Note: Descriptions are shown in the official language in which they were submitted.
x~
IMPROVED METHOD OF LUBRICATING I~ON AN3 8TE~L BEFORE COLD
WORXING
Field of the Invention
This invention relates to a method for forming an im-
proved lubricating layer optimized for cold plastic work-
ing, e.g., drawing of tubing and wire, forging, header
working, and the like, on the surface of objects made of
iron and steel, e.g., low- and high-carbon steels, low al-
loy steel, and the like. The first major stage of the
method is a phosphating treatment with an optimized compo-
sition of phosphating solution.
Description of Related Art
When iron or steel is subjected to cold plastie-work-
ing (generally denoted herein below simply as "cold work-
ing"), the surfaee of the workpieee is usually ~irst sub
jeeted to a lubrieation treatment in order to reduee tool
wear and seizure between the workpiece and tool. In the
ease of relatively light eold-working operations, this
lubrieation treatment conventionally eonsists of coating
the surfaee of the artiele with an oil which contains an
extreme-pressure additive or lubrieity improver. In the
ease of severe eold-working operations, a widely practiced
- . ~
,
. , ,: . . .
.
method consists of the formation of a zinc stearate lubri-
cant layer over a zinc phosphate-based film and the addi-
tional formation of a sodium stearate layer over this zinc
stearate layer. This may be achieved, for example, by dip-
ping the article to be lubricated into a zinc phosphate
based conversion treatment solution (containing sodium
nitrite as accelerator) heated to 70 to 80 degrees centi-
grade, followed by, for example, dipping in a sodium stear-
ate based metal soap solution (for example, Palube~ 235
from Nihon Parkerizing Company, Limited, Tokyo) heated to
70 to 75 degrees Centigrade. Moreover, research has been
carried out on improving the base film with the objective
of improving the performance o such lubricant coatings,
and results in this regard have been disclosed in Japanese
Patent Publication Number 60-20463 talternatively numbered
20,463/85). The conversion treatment in the aforesaid in-
vention is conducted at approximately 80 degrees Centigrade
using a zinc and calcium phosphate based treatment solution
with specified component concentrations.
When these two types of base layer treatments as known
in the prior art are examined, it is found that they both
suffer economically from needing a relatively high conver-
sion treatment temperature and from the generation of rela-
tively large quantities of sludge in the phosphating treat-
ment bath.
It is an object of the present invention to achieve a
reduction in both treatment temperature and sludge forma-
tion compared with that known in the prior art, and it is
another object of the invention to achieve an improvement
in the performance and quality of the film obtained as a
base layer for a final cold worXing lubricant layer.
Description of the Invention and Drawinqs
Except in the operating examples, or where otherwise
expressly indicated, all numerical quantities in this de-
scription indicating amounts of material or reaction condi-
tions are to be understood as modified by the word "about".
It has now been found that the temperature of a phos-
`,
-
,
.
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phating treatment bath can be lowered into the range o~ 35
to 65 degrees Centigrade, that sludge production during
phosphating could be substantially reduced, and that a lu-
bricant film which has a better resistance to cold working
than in the prior ar~ could be formed after phosphating,
through the addition to an otherwise conventional ferrous
ion containing phosphate treatment solution of moderately
oxidizing, water-soluble, aromatic compounds containing
both nitro and sulfonic groups, such as the alkali metal
salts of nitrobenzene sulfonic acid, nitroaniline sulfonic
acid, nitrotoluen~ sulfonic acid, and/or nitroxylene sul-
fonic acid, while at the same time using the other compon-
ents in the treatment solution at specified concentrations
and within particular ranges of composition with respect to
each other, as specified below. Specifically, the phos-
phating solution for use in this invention should contain,
in percentages by weight as are all percentages given here-
in unless other specified, 0.3 ~o 2.5 % of zinc ions, 0.01
to 2.0 % of ferrous ions, 0.5 to 5.0 % of phosphate ions,
0.7 to 12.0 % of nitrate ions, and 0.02 to 0.25 % of water
soluble aromatic organic compounds that contain both nitro
and sulfonic acid or sulfonate salt groups, with the fer-
rous ion and zinc ion contents additionally being such that
the weight ratio of ferrous ions to zinc ions in the phos-
phating solution in within the range from 0.005 to 3Ø
Optionally, the phosphating solution may also contain from
0.2 to 2.0 % of calcium ions, and when it does, the weight
ration of calcium ions to zinc ions in the solution should
also be in the range from 0.7 to 4Ø Also optionally, the
phosphating solution to be used for this invention may ad-
ditionally contain a .chelating agent ~or ferrous ions,
chlorate ions, and heavy metal cations such as n.ickel, co-
balt, manganese, or copper. Preferably the phosphating
solutions consist essentially of only water, the other con-
stituents named above, and any necessary counter ions for
the ionic constituents.
In a process according to the invention, the iron or
- ~
., - . .
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steel object to be treated is contacted with a phosphating
solution as noted above for a time of from 3 to 20 minutes
at a temperature of from 35 to 65 degrees Centigrade. A
final lubricating film is then formed by treating the phos-
phate film thus formed by methods conventional in the artfor treating zinc phosphate based films to produce lubri-
cant films for cold working. Even though the methods used
for forming the lubricating layer are conventional, the
resulting layer gives superior lubrication, apparently as
a result of favorable interactions with the phosphating
layer deposited by a method according to this invention.
Considering the invention in greater detail, the phos-
phating solution used comprises zinc ions and ferrous ions
as its essential cationic components. The zinc ion is to
lS be present at 0.3 to 2.5 ~, because the formation of a film
suitable for cold working becomes problematical at a zinc
ion concentration below 0.3 %; on the other hand, the con-
version treatment is not improved with a zinc ion concen-
tration in excess of 2.5 %, while bath management becomes
difficult and the economics are also undesirable.
The ferrous ion content should be 0.01 to 2.0 ~, and
an additional restriction also applies: that the ferrous
ion/zinc ion (Fe2+/Zn2~) weight ratio should fall within
the range of 0.005 to 3Ø Thus, when the zinc ion concen-
tration is near its lower limit value of 0.3 %, the permis-
sible ferrous ion based on the aforesaid weight ratio would
calculate out to 0.00015 to 0.9 %. However, because the
independent lower limit value for ferrous ion is 0.01 ~,
its content is in fact restricted to 0.01 to 0.9 %. On the
other hand, when the zinc ion is at its upper limit value
of 2.5 %, the ferrous ion content allowable under the con-
straint of its ratio to zinc ions would be 0.0125 to 7.5
~, but in fact the ferrous ion content must be restricted
to 0.0125 to 2.0 % because of the independent upper limit
value for this ion.
At ferrous ion concentrations below 0.01 ~, the phos-
phate film obtained performs unsatisfactorily as a lubrica-
~ ~ .. . . . . . . ................ .. .. ... . . . . .
. . . .
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tion base layer. Moreover, regulation of the iron concen-
tration at such a low level in practice requires precipita-
tion of iron by the frequent addi~ion of an oxidant, such
as NaNO2, H202, or the like, that at the temperature used
can fairly rapidly oxidize ferrous ions to ~erric ions,
which are less soluble in these solutions. This increases
sludge production. Conversely, when the concentration of
ferrous ions exceeds 2 %, a coarse, incomplete film tends
to be formed, and poor film microstructure also results as
a consequence of a substantial decline in the zinc content
of the phosphate film, resulting ~rom substitution of zinc
by iron. The requirement for restricting the ferrous ions
to zinc ions weight ratio as specified above arises from
this consideration.
Phosphate ion (PO43 ) should be present at 0.5 to 5.0
%, with its optimal concentration being determined in part
by the need to provide counter ions for the specified ca
tions present in the solution. Poor quality film formation
is encountered at phosphate ion concentrations below 0.5 %.
On the other hand, while the use of more than 5.0 % of
phosphate is possible, this serves primarily to increase
the cost without improving film formation.
Nitrate ion (NO3 ) is to be present at ~.7 to 12.0 %.
At less than 0.7 %, the film formation rate slows, length-
ening the treatment time, and the film obtained is coarseand poorly adherent. Exceeding 12.0 % nitrate causes an
increase in the Zn(NO3)2 concentration in the treatment
solution, which causes a low Zn(H2PO4)2/Zn(N03)2 ratio.
This results in an unsatisfactory concentration of the
Zn(H2P04)2 required for good film formation and thus a re-
duced conversion-coating capacity.
In addition to the preceding, the phosphate treatment
solution used in the present invention also contains, as an
essential component, 0.02 to 0.25 ~ of water-soluble, nitro
and sulfonic group containing aromatic compound(s). Pref-
erably these compounds are selected ~rom the group of com-
pounds containing a benzene, naphthalene, or anthracene
, ~
.
- . . . . .
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nucleus with at least one each of a nitro and a sulfonic
acid or sulfonate substituent on this nucleus. More pref-
erably, the aromatic compollnds are selected from the gr~up
consisting of nitrobenzene sulfonic acid, nitroaniline sul-
fonic acid, nitrotoluene sulfonic acid, nitroxylene sulfon-
ic acid, and the salts of these acids, with meta-nitroben-
zene sulfonic acid or its salts most preferred. Any of
these compounds will serve to lower the ~reatment t~mpera-
ture for the iron-containing zinc phosphate treatment solu-
tion while also functioning to give a fine, dense phosphatefilm with relatively small crystalline particles. The
treatment bath according to the present invention, having
the above described composition, although containing iron,
nevertheless can produce a fine, dense phosphat~ film with
relatively small crystalline particles on the surface of
iron and steel, with preferred coat weights of 7 to 12
grams per square meter ("g/m2"), through immersion or other
contact for 3 to ~0 minutes at the relatively low tempera-
tures of 35 to 65 degrees Centigrade. This film forms a
base layer adapted to severe cold-~orking operations.
Moreover, because the zinc phosphate based treatment solu-
tion contains iron (Fe2+~, an accelerator such as N02 or
H2O2 is generally unnecessary, and preferably is not used
in the phosphating solutions. As a result, one effect is
the relatively slight precipitation of sludge, such as
FePO4 and/or Zn3(PO4)2, from the phosphating solutions used
in a process according to the invention.
When the aforementioned aromatic compound component is
present at a concentration of less than 0.02 %, the benefi-
cial effect deriving from its addition will either be in-
significant or entirely absent. On the other hand, the
beneficial effects of temperature reduction and development
of a fine, dense phvsphate film are no longer obtained to
any greater degree at concentrations in excess of 0.25 %.
In fact, the use of larger quantities hampers film forma-
tion.
If desired, the phosphate treatment solution according
to the invention may contain a chelating agent for iron to
increase the rate of phosphate film formation. When such
a chelating agent is used, it is preferably present in an
amount of from 0.01 to 0.05 % of the phosphating solution
and is preferably selected from the group consisting of
oxalic acid, citric acid, glycerophosphoric acid, urea,
polyvinyl alcohol, and poly(vinyl pyrrolidone). M~reover,
the phosphate treatment solution used in the present inven-
tion may contain chlorate ions from some constituent such
as NaC103 as additional oxidizer, simple and/or complex
fluoride ions, and heavy metal ions such as nickel, cobalt,
copper, and the like.
As discussed above, the method of the present inven-
tion brings about the formation of a phosphate film on a
clean iron or steel surface upon contact, preferably by
immersion, for 3 to 20 minutes at 35 to 65 degrees Centi-
grade in a phosphate treatment solution with the components
as specified above. This process according to the inven-
tion also preferably includes a water rinse and drying step
or a water rinse and neutralization step after phosphate
film formation, and the process further includes another
step of lubricant treatment after phosphating and preferab-
ly after a water rinse and drying after phosphating. The
lubricant treatment may contain any conventional lubricant
such as molybdenum disulfide, tungsten disulfide, graphite,
highly fluorinated organic resin, or an oil lubricant which
contains an extreme pressure additive. Most preferred,
however, is the lubricating treatment comprising the forma-
tion of a zinc/fatty acid film and an alkali metal/fatty
acid film in layers over the phosphate film by immersion
with heating to 70 to 75 degrees Centigrade in a weakly
alkaline aqueous metal soap solution based on the alkali
metal salts of C16 to C18 saturated and/or unsaturated fat-
ty acids, most preferably sodium stearate.
The final step in a method according to the invention
generally is that of drying the lubricant ~ilm.
When the phosphating solution used according to the
.
:
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55~
invention does not contain calcium, the film formed by
phosphating contains mainly phosphophyllite ~Zn2Fe(PO4)2
4H20~ crystals. When the treatment solution contains cal-
cium ions in the quantity specified above, a uniform, m c-
roparticulate film is formed in which the main component
is scholzite (Zn2Ca(P04)2 2H20} but also contains some
phosphophyllite and hopeite (Zn3(P04)2 4H20} with the
same approximate size as the scholzite crystals. However,
when less than 0.2 ~ calcium ions are present or when their
weight ratio with zinc ions is less than 0.7, crystals
larger than those of the scholzite system, thought to be
phosphophyllite, become an important secondary crystal
phase. Because the size of the phosphophyllite type crys-
tals increases as the weight ratio o~ calcium ions to zinc
ions declines, the crystalline structure of the film be-
comes nonuniform. Since a microhomogeneous film is a par-
ticular requirement for severe cold-working operations,
such an inhomogeneous film is undesirable as the base layer
for severe cold-working operations. Conversely, when the
Ca ion content exceeds 2.0 % or when Ca2+/Zn2+ exceeds 4.0,
relatively soft monetite ~CaHP04) precipitates among the
aforementioned microparticulate crystal types; this reduces
the cold-workability.
~he concentratlons of zinc and ferrous ions for phos~
phating solutions with calcium according to the invention
are preferred to be within the same ranges as for solutions
without calcium, although in some cases the adverse conse-
quences of concentrations outside the preferred ranges are
different in the presence of calcium. For example, with
zinc ion concentrations less than 0.3 %, relati~ely soft
monetite tends to coprecipitate in the conversion film. At
greater than 2.5 % of zinc ions, coprecipitated crystals of
hopeite {Zn3(P04)2 4H20~ and phosphophyllite tend to be
dispersed in the aforementioned scholzite crystals, readi-
ly leading to heteroge.neity in the crystalline structure
of the film. Moreover, at less than 0.01 % total concen-
tration of ferrous ions or when the Fe2 to Zn2+ ratio
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falls below 0.005, the film obtained tends to be unsatis-
factory as a lubrication base layer adapted to severe cold-
working operations. On the other hand, when the ferrous
ion concentration exceeds 2.0 % or when Fe2+/Zn2+ exceeds
3.0, there is a decline in the zinc and calcium content in
the phosphate films due to the excess iron fraction in the
treatment solution, causing a poor coating formation or the
formation of a coarse film of Fe-Hureaulith ~Fe5H2(PO4)4 -
4H2O}-containing scholzite crystals.
The practice of the invention may be further appreci-
ated from the following, non-limi~ing, examples and compar-
ative examples.
Examples and Comparative Examples
Examples and Comparative Examples 1 to 4
Cylindrical test specimens of type S35C steel were
pickle~, rinsed with water, treated with phosphate treat-
ment solution as described in Table 1, then dipped in 70
g/L soap lubricant (Palube~ 235 from Nihon Parkerizing Com-
pany, Limited; main component, sodium stearate; auxiliary
components, sodium borate and sodium nitrite) at 75 degrees
Centigrade for 5 minutes and then dried. The coating
weights of both phosphate and metallic lubricant obtained
are shown in Table 2. The lubrication was then evaluated
by backward punch extrusion under the following conditions:
The critical punch depth for the development of
seizure was determined u~ing backward punch extrusion
as reported by Danno, et al. ~of the Toyota Central
Research Laboratory) in Sosei to Kako [Journal of the
Japan Society for the Technology of Plasticity], Vol-
ume 24, Number 265. This method is briefly described
below.
Equipment and Test Condltions
A 200 ton cold-forging crank press made by Fukui
Kikai Kabushiki Raisha was used at a rate of 30
strokes per minute. Workpieces to be tested were made
of type SKDll steel, which is described in detail in
2~ 5S~
Table 1. Composition of Phosphate Coating Treatment Solutions
examples comparison examples
_ _ ._
components l 2 3 4 1 2 3 4
. . _. ____ _ ___ __ _ ~ ----.~__.A. .V _ .. _ _ _ _ _
zinc ion (%) 0.7 0.7 0.7 0.3 0.2 0.7 0.7 0.7
_ .. _ .. _
calcium ion (%) 1.1 1.1 1.1
._ ................ . _ .. _ _ . . .
iron ion (%) 0.8 0.05 0.5 0.020.9 2.4
. _ _ . _ ~
iron ion (%)
zinc ion (%) 1.14 0.07 0.7 0.074.5 3.4
. ... _ . _ . ___
calcium ion (%)
zinc ion (%) 1.57 3.67 1.57
. ~ .... _ _ ._ .
phosphate ion (%) 1.0 2.0 1.0 1.8 1.2 2.0 1.8 1.0
._ ... .. _. ..
nitrate ion (%) 3.8 4.7 2.5 2.4 1.6 4.9 2.4 1.5
_ _
m-nitro~enzene- 0.05 0.05 0.05 0.05 0.05
sul~nate ion (%)
. .. _ ., . .
ni trox~lene- 0.03 0.07 0.03
sulfonate ion (%)
_ '.
nitrite ion (%) 0.005 0.01
... __ .. ~_
treatment 50 50 50 60 50 50 50 50
temperahlre (C)
... . . _
treatment 10 4 10 5 10 4 10 10
time (minutes) _ _ _ _ .
:
-
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... .
. ~ ` ~ , .
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Table 2. Weight of Produced Coating and Quantity of Metal Soap
No.welght of phosphate quantity of
film metal soap
g/m2 g/m2
. _ ~
1 9.4 3.7
_ . .... ...
2 8.2 3.5
e,xamples . ._ _
3 9.1 2.6
4 8.0 2.2
._ .
1 4.0 1.5
_ . .
comparison 2 7.5 1.9
examples 3 15.0 1.7
. .. ___
. 4 6 8 _
.
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.
Z~ORSS~
Japanese Industrial standard G - 4404. The punch used
to deform the workpieces was made of Hitachi Metals'
high-speed tool steel type HAP40 (made by powder
metallurgical methods and containing in percents by
weight. C - 1.3, Cr = 4.0, W = 6.0, Mo = 5.0~ V = 3.0,
and Co = 8.0). The test method may be further appre-
ciated with the aid of Figures 2 and 3. Figure 2
shows a cross section of part of the test machinery
with a test in progress. A load cell 1 applies pres-
sure through a punch holder ~ to the punch 3. The
punch 3 forces a workpiece 6 to deform as it forms a
hollow space in the originally solid cylindrical work-
piece while pushing it through a cylindrical hole in
the die 4 that has a diameter slightly smaller than
that of original workpiece. When the test is complet-
ed, the deformed workpiece is ejected through the top
of the die by the knockout punch 5. A strain gauge 7
monitors the mechanical force being used in the defor-
mation.
The shape of the punch is shown in greater detail
in Figure 3a. The main shaft of the punch has a diam-
eter of 20.8 millimeters ("mm"), but the leading edge
has a diameter of 21.2 mm and is rounded as shown in
the Figure t with a radius of curvature of not less
than 0.5 mm at any point and a very smooth finish
(meeting the standards described in Japanese Indus-
trial Standard B0601 for marking with the symbol of
four equilateral triangles with adjacent bases) on all
parts of the punch which come into contact with the
workpiece during the testing process. The workpiece
initially has a height ldimension ~ in Figure 3b) of
from 18 - 40 mm and has a diameter (dimension D in
Figure 3b) of 30 mm. The produrtion of a centered
hole with a diameter o~ 21.2 mm in the workpiece dur-
ing testing therefore causes a horizontal cross sec-
tional area reduction of 50 % in the workpiece. As
shown in vertical cross section in Figure 3c, a
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section 10 mm in length at the bottom of the workpiece
remains without any center hole.
\ The results of the tests of critical depth for seizure
generation are shown in Figure 1. The critical depth for
seizure generation was greater in the examples than in the
comparison examples, indicating a superior lubricating per-
formance for the examples. A satisfactory amount of phos-
phate coating and metal soap quantity are also obtained in
Examples 1 to 4, as shown in Table 2.
Examples and Comparative Examples 5 to 8
Samples 10 ~m in diameter by 100 mm long of wire rod
of type S-45C steel were pickled, rinsed with water, treat-
ed with a phosphate treatment solution as described in
Table 3, rinsed again with water, immersed for 5 minutes at
75 degrees Centigrade in 70 g/L of the soap lubricant
Palube9 235, and then dried. Using a Bowden frictional
abrasion tester (Model EFM-4 from Toyo Baldwin Kabushiki
Kaisha), the number of strokes until seizure was measuxed
under the conditions shown in Table 4, with a coefficient
of friction > 0.2. The coating weights of phosphate and
metal soap obtained are shown in Table 5 and the results of
the frictional abrasion test are reported in Table 6. As
Tables 5 and 6 make clear, satisfactory coating quantities
were obtained in Examples 5 through 8, and the Bowden test
results demonstrate that the seizure resistance is far su-
perior to that in Comparison Examples 5 through 8.
Benefits of the Invention
As explained above, the lubrication treatment method
of the present invention achieves the following benefits:
An efficient treatment with an immersion treatment
time of 3 to 20 minutes can be used at a relatively low
temperature of 35 to 65 degrees Centigrade.
The use of a strong accelerator such as NaN02 or H202
can be avoided, so that management of the treatment solu-
tion is facilitated.
A dense, fine phosphate coating with a coating weight
13
.
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7 to 12 g/m2 is formed and provides an optimal base
layer for severe cold-working.
The treatment solution develops only a small quantity
of sludge.
The lubricant film obtained by implementing the pres-
ent invention has excellent cold-working properties. In
particular, the coating obtained has very good properties
when a metal soap film layer is formed on the phosphate
coating using a lubricant treatment solution comprising an
aqueous treatment solution based on the alkali metal salt
of saturated or unsaturated C16 to C18 fatty acid, particu-
larly sodium stearate.
14
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.
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Table 3. Composition of Phosphate Coating Treatment Solutions
examples comparison examples
. . .. _ ~
components 5 6 7 8 5 6 7 8
._ . ___ . ._ . _ . . .
zinc ion (%~ 0.5 1~5 2.0 0.4 0.3 1.0 0.7 0.7
.. ,._ .... _ __
calcium ion (~o) 1.5 0.8 1.5 0.9 0.6
, . __
iron ion (%) 1.5 0.01 0.011.0 0.02
. ~ .... _ . _ ..
iron ion (%)
zinc ion (%) 3.0 0.007 0.005 2.5 0.07
_
calcium ion (æ)
0.752.0 5.0 0.9 0.86
zmc lon (%)
.......................... ....... ........ .... __
phosphate ion (%) 2.9 1.7 4.5 2.0 2.4 1.41.0 1.2
... ._ _ _ . _
nitrate ion (5~O) 9.6 5.0 8.0 5.4 2.72.1 1.5 1.8
. . . . . __
m-nitro~enzene- 0.1 0.07 0.2 0.1 0.03 0.05
sulfona~e ion (%) .
... .. _ .. _ , _. . __
nilrite ion (%) 0.01 0.01 0.01
. . , . _ _ _
trea tment 60 40 40 60 60 50 80 80
temperature (C)
.. . ._ _ . _
treatment 5 7 4 7 5 10 5 5
time (minutes) _ _:
,
z~ss~
Table 4. Bowden Test Conditions
.
pressure element SUJ-~, 5 mm~
. .
load 5 kg
_~ r~
sliding width 10 mm
. . ~
sliding velocity 10 mm/sec
. . .. ~___ . .... .
sliding ~emperature
: 16
. .
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. . .:
.
Table 5.
_ ~ . ___
No. weight of phosphate quantity of
film metal soap
g/m2 g/m2
__ . . ,.. .
S 11.0 3.4
. .... .. _ _
6 10.5 3.6
.. . . ___ . -
examples
7 11.3 28
8 9~4 3.1
.... _ __ ..... ___ _
3.9 0.8
. .. _
comparison 6 4.8 0.7
.
examples 7 7.5 1.9
.. ~ ,, , ._,.. ,, - ..
_ I 6.8 1.7
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Table 6.
. _ . _ _ . . __ _
No.nurnber of strokes mtil
seizure
..... ........ ........ ........... ~
52200
.. .. _. ..
6 2400
examples
~ 2900
___ . _ _ .__
8 2100
_ . _ _ :
1500
_ . .__
comparison 6 1200
.. - --~
examples 7 1700
. -:
8 1900
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