Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a metallic pipe which is provided
with corrosion-protection against chemical and/or mechanical attack,
the said corrosion-protection consisting of a plurality of layers,
at least one of which is a layer made of a metal or a metal-alloy;
and to a method for applying the layers.
Metallic, corrosion-protected pipes of this kind are intended
to remain corrosion-resistant even after being deformed and, during
use, under stress caused by impact, shock and bending. Such
properties are needed for motor-vehicle parts, for example. It
is known to provide a galvanized part with a chromate coating
following a coating on non-wa~ synthetic material, followed in
turn by a heat-treatment. The known me-thod leads to a multilayer
protective coating. See for example, German Patent No. 20 46
~9 or ~.S. Pa-tent No. 3,808,057.
It is also known to apply protective coatings to metal objects
using a reducing agent and compounds of aqueous dispersion
containing hexavalent chrornium, a dispersion being used which
is a hydrophobic resin of a non-waY~ nature, which may be hardenable
or thermoplastic, is added. See German Auslegeschrif-t AS 12 ~6
20 357.
In contrast to this, it is the purpose of the present invention
to provide a metal object with multilayer corrosion protection
in which mutua] adhesion of indivldual layers is sufficiently
flexible to withstand a high degree of deformation, and which
e~hihits still greater resistance to corros:Lon.
According to the invention, this purpose is accomplishecl by
first applying a metal-alloy layer, consisting of low-melting-point
metals, to the surface to be protecter~. Next, an intermediate
layer, both sicles of which are aclapted to adhere, is appli.ed over
the metal-alloy layer. Then, at least one layer of A highly
corrosion-resistant, thermoplastic or thermosetting synthetic
material is formed on the intermediate layer. Multilayer
corrosion-protection o this ~ind adheres firmly to the base (the
metal surEace to be protected), while the individual layers adhere
firmly to each other, said layers being e:tremely flexible and
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able to withstand considerable deformation, as in pipe-bending,
for example. Another advantage of the protection is its great
resistance to base-metal corrosion tests according to DIN 50018/2.0 S
(intensified industrial atmosphere) and ASTM-sll7 (salt-spray
test). This corrosion-protection coating e~hibits homogeneous
behaviour with appropriate resilient adjustment of its components.
These and other beneficial objects of the invention may be
achieved by providiny on a metal surface to be protected: a metal
layer applied to the surface; an intermediate layer, botn sides
of which are adapted to adhere, applied over the layer of metal;
and at least one layer of a highly resistant, thermoplastic or
thermoset-ting synthetic material formed on the said intermediate
layer.
These and other beneficial objects of the inventi.on may also
be achieved by providing on a metal surface to be protected:
a metal or metal-alloy layer, consisting of low-melting-point
metals, applied to the surface; a layer of chromate applied over
the metal or metal-alloy layer; an intermediate layer, both sides
of which are adapted to adhere, applied over the chromate layer;
and at least one layer of a highly resistant, thermoplastic or
thermosetting synthetic material is formed on the said
intermedi.ate layer.
In view of the different mel-ting ranges and temperatures at
wh:Lch the Eilms are formed, the invention may be carried out .Ln
such a manner that, in the case o~ a metal-alloy layer made oE
low-mel-ting-point metals, the intermecliate layer is appli0d as
a short-te.rm heat-insulat:Lng and barrier layer, while the
hiyher-melt:l.ny-point, h:Lyhly resistant, thermoplastic or
thermosettiny synthet:Lc material is appl:Led as the outermost layer.
An important advantaye is that the in-termediate layer makes
it possible to apply hiyh-meltiny-point synthetic or thermosetting
materials, which need higher temperatures to react, to
low-melting-point metal alloys. During the application of the
synthetic material, there is no liquating of the metal alloy and
accumulations of the metal alloy, with the formation of Eree zones
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on the metal object, are avoided. In this case, the intermediate
layer acts mainly as a barrier-layer, preventing the metal alloy
from coalescing. After the synthetic material has been applied,
the intermediate layer effects a particularly intimate union between
the synthetic material and the rnetal alloy. These properties
are eYhibited by mi~.ed polymers, for example, synthetic resins
in which adhesion is also present at high temperatures.
According to one embodiment of the invention, an advantageous
metal alloy is a layer of a lead--tin alloy, since this is soft,
fle~ible and economically viable. The use of a lead-tin alloy
is also supported by the range of equipment available in this
field.
The abovementioned alloy is always effective. However, the
best results are obtained when it comprises, for example, 60 parts
of lead and 40 parts of zinc. This composition is economical
and is also safe and reliable for personnel processing lead.
Moreover, i-t has a relatively low melting point, thus saving power
during processiny.
In the processing of such low-melting-point alloys, a layer
of the metal alloy about a to lO ~Im in thickness is sufficient
to form an initial corrosion-retardant. In practice, a uniform
layer of this thickness is easy to apply and withstands subsequent
deformation of the metal object.
In another embod:iment, a :Layer oE zinc may be applied, which
layer desirably consists of yalvanically cleposited zinc. ~ccording
to another aspect of the invention, :Lt is desirable that the
intermediate layer adhere well to -the unclerlying metal, metal-alloy
or chromate layer. Such an :Lntermecl.Late layer ensures the desired
adhesion anfl, at the same time, const:Ltutes a dense, homogeneous
sur~ace, with which the desired barrier-effect is associated.
E'urthermore, in conjunction with the metal or metal alloy, the
said intermediate layer is sufficiently elastic to withstand higher
degrees of deformation without cracking or even peelin~.
qlhe union between the metal alloy and the intermediate layer
is substantially promoted if the temperature at which the inter-
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mediate-layer film is formed is lower than the melting point of
the underlying metal-alloy layer. Such temperature conditions
also prevent the me-tal alloy from coalescing.
With respect to the relationship between the intermediate layer
and the layer of synthetic material, it is desirable that the
intermediate layer be highly resilient and adhesive, as compared
with the layer of synthetic material.
The resistance of the metallic object to corrosion may be
increased by arranging additional layers of highly-resistant
synthetic material upon the intermediate layer.
According to the invention, the build-up of layers is achieved
in the following manner. The metal or metal-alloy layer is applied
from the molten phase, mechanically or galvanically, in a continuous
operation. The intermediate layer, comprising a primer, is applied
by flow-coating or by spraying from a solvent-phase or dispersion-
phase or electrostatically Erom the solid phase.
The synthetic material is applied by flow-coating, by spraying
from a solvent-phase or dispersion-phase or electrostatically
Erom the solid phase.
Themetal-alloy layer is applied at a temperature of about 190
to 235 C., depending upon operating conditions.
An economical operating process is, therefore, based upon the
highly resistant synthetic material being stoved at about 240
to 270C., being dried and melted onto the underlying lntermediate
layer.
The method according to the invention is particularly suitable
for metal objects in the Eorm oE metal pipes, especially pipes
macle oE steel, used for e~ample, as brake-lines, fuel lines or
a~ hyclraulic l:i.nes Eor motor vehlcles.
In order that the :Lnvention may be reacdily understood, several
embodiments thereof will now be described in detail, by way of
example, with reEerence to the accompanying drawings in which:
Fig. 1 is a cross-sectlon through a pipe with a single coating
of synthetic materLal;
Fig. 2 is a cross-section through a pipe with a double coating
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of synthetic material;
Fig. 3 is a cross-section throu~h a pipe with a chromate layer
and a single coatin~ of synthetic material;
Fig. 4 is a cross-section through a pipe with a chromate layer
and a double coating of synthetic material.
In the eYemplary embodiments, the metal object to be protectively
coated is a seamless, welded or double-walled rolled pipe. Applied
to this pipe is corrosion-protection against chemcial and/or
mechanical attack in the form of a plurality of layers. In Fig.
1, a metal-alloy la~er 3 is applied conventionally to surface
2 of the pipe, designated by the reference numeral 1, said layer
3 comprising, for e~ample, two low-melting-point metals. Lead
and tin are preferably used as the low-melting-point metals in
a 60:~0 alloying ratio. After layer 3 has solidified, an
intermediate layer 5, e.g. a primer, is applied. The intermediate
layer 5 consists of a bonding-agent system comprising a synthetic
resin and containing, among other things, corrosion-inhibiting
fillers. In -this case, the intermediate layer 5 acts as an adhesive
and is therefore highly adhesive on the side facing metal-alloy
layer 3. On the other side, the intermediate layer 5 adheres
to a highly resistant, thermoplastic synthetic-material layer
6, which is now applied; as already indicatecl, this may be replaced
by a thermosetting material. Polyvinyl-fluoride (PVF) and
polyvinyl-difluoride (PVF2) are particularly suitable.
Metal-alloy layer 3 is about 4 to 10 ~m :ln th:lc]cness, thus
providing a hlgh-speecl process. Intermedlate layer 5, i.e. the
so-called primer, in the ~orm Oe a synthetic resin, is such that
it adheres firmly to underlying metal-alloy layer 3.
In one particular exemplary embodlment, both intermecliate layer
5 and layer 6 Oe synthetic materlal are hi.ghly resilient, hi~hly
aclhesive ancl heat resistant.
Accord:Lng to Fig. 2, an additional layer 6 of highly
resistant synthetic material or highly resistant thermosetting
material is provided. The application of an additional layer
6 does not require an additional intermediate layer.
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The advan-tages of the pipe pro-tected, according to the invention,
against corrosion will be apparent if the following tests are
carried oui:
A lead-tin coated steel pipe 1 would not withstand the salt-spray
test according to the ASTM-B117, i.e. after about 360 hours such
a pipe would e~hibit base-metal corrosion (red rust). The test
according to DIM 50018/2.0 S (intensified industrial atmosphere)
would produce poor results with a lead-tin coated pipe. Accordiny
to this test, (corresponding to 2 litres of SO2), only one cycle
is completed before base-metal corrosion becomes visible.
A galvanized steel pipe, carrying a layer of chromate and a
layer of synthetic material, completes more than 50 cycles according
to DIN 50018/2.0 S or more than 5000 hours according to ASTM-s
117 before base-metal corrosion appears.
According to the invention, steel pipes carrying a coating
of lead--tin, an intermediate layer and a layer of syn-thetic material
also complete more than 50 cycles according to DIN 50018/2.0 S
or 5000 hours according to ASTM-B 117.
According to the invention, steel pipes carrying a coating
of zinc, an intermediate layer and a layer of synthetic material
complete more than 60 cycles according to DIN 50018/2.0 S or 7,500
hours according to ASTM-B 117.
Accordiny to E'ig. 3 or 4, it is also possible to apply a layer
of chromate between metal or metal-alloy layer 3 and intermediate
layer 5 which has a positive effect upon resistance to corrosion
in that it prevents sub-migration, such as may arise in the event
oE damage (flying stones).
It will be unclerstood -that the invention is not limited to
the exact constructions shown and described, but that various
chanyes ancl modiications may be made without departing from the
spirit and scope of the invention as deined in -the appended claims.
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