Determining the exact shear bolt

[MossRoad]

Yes, I saw that and replied to you there.

Back to topic...

I would think you would start with the softest shear pin possible in testing to protect your expensive investment in implements and tractors. If the softest works, go up a step. If that works, go up again, until it breaks. All the while making your scientific measurements(of which, I am not familiar). If you started with the strongest shear pin, you could potentially break many implements and/or tractors before you got to a shear pin that would work correctly. I'm no engineer, but that just seems like common sense. Shear pins are dirt cheap and implements and tractors aren't.

<font color="blue"> You need to make it the shear bolt the weaker than any component in this combined system. But, not much weaker as you will not want the bolt broken frequently even when it hits a small stone. </font>

Yes, the shear pin is the safety valve that protects your implement and tractor. How much weaker it should be than the rest of your components is a big question. How would you measure something like that? I'd opt for replacing shear bolts more often than risking my equipment. Pushing a machine to the max all the time is asking for an early retirement of the machine.

 

[HayDR]

MossRoad,
I'm glade you asked. We offer safety clutches on all our equipment or belt slippage safety on our disc and drum mowers. We work with PTO, and gearbox MFGs along with data we have collected with over 30 years of field testing to choose the safety devices we supply for implements we manufacture and import. We test our data to prove our choices are correct. Sometimes it is hard for foreign MFG's to test in the same conditions we have here in the states. For the most part, compact tractors are sold in Asia and the USA markets. The native grasses we have here are different than those in other parts of the world. Testing in the USA is a must if you are to sell a product in the USA market.

 

[nomad]

Villengineer, I'm not saying I am experienced in practical engineering industry as I'm not following which standart bolt does this, which doesn't. But I understand the theoretical backgrounds. I know this (shear bolt) is a small thing to be talked about for engineers. But, we are in a farm machinery forum and there are farmers using Grade5 and happier than using Grade2. So, I consider this small talk about the shear pin selection is like a table meeting at a factory department, in that engineers, farmers and others joining to find a solution. So, I'm not trying to belittle this problem of selection of shear pin. Having said these; let me continue.

</font><font color="blue" class="small">(
First, for most individuals on this site it would be whatever the manufacturer recommends. )</font>
I agree. and they usually recommend Grade2. Some recommends Grade5 and some (rare) do Grade8? But these recommedations are either for zero risks (no care about the farmers' anger everytime the pin is broken) OR for new tractors, pto system and attachments (if they are recommending the higher grades.) But tractors, attachments, ptos are old or weakened in time and manufacturer's recommendation isn't valid anymore. We can stop talking about this and leave the meeting solution table if we really decided to recommend everybody Grade2. Shall we? I will say a last thing before leaving table (after replying your other words.)

</font><font color="blue" class="small">( ...for higher hps,... use clutch systems rather than shear bolts. For two reasons, 1) They are almost always higher priced and therefore easier to justify the expense and 2) It is much easier to set the ideal torque limit useing clutch packs. )</font>
Agree in the clutch system, but some farmers don't prefer them for the reason you mentioned in (1), i.e. the price.
</font><font color="blue" class="small">(
(to find an optimum GradeX)... I would try and design around the most commonly available shear pin. If you are designing the attachment, you should know what the drive system will take and you will be specifying a HP range for the tractor to be used with the attachment. Now it's just a matter of how much torque you are going to allow the tractor to transmit into the attachment. )</font>

This is a solution. But, such a design of attachment (which will use Grade2) can be poorer quality (economical greed will lead to this result) so that making every critical points of this attachment stronger (a little bit more within a tolerance) than the Grade 2. But there is another thing; depending on the field surface conditions of a farmer and their different use of tools with different ages (millions of combinations), no one will be able to design what force/torque will be at the point/section of the shear pin in real conditions of that specific farmer. So, I suggest the shear pin type/size to be determined in real conditions for each farmer. And since we can't do this in that meeting table in the factory for each of farmers, farmers should do that (finding optimum GradeX) themselves. But how will they do? What are farmers currently doing? They are breaking some pins until they find a proper pin for their special application. If they are lucky, they break a few only.

Now, my suggestion; Using a kind of test specimen which can be a "magnified" model of the shear pin. I know modelling the fracture is very difficult, but we don't need to model the fracture. We only need to model the plastic deformation of shear bolt GradeX in consideration. Using that plastic deformation model, we can transfer the results we obtained from that specimen tested under plastic deformation to the shear bolt made of medium/low carbon alloy. Well, don't worry, farmers - you will not use a complex software etc to model the plastic deformation - you will do it in the real field. Hmmm.. What about using an aluminum (very ductile) shear pin speciment to find the deformation, say, D in it? and this deformation amount in specified size aluminum specimen can be transferred (by using a software a design dept. will write) to find out GradeX of the real steel shear pin. Now, the question is; those specialized in material science, what do they think? Is there some analogy between aluminum and steel characteristics so that aluminum can be used to model the deformation in the steel? If this is done, the shear problem is solved;-) [ps: sorry for the long post - i think we can go on further now with shorter posts;0]

 

[MossRoad]

CCI, Thanks.

I have a 5' brush hog on my IH2500b(50PTO HP). The gearbox on the brush hog is rated at 65HP(I think, it's been a while) and it has shear pins. Just out of curiosity, how much would a ballpark figure clutch device be for something of this size? I bust a shear pin about 2-4 times each time I use it on about 8-9 acres. I was hogging this area 2-3 times a year for 5-6 years. So that was about 30-40 times that I had to replace the shear bolt. Took about 10 minutes each time so I spent 300-400 minutes doing this. What I'm getting at, is, for someone like me, my time is worth less than my money, so the shear pins were more practical for me. But for someone making a living doing this kind of activity, it looks like a clutch would be more practical than shear pins.

 

[HayDR]

Are you using the same PTO and gearbox on 48", 60" & 72" cutter? Are you going to use the same shear pin in different size cutters? In the metric bolts there at 5.8, 8.8, 10.9 & 12.9 grades in bolts. Are you bolts CE approved? How do we know what standards you are using for hardness? USA, Canada or CE

 

[nomad]

I'll use the slip instead of the shear pin. I often hear farmers there (here on this forum) asking about their shear pins and i only wanted to make a small contribution. By the way, why shall I answer your irrelevant questions here? (ask them in the cutter thread.) and why trying to change the topic from the shear pin to an irrelevant subject? (to help on closing this thread?) What do you think about my aluminum test specimen idea to model their optimum GradeX of steel shear pin of each farmer? Have any say? Forget it. Speak about the cutter (in the cutter thread) and let me answer you there (if your question is meaningful, however)- back to topic.

 

[HayDR]

There are 5 reasons to have the proper safety device.
Protect the operator
Protect the tractor from damage.
Protect the PTO from damage.
Protect the implement gearbox from damage.
Protect against thrown objects due to breakage of the cutting blade.

I'm sure we could come up with more but these are the main reasons for a safety device to be properly matched to the tractor HP, drive line, implement gearbox and the intended use of the implement.

 

[Villengineer]

</font><font color="blue" class="small">( But these recommedations are either for zero risks (no care about the farmers' anger everytime the pin is broken) OR for new tractors, pto system and attachments (if they are recommending the higher grades.) But tractors, attachments, ptos are old or weakened in time and manufacturer's recommendation isn't valid anymore. )</font>
I don't know about each implement company, but when a customer starts changing parts on our equipment all warranty and liability go out the window. Especially if they try and increase the capacity of our products. I don't recomend trying to out guess the original manufacturer. As far as worn out equipment is concerned then you would definitely being going down in grade if you made a change. Besides if your equipment is in that bad of shape chances are it isn't producing even close to it's original power anyway.
</font><font color="blue" class="small">( But, such a design of attachment (which will use Grade2) can be poorer quality (economical greed will lead to this result) so that making every critical points of this attachment stronger (a little bit more within a tolerance) than the Grade 2. But there is another thing; depending on the field surface conditions of a farmer and their different use of tools with different ages (millions of combinations), no one will be able to design what force/torque will be at the point/section of the shear pin in real conditions of that specific farmer. )</font>
If the shear pin is your weakest point, why do you consider design optimization poor quality. You start with a set of design parameters and stay as close to them as possible, erring on the strong side. Over design is wasteful and in the end hurts the customer as they will be paying for it. Like you stated it's not practicle to design for each farmer. In the same token a single offering practically can't be offered to service every farmer. That's why most manufacturers offer different models with different specifications, or limits. At that point it's the customer's responsibility to determine what they need and purchase accordingly. If you only offer a single model, then state what it can do correctly and the end user has no basis for complaint.
As far as the rest goes:
Aluminum is a pretty poor choice for a test material as it reacts significantly different than ferrous materials.

 

[MossRoad]

I agree and make sure I use the shear pin recommended by the implement manufacturer and a PTO shaft with safety sleeve, etc...

But what is a ballpark figure for a safety clutch across the nation these days? Not asking for a price quote or anything like that... just trying to see where the line of cost of shear bolts and my time meets the line of cost of a safety clutch to figure out how many times I would have to change a shear bolt to justify the cost of the clutch. Or am I missing something like the clutch is safer than the bolts? Not directly related to determining the exact shear bolt, but pretty close.

 

[Junkman]

</font><font color="blue" class="small">( I agree and make sure I use the shear pin recommended by the implement manufacturer and a PTO shaft with safety sleeve, etc... MossRoad )</font>

</font><font color="blue" class="small">( Personally, I think that it is ill advised to experiment with expensive equipment when the correct part is readily available from most equipment dealers... Junkman )</font>

See, we can agree on some things some times!!!!!! <(sticky key) /forums/images/graemlins/blush.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/cool.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/laugh.gif