Insulated roller assembly for a roller furnace

A roller assembly for a roller furnace for heat treating slabs is provided with thermal insulation. A metal roller has carrier rings spaced at intervals thereon for carrying a slab to be treated. A needled first fiber mat surrounds the metal roller between the carrier rings and has a fibrous spraying compound sprayed thereon. A binder in the fibrous spraying compound joins the fiber spraying compound with the first fiber mat. A precompressed second fiber mat is laterally disposed between the carrier rings and the fibrous spraying compound. The result is a thermal insulation arrangement which withstands the dynamic stresses of the roller assembly as well as the chemical stresses due to the presence of a hot slab.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a roller assembly for a roller furnace for 
heat treating slabs of steel, etc. The roller assembly has a number of 
spaced carrier rings for carrying the slabs and thermal insulation between 
the carrier rings. The slabs are transported through the roller furnace by 
the roller assemblies on the carrier rings for heat treatment thereof. The 
hollow cavity of the roller assembly is usually water cooled. The thermal 
insulation is for protecting the roller assembly from the hot slab, as 
well as preventing the hot slab from cooling due to the presence of the 
roller assembly. 
(2) State of the Prior Art 
DE 32 31 736 C2 discloses a sheathing for insulating a cooled slide, skid 
or transverse pipe in a furnace. Moldings for the bottom side of the pipe 
made of a ceramic fiber material and moldings for the upper side of the 
pipe made of a refractory ceramic are provided for adapting the bottom and 
upper sides for the different stresses the sides will undergo. This type 
of an arrangement is unsuitable for a rotating roller assembly. Preformed 
insulating moldings result in joints in the thermal insulation of the 
roller assembly. Such joints have a negative impact on the insulating 
effect of the thermal insulation. 
Moldings for insulating pipes are also described in DE 31 25 440 A1 and in 
DE 36 09 047 A1. The types of moldings described in these disclosures are 
unsuitable for roller assemblies, since the moldings have very little 
ability to withstand the dynamic stresses of a rotating roller assembly, 
and since the joints in the moldings negatively impact on the effect of 
the thermal insulation. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the present invention is to provide a roller 
assembly of the type discussed above having thermal insulation with the 
ability to withstand the dynamic stresses of the roller assembly in use in 
a roller furnace, as well as chemical stresses generated by the material 
being transported by the roller assembly. 
According to the present invention, the above object is achieved by the 
provision of a roller assembly for carrying slabs for heat treatment in a 
roller furnace, having an elongated roller, a plurality of carrier rings 
on the elongated roller at spaced intervals for carrying the slabs, and an 
insulating arrangement on the elongated roller for thermally insulating 
the elongated roller from the slabs. The insulating arrangement comprises 
a fiber mat disposed on the periphery of the elongated roller between the 
carrier rings and a fibrous spraying compound sprayed on the fiber mat, 
the fibrous spraying compound having a binder therein binding the fibrous 
spraying compound to the fiber mat. 
Preferably, the insulating arrangement further has an expansion joint 
disposed between the fibrous spraying compound and the carrier rings for 
expanding in response to shrinkage of the fibrous spraying compound in 
order to maintain thermal insulation of the elongated roller. This 
expansion joint comprises a precompressed second fiber mat disposed 
laterally between the carrier rings and the fibrous spraying compound. 
The fibrous spraying compound has good heat insulating properties. Thus a 
slab transported on the carrier rings of the roller assembly and the 
roller assembly itself are largely thermally unaffected by each other so 
that the slab is not cooled by the roller assembly, nor is the roller 
assembly heated by the slab. 
The fibrous spraying compound extends over the entire circumference of the 
roller assembly, and is in itself jointless. This prevents the scales of 
the slab or alkali residues of continuous casting powders from being able 
to damage the roller assembly. 
The fibrous spraying compound is securely held on the roller assembly, 
because the first fiber mat stabilizes the fiber spraying compound, with 
the binder of the fibrous spraying compound diffusing into the fiber mat. 
The fibrous spraying compound can then withstand the centrifugal forces 
generated by rotation of the roller assembly and forces resulting from the 
acceleration of the roller assembly without breaking or falling off. 
The precompressed second fiber mat serves to permanently close the joints 
resulting between the fibrous spraying compound and the carrier rings. 
Shrinkage of the fibrous spraying compound will not lead to an open joint 
between the fibrous spraying compound and the carrier rings, because the 
second fiber mat is precompressed, and will thus expand to fill the gap 
with the shrinkage of the fibrous spraying compound. 
Preferably, the second fiber mat is precompressed in the direction of 
elongation of the elongated roller by a factor of 5 with respect to its 
uncompressed state. 
Another preferred feature of the present invention is an arrangement for 
stabilizing the fibrous spraying compound disposed on the elongated 
roller. This arrangement includes at least one metal strap disposed about 
the elongated roller, having brackets extending into the fibrous spraying 
compound. Each bracket comprises a locking pin attached to the metal strap 
and a flat shim for attachment to the locking pin. The locking pins extend 
through the first fiber mat from the metal straps into the fibrous 
spraying compound. This helps to further stabilize the fibrous spraying 
compound on the roller assembly. 
Preferably, the metal strap is fastened to the elongated roller by a bolt 
and nut assembly. This is preferred so that welded joints between the 
elongated roller and the brackets are unnecessary. 
The fibrous spraying compound should preferably be made of ceramic fibers. 
The binder can be a colloidal SiO.sub.2 or a hydraulic binder. 
The carrier rings can be composed of two spaced ring segments, the spaced 
ring segments having a non-woven ceramic fabric therebetween, the 
non-woven ceramic fabric having a latex bond. This further helps to 
insulate the elongated roller from the hot slabs. 
If deemed necessary, a ceramic coating can also be provided on the 
peripheral surface of the fibrous spraying compound. Also note that the 
first fiber mat should be a needled fiber mat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A roller assembly for carrying hot slabs for heat treatment in a roller 
furnace has a cylindrical metal roller 1. Distributed over the length of 
the cylindrical metal roller 1 are several metallic carrier rings 2, as 
best seen in FIG. 2. Each carrier ring 2 comprises two spaced flange ring 
segments 3. Between, and on the outer periphery of, the flange ring 
segments 3 are disposed a supporting ring element 4 and a rolling surface 
portion 5 attached to the ring element 4. A plurality of metal straps 6 
are disposed about the metal roller 1 between the carrier rings 2. Each 
metal strap 6 has two bent ends 7, as best seen in FIG. 1. The bent ends 7 
are connected to each other by a bolt and nut connection 8 so that the 
metal straps 6 fit snugly on the metal roller 1. 
A plurality of brackets 9, for example eight brackets, only two of which 
are shown in FIG. 1, are welded on the outer peripheral surface of each 
metal strap 6. Each bracket 9 comprises a locking pin 10 welded to the 
metal strap 6 and a flat shim 11 locked on the locking pin 10. 
After the metal straps 6 have been attached to the metal roller 1, but 
before the shims 11 have been mounted onto the locking pins 10, a first 
needled, binder-free fiber mat 12, made of ceramic fibers in blanket form, 
is disposed about the metal roller 1 between the carrier rings 2. By so 
placing the first fiber mat 12, the locking pins 10 pierce through the 
first fiber mat 12. 
Noting FIG. 2, precompressed second fiber mats 13 made of ceramic fibers 
are placed on the sides of the carrier rings 2. The fiber mats 13 are 
fiber mats which have a low initial density, having a thickness of about 
50 mm, but which are compressed from this low initial density by wetting 
the fiber mat to compress the fiber mat to a thickness of 10 mm. The fiber 
mats 13 are thus put in place about the carrier rings 2 in their 
compressed state. 
The flat shims 11 are then mounted on the locking pins 10, and a fibrous 
spraying compound 14 made of ceramic fibers is sprayed between the second 
fiber mats 13 on the first fiber mat 12 as illustrated in the figures. The 
fibrous spraying compound has a binder therein. This binder can be a 
colloidal SiO.sub.2 binder, which results in a fibrous compound which has 
to be dried in order to attain its final strength. The fibrous spraying 
compound can also be a fiber cement made of ceramic fibers having a 
hydraulically binding binder. The fiber cement can reach its final 
strength even at room temperature. 
The binder of the sprayed-on fibrous spraying compound 14 partially 
penetrates the first fiber mat 12 so that the first fiber mat 12 is 
increased in strength and so that the first fiber mat 12 and the fiber 
spraying compound are bonded to each other, with the result that the 
fibrous spraying compound is securely held about the circumference of the 
metal roller 1. The fibrous spraying compound will thus withstand 
centrifugal forces generated by rotation of the roller assembly as well as 
forces resulting from acceleration of the roller assembly. And since the 
fibrous spraying compound 14 extends over the entire circumference of the 
metal roller 1, and is in itself jointless, scales from the heat slab 
carried on the roller assembly, or alkali residue from continuous casting 
powders, can be prevented from damaging the metal roller 1. The fibrous 
spraying compound also exhibits good heat insulating properties. Note that 
the shims 11 serve to further stabilize the fibrous spraying compound 14 
about the metal roller 1. 
The fibrous spraying compound 14 is sprayed onto the fiber 12 so that the 
fibrous spraying compound 14 will have a significantly larger thickness 
than the thickness of the first fiber mat 12, for example by a factor of 7 
to 10 times as thick. 
After the fibrous spraying compound 14 has been disposed about the first 
fiber mat 12, the earlier provision of the second fiber mat 13 results in 
an effective expansion joint being provided at the carrier rings 2 for the 
protection of the metal roller 1 and the improvement of the overall 
thermal insulation of the roller assembly. Shrinkage of the fibrous 
spraying compound 14 in the longitudinal direction of the metal roller 1 
will be compensated by the expansion of the precompressed second fiber 
mats 13. Thus the second fiber mats 13 permanently close the joints 
between the fibrous spraying compound 14 and the carrier rings 2. The 
total result is crack and joint free thermal insulation of the metal 
roller 1. The fibrous spraying compound 14 withstands jolts and vibrations 
due to the slabs being transported on the carrier rings 2, as well as the 
centrifugal forces generated thereby. 
If necessary, or in an emergency situation, the fibrous spraying compound 
14 can have a further ceramic coating provided on its peripheral surface. 
A cylindrical space is defined between the flange rings 3 of each carrier 
ring 2. A plurality of layers of a non-woven ceramic fabric 15 having a 
latex bond are inserted into the space before assembling the flange ring 
parts 3 on the metal roller 1. As a result, there is provided additional 
thermal insulation between the ring element 4 or rolling surface portion 5 
and the metal roller 1. 
Although the present invention has been described and illustrated with 
respect to preferred features thereof, it is to be understood that various 
modifications and changes may be made to the specifically described and 
illustrated features without departing from the scope of the present 
invention.