spring size

[Flev]

Hello everyone, I have doubts about the following problem (a sketch attached to understand geometry)
you must size the figure spring so that the game between the two vertical profiles can vary between 1 and 6 mm. profiles belong to two weight benches of about 100 kg. in practice when mating the counters screw the screws m6x40 (there are 4 in all, arranged according to the vertices of a square) and the spring should ensure the maintenance of the required game.
in the sketch I did not indicate quotas, however at the minimum game corresponds a spring arrow of 9 mm and to the maximum one an arrow of 4 mm. is also given the diameter of the housing (phi in figure) and the free length of the spring l0. What makes me perplexed is the fact of not having a certain load to be able to dimensional the spring.
to ensure the value of the game that forces should consider? or rather, the forces with which the spring reacts for the required arrow values, which other forces should balance? screw shooting? the force of friction of the first detachment of the docks?
thanks in advance and greetings to all

 

[Mocca]

Then. the screw you have chosen is not good for the dynamic use you have to make to your plates. use a "rected stem screw" in this way use the head of the screw as the end of the stroke of your plate and also avoid making that coupling between the two bushings you have planned by working properly (using the appropriate tolerances) the rectified part of the screw.
for the spring look for tables with which you can check according to their inner diameter (detailed by the screw you have chosen) the load in relation to each compression mm considering that you will have to handle about 100 kg i.e. 25 kg per spring + some kg of margin for the friction.
Finally remember that in the maximum extension situation of the spring you will always have a minimum preload (for your size 3 mm can go well).
I hope all this is enough for you.
We said hello.

 

[Fulvio Romano]

mmmhh... but a healthy locking contradado instead of the spring?

 

[sampom]

. what makes me perplexed is the fact of not having a load to measure the spring.

I think that's the only salient you need for the spring calculation. How can you not know? What are those two "banks"?
if they are put as vertical as you schematized them their weight is influential to the spring. you should know (or estimate) which external forces "horizontal" (if there are) will eventually press normally on those profiles.. and then will crush the springs. as you put them where they are.

to ensure the value of the game that forces should consider?

see above; any horizontal external forces in your design.
How can we know if we don't know the use?

or rather, the forces with which the spring reacts for the required arrow values, which other forces should balance?

again see above; you should tell us

screw shooting?

the force of friction of the first detachment of the docks?

But then are those benches joined together? and what (such as strength.. You see, always there you come back) keeps them together?
But if it were, in that condition, the faces of the benches could not stand together for mutual friction without an external force (always speaking of the directions of your scheme). besides you say that the minimum game must be 1 mm so the faces will never be in contact, and that friction can be there then?. Am I wrong?
to the limit, if you tell me about the first detachment, you will have to refer to the relative one between the bushings threaded one in the other (in your scheme the weight of the benches weighs everything on those).

about the games:
from your installation it is clear that the maximum will be given exclusively by how screwed the screws, regardless of the springs. once the head of the screw is in line in the seat those two profiles more than that will not open (this is clear, no?). then with the screws you will record the maximum game (and precarise the springs by affecting the field of intervention).
the minimum, however, depends on the springs. but here we go back to bomb; what do they have to fight? :biggrin: how much energy should they absorb? How? the minimum game can be given by a end-of-the-race (as for the maximum) or the spring will always have to shock even "at the bottom"?
These things only know the designer.
known those external loads and how they will have to work the 2 counters mutually, you can calculate the spring and then dimensional the various lengths.

Until then everything seems a little cloudy, you should explain better. .
It's very likely that I'm the one who doesn't understand you.

greetings
Marco:smile:

 

[africagia]

In my opinion, from how you can see from the box the only load on which you need to size the spring is the preload of the screw. the other loads seem in other direction. but what friction do you refer to, including surfaces?

 

[Flev]

the friction I referred to was that between benches and floor on which they rest, but I have no information about it (see coefficient of first detachment). .

 

[africagia]

but what are these benches for? How are they loaded?

 

[Flev]

the two profiles belong to modular frames that form the cash counters for supermarkets. above it flows the customer's expense!

 

[africagia]

So these profiles rotate and above is the customer's expense? If so, in my opinion, the only load to dimensional the spring is the preload of the screw.

 

[Flev]

no, the profiles are fixed, at the max there may be the conveyor belt mounted above. I would say that the screw, since it does not tighten the two profiles (because there must be the required game), guarantees me the maximum game by making underhead jokes (if I use another type of screw and not that of the head-to-head sketch). the spring serves for the minimum, as correctly said by sampom. I believe that the only horizontal forces that could undergo the benches are those due to accidental impacts of people. as the bench weighs about 100 kg (981 n), the force necessary to move it should be pairs to 981 x u with u = coefficient of first detachment between bench and floor. According to me, in the minimum game condition the springs (they are 4) will have to endure a force equal to a quarter of that necessary to move the counter. the problem is to baptize a coefficient of first detachment between counter (steel) and floor (??????). correct me if I'm wrong!

 

[sampom]

the two profiles belong to modular frames that form the cash counters for supermarkets. above it flows the customer's expense!

no, the profiles are fixed, at the max there may be the conveyor belt mounted above. I would say that the screw, since it does not tighten the two profiles (because there must be the required game), guarantees me the maximum game by making underhead jokes (if I use another type of screw and not that of the head-to-head sketch). the spring serves for the minimum, as correctly said by sampom. I believe that the only horizontal forces that could undergo the benches are those due to accidental impacts of people. as the bench weighs about 100 kg (981 n), the force necessary to move it should be pairs to 981 x u with u = coefficient of first detachment between bench and floor. According to me, in the minimum game condition the springs (they are 4) will have to endure a force equal to a quarter of that necessary to move the counter. the problem is to baptize a coefficient of first detachment between counter (steel) and floor (??????). correct me if I'm wrong!

..eh, something finally comes out. .
But if you didn't tell us what we know?
and are so vertical on the floor?
So are they part of the external perimeter structure of the cash counter?
and why is he blessed "double wall" with springs, perhaps to absorb any bumps of the shopping carts?
sure that both "pannelli" are leaning on the floor and not perhaps the outer one slightly raised to move?

Now you've got me curious, can't you post a more complete scheme?

I'm going to take a ride to the discount tonight and I'm going through the legs of the cashier to "check" :biggrin::biggrin:

greetings
Marco:smile:

 

[Flev]

the situation is as follows:
those blessed games to satisfy serve to recover the constructive imperfections that you have on the pieces. I'll explain better.
the structures above two edges of the sketch (horizontal surfaces of the benches) must be mounted with a light of 1 mm. in this ideal configuration the game between the two profiles is 3 mm (the g of the sketch). now because of the imperfections of construction or assembly of the pieces this light could not always be guaranteed. then it was thought to install that recovery system games with spring and screw.
It is clear that, in my opinion, a minimum of rigidity the springs will have to have otherwise at the slightest bump that undergoes the counter, I miss the desired game.
Unfortunately the info come to me with the dropper (the job is for an external customer, the drawings make them some of my colleagues, and both I think we don't even know what is a force....), come to me and they tell me, toh look there is a spring to dimensional, the odds are these....however the benches are leaning all on the ground... .

ps: look not to let you tan from the cashier!!!!:biggrin:

 

[Fulvio Romano]

Why don't you do a preload that's a tenth of the screw yielding load?

I think I understand that you need a force as high as possible to prevent the stinging of the benches, but to avoid that by loosening the screw the benches do not flow on the floor. If you do a preload as I say, you have a plentiful static security factor and a force (I think) high enough. Do two accounts and see that it comes out...