Pre-heating furnace for baked amorphous carbon bodies

A furnace for pre-heating carbon bodies prior to pitch impregnation utilizing electrical current flow through the body along its longitudinal axis. The furnace is an apparatus which includes a structural steel framework with roller assemblies to support a carbon body. Electrical contacts and pressing assemblies are provided for establishing pressing forces on the carbon body and the apparatus is configured so that a carbon body can be received on the roller assemblies and contacted by the electrical contact means by adjustment of the pressing assemblies.

BACKGROUND OF THE INVENTION 
The present invention is directed to a furnace for pre-heating baked 
amorphous carbon bodies which are to be densified by impregnation with 
liquid pitch. 
In the manufacture of carbon and graphite electrodes it is a common 
practice to extrude a mixture of coke particles and pitch to form a shaped 
amorphous carbon body. This amorphous carbon body is subsequently baked, 
at a temperature on the order of 800.degree. C. in a baking furnace, e.g. 
a gas fired furnace, to increase the strength thereof. In the course of 
baking, some of the pitch is volatilized leaving a large number of small 
sized pores in the amorphous carbon body. It is important to densify the 
amorphous carbon body by filling these pores with pitch. This is commonly 
achieved by a further pre-heating step at a temperature of about 
275.degree. C., at which temperature the evacuated porous baked carbon 
body is immersed in liquid pitch in an autoclave under pressure. Under 
these conditions, the pitch has a viscosity which enables the filling of 
the pores in the baked carbon body. Following this impregnation step the 
amorphous carbon body can be graphitized by well known techniques, e.g. 
the Lengthwise Graphitization (LWG) procedure which is described in U.S. 
Pat. No. 4,916,714. 
The "pre-heating" of a porous baked carbon body has previously been 
accomplished in gas fired furnaces since the desired pre-heat temperature, 
e.g. about 275.degree. C., is relatively low and readily achievable in 
such furnaces. However, because of the relatively large size of baked 
carbon bodies destined for use as electrodes in electric arc furnaces, the 
"pre-heating" required a relatively long time, and the "pre-heating" from 
the "outside-in" resulted in a non-uniform temperature condition in the 
baked carbon bodies. 
It is therefore an object of the present invention to provide an apparatus 
for rapidly and uniformly "pre-heating" a baked carbon body to a 
temperature suitable for pitch impregnation of the body. 
Other objects will be apparent from the following description and claims.

SUMMARY OF THE INVENTION 
The present invention is a furnace for heating an amorphous longitudinally 
extending carbon body, having the form of an electrode of cylindrical 
cross-section, to a temperature which is below the graphitization 
temperature of the body using an electrical current which passes 
longitudinally, lengthwise through the carbon body. 
The electrical current is about 40,000 A at about 30 volts and is applied 
only long enough for the carbon body to be heated to about 275.degree. C., 
much less than the temperature required for graphitization, i.e. 
2200-3000.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION 
With reference to the drawings, the elevation view of FIG. 1 shows the 
pre-heating apparatus of the present invention at 10 which is adapted to 
pre-heat a cylindrically shaped amorphous carbon body 12 by passing 
electric current from power cable 16, longitudinally through carbon body 
12, to cross-over power cable 18. Power cable 18 applies electric current 
to carbon body 12', positioned alongside carbon body 12, shown more 
clearly in the plan view of FIG. 2. Electric current passes longitudinally 
through carbon body 12' to power cable 22. The apparatus of the present 
invention includes a frame work of structural steel members, e.g. I-beams. 
A vertical steel member 30 is arranged opposite to and spaced from 
vertical steel member 32, both of which are fixed, at 31, 33 to a 
horizontal steel base member 34 which rests on a concrete base 35. 
Horizontal steel member 40 spans vertical members 30, 32 and is affixed 
thereto at 42, 44, to provide a rigid structure. Stationary roller 
assemblies 46, shown in FIG. 3, comprising individual rollers 47, 49, 
mounted in-line on base member 34, extend between vertical steel members 
30, 32. An amorphous carbon body 12 is placed on roller assemblies 46, 
e.g. by using a fork-lift or other conventional device. Rollers 47, 49 can 
be grooved, as shown at 41 in FIG. 3, so that carbon body 12 is nested 
therein and restrained from lateral movement, but can move axially on 
rollers 47, 49. As shown in FIG. 3, roller 47 (49) is pivotally mounted at 
50 in a steel frame 52 which is fixed to steel base member 34 as indicated 
at welds 54. With amorphous carbon body 12 supported on rollers 47, 49, 
electrical contact plate 60 is placed in contact with an end 62 of carbon 
body 12 by actuation of adjustable hydraulic pressing means assembly 64 
which is fixedly mounted on vertical steel member 30. Electrical contact 
plate 70 is concurrently placed in contact with end 72 of carbon body 12 
by actuation of adjustable hydraulic pressing means assembly 74, which is 
fixedly mounted on vertical steel member 32. Contact plates 60, 60' and 
70, 70', completely overly and abuttingly contact the entire carbon body 
surface at ends 62, 72, respectively, as shown in FIG. 7. Electrical 
contact plate 60 is pivotally supported at 80 by spanning horizontal 
member 40 through downwardly depending steel rod 76 which is itself 
pivotally connected to electrical contact plate 60 at clevis 78. 
Electrical contact plate 70 is pivotally connected to steel rod 80 at 
clevis 82 and plate 70 is horizontally rollably mounted on spanning member 
40 by roller assembly 90 which engages steel rod 80 as shown in FIG. 4 in 
which roller 91 is shown supported on flange 93 of spanning member 40. Due 
to the aforedescribed pivotal and rollable support of electrical contact 
plates 60 and 70, and the roller support of carbon body 12, excellent 
electrical contact is made with carbon body 12 since differences in length 
for different carbon bodies are readily compensated by flexible actuation 
of adjustable pressing means 64, 74 and free longitudinal movement of 
carbon body 12. Since it is well known that electrical continuity must be 
interrupted in metal members of the framework, electrical isolation 
devices, i.e. joints 116 are provided in roller support frames 52. 
Isolation device 116 shown in FIG. 5 is conventional and is described in 
U.S. Pat. No. 4,916,714 as comprising a rectangular plate 132 provided 
with holes and is welded at the ends 131 and the butt joints between both 
132 is provided by a bolt and a nut designated by 133 and 134, 
respectively. To interrupt the electrical continuity, a flat rectangular, 
bored plate 135 of an electrically insulating material is arranged between 
plates 132. As the bolts should be insulated as well, they are provided 
with a sleeve having the form of a cylinder with two washers of 
electrically insulating material designated by 136 in FIG. 5. The 
electrical isolation at 161 for support rods 76, 80 is in the form of a 
commercially available strain rod isolator shown in FIG. 6 comprising a 
pair of spaced apart threaded metal inserts 170, 172 which are embedded in 
electrical insulator 174 and receive threaded portions of steel rod 76 as 
shown at 180, 182. Electrical isolation is also provided at 181 between 
contact plates 60, 70 and the respective pressing means assemblies 64, 74. 
This is shown in FIG. 6a, for contact plate 60, where pushing plate 182 is 
electrically separated from contact plate 60 by electrical insulator 184 
and held in place by bolts 186 passing through electrical insulating 
sleeves 188 and washers 189. 
The apparatus of the present invention, in a preferred embodiment, shown in 
FIG. 1 and 2, includes a side-by-side duplicate arrangement, having 
cross-beam support members 95, 97, for simultaneously pre-heating a second 
carbon body 12' which receives electrical current by way of cross-over 
conductor 18. The roller assembly, electrical contact plates and 
adjustable pressing means for the duplicate arrangement for carbon body 
12', operate independently from the arrangement for carbon body 12 so that 
differences in the lengths of carbon bodies 12, 12' are readily 
accommodated. The carbon bodies 12, 12' are exposed to ambient air on all 
sides and the furnace apparatus of the present invention is preferably 
placed with a thermally insulating enclosure, as illustrated at 100 in 
FIG. 8, so that the carbon bodies being heated are surrounded by a static 
environment of ambient air to ensure rapid uniform heating. The enclosure 
8 is suitably made from high insulation wall board with a side being 
removable (as indicated at 102) to enable placement and removal of carbon 
bodies 12, 12'.