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Multiple bolt tightening
2

Multiple bolt tightening

Multiple bolt tightening

(OP)
I'm looking for a device or tool that can be modified or ganged to field tighten four 1/2" bolts at the same time. If it works, I may try eight or sixteen 1/2" bolts and/or another joint with three or six 3/8" bolts. All bolts are closely spaced, the 1/2" bolts are in square groups of four, 1 1/4" apart, the 3/8" bolts are 1" apart in groups of three in straight lines. Currently we use a single 1/2" electric impact. The problem is that the worker has to touch each bolt several times because due to joint geometry and field conditions, tightening one bolt tends to loosen an adjacent one. And the noise makes it simply impossible to communicate besides being a hearing and health hazard. I'm looking for a quieter mode of operation. We recently had a project with (4,000) joints each with (16) 1/2" bolts on one side and (12) on the other side. The worker's time and then mine to inspect all joints was a PITA. I would prefer a hydraulic solution that would apply torque to individual bolts at the same time and could be turned off when the operator noted that all bolts stopped turning. I'm open to any ideas no matter how crazy, I can get almost anything machined or customized. I'd make my own with four 1/2" air or electric impact guns but am looking for a more elegant, quieter and lighter solution. Any thoughts, experience or guidance would be greatly appreciated. If this is not the best forum, please re-direct me...

RE: Multiple bolt tightening

This is commonly done in factory assembly lines but is not practical for field assembly of pipes. Such a tool would be heavy and bulky so moving it around and getting it to fit in a pipe rack with adjacent pipes would be impossible in many cases.

RE: Multiple bolt tightening

I feel your pain. Uniform tightening on a multi-stud flange arrangement with gaskets is an enormously complex engineering challenge, so procedures need to be detailed and enforcement of them rigorous.

And remember, friends don't let friends use impact guns on critical fasteners.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Multiple bolt tightening

Not sure about your bolt sizes, but larger sizes are routinely gang tensioned. You might contact somebody in that line of work.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Multiple bolt tightening

(OP)
This application is not flanges or piping. I have a flat structural connection whose topside bolts are vertical nuts up in four groups of four (1/2") and whose underside bolts are horizontal in four groups of three (3/8"). I've considered Huck style lock bolts but they are not suited for this application. The torque requirements are low and the opportunity to simplify and speedup are there.

Keep the thoughts coming !!!

RE: Multiple bolt tightening

I doubt hydraulic tensioners care what the application is.

EDIT: Superbolts? Exchange torquing 4 bolts for 16 (or more)?

FURTHER EDIT: Didn't see the tool. Duh.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Multiple bolt tightening

IFRs,

Have you thought about the mechanism that loosens bolts when the next ones are tightened? My theory is that you clamped down harder on a gasket. The first bolt was not tight enough to begin with. Your multiple drive needs some sort of ratchet so that when bolt A locks up, bolts B and C continue to tighten. Otherwise, you could have all sorts of loose bolts.

--
JHG

RE: Multiple bolt tightening

(OP)
JHG - the bolts are loosening because the plies are not in intimate contact, but it's just a fact of life for these joints. It's not a gasket but rather the splice plates bending a little due to crossing weld profiles, slight miss alignment, etc. I need each bolt to tighten independently but together at the same time. Right now we hit each of the four with an impact gun and have to go around a few times to make sure all are tight. This takes time and is inefficient besides relying too much on the worker to really care about it. The multiple drive can't be a single motor driving all four, like a multiple spindle drill. Each nut may end up having different numbers of threads exposed. Each bolt needs it's own actuator. They are in a relatively tight pattern but I could, for instance, make four different length impact sockets or extensions and have four impact guns in a box above them. I could conceivably use a single driver with four sockets driven by gears but each would need its own clutch so one, two or three could stop moving and the fourth continue to tighten at which time one or more of the previously tight bolts would need to be re-tightened a little. This image is an old one, the bolts are actually nut side up and we tighten the nuts. Also, the welds in the upper image are not always ground down quite as smoothly as in this model. In the lower picture, the lower left to upper right seams are welded while the others are covered with a strip. Both treatments are among the reasons the bolts need to be repeat tightening.

RE: Multiple bolt tightening

(OP)
Something like that !!!

RE: Multiple bolt tightening

IFRs,

So you are tightening welded flanges tightly against a flat plate. What sort of strain is being imposed on those flanges as you tighten the bolts? That joint is under stress at assembly time, before you apply external force to it.

--
JHG

RE: Multiple bolt tightening

(OP)
I acknowledge that this joint is not without its issues, and appreciate your concern. But it serves its purpose quite well. The flanges and connection plate are of similar thickness and grade, both move a little towards each other when the bolts are tightened, this is what creates loose bolts and requires each bolt to be tightened more than once. With 4,000 of these joints it's no wonder I'm looking for a multi-nut turning gizmo!

RE: Multiple bolt tightening

Whenever I see an assembly like this I think of when CAD users whine about how patterns don't work on such assemblies and how much work it is to click and click and click, when all that clicking is a peek into the future and a suggestion that maybe it's time to prepare something for the actual assemblers to use.

RE: Multiple bolt tightening

How is "tight" determined?

I'm thinking there is a sequence that might make "once thru" work OK. And it is not a "criss-cross".

Basically tighten the two bolts in the welded corners of a single frame first. I'm guessing the bolts further out on the flanges will pull the plate and flanges together on the first try, unless the torque is so puny that the final assembly faying surfaces are 75% air, with only one fastener actually pulling each frame in contact with the gusset plate.

RE: Multiple bolt tightening

(OP)
Mr. Moose - I like your concept and will try it on the next opportunity. Thanks!!!

RE: Multiple bolt tightening

I agree with Tmoose. There are certain joints that require very careful tightening to get a flat joint with uniform compression, such as engine head bolts and raised face pipe flanges. With your joints I can see no problem with applying full torque to each bolt on the first tightening.

I am more bothered by the orientation of the gusset plates. The normal orientation, which uses material more efficiently, is to have the plate corners in line with the tubes. I worry about the skill of a designer who did this.

RE: Multiple bolt tightening

(OP)
Compositepro - Your concerns are 100% valid, as it was my skill (or lack thereof) that you are legitimately worrying about regarding the design of the gusset plates. Originally it was limited by my lack of imagination, experience and design skill as well as available materials and fabrication tooling. The images were from initial mock-ups during development a few years ago, chosen to show the before and after configurations.

The actual joint is much closer to that shown in this image, with the plate corners in line with the channels. This image happens to show a different gusset plate and bolts just hand tight but it's easier to see here that there are gaps that will close up when the bolts are tightened..


RE: Multiple bolt tightening

If you aren't going to grind the weld bead flat before clamping a plate over it you can at least use washers under the plate. There should also be washers under the nuts if you are using steel nuts on aluminum plate.

RE: Multiple bolt tightening

(OP)
Aluminum nuts, SS bolts

RE: Multiple bolt tightening

Are these "critical" connection plates, or are they just used once, to lift an assembly?
The remark by Drawoh and Compositepro is legit if long term: relaxation might (will) happen on the aluminum parts, leaving you with a connection with loose bolts.

Also, aluminum nuts? What torque do you apply on those? Are they strong enough to deform the mating parts during tightening? This looks, ehhh, like there is room for improvement of the design...

RE: Multiple bolt tightening

(OP)
Great comments all!!! Thanks for your time and efforts !!

Although we are getting a little off-topic, I do appreciated the feedback.

If it will put some of you at ease, the chains are used once or twice a year, this is not an occupied structure, in normal operation it does not even support itself and the bolts have no load on them other than the fact that they are tight.

Aluminum nuts are chosen (1) so they don't gall up on the SS bolt, (2) because they gall up on the splice plate tending to act as a locking mechanism and (3) experience has shown that the bolt will break before the nut strips. We tighten them to the limit of a 1/2" electric impact gun, probably 80 ft-lbs +/-.

If the bolts do deform the splice plate given the small movement it is likely to be elastic deformation and the plate will tend to spring up preventing random loosening.

Grinding the weld bead flat would add far more cost than benefit.

Adding washers it not entirely crazy but I'm not sure there is a real value to them other than to make the connection a little closer to "ideal". These bolts are used in single shear, I would not want to complicate it too much.

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