Heat-retaining exhaust components and method of preparing same

A method lining a component of a vehicle which may contact exhaust gases is disclosed, including the steps of applying a thin layer of a heat-resistant compound to an inner surface of the component to form a liner therein and bonding the liner to the surface. The manifold may be in two or more sections when the compound is applied and the sections may subsequently be joined together to form the component. The compound may contain zirconium and/or may be a ceramic material.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to heat-retaining exhaust components and 
methods of preparing such components. More particularly, the present 
invention relates to a method of lining a two-piece exhaust pipe or an 
automotive cylinder head with a heat-resistant compound containing 
zirconium, a ceramic material, or both, and a heat-retaining component 
which is the product of the described process. 
2. Prior Art 
In the automotive industry, it has long been recognized that heat generated 
by the combustion process emanating from hot vehicle components into the 
engine compartment of a vehicle is a problem. Not only does such heat 
degrade the various other components in the engine compartment which are 
not heat resistant, but the heat also causes the hot components themselves 
to become brittle and deteriorate. The problem is exacerbated in today's 
smaller engine compartments since cars are being "down-sized", especially 
when a high-performance engine such as a turbocharged or supercharged 
engine is packed tightly into such a small engine compartment. Heat 
generation in engine compartments is not limited to such high-performance 
engines, however. Heat loss is particularly a problem with any component 
which comes into contact with hot engine exhaust, such as vehicle cylinder 
heads, exhaust manifolds, and exhaust piping. 
Many varied types of heat shields and insulation have been employed in 
prior attempts to alleviate this problem. Ongoing efforts continue to 
channel the maximum possible amount of heat, which has been generated in 
the combustion chambers, from the exhaust ports of the cylinder heads into 
and through the exhaust system, minimizing the amount which is released in 
the engine compartment. 
Another important reason for wishing to channel the maximum amount of heat 
possible through the exhaust system is that by retaining heat in the 
exhaust system, "light off" of the catalytic converter may be achieved 
sooner if more heat is conveyed directly to the converter rather than 
dissipated outwardly. This promotes greater fuel efficiency as well as 
lowered exhaust emissions, which are both high priorities in today's 
market. 
For all of the above listed reasons, it is desirable to retain heat within 
components which contact engine exhaust. 
SUMMARY OF THE INVENTION 
The present invention provides a method of lining a component of a vehicle 
which may contact exhaust gases, comprising the steps of: 
(a) applying a thin layer of a heat-resistant compound to an inner surface 
of the component to form a liner therein; and 
(b) bonding the compound to the surface. 
The component may be an exhaust pipe which may be in two or more sections 
when the compound is applied thereto, and the sections may be welded or 
otherwise joined together after the compound has been bonded thereto. 
Alternatively, the component may be a cylinder head. 
The compound may be applied in a molten state and may be bonded to the 
component by the application of heat thereto. The compound may be a 
ceramic material, may contain zirconium, or may contain both of these. 
Zirconium is a preferred component because of its high heat resistance. 
The application of the compound and the heat bonding may be performed 
substantially simultaneously. The surface to be coated may be treated to 
roughen the surface before the compound is applied, and in one embodiment 
the compound is applied in a layer about 10 to about 15 thousands of an 
inch in thickness. 
The present invention also encompasses a heat-retaining exhaust pipe or 
cylinder head which is prepared by the process of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The above-mentioned copending parent application discloses a heat-resistant 
exhaust manifold which includes a liner formed of a heat-resistant 
material bonded to the interior of a sheet metal manifold. The manifold is 
formed in multiple parts for better access to the interior surface 
thereof. 
The present invention expands on the basic concept set out in the parent 
application. It is desirable to keep as much exhaust heat within an 
automotive exhaust system between the point of combustion and the 
catalytic converter, for the reasons set out in the foregoing description 
of the prior art. It would therefore be advantageous to line other vehicle 
components that come into contact with exhaust gases, in addition to 
lining the exhaust manifold as disclosed in the parent application hereof. 
The present disclosure thus describes a process for lining additional 
components which contact hot exhaust gases. 
Referring to FIG. 1, two sections 11, 12 of an exhaust pipe 10 are 
illustrated, along with a flange 50 for attaching the pipe 10 to an 
exhaust manifold (not shown). 
The flange 50 may be added to the exhaust pipe 10 once a heat resistant 
compound has been bonded thereto and the component parts 11, 12 have been 
joined together as further described herein. The flange 50 or other 
additional components such as hangers, brackets, etc. known to those in 
the art may be attached to the pipe body by laser welding, tig welding, or 
other suitable method. 
The exhaust pipe 10 comprises a lower section 11 which is a first sheet 
metal shell. The pipe 10 also includes an upper section 12 which is a 
second sheet metal shell. The first and second sections 11, 12 are 
alignable, as shown. 
As shown in FIG. 2, the lower section 11 has a horizontal ridge 13 and a 
vertical ridge 14 formed on each side thereof, the vertical ridges 14 
extending upwardly from the horizontal ridges 13 for joining the sections 
11, 12 together as will be described herein. 
Referring to FIG. 3, a metal spraying gun 15 is illustrated in 
cross-section, for applying a thin heat-resistant layer to the inside of 
the shell 11 to form a liner 16 on the inside thereof. In a metal spraying 
application a suitable fuel mixture, such as hydrogen, acetylene, or 
acetylene and oxygen is fed into a fuel inlet 20 of the metal-spraying gun 
15 from a fuel source (not shown). Air or oxygen under pressure is fed 
into an air port 18 of the gun 15, and mixes with the fuel at the outlet 
28 of the gun. The fuel is ignited to form a flame front 30 at the outlet 
of the gun. 
Drive air under pressure is applied to a drive air port 22 and passes 
through a drive air conduit 24 to force a compound 34 in the form of a 
powder out from a reservoir 32 and into a powder conduit 26 and thence 
into the gun 15. The compound 34 is sprayed outwardly from the gun in a 
conical pattern and is bonded to the inside of the sheet metal shell 11 to 
form a first liner 16 on the inside thereof. 
The interior surface 9 of the sheet metal shell 11 may be roughened 
beforehand to promote bonding of the compound 34 to the surface 9, and 
this roughening of the surface 9 may be accomplished by sandblasting, 
machining, or other appropriate method. Alternatively, any appropriate 
adhesive may be applied to the inner surface 9 of the sheet metal shell 11 
to promote bonding of the compound 34 to the inside surface 9 of the sheet 
metal shell 11. 
As seen in FIG. 5, an alternate means of applying the compound 34 to the 
sheet metal shells is achieved using the technique of plasma-arc spraying. 
In plasma-arc spraying, a generally inert gas such as nitrogen or argon is 
fed into a plasma spray gun 48 at a gas inlet 47 and passed between two 
electrodes 40, 41 where it is ionized by a continuous high voltage arc 42 
passing between the electrodes. This ionizes the gas and forms it into a 
plasma capable of attaining temperatures of 20,000.degree. F. or more. The 
electrodes 40, 41 are normally liquid cooled by cooling ports 46, 44 
respectively to prolong their life. A powder 34 which is used to form the 
heat-resistant liner 16 is fed into the gun 48 at a powder inlet 43 and 
enters the plasma downstream of the arc 42, where the powder 34 is melted 
by the plasma and is caught up therein and sprayed from the outlet 45 of 
the gun 48 and applied to the inside of the pipe sections 11, 12. 
Plasma-arc spraying is relatively well known and understood in the art. 
The compound 34 which is used to form the liner may contain zirconium, may 
be a metallic alloy or a ceramic material or may be a powdered glassy 
compound such as zircon. These compounds are used because of their known 
heat-resistant properties. In a first embodiment a zirconium-containing 
compound is preferred. In a second embodiment a ceramic compound is 
preferred. The liner 16 may be bonded to the interior 9 of the sheet metal 
shell 11 by the application of heat thereto. While the thickness of the 
liner 16 is not critical to the present invention, a thickness of about 
0.010 inches to about 0.015 inches has been found to be helpful in 
promoting heat-resistance in the finished exhaust component. 
The upper section 12 of the pipe 10 is treated in a similar fashion to that 
described herein for the lower section, and the gun 15 or 48 is used to 
spray a thin layer of the heat-resistant compound 34 on the inside 
thereof, which is bonded to the shell 12 to form a similar liner. 
Referring to FIG. 4, a cross-sectional view of part of an assembled exhaust 
pipe 10 is illustrated with the upper section 12 joined to the lower 
section 11. The vertical ribs 14 of the lower section 11 are bent in a die 
(not shown) in two operations and clamped around horizontal ridges 19 of 
the upper section 12 and may be welded thereto as at 36 to insure that 
exhaust gas will not leak out of the pipe 10 at the seams proximate the 
ridges 14. The ridges 14 thus provide a means for securing the upper 
section 12 to the lower section 11 in the aligned configuration. 
Alternative methods of joining the two sections 11, 12 may be used, as 
will be appreciated by those skilled in the art. The flange 50 is added on 
as shown in FIG. 1 after the upper and lower sections 12, 11 are joined 
together. The method of the present invention for lining a component of a 
vehicle which may be contacted by exhaust gases of an engine in the 
vehicle is also appropriate for lining portions of a vehicle cylinder head 
such as that shown at 80 in FIG. 6. A metal spraying gun 15 or a plasma 
arc spray gun 48 as described herein before may be used to apply a thin 
layer of a heat-resistant compound 34 which comprises, e.g., zirconium, a 
ceramic material, or both of these, to an inner surface of the cylinder 
head 80 to form a liner 58 therein, and the liner 58 is preferably bonded 
thereto during application of the compound 34. Surfaces of a vehicle 
cylinder head which are appropriate for the application of such a liner 58 
include the combustion chambers 52 and the exhaust ports 54 extending 
through the cylinder head 50 from the exhaust valve seats 56 to join up 
with an exhaust manifold (not shown) at an edge 60 of the cylinder head 
50. 
This lining of various components of a vehicle which may come into contact 
with exhaust gases tends to retain exhaust heat from the combustion 
process within the exhaust system and maximizes the amount of heat 
received at a catalytic converter to promote two important goals, firstly, 
to maximize fuel economy, and secondly, to minimize harmful vehicle 
emissions. This serves to promote conservation of resources and protection 
of the environment. 
The foregoing description is intended to be illustrative, and not 
restrictive. Many modifications of the present invention will occur to 
those skilled in the art. All such modifications within the scope of the 
appended claims are intended to be within the scope and spirit of the 
present invention.