How do baler knotters work?

Answer 1

Knotters to tie twine were developed at the latter part of the 19th century to tie cereal sheaves produced by binders. In principle the same system is still in use today in balers used for hay, straw, silage and haylage.

Twine is fed from balls stored in the 'twine box' into the balers's compression chamber via guides and through the needles. As the crop is fed in, the bale pushes twine along the chamber thus covering end, top and lower part of bale until the preset length of bale is reached. The knotter trip is engaged driving the needles up into the knotter frame thus completing the encirclement of the bale in the chamber. A device called the 'twine retainer' receives the twine delivered by the needles. The retainer consists of notched discs which are rotated by the knotter drive mechanism. Note that the the same retainer also holds the twine while the bale is being formed. The two ends of the twine are thus brought together and are briefly held while the discs rotate and as they do they are gathered by another rotating device known as the 'bill hook' which has a beak which opens to grip the two pieces of twine. As the hook rotates through 360 degrees the twines wrap round the bill hook, the beak closing on them. At this point a device known as the 'stripper arm' sweeps under the bill hook forcing the new knot of the hook. As the beak is still holding the twine the stripping action pulls the held twine through the loop now formed by the rotating bill hook. At the point just before the stripper reaches the end of its travel a knife attached to its end cuts the twine free leaving the new knot holding the bale with the other end held in the twine retainer ready to receive the next charge of crop.

The whole cycle is too fast to observe unless the baler is rotated by hand. Critical points are the grip on the twine held in the 'twine retainers'; the tension on the bill hook beak and the set of the stripper arm which must pass under the lower part of the bill hook just lightly touching it. Another important point is the correct set of the notches in the retainer so that the needles deliver the twine at exactly the right point in the cycle. All these aspects are adjustable and the maker's instructions must be observed for the knotter to give reliable perfomance. In practice it is usual to achieve one or two misses out of one thousand knots.