A client of mine wants me to design a piece of equipment that requires a remotely operated impact wrench to tighten / loosen a clamp bolt, approximately 30 ft from the operator's location.
He also wants pilot air control because retro-fitting electrical wiring is a bit of a nightmare on this existing machine.
Torque requirement is about 300 ft-lb, air supply is practically unlimited (large industrial complex).
For the solution I pick, if any, I'll spot you a case of beer. (or send you a cheque equivalent) I understand you have to trust me on being honest with this.
Air control is common in automatic air nailing systems like pallet manufacturing. We had an air opperated nailer triggered with air supplied by an electric air valve that was triggered by a foot switch. So, ask your local air nailer supplier for the part that replaces the trigger on the impact.
Not sure about the 300 ft lbs, but remote air operated impact wrench is pretty much what a power drawbar on a mill is. Servo, Kurt, and many others make several versions.
Do you have an existing impact driver,or do you need to specify one? if you have an existing one, and simply need to start it and stop it, check out the "Festo" website.
At least I have the pleasure of specifying the driver.....as long as it is not outlandish in $$$$$.
Do you have an idea?
I could use one that the automotive or structural steel people use; I can fix it in place because the bolt it sits on is vertical with the head on top.
It's the remote operation of the thing that has me baffled because the operator has to be able to tighten and loosen the bolt from his remote observation position.
That's why I thought of the power draw-bars....button ON, button OFF...ideal except for the low torque. As I wrote above perhaps the larger milling machine tapers have impact drivers with more oomph.
So look at how a power drawbar is plumbed, and scale it up to your 300 ft lb impact wrench. The drawbars use a little impact wrench. Use a big one!
Depending on time and budget.... A DC motor (or three phase, or servo/stepper as appropriate) and a worm gear reduction drive on the clamp might fill the need. Perhaps a double stage worm reduction for the torque you need. Not so good if it has to operate fast, though.
Well, you can always just brute-force it. A little air cylinder to actuate the direction switch and another to activate the trigger. You got some brackets to make but they'd be simple.
well, what I would do, if it were me (and it isn't), presuming that an impact wrench is required is t he following:
buy a suitable impact wrench and design mounting bracketry
use a small DC gear motor with an eccentric to actuate the reversing switch - or do it pneumatically with a small push pull solenoid - I guess since you say that wiring is a problem, I'd use the push/pull solenoid. if the reversing switch is a round pushbutton (like on my impact wrench), then I'd drill a hole in the pushbutton and tap it and use a ball type connector to link the solenoid and the switch.
a second solenoid can operate the trigger. it only needs to push.
add a master valve in the control room so you can turn it off for sure if something jams
provide a pair of pneumatic push buttons to actuate the reversing solenoid, and a big button for the solenoid that actuates the trigger. see here for example valves
Buy a CP735H impact, ($90 or so, less if you shop around) take it apart. Separate the rear bearing plate from the rest of the gun and look at the passages. Drill through them to the outside of the case, tap for 1/8" pipe, put it all back together, and attach lines to each side from your control valve. Ignore the trigger and control valve. Don't even need to provide exhaust. But you could put a fitting in the exhaust port to reclaim air tool oil if you want. When you put the impact back together, leave the three motor housing screws loose, install the motor, then tighten all of the screws down at once. If the 1/8" pipe is too much restriction you can cram two fittings in per side. But it's just too cramped for 1/4". Or if you have the option, crank the air pressure higher until it works. I don't think any pressure will backfeed out of the intake without the trigger depressed, but you can put in a pipe plug if it's a problem. No promises on how long the gun will last. Might need to change the impact mechanism's oil pretty frequently if it's used a lot. Might try synthetic gear oil in it if you kill too many impacts too quickly. I fill mine with 30wt motor oil, no problems yet. But it's used only intermittently.
On 15 Sep 2006 15:42:48 -0700, with neither quill nor qualm, snipped-for-privacy@hotmail.com quickly quoth:
Let's see, you took a paying job and now want to trade several hundreds or thousands of dollars worth of machine automation design for a whole -case- of beer? Mighty white o' ya, Wolfy.
Liability lies with the designer and your "pay" isn't worth it.
P.S: An impact wrench is too iffy. I'd go with a worm gear drive and limit switches. That tip is worth your "pay" right there.
----------------------------------------------- I'll apologize for offending someone...right after they apologize for being easily offended.
The arrangement is a clamp on a piece of equipment that is manually positioned at some distance from the clamping arrangement. This equipment exists and has been in use for decades. I recently designed a bearing and clamp arrangement for another piece of equipment in the same plant that works well and was very well received by the people who paid for it.
Up to now the clamping was done manually; the clamp was insufficient for the job and I designed a replacement guaranteed to to the job. (While I do make mistakes my clients have confidence in me that I know what I am doing...so far so good).
The proposal sketches were reviewed and money appropriated. Then a bright boy said how about remote operation? (This actually is a great idea and saves lots of running/climbing for the operator). I just wish they had advised me of this up front!
I said "no sweat" we can do this. The restriction imposed was air control, not electrical. I immediately thought of power draw-bars with their simple on/off buttons.
Unfortunately when I reviewed the typical power draw-bar specs they listed torques in the 65 to 85 foot-pound range, way too low for this application.
I will phone KURTZ on monday to find out the torque available for #40 and #50 taper draw-bars. Their web site does not say what it is.
If all else fails I will try to find a large impact driver with lever throttle as advised by Gunner. A couple of small air cylinders to operate the throttle lever via a pilot air operated shuttle valve oughta do the trick.
Mounting the bits is no problem.
I have also thought of air operated torque cylinders. The biggest one I found to date lists 270 ft-lb of torque which is acceptable. The problem is that it requires full air pressure to produce this torque, say 80 psi. To rely on the same pressure to undo the bolt is asking for trouble, even if the same air pressure is available. I would try it if the torque cylinder could produce say 270 ft-lb at 75 psi air to tighten the bolt, and then use full line pressure, 85 to 95 psi to loosen the bolt. I will talk to FESTO on monday about this.
BTW all your suggestions help the thought process; think of it as brainstorming.
Larry wrote: "....several hundreds of thousands of dollars worth of equipment...".
Don't I wish! The equipment may have been worth $1/2 million when new. My modifications will pay the bills for a few days. I don't do the manufacturing nor the installation. I work closely with a small, very sharp fabricator who does the 'heavy' lifting.
Larry, nobody is twisting anybody's arm to 'play' here. If you don't like the rules take a pass. It is still a free country in this regard. I thought a case of your favourite brew, or a bottle of your favourite poison if you prefer, to be an appropriate appreciation for the idea that may save me a little time, and my client a little money.
Read my post above, it may clue you in a little.
As I wrote in the original post the client does not want remote electrical control. In this context the default is pneumatics.
If you believe that the honorarium for your "million dollar idea" is insulting.....feel free to take you idea elsewhere.
It is still a free country in this regard.....I already said that, didn't I? Oh well, it can stand repeating.
Wolfgang
PS.: The liability on this job is ALL MINE because my seal and signature as P.Eng. will be on the drawings and procedures. wfh
Nick, there are several reasons for not doing it your way:
1) the cylinder dia. would be huge at say 90 psi air to supply the 1500 lb of clamping force. (300 ft-lb torque on a 1" dia. bolt). Say, a 6" dia cylinder would do this!
2) should the air supply fail (happens in heavy industry) the clamp would be loose...NOT acceptable. This is really bad, but...a local air tank might alleviate this difficulty.
I therefore opted to torque a 1"-8UNC grade 5 bolt to 300 ft-lb or so to do the job.
I also considered a toggle clamp arrangement operated by an air cylinder. If all else fails I may have to revert to this. The reason it's not my first choice is that the toggle mechanism has of necessity some lateral play, and this would preclude the clamp from holding the base "rock-steady" as it were. Still a good idea, though.
Hi Wolf. Are you sure of the specifications? 300 pounds of torque applied to an unlubricated 3/4-10 zinc plated #5 bolt will create approx. 75% of it's breaking strength or about 69,000 pounds of tension. Is this really required or is 300# meant to be tension and not torque? How much linear motion is required to go from "loose" to "tight"?
In either case how will you keep the proposed (unlubricated?) threads from quickly wearing out? Perhaps a better solution might be to use an air cylinder and a toggle (if a cylinder can not produce the required tension).
Joe, think of a disk brake with caliper. The disk is 40" dia. and forms the base of a rotating column that requires accurate fixing against rotation once its rotational positioning is attained. All this is done manually.
I opted for a 1" dia. bolt because 300 ft-lb torque is very little for this size bolt....to make it ridgid and damage proof. If the torque went up to say 500 ft-lb I doubt anyone would complain....the mountings are heavy, massive, to preclude excessive vibration/movement during use.
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