In the previous part we explained the difficulties of using raw material charged with static electricity in gravimetric dosers in the plastics industry. In this part we’ll see the problems involved in the use of a highly charged additive in the ColorSave-Micro micro-feeder, a product of LIAD Weighing and Control Systems. We’ll also present the way in which we discharged the static electricity in the ColorSave-Micro and what the results were.
The use of a highly charged additive in the ColorSave-Micro
We took a highly charged additive and dosed it by the ColorSave-Micro. The results were reasonable, but we nevertheless encountered undesirable phenomena that posed difficulties for the feeding system.
It was discernible that the granules flowed unevenly in clumps with spaces between them and some of the granules moved backward instead of forward. At times granules jumped randomly in the feeder and some of them got stuck at the outlet of the feeder and didn’t fall into the production machine.
The feeder coped fairly successfully with the challenge and the product was satisfactory, but one could detect occasional minor vibrations that posed difficulties for the control system.
One of the methods for discharging static electricity is the use of an air ionizer. An air ionizer uses high voltage to ionize (or electrically charge) air molecules. In this way the air ionizer creates a balanced source of negative and positive ions that attract the opposite charge of the raw material and discharge its static electricity.
In order to supply ionized air at a steady throughput, the air ionizer receives low-pressure air from the factory’s air system and releases the air at the same throughput, ionized.
Electrostatic discharge in the ColorSave-Micro
In order to solve the problem of charged raw material in the ColorSave-Micro, we added an air ionizer that discharges the additive’s static electricity. One of the important questions that arise in this type of solution is where the optimal place is for using the ionized air to discharge the material.
We must be sure that the material inside the hopper is discharged and will behave normally, flowing freely from the feeder to the production machine. It seems best to discharge the static electricity inside the feeder itself, however the use of air pressure inside a weighing hopper interferes in the weighing process.
Therefore the discharge takes place after the venturi pumping but before entering the weighing hopper. Thus we ensure that all the material that enters the weighing hopper is discharged and on the other hand the process of discharging the static electricity doesn’t affect the weighing process. Indeed, afterwards inside the feeder the granules rub against each other, however since the material is discharged before it enters the hopper and since the hopper is relatively small, as the feeder is small, the friction in the hopper and in the dispenser doesn’t cause a high enough level of charging to make problems.
With the use of an air ionizer in the ColorSave-Micro the additive flowed freely. First of all, it could be seen that all of the material flowed from the receiver to the feeder hopper, as opposed to the situation without the use of an air ionizer, where granules remained on the sides of the receiver.
Inside the feeder as well the granules flowed freely from the hopper through the dispenser, continuously and without gaps, to the production machine, without any granules getting into unwanted places within the feeder.
In comparison with the previous situation in which the material was not discharged, we saw a total elimination of all the static electricity problems and as a result a significant improvement in the feeding quality.
Usually there’s no serious problem with static electricity in gravimetric feeding or even in gravimetric micro-feeding, but sometimes we encounter an especially charged material that may cause problems in feeding.
Our successful implementation of the electrostatic discharge device in the ColorSave-Micro brought about the disappearance of all the side effects of static electricity and a significant improvement in the manufactured product.
You can see a short video about our implementation through the following link: https://youtu.be/PsVk1AQBxfcor scan the code below.