Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3~3~Z
Backqround of the I~vention
Steel ligatures, in the form of wire or strap, are
widely used in induskry and transportion as ties or bands about
packages and bundles. In such ligatures it is desirable to
have substantial tensile strength comblned with good elongation
properties and bend characteristics. It is also desirable for
use in some environments that the ligature have substantial
resistance to corrosion and to discoloration under corrosion
conditions. For steel strap intended for binding bricks, lumber
or tiles, for example, it is desirahle to combine high tensile
streng~h with resistance to corrosion and discoloration.
One method of improving the physical properties of
steel ligatures that has been used with success is a method in
which the ligature i~ advancecl lengthwise through a first and
second lead bath, the baths being at an electrical potential
wi~h respect to each other so that an electric curxent passes
through the travelling ligature~ The electric current heats
the ligature and the second lead bath quenches the hot ligature
to provide desired temper and thereby enhance its physical
properties.
Corrosion resistance is commonly provided to steel
ligatures by coating the ligatures with a layer of a protective
material. Metallic zinc is a preferred protective layer, pro-
tecting the steel by providing a mechanical seal and by its
galvanic action. Zinc may be coated onto a steel ligature either
by hot-dipping which involves passing the ligature through a
bath of molten zinc or by electrodeposition which involve
passing the ligature through an aqueous solution of a einc salt
through which solution a direct current is passed between a
zinc strip serving as anode and the ligature serving ~s cakhode.
37322
The establishment of a zinc coating by electrode-
position is relatively expensive b~cause it r~quixe~ a high
degree of cleanliness in the ligature to be coated and because
the electrodeposition process is relatively slow and does not
permit high speed operation with short residence time in the
electrodeposition bath.
The establishment of a zinc coa~ing by hot dipping
through a molten zinc bath also requires generally a high
degree of cleanliness and also requires high temperatures which
may affect adversely the physical properties of the ligature.
A ligature which has been t~mpered by electrical resistance
heating followed by a lead bath quench may lose some of the
desirable properties imparted by the tempering process when it
is reheated for the h~t dip zinc coating.
In accordance with one aspect of the instant invention
a method is provided for simultaneously heat treating and ~-
galvanizing a steel ligature in which method the ligature is
continuously advanced into contact with an electrical conductor
and thereafter into and through a bath of molten zinc which an
electric current passes through said ligature between said
electrical conductor and said bath.
As the ligature passes through the molten zinc bath
it is wetted by the zinc and, after wiping off any excess
adherent liquid zinc, the remainder, after cool.ing, forms a
smoothl adherent zinc coating on the ligature which serves as
excellent protection against corrosion. It has been found tha~
excellent coatings are obtained in the method of this invention
even when the ligature has not been given a thorough cleaning
or has a surface having a normal residue of rolling mill oil.
It has been found that the physical properties of the
. -, .
~ 373;~:Z
ligature of thi~ invention are superior, particularly wi~h
respect to elongation and bend propertie3, when compared to
liga~ures of the same steel which are tempered by electrical
heating followed by qu~nching in a lead bath. While it i~ not
desired to be bound by any particular theory, it i8 believ~d
that the zinc bath quench is a more rapid quench than a quench
in a lead bath because molten zinc wets the ligature passing
through it and thus provides better heat transfer than molten
lead which does not wet the steel ligature. In addition,
molten zinc is a better heat conductor than molt~n lead, and
in a high speed proce s its superior heat conduction properties
rapidly dissipate the heat in the vicinity of the ligature
path and prevent the accumulation of heat in the immediate
quench zone.
In addition to their superior elongation and bend
properties, the ligatures of the instant invention are charac-
terized by their metallographical configuration and particularly
by a lesser amount of pearlite than in ligatures made of the
same steel but quenched in a lead bath.
In accordance with a preferred aspect of this inve~-
tion the ligature in passing through the zinc bath is subjected
to a rubbing action at its surface at a point within the bath
which is a substantial distance from its exit and. It has
been found that such a rubbing action aids in the consistent
production of a uniform zinc coating despite impurities at the
surface of the ligature.
The invention is best understood by reference to
the drawings in which
FIGURE 1 is a schematic elevation illustrating an
embodiment of the invention; and
. - . ,
~037,;~
FIGURE 2 i8 a schematic elevation of the contact
pot illustrating a preferred embodimenl: of the path of the strap
therewithin.
A8 shown in FIGURE 1, !3trap 11 is contlnuou~ly payed
~ out from feed roll 12 mounted on support 13 which ~8 grounded.
-- ` The ~trap passes through a voltage cancellation device, xhown
~chematically as 14. Suitable voltage cancellation devices
are described in U.S. Patent No. 3,2~7,270, issued to O~car
C. Trautman on October 4, 1966.
me strap then pa~ses over roll 16, energized by
contact 17, then passes downwardly into housing struc~ure 18 and
thence into contact pot 19 containing molten zinc ~1. Within
the contact pot the strap passes over rolls 22 and 23 before
passing out of the molten zinc and over roll 24 and thence to
rewind roll 26. Excess molten zinc is wiped of f the strap a~
it emerges from the zinc bath by wiping devices 27 mounted
at the exit o~ the contact po~
Conduction roll 16 and contact pot 19 are maintained
at an electromotive potential with respect to each other by
the;current generated in winding 27 of transformer 28, the
opposite winding 29 being at~ached to a power source indioated
schematically a~ element 31.
The voltage maintained between conduction roll 16 and
contact pot lg results in a passage of current between them
through strap 11 and specifically through the portion of ~trap
:~-- . 11 moving from the former to the latter and the re ults in the
~ - .
~. resistance heating of that portion of the strap to reach a
.. ,~. :, ....
. ~'. heat txeating temperature in the range of about 1000 ~ to
about 1800F~ ju~t before entering the ~ontact po~.
The s~rap entering the molten zinc in .he contact
~' '': , , ' ` .', ', .' ,
:: ~ , . : : , . .. .
~0373ZZ
pot is rapidly quenched to the temperature of the molten
zinc therein, generally in the range about 825 to about ~25F.
This temperature range is higher than the temperature range used
when molten lead is u~ed as the quench medium; and quenching at
this higher temperature provides improved properties ln the
steel substrate. On the other hand, the differential between
the temperature of the quench bath and the temperature of
the strap entering the quench bath is substantially greater
than is the differential maintained in most conventional
galvanizing systems.
After the strap emerges from the molten zinc and the
excess molten zinc is wiped off, it is important that the strap
be passed to the rewind roll without further heating since
further heating coul~ be detrimental to the enhanced physical
properties of the strap obtained in khe treatment described above.
United States Patent No. 3,758,333 discloses the
galvanizing of wire by subjecting the wire to a rapid heating
just before passage through a zinc bath, then a second rapid
heating, a second zinc bath,and finally an electric shock
treatment to break up the crystalline structure of the coating.
The treatment of the wire in this process does not provide
enhancement of the physical propexties of the steel because
the initial heating is so close to the first zinc bath that
the rise in temperature is confined primarily to the surface
of the wire before entering the ~inc bath. In any case, if
the initial heating followed by the first zinc bath did, in
fact, alter the crystalline structure of the wire and enhance
its physical properties, the subsequent heating step would
disrupt whatever crystalline changes had been effected by the
initial steps.
~03~3~:Z
In a preferred a5pect of this invention, illustrated
ln FIGURE 2, the traverse of the strap through the molten zi~c
in the contact pot includes passage past at least two stationary
guides, or "shoes", which provide a rubbing action on opposite
surfaces of the strap during the deposition of the zinc coating
thereon and thereby aid in assuring an even and 1awless coating
even in instances where the strap entering the zinc bath may
have dirty surfaces coated with rolling mill oil or other
imp~rities.
Specifically, the contact pot contains cradle 31
which is locked in position within the contact pot by means of -
cogwheel 32 and mounted rotatably thereon, so that the cradle
is removable from below the level of ~he molten zinc by rotation ;
in a co~nterclockwis~ direction. Horizontal member 33 is a
position indicator which is positioned just above the inter- `~
face between the molten zinc and the atmosphere above it and
thereby permits proper positioning of the cradle.
Cradle 31 comprises a Y-shaped frame 34 having
rolls 22 and 23 mounted at the lower ends thereof for rotation ~ -
so that the strap can pass through the pot in rolling contact
with rolls 22 and 23. Stationary guide 36, mounted at the -
lower end of vertical spacer bar 37, pushes downwardly on one
surface of the strap as the latter moves across the lower por-
tion of ~he contact pot and thereby provides a rubbing action
on that surface as the surface moves across the curved surface
of the guide.
Similarly, stationary guide 38, mounted at the
lower end of spacer 39 pushes upwardly on the opposite surface
of the strap and thereby applies a rubbing action on said
opposite suxface which i~ again subjected to a rubbing action
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.
~ID37;3;:~2
near the exit of the strap from the zinc bath by stationa~y
guide 41 mounted on the frame by spacer 2a. Both surfaces of
the strap are subjected to the desired rubbing action by
guides 36 and 38 at some distance from the point whexe the
strap leaves the molten zinc. The application of the rubbing
action to the strap at a location which is some distance from
the exit permits continuing action of the molten zinc on the
strap thereafter and is important if the full benefits of the
rubbing action are to be realized.
United States Patent No. 3,499,418 discloses a
galvanizing system in which a continuously moving strap i6
passed through a zinc bath and upwardly past a pair of iuxta-
posed guide member~ located several inches below the surface
of the zinc in the b~th at the location of the emergence of the
~trap from the bath. These guide members are for the purpose of
constraining the strap against loose movement or "fluttering"
as it passes between the gas nozzle wipers which follow but
the patent discloses the guide memhers assist in the bonding
of the zinc to the strap by an "ironing" effect.
The "rubbing" action in the preferred embodiment
of the instant invention differs from the "ironing" disclosed
in U.S. Pa~ent No. 3,499,418 in two important respects, namely
(1) the placement of the guides at a location a substantial
distance from the exit of the strap from the molken bath,
and (2) the placement of the guides to provide contact wi~h
opposing sides of the strap at diferent locations rather than
guides juxtaposed to each other.
Utilizing the rubbing contact of the guide member~
at a substantial distance from the exit end of the bath permits
continuing action of the molten bath on the strap after the
., , . . . : ~
~ 3~
rubbing action has wiped away surface dirt and other impair-
n,ents to complete contact between the liquid zinc and the
steel surface.
Providing rubbing contact first on one side of
the strap and then on the other is advantageous in that it
; permits control of the rubbing action to a greater degree than
simultaneous contact on both sides of the strap. Juxtaposed
guide members set close together will provide varying pressures
on the surface of the strap with random variations in the
thickness within the limits permitted in normal specifications.
By applying the rubbing action at one side of the strap at a
time, as pxovided in the preferred aspect of this invention,
the pressure be~ween the guide member and the strap is dependent
only on the tension ~n the strap and the degree of displacement
of the strap from a straight line path between rolls 22 and 23. .
If it is desired to maintain the strap in the zinc
bath for a longer period than can be provided in a single pass
at high speed through a bath of limited dimension~ one or more
additional passes around rolls 22 and 23 may be provided, as
shown schematically in FIGURE 2 by the dotted line 43. The
strap may, if desired, be subjected to a rubbing action in
each pass by stationary guides 36 and 38. However, it is
generally sufficient to provide the rubbing action in only one
pass of a plurality of passes, either in the first pass or in
a later pass as long as there is still a substantial travel
distance or travel time between the rubbing action and the
emergence of the strap from the zinc bath. Suitably, there is
provided at least about 3 feet of travel, or at least
about 0.5 seconds of travel time, betwee~ the completion o~
the rubbing action at gui~e member 38 and the emergence of the
strap from the zinc bath.
.
_g_
.
-
. The invention has been described above in its sim-
ple3t terms. In practice, there wil:L normally be a plurality
of straps passing simultaneously and side-by-side past the
conduction rolls and through the zinc bath, payed out from a
plurality of feed rolls and taken up onto a plurality of rewind
rolls. In practice housing structure 18 will usually be con-
nected to a source of non~oxidizing gas to provide an inert
atmosphere therewithin. Air nozzles may be substituted for
brushes 27 to wipe off excess zinc. Roll 24 is preferably
cooled and a water bath is provided between roll 24 and rewind
roll 26 to cool the strap rapidly.
EXAMPLE 1
A steel strap 1/2" wide and 0/020" thick containing
0.27% of carbon and 1.30% manganese was passed over a copper
roll located 12-1/2 fee$ above a zinc path and then into the
bath containing molten zinc. The strap after passing the copper
roll passed through an 18l' air gap before passing into a verti-
cally disposed housing supplied with inert gas supplied from a
combustion process. The pressure within the housing was equiva-
lent to 3-1/2" of water and the gas analysis showed about 5% of
combustibles and 0~ oxygen.
The strapping entered the zinc bath at the submerged
end of the housing and was passed over two sets of rolls in
three wraps to provide 26 feet of immersion length in the molten
zinc. In the bath the strap passed over rubbing contact with
guide members, as shown in FIGURE 2. After the strap passed out
of the zinc bath, it passed upward through a 10" gap, then
between two air nozzles, facing each other and delivering
7.5 cu.ft~/min. of air from a distance of 3~4" from the strap.
The hot strap with its molten lay~r of zinc then passed upward
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3ZZ ' ' ' ' '
7 feet and over a 10" water-c~oled ceramic and then aown into a
deep water bath where the zinc coatinq solidified before the
~trap was wou~d onto a take-up roll.
The ~trap temp~ratures, line ~peeds, bath ~emperature~
tensile strengths, elongations and ductility were aB follows:
Quench Line S~rap Tensile ~longa- Ductility
Tes~ Tank Speed Temp. strength tion 90Bends
No. ~ Temp. F . F. P. M. F. M ~/sq . ln . ~ lT
. 1 850F. 150 1320 . 139 6.3 2R
2 850F 150 140n 183 6.3 2R
3 850F. 150 1480 146 6.6 2R
4 850F. 150 1520 151 6.3 2
850F. 150 1550 155 6.3 2
6 850F. 150 1580 156 5.6 2
7 850F. 200 1300 134 2.3 2
8 850F. 200 1380 130 6.6 2R
9 850F. 200 1420 137 7.0 2R
10 . 850F. 200 1510 142 7.6 2R
11 850F. 200 1580 148 5.6 2
12 850~. 200 1600 150 6.0 2 ~ ~
13 850F. 200 1680 156 5.3 2 ~:
14 850~F. 250 1300 120 7.6 3R
850F. 250 1360 126 6.0 . 3R
16 850F. 250 1400 129 6.0 3
17 850F. 250 1450 140 7.0 2
18 850F. 250 1520 141 6.3 2
19 850F. 25~ 1550 154 5.6 2
850F. 250 " 1600 i52 S.3 .. 2
"
.~ ~p~,,' . ' " .
. .
~L037322
TestQue ch Line St:r~p Tensile Elon~a- Ducti.lity
No.Tam~ F. P M. Temp. Stre gth tlOn _ lT_
21850F. 300 1020 121 7.3 4
22 -850F. 300 1350 134 7.7 3R - -
23850F. 300 1400 135 7.7 3R
24850F. 300 1480 159 5.3 lR
25850F. 300 1520 161 5.0 lR
26\ 850F. 300 1600 160 6.0
278~0F. 300 1650 177 5.0 8
28875F. 250 1350 127 6.3 2R
29875F. 250 1400 131 7.0 2R
30875F. 250 1450 140 6.7 2R
31875F. 250 1520 136 7.0 2R
32875F. 250 1580 140 6.7 2
33875F. 250 1640 134 6.0 2
34880F. 300 1300 129 2.3 lR
35880F. 300 1380 120 7.7 3
36880F. 300 1420 139 8.0 2R
37800F. 300 L480 140 8.3 2R
38880F. 300 1520 133 7.7 2R
3~900F. 200 1350 132 8.0 3
40900 ~. 200 1440 130 ~.3 3
41 . 900F. 200 1460 134.5 7. 6 - ' 3 ~
42 900F. 200 1480 131 7.0 3 '`
43 900F. 200 1500 130.5 6.6 3
44 900F. 200 1620 128.5 7.3 3
900F. 250 1320 128~ 5 7O 3 3 `~
46 900F. 250 i400 128 8.3 3
47 900F. 250 1440 133 9.0 3
- - ' ' ~
.~ j ` .
--1 2--
'~ ~ '': .
~: /
.. .. . .
~03732~
No. ~ Spee~ T mp, ~ ~lon~a- ~uctility
48 900F. 250 148û 135 7.6 3
49 900F. 250 1520 134 7. 0 3
900F. 250 1550 134.5 8.0 3
EXAMPLE 2
An additional series of tests were run utillzing
the same general conditior.~ and the ~ame e~uipment arrangement
as in Example 1. In these te~ts the ~trap was al~o 1/2" wide
and 0.020" thick but waq made of a steel-containing 0.29% of
carbon, 1O21% of managane~e, 0.13~ of silicon and 0.81% of
aluminumO
The strap temperature~ line speeds, bath tempera-
tures, ten~ile strengths, elongations and du~tility wexe a~
follow~:
.
Quench Line Strap Tensile Elonga- Ductility
Test Tank Speed Temp. Strength ~ion 9nBend~
N~. ~ F P M. F. ~ % lT
1 850F. 200 1400 134 4.6 3
2 850F. 200 1450 138 4.3 3
3 850F. 200 1500 152 fiO0 2R
4 850F~ 200 1550 155 6.3 2 ~-
850F. 200 . 1620 161 5.6 2
6 850F. 250 1400 106 6.6 2R
7 850F. 250 1450 130 6.3 . 3
8 850~FD 250 1500 142 5O0 2R
9. 850F. 250 1580 157 6.0 2
. 850~. 250 ~1~640 1~3 6 . 0 ' . 2
11 850F. 250 1700 11i6 5. 3 2
12 850F. 300 1350 104 8. 0 4
13 850F. 300 1400~ 119 6.6 3R
. ' ' ' ~
~ 13-
.... . . .
, ' '- ~ .
. ~L03'73;22 ~
Te ~ Qu~nch ~ine Strap Tensi].~ ~lon~a- Duc~ y
s ~n spe~d TemP~ s~n~tl~n C lT
14 850F. 300 1450 129 5.0
850F. 300 1500. 153 6.6 2
16 850~F. 300 1560 145 .7.3 2
17 850F; 300 1620 155 6.6
18 875F. 200 1350 140 7.3 2R
19 875F. 20.0 1420 133 6O3 2R
875F. 20G 1450 . . 136 7~0 2R
21 875F. . 200 1510 136 7.3 2R
22 . 875F. 20D 1550 134 .7.0 2R
23 875~F. 200 1600 136 7.0 2R
24 875F. 250 1350 126 7~0 2R
875F. 250 1380 123 5.7 2R
26 875F. 250 1430 132 6~0 2
2~ 875F. 250 1480 138 8.3 2R
28 875F. 250 1520 134 7.3 2 ` ~:
29 375F. 259 1550 137 8~0 2R
8~5F. 300 1200 106.5 7~6 3
31 875F. 300 1230 116 4.6 3
32 875aF. 300 : 1280 140.5 5.6 2R ~:
33 875F. 300 1350 134 7.6 Z
34 875F. 300 1390 143 7.3 2 ~ ~:
875F. 30Q 1420 143 7.0 2
36 875~F. 300 1450 153 6.6 2
37 875F. 300 1500 156 5.6 2
3~ 900F. 200 1350 135 8.0 2R ~ :
39 900F. 200 1390 133.5 8.6 2R
~ .
900F~ . 200....... 1420 129 7.3 2R
41 900F. 200 1480 132 8.0 2R
42 900F; 20Q 1530 ~26 8.6 2R
I ~ ' ' . . . . .
.
Quench Line Strap T~nsil~ ~longa- Duc~ility
N~ T m~. F. ~Ip M ~mp. ~ tion 90 8end.
~3 . 900F. 200 1600 128 7. 3 2R
44 900F. 250 1280 12i. 5 7. fi 2R
900P. 250 1310 112 6.6 3 - . .
46 900F. 250 13~0 135 8. 3 3
47 9001~. 250 1430 129 B.0 2R
48 900F. 250 . 1480 129 8. 3 2
49 900F. 250 1525 128 8. 6 2
900F. 250 1550 133 8. 0 2R
~il 900F. 300 1280 122.5 2.6 2R
52 900F. 3ûO 132D 133 9. 3 3
53 900F. 300 :L380 130 . 8. 6 - 2R
!;4 900F. 300 1420 130 8.0 2R
900F. 300 1450 139 8. 6 2R
.~ .
~6 900F. 300 1470 140 7.6 2
57 900F. 300 1500 i38 7.6 2
BXAMPLE 3
An addi~ional series of test~ wer~ run util~zing th
~ame general condition¢ and the same equipment arrangement as
in Example 1. In these test~ the trap was 5/R" wide and 0.020"
thiok and wa3 made of a s~eel containing 0.33% of carbon~ 1.54%
of manganese, 0.14~ of siliaon and 0.01% of aluminum.
The strap temperatures, line speeds, bath temperatures,
tensile strengths, elongations and ductility were a followss
.
--15 -
.: .,
. ~ , .. . . .
Quench L.in~s straL Tensile Elon~a- Duc~ility
Test Tan~. .Speed Temp. S~r~ngth tio~ 90D~ends
r~mp. F. ~P~- E. ~ u :in
1 850F. 200 1420 146 6.6 3
2 850F. 200 1500 152 7.3 2R
3 850F. 200 1580 161 .5.6 2
4 850~. 200 1630 176 5.3 1 at 80
850F. 200 1700 190 4.6 1 at 80
6 850F. 20.0 1760 210 1.3 1 at 60
7 850F. 250 1440 152 6.6 2R
& 850F. 250 1480 152 6.7 2
9 850F. 250 1550 155 8.0 2
850F. 250 1550 153 5.6 2 ;
11 850F. 250 1550 195 . 4.3 1 at 70
12 850F. 250 1640 215 .6 1 at 30
13 ~50F. 250 1700 211 1.0 1 at 30
14 850F. 300 1300 140 5.3 2R ~ .
850F~ 300 1350 137 6.3 2R
16 850F. 300 1400 143 6.3 2
17 850F. 300 1450 152 6. 0 2
; :
18 - 850F. 300 1500 183 . 4.0 1 at 60
19 850F. 300 1560 180 5.0 1 at 70
~20 875F. 200 147~ I48 6. 0 3
21 875F. 200 1500 164 6.0 1 at 90
22 875F. 200 1550 165 6.7 1 at 90
23 875F. 200 1550 167 7.7 lR
24 875CF. 200 1620 192 2.3 1 at 45
875F~ 250 1250 144 6.7 2
26 875F. 250 ~ 1320 143 6.7 2R
27 875F. 250 . 1400 147 6.3 2R
28 875F. 2S0 1450 153 8.3 2
29 875F. 250: 1520 ~ 172. ~.o 1 at 90
-16-
:. : . . . .
Test Quench Lin~ S~r.~3p Tensilc Elon~a- D~lcl:ilit:y
No. r~o~. F. P M. l'emp. Stre n . YG 90;Bend~
875F. 250 1550 177 3.7 1 at 70
31 875F. 3dO 1270 134 5. 7 2
32 875~. 300 1320 127 6 . 0 2R
33 875F. ~300 1350 141 6.7 2R
34 875F., 300 1420 155 8. 0 2
3~ ~ 875~. 3~0 1440 16~ 2
36 875F, 300 1480 174 6. ~ 1 at 9~
37 875F. 300 1520 176 5.3 1 at 70
38 900F. 200 1300 141 8. 3 3R
39 900Fo 200 1350 140 7~ 3 3
900F. 200 1400 143 8.3 3
41 900F. 200 1450 143 8~0 3
42 900 F. 200 1500 146 8. 3 2R
'13 900F. 200 1550 . 160 5. 6 1 at ~0
44 900F. 250 1300 144 8.3 3
900 F. 250 1350 146 9 . O 2R
46 900F. 250 1400 150 906 2R
47 900Fc 250 1450 156 7. 3 lR
48 900F. 250 1530 182 4. 0 1 at 70
49 900F. 250 1550 1~8 4. 6 1 at 45
O .900F. 300 1200 134 7.3. . 3
51 900F. 300 1280 139 6. 6 3R
52 900F. 300 1320 . 150 8. 3 3
53 900F. 300 i370 153 7. 3 2R
54 900~. 300 '. 1410 156 7.. ~ 2
~5 900F. 300 1~50 164 6.0 .1 at 90
.
56 900F. 300 1500 186 600 1 a~ 80
57 900P. 300 1530 178 4.6 1 at 60
,
. '
. ' i', .
--17-
_.___ ... .. .
~L~3~73Z;~
In the above-described Examples tha bend tests were
conducted by securing a strap sample into a fixture in a vertical
position and alternately bending thle sample 90 and returning
it to the vertical position until it fractures. Fracture in
the ~trap sample during the first 90 bend is designated as
"1", fracture during the return from the first 90 bend is
designated as "lR", and so on.
As may be seen useful results are obtained when the
strap is preheated to temperatures from about 1000F. and about
1800F. and quenched to a temperature at least 150F. below the
temperature at which the strap enters the bath. For the optimum
combination of tensile strength and elongation properties, ik is
preferred that the strap be preheated to temperatures from about
1300F. to about 1600F. and be quenched to a temperature at -~
least 400F. below the temperature at which the strap enters the
bath, such as to a temperature from about 850F. to about 900F.
The preheating step is of sufficient duration to permit ~;
the temperature to equilibrate between interior and exterior por-
tions of the strap and it generally takes the strap at least two
seconds to traverse the distance between ~he conduction roll
and the zinc bath and generally from about 3 to about 6 seconds.
The quenching step is of sufficient duration to bring
the strap t9 the temperature of the bath, generally at least
about 1 second, and preferably ~rom about 3 to abou 20 seconds.
The invention has been descxibed in connection with a
preferred embodiment~ but it is to be understood that modifica-
tions and variations may be employed within the scope of this
invention. The copper conduction roll~ for example, may be
replaced by a lead bath as the electrical con`ductor at the
upstream end of the preheating path. Lead does not wet steel
-18
.~ . .
~L037322
and passage through a lead bath does not generally make steel
strap unsuitable for galvanizing. Elowever, impurities on the
surface of steel may be wetted by molten lead and small droplets
of lead may be entrained in imperfections on the surface of the
strap. For these reasons it is preferred to utilize he copper
conduction roll rather than a lead bath upstream of the zinc
bath for best results.
In the embodiment described above the zinc bath has
been used as an electrode as well as a quenching medium and
coating medium. If desired, a separate conductor, such as a
copper roll may be employed close to ~he zinc bath and upstream
thereof so that the advancing ligature is still preheated by the
passage of electricity through substantially the entire segment
between the upstream conductor and the zinc bath and does not
have an opportunity to cool before entering the ~inc ba~h~
Other modifications and variations will be apparent
to those skilled in the art.
--19--
