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Watchmakers' Hand Book

Part II,
Page 10


      123. It is well known that a solder is an alloy employed to unite, by the aid of heat, two metallic bodies that are placed in contact. A solder, then, must be much more fusible than the metals it unites, otherwise these latter would be damaged by the degree of heat applied. Solder is all the less tenacious, and melts the more easily according as the proportion of the most fusible metal present is increased.

      This fact is taken advantage of when several solderings have been performed on the same object. The alloy last employed will require to be considerably more fusible than the first, as otherwise the heat would be so great that the earlier joints would melt. In an ordinary lead-tin solder, the fusibility is increased by increasing the proportion of the latter metal till the lead is to tin, as 6 is to 1. This alloy melts at 194° C.(380° F.), and the melting point may be still further reduced by adding a gradually increasing proportion of bismuth.

      As the melting point of the solder approximates to that of the metals to be united, the risk of damaging these latter is of course increased, but, at the same time, the joint will be all the stronger, as the metal will be almost as strong as at any other point, and it can be forged, etc.

      Solders are distinguished as hard or soft; the former requires the application of a red heat, and can therefore only be used for such metals as gold, silver, brass; whereas the latter melt at very low temperature, and can be employed for metals that have a low melting points, or when it is important not to exceed a moderate degree of heat. The joint, however, the more solid as the heat employed approximates to that at which the metal will melt.

      124. Composition of solders. The solders ordinarily employed can be obtained from material dealers, but it is advisable to give here the composition of some of the more important, specifying the metal to which they are applicable.

      125. Aluminum solders.
      I. Zinc, 70 parts; copper, 15; aluminum, 15.
      II. M. Mourey employs a series of aluminium-zinc alloys, commencing with two percent aluminium to 98 percent zinc, and progressing to 20 percent of the former to 80 percent of the latter metal.

      126. Gold solders.
      I. Gold, 6 parts; copper, 1 part; silver, 2 parts.
      II. Gold, 15 parts; silver, 2 parts; copper, 1 part.
      III. Gold, 11.94 parts; silver, 54.74 parts; copper, 28.17 parts; zinc, 5.81 parts. The three first metals are melted together in a crucible, and when thy ave somewhat cooled, a rather greater proportion of zinc than is here indicated (to allow for loss by volatilization) is added, and the alloy constantly stirred.

      127. Silver solders.
      I. Silver, 2 parts; brass (for pin-wire), 1 part.
      II. Silver, 5 parts; pin-wire brass, 1 part.
      III. Silver, 10 parts; pin-wire brass, 5 parts; pure zinc, 1 part.

      128. tin solders.
      I. (Ordinary soft solder.) Tin, 2 parts; lead, 1 part.
      II. (Harder, and known as "Plumbers' Sealed" solder.) Tin, 1 part; lead, 2 parts.
      III. Many other proportions of tin and lead are occasionally used. ranging from tin, 1 part; lead, 25 parts, to tin, 6 parts; lead. 1 part.
      IV. (Very fusible solder, melting in boiling water.) Lead, 3 parts; tin, 5 parts; bismuth, 8 parts. The fusibility is still further increased by adding mercury or cadmium.

      129. Spelter solders. (Used for brazing.) Copper and zinc in varying proportions. It becomes more fusible as the amount of zinc is increased.


      130 A thorough cleaning of the surfaces to be united is always needful, but more especially so in the case of soft soldering. It may be effected by means of acids, or with a graver or scraper, etc.; the cleaned surfaces must not be touched with the fingers, and the soldering should be done at once. If acids are employed, the objects should be thoroughly washed after soldering, in order to avoid rust; and, after drying, they should be rinsed with alcohol.

      The parts to be soldered are held in position with clamps, tweezers, pins, or iron wire. This latter, known as binding wire, is used for delicate objects and should be very pliable. When a high degree of heat is to be applied, all risk of the iron uniting with gold may be avoided by mixing a little sandiver with the borax employed. (See article 153).

      Before heating, if there are already parts united with solder, they should be covered with borax to prevent softening.

      Only a moderate heat should at first be applied, so as to melt the borax, or sal-ammoniac without displacing it. The violent frothing up, which is very liable to displace the parts or the fragments of solder, can thus in a great part be avoided. If a naked lamp-flame is used, or if it is directed on to the object with a blow-pipe, it should be, so to speak, large and soft, and the jet should not be directed to the point of juncture until the solder is observed to have fused. In soldering brass to steal, it is sometimes necessary to direct the flame against the brass only, in order, as far as possible, to avoid softening the steel. The hard solders for gold, silver, etc., require a considerable degree of heat, so that the objects must be heated to redness.

      131. To solder gold and platinum to each other or to themselves. On a hard wetted surface, marble, for example, rub a piece of borax until a white liquid paste is obtained (or the powdered borax sold by chemists can be made into paste direct). Having prepared the borax, the surfaces to be united are cleansed either by scraping or with dilute nitric acid (155); the acid may be previously heated to boiling, as it will then act more rapidly; and the surfaces are subsequently scraped. They are now covered with borax wit a paint brush, set in position, and small pieces of solder placed on the junction. As already observed, the heating must at first be gentle to avoid displacing the solder by the frothing of the borax.

      132. To solder silver. Also for uniting gold to silver, or silver, brass, steel to each other or to themselves. Proceed in the manner already explained for gold and platinum, except that the borax paste must be sensibly thicker.

      133. To solder tin. Also for uniting gold, silver, brass to each other, or to other metals, such as steel, iron, etc. Clean the surface with a graver or scraper; sulfuric or hydrochloric acid may be used, but in this case the cleansing afterwards must not be forgotten.

      The heating is effected as in soldering gold, unless a soldering iron is used, when the directions subsequently given should be followed.

      134. To solder aluminium. M. Mourey recommends the following method.

      One of the series of aluminium solders, No. II. (art. 125), is employed and, as a flux, two-thirds of balsam of copaiba, one-third very pure Venice turpentine, and a few drops of the juice of a citron; these constituents are pounded together in order to secure a perfect admixture.

      The surfaces to be united are covered with solder (employing a soldering iron of aluminium) just as in the case of tinning (137), the flux just mentioned being used. The two surfaces, thus prepared, are placed in contact and maintained in the required position, and, after laying on the joint particles of solder that are richer in aluminium than the one used for preparing the surfaces, the whole is placed over a charcoal fire or heated before the blow-pipe, pressing gently on the pieces of solder, which will soon melt and should be distributed by means of a little tool of aluminium.

      During this second stage of the process, it is necessary to be very cautious in the application of the flux; the pieces of solder should only be dipped in it before being placed in position, for the flux is mainly for use in preparing the surfaces; as soon as the solder has run well, the temperature should be lowered in order not to dry up and burn the solder, which would be apt to become brittle.

      In preparing the solders, the aluminium is first fused and stirred with a small iron rod; then add the zinc and stir again; add a little tallow and cast the solder into rods.

      The zinc must not be too much heated, as it will volatilize, leaving the alloy rich in aluminium and therefore brittle.

      135. Fluxes for soldering. Various substances can be employed as fluxes for cleansing the surfaces to be united:

      Sal-ammoniac reduced to powder and made into a paste with sweet oil, or merely dissolved in water. A paste formed of sal-ammoniac and resin, reduced to powder, with water or oil. Resin alone will suffice for the soft soldering of copper or brass. Venice turpentine, which has the advantage of not causing steel to rust, although it makes the objects sticky so that they require to be afterwards rinsed in alcohol or turpentine.

      Various acid solutions are sold for the purpose and experience will enable the watchmaker to select that which is best adapted to his requirements.

      Lastly, saturated chloride of zinc can be recommended. It is prepared as follows:

      Some dilute hydrochloric acid (which also goes by the name of spirits of salts, or muriatic acid) is placed in a glass flask and strips of zinc are added one by one; the flask must be left un-corked and the zinc added a little at a time, lest the effervescence that occurs should break the vessel. When the zinc added is not acted on by the fluid it may be concluded that the acid is saturated or "killed", and the fluid may then be transferred to a stoppered or corked bottle for use. In using it, a small quantity is spread over the surfaces that are to be united and the solder will be found to run with great freedom. Some authorities recommend the addition of sal ammoniac to the extent of one fourth the weight of acid taken. It is well again to warn the reader that the pieces must be thoroughly washed after employing these liquids, for, otherwise, they will cause tools with which they are brought in contact to rust and will rust themselves if they consist wholly or in part of iron or steel. The vessel containing the fluid must be kept well away from the work-bench.

      The liquid can be used immediately after being prepared as above explained; but all acid reaction may be prevented by evaporating at a moderate temperature until of the consistency of oil; it is then allowed to cool and kept in a bottle.

      136. The soldering iron with a head of copper, such as is used by tin-plate workers, is well known; if made on a small scale it may occasionally be of service to the watch-maker. The tool may be T-shaped, one end of the horizontal portion, the copper head, terminating in a rather thin blade, and the other enlarged, so that, when held in the flame of a lamp, it will store up a sufficient amount of heat. The upright part of the T corresponds of course, to the handle. After the iron has been heated just short of redness in the dark, the end of the blade is moistened with soldering fluid and a small piece of solder attached to it. The object to be united is gently heated and also moistened with the fluid; the iron charged with solder is presented to it, often with the enlarged extremity of the head maintained in the flame of a lamp, and the solder will, as a rule, run without again heating the object, although this might be done while the iron is still in contact. It may be found convenient to fix the iron in a suitable position with the lamp below the large end of the head; the object will then be brought against the iron after being moistened with the fluid.

      137. It is often advisable to tin the surfaces to be united previous to soldering them; in order to do this they are moistened with soldering fluid, small pieces of solder are then spread over, and these are fused by passing the hot iron over the surface; or the solder can be spread after fusion by means of a metallic rod charged with the liquid.

      138. Brazing. This operation consists in soldering iron, steel, brass, or copper, with an easily fusible brass, which is specially prepared in the form of coarse dust, termed spelter solder, or cut in thin strips of convenient shape (129). The method resembles, in all essential particulars, the application of hard solders previously referred to. (131, etc.)

      Heat is usually applied direct by blow-pipe, borax being used as a flux, and the precautions taken that are mentioned in article (130): it is necessary to avoid a greater degree of heat than would melt the brass, since the object might in that case be fused. For fine work, it is better to employ silver solder.

      On an emergency, two pieces of steel can be united by brazing and subsequently hardened, and we have successively practiced this method in such a case as the following: A small portion having been broken off from the quarter-piece of a repeater, we dovetailed into it another piece of steel of the required form, but a trifle too large at the upper side. When the brass had run well into the joint, and the piece was still at a full cherry-red heat, it was hardened, and afterwards cleaned and tempered to a blue color. The upper surface was then brought to shape with a good file, resting it on a wooden block against a projection, and, after making sure that it would act correctly, the whole was smoothed and polished. It has since worked well and does not show signs of wear.

Submitted by: Samuel Kirk (##)

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