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Technology of watch production - part 11

Flat rods and strips of LS6 3 - 3 lead brass are supplied, according to the

TsMTU 4 5 8 9 - 5 5 specifications, with the following mechanical properties :

semihard - 4 5 - 6 5 Rc , s cale B;

hard - 6 5 - 9 0 Rc , s cale B .

B rass grades L62 and L 6 8 are used for the manufacture o f parts by

drawing or bending, since they have good plasticity and can be worked with
out failure.

TABLE 7

Brass 1vire (in mm) (according to GOST 1 066-50)

Tolerance

Wire diameter

standard

high-precision

standard

high-precision

0.10-0 .25

-0.02

1 .0-1 .1

- 0 .04

-0.03

0.30

- 0.03

-0 .02

1 .2-1 .9

-0.045

-0.04

0.35-0 .50

-0 .03

- 0 .025

2 .0-2 . 9

- 0 .055

-0.04

0.55-0.60

-0 .035

- 0 .025

3.0

- 0.06

-0.04

0 .65- 0.90

- 0.035

- 0 .03

3 .2-4.8

- 0.06

- 0 .05

R e m a r k s : The tolerances can be narr01ved if required : for diameters up to 2 .5 mm - down to 0.01 mm,

" " 4.8 mm - down to 0 .02 mm.

TABLE 8

Chemical composition of nonferrous metals used in the manufacture of watch parts

Grade

GOST or TU

Chemical composition

Copper

Lead

Zinc

Nickel

Iron

Antimony

Bismuth

Brass 1..559-1

GOST

57 -60

0.8 - 1 . 9

Balance

0.5

0.005

0.002

1019-47

Brass L62

60.5-63.5

0.03

0.10

0.005

0.002

Brass LS63 -3

62-65

2 .4-3

0.10

0.005

0.002

Brass L68

67 -7 0

0.03

0.10

0.005

0.002

German silver

TUTslviO

Balance

1 .6-2

17-19

16.5-18

lviNTsS

6-42 -51

63-17 -18-2

When machined, thes e types of brass develop large burrs, which are

inadmis sible in watch production .

LS5 9 - 1 b rass contains lead (more than 1 % ), which makes it more s uit

able for machining .

LS6 3 - 3 brass , containing up t o 3 % lead, has even better machinability

and als o higher hardness and brittleness . The hard and very hard bras ses
of this grade have a very good surface quality after being machined .

LS6 3 - 3 brass is use d i n the manufacture o f important watch parts which

require considerable machining.

Less important parts or parts requiri'ng less machining are manufactured

from LS5 9 - 1 bras s .

Bras s o f all grades lends its elf eas ily t o plating.

Leaded German silver has much poorer m ac hinability than has bras s ;

i t i s harder and al so tougher. Its surface quality after machining

4 1

is the refore poorer than that of brass and its tendency to form burrs is
more p ronounced.

Some of the special alloys used in watch p roduction are a nickel alloy

for the spiral springs (hairsprings ) of pocket- and wristwatch balance

wheels, beryllium bronze and cupronickel .

Grade

LS59-1

L6:2

LS63-3

LS59-l

L62

LS63-3

L62-T

LS59-1

L62

L68

LS59-1

L62

L68

TABLE 9

Mechanical properties of the nonfe

rous metals used in '"arch production

GOST or VTU

GOST 1 066-50

GOST 1066-50

TU 303-46

GOST 1066-50

TU 303-46

TUTsMO

6-29-50

GOST 2208-49

GOST 931 - 52

GOST 931 -52

Ultimate tensile strength, in kg/rnm2,

not less rhan

Soft Semihard

Hard

Very

( M)

( PT)

(T) hard (OT)

Percentage elongation, not less than

Soft

(M)

Hard

Very

( PT)

(T)

hard(OT)

W ires, diameter between 2 and 5 mm

50-60

60-70

1 .5

0.5

l<ods, diameter above 5 mm

50-60

60-70

1 .5

0.5

Sheets

Drawing depth, according to the Eriksen test, from 1 to 3 mm

Ribbons

1 0

2.5

Strips

T h e n i c k e l a l l o y N 3 5KhlVIV used for hairsp rings is supplied in the

form of wires of 0 . 2 6 - 0 . 3 0 mm diameter having an ultimate tens ile s trength

of 78 to 8 5 kg/m m2 and a perc entage elongation of 1 7 to 2 0 o/o .

These wires are drawn to the required gage ( 0 . 055; 0 . 07; 0. 0 7 5 m m ) at

the watch plants , after which they are subjected to flattening by rolling.

The tempe rature coefficient of this alloy is 0 . 3 to 0 . 5 sec per

C , which

m eans that when the tempe rature ·varies by 1

oc ,

the modulus of elas ticity

of the spiral changes by a magnitude which will caus e a variation of 0 . 5 sec

in 24 hours . The modulus of elas ticity of the alloy E

1 8 , 5 00 to

1 9, 500 kg/mm 2 and the chemical composition are defined in the MPTU

3404 - 5 3 specifications .

The alloy must satisfy high requirem ents as regards its structure: the

size of the (dispers e d ) carbides must not exceed 6

fl .

Grade B - 4 b e r y l l i u m b r o n z e is used in the manufacture o f the

balance - wheel rim of watches and has the following chemical compos ition:

2 . 26 o/o beryllium , 0 . 4 0 o/o nickel, 0 . 4 2 o/o tellurium , the balance being copper.

TABLE 10

Mechanical properries of beryllium bronze, brass and German silver

Brinell hardness,

Ultimate tensile

Coefficient

Alloy

kg/mm2

strength, k

mm2

of linear

expansion

Brass LS63-3

•

13D-150

43-54

19x lo-6

German silver 63�17-18-2

•

14D-180

38-45

18.4x lo-6

Bery Ilium bronze B-4 . . . .

, ,

340

110

16.5xlo-6

(after aging)

The choice of bronze as the material from which the bal R.nce wheel o f

pocket- and wris twatches i s made i s bas ed o n the following prop e rties o f

this alloy:

a ) high hardne s s , reaching 3 4 0 kg/mm 2 (H8

34 0 ), with a highly stable

fine- grain s tructure, a fact which eliminates the tendency to dis tort, during
or after machining, assembling and adjusting;

b) small co

;

fficient of linear exp ansion ( 1 6 . 5 X l o- 6 ) as compared with

b rass and German silver. This makes it possible to lower the total tempe r

ature coefficient o f the system balance wheel - spiral;

c ) high c orrosion resistance .

The m echanical p roperties o f the B - 4 bronze are p res ented in Table 1 0 ,

together with those o f brass and Germ an silve r .

A small addition o f tellurium improves the machinability o f B - 4 bronze

to the extent that it approaches 8 0 % of the machinability of Ge rman silver.

JZO

-a ZBO

Cl)

c::

:£ zw

200

150

•

200 250 300 350 1;1)0 450

500°

Aging temperature

t C

FIGURE

1 .

The hardness HB of beryllium bronze as a function

of the aging temperature

4 3

The heat treatm ent of bronze consists in heating to between 7 8 0 and

8 0 0°C , quenching in cold water, and tempering for s e ve ral hours at 3 00 to
32 5°C , A s a result of precipitation hardening, which takes place at a tem

pe rature of 3 0 0 to 32 5°C, the beryllium bronze loses the plasticity it had

afte r quenching and becomes hard . Quenched be ryllium bronze has a
hardness H8

1 00; after aging the hardness is H 8

3 2 5 - 3 4 0 .

A ging o f the bronze a t tempe ratures above 3 2 5°C l eads to a decrease

in hardnes s , as can be seen from Figure 1 .

C u p r o n i c k e

is used for the manufacture of the cases of the wrist

watches of the "Zvezda" b rand . It contains , according to GOST 4 92 - 52 ,

2 0 to 2 8 % nickel, the balance being copper. Its m echanical properties are,

according to GOST 5 1 8 7 : ultimate tensile strength from 30 to 40 kg/ mm2 ,
elongation 2 . 5 % .

Cup ronickel strips are s upplied, as are brass strip s , either t o normal

accuracy s tandards or as precision strips according to GOST 5 1 8 7 - 4 9 .

Strips o f thickness up to 0 . 3 0 mm are not s ubjected t o tensile tests,

and their technological prope rties are es tablished by a drawing test.

METAL TESTING

The metals delivered to the plant are subje cted to sampling tests for che m

ical composition, mechanical and technological propertie s, as well a s f o r their

metallurgical structure, in accordance with GOST or VTU .

Depending upon their final use, the metals are subjected to the whole set

of tests or only to s om e of them . The m etals are certified as fit for use in

p ro duction after s atisfactory results have been obtained from the tests .

The m etal tests are class ified as chemica.!, mechanical , technological,

m etallographic, or special tests .

T h e c h e m i c a

t e s t s are conducted in the plant laboratories and

consist in the analysis of the chemical composition of the m etal for the

purpose of determining the perc entage of the various components .

This analysis is called an a s s a y and is conducted on a small sample ,

cut from the bar or strip .

The dete rmination of the chemical composition of m etals by chemical

methods is a lengthy proces s ; however, in many cas e s , it s uffices to de

termine the percentage content of only those components which decisively

influence the p roperties of the alloy: carbon in carbon steel, carbon and
s ulfur in U7A V steel, lead in LS6 3 - 3 bras s , etc .

The percentage content o f certain components can in such cases b e de

termined rapidly, although less accurately than by chemical analysis, by

use of spectral analysis . The instrum ent used for this purpose is the SL- 3

spark spectrograph .

The determination of the chemical composition using the spark spectro

graph takes not more than a few minutes , since it is nondes tructive and can

be conducted directly on the metal bar or strip to be tes ted .

The m echanical tes ts s e rve to determine the ultimate tensile strength

(U. T. S . ), the percentage elongation, and the hardnes s . The tensile -test

specim en

( 1 )

of given dimensions and shape (Figure 2 ), is gripped at both

ends (2 and 3 ) and is set unde r tensile stress by the m achine . The test

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