Biomass Management for Fodder & Energy

Lesson 10. Baler for collection of straw

10.2. Rectangular balers for collection of straw

Field balers for making rectangular bales have been popular for many years. Smaller balers are powered by a tractor PTO and the larger balers are often equipped with auxiliary engines to drive the machine but may be pulled by a tractor.

10.3. Rectangular baler components

The basic functional components or units which make up a baler for rectangular bales are the pickup and elevating unit, feed conveyor, feeder, compression chamber and the tying mechanism. Each of these will be discussed individually.

10.3.1. Pickup and elevating unit 

This unit takes the straw from the windrow and elevates it to the point where a feed conveyor can carry it to the bale chamber. The pickup consists of a series of spring loaded tines which gently lift the windrow and guide it along the stripper bars. At the top of the pickup, the tines retract downward to be ready to lift a new portion of the windrow. On many machines the pickup serves as the elevator but on older machines a separate elevator was used. Balers intended to pickup straw windrowed by mower conditioners may have pickup tines spaced much closer together.

10.3.2. Feed conveyor

This device moves the straw to the side of the bale chamber. Large diameter augers are common feed conveyors. However, on some machines several times extended from the feeder act to convey the material to the bale chamber side. On some older machines, rubber belts were used for this purpose.

10.3.3. Feeder

The feeder takes the straw from the end of the feed conveyor and actually places it into the bale chamber. In most cases the feeder enters the bale chamber when the plunger is forward, for this reason it must be timed accurately with respect to the plunger.

10.3.4. Compression chamber

Straw is compressed in the bale chamber by the plunger which is driven by a large crankshaft and connecting rod. Each new charge of straw is compressed against the previous charges. The partially formed bale moves slowly through the chamber by the plunger forcing new charges against it.

10.3.5. Tying mechanism

The tying mechanism consists of knotters, needles and metering wheel. These parts are responsible for tying each bale when it has reached its correct length. The fingers of the metering wheel extend part way into the bale chamber so the metering wheel turns slowly as the bales pass through the chamber. Rotation of the metering wheel, trip the knotter clutch to engage power to the needles and knotters to tie the bale. The relationship between the metering wheel and the knotter clutch can be adjusted to change the bale length. On most machines this can be done by sliding a collar on the trip arm at the metering wheel. 

10.4. Rectangular pick up baler

It makes bales from the straw windrow left by the combine. The machine consists principally of a pick-up reel, a conveying and feeding system, a compressing chamber,
a bale density adjuster, a bale length controller, a needle and tying mechanism, a crank linkage mechanism and a power transmission and hauling system. It is powered from the power take-off of the hauling tractor. The straw windrow is lifted from the ground by a pick-up reel having spring teeth and transferred continuously to a conveying and feeding mechanism as the baler moves forward along the windrow.

The conveying and feeding mechanism pushes individual charges of straw into the bale chamber from the side at intervals when the piston is withdrawn. The piston reciprocates under the function of the crank linkage mechanism to press the material into the bale. When the bale reaches the required length, the needle and tying mechanism is engaged automatically to bind the bale which is then pushed out from the chamber by successive bales and is discharged to the ground. Rectangular bales can be lifted and loaded either by hand or by a loading machine mounted on the side of a truck and driven by a ground wheel.

10.5. Round balers for collection of straw

Round balers are PTO operated and are pulled directly behind the tractor. It is desirable to use a tractor with a wide front axle to permit straddling the windrow. Large wide windrows are preferred to make round bales which are uniform in diameter. When small windrows are harvested, operators prefer to weave side to side as the bale is formed to avoid tapered bales. Based on the form of working unit, round balers can be classified into long-belt type, short-belt type, chain type and roller type. They are also classified into inside winding type and outside winding type by their working principle. Long-belt and chain types are inside winding; short-belt and roller types are outside winding. According to the chamber size adjustment, balers are classified as expandable chamber round pickup baler, ground roll baler and fixed volume round pickup baler.

10.5.1. Expandable Chamber Round Pickup Baler

The most common type of round baler is the Expandable Chamber Round Pickup Baler. This type of baler picks up the straw windrow with a conventional tooth pick up and moves the straw into the bale chamber using rollers and belts. The straw is then compressed using belts and rollers or apron chains. As the straw is fed into the bale chamber, it expands producing a bale of relatively uniform density. As the bale reaches the desired size, twine is fed into the chamber and wraps around the bale as it turns. After the bale has made approximately one revolution, forward travel is stopped, and twine continues to be fed in while the bale makes 6 to 10 more revolutions. After the wrapping is completed, the tailgate is raised, and the bale is ejected. The tailgate is then lowered, and a new bale is started. Bales produced by this type of baler usually have a high density and weigh from 0.5 to 1.0 tonne. This type of baler is usually easy to use and has overall capacity ranging from 2 to 12 t/h. Power requirements vary from 10 to 25 kW but a tractor with at least 48kW is recommended to fully utilize the baler’s capacity.

10.5.2. Ground Roll Baler

Ground roll balers use the least amount of tractor horsepower of the three types of round balers. A pickup is used to roll the straw forward along the ground and belts, grids or cables are used to form the round bales. Bales made with a ground roll baler tend to be lighter and less dense than bales created by the other two types of round balers. This type of bale can experience significant losses during handling, transporting and storage. Overall capacity with these balers is very dependent on operator experience and can vary from 1 to 5 t/h. Power requirements usually do not exceed 20kW but a tractor with at least 34kW is recommended to fully utilize the baler’s capacity.

10.5.3. Fixed Volume Round Pickup Baler

In Fixed Volume Round Pickup Baler, the pickup lifts the straw into the bale chamber. The bale chamber, however, is of fixed volume and the bale does not take shape until the chamber is nearly full. Bales from this type of machine will have a lower density core than those produced by the expandable chamber balers. Although this type of machine has a capacity similar to the expandable chamber types, the power requirements appear to be higher. Overall capacity for this type of baler is the same as the Expandable Chamber Round Pickup Baler, but power requirements of up to 45 kW have been measured.

10.5.4. Inside winding Round pick-up baler

Figure 10.5 illustrates a belt, pick-up baler that consists of a pick-up reel, a conveying and feeding mechanism, a wrapping and pressing mechanism, a rear door for unloading, a transmission mechanism and a hydraulic operating mechanism. Its working process is shown in Figure 10.6. The windrow is lifted by a pickup reel and rolled up to double smooth rollers where it is pressed into a flat layer, then conveyed to the baler chamber. With the upper belt the straw moves upward by friction to a certain height, then rolls down to the lower belt by gravity to form the core of the bale, which continually rolls, increasing the diameter. When the bale reaches the desired size it is discharged from the lower belt. The springs fixed in the swing arms in the two sides of the bale chamber maintain the pressure of the belt on the bale's surface. The pressure increases with bale size, resulting in low density on the inside of the bale but high density on the outside. Inside wrapping means that the volume of the wrapping and pressing chamber enlarges during pressing to keep a constant pressure on the bale. The bales formed by inside wrapping have much higher density than by outside wrapping and keep their shape for longer during storage. However, the structure of an inside wrapping baler is more complicated. When the bale reaches the desired size, an indicator alerts the driver to engage the hydraulic distributor in order to activate the binding mechanism. The twine is passed by the tube and fed with straw to the chamber. The twine is wrapped around the circumference of the bale and then cut by a blade. The rear door is lifted hydraulically. The bale is then discharged to the ground.

References

1. Kepner, R.A, Roy Bainer and E.L. Barger.1972. Principles of Farm Machinery, 2^nd ed. AVBI Publ. Co., Inc., Westport, Connecticut
2. G.S. Moggach and J.K. Weeden. 1979,  Large package hay equipment -New Concept in Hay Making, Ministry of Agriculture and Food