question: what temperature x forced calettamenti? ? ? ?

[gregario]

a question:

once determined the value of the interference between tree and toothed wheel (hot coupling and without tongue, the pair is transmitted in full by coupling), how do I correctly determine the heating temperature?

reading here and there I found a few formulas, but they are slightly discordant. . .

1- delta t= (i + a) / (lambda * d)

2- delta t= (i + (0.50 * i) / (lambda * d)

where delta t is the thermal jump
i is the max calculated interference
a is the game for assembly (in workshop I recommend 0.05mm)

lambda= expansion coeff hub
d is the diameter of calettamento

which is the most correct?

and what is the maximum permissible temperature for a cemented and tempered material? on the machine organ manual I found max 200°c, but isn't it too low?

thanks in advance for any suggestions

Good day

 

[mtbnicola]

will you submit it to temperatures below 0 heat? in what environmental conditions will work the mechanism?

 

[gregario]

I'm heating up the wheel.

shaft and wheel are components of a plastic machine reducer, operating temperature about 60/70°c

ipoty temperature environment of 20/25°c

 

[meccanicamg]

hi gregarius, the expansion formula is:

dt = imax / (lambda*d)

with dt: delta temperature
imax: maximum interference depending on the torque to be transmitted
d: Hub diameter or shaft depending on what sided

I remember that imax is the theoretical one, while imax,elastic is lower and depends on the roughness of the tree and the photo. see uni 286-1 to choose a coupling where iminimo is greater than necessary imechanic. at the end is imechanical which is imax,elastic + 2*rp(tree) + 2*rp(mode). Remember that rp is about 2*ra.

the temperature for a hardened and cemented material is seen on its characteristic curve or on the material boards. on the internet there is something about temperature. Obviously it is necessary to stay below the tempting temperature and to operate quickly in order not to make the grains honed too much and therefore to lose in superficial hardness.

example look here http://www.nuovabassani.com/it_pdf/18nicrmo5.pdf and see how much the hardness decays with tempering depending on the temperatures.

 

[Meccbell]

I would say that I understand that here the problem is not so much to determine the extent of interference, as we are told that that it has already been defined.

In the specific case the question arises on which the game should be to be given to allow an easy assembly of the wheel on the tree.
not having indicated the diameter of the coupling and not even the dimensions of the wheel, which serve to understand whether or not it is easy to handle and how much it is possible to expand it, I will make a general consideration, starting from the only bond that we can derive from the data in our possession, that is the type of material.

In the case of cemented I agree on the limit of 200° c as it is the temperature at which the finding of such steels is usually performed.
therefore the overcoming of this value would cause the problem of a decrease in hardness of the piece.

so we have the limit value of the wheel heating and, knowing its diameter of the hole, we will have that our piece at 200° c will be dileted of a value equal to dt * 0,0000124 * d
or delta temperature * linear coefficient alloy steels per grade c (in mm) * hole diameter.

Therefore, admitting, for example, that the diameter of the hole is 80 mm and that the interferance has been established in 0.06 mm we will have that at 200° c and with an ambient temperature of 20°c (delta t = 180) our hole will spread by mm 0.178, then about mm 0.12 more than the tree.

at this point the value obtained appears well above the 5 cents that the workshop recommends as a mounting game.
we would therefore be induced to think that it could reduce the temperature, perhaps going down around 130-150° c.

However, it should be considered that the installation of a coupling for interference made possible through the so-called "thermal lift" poses a serious problem about the safety that the operation can take place in a simple, safe and above all fast way.

This is because we are in the presence of the classic operation called "or the go or the split", as it is easy to understand that the mounting conditions must allow to shovel the wheel on the tree in a single stroke, without webbing or worse stops in the middle of the "path".
In fact, at the same time when they mate a hot part with a cold, and therefore with a certain game between them, inevitably at that same time will begin a process of equalization of the temperatures of the 2 pieces, resulting in reduction of the assembly game and the consequent mobility of the parts, up to the real locking.

that is why at first I said that in addition to the extent of the game obtained with the heating, that as seen is easy determination, a very important factor to take into account is that of the size and weight, and therefore of the handling, of the parts to be coupled.
I can now say that couple of pieces of a few kilos of weight and dimensions easily handled by one person is relatively easy, while the same operation made on details of the weight of several tens of kg. and especially of dimensions also "important" becomes very, but much, more delicate and difficult to perform.

In fact, in these last cases, great attention should be paid to the preparation not only of the "theatre of operations", of the means to manipulate the pieces and, often neglected, of the clear predisposition of the tasks to be carried out if the operation is made by two or more people, but should also be previewed in the project place some shortening, like a band of diameter reduced on the tree or increased in the hole to allow the centering and contact of the pieces.

said in extreme synthesis, if during the assembly one of the pieces should be impured (in jargon "ingambare") just at the beginning of the coupling, the thing is resolved to the maximum with some energetic and timely blow of copper sludge, but if the same piece had to stop "road doing", perhaps because being heavy the operator / the crane / the equipment that support it had a momentary hesitation, well...

 

[gregario]

I would say that I understand that here the problem is not so much to determine the extent of interference, as we are told that that it has already been defined.

In the specific case the question arises on which the game should be to be given to allow an easy assembly of the wheel on the tree.
not having indicated the diameter of the coupling and not even the dimensions of the wheel, which serve to understand whether or not it is easy to handle and how much it is possible to expand it, I will make a general consideration, starting from the only bond that we can derive from the data in our possession, that is the type of material.

.

Here are some data:

pair to transmit: mt.
service factor: sr=3
Coeff friction: mu=0.14
calettamento diameter: df=200mm
diameter east hub: de=343.52mm
range: If=205mm
module el: e=206000n/mm2
wheel and tree material: 18nicrmo5

contact pressure calculated: pf=107.32 n/mm2
calculated interference: |p|=0.3152mm

Hole tolerance: h6 (+0.029 /0)

shaft diameter (wheel seat): from=200 (+0.42/ +0.35)

Max interference: imax= 0.42mm
minimum interference: imin=0.321mm

can I be enough to make my job clearer?
now I follow your suggestions and I repeat the calculations