Sizing and selection
Vibrating screens, conveyors and feeders are made to the line. The points below are what a manufacturer needs to size one.
Start from the product
The product group decides most of the machine: raisins, apricots, figs, dates, beans, chickpeas and seeds each need their own deck opening, trough geometry and handling. State the product, its size range, whether it arrives wet or dry, and whether it tends to clump or stick.
Throughput
Capacity is stated as the quantity the machine must handle per hour in normal operation, with the peak if there is one. For a screen, throughput and the acceptable carry-over set the required deck area (see screening efficiency). For a conveyor or feeder, throughput and the layer thickness set trough width and speed.
Task
| Need | Machine |
|---|---|
| Move product between stations, even out batches | Vibratory conveyor |
| Break clumped fruit into single pieces on the way | Vibratory conveyor with internal agitators |
| Meter a batch from a hopper at a set rate | Vibrating feeder |
| Remove coarse trash | Vibrating screen, single or double deck |
| Grade into sizes and remove trash | Double-deck vibrating screen |
| Drain water after washing | Dewatering screen; fan-assisted if the next stage needs drier product |
| Remove leaves, stalks, dust | Vibrating screen with aspiration unit |
Layout
Infeed height, discharge height and direction, the space available and the position of the next machine fix the length, the angle and the outlet arrangement. Each outlet of a sizing screen needs room for a chute or a container.
Material
For food contact the frame and contact surfaces are AISI 304 stainless steel. AISI 316 is specified for contact surfaces where the process requires it, for example with higher salt or acid exposure. Screen panels are stainless steel made for the product group.
Drive and control
Vibratory machines are driven by vibration motors (typically two on screens, running counter to each other for a linear stroke) or by a geared motor on some conveyors. Supply is 380 V / 50 Hz three-phase in the lines described here. Control is either stand-alone or from the line PLC; a frequency controller allows the feed rate to be changed from the panel.
Cleaning and access
State how often the line is washed down and whether panels must be changed between products. Quick-release panels, removable trays and access covers are specified accordingly.
What is not fixed in advance
Deck opening, stroke and angle are set at commissioning with the actual product and adjusted after the first runs. Capacity figures for these machines are stated per project for this reason, not as a catalogue number.