by GJ Stoltz (Reg Eng Tech)

In the final article in our rake and tedder series we focus on rotary tedders and windrowers.

The working principle of a rotary tedder is similar to that of a kitchen egg beater. The primary function of tedders is to spread the cut crop evenly over the field so as to speed up the natural drying process effected by the sun and air movement (see Figure 1).

We thank the ARC Agricultural Engineering in South Africa for making their manual on rakes and tedders available to the readers of ProAgri Zambia.

Main frame and components

Double rotor rakes that can also be used for spreading hay are designed in such a way that the rotor tines can be converted from a horizontal to a vertical angle and vice versa. This is called tedding. When raking is done with this small double rotor rake, the rotor tines are positioned in a horizontal position, and when tedding is done, the tines are positioned in a vertical position. When raking is done, the main frame must be set level with the soil surface, and when tedding is done the main frame must be adjusted slightly forward (see Figures 2, 3, 4 and 5).

A certain amount of tine overlapping occurs between two rotors, also called tedding wheels, allowing the tines to exercise a pulling-apart action on dense, tangled or bumpy material.

A tedder should be used mainly on fast-drying tougher grasses, such as teff, Eragrostis Curvula, and veld hay because all can be baled on the day of mowing, provided the crop is cut early enough in the morning.

Weather conditions play a very important role when using a tedder and where a significant reduction in overall drying time is essential, a hay conditioner should be used while mowing. A hay conditioner is specially designed to overcome the problem of water vapour trapped in the stalks of thick-stemmed forage crops.

By using a tedder, the drying time for certain crops can be reduced by an hour-and-a-half. When lucerne and other forage crops have dried out to below 40% moisture-content level, they are more susceptible to leaf loss arising from the aggressive handling of the crop by the tedder’s fast-rotating tines. The speed of the PTO-shaft is normally set at 540 rpm, but the degree of aggression may be restricted to some extent by reducing the PTO speed.

A swath is the cut material left behind by a mower, and a windrow is formed when two or more swaths are raked together.

The drying time can be considerably reduced by using a tedder in fields where the following conditions apply:

• A very dense swath.

• Swaths which were unevenly formed.

• Where many narrow swaths were formed.

The main advantage of a tedder over a hay rake is its ability to spread the crop uniformity and thereby ensuring an even drying rate. This action eliminates slow-drying patches that could cause a degree of spoilage when the material is baled.

Tedding should commence within thirty minutes after cutting so that tedding can be done over the maximum period of drying time available. Freshly cut grass is relatively heavy and in the process of wilting it is inclined to settle into a fairly dense mat.

Air trapped in this dense mat is quickly saturated with water vapour and the drying rate is consequently depressed. Tedding shortly after mowing effectively reduces the drying rate as the tedder brakes up this dense layer of material.

Tedding

Tedding indicates the spreading of the swaths left by the mower and these swaths are uniformly spread over a wide area in a fluffed-up state, exposing the material to the sun and wind to improve the drying rate (see Figures 6, 7, 8, 9 and 10). The user should always consult the operator’s manual for every specific tedder before making any adjustments.

Spreading

Spreading describes the operation of spreading the crop after the tedding operation, in order to further reduce the drying time (see Figures 11 and 12). It also indicates the use of a tedder to re-spread already spreaded material that became wet. The settings of a tedder for both operations are identical.

Windrowing:

This indicates the formation of a windrow from spread material or the turning of windrows that became damp overnight, by moving them across onto dry ground. It also indicates combining windrows to increase the windrow size (see figures 13, 14 and 15).

Normally, a side-delivery rake will be more effective in combining windrows to improve their sizes because the rake moves more material to its side for every run over a field.

A windrow can be formed centrally behind a tedder by using a cage or deflector tine attachment. The function of this attachment is to retain the material thrown into it by the rotor tines and to form it into a windrow.

Tedding wheel and tine adjustment

The operator’s handbook must be consulted for each application of a tedder, because there are many models and types available and they all differ from each other. The tedding wheel must be set at a flat angle for short crops, wide-spread crops, hay and crops with a moisture content lower than 40% (see Figure 6).

The tedding wheel must be set at a steep angle when tedding long crops, mower swaths, wilted silage and crops with a moisture content higher than 40%. The correct spreading angle will determine how completely the material is taken up by the tines.

Big tedders are usually very adaptable to even the most irregular ground surface. Their chassis are articulated so that they can follow ground contours easily (see Figure 16).

Tine design:

Double tines are mostly used on the tedding wheels because they are exceptionally elastic as a result of their long coils (see Figures 17, 18 and 19).

Operational features

With some tedders, the crop moves through the centre of the tedder wheels. It becomes fluffy and is again teased out so that damp patches are exposed. For a superb windrow, a windrowing cage can be used at the back of the tedder (see Figure 20). When the drying time of the crop is shortened, the nutritional value is better conserved and the high land speed at which a tedder can be operated ensures maximum capacity.

A tedder can be operated at land speeds up to 14 km/h and a 20 kW tractor is suitable to do the job when using a medium size tedder. Eight tedder wheels can be used on one frame, and the working width can go up to 8,85 metres. The power requirements for this type of tedder are 30 kW and the tedder can weigh up to 1 100 kg (see Figure 21). At a land speed of 14 km/h, this tedder can do up to 11 hectares per hour. When transporting such a big tedder, the outer rotors can be pivoted backwards towards the centre of the machine.

This happens with the trailed models. The outer rotors can also be folded upwards into a vertical position that leaves the machine with a transport width of only 2,95 metres (see Figures 22 and 23). When the tedder wheels are folded vertically on some models, the drive shafts are also pivoted by using finger drive constant velocity joints (see Figures 24 and 25). As soon as the tedder wheels are lowered again, these joints couple automatically.

Overload protection

Overload protection is provided on tedders by torque-limited devices, for example slip clutches, in the PTO-drive shaft assembly. Efficient protection from the risk of damage, particularly where the tines are concerned, is also of importance as heavy ground contact or the striking of a sizable obstruction by the rotating tines could result in excessive tine, tine arm and possibly tedder wheel drive damage.

This bring us to the end of a very exciting series. Next month we shall start with a series on balers. 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.