U.S. patent application number 10/830181 was filed with the patent office on 2004-11-11 for method for applying manganese phosphate layers.
Invention is credited to Nittel, Klaus-Dieter, Seifert, Detley, Stickler, Ralf.
Application Number | 20040221924 10/830181 |
Document ID | / |
Family ID | 33420253 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040221924 |
Kind Code |
A1 |
Nittel, Klaus-Dieter ; et
al. |
November 11, 2004 |
Method for applying manganese phosphate layers
Abstract
The invention relates to a method for applying manganese
phosphate layers to iron or steel surfaces using phosphating
solutions containing manganese, phosphate, iron (II) ions as well
as nitroguinidine, as well as its application to workpieces that
are subject to sliding friction.
Inventors: |
Nittel, Klaus-Dieter;
(Frankfurt am Main, DE) ; Seifert, Detley;
(Munster, DE) ; Stickler, Ralf; (Kahl am Main,
DE) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
666 FIFTH AVE
NEW YORK
NY
10103-3198
US
|
Family ID: |
33420253 |
Appl. No.: |
10/830181 |
Filed: |
April 22, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10830181 |
Apr 22, 2004 |
|
|
|
10088840 |
Jul 2, 2002 |
|
|
|
10088840 |
Jul 2, 2002 |
|
|
|
PCT/EP00/09193 |
Sep 20, 2000 |
|
|
|
Current U.S.
Class: |
148/260 |
Current CPC
Class: |
C23C 22/18 20130101;
C23C 22/188 20130101 |
Class at
Publication: |
148/260 |
International
Class: |
C23C 022/07 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1999 |
DE |
199 47 232.7 |
Claims
1-7. (Canceled).
8. A method for applying manganese phosphate layers to iron or
steel surfaces comprising contacting workpieces with a phosphating
solution comprising 0.2 to 4 g/l of iron (II) ions 10 to 25 g/l of
manganese ions 25 to 50 g/l of phosphate ions (calc. as
P.sub.2O.sub.5) 3 to 35 g/l of nitrate ions 0.5 to 5 g/l of
nitroguanidine said solution having 7 to 24 points of free acid, 50
to 140 points of total acid, and an S value of 0.2 to 1, and drying
the workpieces to form a manganese phosphate layer having a minimum
thickness of 2 .mu.m and an average maximum roughness depth
(R.sub.z) of from 1.3 to 2.5 .mu.m.
9. The method according to claim 8, wherein said phosphating
solution that comprises 0.5 to 2 g/l of nitroguanidine.
10. A method according to claim 8, wherein the phosphating solution
comprises not more than 2.5 g/l of iron (II) ions.
11. A method according to claim 8, wherein the workpiece is steel
and said phosphating solution comprises a complex-forming agent for
the alloying constituents of the steel.
12. A method according to claim 11, wherein said coupler-forming
agent is citric acid.
13. A method according to claim 8, wherein said phosphating
solution further comprises at least one metal ion selected from the
group consisting of 0.2 to 4 g/l of nickel ions and 0.2 to 4 g/l of
magnesium ions.
14. A method according to claim 8, wherein at least a portion of
the manganese ions in said phosphating solution are replaced by
manganese carbonate to neutralize free acid.
15. A the method according to claim 8, wherein said workpieces are
subjected to a sliding friction.
16. A method according to claim 8, wherein said workpieces are
selected from the group consisting of axles, gear mechanism parts
and engine pistons.
Description
[0001] The invention relates to a method for applying manganese
phosphate layers to iron or steel surfaces using phosphating
solutions containing manganese, phosphate, iron (II) ions as well
as nitroguanidine, as well as its application to workpieces that
are subjected to sliding, friction.
[0002] On account of their high mechanical resistance, manganese
phosphate layers have proved ideal for various applications, e.g.
in order to reduce the friction of metal surfaces sliding on one
another or to facilitate the cold forming of metals. However,
relatively thick, coarsely crystalline layers were obtained with
the manganese phosphate solutions that were initially commonly
used, these layers being particularly disadvantageous if fine
mechanical parts are to be treated. Numerous proposals have
therefore been made with the object of producing thin, finely
crystalline manganese phosphate layers. For example, it is known
that an improvement in the phosphate layer can be obtained by
adding condensed phosphates. Phosphating solutions based on
manganese phosphate are however generally employed at high
temperatures, which means that, as a result of the considerable
hydrolysis that takes place at high temperatures, the effectiveness
of the condensed phosphates rapidly falls and/or replenishment
condensed phosphate has to be constantly added.
[0003] Another way of obtaining fine-grain phosphate layers is
described in German Auslegeschrift 1109 484. Nitrate-containing
phosphate solutions in which the amount of nitrate is in excess of
the amount of phosphate are used for this purpose. The solutions
should have a ratio of nitrate to phosphate of about 1.5-4.5:1. It
has been found however that in many cases the intended effect is
not achieved.
[0004] Furthermore, a method is known in which an increased amount
of free acid in the phosphating solution is specifically employed
in order to obtain particularly thin layers (DE-C-1246356).
However, on account of their low surface density these layers can,
in practice, only apply to special cases.
[0005] Finally it is known to add to a phosphating solution based
on manganese phosphate or manganese-iron phosphate in which the
concentrations with respect to manganese, iron (II), phosphate and
nitrate ions lie within specific limits, proportionally more free
P.sub.2O.sub.5 in relation to the total P.sub.2O.sub.5 than
corresponds to the phosphating equilibrium in the working
phosphating solution. The aforementioned measure is said to have
the advantages of achieving a significant decrease in the amount of
slurry formed in the phosphating and a reduction of the chemicals
needed to produce a specific amount of coating (DE-B-22 13781).
[0006] A common feature of the known methods is that manganese
phosphate layers are formed having significant roughness depths.
The reason for this is that the etching action in manganese
phosphate systems is already pronounced at the start of the process
and leads to a punctiform removal of metal after an extremely short
action time. On the other hand, the layer formation takes place
relatively slowly compared with zinc phosphate systems. The
pronounced etching action and delayed layer formation can be
observed visually by a large evolution of gas over a relatively
long period, the so-called gas time..
[0007] The object of the invention is to provide a method that
leads to manganese phosphate layers having as low a roughness depth
as possible, but whose layer thickness is in the medium to high
range.
[0008] This object is achieved by the method of the type mentioned
in the introduction and corresponding to the invention in which, in
order to produce a manganese phosphate layer having a minimum
thickness of 2.5 .mu.m and an averaged maximum roughness depth
(R.sub.z) of 2.5 .mu.m, measured after drying, the workpieces are
brought into contact with a phosphating solution containing
[0009] 0.2 to 4 g/l of iron (II) ions
[0010] 10 to 25 g/l of manganese ions
[0011] 25 to 50 g/l of phosphate ions (calc. as P.sub.2O.sub.5)
[0012] 3 to 35 g/l of nitrate ions
[0013] 0.5 to 5 g/l of nitroguanidine
[0014] that has 7 to 24 points of free acid, 50 to 140 points of
total acid, as well as an S value of 0.2 to 1.
[0015] The averaged roughness depth is defined according to DIN
4768, Sheet
[0016] 1, and represents the arithmetic mean of the individual
roughness depths of five mutually adjoining individual measurement
stretches of identical length, defined as
R.sub.z=0.2 (Z.sub.1+Z.sub.2+Z.sub.3+Z.sub.4+Z.sub.5)
[0017] The required maximum value of 2.5 .mu.m refers only to the
roughness depth of the manganese phosphate layer and disregards the
depth of the untreated metal surface.
[0018] The aforementioned total point number is determined in a
manner known per se by titrating 10 ml of the phosphating solution
after dilution with water to about 50 ml using phenolphthalein as
indicator, until the colour changes from colourless to red. The
amount of 0.1 N sodium hydroxide solution used represents the total
point number. Other suitable indicators for the titration are
thymolphthalein and ortho-cresolphthalein.
[0019] The free acid points are determined in a similar way,
dimethyl yellow being used as indicator and the titration being
carried out until the colour changes from pink to yellow.
Interfering metal ions are removed beforehand by adding
hexacyanoferrate (II) or hexacyanocobaltate (III) ions. The S value
is defined as the ratio of free P.sub.2O.sub.5 to total
P.sub.2O.sub.5. (For further details see W. Rausch, "Die
Phosphatierung von Metallen", Eugen G. Leuze Verlag, Stuttgart
1974, pp. 273 ff.)
[0020] More particularly, it is known from GB-A-510684 to produce
manganese phosphate layers using phosphating solutions that may
also contain nitroguanidine in addition to numerous other oxidising
agents. However, it can be calculated from the data relating to the
point numbers of free acid and total acid that the phosphating
solutions contain considerably lower concentrations of
phosphating-active components and--corresponding to the objective
pursued in the known method of improving the corrosion resistance
of metals--can form layers of a very low layer weight. The patent
specification does not contain any kind of information on the
roughness depth of the phosphate layer.
[0021] The investigations carried out on the development of the
present invention have shown that when using nitrate as
accelerator, which autocatalytically forms nitrite as a result of
the normally used high phosphating temperatures, or when using
nitrite or chlorate, the layer formation is disturbed because of
the deficient iron (II) content, or layers are formed having only a
very low layer weight or very low layer thickness. In contrast the
use of nitroguanidine allows the iron (II) concentration to be kept
below specific limits without resulting in an undesirable sharp
drop in the iron (II) content necessary for the formation of a
qualitatively high-grade layer.
[0022] In order to assist the oxidation of iron (II),
oxygen-containing gas, for example compressed air, may be blown
into the phosphating solution. Substances that oxidise iron (II),
preferably potassium permanganate, may also be added. It should
however be borne in mind that the iron (II) concentration should in
no case fall below 0.2 g/l, since otherwise the desired layer
weight will not be obtained.
[0023] A preferred embodiment of the invention envisages bringing
the workpieces into contact with a phosphating solution that
contains 0.5 to 2 g/l of nitroguanidine. Reasons of cost in
particular are decisive in this connection.
[0024] Furthermore it is advantageous to adjust the concentration
of iron (II) ions in the phosphating solution to a maximum
concentration of 2.5 g/l. In this way, finely crystalline layers of
small roughness depth can also reliably be formed in the case of
workpieces that are difficult to phosphate.
[0025] If workpieces with steel surfaces are to be phosphated, a
further advantageous embodiment of the invention envisages adding
complex-forming agents to the phosphating solution in order to
complex the alloying constituents of the steel. In particular
chromium is such an alloying constituent. Suitable complex-forming
agents are for example tartaric acid, but, in particular, citric
acid. The constituents of the steel that might adversely affect the
layer quality are trapped by the addition of complex-forming
agents.
[0026] A further advantageous modification of the invention
consists in bringing the workpieces into contact with a phosphating
solution that additionally contains
[0027] 0.2 to 4 g/l of nickel ions
[0028] or
[0029] 0.2 to 4 g/l of magnesium ions.
[0030] These additions produce an homogenisation of the etching
attack on the metal surface to be treated and thereby achieve a
stronger adhesion of the phosphate layer. Also the appearance of
the phosphate layer is improved as a result of the generally
desirable dark coloration. In addition, the content of magnesium
ions reduces the overall consumption of chemicals.
[0031] Finally, it is expedient to contact the workpieces with a
phosphating solution in which at least a proportion of the
manganese ions have been replaced by manganese carbonate in order
to neutralise the free acid.
[0032] The contact of the workpieces with the phosphating solution
preferably takes place at a temperature in the range from
75.degree. to 95.degree. C.
[0033] The workpieces may be brought into contact with the
phosphating solution in any appropriate way, preferably by
immersion treatment. Treatment times of, in general, 1 to 15
minutes are appropriate.
[0034] As a rule it is necessary to clean the workpieces before the
phosphating. Acidic, neutral or alkaline cleaning agents are used
for this purpose. In general the workpieces are thoroughly rinsed
with water between the cleaning and the phosphating of the
workpieces. Particularly after treatment with alkalis and acids,
the workpieces should be pre-rinsed in an aqueous slurry of finely
divided manganese phosphate in order to promote the formation of
particularly uniform finely crystalline layers in the subsequent
phosphating.
[0035] Phosphate layers having a layer weight of in general 5 to 30
g/m.sup.2 can be obtained by means of the method according to the
invention.
[0036] The phosphate layers produced by the invention may, in a
manner known as per se, be lacquered or provided with plastics
coatings. In conjunction with corrosion prevention oils, these
measures serve to increase the resistance to rust. The main
application of the method according to the invention however is in
the treatment of workpieces that are exposed to sliding friction.
Such workpieces include, for example, axles, gear mechanism parts
and pistons of internal combustion engines and compressors.
[0037] It is possible by means of the method according to the
invention, to produce manganese phosphate layers with average to
high layer thicknesses that, nevertheless, have only a very low
averaged roughness depth. The roughness depth is ca. 30 to 50%
below the values that were hitherto normally obtained. As a result
of the low roughness depth the frictional resistance is
considerably reduced for workpieces that are subjected to sliding
friction. The reduction of the so-called gas time to about half the
hitherto usual time indicates that the duration of the etching
attack of the phosphating solution, and thus the removal of metal
from the workpiece, is considerably reduced. It is assumed that the
content of nitroguanidine in the phosphating solution leads to a
certain passivation of the metal surface, which however permits a
reduced etching attack and/or leads to an earlier start of the
layer formation.
[0038] The invention is described in more detail with the aid of
the following example.
EXAMPLE
[0039] Steel cup-shaped tappets were first of all degreased by
immersion in a strongly alkaline, aqueous cleansing agent, next
rinsed with water, then pre-rinsed in a slurry of finely divided
manganese phosphate, and finally phosphated by immersion in a
phosphating solution at 80.degree. C. for a duration of ten
minutes.
[0040] The phosphating solution contained
[0041] 11.8 g/l of manganese,
[0042] 0.5 g/l of nickel,
[0043] 1 g/l of iron (II),
[0044] 36 g/l of phosphate (calculated as P.sub.2O.sub.5)
[0045] 4.6 g/l of nitrate and
[0046] 0.36 g/l of citrate (calculated as citric acid).
[0047] The total point number of the phosphating-solution was 80,
and the point number of the free acid was 11 (measured with 60 g of
concentrate per 1 l of water). For the determination of the total
acid point number and free acid point number, reference should be
made to the details given above. 183 g of a concentrate containing
6.45 wt. % of manganese, 0.28 wt. % of nickel, 0.05 wt. % of iron
(II), 19.8 wt. % of P.sub.2O.sub.5, 2.5 wt. % of nitrate and 0.2
wt. % of citric acid, which was made up to one litre with fully
deionised water, served as the phosphating solution batch.
[0048] Finely crystalline phosphate layers with a layer weight of 7
g/m.sup.2, corresponding to a layer thickness of 3 to 4 .mu.m, and
an averaged roughness depth R.sub.z of 1.3 to 2.4 .mu.m, were
obtained. The gas time was 2 to 3 minutes.
[0049] A comparative test was carried out under identical
conditions with the above phosphating solution, which however did
not contain nitroguanidine. Phosphate layers were formed which,
although being finely crystalline, nevertheless had an averaged
roughness depth R.sub.z of 5 to 6 .mu.m. The layer weight was 6
g/m.sup.2. The gas time was 6 to 10 minutes.
* * * * *