Shear Pins

I tend to agree with PWSlack on this.

Another possibility... the shear pin mild steel bolt is correctly sized, and your added 30 meters is too far beyond the design of the mechanism. Was there a constant issue of breaking the shear pin mild steel bolt before this modification?

Crystal ball broken? Can't quite see the chain from here?

Never mind, problem solved. See above. No more broken shear pin mild steel bolts.

Agreed!

The direct drive makes me think this isn't intended to tolerate a lot of torque.

[edit] Well, I read again and it says direct drive coupling... it would be useful if we knew more. However, if the advice of PWSlack is followed all will be revealed.

Use a plastic drive sprocket, instead of steel. That'll insure that the shear pin mild steel bolt will not break first.

Now if we only knew how long the conveyor was before the 30 meters of new chain were added, we MIGHT be able to help determine the added stress applied to the system by the additional 30 meters.

Nope, insufficient data for meaningful solution.

Do what Slack said.

Are you binding somewhere?

Yes, thank you.

But, I went to the doctor yesterday/last week (don't remember exactly, time traveling is not without its attendant hazards) and he gave me something to loosen me up. No time travel today, till I get this binding problem fixed.

LOL!

Just weld the f$£%&@ thing up solid, and be done with it.

Careful! You don't want your brain to release the magic smoke out your ears.

Take a dram and relax for awhile. Saving the world is thankless, indeed. But, somebody's got to do it.

Did anyone in their decision to add the 30 meters of extra conveyor. Take into account the additional load?

No.

Is that a Rhetorical Question? I know you know the answer is obvious I think Lyn answered it for us.

Rhetorical or not. We do not know whether they thought about it. Maybe Lyn is right. So the question points them in the right direction. Maybe they did think about it and don't have the skills to compute the additional load. Maybe they did and don't give a s*#t.

The shear pin is there to protect something. Since the 30 meter addition it appears to be doing it job. Now to increase the size of the shear pin it may cause damage to what ever it was to protect. Which could be personnel.

Agreed!

The shear pin is there to protect your motor/gear reducer. Putting a larger shear "device" will put them at risk. If you're habitually breaking shear pins, the motor and gear box are probably already overloaded. One way or another, you need to find out how much practical torque you need to operate the conveyor and size your power components accordingly.

Additionally, if the conveyor is running not-so-smooth, or jerky, then you are probably introducing a shock load onto the coupling as well which will prematurely break the pin.

We don't have sufficient information from the OP to make any intelligent recommendations.

We don't know how long the conveyor was before the 30 meters of new conveyor was added.

By the way, machine bolts should never be use as shear pins. They are not as strong as a smooth pin and may not fail consistently. I liken them to mechanical fuses.

And we dont know if 30 meters is the total length or is it the loop length. The loop could be 15m or the chain length could be 60m.

We don't know what is being conveyed, or if this is a ramp or level conveyer.

I don't know the same things you don't know. I just don't know.

Me too! Me too! I don't know nuffin, But it's my guess that a larger motor, coupling and gearbox are required. Next we know the chain will be breaking instead.

Nah! Then the cable and the supply fuses would need uprating.

Several.

After reading the replies to your question I have also come to the conclusion that there is insufficient information to give you a definitive answer.

What length is the overall conveyor now, what width is it, what material is the chain, did the original conveyor come with a shear pin or a mild steel bolt, is the motor man enough to handle the new loading an extra 30 metres of belt carries, also 30 metres of extra belt equates to an extra 15 metres worth of product.

I assume that the inserted part of conveyor is of the same construction as the original conveyor? All return guides/rollers correctly aligned?

I design conveyors here in the UK for the food and plastic moulding sectors, very rarely do we use shear pins but tend to use a direct drive with the motor/gearbox correctly specced with a torque limiter if necessary.

Ok Ignore all that above, I have just looked at the specs of your conveyor and it is an overhead rail arrangement. Are you working within the manufacturers guidelines for loading? Are the hangers correctly spaced for the lbs/foot loading?

http://www.conveyingsolutions.us/images/Series%202000_2007_rev.pdf

This document provides you with all this information assuming that is the correct series style of conveyor.

I still need to know if the manufacturer supplied a shear pin or a mild steel bolt when the system was originally installed. It could be that a mild steel bolt has a lower shear strength than a shear pin.

If i can help with anything just ask, i will try and help if i can.

Steve

if you're the type of person that finds replacing blown fuses annoying so you wrap new fuses with foil to get them to last longer...you might want to keep going with steel. this is a designed feature to stop excessive loads from damaging your equipment. you would be foolish not to utilize the grade of material the OEM suggests (probably aluminum). the pin broke because you're asking too much of the system.......don't over-ride that, only tax the system to it;s designed limits, not beyond

The questions, the questions.

Who made the decision to add the extra load? I suspect the manager.

Who decided not to clear it with the OEM first? I suspect...

If you don't take all the good advice above, try a high strength alloy bolt of the same size before you drill it out for a bigger one.

NOPE! Just going to a "Higher" grade or "Higher Strenght" alloy bolt, when you have NO IDEA of the shear strenght of the previously used "Mild" bolt is a sure way to find broken parts soon, guaranteed! I have seen people replacing bolts in various pieces of equipment, only to find the equipment now failed at a more critical place or was totally broken. Even changing the physical size (diameter) of the bolt can invite trouble since you cannot easily trace the bolt quality or material... A way to find out would be to devise a MEASURING jig of some kind. I would use an automotive torque wrench and then machine a supporting plate to hold the bolt to be tested, and then apply a shearing force by placing a second plate above, pivoted with a much stronger pin used as a shaft. By applying a torque to that jig, it can be used as an effective shear that can be used together with the torque wrench to quickly find the shearing force limit of the bolt, and then compare several bolts of "mild" vs "strong" materials. But as others have already said, without knowing the strenght and limits of the design, it can be easy to start breaking other things and not the intended "shear-pin". Amclaussen.

All comments are right,but the entering statement;..."using mild steel bolt" - instead of shear pin,is more than maintenance omitment....

Amarquez said he would use an automotive torque wrench to measure the shear strength of the bolt and that got me thinking. You could attach the auto torque wrench to the drive sprocket and measure the torque there, multiply by a factor of your choosing ( based on the overall setup ) and spec your motor, gearbox and coupling from that.

Well, not exactly. My idea was to implement a simple but effective way to get some reliable numbers, (remember the KISS Principle: Keep It Simple S....!).

The first problem is finding how strong the original shear pin needs to be... since we don't know its specs, material, grade, etc. Thus, we can resort to device a simple means to get some numbers. One way to do it, is by comparing the shearing strenght of a known (published) specification common steel bolt to get the number for the (unknown properties) original shear pin.

I was trying to get an easy, repeatable way to compare the shearing resistance of a similarly sized reliable, consistent, good quality bolt, to the shearing strenght of the original shear pin; by improvising a pivoting shear. (Imagine two rectangular steel plates with three holes each one; one hole is a large polished one that houses a short and robust shaft working as a pivot; and two smaller holes located at an identical short distance from the pivot; one hole is threaded and houses a known data common bolt to be sheared (Ouch!), then you can use a smooth hole to house a lengtht of the original pin, which is sheared (Ouch again!) to get a second torque wrench reading value. A simple way of applying a torque to one of the plates while firmly supporting the other, would be a simple square hole to house the square drive of the automotive torque wrench!) That would work as a reliable shearing device that can be used to find the torque value needed to cleanly shear a known strenght bolt, THEN we can use the device to easily and acurately measure the shearing torque needed to cleanly cut (shear) the original shearing pin. By comparing both values and taking into account any sectional area differences, we could establish what was the intended shearing action required in the original design. Amarquez.

Yes I agree. What you describe is a test rig to compare a known component with an unknown one. Given that the unknown component was driving the setup before then a replacement component that has the same shear will be required. Right? NO-wrong! The O.P. says he wants to extend the line and thereby add more load to the shear pin, which is why I suggested using the torque wrench to measure ACTUAL torque required to move the extended line. From that he can derive the REQUIREMENTS for the shear pin and indeed the whole drive train and also for the line itself.

Jim

Well, that would be the best way...

BUT, measuring actual actuating torque at electric motor speeds isn't going to be that easy, or the required instrument won't be cheap or easily available either!

Another indirect, but practical and inexpensive approach would be to measure electric motor running current, and compare the measured value against published data for that exact motor model. End of the problem! (unless the motor was oversized, or the transmission and rest of the mechanism is undersized, and something breaks!)... that perverse Murphy again and again!