Oliver Platinum Series, Руководство по эксплуатации, Страница: 13 / 61

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In addition to the air causing a lifting action to the particles, putting them into a quasi-fluidic state,
the deck also vibrates. The vibration of the deck helps to stratify the particles by moving the particles
that are lighter from around the heavier ones. Once the combination of the two mechanisms of air
flow and deck vibration has stratified the material, only then can the particles be separated properly.
The area in which this stratification occurs is the stratifying area, and it should be kept as small as
possible, and should never be larger than 1/3 of the deck surface. The size of the area it will take to
make the stratification a success is dependent upon the product being separated and the difficulty in
separating the heavier from lighter particles and how large a volume of the product is put on the
deck at one time. The closer the heavier particles are in weight the lighter particles, the large the
area will be.
Once the product has been properly stratified, the tilt of the deck comes into play. The vibration of
the deck begins to push the heavier particles, which are in contact with the deck and each other,
towards the high side of the deck. At the same time, the lighter particles, which are floating and do
not contact the deck, are drawn downwards by gravity. As the product continues to move down the
deck towards the discharge end, the vibration of the deck gradually converts the vertically stratified
material into horizontally graded product. This process of first separating the particles into vertical
stratification with air flow and deck vibration, then using the deck side tilt and end raise to
complement the deck vibration to separate the particles into heavy, medium, and lightweight
particles across the deck is shown in Figure 2.
Figure 2: Stratification followed by separation of the vertical layers into horizontally separate grades
as the particles travel down the deck.
Figure 2 shows a very ideal concept of what a separation will look like. Rarely is it that easy to
separate the particles, and there will still be some vertical stratification even towards the end of the
deck. Typically the area of stratification will not be clearly defined. It will have to be assumed to be
within an area 5 to 15 square feet around the feeder.
As the particles travel down the deck, they are acted upon by three forces. The first two forces are
due to gravity. Once is cause by the acceleration of gravity due to the mass of the particles, i.e the
weight, and the other is due to the pull of gravity across the deck towards the downhill direction of
the deck. The third force is a combination of the vibration and a resistance due to the friction of the
deck opposing the sliding action of the particles in the downhill direction. These forces will interact in
such a way that separation actually starts to occur before stratification is finished. This results in
lighter particles being trapped and sent to the high side of the deck. This makes it important to
stratify the product as quickly as possible. The best way to stratify the particles before they start to
separate is by adding air flow, but not to the point of boiling and remixing the product.. The forces
just mentioned are shown in Figure 3.