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electricpete

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Reply with quote  #1 
When reading the link in the thread I have cracks and breaks in a Screening, I saw mention of a "self-tensioning motor base" (for vee belt drive motor). 

I never heard of that. We might benefit since we seem to have a lot of trouble with belts.  Googling led me to these two links below.  The first (pdf) seems straightforward to me. The 2nd (video ), a I didn't understand exactly how it works.  Anyone have experience or thoughts on a self-tensioning base? 
1 - 
http://www.regalpts.com/PowerTransmissionSolutions/Other/Belt%20Drive%20Monthly's/Form_9887E.pdf

2 - 



John from PA

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Reply with quote  #2 
Video at https://www.rosta.ch/wAssets/videos/ROSTA-self-tensioning-motor-base.mp4
Walt Strong

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Reply with quote  #3 
The Rosta base uses a combination of gravity weight force (offset CG) and torsional spring force from rubber elements. I prefer sheave alignment by laser to correct both angle and offset, especially for multi-belt drives. I prefer the sonic belt tension method. The belt tension should be periodically checked with steel of rubber spring motor base in case of loosening or wear causing reduced tension.

Note the link in the discussion about cracked screening that shows a MEKA vibratory screen with a Rosta motor base!

Walt
electricpete

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Reply with quote  #4 
Thanks Walt, I understand now how that Rosta works. The motor sits on a flat plate. The blue thing below the flat plate is the torsional spring you mentioned. It pushes the flat plate in a direction to tilt away from the opposite sheave. 

I guess the pretensioning devices shown here move the torsional spring to a different part of it's range, which  changes the spring constant and adjusts the target belt tension higher or lower.
https://www.rosta.ch/en/products/docs/Tensioning-Technology/MB_50_Englisch_3.pdf

You mentioned possible loosening. I wonder how much windup there is in the torsional spring (does a small movement from loosening or belt stretch dramatically affect the spring constant).


Walt Strong

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Reply with quote  #5 
"I guess the pretensioning devices shown here move the torsional spring to a different part of it's range, which  changes the spring constant and adjusts the target belt tension higher or lower."

The spring constant does not change (within linear range), since the pretension device changes the angular deflection (position) and thereby the torsional force. The torsional spring force (not spring constant) produces a linear force acting in line with the sheave centers, depending on the torque arm distance.

The document you attached states that belt tension should be checked a few days after new belts are installed. That is pretty standard with most rigid motor bases, so one would expect the Rosta base should accommodate the new belt stretch! Elastomers can behave with nonlinear stiffness whether used as a shaft coupling, vibration isolator (mount) or torsional spring. This should not be a big issue if product is used within rated load/deflection range. Elastomer materials can deteriorate over time and possibly change stiffness. Installation of a constant belt tension device does not eliminate the need for periodic belt tension checks along with visual inspection and condition monitoring by vibrations, ultrasound (preferred), and temperature.

Walt
Dan Timberlake

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Reply with quote  #6 
Hi Epete,

Care to share some specifics about "a lot of trouble with belts" ?

If the troubles are  the vibration dudes issuing reports flagging excessive 1X and belt frequencies, especially inline with the belt strands, then the reports will probably decrease on the driven equipment. But very likely increase on the motor.

Despite the common "mmrrmm  vibration bad"  mantra, I'm of the mind bearing life just might increase due to lessened belt load increases during spike increases from sheave runout and belt fat spots.

I did not study the spring base construction, but it would take a very seriously designed device not to continually wear steel-on-steel pivots from the non-stop oscillation.

** https://www.youtube.com/watch?v=YfT7K7WNpdQ

regards,

Dan T  
RustyCas

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Reply with quote  #7 
Quote:
continually wear steel-on-steel pivots 


Dan, unless I'm seeing it wrong, there is no steel-on-steel pivot... the motor rests on and pivots on the elastomer torsion springs.

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OLi

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Reply with quote  #8 
You have to excuse me I am not happy about mounting motors on structures. We have our fair share of quick swap belt motor mounts and various and some in some cases do work or don't make thins worse but mix it with VFD and I normally get things to add in the reports, maybe I am not lucky with things like that but it is my experience. Add modern motors that maybe now are getting outdated that barely carry their own weight w/o support from a substantial floor and feet long as 80% of the motor..... Sorry I just don't like gadgets like this.
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fburgos

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Reply with quote  #9 

we have couple of Aerzen machines that have a similar arrangement, less sophisticated, just a pivot.

I've aligned those pulleys without the belts and is very easy, when belts are installed alignment is checked but never notice a change, I just assume belt tension is ok.

Dan Timberlake

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Reply with quote  #10 
The  Browning Tenso-Set QR movable base looks have two square tube guides running on round fixed bars.  I'm guessing the "self tensioning" means the base/square tubes is forever sliding back and forth a little bit due to sheave runout and belt thickness variation, and load variations if the load varies. Unless the square tube guides have some space-aged plastic bushings inside I believe they and the rods will have essentially line contact when new, and begin wearing each other immediately.

Like others said, the Rosta design, with the rubber torsional springs, accommodates tension variations with slight rotational motion without metal to metal contact, so is better in regards to wearing out.


RRS_Dave

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Reply with quote  #11 
From the folk who build one of the best, robust motor bases I've ran across, this is their "automatic" base (see link below).
If you're looking for a regular base that is made with acme threads (larger sizes chromed) that absolutely won't rust and foul up with dust, that costs just about the same as one of the "regular" chincy bases, check these dudes out (heavy duty bases).
I don't make a dime off them, but have many happy customers after recommending them.

http://www.overlyhautz.com/automatic1.html

Dave

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