U.S. patent number 3,610,861 [Application Number 05/091,119] was granted by the patent office on 1971-10-05 for induction heating of elongated bars.
This patent grant is currently assigned to Ajax Magnethermic Corporation. Invention is credited to Andrew J. Kocjan, Robert M. Storey.
United States Patent |
3,610,861 |
Storey , et al. |
October 5, 1971 |
INDUCTION HEATING OF ELONGATED BARS
Abstract
There is disclosed herein a method and means for heating a
semicontinuous line of elongated bars passing through a relatively
shorter induction coil whereby the ends of the bars will be heated
to substantially the same temperature as the midportions thereof. A
signal from the generator current is directed to a regulating
device which maintains the generator current at predetermined
values during periods when the lead end portion of a bar is
entering or the trailing-end portion of a bar is leaving the coil
and during passage of the bar through the coil, the heating of the
bar being controlled by voltage regulation when the midportion of a
bar is passing through the coil.
Inventors: |
Storey; Robert M. (Warren,
OH), Kocjan; Andrew J. (Niles, OH) |
Assignee: |
Ajax Magnethermic Corporation
(Warren, OH)
|
Family
ID: |
22226187 |
Appl.
No.: |
05/091,119 |
Filed: |
November 19, 1970 |
Current U.S.
Class: |
219/637; 219/650;
219/665; 219/654 |
Current CPC
Class: |
H05B
6/104 (20130101); H05B 6/06 (20130101) |
Current International
Class: |
H05B
6/06 (20060101); H05b 005/00 (); H05b 001/02 () |
Field of
Search: |
;219/10.77,10.41 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhe; J. V.
Assistant Examiner: Bender; L. H.
Claims
We claim:
1. Induction-heating means for uniformly inductively heating an
elongated workpiece, said induction-heating means comprising an
inductor coil of substantially shorter axial dimension than the
workpiece to be heated; a source of electrical power for said coil
including a generator; means for moving the elongated workpiece
endwise through said coil generally along the axis of said coil;
means for causing the voltage in the coil to rise proportionally as
the leading-end portion of each workpiece enters said coil; means
for maintaining the voltage at a predetermined level and the
generator current at a constant value substantially during the time
the coil is full; and means for causing the voltage to drop off
proportionally as the trailing end portion of the workpiece
approaches the exit end of the coil whereby the generator current
is maintained at predetermined values when any portion of the
workpiece is contained within said inductor coil and the workpiece
is substantially uniformly heated through the length thereof.
2. Induction-heating means for uniformly inductively heating an
elongated bar, said induction-heating means comprising an inductor
coil of substantially shorter axial dimension than the bar to be
heated; a source of electrical power for said coil including a
generator; means for moving the elongated bar endwise through said
coil generally along the axis of said coil; means for maintaining
the generator current constant at a predetermined value when the
leading-end portion of the bar is entering and filling the coil;
means for maintaining the voltage at a predetermined level and the
generator current at a constant value substantially during the time
the coil is full; and means for maintaining the generator current
constant at a predetermined value when the trailing end portion of
the bar is being withdrawn from the coil, whereby the bar is
substantially uniformly heated throughout the length thereof.
3. Induction-heating means for uniformly heating an elongated bar
comprising an inductor coil of substantially shorter axial
dimension than the bar; a source of electrical power for said coil
including a generator; means for moving the elongated bar endwise
through said coil generally along the axis of said coil; control
means for regulating the current and voltage to said coil; trip
means located adjacent to the entrance end of said coil and tripped
by the bar as it enters and progressively fills said coil; said
control means responsive to said trip means to maintain the
generator current constant at a predetermined value substantially
during the time the bar is progressively filling said coil; said
control means responsive to said trip means to maintain a
predetermined voltage to said coil during the time said coil is
full and until the trailing-end portion of the bar progressively
leaves the coil; said control means responsive to the bar moving
away from said trip means to maintain the generator current at a
constant predetermined value substantially during the time when the
bar is being progressively withdrawn from said coil, whereby the
bar is substantially uniformly heated throughout the length
thereof.
4. Induction-heating means for uniformly heating an elongated bar
as set forth in claim 3: said induction-heating means adapted to
automatically successively heat a semicontinuous line of spaced,
elongated bars, said trip means comprising a switch actuated by the
leading end of each bar and released as the trailing end of each
bar rides off of said switch as substantially the time said
trailing end enters said coil; said control means including a first
timer initiating control of the generator current during the time
the bar is progressively filling said coil and a second timer
initiating control of the generator current during the time the bar
is being progressively withdrawn from said coil.
5. Induction-heating means for uniformly heating an elongated bar
as set forth in claim 3: said source of electrical power for said
coil including a high-frequency transformer; said generator
connected to the primary of said transformer and said inductor coil
connected to the secondary of said transformer; capacitors
connected in parallel with said inductor coil; said means for
maintaining the generator current constant at a predetermined value
being responsive to sensing means located between said generator
and said transformer.
6. The method of heating elongated workpieces in an inducted coil
of substantially shorter length than the workpiece, the method
comprising energizing the coil by means including a generator,
passing the workpieces endwise through the coil in a semicontinuous
line with the workpieces spaced apart a sufficient distance whereby
the coil will be at least momentarily empty between workpieces,
causing the voltage in the coil to rise proportionally as the
leading end portion of each workpiece enters the coil; maintaining
the voltage at a predetermined level and the generator current at a
constant value substantially during the time the coil is full; and
causing the voltage to drop off proportionally as the trailing-end
portion of each workpiece approaches the exit end of the coil
whereby the generator current is maintained at predetermined values
during passage of the workpieces through the coil and each
workpiece is substantially uniformly heated throughout the length
thereof.
7. The method of heating elongated bars in an inductor coil of
substantially shorter length than the bars, the method comprising
energizing the coil by means including a generator, passing the
bars endwise through the coil in a semicontinuous line with the
bars spaced apart a sufficient distance whereby the coil will be at
least momentarily empty between bars, maintaining the generator
current constant at a predetermined value sufficient to heat the
leading-end portion of each bar to the desired temperature whereby
the voltage will rise proportionally as the bar fills the coil,
maintaining the voltage at a predetermined level sufficient to heat
the midportion of the bar to the desired temperature while the coil
remains full, and maintaining the generator current constant at a
predetermined value sufficient to heat the trailing-end portion of
the bar to the desired temperature whereby the voltage will drop
off proportionally as the bar is withdrawn from the coil and
whereby the bar is substantially uniformly heated throughout the
length thereof.
8. Induction-heating means for uniformly inductively heating an
elongated workpiece, said induction-heating means comprising an
inductor coil of substantially shorter axial dimension than the
workpiece to be heated; a source of electrical power for said coil
including a generator; means for moving the elongated workpiece
endwise through said coil parallel with the axis of said coil,
there being a first period when said workpiece is filling said
coil, a second period during which said coil is full, and a third
period when the trailing end portion of the workpiece is leaving
said coil; means for maintaining the voltage in said coil at a
predetermined level and for maintaining the generator current at a
constant value during said second period when said coil is full;
and means for maintaining said generator current at predetermined
values during said first and third periods whereby the voltage
rises and falls proportionally as the workpiece enters and leaves
the coil to substantially uniformly heat the workpiece throughout
the length thereof.
9. The method of uniformly heating an elongated workpiece in an
inductor coil of substantially shorter length than the workpiece,
the method comprising providing a source of electrical power for
energizing the coil including a generator; moving the workpiece
endwise through the coil at a uniform speed whereby there is a
first period when said workpiece is filling said coil, a second
period during which said coil is full, and a third period when the
trailing-end portion of the workpiece is leaving said coil;
maintaining the voltage in said coil at a predetermined level and
maintaining the generator current at a constant value during said
second period when the coil is full; and maintaining said generator
current at predetermined values during said first and third periods
whereby the voltage rises and falls proportionally as the workpiece
enters and leaves the coil to substantially uniformly heat the
workpiece throughout the length thereof.
Description
This invention relates to the induction heating of elongated
workpieces such as bars which are moved endwise through an
induction heater coil of shorter axial dimension than the bars and
wherein the line of bars is semicontinuous; that is, the bars are
not positioned end to end, but each bar is spaced from both the
preceding and succeeding bars.
The conventional means for controlling the voltage to the induction
coil is by means of a voltage regulator. In the case of
semicontinuous induction heating, the coil is energized when partly
loaded as the bar enters and also under similar conditions as the
bar leaves the coil. This makes it difficult to keep the ends of
the bar at the same temperature as the middle portions, the
tendency being to overheat the ends which only partly fill the coil
as the bar enters or leaves the coil. Also, with certain
workpieces, not necessarily bars of uniform cross section
throughout, there may be a tendency to overheat the ends. The basic
problem which the present invention solves is the lack of
uniformity of temperature at the ends of the bars or workpieces
heated in this manner due to the changing affect on the load when
the coil is only partially filled. These problems of nonuniformity
occur both at the leading and trailing ends of the bars.
In the heating of each bar, there are three distinct periods
presenting distinctly different heating conditions, the problem of
each period being different from the other two. The first period is
when the bar is first entering and progressively filling the coil
at which time the bar is at ambient or some other, preheated
temperature. The second period is from the time that the coil is
filled with the bar until the trailing end of the bar begins to
enter the coil. The final period of heating is during the time when
the trailing end portion of the bar is leaving the coil. At this
point a substantial amount of the bar has been heated and the
heating of the trailing end portion thereof as it progressively
leaves the coil will normally call for a different control than
that covering the leading end thereof.
The present invention as herein disclosed and illustrated provides
means for sensing or detecting the ends of the bar and switching to
appropriate current regulation for a timed period during the first
and last periods when end portions of the bar are either entering
or leaving the coil. A signal directly from the generator current
is directed to a regulating device which acts on the field of the
generator and maintains the generator current at a predetermined
value or values during passage of the bar through the coil. Under
these circumstances, the voltage will rise and fall as the coil is
being either filled or emptied of the bar, in proportion to the
amount of bar in the coil, thereby controlling the amount of
voltage applied to the bar.
In view of the foregoing, it is the primary object of this
invention to provide an improved means and method for uniformly
heating an elongated bar or workpiece in a coil of relatively
smaller axial dimension than said bar.
Another object of the invention is to provide means for effectively
heating the ends of the bar as they enter or leave the coil to
provide power to the coil in proportion to the amount of bar
disposed in the coil at a given time.
Still another object of the invention is to provide means for
automatically switching between voltage regulation and current
regulation as the bar assumes different positions with respect to
the coil.
Yet another object of the invention is to provide an elongated
bar-heating means wherein the ends of the bar are heated under
conditions of current regulation whereas the midportions of the
bars are heated by voltage regulation.
A still further object of the invention is to provide an automatic
control means for automatically heating successive elongated bars
disposed in a semicontinuous line; that is, with the bars being
spaced from each other whereby there is a period between the
heating of each successive bar when the coil is empty.
Other objects and advantages of this invention will be readily
apparent from the following detailed description of the invention
and the accompanying drawings, in which said drawings:
FIG. 1 is a simplified drawing of an elongated bar at the moment of
entering into an induction-heating coil, the bar being shown
partially disposed within the coil in broken lines;
FIG. 2 is similar to FIG. 1 and shows the bar in a second position
wherein the coil is entirely filled;
FIG. 3 shows a third position of the bar wherein the trailing end
of the bar has just reached the entrance to the coil;
FIG. 4 shows a fourth position of the bar wherein the trailing end
of the bar has just left the exit end of the coil, the trailing end
being shown partially disposed within the coil in broken lines;
FIG. 5 is a diagram indicating the manner in which the voltage
rises, is maintained, and falls as a bar passes through the coil;
and
FIG. 6 is a simplified electrical diagram showing an automatic
control system for heating successive bars in a semicontinuous
production line.
Referring now to the drawings in all of which like parts are
designated by like reference numerals, the simplified drawings of
FIGS. 1-4 show an induction coil 10 adapted to receive and heat an
elongated bar 11. The bar 11 represents one workpiece in a
semicontinuous line of spaced workpieces adapted to move axially or
in the direction of the arrow 12 along a powered conveyor 13
through the coil 10. It will be noted that each bar 11 is
substantially longer than the coil 10 in the axial direction
whereby it is impossible for the said coil to heat the entire bar
at one time. Assuming that the bar 11 is moving in the direction of
the arrow 12 at a constant rate, it will be readily understood that
there will be a period between the position shown in FIG. 1 and
that shown in FIG. 2 when the coil 10 is only partially filled, as
shown in dotted lines in FIG. 1, with the leading end portion of
the bar as the bar moves into said coil. It will be further readily
seen that between the position of FIG. 2 and that shown in FIG. 3,
the coil 10 will be completely filled with the bar 11 whereas
between the positions shown in FIG. 3 and FIG. 4, the trailing end
portion will be progressively leaving the coil thereby
progressively reducing the amount of bar being heated, as shown by
dotted lines in FIG. 4. Thus there are three separate conditions
under which the coil must heat the bar: the entering condition, as
shown by the dotted lines in FIG. 1, between the full-line
positions shown in FIGS. 1 and 2, the full condition between the
positions shown in FIGS. 2 and 3, and the emptying condition when
the bar is, as indicated by the dotted lines in FIG. 4, between the
positions shown in FIGS. 3 and 4.
FIGS. 1-4 also show in diagrammatic form a double-pole switch LS
which will be understood to be the same switch LS as that shown in
the electrical diagram of FIG. 6. The switch LS is disposed just
outside the entrance end of the coil 10 and is tripped at the first
position when the bar 11 is about to enter the coil 10, is held in
the tripped condition through the second position shown in FIG. 2,
and automatically reopens or returns to its normal position when
the bar reaches substantially the third position shown in FIG.
3.
FIG. 6 is a simplified electrical diagram indicating the manner in
which current and voltage are controlled to control the heating
pattern applied to the bar 11 whereby the same will be heated
uniformly throughout. All of the relay contacts of the control
circuitry shown at the left-hand side of the electrical diagram are
shown in their normal condition to which they automatically return
when their respective relays are deenergized, and it will be
understood that energization of the corresponding relays causes the
contacts they control to assume the opposite position. It will be
further understood that the timer contacts may be actuated a timed
period after energization of the timer relays to provide optimum
positioning of the bar within the coil before current regulation is
begun. Because the present electrical diagram has been simplified,
each relay referred to may, in fact, represent plural, interrelated
relays or other known electrical control and switching means. Also,
many safety interlocks and controls not specifically related to the
switching in and out of control means have been eliminated.
In FIG. 6, L1, L2, and L3 represent the main leads to a three-phase
supply, the same being connected to a motor M connected to a
generator G. A control transformer 15 is connected across the leads
L1 and L3 and provides a control circuit to lines 16 and 17.
Current from the generator G is directed through lines 18 and 19 to
the primary of a high-frequency transformer 20, the secondary of
which is directed through lines 21 and 22 to the inductor 10.
Capacitors 23 in lines 24 are connected in parallel with the
inductor 10 and may be controlled by switches 25. A voltage
regulator and voltage and current adjustment control device 26 is
adapted to receive a signal from the generator current by means of
a coil 27 encircling the line 18 leading from said generator. The
control device 26 is also connected to the secondary of a
voltage-regulating transformer 28, connected across the lines 18
and 19.
In operation of the control means for controlling the heating of
bar 11, a main switch 30 in the leads L1 and L3 is closed to direct
current to the main control lines 16 and 17. A manual start switch
31 is then closed to energize a starter relay S across line 32. The
relay S represents motor energizing and sustaining means whereby
the motor M and generator G are started up to supply current to the
inductor 10. The relay S closes holding contacts S-1 in bypass line
33 around the start switch 31 to maintain the current to said
relay. A normally closed stop switch 34 is also disposed in the
line 32 which upon opening will deenergize the relay S which will
immediately be isolated by opening of the contacts S-1 to stop the
motor and generator.
The inductor 10 is energized for heating the bars 11 by a suitable
heat relay H disposed in a line 35 connected across the control
lines 16 and 17. The line 35 is provided with a normally open start
switch 36 and a normally closed stop switch 37, hold-in contacts
H-1 being provided in a bypass line 38 around the start switch 36.
A pair of normally open contacts TEC-2 are also interposed in the
line 35 and would be closed at the time the start switch 36 is
actuated as will hereinafter be fully explained.
As shown in FIGS. 1-4, each moving bar 11 in the semicontinuous
line of bars will, in turn, strike the double-pole switch LS. The
switch LS is connected to the control line 16 at the line 39 and
has two sets of contacts: normally open contacts LS-1 in a line 40
controlling a leading-end timer relay LET, and normally closed
contacts LS-2 in a line 41 controlling a trailing-end timer relay
TET. Thus, prior to any bar 11 entering the inductor coil 10, the
contacts LS-1 will be open and the contacts LS-2 will be closed.
Therefore, whenever current is supplied to the control lines 16 and
17 by closing the main switch 30, the trailing end timer relay TET
will normally be energized. Energization of relay TET closes
normally open contacts TET-1 in a line 42 disposed across the
control lines 16 and 17 and having a trailing-end current
regulation relay TEC interposed therein. Energization of the relay
TEC, in turn, closes normally open contacts TEC-2 in line 35
previously referred to whereby the start switch 36 can be closed to
energize the relay H which will close the hold-in contacts H-1 as
hereabove described. Energization of the trailing end current
regulation relay TEC also opens normally closed contacts TEC-1 in a
line 43 connected across the control lines and having a
voltage-regulating relay VR interposed therein. The relay VR is
adapted to control the voltage at a constant level during the time
when the bar 11 fill the coil 10 as when said bar is moved from the
position shown in FIG. 2 to substantially the position shown in
FIG. 3. The leading end timer relay LET in line 40 controls a pair
of normally open contacts LET-1 disposed in a line 44 connected
across the control lines 16 and 17 and having a leading end current
regulation relay LEC interposed therein. Because the contacts LS-1
of the double-pole switch LS are initially open, the leading-end or
first timer relay LET will be initially deenergized whereby the
contacts LET-1 will be open and the leading-end current relay LEC
will be isolated. The voltage control relay VR is also isolated by
the now open contacts TEC-1 whereby the empty coil is controlled by
the trailing-end current relay TEC only.
When a moving bar 11 strikes the switch LS, normally open contacts
LS-1 are closed to energize the relay LET of the first timer and
the normally closed contacts LS-2 are opened to isolate and
deenergize the trailing-end or second timer relay TET. The relay
LET closes its normally open contacts LET-1 in line 44 thereby
energizing the leading end current relay LEC. The contacts TET-1 in
line 42 now open to isolate the trailing-end current relay TEC
whereby the contacts TEC-1 in line 43 return to their closed
position. However, the voltage-regulating relay VR is maintained in
the isolated condition because the line 43 also has disposed
therein a pair of normally closed contacts LEC-1 which open
immediately upon energization of the leading end current relay LEC.
At this point, a signal from the generator current is directed to
the control device 26 which now acts on the field of the generator
to maintain the generator current at a predetermined value for
optimum heating of the leading-end portion of the bar as it enters
the inductor coil 10.
When the first timer times out, the leading-end timer relay LET is
automatically deenergized thereby isolating the leading-end current
relay LEC by allowing the normally open contacts LET-1 to open. At
the same time, the normally closed contacts LEC-1 are allowed to
close thereby completing a circuit across the line 43 to energize
the voltage-regulating relay VR. At this time, the control device
26 takes a signal from the secondary of the voltage-regulating
transformer 28, compares it to a constant reference voltage, and
then acts on the field of the generator to maintain the voltage
constant at a predetermined level. The control device 26 also picks
up a signal from the generator current through the coil 27 and
holds the current at a constant predetermined value whereby there
is both voltage and current regulation during the time when the
inductor coil 10 is being filled with a bar 11.
When the trailing end of each bar 11 approaches the entrance end of
the coil 10, said bar rides off the double-pole switch LS whereby
contacts LS-1 return to the open position and contacts LS-2 return
to the closed position as illustrated in FIG. 6. The second timer
relay TET is then energized and after a short time delay which
allows the trailing end of the bar to reach the entrance to the
coil 10, the contacts TET-1 in line 42 close to energize the
trailing-end current regulation relay TEC. It will be readily seen
that at this time, relays LET, LEC, and VR are isolated, the
last-mentioned relay being isolated by the opening of normally
closed relay contacts TEC-1. The control device 26 again picks up a
signal directly from the generator current through the coil 27 and
acts on the field of the generator to maintain the generator
current at a predetermined value as the trailing-end portion of the
bar is withdrawn from the inductor coil 10. The next succeeding bar
11 will again actuate the double-pole switch LS and repeat the
heating cycle for the next bar.
During heating of the leading and trailing ends of the bars, the
generator current may be held at a predetermined constant value or
it may be caused to vary or swing through an arc of predetermined
values whereby the optimum heating conditions are obtained for the
particular bar or workpiece to be heated. Such optimum conditions
of constant or predetermined varied values would be obtained by
experimentation with any given bar or workpiece. As hereinabove
described, the remainder of the time when the coil is full as the
bar passes therethrough, both current and voltage are maintained at
a constant value.
As a substitute for the control device 26 and its circuitry, a
programmed numerical computer can be used to control the
temperature regulation and resultant temperature of the bars, and
it will be readily appreciated that this will eliminate need for
timing mechanism, the current regulation being dependent upon
distance rather than timing.
FIG. 5 represents diagrammatically the voltage level throughout the
heating of a single bar 11. The vertical axis E represents the
voltage level and the horizontal axis represents the time elapsed
and the distance covered by the traveling bar. The numerals 1, 2,
3, and 4 of the horizontal axis correspond to the positions 1, 2,
3, and 4 shown in full lines in the FIGS. 1, 2, 3, and 4,
respectively. It will be seen that during the time interval between
positions 1 and 2 during which the generator current is maintained
at predetermined values, the voltage swings upwardly with a greater
amount of bar entering the inductor coil. Between positions 2 and 3
when voltage regulation is being used, the voltage is maintained
constant at a desired level and the generator current is maintained
at a constant value. Between positions 3 and 4 a return to control
of the generator current is made at which point the voltage drops
off or swings downwardly as the bar leaves the inductor coil. It
will be noted that the voltage patterns in the areas designated by
positions 1 and 2 and positions 3 and 4 vary and that, therefore,
the leading end portion and the trailing-end portion are preferably
separately controlled to attain the desired uniform heating
pattern. It will be further understood that the voltage patterns in
the areas designated as positions 1 and 2 and positions 3 and 4 can
be varied from that shown to provide optimum heating patterns for
workpieces of different shapes.
Thus the present invention provides effective means for eliminating
the nonuniformity in the heating of bars of the type and in the
manner herein disclosed. It enables the user to take advantage of
the built-in protection of conventional voltage regulation
throughout the midportion of the bar while at the same time
eliminating the danger of overheating or underheating the ends
thereof.
It will be understood that many changes in the details of the
invention as herein described and illustrated may be made without,
however, departing from the spirit thereof or the scope of the
appended claims.
* * * * *