翻译后的内容

Sampling Strategy取样策略A typical sampling strategy consists of two basic steps: (1) the primary or gross sample, followed by (2) the secondary sample, which reduces the primary sample to a size that is suitable for laboratory measurement. In short, the goal is to select from the lot a quantity of material suitable for measurement without significantly changing the attribute for which one is sampling. In parallel with the sample size reduction, sample size calculations must be done in such a way that the sampling strategy has sufficient statistical power to determine whether the attributes of interest lie within the specification ranges with a reasonable degree of certainty. Each step must be done correctly, or the sampling strategy as a whole will not provide a sample that is representative of the original population.取样方法包括两个基本步骤：（1）首次取样或粗略大量取样（2）二次取样，能够减少首次取样量，使取样量较适合化验室分析。

总之，我们的目标是从批量中取出适合检验量的产品而不该产品的属性。

在取样量减少的同时，取样量的计算必须能够满足检验量，以合理的程度检测出产品质量范围。

取样中每个步骤必须操作正确。

每此取样必须能够代表批次的属性而不是的代表样品本身的属性。

To successfully withdraw a sample from a bulk container that is representative of the population, one needs to have an idea of the population's heterogeneity, i.e., how segregated or stratified the system is. Knowing what factors can accentuate segregation and knowing the patterns of segregation that are likely will help one to account for segregation in a powder bed and to take better samples.为了能成功的从容器中取出具有代表性的样品。

首先需要有多相性的概念。

也就是如何隔离或分层系统。

知道那些因素会影响隔离和了解哪种分离方式能够尽可能帮助在粉末层中取出更好的样品。

Many factors can affect the degree of powder bed segregation. For segregation to occur, sufficient energy needs to be put into the powder bed to induce motion between particles. When a sufficient amount of energy is supplied, segregation can occur via three modes: percolation (in the powder bed), rolling (on the free surfaces of a powder bed), and free flight (when the powder bed is fluidized). These modes are illustrated in Figure 2.很多因素会影响粉末层的分离。

为了更好的分离粉末层，需要在粉末层中使用足有的力道加速粒子之间的运动。

当给出足够的力道，粉末层将会以三种形式分离：渗透（粉末层），滚动（自由表面的粉末层）以及自由飞行（当粉末床流）。

这些模式中在图表2中被显示。

Figure 2. Illustration of the three modes of particle segregation: percolation, rolling,and free flight.Within the powder bed, segregation can occur by means of percolation, also called sifting segregation, as well as through the movement of coarse particles to the top via vibration. During sifting segregation, smaller particles acting under the influence of gravity can more easily migrate downward into the void spaces between larger particles when the particle bed is perturbed.在粉末层中，分离可以通过渗透的方式进行，也可以被称之为“过筛分离”。

粗颗粒可以通过振动运动达到顶端。

在过筛分离的过程中，在重力作用下，当粉末层振动的时候，小颗粒可以进入大粒子之间的空隙空间。

The net effect of these movements is that the smaller particles percolate down into the powder bed, resulting in the top of the powder bed having a higher proportion of larger particles. A common example of sifting segregation is unpopped corn kernels that are found at the bottom of a bag of popped popcorn. For free surfaces, rolling segregation can occur any time that particles can roll down a free surface. In other words, segregation can occur on any non-level surface that allows the relative movement of particles. When particles roll down these free surfaces, larger particles tend to tumble farther down the surface than the smaller particles (see Figure 3).这些运动的净效应就是，小颗粒可以进入到粉末层中，导致粉末层的顶部存留了较大部分的颗粒。

振动分离较普遍的例子就相当于在爆米花袋子底下未爆开的苞米粒。

对于自由表面，滚动隔离随时可能发生。

出现的颗粒可以滚下来自由表面。

换言之，此类型的隔离可以发生在任何非水平的表面，并允许粒子进行相对运动偏析。

当颗粒滚下这些自由表面，大颗粒能比小颗粒从表面上滚动的更远些。

如图3For example, if a conical heap or pile is formed in the middle of a hopper during loading, larger particles are more likely to roll farther down the heap, toward the outer edge of the hopper. This creates a situation in which the smaller particles tend to be in the center of the hopper, and the larger particles accumulate toward the outer wall of the hopper. The formation of these free surfaces can be a major factor in segregation.例如，如果在装载过程中，料斗的中间形成一个圆锥形堆或桩。

较大的颗粒向着料斗的外边缘滚得更远。

这同时也创造了一种条件：小粒子更容易在料斗中间聚集而大粒子更容易在料斗外边聚集。

这些自由表面的形成是分离中的一个重要因素。

Figure 3. Example of extensive powder segregation within a drum.When powder beds are fluidized, a large amount of air is incorporated into the powder bed and, when this air is moving, the air velocity may exceed the terminal velocity of the smaller particles. When this happens, the fine particles are suspendedin the air stream while the coarse particles settle out. The fine particles eventually settle on top of the powder bed, forming a top layer that has a higher concentration of fine particles. This type of segregation, sometimes called elutriation segregation, can occur when a powder is discharged from a hopper, or is poured into the top of a hopper, and a large volume of air is displaced.当粉末层开始流动，大量的空气将会进入到粉末层中。