Sieve analysis (also known as sieving analysis or test sieving) is used to determine the particle size distribution of various bulk materials. Its handling and evaluation is described in a variety of international standards. It is also considered an important and indispensable quality assurance procedure to this day. Sieve analysis is divided into dry sieving and wet sieving. The sieving motion can be based on the principles of throw sieving, plan sieving, tapping sieving, air jet sieving and ultrasonic sieving. Manual sieving is not easily reproducible due to the individual influences of the operator (stamina, speed, strength).
다양한 형상과 입도를 갖는 벌크 제품의 특성을 위해 입도 분포에 대한 지식이 필수적으로 요구됩니다. 입도 분포 즉 크기가 다른 입자 수는 용해도, 유동성, 및 표면 반응과 같은 중요한 물리적, 화학적 특성에 관련이 있습니다.
식품, 제약 및 화학과 같은 많은 산업에서 전통적 분체 분석은 분말 및 과립의 생산 및 품질 제어의 표준 입니다. 분체 분석의 장점은 취급 용이성, 낮은 투자 비용, 비교적 짧은 시간에 정확하고 재현 가능한 결과 및 입도 분획의 분리 가능성을 포함합니다. 따라서 이러한 방법은 레이저 또는 이미지 분석 방식의 대안으로 수용 됩니다.
높은 비율의 재현성과 신뢰도를 보증하기 위해 분체 및 액세서리는 국내 및 국제 표준의 요구 사항을 충족해야 합니다. 이는 입도 분포 특성을 결정하는 시험 분체, 분체기 및 기타 측정 장치 (예. 저울)가 보정되고 품질 관리 시스템의 일부로 테스트 에이전트 모니터링을 받아야 함을 의미합니다. 이외에도 시료 준비를 신중하게 수행하는 것이 매우 중요합니다. 이러한 과정이 준수되면 제품 특성의 신뢰 가능한 분체 결과가 달성될 수 있습니다.
분체 중 시료는 수직 운동 (수직 운동 분체) 또는 수평 운동 (수평 운동 분체)의 대상이 됩니다. 탭 분체기를 사용하면 두 움직임이 모두 중첩됩니다. 이러한 과정을 통해 입자들은 각 분체의 공극과 비교되게 됩니다. 입자가 분체의 매쉬를 통과할 가능성은 분체 공극, 입자의 방향 및 입자와 매쉬 공극 간 접촉 수의 비율에 의해 결정됩니다. 올바른 분체 방법은 시료의 섬도에 의해 결정됩니다 (그림. 1). 건식 분체 방법은 40 µm에서 125 mm 사이의 입도 범위에 선호되는 방법입니다. 그러나 측정 범위는 입자의 응집성, 밀도 또는 정전기 반응성과 같은 특성에 의해 제한됩니다.
The sample is thrown upwards by the vibrations of the sieve bottom and falls back down due to gravitation forces. The amplitude indicates the vertical oscillation height of the sieve bottom.
Due to this combined motion, the sample material is spread uniformly across the whole sieve area. The particles are accelerated in vertical direction, rotate freely and then fall back statistically oriented. In RETSCH sieve shakers, an electromagnetic drive sets a spring/mass system in motion and transfers the oscillations to the sieve stack. The amplitude can be adjusted continuously to a few millimeters.
수평 분체기의 분체는 평면 상에서 원형으로 움직입니다. 수평 분체기는 침상형, 평형 또는 섬유질 시료에 사용됩니다. 분체의 수평 운동으로 대부분의 입자가 체에서 방향을 변경하지 않습니다.
In a tap sieve shaker a horizontal, circular movement is superimposed by a vertical motion generated by a tapping impulse. Tap sieve shakers are specified in various standards for particle size analysis.
The number of comparisons between particles and sieve apertures is substantially lower in tap sieve shakers than in vibratory sieve shakers (2.5 s-1 as compared to ~50 s-1) which results in longer sieving times. On the other hand, the tapping motion gives the particles a greater impulse, therefore, with some materials, such as abrasives, the fraction of fine particles is usually higher. With light materials such as talcum or flour however, the fraction of fine particles is lower.
The air jet sieve is a sieving machine for single sieving, i.e. for each sieving process only one sieve is used. The sieve itself is not moved during the process.
The material on the sieve is moved by a rotating jet of air: A vacuum cleaner which is connected to the sieving machine generates a vacuum inside the sieving chamber and sucks in fresh air through a rotating slit nozzle. When passing the narrow slit of the nozzle the air stream is accelerated and blown against the sieve mesh, dispersing the particles. Above the mesh, the air jet is distributed over the complete sieve surface and is sucked in with low speed through the sieve mesh. Thus the finer particles are transported through the mesh openings into the vacuum cleaner or, optionally, into a cyclone.
In air jet sieving, only a single sieve is used at a time, and it is not moved during the sieving process. A rotating nozzle below the sieve directs a jet of air onto the material to be sieved, causing particles to deagglomerate and then be sucked through the sieve. Air jet sieving is suitable for size ranges from 10 µm to 4 mm.
Dry sieving is the most popular method of reproducible sieve analysis, including vibration, horizontal and tap sieving. Air jet sieving is also considered a dry sieving method, but it is a special process (see below). If necessary, the sample is dried in advance to avoid clumping. Before sieving, the sample is weighed, then placed in the sieving system and weighed again at a later point in time.
Sieving is used to determine the percentage of the sample that remains on the sieve or is smaller than the selected mesh size. If a particle size determination of the various fractions is to be carried out (set sieving), a sieve stack is used that contains several sieves with different mesh sizes (40 µm – 125 mm).
However, to ensure that the results are reproducible beyond doubt, the machine should be set up completely digitally. Furthermore, the integrated control unit should be constantly monitored to avoid unintentional changes and deviations during the test.
Wet sieving is used to determine particle sizes in moist, greasy or oily samples. It is also the method of choice when the material to be analyzed is already present as a suspension and cannot be dried, as well as for particles that tend to agglomerate (usually < 45 µm), which would otherwise clog the sieve openings.
The material to be sieved is suspended and, as with dry sieving, applied to the uppermost sieve and then rinsed with water under vibration until the liquid emerging from below the sieve stack is unclouded. Wet sieving is carried out in the range 20 µm - 20 mm.
The formal size of individual particles in a mixture is referred to as the “grain size”, and grain size analysis is used to determine this size. The subsequent size distribution of the particles has a significant influence on the properties of a material, both scientifically and technically.
Due to numerous differentiations and even different methods of determination, grain size analysis is considered an independent discipline of granulometry.
Although there are different methods for analyzing and determining grain sizes, the equivalent diameter is always determined in all variants. Which method is ultimately used depends heavily on the question, possible regulations and the grain size range itself.
Larger particles, from a size of about 40 mm, are usually measured by hand or on the basis of photos, while sieving is often used for the particle size analysis of very small particles, down to a size of 10 µm. For sieving, sieves of different sizes are first stacked on top of each other and clamped in a sieving machine. The sample is then placed in the top sieve (with the largest hole size) and subjected to a defined sieving motion for a certain period of time to ensure precise sieving.
The particles of the sample are separated according to their size on the sieves. After that, the percentage of the individual fractions remaining on the sieves with different hole sizes is determined. The percentage mass fractions of the individual fractions are referred to as p3. The cumulative distribution curve Q3 provides information about the added masses of the individual fractions. It is common to provide information about the size of the sample smaller than 90%, 50% and 10%.
The particle size analysis can also be carried out using optical measurement technology. Depending on the measurement variant, statements can also be made about the particle shape. The measuring range is between 0.3 nm and 30 mm, depending on the system. The particle characterization can be carried out in suspensions, emulsions, colloidal systems, powders, granules and bulk materials.
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We all know the term “quality”. It is widely used to describe a product of particularly high value. However, the exact definition of quality is as follows: Quality is the compliance of defined properties with the detected properties of a product as determined by performing tests. A product can be described as high-quality if a test measurement ascertains that the desired properties lie within a given tolerance. If the measured values deviate too much, the quality is lower. Many materials, whether natural or artificial, occur in dispersed form (material which does not form a consistent unity but is divided into elements which can be separated from each other, e.g. a pile of sand). The particle sizes and their distribution within a material quantity - i.e. the fractions of particles of different sizes – have a crucial influence on physical and chemical properties.
입도 분포에 의해 영향을 받을 수 있는 몇 가지 특성의 예:
이러한 예들은 특히 생산 공정을 위한 벌크 제품들의 품질 보증과 관련하여 입도 분포를 아는 것이 얼마나 중요한지 명확하게 보여줍니다. 생산 과정 중 입도 분포가 변하게 될 경우 제품의 품질 또한 변동될 것입니다.
