Note: Descriptions are shown in the official language in which they were submitted.
~ 5~3Z
S P E C I F I C A T I O N
_ _ _ _ ._ _ _ _ _ _ _ _ _
SUMMARY OF THE INVENTION:
My invention relates to apparatus to coat a movlng strip with
uniform coatings of metal on one or both sides. The substrate to be
coated is cleaned, chemically treated and preheated before entering
the coating chamber.
The molten metal is atomized by the combined effect of pressure
and ultrasonic vibration or by pressure alone and sprayed using an ~;
inert gas on the cleaned base metal. The inert propellant gas serves
also to provide a controlled atmosphere within the coating chamber.
~here both sides of the moving metal strip are coated3 different
coating metals and different thicknesses of coat may be applied.
Postconditioning provides additional control of the physical and
chemical characteristics of the final product, with the coated metal
strip passing between compacting rollers~ The inert propellant gas
may be recovered for reuse.
The coated substrate resulting from use of my apparatus and pro-
cess~ has the advantageous properties of several conventional products,
while eliminating the disadvantages inherent in the way of manufactur-
ing the conventional products.
There are several presently known methods to coat metaL strip
with metal in a continuous process. All of these methods have lim-
; itations which limit their use and makes them unsuitable for uni-
versal application~
Coating of metal on an other metal is applied for many purposes,
such as decorative~ anticorrosive and antifrictionD
Some of the conventional techniques hitherto employed are hot `~
dipping, electroplating, flame spraying, detonation gun spraying~
plasma spraying, fused coating and vacuum deposition. ~-
For purposes of comparison, and to indicate the advantages of
my invention, it is desirable to describe briefly the conventionally
83;Z
practiced methods of coating and thelr limitatlonsO
~ lot dipplng is one of the most commonly practiced coating methods.
A metal strip is pulled through a pot of molten metal under controlled
conditions, the excess metal removed by mechanical means or an air
knife and cooled. Some of the disadvantages oE this method are:
1. It is difficult to apply thin coating.
2, The coating is often brittle because of the formation of inter-
facial alloy layer between the coating and the substrate.
3. It is difficult and uneconomical to apply coating on one side
only.
4. It requires longer dwell time in the molten metal pot to apply
thick coating, which in turn results in a more brittle coating, due to
thicker interfacial alloy formation,
Electroplating is also widely practiced process. Some of the
limitations of this process are:
1. High equipment cost as compared to the rate of deposition.
2. High electrical energy cost as compared to the rate of depo-
sltion.
3. Difficulty and cost of depositing coatings comparable in thick-
ness to the hot dipping process.
. The complicated arrangement required to deposit metal on one
slde only. -
Flame spraying, a conventional process, is performed with metal
wire or powder which is melted by high temperature flame, such as an
.,:;
acetylene torch, and propelled toward the substrate. Some of the dis-
advantages of this method are:
1. High porosity of the resultant coating.
2. Slow deposition rate.
3, The requirement of mechanical roughening, such as sand-blast-
ing of the surface coated to achieve satisfactory adhesion of the
coating.
:'~
''-
.'.' ~
.. . ...
, ~: : . . ... . . . .
- ; ~
Detonat$on gun spraying, ~ co~v~h~ional process, is performed by
mixing oxygen and fuel gas with the metal in powder form and igniting
by a spark to propel the particles with very high velocity. It results
in a more dense coating than flame spraying. Some of the disadvantages
of this method are: ~
1. Slow deposition rate. ~;
2. The requirement of mechanical roughening, such as sand-blasting
to achieve satisfactory adhesion of the coating,
Plasma spraying, a conventional process, is performed with loni~ed,
high temperature gases which melt and propel metal particles toward the
substrate at high velocity. Some of the disadvantages of this method are:
; 1. Slow deposition rate.
2. High equipment cost as compared to the rate of deposition.
3. Substrate requires cooling to prevent deformation.
Fused coating, a conventional process, is performed by applying metal
powder on the substrate and then heating the substrate above the melting
point of the metal powder in order to fuse~ Some of the disadvantages
of this method are:
1. The substrate may deform at the melting point of the coating
metal.
- 2. Interfacial alloy layer forms which may result in brittle coating.
Vacuum deposition~ a conventional process, is performed by evapor-
ating metal in vacuum, and condensing the metal vapor on the substrate.
Some of the disadvantages of this method are:
1. Very high equipment cost as compared to the rate of deposition. ; ;~
2. Very slow deposition rate.
3. Poor adhesion of the coating unless the substrate is heated to
high temperature. ~
None of the described conventional methods is suitable without
major modification to deposit a metal coating on a moving, flat metal
~: . - . . . , ~
3~
strlp with the versatility of my invention.
The main advantages of my invention are:
1. Varying thickness of metal can be deposLted on one or on both
sides of the moving metal strip.
2. Different metals can be deposited in one process.
3. The rate of deposition is infinitely variable without propor-
tional increase in equipment cost.
4, The quality of deposition is varlable~ The thickness of the
interfacial alloy layer is controllable. Ductile or brittle coating can
be produced on the same equipment.
5. The porosity of the coating can be controlled by rolling and
consequent compacting to the desired degree.
6. The adhesion of the coating can be readily controlled by chemical ;
means, as is done in the hot dipping process.
70 Due to the flexibility of the temperature ranges of the process,
substrate deformation is minimized.
8. The process can be adopted, with minor modification~ on some of
the existing metal coating equipment.
BRIEF DESCRIPTION OF T~E DRAWING:
The objects and features of the invention may be understood with
reference to the detailed description of an illustrative embodiment of
the invention, taken together with the accompanying drawings in which:
FIG. 1 is a side elevation view of the coating apparatus;
FIG. 2 is a sectional view taken through line II-II of FIG. l;
FIG. 3 is a sectional view taken through line III-III of FIG. l; and
FIG. 4 is a sectional view taken through line IV-IV of FIG, 1
DESCRIPTION OF THE PREFERRED EMBODIMENT:
.
Turning now descriptively to the drawLngs, in which similar reference
characters denote similar elements throughout the several views, FIGS.
1-4 illustrate the substrate 10 in the form of a continuous metal strip,
~-~ being coated in the apparatus utili~ing an airless spraying system.
.. . . . .. . ..
3Z
The substrate strLp 10 is initially chemically cleaned, rinsed,
optionally annealed and temper rolled, pickled and flux washed and pre-
heated prior to entering the apparatus through entering rotating rotls
33 mounted across an opening in the housing 12 which is preferably made
of asbestos board. The coated metal strip 10 exits the apparatus through
similar rotating rolls 23.
The atmosphere within the confines 11 of the apparatus is an inert
gas, preferably nitrogen, maintained at a pressure above that of the
ambient air surrounding the housing 12, and at an appropriate temperature
ranging up to 200 degrees F above the melting temperature of the coating
metalO The housing 12 forms a relatively air-tight enclosure about the
confines 11 in which the metal is sprayed.
Gas is drawn out of the interior 11, through pipe 21 by pump 43 and
forced through heat exchanger 20 whlch is gas fired or electrically en-
ergized~ and returned into the system. Valves 22 in pipe 21 control the
flow of reheated gas.
Make-up nitrogen is replaced through line 24 by pump 53 and preheated
through heat exchanger 51 with valve 52 controll~ng flow of make-up
nitrogen into the interior 11.
The coating metal is melted in pot 15 by heaters 16. The molten
metal is kept at 50 degrees - 500 degrees F above its melting point in
pot 15. Line 55, spraying guns 14 and pump 17 are also kept close to
the temperature of the molten metal to avoid clogging of the system~
with use of exterior insulation, or by additional heating elements, if
required.
A pump 17 pumps the molten metal in each pot through lines 55 to
spraying guns 14 where the molten metal is atomized by the combined
effect of pressure and ultrasonic vibration or by pressure alone. The
spraying guns 1~ are mounted above and below the substrate sheet 10~
The pressure requirement is determined by the specific gravity and
viscosity of the molten metal and the degree of atomizing requlred, and
.:
,-, :
, ~, ' : ': ,,
::
\
3~
ranges to 5000 pounds per inch srluare.
The molten metal is kept as noted at 50 degrees to 500 degrees F
above its melting point in pots 15, with one pot 15 supplying the guns
14 above the substrate sheet 10~ and the other pot 15 supplying ~he guns
14 below the sheet 10.
The temperature of the substrate 10 is maintained at 0 degrees to
800 degrees F below the melting point of the coiating metal~ Lower tem-
perature of the substrate will reduce the fonmation of the interfacial
alloy layer, while higher temperatures of the substrate will increase
its formation.
Higher temperature will also result in a more dense, less porous
and better adhering coating but undesirable substrate deformation can
also be the result.
Lower substrate temperature will result in a more ductile and flex- ;
ible coating.
The end use of the product will determine the proper substrate tem-
perature selection.
By closing valve 57 and opening valve 19 the molten metal is re~
circulated through line 55 and by-pass line 56.
FIG. 4 illustrates the arrangement of the molten metal lines and spray-
ing guns. By opening or closing valves 18, individual lines of spraying
; guns 14 can be connected or disconnected to vary the width of substrate
to be coated. The overspray is caught by asbestos boards 28 shown in
FIGS. 2, 3 and 4, which are positioned at a g5 degree to 105 degree
25 angle to the substrate sheet 10 and are movable sideways as the width -
of the substrate sheet 10 varies.
These asbestos boards 28 do not alloy with the molten metal. Since
the temperature in the coating area is higher than the melting point of
the coating metalg the overspray slowly flows down on the boards 28
; 30 and is collected and reused. ~
: . '.
:
:'~
".
3;~ :~
The molten metal is preferably sprayed in a V or U-shaped flat spray.
Electrostatic spray will result in a more uniform coating.
The sprays are overlapping. The nozzles 14 are positioned in a
staggered fashion in several rows for more uniform and thicker coating.
The guns 14 for spraying above the substrate sheet 10 may be offset
from guns 14 below the sheet 10 so that the top coat of metal initlalty
sprayed on the sheet 10 which then passes through compacting rollers 49A
and 49B prior to passing over the lower guns 14 that spray the bottom
coat of the metal.
The coated substrate initially passes between compacting rollers 49A
and 49B. Roller 49B is a back-up roller and turns with the same surface
speed as the speed of the substrate, while roller 49A, located to roll
newly deposited coating, is coated with a hard, smoth, non-alloying,
`~ high temperature resistant metal coating of refractory metal and turns
at a 1-10% lower surface speed than the speed of the substrate~ The
," .
function of roller 49A is to compact the partially solidified, but still
formable metal coating, and smoothen the surface~ The function of roller ~ ;
49A is also to eliminate pinholes and discontinuities in the metal coat- ~ ~ `
ing. The metal coating must be solid enough not to be removed from the
2~ substrate during the compacting process.
After the bottom coat has been sprayed, the coated sheet 10 passes
through a second set of compacting rollers 49A and 49B and exit rollers
23.
The pressure on compacting rolls is variable. Higher pressure wiil
give more dense coating. The surface temperature of rollers 49A and 49B
is kept 0 degrees to 800 degrees F below the melting point of the coating
metal to prevent metal removal from the substrate, yet hot enough to
produce a uniform and non-porous coating.
If uniform characterist~s of the coatings on both sides are cri ti-
cal, the temperature of the molten metal in the second stage of coating
should be higher than in the first.
. :. . . . :
33;~ -
If different metals~ having very different meltlng points are to be
coated on each side, then two completely separated coating areas are
required with separate controls~ The higher melting point metal will
always be coated in the first zone. Each coating zone will be con-
structed the same way as described above, with optional substratetemperature ad~ustment between the coatlng zones.
The coating unit comprises also the necessary drives, rollers,
guides, furnaces, cleaning, pickling, rinsing and fluxing equipment,
which are not described here, since they are not part of this invention.
Post conditioning of the coated sheet 10 may include heat treating,
temper rolling and pack diffusion, and occurs after the coated sheet 10
has left the exit rollers 23, either before or after cooling coated ;
sheet 10 to ambient temperature.
The main advantage of this apparatus is the flexlbility of the
equipment with the ability to coat different thicknesses of the same
or different metals on the top and bottom of the substrate sheet~ at a
continuously variable deposition rate, with coating porosity controlled
by rolling.
Pumps, spraying nozzles, connecting pipes, rollers, housing~ melting
pot, etc., are constructed of su~h material as does not alloy itself
with the molten metal, has sufficient structural ~ ~ and resist- ;
ance at working temperatures so as no~ to corrode.
Materials suitable for such equipment use include refractory metals,
such as ~ ~ and tungsten, ceramics, ceramics lined steel, and
asbestos for the housing.
Air-spray or airless spray guns can be used, in combination with
.
- other known techniques to acieve the maximum degree of atomizing of the
molten metal. The smaller the size of the molten metal droplets are
the more uniform and controllable the coating will be~
The pressure required in the spraying guns is determined by the
viscosity and specific gravity of the molten metal. The higher the
' ~:'
"
: . . ~ , , ~ ................ : -
~. . , . : ; . ~ . , .
~5431l33;~
specific gravity and viscosity the higher the pressure will be required.
~ here equipment and conditions permit, the use of electrostatic
spraying equipment is des$rable for more uniform coatillg.
If air spray is used, the propelling gas such as nitrogen, must be
inert to prevent the oxidation of substrate or coating metal. Since
the coating and compacting is done also in an inert atmosphere, the re-
covery and recycling of the nitrogen gas is important for economy, and can
easily be done by recirculating pumps.
If airless spray is used, the pump must create enough pressure to
atomize the molten metal.
Ultrasonic atomization of the molten metal in the spraying device
will greatly reduce the pressure required in the spraying system. The
ultrasonic vibrator must be also coated or made of a corrosion resistant
ceramic or refractory material or the life of the vibrator will be re-
duced.
Other advantage of the ultrasonic atomization is that uniform sizedroplets will be sprayed out which will result in a more uniform coat-
ing.
The higher the frequency of the ultrasound is the smaller the dia-
meter of the droplets will be,
Since obvious changes may be made in the specific embodiment of theinvention described herein, such modifications being within the spirit
and scope of the invention claimed~ it is indicated that all matter
contained herein is intended as illustrative and not as limiting in
scope.
. -
' -. ' ' , ' , . " ,
. , ,. . , ~ -
