What is gear pitting?

Gear pitting, also known as contact fatigue, is one of the most common failure modes affecting gear teeth.

It appears as small cavities or “pits” that progressively develop on the tooth surface. These defects are caused by repeated contact stresses acting on the gear surfaces during operation.

Over time, microcracks can develop within the material. As these cracks propagate, small particles of metal become detached from the tooth surface, creating cavities.

As the phenomenon progresses, pitting can alter the tooth geometry, increase vibration and noise, and significantly reduce the service life of the gear.

How does gear pitting develop?

During operation, gear teeth are subjected to high and repeated contact stresses.

Each time a tooth passes through the contact zone, the surface undergoes a loading cycle. After a large number of cycles, these repeated stresses can cause material fatigue.

The process can be summarized as follows:

Repeated loading → crack initiation → crack propagation → material removal → pit formation.

Initially, the damage may be localized and difficult to detect. However, if unfavorable operating conditions persist, the pits can multiply, become deeper and eventually merge.

The tooth surface then becomes increasingly irregular and the contact between the gears is affected.

What causes gear pitting?

Several factors can contribute to the development of pitting on gear teeth.

Gear overload

Loads exceeding the design conditions increase the contact stresses between the teeth and accelerate material fatigue.

Insufficient lubrication

Lubrication plays an essential role in protecting gear surfaces and reducing friction.

Incorrect oil viscosity, insufficient lubricant supply or excessively severe operating conditions can promote surface degradation.

Lubricant contamination

The presence of metal particles, dust or other contaminants in the lubricant can accelerate damage to the tooth surfaces.

Misalignment

Misalignment of the shafts or gear system can result in an uneven load distribution across the tooth width. Certain areas are then subjected to higher stresses, increasing the risk of pitting.

Material and heat treatment

Resistance to contact fatigue also depends on the material properties, hardness and heat treatment of the gear.

Manufacturing defects

Tooth geometry, surface roughness and manufacturing accuracy directly influence the quality of contact between the gear teeth.

What are the different types of pitting?

Initial or mild pitting

Initial pitting, sometimes referred to as mild or corrective pitting, consists of small, localized pits appearing in the most heavily loaded areas of the tooth.

Under certain conditions, the phenomenon may stabilize and have a limited impact on the service life of the gear.

Destructive pitting

Destructive pitting represents a more advanced stage of the phenomenon.

The pits progressively increase in number and depth. They can merge together and cause significant surface spalling.

At this stage, the tooth geometry may be significantly altered and the operating condition of the gear can progressively deteriorate.

What are the consequences of gear pitting?

Pitting can have a significant impact on the reliability of a mechanical transmission.

The main consequences include:

• increased operating noise;
• increased vibration;
• deterioration of the tooth surface;
• changes in the contact pattern;
• increased local stresses;
• accelerated wear;
• reduced gear service life;
• risk of failure when the damage becomes severe.

The phenomenon can also become self-accelerating. Initial pits alter the contact surface, which can lead to uneven load distribution and increased stresses in certain areas.

How can a gear affected by pitting be repaired?

When pitting becomes sufficiently advanced, simply monitoring the gear may no longer be enough.

In some cases, complete gear replacement may be considered. However, this solution can be particularly demanding when the gear is very large, difficult to access or integrated into a major industrial installation.

An alternative is to repair the gear teeth directly on site by machining.

On-site gear tooth re-machining

Our on-site gear tooth re-machining solution makes it possible to work directly on the installed gear, without necessarily removing and transporting it to a workshop, provided that site conditions allow the operation.

The process consists of machining away the damaged surface in order to remove the material affected by pitting, and then recreating the tooth geometry.

The objective is to restore a tooth profile consistent with the original gear geometry, providing a sound surface and suitable contact conditions between the teeth.

Repair directly on the installation

One of the main advantages of this technique is the ability to carry out the operation directly on site.

This can significantly reduce:

• equipment dismantling;
• handling operations;
• transportation of heavy or oversized components;
• plant downtime;
• costs associated with complete gear replacement.

This approach is particularly attractive for large industrial gears or equipment where dismantling would be complex and time-consuming.

Removing pitting and recreating the original tooth profile

Re-machining does not simply consist of removing visible defects from the tooth surface.

The machining process is designed to remove the damaged material and restore the functional geometry of the tooth.

After machining, the resulting profile is designed to provide a regular surface and the appropriate tooth geometry for gear operation.

The objective is therefore to remove the pitting-affected material and recreate the original tooth profile, within the limits imposed by the condition and geometry of the existing gear.

This operation must be preceded by an assessment to determine the depth of the damage and the amount of material that can safely be removed.

Why choose on-site gear re-machining?

On-site gear re-machining offers several advantages compared with complete gear replacement.

Reduced downtime

Performing the repair directly on the installation can reduce dismantling and handling operations and significantly shorten equipment downtime.

No transportation of oversized components

For large industrial gears, transportation to a specialized workshop can be complex and costly.

On-site machining allows the repair to be performed directly on the equipment.

Retaining the existing gear

When the condition of the gear allows it, re-machining avoids complete replacement of the component.

The existing gear can therefore be restored while retaining its original mechanical environment.

Removal of damaged material

The purpose of the machining operation is to remove the material affected by pitting and restore a sound, functional tooth surface.

When should gear re-machining be considered?

The feasibility of re-machining depends on several factors, including:

• pitting depth;
• overall condition of the gear teeth;
• gear dimensions;
• tooth geometry;
• amount of material available for machining;
• mechanical operating requirements;
• accessibility of the equipment on site.

A preliminary assessment is therefore essential to determine whether the operation is technically feasible and to establish the amount of material that can be removed.

Our intervention can begin with an assessment of the tooth condition to identify damaged areas and determine the most appropriate machining strategy.

From inspection to recommissioning

A gear repair operation based on on-site re-machining can be carried out through several stages:

Gear tooth inspection
↓
Pitting assessment and damage measurement
↓
Determination of the material to be removed
↓
On-site gear tooth machining
↓
Tooth profile restoration
↓
Geometrical inspection
↓
Recommissioning

This approach makes it possible to address the immediate cause of the defect by removing the damaged material and restoring the functional geometry of the gear teeth.

How can pitting recurrence be prevented?

Gear tooth repair should ideally be combined with an analysis of the operating conditions that contributed to the initial pitting.

Particular attention should be paid to:

• the load applied to the gear;
• lubrication conditions;
• lubricant cleanliness;
• shaft alignment;
• tooth contact conditions;
• operating conditions;
• vibration and noise monitoring.

Identifying the root causes of the initial degradation helps reduce the risk of pitting recurring after the repair.

Gear pitting: repair or replacement?

When a gear presents significant pitting, complete replacement is not necessarily the only solution.

Depending on the condition of the teeth and the depth of the damage, on-site gear tooth re-machining can provide an alternative to complete replacement.

This solution makes it possible to restore the gear teeth by removing the damaged material and recreating the functional tooth profile, while avoiding, where possible, the challenges associated with dismantling and transporting large industrial gears.

A preliminary assessment is required to determine the feasibility of the operation and the amount of material that can be removed without compromising the mechanical characteristics of the gear teeth.

FAQ: Gear Pitting and On-Site Gear Re-Machining

Can gear pitting be permanently removed?

When the depth of the damage and the condition of the gear allow it, gear tooth re-machining can remove the material affected by pitting and restore the tooth profile. Feasibility must be assessed on a case-by-case basis.

Can a gear be repaired directly on site?

Yes. When site access and equipment characteristics allow it, on-site gear tooth machining can be carried out directly on the installation, avoiding the need to remove and transport the gear to a workshop.

Can re-machining restore the original tooth profile?

The objective of re-machining is to recreate the functional tooth geometry based on the reference profile after removing the damaged material. The achievable result depends in particular on the depth of the pitting and the amount of available material.

Does a gear with pitting always need to be replaced?

Not necessarily. Before considering replacement, it is advisable to carry out a gear tooth assessment to determine the depth of the damage and whether on-site machining is technically feasible.

What is the main advantage of on-site machining?

On-site machining allows the gear teeth to be repaired directly on the installation, potentially reducing dismantling, handling and transportation operations, as well as equipment downtime.

An alternative to complete gear replacement

Gear pitting does not necessarily mean that the entire gear must be replaced.

When the condition of the gear allows it, our on-site gear tooth re-machining solution enables us to work directly on the equipment to remove the damaged material, restore the tooth geometry and recreate the functional tooth profile.

This approach is particularly valuable for large industrial gears, where dismantling and replacement can be time-consuming, complex and costly.

Does your gear show signs of pitting? Contact us to assess the feasibility of on-site gear tooth re-machining.