Feeder Types Selection & Operation
The Generic Feeder Model UPSTREAM MATERIAL INPUT CONTAINMENT & CONDITIONING METERING DOWNSTREAM MEASURING & SENSING CONTROL
Metering Design types Screw Cone Liquid Pump Vibratory Rotary Valves Bulk Solids Pump Belt Smart Flow Meter
SCREW FEEDERS
Screw Metering Principle of Operation Material enters screw positioned at/near the bottom of the feeder bin Advancing flights move the material through tube to discharge. Design Variables Single or twin screws, open-, or closed-flight, diameter, pitch, speed range, etc. Rate Control Adjustment of screw speed
Single Screw Feeders
Twin Screw Feeders
Micro Screw Feeders
Screw Feeder Sizing Product bulk density (bd) (kg/m 3 ) Screw capacity (sc) m 3 /rev Screw speed (ss) rev/min Q (kg/min) = bd x sc x ss rate Set Up 40% < drive command < 60% for constant
Screw Type Selection
Screw Type Selection Screw Type Concave screw Auger screw Spiral screw Diameter Tube length
Screw Selection Chart
Twin Screw Feeder Screw Chart K2MVT35
CONE FEEDERS
Cone Principle of Operation Screw-less feeding mechanism Design Variables Stepper motor Low rate tip Vertical discharge option Rate Control 0.2 to 2 dm 3 /hr (0.007 to 0.07 ft 3 /hr) with extension tip: as low as 0.1 dm 3 /hr (0.004 ft 3 /hr)
Very Good Accuracy
Applications Mainly low rate of granular material, such as color additives Film Injection Molding Plastic Compounding Fiber and Filament Plastic Wood Profile Plastic
Cone Feeder Click on the image to view the video
Advantages Modular design Screw-less rotating cone, no friction Superior accuracy (even at 1 second intervals) Simple mechanical construction Low maintenance costs Minimal spare parts requirements Easy and fast to clean Simple on-machine calibration Visual run check (tube rotation) Interchangeable with BSP-100 for higher rates
LIQUID FEEDERS
Liquid Pump Principle of Operation A metering pump or control valve with liquid supply tank is continuously weighed Discharge rate equals sensed rate of system weight loss Periodic manual or automated refill is required
Liquid Pump Design Variables Selection of pump type, flow range, scale range, holding tank capacity and refill parameters Rate Control Closed-loop modulation of pump speed or control valve position based on sensed rate of system weight loss
VIBRATORY FEEDERS
Vibratory Principle of Operation A specially configured springmounted metering channel is vibrated causing material to advance through the channel to discharge. Vibration offers gentle handling of free-flowing, granular, friable, abrasive or fibrous materials. Periodic manual or automated refill is required
Vibratory Design Variables Hopper design, inlet sizing, tray/tube size and geometry; drive power, spring constant Rate Control Closed-loop modulation of vibrational amplitude based on sensed rate of system weight loss
Vibratory Control Principle Feeder signal Controller Setpoint amplitude Amplitude control (fast) Digital/ analog converter Frequency adjustment (slow) Setpoint frequency Drive Current signal Strokesignal Amplifier Vibratorytray Spool
Vibratory MF = δ x A m x D x Ω where δ = bulk density A m = area of product on tray D = tray displacement Ω = tray cycles per minute
ROTARY FEEDERS
Rotary Feeder Principle of Operation Free-flowing material held in a weighed supply hopper fills the voids of an integral pocketed spool. Rotation advances the confined material to gravity discharge. Periodic manual or automated refill requiredḅsh&e is
Rotary Feeder Design Variables Spool size, number of pockets, rotation speed range, supply hopper type/size, purging and refill requirements Rate Control Closed-loop modulation of spool rotation speed based on sensed rate of system weight loss When used as a pre-feeder only, spool speed may be slaved to feeder rate RUN EDK VIDEO HERE
BULK SOLIDS PUMP
BSP (Bulk Solids Pump) Principle of Operation Inter-particle forces produce a lock-up condition in multi-channel spool As spool rotates, lock-up forces relax at bottom of feeder and material is pushed to controlled gravity discharge Design Variables Rate Control
Lock-Up Principle The BSP principle provides continuous, positive displacement volumetric control by exploiting the phenomenon known as lock-up. LOCK-UP
Zone 1:Consolidation ZONE 1: CONSOLIDATION Interparticle forces produce lockup at the end of Zone 1 Zone 1
Zone 2: Rotation ZONE 1: CONSOLIDATION Interparticle forces produce lockup at the end of Zone 1 ZONE 2: ROTATION Material is in lock-up condition throughout Zone 2 and rotates as a solid body Zone 2
Zone 3: Relaxation ZONE 1: CONSOLIDATION Interparticle forces produce lockup at the end of Zone 1 ZONE 2: ROTATION Material is in lock-up condition throughout Zone 2 and rotates as a solid body ZONE 3: RELAXATION Interparticle forces fall below lock-up threshold Zone 3
Zone 4: Active Discharge ZONE 1: CONSOLIDATION Interparticle forces produce lockup at the end of Zone 1 ZONE 2: ROTATION Material is in lock-up condition throughout Zone 2 and rotates as a solid body ZONE 3: RELAXATION Interparticle forces fall below lock-up threshold ZONE 4: ACTIVE DISCHARGE Flexible guide aids material discharge Zone 4
BSP Video Clip click on the graphic to start the video
BELT FEEDERS
Purpose Meter relatively high volumes of granular or freeflowing product into the process with an accuracy of +/- 0.5% with good precision SWB 300 WF 300
Belt Principle of Operation Material enters upstream end of advancing belt and is sheared into a shallow, reasonably uniform bed Material discharge by gravity off end of belt. Scraper assures complete discharge Design Variables Belt width, inlet gate geometry, belt speed range Rate Control Continuous feeding according to set point Batch feeding according to batch time Belt speed constant metering of a bulk material flow
WBF Control Principle I Single scale version Belt load (q) Weigh bridge q Mass flow Q = q * v Setpoint speed pick-up Speed feedback (v) Controller Drive command Controller Weigh Bridge Motor drive
WBF Control Priniciple II Twin scale version Belt load (q) Weigh bridges Shift register Tare Brutto Netto speed pick-up q Weigh Bridge Mass flow Q = q * v Setpoint Motor drive Controller Speed feedback (v) Controller Drive command
Weight Belt Feeder Sizing Capacity Product Bulk density (BD) Shear gate area (GA) Bed depth Belt speed (BS)
Inlet Section Raise or lower to set belt loading
WF Speed and Slip Sensors Belt Slip Detector Sensor WF300 Speed sensor and In-Line Gear Reducer
SWB Optical Belt Speed Encoder SWB300 Belt Optical Tachometer 2000 pulses per revolution
Belt Feeder Sizing Kg/hr Lb/hr dm3/hr ft3/hr SWB-300 20 20000 44 44000 10 40000 0.4 1400 SWB-600 40 40000 88 88000 20 80000 0.7 2800 Belt Speed controlled to within +/- 1RPM over a 100:1 range full motor speed Inlet SWB-300 SWB-600 Small 75mm (3 ) 300mm (6 ) Medium 150mm (6 ) 375mm (9 ) Large 230 mm (9 ) 450mm (18 ) Drive reducers: 20:1, 40:1, 80:1 Material Bulk Densities: 0.5 to 2.5 Kg/l (31 to 156 lb/ft3) Maximum Material Particle Size: 10mm (0.4 )
Weigh Belt Feeding Advantages High gravimetric accuracy on most free flowing materials; suitable for high-rate applications Accommodates larger particle size materials Compact, low headroom Disadvantages Floodable or hard-to-flow materials may require the use of a pre-feeder Requires periodic calibration Relatively mechanically complex; potential cleaning/maintenance concerns
Smart Flow Meter
Smart Flow Meter The K-SFM provides accurate and reliable gravimetric flow measurement of the resin Models for rates up to 200 m 3 /hr (7,000 ft 3 /hr) Two strategically placed digital Smart Force Transducers are combined to produce the flow rate measurement F R F P
Theory vs. Practice Easy Flowing Single screw feeder Twin screw feeder with intermeshing augers Weigh belt feeder with standard shear gate Bulk solids pump Vibration tray Difficult Flowing Single screw feeder that has an undersized screw in reference to the tube Twin screw feeder that has non intermeshing screws Belt feeder with a modified inlet section
Theory vs. Practice Floodable (1) Twin screw feeder with concave screws Adhesive & Cohesive (2) Twin screw feeder with augers or twin spirals Belt feeders with screw pre-feeders (1) For refill devices avoid slide gates and butterfly valves. A rotary feeder provides a nice even drop of materials without inducing a lot of air (2) Most difficult material to handle. Most likely require the use of flow-aid devices
Comparison Summary Attribute True positive Displacement Action Linear over full operating range Uniformity of discharge Active discharge (no residual material) Unaffected by differential pressures Mechanical & maintenance simplicity Screw Feeder No Poor (screw fill dependent) Poor (pulses) Belt Feeder Dependent on material Dependent on material Dependent on material limited (product plug at screw flight) limited M (product plug at belt) Rotary Feeder Vibratory Feeder BSP No No Yes Poor No yes Poor (pulses) Bad (product plug at the rotary wall) Good Bad Good Good Limited No Yes No Yes Yes No Yes Yes yes M