Rotary furnace for melting metal

A rotary furnace for recovering metals, such as aluminum. The furnace includes an outer cylindrical, open-ended drum which is mounted for rotation about its axis. Secured within the drum is a tapered kiln and the kiln is spaced inwardly of the drum to provide an annular chamber therebetween. Salt and aluminum dross and skimmings are introduced into the small diameter end of the kiln and heated, and the molten aluminum and salt are separately withdrawn from the large diameter end of the kiln. The construction of the furnace provides precise concentricity for the rotating kiln, thereby reducing bearing loads and the energy requirements for driving the kiln.

BACKGROUND OF THE INVENTION 
Various types of furnaces have been used in the past to recover aluminum 
from dross and skimmings. In the conventional aluminum recovery procedure, 
salt is initially introduced into a rotating furnace or kiln and heated to 
the molten state. Aluminum dross and skimmings are then added to the 
furnace and melted. The molten aluminum stratifies as a layer beneath the 
molten salt, and the salt layer protects the molten aluminum from 
oxidation. After the materials have been melted, rotation of the furnace 
is stopped and the molten aluminum is withdrawn from a tap hole in an end 
of the furnace. After withdrawal of the molten aluminum, the salt is 
similarly withdrawn from the end of the furnace by gravity. 
The conventional aluminum recovery furnace is cylindrical in shape and in 
order to drain or withdraw the molten aluminum and salt from the furnace, 
a hydraulically actuated tilt mechanism is employed to tilt the furnace. 
As the furnace has substantial weight, up to 60,000 lbs. the tilt 
mechanism is complex and adds considerable cost to the unit. 
Other commonly used furnaces have an outer cylindrical drum and a tapered 
refractory lining. By use of the tapered refractory lining, the molten 
materials can be drained from the furnace without the necessity of a tilt 
mechanism. 
To rotate the conventional furnace, a pair of guide rings and a gear ring 
are welded in spaced relation to the outer cylindrical surface of the 
furnace. As the furnace has a substantial diameter, generally in the range 
of 8 to 10 ft., it is very difficult to precisely position the guide rings 
and drive ring on the outer surface of the furnace with the result that a 
certain amount of eccentricity inherently results. The eccentricity 
produces a substantial load on the bearings and also increases the energy 
requirement for rotating the furnace. 
As a further disadvantage, the guide rings and gear ring, which are welded 
to the outer metal shell of the furnace, tend to restrict the thermal 
expansion of the shell during the heating process. As expansion of certain 
areas of the metal shell is restricted, the refractory lining in these 
areas tends to crack and deteriorate, thereby resulting in serious 
maintenance problems. 
SUMMARY OF THE INVENTION 
The invention is directed to an improved rotary furnace for recovering 
metals, and has particular use as a salt-aluminum melting furnace. In 
accordance with the invention, the furnace includes an outer cylindrical 
open-ended drum which is mounted for rotation about its axis. Located 
within the drum is a tapered, refractory lined, kiln, and the kiln is 
spaced inwardly of the drum to provide an annular chamber therebetween. 
The outer drum and attached kiln are rotated by a roller chain which is 
secured to the outer surface of the drum and is engaged by a drive 
spocket. The drum is guided in rotation by a pair of guide rings that are 
welded to outer surface of the drum and ride on rollers that are supported 
by the foundation. 
In use of the furnace, the salt is introduced into the small diameter end 
of the kiln through a charging opening and a conventional gas or oil fired 
burner is utilized to heat the salt to the molten state. The aluminum 
dross and skimmings are then fed into the kiln and melted, with the molten 
aluminum forming a stratified layer beneath the molten salt. The large 
diameter end of the kiln is provided with discharge openings through which 
the molten aluminum and salt can be individually withdrawn. 
As the guide rings and drive ring are located on the outer surface of the 
drum and not attached directly to the kiln or furnace, the rings can be 
precisely machined to provide concentricity for the drum and the 
subsequently attached kiln. The improved concentricity of the unit reduces 
bearing loads and correspondingly reduces bearing maintenance. 
As the kiln is tapered, no complicated and expensive tilting mechanism is 
required to discharge the molten aluminum and salt from the kiln. 
As a further advantage, the guide rings and drive rings are not secured 
directly to the kiln, but are secured to the outer drum which is spaced 
from the kiln. With this construction, the rings do not restrain thermal 
expansion of the metal shell of the kiln and thus, there is less 
deterioration of the refractory kiln lining. 
Other objects and advantages will appear in the course of the following 
description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawings illustrate a rotary furnace that can be used for the melting 
and recovery of metals, and has particular application for use in an 
aluminum recovery system. The rotary furnace 1 includes an outer, 
open-ended, cylinder shell or drum 2, and a tapered refractory lined kiln 
3 is spaced inwardly and connected to the drum 2. 
The drum 2 and kiln 3 are mounted for rotation with respect to the 
supporting base 4 by a pair of guide rings 5 that are secured to the outer 
surface of the drum 2 adjacent the ends of the drum. Each guide ring 5 is 
mounted to rotate on a pair of rollers 6, and each roller is mounted on a 
horizontal shaft 7 that is journalled within bearing assemblies 8 mounted 
on plates 9. The plates 9 are supported through supports 10 from the base 
4. 
To adjust the position of the support rollers 6, adjusting studs 11 are 
threaded within lugs 12 secured to plates 9 and bear against the bearing 
assemblies 8. By threaded adjustment of the studs 11, the position of the 
bearing assemblies 8 and rollers can be adjusted, as desired. 
Suitable guards 13 cover the rollers and prevent objects from being pinched 
in the nip between the rollers 6 and the guide rings 5. 
To drive the drum 2 and kiln 3 about the axis of the drum, a conventional 
roller chain 14 is secured to drive ring 15 that is located centrally of 
the length of the drum 2. As best illustrated in FIG. 2, a drive sprocket 
16 is engaged with the chain 15 and rotation of the sprocket will drive 
the chain to rotate the drum about its axis. 
Sprocket 16 is mounted on shaft 17 which is journalled within bearing 
assemblies 18 mounted on the base 4. In addition to sprocket 16, a pulley 
19 is secured to the shaft 17 and the pulley is connected by belt 20 to 
the output shaft 21 of gear reduction box 22. The input shaft 23 of gear 
reduction box 22 is connected by chain drive 24 to the drive shaft 25 of 
motor 26. With this drive construction, operation of the motor 26 will 
drive the sprocket 16 to thereby rotate the drum about its axis, at a 
speed up to 8 rpm, and normally at a speed of about 3 rpm. 
To prevent longitudinal displacement of the drum 2 and kiln 3, thrust 
rollers 27 are mounted on brackets 28 and ride against the opposite sides 
of the guide rings 5, as best illustrated in FIGS. 1 and 4. 
The kiln 3 is composed of a tapered metal shell 29, the large diameter end 
of which is enclosed by a head 30, and the small diameter end is enclosed 
by head 31. Head 31 is provided with a central opening bordered by flange 
32 which defines a charging opening 33 into which the material to be 
heated is introduced into the kiln. The inner surface of the shell 29, as 
well as the heads 30 and 31, is lined with a conventional refractory 
material 34. 
To support the kiln 3 in spaced relation within the drum 2, a plurality of 
brackets 35 are secured to the outer surface of the kiln and are connected 
to corresponding brackets 36 which depend from the drum 9. The connection 
between the kiln and the drum is best illustrated in FIG. 5. Brackets 35 
include parallel side plates 37, which are secured edgewise to the outer 
surface of the kiln, and a web 38 is secured between the side plates 37. 
Similarly, each bracket 36 includes a pair of generally triangular side 
plates 39 connected by a web 40. The webs 38 and 40 are secured in 
flatwise relation by bolts 41. With this connection, the kiln is secured 
to, but spaced inwardly of, the drum to provide an annular chamber 42 
therebetween. 
To heat the materials within the kiln 3, a conventional burner 43 is 
mounted within an opening in the head 30. Burner 43, which can be gas or 
oil fired, is mounted on the outer end of an arm 44 which, in turn, is 
pivotally connected through arm 45 to a vertical pedestal 46. Through this 
connection, the burner can be withdrawn from the opening in head 30 and 
moved to a storage or inoperative position. 
To discharge the molten aluminum from the kiln, the head 30 is provided 
with a series of aluminum drain holes which are enclosed by plugs 47. The 
molten salt is also withdrawn from the head 30 through an opening which is 
enclosed by a hinged cover or lid 48. 
As shown in FIG. 3, the head 30 is reinforced by a series of radially 
extending ribs 49. 
In operation of the furnace, salt is introduced into the kiln through the 
charging opening 33 in head 31 and heated by the burner 43 while the drum 
and kiln are rotated. After the salt has melted, the aluminum dross or 
skimmings is fed into the kiln through the opening 33 and the aluminum is 
also melted. The molten aluminum, being heavier than the salt, will 
stratify as a layer beneath the molten salt, and the molten salt which 
protects the molten aluminum against oxidation. 
Subsequently, rotation of the drum and kiln is stopped with one of the 
aluminum discharge holes located at the bottom end of the kiln. The plug 
47 is removed from the drain hole enabling the molten aluminum to flow by 
gravity from the unplugged drain hole. After the aluminum is removed, the 
drum and kiln are again rotated to position the salt tap opening at a 
level adjacent the level of the salt in the kiln, and the cover 48 is then 
removed to permit the salt to drain from the kiln. As the salt drains from 
the kiln, the drum and kiln are rotated to maintain the salt tap opening 
at a level corresponding to the level of salt in the kiln. 
As the guide rings 5 and drive ring 14 are mounted on the outer drum and 
not on the kiln, the rings can be precisely machined to provide 
concentricity for the drum and kiln. In addition, the plates 9 which 
support the bearings are machined so that they lie precisely in a common 
plane, and this also aids in obtaining concentricity for the unit. By 
virtue of the improved concentricity, the loads on the bearings are 
reduced and the energy requirements to rotate the unit are correspondingly 
decreased. 
As the guide rings 5 and drive ring 14 are not attached directly to the 
kiln, but instead are mounted on the outer drum which is spaced from the 
kiln, the rings do not restrain thermal expansion of the metal shell 29 of 
the kiln during the heating operation. As there is no restriction to 
expansion, the tendency for the refractory lining to deteriorate because 
of such restriction is eliminated. 
As the kiln itself is tapered, the aluminum and salt can be discharged by 
gravity from the large diameter end of the kiln and no tilting mechanism 
is required. 
Various modes of carrying out the invention are contemplated as being 
within the scope of the following claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as the invention.