Pneumatic distributors(spreaders)

In a pneumatic fertilizer spreader (Fig. 1.228) the fertilizer is fed from the metering rollers via injectors into streams of air. These metering rollers are, for example, driven by a hydrostatic motor. With the aid of an electric remote control this way a simple, stepless rate adjustment during the operation is possible.

The metering rollers are divided into segments which can be switched on or off in any order. The working width is in this way variably changeable in part widths (part width control). It is possible to accurately spread plots, spreading losses along field sides and odd-shaped field side endings can be reduced to a minimum. The complete metering rollers can be exchanged for special metering units for the application of microgranules (pesticides) and fine seeds.

The fertilizer is transported by the stream of air through tubes which are fixed to the distributing booms. The bends with deflector plates mounted to the end of the tubes produce small overlapping spread fans and distribute the fertilizer evenly across the field surface. Depending on the working width and mechanical execution, the spacings of the jet outlets are between 50 cm and 100 cm. The conversion of the machine from normal fertilizing to late top dressing into taller crops can be done by turning around the deflector plates so that the fertilizer is deflected upwards and will therefore drop with reduced energy from above into the crop. For road transport the booms are folded into vertical position to the sides of the machine’s hopper

Pneumatic distributors meter the fertiliser with an adjustable roller feed mechanism into a high speed stream of air from a power take-off driven fan. The roller feed unit is similar to that used in a pneumatic grain drill. Once in the air stream the fertiliser is carried by the air along pipes or tubes to outlets spaced at intervals along folding booms.

Plate 12.17 A trailed pneumatic fertiliser distributor with the booms folded for transport. The rear cover is raised to show the fan housing.

Plate 12.18 A pneumatic fertiliser distributor with 24 m boom and 4000 I hopper capacity.

A typical pneumatic spreader can have a 12, 18, 20 or 24 m wide hydraulic folding boom to match the more popular tramline spacings used in cereal crops. One example has twenty outlets with spreader plates equally spaced across a 24 m wide boom which spread the fertiliser evenly over the ground. Another design has four widely spaced distributor heads on the boom, but each one spreads fertiliser over a wide area to give a 12 m working width. A 20 m version of this machine has six distributor heads. Pneumatic spreaders, like crop sprayers, have booms which are folded for transport, either manually or with hydraulic rams. Break back mechanisms in the mounting brackets allow the booms to swing backwards if the}- hit an obstruction. One half of the boom can be shut off for working on headlands and when a narrow strip is left to complete the field.

Hopper capacity ranges from 1 to 6 tonnes or more depending on model and the hopper is large enough to be filled from big bags sus­pended over it by a tractor loader or fork lift truck. A screen in the hopper prevents lumpy fertiliser entering the metering mechanism.

Application rateis varied by changing the speed of the feed roller or shutting off part of its length. One model of pneumatic distributor has a gearbox which provides 80 different feed roller speeds. Forward speed, altered with the gearbox, will also affect application rate, which on a typical machine ranges from 40-1,600 kg per hectare for fertiliser down to as little as 5 kg per hectare when broadcasting seeds.

Using pneumatic distributors.Pneumatic fertiliser spreaders are calibrated in a similar way to broadcasters and most models are supplied with a calibration bag for collecting the fertiliser from the metering unit.

Tramlines simplify the operation of full width spreaders and where they are not available, marker stakes are required to ensure accurate joins between bouts.

Figure 1.229. Auger spreader.

Auger Spreaders

Auger spreaders (Fig. 1.229) are prefered for application of high rates of dusty fertil­izers, e.g., for the basic fertilizers such as basic slag, potash, ground lime and lime marl. For the uniform distribution of granular nitrogen containing fertilizers they are not suited. Very often, therefore the auger unit of a spreader is designed to be exchangeable with a centrifugal disc spreading unit so that grain-like granular fertilizers can be distributed with a high work rate. There are also spreaders available with a reversible (redirectable) floor belt. The running direction of the auger belt can be switched from forward running to reverse running. This way it is possible without exchanging spreading units on the machine to spread powdery (dusty), soil moist, or granular fertilizer with a large working width. The distributor auger boom is mounted to the front of the machine, the twin disc spreader unit to the rear.

Auger spreaders are preferably available as trailed implements with payloads from 2– 16 tons and working widths from 6–12 m. The fertilizer is delivered from the hopper by scraper floor chains, rubber auger belts or honeycomb floor belt chains to the spreading auger booms. The use of rubber floor auger belts is getting more popular as they react less sensitively to foreign particles in the spreading material.

Due to uneven loading or when traveling alongside slopes the rubber auger floor belts tend to shift sideways when they become prone to damage. By an automatic belt steering consisting of a steering frame with steering rollers and return roller with swivel pivot, it is possible to keep the floor belt aligned in central running position. The metering of the spread rate is controlled by adjustable shutter slides in front of the outlet openings and by the adjustable floor belt speed. If the floor belt and spreading auger boom is driven by a universal joint shaft, a synchronous run results whereby when changing engine speed the ratio of the spread rate remains constant in the worm auger spreading booms and on the floor belt. Alternatively the auger and spreading mechanisms can also be driven by hydrostatic motors. The effort in design is simpler than for the mechanical drive. At a ground wheel drive the floor belt is driven ground related. At varying forward speeds due to changing tractor gears, the spread rate remains constant.

The driven worm auger booms deliver the fertilizer into tubes with adjustable outlet openings. To achieve a uniform distribution of the fertilizer within the working width the opening diameters of the outlets must be adapted. In the outer range of the auger booms the pressure within the stream of fertilizer is lower than within the central area of the auger boom. That means, that the opening diameters of the outlets will have to be set progressively larger.

The dust development can be reduced considerably by such options as dust-protective covers, especially with drag hoses.

Aerial Spreaders

In some crops and under certain conditions, for example, rice, dry fertilizers and other chemicals are spread with aircraft (Fig. 1.230). The most widely used type of distributor is the ram-air or venturi spreader. These spreaders are mounted under the aircraft.

Venturi spreaders consist of an air entry section, a throat and material entry gate, and a vane expansion and redirection section. The throat-and-vane expansion area usually are referred to as venturi. Internally the spreader is broken down in to 5 to 13 ducts. These are straight in the front and curved toward the rear to direct the discharged material toward a lateral path. The discharge directions with respect to the flying path increase from about 10^◦–20^◦ for the center vanes to 45^◦ or more (up to 70^◦ for wider spreaders) for the outer vanes. For most spreaders these rear vanes are adjustable.

The inlet vanes are adjustable for most venturi spreaders. This is necessary to fine-tune the spreader to a particular aircraft to achieve a uniform distribution pattern. Shifting the front vane position influences the amount of material deposited in the area served by the particular opening and the volume of air to be forced into this vane, and hence influences the velocity of air and exiting material.

Figure 1.230. An aerial spreader

Electronic Monitoring Systems.The performance of a fertiliser distributor can be checked with an electronic monitoring and control system with a digital display in the tractor cab. This indicates fertiliser level in the hopper, forward speed, area covered and the speed of the feed roller or spinning disc(s). The unit also has a remote control system for shut­ting off sections of the boom of pneumatic machines and on some machines the driver can use the system to increase or decrease the appli­cation rate on the move.

More complex control systems automatically increase or decrease application rate to match variations in forward speed and thus maintain the required application rate at all times. Such speed variations may be caused by driving up or down an incline, wheelslip or changing field conditions.

The cab display unit shown in Figure 12.3 is part of an on-board computer control and moni­toring system for a twin disc broadcaster which has even more functions than those listed above. Sensors monitor tractor forward speed and spinning disc revolutions and an electronically controlled actuator ram is used to vary shutter setting.

Details of forward speed, spinning disc speed and the required application rate are pro­grammed into the computer. With this informa­tion the spreader can be calibrated for various application rates and the setting for each is stored in the computer memory.

With calibration completed and the computer programmed, the spreader automatically adjusts the remote controlled shutter to maintain a con­stant application rate irrespective of forward speed, within a limit of 50 per cent variation. If, for example, a forward speed of 13 km/h (8 mph) was programmed into the computer, it can be increased or decreased by 4 km/h (2.5 mph) and the actuator will maintain the required rate of spread.

Figure 12.2 The display panel of an electronic monitoring system on a spinning disc fertiliser spreader. (Lely)

A further refinement includes a load cell on the hopper frame which measures the fertiliser content and converts this information into the distance the tractor can travel before the hopper is empty.

These advanced monitoring systems can be used in conjunction with a yield map produced by a combine harvester to vary the amount of fertiliser applied to match the yield potential of any part of a mapped field. When the computer is linked to the ground positioning satellites used to make the yield map, application rate is automatically increased or decreased according to a pre-determined plan recorded on disk.

Maintenance.Daily lubrication is important and careful cleaning after use is essential to ensure a long working life. All traces of fertiliser must be removed to prevent corrosion. When using a hose pipe or pressure washer, make sure that water is not left in the machine. After washing a pneumatic spreader, run the machine to let the fan blow any trapped water away.

Plate 12.19 This spinning disc broadcaster hopper has a levelling ram and a load cell to monitor the amount of fertiliser in the hopper.

Check that all drives, especially vee-belts, are correctlv tensioned. When storing the spreader after use it is advisable to coat any bright parts which come into contact with fertiliser with a rust preventative solution or oil. However, do not let oil touch rubber parts or get into the air tubes.

Plastic is used extensively in the manufacture of fertiliser spreaders, which has considerably reduced the corrosion problem.

SAFETY CHECK

Always stop the engine before attempting to clear a blockage in a farmyard manure spreader or any other power take-off driven machine.

Date: 2015-12-17; view: 1353