Take the right steps to ensure proper drive belt alignment

Misalignment is one of the most common causes of premature belt failure. Depending on its severity, misalignment can gradually reduce belt performance by increasing wear and fatigue. Or, it can destroy a belt in a matter of hours or days. While the forms of misalignment may be fairly well understood, accurate measurements and acceptable limits must be determined if maintenance personnel are to...

06/01/2006



Misalignment is one of the most common causes of premature belt failure. Depending on its severity, misalignment can gradually reduce belt performance by increasing wear and fatigue. Or, it can destroy a belt in a matter of hours or days.

While the forms of misalignment may be fairly well understood, accurate measurements and acceptable limits must be determined if maintenance personnel are to take corrective action.

Types of alignment

Basically, any degree of misalignment, angular or parallel, will decrease the normal service life of a belt drive (Fig. 1).

Angular misalignment results in accelerated belt/sheave wear and potential belt stability problems with individual V-belts. A related problem, uneven belt and cord loading, results in unequal load sharing within multiple belt drives, and can lead to premature failure. Joined V-belts can suffer tie band separation when operating under misaligned conditions. Belt application engineers caution that angular misalignment has a severe effect on the performance of synchronous belt drives.

Symptoms such as high belt tracking forces, uneven tooth/land wear, edge wear, high noise levels, and tensile failure due to uneven cord loading are typical indicators of misalignment. Also, wide synchronous belts are more sensitive to angular misalignment than narrow belts.

Parallel misalignment results in accelerated belt/sheave wear and potential belt stability problems with individual V-belts. Uneven belt and cord loading is not as significant as with angular misalignment. Parallel misalignment affects V-belts more than synchronous belts. V-belts run in fixed grooves and cannot free float between flanges as synchronous belts can to a limited degree.

Parallel misalignment is generally not a critical concern with synchronous belt drives as long as the belt is not trapped or pinched between opposite flanges, and as long as the belt tracks completely on both sprockets.

Synchronous sprockets are designed with face widths greater than belt widths to prevent problems associated with tolerance accumulation, and to allow for a small amount (fractions of an inch) of mounting offset.

As long as the width between opposite sprocket flanges exceeds belt width, the belt will automatically align itself properly as it seeks a comfortable operating position on both sprockets. It is normal for a synchronous belt to lightly contact at least one of the sprocket flanges in the system while operating. Synchronous belts rarely run in the middle of the sprockets.

Measuring misalignment

The best tool for measuring misalignment is a laser alignment device. However, if one is unavailable, the next best tool is a straightedge such as a long level, a strip of extruded aluminum, a ruler or, as a last resort, a piece of string, depending on the center distance of the drive (Fig. 2). The straightedge is used to project the orientation of one sheave or sprocket face with respect to the other.





When preparing to measure parallel misalignment, the maintenance technician must first verify that the edges of both sheaves and sprockets are of equal thickness, or quantify the difference in thickness. It is important to align the sheave grooves or sprocket faces directly in line with one another, rather than just the outside surfaces of the sheaves or sprockets flanges. It may be necessary to mount sheaves or sprockets with the outside surfaces offset with respect to one another to properly align the grooves or sprocket faces.

Sprocket flanges should also be inspected to be sure they run true. A bent flange could result in erroneous measurements if the straightedge rests against the outside edge of the damaged flange during the inspection process.

To determine how much misalignment is acceptable and at what point it becomes excessive, the alignment must first be measured, quantified and compared to the belt manufacturer’s recommendations for the particular type of belt. These recommendations can be found in drive design manuals.

Quantifying misalignment

Misalignment can either be quantified mathematically, or compared to general rules of thumb for quick and easy results. While using a straight edge to project the plane of the outside face of sheave or sprocket #1 with respect to sheave or sprocket #2, angular misalignment can be quantified as the difference in clearance between the straightedge and the outside surface of the sheave or sprocket #2 across the diameter (Fig. 3).

Parallel misalignment can be quantified as the difference in clearance between the straightedge and the outer surfaces of the two sheaves or sprockets across the separation distance (Fig. 4).

The total allowable misalignment recommended for V-belts is generally

The total amount of misalignment recommended for synchronous, urethane 60-deg belts and poly-V belts is

When determining if a V-type drive system is aligned within these recommendations, the angular and parallel misalignment must be measured and quantified individually, and then added together. The sum of angular and parallel misalignment can then be compared to the belt manufacturer’s recommendations for the particular type of drive.

Sprockets for synchronous belts are made with face widths greater than the belt width to prevent belt fit problems from tolerance accumulations. This additional sprocket face width allows the belt to free float across the sprocket faces.

Because synchronous belts are particularly sensitive to being pinched or trapped between opposite sprocket flanges, sprockets must be installed so there is clearance between the edge of the belt and the flanges on both sides. If clearance between opposite sprocket flanges and the edges of the belt is present, parallel misalignment does not need to be quantified and added to the angular misalignment.

Rules of thumb

Maintenance technicians may not always find it practical or possible to accurately calculate the total misalignment in a system while determining if it is in acceptable alignment. It is also difficult to visualize small fractions of an angle such as

For V-belt drives:

 

For synchronous, 60-deg angle, and V-ribbed drives:

 

These rules can be used to estimate the amount of angular and parallel misalignment visually rather than having to calculate actual numerical values.

For example, for a synchronous belt drive to be within the belt manufacturer’s recommendations for angular misalignment, the distance from the outside surface of the sprocket to the straightedge should not differ by more than 1/16-in. across a 12-in. diameter.

For a sprocket with a 6-in. diameter this difference should not be more than 1/32-in. If the difference is greater than this, or the calculated angle is in excess of the maximum recommended value of

Misalignment can be an obstacle for satisfactory synchronous and V-belt drive performance. In many cases it is not easily detectable in complex drive applications. Maintenance technicians should also check related components, such as brackets and platforms, for proper design and placement. These parts must be strong enough to withstand the peak forces exerted by the belt drive without bending or flexing.



The Bottom Line...

Misalignment can reduce belt performance or destroy a belt.

Two types of misalignment must be checked for, angular and parallel.

Misalignment can be checked with a straightedge or a laser.

Misalignment can be quantified mathematically or quickly by using rules of thumb.

Gates Belt Preventive Maintenance and Safety program provides user tips ranging from inspection to installation of V-type and synchronous belt drives. Also included is information on reducing downtime, controlling parts replacement costs and increasing energy savings. To schedule a free belt preventive maintenance seminar at your facility, download a copy of Gates 48-p “Belt Drive Preventive Maintenance and Safety” manual or sign up for Gates free weekly “Belt Tips” e-mail service atptpasupport@gates.com.

Article edited by Joseph L. Foszcz, Contributing Editor, Plant Engineering magazine, (847) 657-8933,malfoz3@comcast.net.

Power trans, motion control sales are showing strength

Sales of power transmission and motion control products showed continued strength in the first quarter of 2006, according to a report from the Power Transmission Distributors Association.

The March trend data for distributors and manufacturers of power transmission/motion control products showed year-to-date sales up 11.7% as compared to sales for February through March 2005. Sales increased 3.9% over the previous month and were up 12.6% compared to March 2005.

For March, the confidence level of U.S. distributors rose to 7.3 from 7.0 in February on a 10-point scale.

In March, U.S. manufacturers’ year-to-date sales of power transmission and motion control products grew 10.2% as compared to sales for February through March 2005. Sales were up 4.4% over the previous month and increased 9.4% as compared to March 2005. As compared to February, sales of mounted bearings, unmounted bearings, standard industrial motors, variable speed drives, positioning system/linear motion products, gear products, mechanical drive systems and other power transmission products, clutches and brakes, and shaft couplings increased.

Year-to-date orders from U.S. manufacturers grew 9.6% as compared to 2005. March orders decreased 9.4% over February, but were up 5.4% as compared to March 2005. The confidence level of U.S. manufacturers rose to 5.7 in March from 5.6 in February on a 10-point scale.

For more on the Power Transmission Distributors Association, go to

Honeywell’s Jack Bolick: Changes will transform plant operations

As president of Honeywell Process Solutions, Jack Bolick heads one of the leading solution providers on the plant floor. Bolick joined Honeywell in 1998 and has more than 20 years of diverse business experience with a focus on semiconductor and manufacturing materials supply, global marketing, and manufacturing strategies that support high-growth markets. Bolick is Six Sigma Black Belt-certified and holds a master’s degree from North Carolina A&T State University. Bolick talked with PLANT ENGINEERING editor Bob Vavra about how new solutions are leading to rapid change on the plant floor.

Q: Your 2006 User Group meeting in Phoenix in June was called, “Adapting to Change”. The pace of change in process automation seems to be accelerating today, and it was pretty fast to begin with. What’s driving the change?

Bolick: Economics, economics, economics: energy costs are rising, the availability of natural resources is declining, global demand is growing, and environmental controls are tightening. Processors around the world are challenged to produce more with fewer inputs, greater efficiency and less impact on the environment. Furthermore, as companies merge and acquire disparate global facilities, they need an enterprise-wide view of the supply chain to meet these challenges.

Technology enables processors to gain that enterprise-wide view and more rapidly adapt to the changing dynamics of the marketplace. Most of these challenges can be dealt with more quickly through open systems, which in and of themselves are driving change at the plant-floor level.

Q: We’ve seen the emergence of manufacturing execution systems. What impact will these systems have on the plant-floor level workers? What changes should plant managers and plant engineers be prepared for?

Bolick: It depends on the degree to which a company takes advantage of the business transformation opportunity that MES offers. Plant-floor level workers might simply be doing the same tasks they’ve always done, except with new tools that automate the process. Or, their tasks and workflow could be completely transformed %%MDASSML%% instead of collecting data they will be managing information and making decisions.

Regardless, in the short term, workers will definitely see a greater amount of data and more frequent data exchange with the plant floor. Longer-term, we expect plant-floor workers will be performing more and more MES-level functions and having more direct impact on and responsibility for business results.

It’s important to note that MES integration is a great opportunity for plant managers and engineers to identify ways to make the plant run better and the information required to do it. Since the success of an MES depends on its acceptance by plant-floor workers, plant managers and engineers should be prepared to lead the transformation with substantial input from plant-floor workers

Q: Where do you see the manufacturing growth coming from? How do companies such as Honeywell prepare to meet the emerging technology needs of these new markets?

Bolick: In today’s manufacturing world, knowledge is power and technology holds the key. Manufacturing companies grow when they have the ability to capture knowledge and make decisions rapidly. For the foreseeable future, we anticipate that our customers will need to embed more knowledge in their systems and they will depend on those systems to help them more effectively and efficiently manage their facilities.

We also expect continued demand for technology that will help customers become more operationally competitive %%MDASSML%% for example, by doing a better job of managing resources or anticipating supply and demand.

At Honeywell, we keep in touch with our customer’s emerging technology needs by staying in touch with our customers. That may sound simple, but the degree and frequency with which we maintain that contact really sets us apart. We hold Users Group Symposiums at five locations around the world each year including this year’s kick-off event for the Americas in Phoenix.

In addition to having a User Committee that drives the symposium content; we also have several customer advisory boards that provide direct input into Honeywell’s long-term technology roadmap. Our User Input Subcommittee decides which specific enhancements we design into current and future releases.

Our customers make significant commitments to working with us on future features and architectures %%MDASSML%% and we’ve made a significant commitment to them.

Q: Is there’s something still revolutionary out on the horizon?

Bolick: Wireless is, of course, the wave of the future. I predict we’ll see rapid adoption across all process industries as users see more and more proof that the technology is effective, secure and reliable. Furthermore, we’ll see wireless applied in new and creative ways as a problem-solving tool for automation.

The best example of this is the use of wireless to predict and detect corrosion for highly profitable, yet highly corrosive processes. Case in point: Wireless corrosion sensors that help refineries take advantage of cheaper, more corrosive crude oils while protecting their equipment.



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