Extra Edition / Technical

Explaining Static vs. Dynamic Sheave Balancing

April 19, 2010
/ Print / Reprints /
ShareMore
/ Text Size+

BALANCING

Before detailing the differences of static vs. dynamic, let’s first explore balance and its importance to sheaves and the overall drive. When an object like a sheave or even the wheel on a car rotates, centrifugal force causes the mass to naturally move away from the axis of rotation. If a sheave is not balanced, it will have an inherent uneven distribution of weight. This uneven weight distribution (even very minimal) magnifies vibration and noise when rotated and as speed of rotation increases. Unbalanced sheaves can also lead to premature life of other drive components due to the vibration and stresses placed on the components. In order to balance the sheave, we must remove small amounts of material (weight) so that the center of the sheave becomes optimally concentric with the axis of rotation.

STATIC BALANCE

The Mechanical Power Transmission Association (MPTA) is a body of manufacturers, including Browning, that defines criteria for the manufacture of power transmission products including sheaves. Static sheave balance is defined by MPTA as “one plane or static balance.” MPTA states, “A rotating body is said to be in static balance (sometimes called standing balance) when its center of gravity coincides with the axis upon which it revolves.” One plane balance is the recommended norm for most sheave products. As a result most sheaves, such as Browning’s, are statically balanced. The MPTA body corrects for static imbalance by removing weight (typically a drilled hole) from the heavy spot.

NOTE: MPTA one plane balancing guidelines are based on the allowable peripheral speed of cast iron (6,500 ft/min or 33 m/sec).

DYNAMIC BALANCE

With dynamic unbalance vibration also occurs when the part is rotated. MPTA states “dynamic unbalance is a condition where opposite radial centrifugal forces are acting on a sheave but not in the same radial plane. These centrifugal forces form an unbalanced ‘couple’ tending to cause vibration at each end of the sheave, but in opposite directions as shown below.”

Correcting this condition requires a machine that can balance each end independently of the other end. For critical applications or when the sheave is to be operated at a high rpm, a two plane dynamic balance is recommended.

Warning: MPTA and Browning stress - When belt speeds exceed 6,500 feet per minute, special materials must be used. Contact the manufacturer for assistance in selection.

SUMMARY

Static balance is the most common form of sheave balancing and most applications do not require dynamic balance. For those applications that do, manufacturers such as Browning can perform dynamic balancing for an added charge. However, it is best to speak with an application engineer to determine if the application is a candidate.

Reprinted with permission from the Browning Belt Drive Monthly published by Emerson Industrial Automation. For more information, visit www.emerson-ept.com.

Publication date: 04/19/2010

Did you enjoy this article? Click here to subscribe to The NEWS Magazine

Recent Articles by Don Sullivan

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

2014 ACI Home Performance Conference

The 2014 ACI National Home Performance Conference & Trade Show was held in Detroit.

Podcasts

NEWSMakers: Michael Willburn

Michael Willburn, president, Infloor Heating Systems, joins the program to discuss his company, radiant heating, industry trends, and whether contractors are becoming more interested in radiant heating. Posted on July 11.

More Podcasts

ACHRNEWS

NEWS 07-21-14 cover

2014 July 21

Check out the weekly edition of The NEWS today!

Table Of Contents Subscribe

R-22 PHASEOUT POLL

Some in the industry are calling for the EPA to halt production of R-22 as of 2015. What do you think?
View Results Poll Archive

HVACR INDUSTRY STORE

plumbing-hvac.gif
2014 National Plumbing & HVAC Estimator

Every plumbing and HVAC estimator can use the cost estimates in this practical manual!

More Products

Clear Seas Research

 

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

DON'T MISS A THING

Magazine image
 
Register today for complete access to ACHRNews.com. Get full access to the latest features, Extra Edition, and more.

STAY CONNECTED

facebook icontwitter iconyoutube iconLinkedIn i con