TECHNICAL FIELD
[0001] The invention relates to a method for pre-treating a galvanized fence panel to be
coated. In a second aspect, the invention relates to a pre-treated galvanized fence
panel.
PRIOR ART
[0002] Fence panels, and more specifically fence panels for outdoor use, must have sufficient
anti-corrosion properties. In addition, fences often need to have an aesthetic and
attractive appearance.
[0003] Applying a powder coating can provide a solution to both problems. By applying a
powder coating to a galvanized fence panel, not only a more aesthetic and attractive
result is achieved, the corrosion resistance of this so-called duplex system is also
considerably better. However, zinc is one of the most difficult surfaces to apply
a paint system to. The reason for this is that the quality of the hot-dip galvanized
material can vary greatly. In addition, many contaminants can occur on the zinc surface,
such as corrosion products, passivation layers, rolling oil, etc.
[0004] A problem with the known pre-treatment methods is that they are not aimed at treating
complete galvanized fence panels. Known methods fall short in providing an adhesion
layer on the fence panel that provides sufficient adhesion of the coating and has
sufficient anti-corrosion properties.
[0005] US2014120369 discloses a continuous galvanization process for a long steel product consisting
of a single immersion step, wherein prior to this single immersion step the long steel
product has undergone one or more treatment steps, selected from the group consisting
of alkaline cleaning, rinsing, pickling and drying, and furthermore a fluxing step,
consisting of immersing in a fluxing agent composition consisting of a) more than
40 and less than 70 wt% zinc chloride, (b) 10 to 30% by weight ammonium chloride,
(c) more than 6% and less than 30% by weight of a group of at least two alkali metal
chlorides, including sodium chloride and potassium chloride, d) 0 to 2% by weight
lead chloride, and e) 0 to 15 percent by weight tin chloride, provided that the KCl/NaCl
weight ratio of this group of at least two alkali metal chlorides is between 2.0 and
8.0.
[0006] The present invention aims to find a solution for at least some of the above problems.
[0007] There is a need for an improved method for pre-treating galvanized fence panels.
SUMMARY OF THE INVENTION
[0008] The invention concerns a method for pre-treating a galvanized fence panel to be coated
according to claim 1. Preferred forms of the method are set out in claims 2-13. In
a second aspect, the invention concerns a pre-treated galvanized fence panel according
to claim 14.
[0009] It is an aim of the invention to optimize the pre-treatment of galvanized fence panels
that require coating.
[0010] It is also an object of the invention to increase the pickling speed and the pickling
transfer on the metal surfaces of the fence panels. Moreover, it is an aim of the
invention to achieve a faster deposition kinetics of the thin adhesion layer consisting
of elements of the metal ions and to obtain a more homogeneous coating of the metal
surface.
[0011] By applying a powder coating to the galvanized steel, not only an aesthetic and attractive
result is achieved, the corrosion resistance of the fence panels is also significantly
better. However, zinc is one of the most difficult surfaces to apply a paint system
to. The reason for this is that the quality of the hot-dip galvanized material can
vary greatly. In addition, many contaminants can occur on the zinc surface, such as
corrosion products, passivation layers on sendzimir galvanized steel, rolling oil,
etc. The addition of fluoride is particularly advantageous when hot-dip galvanized
steel surfaces are treated in a method according to the invention.
[0012] The adhesion layer on the fence panel over which a coating is applied in a next step
improves both the adhesion of the coating and the anti-corrosion properties of the
fence panel.
DETAILED DESCRIPTION
[0013] The invention concerns a method for pre-treating one or more galvanized fence panels.
[0014] Unless otherwise defined, all terms used in the description of the invention, including
technical and scientific terms, have the meaning as commonly understood by a person
skilled in the art to which the invention pertains. For a better understanding of
the description of the invention, the following terms are explained explicitly.
[0015] In this document, "a" and "the" refer to both the singular and the plural, unless
the context presupposes otherwise. For example, "a segment" means one or more segments.
[0016] When the term "around" or "about" is used in this document with a measurable quantity,
a parameter, a duration or moment, and the like, then variations are meant of approx.
20% or less, preferably approx. 10% or less, more preferably approx. 5% or less, even
more preferably approx. 1% or less, and even more preferably approx. 0.1% or less
than and of the quoted value, insofar as such variations are applicable in the described
invention. However, it must be understood that the value of a quantity used where
the term "about" or "around" is used, is itself specifically disclosed.
[0017] The terms "comprise," "comprising," "provided with," "contain," "containing," "include,"
"including" are synonyms and are inclusive or open-ended terms that indicate the presence
of what follows, and which do not exclude or prevent the presence of other components,
characteristics, elements, members, steps, as known from or disclosed in the prior
art.
[0018] The terms "consist of," "consisting of," "being composed of," "composed of", are
synonyms and are exclusive or closed-ended terms indicating the presence of what follows,
and excluding or precluding the presence of other components, features, elements,
members, steps known or described in the art.
[0019] Quoting numeric intervals by the endpoints includes all integers, fractions, and/or
real numbers between the endpoints, including those endpoints.
[0020] In a first aspect, the invention concerns a method for pre-treating one or more galvanized
fence panels to be coated, wherein the one or more galvanized fence panels are sequentially
immersed in baths in a suspended condition.
[0021] In a preferred embodiment, the method comprises the following sequential steps:
- i. degreasing, whereby the fence panels are immersed in a degreasing bath containing
degreasing agents;
- ii. rinsing, wherein the fence panels are immersed in a first rinse bath comprising
water;
- iii. pickling, whereby the fence panels are immersed in two successive pickling baths
containing pickling agents;
- iv. rinsing, wherein the fence panels are immersed in a second rinse bath comprising
water;
- v. demi-rinsing, whereby the fence panels are immersed in a demi-rinse bath containing
demineralized water;
- vi. applying an adhesion layer, wherein the fence panels are immersed in a polymer
bath, and wherein the fence panels are subsequently dried in an oven, and wherein
the pickling agents comprise hydrogen fluoride and phosphoric acid, in a ratio between
1/320 and 1/80.
[0022] The method optimizes the pre-treatment of galvanized fence panels that need to be
coated. Applying a powder coating to the galvanized steel not only results in a more
aesthetically pleasing result, but also significantly improves the corrosion resistance
of the fence panels. However, zinc is one of the most difficult surfaces to apply
a paint system to. The reason for this is that the quality of the hot-dip galvanized
material can vary greatly. In addition, many contaminants can occur on the zinc surface,
such as corrosion products, passivation layers on sendzimir galvanized steel, rolling
oil, etc.
[0023] In an embodiment, the pretreatment is applied to a plurality of fence panels. In
a preferred form, between 2 and 100 fence panels are pre-treated at the same time,
preferably between 10 and 90, more preferably between 20 and 80, even more preferably
between 30 and 70, most preferably between 40 and 60. In case the method takes place
continuously, it will be apparent to one skilled in the art that in each step of the
method between 2 and 100 fence panels, preferably between 10 and 90, more preferably
between 20 and 80, even more preferably between 30 and 70, most preferably between
40 and 60, can be treated simultaneously. In this embodiment, the fence panels are
positioned parallel in a suspended state.
[0024] In an embodiment, the fence panel is made of unalloyed steel, low-alloy steel or
high-alloy steel. The fence panel can be manufactured from high or low carbon steel.
Unalloyed steel contains a maximum of 1.5% of alloying elements (excluding carbon
(C)). Unalloyed steel has a carbon percentage of 0.5% to 2%. Low-alloy steel contains
between 1.5 and 5% alloying elements (excluding carbon). High-alloy steel contains
more than 5% of alloying elements. The fence panel is preferably made of unalloyed
steel. The term "alloying elements" refers to the elements that are present in the
alloy in addition to iron and carbon. In a preferred form, the fence panel is made
of an alloy comprising iron (Fe), carbon (C) and alloying elements. Preferably, the
alloy comprises a maximum of 1.5% alloying elements, more preferably a maximum of
1.4%, even more preferably a maximum of 1.3%, even more preferably a maximum of 1.2%,
most preferably a maximum of 1.1%. Preferably the alloy comprises at least 0.5% alloying
elements, more preferably at least 0.6%, even more preferably at least 0.7%, even
more preferably at least 0.8%, even more preferably at least 0.9%, most preferably
at least 1%. In another preferred embodiment, the alloy comprises between 0.5 and
1.5% alloying elements, preferably between 0.6 and 1.5%, more preferably between 0.7
and 1.4%, even more preferably between 0.8 and 1.3%, even more preferably between
0.9 and 1.2%, most preferably between 1 and 1.1%.
[0025] In an embodiment, the alloy comprises a maximum of 0.1% C, more preferably a maximum
of 0.09%, even more preferably a maximum of 0.085%, even more preferably a maximum
of 0.08%, most preferably a maximum of 0.075%. Preferably, the alloy comprises at
least 0.025% C, more preferably at least 0.03%, even more preferably at least 0.035%,
even more preferably at least 0.04%, most preferably at least 0.045%. In another preferred
embodiment, the alloy comprises between 0.02 and 0.1% C, preferably between 0.025
and 0.09%, more preferably between 0.035 and 0.085%, even more preferably between
0.04 and 0.08%, most preferably between 0.045 and 0.075%.
[0026] In a preferred embodiment, the alloy comprises alloying elements selected from the
list of: manganese (Mn), silicon (Si), sulfur (S), phosphorus (P), nitrogen (N), copper
(Cu), chromium (Cr), nickel (Ni), niobium (Nb), tin (Sn), aluminum (Al) or any combination
thereof. Preferably the alloy comprises manganese (Mn), silicon (Si), sulfur (S),
phosphorus (P), nitrogen (N), copper (Cu), and optionally chromium (Cr), nickel (Ni),
niobium (Nb), tin (Sn), aluminum (Al).
[0027] Preferably, the alloy comprises Mn in an amount between 0.3 and 0.5%, more preferably
between 0.35 and 0.45%, Si in an amount between 0.05 and 0.25%, more preferably between
0.1 and 0.2%, S in an amount between 0.01 and 0.045%, more preferably between 0.015
and 0.04%, P in an amount between 0.005 and 0.03%, more preferably between 0.005 and
0.025%, Cu in an amount between 0.2 and 0.4%, more preferably between 0.25 and 0.35%,
N in an amount between 0.005 and 0.02%, more preferably between 0.005 and 0.015%,
and Cr in an amount of up to 0.15%, more preferably up to 0.1%, Ni in an amount up
to 0.15%, more preferably up to 0.1%, and Nb in an amount up to 0.005%, more preferably
up to 0.002%, Sn in an amount up to 0.05%, more preferably up to 0.03%, and/or Al
in an amount up to 0.005%, more preferably up to 0.003%.
[0028] In a preferred form, the fence panel is a twin-wire or double-wire fence panel. With
double-wire fence panels, parallel vertical bars (wires) are welded to horizontal
bars (wires), whereby the vertical bars are welded at the same height between two
horizontal bars. The fence panel preferably has between 50 and 55, preferably 51,
vertical bars and between 1 and 20 horizontal bars.
[0029] In an embodiment, the fence panels are galvanized prior to pre-treatment. In a preferred
form, the fence panels are hot-dip galvanized, whereby a zinc layer is deposited on
the fence panel. In a further preferred form, the fence panel is provided with a zinc
layer with a thickness between 40 and 120 mu. In a further or other preferred form,
the average thickness of the zinc layer on the wires of the fence panels is between
60 and 80 mu.
[0030] In an embodiment, the vertical wires have a length between 500 and 2500 mm, preferably
the vertical wires have a length selected from the list: 630, 830, 1030, 1230, 1430,
1630, 1830, 2030, 2230, 2430 mm. It will be apparent to one skilled in the art that
the length of the vertical wires corresponds to the height of a fence panel. In an
embodiment, the horizontal wires have a length between 2000 and 3000 mm; preferably
between 2400 and 2600, even more preferably between 2500 and 2550 mm, most preferably
2508 or 2510 mm. It will be apparent to one skilled in the art that the length of
the horizontal wires corresponds to the length of a fence panel.
[0031] In a preferred embodiment, the distance between two adjacent vertical wires is 40-60
mm c.t.c., more preferably between 45 and 55 mm, even more preferably between 49 and
51, most preferably about 50 mm.
[0032] In another embodiment, the distance between the adjacent horizontal wires is 100-300
mm c.t.c., preferably 150-250 mm, more preferably 180-220 mm, most preferably about
200 mm.
[0033] The term "c.t.c." (center to center) refers to a distance between the center (the
heart) of a circular cross-section of one wire and the center (the heart) of a circular
cross-section of another wire.
[0034] In a preferred form the method takes place continuously. The one or more fence panels
in a suspended state are sequentially immersed in the various baths. The fence panels
are hung using suspension means that allow upward, downward and forward movement.
In this way, the fence panels are moved and positioned forwards above the various
baths by means of the suspension means, after which a downward and then upward movement
makes immersion possible. Multiple suspension means can immerse one or more fence
panels in different steps of the method, so that continuous operation is possible.
[0035] The first step in the method is degreasing the one or more fence panels, whereby
the fence panels are immersed in a degreasing bath containing degreasing agents. The
degreasing is carried out to remove an oily matter or stain adhering to the surface
of the fence panel and the immersion treatment is usually carried out at a temperature
between 35 and 55°C, preferably a temperature between 40 and 50°C, more preferably
between 41 and 49°C, even more preferably between 42 and 48°C, even more preferably
between 43 and 47°C, most preferably between 44 and 46°C.
[0036] In a preferred form, degreasing continues for 0.5-2 minutes, more preferably for
0.6-1.9 minutes, even more preferably for 0.7-1.8 minutes, even more preferably for
0.8 - 1.7 minutes, more preferably for 0.9-1.9 minutes, most preferably about 1 minute.
[0037] The degreasing agents preferably comprise sodium hydroxide. Preferably, the degreasing
agents comprise at least 50 m% sodium hydroxide, more preferably at least 60 m% sodium
hydroxide, even more preferably at least 70 m% sodium hydroxide, even more preferably
at least 80 m% sodium hydroxide, even more preferably at least 90 m% sodium hydroxide.
In a further preferred form, the degreasing agents also comprise wetting agents.
[0038] In a second step (ii) of the method, the one or more fence panels are rinsed, wherein
the fence panels are immersed in a first rinse bath containing water. This involves
rinsing the remaining degreasing agents from the fence panel.
[0039] In a preferred form, rinsing continues for 0.5-2 minutes, more preferably for 0.6-1.9
minutes, even more preferably for 0.7-1.8 minutes, even more preferably for 0.8-1.7
minutes, even more preferably for 0.9-1.9 minutes, most preferably about 1 minute.
[0040] In an embodiment, rinsing continues between room temperature and 80°C, preferably
at room temperature.
[0041] In a third step (iii) of the method, the one or more fence panels are pickled, wherein
the fence panels are immersed in two successive pickling baths containing pickling
agents. In an embodiment, the pickling agents are dissolved in water, so that the
pickling baths comprise water and pickling agents.
[0042] The pickling agents are preferably acidic pickling agents. The hydrogen formed by
the action of the acid can be absorbed in atomic form into the steel of the fence
panel and cause pickling embrittlement (actually hydrogen embrittlement). In an embodiment,
the pickling baths can therefore contain a pickling inhibitor or an inhibitor, which
slows down the acid-metal reaction compared to the acid-metal oxide reaction, so that
hydrogen formation and thus the risk of hydrogen embrittlement can be reduced. In
addition, a pickling inhibitor protects both metal and pickling acid without significantly
extending the pickling time.
[0043] The pickling agents are preferably selected from the list of: hydrochloric acid,
sulfuric acid, phosphoric acid, sulfamic acid, citric acid, acetic acid, acid sodium
sulfate (sodium hydrogen sulfate), hydrogen fluoride, pickling pastes, or a combination
of these. In an embodiment, the pickling agents are selected from the list of: hydrochloric
acid, sulfuric acid, phosphoric acid, hydrogen fluoride, or a combination thereof.
In a further embodiment, the pickling agents are selected from the list of phosphoric
acid, hydrogen fluoride, or a combination thereof.
[0044] In a preferred form, the pickling agents comprise phosphoric acid and hydrogen fluoride.
[0045] The addition of fluoride is particularly advantageous when, in a method according
to the invention, step (iii) immediately follows the rinsing in step (i), with intermediate
rinsing (ii), and in particular when hot-dip galvanized steel surfaces are treated.
In that case, the pickling speed on the metal surfaces increases and a faster deposition
kinetics of the thin layer consisting of elements of the metal ions is achieved and
a more homogeneous coating of the metal surface is the direct result.
[0046] In a preferred form, the pickling agents comprise phosphoric acid and hydrogen fluoride.
In a preferred form, the pickling baths comprise hydrogen fluoride, in an amount of
at least 0.001 m%, more preferably in an amount of at least 0.002 m%, even more preferably
in an amount of at least 0.003 m%, even more preferably in an amount of at least 0.004
m%, most preferably in an amount of at least 0.005 m%. In a further or other preferred
form, the pickling baths comprise hydrogen fluoride, in an amount of up to 5 m%, more
preferably in an amount of up to 4 m%, even more preferably in an amount of up to
3 m%, even more preferably in an amount of up to 2 m%, most preferably in an amount
of up to 1 m%. In another preferred form, the pickling baths comprise hydrogen fluoride,
in an amount between 0.001 m% and 5 m%, more preferably in an amount between 0.002
m% and 4 m%, even more preferably in an amount between 0.003 m% and 3 m%, even more
preferably in an amount between 0.004 m% and 2 m%, most preferably in an amount between
0.005 m% and 1 m%.
[0047] Below a total amount of 0.001 m% hydrogen fluoride the additional positive effect
is not well developed, while above 5 m% no further increase in the deposition kinetics
occurs, but the precipitation of insoluble fluorides becomes detrimental.
[0048] In a preferred form, the pickling agents comprise phosphoric acid and hydrogen fluoride.
In a preferred form, the pickling baths comprise phosphoric acid, in an amount of
at least 1 m%, more preferably in an amount of at least 2 m%, even more preferably
in an amount of at least 3 m%, even more preferably in an amount of at least 4 m%,
most preferably in an amount of at least 5 m%. In a further or other preferred form,
the pickling baths comprise phosphoric acid, in an amount of up to 25 m%, more preferably
in an amount of up to 24 m%, even more preferably in an amount of up to 23 m%, even
more preferably in an amount of up to 22 m%, most preferably in an amount of up to
21 m%. In another preferred form, the pickling baths comprise phosphoric acid, in
an amount between 1 m% and 25 m%, more preferably in an amount between 2 m% and 24
m%, even more preferably in an amount between 3 m% and 23 m%, even more preferably
in an amount between 4 m% and 22 m%, most preferably in an amount between 5 m% and
21 m%.
[0049] The pickling transfer during pickling is preferably at least 1 g/m
2, more preferably at least 1.5 g/m
2, even more preferably at least 2 g/m
2.
[0050] In a preferred form, the pickling continues for 1-15 minutes, more preferably for
2-14 minutes, even more preferably for 3-13 minutes, even more preferably for 4-12
minutes, most preferably for 5-11 minutes.
[0051] In another preferred form, the fence panels are immersed for 1-5 minutes per pickling
bath, more preferably for 1.5-4.5 minutes, even more preferably for 2-4 minutes, even
more preferably for 2.5-3.5 minutes, most preferably about 3 minutes.
[0052] In an embodiment, pickling takes place between room temperature and 80°C, preferably
at room temperature.
[0053] To prevent or minimize acid residues being carried along with the fence panel, a
rinsing step (iv) is carried out after the pickling treatment. The rinsing preferably
takes place in a rinse bath filled with water, whereby the fence panels are immersed
in a second rinse bath containing water.
[0054] In a preferred form, rinsing continues for 0.5-2 minutes, more preferably for 0.6-1.9
minutes, even more preferably for 0.7-1.8 minutes, even more preferably for 0.8-1.7
minutes, even more preferably for 0.9-1.9 minutes, most preferably about 1 minute.
[0055] In an embodiment, rinsing continues between room temperature and 80°C, preferably
at room temperature.
[0056] In a fifth step (v) of the method, the fence panels are rinsed with demineralized
water, whereby the fence panels are immersed in a demi-rinse bath containing demineralized
water.
[0057] In a preferred form, demi-rinsing continues for 0.5-2 minutes, more preferably for
0.6-1.9 minutes, even more preferably for 0.7-1.8 minutes, even more preferably for
0.8-1.7 minutes, even more preferably for 0.9-1.9 minutes, most preferably about 1
minute.
[0058] In an embodiment, demi-rinsing takes place between room temperature and 80°C, preferably
at room temperature.
[0059] Demineralized water, or called demi water for short, is water from which just about
all the salts (minerals) usually present in water have been removed.
[0060] In a sixth step (vi) of the method, an adhesion layer is applied to the fence panels,
wherein the fence panels are immersed in a polymer bath.
[0061] In a preferred form, the demi-rinsing continues for 1-3 minutes, more preferably
for 1.1-2.9 minutes, even more preferably for 1.2-2.8 minutes, even more preferably
for 1.3-2.7 minutes, more preferably for 1.4-2.6 minutes, most preferably about 1.5-2.5
minutes.
[0062] In an embodiment, the adhesive layer is applied between room temperature and 80°C,
preferably at room temperature.
[0063] The adhesion layer is formed by a chemical reaction of the steel surface with the
components in the polymer bath. This layer also has the properties of being insoluble
in water. The adhesion layer over which a coating is applied improves both the adhesion
of the coating and its anti-corrosion properties.
[0064] In an embodiment, the fence panels are then dried in an oven. In a preferred form,
the oven operates at an air temperature between 110 and 130°C, preferably between
111 and 129°C, more preferably between 112 and 128°C, more preferably between 113
and 127°C, even more preferably between 114 and 126°C, most preferably between 115
and 125°C.
[0065] In a preferred form it continues to dry for 10-30 minutes, more preferably for 11-29
minutes, more preferably for 12-28 minutes, more preferably for 1.3-2.7 minutes, even
more preferably for 14-26 minutes, most preferably about 15-25 minutes.
[0066] In an embodiment, a coating is then applied to the fence panel, whereby all wires
are provided with a coating, preferably a powder coating.
[0067] In a further embodiment, the coating comprises one or more components that form a
protective coating on the object when heated. Powders can, for example, be polyamides,
polyolefins, epoxies, polyesters, or a combination of these, preferably the coating
comprises one or more polyesters.
[0068] In a second aspect, the invention concerns a pre-treated galvanized fence panel.
[0069] In a preferred embodiment, the fence panel is provided with an adhesion layer with
a thickness between 1 and 15 mu.
[0070] In a preferred form, the adhesion layer is a layer selected from: a chromate layer,
phosphate layer, molybdate layer, wolframate layer, titanium layer or zirconate layer.
[0071] In what follows, the invention is described by way of non-limiting examples illustrating
the invention, and which are not intended to and should not be interpreted as limiting
the scope of the invention.
EXAMPLES AND DESCRIPTION OF THE FIGURES
[0072]
Figure 1 concerns a preferred embodiment of a method according to the first aspect of the
invention.
Figure 2 shows a perspective view of a double-wire fence panel.
Figure 3 shows an enlarged perspective view of a double-wire fence panel (section A in Figure 2).
[0073] Example 1 concerns a method for pre-treating a plurality of hot-dip galvanized fence panels
to be coated as shown in
Figure 1. Fifty or sixty parallel positioned galvanized fence panels are degreased in a first
step (1) in a suspended state, by immersion in a degreasing bath for one minute at
45°C. The degreasing bath is equipped with degreasing agents. The pickling transfer
is 1 g/m
2. In a second step, the fence panels are rinsed (2), by immersion in a first rinse
bath for one minute. The first rinse bath is supplied with water. In a third step
of the method, the fence panels are pickled (3), by immersion in two successive pickling
baths (3a, 3b), whereby the fence panels are first immersed in a first pickling bath
(3a) for three minutes and then immersed in a second pickling bath (3b) for three
minutes. The pickling baths are provided with a pickling solution comprising water,
phosphoric acid and hydrogen fluoride. In a fourth step, the fence panels are rinsed
a second time (4), by immersion in a second rinse bath for one minute. The first rinse
bath is supplied with water. In a fifth step, the fence panels undergo a demi-rinse
(5), by immersion in a demi-rinse bath for 1 minute. The demi-rinse bath is equipped
with demineralized water. The fence panels are then immersed in a polymer bath so
that an adhesion layer is applied (6) to the fence panels. In a final step, the fence
panels are dried (7) in an oven at 120°C for 15-20 minutes. A pre-treated hot-dip
galvanized fence panel is obtained which can then be coated.
[0074] Figure 2 and
Figure 3 show a double-wire fence panel that can be pre-treated according to the method of
the first aspect.
[0075] A twin-wire fence panel (108) consists of parallel vertical wires (104) welded to
horizontal wires (101, 102) with the vertical wires welded at any height between two
horizontal wires (101, 102) forming a double pair (103). The distance between two
adjacent vertical wires (106) is about 50 mm c.t.c. The distance between the adjacent
horizontal wires (105) is about 200 mm c.t.c.
1. A method for pre-treating one or more galvanized double-wire fence panels to be coated,
wherein the one or more galvanized fence panels are sequentially immersed in baths
in a suspended state, wherein the method comprises the following sequential steps:
a. degreasing, whereby the fence panels are immersed in a degreasing bath comprising
a degreasing agent;
b. rinsing, wherein the fence panels are immersed in a first rinse bath comprising
water;
c. pickling, whereby the fence panels are immersed in two successive pickling baths
comprising pickling agents;
d. rinsing, wherein the fence panels are immersed in a second rinse bath comprising
water;
e. demi-rinsing, whereby the fence panels are immersed in a demi-rinse bath comprising
demineralized water;
f. applying an adhesion layer, wherein the fence panels are immersed in a polymer
bath, and
wherein the fence panels are subsequently dried in an oven, and wherein the pickling
agents comprise hydrogen fluoride and phosphoric acid, in a ratio between 1/320 and
1/80.
2. Method according to claim 1, wherein the fence panels are immersed for between 100
and 260 seconds per pickling bath during pickling.
3. Method according to any one of the preceding claims, wherein the pickling agents comprise
phosphoric acid in an amount of a maximum of 5 m% of the total mass of pickling agents.
4. Method according to any one of the preceding claims, wherein the pickling agents comprise
hydrogen fluoride in an amount of a maximum of 0.1 m% of the total mass of pickling
agents.
5. Method according to any one of the preceding claims, wherein between 40 and 60 fence
panels are pretreated simultaneously, wherein the fence panels are positioned parallel.
6. Method according to any one of the preceding claims, wherein the pickling transfer
during pickling is at least 1g/m2.
7. Method according to any one of the preceding claims, wherein the oven operates at
an air temperature between 110 and 130°C, preferably between 115 and 125°C.
8. Method according to any one of the preceding claims, wherein the residence time in
the oven is between 10 and 30 minutes, preferably between 15 and 25 minutes.
9. Method according to any one of the preceding claims, wherein degreasing takes place
at a temperature between 35 and 55°C, preferably a temperature between 40 and 50°C.
10. Method according to any one of the preceding claims, wherein immersion in the polymer
bath continues for 1-3 minutes, preferably for 1.5-2.5 minutes.
11. Method according to any one of the preceding claims, wherein the fence panels are
immersed for between 1 and 5 minutes per pickling bath, preferably between 2 and 4
minutes.
12. Method according to any one of the preceding claims, wherein immersion in the degreasing
bath continues for 0.5-2 minutes.
13. Method according to any one of the preceding claims, wherein the degreasing agents
comprise sodium hydroxide.
14. A pre-treated galvanized fence panel obtained according to any one of claims 1-13.