Comminution Equipment and Selection Techniques Lawrence Novotny Midwest AOAC June 6, 2018

Hand Tools mainly used to cut material to be fed into equipment scissors clippers pruning shears knives paper cutter saws salad choppers

Selection Techniques Selection process is the physical selection of a smaller mass from a larger mass to obtain a subsample or a test portion. Mass Reduction – selection of a smaller mass from a larger mass Splitting – division of a mass into 2 or more equal portions

(grouping & segregation error)2 = distributional heterogeneity Selection Techniques (grouping & segregation error)2 = distributional heterogeneity number of increments Technique No. of increments RSD2 Est max error, % coning and quartering 2 6.81 22.7 should never be used stationary splitting 10–12 1.01 3.4 rotary splitting >100 0.125 0.42

Stationary or riffle splitting Selection Techniques for Flowable Solids dry ground feeds and forages, grains, oilseeds, mineral mixes, solid fertilizers and dry soils Rotary splitting Fractional shoveling Stationary or riffle splitting

Criteria for Selecting Splitters chute width be 2X the diameter of the largest particle + 5 mm constructed of inert material easy to clean fine powders may have a tendency to stick

Rotary Splitter

Rotary Splitter

Fractional Shoveling

Fractional Shoveling Advantages used in lab or field bo extra equipment minimal clean-up and decontamination any number of splits can be generated Critical mass of each increment must be consistent same number of increments in each split

Stationary or Riffle Splitters

Stationary or Riffle Splitters operator dependent and must be used properly gated rifflers are preferable material must be distributed and fed evenly across the chutes material is to be fed perpendicularly to the longitudinal axis of the chutes do not feed to fast to avoid overflowing and clogging of chutes

for Nonflowable Solids Selection Techniques for Nonflowable Solids wet soils, semi-moist fertilizers, solid manures meat and food products, slurries can also be used for flowable solids 1-dimensional slab cake 2-dimensional slab cake

1-dimensional slab cake create elongated pile as entire sample is poured from container can be poured in single pass or in back & forth motion each increment is taken by removing a slice across the entire width & depth of the pile each increment must be of uniform mass or volume slab cake can be reformed perpendicular to original slab cake to collect additional increments

1-dimensional slab cake

2-dimensional slab cake formed by flattening entire sample using a straight edged tool final shape not critical uniform depth is critical, < 1 cm formed with minimal manipulation to avoid segregation of fines select increments of equal mass from random locations across entire surface of slab cake try to remove a perfectly vertical column in each increment

2-dimensional slab cake

Sampling Tools flat blade spatula rounded scoopula square scoop bias small particles bias large particles no bias

pour out test portion needed or remove single increment by pipet Selection Techniques for Single-Phase Liquids without Solids water, oil, molasses, liquid fertilizer pour out test portion needed or remove single increment by pipet

Selection Techniques for Multi-Phase Liquids without Solids whole milk, salad dressing oil contaminated water some cases, do thorough mixing, provided phases do not immediately separate (milk) complete separation of phases; sample each phase as single phase liquid selection of cylindrical core through entire depth of all phases

Selection Techniques for Multi-Phase Liquids without Solids

Selection Techniques for Liquids with Solids water containing sediment, liquid manure juices containing pulp mixing does not work since segregation immediately starts when mixing stops separate solids from liquid (centrifuging or filtering), analyze separately, and combine results mathematically lab churn

Lab Churn

Achieve Sample Correctness Conclusion Achieve Sample Correctness reducing particle size thru comminution selecting numerous increments using the correct techniques and tools

Laboratory Sampling Resources https://www.aafco.org/Laboratory Questions?