UDC 62-272

INFLUENCE OF THE PARAMETERS

OF CERTAIN TECHNOLOGICAL OPERATIONS

ON THE STABILITY OF S-SHAPED SPRINGS

FOR WRISTWATCHES

V. I. Kalyagina, Yu. Ya. Kovylin

(Presented by the scientific-methodological seminar of the Department of Applied Mechanics)

By the stability of a watch mainspring is meant the constancy over time of the values of the torques at the corresponding points of the characteristic curve and of the free form of the spring.

Stability is the most important indicator of spring quality and has a substantial effect on the quality of watches.

In order to identify possible reserves for increasing the stability of springs, we investigated two operations provided for by the existing technology of their manufacture, namely, the operations of the first and second setting.

The operation of the first setting includes winding the spring onto a mandrel in the direction opposite to the first two coils, and setting in a ring in combination with heat treatment. The existing technology for springs of all thicknesses in this operation recommends two mandrels and two rings. For springs whose thicknesses vary from 0.07 to 0.085 mm, the ring diameter is 8.6 mm and the mandrel diameter is 6 mm; for springs whose thicknesses vary in the range 0.085–0.12 mm, the diameters are 11.5 and 9 mm, respectively.

The operation of the second setting includes winding the spring onto a mandrel in the direct direction and holding it in a ring for 3–5 days.

In this connection, the objective of the investigation was formulated as follows: to study the influence of the diameters of the mandrels and rings in the operation of the first setting, and of the duration of the second setting, on the stability of springs.

To solve the problem, we tested two experimental batches of S-shaped springs of sizes 0.085 × 1.35 × 220, 0.105 × 1.38 × 325, and 0.12 × 1.50 × 335 mm made of cobalt alloy K40Yu. Both batches of springs were manufactured in accordance with the existing technology, but the first with the aid of a series of mandrels and rings that included both those specified by the technology and additional ones; the second with the duration of the second setting varied up to 10 days.

Since we had no possibility of evaluating the stability of the springs over time by means of prolonged testing directly in watches, we base our conclusions on the results of accelerated cyclic tests that imitate the operation of the springs in watches.

Tests of the experimental springs up to 10, 100, and 1000 winding–unwinding cycles were carried out successively on the equipment of the Scientific-Research-

of the Scientific-Research Institute of the Watch Industry in the barrels of serially produced wristwatches “Slava 1601,” “Polet 2409,” and “Vostok 2602.”

Processing and analysis of the experimental data showed that:

— no definite dependence is observed of the torque of the springs on the diameters of the rings and arbors (Fig. 1);

Fig. 1. Torques \(M'_{n-1}\), \(M'_{n-4}\) of springs as a function of the diameter \(D\) of the ring for the first setting and of the diameter \(d\) of the arbor for reverse winding:
a—springs \(0.085 \times 1.35 \times 220\) mm; b—springs \(0.105 \times 1.38 \times 325\) mm; ——— \(N=0\), - - - - - - \(N=1000\) winding–unwinding cycles

— the instability of the torques \(M'_{n-1}\) and \(M'_{n-4}\) (after one and four revolutions of the barrel) for the varied diameter values differs insignificantly, which gives no grounds for preferring any of the diameters from the standpoint of its influence on the indicated parameter;

— the smallest of the investigated ring diameters provide the springs in the as-supplied condition with 70% (0.6 turn) reverse coils

greater than the largest. However, this difference is not constant over time, and by 100 winding–unwinding cycles it is reduced by half;

— the arbor diameter has no effect on the number of reverse turns of the spring;

— the duration of the second seasoning does not affect the stability of the spring torque over time (Fig. 2). From Fig. 2

Fig. 2. Torques \(M'_{n-1}\), \(M'_{n-4}\), straight turns \(i_c\), and reverse turns \(i_s\) as functions of the number of winding–unwinding cycles, for different durations of the second seasoning in days: solid line — 0 days, dashed line — 10 days; a—springs \(0.085\times1.35\times220\) mm; b—springs \(0.105\times1.38\times325\) mm; c—springs \(0.12\times1.50\times335\) mm

it follows that a spring subjected to a second seasoning for 10 days behaves during accelerated tests up to 1000 winding–unwinding cycles in exactly the same way as a spring that has not undergone this seasoning at all;

— springs seasoned for 10 days have, in the delivery condition, a maximum number of straight turns \(i_c\) greater by 0.4, and of reverse turns \(i_s\) smaller by 0.13, than springs not subjected to this operation. However, this difference is not constant over time and by 100 winding–unwinding cycles amounts to 0.2 and 0.03 turns, respectively (Fig. 2);

— stabilization of the torque and of the free form of the spring is practically completed by 100 winding–release cycles, which provides grounds, in future evaluations of the stability of particular experimental springs, for testing them only up to 100 winding–release cycles. In addition, it appears possible to recommend to watch factories preliminary running-in of springs in barrels for 100 winding–release cycles before installation in watches, in order to ensure the stability of the spring parameters from the beginning of operation of the watch.

In conclusion, we note that no appreciable influence of the technological parameters investigated on the stability of the springs was found. In this connection, it may be recommended to increase the diameters of the rings for the first scragging as one of the possible means of combating spring rejection due to waviness, without fear of impairing the stability and other parameters of the springs. The purpose of the second scragging operation should be regarded only as revealing hidden defects in the metal.