Screw conveyors are a critical component of many material handling systems. They are used to transport a wide range of materials, including powders, granules, and pellets, from one location to another. When operated correctly, screw conveyors are reliable, efficient, and cost-effective. However, when they are not properly designed, installed, or maintained, they can cause problems that can lead to significant downtime, loss of production, and high maintenance costs.
We will examine some of the common mistakes made when using screw conveyors. We will provide recommendations for avoiding these mistakes, and highlight the importance of proper design, installation, and maintenance.
Running the Screw Conveyors Too Fast
Screw conveyors are commonly used in material handling and processing industries, but many operators make the mistake of running them too fast. When a screw conveyor is operated at a high speed, there is one major problem, HEAT. Heat causes increased wear and tear on the conveyor components, leading to maintenance and replacement costs. Hanger bearings and ball bearings are the typical failure points when systems are operated at excessive speed. Because of the hanger bearing failure point, the heat generated can also result in conditions that could lead to fire.
To avoid these issues, it's important to properly size the equipment to handle the volume of material needed to move. A properly sized screw conveyor will operate between 30 and 120 RPMs. Often, we operate screw feeders at less than 30 RPMs based on the volume of material needed to feed into a subsequent process. Factors such as the size of the conveyor, the type of material being transported, and the desired throughput rate affect the RPM selection. It's important to note that running a screw conveyor at the ideal speed not only reduces the wear and tear on the components but also increases efficiency.
Overloading the Trough
Another common mistake is overloading the trough. This can occur when too much material is fed into the conveyor at once, causing the trough to become packed and the screw to become jammed. This can cause significant damage to the conveyor components and result in significant downtime. To avoid this problem, it is recommended that the trough loading should not exceed 45% at the discharge. If this is not respected, the material can bypass the discharge, build up at the trough end, and eventually break coupling bolts or push the trough end away from the trough in a catastrophic failure. This goes back to properly sizing the conveyor system with proper RPMs. When reviewing quotes, ask the manufacturer what the trough loading is. If that value exceeds 45%, a change may be needed.
A similar issue on feeders would be material bridging out at the inlet. This is where material would settle in an inlet hopper on a screw feeder or live bottom feeder and would stop falling down to the screws. This is common across all types of feeders, not just screw feeders. It is important to consider the angle of repose, the material density, and moisture content when designing an inlet for a feeder.
Over Torquing the Parts
Over torquing the parts is another common mistake that can lead to problems with screw conveyors. This can occur when too much horsepower is applied at too low a RPM. Over torquing can lead to sheared bolts, shafts, and screw pipes. Torque failure should be seen in the coupling bolts. Coupling bolts should be sized to handle just above the designed torque. This will create a failure point that is relatively easy and cheap to fix. When performing maintenance on equipment, it is important to select the same materials for coupling bolt replacement.
To avoid over torquing, it is recommended that the horsepower and RPM of the conveyor be carefully selected based on volume, material density, and conveyor size. This will ensure that the conveyor is operating within the manufacturer's design recommendation.
Mistake #4: Using Too Small of a Discharge Size
Using too small of a discharge size is another common mistake that can lead to problems with screw conveyors. This is in the same vein as overloading the trough. This can occur when the discharge opening is too small for the material being transported, causing the material to become packed and the screw to become jammed. This can result in significant damage to the conveyor components and result in significant downtime. To avoid this problem, it is recommended that the discharge size be selected based on the type of material being transported and the desired throughput rate.
When tapering into transition discharges, like going from a square to a smaller dia round discharge, it is important to maintain a steep slope on the transition. Material can bridge out in a discharge the same way it can bridge out in the inlet. The results can be the same. The material will back up through the discharge and into the conveyor.
Mistake #5: Not Servicing the Conveyor Regularly
Finally, another common mistake made with screw conveyors is not servicing them as often as they should be. This can result in increased wear and tear on the conveyor components, decreased efficiency, and increased maintenance costs. To avoid this problem, it is recommended that a maintenance plan be developed and executed on a regular basis. This plan should include regular inspections, lubrication of moving parts, and replacement of worn or damaged components as necessary. Inspection methods can include electrical load sensing on the motor, listening for out of the ordinary sounds in the system, and feeling the trough for odd vibrations or heat. Hard iron bearings are known for the amount of noise they make, so it is good to consider the materials of construction before jumping to conclusions. Contact the manufacturer for potential issues as needed.
In conclusion, screw conveyors are a critical component of many material handling systems. When operated correctly, they are reliable, efficient, and cost-effective. However, when they are not properly designed, installed, or maintained, they can cause problems that can lead to significant downtime, loss of production, and high maintenance costs. By avoiding the common mistakes discussed in this article and by properly designing them.
WHO WE ARE
ISC Manufacturing has been designing and manufacturing technologically advanced products for over four decades. We provide innovative solutions to complex problems for a variety of industries. Our experience and knowledgeable team contribute to state-of-the-art, custom manufacturing systems. We also provide commonly used products such as material handling, conveyors and processing equipment. When you work with us, you can expect quality craftsmanship, great communication, and a full-service experience you can count on. We are located just outside of Fort Worth, Texas. With over 200,000 square feet in manufacturing space, across 75 acres, we have the capacity to handle any size project.