Sieves

Sieves and screens control particle size. In tablet and capsule manufacturing, powders are sifted to remove lumps and foreign matter before mixing, and wet or dry granules are milled through a screen so that every granule is close to the same size before drying, blending and compression. The sieve is the part that decides the size, so its hole or mesh size, its condition and its fit in the machine matter directly to the product.

Different machines use different sieves. A co-mill (conical mill) uses a cone-shaped perforated screen: a rotating impeller throws the granules against the screen, and they leave once they are small enough to pass through the holes. A multimill uses a flat or curved perforated screen with rotating knife and impact blades that cut and break the material until it passes through. A sifter, or vibro sifter, uses a flat round mesh screen that vibrates so fine particles fall through and oversize material is carried off the top.

Sifter screens are often made as silicone moulded sieves: the wire mesh is held in a moulded silicone rim, which seals against the sifter and leaves no gap for material to bypass the mesh. Because a torn sieve lets oversize particles or foreign matter through, GMP practice is to check sieve integrity before and after each use and record the result. Spare sieves of each size should be kept so a damaged one can be replaced at once.

We make sieves for co-mills, turbo mills, cadmills and multimills, and silicone moulded sifter sieves in 12, 14, 28 and 30 inch diameters. Our sieves are made in SS 304 with a matt or mirror finish. Tell us the machine make and model, the screen or mesh size and how many you need, and we will make sieves to fit.