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With so many feeding and metering devices available in the market, how does a plant operator know which is the right one to select for bulk material processing? Our team at Palamatic Process has 29 years of experience in the powder handling and bulk solids industry. With our experience, we will give you the necessary information needed in 5 easy to answer questions to help you select the right dosing equipment.
1- What type of material are you dosing?
This may seem like and obvious question, but it is still an important one. Different materials can have a wide variety of characteristics. Does your material flow well or is it cohesive and tend to stick to surfaces? Is it dusty, abrasive, friable?
Vibrating feeders are a great dosing mechanism for materials that are considered either friable or abrasive (or both). This metering equipment utilizes an open or closed trough that conveys the material into the downstream process. By shaking or vibrating the trough conveyor, the material’s integrity is kept intact. Also, there is much less wear and tear from abrasion extending the life of the feeder and resulting in less maintenance requirements. An adjustable feed flap allows the operator to slow down or speed up the feed rates.
Example of vibrating feeders dosing dry fruits into a belt conveyor.
Vibrating feeders are also commonly used on pellets, granular materials and capsules.
Screw feeders are considered all-purpose metering devices and are extensively used where friability and abrasiveness are not as much of a concern. If the material has poor flow properties, screw feeders can be supplemented with mechanical agitators to stir and promote material flow in the storage chamber of the equipment.
2- How accurate does your dosing need to be?
Some processes call for greater accuracy in how much powder is being dosed into packages, storage bins, containers, etc. You may be dealing with a processed material that has high value and therefore need to prevent profit loss by packing too much or too little. Screw Feeders excel at providing the necessary precision to significantly minimize material overfeeding. Palamatic Process offers screw feeders that in some instances can dose within -/+ 1 gram of accuracy.
Range of D10, D11, D12 and D13 screw feeders from Palamatic Process
However, you may be more concerned about rates and high-volume production on low value materials. In this instance, a butterfly valve with a positioner most likely will suffice. Using a butterfly valve with a positioner and pneumatic actuation allows the operator to have a measure of control over the flow rate of the material by adjusting the angle of the butterfly valve disc. By slowly closing off the valve, you get a degree of flow control as you approach your desired target fill weights.
3- Do you need to dose by volume or weight?
It is a common part of most processes for the operator to know how much material is being fed to the downstream process. This question, can be followed with additional questions to fine tune which measuring method is best suited. For example, do you have packages that are already pre-measured to a specific volume? By utilizing instruments such as level probes and sensors, we can tell the metering device to unload material until a certain level either within the feeder itself, or the container below has been reached.
On the other hand, if you need to set a target weight for the material being dispensed, integrating load cells on the feeding equipment will help achieve a loss-in-weight functionality. Or, you could use a gain-in-weight setup by putting the load cells on the station under the receiving container.
Palamatic Process has experience with both applications and can implement load cells, sensors, or level probes on our screw feeders and vibrating feeders.
In this illustration we see two feed screws on load cells dosing powder into a storage hopper below. The load cells allow the control system to measure the material dispensed by weight loss into the storage of the screw feeder.
4- What is the equipment that you are feeding material into?
Another very common practice for having the need to meter bulk solid product, is the introduction into a pneumatic conveying system. Rotary airlock valves provide the ability to both feed material from a bulk container above (bulk bags, sack, drums, etc.) into pressure or vacuum conveying systems. A multi-lobed rotor spins on its axis via a direct drive motor. As the rotor spins, material fills the empty pockets which are then exposed to the conveying system where the material evacuates and is swept away by the air conveyance. The rotor isolates the feed from the pressure or vacuum, therefore safely and effectively introducing the material into the transfer system. Rotary valves can implement VFD’s in order to slow down or speed up the rates at which the powder is dispensed. Caution must be exercised as speeding up the rotary valve too much may cost the operator filling efficiency of the rotors pockets and therefore defeat its purpose. Another common use for rotary valves is unloading raw materials from bulk storage equipment such as silos and bulk bags.
An example of a rotary valve on guide tracks to help implement the disassembly for cleaning and maintenance.
Perhaps you have to isolate the material under pressure, or you are dealing with an extremely abrasive or high temperature product. Dome valves with inflatable seals are a great option for dosing product under these conditions. As the valve closes, the seal inflates trapping product against the dome. The design and functionality provide the necessary seal against pressure and minimizes wear and tear on the valve itself. Palamatic Process offers the Inflatek® valve for ideal sealing and total containment with temperatures up to 350°C.
If you are simply looking to meter powders and bulk solids into a type of process equipment (e.g., mills, screeners, mixers, etc.) then most types of dosing equipment will be up to the task. Screw feeders, vibratory feeders, rotary valves all can provide the necessary metering this type of process equipment requires. With careful consideration, even screw conveyors may be able to provide the necessary rates for value-adding equipment to effectively process the material.
5- Does your process have strict hygienic requirements?
If so, you may want to look into feeding and dosing equipment that is designed with the intent of minimizing downtime due to cleaning and maintenance cycles. Feeding equipment is widely used in all dry process industries including mining, chemical and energy. However, the food, dairy, pharmaceutical, nutraceutical and cosmetic industries often require equipment that is made to prevent material trap points and can be easily sanitized between production runs. Palamatic Process offers a line of feeding and processing equipment we refer to as the ECD Range – Easy Clean Design sanitary equipment.
For example, our ECD rotary valve can be integrated with guide rails and clamping flanges to quickly pull the rotor out of its housing for inspection and cleaning. The Screw Feeder ECD offers the same design concept with the screw bearing and flights being supported by a quick release guide track for the same benefits.
The Palamatic Process ECD Screw Feeder with quick assembly features.
With 29 years of experience and over 2,000 installations in more then 30 countries, Palamatic Process can offer a full range of feeding and dosing equipment to meet any industry and material-handling process. Our equipment can be offered in mild/carbon steel, 304 stainless steel or 316 stainless steel fabrication with standard bead blast or special fine grit internal finishes. In order to determine which is the best feeding equipment for your powder process, please contact one of our sales representatives to discuss your project requirements.
