Stroke Alert
Check for material buildup on conveying surfaces inside the pan (pan bottom, flat decks, screens, and below the screens in the sub-pan). If equipped with a flexible sub-pan liner, check for tears and material buildup under the liner.
Inspect the conveyor for broken, loose, or missing reaction springs.
Are all rocker arm bushings in good condition and are the bushing bolts tight?
Verify the eccentric shaft operating speed matches the design RPM.
Have any modifications been made to the pan or balancer (weight added or removed)?
If parts have been replaced, are they the correct components and do the part numbers match what is shown on the General Arrangement drawing machinery list?
If equipped with a Stroke Control Unit (SCU), check to be sure it is functioning properly and no errors are indicated.
PAN WEIGHT
Pan weight increase will increase stroke.
SPRING RATE
Broken springs will increase the stroke.
RPM
Motor / Shaft RPM sets the operating frequency of vibratory equipment. Less RPM gives less stroke.
Natural Frequency Vibratory Equipment
Vibratory equipment requires a balance between weight, speed and spring rate.
Remove shipping braces before startup.
Check springs for damage, broken coils.
More detail stroke alert
Vibratory equipment is designed for optimal performance and longevity based on an ideal peak to peak stroke. Variations outside the recommended operating stroke value can cause damage to components and the structure of the machine. Operating strokes should be checked frequently and maintained.
High stroke (overstroke) is a serious operating condition. Operating strokes substantially higher than the design stroke will result in increased stress on components and the overall structure of the machine.
Examples of component damage related to high stroke: Broken drive springs, bearings overheating or failing, damaged drive arms or drive spring connecting brackets, broken reaction springs, shortened rocker arm bushing life or failure, stress cracks on the pan, base or balancer.
Low stroke (understroke) is a less serious operating condition, but it is important to understand that it increases the stress on drive components. Stress on all other components will be reduced.
Examples of component damage related to low stroke: Broken drive springs, bearings overheating or failing, damaged drive arms or drive spring connecting brackets.
Operating strokes that deviate from the design value are commonly caused by a change in weight, change in eccentric shaft speed, damaged components, and modifications or repairs that result in a change in configuration from the original design.
Change In Weight
There are conditions where a portion of the material being conveyed can stick to conveying surfaces (such as “fines” with high moisture content). As material buildup increases, the weight of the pan increases resulting in overstroke. Conveying surfaces should be cleaned periodically to maintain the proper operating stroke. Adjust your cleaning schedule to a frequency that suits your operating conditions and prevents overstroke. Also see Change in Configuration section for additional information.
Change in speed
Vibratory equipment utilizing reaction springs (natural frequency design) depends on a specifically calculated operating speed (eccentric shaft RPM or vibratory motor RPM) and natural frequency to function properly. A change in the operating RPM affects the operating stroke dramatically. As compared to other types of equipment, a 10 RPM variation on natural frequency vibratory equipment can be too much for proper operation.
If no other changes have been made, reducing the operating RPM decreases the stroke, while increasing the RPM increases the stroke. Some RPM changes can be accommodated by re-tuning the machine (adding or removing springs). However, always consult ACTION before making a speed change to be certain it does not exceed design parameters.
One often overlooked cause of RPM loss is wear on the drive belts and sheaves. Over time in a harsh, dirty environment, the V-grooves on the sheaves can wear causing a gradual reduction in the pitch diameter. This (or belt wear) allows the belts to drop in the grooves resulting in a lower operating RPM and lower stroke. Check the RPM with a tachometer or strobe light. If low, replace the belts and sheaves, especially if you are troubleshooting an older machine.
RPM variation from design can also be caused by component replacement such as a mismatch between belt cross-section and sheave V-groove cross-section or installing a sheave with a different pitch diameter. For example, BX belts will run differently than B section belts, or variations between belt manufacturers are possible.
Always verify the part number and pitch diameter is correct as shown on the General Arrangement drawing machinery list if replacing sheaves. Sheaves one incremental size apart may look alike but result in a very different operating RPM.
Change in Configuration
Mechanical modifications that result in a weight increase, such as adding an extension, skirting, diverter, liner, heavier screens, etc. will increase the operating stroke. This should not be done without consulting ACTION. Likewise cutting structure off the pan will reduce the weight of the pan and should not be done without consulting ACTION.
ACTION can guide and assist with re-tuning the conveyor if modifications are required or verify if the desired changes exceed the capacity of the conveyor.
Always verify the part number when replacing springs. Do not substitute with a spring from another manufacturer or one that simply fits. Springs with different spring rates may look similar but will cause unexpected results in performance. Any change in spring rate affects the natural frequency and changes the calculated relationship of speed, weight and spring rate. Increasing the total spring rate reduces the stroke. Decreasing the total spring rate increases the stroke.
If you are in doubt, consult ACTION before making a modification or changing the quantity of springs.