Metal 'fatigue'?

[Ty Korrigan]

Hello,

 Question for the engineers out there.

The effects of cold bending/redressing steel.

If steel deforms through use, even slightly and is bent back to correct it, does this weaken or strengthen the metal?

        Stuart

  

 

 

 

[Khriss]

...only clicked on this cos thought it was ' mental fatigue' ..... however  !  All stresses / bending / shocking and vibration affect the structure of metals. Heat treating is possible with certain methods  ( sawdust on aluminium for example ) or welding extra support in . Which also eases stressed parts.  K

[Ty Korrigan]

Metal fatigue has given me mental fatigue...

  Stuart

[openspaceman]

22 minutes ago, Ty Korrigan said:

If steel deforms through use, even slightly and is bent back to correct it, does this weaken or strengthen the metal?

If the steel has bent cold it means the strain has gone beyond its elastic limit and it has entered the plastic deformation zone . I think it has been weakened both initially and when bent back. The problem is when it is repeated cracks develop along the crystal boundaries. Steel copes with this better than aluminium which always eventually fails if stressed this way (hence Comets falling out of the sky and no aluminium suspension springs.

[Khriss]

@Ty Korrigan  best post a pic of part in question cos it's a broad subject. Remember seeing the steel castings of Chieftain tank turrets in Leeds sitting there for 2 yrs whilst the casting stresses left them - so they could be machined to fit properly.  K

[spudulike]

In real terms I would say it weakens it. Without looking I would say the hardness would increase in the bent area but if bent repeatedly, it will snap! Bending any metal repeatedly will break it.....apart from mercury in its fluid state

[Ty Korrigan]

I'll post an image when I return home.

The subject is sliding roller rails on a GM150

They splay subtly upwards.

I am led to believe by GM the slight deformation has lead to the rollers drop off in performance and the solution is simply to bend them back.

  Stuart

  

[doobin]

54 minutes ago, Ty Korrigan said:

I'll post an image when I return home.

The subject is sliding roller rails on a GM150

They splay subtly upwards.

I am led to believe by GM the slight deformation has lead to the rollers drop off in performance and the solution is simply to bend them back.

  Stuart

  

To have splayed they can’t have been built strong enough in the first place. Bend them back, then they will slowly splay themselves back the other way. Repeat until failure....
 

sound like the usual gm crock of shite excuses. 

[Ty Korrigan]

I am plagued by the rollers refusing to draw material in.

They are sharp, I see to that.

The spring is weak though, I can draw the rollers apart.

They just do not seem to have much bite.

Now larger wood is drawn in fine, generally.

But leafy twiggy and smaller stuff just sits there between the rollers as they spin to the sound of my swearing.

I have also caught the rollers jamming open and stopped the machine to take images of clean roller rails.

GM think the roller carriage is twisting in the rails and jamming.

They propose to redress the rails.

I can see a slight upward bend in the rails and a curve in the metal upright panel.

Seems like nothing at all but I'm led by the manufacturers advice.

There must be other GM150 owners with similar issues as I cannot believe that I am lucky enough to have ALL the problems to myself.

 

 

[Ty Korrigan]

I worry that I'm being over particular about the performance of the machine and that these issues are perhaps perfectly normal even acceptable.

Like trying to sleep with a mosquito in the room, trying to 'enjoy' effective and efficient chipping or having 'pride in ownership' certainly is difficult for me to manage given the cumulative issues which seem out of my control.

   Stuart