Optimal control sifting of plastic granules with the SIFTOMAT plansifter
Sifting plastic granules and especially master batches aims to separate granules that are too big, so-called longs, and grains that are too fine, from the "good" product. The sifting process tends to increase the quality of the granule in order to sell it easier or at a better price.
Nevertheless, sifting is not a very simple process and a thorough analysis of the problem was required, as well as a high number of trials until theory could be converted into practice in order to achieve the desired result.
The problem
The sifting problem lies in the fact that plastic granules do not behave in the same manner as many other materials. In fact, most of the sifting machines do not operate in a satisfactory way when used for sifting plastic granules. The problem is that granules, which are too long and which should be sifted out, remain with the desired end product. The reason is that the sifting surface is too big, or that the selected sifting technique is inadequate. Often both reasons apply.
In most cases, the bigger the sifting surface, the higher the quality or the throughput of the sifted material. However this will not be the case, when plastic granules, which are too long, are sifted out. The reason for this being that with increased sifting surface, the probability of having a too "long" granule falling vertically through a "hole" in the sieve increases. In addition to this, by using inappropriate sifting techniques (for instance a vibrating sieve), these granules will increasingly "jump", into a vertical position and fall through a hole of the sieve.
By trying hard to fully understand the problem, FUCHS Machines Ltd discovered the following facts (as the sifting of fine products is unproblematic, we shall only mention the sifting of coarse particles):
1.If possible, the thickness of the product-layer should be constant on the whole surface of the sieve at the start of the sifting process (in this case a perforated plate) and in the order of 2 to 5 cm. It is then possible to avoid long granules getting into a vertical position and falling through a hole.
2.The thickness of the layer should ideally remain constant throughout the whole sifting process. If this cannot be guaranteed, for instance with long sifting surfaces, some of the granules will show a tendency for jumping over the remaining surface in a non controlled manner, increasing the probability of having vertically positioned granules falling through a hole in the sieve. The sifting surface should therefore not be too big and well adapted to the corresponding throughput of the sieve.
3.The sieve movement should not contain vertical components. These would only exacerbate the "jumping effect".
4.The frequency of the sieve movement should be as low as possible. It is a fact that the best sifting results are obtained with low-speed sieve movements and the "jumping effect" of the granules gets worse with increasing frequency.
Nevertheless, a certain movement is necessary to guaranty the conveying of the sifting material, especially on the "fine" sieve.
The solution
By taking these findings into account, it became clear that the FUCHS SIFTOMAT plansifter offers the best possible conditions for sifting plastic granules, as the sifting movement has no vertical component. Additionally, the rectangular shape of the sifter has the advantage that compared to circular units, the sifting width does not increase during the process. Additionally, FUCHS subdivides the sifting surface, the perforated plate, into several segments with perforated and imperforated plates. Thus, it is possible to adjust the surface of the perforated plates to the required capacity by inserting only as many perforated segments as necessary. The rest of the segments are imperforated and sieve surfaces that are too large can be avoided.
The frequency of the plane circular sifter movement is kept as low as possible, without interfering with the conveying of the material to be sifted. The low frequency accelerates the process and prevents the long granules from getting into a vertical position and falling through the holes into the "good" products. By using a frequency converter the process can be adapted to the specific requirements and optimised.
(double click on picture to open in new window)
SIFTOMAT, the universal plansifter
The slope of the sieve can also be adapted. For high throughputs requiring a fast transport of the material to be sieved, the slope of the sieve can be increased.
Additionally, the sieve case and the sieves are modularly built. For cleaning the sieve case and changing the sieves, for instance in order to process other plastic granules, the sieves and the spacer frames can be removed and replaced very easily.
The SIFTOMAT plansifter is the result of a long development process based on the above described findings. It is used in the plastics industry and can be customised.
Final remarks
Trials in FUCHS's own laboratories as well as with well-known leading producers of granules have led to highly convincing results. It has been proven that the FUCHS SIFTOMAT is the most effective sifter for plastic granules among all vibratory or circular sifters.
Summary
•In order to avoid problems, the sifting surface should be as highly adapted as possible to the sifting capacity.
•Excessive frequencies of the sifting movement have a negative effect on the sifting quality.
•The thickness of the material layer on the sieve should be kept as constant as possible, in order to avoid "jumping" of the granules.
•The sifting movement should not have vertical components, which exacerbates the "jumping effect".
Optimal Sifting of Plastic Granules
Optimal control sifting of plastic granules with the SIFTOMAT plansifter
Sifting plastic granules and especially master batches aims to separate granules that are too big, so-called longs, and grains that are too fine, from the "good" product. The sifting process tends to increase the quality of the granule in order to sell it easier or at a better price.
Nevertheless, sifting is not a very simple process and a thorough analysis of the problem was required, as well as a high number of trials until theory could be converted into practice in order to achieve the desired result.
The problem
The sifting problem lies in the fact that plastic granules do not behave in the same manner as many other materials. In fact, most of the sifting machines do not operate in a satisfactory way when used for sifting plastic granules. The problem is that granules, which are too long and which should be sifted out, remain with the desired end product. The reason is that the sifting surface is too big, or that the selected sifting technique is inadequate. Often both reasons apply.
In most cases, the bigger the sifting surface, the higher the quality or the throughput of the sifted material. However this will not be the case, when plastic granules, which are too long, are sifted out. The reason for this being that with increased sifting surface, the probability of having a too "long" granule falling vertically through a "hole" in the sieve increases. In addition to this, by using inappropriate sifting techniques (for instance a vibrating sieve), these granules will increasingly "jump", into a vertical position and fall through a hole of the sieve.
By trying hard to fully understand the problem, FUCHS Machines Ltd discovered the following facts (as the sifting of fine products is unproblematic, we shall only mention the sifting of coarse particles):
1.If possible, the thickness of the product-layer should be constant on the whole surface of the sieve at the start of the sifting process (in this case a perforated plate) and in the order of 2 to 5 cm. It is then possible to avoid long granules getting into a vertical position and falling through a hole.
2.The thickness of the layer should ideally remain constant throughout the whole sifting process. If this cannot be guaranteed, for instance with long sifting surfaces, some of the granules will show a tendency for jumping over the remaining surface in a non controlled manner, increasing the probability of having vertically positioned granules falling through a hole in the sieve. The sifting surface should therefore not be too big and well adapted to the corresponding throughput of the sieve.
3.The sieve movement should not contain vertical components. These would only exacerbate the "jumping effect".
4.The frequency of the sieve movement should be as low as possible. It is a fact that the best sifting results are obtained with low-speed sieve movements and the "jumping effect" of the granules gets worse with increasing frequency.
Nevertheless, a certain movement is necessary to guaranty the conveying of the sifting material, especially on the "fine" sieve.
The solution
By taking these findings into account, it became clear that the FUCHS SIFTOMAT plansifter offers the best possible conditions for sifting plastic granules, as the sifting movement has no vertical component. Additionally, the rectangular shape of the sifter has the advantage that compared to circular units, the sifting width does not increase during the process. Additionally, FUCHS subdivides the sifting surface, the perforated plate, into several segments with perforated and imperforated plates. Thus, it is possible to adjust the surface of the perforated plates to the required capacity by inserting only as many perforated segments as necessary. The rest of the segments are imperforated and sieve surfaces that are too large can be avoided.
The frequency of the plane circular sifter movement is kept as low as possible, without interfering with the conveying of the material to be sifted. The low frequency accelerates the process and prevents the long granules from getting into a vertical position and falling through the holes into the "good" products. By using a frequency converter the process can be adapted to the specific requirements and optimised.
(double click on picture to open in new window)
SIFTOMAT, the universal plansifter
The slope of the sieve can also be adapted. For high throughputs requiring a fast transport of the material to be sieved, the slope of the sieve can be increased.
Additionally, the sieve case and the sieves are modularly built. For cleaning the sieve case and changing the sieves, for instance in order to process other plastic granules, the sieves and the spacer frames can be removed and replaced very easily.
The SIFTOMAT plansifter is the result of a long development process based on the above described findings. It is used in the plastics industry and can be customised.
Final remarks
Trials in FUCHS's own laboratories as well as with well-known leading producers of granules have led to highly convincing results. It has been proven that the FUCHS SIFTOMAT is the most effective sifter for plastic granules among all vibratory or circular sifters.
Summary
•In order to avoid problems, the sifting surface should be as highly adapted as possible to the sifting capacity.
•Excessive frequencies of the sifting movement have a negative effect on the sifting quality.
•The thickness of the material layer on the sieve should be kept as constant as possible, in order to avoid "jumping" of the granules.
•The sifting movement should not have vertical components, which exacerbates the "jumping effect".
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