Tip #6: Don’t Overload the Belt
When operating a mesh-belt conveyor furnace, the goal should be to maintain a consistent temperature profile and uniform belt loading for any given part number over time. Premature or abnormally short belt life is often signs of overloading, misapplication, abuse or neglect. It is not uncommon to find mesh belts used in carburizing or carbonitriding fasteners lasting anywhere from 6-18 months and hardening (only) belts up to 24 months.
1. Know your belt speed by actually timing the belt movement. Do not assume it is what is stated in the instruction manual or what is displayed on a digital indicator. Calibrate the speed control (typically a magnetic or inductive pickup device) as often as your temperature instruments.
2. Determine your belt loading over time. Improperly adjusted vibratory feed systems and weigh scales that do not read correctly are two of the most common causes for improper loading of furnace belts. Load as uniformly as possibly to evenly distribute wear across the bottom of the belt and help to prevent camber and other belt distortion problems.
3. Avoid using skid plates or belt guide rollers to help belt tracking. These items tend to do more harm than good. Where skid plates must be used, consider coating them with laminated plastic strips. Observe the motion of the belt. It should be smooth, not jerky, and maintain a consistent speed and tracking over time. Remember, a metal mesh belt has flexibility along its length, semi-rigidity across its width and rigidity in its thickness.
4. Work with your equipment or belt suppliers to select a belt weave and belt alloy best suited for your process and parts. Be aware that some belts using heavier wire or larger crossrods actually decrease furnace throughput. Avoid upturned-edge belts whenever possible.
5. Flip and/or reverse the belt at frequent intervals as signs of wear or camber become evident. Only flip and reverse the belt when the belt is sufficiently flexible to ensure that reversing of the belt does not create a fatigue problem. Keep the belt clean (free of oxidation and scale) by running it under protective atmosphere above 760°C (1400°F).
6. Be sure that the belt is properly supported over its length. Watch for signs of premature belt failure such as abnormal distortion of the crossrods, flat spots, deterioration of belt edges, contamination/buildup of foreign residue and tracking problems.
7. Check the tension on the belt frequently or as dictated by production usage. Some systems rely on springs to maintain tension, so check their length. Other systems rely on cylinders, so verify that plant air pressure does not fluctuate significantly.
8. Have your belt-drive system analyzed by a furnace manufacturer or belt company at least once a year.
9. Keep loading consistent. Fasteners are often loaded on the belt in such a way as to leave space along the edges to prevent parts from moving off the edges.
10. Understand that maintenance is different between front-end drive systems having pinch and tangential rolls (for tracking) and rear-end drive systems having only pinch rolls.