Method to prevent specks or hairline cracks in, and premature failure of, airplane cylinder barrels

• US 20030031810A1
• Filed: 05/09/2001
• Published: 02/13/2003
• Est. Priority Date: 05/09/2001
• Status: Active Grant

• Current Assignee: Textron Lycoming Corporation (Textron Inc)
• Original Assignee: Textron Lycoming Corporation (Textron Inc)
• Inventors: Kim, Yoon Sam
• Granted Patent: US 6,585,832 B2
• Time in Patent Office: Days
• US Class Current: 428/34.1
• CPC Class Codes: C23C 22/62 Treatment of iron or alloys based thereon
• CPC Class Codes: Y10T 428/13 Hollow or container type article [e.g., tube, vase, etc.]

Abstract

The present invention relates to an improved method for the manufacture of aircraft engine cylinder barrels to prevent their premature failure due to hairline cracks or specks thought to be caused by caustic stress corrosion cracking during black oxide treatment. Machined aircraft cylinder barrels immersed into a black oxide chemical bath composed of a solution containing about 60% sodium hydroxide, about 0% sodium nitrate, and about 40% sodium nitrite most effectively prevents specks and hairline cracks. Since residual stresses from machining also contribute to the probability that specks or hairline cracks will occur during black oxide treatment, the maximum selected number of cylinder barrels essentially free of detectible specks or hairline cracks determines the maximum number of cylinder barrels to be machined on a given set of tool bits.

Claims

1. An improved method of manufacturing aircraft engine cylinder barrels wherein the improvement comprises the step of immersing a machined cylinder barrel in a black oxide chemical bath, wherein the bath is comprised of a solution comprised of about 60-80% sodium hydroxide, about 0-20% sodium nitrate, and about 20-40% sodium nitrite.

2. The process of claim 1, wherein the solution is comprised of about 60% sodium hydroxide, about 0% sodium nitrate, and about 40% sodium nitrite.

3. The process of claim 1, wherein the solution is comprised of about 60% sodium hydroxide, 20% sodium nitrate, and 20% sodium nitrite.

4. The process of claim 1, wherein the solution is comprised of about 80% sodium hydroxide, and 20% sodium nitrite.

5. The process of claim 1, wherein the solution is comprised of about 60% sodium hydroxide, about 10% sodium nitrate, and about 30% sodium nitrite.

6. The process of claim 1, further comprising machining no more than a selected number of cylinder barrels on a given set of tool bits, the number selected such that a surface of the barrels is essentially free of detectible specks or hairline cracks after black oxide treatment.

7. A cylinder barrel manufactured according to the process of claim 1 wherein a surface of the machined cylinder barrel is essentially free of specks or hairline cracks.

8. A cylinder barrel manufactured according to the process of claim 2 wherein a surface of the machined cylinder barrel is essentially free of specks or hairline cracks.

9. A cylinder barrel manufactured according to the process of claim 3 wherein a surface of the machined cylinder barrel is essentially free of specks or hairline cracks.

10. A cylinder barrel manufactured according to the process of claim 4 wherein a surface of the machined cylinder barrel is essentially free of specks or hairline cracks.

11. A cylinder barrel manufactured according to the process of claim 5 wherein a surface of the machined cylinder barrel is essentially free of specks or hairline cracks.