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Old 01-13-2013, 06:53 AM
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Default Bolt Torque Reduction with Anti Seize

Is there an actual accepted percentage to drop torque values when using an anti seize product? I have always used 20% but would like to know the proper way to calcualte or a accepted amount to reduce
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Old 01-13-2013, 11:00 AM
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Quote:
Originally Posted by Cavalry View Post
Is there an actual accepted percentage to drop torque values when using an anti seize product? I have always used 20% but would like to know the proper way to calcualte or a accepted amount to reduce
Good question. I'd be interested in an answer to this one too.
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Old 01-13-2013, 11:28 AM
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Years back, I took a Bowman-Barnes bolt course. I thought it would be boring as heel, but I was getting paid to, so....
It was fascinating. They had load cells to demonstrate torque and what happens when you re-use a bolt. We each had a cell and the instructor had us do this and record our readings.

With a new 3/8 bolt torqued down to spec, the load cell read.....lets say 400lb.

Now we took a new bolt, and wiped it through our fingers once, to get skin oil on it. Then it was put through the load cell and torqued to spec. Now the load cell read 550 lb pressure.

Then we took the original bolt that was used right out of the box and torqued down only once.
It was put back into the load cell and torqued to spec. Now the load cell read 380lb.

It was loosed off and the bolt then re-torqued. Now the load cell read 360 lb.

They explained that any tiny bit of lubrication will drastically increase the pressure of a torque spec. They said that bolts are manufactured to have a thread edge that folds and flattens at tightening, so that way more surface contacts the nut thread face. When you re-use the bolt, the thread is already deformed, and it takes more torque because of the increased sliding resistance, to achieve the same pressure.

Which is why you always throw away head bolts, because they will not properly pressurize a head gasket if re-used.

So Cav, it will definitely take less torque to tighten a lubricated bolt, but as to how much less, only a load cell would know.

You could develop a number by making a couple of L brackets, and joining them with a dry bolt and attach a chain to each of the other legs. Then hoist up a weight of 200 lbs. and attempt to lift the weight by tightening the bolt with a torque wrench. Save the reading, and repeat with a lubricated bolt. The difference will be the reduced torque number you need.
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Old 01-13-2013, 11:39 AM
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Well, fancy this. I roamed through my resource info and I found a chart. May not apply for your size, but it gives you a median number to play with.



EDIT
Looking at the chart torque numbers, this cannot be for mild steel bolts, so is probably Gr 12 or Titanium. Sorry
I did find this chart that will help Cav in this matter, as it is for normal mild steel bolts
Attached Files
File Type: doc Lube bolt specs.doc (23.0 KB, 167 views)
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Last edited by Ironman; 01-13-2013 at 11:50 AM.
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Old 01-13-2013, 03:01 PM
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Look for tables on wet and dry torque. I was in aircraft maintenance where torque is very critical..Technical orders were very specific about its application.
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Old 01-13-2013, 08:43 PM
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Cav with antiseize I don't sweat it much. It's more like a grease than oil and I'm sure it affects the torque value but I doubt it's going to allow you to stretch a bolt or pull threads. At least it hasn't been an issue for me so far.

In my world anything that needs a super crucial torque value tells what oil is to be used to lube the threads on new fasteners.

Here's a torque chart I have bookmarked in my phone for quick reference.
http://www.cncexpo.com/MetricBoltTorqueNm.aspx

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Old 01-13-2013, 11:38 PM
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Handy charts to have around. Thank you for the information. I'm sure the next time I snap off a bolt, I will be able to tell at what torque value it happened, just by looking at the charts.
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Old 01-13-2013, 11:53 PM
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Cav you asked about anti-seize and about an accepted torque drop value when using it.

We use Kopr-Cote on almost everything we repair in our shop. We use a reduction in torque value of about 35% because we stretched grade 8, 1/2 inch bolts when we tried to go to the recommended dry torque value.

When I first noticed we were stretching bolts and not even able to reach the dry torque value I did some research. There is an Engineering forum that I think is where I found the info. Someone had tested many types of lube and anti-seize products on actual clamping force and torque values. I should have saved that info to a pdf but I didn't.

The info from this test, if I remember correctly, showed about 30-40% less torque was required for most anti-seize products with some silver ones hitting 60%.

We don't work on aircraft but we don't want to stretch bolts or strip threads either.
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Old 01-14-2013, 12:36 AM
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Generally you reduce torque by 10% for lubrication. However, torque on a
fastener is not a very exact method to measure clamping force. Way to
many variables to account for.

When we had very critical specifications the best way to measure short of
a load cell is by measuring bolt stretch. Kind of tough on a blind hole. But
it is the only very accurate method.

Now why don't we discuss TTY fasteners...
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Last edited by Shade Tree Welder; 01-14-2013 at 01:53 AM.
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Old 01-14-2013, 01:03 AM
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Quote:
Originally Posted by Shade Tree Welder View Post
Generally you reduce torque by 10% for lubrication. However, torque on a
fastener is not a very exact method to measure clamping force. Way to
many variables to account for.

When we had very critical specifications the best way to measure short of
a load cell is by measuring bolt stretch. Kind of tough on a blind hole. But
it is the only very accurate method.

Now why don't we discuss TTY fasteners...
Why TTY?... From what I have read or have been told, TTY head bolts in automotive applications reduced the number of warranty claims... And they can sell more parts... And the bolts are slightly smaller, so less material they have to pay for...

Bean counters gave us TTY...
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Last edited by Shade Tree Welder; 01-14-2013 at 01:53 AM.
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