Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-06-11
2003-03-18
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C148S516000, C148S528000, C228S111500, C228S200000, C228S225000, C228S226000, C228S262900, C428S658000, C428S926000
Reexamination Certificate
active
06534195
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a connection structure for metallic members, which is, for example, suitable as a connection structure between a tank and a pipe of a fuel tank for automobiles, etc., and in particular, relates to a technique in which corrosion resistance and sealing can be improved without using Pb.
BACKGROUND ART
For example, in a fuel tank
1
for automobiles, as shown in
FIG. 10
, pipes such as a filler neck pipe
2
for refueling, a breather pipe
3
for breathing air in refueling, and a venting pipe
4
for releasing pressure in the fuel tank
1
, are connected. In the case in which such pipes are connected to the fuel tank
1
, one end of a pipe P is press-fitted in the fuel tank
1
, as shown in
FIG. 11
, then ring shaped solder S is adjacently placed at a boundary between the pipe P and the fuel tank
1
, and this solder S is heated and melted by an electrode
6
for high frequency induction heating. Then, the melted solder S solidifies at the corner portion of the boundary between the pipe P and the fuel tank
1
, as shown in
FIG. 12
, and both members are thereby airtightly connected.
As a conventional solder, Pb—Sn alloy has generally been employed. However, it is not desirable to use Pb since there are environmental regulations on Pb leached from industrial waste such as shredder dust, etc., and substitutes for Pb have been required. Therefore, Ag alloys, Cu or Cu—Zn based alloys, Zn—Al alloys, etc., have recently been used, and in Japanese Unexamined Patent Publication No. 71488/98, a Sn alloy solder (Sn—Ag based) has also been disclosed.
On the other hand, as a material for fuel tanks and pipes, surface treated steel sheets which are subjected to Zn plating, Al alloy plating, Zn alloy plating, etc., may be used. Alternatively, after-treatment plating which is carried out after material is processed from a steel plate, may be carried out. In any case, a fuel tank
1
and a pipe P on which are formed platings M
1
and M
2
, are connected together by solder S, as shown in FIG.
12
. The solder S is applied to such connections since the heating temperature thereof is lower than those of other methods such as welding, etc., the heat distortion at a position where dimensional accuracy is required can be suppressed in a thin layer, the sealing thereof is superior, equipment can be miniaturized, etc.
In a fuel tank for automobiles, seals which can withstand high internal pressure are required at soldered portions since internal vapors of fuel expand with increasing temperature, and in addition, reliability and durability in which functions thereof are not damaged by vibration and acceleration during driving of the automobile, are also required. The fuel tank is often installed under the floor of the car body, and therefore, a high level of coating and high corrosion resistance are required, even at the soldered portions, since they are exposed to severe road environments and climatic conditions, such as snowmelt salt, mud, water, humidity, are splashed gravel. Furthermore, corrosion resistance of the inner surface is also required, since corrosive components such as acids and peroxides are produced when gasoline decomposes in a fuel tank.
However, there was a problem in that surrounding plating is heated by heating during soldering, and the plating is thereby heat-deteriorated. That is, it is necessary to heat to a temperature 50° C. or more (preferably 100° C.) higher than the melting point of solder, in order to securely fix members by increasing the solderability (wettability). In particular, a pipe wall portion just above a high frequency heating electrode is heated to a high temperature by this heating and plating metal is alloyed with Fe material, and the corrosion resistance is thereby lowered and the plating is weakened thereby. Depending on conditions, a plating M
2
may melt and flow down, as shown in FIG.
13
(
a
), or a porous oxide film M
3
may be formed by oxidizing the plating M
2
, as show in FIG.
13
(
b
), and corrosion resistance is thereby drastically lowered, and the application property is also lowered in the latter case.
In addition, in the case in which the solder material is different from the plating material, there was a problem in that the corrosion resistance is lowered by contact corrosion occurring in which the base metal acts as an anode. Therefore, it is an object of the present invention to provide a connection structure for metallic members and a connecting method in which high reliability and high durability can be ensured even in use under severe conditions. Specifically, in the present invention, plating and solder materials are selected in consideration of following points.
{circumflex over (1)} A solder having superior solderability to plating is selected in order to obtain a connection structure having superior qualities in which a soldered portion thereof has high strength and there are few internal defects.
{circumflex over (2)} Materials for the solder and the plating having small differences in corrosion potential are selected in order to reduce contact corrosion between the solder and the plating.
{circumflex over (3)} A plating having high corrosion resistance to saltwater or decomposed gasoline is selected in order to improve the corrosion resistance of the plating.
{circumflex over (4)} A solder having a low melting point is selected in order to reduce heat deterioration of the plating caused by heating during soldering and to increase thereby adhesion of films. In particular, it is desirable that melting points of the solder and the plating be 180° C. or more in view of the fact that baking finishing is carried out at 150° C. or more in a subsequent process.
DISCLOSURE OF THE INVENTION
(1) Prevention of Heat Deterioration of Plating
The present inventors researched materials for plating and solder from the above points of view. Firstly, melting points of various alloys or metals were enumerated in the following, in order to take into account the heat deterioration prevention of the plating. In comparison with properties shown in Table 1, Zn to Cu—Zn based alloy (lines 6 to 10) have high melting points, and it is therefore anticipated that heat deterioration, such as oxidation, etc., of the plating material (Pb—Sn alloy, etc.) will occur.
TABLE 1
Melting
Evalua-
Alloy Names
Symbols
Points
Primary Uses
tion
Lead-tin alloy
Pb—Sn
200
Soldering, Plating
Good
Tin-silver alloy
Sn—Ag
215
Soldering
Good
Tin-antimony alloy
Sn—Sb
220
Soldering
Good
Tin-zinc alloy
Sn—Zn
230
Plating
Good
Zinc
Zn
420
Plating
Bad
Zinc-aluminum alloy
Zn—5Al
361
Soldering, Plating
Bad
Aluminum-silicone
Al—Si
585
Plating
Bad
alloy
Silver-copper alloy
Ag—Cu
780
Brazing
Bad
Copper-zinc alloy
Cu—40Zn
890
Brazing
Bad
(2) Corrosion Resistance of Plating
In a fuel tank for automobiles, corrosion resistance to the external environment and corrosion resistance to acids and peroxides produced by the degradation of fuel are required. Then, with respect to the internal corrosion resistance which prevents Fe in a saltwater environment from causing corrosion and the external corrosion resistance which has resistance to gasoline degradation products including formic acid or acetic acid, the evaluations of various metals are described in Table 2. As is apparent from Table 2, Al—Si alloy and Sn—Zn alloy are preferable as a plating material.
TABLE 2
Plating Metal
Zn
Zn—Ni
Al—Si
Sn—Zn
Sn
Cu
Ag
Internal
Bad
Average
Good
Good
Bad
Bad
Bad
corrosion
resistance
External
Bad
Bad
Good
Good
Good
Bad
Good
corrosion
resistance
(3) Contact Corrosion Resistance and Solderability
The order of corrosion potential of various metals in a saltwater is shown in FIG.
1
. In the case in which two metals shown in
FIG. 1
are employed for soldering and plating, if the locations of the corrosion potential of the two metals are far apart, the difference in the corrosion potentials is high, and the base metals are easily corroded. According to this rule as a standard, the contact corrosion resistances of the combinations of various metals were evaluated and t
Narita Masayuki
Takikawa Kazunori
Arent Fox Kintner & Plotkin & Kahn, PLLC
Koehler Robert R.
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