dimension to oblique fatigue beats.

[Ritberger]

Hi, I'm new, and I hope I'm not wrong section.
My question arises from the classic project of construction of machines and I hope to be able to post it here.
I should dimensional a double row oblique roller bearing.
the bearing is mounted on the shaft of a small angle head (6n*m to 500 rpm maximum torque).
I schematized the cinematic bond provided by the bearing as a zipper and a spaced trolley of the distance provided by the catalog (hinge point).
I solved the system 1 time hyperstatic, resulting from the bond provided also by the other bearing and got the binding reactions of the two hinges, which of course are opposite.
I ask you how it would be more appropriate to behave for the fatigue dimensioning of the bearing, what load value do I take the largest? or should I also consider the opposite that is smaller than a 30%?
the two reactions should spring from two different tracks then to the most there will be on a track the maximum action, or is it wrong?

Thank you very much and apologize for any errors due to inexperience.

 

[meccanicamg]

Hello Ritberger,
If you had read the forum rules, you would have answered the first question alone.

first I didn't understand what bearing you need to check: you write double row oblique rollers. I think there's no bearing like that.

if it is an oblique to 2 crowns balls is not an oblique roller. It is true that both are adjustable and hinge while roller toroidals (skf carb) do as a cart.

if the system is formed by hinge and cart is isostatic and not hyperstatic 1.

if you have two hinges is hyperstatic 1.

pay attention to the axial constraints that are placed on the tree and the hub, because I tell you that if you do well the bonding systems arrive to make hyperstatic 2 and 3. increasing hyperstaticity requires the mechanics of the shaft to be sufficiently insensitive to the load.

fatigue testing and/or sizing are based on the canonical formulas indicated in the catalogues of the major bearing manufacturers. Keep in mind that each bearing will have to bear a certain load and not the maximum for both (if you have calculated the equivalent reactions and loads you will know that forces gravitate on each cux).

If you need some theory and books/manuals at your disposal there is no sufficiency I suggest you look at the site of theskf which has the explanation section and modules for calculation of duration.

If you need more, be clearer and receive more targeted explanations:finger:

 

[Ritberger]

Hello Ritberger,
If you had read the forum rules, you would have answered the first question alone.

first I didn't understand what bearing you need to check: you write double row oblique rollers. I think there's no bearing like that.

if it is an oblique to 2 crowns balls is not an oblique roller. It is true that both are adjustable and hinge while roller toroidals (skf carb) do as a cart.

if the system is formed by hinge and cart is isostatic and not hyperstatic 1.

if you have two hinges is hyperstatic 1.

pay attention to the axial constraints that are placed on the tree and the hub, because I tell you that if you do well the bonding systems arrive to make hyperstatic 2 and 3. increasing hyperstaticity requires the mechanics of the shaft to be sufficiently insensitive to the load.

fatigue testing and/or sizing are based on the canonical formulas indicated in the catalogues of the major bearing manufacturers. Keep in mind that each bearing will have to bear a certain load and not the maximum for both (if you have calculated the equivalent reactions and loads you will know that forces gravitate on each cux).

If you need some theory and books/manuals at your disposal there is no sufficiency I suggest you look at the site of theskf which has the explanation section and modules for calculation of duration.

If you need more, be clearer and receive more targeted explanations:finger:

Thank you very much.
I was wrong to write I jumped out reels not so why.

the bearing is oblique ball bearing two crowns skf 3205 a
I schematized his bond with a zipper and cart.
the system is hyperstatic 1 because on the other side of the tree there is the radial ball bearing skf 6004 that I schematized with a cart.

I used skf fatigue sizing formulas but with regard to the radial load agent on the single double crown bearing I didn't know what to use, I hypothesized precisely that the fatigued load was the highest agent on the zipper that patterned part of the bearing.
my problem derives precisely from having schematized the bond of the bearing in two constraints and therefore having two reactions I was undecided on how to behave .
I used the greatest reaction because in the worst case on a track it will act that load and on the other track will act the other reaction.
I wanted to know if the reasoning is correct.
I turned to you because it is two days that scartabello books but beyond 4 words on the cross on the assembly to "o" or the assembly to "x" I did not find.

thanks to everyone for the attention

Have a good day.

 

[meccanicamg]

Please. then the skf 3205 a bearing is an oblique ball bearing, with two crowns, without non-adjustable seals, so if binding suit on both the shaft and the hub becomes a whole allowing only the rotation of the shaft. defined as this is not schematizable as a double-winner (circum + cart) but it will be a recess with vertical reaction, horizontal and moment. the skf 6004 bearing is a radial bearing to a ball wreath and if tied axially stuck on the shaft and free axially in the hub or vice versa can be schamatized by a cart constraint.

It should be noted that both bearings do not allow hinge style rotation (except a small fraction of degree) therefore if subjected to strong loads it is good to evaluate hyperstaticity 3 (incastro-incastro). Keep in mind that using non-adjustable bearings and load strongly you go to increase the axial force on the rolling slopes of the desired elements leading to a premature break of the bearing itself.

to verify the type of constraint hypothesis should be evaluated the bending and therefore the angle of rotation near the bearings and compare them with the maximum value admitted by the bearing itself.

the practice says: short and big tree can be loaded so much and not flet. long and fine tree, loaded little or so it stings. if loaded little ok, otherwise use adjustable bearings.

with adjustable systems increase deformations on the tree but become less dangerous on the supports. It is always a matter of designing an element that breaks before the other creating less physical and economic damage.

ps: I believe that a fundamental error in teachers and in some texts is: It is not that a radial bearing is a cart and a conical roller is a zipper only because the first has radial predominant reaction and the second has almost equal in two directions. There are always assumptions upstream of a more or less realistic bond choice according to circumstances. If you're wrong to think something breaks.

 

[atofras]

hi to all I found interesting the discussion and I introduce myself given my little knowledge on the bearings to ask you that you are prepared as I can do to understand how to choose, I don't think just take a catalog to do it. how to calculate the forces that act and how to place it on the trees where they are stuck? I know there must be some tolerance, so how do I move?

 

[Zanna91]

hi to all I found interesting the discussion and I introduce myself given my little knowledge on the bearings to ask you that you are prepared as I can do to understand how to choose, I don't think just take a catalog to do it. how to calculate the forces that act and how to place it on the trees where they are stuck? I know there must be some tolerance, so how do I move?

hi, I found this file in pdf very intuitive: http://nazzarenocorigliano.interfree.it/calcolocuscinettivolv.pdf :finger:

 

[meccanicamg]

hi to all I found interesting the discussion and I introduce myself given my little knowledge on the bearings to ask you that you are prepared as I can do to understand how to choose, I don't think just take a catalog to do it. how to calculate the forces that act and how to place it on the trees where they are stuck? I know there must be some tolerance, so how do I move?

Hello atofras,
definitely the link they posted to you is intuitive and is quite simplified calculation procedure. if you go to the skf site there is the part of theory and you will see how to make calculations, duration verification etc.

for the choice of bearings, I would say that it depends a lot on applications and costs. of course also from the inherent characteristics of the bearings: orientation possible or not, decrease games on axial load, high speed applications, reduced encumbrance etc etc.

I would say it is worth turning some site of bearing manufacturers and integrating with a manual.

I do not know how much it can give you an exhaustive overview.

 

[atofras]

even if I can choose the bearing we remain a doubt at the base on how this should be placed on which bond at a certain point and to which I allow an axial movement more I do not know what game there must be between bearing and tree

 

[meccanicamg]

even if I can choose the bearing we remain a doubt at the base on how this should be placed on which bond at a certain point and to which I allow an axial movement more I do not know what game there must be between bearing and tree

tolerances see catalog skf... go to the site and look for.... there is table trees and table holes