This is the second article in a series of ten that present insights into the challenges faced while packing powders. In this article we try to understand the characteristics of powders and their implications on the selection and management of packaging solutions.

1. Understanding Powder Types

• Free-Flowing Powders — Excellent flow characteristics, relatively easy to handle. Examples: sugar, salt, suji, certain pharmaceutical powders and granular products.
• Non-Free-Flowing Powders — Poor flow characteristics; generally require a screw to assist movement and filling. Includes flour, milk powder, cocoa, and certain chemical powders.
• Hygroscopic Powders — Absorb moisture, which can change flow property and bulk density. Lumping and surface sticking are common challenges.
• Abrasive Powders — Cause wear and tear on equipment over time. Require durable materials and proper maintenance practices.
• Agglomerated Powders — Larger particle size with benefits including improved flowability, improved solubility, reduced dust, and easier packing — though at additional processing cost.

2. Key Powder Attributes — Bulk Density and Differential Flow Rate

Bulk Density refers to the mass of powder per unit volume. Understanding it is essential for determining filling equipment and optimising the process.

Differential Flow Rate is the rate at which powder flows under gravity at an angle greater than its angle of repose. Powders with low differential flow rates may require additional assistance such as vibration or agitation.

3. Powder Storage Guidelines

• Environmental Control — Store in a controlled environment, avoiding extreme temperatures and humidity.
• Container Integrity — Use airtight containers to prevent moisture ingress and contamination.
• Segregation Prevention — Store powders to prevent segregation, especially blends where different particle sizes may settle at different rates.
• Labelling — Clearly label with powder type, batch number, and storage conditions.
• Regular Inspection — Periodically inspect for caking, clumping, or changes in colour or texture.

4. Guidelines for Powder Conveying

• Equipment Selection — Pneumatic, screw, and vibratory conveyors each have advantages depending on the powder's flowability and sensitivity.
• Minimise Air Velocity — In pneumatic systems, control air velocity to prevent turbulence and powder degradation.
• Moisture Control — Use dry air and moisture removal systems when conveying hygroscopic powders.
• Avoid Segregation — Select methods that minimise segregation risk.
• Cleaning and Maintenance — Regularly clean conveying equipment to prevent cross-contamination.

5. Tailoring Equipment to Powder Characteristics

• Auger Fillers — Ideal for non-free-flowing powders like spices and powdered milk. Deliver constant volume, making consistent bulk density paramount.
• Volumetric Cup Fillers — Well-suited for free-flowing powders that move easily with gravity.
• Gravity Fillers — Cost-effective for free-flowing products like granulated sugar or salt.
• Net Scales — Excellent for high-accuracy requirements where product cost is significant.
• Loss-in-Weight Augers — For non-free-flowing powders requiring high accuracy; ideal for larger pack weights.

Summary

Success in powder filling lies in understanding and managing diverse powder characteristics. The powder determines how it will be conveyed and dosed — it is therefore important to understand the suitability of various types of dosers before making equipment decisions.