A manufacturer of plastic bottles had a problem with static charge. Right after the bottles are extruded and cooled, they have an apparatus that “unscrambles” them and places them, single file, onto a conveyor. It does so with some fabric belts and plastic rollers. If you know anything of static electricity, dear reader, you probably recognize that there aren’t too many better ways to generate a static charge than to rub plastic against plastic, or (even worse) plastic & fabric together. Here’s a prime example of the kind of static charge you can get, just from unrolling plastic film.
Now, the bottle makers didn’t have a static meter, but they didn’t need one to know they had issues: the bottles that the “unscrambler” was putting on the belt were still very much “scrambled.” They installed a Model 112209 9″ GEN4 Super Ion Air Knife Kit, to blow ionized air up from under the bottles as they entered the belt conveyor, and they did see what they’d call an improvement, but not quite what they’d call a solution.
Unfortunately, dissipating the static from just about half of the surface area of the bottle was still leaving them with half a problem. However, by adding a Model 112009 9″ GEN4 Super Ion Air Knife (the 112209 Kit’s Power Supply has two outlets, and its Filter Separator & Pressure Regulator are capable of handling the flow to two 9″ Air Knives,) they were able to blow ionized air down from the other side, and up from where the first one was installed. A soft “breeze” was all it took…a stronger air flow would have worked against the “unscrambler” anyway…because even at very low supply pressures, the Super Ion Air Knives produce an extremely fast static dissipation rate.
The temperatures have been dipping a bit in Cincinnati. One day it might top 80F (26C), the next it could only get up to 60F (15C). So, its typical Cincinnati weather.
With the fluctuation in ambient temperatures comes a fluctuation in humidity and varying propensity for static. Lower temperatures, and the corresponding aridity in the air which usually accompanies them, are prime conditions for generating static. This is because the relative humidity (which is a percentage of moisture held in the air compared to the maximum it could hold (at a given temperature)) normally drops below 30%, which promotes static.
Lower relative humidity essentially means less moisture (water) in the air. And, water conducts electricity very well. So when relative humidity is above 30%, the surfaces and materials in a given environment will absorb the moisture in the air or they will form a very thin surface layer of moisture which dissipates accumulated static charges. The thickness of the moisture layer increases with increased relative humidity, so when relative humidity drops, so does this layer on surfaces and materials. Then, when this layer of moisture is no longer present, static can easily build up.
Such was the case for the end user in the application photos shown below.
This system began experiencing a process disturbance when separating stacked plastic sheets. The operation is supposed to remove a single sheet at a time, but static was causing the machine to pick up multiple units in each pass. (Separating two insulators such as these sheets is enough to create a static charge in any environment, let alone when humidity drops and static is more prevalent.)
For this application, we recommended a set of Super Ion Air Knives with the ionized air stream aimed along the short edge of the sheets. As the sheets begin to separate, the ionized air flow from the Super Ion Air Knife has a chance to penetrate in between the sheets and eliminate the static charge. This prevents the machine from picking up more than one sheet at a time.
As the temperatures and humidity drop it is common to experience static problems. For help with a solution, contact an EXAIR Application Engineer.
One of the well known truths in the industrial world is that lower temperatures increase the potential for static. Another truth is that static problems wreak havoc on industrial processes.
Sometimes the process disturbance repels a label or a printing onto a material, sometimes the static causes shock hazards, and sometimes the problem is with material flow. In the photo above, their problem was the latter of those three.
The problem for the end user was the clinging of material, preventing proper conveyance into the machine on the other side of the hopper that we can’t see. But, looking closely at the reflection in the glass and noting the attire of this employee, we can see that this is a clean room application.
In discussing options with the end user, we determined that using an air assisted solution, such as a Super Ion Air Knife or Ion Air Cannon, posed a risk of taking any existing dust airborne without adding suitable dust collection. Given that the problem was localized to the hopper, and that adding dust collection would increase the complexity of the solution, we sought to remove the static without air.
This left us with the tried-and-true solution of static removal without air – an Ion Bar. The Ion Bar can eliminate a 5kV static charge in 0.30 seconds at a distance of 50mm (2″). In this application that decay rate was more than adequate and installation of two bars across the top of the hopper “raining” ions down onto the caps was the final choice of the end user. To allow for adequate treatment of all caps, the personnel using the machine intermittently “mix” the caps, allowing static eliminating ions to contact more of the material.
This application was a great example of how an EXAIR solution can solve a problem to increase machine throughput. If you have an application with a similar need, contact an EXAIR Application Engineer.