August 8, 2018
There are a number of different materials being conveyed around a cement plant, ranging from dust to large, sharp rocks, and each have different abrasiveness and moisture contents. If you can succeed in getting all these materials moved around without spilling off the belt, maintenance efforts and dollars can be focused elsewhere. That said, the load zone is easily one of the most important parts of your belt conveyor system and should be looked at closely.
So let’s do just that. Here are the Top 5 load zone issues you may see at a cement plant, why they happen, and how you can address them before they affect production.
Issue: Premature wear of belt and splices in the load zone.
Diagnosis: Incorrect materials used for sealing the impact area and the following section of conveyor after the load zone is the likely culprit here. Using incorrect skirting materials leads to premature wear on other components and requires additional maintenance. It is extremely common for plants to use belting as skirting material, which leads to belt and splice damage and requires the premature replacement of both. Abrasive dust like clinker gets trapped in the carcass of the belt being used for skirting and acts like a big piece of sandpaper. This can wear through belts and splices in a matter of weeks.
Solution: Instead of using old belting, consider urethane skirting, which has a lower durometer, reducing friction, and providing 3-4 times the wear life over traditional rubber. A lower coefficient of friction reduces strain on the system and soft durometer urethane offers exceptional tear resistance to ensure a good seal and long belt life.
Issue: Worn skirting systems in impact area, causing long maintenance delays.
Diagnosis: Homemade skirt clamping systems, as well as those made by OEMs, may be hard to adjust, requiring unbolting/reassembling or torching/re-welding the entire clamp bar to adjust the skirting as it wears. This requires the belt be stopped for a longer period for maintenance. Belts handling things like raw materials and taking clinker to the finish mills may have skirting running the full length of the conveyor, so the maintenance time required for adjustments adds up quickly when the system is not designed for easy adjustments.
Solution: An engineered skirting system that that can be adjusted quickly and utilizes urethane skirting is the best choice for the belt. With correct installation, the skirt rubber will not drag on the belt, causing premature wear or gouge marks in the belt cover, which can reduce belt cleaning efficiency and the life of the belt. Your engineered skirting system should be designed with maintenance in mind, so find one with safe service access from the side of the conveyor and is made of corrosion-protected components. Pairing quick adjustments with long-wearing urethane means minimal time spent ensuring the load zone stays sealed.
Issue: Containing material on the belt.
Diagnosis: This problem is associated with chute height. Oftentimes, OEM and homemade chute systems that are mounted too high off the belt require the skirting system to take on more work to contain the material. Ideally, a chute will only be a couple of inches above the top of the belt and the skirting should seal up the small gap. When the skirting is mounted too high, the plants tend to add too much skirting material that can flip outward and allow material to spill. This is an issue found throughout the plant on belts under the crusher, belts transferring raw materials, belts carrying clinker, etc.
Solution: Assess your chute system and make adjustments as needed. Additional material may be required at the bottom of the chute to reduce the gap down to a couple inches. Also make sure the sealing material is mounted close enough to the belt and is supported so it cannot flip out and allow material to escape.
Issue: Fugitive dust in the load zone.
Diagnosis: Sites may only be looking at skirting as the cause of spillage around the load zone as mentioned above, but the components that are supporting the belt are also very important to consider. Sometimes an incorrect choice of load zone support can lead to increased spillage and fugitive dust. Many cement plants are only using impact idlers in the load zone. With impact idlers, the skirt systems do not have a continuous flat surface to seal against, so material escapes between the idler sets. This also puts pressure on specific areas of the skirting material, wearing the spots where the belt contacts the idlers faster than the gaps in between idlers. This action breaks the continuous seal and eventually dust and material will start to escape.
Solution: Slider beds are engineered to provide containment around load zones. In areas where low impact affects productivity, such as in raw materials storage and proportioning and after pyroprocessing, slider beds with impact idlers and adjustable idler sets with impact rolls are key. When combined with skirting systems, slider bars effectively seal the load zone. When paired with impact beds, slider beds create a holistic load zone.
Issue: Spillage at the load zone and beyond.
Diagnosis: When you load a mistracked belt in the load zone, it has a tendency to hold the belt in the mistracked position the full length of the conveyor. Off-centered belts going through the load zone can cause a gap between the skirting system and belt that will let material drop out. In severe cases, the belt can become trapped in this position by the skirting. On clinker belts, this leads to seized idlers and possibly buildup around the load zone that requires a lot of effort to break down and remove the fugitive material.
Solution: Installing a trainer before the tail pulley will center the belt before it goes through the tail and load zone, minimizing the issue. Look for a trainer 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 more effective than a pivot tracker at restoring belts back to the center of the conveyor.
Dust, spillage, and equipment damage at the load zone is avoidable. Evaluating and optimizing the belt conveyor at load points can do wonders for a belt conveyor system and its productivity. Take the time to do a proactive evaluation of your system and tackle the challenges before they become real issues that affect your productivity and bottom line.
Authored by: Franklin Moore, Industry Manager
Moore identifies focus markets, researches chosen industries, and concentrates on the voice of the customer. He develops sales tools and programs to help our teams better understand the pain points present in each industry. Currently, Moore is focusing on Flexco solutions for the cement industry now and in the future. Moore holds a bachelor’s degree in finance from Michigan State University.