Content .. 8 9 10 11 ..

Technology of watch production - part 10

C h a p t e r II

METALS USED IN WA TC H PRODUCTION

The mechanical p rope rties of metals used in watch production must

s atisfy definite t�chnical requirements

(

speci

fications

)

which have been

worked out o ver a long period of time . In mass production, deviations from
the specified properties lead to the deteriorat�on of the quality of the watches

p roduced and complicate the production process .

Chemical compos ition, mechanical properties and other requirem ents

relative to the metals are defined in the All - Union Gove rnment Standards

(GOST) and the interdepartmental technical specifications (TU ).

A wide range of metal profiles and dimensions are us ed in the manufacture

of watch parts . The number of m etal grades is , however, relatively limited .

FERROUS METALS

':(he dimensions , tolerances and surface conditions of round wires and

bars , as well as of rectangular bars and strips used in watch production

are specified (with reference to GOST and TU ) in the order specifications .

In exceptional cases the materials are proces sed to the required dimen

s ions in the watch plants thems elves : flat bars and strips are rolled and

rods are drawn and then ground and polis hed.

The range of grade U l OA and U7AV steel rods is given in Table 1 , and

Table 2 lists the range of high - carbon s teel strips . Steel rods of a dia

meter of less than

mm can be supplied with a tolerance of 0 . 005 mm if

required.

TABLE

Polished steel rods• (in mm)

Diameter

GOST or TU

Tolerance on diameter

From

0.2

0 .45

GOST

2 5 89-44

- 0 . 0 1 5

. .

0 .5

The same

- 0 .02

3 .05 ..

- 0 .025

0 .6

0 . 9

MPTU

. .

2283-49

- 0 . 005

0 . 9

. . 3

MPTU

2236-49

- 0 .01

• A bridged list.

.. Metallurgicheskaya promyshlennost' . Tekhnicheskie usloviya (Metallur

gical Industry . Technical Specifications).

3 7

The range of low- carbon cold- rolled steel strips is given in GOST 5 0 3 - 4 1 .

The grades and chemical compositions of the carbon steels and special

steels used in watch production are given in Table 3 .

The mechanical properties o f these s teels are listed in Table 4 .

The steels most widely used i n watch production are grades U7 A V and U 1 OA .

A n order for metals used in the manufacture of watch parts must specify the

metallurgical state and characteristics of the m etal in addition to the specifica
tion of mechanical prope rties . Thus , low- carbon cold- rolled s teel strips

(GOST 50 3 - 4 1 ) can be s upplied with different hardnes s e s , depending on the de

gree of cold working resulting from rolling (Table. 5 ) . Degrees of hardness have
als o been es tablished for rods : s oft (symbol M ), semihard (symbol PT), hard

(T), very hard (OT ) .

Steel , aside from its mechanical prope rties , is characterized b y its m i

crostructure . Grades U 1 0A and U 7 A V steel must have a microstructure of

uniformly distributed fine- grain pearlite, corresponding to numbers 2 - 3 on

the GOST 8 0 1 - 4 7 s cale . A cementite lattice or lamellar pearlite are not accept
able . Nonmetallic inclusions , oxides and s ulfide s , are permitted for U 1 OA

steel within the limits of numbers 2 - 2a on scale No . 5 of GOST 8 0 1 - 4 7 .

The sulfide inclusions must b e uniformly distributed within the grains of

the metal . Steel in a decarburized condition is not acceptable .

TABLE

Bright

cold-rolled tool-steel strips• (in

mm)

( according to

GOST

2284-43)

Thickness

Thickness tolerance

Thickness

Thickness tolerance

0 .1 - 0 .1 5

- 0 .015

0 .9 5 - 1 .35

- 0 .06

0.15- 0 .2 5

- 0 .02

1 .35- 1 .75

- 0 .08

0.25- 0 .4 0

- 0 .03

1 .7 5 - 2 .30

- 0 . 1 0

0 .4 0- 0 .7 0

- 0 .04

2 .3 0 - 3 . 0

- 0 .1 2

0 . 7 0- 0 .95

- 0 .05

• High-precision strips

The surfac e quality of the steel and its tolerances are of great impo rtance in

watch production. In most cases thes e parameters directly influence the quali
ty of the parts and the production process . Thus , the yoke and the bridge of the

hand-s etting movement, for example , are blanked from a strip with final thick

ness dimensions and a s urface suitable for plating. Less important parts, which
are not subjected to heat treatment (hardening), are manufactured from rods

and strips of grades 1 0 and 50 s teel . Most turned parts and bla-nks, including

thos e to be hardened, are m ade from rods of grade U7A V s teel (automatic ). Ow

ing to the p resence of s ulfur and phosphorus in this grade of steel, it ma

chines easily and is particularly s uitable for fine threading.

Its high s ulfur content, however, reduces its corros ion resistance and

makes it b rittle, C ritical parts , such as the balance staff, are therefore

preferably m ade of grade U 1 0A steel. USA steel strips are s upplied in a

hardened state and are us ed for the m anufacture of flat springs .

Grade E 1 6 9 9 steel is characterized by a high co rrosion res istanc e . Its ma

chinability in turning and drilling is lower than that of grades U 7A V and U 1 0A ,

reducing m achine output by roughly 1 0 o/o . This steel i s s upplied with a polished

surface . Grade 1 Kh 1 8N 9 steel is used mainly for external parts such as covers,

etc . This steel is very hard and tough, which makes its m achining very difficult.

3 8

TABLE 3

Chemical composition of steel grades used in the manufacture of watch parts

Steel grade

GOST or TU

Chemical composition, in

o/o

Carbon

Manganese

Silicon

Sulfur

Phosphorus

Nickel

1 0

GOST 1050-52

.0 .07 -0.01 5

0 .35-0 .65

0.17- 0.37

0 . 045

0.04

0.30

The same

0 .47-0.55

0 .50- 0 .8 0

0.17- 0.37

0 . 045

0 .04

0.30

U S A

GOST 1435-54

0.75-0.84

0.25- 0.30

0.30

Not more than 0.02

0.03

U1 0A

GOST 1435-54

0.95-1.04

0.15-0 .30

0 .30

Not morethan 0.02

0 .03

U7AV

MPTU 2242-49

0. 7 - 0. 8

0.4-0.7

Not more

0.16- 0.24

0.04-0.08

Not more

than 0.3

than 0.25

1 Kh18N9

GOST 5632-51

,;;; o.14

<o.8

,;;; 2.0

0.03

0.035

8.0-11.0

El699

ChMTU*

0.32- 0 .4

0.4- 0.7

,;;; o.7

0.2- 0.3

0.02-0.05

• [Chernaya metallurgiya. Tekhnicheskie usloviya (Ferrous Metallurgy. Technical Specifications)]

TABLE 4

Mechanical properties of steel grades used in the manufacture of watch parts

Ultimate temile strength, in kg/mm2

Percentage elongation

Steel grade

GOST or TU

rods

strips and flat bars

up to 4 mm

above 4 mm

up to 4 mm

above 4 mm

1 0

GOST 503-41

28-80

1982-50

Not more than 80

2284-43

75-11 0

USA

GOST 2283-43

75-120

U10A

M PTU

2242-49

8 0- 90

70-80

75-120

U / A V

1\ 1 PTU

:2242-49

70-80

Not less than 4

1 Khl�N9

ChMTll 3715-53

Not more than 72

F.I699

ChMTU 4825-54

70-75

Chromium

0.15

0 .30

0.25

1 7 .0-20.0

12 .5-14

strips and flat bars

4-30

1 .5

Not less than 1

Not less than40

Not specified

TABLE

Mechanical properties of low-carbon cold-rolled steel strips (GOST

5 0 3 - 4 1 )

Very soft

State

•

0 .

Soft

. . . .

. . . . . .

. . .

Semisoft

. .

•

Reduced hardness

. .

. . . .

Hard

. . .

. .

. . .

. .

U !tim are tensile

Percentage

Symbol

strength, in

kg/mm2

elongation

2 8 - 4 0

3 0

33-45

3 8 - 5 0

1 0

42 - 55

5 0 - 8 0

Not specified

NONFERROUS METALS

The nonferrous m etal most widely us ed in watch production is b ras s .

Plates and b ridges , gears , cas e s , mainspring barrel caps , dials and other

parts are made of bras s .

German s ilver (nickel s ilver ) occupies s econd place in impo rtanc e .

C a s e pa rts , the balance-wheel rim and other parts a r e made f rom it . C op

per, tombac , and aluminum are used t o a small extent.

Flat bars and strips of grade LS6 3 - 3 b rass are listed in Table 6; Table 7

gives the range of b rass wire of grades LS59 - 1 , L62 and LS6 3 - 3 .

Strip thickness

0 .1 8 - 0 .2 3

0 .2 5 - 0 . 3 0

0 .3 5 - 0 .38

0 .40- 0 .47

0 .5 0

0 .5 5 - 0 . 6 0

0 .6 5

0 . 7 0 - 0 .85

0 .9 0 - 0 .95

TABLE

Flat bars and strips of grade

LS6 3 - 3

lead brass (in mm)

(according to GOST

4442 -48)

Tolerance

Strip thickness

standard

high-precision

standard

high -precision

- 0 .03

- 0 .02

1 .0 - 1 .1

- 0 . 0 8

- 0 .06

- 0 . 04

- 0 .02

1 .2 - 1 .4

- 0 .09

- 0 .06

- 0 .04

- 0 .03

1 .5 - 1 .7

- 0 .1 0

- 0 .08

- 0 . 05

- 0 .03

1 .8 - 1 . 9

- 0 . 1 2

- 0 .08

- 0 . 06

- 0 .03

2 .0 - 2 . 5

- 0 .1 2

- 0 .1 0

- 0 .06

- 0 .04

2 .75 - 3 . 0

- 0 .1 4

- 0 .1 2

- 0 .06

- 0 .05

3 .2 5 - 3 . 5

- 0 . 1 6

- 0 .12

- 0 .07

- 0 .05

3 .7 5 - 4 . 0

- 0 . 1 8

- 0 .1 2

- 0 .08

- 0 .05

4 . 5 - 5 . 0

- 0 .20

- 0 .14

It should be noted that the tabulated data p res ented refer to the period

1 9 54 to 1 9 5 5 and that m echanical properties and attainable accuracy are

cons tantly b eing improved.

The chemical compositions of the basic grades of nonferrous metals us ed

in the manufacture of watch parts are given in Table 8 .

I n order to improve machinability, lead i s added to LS5 9 - 1 and LS6 3 - 3

b rass and to German silve r MNTsS6 3 - 1 7 - 1 8 - 2 .

Nonferrous metal s mus t satisfy the requirem ents specified by GOST and

VTU and pres ented in Table 9 .

Content .. 8 9 10 11 ..