As a design engineer you will be able to follow the principles below :

The shear pin material will have a shear strength of q N/mm2.

The shear pin will have a neck diameter of d mm.

Thus the shear load L (N) will be the shear strength * the neck area.

The shear load will act a radius r mm, so the shear torque will be the the shear load * the radius.

Naturally, you will select a suitable material for the shear pin having tested its shear strength.

I don't think a design engineer needs any more guidance than this. Of course when applying these principles it may be necessary for you to establish an application factor to suit the chain conveyor you have designed, but that is down to you as the designer. ■

Usually, the pin is supported from two sides and therefore the load is distributed onto the shaft at two locations. Don't forget to divide the total load by the number of shear zones. ■

?? This is my understanding of a shear pin.

http://www.howdon.co.uk/images/PDFs/0030505.PDF ■

OK, which is "usually"? I offered for those of us that don't know "usually" from less than "usually". ■

Shear pins are simple but at least in my experience using shear pins in chain drives and similar equipment ,.

They can be dangerous and should be used as a last resource. To protect the instalation from further or greater damage .

Can you better use an electrical trip in your drive , or a torque limiting device , sumitomo can provide some really excelent devices that have worked for me in very large, very hot rotary and svrew dossifiers .

Even a smaller motor will work better , nothing breaks , nothing moves , nothing falls.

Marco ■

I must beg to differ on the subject of electronic devices.

My experience is that mechanical shearing devices are the most effective at protecting the driven machine as they are fitted AT the machine drive shaft and not at some distance from it relying on some sensing device on the input power supply to the motor. ■

let me elaborate .

A cluster braking dossifier valve at the bottom of a reactor is designed to give a 6000lbs force at the end lip , the dossifier runs at 1 rpm , feed vary 45 to 200 ons per hr although it is volumetric the density of the product at 800ºc does not vary much , the original shaft design (designed by me) asked for a 7 Hp motor , a smart purchasing engeneer desided that as a 10 hp motor has the same price as a 7 hp , and they are readiliy available , thaT IT WAS A BETTER DEAL. so the dossifier was set with a 10 hp motor , then the reducer gear was installed with a large design factor because of the impacting nature of the load , so the reducer bought was a sumitomo with a 500% factor .

After this ,( and after severall un nice meetings) to protect the shaft we instaled shear pins .

Not once but several times in different instalations, as redundancy we installed a microphone in the discharge line , a pilot plant contraption that worked well there.

One day the pins sheared and nobody noticed until the reactor outlet temperature increased (then it was too late , the material inside the reactor had becomed a 1000 metric tons metheorite .

The microphone was silent and we(I was there) all tought how nice the plant felt that day (no noise is not an alarm)

It took us one week to clear the mess ( and $700,000 dls production loss ). we installed electronic backups, torque limiting devices , first only changed the fuse (it didn't work as when the fuse blew , somebody came with a larger fuse and we got the pins sheared aghain , finally the electronic system was installed and it has worked fine for 20 years. No need to extract and replace shear pins, in the New installations the shear pins were removed . They have not had problems , unfortunately I was unable to convince the organisation that a 7 hp motor would have been the solution. , they kept the 10 hp nevertheless.

In Fibrasin , a plant where i Briefly consulted , they followed the same track only that the shear pin was installed in a chain drive , they also increased the motor size , ( the problem was uneven feed at the starting point , not the motor) the pin sheared and the chain flew .

Please do be carefull where you install shear pins , yo might be saving the equipment but might be injuring someone else.

Marco ■

I have no concept of "A cluster braking dossifier valve at the bottom of a reactor", in the original post he was asking about a CHAIN CONVEYOR about which I do have a little knowledge. ■

sorry got carried away ■

Either the machine is strong enough for the duty or it isn't. Downsteam procurement faults are only part of it. If the shear pin kept cracking then a bigger pin should have been used from the start.

I am entertained daily by bidders who confidently talk about rope breaking strain, wheel tread pressure in kN & the way torque demand increases because the speed decreases.

Electronic v's mechanical is a non starter. If you have to ultimately protect a machine against heavy damage you need a shear pin.

I have previously argued that, lets say, a reclaimer should stall under oversize material feeds. It can be stalled by the limiting fuses in the motor. This throws the Mechanics into the province of the Sparks & the machinery has to be strong enough to suit the whims of some distant PCB. That means a lot of extra money must be spent to suit a PCB costing a few bob. Better to save the money & spend a few bob on a shear pin.

I'm currently trying to get thickener manufacturers to tell me the "and then" after the rake arm has been lifted because it encountered a submerged obstruction. Like the brick on the bottom of the pond I'm still waiting. With a shear pin the rake wouldn't have to lift.

Neither solution helps me to clear the obstruction; hence the wait.

That wasn't about bucket elevator either but the feeling is the same. ■

The case is clear ,

Some years ago , at a large sugar cane fiber board factory, the equipment failed frequently , the solution shear pins . the cause the feed to the first conveyor belt was made with a front loader so the equipment was overloaded , this was in turn , a belt conveyor , a washer , a screw feeder-drainer , a second belt conveyor then a chain conveyor then a fiber breaker and so on . Motors stalled and the protections tripped , only to have the protections over sized , then the motors beefed up , util the shear pins in the chain conveyor strainer gave up.

the solution , change the feeder . feed at a constant rate ,

I know this sounds out of the request of the tread starter ...

the design of a shear pin , shearing force divided by shearing area = to stess use your mohr circle and calculate the either the metal strength or the diameter of the pin if you can change that ,

the pin should be the weakest point in the chain , ideally the motor should stop before the pin shears . and then the root cause should be found and eliminated .

otherwise you better have a good stock of pins .

Marco ■

Regretfully you can't design out the engineering ignorance of an end user. No matter what, such people will screw up anything. ■