In-situ cavity coating method

Method for the in-situ deposition of a coating onto internal surfaces and matrix substrates of a body which defines one or more cavities. The single cavity, or the respective cavities packed with suitable substrates are provided with a predetermined amount of a solid reacting component to produce a suitable coating. The cavity is furnished with a liquid component which contacts the solid component, thereby forming a desired liquid coating reaction mixture. The latter is brought into contact with the cavity walls as well as with materials contained within the cavity, to achieve the desired coating of walls and matrix material.

BACKGROUND OF THE INVENTION 
The art of coating a layer of material onto a substrate to achieve certain 
characteristics in the material, is used in many industries and fields of 
commerce. One procedure for coating such an article resides essentially in 
depositing a layer of the desired material across the surface, or part of 
a surface of the object being coated. Normally the deposited layer is 
sufficiently thin as to not add substantially to the thickness of the 
entire surface. However, the coated area will possess characteristics that 
are essential to the desired function or operation of the object being 
coated. 
As an example of the coating process, in the automotive art certain exhaust 
gas filters and reactors are provided with a catalytic material or a 
substance adapted to promote reaction of the exhaust gas. This reaction is 
followed with the intention of treating the gas prior to its discharge 
into the atmosphere. Usually for such an article as an exhaust gas filter, 
the entire unit is dipped or immersed into a bath of coating solution. The 
unit is then maintained at a desired temperature to best achieve 
deposition of the coating material. 
Generally, in such a process there are a number of factors to be considered 
for the filter's coating layer to be properly applied and held to the 
inner surface. Primarily, the coating ingredients must be brought to, and 
maintained at an optimum concentration and strength. Further, during the 
coating process, the solution's strength should be maintained by the 
periodic addition thereto of amounts of the coating elements as the latter 
leaves the solution to form the coating. 
Also, it is desirable to maintain the applied layer at a relatively uniform 
thickness. This latter requirement, however, becomes difficult in the 
instance of objects or articles which are of an irregular shape or 
configuration. Lack of layer uniformity will result for example when the 
solution does not contact all exposed surfaces for the same period of 
time. 
As is well known, to achieve a proper coating or layer, it is necessary to 
maintain the coating solution within a preferred temperature range, and to 
sustain the process over a set period of time. 
As mentioned above, a primary defect or fault normally encountered in this 
type of coating process resides in the shape of the object being coated. 
Normally, the article is simply dipped into a bath such that it is 
immersed and consequently all exposed and wetted surfaces in contact with 
the reacting materials will become coated. Such a process however, could 
require the removal of excess coating material from certain surfaces that 
have been exposed to the solution but do not require coating. This latter 
step of course adds to the overall cost, and the time involved in 
producing the product. 
Other limitations normally embodied in the coating process reside in the 
capacity of the coating bath to accommodate a limited number of articles. 
This facet also leads to the problem of irregularity of the coating. 
Notably, all exposed surfaces will not necessarily be subjected to the 
same degree of contact time with the solution even though they are 
completely immersed in the latter. 
Toward overcoming these above stated problems as well as to provide a 
commercially acceptable coating method, the following method is provided. 
The method herein disclosed is addressed primarily to the coating of 
irregularly shaped members which normally define an internal filled or 
unfilled cavity, into which a uniform coating is difficult to apply and 
for which the coating needs to be restricted to the inside walls of the 
unit. The term "matrix" as herein used, refers to a bed or mass of a 
mesh-like material such as steel wool. The function of the latter is to 
contact the gas for prompt treatment. 
Thus, the article, although irregular in shape, and filled with matrix 
substrate material, is nonetheless adapted to be sealed such that the 
internal cavity can be made liquid tight. To achieve the in-situ coating, 
the cavity or cavities will also have previously been provided with 
separate charges of unmixed solid and liquid components which make up the 
coating composition. Said components are thereafter mixed, and react to 
form a coating solution. When said solution is caused to contact the 
internal cavity walls and matrix, such surfaces will receive a deposit of 
the coating element. 
To achieve the proper degree of such internal coating, each article in 
sealed condition, can be immersed in a bath or other temperature 
controlled medium. In the latter, the article is maintained over a period 
of time, exposed to the solution at a prescribed temperature. 
It is therefore an object of the invention to provide a novel method for 
depositing a uniform coating layer onto an inner substrate surface. A 
further object is to provide a method for in-situ coating of discrete 
surfaces of an irregularly shaped article. A still further object is to 
coat the inner surfaces, including a matrix contained therein, of an 
exhaust gas manifold or filter.

To illustrate the novel method, a coating as hereinafter disclosed, is 
applied to inner surfaces of a manifold member 10 of the type normally 
used in conjunction with an internal combustion engine. The manifold as 
shown, is provided with means for removably engaging the block of a four 
cylinder engine. When so positioned it receives four distinct exhaust gas 
streams, each of which is discharged from an engine combustion chamber. 
Said manifold 10 is provided with a plurality of internal beds 11 adapted 
for contacting and treating hot exhaust gases. Thus, the manifold 
comprises four elongated, tubular arms or segments 12, 13, 14 and 15. The 
end of each segment, such as 12, is provided with a flange 16 which is 
shaped to fasten to a corresponding flange or surface at the engine block. 
Thereafter the flow of hot exhaust gas will pass from the engine block, 
into manifold 10, and thence to a muffler or a gas treating unit. 
The respective elongated manifold segments or arms are sufficiently curved 
to be attached to the block at space apart locations. Further, they are 
brought together at a juncture to form a common gas stream within manifold 
body 17. The latter is likewise provided with a connecting flange 18. Body 
17 is internally structured to concurrently receive the four separate arms 
and gas flows, and can be shaped at its outlet to further direct the gases 
in a desired direction. 
To enhance the efficiency of any gas treating unit connected downstream of 
manifold 10, the hot exhaust gas can be pretreated while still within the 
manifold. Thus, and as here shown, the respective manifold arms 12, 13, 14 
and 15 are each provided with a bed 11 or mass of a packing material which 
defines a gas pervious section. 
Physically, bed 11 can comprise any one of a number of shapes and 
configurations to achieve the desired function. Here, the bed is formed of 
steel or alloy wool in a manner to define passages capable of guiding and 
contacting the hot gas passing therethrough. Further, to promote the gas 
treating or catalytic effect, the exposed surfaces of bed 11 as well as 
those of the cavity which confines the bed 11, are provided with a 
suitable coating of alumina. The latter can comprise for example, a 
coating of alumina which provides a catalytic effect and to which can be 
added other catalysts by solution impregnation or other means. 
Operationally, as hot exhaust gas flows through the respective manifold 
arms 12 to 15, the gas will be contacted and react with the alumina or 
other catalyst which is disposed along the bed 11 surfaces. Bed 11 can 
extend for only a portion of the arm's length; however it preferably 
extends the entire length of the arm and is retained in place by any 
suitable means. The bed thereby has ample opportunity to be contacted by 
the hot, flowing exhaust gas. 
As previously noted it is desirable to apply the uniform thickness of the 
catalytic material or coating layer only to the manifold 10 inner walls or 
the cavity formed in the respective arms. Thus, each cavity as defined by 
a manifold arm, is exposed to a solution of comparable concentration as 
are other cavities. Further, the time of exposure, as well as the 
temperature of the coating solution are readily maintained at a relatively 
uniform level. 
After the packing material or bed 11 has been positioned within each 
manifold arm such as 12, a canister or container 21 is removably fastened 
to each arm flange 16. To achieve a liquid tight joint, a resilient gasket 
22 can be pressed between arm flange 16 and the corresponding flange 23 of 
canister 21. The respective flanges are held in fluid tight engagement 
about gasket 22 by two or more bolts 24 which pass through the respective 
flanges and are drawn tight. 
To achieve a desired concentration of the coating solution in each arm 12 
to 15, the container 21 which is adapted to a particular arm, is provided 
with a quantity or solid charge of aluminum pellets. These pellets are 
provided in a predetermined amount sufficient to coat the walls of the 
cavity as well as the various passages of the bed 11 disposed within the 
arm cavity. 
In the present arrangement, the respective arms 12 to 15 are of 
substantially equal lengths and consequently will have equal areas of 
internal coating surface. Thus, the amount of aluminum pellet charge which 
is provided in the respective canisters 21 will be substantially equal. 
However, should there be variations in the coating surfaces of the 
respective arms, the volume of aluminum pellet charge will be 
commensurably proportioned for each of said arms. 
The respective canisters 21 are preferably fastened onto the manifold arms, 
with the manifold positioned in a way that the canisters will be at the 
manifold's lowest point or points. Thereafter, alkali hydroxide which is 
introduced to manifold 10 to form the coating slurry or mixture, will 
gravitate downwardly and into the canisters and react with the aluminum 
pellets. 
The coating operation is carried out with manifold 10 in a substantially 
liquid tight condition. It is understood, however, that the manifold 
interior is vented to release gas which is generated during the process. 
The alkali liquid is added to the cavity by means of a suitable container 
26 or similar receptacle which includes a flange 28 that attaches to 
flange 18. As in the previous instance, the flanges are brought together 
with a gasket compressed therebetween to assure a liquid tight seal. 
Container 26 includes a body 27 that can be internally channelled to define 
separate passages for each of the respective arms 12 to 15. However, the 
container can also be provided with an external attachment adapted to 
receive a hose or conduit for metering liquid. 
Functionally, manifold 10 can be initially disposed to place the liquid 
holding container 26 at the lowest point. Thereafter, the manifold is 
adjusted to prompt forming of the coating slurry. Thus, container 26 is 
fastened in position with bolts 29. The amount of liquid retained in said 
container is proportioned to mix with the solid aluminum pellets, and 
thereby form a desired concentration for optimum coating rates. 
In the instant example, a sufficient amount of one molar sodium aluminate 
was added to react with the aluminum pellets, and form a desired solution 
concentration. 
When the manifold is optionally placed into the temperature controlled 
heating medium, the sodium aluminate will gravitate downwardly and into 
the respective canisters 21 to meet aluminum and form the alumina coating. 
To best foster the coating process, the water bath, if utilized, is 
maintained at a temperature of 180.degree. F. 
With the coating solution thus formed manifold 10 can be fixedly positioned 
or it can be articulated to prompt flowing of the solution or slurry about 
the cavity and bed. However, the normal reaction, as well as the upward 
flow of H.sub.2 gas also prompts circulation of the solution. 
Thereafter, when the coating period has terminated, the manifold is removed 
from the heating bath. After removal of the respective container 26 and 
canister 21, the unit is calcined at 700.degree. to 1,000.degree. F. and 
is in condition for use. 
The resulting manifold with coated matrix or bed is now in condition to be 
used as a filter, or a particle trap for treating particle laden exhaust 
gas as would be the instance particularly in diesel engines. 
Other modifications and variations of the invention as hereinbefore set 
forth can be made without departing from the spirit and scope thereof, and 
therefore, only such limitations should be imposed as are indicated in the 
appended claims.