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COMPANY PROFILE
essential to identify many small problems with the tyre. The tyre inspection staff have up to a year of special training and can identify internal damage by feel, they can tell whether a puncture has resulted in corrosion in the wires, or if it is a clean hole, just by feeling and listening.
The role, at every stage in the process is to maximise the efficiency of casing recovery. If a casing can be saved then it will be saved.
After visual inspection and marking up, and being given a bar code the tyre will go through shearography, three machines operating in parallel ensure that the flow is maintained. If the tyres are deemed to be dirty they are cleaned before being placed into storage.
At this stage Michelin uses its advantage as a tyre manufacturer to optimise retread performance.
Michelin has access to
the production data for
millions of tyres, each
one having its own
matriculation number.
When those tyres come
back to Michelin, the
company can dial in the
matriculation number
and it already knows
certain information
about that casing. It
knows when and where
it was built, on what
machines, using which
compounds. It may
know what its use has
been. However, the real
trick is that in testing
tyres over the years,
Michelin has built up a
huge database of
information on the
condition and
deformations of any
particular tyre. It can
judge from its
matriculation number,
how that tyre will have deformed in use. So, tyres are stored in stillages of like deformation, as well as similar sizes. So for any given size, there may be three or four sub divisions of casing deformation.
This is critical when it comes to the stripping and buffing process, as rather than buffing a casing to match a set profile, Michelin buff a casing taking into account its deformation. This, according to Jérémie, ensures the optimum retread for any given casing. Buffed casings are given an RFID tag for the rest of the retread process. This ensures that the manufacturing data is allocated to the right tyre and that the right tyre is retreaded as it should be. All repairs and skiving are recorded
against the individual tyre.
From this point on, no casing is supposed to touch the ground.
The casing receives a coating of bonding rubber before the tread rubber is applied by automatic extruders, using the RFID tag to ensure that the rubber is applied to comply with the casing deformation, so that there is sufficient rubber to mould the tyre properly. Then the sidewall rubber is applied and the casings are fed to the moulds. There are 100 mould presses at the Combaude plant.
After, the tyres come out of the moulds, they continue to cure as they cool as they proceed to the final trimming and pressure testing before being sorted and sent to the dispatch warehouse. Even the team doing the trimming and final inspection have six months individual
training, and there is as much physical contact with the tyre at this stage as there was at the outset. The skilled operator can still feel more than the machine can see at this stage. A final check is to use the nail hole detector to identify any porosity in the finished tyre. All this is a finely honed process and it was noticeable throughout the plant that housekeeping was a priority. The plant was clean, the floors polished, the equipment as clean as possible: The whole process cleaner than some catering establishments can be. The attention to the process was exacting in every detail. Any tyre falling short at any point is sent back to go through the whole process a second time.
This single plant in Clermont Ferrand
Everybody in the retread business knows that a retread can vary in quality. That the quality depends upon the condition of the casing, the skills of the workforce, the standard of the factory, the level of retreading technology utilised, the compounds used, the raw materials, the additives and the working conditions. This is true from the back street retreader operating in arduous conditions in Nepal or Nigeria, to the most modern facilities in Europe or the USA. However, when one of the world’s leading tyre manufacturers produces retreads, one can expect something ahead of the game.
Retreading Business was invited to visit Michelin’s truck tyre retread plant at Clermont Ferrand, France. On arrival in Clermont, one gets the impression that without Michelin, this would still be a sleepy Auvergne town struggling to find a reason for existing. The importance of Michelin to the town cannot be over stressed. The company built much of the town and was advanced in its social care for its employees, building housing between the wars that was more advanced than the social housing built at that time across the UK. That history
of being at the forefront, highlighted by a visit to the Michelin Adventure, guided by Gonzague de Narp a curator at the centre, where a display of the progress of Michelin over the past 100 years or so underlines the key to how Michelin produce hot cure retreads just that step above its competitors.
Readers are familiar with the general process, tyres are collected, sorted, good casings delivered to the retreader, who sorts, rejects or selects, tests, buffs, rebuilds, moulds and tests and a retread rolls off the production line.
According to Planning Manager at the Combaude retread plant, Jérémie Wojcik, Michelin’s process varies from the outset. At the Clermont Ferrand plant all Michelin casings collected are brought to the plant. Collection is by the same trucks making the delivery, and Jérémie reports that the return load of casings is always greater than the outgoing delivery. All casings collected, regardless of condition are brought to the factory, where skilled tyre inspectors examine, prod, probe, stretch, and feel the casing for flaws. The personal contact, the hands on approach is very important and according to Jérémie is
Michelin – Setting the Standard for Retreading
44 Retreading Business