What Is a Balance Wheel?

The balance is the name of a mechanical part. It consists of a wheel with a shaft arm that can swing back and forth, with a spiral hairspring inside.

Balance wheel

Right!

The balance is the name of a mechanical part. It consists of a wheel with a shaft arm that can swing back and forth, with a spiral hairspring inside.

Chinese name

Balance wheel

Foreign name

Balance

Temperature changes have a negative effect on the watch, because temperature will change the elasticity and effective active length of the steel hairspring. High temperature will cause the hairspring to expand and the balance speed will decrease, while low temperature will accelerate the balance. Therefore, before the invention of the automatic compensation hairspring, Swiss watchmakers used bimetallic compensation balances. That is to rely on the different expansion coefficients of the two metals to achieve the purpose of temperature error compensation.

More than 200 years ago, the British John Arnold invented the truncated bimetal compensation balance wheel: there are two truncations near the shaft arm, which serve as a buffer for metal thermal expansion and contraction. The outer layer of this balance is copper, which accounts for about 2/3 of the thickness of the balance, and the inner layer is steel, which accounts for 1/3. The two metals have different expansion coefficients. When the temperature rises, the outer layer of copper has a larger expansion coefficient than the inner layer of steel, forcing the balance ring to bend inward at the truncation, reducing the balance radius and reducing the moment of inertia, thereby compensating for the Changes in hairspring that change elasticity and length as temperature rises. When the temperature decreases, the shrinkage coefficient of the copper outer layer is greater than that of the steel inner layer, forcing the balance ring to bend outward, the effective radius increases, and the rate of torque increase slows down, which compensates for the change of the hairspring accelerated due to low temperature.This is the cold Cold and Heat Adjust.

It is worth mentioning that the light pendulum is widely used in observatory-grade movements. Before copper beryllium nickel alloys were used on balance wheels, most of them were made of copper, but because copper itself is affected by temperature, the error changes greatly. And the specific gravity is not uniform, so the observatory movements use copper-beryllium-nickel alloy as the balance material, which is uniform, stable, and less affected by temperature changes, is an ideal material. ^[1]

Whether the balance is running or not directly affects the accuracy of travel time. Whether the balance is even depends on whether its texture is uniform or not. It is also related to its roundness, which is related to the number of balance arms. We usually have two arms, three arms, four arms. That is to say, the more the arms of the balance wheel, the closer the balance wheel that it encloses is to the theoretical true circle, the more stable it is to run, and the more accurate the travel time.

In addition to good design and adjustment, a good movement must also have excellent craftsmanship. The Geneva Twelve Principles most authoritatively stipulates the highest standards for the manufacture of movements. This production is currently only used on high-end movements. ^[1]

Glucydur balance

Ordinary balance wheel

Although the design is simple, it has been adopted by many COSC chronometers. It is made of a new alloy Glucydur-ingredients: beryllium, copper and berrylium bronze. Its advantages are very hard and stable, resistant to deformation, magnetic and rust. Parity tables are also useful for this design, but they use parity materials.

ETA2824 movement

The commonly used balance wheels of ETA2892, 2824 and other movements are made of Glucydur alloy.

Bimetal screw balance

The screw on the side of the balance wheel can be adjusted in or out, changing the position, and the screw cap under the screw can also be increased or decreased. The effect is a balance wheel. When adjusting the entry and exit of the screws placed next to the cutting position, the effect of temperature changes on the balance wheel can be compensated. When adding weight or moving the screw closer to the cutting edge, the temperature difference compensation ability will increase. At the same time, the balance wheel is also made of two alloys to compensate for temperature changes.

Screw balance

Omega balance

Around 1930, many alloys became the material of the balance wheel. The most famous alloy is Nivarox, consisting of nickel, chromium, berrylium, titanium, aluminum and iron. The highest-level Nivarox I Highest has a temperature error of +/- 0.3 seconds per degree per day. The new alloy allows a single-material balance because the balance no longer needs to compensate for the influence of the hairspring on temperature.

French balance

There are several weights on the balance wheel

Because the slot on the code will reduce the weight at that point, turning the code can change the weight distribution of the balance wheel. If a pair of opposite codes are adjusted in the same way, the watch's day difference can be adjusted. The more code points to the outside of the balance (the crack points to the center of the balance) will increase the effective diameter of the balance and slow down the time of the watch. The weight can also be adjusted independently to serve as the balance wheel itself. This design is heavily used by Patek Philippe.

Rolex balance

Exclusive to Rolex, adjustment requires special tools.