Refractory lined cylindrical article

A refractory lined cylinder or tube is produced by causing an aluminothermic reduction reaction therein, such that the metallic reaction product forms a layer within the cylinder and the slag reaction product forms a second layer overlying the first layer thereby presenting an abrasion-resistant refractory lining.

BACKGROUND OF THE INVENTION 
This invention relates in general to refractory-lined tubes, pipes or 
cylinders, and more particularly to a method for producing a 
refractory-lined cylinder by an exothermic reduction reaction, such as 
aluminothermic reduction. 
Tubes, pipes, cylinders, and tanks lined with acid-resistant, 
corrosion-resistant or abrasion-resistant materials intimately bonded to 
the metal shell are required in many industrial applications. The shells 
of some tanks used in the oil industry, for example, are protected by a 
cured mixture of furnace cement and sand containing short asbestos fibers. 
The interiors of steel pipes and tanks exposed to corrosive water, salt 
solutions, or oils containing sulfur compounds are also often coated with 
cement to inhibit the attack on the steel. In cases where tanks are not 
subjected to high abrasive wear, but still require protection from an 
agressive environment, expensive stainless steels are often used in place 
of carbon steel. 
In other applications, glass lined vessels and pipes are used despite their 
obvious disadvantages and limitations. Thin impervious linings for steel 
vessels are also obtained through the used of vitreous enamels. This 
material is essentially a borosilicate glass containing fluorides which is 
finely ground, suspended in water or an organic solvent, and applied to 
the surface of the steel by dipping or spraying. The assembly is then 
dried by warming and finally heated in a furnace to near 1600.degree. F. 
to melt the enamel so that the particles flow together to form a 
continuous coat. The operation is often repeated to obtain a sufficiently 
thick coat. In addition to the complicated and tedious procedure, the 
substrate steel must be carefully cleaned by degreasing and pickling to 
assure satisfactory bonding. These treatments are costly and time 
consuming. 
In steelmaking operations, tuyeres and lances are lined with high alumina 
or mullite linings, which are held in place by refractory cement, to 
reduce damage from abrasion. The linings are expensive and subject to 
breakage prior to and during installation in the tuyeres. 
We are aware of the following prior art concerning aluminothermic welding 
processes and centrifugal casting: Adams U.S. Pat. No. 1,796,819, Touceda 
U.S. Pat. No. 2,011,955, Carpenter et al U.S. Pat. No. 2,515,191. 
SUMMARY OF THE INVENTION 
It is the primary object of this invention to provide a single, rapid, and 
effective method for coating the inside of cylinders, pipes, or tanks with 
an abrasion-resistant, corrosion-resistant, and oxidation-resistant layer 
of refractory. 
It is also an object to provide a method for fusing such a refractory layer 
to metal cylinders. 
It is a further object of this invention to deposit such a refractory 
without cleaning, pickling, or otherwise conditioning the inside surface 
of the cylinder. 
It is also an object of this invention to provide a coating method which 
will require relatively little capital expenditure for a coating facility. 
It is another object to provide a method by which a wide range of coating 
thicknesses can be applied to pipes, cylinders, and tanks in a single 
operation, eliminating the need for several applications to obtain any 
required coating thickness. 
Another object of this invention is to provide a method for depositing a 
ceramic layer in a cylinder using relatively low cost materials and one 
which requires no furnace firing or baking to fuse the ceramic particles 
into a continuous impervious coating. 
It is also an object to provide a method of making a refractory-lined 
tuyere. 
It is another object to provide a refractory-lined tubular article, such as 
a tube, pipe, tuyere or cylinder. 
These and other objects of our invention will become apparent from the 
following detailed specification and the appended drawing in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiment of this invention consists of filling a metal tube 
with an exothermic reduction reaction mixture such as an aluminothermic 
reduction (ATR) mixture rapidly rotating the filled tube about its 
longitudinal axis, initiating the ATR reaction, and continuing to rotate 
the tube until the reaction products have solidified. The centrifugal 
forces developed effect a separation of a metal phase from a slag phase, 
propelling the heavier metal phase toward the tube wall where it bonds 
metallurgically to the metal. The lighter molten slag layer, being 
displaced toward the center of the pipe by the metal phase, subsequently 
solidifies to form a continuous layer of refractory. Upon cooling, the 
metal pipe walls will contract to a greater extent than the ceramic liner, 
thereby locking the liner into the pipe. The chemical reaction involved in 
this method includes the very energetic reduction of oxides by such metals 
as aluminum, magnesium, silicon, and calcium-silicon alloys and mixtures 
thereof and can be generally represented by: 
EQU 2Al + 3MeO .fwdarw. Al.sub.2 O.sub.3 + 3Me + .DELTA.H 
where .DELTA.H represents the evolution of a large quantity of heat per 
mole of reductant (Al). The metal oxide (MeO) should be low in cost, 
readily available in a dry form and easily reduced by the reductant (Al, 
Mg, Si, or SiCa) to generate a substantial heat of reaction. Common iron 
ores, containing magnetite (Fe.sub.3 O.sub.4) or preferably hematite 
(Fe.sub.2 O.sub.3) are well suited for the process, and a stoichiometric 
mixture of iron ore fines and aluminum is preferred for most applications. 
In some applications, particularly where the pipe wall is rather thin and 
in danger of being burned through by the ATR reaction, it is preferable to 
include a small amount of alumina, typically up to about 20%, to retard 
the ATR reaction, and thus minimize the risk of burn-through. 
The metal oxide preferably has a size at least as fine as -35 mesh, and 
advantageously is no finer than +200 mesh. The fuel powder should have a 
size at least as fine as -100 mesh, but no finer than +325 mesh. 
As shown in FIG. 1, a metal cylinder or tank 10 is first fitted on one end 
with a retaining flange 12. An inner sleeve 14 in then positioned in the 
assembly and the annular space 16 thus formed is filled with an ATR 
mixture 18. A second retaining flange 20 is then fitted on the open end of 
the cylinder 10 to contain the charge mixture. Either sleeve 14 or 
retaining flange 20 or both is provided with holes 22 or 24 to provide 
access to the charge to initiate the reaction and vent the combustion 
products. The charged cylinder 10 is then placed on motor driven rolls 26 
and the entire assembly rotated about the cylindrical axis at such an 
angular velocity that the centrifugal force maintains the charge tightly 
against walls of the cylinder 10. When the cylinder is rotating at the 
proper speed, the ATR reaction is initiated by igniting the mixture. 
Centrifugal force, acting on the molten reaction products, separates the 
metal phase from the slag phase by forcing the heavier, more dense metal 
phase against the wall of the cylinder. Because the aluminum-iron ore 
reaction is a very energetic one, the metal phase melts and fuses to the 
cylinder wall and, in turn, is covered by a layer of molten slag of 
uniform thickness. The materials quickly solidify, and on cooling to 
ambient temperature, the slag phase is locked into the cylinder due to the 
differential thermal contraction of the metal-slag system. When aluminum 
or magnesium is used as the reductant, a highly refractory, chemically 
inert, corrosion-resistant and abrasion-resistant alumina or magnesia 
layer is formed which is useful in many chemical petroleum and steelmaking 
applications. 
Alternatively, the ATR mixture is suspended in an inert vehicle having a 
suitably low volatility or mixed with a binder to form a thick paste or 
slurry. Suitable binders include resinates of metals, asphalts, 
polyvinyl-chloride ethyl cellulose, plastics and waxes. Retaining flanges 
12 and 20 are attached to the ends of cylinder 10 and the inside of the 
cylinder is coated with the ATR mixture 18 in the paste form. The paste is 
dried and the coated cylinder can either be stored for future use or used 
immediately. The coated cylinder is rotated and the mixture is ignited as 
described above. Upon cooling, an abrasion-resistant refractory-lined 
cylinder has been produced. 
In another alternative, retaining flanges 12 and 20 are attached to the 
ends of cylinder 10, the assembly is placed on rollers and it is rapidly 
rotated. When the assembly is rotating at the proper speed, dry ATR 
mixture 18 is uniformly metered into the cylinder where it falls to the 
cylinder wall and is held tightly against the wall by centrifugal forces. 
When a sufficient amount of the mixture has been charged to the inside of 
the cylinder, the mixture is ignited and the coating process proceeds as 
described above. 
FIG. 2 illustrates the invented method for coating small diameter pipes, 
tubes, tuyeres, and tanks. Tube 30 is fitted with plugs or retaining 
flanges 32, each having hole 34 therein, then filled with an ATR mixture 
36. The charged assembly is placed into a motor driven chuck 38 and 
rapidly rotated about its axis. The ATR charge is ignited through hole 34 
generating the slag and metal phases as described above. The centrifugal 
forces generated in the system cause the slag phase to separate from the 
metal phase thereby forming a continuous slag layer covering the metal. 
Upon cooling, the reaction products solidify to form a metal coating 40, 
and an inner refractory coating 42 (FIG. 3) intimately bonded to the 
inside of the tube 30. 
The primary embodiment of this invention, as described above, requires a 
relatively rapid rotation of the pipe, e.g. at least 1,000 to 2,000 rpm, 
so that centrifugal forces will separate the metal and slag phases in the 
molten ATR mixture. As noted, this will cause the metal phase to solidify 
as an intermediate layer between the original pipe wall and the slag 
layer. In some applications however, particularly where large diameter 
pipe is to be coated using a sizable mass of ATR mixture, equally good 
results can be achieved by using a relatively slow rotation, i.e., slow 
enough so that centrifugal forces do not hold the ATR mixture against the 
pipe wall. In this embodiment, the ATR mixture is of sufficient mass that 
the metal and slag phases are separated by gravity, with the metal phase 
lying on the bottom pipe inner surface and the slag phase thereover. If 
the pipe is rotated slowly so that centrifugal forces do not disturb the 
molten ATR phases, e.g. 100 to 200 rpm, the slag phase will solidify 
first, being deposited against the original pipe inner surface. That is, 
as the pipe rotates more slowly, any given point on the pipe inner surface 
will rotate into and out-of contact with the two molten phases, but always 
last contacting the slag phase. As the temperature of the two phases 
begins to drop, the slag will start to solidify against the pipe surface, 
as surface rotates through the slag layer. In this manner, the slag phase 
can be substantially completely deposited against the pipe's inner surface 
before the metal begins to solidify. At this point, the molten metal phase 
may be poured out of the pipe or rotation continued until the metal phase 
does solidify, usually as easily removable beads or droplets which do not 
strongly adhere to the slag layer. By this embodiment then, the pipe is 
given a slag inner coating without the intermediate metal layer. 
EXAMPLES 
As an example of our method, a 11/4 inch OD by 4 inches long steel pipe was 
packed with a stoichiometric mixture of powdered aluminum and hematite 
iron ore (Fe.sub.2 O.sub.3) without cleaning or preparing the pipe in any 
manner. The ends of the pipe were partially closed with pipe reducer 
sections, thus providing a 1/4-inch high lip to contain the molten 
reaction products. The pipe was then rotated at 1500 RPM. Upon igniting 
the charge, the ATR reaction rapidly propagated through the charge. When 
the reaction was complete, and the products had solidified, rotation was 
stopped and the assembly was allowed to cool to ambient temperature. The 
pipe was then sectioned to show a fairly uniform and continuous slag layer 
firmly attached to the inside of the pipe as depicted in FIG. 3. 
As another example of our method, 115.7 grams of a mixture consisting of 
88.9 grams of nickel oxide sinter, 21.3 grams of 20 mesh aluminum and 5.5 
grams of powdered alumina was charged into a length of 1 inch steel pipe. 
The pipe was not cleaned or prepared in any manner. The pipe was then 
rotated at a speed of 2250 RPM in a horizontal position, and the ATR 
reaction initiated. Rotation was continued until the reaction was complete 
and the reaction products solidified. The resulting ceramic alumina layer 
was firmly secured inside the pipe. 
In still another example, 101.7 grams of a mixture of 71.0 grams of cobalt 
oxide (Co.sub.3 O.sub.4), 21.4 grams of 20 mesh aluminum and 9.3 grams of 
powdered alumina was identically processed in a 1 inch steel pipe as 
described above for the nickel oxide. Again a secure ceramic alumina 
coating resulted within the pipe. 
We have also found that a small diameter (less than 6 inch) tube can be 
coated with a refractory-lining by another modification of our method 
illustrated in FIG. 4. Tube 50 is covered at one end by a cap 52, such as 
aluminum foil, filled with an ATR charge mixture 54, and placed in a 
vertical position on a refractory solid or in a granular refractory bed, 
such as sand bed 56. The sand acts as a receptacle for the reaction 
products. The cap 52 prevents sand from entering the tube 50 prior to the 
reaction. The ATR reaction is initiated by igniting the mixture whereupon 
the extremely violent nature of the reaction throws molten reaction 
products against the walls of the tube to form a metal-slag layer 
(commonly termed "skull") on the tube. The skull moves downwardly and into 
the sand, but coats the tube with a substantially ceramic 
abrasion-resistant coating containing some metal. The sand bed may have a 
recess or a receptacle in it to receive the molten skull that leaves the 
tube. The resulting tube has an intimately bonded single layer lining 
rather than the two-phase or two-layer lining of the method which includes 
the rotating step. 
Our coating methods can be used on a large variety of metals including, but 
not limited to nickel, chromium, bronze, brass, iron, steel, stainless 
steel, copper, cobalt, molybdenum, tin, and aluminum. 
It is readily apparent from the foregoing that our invention provides a 
simple, rapid, and reliable method for coating the inside of cylindrical 
or tubular articles with a hard, corrosion-resistant, oxidation-resistant, 
and abrasion-resistant refractory-lining. The method is simple, reliable, 
relatively inexpensive, and does not require large capital expenditures to 
practice. Further, the method does not require the careful cleaning or 
other conditioning or preheating of the metal surfaces, and can be 
utilized to place a variety of fused refractory coatings onto the inside 
surfaces of tubes, tuyeres, pipes or tanks in any desired thickness in a 
single operation.