Mine Door Maths Question.

It's a bit early in the day for my brain, but how about a different arrangemet ; A small sliding panel in each door can be opened to reduce preassure on the doors.The doors can then be opened against the air flow. It takes a fair bit of muscle to get them moving, but is common practice in mining. There doesn't seem to be much keeping them shut in your diagram ?

Hi Kris.

The idea is that the doors must restrain either wind or blast loading, we don't want to let either pass at a high velocity. Yes, there is , however, a panel that will let go under extreme pressure.

The quick sketch I did was only to show the mechanics of where the forces would act. In fact, it will only be the hydraulics that will lock the doors as far as the plans go at the moment. There may need to be lock pins added later.

Provided an expert can provide me with the forces likely to be imposed on the cylinder (and hopefully show how the calculation was achieved, so that I don't have to embarrass myself again by asking) I can deal with all the hydraulic implications.

Go and scruff yourself a quick coffee and maybe you can solve the conundrum! Thanks all the same!

Hi beej50,

hee hee, I do need my coffee in the morning ! Looks like caramba has come to your rescue though. Anyway, here's a handy converter - I'm with you on using KPa, but there are so many units out there.

What I'd had in mind was the kind of doors seen at the pit-head where forced ventilation is used. The doors are kept tight shut by the force of the venting air. To pass through them, a hatch is slid ( the air rush nearly taking your head off ), and you can then just manage to fully open the door to pass through. I neglected to add that this arrangement is like an air-lock with two sets of doors. You need to pant to avoid your ears popping as well !

These are kind of neat, but hopefully you can progress your solution with carambas calcs.

Kris

Good morning Kris, hope you've enjoyed your coffee,

I do find your comments have been said to the point of issue. I am sure you're a good specialist, even very good regardless your sarcasm toward me. Where was I wrong when on direct question had provided a direct answer with reminding that it's so dangerous construction to be applied without detailed study with help of expert? Why not with you, Kris? Your remarks about two sets of doors and etc are looking very relevant and useful.

I do see your last comment is provoked by my location. So in capacity of my location I assure you that your "hee,hee" didn't touched me not a bit though it could touch beej50 maybe. I have not any idea about. If you need get a class of sarcasm irony and curses. Welcome to my home. I guarantee your safety and returning back home being healthy and profoundly educated. Really write me! Welcome!

Sarcasm is weapon. Take a care with any weapon. It's my kind advice to you.

Truly the best regards to you and your closely one.

Hello caramba,

I'm truly sorry if you interpret my coment as sarcasm, and also slightly baffled. I was commending your post, and rated your post as good by voting for it. If you find my comment to have been offensive, then please utlize the report button and have the site Administrators look at it.

Sincerely (but bewildred)

Kris.

Kris, it's my return to say you sorry.

Unfortunately I have had not quite well experience in my life with some kind of people owing to only my residence. But in any case as you noticed I had confirmed your high professionalism at all. And your comments was to the point. I had base (practically forgotten now) mining education and I worked in mine for the short time. So you're absolutely right with your warnings about design.

Thanks for your vote and I've voted for nick name to my return as we are here to share our duty help each other. Aren't we?

And my invitation to you was really from the bottom of my heart.

I am not an angel, sorry again.

All my respect and regards to you. Hope your weekend goes fine.

Hi Caramba

Many thanks for your contributions. It is not your fault that you miss interpreted my drawing. One of the other contributors further down has tipped me off how to get the drawing more clear from AutoCAD. It was a good tip.

Your maths was spot on and I know Kris was definitely not having a go at you! As for me, I don't mind where I get useful help from. Maths is the same in every country. Talking of which, my brother is in charge of English Education in your country (working for the British Council). It is only a two year posting and he happily goes from place to place. Unfortunately, he will never visit me in Oz as we are supposed to already have a grip of English! Uhm!

Have a good day and thanks again for you help! It is much appreciated!

As we have here equal doors we can consider only one of twos.

So P=4kPa=4000 P/m^2

a=2.25 m; b=4.855 m;

----------------------------------------------

Square of one door is S=a*b=2.25*4.855=10.92 m^2. From this it's easy to find wind force affecting the door as

Fw=P*S=4000*10.92=43695 N (Newton). It's not look quite properly but we can use for convenience mass units instead force,i.e.

Fw=4369.5 kg or about 4.4 metric ton.

Unfortunately you didn't represent complete dimensions so I give you general resolving.

Kinematic configuration is shown in fig.1.

Fw applied to point B should be compensated by response reaction of cylinder Fc.

Fc is consist of its projections on horizontal and vertical axes' Fv, Fh.

Torque moment Mv=-Fw*|OB|=-Fw*a/2 is caused by wind pressure should be compensated sum of response moments Fh*h2+Fv*d, that is we get equation of momentum

Fw*a/2=Fh*h/2+Fv*d; (1)

At the same time Fh=Fc*cos(alpha) and Fv=Fc*sin(alpha);

So equation (1) can be rewritten as

Fw*a/2=Fc*[h/2*cos(alpha)+d*sin(alpha)];

So reaction of cylinder can be obtained as

Fc= Fw*a/2/[h/2*cos(alpha)+d*sin(alpha)]

Angle "alpha" can be obtained easy as tg(alpha)=(h2-h1)/d

If I were you I would prefer write short program to find optimal parameters for system. Really Fc believed to be very significant as angle alpha is so small.

I suppose there are one more cylinders beneath which would share wind load.

Every good luck to your project.

P.S. Check my calculations carefully. I could pass by a mistake.

Hi Caramba!

Is this a Caramba moment! Thanks very much for that.

I hoped I had included all the relevant details as I get frustrated with others who don't.

The way I looked at it, we only have to consider the force on the cylinder when the doors are closed. The connecting arm is 300mm long between pivots and is at an angle of 45° from the door (and 135° from the cylinder). This places the cylinder inline but offset from the door pivot by 212.13mm.

There is no second cylinder at the bottom. There will only be the overhead cylinders hence we will probably provide lock pins.

Please tell me how you did your exceptional diagram. It's very clear and informative. Many thanks for your contribution!

I do not think that my contribution is so great as it's task for student. Have you treat my formulas for assessment? Without any calculation it's obvious cylinder will be affected a great force far beyond safety level. Though I am not expert in door manufacturing as well as hydro cylinders at all. But I suppose obtained formulas (if there are not bugs) quite enough to evaluate plausible strengths.

I'll see your new parameters and try to help you, though I think I had given you direction where and how to dig.

Your welcome every time.

Have I understood your correct?

I some confused where should be placed 45, 135 angles ( is alpha 45 degree?). Would you like to confirm either send me one more draft. As my English is not perfect.

Hello nick name. I do find your kinematic configuration and end decision quite proper. It wasn't clear for me what part of shown doors to get for consideration. Your calculations are good.

Hi Guys

Thanks very much for you work. Sorry I dropped out, I needed some zzzzZZZZZzzz! Score another 'Good Answer'!

It would have been easy for Caramba to misinterpret my drawing. I just can't get AutoCAD to show up very clear!

Thanks to all contributors. Done good!

Hi Nick Name.

Perhaps I didn't quite get over to you what a dunce I am at Maths. I'm afraid your speaking another foreign language when you use lots of e's in equations. When I have the miss-fortune to have them pop up in excel, I have to expand the cell until it gives me the real numbers!

Once I've got the force (in nearly any flavour other than the technical way you have posted) I'm away!

In Dry-Bollocks (hydraulics) I only use pressure, flow, velocity, temp etc, and NEVER use e's cos they suck, and my Mummy say's I get too many of them! Oh, and 'raised to the power of' is treading on thin ice too! That is what that 'top hat thing' is, isn't it?

Anyway, to cut to the chase, could you please (pretty please) translate, I don't care if the number is humongous, so long as it is a number, without Egyptian hieroglyphics!

Oh, and then you can score another coffee! Good man!

Hi, sorry for the delay but i did not open my connection.

I had no troubles interpreting your drawing it was clear to me from the start i did only react delayed because i saw that to many question did arouse.

Now for the E-s there is a computer derived notation: 1000= 1E3 which groups the power of 10 under the notation Ex= 10^x and the number between 0 and 10 multiplying it.

It is very convenient for estimations when only the order of magnitude has to be known not the exact value.

I shall be glad to answer any other question.

I would like to make a comment the torsion load on the shaft is quite important and could under circumstances deform even the door. I would dimension the shaft on torsional deformation and not based on the admissible shear stress.

Hi again Nick Name!

I would dimension the shaft on torsional deformation and not based on the admissible shear stress.

Thankfully, I am only tasked with the hydraulic system and a engineering consultancy company are designing (hummm) the doors! Provided that my bit works as expected, I should smell of roses! HOWEVER, I actually do want to understand what you are suggesting. I am fairly familiar with pins in (say) double shear (such as hydraulic cylinder pins). Torsional deformation, however, is beyond me although I understand what you mean! I couldn't do the numbers on that one.

From the provisional drawings I have seen, there will be three Ø 40mm pins on each door. I think (but not quite sure) that the pins will be able to freely rotate on both door and frame mounting. I could imagine that if one side was fixed then torsional deformation could be an issue! Would it also be a consideration if the pins were free to rotate (or not) as they saw fit? I'm not sure if I'm on the right wicket here!

Thanks very much with your explanation. Now if I've understood you correctly:-

Fh=2.3173E5N = 231730N = 23629.9kgf = the answer (force on cylinder)?

Trust me! I'm trying very hard here! Jessss, I hope this looks good.

Hydraulically, thats looking like a 5.5" cylinder to hold (by itself) on the annulus area @ 200 Bar! This is a bit larger than I had anticipated! BUT it only has to hold against the overpressure so, provided a Pilot Operated Check valve (or counterbalance) can do the holding and a (say) 4" cylinder is utilised, we should still be good provided the 4" cylinder can stand the intensification (of pressure)?

If you can think of any concerns, please get back to me, especially if I am magnitudes out!

Thanks for your input!

Hello Beej50! Hope life is treating you good,

Excuse me for my post came up too late. I have not access to inet being at work. Nevertheless and for me and for Kris at once it was clear that cylinder loading will be very significant. Without any calculations.

Therefore take a care with end decision.

Say salute your brother! Really Earth is bloody small planet!

Hi Caramba

Many thanks for your contributions that helped me significantly! Also, thank you for your general good wishes. Its always nice to receive these from CR4 members.

All the best to you and yours as well!

Hi, I shall try to answer as well your questions as to the comment of our specialist in physics.

Start with yours: The load is uniform on the door height. The cylinder is for different reasons at the top above the door. The door is on several pins (hinges) 2 or 3.

The whole load on the door is transmitted by the door itself to the level to which the ram is connected. So that the door will be under a torsion moment and will deform in space as a sheet of paper you keep on both sides and make an angle between the hands. Even if the shaft goes all the height long the same effect will be noticed.

Either the door frame has to be designed as well for this torsion or the shaft if it goes all a long. Important will be the stiffness so that the angular deformation will not be too big.

Now with respect to that other objection. The lowest force will be obtained for 90° between the cylinder center line and the level. Not knowing any thing about the cylinder dimensions or the reasons for the dimensions choice I limited my answer to your question. I thought that you have good reasons to choose as you did so that i did not go into other details. I try every time to give the requested answer since i noticed too often that the answers are all but what is asked for. I consider that the person asking for an answer deserves the respect and i have to assume that he knows why he put the question and i have not to underestimate his knowledge or his value teaching how i would do it better.

Hi NN

You've all done very well. I now have a better understanding of basics that I forgot a long time ago (or never fully grasped in the first place).

I think all my dilemmas have been cleared up and I can go forward. Thats what its all about. CR4 worked for me this time! Thanks to all!

Hi Beej50.

I enjoyed the discussion but couldn't figure why your original drawing showed the right hand piston support vertical to the door and the left hand one at about 45 degrees to the door.

This suggests the piston supports pivot around the same pivot as the door, in which case they can't function as a base for the piston. If they are fixed, what are they fixed to? Why is the door pivoting at the same point?

Maybe I misread your drawing.

Regards.

Hi Fredin

I'm beginning to curse my Cad drawing. I used the 'print to jpg' option and as another contributor has told me, I should have used 'alt-printscreen'! Nice tip! Anyway, yes you did Miss-interpret the drawing!

The right hand door is shown half open making the connecting arm look at 90° to frame. Left hand door is closed showing it's connecting arm at 45°. Had the drawing been clearer, I think you would have spotted that one.

Please don't make me feel any more about my drawing. I promise not to do it again!

Have a nice day though and thanks!

nick-name's contribution looks good to me. My one additional observation (I haven't read all the posts, so I apologise if it's a duplication) is that if the opening is limited to 90^O and the worst force is experienced when the doors are closed, you could comfortably increase the angles between the doors and the arms**. If the factor is as high as 4:1, it could be 75-degrees, which would reduce the force on the arms by a factor of about 1.35. It would also reduce the 'throw' by a factor of about 1.15, so you could in principle lengthen the arms by this factor as well. Doing both would reduce the force on the piston (when the doors are closed) by a factor of 1.55.

However, good as hydraulics can be at absorbing surges, etc, I would still be inclined to go for some "braces" to go with this "belt".

Fyz

**The limitation would be if the arms foul the ground when the doors are open - you don't give the diameter of the pistons

Hi Physicist

No, I hadn't included piston size as this was the object of the original calc', i.e. to determine the forces imposed on the cylinder.

With regards to your other comments, yes, we are in the process of re-jigging the dimensions of the arm (almost exactly) to your suggested angles and increasing the length from 300mm to 488mm.

The result is that the forces imposed are now almost a half of the original calc' and make the cylinder easier to find a home for it and also more cost effective!

Many thanks for your contribution. Keep 'em coming!