Guidelines for tracking conveyor belts

Conveyor belts are often accused of belt tracking problems, which in most cases is unreasonable. The cause of the failure is usually found in the installation itself, which may be due to poor adjustment of the pulleys and rollers, incorrect application of tracking measures or incorrect design. In order to use belt tracking methods correctly, it is therefore essential to fully understand their basic characteristics.

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It is necessary to distinguish between basic measures and additional measures for belt tracking. The former is suitable for keeping the correctly aligned belt in its center position, as long as there is no great external influence, such as lateral forces. It is necessary to use the latter when the basic measures do not suffice.

No matter what measures are taken, the following conditions are necessary to achieve problem-free belt tracking:

• Stable and strong support is essential. Various forces can act on it, such as belt tension, the load to be transported, or uneven ground.
• All pulleys and rollers must be installed at right angles to the belt running shaft. Adjustable pulleys and rollers can only be adjusted after the belt is running normally.
• All installation parts in contact with the belt must be protected from dirt and grime, and cleaned if necessary

What happens if the conveyor belt has no tracking measures at all?

When the transmission belt runs on a cylindrical pulley that is at right angles to its direction path, the force acting on the transmission belt will be parallel to the running direction of the transmission belt. No tracking force is applied to the conveyor belt.

In fact, the belt operation is in an unstable state of equilibrium, as long as it is affected by the slightest external factors such as eccentric loading of the product, dirt between the belt and the pulley, belt deformation, lateral feeding or deflection of the goods, etc., it will immediately run away .

The same situation applies to the belt running shaft if one or two pulleys are not accurately positioned at right angles. The belt will inevitably run to the less tight side.

1. Tracking rule 1

The belt crawls to one side with minimal tension. Tracking effect of cylinder-cone or radial top pulley. The cloth belt conveyor is usually equipped with at least one and sometimes several pulleys with conical or radial top. This basic measure is usually sufficient to achieve straight and stable operation.

The pulley of this shape has a self-tracking effect. If there is a changing runoff trend, or a reversal of the running direction, the belt is centered and there is no need to adjust the shaft. Detailed cylindrical conical pulley information

In a simple two-pulley conveyor that determines the running direction, the head pulley is usually the driving pulley. It is designed into a cylindrical-cone shape. When the conveyor length-to-diameter ratio (conveyor belt length to conveyor belt width) exceeds about 5 to 1, and in a device with reversing operation, it is advisable to place both the head pulley and the tail pulley on the top.

In this way, as long as the pulleys are not excessively deflected, the correctly aligned belt can remain in the center position.

Additional belt tracking measures:

For devices with obvious runoff trends and considerable lateral forces (side feeds, steering rods, a large number of belt paths, etc.), the basic use of cylindrical-cone pulleys is not enough. Additional belt tracking measures are required, but these measures will be determined by the application and operating conditions.

Guide wheel

Guide pulley, also known as control pulley, is an adjustable buffer pulley.

The guide pulley is usually cylindrical. Observe the minimum diameter of the back bend according to the instructions in the product data sheet. In order to achieve good tracking, the contact arc at the guide wheel should be at least 30°. For belts with non-sticky surfaces, wear-resistant rubber or synthetic material (recommended hardness 80-90 Shore a) friction cover can be used to improve the tracking effect.

2. Tracking rule 2

The larger the contact arc, the higher the friction and the greater the tracking effect. Keep the belt tension as low as possible and rotate the movement, whenever possible, perpendicular to the middle line of the arc of contact (plane ' B). The center distance between the end pulley and the guide pulley should be at least twice the diameter of the larger pulley. Unlike cylindrical-tapered pulleys, adjustable cylindrical rollers cannot track themselves.

This means that when the running direction of the belt changes, the pivot position of the cylindrical pulley must be reset. Since this is not feasible, it is not recommended to use adjustable cylindrical roller belt tracking reversing operation. However, exceptions can be made for long conveyors. If there is enough distance between the pulleys, they can even be used for reversing operations.

The guide wheel A tracks the belt correctly in the A direction, and the guide wheel B tracks the belt correctly in the B direction.

3. Tracking rule 3

In a set of pulleys and rollers, the roller that first comes into contact with the belt has a greater tracking effect (in the adjacent example roller A).

Return side tilt roller

If the return side skew roller is installed on the running side (head drive) before the tail pulley and the drive side (tail drive) before the tail drive wheel, the tracking effect of the return side skew roller is the greatest.

The idler is positioned below the conveyor belt, that is, on the conveying side of the conveyor belt. Due to the high friction coefficient, the tracking effect is better, but the possible tracking traces on the belt cover must also be considered.

Rollers can also be installed above the running side of the conveyor belt. It is ideal that the belt has a delicate or highly structured conveying side, or transversely mounted profiles.

It is recommended that the belt surface contact of the idler be approximately 14% of the bandwidth, and the idler inclination should be 5°*10° to achieve a satisfactory tracking effect.

If the inclined roller is at right angles to the running direction of the tape, the tape will automatically correct its position when the running direction of the tape changes. This measure also applies to commutation operations.

In the running direction of the belt, the inclined roller is tilted 8° to 10° forward at the edge of the belt, which further improves the tracking performance of the belt. Their effect can be enhanced by adding a friction cover.

However, the forward-inclined rollers cannot be used for reversing operations, because the centering force of the belt is therefore reversed.

Tilted rollers on the return side have also proven successful in tracking wide, short and thin belts at high speeds. In this case, the drive pulley and tail pulley should be installed cylindrically to avoid folding or creases.

4. Guidance profiles

The guide profile is usually v-shaped, welded or glued to the running side of the conveyor belt. Sometimes rectangular and semicircular contours are also used.

Due to higher production costs and limited effects, guide profiles are not recommended as a general belt tracking measure. Especially not suitable for guide profiles in high-speed applications, because they have a tendency to be forced out of the groove, allowing the belt to continue to run away.

The guiding profile is very suitable for counteracting local lateral forces. In this regard, the term 'lateral forces' refers to those forces that are applied to one side of the conveyor belt temporarily, such as during side loading or turning.

General rules

In principle, the belt must be tracked by the usual methods, usually cylindrical-cone pulleys. If the belt should run away, it must be prevented only by the guide profile in lateral forces.

This means that the groove size should have different sizes:

1) A groove on a guide section should be very wide, roughly 8 to 10 mm/0.31 to 0.39 mm wider than the area of no lateral force. The larger gap allows the belt to be adjusted without the guide profile permanently running the groove on the opposite side.

This is particularly true for driving, head and tail pulleys. As an exception to this general rule, the guiding profile must be considered, in short, but a wide conveyor. In this case, it is recommended to make the groove on the pulley narrower than the groove on the slider bed.

2) In the area where the lateral force occurs, that is, on the slider bed or the bearing roller, the groove should be narrow, that is, only about 4mm / 0.16 wider than the guide section.

Need to consider:

• The conveyor belt must have sufficient lateral rigidity to prevent the conveyor belt from being thrown out of the groove by the lateral force
• The minimum pulley diameter of the profile must be observed
• Under normal circumstances, it is sufficient to place a v-shaped line in the center of the belt
• For thin belts and wide bands with low lateral rigidity, two guide profiles should be used and positioned as close to the edge of the belt as possible. In these cases, both v-type and flat-type can be used.
• Bandwidth and fast running speed, it is recommended to use idler to prevent the profile from climbing out of the groove
• The edge of the groove must have a chamfer of 2 to 4 mm / 0.08 to 0.16 to prevent damage to the guide profile
• Ensure that all grooves on the belt are aligned correctly before installation. Be very careful when running in. The belt should adopt appropriate tracking measures, such as cylindrical-cone pulley. When there is no lateral force, the guide profile should not touch the sides of the groove.
• If there is sufficient clearance between the belt edge and the end of the pulley and/or adjacent frame work to prevent the belt from running the end of the pulley or colliding with the frame, the groove may be wider than specified. In addition, any required tolerances must be taken into account, product placement with the centerline or edge of the belt.

5. With automatic control

Even the most severe belt tracking issues can be solved by automatic belt control. However, this is a relatively expensive option, so the use of belt tracking behavior is either highly critical and/or where other belt tracking methods have proven ineffective, for example, long-term accumulation of contaminated rollers/pulleys.

Automatic belt control is realized by sensing the edge of the belt, and can use non-contact sensors or mechanical methods. The signal is sent to a control mechanism that drives a guide wheel to accurately position the belt.

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It is recommended to make the tail pulley into a cylindrical shape. For the cylindrical-cone tail wheel, the conflict between the two adjustment systems may cause the belt to run quite turbulently.

• Optical scanner (photocell, light barrier)
• Pneumatic sensor (air jet)
• Electric sensor (capacitive sensor)
• Mechanical sensor (micro switch, stylus)
• Control mechanism: electric (servo drive), pneumatic or hydraulic (pressure cylinder)
• Guide wheel

It is recommended to equip one side of the guide/control roller with a standard adjustment device so that the tracker assembly can be initially aligned manually. When doing this, the automatic control should be in a neutral position.

Many companies supply automatic belt tracking products, and we recommend that experts who require these devices in the installation recommend taking them.

In addition to the belt tracking measures described above, other options can be used according to specific prerequisites and application types. The advantages and disadvantages of several alternatives will be described in detail below.

Extra band packaging

Additional belt windings will be used to stabilize the track in areas experiencing lateral forces. This effect can be enhanced by covering additional pulleys. The running belt can be tracked by adjustable rollers. Horizontal adjustment (A) is only applicable to one running direction. Vertical adjustment (B) will also track belt reversing operations.

Roller with rubber

Local lateral forces can also be handled by installing multiple load-bearing rollers with friction covers. This method is not only suitable for sliding table installation, but also for roller installation. The running direction of the roller and the belt is adjusted vertically, and the tracking can also be reversing operation.

Pivot roller on load side

Cylindrical rollers are installed on the edge of the belt and tilt forward along the belt running direction. The oblique angle γ should be 3° to 12°, depending on the tape load, the friction between the roller and the tape, and the tape speed.

This method is not recommended for thin belts with low lateral rigidity. Since the belt not only runs on the drum, but also slides, there is friction, which increases the wear of the belt. This tracking method only centers the belt in the running direction. This method is only suitable for centralized and evenly distributed cargo transportation.

Combination of belt sensor and shaft rotating roller

The tracking device is suitable for heavy belts and belts with high lateral stability. These units provided by professional manufacturers can also be equipped with adjustable sensors to greatly reduce the wear of belt edges. This tracking method is only suitable for one running direction.

Horizontal guide belt and guide roller

The belt edges will wear more quickly if some measuring device is used, but only for belts of adequate lateral rigidity and edge integrity. In this respect, guide rollers are superior to transverse wear belts.

Tracking measures also apply to commutation operations. Edge guide belts are most suitable for relatively clean conveying operations, because debris may get stuck between the belt and the guide belt, causing serious belt damage and other performance problems.

The entrance of the edge guide must be radiused to reduce potential edge damage. The edge of the belt can be polished by itself. Therefore, it is wise to consider the use of durable low-friction material edge guides, such as stainless steel, phenolic (such as Delrin) and so on.

6. Short-width belt guide

The width of the conveyor belt installed on the conveyor belt is equal to or greater than the conveyor length, and it is becoming more and more difficult to guide. That is, thin belts with low lateral stiffness, especially at high speeds, have a tendency to bend and fold when cylindrical-cone pulleys are installed on a short conveying distance. Accurate industry recommends that the head and tail pulleys should be cylindrical and must be installed with absolutely parallel and square belt running directions.

The following recommended further measures should be considered to ensure effective belt guidance in these situations.

Return side tilt roller

It is suitable for wide conveyor belts with short conveying distance and adopts inclined rollers on the return journey. In order to achieve a satisfactory tracking effect, the roller inclination γ should be at least 5° to 10°, and in some cases up to 45°. This configuration provides a belt with a self-centering effect.

Likewise, this arrangement is effective for reversing operations if the roller is installed at right angles to the belt's running direction.

Center drive

It is recommended to use center drive when commutation. The drive pulley should be cylindrical-conical and, if necessary, lagging. The head and tail pulleys and the deflection rollers are cylindrical. For low speed belts, the head and/or tail pulleys can be cylindrical-conical.

Guidance profiles

If there is sufficient lateral rigidity and low speed, short and wide belts can be effectively guided by using guiding profiles. It is recommended to guide the belt on the pulley instead of the slider bed. This means that the groove on the pulley should be narrower than the groove on the slider bed.

In order to compensate for deflection at the bottom of the groove, the grooving roller must be large enough to offset it. By moving the groove to the edge of the roller, the deflection is significantly reduced. Therefore, a smaller diameter roller can be used without excessive deflection (the minimum diameter of the guide roller must be considered).

Alternative A: Parallel operation of narrow belts

In situations where a wide belt is not required, it is recommended to use several narrow belts. Tracking is easier to control.

Note: Unless elastic belts are used, each belt must be guided and tensioned separately.

Alternative B: Plastic Modular Belt

For short and wide conveyor belts, plastic modular belts are a common alternative to traditional fabric belts. The plastic modular belt is driven by a sprocket, so that the position is determined by the fixed position of the drive sprocket. When designing a modular belt, the special requirements of the conveyor must be considered.

7. Overview of follow-up measures and recommendations

We recommend that at least one and sometimes several pulleys be equipped with cylindrical-conical or crown shapes as a base measure. If this basic measure is not sufficient to achieve straight and stable operation, additional tracking measures need to be considered.

8. Checklist for design issues to avoid tracking issues

Belt tracking is a pain point for you, for your maintenance team, and for your customers. Incorrect tracking can cost you time, money and a lot of frustration, but there are a few fairly simple ways to diagnose and correct the tracking in your belt. To troubleshoot a belt that isn't tracking properly on your conveyor, use the following steps to fix the problem.

Belt issues

Continually tracking off

A belt must be cut squarely, or at a consistent angle if cut on a bias, and laced properly in order to track perfectly. If either of these are off, the belt will track off each time the lace comes around the end of the conveyor. If this is the case, you can recut the ends and relace the belt as a solution.  Sometimes belts are intentionally cut and laced on a bias angle in order to quiet the belt as it flows through the conveyor.  In these applications make sure to cut each end at the exact same angle prior to installing new lacing.  Make sure to install the correct lacing size and type for the belt and the application.

Tracking over and back

If your belt is tracking over and back with each revolution and it doesn't appear to be at the lace then the belt may have been slit to width from the manufacturer with a bow, or camber, in it. Unfortunately, if this is the case the belt will need to be completely replaced.

Visible signs of damage

Over time, a belt tracking improperly may result in the belt becoming severely damaged in structure. Again, if this is the case, the belt will most likely need to be replaced in order to achieve proper tracking. If this has occurred, the belt will show visible signs of damage, such as rips, tears, fraying edges, or discoloration on one side where it may be been folded or stretched beyond allowable limits.

Conveyor issues

If you've checked the belt for these issues and you're still having issues troubleshooting the problem, the issue may be with your conveyor. Conveyor issues can include any of the following.

Frame squaring

If your conveyor is a belt over roller or belt-driven live roller conveyor, the issue may be that your frame is out of square. When this happens, the rollers under or over the belt will not be perfectly perpendicular to belt travel.  This will cause the rollers to steer the belt to one side as it travels through or over the rollers.

You can check or confirm this by measuring the diagonals of each conveyor section'if the diagonals don't match measurements, your frame is not square. You can also check using a framing square to measure for a perfect 90-degree angle between the frame and rollers.  The sections may not have been installed squarely or may have suffered from damage caused by force placed on the conveyor by something such as a lift truck.   

False crowns

End pulleys and take up pulleys typically utilize a crown in the center to assist with belt tracking.  The crown is simply a larger diameter in the center of the pulley which tapers off to a slightly smaller diameter near the ends of the pulley. The crown generates forces in each side of the belt toward the center to keep the belt tracking in the center. However, if shipping labels, cardboard, strapping or other debris have wrapped around the pulley or stuck to the pulley, this can produce a false crown and cause the forces in the belt to be uneven from each side and track the belt off to one side. To fix this, the pulley must be cleaned to reestablish the original intent and purpose of the factory crown.

Return roller adjustments

Return rollers are generally used on the underside of the conveyor to support the belt as it returns.  Return rollers are normally adjustable in squareness to frame.  Adjust these as needed to be square with the frame, consulting your maintenance manual for further instruction.

Snub roller adjustments

Conveyors utilize rollers on the underside of the unit near the pulleys where the belt needs to change angles of flow to feed the belt to the pulley which is typically larger in diameter.  These are referred to as snub rollers or snub idlers. These have a lot of control over the belt. These rollers should be adjusted to be square with the frame, therefore perpendicular to belt travel. At this time, also adjust the pulleys to be square with the frame. Once you're sure everything is square, the snub roller on the infeed end of the belt conveyor or on the discharge end of a belt-driven live roller conveyor may be adjusted.  Adjust to steer the belt to the center; the forces created by the crown should hold the belt in a center once the belt is steered to the center tracking position.

Belt tension is important for proper tracking.  The belt must be sufficiently tight to conform to the crown in the pulley. This tension varies with belt type and severity of crown; if you're not sure, consult your manufacturer for proper tension measurements.

Conveyor belt tracking is important for the smooth running of your operation and long useful life of the conveyor belts in your operation; using these troubleshooting steps, you'll be able to maintain your belt and save a lot of headaches down the line.

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