WO2004037454A2

WO2004037454A2 - Double wall nickel or nickel alloy coated stainless steel tubing

Info

Publication number: WO2004037454A2
Application number: PCT/US2003/033817
Authority: WO
Inventors: Duane Pontbriand; Jeffrey W. Clawson; Tom White
Original assignee: Cooper Technology Services, Llc.
Priority date: 2002-10-23
Filing date: 2003-10-23
Publication date: 2004-05-06
Also published as: WO2004037454B1; AU2003284915A8; WO2004037454A3; AU2003284915A1

Abstract

Tubing material (10) is rolled into a double wall tubular member (34) to form a vehicle fluid line. The tubing material includes a stainless steel sheet metal (12) having a nickel or nickel alloy coating. The double wall tubing member is then heated to a brazing temperature to melt the nickel or nickel alloy coating (14, 16) and secure the tubing material into the double wall shape. A cooling process may be used to obtain desired mechanical properties.

Description

DOUBLE WALL NICKEL OR NICKEL ALLOY COATED STAINLESS STEEL TUBING

BACKGROUND OF THE INVENTION The present invention relates generally to double wall stainless steel tubing having a nickel or nickel alloy braze layer.

Motor vehicles utilize numerous fluid lines to carry fluids from one component of the vehicle to another. The fluid lines must have mechanical properties that accommodate fabrication, be resistant to corrosion and capable of withstanding pressures without bursting.

Vehicle fuel lines are typically subjected to pressures of approximately 15- 100 psi. Stainless steel single wall tubing having a thickness of approximately 0.028 inch has been welded using the TIG welding process to produce fuel lines and carry fuel within a vehicle. Stainless steel provides resistance to corrosion. The single wall tubing is typically welded at the seam using a tungsten inert gas (TIG) welding process. Typically, only 11 meters of tubing may be produced per minute utilizing the TIG welding process for this type of tubing. A drawback to this process is that it is undesirably slow.

Vehicle brake lines are typically subjected to much higher pressures than fuel lines, as much as 3000 psi. As a result, double wall tubing has been utilized to withstand the higher pressures within the tubing and to reduce fatigue failures. Double wall low carbon steel has been utilized for the production of double wall brake line tubing. However, the tubing is not corrosion resistant and the tubing must be coated with various materials to provide the needed corrosion and impact resistance. These materials can be corrosion resistant metallic coatings, such zinc or electrozinc. A top coat of extruded polymer or cured paints can be used to provide additional corrosion resistance.

Fluid lines have also been formed of a stainless steel material having a nickel flash layer less than 1 micron in thickness on the stainless steel material and a copper layer on the nickel flash layer. Copper is a prevalent brazing material. When heated, the copper layer melts to adhere the tubing in shape. The nickel flash layer is used to adhere the copper layer to the stainless steel material. As nickel has a higher melting temperature than copper, the nickel does not melt to form the brazed joint. Additionally, the less than 1 micron thickness nickel layer is not sufficient to form a joint. A drawback to this tubing is that a nickel flash layer is required to adhere the copper layer on the tubing, requiring two layers. Hence, there is a need in the art for a fluid line that is corrosion resistant and that may be produced rapidly.

SUMMARY OF THE INVENTION

A tubing material is rolled into a double wall tubing to form the vehicle fuel line of the present invention. The tubing material includes a flat stainless steel sheet metal having a nickel or nickel alloy coating on both sides of the stainless steel sheet metal. In one example, the nickel or nickel alloy coating has a thickness of approximately 4 to 5 microns, and the total thickness of the tubing material is 0.011 inch. The tubing material is first tapered at both ends and then rolled into a double wall tubular member having the desired diameter. When rolled, the tubing material extends at least 720° around a central axis of the tubing to define the double wall tubular member. Preferably, the tapered ends slightly overlap such that the tubing material extends approximately 740° around the central axis. When rolled into the double wall tubular member, the nickel or nickel alloy coating on the first surface of the tubing material contacts the nickel or nickel alloy coating on the second surface of the tubing material for at least 360° around the central axis of the tubing.

The double wall tubular member is then heated to a braze temperature to melt the nickel or nickel alloy coating. The contacting nickel or nickel alloy coatings melt together to secure the tubular member into the double wall tubular member. The nickel or nickel alloy coating proximate to the tapered end on the exterior of the tubing melts to form a seam that adheres the tapered end to the exterior outer wall of the tubing.

The tubing is then cooled to obtain desired mechanical properties, such as hardness, yield strength, and elongation. The tubing may be cut to a desired length and then further fabricated, such as bending and end forming, to produce the final tubing. Once finished, the rolled tubing has a thiclαiess of 0.022 inch, or twice the thickness of the tubing material.

These and other features of the present invention will be best understood from the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 schematically illustrates a cross-sectional view of a stainless steel sheet metal having a nickel or nickel alloy coating;

Figure 2 schematically illustrates the process utilized to form the tubing of the present invention;

Figure 3 schematically illustrates a perspective view of the double wall tubing member;

Figure 4 schematically illustrates a cross-sectional view of the tubing of the present invention; Figure 5 schematically illustrates an enlarged cross-sectional view of the seam of the tapered end to the outer wall of the tubing;

Figure 6 schematically illustrates a cross-sectional view of another embodiment of the tubing of the present invention; and

Figure 7 schematically illustrates an alternate embodiment of the tubing of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a tubing 34 suitable for use in vehicle fluid lines, such as brake lines and fuel lines. The inventive tubing 34 is more corrosion resistant and of lighter gage than the prior art vehicle fluid lines, keeping the tubing 34 cost effective. The tubing 34 may also be produced more rapidly than the prior art single wall tubing.

Figure 1 schematically illustrates a cross-sectional view of a tubing material 10 used to form the tubing 34 of the present invention. The tubing material 10 includes a flat stainless steel sheet metal 12 having a nickel or nickel alloy coating 14, 16 on both the first surface 18 and the opposing second surface 20, respectively, of the stainless steel sheet metal 12. Preferably, the nickel or nickel alloy coatings 14, 16 each have a thickness of approximately 4 to 5 microns, and the total thickness of the tubing material 10 is 0.011 inch. However, it is to be understood that any thickness can be utilized and one skilled in the art would know what thickness to use. The tubing process 26 of the present invention is schematically illustrated in

Figure 2. The tubing material 10 is tapered at both ends to form a first tapered end 22 and an opposing second tapered end 24 by a tapering machine 8. When tapered, the ends 22 and 24 have an angle of approximately 12°, shown as angle B.

The tubing material 10 is fed into a rolling machine 28, which is known in the art. The rolling machine 28 rolls the tubing material 10 into a double wall tubular member having a desired diameter (as shown in Figure 3). Preferably, when rolled, the tubing material 10 extends at least 720° around a central axis A of the tubing 34 to define the double wall tubular member. Preferably, the tapered ends 22 and 24 overlap to ensure a consistent wall thickness (shown in Figure 5). More preferably, the tapered ends 22 and 24 overlap 20° such that the tubing material 10 extends at least 740° around the central axis A of the tubing 34.

When the tubing material 10 is rolled into the double wall tubular member and heated, the nickel or nickel alloy coating 14 on the first surface 18 contacts the nickel or nickel alloy coating 16 on the second surface 20 for approximately 360° around the central axis A of the tubing. Preferably, the nickel or nickel alloy coating 14 on the first surface 18 contacts the nickel or nickel alloy coating 16 on the second surface 20 for approximately 380° due to the 20° overlapping of the tapered ends 22 ad 24. As shown in Figure 4, the first tapered end 22 is on the interior surface of the double wall tubular member, and the second tapered end 24 is on the exterior surface of the double wall tubular member.

Returning to Figure 2, the double wall tubular member is then heated 32 to a braze temperature to melt the nickel or nickel alloy coatings 14, 16. The contacting nickel or nickel alloy coatings 14, 16 melt and fuse together to form a nickel or nickel alloy layer 30 (shown in Figure 4 as hatching). When the contacting nickel or nickel alloy coatings 14, 16 cool, the fused nickel or nickel alloy coating 30 retains the shape of the double wall tubular member. The braze temperature depends on the nickel or nickel alloy employed, and one skilled in the art would know what braze temperature to utilize. Preferably, the braze temperature is between 1500°F and 2500°F. The double wall tubular member of tubing material 10 can be heated by a resistance circuit, an atmospheric furnace, or frequency induction.

Figure 5 schematically illustrates an enlarged cross-sectional view of a portion of the tubing 34 after heating 32. The contacting nickel or nickel alloy coatings 14, 16 (not shown) melt together to form a nickel or nickel alloy layer 30 that secures the double wall shape of the tubing 34 when cooled. The nickel or nickel alloy coating 14 proximate to the tapered end 24 of the tubing material 10 melts to form a seam 36 that adheres the tapered end 24 to an outer wall 38 on the exterior surface of the tubing 34.

Alternately, as shown in Figure 6, a brazing section 40 can be employed to braze the tapered end 24 of the double wall tubular member of tubing material 10 to the outer wall 38 to form a brazed lamination 42 that seals the tapered end 24 to the outer wall 38. The brazed lamination 42 is deposited onto the tubing 34 by a braze welding or torch brazing process 40. The brazed lamination 42 can be formed using a nickel-silver braze or other suitable braze. For example, the brazing process 40 can include heating by electric resistance, induction, or employing a gas or an electric furnace. However, it is to be understood that any suitable brazing process 40 may be used.

Returning to Figure 2, the tubing 34 is then cooled 44. The cooling process 44 is utilized to obtain desired mechanical properties, such as hardness, yield strength, and elongation, among other properties. The tubing 34 can be finished by cutting to a desired length and then further fabricating the tubing by bending and end forming. Alternatively, the tubing 34 may be coiled 46 for transportation and offsite processing.

The heating 28 and cooling 44 occurs in a controlled atmosphere preferably containing nitrogen, hydrogen, or a mixture of nitrogen and hydrogen. However, it is to be understood that other suitable shielding gases can also be used. The controlled atmosphere does not include oxygen. By employing a controlled atmosphere, the metal material of the tubing 34 is prevented from oxidizing at the elevated braze temperature.

Figure 7 illustrates an alternate embodiment of the tubing 134 of the present invention. The ends 122 and 124 of the tubing material are not tapered. When rolled, the tubing material between the ends 122 and 124 extends approximately 700° around the central axis A. The ends 122 and 124 contact a portion 132 of the tubing material that extends approximately 20° around the central axis A. The tubing 134 is heated to form the nickel or nickel alloy layer 130 between the layers of the tubing 134. The lamination in the final tubing 34 creates a nickel or nickel alloy interface that inhibits the propagation of cracks, minimizing fatigue failure. As a result, a thinner stainless steel sheet 12 may be utilized. In one example, the thickness of the tubing 34 is approximately 0.022 inch, or twice the thickness of the tubing material 10. The thinner tubing material 10 is less expensive than the higher gage material previously employed in prior art tubing. Uncoated stainless steel material is not compatible with a brazing process. Accordingly, the nickel or nickel alloy coating 14, 16 enables brazing to be used with the stainless steel sheet 12 so that the production rate of the tubing 34 may be increased, while providing a tubing 34 having corrosion resistance. Additionally, the tubing 34 of the present invention may be formed at a speed in excess of 20 meters per minute, thereby more rapidly producing tubing 34 in comparison to the prior art TIG welding process.

The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the above description that the invention may be practiced otherwise than as specifically described.

Claims

1. A tubing comprising: a sheet of stainless steel including a first surface and an opposing second surface; a brazing material including nickel coated on said sheet of stainless steel; and a joint of said brazing material to secure said sheet of stainless steel into a fluid conduit to adjoin said first surface and said second surface.

2. The tubing as recited in claim 1 wherein said brazing material is coated on both said first surface and said second surface.

3. The tubing as recited in claim 1 wherein said tubing has a thickness of approximately 0.022 inch.

4. The tubing as recited in claim 1 wherein said brazing material on said sheet of stainless steel has a thickness approximately between 4 microns and 5 microns.

5. The tubing as recited in claim 1 wherein said sheet of stainless steel includes a first tapered end and an opposing second tapered end.

6. The tubing as recited in claim 1 wherein said sheet of stainless steel has a first tapered end and an opposing second tapered end and said tubing has an outer wall, and one of said first tapered end and said second tapered end contacts said outer wall of said tubing at a seam.

7. The tubing as recited in claim 6 wherein said tubing has an inner wall, and the other of said first tapered end and said second tapered end contacts said inner wall of said tubing.

8. The tubing as recited in claim 1 wherein said sheet of stainless steel extends substantially at least 720° around a central axis of said tubing to define said fluid conduit.

9. The tubing as recited in claim 8 wherein said brazing material is coated on both said first surface and said second surface, and said brazing material on said first surface and said brazing material on said second surface contact at a contact surface extending substantially at least 360° around said central axis of said tubing.

10. The tubing as recited in claim 9 wherein said brazing material at said contact surface fuses together to form said joint and to secure said sheet of stainless steel into said fluid conduit.

11. The tubing as recited in claim 6 further including a brazed lamination along a length of said tubing at said seam.

12. The tubing as recited in claim 11 wherein said brazed lamination is nickel-silver.

13. The tubing as recited in claim 1 wherein said brazing material is a nickel alloy.

14. A method for forming a tubing comprising the steps of: rolling a sheet of stainless steel having a first surface, an opposing second surface, and a coating nickel into a tubing; and heating said tubing to melt said coating; and adjoining said first surface and said opposing second surface.

15. The method as recited in claim 14 further including the step of cooling said tubing.

16. The method as recited in claim 14 wherein the step of heating includes employing one of a resistance circuit, an atmospheric furnace, and frequency induction.

17. The method as recited in claim 14 wherein the step of heating includes heating to a temperature between 1500 and 2500°F.

18. The method as recited in claim 14 further including the step of finishing said tubing.

19. The method as recited in claim 14 wherein the step of rolling including rolling said sheet of said stainless steel substantially at least 720° around a central axis of said tubing to define said fluid conduit.

20. The method as recited in claim 14 further including the step of brazing a lamination along a length of said tubing.

21. The method as recited in claim 14 wherein the step of heating occurs in a controlled atmosphere.

22. The method as recited in claim 21 wherein the controlled atmosphere includes at least one of nitrogen, hydrogen, and a mixture of nitrogen and hydrogen.

23. The method as recited in claim 14 wherein said coating is a nickel alloy.