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Conditioning the powder in a packaging that will be convenient for the customer is a key process step. The powder must be brought in the right conditions to a filling machine in order to be filled typically either in small packs (retail), bags or Big Bags when delivering product to other industries.
Filling machines are quite complex machines that can be also sensitive to small variations in the powder, particularly if small sticks / sachets are filled.
Fillers are not managing well start and stop, the main task of the process feeding the fillers will be to ensure that the fillers have always product available for running. The process must be designed so that the bottleneck is the fillers, not any process step prior to them. Fillers must be placed below a buffer that will ensure that powder is always available. The process must be such that the buffer never runs empty. If the process is continuous, then the buffer shoudl be sized to absorb process upsets that can happen (to be estimated during design), if it is running per batch, then the buffer will have to be large enough to not get empty in between the delivery of batch n and batch n+1.
For Big Bag fillers or bag fillers, this aspect is not that important, the objective is actually there to fill the bag as quick as possible. Therefore it is often done simply by gravity or with a very fast dosing equipment. What matter here is to not delay the filling of the bag, and especially to manage to remove the false air from the bag when the powder is dropped. A filter must then be installed on the filling head, large enough to evacuate the air and avoid any back flow of air to the process that could reduce the flow of material.
Filling machine can be equipped with the following features :
- Conveyors to bring and remove the bags
- Inflation fan, to form the bag prior to filling
- Clamping system, filter and fan to ensure filling without dust emission
- Load cells to measure weight of bag
- Vibrating table to compact the bag and fill more powder
It is also possible to gas the bags / Big Bags if the packaging is designed for such purpose
Such fillers are very different than bags or BB fillers. The intake of powder is of primary importance here, since any upset will lead to losses and / or stoppages. Such fillers are usually equipped with a small hopper that ensure an almost constant supply of powder to the filler by ensuring that the level is varying slightly in between 2 levels defined. The process upstream has to be designed to gently provide powder to this hopper whenever it needs it, without overfilling it. It is therefore essential to dose the powder supplied. The worst system is to provide powder very roughly following an on-off way (typically done by a butterfly valve). Typical systems to feed the filler will be screw conveyors, rotary valves or vibrating valves.
Dosing the powder gently supposes that the powder above the dosing
equipment is available : the buffer above the dosing equipment must be
designed in such a way that there is always at least a minimum level
of product inside. Key design characteristics will be the following :
- Interuption time of powder infeed to the buffer must be estimated so that the volume of the buffer can be calculated
- Single outlet buffer is preferable to avoid segregation effets (for powder sensitive)
- Outlet diameter and cone angle must be determined for the product processed
The loose density of the product to be filled is of importance to design the filling process. Indeed, one basics, but often challenging, is that the powder must fit in the packaging foreseen. The loose density must be considered, if the filler is equipped with a vibrator, then the density after vibration could come closer to the tapped density.
The amount of fines in the product is another key element to assess. Besides the fact that the processing area can be dirty if dust is not properly controlled (see ATEX page), fines deposits on the packaging material can have a very disturbing effect on the sealing. Dusty products may cause sealing issue that, in return, will decrease the efficiency of the line. If it is a problem, fines must be sucked and filtered.
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