CONVEYOR SAFETY AND PREVENTIVE MAINTENANCE
Most accidents causing personal injury can be traced to unsafe work practices by either operating or maintenance personnel. Many accidents occur because the personnel concerned do not realize the danger of improper practices. Frequently however, the proper practice is known but ignored because the employee is in a hurry or is careless. Maintenance personnel can contribute greatly towards the success of a safety program. They are familiar with product processing equipment and know the dangers inherent in such equipment. In addition, they realize the hazards resulting from incorrect use of the equipment. Maintenance personnel should be trained to recognize and report promptly unsafe practices in the operational use of this equipment, as well as any dangerous condition in the equipment itself.
The following precautions must be observed:
The following precautions must be observed:
To obtain the optimum return on conveyor systems, the following components that typically make up a conveyor system must be maintained:
Here is a quick list to help you stay on top of maintenance for your conveyor system. While the system is in operation, check the following issues and refer to all relevant safety warnings and information:
'''Note''': A rise in amperage levels above previous levels may be an indication of increased drag within the system, perhaps due to failed or unlubricated bearings. This should be further investigated when the system is at rest and electrically locked out.
-Confirm that components are in proper alignment and make necessary adjustments.
-Closely inspect suspect components and take corrective action as appropriate (i.e., if rolls are not revolving freely, relubricate or replace).
-Check all safety systems.
-Test control equipment.
-Check for belt wear — especially at edges and splices — and belt stringing.
-Check for damage or wear at loading and transfer points.
-Check clearances at chute and skirting areas.
-Remove any material buildup on components and clean up any spills along the system.
'''Note''': The causes of such should be investigated and corrected.
-Relubricate all pillow block bearings per the manufacturer’s schedule or the specific requirements of the installation.
-If relubricatable, relubricate troughing and return rolls per the manufacturer’s schedule or the specific requirements of the installation.
-Check the condition and functionality of belt scrapers, and adjust or replace as needed.
-Confirm that all guards and covers are in place.
-Replace motor brushes as specified by the manufacturer.
The preventive maintenance procedures listed below provide an easy means of determining the operational status of the conveyor. The preventive maintenance procedures result in identification of possible trouble areas so the condition will not deteriorate to the point where a failure is likely to occur.
The objectives of the preventive maintenance checklist are to ensure the equipment is working at maximum efficiency over long periods of time and eliminate costly repairs and downtime.
To ensure effective control over maintenance operations and to permit comparability between equipment as a means of evaluating the maintenance program, preventive maintenance procedures are criteria that may be applied at all equipment locations.
Preventive maintenance can be divided into three categories, each of which is represented by a separate type of checklist.
These checklists specify those activities that call for the highest level of mechanical and electrical skill. These checklists are primarily concerned with inspection and adjustments, though tightening and cleaning activities may be included when delicate or complex equipment is involved. Inspection checklist activities are limited to weekly, monthly, quarterly, semiannually, and annual intervals. During an inspection, never touch a moving belt or rotating part.
These checklists are primarily concerned with cleaning, lubricating, and tightening activities. These jobs do not require as high a level of technical skill as those appearing on inspection checklists. Performance frequencies for cleaning and lubricating checklist activities are also limited to monthly, quarterly, semiannual, and annual intervals.
These checklists are concerned with all of the activities listed above, but are normally directed at a level of skill between that required for inspection checklists and that required for cleaning and lubricating checklists. Inspection and adjustment work assigned at this level is less complex than work listed on inspection checklists. Performance frequencies for routine preventive maintenance checklist activities are, in most cases, limited to daily, weekly, and biweekly intervals.
It is recognized that conveyors may be installed in locations not staffed to carry out the complete maintenance program. Where qualified personnel are not available, the preventive maintenance program should be limited to performing the cleaning and lubricating and routine preventive maintenance routes only. The inspection routines can be assigned to the operator.
'''Note''': Preventive maintenance instructions and checklists should be followed.
Performed by Operator
Cam Roller Lubrication and Adjustment - Inspect and adjust cam rollers. Both front and rear cam support blocks have provisions for lubrication. Front blocks can be lubricated without guard removal. To lubricate rear cams, the rear guard must be removed. All cam rollers should be checked for proper adjustment (see boom alignment instructions). The machine should be locked out for this procedure.
1. Change fluid in gear boxes - Twice a year the gear head lubricant should be changed. The gear cases should be drained and cleaned. When adding oil to any gear box, use the following procedure: a. Remove the oil level plug in the side of the box that controls the oil level height. b. Remove the fill line plug located on the top of the gear box. c. Add lubrication through the top fill line port. d. Add lubricant until it runs out of the fluid level line hole. '''Caution: Do not over-fill gear box with oil.''' e. Replace both plugs in gear box. '''Electrical lockout is required.'''
2. Examine master control panel - Wipe dust from exterior of panel. Open panel door. Remove dust from the interior of the panel. '''Do not touch wires.''' Look for burned wiring and loose terminal connections. Close panel.
3. Observe drive section - With the conveyor running, carefully contact motor and reducer housing with metal rod to detect excessive vibration from bearings or gears. Listen for evidence of wear or damage to internal parts. Do not go near moving parts.
5. Wheel bearing inspection and lubrication - If the conveyor is a traversing unit, each wheel bearing should be inspected for wear, proper alignment, and tightness in the wheel mount. All wheel bearings should be lubricated at least twice a year, and quarterly if unit is traversed regularly. '''Lock-out is required. '''
6. Track clean out - If the unit is of the traversing type with a floor mounted track, the rear track should be checked for build-up of dirt and debris. This should not be allowed to build up where it interferes with conveyor wheels. Clean-out slots are provided at each end of the track for removal of debris.
Lubrication points on the conveyor are confined to:
Each bearing has its own grease fitting and is accessible from either the front, rear, or each side of the conveyor section. In order to lubricate the rear cam rolls and followers, the rear cover of the machine must be removed. All greasable joints have standard grease fittings and can be reached from one of the above locations.
An inspection system must provide for the carrying out of periodic inspections of each operating belt conveyor in the plant.
Belt conveyor inspections must include inspections of the following:
Belt drive misalignment is one of the most common causes of premature belt failures. This problem reduces belt drive performance and greatly increases wear and fatigue on belts. A belt can be destroyed within a matter of hours or days if the belt drives have been aligned incorrectly during their installation.
If the belt drives are correctly aligned when installed, the service life of the belt is greatly increased. Angular misalignment ('''Figure 1''') results in accelerated belt/sheave wear and potential stability problems with individual V-belts. Uneven belt and cord loading or unequal load sharing with multiple belt drives results in, and leads to, premature belt failure.
'''Figure 1: Angular Misalignment'''
Angular misalignment has a severe effect on synchronous belt performance. Symptoms such as tracking forces, uneven tooth/land wear, high belt wear, high noise levels, and potential tensile failure due to uneven cord loading are possible. Also, wide belts are more sensitive to misalignment than narrow angular belts.
Parallel misalignment ('''Figure 2''') also results in belt/sheave wear and accelerated potential stability problems with individual belts. Uneven belt and cord loading is not as significant a concern as with angular misalignment. However, parallel misalignment is typically more of a concern with V-belts than with synchronous belts. V-belts run in fixed grooves and cannot free float between flanges.
'''Figure 2: Parallel Misalignment'''
Parallel misalignment is generally not a critical concern with synchronous belt drives as long as the belt is not pinched between flanges and the belt tracks completely on both sprockets.
Synchronous belt 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 the belt widths, the belt automatically aligns 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 sprocket flange in the system.
The most common tools for measuring misalignment are a straightedge or string ('''Figure 3'''). The improper use of a tool, especially a string, can result in erroneous conclusions.
'''Figure 3: Measuring Misalignment'''
A straightedge or string should be used to project the orientation of one sheave or sprocket face with respect to the other. Sprocket flanges should be inspected. A bent flange could result in erroneous measurements if the straightedge is bent or rests against the outside edge of a damaged flange.
To determine how much misalignment is acceptable and at what point it becomes excessive, alignment must be quantified and compared to the belt measured; check the manufacturer’s recommendations for various drives.
Misalignment is either quantified mathematically or compared to some general rules of thumb for quick and easy results.
Angular misalignment is quantified into a real value by measurements. The actual angle of misalignment is defined by the difference in clearance between the straightedge or string and the outside surface of the sheave or sprocket across the diameter. The angular relationship is:
A = ArcTan, deg
D = diameter of sheave or sprocket, in.
X = distance from straightedge to sheave flange, in.
The angle of parallel misalignment is defined by the difference in the clearance between the straightedge or string surfaces of the two sheaves or sprockets and the outer edge across the length of the belt. The mathematical relationship is:
P = parallel straightedge to sheave, in.; misalignment, deg;
Y = distance from belt edge to center
L = center distance between sheaves, in.
It may not be practical or possible to accurately calculate misalignment in a total system while determining if it is within acceptable alignment. It is also difficult to visualize small fractions of an angle such as 1/4 or 1/2 a degree. These angles are illustrated with the following rule of thumb:
The processes described above permit alignment checking in one plane only. Shafts may be misaligned in either of two different planes or both.
Parallel misalignment is difficult to determine since an accurate common reference plane is not always available. Synchronous belt drives are checked by making sure the belt is not pinched between opposite flanges or does not track off any unflanged sprockets. If the shafts are horizontal, and one is located vertically above the other, a plumb bob or bubble level is used to determine if the sheaves or sprockets are in line with each other. A single V-belt could also be hung in an outside sheave groove from the upper shaft to indicate the proper position of the lower sheave.
After the alignment and tension of a synchronous belt drive are set as accurately as possible, a simple test is used to make sure the system is lined up properly.
Carefully turn the drive over by hand and observe which direction and how fast the belt tracks toward one flange. The belt should move slowly enough that several revolutions are required for the belt to move from one sprocket flange to the other. The drive should then be stopped and the rotation reversed. The belt should track in the opposite direction at about the same speed as before. Related components such as brackets and platforms should be checked for proper design and ability to withstand peak forces without flexing.