US2321731A - Method of making repairs and joints in cable sheaths - Google Patents

Description

June 15, 1943. G. M. BOUTON ET A1.

METHOD OF MAKING REPAIRS AND JOINTS IN CABLE SHEATH Filed Dec.

m H N ,M mmM umu OHMv BPS MSE. 66.5 w. m n m Wj. ac mail( ATTORNEY Plantea June 1s, 1943 OFFICE Marilou or MAxrNd nsrams AND Jom'rs 1N canut snalrrns George M. Bouton. Madison, George S. Phipps,

Chatham, and Earle E. Schumacher, Maplewood, N. J., assignors to Bell Telephone Labo- Y ratories, Incorpora poration of New York Application December 18, 1941, Serial No. 423,414

2 Claims.

This invention relates to a method of making repairs-or Joints in lead-antimony and other cable sheath such as is used, for example, in telephony.

Such repairs andjoints are now made by hand wiping methods which require skilled operators and the repairs and joints so made result in certain deleterious eiects on the lead-antimony or other precipitation hardened sheath. 'I'hese harmful effects are due to the solution .and coalescence of the hardening ingredient caused by the heating of the sheath above the eutectic point l83.3 C. of the lead-tin solders. In fact, sheath temperatures under wiped joints may reach over 300 C. during wiping.

Such heating of, for example, old lead 1 per cent antimony sheath causes partial solution of the precipitated antimony, the amount redissolved depending on the time and temperature of heating and the size of the precipitated particles. Unfortunately,l the nner particles which are responsible for most of the dispersion hardening dissolve most readily and leave the alloy mechanically weak. The larger particles of precipitated and coalesced antimony which, because of their size, do not dissolvecompletely during the brief heat treatment contribute practically nothing to the strengthening of the cable sheath alloy. Their presence, on the other hand is distinctly harmful when theantimony which was dissolved by the heat treatment st arts to reprecipitate. These large particles act as nuclei upon which the antimony precipitates and loses most of its strengthening eil'ect instead of carrying out as an evenly dispersed phase throughout the alloy and thereby producing dispersion hardening. A1- though heating partially coalesced lead-antimony sheath causes some antimony solution at all temperatures, the rate of solution becomes rapid above 175 C.V Laboratory study has shown that the-tensile strength drops from about 3400 per square inch to about 2400 per square inch after i heat treatment. Similar eiects can benoted when using other cable sheathing alloys such as lead-calcium.

The method of this invention produces repairs and joints in which vthe sheath adjacent to the repairs is as durable as untreated sheath.

When any -physical discontinuity is placed on sheath which, because of its environment, is subject to cyclical-stress an added strain is put on the sheath directly adjacent to the discontinuity. Thus it becomes doubly important that the sheath in the immediate vicinity of the repairs, should in no way have its mechanical strength impaired.

Full size sheath having repairs made in this ted, New York, N. Y., a cornew method has been compared directly with sheath repaired by old conventional methods by subjecting both to mechanical tests closely simulating iield environment. The new method was demonstrated to be greatly superior to the old method.

In practicing the method of this invention the surface of the cable to be repaired is cleaned in any suitable manner as, for example, by means of a wire brush, is then coated with stearin or some other suitable flux and covered with a preshaped flexible mold, which may be made of rubber or convas. If the repair is a ring cut, only the lower half of the sheath is covered by the mold, leaving the open ends exposed on either. side. The mold is secured to the cable sheath by means of friction tape, for example. Solder is then poured alternately into each side oi the mold so as to give overflow of solder from the joint until the sheath is heated to a satisfactory wetting temperature. After a definite amount of solder has been poured into the mold, the joint is allowed to solidify and the mold removed. Y

The character of the solder is important. Among the requirements of a solder for casting are:

A low enough melting point to allow iluid casting with overilow without heating the sheath at the edge of the Joint above C,

A high ailinity for the lead sheath to insure easy and complete wetting.

The oxides of the alloy must be readily reduced by some acceptable relatively non-corrosive ilux.

'Ihe alloy should be chemically stable.

A suitable solder which most nearly meets the above requirements is a lead-tin-cadmium eutectic falling within the range of 30 to 34 per cent lead, 16 to 20 per cent cadmium and 48 to 52 per cent tin, for example 32 per cent lead, 18.2 per cent cadmium and 49.8 per cent tin. This solder melts at l45.5 C., possesses excellent fluidity sligh above'this temperature, and readily wets the l able sheath. Its chemical stability is of the sam'e order as that of lead-tin solders. At soldering temperatures'a stearin ilux, which is acceptable for cable use, was found to reduce effectively any oxide formed by this solder.

Measurements of the sheath temperature at the edge of a repair during casting has shown that with the sheath at room temperature, the

alloy can be cast at 240 C. without heating the sheath at the edge of the joint over 175 C., the

.critical solution temperature for precipitates such as antimony. Microscopic examination of adjoining solder and sheath sections has shown 2 that the alloy wetted the sheath wen and unlformly. Further examination of the sheath near theedge of the joint has shown no discernible evidence in the case of antimonial-lead alloy of antimony solution thus indicating no damage has been done to the sheath. Under commercial conditions the casting temperature and the quantity of solder to be overflowed through the mold can be adjusted according to the sheath temperature.

Fig. 1 is a fragmentary perspective view of a elastic Wrapping or gasket 24 of suitable heat resisting material. After the sleeve 2U has been beaten down the gasket 24 positioned and thev tion, molten solder is introduced into the interior of the mold through-the port'30 to completely fill the interior thereof with solder as shown at 3| in Fig. 4. An additional port 32 is g provided for the escape of air as the molten solportion of a lead-antimony sheath cable with the flexible mold about to be positioned over the ring cut or damaged portion;

Fig. 2 shows the mold in position on the underside of the cable and secured thereto by means of suitable tape and the cavity of the mold filled with molten solder;

Fig. 3 shows the cast boss on the bottom of the cable sheath after the mold has been removed:

Fig. 4 is a fragmentary view, partly in section, illustrating a modified form of the invention in which a flexible mold is used to cast a joint between the sleeve and the cable sheath;

Fig. 5 is a reduced perspective view of the flexible mold used for making the joint shown in Fi 4.

its shown in Figs. l and 2, a flexible mold I0 having a depression II therein is secured in position on the cable sheath I2 so that the damaged portion I3 is approximately centrally located with respect to the depression II. The mold IG, which is provided with feather edges I4 and i5, is secured in place on the cable sheath I2 by means of the tapes I6 and I'I which are Wrapped around the feathered edged portion of the mold and around the cable sheath. This provides a tight fit for the mold and prevents the escape of any solder from the sides of the mold during the casting operation,

After the mold I0 has been secured in `place, the cavity between the sheath and mold is filled with molten solder I8 as shown in Fig. 2. and overflowed suciently to heat the sheath to the desired wetting temperature. When this operation is completed and the solder cooled, the mold is removed and a lug or boss I9 as shown vin Fig. 3 is the result.

In the modified form of our invention shown in Fig. 4, a lead sleeve is positioned over the cable sheath 2| and the exposed conductors 22 and the end portion 23 is beaten down in the customary manner. However, to form a tight closure there is interposed between the beaten ends of the sleeve 20 and the cable sheath 2| an der is poured into the mold and to permit the desired amount of overflow. After the solder has cooled, the mold is removed and a perfect joint is the result.

We do not wish to limit our invention to the exact details of construction herein set forth, as various modifications thereof may be made without departing from the scope of the appended claims. For example, in place of the rubber mold illustrated, baked varnished canvas, Wire cloth or other reenforced textiles could be used. In fact the mold may be made of any material which will result in its being flexible within relatively narrow limits and` resistant to chemical change at the casting temperature.

What is claimed is:

1. A method of making joints or repairs in dispersion hardened lead cable sheaths which consists in securing a preformed flexible mold to the cable where the joint or repair is to be made, pouring into said mold, a molten solder comprising 30 to 34 per cent lead, 16 to 20 per cent cadmium and 48 to 52 per cent tin, said solder having a melting point low enough to permit fluid casting without heating the sheath at the edge of the joint above the temperature which would O cause appreciable quantities of the precipitated and partially coalesced antimony particles in the lead sheath to go into solution.

2. A method of making joints or repairs in dispersion hardened lead antimony cable sheaths which consists in securing a preformed flexible mold to the cable where the joint or repair is to be made, pouring into said mold a molten solder having a high affinity for the sheath, said solder comprising 30 to 34 per cent lead, 16 to 20 per cent cadmium and 48 to 52 per cent tin, said solder having a melting point low enough to permit fluid casting without heating the sheath at the edge of the joint above the temperature which would cause appreciable quantities of the precipitated and partially coalesced antimony particles in the lead sheath to go into Solution.

GEORGE M. BOUTON. GEORGE S. PHIPPS. EARLE E. SCHUMACHER.

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