Method of and system for cleaning the surface of furnace rollers of a roller hearth furnace

A roller hearth furnace (1) is subdivided into detachably assembled sections (2). In order to clean the rollers, one of the sections (2) of the assembly is removed and replaced by a replacement section (7) previously heated to the furnace operating temperature. The section (2) removed can therefore cool before being cleaned. The sections (2, 7) are transported along a stretch of rails (3) parallel to the roller hearth furnace (1).

The invention relates to a method and a device for cleaning the surface of 
the furnace rollers of a roller hearth furnace. 
It was hitherto necessary to shut down the roller hearth furnace and to 
cool it down to ambient temperature when it became necessary to clean the 
surface of the furnace rollers. This practice caused especially in the 
case of long roller hearth furnaces which have a length of 100 m to 150 m, 
considerable shutdown times of an order of 8 to 10 days. The loss of 
production was correspondingly high. 
It is the object of the present invention to substantially shorten the 
shutdown times of the roller hearth furnace necessary for cleaning the 
furnace rollers. 
To achieve this objective, the method referred to hereinabove is 
characterized by the removal of at least one of a multiplicity of furnace 
sections detachably assembled to form the roller hearth furnace from the 
furnace assembly in a direction which is transverse to the direction of 
travel through the roller hearth furnace, the integration in the furnace 
assembly of a replacement furnace section preheated to operating 
temperature to replace the furnace section so removed and the cool-down of 
the furnace section so removed to a temperature allowing its furnace 
rollers to be cleaned and their cleaning being carried out. 
The roller hearth furnace must hence be shut down only until one of its 
furnace sections has been replaced by a preheated replacement furnace 
section. It is of essential importance that no cool-down or heating-up 
times are required. The time of such a shutdown may be reduced to 
approximately 20 to 30 minutes. 
The method proposed by the present invention is particularly important in 
the case of high-temperature methods in which the temperature is above 
approximately 700.degree. C. The forward or reverse travel of plates or 
slabs then causes, through scale carried into or formed inside such a 
furnace, the build-up of lamination-type deposits on the surface of the 
furnace rollers commonly referred to as pickups or scale pickups. They 
damage the charge to be processed and must hence be removed. The build-up 
of pickups is a function of time. A complete cleaning operation is 
normally required at intervals of one to two months. 
Using the method proposed by the present invention, such cleaning 
operations may be carried out in cycles. If a roller hearth furnace 
comprises, for example, twelve furnace sections of a length of 10 m each, 
then on average two furnace sections must be replaced and cleaned each 
week. 
A typical application is provided by a continuous furnace for reheating 
thin slabs. The slabs are cast, passed through the roller hearth furnace 
and are thereafter rolled. Since the travel of the slabs must be 
accelerated inside the furnace, the alternative use of a walking-beam 
furnace where scale pickup problems are not encountered, is not possible. 
The plant operates continuously around the clock. It is only sometimes 
shut down when an empty ladle is replaced by a full ladle. The shutdown 
times take approximately 30 minutes. The method proposed by the present 
invention is in such cases the only method of avoiding longer shutdown 
times. 
Preferably, the furnace section removed is preheated to operating 
temperature after its furnace rollers have been cleaned and is kept ready 
as a replacement furnace section. It is hence only necessary to have a 
single additional furnace section to apply the method proposed by the 
present invention. 
It is also advantageous for the furnace section to be preheated to 
operating temperature to be connected with services for water, 
electricity, fuel, exhaust etc. and preferably with those of the roller 
hearth furnace. Heat-up is hence by the equipment such as burners etc. 
forming anyway part of the furnace section. 
To minimize heat loss and to prevent a cool-down of the furnace rollers 
located close to the face sides, the present invention proposes that the 
face side of each of the two furnace sections adjacent to the furnace 
section removed from the furnace assembly and exposed by the removal and 
the face sides of the replacement furnace section to be preheated to 
operating temperature are kept closed until the replacement furnace 
section has been integrated in the furnace assembly. 
The device for cleaning the surface of the furnace rollers of a roller 
hearth furnace proposed by the present invention is characterized in that 
the roller hearth furnace is subdivided into a multiplicity of detachably 
assembled furnace sections and at least one stretch of rails runs parallel 
to the roller hearth furnace, at least one car designed to accommodate at 
least one furnace section running thereon. This car is used to carry away 
the furnace section removed and to bring the replacement furnace section. 
It is possible to make arrangements for two stations on the car allowing 
both furnace sections to be accommodated simultaneously. Normally, two 
cars will be used. 
The latter arrangement will in particular be used, if, according to one of 
the embodiments of the present invention, the stretch or rails extends 
beyond each end of the roller hearth furnace by at least the length of one 
furnace section and a preheating station is arranged at at least one of 
its two ends and preferably at both ends. Such an arrangement allows in 
any case an extremely rapid replacement irrespective of the location at 
which a furnace section is to be replaced. 
Space conditions often do not allow the stretch of rails to be extended 
beyond the ends of the roller hearth furnace. To allow nevertheless an 
easy replacement of the outer furnace sections at the two ends of the 
roller hearth furnace, the present invention proposes that holding 
stations for at least two furnace sections are arranged adjacent to the 
stretch of rails and that a preheating station is arranged at at least one 
of the holding stations. This embodiment of the present invention offers 
the additional advantage that a single car may be used on the stretch of 
rails without increasing time requirements. 
Preferably, each furnace section is movable on wheels at least in a 
direction which is transverse to the direction of travel through the 
roller hearth furnace. 
According to another advantageous characteristic, each furnace section is 
provided with its own metering and control system. It may hence tie into 
services at all points where the latter are accessible, in particular over 
the entire length of the roller hearth furnace. 
The present invention also provides for each furnace section to have its 
own roller hearth drive. It is well known that due to drive reasons the 
roller hearth drive of long roller hearth furnaces is sub-divided into 
sections, but in the present case the characteristic serves to simplify 
and to accelerate the disassembly and the assembly of the detachably 
assembled furnace sections. 
The latter is also facilitated by the face sides of the furnace sections 
each being provided with a channel around its circumference outwardly open 
in the axial direction wherein a fiber module displaceable in the axial 
direction is arranged around the circumference. If the coupling between a 
furnace section and its adjacent furnace section is to be detached, the 
fiber modules are retracted. A gap is thereby created, as the channels are 
not in contact with each other. For assembly, the fiber modules are 
pressed against each other, thereby instantaneously sealing the roller 
hearth furnace.

According to FIG. 1, a roller hearth furnace 1, consisting of separate 
furnace sections 2 is proposed. The latter are detachably assembled. A 
stretch of rails 3 on which two cars 4 and 5 run, runs parallel to the 
roller hearth furnace 1. The stretch of rails extends beyond the ends of 
the roller hearth furnace by more than the length of one furnace section 
at each of its ends. Provision is thereby made to allow the replacement of 
the furnace sections 2 located at the furnace end. 
Car 4 is empty and ready to take the opposite furnace section. Car 5 is 
stationed in a preheating station 6 at the right-hand end of the stretch 
of rails 3. A replacement furnace section 7 located thereon is connected 
with utility supply and disposal services 8 for fuel, water, electricity 
and exhaust. The disposal services are the services of the roller hearth 
furnace. The replacement furnace section 7 has been preheated to operating 
temperature using its own burners. 
A preheating station 6 with utility supply and disposal services 8 is also 
arranged at the left-hand end of the stretch of rails 3. 
As soon as car 4 has received the opposite furnace section, car 5 takes 
replacement furnace section 7 to the empty space which is thereupon 
closed. The furnace section carried away by car 4 may cool down so that 
the rollers may thereupon be cleaned without problem. During the 
replacement, all faces of the heated furnace sections remain closed as 
long as possible. Covers not depicted are used therefor. 
As soon as the rollers of the furnace section carried away by car 4 have 
been cleaned, the furnace section is taken to the left-hand side 
preheating station 6 and heated there to operating temperature. 
Each furnace section disposes of its own metering and control system 9 to 
allow tie-in with utility supply and disposal services wherever the latter 
are available. 
In the embodiment according to FIG. 2, the stretch of rails ends at both 
sides at the ends of roller hearth furnace 1. To make nevertheless 
provisions for replacement of the furnace sections 2 located at the ends, 
holding stations 10 and 11 for furnace sections are arranged adjacent to 
stretch of rails 3. Holding stations 10 and 11 are at the same time a 
preheating station 12 with utility supply and disposal services 8'. 
As soon as car 4 has received the opposite furnace section, it takes it to 
holding station 10 and thereupon picks up replacement furnace section 7 
from holding station 11. It takes it back to the empty space which is 
thereupon closed. The furnace placed at holding station 10 cools down and 
is thereupon cleaned. 
As indicated schematically in FIG. 2, each furnace section disposes of its 
own roller hearth drive 13, whereby the removal of furnace sections from 
the furnace assembly and the re-integration are facilitated and 
accelerated. 
The same purpose is served by the design according to FIG. 3. The top part 
shows the roofs 14 and 15 of two adjacent furnace sections 2. The face 
sides of the furnace sections feature channels 16 around their 
circumferences facing each other wherein fiber modules 17 are dispaceably 
arranged. They are supported by metal plates 18. 
FIG. 3 shows the sealed condition wherein the fiber modules 17 are pressed 
against each other. To remove one of the furnace sections 2, the fiber 
modules 17 are retracted into the channels 16. The removal may then be 
completed without any problem as an appropriate space is provided between 
the channels. 
In the bottom part of FIG. 3, the floors 19 and 20 of the two furnace 
sections 2 are shown. The floors are provided with brackets 21 extending 
downward which serve to carry wheels 22, as shown schematically. On the 
wheels, each furnace section 2 may be moved in a direction which is 
transverse to the direction of travel through roller hearth furnace 1. It 
may be moved out of the furnace assembly onto car 4 and therefrom to one 
of the holding stations 10, 11, if desired. 
It is also possible to vary the arrangement such that the furnace sections 
2 may also be moved in the direction of travel through roller hearth 
furnace 1. They may then be moved from one of cars 4, 5 to the other one 
or from one of holding stations 10, 11 to the other one.