shot peened rods
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14-12-2008, 12:08 AM
#8
Little metal balls fired at high speed mottles the surface of the metal.
Reduces stress raisers and places cracks can start.
Think of small radiuses everywhere no sharp edges.
Well that is my take anyway.
Shot peened stuff looks like sand blasted metal.
Reduces stress raisers and places cracks can start.
Think of small radiuses everywhere no sharp edges.
Well that is my take anyway.
Shot peened stuff looks like sand blasted metal.
14-12-2008, 11:40 AM
#10
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Theres a bit more theory behind shot penning, although what Lincoln said is true. It actually gives a thin layer of residual compressive stress on the surface of the metal left over by the plastic deformation, in comparison to the tensile stresses already in the rods (from the forming, cooling and grinding processes they undertake).
In short it helps fatigue life, sometimes drastically..like up to 600% IIRC (was long time since college to remember numbers), we use it extensively at work with every welded assembly going through an automated shot blast facility for stress relief.
Basically polishing the rods is not as good as penning the rods, as the very act of polishing is infact grinding, just ona finer scale, this leaves a buildup of tensile stress in the components surface, whereas penning doesnt, it produces residual compressive stress which is benficial.
*** polishing is still much better than std though, as your removing all of the possible failure points like high spots, grinding scores, sharp edges and angles. ***
Maybe the best would be a polished rod thats then penned to give perfect smoothness in shape and penned surface finish for strength and fatigue life???
Hope my ramblings helped, i enjoyed typing it :P
Dan
In short it helps fatigue life, sometimes drastically..like up to 600% IIRC (was long time since college to remember numbers), we use it extensively at work with every welded assembly going through an automated shot blast facility for stress relief.
Basically polishing the rods is not as good as penning the rods, as the very act of polishing is infact grinding, just ona finer scale, this leaves a buildup of tensile stress in the components surface, whereas penning doesnt, it produces residual compressive stress which is benficial.
*** polishing is still much better than std though, as your removing all of the possible failure points like high spots, grinding scores, sharp edges and angles. ***
Maybe the best would be a polished rod thats then penned to give perfect smoothness in shape and penned surface finish for strength and fatigue life???
Hope my ramblings helped, i enjoyed typing it :P
Dan
Last edited by SillyFezzaMk1; 14-12-2008 at 11:57 AM.
14-12-2008, 12:41 PM
#16
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Jimbo, polishing is very good for the rods, I dont see how rods recieve a true cyclic load (fatigue state) most of the time they're under compression. The only time I can think of them being under tension is dragging the piston down the cylinder sucking fuel/air into chamber ont he 1st of the 4 strokes....
Polishing greatly reduces the risk of failure as it removes (if done properly) all of the main stress concentration points, the finer the polish the less likely it is to fail. It's more effective to polish a rod than it is to Penn it, thats probably why you see your old man using polished over penned rods.
You mentioned Beam rods, do you mean I beam section? If so then these are different rods with diff materials and structure to a std forged rod.
Cheers
Dan
Polishing greatly reduces the risk of failure as it removes (if done properly) all of the main stress concentration points, the finer the polish the less likely it is to fail. It's more effective to polish a rod than it is to Penn it, thats probably why you see your old man using polished over penned rods.
You mentioned Beam rods, do you mean I beam section? If so then these are different rods with diff materials and structure to a std forged rod.
Cheers
Dan
14-12-2008, 12:48 PM
#17
Colossal Pervert
Shot-peening and polishing rods does very little to prevent damage caused by excessive compressive loads.. they're both practises more useful in high-tensile-loading applications like buzzy atmo engines.
14-12-2008, 12:58 PM
#18
Jimbo, polishing is very good for the rods, I dont see how rods recieve a true cyclic load (fatigue state) most of the time they're under compression. The only time I can think of them being under tension is dragging the piston down the cylinder sucking fuel/air into chamber ont he 1st of the 4 strokes....
Polishing greatly reduces the risk of failure as it removes (if done properly) all of the main stress concentration points, the finer the polish the less likely it is to fail. It's more effective to polish a rod than it is to Penn it, thats probably why you see your old man using polished over penned rods.
You mentioned Beam rods, do you mean I beam section? If so then these are different rods with diff materials and structure to a std forged rod.
Cheers
Dan
Polishing greatly reduces the risk of failure as it removes (if done properly) all of the main stress concentration points, the finer the polish the less likely it is to fail. It's more effective to polish a rod than it is to Penn it, thats probably why you see your old man using polished over penned rods.
You mentioned Beam rods, do you mean I beam section? If so then these are different rods with diff materials and structure to a std forged rod.
Cheers
Dan
no im talking about standard rods
when using anything other than standard then they dont have any thing done to them iirc
14-12-2008, 01:12 PM
#19
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Pa Sjo You could categorise some of the high revving YBs around here as 'buzzing'!
I dissagree to be honest, the process of polishing and penning helps prevent failure due to adding strength to the rod, that you can't deny.
I dissagree to be honest, the process of polishing and penning helps prevent failure due to adding strength to the rod, that you can't deny.
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