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Defects treated

Novexa intervenes up-stream and down-stream in order to treat different types of defects.

Excessive wear speed

This type of damage is often connected to :

Insufficient hardness

Pollution of the lubricant (carter or poorly adapted joints)

A bad choice of lubricant or flow

Novexa can help you to reduce this wear speed, which conditions shelf life of the harness

pinion/crown while at the same time reducing maintenance problems.

Novexa is able to quantify wear speed to 0.05 mm.

The control template can be provided to you in order to carry out the follow up process yourself.

Profile deformation

Our training program gives details about the origin of vibrations, which are linked to profile

deformation. We have found out that on average 80% of generated vibrations are linked to the

meshing frequency of pinion/crown.

While deforming a profile (at a constant angular speed of the pinion), a minor angular delay can be

observed in the dale areas of the crown as well as an adjustment in the hill areas.

This movement generates an irregular dislocation between pinion and crown and creates thus

vibrations and acceleration. Measured vibrations can be horizontal, vertical or axial.

Reasons for these vibrations could be :

Meshing interferences on gear and/or profile deformation

Poor distribution of loads

Bad contact ratio linked to pitch gaps (wrong transfer of loads)

Lateral step on pinion / crown, 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 (meshing on the step)

Alignment error on pinion axe / gearbox axe

Problem of balance on the reach

Shocks on meshing gear already observed on harnesses are very destructive for the whole kinematic

chain.

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Wrong temperature distribution

An alignment defect can be brought to light by an irregular temperature distribution on gear teeth

(excessively tightened joints during assembly can explain these gaps)

Up to 4C, the situation is normal (green code)

Beyond 4C, an adjustment is useful (yellow code)

Beyond 8C, an adjustment is necessary (red code)

Beyond 12C, an adjustment is vital (black code)

In the case of temperature gaps, it is necessary to address the question of wear of pinion bearings or

trunnion bearings.

Short and medium term effects of this kind of defect left untreated include always cracking which

entails a later replacement of the harness.

Concerning regulated bearings, temperature controls with thermocouples of the type PT100 together

with relief measurement once a year are sufficient to anticipate breakages.

Pitting

Pitting is a destruction of the surface often caused by wear not exceeding 0,3 0,5 mm in depth.

Pitting is not dangerous for the gear. It does not justify any flipping or replacement.

However, it can be slowed by a most suitablelubricant choice.

On the contrary, pitting caused by creeping (which in turn is linked to slipping) will foster profile

deformation. It is thus essential to exactly quantify this profile deformation.

Chipping

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Chipping is a dangerous kind of damage where metal comes off in plates. This damage is linked to an

excessive Hertz pressure. This elevated pressure can be explained by a poor distribution of loads.

Concerning this type of damage, detaining an intervention is detrimental because the extension is

carried out in the underlying layer. An in-depth analysis of the problems' cause is vital, followed by an

intervention through an appropriate routing.

If the chipping reaches 50% in width on straight gear teeth and 70% on inclined gear teeth (variable

depending on the helix angle), a flipping or a replacement should be scheduled.

Scuffing

Scuffing is a type of damage linked to contact of metal on metal caused by meshing of gear entailing

a wrenching of material.

We consider 2 types of scuffing :

1. Scuffings which have generated an increase in temperature

These ones cover the whole surface of the teeth.

Action : a halt of the equipment is necessary. The temperature needs to be reduced and the harness

must be cleaned. A restart of the equipment can be considered under the condition of a forced

lubrication.

However, it would be preferable to contact us. Novexa will assist you in order to identify your most

appropriate options.

2. Scuffings located in areas of slipping

These scuffings are less dangerous than the previous ones. They often contribute to an enlargement

of profile deformation. However, vibration risks are the same.

An extensive lubrication can slow down or even stop this type of damage.

Fissures or tooth breakages

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The treatment of a fissure is necessary in order to stop further spreading. Tooth breakages should be

considered case by case, however all cases can be repaired. The urgency of reparation intervention

depends on the total contact ratio, which only an expert can calculate.

The limits of fissures or breakages which should not be exceeded are :

50% for straight gear teeth

70% or inclined gear teeth (depending on the helix angle)

The absence of a contact pattern, which results in a tooth breakage, does not impede the functioning

of equipment in the medium term. However it is recommended to intervene through welding repair

and reprofiling of the teeth concerned.

This kind of reparation should be carried out with special attention to the pitches and the profiles. The

non-respect of this total contact ratio (transfer of loads) will lead to shocks and new breakages in the

short term.

Novexa has got the necessary experience required for this type of interventions. Our references are

numerous and our reparationsare durable.

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