Bulk Solids Materials & Characteristics
Our original page had lists of the materials Trantec has successfully dosed going back to 1997. Over time this list has grown extensively and become difficult to utilise, primarily since some products are known by different names but are the same material. Instead, we have produced an overview of specific material properties, including some of the popular bulk solids handling terms and powder characteristics which are the most useful when considering how a particular product will behave.
Material Bulk Density
Bulk density is the mass of bulk solid that can be fitted into a defined volume. For example, how many Kgs can be accommodated in a hopper of one cubic metre. The manner in which the product is loaded into a hopper and what the material is subjected to can significantly impact the bulk density. In laboratory conditions, three classes of bulk density are widely recognised:
Aerated: Powder volume is increased by adding air to the point of almost destroying the bulk.
Poured: Powder is poured into the receiving vessel from a specific height and rate.
Tapped: Powder is densified by “tapping” the receiving vessel to reduce voids within the material.
Angle of Repose
The maximum angle from the horizontal, where a bulk solid remains in place. The angle is formed when a bulk solid is “poured” steadily to create a “mountain shape.” This angle is a good indicator of the degree of flowability in the material. Free-flowing products produce a small flat-shaped peak, while cohesive materials create tall, sharp profiles with high angles of repose.
Here are some key material characteristics types that Trantec metering screw feeders successfully handle.
Abrasive/Corrosive materials: Trantec manufactures volumetric and gravimetric screw feeders from 316 stainless steel, built to withstand highly acidic environments, corrosive material handling, and extreme temperatures. Due to the formation of chromium-rich oxides on 316 stainless steel, this gives increased oxidation protection against corrosion, rusting, and stains, ideal for food, chemical, and pharmaceutical application where frequent sterilisation with strong disinfectants is applied.
Fine powders and fibrous materials: Trantec’s screw feeders include a variable function 360 degrees rotating agitator for fine powders and fibrous materials. When used in continuous operation, the agitator eliminates bridging, keeps fibrous materials loose, or de-aerates and densifies fine powder.
Delicate and friable materials: Materials with these characteristics may bridge unless gently and regularly activated. When the feeder’s agitator is used in a slow, intermittent operation, this allows successful feeding of delicate and friable materials.
Sanitary materials: Trantec hygienic feeders are constructed from materials that meet every EC and FDA food contact regulations and for sanitary material handling are manufactured crevice-free with a mirror finish (0.2Ra). As standard, our feeders include blue, metal detectable silicone gaskets, PTFE based cartridge shaft seals, and are comprised of autoclave-friendly removable parts to ensure a contamination-free metering process. In addition, optional quick-release, easy-clean features are available across all our feeder ranges, enabling rapid dismantling and non-problematic cleaning.
Sticky and cohesive characteristics: Materials with these characteristics are particularly susceptible to bridging, forming congealed lumps and causing blockages. For effective feeding, Trantec’s agitators adopt proven technology from the mixing industry with left, and right-hand contra-rotating scroll blades This ensures the material is evenly and continuously stirred to prevent bridging or rat-holing. For extremely sticky and cohesive materials, vibration can be added on the outer side of the hopper for further agitation.
Free-flow materials: Trantec screw feeders are manufactured without the agitator for very free-flow powders and granules. The conditioning section geometry ensures a smooth material flow is evenly distributed within the rotating auger screw for effective feeding.
Materials that fluctuate in density: Trantec’s gravimetric screw feeders is ideal for materials that fluctuate in density. The self-calibrating system uses an advanced loading cell and controller combination to achieve extremely high accuracies of 1 to 2%. In operation, as the material in the feeder is discharged, the weight of the feeder is constantly monitored and converted into a weight per unit of time. If there is a deviation between the dispensed material value and setpoint, the gravimetric controller automatically adjusts to deliver the correct dispensing rate. Therefore, fluctuation in density does not affect the end result.