dimensioning toothed wheels to helical teeth

[Raffaele98]

hello to everyone, after reading the various discussions on the forum, I have a doubt arisen:
If the hertz test was not satisfied and we already use a cemented steel as a material, is it correct to change the form to return to the verification or is it more appropriate to look for another steel?

 

[PiE81]

I believe that both solutions are valid, if the sizing will be satisfied. In short, either change geometry or choose a material with greater mechanical properties. I imagine that your question is related to a university exam and therefore you do not go beyond other considerations as cost of materials.

 

[TETRASTORE]

confirming what is expressed in the previous post, in the industrial field for serial products (e.g. reducers), it is generally preferable to intervene on the module to maintain uniformity in the processes of processing and supplying materials. Then obviously in specific cases, such as for example for special encumbrance needs or applications, it intervenes on the material.

 

[meccanicamg]

hello to everyone, after reading the various discussions on the forum, I have a doubt arisen:
If the hertz test was not satisfied and we already use a cemented steel as a material, is it correct to change the form to return to the verification or is it more appropriate to look for another steel?

if the flexional fatigue test with lewiss is positive and normally is with good margin due to exercise considerations not by uniform force, when switching to wear assessment i.e. with hertz pressure you can act differently:
- change x profile shift factor
- helical angle change if they are helical wheels
- increase in the engraving belt
- increase in oil viscosity
- increased module

depending on what you are doing and what you can do, depending on the encumbrance, exact or not relationship, application and entity of the non-verification of hertz you can act in various ways.

in the classification of materials in iso 6336 cemented steel is that with superior mechanical characteristics. you can choose to use excellent quality material and with certificates to have slightly higher values. See you qui all the post.

I'll give you the summary scheme.

 

[Raffaele98]

thanks to all for the answer, it is a university project and for the accuracy of a speed reducer. as a material for wheel and pinion I had chosen a cemented steel on 17crnimo6 with sh=1300 and sf=312, from the calculation of the normal module according to lewis I exit a minimum module of 3; but going to do the verification with hertz comes out a value of sigmah that is almost half the permissible value. for this reason I had opted for a module of 6, thus returning to the verification.

 

[Raffaele98]

thanks to all for the answer, it is a university project and for the accuracy of a speed reducer. as a material for wheel and pinion I had chosen a cemented steel on 17crnimo6 with sh=1300 and sf=312, from the calculation of the normal module according to lewis I exit a minimum module of 3; but going to do the verification with hertz comes out a value of sigmah that is almost half the permissible value. for this reason I had opted for a module of 6, thus returning to the verification.

Sorry I was wrong to write sigmah is almost double the sigmahamm

 

[meccanicamg]

thanks to all for the answer, it is a university project and for the accuracy of a speed reducer. as a material for wheel and pinion I had chosen a cemented steel on 17crnimo6 with sh=1300 and sf=312, from the calculation of the normal module according to lewis I exit a minimum module of 3; but going to do the verification with hertz comes out a value of sigmah that is almost half the permissible value. for this reason I had opted for a module of 6, thus returning to the verification.

Sure that switch from module 3 to module 6.... there is in between at least 4 and 5. Are you sure the band is wide enough? If you place the input n and kw interasses we can reason.
but are you using iso6336 or are we left to pure lewiss and pure hertz?

 

[Raffaele98]

Unfortunately we stayed at lewis and hertz pure.
the input power is 100 kw, while n=1400 rpm

 

[Raffaele98]

Unfortunately we stayed at lewis and hertz pure.
the input power is 100 kw, while n=1400 rpm

the transmission ratio is 28

 

[Raffaele98]

Sure that switch from module 3 to module 6.... there is in between at least 4 and 5. Are you sure the band is wide enough? If you place the input n and kw interasses we can reason.
but are you using iso6336 or are we left to pure lewiss and pure hertz?

even if I read on the niemann that for a ratio b/d less than 1 and for cemented steels the module is included 5 and 6

 

[meccanicamg]

with ratio 28 I would say that being at the maximum feasible ratio for each stage i≈6 I would say that at industrial level it is usually done with three Sit down. I often do it with two stages but keep in mind that overcoming i≈3 you will have a strong exasperation of hertz. the pinion will be small and the wheel will be a very large and potentially unstable disk. in these conditions it would take a good job on the propeller by changing the angle and one of the profile correction.
this condition confirms that the way to pass to larger modules can better solve the problem, especially if you do not have the most complete and advanced calculation regulations. clearly you will have a quite overflowing bending factor.

 

[Raffaele98]

I have hypothesized two stages; Following the niemann I calculated, through the optimization for the minimum volume, the transmission ratio of the first stage that exits me 7,4 and I went ahead with the sizing.
is it correct as reasoning?

 

[meccanicamg]

I have hypothesized two stages; Following the niemann I calculated, through the optimization for the minimum volume, the transmission ratio of the first stage that exits me 7,4 and I went ahead with the sizing.
is it correct as reasoning?

In principle, however, it is not said that it is really the best solution. is quite challenging a 7.4 reduction report....
what procedure and formulas did you use to determine the minimum volume?

 

[Raffaele98]

good morning the formula I used is:

 

[meccanicamg]

I tried sometimes to use that foula but eventually you have to impose the first reduction report.
then it would be to see whether it is verified or not and also here...they come into play a lot of factors that can change the destiny.... However case it wants us to pass 100kw-1400rpm with corners 12° of helix and cementing steel.
but are we sure that there is not a pair of gears that occupies less volume?
in your case you can also put i=8 in the first stage and the second will always be 28/8.

I can't understand how and when the formula can work properly. that of the three stages is even more unbalanced and I still find less applicability. I saw that with total 12 ratio then he imposes an i1=6,something.... then there makes sense.

Did they explain something more to you?

 

[Raffaele98]

hi, the prof told us only to choose the material and apply the 22.1/8 to calculate u1; once chosen the material we can fix b/d1 and then find lambda and then proceed with the verification.

 

[Raffaele98]

Ah, I forgot, good party to everyone.

 

[Raffaele98]

having chosen a cementing steel, b/d1<=1,1 and I chose 0.8.

 

[meccanicamg]

having chosen a cementing steel, b/d1<=1,1 and I chose 0.8.

Indeed, since there is this variability I am not convinced that at the end there is the least volume of the reducer because it is not said that if I use b/d1=1,1 has the same characteristics of resistance of b/d1=0,2.

 

[Raffaele98]

I understand what you mean, but I don't know how to proceed now. the prof so showed us and neither did I, sincerely I am so convinced.