Maintenance Tips For Cross Belt Samplers

Adam Orner
By: Adam Orner June 14, 2019
Routine maintenance plays an important role in keeping Cross Belt Sampling Systems operating effectively. Here are some tips to help you maintain your Cross Belt Sampler.

Cutter Wiper

The most common maintenance item for Cross Belt Samplers is the adjustment of the cutter wiper. The cutter wiper is attached to the outside surface of the rear plate on the sample cutter, and is intended to provide positive contact with the conveyor belt during the collection of a sample increment. 

Cross-Belt-Sampler-Cutter-Wiper.jpg?mtime=20190612142305#asset:41420

The rear of a sampler cutter with cutter wiper installed.

The cutter wiper is subjected to a significant amount of wear. The cumulative amount of wear is primarily dependent upon the frequency of sample collection and the type of material being sampled. 

Correct adjustment of this wiper is crucial because it ensures that fine material that may be present on the conveyor belt surface is collected with the sample increment. 

When the cutter and cutter wiper are adjusted properly, a high-quality increment extraction is possible – to the point where a clearly defined belt swipe can be demonstrated during stopped belt testing. 

High-quality-increment-from-correct-adjustment.jpg?mtime=20190612142334#asset:41429

High-quality increment resulting from correct adjustments. Note the cutter wiper contact path across the conveyor belt. 

Cutter wipers are accessed through a door or panel in the upper housing of the sampler on the side of the machine opposite the discharge. The cutter assembly is manually jogged until the rear of the cutter is in the area of the access panel, and then the machine is de-energized and made safe using lockout/ tagout procedures. 

When a sampler is installed and initially adjusted, a measurement is made from the bottom of the cutter to the end of the cutter wiper (the wiper extends below the cutter by 3/8in [10mm] or less). This measurement serves as the baseline for future adjustment. After the wiper is worn, it is simply adjusted to maintain this measured distance. 

Alternatively, a template that fits against the cutter with an outline of the correct position of the cutter wiper can be made. This allows an operator to quickly reference the wear on the wiper and make a determination as to whether or not wiper adjustment is necessary.

Cut Zone

The Cut Zone belt contouring system is a critical part of collecting a correct, high-quality sample increment. 

To assure that the Cut Zone system is performing correctly, Cut Zone components should be kept in proper adjustment – the impact deck portion of the system in particular. 

A Cut Zone system typically is comprised of three parts: an impact deck that is located at the centerline of the sampler, and two multi-segment idlers, one of which is located at either side of the sampler enclosure. 

Cut-Zone-System.jpg?mtime=20190612142306#asset:41421

A Cut Zone system is installed on a conveyor structure as shown (the primary sampler is not shown for clarity). This system is intended to conform the conveyor belt to the radius of the sampler cutter and provide support to the conveyor belt so that it does not deflect downward while a sample increment is collected.

The multi-segment idler component of the Cut Zone system should be adjusted so that the center roll of the idler is at the same height as the center roll of the standard carry idlers that are installed on the conveyor. This is usually done at installation, and adjustment is not normally necessary until rollers are replaced.

The impact deck component of the Cut Zone system should be adjusted so that the slide bars are approximately 1/8in (3mm) below the center roll height of the multi segment idlers. This slightly lower orientation is intended to minimize wear of the slide bars while still providing adequate support and contouring action to the belt. 

As the slide bars wear, the impact deck should be adjusted upward to maintain the 1/8in (3mm) nominal distance. When the slide material is worn to the point where it is close to the impact material that supports the slide material, the slide bars should be replaced. 

Brake

After a Cross Belt Sampler has been in operation for a period of time, the stopping distance of the sampler cutter assembly will slowly increase. 

The stopping distance is the angle of travel that the cutter assembly will rotate through from the time the brake is applied until the cutter assembly comes to rest. This distance is important because if it becomes too large, the sampler will stop outside its designed stopping window and cause an alarm. 

This alarm is called a “failed to park” alarm and indicates that the sampler is not in its correct parked position. This alarm should also be interlocked with the customer’s controls so that if this alarm is set, the conveyor will stop, thereby preventing problems that can occur if the sample cutter is stopped in the material flow. 


Sampler-brake.jpg?mtime=20190620170456#asset:41425

Sampler brake with fan cover and dust seal removed. Feeler gauges (right side, circled in blue) are inserted into the air gap to check the distance. The air gap is adjusted by tightening the brake mounting bolts (shown with yellow paint at the bottom and circled in yellow).

Regardless, if the stopping distance of the sampler is observed to increase to a point where the sampler may fail to park, the brake can be adjusted to bring the stopping distance back to its original value. 

The brake is adjusted by removing the motor fan cover to gain access to the brake. Next, a rubber dust seal must be removed to expose the brake discs. From this point, the brake air gap is measured. 

Sampler-brake_rear.jpg?mtime=20190612142320#asset:41426

The rear end view of the sampler brake. In this case, the air gap has been measured at .012" (.305mm), which is the factory setting for the brake shown.

The measured value is checked against manufacturer’s literature for the brake size in question, and the air gap is adjusted to meet the literature values by tightening (or possibly loosening) the brake mounting bolts to achieve a uniform distance around the brake assembly. 

At some point, the brake discs will wear out. When this occurs, individual brake discs or the entire brake assembly can be replaced. 

Enclosure End Seals

There are two types of external enclosure end seals – upper and lower. 

The upper end seals are a more common maintenance item for cross belt samplers, though some periodic adjustment is also required for lower end seals. 

Neither the upper or lower end seals have a direct impact on the quality or correctness of samples collected, but they do play a key role in minimizing the amount of fugitive material created by a cross belt sampler. 

A Cross Belt Sampler is essentially designed to fit around a moving conveyor belt, so the areas where the conveyor belt enters and exits that sampler enclosure must be large enough to permit belt movement that occurs during normal operation.

Unfortunately, the clearance necessary to accommodate the conveyor belt also allows the escape of particles that are separated from the material flow during the collection of a sample increment. The potential for the escape of fugitive material is greater in the areas covered by the upper end seals, so adjustment of these seals is key. 

The lower end seals close off openings in the sampler enclosure below the belt, but the key function of these seals is to provide support to the bottom of the conveyor belt edges so the belt does not deflect away from the upper seals and limit the effectiveness of the sealing arrangement. 

upper-and-lower-enclosure-seals.jpg?mtime=20190620170458#asset:41428

Upper and lower enclosure seals on a primary Cross Belt Sampler (circled in blue). Note how the upper seal closes off the region above the conveyor belt and the lower seal supports the belt to allow for a good contact between the upper seal and the belt. The slot between the upper and lower seal allows for lateral belt movement.

Upper and lower seals are accessed from either side of the sampler, ideally from a conveyor walkway. 

Since adjusting these seals will require maintenance personnel to be in close proximity to the conveyor belt and conveyor idlers, it is necessary to de-energize the conveyor and follow lockout/ tagout procedures. 

Once the conveyor is secured, seals can be adjusted by loosening the mounting hardware, reorienting the seals and retightening the mounting hardware.

With a few exceptions, Cross Belt Samplers are also provided with an internal end seal. This seal is located inside the sampler enclosure on the discharge side, outbound conveyor belt cutout. 

As shown in the external end seal picture, a slot exists that allows for conveyor belt lateral movement. The internal seal is meant to cover this slot while moving laterally with the belt. It is only located in this one location, as this is the area in which the majority of fugitive material will escape if it is not sealed correctly. 

Since this seal is in contact with the conveyor belt, it also is a high wear item. Replacing this seal requires that the conveyor and sampler be locked out and tagged out, and access to the inside of the sampler is necessary. 

An operator must evaluate whether or not the amount of fugitive material in their application requires the investment in time and resources to maintain this extra seal. 

internal-end-seal.jpg?mtime=20190620170850#asset:41989

Internal end seal (right, circled in blue). This seal hangs over the slot left between the external upper and lower end seals on the outbound discharge end of the sampler. As the belt tracks laterally, the internal seal is able to pivot and maintain coverage of the belt clearance slot. 

Internal end seals are accessed through by removing the small enclosure hood above the discharge of the sampler. The seal is essentially self-adjusting, so maintenance for this seal would simply be to replace it. 

Replacing this seal involves removing the remnants of the old seal material from the pivoting bracket and replacing it with a new piece of seal material. 

Skirtboard Seals

Skirt board seals are another maintenance item on cross belt samplers that do not directly affect the samples collected, but do play an important role in preventing the escape of fugitive material. 

skirt-board-seals.jpg?mtime=20190620170725#asset:41427

Skirtboard seals close the space left between the steel portion of the sampler skirtboard and the conveyor belt (circled in blue). This prevents material on the conveyor from escaping from the material flow on the conveyor while it is within the sampler area.

Since adjusting these seals will require maintenance personnel to be in close proximity to the conveyor belt and conveyor idlers, it is necessary to de-energize the conveyor and follow lockout/ tagout procedures. 

Once the conveyor is secured, seals can be adjusted by loosening the mounting hardware, reorienting the seals and retightening the mounting hardware.

The outbound section(s) of sampler skirt board also have a second type of skirt board seal. This second seal is a steel internal seal, and it is designed to prevent material from contacting the more pliable rubber seal on the outside of the skirt board. 

These internal seals direct material back onto the belt in an effort to minimize potential spillage during and immediately following a sample increment.   

internal-skirt-board.jpg?mtime=20190620170957#asset:41990

The internal skirtboard seals (circled in blue) direct material that is distributed during sample increment collect and direct it back onto the conveyor belt, away from the external skirtboard seals. This provides a more effective sealing arrangement than traditional external sealing only type arrangements.

These seals will require maintenance personnel to on the conveyor belt and under the sampler skirt board, so it is necessary to de-energize and secure the conveyor and sampler using appropriate lockout/ tagout procedures. 

Seals can be adjusted by loosening the mounting hardware, reorienting the seals and retightening the mounting hardware. The seal is intended to be within 1/16in (2mm) of the conveyor belt. Light contact with the conveyor belt is also acceptable. 

Lubrication

Like most machines, Cross Belt Samplers have some lubrication requirements. 

Fortunately, these requirements are very reasonable. Rollers for multi-segment idlers used in the Cut Zone system are sealed for life. The only remaining components that require maintenance for lubrication purposes are the bearings and the gearbox.

Bearings are subjected to one rotation on an intermittent basis, ranging from roughly 30 seconds to several minutes between rotations. 

Given this, frequent lubrication is not required. Generally, adding grease to the bearing every couple of weeks is sufficient. 

Since bearings are enclosed in an area that is guarded to prevent access to rotating components, grease lines are provided to a convenient point on the side of the machine so grease can be added to bearings without removing any guards.

Gearboxes will require oil replacement at an interval of every six to 12 months. 

Gearboxes are also used on an intermittent basis, with one rotation of the gearbox output shaft occurring at the same time intervals mentioned for the bearings.

 Gear oil replacement is generally based on the amount of time that has elapsed since the preceding oil change as opposed to the amount of use the gearbox has received or the need to replaced degraded oil.

Cross Belt Samplers generally don’t require a significant amount of maintenance. The main items have been outlined above, and will hopefully allow maintenance staff to be more confident and successful in completing these common maintenance tasks associated with cross belt samplers.

View Cross Belt Sampling System Best Practices
Tags: Mining, Sampling, Aggregates, Minerals