The picture that you see of me as "Ask Joe" on Powder and Bulk Dot Com's home page and above, shows me holding something. Some people have told me it is a coffee cup, dish, etc. In fact, it is the bottom half of a Jenike shear cell filled with corn grits. The Jenike Shear Tester is the device that is recognized as one of the standards for testing bulk solids by ASTM (D-6128-97) in the US and in Europe.

Although there are additional means to characterize solids flow properties, the Jenike method has been scrutinized and perfected over the years and remains the preferred approach. It is classified as a direct shear tester that is capable of providing information on a solid's "cohesive strength" as well as its "wall friction" properties. These are the two main considerations when designing a bin or hopper to ensure reliable material flow.

Our first photograph (above) shows a Jenike Shear Tester, which is composed of a strip chart recorder that records a signal from a load cell located in the blue rectangular box (shear unit), mounted on the front. This unit also contains a small motor that drives the load cell horizontally into a sample located on the stainless steel circular base (shear cell not shown).

The second photograph shows a shear cell in place. Notice the protrusion from the box that is the load cell stem. The shear cell is in two parts that allow the top to be sheared across the bottom, while a normal load is applied by the weight hanger. A shear cover comes in contact with the load cell stem to provide the linear motion.

This test allows us to measure the strength of a bulk solid as a function of pressure applied to it. This information is then used to determine the opening size required to prevent arching and ratholing in a bin or hopper. In subsequent articles we will describe this evaluation in more detail. This test can be run to simulate the affect of several environmental conditions on material flowability, namely, the affect of moisture, particle size reduction, temperature, and time of storage at rest. All these factors come into play when evaluating a material's flowability.

The Jenike Shear Tester is also used to measure wall friction properties. From previous articles, you will remember that friction is developed between a solid and the walls of a bin or hopper. This friction determines whether the solid will slide on the wall (mass flow) or adhere to the wall and preferentially slide on itself (funnel flow).

Our final photograph shows that the bottom "cell" of the shear cell arrangement has been replaced with a sample of wall material. The weight hanger applies the load simulating pressures acting in a bin and shear force is recorded as a function of this pressure. The information gathered during this test, results in a wall friction angle that is subsequently converted to a hopper slope for mass flow.

The test procedure should not be considered simple, because it requires constant practice to maintain skills. As well, the testing process can be time consuming and as such, you should evaluate your testing requirements before adding this type equipment to your laboratory.

Help others by posting your comments, suggestions and experiences with bulk solids feeding or any other materials handling concerns you may have on our On-Line Help Forum.

For past Ask Joe ! Articles, visit the Ask Joe! Archived Articles.

Guest articles for the Ask Joe! Column are always welcome, for more information please contact Joe Marinelli directly at his email address:  joe@solidshandlingtech.com.