Powder sieve classification

Sieving is the simplest and most widely used technique for powder classification. This method is based only on the size of the particles and is independent of other particle properties (e.g., density, optical properties, and surface roughness). 

Such sieves were used solely for powder classification, and the inception of test sieving did not arise until sieve aperture sizes were standardized. Standard apertures were first proposed by Rittinger [2] who, in 1867, suggested a V2 progression of aperture sizes based on 75 pm thus, similarly shaped particles passing consecutive apertures, are in a 2 1 surface ratio. Modem standards are based on a fourth root of two progression, apart from the French AFNOR series, adopted in 1938, which is based on a sieve aperture of 1 mm in a tenth root of ten progression this is known as the RIO or Renaud series. 

Sieves and screens are widely used for the classification of relatively coarse materials. For very large particles (>0.5 in.) a robust plate perforated with holes is used. However, the pharmaceutical applications of screening are for much smaller particles and screens are in the form of woven meshes. Unless special methods are used to prevent clogging and powder aggregation, the lower useful limit is in a cloth woven with 200mesh/in. (70-80 pm). Fine screens of this type are extremely fragile and must be used with great care. 

Soaps Soaps in a finely divided form may be classified as soap powder, powdered soap, and chips or flakes. The term soap powder is applied to a granular product. No. 12 to No. 16 sieve size with a certain amount of fines, which is produced in hammer mills with perforated or slotted screens. The oleates and erucates are best pulverized by multicage mills laurates and palmitates, in cage mills and also in hammer mills if particularly fine division is not required. Stearates may generally be pulverized in multicage mills, screen mills, and air classification hammer mills. 

Classification. The subdivision of a powder according to its particle size distribution or its separation into fractions of differing particle sizes. See also sieves, air separations, etc. CLAW. Control of Lead at Work Regulations, 1980. 

Fines n In the classification of powdered or granular materials according to particle size, fines are in portion of the material whose particles are smaller than a stated minimum size. When the particle-size distribution is determined by Sieve Analysis, the fines are those particles passing the finest sieve and found on the pan, usually designated as minus 000 mesh, where 000 is the mesh number of that finest sieve (Provder T, Texter J (eds) (2004) Particle sizing and chacterization. American Chemical Society, Washington, DC). 

The size of the particles in a solder paste determines the print characteristics, amongst other things. The particles are produced by a variety of methods, but they are most commonly made by dispersion of a stream of molten solder onto a rotating disk. The particles fall into a tank filled with an inert atmosphere where they solidify and then are collected at the bottom of the chamber. The collected particles are separated by size utilizing in a series of wire-mesh sieves. The mesh size is typically given in wires or holes per square inch. The Joint Industry Standard, J-STD-005, provides for solder paste particle size classification as listed in Table 1. The choice of solder-powder particle size for SMT applications is based on component pitch, part mix and pad arrangement. For example, the paste particle size required for an area array device is smaller compared to a peripheral-leaded device with the same pitch. A 0.5-mm pitch area array device may have 0.25-mm diameter pads which require a 0.25-mm to 0.3-mm stencil aperture to print a Type rv solder paste with an approximately at 60-80% transfer efficiency. Comparatively, a 0.5— mm pitch quad flat pack device would typically have an 0.2 mm to 0.2.5mm wide pad, but require a 0.15 to 0.2mm wide stencil aperture to print a Type III paste with approximately a 80 90% efficiency. 

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