Factors affecting the smoothness of flow rate of a screw feeder and a rotary table feeder

Abstract

Screw feeders and rotary table feeders are used extensively in bulk materials handling and powder processing industries. Generally, the instantaneous discharge flow rates from the screw feeder and the rotary table feeder exhibit some degree of rapid fluctuation and possible medium-term flow variation. The present work experimentally investigates the effects of various factors on the smoothness of the discharge flow rate of a typical screw feeder and a rotary table feeder. In the case of the screw feeder, the factors investigated are two types of test material, four configurations of outlet ports, applied back pressure, and the rotational speed of the screw. In the case of the rotary table feeder, the factors are the same types of test material, the vertical gap between the coarse scraping plate and the tumtable surface, the insertion depth of the fine scraping plate from the tumtable edge in the radial direction and the rotational speed of the turntable. In addition, the effect of stearic acid lubricant is also investigated. From the experimental results, it has been found that in the case of the screw feeder the suitable conditions for LLDPE resin are: screw speed of 50 rpm with back pressure of 2 kg/cm[superscript 2] and trapezoidal outlet (the resulting flow rate is 7.16 g/sec and flow variation is 4.694x10 [superscript -3]). For LLDPE pellets and gypsum powder, the suitable conditions are: screw speed of 38 rpm without back pressure and circular outlet (the flow rate is 1.10 g/sec and its variation is 1.143x10 [superscript -3]) and screw speed of 50 rpm without back pressure and circular outlet (the flow rate is 17.5 g/sec andits variation is 3.010x10 [superscript -3]), respectively. In the case of the rotary table feeder, the suitable conditions of LLDPE resin and gypsum powder are: the insertion depth of the fine scraping plate 12.0 mm, the vertical gap of the coarse scraping plate 1.95 mm, and the optimal rotational speed of the turntable 3 rpm (the flow rate is 1.8 g/sec and its variaton is 6.526x10 [superscript -2]), and 9 rpm (the flow rate is 3.444x10 [superscript -1] g/sec and its variation is 1.201x10 [superscript -2]), respectively. As for the lubricating effect of stearic acid in the case of the screw feeder, LLDPE pellets exhibit a smoother flow and pulsing is reduced. This trend is reverse when back pressure is not applied and when stearic acid is mixed into gypsum powder. Similarty, in the case of the rotary table feeder, both the LLDPE resin and gypsum powder also exhibit less smooth flow and amplitude of the flow fluctuation is increased ;เครื่องป้อนแบบสกรูและเครื่องป้อน