Novexa 55 rue Linné 26500 Bourg les VALENCE
Contact us+33 (0)4 75 25 14 18 France

Defects treated (gears)

Novexa intervenes either as prevention or follow up in order to treat different types of defects.

Excessive wear speed

This defect is often linked with:

  • Insufficient hardness
  • Lubricant pollution (improper casing or joints)
  • Wrong choice of lubricant or output

Novexa can help you reduce wear speed in cooperation with lubrication professionals. Lubrication is an essential factor in the pinion/crown harness durability and prevents maintenance problems as well.
The control template can be supplied to you in order for you to complete the controls yourself.

Profile deformation

Our training programme specifies the origin of vibrations which are linked to profil deformation. We have observed that on average 90% of the generated vibrations are linked to the pinion/girth gear meshing frequency.
By deforming a profile, at a constant angular speed of the pinion, a slight angular delay can be observed in the dale areas of the girth gear as well as an adjustment in the hill areas. Following this theory, irregular movements are generated between the pinion and the girth gear, and therefore also vibrations and accelerations.
Shocks during meshing that can be observed on many harness very harmful to the entire kinematic chain.
The measured vibrations can be expressed axially, horizontally or vertically.
The reasons can be:

  • Meshing interference and/or profil deformation
  • Surface bearing defect
  • Poor contact ratio linked to pitch gaps (wrong transfer of loads)
  • Lateral step on pinion / girth gear, gear teeth couplings
  • Lack of backlash on a free standing bearing or lack of steadiness on a fixed bearing
  • Poor adjustment of root clearance
  • Pinion tooth root step combined with an expansion or out-of- round (interference)
  • Poor alignment on pinion axe / gearbox axe
  • Balance problem of on the reach

Poor temperature repartition

An alignment defect can be brought to light by an irregular temperature repartition on gearings (joints too tightly set during assembling can be a reason for such differences)

  • Up to 4°C, the situation is normal: code green
  • Beyond 4°C, an adjustment is useful: code yellow
  • Above 8°C, an adjustment is required: code red
  • Beyond 12°C, an adjustment must be made: code black

Pitting

Pitting consists of the surface being damaged often by wear and it usually does not exceed 0.3 to 0.5 mm in depth. Pitting is not harmful to a gear. It does not constitute a reason to flap or replace the part.
However, it can be slowed down by choosing a more suited lubricant.
On the contrary, when pitting is caused by creeping, it enables profil deformation. It is therefore essential to exactly quantify profil deformation

Chipping

Chipping is a dangerous kind of defect which consists of metal coming off in plates. It is in direct relation with an excessive Hertz pressure, often linked with a poor load distribution.
Not acting right away on this kind of defect is detrimental as the extension is carried out in the underlying layer. An analysis of the problem's origin is necessary as well as an intervention using an appropriate routing.
If the chipping reaches 50% of the spur gearing and 70% of the inclined gear teeth (it varies following helix angle), then flapping or replacing the part is required.


Scuffing

Scuffing is a defect that is linked to metal to metal contact during meshing, which causes a wrenching of material.
We consider 2 types of scuffing:
1. Scuffing which caused a temperature elevation
This type of scuffing concerns the whole teeth surface.
Action: bringing the equipment to a halt. The temperature must be lowered and the harness must be cleaned. A restart can be considered under the condition of a forced lubrication.

1. Scuffing which caused a temperature elevation

This type of scuffing concerns the whole teeth surface.
Action: bringing the equipment to a halt. The temperature must be lowered and the harness must be cleaned. A restart can be considered under the condition of a forced lubrication.

2. Scuffing located in slipping areas

This type of scuffing is more dangerous than the previous one. They often contribute in amplifying the profil deformations and the risk of potential vibration is the same.
An extensive lubrication can slow down or even stop this type of damage.

Cracking of tooth breakages

Treating a crack is necessary in order to prevent it from spreading further. The urgency of a repair depends on the contact ratio which only an expert can calculate.
Limits to no exceed for cracks of breakages are:

  • 50% for spur gear
  • 70% for inclined teeth (depending on the helix angle)
The absence of a contact pattern which results in a partial tooth breakage does not prevent the machine from operating in the medium term.
It is however strongly advised to intervene using welding and reprofiling repairs on the concerned teeth
If the tooth is entirely broken, operating the machine is impossible and repairing it is required.
For such repairs, extra attention must be paid to pitches and profiles. Novexa has the experience required for such interventions.
We have many references and our repairs are always durable.