THE TRAINING CENTER

During the servicing of a watch, one of the areas requiring particular attention is the threading of the case and screw-down case-back. Repeated assembly and disassembly, combined with contact between two metal surfaces, can lead to a phenomenon known as Galling.

Galling is a form of adhesive wear. It occurs when two metal surfaces under pressure slide against each other and microscopic bonds form between the surfaces. As the movement continues, these bonds break, causing metal to be transferred from one surface to the other. The result is the formation of irregularities in the thread and, at an advanced stage, seizure of the case-back.

How does it occur in a watch?

In watches, the phenomenon mainly concerns screw-down case-backs. During rotation of the case-back, the surfaces of the two threads are continuously sliding against each other while being subjected to significant local pressure.

If lubrication is inadequate, if the surface condition is poor, or if excessive force is applied, the metal surfaces may come into significant direct contact. Friction increases, heat is generated, and material transfer may begin.

Initially, the problem may be almost imperceptible. However, the case-back gradually becomes more difficult to turn and the movement becomes rough. If the watchmaker continues to apply force, Galling can progress rapidly and eventually lead to complete thread seizure.

What causes it?

Galling is not caused by a single factor. The most important contributing factors are:

Lack of or inadequate lubrication

When the thread is assembled dry, direct contact between the metal surfaces increases and, consequently, so does the possibility of adhesion.

Excessive pressure and torque

Over-tightening increases the loads acting on the surfaces of the threads.

High rotational speed

Rapid tightening increases the heat generated by friction and can accelerate the phenomenon. For this reason, controlled and smooth rotation is recommended.

Poor thread condition

Burrs, deformation, scratches, or remnants of previous wear create areas of increased local pressure.

Dirt and metal debris

A thread that has not been properly cleaned before assembly may experience increased friction and wear.

Incorrect engagement of the case-back

If the case-back is not positioned correctly and the threads are not properly aligned, cross-threading may occur. This is not Galling, but it can create significant local stress and damage the thread.

Cases made of white gold and platinum

Particular attention is required when working with cases made of white gold and platinum, as these are precious metals and repairing a severely damaged thread can be difficult.

However, Galling should not simply be attributed to the fact that a metal is “soft.” Its behavior depends on the combination of materials, surface finish, contact pressure, sliding speed, and lubrication.

In practice, this means that the thread of a case made from a precious metal must be handled with particular care, regardless of whether it is made of gold, white gold, or platinum.

Prevention is the best approach

Preventing Galling is relatively straightforward and should be an integral part of the correct watch servicing procedure.

Before fitting the case-back

1. Thoroughly clean the thread.
2. Inspect its condition for burrs, scratches, or signs of metal transfer.
3. Use a suitable lubricant for the particular thread.
4. Apply the lubricant in a small and controlled quantity.
5. Position the case-back correctly, without applying pressure.
6. Rotate it slowly and smoothly.
7. Do not increase the applied force if unusual resistance is encountered.

Thread lubrication is one of the most important methods of preventing Galling, while reducing the speed of assembly is also an effective preventive measure.

Fomblin

In watchmaking, Fomblin, a lubricant belonging to the PFPE family, is also used for this purpose. Its use on case threads is an established practice in watchmaking for preventing seizure during the closing and subsequent opening of the case-back.

The important point is to apply a very small amount and only to a clean thread. Excessive lubricant does not provide better protection and may attract or retain contaminants.

Fomblin, like any other suitable lubricant, does not repair an already damaged thread. Its primary purpose is prevention. In the case of a severely worn or damaged thread, a technical inspection is required first and, if necessary, the thread must be properly restored.

What should a watch owner be aware of?

Galling is not a problem that a watch owner can easily identify before it has progressed. However, an important warning sign is unusual difficulty when opening or closing a screw-down case-back.

If a case-back that normally turns smoothly suddenly develops significant resistance, it should not be forced open.

Applying additional force may worsen the wear and turn a minor problem into serious thread damage.

For this reason, the work should be carried out by a qualified watchmaker using the appropriate tools and procedures.

Conclusion

Galling is a phenomenon that can cause significant damage to the threads of watch cases, particularly those of screw-down case-backs.

Cleanliness, thread inspection, proper lubrication, correct positioning, and controlled rotation are the key measures for preventing it.

Prevention is especially important in watches made of white gold and platinum, where the value of the case is high.

For the watchmaker, the basic principle is simple:

If a case-back does not rotate smoothly, do not apply more force. Stop, inspect, and identify the cause.

By following this principle, it is possible to prevent not only Galling, but also one of the most unpleasant and costly forms of damage that can occur during the servicing of a watch.