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Ultrasonic Deblinding

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Ultrasonic Deblinding

Post by ioncube on Thu Jul 05, 2012 6:02 pm

A Blinding Problem
Screen blocking or blinding is a common problem when sieving difficult powders on screens of 300 microns and below. It 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 companies try to clean their screens manually, but this often results in the mesh becoming damaged or broken. Other companies use screening systems that incorporate mechanical devices, such as discs or balls, which bounce up and down, hitting the screen and shaking free any blockages. Unfortunately, the action of these discs can also damage and reduce the life of the mesh. Even more seriously, as these devices wear down, pieces of their rubber or plastic construction can fall off and contaminate the powder being sieved. Another disadvantage with mechanical deblinding systems that is becoming increasingly relevant in today’s health- and safety-conscious manufacturing environment is the noise these devices generate—noise levels of over 90 dB(A) have been recorded with some deblinding disc assemblies.

Mechanical deblinding methods

In a typical sieving operation, particles often combine to blind the stainless steel wire mesh. Ultrasonic deblinding systems can eliminate this problem.
An Ultrasonic Solution
An ultrasonic deblinding system can eliminate all of these problems. In ultrasonic deblinding, an ultrasonic frequency is applied to the sieve mesh using an acoustically developed transducer. The frequency breaks down the surface tension, 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;The control unit, which houses all of the electronic components driving the system;
  2. The control unit, which houses all of the electronic components driving the system;The control unit, which houses all of the electronic components driving the system;
  3. The mesh screen, which includes a special velocity transfer plate (VTP) to which the probe is connected.The mesh screen, which includes a special velocity transfer plate (VTP) to which the probe is connected.

The components of an ultrasonic deblinding system.

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 was almost impossible with conventional deblinding technologies. With the newfound ability to produce accurately sized batches of powder of very small particle sizes, many companies have been able to improve the quality of their final product or even introduce new products with a higher quality or specification.
Works are in progress on reducing the level of noise produced by the equipment. Other efforts include a screener design that allows the equipment to fit into smaller spaces, and systems that allow for enclosed streams, for harmful materials, and those that convey solids through screens with the aid of vacuum or positive pressure rather than relying on gravity.

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