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Technology of watch production - part 80

with intermediate annealing for which purpose the s trip ends are conn

cted

to terminals , and the strip is heated by electric current to red incandescence .

The strip surface i s c oated with a n ochre paste t o prevent oxidation.

The c ompleted rolled strip consists of three rigidly bound layers: outer

layers of gold 2 0 ft and

0 ft thick, and a core of 0 . 3 5 to 0 . 5 mm thicknes s .

Stamping and other mechanical operations similar t o those used i n producing

gold cases are performed on the strip . Blanks are annealed after stamping
operations in furnaces with a neutral medium .

The gold layer thickness is reduced from its original 2 0 ft to 1 0 ft on pro

tuberances, acute angles and transitions which result from drawing and
forming operations . The layer thickness on these features is s ometimes

as little as 3 to 4 /t , which corresponds to 3 to 4 years wear . Bright points

appear at the spots where the gold is thin (the nickel silver shows through),

and, in order to obtain a uniform hue, the case is galvanically gold-plated

( 1 -2ft ).

The galvanic layer is rapidly worn, however, and hues appear on

the watch case. To avoid these problems s harp transitions should be avoid

ed in gold-plated cases and they should have a streamlined form .

The quantity of gold used in a thermally-plated case is only 1 0 to

o/o,

the quantity required for a s olid- gold cas e . It is , howe ver, difficult to de

termine the exact amount of gold in a case gold-plated by the thermal method.

Wristwatch cases have s ometimes backs made of stainless steel . The
middles of such watches are so designed as to make the back invisible from

the side. The amount of gold required for a watch of this type is only 0 . 4 g.

A variation of the thermal-plating process involves the separate blanking

of nickel- silver and gold parts which are then soldered with tin or bound

together by means of a special compound, after

which they are subjected to the subsequent ope rations .

This method has the advantage that the gold sc rap

is s eparate from the nickel - silver scrap and s o can

be salvaged. The scrap from the bim etallic strips
has to be subjected to etching to remove the nickel

FIGUR£ 47. Winding crown

silver so that the gold can be recuperated.

with gold envelope

Galvanic gold- plating of watch cases is not widely

p racticed because galvanic baths only work satis

factorily with pure gold , and a pure- gold coating is

of low durability. Electrolytes containing 1 4 - and 1 8 - carat gold are unstable

in operation and p roduce a low-quality coat. The thickness of the gold layer

produced by such baths does not excee d 5 to 7 ll and repeated plating oper

ations are the refore necessary in order to obtain a 2 0 ft thick layer .

A mechanical gold-plating method involves clos ely fitting a gold foil to

the case and the winding c rown. This requires a larger amount of gold than

that required by the thermal or galvanic methods . This mechanical method

is now being used only for coating the winding crown, to which end gold foil

is used, 0 . 0 5 - 0. 1 0 mm thick and having the same color and the same carat
number as the case (Figure 4 7 ).

3 1 7

DIALS AND HANDS

The dials

of wrist- and pocket- watches are made of L- 6 2 brass or L - 9 0

tombac . Their design and finish are very diverse. The dial field can be
white ( silvering ), pink (alloy gilding), or black (oxidation or black- nickel

plating). The marks on the dial may be flush or raised and include the

watch-scale figures or the symbols which replace them , and the divisions
of the minute and second scales with incomplete (or completely lacking)

numbering (Figure 48). The figures are p rinted by using printer ' s ink or

luminous paste , or are embossed in dies (raised figures ).

FIGURE 48. W atch dials:

a-" Zvezda" ; b-" Mayak" ; c-"Sportivnye" .

The process of dial manufacture consists basically o f the following oper

ations : blanking, soldering the feet, recessing, p reparing the surface for

coating (de greasing and etching), silvering or gilding, varnishing, printing

and drying.

FIGURE 49. Dial blank ( first operation)

3 1 8

For example , the dial blank for caliper K - 2 6 wristwatches is blanked

with two through holes for the axes of the hands , and two blind holes for

the feet (Figure 4 9 ) . The operation is performed on a 1 5-t crank press by

a c ompound die (Sh- 04 ). The permissible run- out of the outer diameter

relative to the central hole is 0 . 02 mm.

The blank is ground on the S - 2 9 machine, the object being the leveling

of its face, after which it is degreased in an organic solvent.

Two feet are pressed into the blank and s oldered using PSR- 45 silver

solder (Figure 5 0 ). The ring-shaped s older preform is placed on the dial foot;

the soldering location is m oistened with borax; and the foot is s oldered in
a gas burner . In some plants the feet are welded on an electrical welding

machine .

FIGURE 50. Soldering the feet

FIGURE 51. Sizing the feet

The soldered joint is then cleaned , and the feet and the dial face are

straightening (Figure 5 1 ). The cleaning is performed by m eans of a hollow

mill in a vertical drilling machine, while the straightening is performed

on a special semiautomatic m achine. The dial - face flatness is tested using
a ruler.

Section AA

�;"

FIGURE 5 2 . Machining the recesses for the
winding pinion and the balance cap

3 1 9

0. OS

FIGURE 53. Pol

ishing the dial face

The slot for the winding pinion is then milled, and the recess for the

balance cap bored on horizontal and vertical milling machines , respective

ly (Figure 52 ). The machines are adjusted using an adjusting or position
ing template , and the two holes for the hands serve as a referenc e .

A fter the edges are bent, the dial face is ground and polished (Figure 5 3 )

o n the S-42A machine by felt disks charged with emery paste o f grain- size

2 8 0 to 3 2 0 and with chromium - oxide paste. The surface - finish quality must

be grade"\7'\i"V\7 1 0, and no scratches, dents , or other defects visible under

a 5 X magnifying glass are permitted.

The dials are washed before inspection in four baths with "Galosha "

brand benzine (GOST 44 3 - 4 1 ) and are bushed using a soft-hair brush.

Dials which pass inspection move on to the next operation, which is the

boring of the s econds-hand recess (Figure 54 ) . The operation i s performed

at a high tool-feed rate of 0 . 1 0- 0 . 1 5 m m / rev in order to obtain a clean A r

chimedean spiral on the recess surface (Figure 54, b ). The central part

of the dial field is sometimes faced, using the feed rate mentioned, in order

to obtain an aesthetic design.

FIGURE 54. Seconds-hand recess

The blank is again washed in four benzine baths and is then subjected to

silvering. Silver plating is preceded by electrolytic degreasing, washing

in very hot and in cold water, and brushing of the face in order to remove

the oxides and give it a uniform hue . The blank is then suspended from a

frame and charged into the silver-plating bath where a 1 . 5 to 2

thick silver

layer is deposited. Three baths wash off the remainder of the electrolyte,

and the dials are then rins ed in cool running water after which they are

spread, faces down, on tissue paper for drying.

V a r n i s h i n g is a critical operation, as it must protect the silver sur

face against the effects of air and so preserve its appearance for many years.

The varnish must resist the action of sun and that of other light sources .

It must be colorless, and must not distort the dial field or change its color.

The thickness of the varnish coat must be 5 - 6 ft , so as to be invisible to

the eye .

These requirements are satisfied, to a ce rtain extent, by the BMK- 5

resin, which is soluble in amylacetate and in acetone. The dials are dried

before varnishing by consecutive dippings in three acetone baths and are

then varnished in a centrifuge, and dried at 4 0 - 4 5°C in a glass cupboard

in order to prevent dust from setting on them.

320

Content .. 78 79 80 81 ..