PH—Postharvest Technology: Friction of Wheat on Corrugated and Smooth Galvanized Steel Surfaces
✍ Scribed by M. Molenda; S.A. Thompson; I.J. Ross
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 281 KB
- Volume
- 77
- Category
- Article
- ISSN
- 0021-8634
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✦ Synopsis
A new modi"ed direct shear device was constructed and experiments performed to estimate the coe$cient of friction of soft red winter wheat on corrugated and smooth galvanized steel surfaces. The modi"ed direct shear test device is slightly di!erent from most conventional direct shear testers in that the metal test specimen is pulled to create a shear plane as it is moved within stagnant granular material. In most conventional direct shear test devices, the granular material is sheared across the metal test specimen by a force applied laterally to the grain compartment. The e!ects of steel sample size, sliding speed and normal pressure on the coe$cient of friction were studied for the corrugated sample using the modi"ed direct shear device. Four speeds of 0)05, 0)5, 5, and 50 mm/min were tested. Tests were conducted at three di!erent normal pressures of 6)9, 27)6, and 48 kPa. Using the modi"ed shear tester the coe$cient of friction of wheat on the corrugated surface increased with an increase in speed and decreased with an increase in normal pressure. &Slip-stick' behaviour was observed for tests with sliding speeds lower than 2 mm/min. Coe$cients of friction determined with the shortest and/or the narrowest steel sample were signi"cantly higher ( "0)05) than the values obtained with larger steel samples.
The test device was also adapted to enable measurements of the friction force of wheat on smooth galvanised steel. Friction was measured for two sliding speeds (0)5 and 5 mm/min) and three normal pressures (6)9, 27)6 and 48 kPa) At low speeds, slip-stick was observed that ceased after the speed increased to a critical value of 0)2 mm/min. Coe$cients of friction were found to decrease with an increase in vertical pressure.
Friction was measured using a tilting table test method on the same steel samples which had been used for the tests with the modi"ed shearing device. The coe$cient of friction had a tendency to decrease with an increase in normal pressure. Values of the coe$cient of friction determined using the tilting table test method were in the same range as those determined for test conditions using the modi"ed shearing device at the lowest normal pressures and sliding speeds.
Results from either the tilting table method or the modi"ed shearing method can be applied to design conditions at low pressures and low sliding speeds. For higher normal pressures and greater sliding speeds, the modi"ed shearing method should be applied. For practical applications the modi"ed shearing method should be used because it most closely smulates the actual conditions at the frictional interface in a grain bin when grain slides down the wall.