Richwood: Containing Material at Load Zones
For any conveyor, the most vulnerable points are the load zones. The load zone has always provided a host of issues that concern those who work on conveyor belts. These concerns will often include, impact, belt wear, and sealing. Together, these issues make the load zone the most expensive and problematic section of the conveyor.
Perhaps most readily apparent is the problem of material spillage. The fact is, spillage clean-up is often one of the greatest cost factors in the use of conveyor belts. Hauled product can fall from high speed belts, escape from transfer areas during loading, or stick to the belt as carryback that can be deposited down the belt line.
Any spilled material is wasted material, whether it has to go through process again or is simply factored as a loss. In addition, any displaced material can also shorten the life of components. When material becomes trapped between the belt and idlers, for example, it can lead to idler failures as well as damage to the belt carcass.
Escaping material not only requires extra clean up personnel but can also cause significant issues in regard to safety. The Mine Safety and Health Administration (MSHA) in the U.S. sets the regulatory limits on dust and debris in the mining environment and it is imperative that new conveyor systems and transfer or load zones meet these types of requirements – or similar ones – in many countries. The MSHA studies have concluded that conveyors with a greater degree of spillage also have the greatest number of accidents. Prevention of spillage and successful sealing are non-negotiables at productive mines.
Be Wary of Belt Wear
Impact and belt wear can be just as problematic in the loading area and must not be overlooked. Material impact or other jagged materials have the potential to penetrate and rip the belt, delivering belt stopping damage to the cover and carcass. Loading materials can often nick or cut the belt. Frequent heavy loads can weaken the belt carcass. Because of this, an investment in belt protection can be the difference between a moving belt and a stopped one and a productive mine does not have the option of unnecessary downtime.
Finding the Right Answer for You
Though often easy to identify, the issues concerning spillage, sealing, and belt wear require viable solutions and numerous attempts have been made over the years to tackle these expensive and time-consuming issues; all with varying degrees of success.
Taking a step back and looking at the overall conveyor design is one place to start. New design methods for loading areas focus on designs that control the material flow and diminish the percentage of belt sag, two of the major factors in loading area inefficiencies. These methods are aimed at reducing the common problems experienced in the vulnerable loading and transfer zones. Controlling material flow and achieving zero per cent belt sag attempt to halt the problems before they occur.
Everyone can benefit when these new types of design technologies are implemented, in that it will lead to the creation of more efficient work areas. In the majority of applications, however, the conveyor system is already in place or a company will find that the innovative design alone will not solve the problem as effectively as required. Because of this, additional methods are needed in order to control the safety, housekeeping, and cost issues associated with material flow and material containment.
Other attempts to improve the load zone have included using some kind of metal, urethane, or other type of skirting to try to seal the area. Impact idlers are also often used – as are slider beds – to deal with material impact. The Conveyor Equipment Manufacturer’s Association (CEMA) recommends that some type of impact absorbing protection is used in loading areas, such as impact idlers, impact beds, or cradles.
A truly effective solution will resolve both the impact issues and containment problem simultaneously.
Mines around the world that have found success in their load zones share a few commonalities and Richwood, a thirty-year veteran of the mining industry as a developer of conveyor accessories, recommends following three basic fundamentals for optimal load zones.
- Straight line, consistent belting elevation support under skirtboards.
- Internal wear liner installation for maximum containment of bulk material load.
- The use of a high-quality skirting rubber for dust seal outside of skirtboards at conveyor transfers.
In Richwood’s experience, these fundamentals have proven to be real world solutions even in the most severe applications.
Real World Applications
A recent example of this comes from the northern United States where a mine had been using internal steel wear liners – many of which were installed several inches above the belt – with a hard urethane skirting material attached to the outside. Though the steel wear liners had been lowered in a couple of areas, there was still a clearance gap between the liners and belt which placed an overload demand on skirting material to contain the product. Additionally, conventional impact idlers were in use under the belt load zone and there were two kinds of bar type impact beds that were reinforced and repaired on several occasions, yet still were not holding up to demands of the application. As a result, the belt was regularly punctured and damaged by the severe impact and material would often get caught in the gap between the skirting and belt, creating premature belt wear.
In this instance, Richwood recommended a system that would stand up to the heavy-duty requirements of the location, providing a reliable and long-term solution.
Step One: Richwood Impact Saddle® Provides a Solution
This meant starting with Step One; Creating a consistent straight line of belt support. In order to accomplish this, patented Richwood Impact Saddle was required. When choosing the right type of impact protection for a transfer point, CEMA recommends calculating for the force of the ‘impact from a single lump… as the criterion for selecting the duty rating of an impact bed.’ The Impact Saddle fits the bill as it exceeds CEMA ratings for impact and is in a completely different category from both idlers or slider beds. The Richwood Impact Saddles are not considered idlers because they do not use rolling cans and they are not typical slider beds because the Impact Saddle cradles the belt to provide full belt support.
Ideally suited for impact areas, Richwood Impact Saddles are built to control the impact energy by three mechanisms: distribution, isolation, and absorption. When the material falls, its force is spread to a Ultra High Molecular Weight (UHMW) saddle segment, where it floats on a rubber cushion that is molded to a steel frame. Not only do Impact Saddles protect the belt from impact, they also become an important partner in a reliable Material Containment System and create a belt free of sag, which is a precursor to successful sealing. Richwood Impact Saddles are built as a direct replacement for any standard idler and are designed in any idler profile. When butted together, Impact Saddles provide a continuous impact bed and the full belt support provides the ideal skirt seal. The continuous curve does not have any gaps in the cradle, but provides complete trough support. For this particular application, it was recommended that a series of Impact Saddles be placed under the transfer point on 12-inch centers to create a solid UHMW-Polyethelene (UHMWPE) impact surface.
Step Two: The Addition of Richwood Canoe Liners®
Once the foundation was laid with a straight line of elevation, the next step was to add Richwood Canoe Liners to the inside wall. Richwood Canoe Liners use a specially formulated rubber (with optional ceramic matrix) to deal with the problem of abrasion from passing material, as well as providing impact protection and containment of fines and material. Canoe Liners are unique in that they reliably handle abrasion and sealing while being easy to work with. In contrast to most liners, Richwood Canoe Liners come in standard sizes that are easy to install, with a bolt-on feature and manageable sizes. Richwood liners can be furnished up to four inches thick as required by the application and custom sizes are also available. For the northern U.S.A. application, 14” x 1 ½” liners were recommended to replace the one inch steel and the Canoe Liners used were ceramic with ceramic bevel, where the beveled edge helped to assure best sealing with the belt.
Lastly, for a complete Material Containment System, Combi-Clamp ®Skirt Clamps and Rock Flex ®Skirt Rubber were added. RockFlex is a proprietary rubber blend that is long lasting yet self-sacrificing so that the conveyor belt is not in danger of being grooved or worn by the skirting. By using RockFlex’s specially formulated rubber skirting, the area was safely sealed while belt cover damage was eliminated. To partner with the skirt rubber, Richwood Skirt Clamps were recommended and were specified for their long wear life and ease of use. When adjustment of rubber is required, the clamps will allow for easy release and repositioning of the skirt rubber as needed.
There are no special tools required to install or move the skirt rubber. Simply lift the clamp handle, place and clamp down again. This simple system keeps product and debris where it belongs, off the floor and on the belt.
An alternative option that is available, but not specified for this application, is the complete material containment system called the Loading Station Tailpiece, or LST. The LST is available as a complete, stand alone, prefabricated system that contains Impact Saddles, Clamps and Skirting, and built in support structure.
At the northern U.S. mine, all of the recommendations were implemented and, as a result of these changes to the loading areas, the mine has experienced worry free load zones with no more clean up under loading areas and no more problems with belt punctures, demonstrating that prevention the best form of maintenance. The right philosophy of containment and impact protection, combined with the correct application of equipment help to keep hard working mines running both profitably and efficiently.
- CEMA 6th Ed. Belt Conveyors for Bulk Materials
- International Energy Agency (IEA) statistics – 2008
- Mine Safety and Health Administration (MSHA)