Flour
Laboratory Viscometer Application Data Sheet
USE
Used for baking and cooking
Test Equipment
- Instrument: Powder Flow Tester (PFT)
- Trough: 230 cc, 6-inch diameter
- Lid Type: Vane Lid, 304 s/s, 33cc, 6-inch diameter (Flow Function)
Wall Lid, 304 s/s, 2B finish, 6-inch diameter (Wall Friction) - Type of Test: Flow Function Test, Wall Friction Test
- Temperature: Room Temperature (70-72° F)
- Humidity: 24%
Method
A Brookfield Powder Flow Tester, equipped with Powder Flow Pro software for automated instrument control and data acquisition, was used to test this name brand flour. The flour was scooped into the trough, and the scraping tool was then used to evenly distribute the powder throughout the trough. After recording the sample weight and entering it into the software, a standard flow function test and then a wall friction test were run. Time required for each test was 35 minutes and 20 minutes respectively.
Parameters Measured
- Flowability: Very Cohesive to Cohesive
- Wall Friction: 12° (0.5 kPa) to 9.5° (4.75 kPa)
- Bulk Density: 530 kg/m³ to 880 kg/m³
Analysis
- Hopper Shape: Conical
- Arching Flow Factor: 1.40
- Critical Arching Dimension:
- Rathole Diameter: Dependent on bin diameter
Results
Figure 1: Flour Flow Function Graph
Figure 1 shows the flowability of the flour at different levels of consolidating stress. These results show that the flour is generally cohesive except at very low levels of consolidating stress where it begins to fall into the very cohesive range (below 2 kPa).
Figure 2: Flour Wall Friction Graph
Figure 2 represents the angles of wall friction at different levels of normal stress. Angles of wall friction represent the friction between the sliding powder and the wall of the hopper or chute at the onset of flow. In this test a stainless steel lid was used, illustrating what the friction would be like if the flour was in a stainless steel hopper. At a low normal stress of about .5 kPa, the effective angle of wall friction is about 12º and goes down to about 9.5º at higher levels of normal stress (4.75 kPa).
Figure 3: Flour Bulk Density Graph
Figure 3 shows the bulk density of the material at different levels of consolidating stress. This graph tells us that the flour has a fill density of about 530 kg/m³ and rises to about 880 kg/m³ at around 4.5 kPa of consolidating stress. In general, a free flowing powder will show very small changes in bulk density, whilst a cohesive or poor flowing powder will generally show a large increase in bulk density.
Conclusion
The flour is a very cohesive powder at low consolidation stress levels and cohesive at high consolidation stress levels. This means that the flour may have flowability issues as the hopper empties. Possible problems include arching (when the powder forms a cohesive bridge over the outlet) and ratholing (when the powder flows out only from the center leaving the rest of the material static against the walls). The critical arching dimension, of 4.192 inches (104.8 mm) provides a conservative estimate to prevent arching from happening, provided the minimum outlet dimension of the hopper exceeds this value. The critical ratholing dimension is dependent on the diameter of the bin. Powder Flow Pro can automatically calculate the rathole diameter once the bin diameter is entered.
