Effects of corn kernel hardness and grain drying conditions on particle size when grinding using a roller mill or hammermill
Published:March 11, 2020
By:Hernan Cordova-Noboa, Edgar Oviedo-Rondón, Ivan Ospina-Rojas, Adam Fahrenholz, Viviana San Martin, Miguel Chico, Yilmar Matta-Lozano, Andres Ortiz-Diaz, Lina Peñuela-Sierra. / Prestage Department of Poultry Science, North Carolina State University.
Summary
Corn kernel hardness and grain drying conditions may affect particle size and distribution subsequent to grinding, which could affect feed mill productivity and animal performance. In the present study, the effects of two corn hybrids (Dekalb 68-05 and Dekalb 65-20) with differing kernel hardness (average and hard respectively) and three grain drying conditions (35, 80, and 120°C) on the geometric mean (Dgw) and standard deviation (Sgw) of particle size were assessed by the sieving method. For roller milling, four combinations of roll gap settings were studied (0-0, 25-20, 30-30, and 35-35.) For hammer-milling, three hammermill speeds were evaluated (900, 2,400 and 3,600 rpm) in each case grinding through a 12-12 screen combination. Treatments were arranged in a 2 x 3 factorial design with two corn hybrids and three grain drying temperatures. There were three replicates per treatment combination. Data were analyzed in a completely randomized design and mean separation was done using Tukey’s test. Results obtained by roller milling with 0-0 and 35-35 roll gaps showed that harder corn kernels yielded higher (P < 0.001) Dgw values in comparison to corn with average kernel hardness when dried at 35°C. Similar response was observed when the corn was dried at 120 °C.
In addition, the Sgw was reduced (P < 0.001) when using corn with harder kernels that was dried at 80 and 120°C and milled at 0-0 (2.39 vs. 2.53), 30-30 (2.41 vs. 2.65), and 35-35 (2.34 vs. 2.69), respectively. In contrast, no effects (P > 0.05) were observed on Sgw when corn dried at 120°C was ground by the hammer mill. Higher (P < 0.001) Sgw was detected in the corn with average hardness that was dried at 35 and 80°C and milled at 2,400 and 3,600 rpm (3.84 vs. 3.45; and 3.21 vs. 3.03 respectively). The Dgw was higher (P < 0.001) in corn with harder kernels dried at 120°C when ground at 2,400 (744 vs. 594 µm) and 3,600 rpm (556 vs. 424 µm) respectively. Generally, corn with harder kernels and dried at 120 °C had higher Dgw and corn with average hardness had greater Sgw independently of the grinding method. In conclusion, kernel hardness of corn and grain drying temperatures affected the particle size and distribution subsequent to grinding in both a roller mill and hammermill.
I would like to propose my opinion to all interested parties as follows.
I also think that the grinding process is very important.
The reasons are 1) the generation of powder in the feed 2) the decrease in moisture in the grain 3) the particle size preference of animals.
-For pellet feed, a 2.4 mm screen for corn and a 2 mm screen for wheat should be selected and the other stripping grain 3.2 mm and hull grain 4 mm.
To do this, it is necessary to manage the temperature of all grains below the atmospheric temperature, and the moisture of the grains must be managed at 15 degrees? or below, and this must be done at the entrance to the Hammer Mill.
- During grinding, the filling rate inside the hammer mill should never be 100%, and my suggestion is to operate at a filling rate of 85%, because the air in the handle does not circulate, so the risk of fire and yield increase due to temperature increase.
Check this with the outlet temperature of the handle and the temperature after grinding, and grind it below the ambient temperature.
-Select the thickness of the hammer tip. For pellet feed, select 6 or 8 mm and set the rpm to about 1750.
We suggest 4 mm of Pig baby feeds and weaned pig feeds.
- The screen and tip spacing is 25 mm for the inlet, 12 mm for the middle, and 6-7 mm for the bottom.
- For laying hens and breeders, the screen hole is 6-8 mm and the rpm is 550->759.
Of course, in order to reduce the generation of powder, I mixed it with a roller mill grind and a hammer mill grind 50:50.
-Of course, it is suggested that the dust collector be selected, that is, the bag filter area vs air volume should be about 9 : 1.
-In order to operate as above, the analog thermometer must be installed in the following place.
1) Hammam wheat surge hopper Area
2) After grinding Area
3) Inside the hammer mill Area
4) fan outlet Area
If you have any questions regarding the above, please feel free to contact us by e-mail.
Thanks, Choi
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