the invention has been described with particular reference to its application to tubing, it will be understood that the principles of the invention are also applicable to the expansion of containers of other shapes.

It will be further understood that instead of using water as the freezing medium, various liquid chemicals may be used having the desired degree of expansion upon solidification. Furthermorefthe expansion may be accomplished by using chemicals which will react with increased volume to cause expansion of the tube. Furthermore, metal alloys may be used which will expand when cooled, such as in the case of certain alloys of antimony. These, for example, may be poured into the tube when hot and on .cooling,

would expand. Thereafter the alloy may be remelted in order to remove it from the expanded tube. One commonly known example of such a metal alloy is so-called type metal which normally consists of about 15% antimony, 82% lead and 3% tin.

The method of expanding tubes or other containers by freezing liquid therein, in accordance with this invention, has substantial advantages over methods heretofore proposed for the use of hydraulic pressure for the purpose. Expansion by hydraulic pressure will cause the weakest spots or areas in the tube to expand more than other parts and thus result in irregularities. Also hydraulic pressure for such purposes has to be closely controlled or over-expansion will result because of the fact that as the walls expand, they will become progressively weaker and thus more susceptible to over-expansion.

When it is desired to use a plurality of the finned tubes assembled with headers, it may sometimes be found convenient to used the headers as the end closures or sealing means for the tubes during the freezing step. In such cases, plastic bushings may be desirable for connecting the tubes to the headers and to provide insulation therebetween to afford more uniform expansion throughout the length of the tubes.

While the invention has been described in detail with respect to particular preferred examples, it will be understood by those skilled in the art after understanding the invention that various changes and modifications may be made without departing from the spirit and scopeof the invention, and it is intended therefore in the appended claims to cover all such changes and modifications.

I claim:

1. Method for securing annular fins in positions surrounding a metal tube, which comprises confining within the tube a predetermined volume of a liquid medium partially and substantially to the" same extent filling each cross-sectional portion of the tube, said medium being capable of expanding on solidifying, limiting the amount of said liquid medium by substantially filling the remainder of the space of each said cross-sectional portion within the tube by inserting a substantial- 1y non-compressible material which is notsubject to a change in state at the temperature of solidification of said liquid medium, then subjecting said liquid medium to a temperature causing such solidification thereof, the volume of said liquid medium being made sufficient to cause upon such solidification permanent expansive deformation of the tube into firm contact with the surround-v ing fins, and the volume of said material being sufiicient to so limit the volume of said medium upon solidifying that no rupture of the tube I occurs.

2. Method for forming corrugations in the walls of metal tubing which comprises surrounding the tube with means which will tend to retain the tube relatively rigidly against substantial expansion along portions corresponding to the valleys of the desired corrugations, as compared with portions on the tube corresponding to the ridges of the desired corrugations, confining within the tube a predetermined volume of a liquid medium partially and substantially to the same extent filling each cross-sectional portion of the tube, said medium being capable of expanding on solidifying, limiting the amount of said liquid medium by substantially filling the remainder of the space of each said crosssectional portion within the tube with a substantially non-compressible material which is not subject to a change in state at the temperature of solidification of said liquid medium, then subjecting said liquid medium to a temperature causing such solidification thereof, the volume of said liquid medium being made sufficient as compared with that of said material to cause upon such solidification the formation of said corrugations, but being so limited by the presence of said material that no rupture of the tube occurs.

3. Method for causing tubing to be permanently expanded to a predetermined degree, which comprises introducing an axially extending solid and substantially non-compressible rod into a tube to provide a space of predetermined volume between said rod and the interior tube walls, substantially filling such space with a liquid medium capable of expanding on solidifying, then subjecting the liquid medium to a temperature causing such solidification with consequent expansion of the tube walls, the volume of said liquid medium as compared with that of said rod being made suiilcient to cause upon such solidification said predetermined permanent degree of file of this patent:

- expansion, but being so limited by the presence of said rod that no rupture oi the tube occurs.

4. Method for causing tubing to be permanently expanded to a predetermined degree, which comprises confining within the tubing a predetermined volume of a liquid medium partially and substan-.

- tially to the same extent filling each cross-sectional portion of the tubing, said medium being capable of expanding on solidifying, limiting th amount of said liquid medium by substantially filling the remainder of the space of said crosssectional portions along and within the tubing by introducing a material which is not subject to a change in state at the temperature of solidiflcation of said medium, but which will resist any substantial compression upon solidification of said medium, then subjecting said liquid medium to a temperature causing such solidification thereof, the relative volumes of said medium and material being such as to cause upon such solidification the said predetermined permanent degree. of expansion of the tubing but without rup-' ture of same. 1

DAVID E. MORGAN.

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