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What is an Ultrasonic Screen?
Most people are familiar with a vibrating screen. It is comprised of a wire or plastic mesh held in a frame that is continuously shaken to and fro or in a circular fashion. The shaking of the screen can be accomplished by hand or by machine. Any sieving done on a commercial basis is shaken by a machine.
There are several inherent problems with typical sieving process. Screen blocking or blinding is a common problem when sieving difficult powders on screens of 300 microns and below, which is always the case when sieving cannabis.
Screen blocking or blinding occurs when one or a combination of particles sits on or in an aperture of the mesh and stays there, preventing other particles from passing through these openings, and it is particularly common with powders that are sticky or that contain a lot of particles that are similar in size to the mesh apertures. When blinding occurs, the useful screening area and the screen’s overall capacity are reduced, slowing down production levels.
Many people try to frequently clean their screens manually, but this often results in the mesh becoming damaged or broken. Additionally the processing time is slowed considerably when the screens must be constantly cleaned to maintain their efficiency.
An ultrasonic deblinding or screening system can eliminate all of these problems. In ultrasonic screening, an ultrasonic frequency is applied to the sieve mesh using an acoustically developed transducer. The frequency breaks down the surface tension of the mesh, effectively making the stainless steel wires friction-free and preventing particles that are slightly greater and smaller than the mesh from blinding or blocking the screen mesh.
The system is composed of three parts:
1. The control unit, which houses all of the electronic components driving the system;
2. The acoustically developed transducer (often referred to as the probe); and
3. The mesh screen, which includes a special velocity transfer plate (VTP) to which the probe is connected.
The probe is bolted to the VTP, which, in turn, is bonded to the stainless steel wires of the sieving mesh. When the system is activated, the control box sends signals to drive the piezoelectric element in the probe through a single cable, and the probe is excited at its resonant frequency of 35,000 Hz. This frequency excites the velocity transfer plate, which, in turn, vibrates each individual wire of the mesh and prevents the powder from sticking to them.
Ultrasonic systems have no mechanical or wearing parts, so there is no risk of mesh damage or product contamination. Because they keep the mesh from being blocked or blinded, these systems ensure that screening capacity and throughput remain constant throughout the production process. They also dramatically reduce downtime for cleaning while increasing mesh life due to the reduction in manual handling.
Screening very fine powders accurately on a production scale using mesh screens of less than 100 microns is almost impossible with conventional deblinding technologies. With the newfound ability to produce accurately sized batches of powder of very small particle sizes, many people have been able to improve the quality of their final product.
Current systems offer the ability to change the intensity of the ultrasonic activity—a feature that is especially useful with light-density powders. If the wires vibrate too strongly, the powder tends to bounce off them and stay suspended above the mesh. By allowing the system to automatically turn the activity on and off in short bursts (pulsing) or vary the activity unevenly (modulation), the system enables the powder to settle on the mesh and sieve while the ultrasonic activity is off, and it disperses any blinding when the activity pulses on again.
Screening with an ultrasonic vibrating screen can:
(i) Increase sieving capacity by up to 10 times by enabling cannabis trim to pass through the screens faster.
(ii) Reduce production downtown by preventing screen overload and reduces the frequency of screen cleaning.
(iii) Improve the quality of the kief collected, as more correctly-sized granulate is recovered from the screenings.
(iv) Lowers costs by reducing screen damage and the need for repairs.