Part 4: The double rotor rake

by GJ Stoltz (Reg Eng Tech)

The double rotor rake is designed with two rotors next to each other, rotating in opposite directions to form a windrow between them. Double rotor rakes can also have their rotors placed behind each other (trailed) to form the windrow on one side.

This month we take a look at the main frame, hitch components, PTO drive shaft and rotors of the double rotor rake. We thank the ARC Agricultural Engineering in South Africa for making their manual on rakes and tedders available to the readers of ProAgri Zambia.

This type of rake is driven from the PTO-shaft of the tractor and consists of the following:

• Main frame
• Hitch components
• PTO drive shaft
• Rotors
• Windrow screen
• Guide wheels and land wheels

(See Figure 1).

Main frame:

The main frame must be strong enough and designed in such a way that the rake can be operated smoothly, es-pecially on rough terrain. The frame must have a high clearance, so that voluminous windrows can be formed without dragging the material along.

Hinges, pivots and hydraulic components are attached to the main frame.

Drive shafts are sometimes enclosed in members of the main frame, and for maintenance these members are bolted together with high tensile bolts. Gearboxes and safety guides are also mounted onto the main frame (see Figure 2).

Hitch components:

Some of the double rotor rakes are hitched to the two lower links of the tractor’s three point linking system (see Figures 3a and 3b).

Other double rotor rakes are hitched to the tractor’s drawbar by means of a clevis (see Figure 4). It is also called a trailed double rotor rake. Smaller double rotor rakes have three-point hitch points and are therefore hitched to a tractor’s three-point linkage system. These rakes also have pivoting three-point frames and the PTO-drive shaft operates through the three-point hitch of the rake (see Figure 2).

PTO drive shaft:

Where the rotors are positioned next to each other, the rake consists of a main PTO drive shaft that is connected to the tractor’s PTO shaft. This main drive shaft terminates in a gearbox, mounted on the main frame of the rake. From this gearbox, two side shafts are used to drive the rotors. The shafts driving the rotors, are positioned in such a way that the rotors can be lifted vertically without damaging the shafts.

On rakes where the rotors are staggered, the PTO drive shafts are partly enclosed in the boxed frame and these shafts will line up automatically when the rake is prepared for transport (see Figure 4).

Rotors:

The double rotor rake is equipped with two rotors and can have a working width of up to 6,8 metres. The rotors are designed and operated the same way as the rotor on a single rotor rake. The one type of rake has the two rotors positioned next to each other while the other type has the rotors staggered (see Figures 2 and 3).

Where the rotors are positioned next to each other, the rake is stabilised by two land wheels at the back and each rotor has two guide wheels for height adjustment. Each rotor is therefore independent and adaptable to ground contours. The rotors are lifted hydraulically from the tractor seat for transport purposes (see Figure 5). Sometimes it is necessary to lift one rotor for headland turns and that can also be done hydraulically from the tractor’s seat (see Figure 6).

With double rotor rakes, where the rotors are staggered, the height of the tines above the ground can be adjusted hydraulically and the rotors can also be shifted hydraulically to follow in a straight line behind the tractor for transport purposes. The windrow screen folds away automatically and the transport width will be about 2,8 m (see Figure 4).

Next month we shall discuss the windrow screens, guide wheels and land wheels, transport techniques and operational features of the double rotor rake. Published with acknowledgement to the ARC Agricultural Engineering for the use of their rakes and tedders manual. Visit www.arc.agric.za for more information.