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Clamping Unit Needed

08/27/2017 10:31 AM

Hello :) (sorry for the bad english, but I really am in need of help)
I currently attend a mechanical school in Austria and have to design a new clamping unit for a lid.
The circular lid is loaded with a force of 60kN (the force acts on the center) and clamped with 4 units.
The currently existing units are equipped with star-shaped grips which have to be turned clockwise to clamp the lid.
The problem here is the particle generation of the thread.
Therefore, i am looking for another solution, which can applie the force needed to clamp the lid, but without the particle generation.
It has to be a manually operated solution.
I am thankful for every kind of advice you can give me and am thankful for you spending your time helping me.

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#1

Re: Clamping unit needed

08/27/2017 11:55 AM

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#6
In reply to #1

Re: Clamping unit needed

08/28/2017 12:48 AM

Good concept, but I don't think any of those could safely handle 15kN (60kN/4)!

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#2

Re: Clamping Unit Needed

08/27/2017 4:10 PM

New nuts and bolts that are durable?

Particle generation of the thread is a component failure, not a reason to ditch the design.

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#3

Re: Clamping Unit Needed

08/27/2017 7:12 PM

These clamps should work ....

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#9
In reply to #3

Re: Clamping Unit Needed

08/28/2017 10:16 AM

Firstly, thank you for replying to my post, i really am grateful

Could you tell me the name of these clamps or perhaps message me a link of them

Thank you

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#12
In reply to #9

Re: Clamping Unit Needed

08/28/2017 10:37 AM

Over center latches, draw latches and other names.

Simply hover your cursor over the pictures and click your mouse and all the information is linked to the photographs.

Good luck.

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#15
In reply to #12

Re: Clamping Unit Needed

08/28/2017 12:25 PM

Oh, my!!!! Guess I am amused because I know what those clamps are.

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#17
In reply to #15

Re: Clamping Unit Needed

08/28/2017 12:46 PM

OP said, "have to design a new clamping unit for a lid."

I was merely providing a concept that he can scale up or not. Picky, picky, picky.

Some of these are good for 16,000#. Like I said, just a thought.

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#20
In reply to #17

Re: Clamping Unit Needed

08/28/2017 3:26 PM

I meant to reply to #3. Those are not clamps for a lid........

Unfortunately because of one the ex-wife's brilliant web store ideas (failed), I know exactly what those are.

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#24
In reply to #20

Re: Clamping Unit Needed

08/28/2017 4:22 PM

So, I did all that brilliant research and explaining for naught?

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#25
In reply to #24

Re: Clamping Unit Needed

08/28/2017 4:36 PM

Sorry, all I can say those clamps rhyme with ripple. Really surprised nobody else said something or they were moderated out. If we posted it, it would have been.

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#31
In reply to #25

Re: Clamping Unit Needed

08/28/2017 6:22 PM

Really?

I thought it was something the went around your neck to hold a sweater when it was just hanging on your back.

I've lead a sheltered life I guess.

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#37
In reply to #31

Re: Clamping Unit Needed

08/28/2017 8:19 PM

They will hold your sweater up, from the inside out....

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#70
In reply to #15

Re: Clamping Unit Needed

08/30/2017 3:16 PM

Me too....

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#27
In reply to #12

Re: Clamping Unit Needed

08/28/2017 5:08 PM

Lyn. please explain how you made those photos become links...

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#29
In reply to #27

Re: Clamping Unit Needed

08/28/2017 5:20 PM

Sublime ignorance is how.

I googled "overcenter clamps" and went to images. I then chose a photo, clicked on it to get a larger, single image and then just cut and pasted the pictures, one at a time.

That linked them, at least for me.

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#30
In reply to #29

Re: Clamping Unit Needed

08/28/2017 6:02 PM

Oh really!? I haven't tried pasting an image into CR4 for years; I've always created a jpg and used the camera icon to link to it.
Back when I tried to paste an image, it didn't work... I'll have to try it now...

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#4

Re: Clamping Unit Needed

08/27/2017 8:15 PM
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#11
In reply to #4

Re: Clamping Unit Needed

08/28/2017 10:27 AM

You are right that these would probably better, but i was tasked with finding a clamping unit that can be manually operated

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#48
In reply to #11

Re: Clamping Unit Needed

08/29/2017 1:32 AM

haha.... that's why I included the manually operated pump link....

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#13
In reply to #4

Re: Clamping Unit Needed

08/28/2017 12:18 PM

Very interesting. I did not know those existed. Will send the link to myself.

Do you happen to know the upper limit of force these can withstand per clamp?

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#19
In reply to #13

Re: Clamping Unit Needed

08/28/2017 2:24 PM

Well they have several models, the one pictured is rated at 2.1kN to 33.8kN....but I see one up to 50kN....truth be told they can probably make whatever you want...They have dozens of different models...

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#5

Re: Clamping Unit Needed

08/28/2017 12:34 AM
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#16
In reply to #5

Re: Clamping Unit Needed

08/28/2017 12:29 PM

Beats the rubber band band (and the rubber band man) by miles.

I would not trust a band clamp to hold such force though.

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#7

Re: Clamping Unit Needed

08/28/2017 1:05 AM

I presume the 60 kN force is NOT applied until after the lid is in place. Is that correct?

How big is the lid? Does it need to resist corrosion? High temperature?

I assume that by particle generation, you are referring to thread wear. Is that wear occurring on the bolt, the nut (star-shaped grip), or both? Perhaps, as someone else hinted, the problem is not with the design, but with the material(s) chosen for the bolt and nut, or the heat treatment of those materials.

Since this clamping system only has to exert force in a single direction, consider changing to a buttress thread form, and perhaps lubricating those threads.

Take a look at several pressure cookers for additional ideas.

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#10
In reply to #7

Re: Clamping Unit Needed

08/28/2017 10:25 AM

Hello and thank you for spending your time helping me

The lid has a diameter of 320 mm
There is no high temperature in the process and it's all happening in a cleanroom so corrosion is hardly a problem

You are right about the particle generation, it's the thread wear. The particle generation is occuring on the nut, at least, that´s what I was told.

And again, thank you for helping me

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#18
In reply to #10

Re: Clamping Unit Needed

08/28/2017 1:12 PM

You're welcome!

If it is in a clean room, then thread lubrication may be verboten.

JStewart correctly converted the 60kN to close to 13,500 pounds, which means over a ton and a half of tension on each bolt. I also agree with him that there ought to be more than 4 clamps!

Now I'm beginning to think the problem may not be the device, but rather the procedure. If the threads are wearing sufficiently to create visible particles, then those clamp nuts must currently be moved while the unit is under pressure. If so, why? I sure as heck wouldn't want to fiddle with them with that kind of force applied.

There may be something I haven't thought of, but I can't imagine a reason for adjusting those clamps while under pressure. The pressure should always be released before loosening those clamps, and should not be applied before they are tightened appropriately.

I have no idea how your instructor might react to the above concept, since your assignment was to change the design, but a good engineer should always consider alternative methods of solving a problem.

And by the way, your English has shown to be MUCH better than that of many we see here, even for quite a few whose first language is English!

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#21
In reply to #18

Re: Clamping Unit Needed

08/28/2017 3:37 PM

Again, thank you very much for your reply.

Firstly, no, the clamps are not moved under pressure, there are sensors on every unit that prevent the process to start before every unit clams the lid.
And the clamps are opened after the process is over and the lid isn't under pressure anymore.
Also, the current particle generation is only slightly, really hardly anything.

In all honesty, this project is for my thesis since I am finishing the school I currently attend, so the company gave me this project..... well,justso I can work on something for my thesis.
Therefore, it is no special project, the current clamps are fine, but they would like to see some alternatives, maybe one without particle generation, and thats my job, finding some alternatives that hopefully prove to be better than the already existing clamps.

I hope the information i provided you with now is enough, and again, thank you for spending your time helping me.

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#26
In reply to #21

Re: Clamping Unit Needed

08/28/2017 5:02 PM

OK. If these clamping nuts aren't moved while under tension, then I can only think of a few possibilities:

1. The nuts, the bolts, or both, are made of a material which is too soft.

2. The particles are not really coming from the threads, but from the contact area between the nuts and the top of the lid "ears". Add a hardened and polished washer to each nut. Ideally, those washers would be retained by a swaged ring on the bottom of the nut.

3. There is a misalignment or insufficient clearance somewhere, so some part of the clamping nut is rubbing on something other than the bolt.

4. The bolts are really too small, so are stretching inside the nut when pressure is applied. If so, this is definitely a safety issue that should be addressed immediately!

5. The particles are actually being created while the lid is being placed, by the rubbing of the bolts on the sides of the lid "ears".

Obviously, in a clean room, any particles are a potential problem, so this is indeed a problem that needs to be corrected. Do you know for sure when the particles are being generated? You might find it useful to use a loupe or other magnification to check at each step of the operation.

Good luck!

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#51
In reply to #26

Re: Clamping Unit Needed

08/29/2017 8:13 AM

What SolarEagle posted later on has the same solution as the one I have to improve.

I was told the particle generation happens when the clamping takes place. It comes from the nut. That probably comes from, as you already listed, too soft materials. I will look into this further, but in the meantime, would you maybe know a different kind of solution to the picture already mentioned?

Thank you very much, it really is nice of you helping me like that.

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#57
In reply to #51

Re: Clamping Unit Needed

08/29/2017 11:20 AM

I agree with you on the probable cause. Determine the diameter and pitch of the threads, then procure or make a set of nuts of hardened/hardenable steel. Polish the threads inside the nuts and the bottom contact surface before and after hardening. One possible source: https://www.mcmaster.com/#case-hardened-nuts/=195hfbj

Doing this has the MAJOR advantage of requiring no modification of the existing container or lid.

The method shown in the illustrations has quite a few positive attributes, but at least a couple of negative ones:

1. The nuts can be tightened unequally buy a careless operator, potentially warping the lid.

2. The nuts are above the lid, so there is a greater possibility of any particles generated contaminating the interior of the container. Putting the bolts on the lid and the nuts underneath would reduce that possibility, but would be considerably less convenient for the operator.

Every other method I can imagine would require major modification of the container and lid. It would probably be better to start from scratch with a new container and lid, and add to it. In any case, it will be expensive.

I definitely like the RapiDoor™ solution shown by Lyn.

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#71
In reply to #10

Re: Clamping Unit Needed

08/30/2017 3:19 PM

Modify your existing threaded rods and nuts with BALL SCREWS and BALL NUTS. Absolutely no thread wear particles.!!!

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#72
In reply to #71

Re: Clamping Unit Needed

08/30/2017 3:34 PM

This appears to me to be a viable idea also. Is it possible to support that much load on just a few lead screws (ball screw type)?

At least this option has one more advantage: easy to synchronize four ball screws turning using a simple drive mechanism - removes the human error factor.

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#73
In reply to #71

Re: Clamping Unit Needed

08/30/2017 4:42 PM

I thought about suggesting that a few days ago, but then it occurred to me that there would have to be some form of locking mechanism. The balls would have to be pretty good sized to withstand the ton-and-a- half axial force per screw, and large balls would require a relatively large pitch, so at that thread slope there would not be enough friction for them to be self-locking like an ordinary nut. The bottom of the nut would still have to rub on the top of the "ear", or on a washer. If you tried a ball or roller thrust washer to eliminate that rubbing, then you'd really need a locking mechanism to prevent the nut from loosening.

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#74
In reply to #73

Re: Clamping Unit Needed

08/30/2017 4:47 PM

Hey.... I'm just the idea guy..... Someone else has to fab and implement it!

Though it would be a LOT easier to suggest a solution with a diagram or even better... A PICTURE!!!!

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#75
In reply to #74

Re: Clamping Unit Needed

08/30/2017 5:26 PM

As the ranking member of the names committee, it is only fair to warn you that the statement, "Someone else has to fab and implement it" may be grounds for the revocation of your current name: Original_Macgyver.

The following names are being considered as your name replacement: Wannabe Macgyver, Pretend Macgyver, Would-be Macgyver, Macgyver in my mind, Macgyver, I'm just the idea guy.

You have the right to protest this proceeding, but I would suggest throwing yourself at the mercy of the Council and begging for a second chance.

Ranking Member lyn.

(A copy of the proceedings is available on request)

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#76
In reply to #75

Re: Clamping Unit Needed

08/31/2017 9:31 AM

I was being Facetious_Macgyver there!

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#77
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Re: Clamping Unit Needed

08/31/2017 9:36 AM

Duly noted.

Committee adjourned!

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#32
In reply to #7

Re: Clamping Unit Needed

08/28/2017 6:28 PM

On a larger scale:

Hover your cursor and click.

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#33
In reply to #32

Re: Clamping Unit Needed

08/28/2017 6:56 PM

Looks pretty much like a pressure cooker lid on its side... I mentioned those before...

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#34
In reply to #33

Re: Clamping Unit Needed

08/28/2017 7:05 PM

Yes, that's why I responded to your # 7 post.

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#35
In reply to #34

Re: Clamping Unit Needed

08/28/2017 7:51 PM

Sorry - I missed that detail. Now it just occurred to me: are pressure cookers known by the same name on your side of the pond?

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#36
In reply to #35

Re: Clamping Unit Needed

08/28/2017 8:05 PM

That's what we call them in Arizona, which is where I live.

It must be my accent that threw you off.

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#44
In reply to #36

Re: Clamping Unit Needed

08/29/2017 12:32 AM

Oops! I was thinking of the bowman in GB. Come to think of it, I believe he spells it with two n's.

It is amazing how written language hides accents. A couple of years ago, I made phone contact with a person from GB who I had 'met' on CR4. I had zero problem understanding his written posts, but it was a major struggle to understand him over the phone. Unfortunately, it appears that he is no longer with us...

BTW, welcome back! I missed you for a while...

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#45
In reply to #44

Re: Clamping Unit Needed

08/29/2017 12:58 AM

Del the Cat is the only English bowman of which I am aware, here on this forum.

Thanks, by the way.

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#46
In reply to #45

Re: Clamping Unit Needed

08/29/2017 1:07 AM

That indeed is who I was thinking of. I have no idea why I thought of him as Lynn...

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#47
In reply to #46

Re: Clamping Unit Needed

08/29/2017 1:25 AM

I take that as a compliment. I can't speak for him the other way round.

He is still on the forum.

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#54
In reply to #36

Re: Clamping Unit Needed

08/29/2017 9:01 AM

It had to be the accent'.

Nice job finding Rapidoor clamp ring closures.

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#8

Re: Clamping Unit Needed

08/28/2017 3:49 AM

You could try a Destec clamp if your budget allows.

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#14

Re: Clamping Unit Needed

08/28/2017 12:23 PM

I checked that force and it is 13,480 lb. force. The equivalent in Kg (in gravity) of 6118 Kg. Just 4 units holding that back? What is the diameter of said lid?

Who is the fool charged with opening this thing? Will the container still be pressurized?

Is this an industrial coatings pot (paint pot)?

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#22
In reply to #14

Re: Clamping Unit Needed

08/28/2017 3:45 PM

Thank you for the reply and spending your time helping me.

Ther is some kind of waver bonding happening inside, that's all the information I was told regarding the process.

And no, the pressure will be gone and after that the conainer is to be opened

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#23
In reply to #22

Re: Clamping Unit Needed

08/28/2017 4:17 PM

I think you mean "wafer" bonding?

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#28
In reply to #23

Re: Clamping Unit Needed

08/28/2017 5:11 PM

Vanilla wafer bonding, or chocolate?

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#49
In reply to #23

Re: Clamping Unit Needed

08/29/2017 7:40 AM

You're right, it's wafer ^^

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#38

Re: Clamping Unit Needed

08/28/2017 9:05 PM

I would still go with the hydraulic clamps....

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#40
In reply to #38

Re: Clamping Unit Needed

08/28/2017 10:00 PM

Not in a wafer fab facility!

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#41
In reply to #40

Re: Clamping Unit Needed

08/28/2017 10:15 PM

None of the hydraulics need be exposed....

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#42
In reply to #41

Re: Clamping Unit Needed

08/28/2017 10:47 PM

If the pressure vessel is in the clean, so are the hydraulics.

In semiconductor manufacturing, wafer fab processes usually require a sub-Class 1 to Class 10 clean room.

Class Name

0.1 micron

0.2 micron

0.3 micron

0.5 micron

5 micron

1 35 7.5 3 1 N/A

If you've never suited up and gone inside one, it's very intense.

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#43
In reply to #42

Re: Clamping Unit Needed

08/28/2017 11:16 PM
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#50
In reply to #38

Re: Clamping Unit Needed

08/29/2017 7:53 AM

Wow, that looks like the clamping solution I have to improve, may I ask how you found such a good picture, not even I found a good one like that

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#52
In reply to #38

Re: Clamping Unit Needed

08/29/2017 8:22 AM

Oh, and also, you are right about something hydraulic being better, but sadly I was tasked with finding a mechanical solution.

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#53
In reply to #52

Re: Clamping Unit Needed

08/29/2017 8:29 AM

*manual

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#39

Re: Clamping Unit Needed

08/28/2017 9:27 PM

What? Oh.. Misunderstanding

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#55

Re: Clamping Unit Needed

08/29/2017 9:19 AM

Pretty much, every solution you come up with where metal threads down on something, the nut has to have sliding friction against something as it turns. Rule those out.

Any locking ring closure still involves sliding friction as the lock ring is rotated into position, however, the degree of sliding friction pressure should be a lot less, due to much larger surface area to spread out the force of closure of the vessel. Not ruled out.

Hydraulic clamping unit: IMHO this is a simple solution with extremely low sliding friction (to general particles), as one merely rotates the "dogs" into position, and pumps up the closure device with a manually operated hydraulic pump. I would look into what fluids can be utilized with the pump, and what is allowed into the clean room (by the local operations group) before proceeding with this. I would also check into possible failure modes of these units, such as leak down (if that can take place, and I do not know that it can), leaking from pump connection during attachment/removal/pumping.

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#56

Re: Clamping Unit Needed

08/29/2017 10:20 AM

Well I think the solution is 2 parts, one the particles generated should be inert, that means changing from steel to thermoplastic threads and/or nuts....and the second is a cleaning maintenance program or service that provides the deep cleaning needed on a regular basis...

...any particles that exist in the clean room must be non-conductive and inert. This is one reason why a lot of ultra high molecular weight (UHMW) plastic bearing materials are used in clean room machinery for that industry.

These industries also are concerned about ionic contamination, as well as particulate contamination. The release of metallic ions during many stages of semiconductor production can cause a short circuit on the semiconductor because of the submicrometre conductor widths now used in the newer devices and the conductivity of copper."...

https://www.clipnuts.com/torlon/what-is-torlon.html

http://www.hydraulicspneumatics.com/200/TechZone/PneumaticValves/Article/False/21750/TechZone-PneumaticValves

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#58
In reply to #56

Re: Clamping Unit Needed

08/29/2017 11:37 AM

Could a Teflon washer solve this without being pushed out of the way during strap down with those dog bolts shown in your picture?

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#59
In reply to #58

Re: Clamping Unit Needed

08/29/2017 12:10 PM

Teflon is too soft. It would take a pretty large washer to withstand the ton-and-a half force repeatedly.

These folks have some amazing plastics... Their type X6 and Type Z plastics are rated at 21,750 PSI and 482°F; they have at least some sizes of washers in stock! I believe they also sell bar stock plastic. I haven't done any of the math, but it just might be possible to replace the bolts with polished buttress threads and fabricate plastic nuts.

I didn't quickly find PSI values for UHMW to compare...

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#60
In reply to #59

Re: Clamping Unit Needed

08/29/2017 12:32 PM

Yes, I am pretty sure UHMW PE would pull out really easily.

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#61
In reply to #59

Re: Clamping Unit Needed

08/29/2017 1:10 PM

There are any number of engineered composite nuts and bolts that would work....and you can always go with larger size nuts & bolts to increase strength rating...I suspect it's a tradeoff between cost and working space available...

http://www.insulect.com/fasteners/

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#62
In reply to #61

Re: Clamping Unit Needed

08/29/2017 6:28 PM

I have to thank you all so much for spending your time helping me and providing me with some really high class information. It really helped me a lot and I will try to replace the current nuts with some composite ones.
But one last question I may ask, if just changing the materials wasn't enough ( there is a set amount of time I must work for my thesis ), would swing clamps also work, next to the Rapidoor solution I will also look further into

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#63
In reply to #62

Re: Clamping Unit Needed

08/29/2017 6:53 PM

If correctly sized and designed, of course they would. In addition to the several suggestions already presented, you might find it worthwhile to investigate the swing levers that truckers use to tighten their straps and chains.

In all kinds of clamping devices, it will be important to pay attention to the qualities of the materials used to avoid/minimize wear.

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#64
In reply to #63

Re: Clamping Unit Needed

08/29/2017 7:22 PM

Like these?

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#65
In reply to #64

Re: Clamping Unit Needed

08/29/2017 8:42 PM

Yep! Although the ones I had in mind are slightly different, they all use the snap-past-center concept, as do many, if not all, of those posted in your post #1.

I think all of those in your post #1 are too light for this task, but any of them could be re-engineered to do this job, and they've all been around long enough that I presume there would be no danger of patent infringement...

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#66
In reply to #65

Re: Clamping Unit Needed

08/29/2017 9:22 PM

Yep, too light, but conceptually they are feasible with mods.

Th kid's working on solving, "the particle generation of the thread" so get rid of the threads and use an over-center clamp. Even the pressure cooker/Rapdi-door has metal to metal contact.

It's up to him to re-design/refine the existing solutions.

I think the forum has provided plenty of food for thought.

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#67
In reply to #66

Re: Clamping Unit Needed

08/30/2017 7:29 AM

I thank every single one of you for providing me with some first class information, and spending your time helping me.
Thanks to all of you I can now work on my thesis a lot better with much better ideas.

Thank you again very much

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#69
In reply to #67

Re: Clamping Unit Needed

08/30/2017 11:58 AM

Thanks for that! So many times posters simply disappear without a parting word, and we don't know whether we have been of any help or not. Good luck on your thesis!

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#68

Re: Clamping Unit Needed

08/30/2017 10:09 AM

All mechanical clamp down methods can produce particles. Otherwise there would be clamps with transferable lifetime warranties. And I haven't heard of that.

I'd look at what's currently being used for the application by the leaders in that field for the most appropriate methods.

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