contract powder sieving services

Material is passed over or through flat sieve screens which are either eccentrically oscillated or vibrated to move the material through the sieve.
Minox and Allgaier sieves can provide gentle rolling action suitable for more friable products. With screen sizes ranging from 90 microns to 10mm and the capability of single to triple decks, these machines are versatile and can achieve accurate sieve cuts often at high throughput. Self-cleaning systems maintain efficient operation with challenging materials which would rapidly blind lesser quality sieve units.
Russel and Kaison vibrating sieves are available in a wide size range. These are simpler machines to set up and can also achieve accurate particle size cuts between 90 microns and 10mm. These units can offer advantages in screening fibrous materials which can roll up into balls on oscillating sieves. Self-cleaning systems are available for use with vibrating sieves but are not always as effective with challenging materials as those used with oscillating sieve. Vibrating tray sieves are frequently used for check screening prior to packing.

Based on Kek air swept sieve technology, these machines can screen from 32 microns up to 5mm. The finer the screen the slower the throughput. The sieve can only achieve 2 streams per pass.
At the finer particle sizes, this technology excels at separating low density cohesive powders. These would be difficult if not impossible to achieve on flat deck screens at a reasonable throughput.
These sieves are also used for check screening either pre-process or post process to remove any coarse material which is potentially a contaminant to the end product.
A coarse feed screw transfers powder into the sieve where the screen is in the form of a tube. Rotating sweeper blades then aerate the material and the action of the blades and air flow generated, propels material smaller than the screen size through the screen into the main outlet. Oversize passes along the sieve tube and falls out of the end as a separate oversize stream.
While these sieves offer advantages highlighted above they have limitations and are not suited to removing high levels of oversize, they are also not ideal for dense, friable granules, abrasive materials or fibrous products.

In 35 years of contract processing powders and granules, Custom Powders Ltd has faced a huge range of exceptional requirements for finished product performance. Many of these have included requirements for low dust content whether required for aesthetic reasons, customer or user experience or critical to the end product performance.
Sieving has an important use here but is not always the answer. Air classifying has been extremely effective but depending on the raw material may be impractical.
As a result of this Custom Powders Ltd has developed a range of bespoke de-dusting systems and unique product tests, to ensure we have achieved consistent performance to the most demanding low dust products.
The most common application for de-dusting systems is within a value adding process eg agglomeration or compaction. Here the de-dusting not only has to achieve the end product requirement, it must be compatible with the speed of the process being operated.
De-dusters operate with both mechanical and air agitation to ‘knock’ fines off the product particle and then to remove the dust particle via air conveying. Whenever possible, dust extracted is recycled continuously to the process, for example in compaction or agglomeration.
A further option available to some products is by post treatment of a granule or powder with low levels of a suitable liquid, often oil. A suitable dosing and blending system is required often followed by a sieve system to remove or break down any agglomerates formed prior to packing.

Air classifying is suitable for high volume processing where a single product cut is required, to remove oversize or fines, typically between 10 and 300 microns. It is therefore capable of a smaller particle size cut than sieving.
The accuracy of cut achieved is very material dependant and requires extended development time.
Material is air conveyed into the classifier. This process is best suited to free flowing powders but sometimes it can accommodate cohesive powders. The vigorous air conveying and classifier action makes this process less suitable for hygroscopic or friable materials.
Once the material enters the classifier an adjustable but static baffle system combined with variable speed classifier wheel achieves the separation. Fine material passes out of the classifier with the air flow and is separated in a filter unit, from where it can be packed into big bags or sacks. Oversize drops out of the air flow in the classifier and is discharged via a rotary valve. Air classifying is commonly used in Protein Shifting where precise particle size control is essential to provide consistent high protein content in the fine fraction.