Note: Descriptions are shown in the official language in which they were submitted.
M~l`HOD FOR IND[1CrrIVELY HEATING VALVE ~5EAT INSE~RTS
Background of the Invention
This invention relates to the art of induction heating
and, more particularly, to a method for inductively heating
valve seat inserts for an engine component such as an engine
head or the like.
The invention is particularly applicable to heating
exhaust valve seat inserts in a cast aluminum engine component
and will be described with particular reference thereto;
however, it will be appreciated that the invention has broader
~0 applications and may be used for heating a variety of conically
shaped metal surfaces in other environmentsO
Internal combustion engines generally employ conically
shaped valve seats which coact with reciprocating poppet valves
for controlling the flow of gases to and from the engine
cylinders. The Yalve seats for the exhaust valves must have
extre~ely high wear characteristics at high engine operating
temperatures. To coun~eract such wear and increase desirable
physical properties in the valve seats~ the conical seat
surfaces are inductively heated during engine manufacture and
t}-en quench hardened by conventional liquid or mass quenching
techniques D
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Induction heating of multiple valve seats in an engine
component may be adapted to automatic processing in a single
operation where, for example, a plurality of single turn
inductors are positioned immediately adjacent the conically
shaped exhaust valve seat. Such apparatus and methods are
disclosed in U SO Pat~ Nos~ Re 29,046 and 3,837,934. There,
the inductors are independently movable on a common frame
relative to the engine component and are biased toward the
valve seats~ The frame itself is moved into contact with the
engine component so that each inductor contacts the valve seat
which it is to heat. The inductors are then locked in position
and the frame retracted slightly for purposes of establishing a
desired magnetic coupling distance between the inductors and
valve seats. The foregoing patents disclose methods which have
provided extremely good results when induction heating ferrous
exhaust valve seats in cast iron engine componentsO
However, recent efforts to improve gasoline mileage
and obtain vehicle weight reductions have brought about an ever
increasing use of aluminum for major engine components.
Although use of aluminum for manufacturing such major
components provides substantial benefits insofar as weiyht
reduction is concerned, attendant difficulties and problems
have been encountered in several areas, including exhaust valve
seats~ Aluminum does not have sufficient strength and hardness
properties to itself accommodate or comprise the valve seat
surfaces~ As a result of these shortcomings, it is necessary
that the exhaust valve seat surfaces be provided through use of
seat ring inserts constructed of a hardenable material
installed in the cast aluminum engine component by suitable
means such as, for example, a force Eit or the like. For cost
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reduction purposes as well as for purposes of assuring accurate
location and concentricity of the valve seat surfaces~ it is
highly desirable that machining of the inser~s for obtaining
final valve seat con~ormation take place subsequent to mo~nting
of the inserts into the engine component.
While machining of the conical valve seat surfaces
does not present any significnt problems, subsequent surface
hardening must be performed in a manner which will not
deleteriously affect the aluminum engine component and/or the
pressure fit between the engine component and the ferrous metal
insert. Because it is customarily necessary to harden exhaust
valve seat surfaces at approximately 1700F and since the
melting point of typical aluminum alloys employed for engine
components is generally in the range of 1200 ~ 1400 F,
heating of and heat transfer through the seat inserts must be
carefully controlled during the hardening process. Without
appropriate control, the inserts may radially expand against
the associated receiving bores in the engine component to
destroy the pressure fit relationship therebetween and/or
~ otherwise damage the integrity of the engine component metal
adjacent thereto. In more severe cases, the aluminum engine
component metal could be unacceptably brought close to its
melting temperature. Both of the foregoing situations are
extremely undesirable in that they can ultimately adversely
affect engine operation or expected engine life. The specific
heating methods disclosed in U. 5 Pat. Nos. Re 29,046 and
3,837,934 are useful in inductively heating valve seats and
valve seat insert surfaces when conventional gray cast iron
engine components are involved. They are not, however, as
effective for use with aluminum or the like components because
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of the above noted problems and characteristics which are
generally associated therewith. In view of these factors, the
inserts ~ere often made of expensive steel and hardened in
furnaces before assembly into the engine component. This
S involves costly materials as well as costly post assemb~y
machining of the hardened seat inserts.
It has, thereore, been considered desirable to
develop a method for inductively heating the seat surface of
ferrous seat ring inserts installed in aluminum engine
components for purposes of overcoming the foregoing problems.
One such method and apparatus is disclose~ in the commonly
assigned,Canadianpatent applica~ion 5er. No. 376,487, filea
April 29, 1981,and which involves method conceived subsequent to
conception of the subject invention. The foregoing application
generally relates to use of a conducting ring or shield in
operative association with each heating inductor for shielaing
the inductive energy of the inductor from the aluminum engine
component. This then prevents or controls heating of the
aluminum engine component around and adjacent to the valve seat
insert. The method in this prior application did not solve the
problem of undue seat insert expansion during heating. Although
providing a solution to one o~ the major problems~ the subject
new method is deemed to provide another approach for enhancing
the ability to harden ferrous seat rings in the general
environment of aluminum engine components~
Brief Summary of the Invention
The present invention relates to inductively heating a
metal valve seat insert within an engine component such as an
3~ engine head or the like subseqLIent to 1nstallation and
machining of the insert within the component.
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The invention further relates to a method for
inductively heating the inse~t prior to quench hardening while
maintaining a peessure fit between the metal insert and a
non-ferrous engine component. The method utilizes high power
induction heating techniques which facilita~e obtaining the
necessary insert heating to a satisfactory preselected depth in
a very short time interYal.
According to the present invention, the method
comprises the steps of:
(a) locatiny a generally circular inductor adjacent
the insert;
(b) energizing the inductor with a primary power
source having a frequency of at least greater than 200
kilohertz and a selected power greater than approximately 12
kilowatts and providing a power source density at the seat of
at least 25 kilowatts per square inch;
(c) maintaining the inductor in an energized condition
for some predetermined period of time less than 3 seconds to
transform the metal forming the valve seat into an austenitic
2Q structure to some predetermined depth; and,
(d) thereafter quenching the valve seat mateeial.
According to a more detailed aspect of the invention,
the step of energizing is performed at a frequency generally in
the range of approximately 250-500 kiloheetz at a selected
power generally in the range of 15-25 kilowatts and with said
step of machining being performed in a time period of less than
1 second. In the preferred arrangement for practicing the
method, the frequency is approximately 400 kilohertz at a
selecte~ power of approximately 20 kilowatts.
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According to a further aspect of the invention, the
step of maint,alning continues until the metal forming the valve
seat is Eormed into an austenitic s~ructure to a depth of
generally no greater than 0.035 inches. In the preferred
method, this depth is maintained at approximately 0.024 inches.
The principal object of the present invention is the
provision of a new method which is extremely reliable and
effective for purposes of inductively heating a conical surface
on a ferrous ring insert~ such as a cast iron insert, disposed
in a non-ferrous component and, in particular, an internal
combustion engine component.
Another object of the invention is the provision of
such a method which will not cause deleterious heat transfer
through the insert and/or to the component metal immediately
surrounding and adjacent to the insertr
Still another object of the invention is the provision
of a new method for inductively heating a ferrous valve seat
insert having a pressure fit in an aluminum engine component so
that such heating will not deleteriously affect the pressure
fit and wherein an inexpensive ferrous material like cast iron
may be used for the insert.
Further objects and advantages for the invention will
become readily apparent to those skilled in the art upon a
reading and understanding of the following specification.
Brief Description of the Drawings
The invention may take physical form in certain parts
and arrangements of partsS a preferred embodiment of which will
be described in detail in the following specification and
illustrated in the accompanying drawings which form a part
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hereof and herein:
FIGURE 1 is a partial cross-sectional view
illustrating the preferred manner of practicing the subject new
method; and,
FIGURE 2 is an enlarged cross-sectional view of a
portion of F~GURE 1 for bet~er showing ~he relationship between
the inductor and valve seat surface to be heated.
Detailed Description of the Preferred Embodiment
Referring now to the drawings wherein the showings are
for purposes of illustrating the preferred embodimen~ of the
invention only and not for purposes of limiting same, FIGURE 1
shows an induction heating deYice A disposed in operative
communication with a cast aluminum engine component B.
Specific details of the features and operation of induction
heating device A are disclosed in detail in the commonly
assigned United States Pat. No. Re 29,046
More particularly, engine component B includes at
least one exhaust passageway 10 having an annular valve seat
insert 12 formed of cast iron and closely disposed coaxially
within a recessed cylindrical e~haust port 14. A g~ide opening
or port 16 is coaxial with exhaust port 14 and receives the
stem of a conventional poppet valve (not shown) when the engine
is assembled.
Annular valve seat inser~ 1~ includes a conically
shaped valve seat surface 30 which is installed into the engine
3Q component, machined and thereafter hardened in accordance wi~h
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the subject invention. Insert 12 comprises a standard
component typically constructed from steel or cast iron;
however, cast iron is preferred because of costs. Installation
of insert 12 into the receiving bore at exhaust port 14 may be
by any one of a number of conventional methods including, for
example, a pressure or force fit and the likeO When a pressure
fit technique is employed, the insert is normally chilled to
obtain some degree of contraction and thereby more readily
accommodate installation. Following ins~allation, the insert
is fixedly retained in port 14 by opposed forces particularly
occurring at interface area 32 between the outer side wall o~
.he insert and the receiving bore side wallO It will be
readily appreciated that a plurality of exhaust ports with
associated inserts A are typically involved with any engine
component B in the same manner best described in U. S. Pat. No
Re 29,046.
Continuing with reference to FIGURE 1, induction
heating device A includes a generally cylindrical electrically
insulated body 40 having a somewhat smaller cylindrical
electrically insulated body insert 42 extending coaxially
outward from the inner end thereof. A locating pin or nose 44
extends coaxially outward from body insert 42 to accommodate
locating the induction heating device coa~ially of exhaust port
14 in a known manner~
Interposed between body 40 and body insert 42 of the
induction heating device is a single turn inductor generally
designated 50. This inductor comprises a split circular ring
of copper of generally rectangular cross-section and includes a
pair of spaced legs S2,54 e~tending therefrom axially through
body 4U and outwardly from the body outer endO Inductor 50 as
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well as legs 52,54 are hollow and communicate with each other
in such fashion to define a continuous fluid passageway
therethrough. This passageway accommodates passage of a
suitable coolant from a source (not shown~ disposed adjacent to
or spaced from the overall induction heating device as is known.
A power source 60 is operatively connected by leads
62,64 to conductor 50 as at, for example, legs 52,5~,
respectively. In accordance with the present invention, the
power source comprises an oscillator having an output frequency
capability generally in the range of 200-500 kilohertz (kHz)
and a power capability of generally between 12-25 kilowatts
(kw). In practice, it is preferred to use an oscillator having
an output frequency of approximately 400 kHz to provide a radio
frequency which will create a relatively low reference depth in
the heating pattern caused by flux generated around conductor
50. Also, the preferred power is approximately 20 kw. Since
the heated area of conical surface 30 is about 0.5 square
inches (in ), the power density is in the general range of 40
kw/in2. This is drastically higher than any power density
previously used for heating the valve seats of internal
combustion engines. A time delay device is advantageously
incorporated between leads 62,64 for turning the power source
60 off after a preselected heating time or intervalO In
accordance with the present new method, this heating time is
quite short and is ~ypically less than 1 second.
In practicing the new method, aluminum engine
component B will typically have a plurality of exhaust ports 14
which all have similar inserts 12 which are to be inductively
heated in a simultaneous manner. Apparatus adapted for this
purpose is shown in U. S. Pat. NoO Re 29~046 and includes means
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for causing induction heating device A to be positioned in an
associated exhaust port 14 with locating pin 44 coaxially
aligning the device relative to the exhaust port. Device A is
bottomed out with inductor 50 engaging conical valve seat
surface 30 of seat insert 12. Thereafter~ the heating device
is backed out slightly so that some preselected gap is present
between the inductor and conical valve seat surface 30 to
effect a desired coupling relationship therebetween.
With reference to FIGURE 2, this gap is generally
~esignated by letter ~ and comprises a distance of
approximately 0.040 inches. While this particular gap has been
found particularly suitable in most cases where a ferrous valve
seat insert disposed in an aluminum engine component is to have
a conical valve seat surface hardened, it will be appreciated
that it may be varied somewhat as deemed necessary or
appropriate for a specific application ~f the new method. The
side or flat surface 70 of inductor 50 is generally parallel to
seat surface 30 and has a width at least slightly greater than
that of the seat surface.
As previously noted, it is necessary to prevent
deleterious heating of or heat transfer through the entirety of
insert 12 in the preferred environment here under discussion.
It has been discovered that acceptable heating results could be
obtained if seat surface 30 was quickly brought to temperature
~5 and then quenched prior to the time that any deleterious heat
transfer could occur~ Moreover, it is necessary at the same
time to obtain a suitable depth of heating to assure that the
haxdened seat surface will have sufficiently high wear
characteristics at high operating temperatures. To that end,
it has also been discovered that a depth of generally no
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yreater than 0.035 inches will provide wholly satisEactory
results without in any way impairing engine operation or engine
life. In practice, a depth of approximately 0.024 inches has
been found entirely satisfactory and is preferred when using
the subject new method.
Thus, and in accordance with the invention, a high
powerl low time induction heating metho~ is employed whereby
seat surface 30 of seat insert 12 is sufficiently heated to an
acceptable depth for purposes of transforming the seat material
into the austenitic range for subsequent transformation into
the martensitic range. As shown in FIGURE 2, the depth o~ such
transformation is generally designated by the letter d and may
comprise a depth of up to approximately Q.035 inches, although
0.024 inches is generally preferred. By using the preErred
frequency of approximately 400 kHz, a relatively shallow
reference depth is heated in the seat surface and by using the
preferred power of approximately 20 kw to obtain a power
density of about 40 kw/in2, the valve seat is heated to an
acceptable transformation temperature at a very rapid rate~
Indeed, and when using the prefereed ranges noted, it has been
found that a time interval of approximate~y 0.5 seconds will
provide entirely satis~actory heating and hardening results to
a depth of approximately 0.024 inches.
On completion o the induction heating cycle, the seat
rings or the entire engine component are subjected to quenching
in a manner known in the art. Because heating of seat surfaces
30 is so rapid and is substantially limited to or isolated at
these surfaces to a preselected shallow depthl there is no
deleterious heating of the whole insert or heat transfer
through seat inserts 12. These factors might otherwise
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adversely affect or alter the close fitting relationship
between the seat inserts and exhaust ports. This result
represents a substantial improvement over results obtained from
prior known techniyues in inductively heating valve seats or
valve seat inserts.
Example
In using the foregoing new method, cast iron valve
seat inserts have been successfully hardened to a case depth of
0.030 inches using a hea~ cycle of 0O5 seconds with a radio
frequency oscillator (400 kw) and a power density of 40
kw/in . The advantages of using a soft cast iron insert in
an aluminum cylinder head rather than a prehardened alloy steel
insert resides in the fact that it permits easy machining of
the soft cast insert with subsequent hardening of the valve
seat by induction hardening techniques. This then achieves the
requisite seat durability while, at the same time, yielding
considerable improvement by way of increased productivity.
Valve seat inserts have also been hardened at a 0.2
second heat time with this new me~hod to approximately the case
depth of 0.030 inches by using considerably more than 40
kw/in2 power density. ~ven though it reduces the tendency to
induce heat into the insert, the 0.5 second heating cycle is
considered somewhat more tolerable in that it provides a more
uniform and constant case depth.
By way of comparison, the preferred parameters of the
subject method using a primary power source having a frequency
ot approximately 4~0 k~lz and a power of approximately 20 kw
with a heating cycle of approximately 0.5 seconds provides a
case depth of approximately 0.024 inches and a hardness of "58
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on the Rockwell C scale in cast iron seat inserts. Prior
techniques which typically employ the same frequency at a power
of approximately 7 kw with a heating cycle oE approximately 7-8
seconas provides a case depth of between 0.050-U.060 inches an~
a hardness of "58" on the Rockwell C scale. Such parameters,
while acceptable for gray cast iron engine components having
integral cast iron valve seats simply will not provide suitable
results in the environment of cast aluminum engine components
utilizing ferrous seat ring inserts.
I~he invention has been described with reference to a
preferred embodiment. Obviously, modifications and alterations
will occur to others ~ipon a reading and understanding of the
specification. It is intended to include all such
modifications and alterations insofar as they eome within the
seope of the appended claims or the equivalents thereoE.
