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Caking
The Johanson Hang-up Indicizer is used to: Determine the amount of additives needed to eliminate caking. Predict storage limitations. Identify how processes affect caking potential. And identify temperature/climate effects on stored materials.
Caking, for the most part, is associated with crystal growth in solids with water-soluble components. Crystal growth requires conditions that leave super saturated solutions on the particle surfaces. Changes in temperatures and the associated moisture migration produce conditions for crystal growth. The Temperature Cycle Hang-up Indicizer allows the user to impose controlled temperature variations. In this way, it is possible to simulate typical day/night temperature conditions in the test cell and to measure the RI for these conditions. The number of temperature cycles is the most important variable in building crystal growth strength in bulk solids. The Temp Cycle feature allows for a one-week time test to be completed in one day to get answers quickly.
The RI index simulates conditions in railcars, trucks and supersacks. RI values, measured under controlled temperature conditions, predict caking of material received at the customer�s plant. Caking can be expected as RI increases.
The following case histories show how the Hang-up Indicizer is being used to solve caking problems.
Identify Processes That Affect Caking Potential
Adipic acid, which is used to make nylon, is frequently transported by railcar.
Because it readily cakes, railcar unloading is sometimes difficult. Some adipic acid discharges in 5 hr, while other shipments require 24 hr or longer to unload because of severe caking problems that require poking, prodding, pounding, and even air lances to break up lumps and initiate flow.
The cake-type adipic acid was easily identified by measuring the ratholing index (RI) for the various samples when they were subjected to temperature cycles, Those with a RI greater than five showed increased unloading times. AI greater than 15 caused extreme unloading difficulties.
In the sample, RI changed from 3 to 17 with fines addition. The flowrate index (FRI), which is a combination of permeability and compressibility, decreased from 2,200 to 1 with the fines addition. A low FRI decreases as a high fines content increases.
Caking
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