Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-11-23
2001-07-24
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C029S458000, C029S527200, C427S433000, C427S436000, C428S628000, C428S678000, C428S679000, C428S680000, C428S682000
Reexamination Certificate
active
06265087
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a structure and method for joining panel sheets, and more particularly to such structure and method for joining Zn-plated steel panel sheets with non-plated steel panel sheets.
2. Description of the Related Art
Conventionally, at least one surface (outer surface) of a steel plate (base member or material) is plated with Zn or its alloy in order to prevent corrosion and maintain decent appearance when the steel plate is used as a panel sheet for an automobile body. A common Zn-plated steel panel sheet for an automobile is manufactured by hot or cold rolling a steel plate, and electroplating or hot dipping the steel plate to form a Zn or Zn-alloy plating (collectively referred to as “Zn plating”) over a surface of the steel plate.
Referring to
FIG. 9A
of the accompanying drawings, illustrated is one example of automobile panel sheet
91
a
that incorporates a steel plate coated with Zn plating. The base member (steel plate) is first plated with Zn or its alloy
95
to provide a Zn-plated steel panel sheet (corrosion-proof steel plate)
94
. The steel plate
94
is then subjected to chemical conversion coating treatment with phosphate liquid to create a chemical conversion coating (Hopeite)
96
over the Zn coating. On the phosphate coating
96
, a first coating or undercoating
97
is formed by electrodeposition to provide an inner plate
92
a
. An intermediate coat
98
is further formed over the undercoat
97
, and a finish coat
99
is then formed over the intermediate coat
98
to provide an outer plate
93
a
. This outer plate
93
a
is the panel sheet
91
a
. It should be noted that the steel plate
94
has the Zn coating
95
on both surfaces, but only one surface is illustrated.
Referring to
FIG. 9B
of the accompanying drawings, illustrated is another example of automobile panel sheet
91
b
that contains a steel plate without Zn plating. A non-plated steel panel sheet
102
is first coated with a chemical conversion coat (Phosphophyllite)
103
by phosphate liquid. Then, an undercoat
97
is applied over the phosphate crystal coat
103
by electrodeposition to provide an inner plate
92
b
. An outer plate
93
b
is obtained by further coating the inner plate
92
b
with an intermediate coat
98
and finish coat
99
. The outer plate
93
b
is the panel member
91
b.
It should be noted that an appropriate kind of intermediate coat
98
is selected according to, for example, the type of the automobile. Therefore, it should also be noted that the intermediate coat
98
may be dispensed with if unnecessary.
In general, an automobile panel member is made from a plurality of panel sheets. If an entire panel member of an automobile body is made from a plurality of Zn-plated steel panel sheets
94
only, a cost is raised considerably. Therefore, as illustrated in
FIG. 8A
of the accompanying drawings, the expensive Zn-plated steel panel sheet is connected to the inexpensive non-plated steel panel sheet in a partly overlapping manner such that the Zn-plated steel panel sheet is located at an area of the body which requires high resistance to corrosion.
FIG. 10
of the accompanying drawings illustrates an overlapping portion of the two sheets in an enlarged scale.
Referring now to
FIGS. 11A and 11B
of the accompanying drawings, a chemical conversion coating (Hopeite)
96
is formed over the surface of a Zn plating
95
a
by phosphoric acid etching, and another chemical conversion coating (Phosphophyllite)
103
is formed over the surface of the non-plated steel panel sheet
102
(“Normal Area” in
FIG. 10
) by phosphoric acid etching. Anode and cathode exist microscopically (they are present very closely), and therefore an anode reaction (phosphoric acid etching) and a cathode reaction (generation of chemical conversion crystal around the etched area) take place on the same steel plate. As a result, the crystal precipitates and grows to extend over the anode-etched surface which is fresh and reactive (zones designated at
101
in FIG.
10
). Thus, the Zn plating
95
a
and chemical conversion coating (Hopeite)
96
are firmly joined with each other, and the non-plated steel panel sheet
102
and chemical conversion coating (Phosphophyllite)
103
are also firmly joined with each other.
As depicted in
FIG. 10
, however, the panel member always has at least one connection of the Zn-plated steel panel sheet
94
and non-plated steel panel sheet
102
. In the vicinity of the connection, a voltage difference is produced due to contact of different metals when dipped in the chemical conversion treatment liquid.
Referring to
FIGS. 12A and 12B
, consequently, Zn (base metal) becomes an anode in the surface of the non-plated steel panel sheet
102
near the two-sheet connection on the connection side (“Weak Adhesion Area” in FIG.
10
). Therefore, Zn is only dissolved by the anode reaction, and crystal precipitates and grows on the non-etched steel surface. In other words, although a chemical conversion crystal is formed on the Fe-based steel plate in the range of about 20 mm from the two-sheet connection, it is not the chemical conversion coating (Phophphyllite)
103
but the chemical conversion coating (Hopeite)
96
having no Fe.
The chemical conversion coating (Hopeite)
96
is difficult to adhere onto the non-plated steel panel sheet
102
and easy to exfoliate. Therefore, connection of the Zn-plated steel panel sheet
94
and non-plated steel panel sheet
102
(different metal connection) is not applicable to those areas of a vehicle body panel which are subjected to an external stress. Such areas of the vehicle body are, for example:
(1) Front and roof panels of a vehicle body, which often experience pitching movements;
(2) Panels near vehicle doors, which frequently experience vibrations and frictions due to opening and closing;
(3) Panels of which two-sheet connection is often exposed to water or moisture due to an inherent structure of the vehicle (areas where edge corrosion tends to occur);
(4) Panels which a service man's legs, hands and body tend to touch or hit; and
(5) Panels onto which optional parts such as ski carriers are mounted.
Therefore, even if the non-plated steel panel sheet
102
itself possesses a corrosion resistance required by the vehicle body, it cannot be used for those areas such as mentioned above. Instead, the expensive Zn-plated steel panel sheets
94
should be used. The Zn-plated steel panel sheets are joined with each other to provide a panel member for such areas because the same metal connection does not produce a voltage difference in the chemical conversion treatment. Accordingly, a Zn-plated steel panel sheet utilization ratio is high in the conventional body panel.
SUMMARY OF THE INVENTION
An object of the present invention is to eliminate the above-described problems of the conventional auto body panel.
According to one aspect of the present invention, there is provided a panel member including a steel plate, two layers of Zn plating formed over two opposite surfaces of the steel plate respectively, another layer of plating formed over at least one of the two layers of Zn plating, so as to form a plated steel panel sheet, and a non-plated steel panel sheet joined with the plated steel panel sheet in a partly overlapping manner such that the another layer of plating contacts the non-plated steel panel sheet. The another layer of plating is made from a metal or alloy having a standard electrode potential equal to or more than Fe. Since the connection between the plated steel panel sheet and non-plated steel panel sheet is connection of the metal (or alloy) plating and Fe, the connection of the plated and non-plated steel panel sheets is less influenced by the voltage difference caused in the chemical conversion treatment bath due to different metal connection. As a result, a chemical conversion coating (Phosphophyllite) is formed at an area near the two-sheet connection (“Weak Adhesion Area” in FIG.
10
). Unlike the conventional st
Matsumi Yutaka
Suzuki Masaru
Isuzu Motors Limited
Jones Deborah
Koehler Robert R.
McCormick Paulding & Huber LLP
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