Grain Cleaning Machine

Overview

A grain cleaning machine takes raw grain straight off the field or out of storage and removes everything that is not sound grain: straw, chaff, dust, weed seed, sand, stones, mud balls and tramp metal. It is the first machine in almost every flour mill, seed plant, malthouse, feed mill and grain terminal, because nearly every later step assumes a clean, uniform feed. Dirty grain abrades milling rolls, dilutes the product, harbours insects and downgrades the sale. This machine cleans by stacking several physical separations that each exploit a different property: size, terminal velocity, density and magnetism. The model here combines a vibrating screen separator with closed aspiration, a gravity destoner and a magnetic grate in one frame.

Grain enters through the Feed Section, drops onto the Sieve Box, passes the Aspiration System loop, crosses the Gravity Destoner deck, runs under the Magnetic Separator and leaves through the Outlet Section. The whole shaking deck rides on the Anti-vibration Suspension, everything bolts to the Frame Body, and the Control Panel runs the drives.

Feeding and distribution

Even cleaning depends on an even feed. The Feed Section spreads incoming grain across the full screen width and meters it to a thin, steady layer. The Distribution Hopper fans the stream out sideways, the Feed Gate sets layer thickness, and the Spreader Roll turns slowly to break clumps. A Feed Level Sensor tells the panel to throttle the feed when grain backs up, so the screens are never flooded. A flooded screen cannot grade, because grain rides over the apertures instead of presenting itself to them.

Scalping and grading by size

Size separation happens on the Sieve Box, a stack of two decks given a controlled linear stroke. The upper Coarse Scalping Screen has large apertures, typically 6 to 12 mm. Good grain falls through it while straw, cobs and other oversize ride over the top and leave as scalpings. The lower Fine Grading Screen has small apertures, typically 1.5 to 3 mm. Now the logic flips: sand, dust, broken kernels and small weed seed drop through as undersize, while the sound grain is carried over the screen to the next stage. Each screen sits in a tensioned Screen Frame held flat by Screen Tension Hook hooks, because a slack cloth blinds and grades poorly. Below each deck a layer of Rubber Cleaning Ball cleaners bounces against the underside, knocking out kernels lodged in the holes and stopping the screen from blinding. The balls stay in their compartment on a Ball Retention Tray.

Aspiration by terminal velocity

The Aspiration System system separates by weight rather than size. As grain falls through the Aspiration Channel, an upward airstream lifts anything whose terminal velocity is below the air speed: husk, dust, empty hulls and the lightest weed seed. Sound grain is heavier and falls straight through. The Centrifugal Fan sets the air speed, usually 4000 to 9000 m3/h, and an Air Volume Damper trims it so each grain type is cleaned without blowing away good kernels. The dusty air slows in the Expansion Chamber and then the Settling Chamber, where the carried material drops out and leaves through a Rotary Airlock. The cleaned air returns to the fan through the Air Recycle Duct, so the loop runs nearly closed and most dust stays inside the machine instead of in the room.

Destoning and magnetic removal

Stones and mud balls are close to grain in size, so screens cannot catch them. The Gravity Destoner separates them by density. Air blown up through the Destoner Deck fluidises the bed: light grain floats and slides down the incline to the outlet, while dense stones lose contact with the air cushion and walk uphill on the deck vibration to the Stone Discharge Channel. The Incline Adjuster balances grain travel against stone climb. Last, the Magnetic Separator pulls ferrous tramp metal, nuts, nails, wire and bolts, onto rare-earth Magnetic Grate Bars bars of 9000 to 11000 gauss, protecting the rolls and hammers downstream. The grate is cleared from a Cleanout Drawer.

Drive, vibration and isolation

The deck is shaken by the Vibratory Drive. Two counter-rotating Vibromotor units, or an Eccentric Shaft with adjustable Adjustable Counterweight weights, give a linear stroke of about 6 to 10 mm at 900 to 1500 rpm. That stroke does two jobs: it conveys grain along the deck and it stratifies the bed so heavy kernels settle onto the screen and light trash rises. None of this shaking should reach the building. The Anti-vibration Suspension hangs the sieve box on eight Coil Spring units that store and return the stroke energy, so the dynamic load seen by the Frame Body and the floor is small.

Materials, capacity and use

Surfaces that touch grain are usually mild steel, with stainless used for the magnet housing and food-contact spouts. Screens are perforated steel or woven wire. The frame is box-section steel sized for the cyclic load. Throughput on a combined cleaner runs from about 5 t/h on a seed-plant model to 30 t/h on a terminal unit, and it depends heavily on the grade demanded: a cleaning pass for storage runs faster than a fine seed grade. Installed power is modest, roughly 4 to 11 kW across the vibromotors and the fans, because the work is separation rather than size reduction. A plant matches screen apertures and air settings to each crop, wheat, maize, paddy, soybean or sunflower, then leaves the machine to run continuously ahead of milling, seed treatment or storage.