michelin tyre inspection

Annex - Inspection / 26

Types of Plies

Ply categories The main types of ply are as follows:

Nappes Sommet de Protection (NSP) (breaker strip) = elastic cables.

Nappe Sommet de Travail (NST) (bracing plies) = fretted or unfretted

cables.

Nappe Carcasse (NC) (casing ply) = fretted, unfretted cables.

Cable Visual characteristics for each type of cable:

elastic

fretted

unfretted

Damaged cable A cable is damaged when it shows at least one of the following features:

Metallic cable Textile cable

Separated from the surrounding

rubber

Oxidized in depth

Unfretted

Worn

Broken

Separated from the surrounding

rubber

Frayed

Worn

Broken


Verification of casings

Crown The crown represents the external part between points (B): joint of the tread with

the sidewalls.

The crown includes the tread area and the shoulder area.

Sidewall The sidewall is the external part between the tread / sidewall joint (B) and the

guide rib (A).

Bead The bead is the part between the guide rib (A) and the bead point rubber (F).

FE zone

The FE zone is the part between the bead point rubber (F) and a point (E)

inside.

This FE distance is 75 mm for 10.00R20 and 295/80R22.5.

Interior The interior is the internal part between points (E).

Cables injuries can NOT be repaired

in FE area


Verification of casings (continued)

Remarks on inspection

Inspection is both visual and with hands / fingers.

Inspection of each zone entails a complete rotation of the casing.

Correct examination of the interior requires spreading the beads and adequate

lighting of the zone to be verified.

All damage must be carefully identified.

Take care against projected shadows (work at a station with good lighting).

It is important to draw up a "monitoring" document for the casings shown.


Cleanliness of "interior / exterior" casings

Obstacles to optimum inspection

Any casing coming in for retreading may show a level of dirt incompatible with

the acceptable limit for verification.

If the amount of dirt is excessive, faults in detection may occur.

The innerliner may show locally adhesive materials or not, which might prevent

the detection of a crown perforation or GI damage.

Beads covered with assembly grease or rim calamine and sidewalls full of dirt

do not ensure conditions for an optimum inspection.

Any detection is made impossible.

The pollution is too concentrated to enable quality verification.

Obligation

The casings must be dry before inspection.


Cleanliness of "interior / exterior" casings (continued)

Examples of dirt Examples of dirt not acceptable without washing:

Dry crust Dust layer

Assembly lubricant Grease runs


Inspection of sidewall and shoulder

Examination of shoulder

Verify if there are deep cuts or cracks.

Search for signs of previous retreading(s)

Examination of

sidewall area Reading the markings (engravings) enables identification of the casing.

Decoding of the DOT code indicates the place and date of manufacture

of the tyre.

Verify the condition of the rubber (cuts, scratches, cracking, alteration by

hydrocarbons).

Verify the condition of visible cable.

Search for indications of previous retreading(s)

Technical specifications:

The casings are rejected in the following cases:

DOT older than 8 years.

Markings of size, load and/or speed index illegible.

Heavy buffing on the sidewall.

Rubber cracks with a depth greater than 1 mm.

Rubber damaged by hydrocarbons

Cracked rubber.

Surface irregularities detected by touch or using incident light (deformations

unrelated to presence of a patch).

Rubber / cable separation following damage causing infiltration of inflation

air.

Break in the casing ply in sidewall: LxW = 90 x 20 mm or 120x10 mm (L

taken in the cable direction).

Maximum 5 patches (total of 2 existing and 3 to be done) AND Maximum 2

patches per sidewall.

Examples of defectiveness

The photos below illustrate the cases of defectiveness identified above.


Inspection of sidewall and shoulder (continued)

Buffing Examples of buffing:

pronounced sidewalls

sidewalls with cables visible



Rubber Examples of rubber:

Damaged (hydrocarbons)

Cracked (ageing)



Sidewall damage

Size measurement

Out-of- tolerance damage

L

L*l=90*20

L*l=120*10



Wear well Example of wear well (cracked at bottom or peripheral):

Perform a skiving operation to check the condition of the NC.

In presence of "oxydation DECHET", there is a risk of "Rupture NC circulair"

(CASING PLY circular rupture).


Inspection of a bead

Examination to be carried out

Guide rib area Detect deformations by touch or using incident light (bumps and dents).

Verify if there are deep circular cracks.

Bead area Search for deformations (surface, profile).

Verify the condition of the rubber (separation, bakelization) and the presence of

visible cable.



Deformations (by touch or using incident light).

Circular cracks with a depth greater than 2 mm.

Visible cable.

Deterioration caused by a wheel in poor condition.

Rubber tearing or cracking reaching the cables.

Deformation of the bead point rubber greater then the limits specified (case

of flat seat and drop centre).

Twisted bead.

Tearing of bead point rubber greater than 80 mm, or more than 3 tears per

side, or two tears distant by less than 75 mm.


The photos below illustrate the cases of defectiveness identified above.


Inspection of a bead (continued)

Examples of defectiveness (contd)

Irregularities (bumps)

Irregularities (dents)




Deep circular cracks

Visible cable




Deterioration (wheel in poor

condition)

Cracks reaching

cables




Flat seat deformations

Good Deformed Overturned

Excessively deformed or overturned beads (B>5mm) must be refused.

Drop centre deformations

The diagram below shows the limits beyond which the casing is rejected for

retreading

Beads not overturned

Beads overturned max. acceptable




Twisted bead

Tubeless bead point rubber tearing


Inspection of internal area

Examination of internal area

Examination of internal area (sidewall and crown):

Check condition of innerliner (perforations, cracks, mottling).

Check condition of casing ply (folding, perforation).

Verify the condition of existing repairs.

Detection method Visual observation and direct lighting.

Tactile In the Crown / Shoulder joint using back and forth movements of the hand.

Search for deformations (separation between casing ply and crown), then validate

the separation using incident light.

Tuning fork method Is performed on a station free of disturbing noise.

Search area Crown / Shoulder joint (under end NST1).

Methods Using short and consecutive strikes, with a pick hammer, hit the interior of the

casing in the search area, every 3 to 5 cm approximately and on the whole of the

circumference of the casing.

If areas of separation are present, a change in tone will be heard when passing

through the area.



The innerliner is coated with an anti-puncture product or a balancing product

(excluding balance patch).

Maximum 5 patches (total of 2 existing and 3 to be done) AND Maximum 2

patches per sidewall.

A repair using patch in poor condition.

Deterioration of the innerliner: mottling, "plucking", cracks.

Deformation, folds, cable deviations.

Separation between casing ply and crown.

Calendering of oblique or radial cracking or small cracks.

Opening of the innerliner joint.


Inspection of internal area (continued)


The photos below illustrate cases of defectiveness identified above.

Anti-puncture product

Repair in poor condition




Mottling Wipe off systematically, using the following: bare or gloved hand,

cloth, paper.

Any other resource is PROHIBITED

Only the mottling still visible after wiping will be addressed.

"Mottling then plucking"




Cracks at base of membrane ribs

Cracks



(contd)

Radial cracks

Opening of the innerliner joint




Fold in the casing ply


Inspection of crown

Examination of

crown area Check the condition of the tread (abnormal wear, cuts, separations).

Check the condition of the crown (perforations, visible cable, oxidation).

Important: Remove any metallic or other visible object, foreign to the casing,

remaining in the damage to the crown (pin, screw, bolt…).



Deterioration of the crown with diameter greater than 25 mm (diameter

measured on the casing ply).

More than 1/3 of breaker strip visible or damaged, following excessive re-

grooving or excessive wear.

Crown scarred with many cuts.


The photos below illustrate cases of defectiveness identified above.


Inspection of crown (continued)


Deterioration of crown

(interior view)

Deterioration of crown greater than 30 mm (seen from interior)

Deterioration of crown

with oxidation




Excessive wear

Abnormal wear with deterioration

of ply




Scarred crown

Excessively deep re-grooving

michelin tyre inspection

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inspection of sidewall

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sidewallthe sidewall

rubber cable separation

rubber cracks