Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
This in~ention generally relates to a method of spec-
ialized induction heat treating and restraint quenching of
structural members whic~ generally are in the shape of a channel
but can be any member having a web and at least one flange. The
objec~ of this specialized heat treatment would be to produce
certain physical properties which are required in the design of
truck side rails, as a means of increasing strength of a given
side rail section such that the payload capability of a truck
is increased with no additional weight penalty in the side r~il
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effecting a more efficient vehicle. Truck side rails are long
structural channel members generally 18 to 40 feet in length,
.250" to .3751' thick. Due to the lean alloy composition of the
low carbon steel specified in this invention, a rapid efective
quench is necessary to obtain the required minimum physical
properties and micros~ructure AS the truck side rail is a
long, thin section member, generally cold formed into its
channel shape from a flat strip, considerahle residual stresses
are present due to the forming operation. During the heating
and rapid quenching of these thin section members, considerable
distortion occurs due io the interaction of the residual stresses
and the severe thermal action of the quench; distortion is evi-
dent in the member as bow, twist, and camber, as well as growth
- experienced along the length of the side rail due to the mater-
ial grain size enlargement as a result of the heat treat opera-
tion.
This invention further relates to a method of induc-
tion heat treating and restraint quenching structural members
such that the total system represents a more economical invest-
ment than do existing conventional methods of restraint quench-
ing, in particular, restraint quenching truck side rails. These -
other ~echniques for restraint quenching truck side rails are
taught in the Kuchera Patents 3,252,695 and 3,294,597 in which
are employed large movable die quench sections constructed with
a vast network of quench fluid passages to simultaneously allow
quench ~luid passage and provide restraint, such that the overall
effect is akin to a large forming press complete with dies, re-
presenting a sizeable investment. The method of restraint taught
in conventional methods must be elaborate as the entire member
is quenched at the same time, setting up significant thermal
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970
gradients along the member length,greatly increasing the pro-
pensity to disto-r~. This invention does not reyuire the large
quench press and its attendant special die sections as rela-
tively short sections of the rail are heated in stages to aus-
tenitizing temperature and t~en immediately restraint quenchedon a continuing basis as the member travels longitudinally
through the system,necessitating only a relatively short re-
straint quench system which,in this invention,employs restraint
rolls similar to those ound in roll forming operations
It is known generally to produce induction heated,
quenched and tempered, hlgh strength steels for tubular products
but not necessarily for structural members, more specifically
channel members. One method of making these is described by
Tom Allan in a paper entitled "Production of High Strength
Quenched and Tempered ERW Tubular Products Utilizing Induction
Heating Equipment," 13th Mechanical Working and Steel Process-
ing Conference, January 20, 1971, Pit~sburgh, Pennsylvania
Generally others have taught various techniques for
rapid heat treating of steel and quenching. Examples of this
are R. A. Grange, "The Rapid Heat Treatment of Steel",
Metallurgical Transactions, Vol. 2, January 1971, p. 65-7~.
More generally, of course, the induction and flame hardening of
metal is known in the Metals Handbook, Vo.. 2, 8th Edition,
"Induction and Flame Hardening", pages 167-202. The particu-
lar type o~ hardening taught in this instance is known as"through hardening," Other developments of bar quenching fix-
tures are taught in patent No 3,738,629. Various inductor
coil designs are taught in patents, such as 3,699,302 and page
171 o the Meta~ Handbook, Vol, 2.
- Su~nary of the Invention
This invention is directed to the selecti.on of a gen-
erally low alloy steel using a special heat treat and restraint
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quench operation to increase the physical properties of the steel
so that it will provide ~avorable strength characteristics for
effective truck frame designs. In general, it i5 contemplated in
~his inven~ion that a typical low alloy steel will have a steel
content of carbon .22 30%, manganese 1.00 to 1.35%, sulfur .05%
max., phosphorus .04% max., and ~his would be expected to have a
full martensitic structure after heat treat. These steels are
generally known as SAE 1025 or SAE 1027 with increased ma~ganese
content. The minimum physical properties after heat treatment
would be the yield strength of 110,000 psi minimum and a ten-
sile strength of 125,000 psi. The hardness of this material
after completing the tempering would be in the range of 269 to
331 Brinell. The method of heat treating would consist of taking
- a formed channel member, though it could be other shapes, such
as a T J an I-Beam or even bars or flats, and rapidly heating
and ~uenching this member by causing it to pass through a series
of preheat steps. In these preheat steps, the member is heated
up to about 400 in the first preheat step and possibly to 950
in the second preheat and then in one or more steps to a final
preheat to austenitizing temperature-about 1450F. to 1750F.
The member is then quenched, in which a large quantity of water
is poured frequently at a rate in excess of ljO00 gallons per
minute onto all faces of the member and this is then cooled to
about 900-to avoid distortion. After quenching, the hardness
of this material will be as much as 440 to 460 Brinell. Immed~
iately preceding and immediately ~ollowing the quench, the mem-
ber is restrained by passing it through restraining rolls that
have a roll on the web, both above and below it, and on the
flange members to restrain the web and ~lange so that they do
not distort. Subsequent to the restraining of the member, it
is then tempered by again inductively tempering the member to a
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temperature in the range of 750 to 1000F. and restraining
the member after heating while cooling to avoid distortion by
passing it t~rough a set of restraint strands.
The invention is particularly direct~d to the method
and it will be characterized by various inductor shapes which
include that of an oval, pancake coil or hairpin coil. Basic-
ally, this apparatus and method ~hen provides for rapid induction
heating of a member, such as a channel member or truck side
rail. It provides a rapid quenching o~ the section of the
workpiece as it travels longitudinally and distortion is mini-
mized by the quenching of a relatively small section at a time
as the member travels longitudinally through the line. This
position of the quench water being such by means of pressure,
flow rates and direction of the water spray so that the distor-
~ion is controlled. During quenching and before distortionsets in, the distortion is controlled by incorporation of roll
stands which are interspersed in the quenching mechanism and
the heating areas if required which, without rerolling the pro-
duct, restrains the movement of the channel. This is done by
having a roll stand effect the web of the channel and by having
side rolls to prevent side distortion. This apparatus and
method then provides flexibility as it can be adapted through
coil design of the inductors, both the preheat and temper induc-
tors, to selectively heat treat a portion of the length of the
2~ wor~piece or only certain areas of the workpiece which are
highly stressed, such as the flanges and the part of the web,
as was taught in McNitt, 3,352,724.
Brief Dg~ 5~l5~l~Ll ~L~ Y~5--
Fig. 1 and l~ are schematic views of the entire
line showing the preheat, the heat sections, quench and temper
sections, as well as the feed roller conveyor and the cooling
-~ table;
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Fig. 2 is a cross-sectional view through the quench
section;
Fig. 3 is a longitudinal cross section through the
quench apparatus;
S Fig. 4 is a cross-sectional view through one form of
the inductor;
Fig. 5 is a side view of said cross section in Fig.
4;
Fig. 6 is a further cross-secti,onal view of the modi-
fication showing an oval inductor;
Fig. 7'is a side view of said inductor of Fig. 6;
Fig. 8 is a top plan view of a pancake inductor on
the web and additional pancake inductors on the flanges;
Fig. 9 is a cross-sectional view o said pancake
inductors of Fig. 8;
Fig. 10 is a top plan view of a pancake inductor in
an L-shape, leaving an open section substantially unheated;
Fig. 11 is a cross-sectional view of said L-shaped
pancake inductors of Fig. 10;
Fig. 12 is a cross-sectional view of the pinc:h and
guide rolls of this invention;
Fig. 13 is a longitudinal view of the rolls of Fig.
12;
Fig. 14 is a view of the restraining rolls that are
used upon quenching of the channel to restrain movement of the
flanges, ~oth inwardly and outwardly,
Fig. 15 is a side vlew of said restraining rolls
shown in Fig. 14.
DescriRtion of the Preferred Embodiments
Figs. 1 and Fig. l(A) are an overalL plan view of
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this pre~eat, quench, temper line for truck side frame rails.
10 shows generally the roller conveyor and l~ading table on which
l~n~ channel shaped members would be fed to the line. These
channel shaped members would be 9-1/8" on ~he outside of the
channel to as much as 12-1/4" on some very large channels. Each
leg of the channel would be 3~' to 47' and would generally be of
stock up to 1/2" and more frequently in the range o .250" to
.312". This would then pass to the conveyor line itself 11,
which is driven by a drive unit 12 Various guide rollers for
the conveyor are shown at 13, 14, 15 and 16. Some of these
truck side rails are as long as 40 feet. These then pass
through a pinch and guide roller shown generally at 17. It
is more particularly seen in Fig. 12. Providing heat for the
first preheat stage which would be an inductor produci.ng power
at possibly 180 cycles to as much as 3,000 cycles and would heat
the channel member up to approximately 400F, This is seen in
the first inductor at 18 and the inductor power supply seen at
l9. We then go to a second stage of pinch and guide rolls, one
of which is shown at 21, and the second i.nductor would be 22
and its power supply would be 23. At this stage the channel would
be heated to approximately 950F. To the final heat stage which
could be one or more stages, we see a pinch and guide roll of
the type shown in Fig. 12 at 24 and an inductor 25 which now may
be o~ higher frequency, possibly 10, 000 cycles and its power
supply is seen at 26. The other pinch and guide roll is seen
at 27 and a further inductor is seen at 28 and its power supply
at 29.
The temperature o the channel has now ~een raised
to about that o the austenitizing temperature 1450 to 1750F.
These now pa s to the 1rst of the restraint and roll stands,
the first one of which is seen at 30 and the cross section of
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which is seen in Figs. 14 and 15. Immediately following this
is the quench section seen generally at 31 wh:Lch will be
described in connec~ion w;th Fig. 2 and a ~urther restr~int and
roll stand 32, the type shown in Fig. 14.
Next follows the temper section in which we have a
restraint and roll stand 34 and the first inductor 35 with its
power supply 36. The inductor for ~he temper section may be
in a series of stages so we have sho~m another restraint roll
stand 37,an inductor 38 in the second stage and its power sup-
ply 39, and a final restraint roll stand 40 This then passes
to the temper quench which may be necessary. Sometimes it is
planned to air cool the channel members but if it is necessary,
then we would ha~e a restraint roll stand 42, a possi~ly li~uid
quench 43 of the type shown in connection with Fig. 2 and a
final mill straightening roll which is shown diagrammatically
at 44, the type shown in Fig 14 There might be as many as
three straighteners at this point. Finally~ the channel mem-
ber passes to the last conveyor table 45 and is pushed aside
to the cooling table 46. In connection with the specific fea-
tures of the inventionJ the quench section is probably the
most critical.
Specifically, Fig. 2 shows the quench which is shown
in connection with Fig. 1. We would have a multiplicity of water
supplie~ which the upper one would be shown at 51 and a pair
of lower supplies at 52 and 53 would generally be a housing
member of rectangular cross section at 54 and inside this would
be a perforated member shown generally at 55, ha~ing apertures
approximatel-y 1/8" in diameter that are angle~ toward the
direc~ion of movement and that impinge on all surfaces. They
are seen, for example, impinging on the right flange as seen
at 56 and the left flange as seen at 57, besides the web which
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would be seen at 58. Additionally, the inside flanges opp~site
these flanges would be covered by ~he lower section of the quench
shown generally at 59. Over 1 J 000 gallons per minute would pass
onto the channel mcmber so that it would be evenly quenched in
a very few secon~s. The spacing and size of the apertures shown
generally at 55 and S9 will vary such ~hat the amount of quench
water inpinging on a given area of the channel will tend to con-
trol the distortion developing from ~he quench process. Also,
the amount of incoming water supplies at 51, 52, and 53 can be
varied during operation to further e~fect distortion control by
directing ~ore or less quench liquid to either outside or inside
of web, channel right or left sides to control distortion such as
bow and camber. The object is to get the temperature of the
channel down to below 900F. and minimize distortion in the
restraint roll stands that follow. Generally the web would be
up and the flanges depending.
Fig. 3 shows the cross section along the line 3-3
of Fig. 2 and shows the housing me~ber 54 and the inner housing
55 having apertures, one of which is shown at 61 therein and
these are proejcted at about a 30 angle to the channel mem~er
so that the water is carried away along the direction of movement
of the channel. The web of the channel itself is shown at 58.
Fig. 4 shows a typical type of loop inductor that
has connections coming in at 65 and a single loop having a
first member 66 extending across the channel, a connecting link
67 and a return loop 68. This would induce curr~nts i.nt~ the
channel mem~er shown generally at 69 and heated up to the appro-
~priate temperature. A varient ~orm of inductor is shown in
Fig. 6 and the dlfference here ls that lt i~ an oval inductor
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having a pair of input connections as seen at 70 and 71 and
multipllcity of loops which are shown gen~rally at 72. It can
be seen that these are in close proximity to the channel member
73 and in this case the channel differs in that it might be
bowed outwardly as seen a~ 74 because certairL truck side rails
have to be bowed over a confined area ~o permit mounting of
certain components, such as an engine and the like, and adequate
clearance is provided on the side so that varying shapes of
channel members may be fitted through the line. The proximity
of the coil to the channel member will be determined by the
amount of bow out in the member and the attainment of a uni~orm
heating pattern in the mem~er. Fig. 7 shows a side view of
this multi-turn oval coil that would be used in connection
with this invention. Fig. 8 is a pancake coil having in con-
nection with this view, as seen at 76, a single loop in theshape of a pancake, possibly rectangular in shape though, cov-
ering the web of the channel. Another loop is seen at 77 which
would cover one flange and a further loop at 78 which would
cover the other flange. The main object of all three of these
~oil assemblles is to produce even heating without excessively
raising ~he temperature of the channel m~mber in any portion
of the channel so that the austenitizing temperature can be
reached as exactingly as possible without damaging the metal-
lurgical structure of the steel. Figs. 10 and 11 show an
L-shaped pancake coil. In this instance the let pancake coil
80 is L-shaped and surrounds both the web and the flange. The
right pancake coil 81 surrounds both the web and the f1ange,
leaving a gap of many inches between the coils because this will
be a portion o~ the charmel which on end will have the neutral
axis passing 'Lhrough it and the 9 tresses will be of lower order
of magnitude. The reasons for this structure are sho~m in
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McNitt patent No. 3,352,724 Now as to the various pinch and
guide rolls, Fig. 12 shows a view of these. ~0 shows th~ top
pinch roll moving and 91 diagrammatically shows the axis of
such pinch roll. The channel member itself is shown at 92
having flanges 93 and 94. Guiding the flanges would be web
idlers shown at 95 on the right, 96 on the left. ~he lower
pinch roll is shown at 99 about its center 100 and it would
adapt to pinch the channel member 92 between the upper pinch
roll 90 and the lower pinch roll 99.
Fig. 14 shows a view of the restraint rolls. The
upper restraint roll yenerally shown at 105 has a flange
member 106 with a series of spacers between the roll 105 and
the flange 106, one of which is shown at 107. This adapts it
to webs of any width, as well as allowing adjustment to suit
the growth of a "hot" section as would be the case at stand 30
compared to a "cold" or quenched section as would be the case
at stand 32 to further effect distortion control, and has a
flange portion 108 which restrains the lateral movement of the
flange shown generally at 109. The web of the channel is shown
at 110. The lower roll is shown generally at 111, having a
center portion 112 and variable sized right and left-hand roller
portions 113 and 114. This equips the roll to fit various size
channels and it will be seen that in movement of the rolls, the
channel will be restrained both on its web 110 and on its flange
as at~109, so that it cannot buckle or distort. This was described
in connection with the schematic diagram of the induction heat-
ing, quench and tempering line, A~ter the channel member becomes
hot, it would generally be restrained in order to keep the flanges
and the web straight. During the initial section it would be
guided through the inductorg until it reached a temperature at
which the residual stresses would be relaxed such that the
section could warp.
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Generally, in connection with this invention, the
preheating takes place in a number o~ steps and the inductors
would be desi~ned with the frequency tha~ wauld produce the
grea~est heat efficiency~ Most probably the lower temperature
preheat coils would be about 180 cycles ar m~ltiples thereof
up to a ~aximum of 3,000 cycles. In the final preheat stage,
probably a 10,000 cycle coil would be used to heat the member
to austenitizing temperature~ ~n one design we intend to
revert to 180 cycles for tne final heat, although a range of
180 to 3,000 cycles could be employed. In the temper induc-
tors, the frequency might be 180 to as much as 3,000 cycles to
reheat the channel up to 750 to 1000F. to temper ~he channel
member. It is generally recognized that the frequency selected
in the preheat, austenitizing and temper will depend upon the
size of structural section processed to achieve optimum heat
efficiency. It is the intent of this invention to utilize
dual frequencies in the preheat, austenitizin~ and tempering
phases as determined necessary to obtain that optimum heating
efficiency for the required production rates.
One of the particular problems in connection with
heat treating, quenching and tempering channel members is that
they both bow and twist and besides there will be camber.
These are conditions that generally exist in the metal in the
cold state as received from the steel mill which mani~est them-
selves as residual stresses in the formed part, plus additional
- residual stresses added as a result of the cold forming of the
member, which are relaxed in the thermal cycle of the heat treat-
ment process such that distortion occurs; in effect, the steel
has a "memory" and it will tend to revert to its relaxed con-
dition.
It is a further ob;ect of this invention that adjust--
me~ts must be made to a truck side rail which has portions of
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the flange removed at points of lower stress. Thls is, of course,
in keeping with typical truck side rails as cutouts are also
required to provide clearance for certain components such as the
engine. It is planned that in heating these truck side rails
by induction heating, in order to avoid localized overheating in
the lesser sections of the member where the flange has been
removed J means can be provided such that the amoun~ of current
passing through any section of the channel shall be proportional
to the cross section o the member in said section. This means
that the inductors would have to be prograrnmed to change along
the length of the product as it was going through the line. It
is further contemplated thatJ in general,the rapid movement of the
structural member with respect to the induction preheating and
austenitizing limits the overheating that might take place in
connection with the induction heating and tempering stages.
Having thus broadly explained the concepts of my in-
vention, what I wish to claim is appended as follows but I do
not mean my invention to be limited anything more than by the
claims o~ this case.
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