US3453721A - Soft solder joints and methods and materials for producing the same - Google Patents

Description

July 8, 1969 T. D. JAYNE SOFT SOLDER JOINTS AND METHODS AND MATERIALS FOR PRODUCING THE SAME Sheet L of 4 Filed Nov. 22, 1965 TEST SPECIMEN 1 O O 5 2 m 0 TIME-HOURS DATA v2 M COPPER TUBlNG 3 WROUGHT S 3 CAST COUPLINGS 66% COPPER I SHEAR-.370 LB/IN2 LOAD: 87 LB.

TEST SPEC! MEN 2 O O 3 2 m o TIME HOURS DATA 1/2 M COPPER TUBING 3 WROUGHT S 3 CAST COUPLINGS 66 COPPER A INVENTOR' THEODOfi/I D. JAY/V5 7 BY SHEARi 57o LB/IN2 LOAD: I46 LB.

July 8, 1969 EXTENSION- INCHES SOFT SQLDER JOINTS AND METHODS AND MATERIALS Filed Nov. 22. 1965 T D. JAYNE 3,453,721

FOR PRODUCING THE SAME Sheet 2 014 TEST SPECIMEN #3 Fig. 3

TIME-HOURS DATA /2 M COPPER TUBING 5 WROUGHT 8. 3 CAST COUPLINGS 50 COPPER 2 SHEAR: 370 LB/IN LOADI 808 L8.

TEST SPEcIM EN 4 Fig. "4

4000 TIME HOURS DATA l/ZM COPPER TUBING 3 WROUGHT 8 3 CAST COUPLINGS 50% COPPER SHEAR: s05 LB/IN.2

LOAD 1 I60 LB.

INVENTOR. THEODORE 0. JAYNE BWMSIWWL/W T. D. JAYNE SOFT SOLDER JOINTS AND METHODS AND MATERIALS July 8, 1969 FOR PRODUCING THE SAME Sheet 1 014 Filed Nov. 22, 1965 TEST SPECIMEN 5 TIME HOU RS DATA 1/2 M COPPER TUBING 3 WROUGHT 8. 3 CAST COUPLINGS 34 COPPER.

SHEAR! 37o Lia/1N? LOAD: 8.8

TEST SPECIMEN s O O O mmIuz I zQmzwFxw TIME HOURS DATA M mY WA w m P O S w G E .N. H L P T U 0 C mw 8% N U l T3 8 WS B PTMI HP 6 O G 0 5 M R A 4 m H33SL T. D. JAYNE 3,453,721 SOFT SOLDER JOINTS AND METHODS AND MATERIALS Filed Nov. 22', 1965 Sheet g of 4 TEST SPEClMEN 7 July 8, 1969 FOR PRODUCING THE SAME a .8 7 S N g 0 G .N M w W O O O C S T m M m w n T O U T3 B O nHv A RCQRLB. 4 N W T E D WWT 0 OG 1 O M CU OD O 2 a 2 O lll lllli V32%. L J I 0 w m m 0 q 0. O w w m 0 SIUZTZQWZEXM O $1 02 I zgmzmtm INVENTOR. THEOUO/if. D.JAYNE Wad MW TIME HOURS DAD.

1/2 M COPPER meme EWROUGHT a 5 CAST COUPLINGS 20% COPPER SHEAR: 605 LB/IN2 LOADI 10.0 LB.

United States Patent Ofice 3,453,721 Patented July 8, 1969 US. Cl. 29-489 8 Claims ABSTRACT OF THE DISCLOSURE A mixture of a paste flux and copper particles for use in forming soft solder sweat joints. A method of forming soft solder sweat joints connecting tubular copper members including the steps of introducing into the joint area around one of the members a solder-reinforcing agent consisting of copper, and thereafter introducing a molten soft solder.

This invention relates generally to the soldering art, and more specifically to the formation of soft solder joints. It is particularly concerned with sweat joints connecting copper fittings and tubing such as those found in plumbing systems, and with methods and materials for forming such sweat joints.

The resistance of a soft solder joint to substantially constant or static forces as distinguished from transient forces, is known as creep strength. Because of its poor creep strength which may be less than one-eighteenth of the short term loading of the joint, the soft solder sweat joint is the weakest part of present copper plumbing systems. This weakness in soft solder sweat joints results primarily from the low strength of current solder materials. It is believed this weakness is also due to defects in the form of voids which occur in the solder space.

Prior efforts have had little success in increasing the strength of solder materials and joints. Instead, copper plumbing systems, as they are now generally assembled and constituted, are overdesigned structurally, particularly in the length of the solder cup, in an effort to assure adequate all-over joint strength. Some idea of this over design may be had by noting that the 50-50 soft solder sweat joint creep load for one-half inch size plumbing is on the order of one hundred pounds in hot water service, while the creep load for the copper tube and fittings themselves is on the order of three thousand pounds or more, a factor of thirty or greater. The factor is greater still for larger size plumbing.

In spite of the over design of the solder cup to provide greater total strength in the joints, the unit creep strength afforded by the present solder materials is so low that the conventional soft solder joint operates at a calculated safety factor level of 2.8 which is one of the lowest in building construction. If the long term joint strength in conventional systems were to have a safety factor equivalent to that in the rest of the system, the length of the solder cup would have to be several times its present length.

It will be apparent from the foregoing that important advantages can be obtained by increasing the creep strength of a soft solder sweat joint. An improvement in the unit creep strength would improve the entire general strength of sweat plumbing systems. Concomitantly, it would be possible to eliminate much of the conventional over design by decreasing the solder cup length, as well as lightening other components including the tubing, and thereby provide for substantial cost reductions. An improvement in the joint strength would also afford increased reliability and safety factor and reduce the occurrence of service failures.

Known prior art joints, such as brazed joints, exist which hve substantially greater creep strength than soft solder joints. These stronger joints require higher forming temperatures than do soft solder joints. This is a factor that may make brazed joints undesirable, especially in frame constructions where high temperatures may be dangerous. Thus, in spite of its poor creep strength, the soft solder joint is preferred and used because of ease of installation, its low temperature melting, and also because of its good capillary flow characteristics at low temperatures.

The present invention provides new and useful improvements which greatly increase the strength of copper sweat joints, particularly the unit creep strength under long term loading conditions, without affecting the good low temperature and flow characteristics of soft solder. This invention makes it possible to improve the overall strength of copper plumbing systems and obtain all of the attendant advantages mentioned above. The invention resides in the structure of the improved sweat joints and in the methods and materials used in the formation of such joints.

-In general, the invention contemplates the introduction of a strengthening agent into the joint in order to improve the strength properties of the solder layer. The strengthening agent may be dispersed throughout the joint and is preferably introduced in the form of discrete solid particles. In order to avoid problems of electrochemical corrosion which may be caused by the introduction of atoms into the solder-copper system, particles of copper substantially free of alloying elements are used as the preferred dispersion strengthening material.

Various techniques may be employed for introducing the particles of copper or other reinforcing material into the joint. A preferred technique is by means of a flux vehicle. This may be accomplished by mixing or blending copper powder in a suitable flux, for example, a commercially available corrosive paste flux, and applying the copper-flux to at least one of the parts to be joined. Thereafter, a molten soft solder, which may be a standard 50-50 tin-lead solder, is provided at the junction between the parts being joined and the assembly cooled to form a strong solder joint in which the copper powder is dispersed throughout.

The novel copper-flux material which comprises one aspect of the invention has several important advantages. The flux can be wiped onto a fitting in. a manner similar to conventional flux and the major portion of the powder will remain in the joint to strengthen the subsequently applied solder. However, as distinguished from prior attempts to add a strengthening agent directly to the solder, the application of the preferred copper powder in a flux vehicle does not adversely affect the flow characteristics of the solder and the times and temperatures of the soldering operation. The invention therefore provides a new flux material and soldering technique which result in greatly improved strength characteristics of the formed joint and yet do not require significant modification of standard soldering practices. Thus, the methods and materials of the invention can be used without special handling by both skilled and unskilled persons to form improved copper sweat joints.

Among other advantages are that the new copper-flux can be used without changing the design of the usual plumbing fittings. The new flux material of this invention is relatively inexpensive and does not require special equipment, know-how or materials to produce. Further, it is characterized by a long shelf life and can be stored prior to use without deterioration.

Accordingly, the objects of the invention are to provide sweat joints of improved strength and methods and materials for making such joints.

Other features, objects, advantages and a fuller understanding of the invention will be apparent from the following detailed description and the accompanying drawmgs.

In the drawings, FIGURES 1 through 8 are graphs showing creep strength data of joints formed in accordance with the invention compared to creep strength data of conventional copper sweat joints.

As generally descirbed above, the invention resides in the formation of soft solder joints containing a strengthening agent in the solder layer. The agent is preferably in the form of dispersed particles. The invention also pertains to methods and materials for introducing the particles into the joint. In the preferred embodiments to be described, the particles are added to the flux and the flux is applied to the metal parts in a manner similar to standard practice. The specific composition of the flux itself is not of significant importance and various commercial fluxes. can be selected depending upon the particular soldering application. Similarly, the soft solder which is used can be any conventional type.

A primary requirement of any commercially acceptable technique and material for reinforcing copper sweat joints is to avoid altering the basic solder-copper system by introducing a new atom that might result in electrochemical corrosion. Because of this consideration, commercially pure copper particles are a preferred strengthening agent. Electrolytic copper powders which have a low percentage of alloying elements and may be considered commercially pure are particularly well suited for the purposes of the present invention. Although copper is disclosed as a preferred strengthening material, it is contemplated that alloys containing copper could be used, as well as inert materials, such as glass or the like, which will not induce corrosion or other detrimental actions in the joint.

In forming sweat joints, the maximum particle size is determined by clearance of the fitting. The average clearance of most fitting designs is approximately 0.006 inch, and in such designs it is preferred that the maximum particle size be 0.003 inch (100% minus 200 mesh). Particles having a maximum size of 0.003 inch can be distributed around the end of the tube or the inside of the solder cup and the two members maintained in concentricity in accordance with good soldering practice.

There are several commercially available copper powders which can be used as the strengthening agent in accordance with the invention. The following are three typical electrolytic copper powders which have been used successfully:

l) AMAX Type B electrolytic copper powder (American Metal Climax, Inc.) 99.5 min. Cu., apparent density 2.5-2.6 gm./cc.-

Screen analysis (mesh): Percent On 100 (max). 0.2 On 150 1.11 On 200 13-23 On 250 3-10 On 325 17-38 Minus 325 45-53 (2) MD 201 granular copper powder (Metals Disintegrating Corp.) 99.0% Cu, apparent density 2.4-2.8 gm./cc.

Screen analysis (mesh): Percent Minus 200 100 Minus 325 85 (3) Screened electrolytic copper powder- Screen analysis (mesh): Percent On 100 0.0 On 150 1.1 On 200 12.7 On 250 9.5 On 325 19.8 Minus 325 555+ Copper powders can be readily mixed or blended into a flux without requiring any special handling techniques or equipment. The resulting composition has a long shelf life and can be stored for a year or more before use. Fluxes containing as little at 5% by weight copper powder have been used successfully to produce sweat joints exhibiting improved strength. Large amounts of powder can also be added to the flux and will result in strengthening of the joints, but it has been observed that paste fluxes containing large amounts of the powder apply somewhat more stifily than the usual paste flux.

In use the copper-flux can be applied to at least one of the parts to be joined in nearly the same manner as conventional fluxes. The subsequently introduced soft solder is readily accepted into the joint and the finished joint will have an exterior appearance similar to that of an ordinary one. The soft solder may be placed in the joint in accordance with conventional practices, such as melting the solder by bringing it into contact with a surface heated to the soldering temperature, allowing the molten solder to flow into and fill the joint space, and then cooling the metal surfaces. The invention also can be practiced in conjunction with the constructions and methods disclosed in copending applications Ser. No. 429,562, filed Feb. 1, 1965, now Patent No. 3,334,925, and entitled, Sweat Soldering Apparatus, and Ser. No. 462,673, filed June 9, 1965, and entitled, Sweat Soldering Invention.

Accelerated screening creep tests of copper sweat joints formed by using the above-described copper-flux and method have shown a large improvement in the strength of the reinforced solder layer. In one such accelerated test, a test section of /2-inch wrought coupling joints placed under a load of 1000 pounds per square inch shear and containing three conventional joints made with 50-50 tin-lead solder and three joints in which the solder was reinforced by a copper-flux containing 66% by weight of the copper indicated a minimum improvement in strength of a factor of 7:1. The maximum strength improvement has not been determined, since this test is still in progress at the time of this writing. All three of the conventionally soldered joints failed at the end of 292 test hours, the first having failed after only 101 hours. One of the copper-flux coupling joints failed after 725 hours, but all of the remaining reinforced coupling joints have withstood over 3000 test hours.

Another accelerated test produced results similar to that set forth above. In this test, a /2inch wrought fitting was made using 66% by weight copper-flux. A shear load of 600 pounds per square inch was applied to the fitting and the test is still in progress with no sign of failure after over 4000 hours. A similar load on a conventional 50-50 tin-lead solder joint failed at the end of 1500 hours.

Extensive long term creep tests have also been conducted to show the improved creep strength of copper reinforced sweat joints under long term static shear loading. The test procedures which have been followed are similar to those described in the Building Materials and Structures (BMS) Report No. 58 by Swanger and Maupin, published Dec. 20, 1940 by the National Bureau of Standards. For the most part, higher loads were chosen than by Swanger and Maupin because of the increased strength of the copper-flux joints and the desire to reduce the total test time.

The following table summarizes the long term test results of several examples of copper-flux joints made in accordance with this invention. In each of these examples, the copper powders were mixed in a conventional corrosive paste flux sold under the trade name Oatey #5 by The L. R. Oatey (10., Cleveland, Ohio. The copper powder was the previously identified AMAX Type B electrolytic copper powder sold by American Metal Climax, Inc. in which all powder larger than minus 200 mesh (.003 inch) was screened out. The soft solder used in forming the joints was a standard 50-50 tin-lead solder. The flux and solder material were selected simply because they are presently widely used in copper plumbing systems, and it is to be understood that the exemplary flux and solder are not limiting of the invention.

Referring to the drawings, FIGURES 1-8 show plotted data for each individual example listed above in the table in comparison with plotted data calculated from the re sults of Swanger and Maupin. The solid lines in FIG- URES 1-8 indicate the test results on the examples of the invention, while the dotted lines are based on the Swanger and Maupin data and indicate the average expected creep data for the test shear load or estimated data in the case of heavier loads.

The following Table II reports the results of modified short term tensile tests of conventional copper sweat joints and reinforced copper sweat joints made in accordance with this invention. By Way of explaining the test procedures, it should be noted that ordinary tensile testing by standard rates of applied stresses does not reveal much about the strength of soldered joints. This is because the tube will fail under short term loads before the joint does unless there are extraordinary flaws in the joint. If a solid bar is substituted for the tubing, the fitting will frequently shear. Consequently, in conducting short term tensile tests, the procedure was to reduce the solder area of standard fittings by cutting down the cup length until the joints failed in the solder area. Joints of the same size were then made using the new copper flux and it was found that the average increase in reinforcement was from %to AVERAGE TENSILE It will be seen from the above that the strength improve ment in the ordinary copper sweat joints is substantial, and that this improvement can be obtained in a practical and easily accomplished manner by applying a flux containing particles of copper or other reinforcing material to the parts to be joined and then introducing a molten soft solder in the usual Way. The copper powder or other particles remain unalloyed in the joint and are dispersed throughout the solder layer to afford a substantial strengthening effect.

While the use of a flux vehicle has been described as the preferred manner of introducing the strengthening agent into the joint, it is to be understood that alternative techniques can be employed. By way of example, it is contemplated that metal particles, such as copper, can be electrodeposited in the fitting. Alternatively, a quantity 01 particles could be preplaced in the fitting with a paste flux. Still another technique contemplated by the invention is to place mesh formed of copper or other material compatible with a solder-copper system around the end of the tube prior to the introduction of the molten solder.

As used herein, the term free in referring to the dis persion strengthening agent is intended to means that the agent is substantially unalloyed in the solder layer. The term copper is used in the specification and claims in a broad sense and includes commercially pure copper as well as metals and alloys containing copper.

Many modifications and variations of the invention will be apparent to those skilled in the art in view of the foregoing detailed disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically shown and described.

What is claimed is:

1. As a new article of commerce, a prepared composition of matter for use in forming a reinforced soft solder joint between copper parts, said composition of matter consisting essentially of a mixture of a paste flux and copper particles.

2. As a new article of commerce, a prepared composition of matter for use in forming a reinforced soft solder joint between copper parts, said composition of matter consisting essentially of a mixture of a paste flux and at least 5% by weight copper particles.

3. A composition of matter as claimed in claim 2 wherein said copper particles are a commercially pure, electroyltic copper powder.

4. A method of forming a soft solder sweat joint connecting tubular copper members comprising the steps of introducing into the joint area around one of the members a solder-reinforcing agent consisting of copper in a divided state which can be permeated with molten solder, subsequently introducing a molten soft solder, and thereafter allowing the solder to cool and form a joint between the members which is reinforced by free copper.

5. A method as claimed in claim 4 in which the solderreinforcing agent consists of copper particles.

6. A method as claimed in claim 5 in which the solderreinforcing agent is introduced into the joint area by applying to at least one of the members a paste flux containing the copper particles.

7. A method as claimed in claim 6 in which the flux contains at least 5% by weight of copper particles.

8. A method as claimed in claim 7 in which the copper particles consist of commercially pure, electrolytic copper powder.

References Cited UNITED STATES PATENTS 893,207 7/1908 Tabet 294% 1,722,025 7/1929 Wagener 29495 1,966,260 7/1934 Munson 29-496 L. DEWAYNE RUTLEDGE, Primal y Examiner. W. W. STALLARD, Assistant Examiner.

US. Cl. X.R.

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