Material handling continued

In the last installment of the series, drying was discussed.  Though drying problems are many, that subject will be address in a separate article. What we now have is properly dried material to be loaded into the hopper of the machine.  The question to ask is how do we load the material into the hopper.  Is it by vacuum, air, gravity or some other method?

The other issue is what is the amount of the material transferred and what is the residence time in the hopper itself. Given the fact that at 50% humidity, we can pick up enough moisture in 15 minutes to destroy what has taken possibly 4 hours or more to achieve the system or amount of material loaded in the hopper is critical.

If the dryer is mounted on the press than the only concern is proper support of the dryer. If we are conveying the material than the how becomes important, along with the amount.

Bucket method: In this case we transfer from our dryer by bucket and place a specified amount into the hopper of the machine.  What is the amount? Longer than 15 minutes, there may be a problem.  Does the hopper have a sealable lid or a lid at all? If this is the method than the procedure of minimum material means loading material all day long. The solution may be to load the hopper full, than place the lid onto the hopper and seal the lid to the hopper by means of tape, gasket or whatever to prevent atmospheric air form being absorbed into the material.  Further, the bucket can be a great source for contamination.  Hopefully a tack rag of some sort is used to clean it inside and out.

Vacuum Method: If using a vacuum to load the material than it again gets down to the time of material in the hopper. The seal between the hopper and the vacuum unit / loading area is critical.  If in fact they are sealed correctly there is usually no problems. The hoses are critical though, if there are gaps and holes within the hose the atmospheric air and the moisture held within it can be introduced to the dry material.

Air; the use of the venturi air type system can work rather well if the air is dry. If we do not dry the air or have moisture traps that are not maintained within the system, we can contaminate the material with moisture.

It comes down to how the material is loaded into the hopper of the machine and type of hopper in use. Filter cleanings, maintenance of the equipment tend to be low on the priority for loaders and the lids all tend to disappear. Look around the shop and run the fingers over the surfaces, are they clean?  Now think of that open box or hopper with out a lid and visualize a giant magnet just attracting the particles and or moisture into the raw material. Don't disregard the safety aspects of loading materials.  Are there ladders and safety procedures in place? Again, it’s the little things that add up that cause the most trouble.

Thanks for the time.

Steven L Silvey
Sr. Technical Service
General Polymers Division
Ashland Distribution