If there is one industry that really needs hygienic and efficient processes it is the pharmaceutical industry. The approval of the use of any drug must follow strict biosafety protocols to guarantee the purity of its components, both active principal ingredients and excipients.
One of the main processes used by the pharmaceutical industry to achieve the required quality is sieving. This is a physical method of separating mixtures of particles of different sizes by passing them through meshes of different aperture sizes. This screening method allows particles larger than a certain size to be retained, while particles of the appropriate size can pass through.
Screening or sieving is a particle separation technique used since ancient times, which today has reached great sophistication of the equipment used. Also, there are different standards that regulate some of their operation features, like the sieve opening diameter regulated by ISO standards.
In the pharmaceutical industry, screening or sieving has applications in the control of powdered ingredients before mixing, in the elimination of contaminants and in the classification of the granules produced.
Non-vibrating screens vs. vibrating screens
What are non-vibrating screens?
As their name indicates, non-vibrating screens perform their function without the use of vibrating movements, only based on the force of gravity. They were traditional forms of screening until recent times, consisting of a fixed screen with a steep inclination. Today the non-vibrating screens have been displaced by vibrating screens in which gravity is combined with the vibration movement.
What are vibrating screens?
In Vibrating Screens, the vibratory motion is coupled with gravity to make the screening process more efficient. With vibration, the particles of the product placed on the screen mesh jump and hit against the screen openings, more likely to pass through.
Process efficiency is expressed as a percentage. The vibrating screen never reaches 100% efficiency because it would require an extremely long process. However, the most modern equipment achieves high percentages, acceptable for what is required.
Efficiency is calculated as the proportion by weight of the particles that passed out of the total weight of product placed on the screen, expressed as a percentage.
What is a Vibratory Feeder?
Vibratory feeders are short conveyors used to transport bulk materials utilizing a controlled vibratory force system and gravity. The vibrations impart a combination of horizontal and vertical acceleration through tossing, hopping, or sliding-type of action to the materials being handled. Gravity counters some of the acceleration from the vibration and helps move the materials in a certain direction.
A basic Vibrating Feeder consists of a trough supported by springs, hinged links, or other force-dampening mechanical components. These isolate the vibratory feeder from the structural members of the building which can cause unwanted reaction forces. Attached to the trough is a drive unit that produces high frequency, low amplitude oscillations. These oscillations are tuned to create the desired movement of the material.
A vibratory feeder is one of the many pieces of equipment designed for bulk handling. Bulk handling materials have certain properties that separate them from fluids (liquid and gas). Other equipment used for transporting bulk materials are screw conveyors, belt conveyors, apron conveyors, flight and drag conveyors, pneumatic conveyors, reciprocating plates, and so on.
Dosing Feeders and conveyors have operating frequencies that range from 200 to 3600 vibrations per minute with an amplitude of 1 to 40 mm. The vertical acceleration component is usually near gravitational acceleration (9.81 m/s2). This is enough to transport materials with a gentle shuffling motion producing minimal impact and noise. Because of this, the material moves across the trough by sliding action. The material does not actually leave the surface of the trough when the pressure between the surface and the material is at a minimum. In applications where the material has to lift from the trough and then impact again as it falls, special considerations must be made to counter the impact force and the increased noise levels.
Vibratory feeders are distinct from other bulk material handling equipment because the material moves independently from the conveying medium. This contrasts equipment such as conveyor belts and aprons where the material is static relative to the conveying medium. This enables additional processes to be integrated while the material is in transit. Below are some of the processes that can be performed while transporting using vibratory feeders.