by GJ Stoltz (Reg Eng Tech)

The inside of a square baler is packed with intricate mechanisms. This implement should be able to produce a suitable animal feed source which is compacted sufficiently to not fall apart or allow air inside.

Plunger:

A crank arm and pitman drive the plunger back and forth in the bale chamber at about 80 times per minute. As the plunger moves down the bale chamber, the plunger knife moves past a stationary knife to slice off hay that is still outside the chamber. The plunger then compresses the hay in the bale chamber (see Figures 1, 2 and 3).

Hay dogs:

The hay dogs engage the bale to keep the partly formed bale compressed when the plunger retracts (see Figures 4 and 5).

Bale chamber:

The process of feeding hay into the bale chamber and compressing it with the plunger is repeated until the bale is formed. The density of the bale is determined by adjusting the spring-loaded upper and lower tension bars on the bale chamber. On some models the tension bars are controlled hydraulically (see Figure 6).

Bale measuring wheel:

The bale measuring wheel rotates as the bale moves through the bale chamber.

When the wheel completes a cycle, the tying mechanism is tripped. The bale length may be changed by adjusting the bale measuring cycle (see Figures 8 and 9).

Needles:

The tying mechanism is timed to synchronise with the plunger movement.

When the plunger is at the rear of the baler and the hay is fully compressed, needles deliver the wire or twine to the tying mechanism. As the wire or twine is grasped by the tying mechanism, the needles retract and the bale is tied (see Figure 10). It is important to study the operator’s manual first before making any adjustments.

The process is repeated as each bale passes through the bale chamber and drops off the baler. Forming proper bales is useless unless the hay is tied properly by the tying mechanism (see Figures 11 and 12). The measuring wheel cam, or bell crank, operates a trip rod which starts the tying mechanism. First the needles pass from the bottom of the bale chamber to the top of the bale chamber, carrying with them the wire or twine.

There the knotting, or twisting device ties the twine. Then the needles withdraw to their home position until the metering wheel hits the trip rod again. The needles do not penetrate the hay. They go through slots in the plunger head. The needles are protected by spring action or a shear bolt. They will not enter the chamber if there is an obstruction in the chamber or if the plunger is not in position. There is a plunger safety stop to protect the needles from damage by the plunger if the needles enter the chamber too soon or if they remain in the chamber too long (see Figure 13).

The safety stop alternatively enters through the bottom of the bale chamber at the same time that the needles start to enter the bale chamber. The stop then remains in position until the needles are fully withdrawn to the home position. If the plunger should move at the wrong time, and is stopped by the safety stop, a shear bolt in the plunger drive is sheared to prevent damage to the baler (see Figure 14).

Therefore, if the position of the plunger is properly timed, the hay will be compressed into a well formed bale and at the same time the needles will go through the plunger slots and through the bale chamber with the minimum needle-to-hay contact (see Figure 15). The needles will then be in the bale chamber only for a fraction of a second while the plunger is at the end of its compressed stroke and the entire tying operation is performed in about 3 seconds. The twine knot, or twisting, takes less than a second and one must look very carefully to follow the entire process with the eye (see Figure 16).

Next month we shall discuss the knotter, wire twister, bale preparation and the wire-tie baler. Visit www.arc.agric.za for more information.

We thank the ARC Agricultural Engineering in South Africa who made the information on square balers available to the readers of ProAgri.