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Most common problem

Rope assemblies breaking prematurely.

 

The Aero-Mechanical conveyor uses a wire rope usually ¼” to 3/8” diameter, as the carrier for the discs. The wire rope is usually supplied in 304 S/S, 316 S/S, or galvanized C/S. Plastic coating is also available from some manufacturers on the exterior of the rope. The user should be instructed that a rope assembly definitely has a limited life. On average, the rope assembly will require replacement every 1500 – 3000 hours of operation. Every manufacturer will vary somewhat, but the user should know that the rope has a defined life. During its operation, the rope travels around the sprockets millions of times which results in fatigue of the rope. It is important that the rope be flexible, and strong. Every manufacturer has their own rules and guidelines concerning conveyor length, but remember that the longer the conveyor, the more the rope will stretch and cause the pitches ( length between each disc) to change over its life. On very short conveyors, the rope stretch may not be a consideration, but with the shorter length, the number of cycles around sprocket increases which also causes fatigue.  As a general statement, it can be said that the Aero-Mechanical Conveyor is an excellent choice for batch type operations, due to its high capacity and low power consumption. For continuous service the rope replacement factor should be considered. Some items to consider if rope breakage is occurring frequently.

 

  1. Conveyor run time – Many times the user does not turn off the conveyor after product conveying is complete. It is important that the conveyor be stopped when not in use. The rope assembly will wear  as fast when running empty as when running with product.
  2. Starting frequency – If frequent starting and stopping is occurring, a soft-start motor starter is preferred. The soft-start gradually increases the speed of the conveyor when started, instead of the normal motor starter which instantly brings the conveyor up to speed. The soft start puts much less stress on the rope when starting.
  3. Product characteristics – As discussed earlier in this article, cohesive, fatty, or moist products can cause problems. Along with this, larger size particles can be a problem. Most suppliers recommend a maximum particle size to be conveyed be 3/8” – ½” size. It is important to realize that the conveyor has “pinch points’. Areas that larger particle can pinch between the disc and sprocket housing. The larger the particle, the greater the chance of pinching. If the particle is friable, this is not a problem. If the particle is hard, problems may occur. In the area of the pinch point, normally where the discs enter into the convey tubes, the constant interference between these particle and the disc can cause disc wear, or fatigue of the rope due to constant flexing of the rope. Some manufacturers offer various size discs (smaller diameter) which reduce the pinching effect.
  4. Sprocket wear – The sprockets on which the rope engages are normally fabricated of various grades of stainless steel or carbon steel. Abrasion resistant materials are also sometimes used. The Aero-Mechanical conveyor sprocket has guides on each side of the surface on which the discs seat, to assure that the rope assembly stays engaged with the sprocket. Over the life of the conveyor the sprocket edge where the rope rides will wear. For the user that is not familiar with the conveyor, it may be hard to tell. Normally the edge of the sprocket is flat, without groove. When the sprocket edge wears, there will be a groove around the periphery of the rim. Sometimes this groove is so smooth and uniform that it appears to have been machined in the rim by the manufacturer. Keep in mind that as the diameter of the sprocket wears, the engagement of the discs in the sprocket changes and causes the bosses ( front and rear sections of disc ) to wear. Consult the supplier is excessive wear is an issue.
  5. Rope tension - For many current users of Aero-Mechanical Conveyors reading this article, you can appreciate the difficulty explaining proper rope tension. The tensioning of the rope as simple as it may be is also the most difficult to define. The method of tensioning the rope is to basically slide one of the sprocket housings on the tubes to stretch the rope assembly. That is the easy part. The first thing to remember is that it is better to have a slightly slack rope than a rope tensioned too tightly. Also remember that the conveyor cannot be properly tensioned by sound or lack of sound. I have seen instances where maintenance personnel increase the tension on the rope assembly to a point where the plastic discs do not touch the tubes. That is totally wrong. Under normal circumstances the discs will contact the tubes making an intermittent “pinging” sound.

    The best method to adjust tension is to have access to all sprockets. The tension on the tensioning sprocket should be adjusted until the rope on the inlet sprocket rests snuggly on the very bottom of the sprocket. In many cases the conveyor tension is only adjusted and monitored from the discharge housing, which is normally used as the tensioning sprocket. On long conveyors this may give a false sense of tension, due to the weight of the rope assembly. Many times the rope assembly will appear to be in proper tension, when actually the rope is not even seated on the inlet sprocket. The rope tension should always be adjusted when there in no material in the tubes. In general, checking the rope tension should be part of the preventative maintenance program. The tension may not need to be adjusted, but it should be checked. The supplier of the conveyor can give recommendations for frequency.
  6. Disc Wear - The discs of the conveyor are manufactured from various plastics. Polyurethane, Nylon, and Polycarbonate being common materials. Under normal operation with non-abrasive powders, disc wear is not a factor. If the material is abrasive, the wear may be excessive. Because of the velocity of the discs, wear is a factor when handling abrasive materials. Normally due to the high velocity, the Aero-Mechanical conveyor is not used for conveying abrasive products.

    Disc wear can also be a result of other factors. If the disc becomes almost egg shaped, it is quite possible that the rope assembly is too loose, and the discs are contacting the sprocket housing wall. If the bosses (front and back) of the disc are wearing, the tension may not be correct, or the sprocket may be worn. If each disc shows uniform wear around the outside diameter, it is probably product abrasion causing the problem. If this occurs, work with the supplier to evaluate the best material for the disc. There are plastic materials available to reduce disc wear.

Conclusions

 

It is important to evaluate the application in which you intend to use the conveyor. Testing a machine is always a good idea. Testing will give you a good idea how well the product will convey and many times will give you an indicator if and where you may experience problems. Keep in mind that in general the conveyor is meant for batch type operations due to the operating life of the rope and disc assembly. Always be sure the discharge of the conveyor has a clear path in which to discharge. Allow enough room in the receiving vessel to be assured that product will never build up from the vessel to the conveyor discharge. Put the conveyor on a regular maintenance schedule to check the rope tension. In the correct application, the aero-mechanical conveyor should give good reliable service.

 

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