Knotter damage - help

[maciejka85]

Hello everyone,
I'm a Material Science and Engineering faculty student from Warsaw (Poland). I've found your forum looking for some data concerning machine parts destruction analysis.
Now I'm working on project which goal is to find the way the part was destroyed.
The part which I'm analysing is a part of baler (part of knotter). Materials testing (hardness testing, microstructure analysis)shown that everything was ok with material used in this case but I still don't know what might be the cause of destruction.
Did you ever had a situation when knotter was damaged in this way?(pictures are in attachement)
What kind of situation it might have been?
I'm not a farmer so I'm not familiar with using this kind of machines.
Than you for your help.
Regards
Maciek Karabin

 

[aczlan]

Here are the pictures attached directly to the post (that way people dont have to worry about getting a bug from the zip file)


Aaron Z

 

[zzvyb6]

The part you are showing is called a "knotter frame". The damage it is showing in the photos is consistent with a secondary impact from the baler needles after they themselves have been struck by the plunger mechanism. It occurs quite frequently when either the baler falls out of "timing" or it injests unacceptable material. The fundamental cause is that during the knot tying sequence, the needles do not retract properly as they become jammed between the plunger (and its fresh load of hay from the feeder), and the the previous flake of hay already in the bale case. If the current flake is wet, too large, contains material other than hay, or the charge is too fast, or the bale retention pressure is too great, then the needles get stuck in the fully inserted position and then the needle drive shear pin breaks to save the main drive, gearcase and other parts. The needles are already in very close proximity to the knotter frame when this happens. And in fact are very tightly wrapped by cast metal around the twine disk, billhook, and wiper arm bearing holders. When the plunger slams the needles, they are strong enough to impact the knotter frame in several areas and fracture the frame. The microstructure in the breakage area should be expected to be of impact nature and you should look for the tell-tale marks of the needle strike on the forward portion of the frame. Needles can be cast or forged steel. You should also look for metal pieces of a dissimilar material in the parent metal of your sample piece. Usually the needles are destroyed in this unitended operation and pieces of them are found in the struck object.

Hows, that?? I don't usually do homework problems, but if you look thru this forum, a lot of damage to parts is done by bending, not fracturing, so this is a relatively rare deal.

 

[RickB]

The part you are showing is called a "knotter frame". The damage it is showing in the photos is consistent with a secondary impact from the baler needles after they themselves have been struck by the plunger mechanism. It occurs quite frequently when either the baler falls out of "timing" or it injests unacceptable material. The fundamental cause is that during the knot tying sequence, the needles do not retract properly as they become jammed between the plunger (and its fresh load of hay from the feeder), and the the previous flake of hay already in the bale case. If the current flake is wet, too large, contains material other than hay, or the charge is too fast, or the bale retention pressure is too great, then the needles get stuck in the fully inserted position and then the needle drive shear pin breaks to save the main drive, gearcase and other parts. The needles are already in very close proximity to the knotter frame when this happens. And in fact are very tightly wrapped by cast metal around the twine disk, billhook, and wiper arm bearing holders. When the plunger slams the needles, they are strong enough to impact the knotter frame in several areas and fracture the frame. The microstructure in the breakage area should be expected to be of impact nature and you should look for the tell-tale marks of the needle strike on the forward portion of the frame. Needles can be cast or forged steel. You should also look for metal pieces of a dissimilar material in the parent metal of your sample piece. Usually the needles are destroyed in this unitended operation and pieces of them are found in the struck object.

Hows, that?? I don't usually do homework problems, but if you look thru this forum, a lot of damage to parts is done by bending, not fracturing, so this is a relatively rare deal.

The plunger won't contact the needles unless the needles are well out of adjustment. The needles are inserted into the chamber when the plunger is in the closest proximity to them each and every time without contact. In fact, the needles are protected by slots in the plunger face most of the time they are in the chamber. Broken needles are the result of the plunger delivering a charge of crop and possibly foreign matter while the needles are inserted at the wrong time, or remain inserted when they should be retracted.

Broken knotter frames are often the result of the loss of the knotter frame anchor bolt or or pin. The needle contacts the frame, rotating it upwards, usually breaking the tip from the needle and often breaking the frame as well.