Torque control of impact wrench
Torque control of impact wrench
(OP)
Want to use an air impact wrench to torque bolts to an approx torque of 1200N-m (about 900 ft-lb). Is there any proven method available of doing this? Desire to use impact wrench because of speed of operation. Bolts are 1 inch diam.





RE: Torque control of impact wrench
The use of a calibrated torque wrench can provide this data. This method provides a torque value used to tighten the fastener under specific conditions. A multiplier may be needed if there are numerous fasteners to torque or if a wrench with that capacity is not available, 900ft-lbs is quite a bit.
A Wilhelm-Skidmore fastener-tension tester can also be used to correlate the required torque with a tensile load applied to the fastener.
The turn of the nut method can also be used to achieve a target tensile value based on the number of turns after the fastener has reached a "snug-tight" condition.
RE: Torque control of impact wrench
RE: Torque control of impact wrench
You may want to check with an automotive repair shop the specializes in tire installation... like Discount Tire, etc. I remember having some tires changed, and they use impact wrenches to put the wheels on. Their wrenches had a series of special bars that limited the torque for installation. The selection of the bar was based upon the vehicle type. They may be able to tell you where they got the tooling, and you may be able to find one for your torque range.
Let us know what you find.
jetmaker.
RE: Torque control of impact wrench
Blacksmith
RE: Torque control of impact wrench
Nick
RE: Torque control of impact wrench
I think CWIC's point is that unless you calibrate your equipment, you don't know what you have as far as "torque" values go. The numbers are meaningless unless you bounce the equipment, torque-limiters, et.al. against a known standard such as the pressure gauge on the calibrated Skidmore. I thinke even turn-of-the-nut needs qualification because of the variation in material such as the plies mentioned above. At those torque values, I'd want calibration of my torque wrench, unless it was for in-plant use. Are there TC bolts available for this torque value? You could use the manufacturer's certs.
Koz
RE: Torque control of impact wrench
Where did the 900 ft-lb value come from if the system
is highly unpredictable.
RE: Torque control of impact wrench
The torque applied to most passenger car wheels is in the range of 70 to 90 ft-lb. Just for a little perspective I note that the Ferrari F50 with a 286 cubic inch V-12 develops 347 ft-lb of torque at 6500 rpm. This allows it to achieve 60 mph in 3.7 seconds! But 900 ft-lb of torque... we'd have to talk Cummins and Kenworth for a good comparison.
RE: Torque control of impact wrench
A torque wrench can be somewhat calibrated with a DTI. As you have a flexible connection this should be adequate.
Being a joint with flexible components we could use crush tubes.
One could also go to DTI Bolts or use it as calibration method.
A good approximation can be had if you can gauge the bolts with a micrometer. A lot depends on the grip length.
RE: Torque control of impact wrench
Several units from hand operated (porta-power) to power driven pump units are available at most of the larger construction/industrial rental companies.
As to wheel torque---my Dodge D-350 wheels torque to 350 ft/lbs OEM specs.(I don't go quite this high and I use anti seize, both deals definately NOT approved by the OEM!)
Rod
RE: Torque control of impact wrench
We have worked on this issue for a number of years. Pneumatic torque wrenches are not repeatable to any degree. That is why you occasionally hear of wheel studs snapping off. The adjustment is far too gross. There are some electric drivers that will work somewhat better while electric torque wrenches are nearly as bad as air.
Do yourself a favor and buy an tool designed for consistency. We use an Atlas Copco air torque ratchet that has served us well. Desoutter also has these.
RE: Torque control of impact wrench
We have used the RAD pneumatic torque wrenches (non-impact wrenches) from Global Bolting Technologies (http://www.radseries.com/) with good success on high pressure equipment. Accuracy (to the desired bolt torque) is +/- 5%, repeatability from bolt to bolt is +/- 1.5%.
KST
RE: Torque control of impact wrench
RE: Torque control of impact wrench
Nick55
RE: Torque control of impact wrench
Using a DTI you might want to match mark the bolt and nut on a couple of joints and see where the nut side ends up. You can get a pretty good Idea of the torque. It might be good enough for your application.
http://www.appliedbolting.com/
RE: Torque control of impact wrench
I had faced the same problem with you. Let me describe myself first. I work with an offshore-contractor company. As usual, the project specification sometimes call for a bolt to be torqued (sometimes to be tensioned) to a certain value.
If this is above water surface work, I am willing to use a torque wrench. But, once we are requested to use torque wrench under water (diving job), our diver are reluctantly to use it(in-practical). So, we always come out with an idea to calibrate the (air/hydraulic)impact wrench.
How? I believe this is the question you raised before.
We can use impact wrench to replace tensioner or torque wrench. The way is as follows:
1. Provide the tensioner or torque wrench (yes, you have to have this tool to perform the calibration. The idea of this is we want to perform quicker and practical way to tighten the bolt. I am not trying to save money by avoid in providing the torque or tensioner. Eventhough, you might end up saving money since your job will be completed quicker than suppose to be)
2. Provide a sacrificial bolt (with all appurtunances).
3. Tighten the bolt to the required tension or torque tool by the torque/tension tool.
4. Try to UNBOLT/untighten the bolt with impact wrench by adjusting the released pressure (gradually increase the pressure).
5. Once you have the "correct" released pressure, re-tighten the bolt with the correct released pressure.
6. For final confirmation, try to un-bolt AGAIN it with an increasing torque or tension value until achieve the required value. If the bolt is loose on the required tension/torque, than you have calibrated your impact tool.
The reason why some client refuse to perform this way is that we are hardly to ensure that the impact wrench will not exceed the bolt's breaking load, thus we can not guarantee that we will not damage the bolt. However, by a slow increment on the pressure, we might be able to get the "most correct" pressure value.
Hope this answer your query.
RE: Torque control of impact wrench
The reuse of a fastener for more than one test is ususally prohibited. It is normal to use 3 bolts of each size to set a tightening device. Then 3 new ones to verify.
How does the torque values change at 100' with an air impact wrench? Do you have a special type wrench?
RE: Torque control of impact wrench
Nick55
RE: Torque control of impact wrench
Having gone through this post (late I know, but Im new here)first of all I would like to say, your final choice is slightly better than your original, yes the tool that you have selected is expensive, but is it acurate?
I have faced this argument many times in the field, basicaly the impulse gun is a modified impact wrench, and the torque control specified by all the manufacturers is some what dubious to say the least. I have tested many brands on torque transducers fitted with rundowns to recreate a bolt being tightened, and each time, I have been left nothing short of dissapointed.
The only time I would advocate the use of such tools is when being employed to break out bolts, even then I am not happy with the use of them.
the problems arise with these tools from the very nature of their running, basicaly, most manufacturers use a kind of relief valve for the impulse wrenches, and is usualy colour coded, the problem with this is, the changing properties of the oil used in the impulse chamber, on start up it is thicker due to it being cold, through use it thins down, as you may know, with a direct operating relief valve on any hydraulic system, cracking pressures vary from 50% to 25% of the set load, and this is so with the impulse wrench and this is the very reason why they are not reliable as true torque tools, and I wont even get into repeatability.
I see mentioned above that some one says that no pneumatic tool can give good repeatability, this is wrong, there is a manufacturer in the UK who Rad have based their tool on that have repeatability to +/- 3% on their pneumatic torque guns, and they have very smooth action, dont cause white finger vibration problems, and they are not noisy, but above all, after many tests, I find that although slower than the impact/impulse tools, it does give a finished torque figure that can be trusted, and this unit does not keep going, when it has reached the set torque, it stalls, Impact/impulse wrenches do not, the motor keeps banging away, and the final outcome of the bolt is very uncertain, the problem that I find with the rad tool is again the motor driving it, i dont know if they have changed this in recent years, but it used to be a motor from an impact gun, and the problems occured because the motor is not designed to stall.
As for costs, the tool i am talking about comes in slightly cheaper than the one you have selected, and like all torque wrenches, the one I would choose has to be calibrated every year.
I hope this throws some more light on the subject for you, and I wish you luck with your adventures into torque and the many methods to apply it.
RE: Torque control of impact wrench
I misspoke & I apologize. I meant to say that pneumatic impact wrenches are not repeatable. We have pneu. torque wrenches and are happy with them.
When we were developing our requirements we looked at the impulse wrenches but decided that the value vs performance was not good enough.
Nick,
One step we took, and I recommend, is to define a torque range when selecting the wrench rather than a specific torque. It makes a huge difference in the tool selection. If your required range is 800-1000 ft# then a suitable tool may be significantly less money than one needing to meet 875-925.
Hope to hear of your experience.
Griffy