Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS OF PRODUCING PHOSPHATE COATINGS ON METALS
Bach~lou~d of In~vention
The pre~ent in~ention i8 in a process for producing a
phosphate coating on a metal ha~ing a surface which consists at
lea~t in part of iron or ~teel by a treatme~t with an aqueou~
phosphatizing solution, which contains zinc ions, P04 ion~,
nitrate ions, magne~ium ions and if ~eing in working condition,
iron(II) ion6 and to the use of that process for preparing metals
for sub~equen~ cold working operations such a~, ~o~ example, wire
drawing, tube drawing, cold heading and cold extrusion.
The use of phosphatizing solutions which contain mangane6e,
iron(II) and zinc pho~phate and are at temperature~ of from 50 to
98 C to pho~phatize metals, particularly iron and steel, i~
known. The resulting phosphate coatings are useful for varioug
applications such a~ ru~t prevention, priming for the applica~ion
of paint, electric insulation, reducing sliding ~riction and
facilitating cold working (Published German Application 30 2
479; EP 42 631),
The performance of the known phosphatizing proce~ses at
relatively low temperatures, e.g., between 30 and 50~ C, often
gi~es rise to difficultie~ which include, among others, the
formation of phosphate coatings which only incompletely cover the
metal ~urface and/or which become progressi~ely more coar~e as
the iron (II) content in the phosphatizing ~olution increases.
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Certain impro~ements can be obtained by a preliminary acti~ating
rinsing ~tep, e.g., with titanium pho~phate, but the results thus
produced are not en~irely sati~factory. On the other hand, low-
temperature processes are urgently required because they save
energy. Additio~ally, the pro~esses which involve the pre~ence
of iron(II) are superior to the u~e of pho~phatizing solutions
which are free of iron(II) because much less sludge is formed and
the consumption rates are fa~orable.
It has been ~ound the component solution~ for the
phosphatizing bath periodically become un~table when supplied in
commercial quantities. The lack of sta~ y sometime~ re~ults
in the formation of precipitates which can ad~er~ely affect the
coating. Also, the component solutions sometime~ exhibit a
gassing which i9 believed to be ~a~ed on the ~ormation of NOX in
gaseous form causing the expa~sion or -~welling of the container
and resulting in the emission of a browni~h ~ume. One approach
to a~oid such pro~lems is to use a number of separate concentra~e
or make-up solutions and to mix the sol~tions on site as the need
arises. Howe~er, on site m; ~; n~ can be inconvenient and requires
the expenditure of additional time, effort and resources as the
number of such component 601utions required to make the bath
increases.
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The In~rention
It i~ an object of t~e in~ention to pro~ide a process for
the produc~ion of phosphate coatings on metal~ ha~ing surfaces
which conQist at least in part of iron and steel, which can be
carried out at low temperatures and in the ~resence of iron(II)
and which results in the formation of uniformly covering
phosphate coatings but without an un~sually high proces~
expenditure.
It i~ a further object o~ the in~ention to pro~ide a process
~or the preparation of such a metal ~ur~ace for cold working.
Another object of the invention is to provide a process
which requires a minimum number of ~eparate components to prepare
the phosphatizing bath.
It is another object of the in~ention to provide
compositions for use in ~uch a proce~ that are consi~tently
stable and which remain stable o~er an extended period of time.
It is a further object of the invention to pro~ide component
solutions which are not subject to gas~ing and which do not form
precipitates.
The proce~ o~ the invention overcomes the above-discussed
disadvantage~. In the in~ention the metal 6ur~ace is contacted
with a phosphati~ing ~olution which i-~ at a temperature in the
range of from about 30 to 65 C and contain~ about 5 to about 25
g/l zinc, abou~ .5 to about 5 g/1 of magnesium, about 0.1 to
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about 13 g/l iron(II), a~out 5 to about 40 g/l pho6phate
(calculated as PzOs), about 5 to about 50 g/l nitrate, about 0.5
~o about 5 g/1 fluoroborate (calculated as BF~) and which ha~
been adjusted to weight ratios of Zn : P20s of (~.5 to 3) : 1 and
of Mg : Zn of (0.04 to 0.5) : 1 and to a raeio of free acid to
total acid of (0.04 to ~.2) : 1. Optionally the solu~ion may
contain about 0.05 to about 3 g/l of tartaric acid and/or of
citric acid. The phosphatizing solution, and the conce~trate
solution(~) used for make-up and repleniQhment are e~sentially
free of manganeQe.
The process of the invention is especially useful to treat
iron and steel which contain up to a~out 5~ alloying additions
It al~o ifi possible to treat other metals, e.g., of zinc and zinc
alloys, together with iron and steel, whether such other metals
are in the form of compact workpiece~ or merely coatings on
workpieces.
The selJeral component3 o~ the phosphatizing l;olution, such
as zinc, magnesiu~, phosphate, etc., are jointly predi~sol~ed ~o
form an acid phosphatizing concentrate, a~ is usual in
pho~phatizing technology, and are added to the phosphatizing
solution in that form. The several component~ are added in such
quantities that the required con~Pntration ranges are obtained in
the phosphatizing solution. If nece6sary, the required ratio of
free acid to total acid may be obtained by the introduction of
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additional ions of the group con.~isting of the alkali and
ammonium ions.
In a preferred emboA;~nt o~ the in~ention, the metal i~
contacted with a phosphatizing ~olution which also contains abou~
O . 05 to about 2 g/l Ni and/or about o . 001 to about 0.1 g/l Cu
and/or about O . 5 to about 2 g/l Ca. A nickel content will
promote layer formation, particularly on ~inc and on materials
which ha~e a relatively high resistance to the attac~ by the
colution. An addition of copper ions will accelerate the
phosphatizing proces~. Added calciu~ ion~ will modify t}le
phosphate coating and will effect ~uch a conditioning o~ the bath
~ludge ~or~ed in a small amount that the sludge is still les~
disturbing in the pho6phatizing bath and can be remo~ed f~nm the
system more easily.
The phosphatizing solutions used in the proce~s in
accordance with the in~ention need not initially con~ain iron(II)
ions. The bath will become enriched in iron(II) durin~ the
treatment of iron and steel by di~solution of iron from the
sur~ace. The ph~sphatizing ~olution may also be artificially
aged by addition of an iron(II) sal~ compatible with the other
components of the solution, e.g., iron(II) ~ulfate. While the
phosphatizi~g solution ~ay ha~e an iron(II) conten~ of up to
about 13 g/l, the ~olutionæ are pre~erably ~sed in such a m~n~
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that the concentration of iron(II) ions does not exceed 10 g/l
and is preferably in the range o~ from 4 to 7 g/l.
In order to prevent an undesirable increase of the iron(II)
concentration, a portion of the iron(II) ions which have entered
the solution a~ a re~ of the pickling action are preferably
oxidized to form irontIII) ~ons. The iron(III) ion~ are
precipitated as difficultly soluble iron(III) phosphate sludge
In a preferred embodiment of the ~nvention, ~urplu~ iron~II)
is transformed to tri~alent iron by contact with an oxygen-
containing gas or by mean-~ of chlorate and i9 precipitated as
iron(III) phosphate ~ludge. In the first case, iron kI) can be
removed, e.g., in a separate aerating container, which i5
s~cceeded by a filter.
Sodiu~ carbonate, zinc oxide and/or zinc carbonate are
preferably used to adjust the ratio of free acid to total acid to
(0.04 to 0.2) : 1. The~e co~ponent-~ are added to the
pho~phatizing 601ution ag a powder or in an aqueous ~uspen~lon.
To determine the contents of free acid and of total acid, bath
sample~ of 10 ml are titrated with NJ10 ~aOH to the fir~t and
~econd tran~itions of pho~phoric acid a~ indicated by a color
change, e.g., with dimethyl yellow (free acid test) and
phenolphthalein ~total acid test) ~sed a~ indicator~. The
consumption of Nt10 NaOH in milliliters corresponds to the points
of free acid or total acid.
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It ha~ also been found desirable to contact the metals with
a phosphatizing solution which contain~ a nitrite-destroying
su~tance, such as urea or amidosulfonic acid. This will inhibit
the autocatalytic formation of nitrite from the nitrate and will
preclude a turrlover of the bath from the iron side to the nitrite
ide .
In prior art ~igh zinc phosphatizing processes, it ~as been
~ound that the addition of tartaric or citric acid to the
pho~phatizing solution re~ulted in a coating having a finer
crystal ~ructure than obtained by the u~e of the same solution
without those acid addition~. Howe~er, in the process of the
invention, such substances are not necessary to obtain a fine
crystal structure and their presence, whic~ is optional, ha~
li~tle or no ef~ect on the finenes~ of the crystal 6truc~ure.
The addition of the tartaric or citric acid can result in a lower
coating weight. The fine coatings produced by ehe proces~ o~ the
invention have a ~ood drawing ability, exhibit good coating
retention during drawing and consume less drawing lubricants,
i.e., drawing soap~.
During the phosphatizing proces~, co~ponents o~ the ~olution
are con~umed by the formation of the coating, the formation of
~ludge, and by the mechanical discharge of pho~phatizing
solution. The pho~phatizing solution must be repleni~hed wieh
the con~umed components. The replenishing i~ preferably by means
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2149721
of a replenishing concentrate containing a number of, or all of,
the individual component~. The phosphatizing solution can be
replenished i~ a particularly desirable manner by an addition of
zinc ion~, magnesium ions, phosphate ion~ and nitrate ions in the
form of at least one concentrate which has been adjus~ed to
weight ratios of Zn : P2O5 = (0.3 to 0.8) : l, o~ Mg : 2n =
~ 05 to 0.2) : 1 and of NO3 : P2Os , (0.2 to 1) : 1. Any other
components of the phosphatizing solution to be replenished should
be added in weight ratios of Ca : Zn - (o . 00~ to 0.1) : l, of Ni
: Zn - (0.005 to 0.05) : l, of Cu : Zn = (0.001 to 0.03~ : 1, and
of BF4 : P205 - ~0.008 to 0.04) : l. When the solution is to
contain tartaric and/or citric acid, the ratio of tartaric and/or
citric acid to P2O5 is (0.05 to 0.3) : 1. The concentrates of
the invention need not contain stabilizing agents ~ut, if
de~ired, the ~sual stabilizers may be added.
The metal surface may be contacted with the pho~phatizing
solution by dipping, flooding or spraying. In mo~t cases the
501ution is applied by dipping with treatment ti~es of, e.g., 5
to 15 minutes. If the flooding technique is used the trea~ng
time i~ the ~ame as with the dipping treatment. In case of
~praying the treatment time is in general in the range o~ 0.5 to
3 minutes.
In dependence on the ~pecific compo~ition of the solution,
the treating temperature, the treating time and the sequence of
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operations, the pho~phate layer~ produced by the process in
accordance with the invention will have a weight of about 3 to 18
g/m2 ~
sefore ~he pho~phatizing proces~, ~he ~etal6 are pretreated
in ~he conventional manner. ~or in~tance, the metal~ may be
degreased by means of an aqueou~ alkali~e cleaning solution which
contains suita~le surfactants. Any ~cale or rust which may be
present should be removed by a pi~kling treatment, e.g., with
~ulfuric acid or hydrochloric acid.
Before the workpieces are phosphatized, they may be
prerin~ed in a manner kno~n per se, e.g., with an acti~ating bath
which contains titanium phosphate, in order to promote the
formation of finely cry6talline phosphate coa~ing~. Such a
treatment is not compulsory.
The phosphatizing treatment i~ usually ~ollowed by a water
rinsing and by an optional aftertreatment and drying, if
required. The re~istance to corrosion can be increased by an
aftertreatment, e.g., wi~h chromic acid and/or corrosion
protecti~e emulsions. Workpieces to be cold-worked may be
aftertreated, e.g., with a ~oap-applying bath.
The pho~phate coatings produced by the proces~ in accordance
with t~e in~ention can be used to advantage in all fields in
which phosphate coatings are u~ed and are particularly suitable
for preparing metals for a sub~equent cold working.
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2149721
The invention will be explained more in detail by the
following E~ample.
ExamDle
Steel wire having a carbon content of from 0.5 to 0.9~ i9
acid treated to remo~e ruQt and ~cale and is then thoroughly
rinsed with water. The rinsed wire is pho~phatized by dipping
for 6 to 10 minutes in a phosphatizing ~olution which is at 45C
and compo~ed as follows:
15.0 g/l Zn,
1.6 g/l Mg,
7.0 g/1 Fe(II),
0.5 g/l Ca,
g/l ~i,
0.01 g/l Cu,
0.3 g~1 Na,
30.0 g/l NO3,
12.0 g/l P20s
1.6 g/l BF"
0.5 ~/l Urea,
5.4 points free acid, and
points total acid.
The pho~phatizing treatment is followed by another rin~ing
with water, which i~ followed by neutralization in a hot a~ueous
borax solu~ion and by o~en-drying. After that ~equence o~ Qteps,
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2149721
the phosphate coating ha~ a weight of 8 to 12 g/m2. Although
there had been no activating prerinse with titanium pho~phate,
the phosphate coating i6 ~inely cry~talline and pro~ides a
uniform coverage.
After that treatment the wires could ~e fiatisfactorily
~haped in up to lO to 13 drawing passes to a ~ximl~m reduction in
cro~ ection by 93.5~ with a very low wear of the drawing dies.
After drawing, the qurface o~ the wire continues to have a
uniform re~idual phosphate layer and is free of groove~.
Air is blo~n into the phosphatizing bath during the
treatment to maintain the iron(I~) ion content in the range of
from 2 to 7 g/l under the existing condition~. ~o maintain as
constant the point~ of total acid in the bath, the solution i6
replenished with a replenishing concentrate containing, on a
weight percent ba~
10.1 ~ Zn,
,163 ~ Mg,
o.o9 ~ Ni,
O.021 ~ Cu,
19.5 ~ P2Os,
10.6 ~ NO3,
0.~ ~ BF" and
0.15 ~ Ca.
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secause the bath i~ operated on the iron side, only a small
amount of bath sludge forms. Repleni~hing concentrate i9
consumed at the very low rate of about 27 g per m2 of metal
surface area.
It ~ill be understood that the ~pecification and examples
are illustrati~e but not limitati~e of the present invention and
that other embodiments within the Qpirit and scope of the
invention will suggest themselve~ to those skilled in the art.
