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Патент USA US3071188

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Jan. 1, 1963
M. s. HOWETH
3,071,178
APPARATUS FOR CONTROLLED ETCHING OF METAL
Filed Dec. 31, 1958
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Jan. 1, 1963
V
M. s. HOWETH
39719173
APPARATUS FOR CONTROLLED ETCHING OF METAL
Filed Dec. 51, 1958
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JNVENTOR.
MAQV/M i HOWETH
BY
ATTOEL/EY
ilnitc .
Qcares Patent O??ce
Fatented Jan. 1, i963
rt,
41
controlled chemical corrosion of metal workpieces where~
in the corrosion solution is applied thereto in vapor form
within an atmosphere, the temperature and pressure of
which are controlled at their optimum values.
The present invention offers several advantages over
previous etching devices. The metal removal rate of
,~\ .‘
APE’ARATUS
E
* ‘
CGNTRGLLED
‘TEAL
Marvin S. Hewett], ftlort v-Jorth, lien.7 assignor to General
Dynamics Qorpor ‘ion,
Diego, Calif., a corpora
tion of
Dec. 31,
ll (Iinims.
this apparatus is much greater than prior devices, thereby
making the operation more economical. Moreover, there
is no contamination of the corrosion solution; hence the
The present invention relates generally to metal re 10 rate of removal of the metal is constant. This invention
is further advantageous in that corrosion agent, corrosion
duction; more particularly it relates to the dimensional
reduction of metal objects by controlled chemical action.
agent concentration, pressure and temperature may be
In recent years the complexity of aircraft con?gura
tional design has increased to the extent that it has be
controlled and varied to suit the metal or alloy to be cor
roded in a particular operation. The present apparatus
come necessary to evolve and develop new manufactur
15 in addition to the metal removal operation also lends
ing techniques for the fabrication of the components of
such designs. For example advanced aircraft employ
itself to such associated operations as degreasing, rinsing
and brightening, all of which may be accomplished in
large contoured wing panels of a sandwich type con
a single container. And, since a single container is em~
struction. (Joe of the elements of such a panel is an
ployed, the manufacturing floor space required is sub
external skin which is fabricated from a solid metal plate 20 stantially less than that previously required for operations
of which the thicknesses of certain areas are reduced in
of this type.
order to permit the placement of cellular type core mate
it is, therefore, an object of the present invention to
rial therein. Such skin is integrally reinforced and stiff
ened by the unreduced areas between suct reduced areas.
A structure of this character is extremely dif?cult to
fabricate by conventional mechanical machining meth
ods. if the curvature of the skin is formed after the
areas have been reduced, undesirable deformation very
often results in these areas. if the curvature is formed
provide an apparatus for the useful, controlled corrosion
of metal objects wherein such metal objects are exposed
to the chemical action of a corrosive soltuion in vapor
form within an atmosphere wherein the pressure and
temperature are controlled at their optimum values.
Another object resides in the provision of an apparatus
for the controlled corrosion of metal workpieces, such
before the at as are reduced, such reduction is very diffi 30 apparatus affording a greater rate of removal of metal
cult and expensive.
from such workpieces than heretofore possible.
By utilizing chemical action, however, it is relatively
Yet another object is to provide an apparatus for the
easy and comparatively simple to fabricate such a struc
useful and controlled corrosion of metal objects which
ture. A plate, the thickness of which is equal to the
is economical in operation.
thickness of the unreduced areas, is ?rst formed to the
Still another object of the invention is to provide an
desired curvature. The stiffening areas are next masked
apparatus for corrosion of metal workpieces at a constant
with a suitably chemically inert synthetic material. The
rate.
metal of the unmasked areas is then subjected to the
A further object resides in the provision of an appa
action of a chemical agent which reacts with such metal
ratus for the controlled corrosion of metal objects which
and reduces the thickness thereof to the desired di
is also adapted to perform such associated operations
mension.
as degreasing, cleaning, rinsing and brightening.
l‘cretofore the chemical reduction of metal work
A still further object is to provide an apparatus for
pieces has been accomplished by immersing a plate or
the corrosion of metal objects of various composition,
workpieces in a suitable etchant solution contained with
in a tank. When the workpiece has been immersed for
a period of time sullicient to yield the desired depth of
etch, it is removed from the ?rst tank containing the
etchant solution and immersed in a second tank con
taining water, such water immersion terminating the etch
reaction. After the usual etch operations the workpiece
is covered by an undesirable, black residue or “smut,"
which necessitates the immersion of the workpiece in a
third tank containing a brightening or “desmutting”
agent.
Several disadvantages are inherent in such etching ap 55
paratus.
The etch-rate or rate-of-removal of metal is
comparatively low, on the order of .001 inch per minute.
Moreover, continued use of the etchant solution results
in the contamination thereof by a precipitate formed of
the removed metallic cations and the anions present in
the etchant solution; such contamination further reduc
ing the effectiveness of the solution and resulting in a
continually diminishing etch-rate. Eventually, when the
etchaut solution reaches a certain contamination level,
such apparatus including means for varying the corro
sion agent composition, the corrosion agent concentra
tion, and the temperature and pressure of the atmosphere
surrounding such metal objects.
These and other objects and advantages will be more
apparent to those skilled in the art from the following
description of the appended drawings wherein:
FlGURE 1 is a perspective view of the preferred em
bodiment of the invention; and
FIGURE 2 shows the apparatus of FIGURE 1 in cross
section.
The present invention comprises four basic compo
nents: A receptacle having a chamber therewithin wherein
is contained the workpiece to be corroded, a corrosion
agent supply system for injecting such corrosion agent
into such chamber, a pressurization system for pressuriz~
ing such chamber, and a calefaction system for heating
such chamber.
Referring now to the drawings, the autoclave receptacle,
generally indicated by the numeral 10, is of a substan
tially cylindrical con?guration, open at one end in order
to receive the workholding device 11 therein; which device
in turn, supports, in vertical position, a workpiece 12.
etching operations must be suspended and the contami
nated solution replaced, which is both time consuming
and expensive. Another serious disadvantage is that the
The open end of autoclave it? is provided with a door 13,
tanks containing the various solutions are generally large
hinged at 14, the closure of which effects an airtight
and require an excessive amount of manufacturing floor 70 seal of the autoclave receptacle. Blocks 15 serve to ?x
space.
The present invention comprises an apparatus for the
edly support the receptacle 10.
The receptacle ltl (FIGURE 2) comprises two con
3,071,178
3
centric, cylindrical members, an outer ‘cylinder 16 and
an inner cylinder 17.
The inner cylinder 17 is supported within outer cylin
der 16 by means of spacer blocks 18 therebetween. Such
concentric cylinders 16 and 17 divide the interior of the
receptacle into two chambers, a central chamber 1? de
?ned by inner cylinder 17, and a peripheral chamber 21}
intermediate cylnders 16 and 17. It is to be noted that
such chambers are entirely distinct and separate, each
nism 41 which may be set to the desired pressure by
means of handle 42. Such pressure relief-?lter mecha
nism communicates with central chamber 19 through con
duit @3. Should the pressure in chamber 19 become
higher than the desired pressure, the valve of the pres
sure relief-?lter device opens and some of the vapor en
ters the ?lter where such vapor is reacted with a suitable
chemical agent thus transforming it into a harmless com
pound, which then exits through exhaust conduit 44 to
from the other. The external cylinder 16 is inclosed 10 the surrounding atmosphere, thereby reducing the pres
within a layer of suitable insulating material 21 which
sure of chamber 19.
serves the purpose of safety as Well as to minimize heat
loss to the ambient atmosphere. A drainpipe 22, the
purpose and function of which will be explained herein
after, enters internal cylinder 17 at the lowermost posi
tion thereof.
Along the lower surface of inner cylinder 17 there are
positioned a pair of step ledges 23, which extend sub_
stantially the length of receptacle lttl and which serve to
support rails 24. The top surfaces of such rails 24 are of 20
convex curvature, such as will conform to the concave
surfaces of Wheels 25 of Workholding device 11. inas
much as many of the workpieces to be fabricated by
The temperature of central chamber 19 is raised by
means of circulating superheated steam from a suitable
earn generator (not shown) through peripheral cham
er 20.
The steam is admitted thereto through a steam
onduit
A drain pipe 46 at the lowest point of ex
ernal cylinder 16 is provided for draining off the con
densed steam. An adjustable thermostat 4'7 (FIGURE
1) maintains ‘he desired temperature within the chamber
19 (FIGURE 2) by controlling the output of the steam
generator. in the event that a low temperature is de~
sired, a suitable refrigerant gas may be circulated in
means of the present apparatus are of considerable size
peripheral chamber Ztl.
The console control unit 23 (FIGURE 1), in addition
and weight (of the order of several hundred pounds), it
is desirable that a track of rails, similar to those described,
be provided external to the apparatus so that the work—
encases a pair of pyrometers 43 which indicate the tem
perature within chamber 19, a row of pressure gauges
to housing the feeder line valves as described above, also
piece 12 may be loaded into the workholding device 11
1'29 which indicate the air pressure at representative posi
while such device remains on the track, and the work
holding device then rolled into the chamber 19. A later
tions within chamber 19, and a row of feeder line pres
sure gauges 59 which indicate the pressures in the re
ally movable track section is provided immediately adja
spective feeder lines 27.
cent the opening of receptacle 10 in order to permit
closure of door 13.
it is to be understood that the surfaces of those ele
ments of the invention which would be exposed to the
corrosive solutions are protected by coatings of such
The corrosive agent supply system comprises a plural
ity of feeder lines 27 (FIGURE 1) from a corresponding 35 chemical nature as will successfully resist corrosion from
number of suitable storage tanks (not shown). The stor
such solutions. in general it is desirable to line or cover
age tanks are provided with pumps so that the corrosive
exposed surfaces with a chemically inert, synthetic ma
solutions are delivered under pressure. The invention
terial such as an unplasticised polyvinyl compound of
anticipates the use of caustic and acidic corrosive agents,
which the commercially available “Teflon” and “Kel-F”
degreasing agents such as trichloroethylene, “desmut 40 are examples, In some instances, howe er, it may be
ting” or brightening agents such as a low concentration
mixture of nitric and hydro?uoric acid, and water which
is utilized to terminate all chemical reactions and to
more practicable to utilize a plurality of separate mani
fold systems, each of which is fabricated of a metal which
resists or inhibits corrosion by the particular corrosion
agent to be circulated therethrough.
Feeder lines 27 enter the control console unit 28, to be
The preparation of an object, such as the workpiece 12,
described in greater detail hereinafter, wherein are dis 45 for the controlled corrosion thereof, involves the steps of
posed a plurality of valves, the number of which is equal
rigorously cleaning the object and masking certain areas
to the number of feeder lines. The opening and closing
thereof with a suitable inhibitive substance, unreactive
of such valves are effected by means of hand wheels 29
with the corrosive agent to he used, in order to prevent
which extend through the forward face of console unit
the corrosion of such areas.
28. Each of the valves communicate with a manifold
Cleaning is normally accomplished by first manually
36. Such manifold 39, in turn, communicates with one
wiping the object with a cloth dampened with a suitable
of the longitudinal conduit manifolds 31 as indicated at
solvent such as methyl ethyl ketone. The workpiece is
32 (FlGURE 2). Such longitudinal manifolds 31 (FIG
then placed in a workholding device 11 and enclosed with
URE l) are spaced about the external surface of re
in central chamber 19 of autoclave receptacle 19. When
55
ceptacle it) and extend substantially the length thereof.
the appropriate temperature and pressure have been ob
Near the aft end of the receptacle ill a transverse, cir
tained, a degreasing agent, for example trichloroethylene,
cumferential conduit 33 joins the longitudinal manifolds
is injected in vapor form into the chamber 19. When the
31. At ‘spaced intervals along longitudinal manifolds 31
object has been degreased for a predetermined time, a
inwardly directed radial members 34 extend through 60 clenaing agent, such as a very mild solution of nitric and
receptacle lltl into central chamber 19 (FIGURE 2).
hydro?uoric acids, is similarly applied thereto. The ob
Vaporizer nozzles 35 are affixed to the ends of such ex
ject is then rinsed with water vapor, removed from the re
tensions 34, such nozzles serving to vaporize the corrosive
ceptacle and allowed to dry.
agent as it enters the chamber 19. Sealing glands 36 serve
The masking substance is next applied to the surface of
rinse the workpieces.
to effect an airtight seal between radial members 34 and
65 the object. The areas to be reduced or corroded away,
inner cylinder 17.
as indicated at 51 (FEGURE l), are trimmed and re
The pressurization of the central chamber 19 is ef
moved from the workpiece 12 leaving areas 52 covered by
fected by means of a suitable, conventional air com
the masking substance. in the example shown, the work
pressor unit 38 (FIGURE 1). A cylindrical pressure
piece 12 is a plate, whereby it is desired to reduce the
reservoir tank 39 initially accepts the compressed air 70 thickness of the unmasked areas 51 a predetermined
from compressor unit 38. From the reservoir tank 39
the compressed air is admitted into central chamber 1%
(FIGURE 1) through the pressure conduit 43.
The desired pressure is maintained within central
chamber 1? by means of a pressure relief-?lter mecha
amount, leaving the masked areas 51 intact.
When the workpiece 12 has been cleaned and masked
as described above, it is ready to be corroded in a pre
cisely controlled manner. in the actual corrosion opera
tion, as in the degreasiug and cleaning operations referred
3,071,178
5
to previously, the workpiece i2 is sealably enclosed With
in the central chamber 19 of receptacle it}. The desired
temperature and pressure are set on thermostat 47 and
inner cylindrical member de?ning a central chamber, an
outer cylindrical member around said inner member to
de?ne a peripheral chamber, and a workholding device
for holding a workpiece in position in said central cham
ber for exposure to said corrosion agents, said corrosion
agent supply system including a plurality of feeder lines
communicable with separate sources of pressurized fluid
and extending from said sources to said receptacle, in
pressure relief-?lter device ‘til respectively and the opera
tion of the heating and pressurization systems is initiated.
The operation of the pressure pump for the corrosive
agent to be employed is also initiated. When the re
quired temperature and pressures have been obtained, as
indicated by pyrometers 48, chamber pressure gauges 49
wardly directed radial members extending through said
and the appropriate feeder line pressure gauge 50, the 10 receptacle and having vaporizer nozzles thereon posi
valve within control console unit 23 which corresponds
tioned within said central chamber, and valves in said
to the feeder line supplying the corrosive agent to be used
feeder lines for selectively releasing ?uid from certain
is opened by means of the proper handwheel 29, thus
of said sources to said receptacle, said pressurization sys
allowing the corrosive agent to ?ow through manifolds
tem including conduit means in communication with said
3t) and 31, conduit 33, radial members 34 and nozzles
central chamber for pressurizing said central chamber
35. The corrosive agent is vaporized by nozzles 35 as it
to a predetermined value, pressure relief means to pro
enters the central chamber 19. There is thus effected
vide for the escape of gases and vapor from said central
within the central chamber 19 and about the workpiece
chamber including a suitable ?lter mechanism to render
12, an atmosphere of which the chemical composition,
said escaping gases and vapors harmless, and an exhaust
cencentration, temperature, and pressure are controlled at
their optimum values. The workpiece 12 is subjected to
the chemical action of the corrosive agent for a prede
termined time, such time being determined by dividing
conduit to permit passage of said gases and vapors un
der pressure, said temperature control system including
means for circulating superheated steam in said periph
eral chamber and a suitable drain at the bottom thereof
to drain condensed steam vapor.
the desired depth of metal removal in areas 51 by the
known rate of removal of the particular corrosive agent 25
2. Apparatus for controlled chemical corrosion ‘of
under the prevailing conditions of pressure and tempera~
metal workpieces comprising a receptacle for receiving
ture.
said workpieces, a corrosion agent supply system for
As the corrosive agent reacts with the metal of the work
supplying said receptacle with corrosion agents, a pres—
piece, a liquid precipitate is formed which collects at the
surization system for pressurizing said receptacle and a
bottom of the chamber 19 Such precipitate is drained off 30 temperature control system to regulate temperature with
through drainpipe 22 (FIGURE 2).
in said receptacle whereby said workpieces may be cor~
When the required time has elapsed, the corrosive agent
roded to remove metal from selected portions thereof
supply valve is closed and the water line valve is opened,
under controlled conditions of agent concentration, pres
and water vapor is injected into chamber 19, thereby
sure and temperature, said receptacle including an inner
terminating the corrosion reaction and rinsing the work 35 cylindrical member de?ning a central chamber, an outer
piece. If necessary the workpiece is similarly subjected
cylindrical member around said inner member to de
to the action of a brightening agent after which it is again
?ne a peripheral chamber, and a workholding device for
rinsed with water vapor. The operation of the heating
holding said workpieces in position in said central cham
and pressurization systems are then terminated, and the
ber for exposure to said corrosion agents, said corrosion
pressure withinthe chamber 19 released by opening the
agent supply system including a plurality of feeder lines
valve of pressure relief-?lter device 41.
communicable at one end with sources of fluid under
The workpiece l2 and workholding device 11 are there
pressure and at the other end with means for conducting
upon removed from the receptacle 10. When it has cooled
said ?uid interiorly of said receptacle and for vaporiz
sufficiently, the workpiece 12 is removed from the work
ing the ?uid therein to effectively expose said workpiece
holding device ill, stripped of masking material and, if 45 to the ?uid, and valves interposed in said corrosion agent
necessary, trimmed to desired size. This having been ac
supply system to selectively control the ?ow of said ?uid
complished, the workpiece is now ready for its intended
from said sources into said receptacle, said pressurization
end use.
system including conduit means in communication with
As thus described the present invention resides in a
said central chamber for prcssurizing said central cham
novel, e?icient and economical device for performing op 50 ber to a predetermined value, pressure relief means to
erations on metal objects wherein it is desired to pre
cisely reduce certain dimensions of such objects; such de
vice comprising, in combination, a receptacle de?ning a
chamber wherein is placed the metal object to be reduced,
provide for the escape of gases and vapor from said cen
tral chamber including a suitable ?lter mechanism to ren
der said escaping gases and vapors harmless, and an ex
haust conduit to permit passage of said gases and vapors
means for delivering to such chamber a vaporized cor 55 under pressure, said temperature control system includ
rosion solution, means for controlling the pressure of
ing means positioned in said peripheral chamber for ef
such chamber, and means for controlling the tempera
ture of such chamber.
Although only the preferred embodiment of the inven
tion has been herein disclosed, it is to be understood that
the invention is not limited thereto, as many modi?cations
and variations will be apparent to those skilled in the art,
and the invention is to be given the broadest possible
fecting the temperature condition within said receptacle.
3. Apparatus for controlled chemical corrosion of
metal workpieces comprising a receptacle for receiving
said workpieces, a corrosion agent supply system for sup
plying said rcceptacle with corrosion agents, a pressuriza
tion system for pressurizing said receptacle and a tem
perature control system to regulate temperature within
said receptacle whereby said workpieces may be corroded
interpretation within the terms of the following claims.
I claim:
65 to remove metal from selected portions thereof under
1. Apparatus for controlled chemical corrosion of
controlled conditions of agent concentration, pressure and
metal workpieces comprising a receptacle for receiving
temperature, said receptacle including an inner cylin
said workpieces, a corrosion agent supply system for
drical member de?ning a central chamber, an outer cylin
supplying said receptacle with corrosion agents, a pres
surization system for pressurizing said receptacle and a
drical member around said inner member to de?ne a pe
ripheral chamber, and a workholding device for hold
temperature control system to regulate temperature with 70 ing said workpieces in position in said central chamber
in said receptacle whereby said workpieces may be cor
for exposure to said corrosion agents, said corrosion
roded to remove metal from selected portions thereof
agent supply system including means for selectively feed
under controlled conditions of agent concentration,
ing ?uids under pressure into said receptacle and for
pressure and temperature, said receptacle including an 75 vaporizing said fluids to effectively expose said workpiece
3,671,178
7
to same, said pressurization system including conduit
means in communication with said central chamber for
pressurizing said central chamber to a predetermined
lines and extending through said receptacle and having
vaporizer nozzles thereon positioned within said central
chamber, and valves in said feeder lines for selectively
value, pressure relief means to provide for the escape of
gases and vapor from said central chamber including a
releasing ?uid from certain of said sources to said re
suitable ?lter mechanism to render said escaping gases
means in communication with said central chamber for
pressurizing said central chamber to a predetermined val
ue, pressure relief means to provide for the escape of
gases and vapor from said central chamber including a
suitable ?lter mechanism to render said escaping gases
and vapors harmless, and an exhaust conduit to permit
passage of said gases and vapors under pressure, said
temperature control system including means for cir
and vapors harmless, and an exhaust conduit to permit
passage of said gases and vapors under pressure, said
temperature control system including means acting with
in said peripheral chamber to bring about the tempera—
ture condition desired Within said receptacle.
4. Apparatus for controlled chemical corrosion of
metal workpieces comprising a receptacle for receiving
ceptacle, said pressurization system including conduit
culating superheated steam in said peripheral chamber
plying said receptacle with corrosion agents, a pressuriza 15 and a suitable drain at the bottom tnereof to drain con~
densed steam vapor.
tion system for pressurizing said receptacle and a tem
perature control system to regulate temperature Within
References Cited in the tile of this patent
said receptacle whereby said workpieces may be corroded
to remove metal from selected portions thereof under
UNITED STATES PATENTS
controlled conditions of agent concentration, pressure 20
1,255,643
1918
and temperature, said receptacle including an inner cylin~
1,313,233
1919
drical member de?ning a central chamber, an outer
1,328,657
1920
cylindrical member around said inner member to de?ne
2,235,658
1941
a peripheral chamber, and a workholding device for
1951
holding said workpieces in a generally upright position 25 2,566,142
2,651,869
1953
in said central chamber, said corrosion agent supply
2,664,402
Cromeans ___________ __ Dec. 29, 1953
system including a plurality of feeder lines communicable
said W rkpleces, a corrosion agent supply system for sup
with separate sources of pressurized ?uid and extend
ing from said sources to said receptacle, inwardly di
rected radial members communicating ‘with said feeder .30
2,328,192
Langsfeld ___________ __. Mar. 25, 1958
2,884,728
__ May 5, 1959
2,895,814
Clark ________________ __ July 21, 1959
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