Nitriding Valve Springs - Daily Driver
12-15-2005, 07:03 AM
#1
Nitriding Valve Springs - Daily Driver Have been looking at the PSI springs, and the 1500 series spring is nitrided for circle track use. The nitriding hardens the outer surface and is supposed to increase fatigue life. I am wondering how a harder outer surface, which is likely more brittle, increases the fatigue life unless the outer fiber stress is held constant by the design of the spring while the nitriding operation increases the material yield strength.
Any materials folks here that can provide a more in depth discussion of the nitriding affect on the spring life?
These springs are an option on ETP heads and Dart is using them also, so the springs will be hitting the street in large numbers in the coming months.
Any materials folks here that can provide a more in depth discussion of the nitriding affect on the spring life?
These springs are an option on ETP heads and Dart is using them also, so the springs will be hitting the street in large numbers in the coming months.
12-16-2005, 03:25 PM
#5
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I work for a spring manufacturer.....Don't do any automotive applications, however.
Consulted a couple of the industry standard references looking for info on Nitriding. Didn't find any. The reference books aren't exactly new (Mechanical Springs, Wahl, 1963, and Spring Designer's Handbook, Carlson, 1978) but neither is Nitriding as a process (its detailed in my 1964 Machinery Handbook, have to look in my 1944 edition one (its at home where its safe)).
Shotpeening has a number of advantages, but the principle one is the introduction of compressive stresses in the surface of the material. Therefore, when the spring is put under load (which creates lots of tensile stresses) you first have to overcome the compressive stresses. Also, shotpeening cleans, deburrs, and generally smooths the outside surface, helping to eliminate potential stress risers from which fatigue cracks can propagate. Shotpeening can improve the fatigue life by 30% (average minimum) to 2 to 10 times (depending upon exact application). One of the things I found interesting is that shotpeenings impact is most important on the inside diameter of the spring. And that setting the spring (if setting is required) should be done prior to shotpeening (which may not always be the order that its done in) because there is a strength advantage.
From what I understand, Nitriding really only makes the surface harder, basically a case hardening process. This would make the surface stronger (which would make the spring stronger), but potentially more brittle (think crack propagation). I couldn't find any discussion of it in any of my texts, so I went searching.
Found this reference: http://www.shotpeener.com/library/pdf/2001000.pdf Was a bit of interesting reading. They're using extremely small shot to get even better results than conventional shot peening & nitriding.
'JustDreamin'
Consulted a couple of the industry standard references looking for info on Nitriding. Didn't find any. The reference books aren't exactly new (Mechanical Springs, Wahl, 1963, and Spring Designer's Handbook, Carlson, 1978) but neither is Nitriding as a process (its detailed in my 1964 Machinery Handbook, have to look in my 1944 edition one (its at home where its safe)).
Shotpeening has a number of advantages, but the principle one is the introduction of compressive stresses in the surface of the material. Therefore, when the spring is put under load (which creates lots of tensile stresses) you first have to overcome the compressive stresses. Also, shotpeening cleans, deburrs, and generally smooths the outside surface, helping to eliminate potential stress risers from which fatigue cracks can propagate. Shotpeening can improve the fatigue life by 30% (average minimum) to 2 to 10 times (depending upon exact application). One of the things I found interesting is that shotpeenings impact is most important on the inside diameter of the spring. And that setting the spring (if setting is required) should be done prior to shotpeening (which may not always be the order that its done in) because there is a strength advantage.
From what I understand, Nitriding really only makes the surface harder, basically a case hardening process. This would make the surface stronger (which would make the spring stronger), but potentially more brittle (think crack propagation). I couldn't find any discussion of it in any of my texts, so I went searching.
Found this reference: http://www.shotpeener.com/library/pdf/2001000.pdf Was a bit of interesting reading. They're using extremely small shot to get even better results than conventional shot peening & nitriding.
'JustDreamin'
Last edited by 'JustDreamin'; 12-16-2005 at 03:43 PM.
12-16-2005, 03:55 PM
#6
Does anyone know what the TST (Tuned Surface Treatment) from PSI is ? I know some springs are Electro Polished , is that kind of like EDM but applied strictly to the surface ? I think some of those reference materials while a great read , would really be lacking compared to the technology being utilized in material processing these days . It's amazing what we have available to us today .
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12-16-2005, 05:36 PM
#8
Springs aren't usually for a dedicated application . They come in a myriad of sizes and rates . Find the appropiate spring for your needs and thats about it . Since PSI makes so many diiferent springs I'm sure you can find something to suit your needs . I believe Manley's NexTek springs are made by PSI . Be prepared to pay , CV is the sole distributor but other sources are out there . I was really impressed with the quality of the springs . They look beautiful , very close when checked on a spring tester and should last a long time . So any info on TST or other surface enhancing treatments ?
