Leaf spring and method of manufacture thereof having sections with different levels of through hardness

Patent metadata

Field	Value
Publication number	US-9890440-B2
Application number	US-201715431480-A
Country	US
Kind code	B2
Filing date	Feb 13, 2017
Priority date	Oct 1, 2013
Publication date	Feb 13, 2018
Grant date	Feb 13, 2018

Abstract

Leaf springs, and methods of manufacturing thereof, having first and second sections, spaced apart along the length of said leaf spring, said sections are through hardened and tempered to achieve, respectively different levels of finished through hardness, are disclosed.

First claim

We claim:

1. A method of selectively tempering to a finished through hardness one or more sections of a leaf spring having at least a first section and a second section spaced apart longitudinally along said leaf spring, each of said first and said second sections extending across an entire transverse cross section of and along said leaf spring, after primary tempering of said leaf spring has commenced, said method comprising the acts of:
applying localized heat to said second section of said leaf spring at a temperature that is above a temperature at which the leaf spring underwent primary tempering and below austenitic transformation temperature,
maintaining said localized heat to said second section for a period of 20 seconds or longer, and
quenching the leaf spring with an aqueous solution to rapidly cool the second section from a temperature of at least 50° F. above the temperature at which tempered martensite embrittlement can occur to a temperature less than 150° F. and to reduce heat migration into any section to which said localized heat was not applied,

resulting in said first section being through hardened and tempered to a finished through hardness and said second section being through hardened and selectively tempered to a finished through hardness that is less than the finished through hardness of said first section.

2. The method of claim 1 wherein the temperature at which tempered martensite embrittlement can occur is 600° F.

3. The method of claim 1 wherein the leaf spring is a parabolic leaf spring wherein said first section thereof includes at least one parabolic arm and has a finished through hardness of between about 466 BHN and 510 BHN, and said second section thereof comprises a first eye or a seat of said leaf spring.

4. The method of claim 1 wherein said localized heat is applied to the second section of the leaf spring to maintain the heated areas of said second section at a temperature between 1000° F. and 1200° F. for a period of time between 45 and 60 seconds.

5. The method of claim 1 wherein the second section of the leaf spring includes at least one eye and said localized heat is applied to said second section across an entire width of a 180 degree zone across the top of said at least one eye.

6. The method of claim 1 wherein the second section of the leaf spring comprises at least one eye and has a finished through hardness of between about 401 BHN and 444 BHN.

7. The method of claim 1 wherein the second section of the leaf spring comprises at least one eye and has a finished through hardness of about 388 BHN or 406 BHN or 434 BHN.

8. The method of claim 1 comprising the additional steps of applying localized heat to a third section of said leaf spring at a temperature above and maintaining localized heat to a third section of the leaf spring, said third section spaced apart longitudinally along said leaf spring from each one of said first section and said second section and extending across an entire transverse cross section of and along said leaf spring, and wherein said second section and said third section respectively comprises a first eye and a second eye, or alternatively, a first eye and a seat of said leaf spring, and said third section is through hardened and tempered to a finished through hardness that is less than the finished through hardness of said first section.

9. The method of claim 1 wherein said localized heat is applied by electric heat induction.

10. The method of claim 1 wherein said second section or said third section is a seat of said leaf spring and said step of applying localized heat to said seat further comprises applying localized heat to zones on top and bottom surfaces and across the seat and within about a half inch on either side of a center of the seat.

11. The method of claim 1 wherein after primary tempering has commenced, the leaf spring is not quenched until after said step applying located heat to said second section.

12. The method of claim 1 comprising a further step of quenching said leaf spring after primary tempering to reduce the leaf spring to ambient temperature before said step of applying localized heat to said second section.

Assignees

• Hendrickson Usa Llc
• Hendrickson Usa Llc

Inventors

• Wilson William
• Farrell Brian

Classifications

• C21D2211/008

  Martensite · CPC title

• C21D1/25

  Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten") · CPC title

• C21D2221/00

  Treating localised areas of an article · CPC title

• B60G11/02

  having leaf springs only {(B60G11/006 takes precedence)} · CPC title

• B60G2206/8402

  Quenching · CPC title