Method of brazing titanium to stainless steel

• US 6,168,069 B1
• Filed: 07/06/1998
• Issued: 01/02/2001
• Est. Priority Date: 07/18/1997
• Status: Expired due to Term

• Current Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Original Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Inventors: Lorenz, Rainer
• Primary Examiner(s): Ryan, Patrick
• Assistant Examiner(s): EDMONDSON, LYNNE RENEE
• Application Number:
  US09/110,606
• Time in Patent Office: 911 Days
• Field of Search: 228/121, 228/131, 228/126, 228/208, 228/221, 228/262.42, 228/262.72, 420/502, 294/69
• US Class Current: 228/131
• CPC Class Codes: B23K 1/0008 specially adapted for particular articles or work
• CPC Class Codes: B23K 1/19 taking account of the properties of the materials to be soldered
• CPC Class Codes: B23K 2103/24 Ferrous alloys and titanium or alloys thereof
• CPC Class Codes: B23K 35/3006 Ag as the principal constituent
• CPC Class Codes: G01F 1/8404 details of flowmeter manufacturing methods
• CPC Class Codes: G01F 1/8409 constructional details
• CPC Class Codes: G01F 1/8413 means for influencing the flowmeter's motional or vibrational behaviour, e.g., conduit support or fixing means, or conduit attachments
• CPC Class Codes: G01F 1/849 having straight measuring conduits
• CPC Class Codes: Y10T 428/12812 Diverse refractory group metal-base components: alternative to or next to each other
• CPC Class Codes: Y10T 428/12896 Ag-base component

Abstract

Surprisingly, silver-copper-palladium brazing alloys, which have hitherto been used only for the brazing of components of the same material, are also very well suited for brazing directly titanium to stainless steel if, the latter component clasps the titanium component tightly, so that the cold joint is under constant compressive stress. In a method for forming the titanium-steel compound the titanium component is provided with a cylindrical end which has a smaller out-side diameter than an adjacent main portion whose external surface is a first surface to be brazed. The cylindrical steel component is a sleeve whose inside diameter is equal to the outside diameter of the main portion and whose internal surface is a second surface to be brazed. A silver-copper-palladium brazing alloy is placed around the end of the titanium component. The steel sleeve is slipped thereover. The whole is heated in a vacuum or an inert gas until the silver-copper-palladium brazing alloy melts and wets the surfaces to be brazed, and is then allowed to cool down.

Claims

1. A method for forming a compound arrangement by brazing a first component of titanium to a second component of unplated stainless steel using silver-copper-palladium brazing alloys, wherein

the first component of titanium is provided with a cylindrical first end

which has a smaller outside diameter than an adjacent main portion

whose external surface is, at least in part, a first surface to be brazed;

the second component is a cylindrical steel sleeve

whose inside diameter is equal to the outside diameter of the main portion of the first component and

whose internal surface is, at least in part, a second surface to be brazed the second surface being unplated stainless steel;

a silver-copper-palladium brazing alloy is placed around the first end of the first component;

the steel sleeve is slipped over the main portion of the first component;

the first and second components and the silver-copper-palladium brazing alloy are heated in a vacuum or an inert gas until the silver-copper-palladium brazing alloy melts and wets the surface to be brazed; and

the first and second components and the brazing alloy are then cooled so that the steel sleeve exerts compressive stress on the first surface of titanium and is brazed directly to the first surface of titanium;

whereby the compound arrangement is formed.

2. A method as claimed in claim 1 wherein

the steel sleeve has an end projecting beyond the first end of the first component of titanium;

the first component has a tapped blind hole at the first end;

a tube of stainless steel which has an outside diameter equal to the inside diameter of the steel sleeve is provided at a first end with an external thread fitting the thread of the tapped blind hole; and

the projecting end of the steel sleeve is brazed to the tube.

3. A method as claimed in claim 1 wherein the main portion of the first component of titanium is provided with a collar remote from the first end, said collar being covered by and serving as a stop for the steel sleeve.

4. A method as claimed in claim 2 wherein the main portion of the first component of titanium is provided with a collar remote from the first end, said collar being covered by and serving as a stop for the steel sleeve.

5. A method as claimed in claim 2 wherein

the first component of titanium is provided with an axial bore whose diameter is equal to the inside diameter of the tube of stainless steel;

a titanium tube whose outside diameter is virtually equal to the inside diameter of the tube is inserted into the tube and into the axial bore; and

the titanium tube is electrically welded to the first component in an inert-gas atmosphere.

6. A method as claimed in claim 3 wherein

a tube of stainless steel which has an outside diameter equal to the inside diameter of the steel sleeve is provided at a first end with an external thread fitting the thread of the tapped blind hole;

the first component of titanium is provided with an axial bore whose diameter is equal to the inside diameter of the tube of stainless steel;

a titanium tube whose outside diameter is virtually equal to the inside diameter of the tube is inserted into the tube and into the axial bore; and

the titanium tube is electrically welded to the first component in an inert-gas atmosphere.

7. A method as claimed in claim 1 wherein the silver-copper-palladium brazing alloy has a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5 wt. % palladium and is as free from residues as possible.

8. A method as claimed in claim 2 wherein the silver-copper-palladium brazing alloy has a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5 wt. % palladium and is as free of residues as possible.

9. A method as claimed in claim 3 wherein the silver-copper-palladium brazing alloy has a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5 wt. % palladium and is as free of residues as possible.

10. A method as claimed in claim 4 wherein the silver-copper-palladium brazing alloy has a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5 wt. % palladium and is as free of residues as possible.

11. A method as claimed in claim 5 wherein the silver-copper-palladium brazing alloy has a composition of 68.5 wt. % silver, 26.5 wt. % copper, and 5 wt. % palladium and is as free of residues as possible.

12. A method of brazing titanium directly to unplated stainless steel, the method comprising the steps of:

a) providing a first surface of titanium to be brazed;

b) providing a second surface of unplated stainless steel to be brazed;

c) forming with the first surface of titanium and the second surface of unplated stainless steel a cold joint;

d) applying a brazing alloy adjacent to the cold joint;

e) heating the cold joint and brazing alloy so that the brazing alloy melts and penetrates into the cold joint between the surfaces to be brazed and wets the surfaces; and

f) cooling the cold joint and brazing alloy so that the second surface of unplated stainless steel exerts compressive stress on the first surface of titanium and is brazed directly to the first surface of titanium.

13. The method of claim 12, wherein the cold joint and brazing alloy are heated in a vacuum.

14. The method of claim 12, wherein the cold joint and brazing alloy are heated in an inert gas.

15. The method of claim 14, wherein the brazing alloy is a silver-copper-palladium brazing alloy.

16. A method of brazing titanium directly to unplated stainless steel, the method comprising the steps of:

a) providing a first surface geometry of titanium to be brazed;

b) providing a second surface geometry of unplated stainless steel to be brazed, the second surface geometry of unplated stainless steel selected to form a cold joint under compressive stress with the first surface geometry of titanium when the geometries are cooling after heating; and

c) forming with the first surface geometry of titanium and the second surface geometry of unplated stainless steel a cold joint.

17. The method of claim 16, further comprising the step of applying a brazing alloy adjacent to the cold joint.

18. The method of claim 17, further comprising the step of heating the cold joint and brazing alloy, whereby the brazing alloy melts and penetrates into the cold joint between the surfaces to be brazed and wets the surfaces such that the first surface geometry of titanium is brazed directly to the second surface geometry of unplated stainless steel.

19. The method of claim 18, wherein the first surface geometry of titanium to be brazed is the outer surface of a titanium cylinder.

20. The method of claim 19, wherein the second surface geometry of unplated stainless steel to be brazed is the inner surface of a stainless steel cylinder.

21. The method of claim 20, wherein the cold joint and brazing alloy are heated in a vacuum.

22. The method of claim 21, wherein the cold joint and brazing alloy are heated in an inert gas.

23. The method of claim 21, wherein the brazing alloy is a silver-copper-palladium brazing alloy.