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Type of Bolt

06/18/2020 2:36 AM

Hi all,

I'm new. I've just been graduated the last year and I work in a mining industry as a graduate mechanical engineer now. I'm learning about plant equipment and I would ask you about this type of bolt I found on a vibrating screen in a dry mill. Do you know it? What is its material? I need your help because I can't find spare parts for it. what I've replaced has been cut by shear load.

Thanks in advance

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#1

Re: Type of bolt

06/18/2020 3:52 AM

The three tick marks on the head indicate that it is a Grade 5 bolt or cap screw made of steel. The silvery color suggests that it is electroplated with cadmium or zinc.

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#2
In reply to #1

Re: Type of bolt

06/18/2020 4:46 AM

thank you for your answer . however, does the plating affect the shearing of these bolts?

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#9
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Re: Type of bolt

06/18/2020 7:12 PM

If it is electroplated, the strength would be very little affected, if at all. On the other hand, if it hot-dip galvanized, the bolt has to be a bit undersized to accommodate the zinc thickness. This would reduce its strength.

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#23
In reply to #2

Re: Type of bolt

06/22/2020 12:05 AM

Not normally, but please note that the Triangle indicates that it is a close tolerance bolt which could be very important in your application.

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#24
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Re: Type of bolt

06/22/2020 7:53 AM

This guy

https://www.youtube.com/watch?v=G3eH_YFTcFo

Says the triangle is just a "manufacturer's mark" (within the first 90 seconds).

Is he wrong?

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#25
In reply to #24

Re: Type of bolt

06/22/2020 10:47 PM

I think he is right, the triangle in this case is the makers mark of Enfrasco.

I am used to a triangle meaning close tolerance, but having said that it usually surrounds the identifier which is not the case here. My bad.

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#8
In reply to #1

Re: Type of bolt

06/18/2020 11:35 AM

I agree. Grade 5 plated bolt.

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#3

Re: Type of Bolt

06/18/2020 5:23 AM

Maybe the failed bolt was an incorrect replacement anyway, so replacing "like for like" will see the failures continue.

My suggestions

  • Check some of the bolts that haven't failed to see if they are higher spec material.
  • Check original machine specs from supplier and see if there are some hints there.
  • Be cautious not to just select a stronger bolt. The failures might be the least expensive symptom of something else wrong with the machinery.

There are some others here that are fastener specialists. I seem to remember long time ago about sheared bolts from being too tightly tightened, such that the tensile stress in the bolt compromised the effective strength.

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#16
In reply to #3

Re: Type of Bolt

06/19/2020 7:56 AM

A lot of people think a bolt is a bolt. But if the failiers are frequent , the easiest is to upgrade to a Grade 8 bolt - which are readily available from any fastener store. Your point about upgrading is taken but in this application I don't think the bolts were meant to fail like a shear pin.

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#4

Re: Type of Bolt

06/18/2020 6:42 AM

You might want to test a small sample of the bolts you source.

That's what we've done.

You might find that one manufacturers quality is better than another.

You might also help the manufacturer by pointing out batch quality issues. Which could lead to ..bolt samples!

I've heard that hot dipped galvanization can weaken a nail or screw ...but make it last longer.

It seems to be correct, but I have not tested that with a strain gauge.

Can a larger fastener be utilized?

Shear Madness.

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#5

Re: Type of Bolt

06/18/2020 6:42 AM

The triangle is just a manufacturers idendity mark

https://www.engineersedge.com/hex_bolt_identification.htm

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#6
In reply to #5

Re: Type of Bolt

06/18/2020 8:09 AM

Excuse Please!

This comment was meant for the OP!

--------------------------------------------------------------------------------------------------

Check the diameter of the hole that the bolt goes through.

Excessive clearance here will cause a shear failure.

An oval shaped hole usually develops before a bolt failure,and the slop increases the shock load on the bolt,eventually causing failure.

If clearance is excessive,drill to the next bolt size.

Just make certain you have sufficient clearance for the larger head and nut and be sure to torque to proper value.

A chemical thread locker is recommended,using the proper prepping method.

No notches on a bolt head indicates a grade 2 bolt.

3 notches is grade 5,etc.All the way up to a grade FNL 9,which is used in heavy earth moving equipment.

Here is a link to a hand y chart for future reference.

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

And just to muddy the water a bit,here is another:Some bolts may have same markings,but different strengths.

https://www.engineersedge.com/hex_bolt_identification.htm

Miles to go before you sleep.

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#19
In reply to #6

Re: Type of Bolt

06/19/2020 12:30 PM

A phone call to the equipment manufacturer will be useful. I am sure they have seen this failure before. Ask for the field service manager.

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#20
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Re: Type of Bolt

06/19/2020 12:53 PM

You're assuming the OEM still exists.

I have a 40-yr old electric over hydraulic pyramid roller in my shop that I and my guys use regularly. Repairs are always a challenge, because the OEM went out of existence in the late 1980's with no successor. In fact I had to build my own set of hydraulic system schematics from scratch. My state-of-the-art Master Electrician/ PCM expert took one look at my AEG controller box and said "pray this thing never goes bad" I THINK I can get schematics on the box, because AEG is German and they are real anal about keeping historic technical documents.

FYI: Mining equipment is run until "the wheels fall off" and the CAT uses it's 9 lives and dies.

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#21
In reply to #20

Re: Type of Bolt

06/19/2020 8:46 PM

1980's! Ok.That was during the period of discreet components that can be easily replaced.

Barring a catastrophic failure,most of the electronics can be repaired.

I have even repaired boards with vaporized traces..not easy..not cheap..but doable.

I have repaired boards with no schematics by testing individual components and replacing as necessary.

My training came from the days of vacuum tubes,transistors,and experience as technology advanced.

Board replacement is easier to troubleshoot and replace than it is to repair.

I don't think they teach component level troubleshooting and repair anymore,just board level..and most modern boards are non repairable due to surface mount components becoming so small as to require a microscope and brain surgeon skills to replace.

I guess I am part of a dying breed,unless a CME or EMP wipes out the modern circuitry.

I am comfortable with progress;that is as it should be.

I can look back over 60 years of experience and the technological progress is amazing in all areas.

I have served my purpose during it's time slot and I am contentedly retired.

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#22
In reply to #21

Re: Type of Bolt

06/20/2020 8:42 AM

My E-Power guy didn't say it couldn't be replaced or repaired. He said to fear having to do it. It is a big board 18" x 24" chock full of transistors, resistors, capacitors, relays and such. Given the multi-dimensional functions, stacks of spool valves and hydraulic sensors, and remote operator's console of the machine the board is probably a dedicated custom design. If necessary I could source all the components off the net, BUT sourcing a guy with your capabilities would be a challenge even here in Houston.

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#7

Re: Type of Bolt

06/18/2020 10:48 AM

I agree that the first step in troubleshooting a repair is to identify the cause of failure, this separates the mechanics from the parts changers...knowing if the bolt is the proper one for the task at hand is the engineers job...you must be all three...so a forensic examination of the bolt is necessary..

Very important to know if this failure has occurred more than once, or is just a one time thing, so the age of the equipment must be considered and the maintenance procedures performed if any....it's possible the bolts are recommended to be changed at intervals...and if the machinery is being used properly...

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#11
In reply to #7

Re: Type of Bolt

06/18/2020 11:32 PM

In the forensic:

  1. Is it a reoccurrence event?
  2. If so, is the failed bolt you have the right repair bolt for the prior failure? If a Grade 5 keeps shearing should a Grade 8 be the right bolt? Since the young grasshopper is new to the world of industrial parts failure and repair he may be very well be naive to the fact some repairmen simply take the most available part (bolt) and shade tree make do.
  3. If it is the right repair bolt, then something as simple as a bearing being worn causing the body that the bolt anchors to have a high frequency - low amplitude harmonic that slowly fatigues the bolt.
  4. Let us not forget the little devil named torque. Even with the right bolts repairs done with regular mechanics wrenches and not torqued to manufacture's specs will have a high probability a reoccurring shear failure. The quickest way to dynamite a high powered engine is to improperly torque tighten ANY of the primary bolts.
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#12

Re: Type of Bolt

06/19/2020 2:40 AM

All the above is good stuff.

Adding some personal experience - if there is reversing torque, by design or due to resonant machine frequencies etc, then if the shear of the fixture occurs at the threads or if a clearance fit for the bolt was used instead of a close fit, then the shear problem is amplified.

I saw this in a bolted coupling where there was an AC drive and the system went into instability. Even though the drive was limited to 100% torque the resonant phenomenon created very large shear loads. It sheared 6 bolts all at once in the coupling. Part of the solution was to use high tolerance shoulder bolts where the shoulder was presented at the shear plane, and the holes in the coupling reamed to match the shoulder as a close fit. We never sheared any more bolts.

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#13
In reply to #12

Re: Type of Bolt

06/19/2020 6:17 AM

Good solution.

Threads should never be presented at a shear line.

Threads are stress risers where stresses will concentrate and focus and are especially vulnerable in high vibration applications.

The elimination of "slop" or excessive clearance in the hole is also important to prevent a hammering effect on the bolt and hole.

Even with the best possible engineering a high G force vibration application has a relatively short cycle life.

I recall an instance where a 10 hp vibrator was used to shake frozen coal from a rail car.

Very high maintenance indeed,even when using the best practices.

It actually shook buildings several hundred feet away when running.

They had recurring generator bearing failures that were unexplained.

The generator was a GE 3.125 MW co-generator on the 2nd floor of a boiler room near the coal pit.

The plant has long since shut down,and the generator has been sent to who knows where.

I am convinced that the box car vibrator was the source of their constant misery.

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#14
In reply to #13

Re: Type of Bolt

06/19/2020 6:54 AM
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#15
In reply to #14

Re: Type of Bolt

06/19/2020 7:44 AM

True! True!

But in that era of poured Babbit bearings, slide rules and long hand math on paper,or in your head,such devices were not even imagined.

"Return with us now to those thrilling days of yesteryear..."(The Lone Ranger)

A few years later,the Z80 was the big kid on the block,then later,the 99000- 16 bit CPU.WOW What a screamer!

Modern technology is great is some respects,but not all.

It tends to make one mentally lazy,in the sense of having to analyze and figure things out.

Just Google it.

I am guilty as charged of taking mental short cuts also.

But I do remember being able to factor multiple inputs in my head,without writing them down, and memorizing a schematic at a glance,but it has become harder to do with disuse.

Use it or lose it is so true.

I realize how much expertise and programming goes into modern devices,and I know there are many very smart people out there.

It takes a good team of engineers and programmers working together to develop a built-in expert system in a machine.

I am simply amazed at how much low level code it requires to generate and move an image on screen,much less video games.

The problem I see it is that in the future there will be a dependence on the AI answers,without questioning their validity.

If I perform a calculation,and the answer does not "look right" I do it over again,and uncover my error.

If I just accepted the result without question,it would lead to many problems.

IMHO,that is the danger of too much reliance on AI.

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#18
In reply to #15

Re: Type of Bolt

06/19/2020 12:29 PM

Well we already have engineering failures everyday it seems, and over time everything seems to be getting better, so I must conclude the trend will continue, with minor glitches along the way...

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#17

Re: Type of Bolt

06/19/2020 8:17 AM

As a Senior Test and Development (mechanical) engineer in the auto industry for more than 30 years, getting to know the means of identifying material properties of parts was essential to me. That also applies to the head markings of bolts. This is a skillset that you need to acquire. Try using Google to do this. Here is a good start:

https://www.google.com/search?rlz=1C1GCEU_enUS821US821&sxsrf=ALeKk01NwFfV5fluP0JTidkc2A7NfZgbEQ:1592568738586&source=univ&tbm=isch&q=head+markings+on+bolts&sa=X&ved=2ahUKEwjv_8Xv7I3qAhVSZ80KHUI6AyMQsAR6BAgIEAE&biw=1745&bih=886

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