Re: Pulley Shaft Bm Vs Locking Element
Yes, but where did you get 20%? Most, but not all locking devices take more than 20%. More important, what type of locking device are you talking about?
We have a strong expertise in the design and application of various locking devices and their design criterion.
The solution maybe:
1. larger diameter shaft
2. wider locking element
3. lower locking pressure
4. more flexible end disk
5. shallower angle of locking wedge
6. different locking device
If you are talking about a Ringfeder type, the failure results in bolt loosening and then fatigue failure, wedge ring fatigue failure, plasticity of the shaft and/or hub which leads to a number of failures, and/or bolt tension failure.
Also important is how you quantify the bending moment. This analysis is complex and includes the stiffness properties of the shaft, locking device, hub, end disk, and shell.
I do not know why you question the locking device deflection requirement. No one knows what the deflection properties of the locking device is. No one has tested these properties on a significant scale.
I asked this question of the manufacturers about 20 years ago. I proposed to analyze the same. I estimated it would then take about a year to catalog all with a generalized parametric model. I further asked if the mfgrs. would be willing to bench test them so the results could be applied to pulley design. Nada! ■
Re: Pulley Shaft Bm Vs Locking Element
It is a Mav locking element. 6903. Literature states 22%. I just used a rough value for converstational purposes.
To comment on your solutions
1. larger diameter shaft (This is what I am trying to avoid)
2. wider locking element (Means wider end disk which will add further complications)
3. lower locking pressure (Does this mean not applying design torque to the bolts. This I would imagine would lower the transmissible torque which would then lower the allowable bending moment torque. Please explain?)
4. more flexible end disk (Already grade 250 on a standard design shape. Are you suggesting a profiled end disk or similar. How would this help the locking element bending moment.)
5. shallower angle of locking wedge. (Reliant on device see point 6)
6. different locking device ( Not my design I only looked over it. However most locking devices of this thickness are roughly the same as because of points 2 and 5 shown above.)
Are all of the faluires fatigue failures? Hence only loads that fall under fatigue loading need to be used.
I know how complex the analysis can get. I am just doing some quick ball park checks of others work.
Diameter of the shaft changed from 100 to 130 because of the locking assembly design.
Best Regards,
Gareth Blakey
blakeyg@conwag.com ■
Re: Pulley Shaft Bm Vs Locking Element
Dear Sir,
depending on the relation of stiffness of pulley body (shell+discs) and shaft only a certain amount of the 100% bending moment is transferred through the locking elements. Due to the structure and the design of the locking device itself PLUS the additional stress that is occuring when a hub to shaft connection is carrying a rotating bending moment, the trasferrable bending moment is limited to a value that the locking device manufacturer should tell. In my opinion it does not make sence to use high strength steel for the shaft and combine it with a locking device (of a smaller size) that can not carry the load. As a rough guideline: use low strength steel in combination with locking elements with lower bending moment capacities and vice versa. In case of further information or details required, please let me know. ■
Re: Pulley Shaft Bm Vs Locking Element
Points:
2. Wider locking device does not equal wider end disk - maybe wider hub
3. You have not stated if it is a drive or non-drive - lowering the bolt torque does lower the contact pressure that may alleviate excessive bending stress concentration. We are talking generalities used in design
4. End disk flexity has nothing to do with steel strength - elastic modulus does not vary. It only has to do with geometry
5. Locking devices have differing taper angles - by example Ringfeder narrow verses wide device. Their short width device does not have a self locking taper and therefore can put undesirable tensile cycling load on the bolts. Their wide seris 1012 and 1015 have self-locking tapers and do not put unacceptable bending cyclic loading on the bolts.
Just doing some ball park assessments.
Hiring an expert can be an education. ■
Re: Pulley Shaft Bm Vs Locking Element
2. True but the way this pulley is designed is very basic. Uses the same width at the hub.
3. Yes it is a drive pulley
4. Realised my mistake as soon as I pressed submit. As stated in point 2 using very basic pulley design for this conveyor so would not want to complicate manufacture by using a fancy end disc.
5. Did not think about the cyclic loading of the bolts. I would hope the manufactures took this into account when rating the locking element.
If I am ever given the money I will hire an expert. I would prefer an expert on a more exciting topic however.
Unfortunately small, non revolutionary, projects do not get the time or money you would be used to on the more prestigious project.
Thanks for your assistance. This forum would not be as useful without you.
Best Regards,
Gareth Blakey
blakeyg@conwag.com ■
Re: Pulley Shaft Bm Vs Locking Element
The control of the bending moment is a bit tricky. You can, and some have, use a wider locking device than the flat plate end disk width. The critical condition for the locking device and pulley assembly is the shaft notch stress concentration at the initial contact between shaft and locking device. This is not the critical condition of the locking device. You may ask more about this. I will not answer.
I do not wish to open a can of worms. Just a note that not all suppliers of pulleys do the necessaries on the point of failure of the shaft. Not all understand the locking device. They rely on others to guide them and so on.
Fancy. who makes it fancy. How about appropriate. Everybody competes for the same business. Caveat Emptor (CE). How do you know the pulley design is adequate unless you can evaluate it with accuracy.
Regarding the bolt failures. The more conservative "big houses" select weeny shaft deflection criteria without contribution of the end disk and shell stiffness. Its not their money. Smaller OEM's let the mfg. do the work and gets a more competitive $$$. Which is right? If the mfg. does not have the capacity to do the complex analysis and know what the controls are, CE. Big Houses use belts and suspenders.
I do appreciate your compliment and patience with my acerbic attitude.
. ■
Re: Pulley Shaft Bm Vs Locking Element
Dear Mr. Blakey,
if it is helpful for you please let me know the following:
-pulley load (T1+T2)
-torque
-pulley diameter
-shell length
-centre to centre of discs
-centre to centre of bearings
-is there any load to consider from the drive?drive connected rigid to the pulley shaft (hollow shaft gear box or flange coupling)?
and it would be my pleasure to carry out some calculations and inform you about the result (shaft diameters, shell and disc thickness, type of locking device).
Best Regards from Germany, ■
Re: Pulley Shaft Bm Vs Locking Element
Alex Witt,
What method do you use to analyse pulleys?
Being from Germany I hoping you have the Shitzwohl paper as I believe that is were it originated from.
I have a few simplified methods I use for ball park work with some many flaws.
I started looking at creating a program for a full analysis but got lost in the maths and gave up. I will hopefully, when got time, setup something using an existing FEA package as the template.
Best Regards,
Gareth Blakey
PS. I would have thought you need contact angles and angle of wrap? ■
Re: Pulley Shaft Bm Vs Locking Element
Gareth Blakey,
the basic foundation of my program is the theory of Lange and Schmoltzi, but I have added a lot more, such as the calculation of the allowable stresses in the pulley weldings, because this is the area where the most problems are. Further some material specific data are considered, since it is not only necessary to know the existing stresses, but also the allowable stresses in order to be able to design and fabricate optimized pulleys for all applications.
I assume a wrap angle between 180° and 210° (drive pulley).
The paper you are talking about is not in my hands.
Regards, ■
Re: Pulley Shaft Bm Vs Locking Element
Alex,
I am impressed. Did you write the program yourself? Did you buy it? Did you modify any of the Lange formulas as I have been told that there are errors in them. That is where I got lost in the maths. What did you write the program in? How long did it take you?
Sorry for the bararge of questions, it is just that I attempted to write one myself.
Pulley information. (Bit of a strange one as it in a shuttle module)
T1 = 23kN @ contact angle of 13 deg from 3 O'Clock
T2 = 9kN @ contact angle of 13deg from 3 O'Clcok
Wrap angle = 180deg
Dia = 540mm
Locking assembly width = 600mm
Shell Face Width = 750mm
Bearing Centers = 1168mm (I did not come up with this dimension)
Distance from bearing to start of hollow gearbox = 323mm
Shaft mounted drive
Torque arm length = 400mm
Torque arm angle with horizontal = 238 Deg from 3o'clock
Center of Gravity = 520mm
Overhang = 358mm
Think that is everything.
Thanks I look forward to hearing more about your program.
Best Regards,
Gareth Blakey
blakeyg@conwag.com
ps. If a drawing makes it easier send me an email address. ■
Pulley Shaft BM vs Locking Element
Dear All,
Does anyone understand why the locking element should only support 20% (Depends on brand and type) of it rated torque in bending?
What failure mechanism does this cause? How is this different to the deflection requirement of locking elements?
What is the best locking solution when the bending moment is high.
Best Regards,
Gareth Blakey
blakeyg@conwag.com ■