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Bulk Handling Global - Storage and flow of solids solutions

Q. Why do I need to have the product tested for its handling characteristics?

A. There are very important reasons:-

  • Determining the flow and handling characteristics of the product. The measured characteristics are important in evaluating silo design and establishing the process / plant design requirements. Without measuring the bulk solids flow properties, one can only design equipment and silos based on assumptions. This often leads to having undergo major equipment modifications and long commissioning times; de-rate the plant, or worst case having the plant mothballed. The result of not understanding the material flow characteristics, and not interfacing bulk solids test results with silo, hopper, process and equipment design, will lead to major consequences in plant performance and reliability.
  • Shear values. Most process equipment, handling equipment, feeders and dischargers shear the product. Once shear values are known, accurate design can be carried out. By knowing measured shear values, you can easily avoid having to upgrade equipment drives and components, electrical cabling and motor contactors.
  • Measures cohesion of the product. This is important for equipment design, and how the product will behave. As a result of not going through the simple process of having cohesion measured, not only have some process plants experienced major equipment modifications, but plant reliability is jeopardized and some plants have been mothballed as a result.
  • Defines major principal stress, unconfined compressive stress and flow function of the product. These values are used in silo design, predicting loads at the silo outlet and estimating flow properties. So you can ensure that material will easily and reliably discharge properly from the storage silo or hopper.
  • For quality assurance purposes.

If your company operates to ISO 9001, you need an alternative source to measure and check measurements and results of bulk solids flow testing. If you are a project leader, rather than having your team engineers and design drafters make assumptions on plant process and equipment design, they will have the knowledge to apply proper design effectively.

Purchasers of bulk solids for processing plant, check the quality of the product as plant reliability depends on the quality of the product. Ensure that the product meets specification by specifying a flowability index. Why should your production plant loose efficiency because of poor quality product from a supplier?

Q. Our reputable equipment vendor states in their literature, that the flow properties of the product are important in the design of their equipment. Why is this so, and who’s responsibility is it to supply the product properties?

A. In just about all instances for feeder, discharger and conveyor design, with the exception of belt conveyors and bucket type conveyors/elevators that carry material, feeding or conveying requires shear of the bulk solids or powder.

As all products vary in characteristics the shear values must be known to determine energy requirements. For all equipment, the cohesive properties have a great impact on selection of suitable equipment type, sizing of equipment, as well as the use of materials of construction.

It is recommended that the party issuing the enquiry for the equipment supply the bulk solids and powder flow properties testing information.

Your reputable equipment vendor can apply the values obtained in the shear test results in their equipment design, thereby, eliminating any need to use theoretical values or guess the values for material properties and characteristics and equipment selection, and verify their design of equipment.

It is not possible to guess how a product will behave under various consolidation pressures.

Q. Can bulk solids and powder flow properties testing be done on site?

A. Yes – The Peschl Rotational Shear tester is easily transported to site. On site shear testing provides results which are true to use. Some materials loose their characteristics between the time they are collected and tested in the laboratory. So, in most cases, it is important to test the material at the supply source.

On site bulk solids flow testing also can assist in expediting commissioning as well as trouble shooting investigations.

Q. What is the difference between axial testers and the Peschl Rotational Shear tester?

A. Axial shear testers are limited in movement, and measure only one pass of the product. As translation movement of the axial - single pass shear testers is limited to a few millimeters, for some products, this short movement only shears the product within its elastic range, and well below the point of plastic deformation i.e., it never reaches the point of plastic deformation. The Peschl Rotational Shear tester continually shears the product sample, until the maximum shear of the product is measured at its plastic range.

This is reflected in the development of the Mohr’s circle – major principal stress (which has a major impact on silo, hopper and equipment design). Some products achieve maximum shear quickly, and others take longer – it really depends on the characteristics of the product.

Also, due to linear movement of the circular shear cells, the function of pressure applied to the sample varies due to uneven displacement of sample particles during the linear movement. These issues place limitations on an axial shear tester’s ability to measure the true shear stress as function of pressure.

So you can easily see, as shown in the product shear profile results, that the Peschl Rotational Shear tester easily identifies maximum shear values by using the continual rotational shear process. This eliminates the risk of non-accurate measurement.

Q. What is important about measuring peak and dynamic yield as shown on the shear profile graphs? There doesn’t appear to be too much difference.

A. There are major issues. Whilst the peaks as measured for initial/static shear appear relatively small and insignificant, they have a major influence on the development of the Mohr’s circle and the values for cohesion and flow function of the product. This is also reflected in the outcomes in silo design. The Peschl shear test results include the shear profile graphics. This ensures your equipment and plant is designed properly. Always ask for your shear profile when having bulk solids flow characteristics carried out which will ensure maximum shear of the product is achieved.

The outcome of not measuring the maximum peak shear results in incorrect calculation of silo arching dimensions, ratholing of product, additional feeder loads and poor plant reliability.

Q. We handle large lumps on site. Is it possible to carry out shear testing?

Shear testing is carried out on fines. Fines dominate the handling characteristics of the product, and have a more adverse effect on equipment than large lumps. By testing the fines, it also provides safe design. Common methods of side discharge of feeders and improper silo design tend to segregate the product, and concentrate the fines towards the centre.

Q. How long does it take to do a shear test?

A. Depending on the type of product, a single shear test can take approximately 1 hour to carry out, including pre-consolidation. Ideally, at least 3 to 4 shear tests are required to form a family of yield loci, to properly evaluate material characteristics. Some products, especially if they are elastic, can take 1.5 to 2 hours to reach plastic shear.

Q. Can you carry out wall friction tests?

A. Most easily and accurately. It is a separate test to the shear test, and a wall sample is carried out by shearing the product on a wall sample.

Q. Can Bulk Handling Global provide audits of my equipment suppliers design?

A. Absolutely. In fact most of Bulk Handling Global’s repeat clients specifically request that we do carry out design audits. Typically, we review the design process requirements, including silos, hoppers, feeders, conveying equipment and process design requirements. As we take a totally unbiased approach, we easily interact with specialist equipment suppliers as well.