Definition: Drying: to make dry, free from moisture. Tip: to inform

One of the issues with drying is the residence time needed for the material.  In too many cases the material has not seen proper residence time even though all components within the system are operating properly.

The understanding of the statement that "residence time is 2 to 4 hours is necessary" what is intended by such a statement is that it is 2 to 4 hours at temperature.  So the question to ask is how long does it take to get to temperature? This time should be added to the initial start up.  Thus when prepping a dryer to run a job, it may have to be in the dryer for 5 hours, thus using 1 hour to get to temperature and the 4 hours to dry it.  If in fact the supply of material is received in a hermitically sealed bag ready to process than the preheat time may be eliminated.

In a shop that is processing many materials the drying capacity must be accessed so that material is ready when a change is to be made. This in itself will require an extra dryer or two in the plant. The whole concept of volume of material to be processed and set-up of the drying system may require a bit of math and organization of all parties and shifts.

Using a smaller than normal dryer to start a job. In many cases some math must be done to get a job up and running. For example let us assume that the dryer needed to run a job has a capacity of 400 pounds, with an estimated through put of 75 to 90 pounds per hour, and a drying time of 2 to 4 hours. The issue being is that it is currently running a job. By predrying in another hopper and system the material can be ready when the job is ready in the machine, followed by the standard dryer. The steps involved would be:

1-      Set up a separate hopper and dryer to get 2 hours or more of material dry

2-      Start this up at least 3 hours prior to starting of this job. (possibly longer dependant on materials)

3-      At the completion of first job the primary dryer must be cleaned and prepped for new job

4-      2 choices now exist,

a.       either load the hopper with predried material (#1 option)

b.      Set up the initial dryer to load the machine first and when empty switch to full capacity dryer which by that time should have had sufficient time to dry materials.

5-      In either case remember to recycle the material below the cone to the top of the hopper so as to dry properly.

The above is just an example, but allows for prep and efficient change over not waiting for material to dry while the machine is just setting there idle ready to run. Communications and education of all personnel is required to achieve this and over time should become standard. Equipment, room and space must also be available to proceed with the process listed above. Each plant is different in their space and material handling process.

The points to keep in mind which ever process is used is to minimize the handling of material, optimize the usage of personnel in material handling, and to have a production schedule that can be followed.  

SL Silvey

silveysplastics@hotmail.com