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Патент USA US3056750

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Oct- 2, 1962
Filed on. 10, 1957
4 Sheets-Sheet 1
Fl G. I
Oct. 2, 1962
Filed Oct. 10, 1957
4 Sheets-Sheet 2
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Oct 2, 1962
Filed Oct. 10, 1957
4 $hee’cs-Sheet‘3
Oct. 2, 1962
Filed OO'b. 10, 1957
4 Sheets-Sheet 4
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United States Patent 0
Patented Oct. 2, 1962
to operate in accordance with the invention and appa
ratus to utilise such sources will now be described, as
Leslie Arthur Holland, Northgatc, Crawley, and Laurence
examples, with reference to the accompanying drawings
in which:
FIGS. 1 and 2 illustrate the invention diagrammatically,
Laurenson, Langley Green, Crawiey, England, assign
ors to Edwards High Vacuum Limited, Crawley, Eng
FIG. 3 shows the addition of a detail improvement,
FIG. 4 shows diagrammatically a form of pump pro
vided with a gettering vapour source embodying the
land, a British company
Filed Oct. 10, 1957, Ser. No. 689,381
Claims priority, application Great Britain Oct. 12, 1956
2 Claims. (Ci. Nib-298)
This invention relates to the vaporisation of metals
and particularly to apparatus in which the heat for effect
ing vaporisation of a metal is produced by electron
bombardment of the metal.
In vacuum vapour metallisation apparatus, it is known
to feed a wire of the metal to be vapourised onto a heated
refractory support. Suitable refractory materials are
however expensive, and further, their useful life is short.
In the speci?cation of the present applicants’ Patent No.
754,102, it is proposed to provide an electron bombarded
FIG. 5 shows diagrammatically a general arrangement
of a developed form of pump embodying the invention,
FIG. 6 is an elevation in section of a practical form of
evaporation source and wire feed mechanism for use in
the pump shown diagrammatically in FIGURE 5, and
FIG. 7 is a plan, partly in section and to a slightly larger
scale than FIGURE 6, of a pump having the evaporation
source shown in FIGURE 7.
Referring to FIGS. 1 and 2 of the drawings, it will be
seen that a Wire 1 is fed downwardly and, for the reasons
now to be explained, the problem already described is
vapour source in which a wire is fed horizontally through
a water-cooled nozzle into the path of an electron beam
not encountered.
and the wire, being bombarded by electrons, reaches a
sufficient temperature to evaporate. Normally a molten
hollow core 3 of a hollow block 4 cooled by water ?owing
The wire 1 is driven by knurled wheels 2 through the
through pipes 11. The end of the wire leaving the core 3‘
globule is formed at the end of the wire unless the metal 25 is heated by electron bombardment from a circular tung
evaporates rapidly by sublimation. This method of
sten ?lament 5 which is energised by the low tension wind
evaporation has the advantage that metals can be evapo
ing of a transformer T and constitutes a. cathode, the
rated which would otherwise react and form alloys and
block 4 being connected to the positive terminal of a
compounds if heated on a support made, for example,
source of supply.
from a metal or ceramic material. In carrying out the
When the end of the wire 3 is heated by electron bom
method referred to, the energy ?owing into the molten
bardment from the cathode 5 the less viscous and high
temperature metal ?ows to the top of the globule, which
globule must be suf?cient, not only to maintain the energy
lost by heat radiation and thermal evaporation of the
is remote from the cooled feed. When the evaporation is
commenced with the wire fed vertically downwards a
metal, but also to maintain the high temperature difference
between the point of evaporation and the water-cooled
globule forms on the end of the metal which remains
suspended by surface tension forces, as shown in FIG. 1.
nozzle. However, this minor disadvantage is more than
outweighed by the simplicity of the source and the avoid
The electron bombardment system is arranged so that the
maximum bombardment occurs on the outer tip of the
ance of the use of costly refractory materials. For some
metals, e.g. titanium, no satisfactory refractory support
materials are as yet known.
globule. Thus, this region of the gobule becomes the
40 hottest zone from which evaporation occurs. The globule
may run back up the wire, depending on thermal conduc
In order to obtain reasonable rates of evaporation with
tion of the metal wire and the length of wire bombarded,
most metals, it is necessary to raise their temperatures
until the globule touches the cooled support where it
above those of their molten state, for example, aluminium
freezes and forms a hemi-spherical droplet as shown,
melts at 650° C. and evaporates rapidly at 1300° C. and
titanium melts at 1750° C. and evaporates rapidly at 45 cross-hatched at 7 in FIG. 2. The wire is fed into the
droplet to maintain the evaporation.
2000° C. Thus, if evaporation is to take place with the
A simple apparatus for melting and evaporating metal
apparatus described a temperature difference must be
by electron bombard-ment can be developed from the dia
maintained between the molten zone of the globule and
grammatic form in FIG. 2. The cathode consists of a
the solid wire, which is of the order of many hundreds of
degrees in temperature. Further, a very high temperature 50 circular turn of tungsten wire and the guide nozzle is
made from copper and water cooled. Care is taken to
diiference will be required between the evaporation point
avoid the use of brazed joints at the end of the water
and the molten zone.
cooled nozzle. This is to obtain the highest thermal con-‘
According to the present invention, a source of metal
ductivity between the nozzle and the cooling water, which
vapour comprises a downwardly fed metal wire and means
is necessary if the nozzle is not to melt when the molten
providing electron bombardment of the end of the wire
evaporant has a temperature in excess of the melting point
to produce a molten droplet which is subjected to the
of the copper or brazing solder used. Where brazed joints
electron bombardment and emits metal vapour. By
are used, they must not form a junction or thermal bar
“downwardly” is meant vertically downwardly, or down
rier in the heat ?ow between the droplet and the ‘cooling’
ward feed at any angle from 0° to such angles approach
ing 90° from the vertical as will result in the formation
A negative electrode in the form of a ring shield 8 sur
of a molten droplet as hereinafter explained.
rounds the ?lament and prevents the electron stream from
In particular forms of metal vapour source according
bombarding any metal ?ttings which may be at a positive
to the invention, the molten droplet is suspended from a
potential and adjacent to the wire and feed tube. The
cooled surface down or adjacent which the metal wire is
fed, the extremity of the wire being subjected to electron 65 shield may be enlarged and formed with a small aperture
9 as shown in FIG. 3 to prevent undue electron bombard
bombardment to produce the molten droplet.
ment of the end of the wire feed nozzle. However, if the
The cooled surface may consist of a nozzle, or the equiv
metal globule has been made to melt back and contact the
alent, through which the wire is fed into proximity with
cool support, as in FIG. 2 then the electron beam need
a ring shaped heated ?lament. It is a feature of the
invention that the source may be used either in vacuum 70 not be greatly restricted because the end of the feed nozzle
will be almost covered by evaporant which is molten on
vapour metallisation apparatus or in a getter pump.
its outer surface. This is an advantage because it is often
Forms of metal vapour sources constructed and arranged
dif?cult to prevent the molten wire contacting the shield
electrode and short circuiting the power supply if the
central aperture is too small.
When the wire melts back and the droplet contacts the
cooled nozzle it partially solidi?es and sticks to the outer
surface of the nozzle. Thus a much larger droplet can
be supported on the nozzle than by the wire alone and
this greater mass of droplet increases the surface area
available for evaporation.
The block 14 is supported from the pump flange 18 by
a cover 19, a sealing gasket 20‘ being provided. The
gasket 20 may also serve as an insulator for isolating the
anode block 14 from earth and may conveniently be
made of polytetra?uorethylene which is an insulator and
a vacuum sealing medium. The wire feed mechanism
is mounted in the block 14 so as to prevent the mechanism
from becoming overheated during the operation of the
The vapour source described has been used by the ap
The wire 1 to ‘be evaporated is fed from a stock reel
21 via a guide nozzle 22 and feed tube 23 through knurled
high vacuum pump known as a getter pump. The evap
driving wheels 2a and 2b which drive the wire on to an
orated metal atoms combine with gas and vapour mole~
inclined plane 24 formed on the block 14. At the ends
cules to form compounds on the walls of a receiver. The
of each of the knurled wheels 2a, 2b are gears 20, 2d
source is then used in a chamber as shown in FIG. 1 fitted 15 which mesh with each other so that drive imparted to one
with a large entry port ‘10 for connection to the vessel to
wheel will cause the other also to be driven. A toothed
be exhausted. The chamber houses a vapour source as
wheel 25 ?xed on the shaft of the wheel 2a is inter
already described. The metal evaporates in a downward
mittently driven by a ratchet 27 carried at the end of a
direction and condenses on the sides and base of the
lever 28 pivoted on the shaft of the wheel 2a. The op
chamber. To obtain the maximum gettering ef?ciency 20 posite end of the lever 28 has attached to it a push rod
the receiver is then arranged to receive more or less equal
29 which passes through a bellows vacuum seal 30 which
plicants for evaporating titanium in a special form of
permits the rod 29 to be vertically reciprocated by the
when the pump is in operation the removal of gas mole
outer casing of a ball race 31 driven by a cam 32 on
cules by absorption at the receiver surface, is more or less
a rotatable shaft 33. A high tension insulator 34 is inter
constant over the whole of the receiver surface. When 25 posed in the rod 29 to isolate electrically the rod driving
the evaporation rate is adiusted to provide a given pump
means from the anode block 14. The bellows 30, driv
ing speed there is no region of the receiver where evap
ing cam 32 and motor, not shown, can thus be at earth
potential. Reciprocation of the rod 29 results in actua
orated metal is condensed without maximum use.
Two further advantages are gained by using this form
tion of the ratchet 27 via the lever 28 to drive the wheels
of apparatus
30 25, 2a and 2b with consequential feeding of a small
lFirstly, there is no obstacle in front of the evaporating
length of wire over the edge of the inclined plane 24.
masses of evaporant per unit area of the receiver.
globule to prevent the complete expansion of the vapour
beam and which would reduce the gettering action. For
The protruding tip of the wire is bombarded by electrons
feed tube and also reduce the amount of metal available
Evaporation may not ‘be con?ned to the single droplet
emitted by a ?lament 35 and a molten droplet 36 is
example one form of pump is known in which a wire is
fed on to an electron bombarded refractory support. Ob 35
In the arrangement described, it will be seen that, as
viously the metal wire must be directed by a nozzle on to
melting of the wire does not occur at the exit of the feed
the anode support and the evaporated metal tends to con
tube 23, that exit cannot be blocked or restricted so that
dense on the end of the feed tube. This may block the
no constraint on the wire will be imposed by the tube.
for gettering purposes.
40 36 and more than one droplet may be formed beneath
Secondly, when a gettering pump has been in opera
the edge of the inclined plane 24, particularly if the under
tion for some time, the thick metal deposit peels from the
side edge is inclined so that the droplets move under
walls of the receiver. With the source in the base of the
chamber evaporating upwards the metal coating may
It has been found advantageous to mount both the
fall on the electrodes and short circuit the supply. With
wheels 2a, 2b on ball races as shown to prevent the high
an arrangement embodying the invention, this cannot
friction which may develop in dry bearings to be operated
under high vacuum. The wheel 2b is mounted on a shaft
If desired, the pumping port may be placed opposite
the dead evaporation zone at one side of the vapour
source as in ‘FIG. 1 or above the vapour source as at 13 .
in FIG. 4.
The latter arrangement is not so convenient
for mounting the source and furthermore the path of
the gas molecules into the pump may be restricted by
the feed mechanism and auxiliary items. However, this
is a matter of practical detail, which can be catered
‘for in the design of the apparatus where it is of advantage
to locate the pumping port as shown in FIG. 4.
The developed form of apparatus embodying the in
vention illustrated diagrammatically in FIG. 5 and of
which essential parts are shown in more practical form in
FIGS. 6 and 7 overcomes a di?iculty which is apt to arise
with the use of a guide tube, namely a tendency ‘for the
wire slightly to melt back by thermal conduction into
the guide tube with the resultant need periodically to
service the tube in order to maintain uniformity of the
bore. Uniformity of the bore is desirable in order that
the feed wire may be smoothly fed without flowing into
irregularities in the tube surface which would cause
jamming of the feed mechanism.
Referring to FIGS. 5, 6 and 7, the water cooled block
4 of the preceding ?gures is replaced by a solid copper
37 which can be adjusted to vary the compression on the
feed wire. For this purpose, the ends of the shaft 37
are supported, below the centre line of the shaft by arms
38 linked by a rod 39 which can be raised or lowered
by a nut 40 (FIG. 6) on a screw-threaded rod 41 which
passes through a support 59. A block 51 at the end
of the rod 41 is carried ‘by the rod 39 and on rotation
‘‘ of the nut 40 in a clockwise or a counterclockwise direc
tion, the rod 39 is raised or depressed respectively. The
arms 38 linked by the rod 39, are ?xed by bolts '52 (FIG
URE 7) to a disc 53 (FIGURES 6 and 7) forming a
pivot bearing and the shaft 37 is rotatable in bearings
54 mounted in the disc 53. Rotation of the nut 40 pro
duces slight rocking of the shaft 37 to vary the grip on
the feed wire between the wheels 2a, 2b, without a?ect
ing the driving connection between the gears 2c, 2d.
In operation of the mechanism there is sometimes a
tendency for backlash in the mechanism to permit the
feed wire to spring upwards after ‘feeding with the result
that only a small quantity of the original wire fed enters
the droplet. To prevent this, a gravity compensation
pawl 42 is mounted above the ratchet wheel 25 and this
pawl permits the ratchet wheel to move forwards but
engages in the teeth if the compression in the feed wire
block 14 formed at its upper end with a cooling water
places a reaction strain on the mechanism,
chamber 15 having water inlet and outlet pipes 16 and
While successful operation can be achieved with the
17 respectively. Heat may also be removed from the
use of a tungsten ?lament electron source, it has ‘been
block 14 by air cooling at its outer end, using a blower. 75 found that the ?lament is subject to erosion due to posi
tive ion bombardment and reaction with active gases, the
effect being intensi?ed with increased gas pressures. Ero
sion is contributed to also by ionised metal atoms striking
the ?lament. Accordingly, as an alternative or in ‘addi
tion to a ?lament source of electrons, an arc discharge
may be used with advantage for evaporation at high pres
sures. An electrode 35a shown in broken lines in FIG. 5
and which may conveniently be a pointed tungsten rod
may therefore be used and will function as the negative
ample ‘when inert gases are admitted to the system being
exhausted. To facilitate such operation, there is shown
in FIG. 5 a single high tension source 43 provided with
a change over switch 44 by means of which either output
terminal 45 or 46 of the source may be connected to the
condensing wall or the contact arm may be left on the
neutral terminal 47. For convenience, the condenser wall
is always at earth potential if this forms part of the outer
casing of the vacuum vessel. Obviously a circuit may
electrode in an arc for-med between it and the positive 10 be used in which two high tension power supplies are used,
block 14.
one for pumping at high pressures and the other for i011
In one method of using the arc and because initial
pumping at low ‘pressures.
striking of the arc may be difficult to achieve, the evapora
In a getter pump it is necessary to remove absorbed
tion is commenced by heating the evaporant using the hot
gases from the condenser walls before commencing
?lament. As the resultant droplet is brought to tempera 15 evaporation and getter pumping. Such absorbed gases
ture by electron bombardment from the wire cathode the
would result from exposure of the pump to atmosphere if
tungsten arc rod begins thermally to emit electrons as its
temperature rises under bombardment of positive ions of
for any reason it has to be opened up, and these absorbed
gases constitute a very serious gas load on the pump‘ until
gas molecules and metal atoms.
An arc discharge then
they are gettered. During this period they drastically
occurs between the negative tungsten rod and the positive
metal droplet and it is possible then to disconnect the
?lament cathode until the pressure of the gas drops to
reduce the pumping speed of the pump and as these
absorbed gases are released from the walls of the pump
below that necessary for an arc discharge to be sustained.
there can be a very undesirable rise in the system pres
as they become heated during operation of the pump
Apart from titanium, the properties of which make it
sure which could be harmful to the system operation.
ideal for evaporation by this method, many metals, for 25 Such pressure rise will persist until the absorbed gases
example, aluminum, copper and nickel-chrome alloy can
are reduced by gettering when, of course, the pump begins
be evaporated from the vapour source described. A low
to getter the gases coming from the system itself, i.e. it
pressure to provide a clean wettable surface on the end
begins to function as a pump in its own right.
of block 14 is required for these metals because, unlike
absorption of atmospheric gases is very much more serious
titanium, the surface oxide skin which forms at high pres 30 in the case of the getter pump than in normal vacuum
sures prevents the droplets from adhering to the block.
apparatus because the walls of the pump, covered as they
It is a known practice when operating a getter pump, in
are by porous layers of gettering material, are ideal for
which the metal is evaporated by electron bombardment
the taking up of enormous quantities of gas. The re
heating, to make the condensing wall surface of the pump
moval of the absorbed gases is usually achieved by heat
a cathode electrode to which positive gas ions may be 35 ing the vessel to a high temperature under vacuum. It
attracted and trapped on the wall by subsequently con
is known that a glow discharge will remove absorbed gases
densing metal atoms. This process is found particularly
from the surface of an electrode under electron or posi
advantageous when pumping inert gases, e.g. argon, etc.,
tive ion bombardment and also absorbed gases if the
which do not chemically combine with the gettering or
temperature of the body rises under bombardment. Elec
condensing metal. However, it is not possible to operate 40 tron bombardment heating of the condenser wall is pre
an electron bombarded source at a high gas pressure, ap
proximately above 0.1 micron of mercury, if both the
metal collecting walls of the pump or other condensing
surfaces disposed in the path of the gettering metal vapour
ferred because if, as is usual, the metal condenser is
grounded than all of the earthed metal ?ttings in the ap
paratus at the same potential would form a cold cathode
discharge if exposed to positive ion bombardment. The
and on which vapour atoms condense, and the electron 45 connection of the condenser wall to a positive source of
emitting ?lament are at the same potential. This is be
supply while the source of bombarding electrons is en
cause the electron beam ionises sufficient of the residual
ergised, results in bombardment heating of the condenser
atmosphere for a cold cathode glow discharge to pass
wall. A preferred method of operating the pump
from the condenser walls and the electron current ?owing
described therefore involves use of the output of a source
from the hot cathode to the anode is usually so reduced 50 or sources of high tension supply to obtain the following
and dispersed that the evaporant cannot be volatilised.
sequence of events, high tension cleaning by removal of
Such a system also becomes unstable because minute
absorbed gases by electron bombardment of the vessel
metal particles on the condenser walls become incandes
and condenser walls while these are at a positive poten
cent under positive ion bombardment and promote the
tial, intermediate pumping and then ?nal pumping which
formation of arc discharges.
may be referred to as chemical and ion pumping.
In applying a further feature of the invention the vapour
Applying the above outline of an operational cycle
source described is operated in a getter pump in which the
to a speci?c case, the vacuum vessel under exhaustion and
metal is evaporated by electron bombardment at a high
the chamber of the getter pump are exhausted to about
pressure, that is to say above about 0.1 millimetre of mer
0.1 millimetre of mercury using a rotary oil pump. The
cury, with the heated cathode insulated from the con 60 cathode ?lament is then energised and the getter pump
denser wall which is connected to the positive side of the
condenser wall is made positive with respect to the ?la
supply. Positive ions of metal or gas atoms cannot then
ment by appropriate operation of the switch 44. The
?ow to the wall and a cold cathode glow discharge cannot
wall is then degassed by electron bombardment at 3,000
occur. Such a stable arrangement of an electron bom
volts with a current consumption of 2 amperes which
barded source has been described by L. Holland in 65 raises the temperature of the wall to about 400° C. in
“Vacuum Deposition of Thin Films” (Chapman & Hall
about ten minutes. Initially the gas pressure rises and
Ltd., 1957, p. 137), land in the speci?cation of Patent No.
754,102. If desired the condenser wall potential may be
then falls as the pump Walls are freed from occluded gases.
The electron bombardment of the pump wall is then
permitted to “?oat” intermediate between that of the
stopped and the getter pump is isolated from the rotary
cathode and anode electrode. Thus if both electrodes are 70 pump. Next the Water ?ow to the cooling pipes 48 sur
insulated from the earthed metal condenser only very
rounding the pump condensing wall is commenced.
Weak currents can flow to the wall.
Positive potential is now applied to the copper block
A getter pump operated as described provides stability
14 with the result that the feed Wire itself is made positive
at high pressures when removing chemically active gases
with respect to the hot ?lament cathode 35. If an arc
and additional ion pumping at low pressures as, for ex 75 electrode is used, the electrons gradually become emitted
from the arc electrode as the gases become ionised and
in design of the apparatus described and, for example, in
order to reduce or eliminate the possibility of melting back
of the downwardly fed wire at the point where it leaves
the cooled block or nozzle, the nozzle exit may be flared
with the result that, while a solid zone of metal may be
produced on the ?ared portion of the nozzle, a liquid zone
will be maintained immediately below the exit. Alter
surface. The wire feed mechanism is then brought into
natively, the nozzle may be mounted slightly out of the
operation and the wire feeds into the molten droplet
vertical so that the bead formed by melting back ?ows to
suspended at the tip of the block 14. Conveniently, No.
20 S.W.G. titanium wire may be used and in this case 10 one side and allows the wire to be fed forwardly without
obstruction from partial solidi?cation of the bottom of
the feed rate may be adjusted from 0 to 1 gramme per
the bead.
minute. A typical evaporation rate of 100 to 200 milli
the ?lament 35 may be disconnected until the pressure
has fallen to about 1 micron of mercury. The condenser
wall of the pump is either insulated from both the anode
block 14 and the ?lament, or is connected to positive
potential so that a glow discharge cannot pass from its
grammes per minute may be obtained with a source in
put of 4 to 6 kilowatts at a potential of 2,000 volts. Dur~
ing the operation at this stage, gas atoms and molecules
are removed by chemical combining with metal atoms in
transit and chemical combination and absorption at the
condenser walls. As already stated, a cold cathode dis
charge cannot occur and the heating bombardment is
stable. This intermediate pumping really embraces two
stages, ?rstly with the arc and secondly with the ?lament
as a source of electrons.
We claim:
1. Apparatus providing a metal droplet as a source of
" metal vapor and comprising: cooling surface means for
supporting a metal droplet, means for feeding metal wire
downwardly through and past said cooling surface means,
and electron bombardment means disposed below said
cooling surface means and arranged directly to bombard
a zone starting at the lower surface of said cooling sur
face means for melting back the end of the wire into con
tact with said cooling surface means to cool and partially
When the pressure in the system is reduced to lower
solidify a droplet thereby formed for providing a droplet
than 10 to —4 millimetres of mercury, the pump wall is
switched to a negative potential so that positive gaseous
of larger size and thus larger evaporation surface area
than a droplet supported solely by said wire.
ions formed by the electron stream from the cathode are
2. Apparatus providing a source of metal vapour and
transported to the condenser wall where they may be
absorbed by deposition or embedded by the condensing
comprising driving means for downwardly feeding metal
wire and means providing electron bombardment of the
end of the Wire to produce a molten droplet which is sub
The method of pump operation described is applicable 30 jected to the electron bombardment and emits metal
vapour, said apparatus including a cooled surface down
to a getter pump in which the metal to be evaporated is
which the metal wire is fed and from which the molten
fed in the manner described or is fed on to an electron
droplet becomes suspended, said cooled surface including
bombarded support or is heated directly by bombardment
a solid block of metal of high heat conductivity and having
as described in the speci?cation of Patent No. 754,102.
an inclined plane on to which said driving means feeds
If the pump system has been degassed by heating by known
said wire and in which said means providing electron
methods other than electron bombardment then the initial
stage of degassing described may be omitted. Again,
bombardment are disposed adjacent the lower extremity
metal in the manner known as ion pumping.
the method of connecting the condenser walls of the pump
either for collecting or repelling positive ions may be
used in pumps in which the number of positive ions pro
duced per electron ?owing through the gas is increased
by the use of more complex electrode systems or elec
trodes combined with a magnetic ?eld.
of said inclined plane.
References Cited in the ?le of this patent
Reinecke et a1 __________ __ May 9,
Berghaus et al. ________ __ July 2,
Calbick ______________ ___ May 23,
Lewis et al. __________ __ Oct. 31,
has also already been made to the use of the invention in
connection wtih vacuum vapour metallisation. In such
Wouters _____________ __ Sept. 13, 1955
Foster et al ______ _'_ ____ __ May 7, 1957
use of the invention, it will readily be appreciated that
Alpert _______________ __ Oct. 8, 1957
Kuhlman ____________ __ Nov. 15, 1960
Great Britain __________ __ Oct. 9, 1939
Great Britain __________ __ Aug. 1, 1956
While some detailed reference has been made to the
application of the invention to getter pumps, reference
objects which are to be vacuum coated in accordance
with well known techniques, may be placed in the path "
of the vapour beam, the objects being either statically
mounted or mounted on rotating jigs.
It may be found desirable to effect various modi?cations
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