TIPS FROM THE PROS ON CONVEYOR ENGINEERING, USAGE, MAINTENANCE AND MORE.
By Mark S. Kuhar
Conveyors are the critical link that keeps material moving in an aggregates plant. While you can’t overstate the importance of crushers and screens, if the material doesn’t get to them efficiently, product doesn’t get made.
Because they are so automatic in service, it is easy to forget that conveyors need regular attention for maximum productivity.
Jason Adams, general manager of Superior Industries’ construction management division, answered our questions on keeping your material handling systems operating smoothly.
What are some of the typical material handling/conveying problems aggregates producers face today? What can they do to prevent these?
General conveyor maintenance:
- Carefully read through all safety instructions in the owner’s manual.
- Check to be sure the reducer is filled to the proper oil level.
- Check all other fluid levels.
- Check to be sure that skirtboards at loading points are installed and adjusted.
- If conveyor has multiple motors, steps should be taken to ensure the conveyor load is shared equally between the motors. Use amperage meters to measure the current drawn by the motors. Adjust the tension of the v-belts on the drives until the readings from the motors are equal. Be certain not to over tighten the v-belts. The drives should be checked periodically to see if the motor load is still balanced.
- When a belt scraper is used, be sure that it is properly installed, tensioned and working.
- Be certain all guards and safety devices are in place and in working order.
- Visually inspect all hoses, lines and belts for leaks, wear and damage.
- Check and remove all tools and any foreign objects from the belt, particularly on the return run side where they may get between the pulleys and belt. Grease on the belt should be removed immediately as it will deteriorate the belt.
- Make certain no parts of the conveyor power, hydraulics, or moving parts have been locked out or tagged out. If they have, determine who placed the lockouts, and have them.
Conveyor belt mistracking:
- Belt training is a process of adjusting idlers and loading conditions in a manner that will correct any tendency of the belt to run off of center. Never attempt to train the belt by unequal adjustment of take-ups. The take-ups are only to be used for keeping the tail pulley square with the conveyor frame and to maintain belt tension. The training of a conveyor belt causing it to travel over the center area of troughing idlers, pulleys and return idlers is vitally important to trouble-free operation and low maintenance cost. Unless a belt itself is warped and curved from improper manufacture, use or storage, it is possible to train it for central running.
Improper loading of the belt:
- When starting a conveyor for the first time, start with a light load and gradually work up to the load that the conveyor was designed to handle. When stopping the conveyor, operate until the belt is clear of material, especially at the end of each working day. During cold weather, material remaining on the belt will freeze to the belt and may cause damage.
- Rubber skirtboards are bolted to the trough to form the load centrally on the belt, to prevent side spillage, and to prevent material from spilling out the back or bottom of the trough. Larger material spilling out the back of the trough has potential to catch in the belt or damage the tail pulley. Skirtboards will require adjustment or replacement as they wear.
- Material should be stilled on the belt before it reaches the end of the skirtboards. If the material particles are still tumbling as they pass the skirtboard ends, belt speed may need to be adjusted, feed arrangement or rate may need to be adjusted, or the skirtboards may need to be extended in order to avoid side spillage of material.
Conveyor belt slippage and sag:
- Conveyors with manual take-ups are equipped with side adjusting bolts at the tail end to maintain the necessary belt tension. With a wrench, loosen the take-up side adjusting bolts to move the sliding bearing assemblies forward. Apply the proper tension to the belt to prevent slippage and excessive belt sag between troughing idlers, and then re-tighten the take-up side adjusting bolts.
- Fasteners can be used to make quick repairs to belt tears or to replace belt sections with new pads of the same belting. Coat all exposed edges or cuts with rubber cementing compound to prevent any moisture or foreign material from entering the belt carcass and causing further damage.
What are the main components of an effective conveyor maintenance program?
The beginning of a good maintenance program for a conveyor starts with the engineering of the equipment. Choosing the correct conveyor components for the given conveying application can reduce or eliminate many maintenance issues. Components such as belt scrapers, impact beds and skirtboards can further reduce maintenance issues and lengthen the time between maintenance tasks.
Since all maintenance issues cannot be resolved through design, a well-run maintenance program is essential to the safety of the operators and maintenance personnel. Each operator or maintenance personnel should be trained in safety procedures and proper maintenance procedures before working on equipment. Personnel should be trained as to what maintenance tasks need to be performed and when they must be done.
When is it time to replace idlers? What should producers consider when replacing idlers?
Idler life is defined as the length of time during operation in which an idler effectively supports and protects the conveyor belt. It can also be stated as the amount of time operating between idler installation and idler failure.
An idler has failed if any one of the following conditions has occurred:
- A roll has stopped turning.
- A roll has a hole worn through its shell.
- The end disc has separated from the shell.
- The bearings are squeaking at an unacceptable decibel level.
- Any portion of the frame has failed.
- The deflection of any frame component is so great that it limits the idler’s usefulness.
How can producers best monitor their conveying systems to make sure they are performing effectively?
Maintenance is an important part of the lifespan of any piece of equipment. The harsh operating conditions experienced by aggregate conveyor systems not only increase the need for proper maintenance but also creates a need for design considerations that facilitate proper maintenance. In many cases, proper design considerations may reduce the cost and time involved with conveyor maintenance.
Design considerations are not able to eradicate maintenance altogether; however, in order to achieve longevity of the equipment maintenance must be performed correctly and according to the recommended maintenance schedule.
Check daily for:
- Spillage around load points.
- Performance of transitions.
- Build up on conveyor truss.
- Incorporate zero-speed switches, belt-alignment switches, ripped-belt detector.
- Use belts scales to prevent overload.
- Confirm belt speed for proper tonnage (improper belt speed will create premature wear of the belt).
What are the advantages of portable stacking conveyors over stationary conveyors?
- Setup time is reduced to minutes for portable versus days for stationary.
- Portable equipment can be employed at multiple sites.
- Portable stackers are often equipped to better control stockpile segregation.
- Portable conveyors have higher resale value on the market.
- Portable equipment can be used in several different applications.
|Many belt tracking devices have guide rollers that help actuate the movememt of the belt tracking device.|
Getting Your Conveyor Back on Track
When your operation is working at full speed, trying to move product or fulfill orders, the last thing you need to worry about is your conveyor belt. Unfortunately, sometimes even the slightest movement or change in the conveyor can throw your belt off track.
According to Ryan Grevenstuk, senior product manager, Flexco, the important thing to remember is that getting your belt back on track isn’t just a matter of slapping a belt-tracking device on the system. It’s a more involved process that includes finding the cause of the mistracking, surveying the problems that have occurred based on the mistracking, and determining what device to use to solve the problem.
Ignoring belt mistracking problems is not wise, as it can result in total replacement of the belt that can hit your pocketbook by way of cost and downtime. More importantly, a mistracking belt can pose a safety hazard, resulting in fines and the possibility of workplace injuries.
If caught early and fixed, a mistracking belt does little damage to the conveyor or the belt. However, if missed or left unfixed, other types of damage can occur. If a belt is constantly hitting a structure, it can not only damage the structure, but it could shave layers off the belt until there is little left. The width of the belt could also be affected, reducing the amount of material it can carry.
What Causes Mistracking?
|If a belt is constantly hitting a structure, it can not only damage the structure, but it could shave layers off the belt until there is little left.|
When trying to fix mistracking, the first thing that needs to be explored is why it is occuring. The best way to go about this is by performing a conveyor assessment. A conveyor assessment is a full inspection of the conveyor that can help determine any problems that need to be fixed or equipment that needs to be updated, replaced, or added.
When searching for the cause of mistracking, special attention should be paid to splices, the conveyor structure, and any material build up on or, damage to, the idlers and pulleys.
Improper belt preparation before splicing can be a major source of mistracking. When going over a pulley, an improperly squared belt has a tendency to wander back and forth on the conveyor structure which can lead to damaged structures, improper loading and other related issues.
In this case, the belt needs to be taken off line and the splice must be replaced, this time using proper belt squaring techniques.
Squaring your belt ends is a job that requires only a few minutes of your time and offers real paybacks in extending your belt splice life. A splice that is applied on a belt that is properly squared will have the tension evenly distributed across the splice. Properly squared splices will help prevent mistracking.
|Mistracking can cause a variety of problems, including materials spillage.|
Prior to any work on your conveyors, make certain that the power has been turned off and the belt is “locked out.” Follow other safety precautions outlined in the operator’s manual. The following steps will help ensure that your belt is properly squared.
- Mark the actual center points in belt width at intervals of 3 to 5 ft., for a distance back from the intended splice area of 15 to 20 ft.
- Using either a steel rule or a chalk line, mark the average center line through the points measured.
- Using a square, draw a line perpendicular to your average center line across the belt width.
- For even greater accuracy in preparing your squaring line and with belts with worn edges, after completion of step two, mark two lines (B&C) equal distance from the center line in the area where you are going to install the splice, running parallel to the center line.
- Measure back from the intended splice area a distance equal to approximately three times the belt width and drive a nail or awl at this point on the center line. Using the nail or awl as a pivot point, swing an arc, marking the belt across the full width.
- Where this arc intersects the two smaller lines marked parallel to the average belt center, align a steel rule through these points. The resulting line is the true square.
- Mark this line and cut your belt at this line using a belt cutter.
The structure of the conveyor can also cause the belt to wander from side to side. Over time, several factors can change the structural integrity of a conveyor structure, including weather.
If the structure was not built to withstand winds blowing across it, the structure may have to be reinforced for stability. Weather can also affect the belt itself, causing it to mistrack.
Strong winds, for example, can blow the belt off to the side if the conveyor is not enclosed. When combined with snow and rain, the resulting pressure on one side of the belt can push it offline. The same is true with the sun shining on one side of the belt and not the other, heating the belt and causing it to wander.
Misalignment of rollers and pulleys can also lead to belt mistracking. Even the slightest difference in one roll can pull the belt off track. Improperly positioned head pulleys, tail pulleys, and bend pulleys can also contribute to mistracking.
Material build up, may be one of the most common cause of belt mistracking. When materials build up on idlers and pulleys, it throws the rollers off, causing the belt to wander.
This buildup can also change the tension of the belt, which can result in shorter life of the actual belting and other components, like cleaners. Belt cleaners are an effective way to keep idlers and pulleys free of carryback material. Installing an effective cleaning system will go a long way toward keeping belt mistracking and other common system problems caused by carryback in check.
The Result of Mistracking
Mistracking can cause a variety of problems, including materials spillage (causing materials to “spill off” the belt). When a belt mistracks, it is common to look at what may be falling off the conveyor because of the change in the belt’s path. Whether conveying larger materials or miniscule materials like sand, spillage represents lost revenue and, in many cases, huge safety risks.
In other cases, belt mistracking can cause damage to your belt and conveyor structure that could lead to serious problems. In some cases, layers of the belt can be shaved off the sides and can spill material off the topside onto the area around it. Plus, as you reduce the width of the belt, you reduce how much material you can carry on the belt, cutting into profits.
Fixing the Problem
Ideally, the way to fix a belt that is mistracking is to go straight to the source and eliminate the problem. And while some fixes are easy and will train your belt to function properly, some are cost prohibitive (moving or remodeling the structure) and some are beyond your control (weather conditions). When permanent structural changes cannot be made, devices must be used to help track the belt correctly.
When you’re on a tight schedule and a large amount of downtime will stall your operation, it can be tempting to employ a quick fix to get the mistracking under control.
One of the most common quick fixes involves tying two rollers to the side of the conveyor to keep the belt running to the center. The problem with this method is that a roller on the edge of the belt is not always effective because belts prefer to pull not push, so the rollers are actually working against the belt.
One way to adjust the belt is to use friction – skewing the roller in comparison to the direction of the belt. Another way is to affect the tension profile. Belts naturally want to “walk away” from a higher tension. If tension is increased on one edge, it will walk the other way.
Field testing has proved that a combination of friction and tension is the best way to put a belt back on track when the structure cannot be aligned.
Many equipment manufacturers offer a steel return roller with an edge roller next to it that causes the roller to pivot or skew relative to the travel of the belt. The friction of the roller on the belt steers it back. The problem with this method is that the edge of the belt strikes the roller with heavy force without much effect, exerting heavy pressure to the belt edge. This situation can generate high force into the roller that can damage the belt.
To avoid exerting heavy pressure, use a design that provides friction and changes the tension profile by tilting as well as pivoting. When both the friction and tension mechanisms work together, they are more than three times as effective at restoring belts back to the center of the conveyor.
Pinpointing the Mistracking
Before finding a device that can help solve your problem, you must first identify what type of mistracking you are experiencing. If your belt is constantly mistracking and moving back and forth, you are experiencing wander.
A belt that runs to one side constantly is simply mistracking. The device you choose depends on which type of mistracking is occurring, along with the belt tension and belt speed, thickness, width, and whether the belt reverses.
|It is important to choose a belt-tracking device that adjusts based on the movement of the belt.|
A proper belt positioner is the simple, reliable solution for problem belts that consistently mistrack to one side of the conveyor. A belt positioner works on the return side belt using simple angled rollers mounted in a fixed position to quickly and continuously funnel the belt into the correct path.
This is a quick, simple solution for belt-tracking problems caused by conveyor misalignment mishaps, ground shifts or on temporary systems.
Belt positioners are not meant to work with top-side belt mistracking, or for belts that mistrack from side to side. Ideal for use on belts with medium-to-high running tensions, a belt positioner is not appropriate for use on belts with low running tensions.
For top side or return side belts that wander from side to side, it is best to choose an active belt-tracking device that adjusts based on the movement of the belt. As noted earlier, an active belt-tracking device that affects both friction and the belt tension will most effectively track the belt. Many of these belt-tracking devices will also have guide rollers that help actuate the movement of the belt-tracking device. If that is the case, it’s important to note that often these devices will not work on reversing belts.
Reversing belts typically need a different style of belt-tracking device designed to work in both directions. Before putting a belt-tracking device on your belt, clarify that it will work on reversing belts if the application warrants, otherwise, it may do more harm than good.
Keeping an Eye on Your Entire System
In most cases, mistracking can be solved by following the procedures listed above, which means you can be back on track in no time. Of course, preventative maintenance can signal some of these challenges before they bring your operation to a screeching halt.
Inspecting and performing maintenance on all of your conveyor system components should be part of an overall maintenance plan. You can save yourself time and money with scheduled work stoppages for maintenance and by replacing equipment before they cause damage to other components in your system.
The amount of effort you put into proactive maintenance will decrease the amount of unexpected downtime, help keep your workers safe, and help your operation run more efficiently.
Engineering a Perfect Solution
When designing a new aggregates plant, or refurbishing an existing one, there are a number of tips to keep in mind with regard to the operation’s material handling systems.
Peter Guttridge, chairman of Guttridge Ltd,
www.guttridge.com, and chairman of Solids Handling and Processing Association, is an engineer with more than 30 years’ experience and unrivalled knowledge of the UK bulk-materials handling industry. He explains some of the key points of conveyor design.
1. Assess supplier experience for your industry and application.
Conveying requirements are constantly evolving in terms of scale and the range of materials handled. Experienced suppliers who know your industry will have the knowledge needed to design and manufacture conveyors uniquely tailored to your specific application. Look out for the option for bespoke systems for highly specialized requirements.
2. Define critical aspects of the material that will impact equipment design.
Some materials need particular consideration during transportation. For example, with fragile food stuffs such as breakfast cereals, avoiding attrition is vital in order to maintain product quality and value. Other materials, in contrast, may be very robust but highly abrasive or prone to entanglement in any conveyor internals.
3. Put figures to reliability.
Reliability requirements are now extremely stringent in certain industries and it is vital to be realistic about expectations. A good conveyor supplier will offer reliability enhancing mechanical features and automated monitoring but these will increase initial capital outlay. Putting value to reliability targets will help to justify the necessary investment.
4. Look for examples of supplier success.
It makes sense to scrutinize the history of your supplier. Look to customer testimonials and case studies for evidence of successful conveyor construction and a healthy track record of project completion. A company with longevity and economic robustness is especially reassuring when it comes to larger projects.
5. Focus on layout.
Distances and changes in height play a significant role in determining which type of conveyor technology is best for any given application. Get site layout well-defined as early in the project as you can to develop an optimal solution.
6. Communicate effectively with the designers.
Make sure any variability within your material is as fully described as possible to ensure that the project is effectively scoped. Streams with variable flow properties require a design with the flexibility to cope.
7. Make the most of specialist expertise.
Good conveyor design relies heavily on experience but technical expertise also has a part to play when it comes to developing right first time solutions. For example, for tricky to handle powders, the best suppliers are increasingly using powder testers to support their design work. Expert interpretation of the test results within the context of conveyor design helps to ensure that even challenging materials are handled efficiently from the outset.
8. Consider lifetime maintenance and the associated costs.
Conveying systems have a long lifetime and costs of operation need to be considered alongside the initial capital sum. Research whether a supplier has the infrastructure in place to provide long-term support.
9. Investigate newly integrated care packages to minimize in-house support requirements.
Consider whether maintenance and any emergency breakdowns can be covered with in-house capability or whether external support is required. Leaders in the field are now offering “cradle- to-grave” care packages that include both routine and emergency maintenance. These can substantially relieve pressure on in-house staff.
10. Decide how you want to implement the project.
Projects work best when each participant plays to their strengths. If a turn-key package is required then find a supplier with the resources to follow through every stage to final commissioning. On the other hand if there is a need for a single conveyor or discrete elements of a project, find a partner who will work productively alongside you.