Friction varies more at the underhead or nut bearing surface than in the threads. If you decide to use something like anitsieze or moly at the point of assembly be sure to have the lubricant applied to both the threads and the flat rotating surface.
Be cautious with electoplated zinc...
Biggadike,
The stress amplitude calculated is for the endurance limit. Below the calculated stress amplitude, no failures should occur. You can run at higher stresses as long as you keep the number of cylces down. You can draw a SN curve on a log-log plot with the calculated endurance limit at...
As Metalguy stated, most bolt strength specs only provide minimum strength numbers, a hardness range, and maybe a loose %content list. It is common to recieve fasteners at the high end of the hardness range, meaning they will have significantly better yield performance than the ones at the...
Biggadike,
Best source I have seen lately for axial fatigue strength in threads is the German spec VDI2230. The major consideration is if your threads are rolled before or after heat treat. If rolled after heat treat you get a higher fatigue strength.
For rolled before heat treat bolts...
Cory summed it up, but here are some other consderations. I recommend looking at Dacromet's environmentally friendly version called Geomet if you need to avoid hexavalent chrome. Geomet is usually applied thicker than Dactromet, but performance is the same.
Advantages
- 5x corrosion protection...
Remember that there are two friction surfaces - the underhead surface and the thread surface. If the 242 threadlocker is only applied to the threads after cleaning, the underhead will still be expected to have higher friction due to solvents removing any lubricants. I have seen extremely high...
Not sure what you meant by remanufacture, I hope it meant replace with more durable/improved part. Threads can be rolled before heat treat (RBHT) or after heat treat (RAHT). RBHT threads have a better root geometry than cut threads and provide a little fatigue improvement. RAHT threads provide...
In my experience there is not a relationship between tightening and loosening torque. Tightening torque is dynamic torque, while loosening torque is determined by the static torque. Static torque has very large variability and is affected by everything including materials, coating, friction...
Some methods to check current torque-
1. Return to mark check - Mark the bolt and abutment with a reference line, then loosen the bolt, retighten the bolt up to the reference line again while monitoring torque. You want the dynamic torque and not the static. (This method has pretty good...
Gerry,
You are correct, most of the setting happens during tightening. Most of the setting has happened before you remove the wrench. After a few minutes it is very hard to measure any further setting.
However, external loading on the joint is the main cause of joint set or embedment. The...
Pardal,
The hydrogenation I think the are referring to is the fact that as part of the plating process the parts are dipped in an acid bath. This bath/chemical reaction provides a source for hydrogen that can enter the metal matrices. Try looking under the subject of "hydrogen...
It has come to my attention that we have been using fatigue data obtained from 1/2" bolts (grade 8). A recent test showed that larger bolts (same class/grade) can have a much reduced fatigue limit. I have been unable to find much information on how to account for size but have heard...
Hello, decided to add two more cents worth
I usually am encouraging designers to have longer bolt stretch lengths. Bolt joints often fail from bolts that have to short a stretch length and almost never from bolts that are to long. Washers 'to me' are a must under both the nut and bolt head. I...
Longer bolts can be beneficial. - The longer length being stretched allows for more relaxation of the joint after it has been tightened. This means you have more clamp load after the joint has set. A single thicker washer is recommended (but probably harder to find than your original bolts) each...
Simon,
Here are two quick source from the web.
(http://www.boltscience.com/pages/vibloose.htm
...conventional spring lock washers are no longer specified, because it has been shown that they actually aid self loosening rather than prevent it.)...
Does anyone know where to find info on washer theory?
Simon
I recommend Bickfords books - they cover almost the full range of bolted joint problems.
On split washers, I recommend not to use them. Studies show that joints can come loose faster with split washers than when regular hard washers...
To prevent thread strip in aluminum, you should usually try for two diameters of thread engagement for grade 8 hardware. Your 1/2" / 3/8" is at the very bottom edge of what I would use but might be ok for grade 5. If you do not have to use a high torque to handle your loading...
