Determining the exact shear bolt

MossRoad · Dec 22, 2003

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.

 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. 

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 · Dec 22, 2003

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 · Dec 22, 2003

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.

(
First, for most individuals on this site it would be whatever the manufacturer recommends. )
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.)

( ...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. )
Agree in the clutch system, but some farmers don't prefer them for the reason you mentioned in (1), i.e. the price.
(
(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. )

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 · Dec 22, 2003

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 · Dec 22, 2003

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 · Dec 22, 2003

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 · Dec 22, 2003

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 · Dec 22, 2003

( 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. )
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.
( 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. )
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 · Dec 22, 2003

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 · Dec 22, 2003

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

( 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 )

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

HayDR · Dec 22, 2003

Safety devices are matched to the torque range of a PTO. The key is knowing what Catagory PTO the application requires and then match the safety device to the PTO.

nomad · Dec 22, 2003

( 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. )

I think we are confused (in communication) here in the steps of design.? The shear pin isn't designed yet, but (in your previous post) you already started with Grade2 (for its price/availability/etc). So, you already selected Grade2. Now, designing of attachment will be affected also by this early selection of the pin and the result (attachment) will be "relatively" poorer quality (which you may call optimum design) since your design travels around Grade2 use. We are saying same thing up to now. But, the problem starts here; the tolerance in the design. This farming field applications (unlike other industries) require larger tolerances in the designs because farmers are using their implements in very different conditions. I agree in that it's in their responsibility of farmers using them in not-mentioned conditions of farmers. But changing an implement just for a shear pin isn't reasonable and isn't practical. So, this problem of selecting the shear pin in real application requires a solution, at least in my opinion based on farmers' complaints here.

( As far as the rest goes:
Aluminum is a pretty poor choice for a test material as it reacts significantly different than ferrous materials. )

As I said before, I'm not good at material science details. Aluminum may not be a good selection as its characteristics is different than ferrous materials like the steel. But I still think there must probably be some sufficient analogy between the deformations of aluminum and steel. I think a rough/approximate mathematical model using some symmetries can be made for the deformation path of aluminum and steel under the same forces. and modelling deformation parts of them only will be sufficient. Anyways, this needs further study, but who cares about farmers' shear pin?, except Nomad;-).

Villengineer · Dec 22, 2003

( I think we are confused (in communication) here in the steps of design.? )
No confusion on my part. I said you start with a set of parameters. Since they are widely accepted, cheap, and readily available it's entirely possible that the use of Gr2 shear pin could be one of those parameters.
( Now, designing of attachment will be affected also by this early selection of the pin and the result (attachment) will be "relatively" poorer quality (which you may call optimum design) since your design travels around Grade2 use )
There is nothing about Gr2 that makes it "poorer quality" than any other grade bolt. Quality is how it's made, not what it's made of. I have seen plenty of poor quality Gr8 bolts. Like I said before you start out with an objective and if it can be accomplished with the use of all basic components and materials, why complicate things?
( We are saying same thing up to now. But, the problem starts here; the tolerance in the design. This farming field applications (unlike other industries) require larger tolerances in the designs because farmers are using their implements in very different conditions. )
What are you talking about? The industry I work in varies MORE than farming in how various customers use our products. Farmers just happen to be a very small slice of our customer base. We design to the specifications set before us, if you want it right on the edge we'll do it, if you want it built like a tank, we can help you out there, too. The very same product might be used by a farmer, in the auto industry, and by a lumber yard. We tell them what it can do and stand behind it.
( But changing an implement just for a shear pin isn't reasonable and isn't practical. So, this problem of selecting the shear pin in real application requires a solution, at least in my opinion based on farmers' complaints here )
Designs are changed for a single component all the time. Especially if our customers find it unsatisfactory. At the same time, if we find that the customer has unrealistic expectations, we may decide not to change anything. If you keep breaking shear pins there are a number of possible reasons and none of them may have anything to do with the shear pin itself.

nomad · Dec 22, 2003

Ok, I'm lost in this communication. I meant by "relatively poor quality" anything from material, size, how it's made because I was trying to use a kind of language that everybody could understand.

Anyways, we can summarize the REAL stiuation as

Farmers are frequently breaking many shear pins if theirs are Grade2 and they are affraid of using higher grade pins like Grade5 or Grade8.

Correct? I think we all agree in that summary (doesn't matter whoever doing the mistake. this is reality) I had a solution in my mind and it was modelling the deformation behaviours by a real field test by using aluminum. Yes, such a model can be made. because generalized equations of stress-strain is same for both of the steel and aluminum. During the elastic deformation, from mathematican's point of view, these equations can be considered linear and nonlinear during the plastic deformation. But the nonlinearity in this plastic deformation isn't so high. Nonlinearity is very high only during the fracture moment. But since we are modelling only deformations small nonlinearity during the deformations will certainly not be a problem for a mathematican. As I said above, their forms of generalized equations are same. The only difference for steel and aluminum equations is the specific constants (or functions of their material properties.) These functions related to material properties can be nonlinear, but with some symmetries, this nonlinear functions can be reduced to lower dimensions unless it's at fracture period. While even fractures which are highly nonlinear are already being modelled, modelling simple deformations certainly won't be difficult. Certainly there must be some symmetry groups which can be applied to specific material functions of aluminum and steel. These symmetry groups will simplify big equations with material emphirical functions. So, as a conclusion, a certain aluminum specimen can be produced for farmers so that they can fix their steel shear pin type and size for their special applications. If the specific deformation functions of steel and aluminum are given to me (any material science professor there;-), I can contribute by writing a small software for aluminum specimen. (its cost? will not be higher than a baler cost;-)

Finally, I'd like to repeat the summary:

Farmers are frequently breaking many shear pins and therefore, they are angry if theirs are Grade2 and they are affraid of using higher grade pins like Grade5 or Grade8.

Egon · Dec 22, 2003

Nomad; have you considered designing a viscous coupling with lock up capability that is torque sensitive for release capabilities.

That would sure eliminate a lot of time spent changing shear bolts.

Egon

nomad · Dec 22, 2003

Egon, viscous coupling is a good idea as it will also absorb/damp the shock which is the main reason in breaking the shear bolt. But the price is a restriction here and we are talking about farmers using the shear pin only. A very simple viscous coupling (which will cost very cheap) possible? Worth to think about it.

Egon · Dec 22, 2003

Time is worth money when the farmer is working. This is really true at planting or harvest time. The less time he's fixing stuff the more time he has to do all the good stuff.

Why not move technology ahead and forget those simple shear pins?

Egon

Villengineer · Dec 22, 2003

( Farmers are frequently breaking many shear pins if theirs are Grade2 and they are affraid of using higher grade pins like Grade5 or Grade8 )
As they should be. If the attachment was designed to use a Gr2 shear pin then they should use a Gr2 shear pin. To suggest that they should do otherwise is irresponsible. Even if you don't get them hurt or killed, chances are you will cause them even more agravation when they start breaking major parts of their attachments.
If they are so put out by having to replace shear pins, then buy attachments with slip clutches. I can't believe that a vicous coupling would be that much cheaper than the clutch systems already available.
Your whole test specimen thing doesn't make practicle sense to me. Are you suggesting that each farmer be given an aluminum shear pin for each attachment to put into use and then have them analyzed to find the best alloy of steel for them to use for each application? 1) The mechanical properties of common aluminums (the only ones that make economical sense) are so much lower than steel that you couldn't get an accurate reading. They would shear way before the loads required to shear any steel, thus telling you absolutely nothing 2) I don't know about Turkey, but here in the US it would be cheaper to install slip clutches on each implement than to go through this process. After all what's the cost difference between them, a couple hundred bucks? You couldn't get a qualified materials test lab to look at them for that kind of money.

nomad · Dec 22, 2003

( If the attachment was designed to use a Gr2 shear pin then they should use a Gr2 shear pin.
)
This is an approach of "sell and forget the rest" (joke.)
You are correct. But whatever happening, they are breaking Gr2 much and this is causing them make angry and waste time. Okay, they should follow the user manuals, but the manuals will not be able to tell them exactly what exact field conditions are designed for that certain implement and also, the conditions of their PTO, engine, etc of tractors will not be (cannot be) considered much. So, they should do somethings else. But, what to? What I am trying to do here is a try to suggesting a solution. Here, our opinions differ.

( I can't believe that a vicous coupling would be that much cheaper than the clutch systems already available.
)
Agree (although didn't think if possible to make a cheap viscous coupling or not)

(
Your whole test specimen thing doesn't make practicle sense to me. Are you suggesting that each farmer be given an aluminum shear pin for each attachment to put into use and then have them analyzed to find the best alloy of steel for them to use for each application?
)
Yes, one test specimen (within the package of implement) will be enough. Once farmer determines his/her steel shear pin type for his/her special conditions he will not need that test specimen anymore.

(
1) The mechanical properties of common aluminums (the only ones that make economical sense) are so much lower than steel that you couldn't get an accurate reading. They would shear way before the loads required to shear any steel, thus telling you absolutely nothing
)
Their magnitudes of their parameters like load capability, etc aren't important in a modelling (as you know.) Even their equations of material functions can be different for aluminum and steel. Whats important is the "form" of their "specific material" functions which are usually linear at low deformations. If their forms and nonlinearities are somewhat close to each other, symmetries can easily be found in their behaviours. Thus, this will absolutely tell me somethings about the shear deformation behaviours of aluminum test pin model and prototype steel pin. "Generalized form" of stress-stress flow relation is same for both of them anyways. So, such an aluminum test specimen is "probably" possible.

(
2) I don't know about Turkey, but here in the US it would be cheaper to install slip clutches on each implement than to go through this process. After all what's the cost difference between them, a couple hundred bucks? You couldn't get a qualified materials test lab to look at them for that kind of money. )
Here the cost difference between them is cheaper. So, shear pin clutch is almost unavailable here. Even if there is $100 difference, I think it's still worth to use the slip clutch economically if we consider time=money. (a real cost analyse will probably prove that.) But there are people everywhere who are hard to change their habits. I guess thats why they are still preferring to use the shear pins.

rambler · Dec 23, 2003

First I gotta say - you folks have some of the best inside jokes in this thread I've ever seen. good job all! /forums/images/graemlins/smile.gif Totally enjoyed them! /forums/images/graemlins/smile.gif And yes you know who you are....

Ok, the aluminimn thing is pointless. If you want to test a pin, test the type of pin that will actually be used.

In my farming career, most farmers drilled out the holes 1/16" and use a slightly larger bolt of the same grade as the previous shear pin. We don't like to change the pin type, but slightly increase the size.

I feel nomad is trying to chang the material (aluminumn) and the diameter (using a gr 8 bolt & grinding a nick in it) and making this terribly confusing & immpossible. Somewhere in there he has a point, that each machine has it's own breaking point slightly different than another machine; but you can't try to find that by starting with a gr 8 bolt & making it skinnier - you MUST start with a gr 2 bolt, and either increase the grade or increase the bolt size. You also cannot easily create the same 'nick' in every gr 8 bolt a farmer makes by himself, so the whole exersize is pointless in the real world as nomad preposes it.

Also, this whole discussion is about changing the bolt grades, and that is not how I'm familiar with this. You increas the size of the hole & bolt slightly; and leave the grade of the bolt the same.

I remember a discussion somewhere here about a company that makes post hole diggers, a regular duty one & a lighter duty one. all components are the same, but the gearbox & pto shaft are lighter on the lighter duty unit. It has a shear pin with one side thicker than the other side, because a thin bolt was too weak, and a thick bolt was too strong - so they used holes in the pipe shaft of 2 dofferent sizes, and a special shear pin of 2 sizes that cost $9.

In the thread they figured out that for the price of 30 shear pins, you could have bought the heavy duty post hole digger & had a better machine.

I think most people drill those holes out to the bigger size & go dig holes......

I'm sure nomad will somehow like this story & think I am agreeing with him, but i'm actually disagreeing with much of what he has said in this thread.

If I were to fine tune my shear pin, I would start with gr 2 bolts, & redrill the holes slightly bigger and use a bigger bolt if the first size sheared too many & I felt my tractor could handle a bigger load & I was not concerned about the warrenty on the machine. However, such 'fine tuning' can cost you a whole lot if you are not careful, & i am not saying I recommend it.

As to slip clutches, they are a problem. For the most part they are much better than a shear pin, but if a slip clutch 'fails' it does not work, and this will destroy your implement or your tractor 50% of the time. So the slip clutch costs more, does a better job, but it is not fail-safe. A shear pin that is defective will break too soon, and only destroy itself. So, which is better, a shear pin or a slip clutch? hum.

--->Paul