Physical properties of powder

“Grasping the powder nature” is something quite difficult. In the engineering field it is called “Powder technology”. We, Tam have built our knowledge and experiences of the powder engineering through our cases of filling machines and we have succeeded in many cases. In this article, we would like to introduce what are the points for handling powders, and our studies and solutions.

Powder Characteristics

Powder can be roughly classified in two types. One is called as “free-flow” that means easy to flow; for example, when you grip the powder in your hand and then open your hand, if the powder is not shaped but just spilled out, it is called free-flow powder. The other is called as “non free-flow” that means the powder remains the shape of gripping when you open your hand. These powder characteristics are the flowability. The flowability of the powder is indicated by “Carr’s index”. The index chart shows the values of the “Compressibility”, “Angle of repose”, “Angle of spatula”, and “Cohesion (Uniformity)”.

Compressibility

Compressibility can be calculated by the ratio of the difference between “loose bulk density” and “tight bulk density”. The “loose bulk density” is the density when pouring the powder into container by free fall and the “tight bulk density” is the density by tapping the container while pouring the powder into container. The smaller the difference, the distance between the powder particles get naturally closer, so it is said the compressibility is low and the flowability is high. The bigger difference, vice versa, the distance between the powder particles isn’t naturally filled, so the compressibility becomes high by external factor. This means the flowability is low and the powder can be classed it doesn’t flow easily.

Angle of repose

The Angle of repose is obtained by the inclination and the horizontal level when the powder is heaped naturally. If the powder has high flowability, the powder easily moves and flows so the pile of powder become low and the angle of repose are low.
If the powder has low flowability, the powder stays in the powder pile, so the angle of repose is to be large.

Angle of spatula

The angle of spatula is obtained by the inclination and horizontal level created when a spatula is inserted horizontally into the pile of powder and then the spatula is lifted up. Same as the angle of repose, the angle becomes low when the flowability is high and it becomes high when the flowability is low.

Cohesion (Uniformity)

The cohesion is obtained by the remaining amount of powder when the powder is sieved. If the powder has high cohesion, the powder particles stick each other and unlikely to fall. The amount of falling powder is small, so this means the powder has low flowability. On the other hand, if the powder has low cohesion, as the powder is easy to fall from the sieve, the amount of fall is large. This means the powder has high flowability.

From the above index values, the flowability is evaluated in 7 levels ; “Very good” if the index is 90- 1oo, “Fairly Good” for 80-89, “Good” for 70-79, “Normal” for 68-69, “Not good” for 40-59, “Bad” for 20-39, and “Very bad” for 0-19.

Other than the powder flowability, in order to offer most appropriate machine for the customer’s product, we investigate the dispersion by dropping the powder from the prescribed height, or check if the powder fracture occurs inside the auger when the particle is large, and if the salt in the product will affect and generate rust on the machine parts.

Problems caused by Powder and solutions.

Depends on the above-mentioned the nature of powder, there might be some problems can be occurred during filling process. Here are the actual problems that could happen when handling powder with the filling machine and how we act for those problems and the solutions we have finally reached.

Powder jamming

The powder with its flowability bad tends to occur a jamming inside hopper. As auger filling machine adjusts the amount of powder to be delivered by the auger rotation, the powder jamming will cause variation for the filling volume. The jamming has two types; one is called as “Rat hole” that creates a hole at the center of the powder as the powder surrounding area become hard like a wall inside hopper. The other is called as “Bridge” that the powder is aggregated in center when it is discharged, and it becomes hard and creates an arch-shaped bridge. For these phenomena, Tam offers the following solutions;

Low speed agitator, High speed agitator

The low speed agitator rotates inside the hopper to stir the powder adheres to the wall. It also works to uniformize the powder flowability by agitating. The high-speed agitator is installed at the lower part inside the hopper, and its rotation in high speed closely the discharging area makes the powder to contain oxygen and the flowability better and prevent generating rat hole or bridge.

The concerns of the low speed agitator are the breakage the granule product or the product contains oil may be kneaded by stirring. Those concerns, however, can be dealt with by changing the agitator shape or adjusting the motion.

Sealing contamination

The seal contamination is as major issue on the powder filling as the powder jamming. The contamination is the phenomenon that powder remains between the sealing joint. When one cycle filling is completed, if the next filling cannot be hold at the end of funnel but a small amount of powder is dropped unintentionally, it gets caught between the seal. This causes the failure of sealing performance and the product deterioration.
Tam offers some options for the contamination by using parts and devices.

Star rings, rings, washers

The star rings, rings and drip washers are the parts to install at the end of the filler’s funnel. These parts are mounted on the purpose to hold the powder and prevent dropping. Accuracy adjustment will be made by changing the size and shape according to the powder nature.

Deairing

Deairing device is used for the non-free flow powder of bad flowabililty. It has an effect to aggregate the powder to prevent dropping by deairing at the end of the funnel. Please see the reference movie from our You tube channel:
https://youtu.be/L1MsQ00vXL4?t=50

TAM Test room

We hope you understand from the above-mentioned explanation, for handling the powder product is very difficult to get to know the nature and it is essential to experience trial- and-error process for filling and packaging. Tam has testing room in our factory and conducts the sample product supplied from the customer for trial on the machine with the properly selected option devices and parts for the product. This is possible because TAM manufactures both filling machine and packaging machine.

If you have problems with packaging powder products, please feel free to ask us and let us support with our long-year history and assured experiences.
Tam Contact to: tam-overseas@tam-tokyo.co.jp