The invention concerns a roller designated for the transfer of a metal strip in a continuous annealing furnace, consisting of a driving shaft encased in a collar that bears the strip.
In general, transfer rollers used in continuous annealing of metal strips made of ferrous and non-ferrous materials are made of alloy steel.
In terms of thermomechanical characteristics, these rollers have a coefficient of thermal expansion of 17.10xe2x88x926/xc2x0 C. and a coefficient of thermal conductivity of around 20 W/m.xc2x0 C.
To compensate for the thermomechanical deformations in rollers, a compromise is sought in the mechanical profile of the generatrix of collars on rollers obtained by machining, such as to avoid the development of folds in wide and narrow format strips, as well as strip offsets when processing narrow-format strips. Rollers are generally cylindrical or manufactured with a slightly curved generatrix, however they become deformed in the annealing furnace due to heat intake from the strip being annealed.
Numerous patents propose rollers featuring a shrink ring, e.g. copper-based. The deformation of the generatrix of this-type of roller, in an annealing furnace, is improved by a factor of around 2 due to the high thermal conductivity of copper. However, these rollers are heavy and exhibit high thermal inertia.
GB patent 945,244 also proposes a roller for a continuous metal strip annealing furnace comprising an envelope consisting of either graphite or a mixture of carbon and metal powder sintered with e.g. a bitumen binder. This type of sintered material does not seem to have been developed for industrial purposes.
The goal of the invention is to minimize deformations of the roller profile with changes in temperature and strip format, in order to broaden the application range and allow both wide and narrow strips to pass without developing folds or offsets and without the need for strip guides, due to the presence of a shape-retaining roller exhibiting low weight and inertia and manufactured at a low cost, as compared to rollers made of e.g. refractory steel with a copper shrink ring.
The object of the invention is to propose a roller designated for the transfer of a metal strip in a continuous annealing furnace, consisting of a driving shaft encased in a collar that bears the strip, characterized in that at least the collar is manufactured of a composite material.
The other characteristics of the invention are:
the shaft is manufactured of a composite material or metal.
the composite material is chosen between a carbon-carbon fiber (CCF) or a silicon carbide-silicon carbide (SiCxe2x80x94SiC) composite.
the composite material comprises fibers woven along at least two dimensions.
the collar comprises a metal or ceramic hard coating.
the coating is chosen between chromium carbide or zirconia.
the coating may comprise an underlayer.
the underlayer material is chosen between IC type carbon or silicon carbide.