Lesson 5. Baling-classification, uses

5.1. Introduction

Off-field utilization of rice straw and other crop residues continues to attract increasing attention due to concerns associated with environmental impacts from open burning for disposal. Straw makes up about 40% to 60% of the dry weight of rice plants according to the cultivar and cultivation method. For every ton of grain harvested, about 1.35 tons of rice straw remains in the field. The proportion of straw recoverable depends on the technique of reaping and harvesting (manual or mechanical) and on the condition of the field or crop (flooded or lodged). About 2.5 to 3 tons per acre of dry straw is an average net production. After combine harvesting, the straw is left on the earth in swaths. The straw should be removed as quickly as possible so that the treatment of the soil preparation can begin thereby establishing next year’s crop. The only method commonly used to handle rice straw is baling. Baling is a packaging operation performed to facilitate handling, transport and storing.

Optimum moisture for baling can range from 15% to 20% depending on size of bale being made. Baling at moisture levels lower than 15% will result in greater harvesting losses because straw losses increases as moisture content decreases. On the other hand, storing straw at moisture levels greater than 20% can result in molding and heating, which translate into discoloration and greater dry matter and nutrient losses.

5.2. Baler and its classification

A baler is a machine used to compress straw into bales for easy transport and storage. Balers are divided into stationary balers, movable and field balers. They are further classified into square balers, rectangular balers and round balers according to the bale shape produced. According to density of bale, they could be high (200-350 kg/m3), medium (100-200 kg/m3) or low density (<100 kg/m3) balers. Based on the power used for operation, balers are classified as pull type balers and self propelled balers. Pull type models are available with either a PTO drive or a mounted engine.

5.2.1. Stationary baler

Stationary baler was grouted at one place and the material for baling was brought to its place.

5.2.2. Movable baler

Movable baler was transportable by attaching it through single point hitch of tractor. It was installed at one place for operation after carrying it to required place.

5.2.3. Field baler

Field baler was pulled by single point hitch of tractor and operated by power from tractor PTO shaft. Three hydraulic lines of the baler were connected to the three hydraulic secondary control valve of tractor. Hydraulic power was used for positioning of baler in rear offset and to adjust the height of finger reel mechanism while operation.

 Functional components of field baler

A plunger type field baler includes the following components:

    1. A unit to pick up straw from the windrow and elevate it.

    2. A conveyor to move the straw to the bale chamber entry

    3. Packers to place the straw in the chamber while the plunger is on its retracted stroke

    4. A reciprocating plunger to compress the straw and move it through the bale chamber.

    5. Means for applying forces to resist the movement of straw through the bale chamber and thus control the degree of straw compression and the resultant bale density.

    6. An automatic metering device for controlling the bale length.

    7. A means of separating consecutive bales and placing the wires or strings around each bale

    8. Automatic tying devices that operate when the bale reaches the preselected length

5.2.4. Square balers

Square balers are classified as small square baler and large square baler based on the dimension of baler. In square balers, the straw enters the baler through the pickup, and the teeth gently rake the straw from the ground to prevent the loss of leaves and ingestion of rocks or debris into the baler. Directly behind the pickup is the compressor bar, which holds the straw in place so the auger can feed it into the bale chamber. The bale chamber contains a plunger that drives in and out, each time packing and compressing straw into the desired shape. The plunger also cuts the ends of the straw to make the bale a uniform size. The chamber feeds into a spring tension section that keeps the bale tightly compressed until enough straw has been processed to complete the bale. When the correct length of bale is achieved, a mechanism wraps the bale with two lengths of twine or wire and ties it securely. The twine is carried on spools and fed through two curved needles that are timed to miss the cycle of the plunger. After the twine is in place, a gear mechanism called a knotter ties the knot and cuts the twine free of the supply spool. After it is tied, the bale is pushed down the bale chute and falls to the ground. Some balers have "kickers," or bale ejectors, which throw the bale onto a straw rack pulled behind the baler.

 Most of the small square balers operate to the right side of the tractor and the wagon follows behind the baler, usually in line with the tractor. However, the large square balers operate directly behind the tractor, requiring the operator to turn around even further than is necessary for the operation of a small square baler to view their operation.

 5.2.5. Rectangular balers

Similar to square balers, rectangular balers are also classified as small rectangular baler and large rectangular baler based on the dimension of baler. Small rectangular bales of conventional type made by a variety of machines have dimensions close to 0.4 x 0.6 x 1.2 m (0.3 m3) and weighing approximately 32 kg (dry matter) each (110 kg m-3). Large rectangular bales have nominal dimensions of 1.2 x 1.2 x 2.4 m (3.5 m3) weighing approximately 600 kg (175 kg /m3) and nominal dimensions of 0.9 x 1.2 x 2.4 m (2.6 m3) weighing 450 kg (170 kg/m3).

In large rectangular balers, packer fingers above a windrow pickup cylinder push the straw through a tapered feeding chute into the bale chamber. The straw is compacted by the front wall of the chamber moving about 13mm into the chamber in a reciprocating motion. A gate on the chamber outlet remains closed while the bale is being formed. When the bale reaches desired density, the operator stops the forward motion and trips the knitters. Three ties are made around the bale, using special polypropylene twines. The rear gate opens automatically when the tying cycle is completed. The tied bale is subsequently pushed out by the next bale being formed, after which the gate closes.

 5.2.6. Round balers

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.

5.3. Baler capacities

Baler capacities depend on machine characteristics and operating factors. Some of the machine characteristics that affect the capacity of the baler are (a) the size of the bale, (b) the number of plunger strokes per minute, (c) capacity limitations of the pickup and feed mechanisms, (d) the amount of power available, and (e) the durability and reliability of the machine. Important operating factors include (a) size and uniformity of the windrows, (b) the condition of the field surface, insofar as it limits the forward speed, (c) condition of the straw, (d) the density of the bales and (e) the skill of the operator.

5.4. Uses of baling

Baling can be applied to improve the characteristics of straw for transportation and storage. The bulk density of rice straw is around 75 kg for loose straw and 100 -180 kg in packed and baled form as energy feedstock. Transport of bailed straw can be up to 50% cheaper than transportation of loosed material. 

Last modified: Monday, 28 April 2014, 11:19 AM