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).
为了表征不同形状和尺寸的散料，必须了解其粒度分布。粒径分布，即不同粒径颗粒的量，决定了重要的物理和化学性质，如溶解度、流动性和表面反应。
在食品、医药、化学等许多行业，传统的筛分分析是粉末和颗粒生产和质量控制的标准。筛分分析的优点包括操作简单，投资成本低，在相对较短的时间内得到精确和可重复的结果，以及粒径分级的可能性。因此，筛分分析法是一种公认的使用激光法或图像法的替代分析方法。 为了保证高度的再现性和可靠性，振动筛和配件必须满足国家和国际标准的要求。这意味着，作为质量管理体系的一部分，用于表征颗粒分布的试验筛、振动筛分仪和所有其他测量仪器（如天平）必须进行校准并接受试验监测。除此之外，非常有必要小心地进行样品前处理。只有这样，才有可能获得筛分结果，从而对产品进行可靠的表征。
在筛分过程中，样品进行垂直运动（振动筛分）或水平运动（水平筛分）。使用拍击式振动筛分仪，两种运动是叠加的。在此过程中，将颗粒与每个分析筛的孔径进行比较。颗粒通过筛孔的概率取决于颗粒大小与筛孔的比率、颗粒的方向以及颗粒与筛孔之间的接触次数。适当的筛分方法取决于样品材料的细度（图1）。对于40µm至125 mm的粒度范围，干法筛分是首选方法。然而，测量范围受到样品特性的限制，例如结块性、密度或静电电荷。
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.
在水平振动分析筛中，分析筛在平面内做水平圆周运动。水平振动筛优选用于针状、扁平、长或纤维状样品。由于水平筛分运动，几乎没有任何颗粒改变其在筛子上的取向。
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.
可受粒径分布影响的一些特性示例：
这些例子清晰地表明，了解粒度分布是多么重要，特别是在生产过程中散装货物的质量保证方面。如果在生产过程中粒度分布发生变化，产品的质量也会发生变化。
