Rather than spending money on feeding, clothing, and housing inmates, the society can adopt a material classifications punishment system. The number of years will now become the number of bags. Having to sort bags of fine sand and smooth flour will be a crime deterrent for sure.
Modern high efficiency classifiers are available today to save anyone from engaging in such extremely tasking activity. This industrial machine is built to classify or separate materials measuring 100 microns or smaller in size (like ground corn from ground wheat, etc). It can also classify based on the size, shape and density of the materials.
A sieve or screen is normally adopted for materials larger than 100 microns. Materials less than 100 microns will likely block the sieve or screen mesh and not allow any sorting to happen
Air classification is thus the choice when separating fine, dry products measuring less than 100 microns. The classification helps to improve efficiency with grinding or milling equipment. In some cases, air classifiers have been used for dedusting.
High efficiency classifiers, especially air classifiers, work by using pressurised air. The materials to be sorted are fed into the chamber of the air classifier. The chamber is already filled with pressurised air coming from an inlet. The pressurised air reacts with the materials by lifting them into the air due to the air drag effect on the materials that forces it to go against the pull of gravity.
Usually, the fine material that needs sorting is lifted into a vertical position, commonly known as the dispersion zone. The materials are then sorted by pushing it down a curved outlet path using pressurised air from another direction.
Air classification works through systematic, continuous streams of air flowing in opposition to each other. The force applied to achieve this opposition is generally uniform, but can be adjusted if required. The opposing air forces originate from two sources, and flow inward and outward through a rotating disk. The outward air flow imparts a centrifugal force on the material particle, at the same time, the inward air flow imparts an inward drag force on the material particle.
These two impart forces will react to either move the material particle up or down, depending on its size, density, or if it is fine or coarse. Where material particles are in clusters, or where air flow and force field is not uniform, there will be poor separation or ineffective random sorting. This means uniform force fields, air flow, and material particles are essential for an effective separation.
Air classifiers are not used just for sorting and separation of materials; they are also a fine powder technology machine used to cut down sorted materials into yet smaller pieces, for example, from 500 microns to 7 microns, or from 250 microns to 3 microns.
Modern air classifiers come in several designs, but the one most commonly used in powder technology particle dispersion is the centrifugal force design. This design also uses rotating plates like the ones discussed earlier.
The centrifugal air force flows in opposition to the drag air force (moving the particles) and then propels the smaller material particles into a field at the centre where they exit through an opening at the centre of the rotating plate. The larger material particles remain outside the centrifugal force field or zone, and also exit the rotating plate by the sides.
The cut size measurement must be strictly accurate because this determines the direction each material particle will go, either fine or coarse. Different centrifugal (outward) and drag force (inward) are used to achieve this, so when the forces become equal, material particles will now have a 50% chance of going either direction.
Materials to be sorted have to be consistently moving for there to be actual separation. Elimination of variations when classifying is achieved by passing material particles through trajectories. All these important features have been fine-tuned in the modern air classifiers.
Fine materials measuring 100 microns and less are not the only materials that can be subject to air classifiers, although they are the most common. Other larger materials can also be easily separated using these air classifiers.
This is why large recycling companies use it to sort out the collected waste mixture of metal, wood, paper, fire, and plastic, before continuing with their recycling processes. Industrial air classifiers do the job speedily while also being efficient, compared with manual sorting.
A detailed understanding of the material to be sorted is needed to help in reaching an economic decision of what type of classifier will be best for your needs.