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Watchmakers' Hand Book

Part II,
MATERIALS EMPLOYED IN HOROLOGY
Page 8

TO ANNEAL BRASS.

      105. When it is necessary to considerably reduce the dimensions of a piece of brass, either with the hammer, rolls or draw plate, it must be annealed from time to time.

      The metal should not be heated to redness; it is supposed, rightly or wrongly, that such a proceeding, especially if repeated, separates a portion of the zinc, or aleast changes the mode in which it is associated with the copper. Brass should be heated slowly and uniformly, in a moderate fire, until the temperature is such that drops of water thrown onto the surface are rapidly converted into vapour, or paper turns yellow and begins to smoke. It is then withdrawn from the fire and allowed to cool.

      Brass is brittle when hot, so that it can only be worked cold

      When brass is annealed, just as when steel is tempered, the metal should not be allowed to rest on a bad conductor of heat, such as wood or stone, because there will be a tendency to uneven distribution of the heat throughout the metal.


CAST BRASS.

      106. This is usually brittle, owing to the fact that the copper employed in its manufacture consists, as a rule, of all sorts of scrap, from good or bad metal; moreover, from motives of economy, the proportion of zinc is generally increase and, in pouring, the precautions essential to avoid the effects of liquation (102), etc., are frequently neglected. Such an alloy must never be used for small objects, it must be entirely excluded from a watch, and in a clock only such pivots as are called upon to perform an insignificant amount of work should be allowed to run in it.

      In order to avoid injuring the file, or embedding in the metal any particles of the hard coating of oxide that always covers rough castings, it is usual to dip the object in dilute nitric or sulphuric acid (155), by which the oxide is dissolved.


TIN.

      107. This is an elementary body, almost as white as silver and having a breaking strain of only 8 kilo. per sq. mm. of section (or 11,300 lbs. per sq. inch.)

      Watchmakers use it in making solder. It is also sometimes used in the form of plates or rods for polishing with rouge, and is said to be much more efficient when very pure.

      If a strip of pure tin is bent, a cracking noise, termed the "crying" of tin, is heard. After frequent bending, the metal loses this property.

      The degree of purity may be judged:

      (1) By the loudness of the "cry," which is found to be greater as the tin is purer;

      (2) By the relative lightness of two balls of equal size, one of which is formed of very pure tin and used as a standard;

      (3) By pouring the metal, when just melted, in a mould 1 or 2 centimeters (about 3/4 inch) in diameter. If tin is pure, when cast into plates or ingots, the surface will be perfectly smooth, without exhibiting any sign of crystallization at the moment of solidification, whereas the presence of small quantities of foreign metals causes it to be covered with a network of needle-formed crystals, which are the more numerous according as the metal is less pure.

      The Banca tin is almost chemically pure; English tin is also very pure; but others contain a small percentage of copper, lead, or arsenic.


BRONZE.

      108. Bronze is an alloy, in very variable proportions, of copper and tin, to which may be added, according to circumstances, a small percentage of lead or zinc, or even iron, when it is desired to increase the hardness or tenacity.

      As a rule, this alloy is tough and hard to work; it is especially used for parts of large machines that are subjected to considerable preasure.

      The fusion and casting of bronze require special precautions, for the proportion between the metals is liable to vary through oxidation of the tin, which then goes to form dross, and the composition may vary throughout the mass. It sometimes results from this that the bronze bearings for the pivots in large clocks are not even as good as ordinary brass, and wear away more rapidly than the pivots.

      Bronze is also use by watchmakers for making plates or small rods for polishers, and for the bells of clocks. Bell-metal contains about 78 per cent. of copper and 22 per cent. of tin; it has a beautiful fracture, and is very fusible and sonorous. The addition of any other metal is rather prejudicial than otherwise; this explains why so many clock bells are wanting sonorousness.

      An impediment to the use of bronze is its want of malleability; but Dronier has recently pointed out that such alloys may be rendered perfectly ductile and malleable by adding from 1/2 to 2 per cent. of mercury. These alloys are said to be less oxidizable than ordinary bronzes, and at the same time more hard, elastic, resisting and sonorous.


STERRO.

      109. This is an alloy containing 56 per cent. copper, 41 zinc, 2 tin and 1 iron. It resembles a reddish-colored brass, and has been much used in Vienna, where it is considered superior to brass from the point of view of ductility, tenacity and malleability.

      An experienced horologist, M. Grossmann, made satisfactory lever escape-wheels of it, and he considers it to be superior to the best brass in regard to both density and elasticity. At the same time he points out that it clogs the cutter, and the color is inferior to that of good hard brass.


LEAD.

      110. A metal with a brilliant bluish grey lustre, which rapidly becomes dull when exposed to the air. It is very malleable and ductile. It breaks with a strain of 2.9 kilo.per sq. mm. section (4,000 lbs. per sq. inch), but possesses extreme flexibility.

      Lead is not used in horology, except as a constituent of solders; in these, however, it plays a very important part. It is occasionally used in the pure state as a lap for applying polishing materials, but more frequently alloyed with tin, by which hardness is imparted to the metal, the alloy being known as "pewter."


NICKEL.

      111. An elementary metallic body of a greyish-white color, resembling that of platinum. With care it can be forged when hot and formed into plates; its structure in that case is fibrous. Its hardness is the same as that of iron, and nickel will take a high polish. Next to iron, it is the most powerfuly magnetic of all metals.

      It can be caused to alloy with many other metals--notably iron, cobalt, copper, zinc, tin, and antimony. According to Stoddard and Faraday, an alloy of 33 parts iron and 1 part nickel is as malleable as the former metal, but less liable to rust. Fleitmann has recently shown that by the addition of about 1/10th er cent. of magnesium, nickel is rendered perfectly malleable and ductile, capable of being drawn into wires or rolled into sheets, and Garnier finds that 3/10ths per cent. of phosphorus has a similar effect.

      Nickel is useful as a coating for objects that are not subjected to friction, for preserving them from the action of air. It takes a beautiful polish, and is not tarnished by being touched.


GERMAN SILVER.

      112. Although the proportion of copper in this alloyis considerable greater than that of nickel, watchmakers frequently apply the latter name to it, doubtless on account of the beautiful polish of which the metal is capable and the comparitive inoxidizability which it derives from the presence of nickel.

      German silver is an alloy of copper, nickel and zinc, with the occasional admixture of a small proportion of iron or tin. When used in the construction of objects that require soldering, 2 per cent. of lead is added.

      The alloy usually employed in horology is very malleable; it has a mean composition; copper, 60 per cent.; nickel, 20 per cent.; and zinc, 20 per cent. That containing 58 per cent. copper, 14 nickel, 25 zinc, and 3 iron, is said to be highly elastic.

      The following useful details with regard to the employment of German silver for watchwork are due to M. C. E. Jacot.

      Watch movements have been made of this alloy for the last thirty years; it was long thought that the taste would die out, but, on the other hand, the demand for "nickel" movements increases each year.

      The alloy is better prepared at the present day; it has a beautiful greyish-white colour, it is more malleable, and better to work than formerly, but still not so easy as brass. The latter alloy is less detrimental to the file, and can be turned and drilled rapidly.

      German silver is only used for the plates, cocks and bars. The barrels and wheels are of brass, and surfaces exposed to friction, such as the center pivot-hole (all other holes being jeweled) are bushed with the same metal, for it is observed that in presence of nickel oil is rapidly blackened and the pivots wear sooner than when working in good brass.

      The color remains unaltered for a long time if the surface has been carefully smoothed in the first instance; and if cleaned with soap and water, its original freshness can be to a great extent restored. Some watchmakers prefer to employ chemical preparations for cleaning the metal.

      The following is recommended as very effective for this purpose; Mix 50 parts alcohol, 1 part sulphuric, and 1 part nitric acid. Allow the pieces to remain in this liquid for 10 or 15 seconds, wash with cold water, and subsequently with alcohol, dry with a soft rag or in boxwood saw dust.


GOLD.

      113. An elementary body, the most beautiful and the most valuable of all the ordinary metals. In the unalloyed state it has a pure yellow color, and when reduced to extremely thin layers, appears green by transmitted light. It is the most malleable and ductile of all the metals, but its tenacity is low.

      Gold resembles platinum, silver, iron, etc., in being capable of welding, that is to say two pieces of the metal can be united without previous fusion. Indeed, by the application of great preasure it can be made to weld when cold.

      It is insoluable except in aqua regia (a mixture of 1 part nitric acid and 4 parts hydrochloric acid), alkaline persulphides and selenic acid. Chlorine, phosporus, and a few other substances can be made to combine with it by the aid of heat.

      It is as a preservative, that is applied in layers termed "gilding," that gold is principally used in watchwork, and some details will be found on this subject under "Gilding," (articles 142--153). Owing to its softness the metal is not used in a pure state, but usually alloyed with copper. The principal alloys in use in this country are:

      22 parts (carats) gold, 2 parts (carats) copper, for coin and wedding rings.

      18 parts gold, 6 parts copper, for high-class jewelry and watch cases.

      15 parts gold, 9 parts copper, for ordinary jewelry.

      12 parts gold, 12 parts copper; and 9 parts gold, 15 parts copper, for common jewelry.

      The alloys used for soldering gold will be described under "Solders" (126).

      Alloys of gold with silver and copper have been employed for making watch wheels; they wear well, and will take a beautiful polish, which is maintained for a longer time than in the case of brass wheels.

      Chronometer balance-springs and the suspension-springs for astronomical clocks have also been made of gold-copper or gold-silver alloys rolled and hardened(666). If carefully prepared, they maintain their elasticity unimpaired for a long period, and there is no liability to rust

      The dilation for a given change of temperature is, however, greater than that of steel, so that a greater compensating effect becomes necessary, but this inconvenience is partly compensated for by its inoxidizability and the fact that it is not liable to become magnetic.

Submitted by: Samuel Kirk (##)

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