How to Ensure Blend Uniformity by Managing Fill Levels (Published in Powder & Bulk Solids)
A guide on how to manage fill levels effectively
Achieving blend uniformity is crucial in powder processing, and one of the key factors influencing this is the fill level of your blender. Here’s a guide on how to manage fill levels effectively, using GEMCO’s guidelines as an example.
Understanding Fill Levels
Optimal Fill Level: The optimal fill level ensures the best blend uniformity. For instance, in a 30-cu-ft double cone blender with a material density of 10 lb/cu ft, the optimal load is 300 lb. This load level typically places the material at the middle of the blender’s center band, considered 100% capacity. Based on this example, anything under 300 lb is technically underfilling the blender.
Underfilling: Loading below the optimal level can decrease blending efficiency. GEMCO recommends not underfilling below 25% of the optimal load. For the example above, this means not going below 75 lb. Underfilling can lead to increased mixing times and poor blends due to factors like particle morphology, lubricity, cohesiveness, and moisture, which could cause the material to “slide” on the blender walls rather than mix. If the blend load moves in a complete mass, it is “sliding” on the walls of the blender and not mixing. Tumble blender sizes are designed to operate at near peak efficiency based on optimal loading. The most uniform blends are achieved if your blender loading is within 5% of the optimal load.
Overfilling: Nothing mixes until it moves. Overfilling poses a risk of damaging the blender and leads to inefficient blending. In this case, there is less “head” or “void” space for powder to move into. The powder at the bottom must wait longer to move and then mix, if at all. The powder acts like a car in a traffic jam. This results in segregated materials and reduced blending efficiency. Unlike underfilling, adding more blending time does not resolve the issue. A good indication the blender is overloaded is that the materials in the blend will remain segregated. As with underloading, the characteristics related to the powder could have deleterious effects on the blend if not recognized as contributing factors.
Practical Tips for Managing Fill Levels
- Calculate the Optimal Load: Determine the optimal load based on the blender’s capacity and the material’s bulk density. For example, a 30-cu-ft blender with a material density of 10 lb/cu ft should be loaded with 300 lb of material.
- Avoid Underfilling: Ensure the load is not below 25% of the optimal level. For a 300-lb optimal load, do not go below 75 lb.
- Prevent Overfilling: Do not exceed the blender’s capacity. Overfilling reduces the available space for material movement, leading to poor blend uniformity and potential equipment damage.
- Monitor Particle Characteristics: Be aware of the material’s properties such as morphology, lubricity, cohesiveness, and moisture content. These factors can affect how the material behaves during blending.
- Conduct Thorough Powder Characterization: Thorough characterization of all powders in the blend is highly recommended to understand their behavior and ensure optimal blending conditions.
By following these guidelines, you can achieve more consistent and efficient blending results, ensuring high-quality blends for your processes.
