Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1995-05-26
2001-06-12
Crispino, Richard (Department: 1301)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S244130, C156S244210, C156S244230, C156S286000, C264S171220, C264S173140, C264S173190, C264S177140
Reexamination Certificate
active
06245183
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a multi-layer coated metal tube, and more particularly to a metal tube having an outer surface coated with a plurality of layers of plastic material securely bonded thereto.
BACKGROUND OF THE INVENTION
Metal pipes often have their outer surfaces covered with a protective coating. These pipes are used for conveying brake fluids, fuel and the like in a motor vehicle. As such, these pipe lines are located under the body of the vehicle. Since they are used in such a harsh environment, the pipes are required to have a high degree of corrosion resistance, scratch resistance, impact strength and mechanical wear resistance. In cold climates, it is not unusual to encounter rock salt sprinkled onto road surfaces in order to prevent freezing of water on the road surfaces and the inherent dangers caused thereby. The popularity of spreading rock salt has created a serious problem of pipe corrosion. The pipes are also vulnerable to damage or wear from stones or mud spattered by rotating wheels of the vehicle. It is, therefore, necessary that the pipes attached to the underbody of the vehicle be coated so as to resist both chemical corrosion and mechanical damage or wear.
A double-rolled steel pipe has been proposed that is made by rolling a steel strip or hoop twice and brazing its longitudinal edges by means of a copper plating layer, or a seam welded steel pipe, where the pipe has an outer surface coated with an electroplated zinc film. The zinc film has an outer surface coated with a relatively thick special chromate film having an olive color. The chromate film has an outer surface coated with a fluorinated resin film. The fluorinated resin film is formed by impregnating the chromate film with a dispersion of polyvinyl fluoride immediately after the formation of the chromate film when it is still in the state of a gel, and drying them under heat, so that the fluorinated resin film may form an intimate bond with the chromate film. When the chromate film is formed by treating the pipe with a solution, it requires large amounts of a chromium compound and an organic acid, such as formic acid, used as a reducing agent. It is necessary to supply the treating solution with the chromium compound frequently, and to renew it at regular intervals of time in order to maintain a constant film forming capacity. The waste solution, however, contains a large amount of chromium having a valence of 6, which is a toxic substance, and its disposal, therefore is very costly. Although the chromate film as formed is highly resistant to corrosion, the heat to which it is exposed during the formation of the resin film deprives it of water and thereby makes it brittle. Any plastic deformation of the pipe, such as the result of bending or double flaring, forms fine cracks in the chromate film which lowers its rustproofing properties.
It has also been proposed to provide a corrosion resistant pipe where a metal pipe is provided with an outer surface coated with a zinc film, a chromate film, an intermediate layer consisting sequentially of an epoxy resin, and a polyvinyl fluoride film formed one on top of another in the order listed. A plastic-coated steel tube has also been proposed where a steel tube has an inner layer of at least one cross-linked polyolefin modified with a hydrolyzable silane and an outer unmodified or soot-blended polyolefin layer on the exposed surface of the inner layer. A process for coating metal tubes with plastic material has also been disclosed where a fixed metal tube is heated to a temperature above the melting point of the plastic material to be employed, thereafter causing a mixture of plastic powder and air to pass through the metal tube whereby the plastic material is fritted onto the inside surface of the tube, thereafter rotating the metal tube and applying to the exterior surface thereof in a plurality of stages a plastic material, the plastic material being electrostatically sprayed onto the rotating metal tube and after each stage of electrostatically applying plastic to the outside surface of the metal tube and applying plastic material to the inside surface thereof, completely melting and smoothing the plastic material.
An automobile tube line for a brake, fuel or hydraulic system has also been disclosed with an interior steel tube having a galvanized exterior layer with an additional exterior olive chromated layer which is wrapped in an additional Nylon 12 layer casing where the plastic casing is a polyamide layer applied by extrusion on top of the olive chromated layer.
SUMMARY OF THE INVENTION
It is desirable in the present invention to provide brake lines and fuel lines, and other lines which could be damaged by the regular use of an automobile, which can meet the continuous demand of traffic conditions, and therefore must have a long lasting durability of ten years or more. In such application areas, resistance to corrosion, resistance against breaking, cracking or bursting due to internal pressure, resistance to stone impact and a high corrosion resistance against winter salt are all desirable characteristics. At this time, tube lines made of steel are currently being used in a large capacity. For brake lines, double-wrap steel tubes are suitable, whereas single wall straight bead welded steel pipes are more appropriate for fuel lines.
The extruded multiple plastic layer coating bonded to a metal tube and the process therefor according to the present invention provides numerous advantages over the prior known tubing configurations. In particular, the multiple layer construction allows greater selection of materials for meeting varying application and environmental conditions. The multiple layers allow the application of a coating on top of the basic corrosion resistant coating to act as a cushion thereby eliminating the necessity of assembling a protective sleeve or heatshrink tube to outside of the tube for stone impingement protection. The multi-layer coating according to the present invention also allows use of recycled materials in the inner layer, sometimes referred to as “regrind” materials in intermediate layers at a substantial cost savings without detrimental loss of external coating properties or internal adhesion of the coatings to the external surface of the metal tube. The multi-layer configuration of the present invention also allows the use of less costly materials in the inner layers which may not have the chemical resistance required of the outer layer. The multi-layer configuration allows for alloying of the layers to improve the adhesion to the base metal tube. A multi-layer configuration, even if of the same material, greatly reduces the probability of apertures or perforations in any one layer reaching through to the base tube. The multi-layer configuration provides more precise control of the coating thickness and concentricity about the base tube. Finally, the multi-layer configuration according to the present invention allows for color selection with protection of the color layer below a clear top layer for protection from ultraviolet light, chemical and heat degradation.
In one form, the tube of the present invention includes a metal tube having an outer surface pretreated to form a surface selected from the group consisting of a zinc plate with chromate, a zinc plate with phosphate and chromate, a galvanized zinc layer with phosphate and chromate, a galvanized zinc layer with chromate, a zinc-metal blend with phosphate and chromate, and a zinc-metal blend with chromate, where the zinc-metal blend is selected from a group consisting of zinc-nickel alloy, zinc-cobalt alloy, and zinc-aluminum alloy, and mixtures thereof; an intermediate alloy or bonding layer applied to the pretreated outer surface of the metal tube selected from a group consisting of Nylon 12, Nylon 6, zinc chloride resistant Nylon 6, thermoplastic elastomers, fluoropolymers, and mixtures thereof, in combination with at least one of the group consisting of a thermoplastic elastomer, an ionic polymer, a polyamide, and mixtures the
Davie Robert M.
Iorio Ralph A.
McDaniel James D.
Mitchell Frank L.
Nie Tao
Crispino Richard
ITT Manufacturing Enterprises Inc.
Seitter Robert P.
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