Knife roller: How they work and what are the differences – agrarheute.com

If you are looking for a tool to chop up catch crops or stubble, the mulcher has had serious competition in recent years: the knife roller. These can be divided into two categories: rollers up to 50 cm and over 80 cm in diameter.

A major difference to other shredding devices (such as mulchers) is the high driving speed that knife rollers allow on the one hand, but on the other hand also require for a satisfactory work result. As a rule, this starts at 12 km/h and can be up to 30 km/h depending on the crop to be processed and the site conditions. This enables high area coverage and low fuel consumption of 3 to 5 l/ha.

The knife rollers with a maximum diameter of 50 cm are relatively light in construction, often in two rows or in combination with other rollers and can also be used as front tools for cultivators or disc harrows. Their larger siblings are heavier and designed as an independent machine, and they always work in one row without an additional roller.

However, driving speed and fuel consumption must be related to the degree of shredding. Knife rollers do not perform such intensive work as that of the mulcher, nor can they. Often this is not even necessary or desired. In many cases, cutting a rapeseed stalk once or twice is enough so that it does not cause any problems for the subsequent grain sowing or so that catch crops can be better worked into the upper layers of the soil. In general, organic material decomposes faster the more it is frayed and its surface area is increased. In the case of winter vegetation, in particular, which serves to protect against erosion and is intended to bind nitrogen for the subsequent crop, less treatment is even positive.

There are also two main types of construction for the rollers themselves, provided that the knives are connected to them by screws. Either the backs of the knives are in contact with the roller core or there is a sufficiently large free space between the knife and the support shaft. The former can be described as closed. Here the knife holders are connected directly to the larger roller core via brackets or flat bars. Its increased diameter ensures torsional rigidity – for example, stones cannot get caught inside the blade cylinder. However, soil can get stuck between the individual rows of knives and minimize the cutting effect, as the usable knife length is reduced.

Open rollers are intended to counteract this phenomenon by allowing cohesive soil to press inwards, not sticking and being thrown out of the roller again. For this purpose, the support shaft is more compact and longer knife holders ensure sufficient free space.

Alternative variants include Knoche and HeKo. For his moveable individual segments, Knoche welds the knives firmly to the outer holders, which also hold the bearings. As a result, a continuous shaft can be dispensed with entirely. HeKo, on the other hand, uses screw connections to connect four knives that run across the entire working width. Viewed from the side, these form a cross with a 90-degree opening angle.

As with any other cutting tool, the shape of the blade largely determines the work. However, the blades of the knife roller have to fulfill two main tasks: On the one hand, they have to cut and shred and, at the same time, they have to guide the entire implement over the field. At speeds of up to 30 km/h, a lot is demanded of the knives. Straight cutting edges can absorb external forces over their entire length and are often more massive. In order to still ensure smooth running, the knives are not mounted in a row across the entire working width, but are subdivided and installed with an offset to one another.

Curved or coiled knives are in constant contact with the ground; depending on the degree of twisting, one or more points of the blade rest on the surface. As a result, the roller rolls over the ground and the weight also only presses at these points. So the cutting pressure can be higher. But loads also inevitably have a more selective effect.

In practice, the good rolling behavior of the roller cannot be seen separately from the later place of use. Uneven ground, furrows and lanes can be found on almost every field. This is hardly relevant for single-row rollers that are run in the floating position. Your ground contact is always ensured and vibrations are only partially passed on to the tractor. If, on the other hand, two rollers are connected to each other via a rigid frame, the upper link should be movable. This allows the machine to move freely and bumps over. Otherwise the rollers would lift each other up at each obstacle and not work satisfactorily at these points. Alternatively, devices are available whose rollers are connected to the coupling points via a movable frame, comparable to the boogie chassis of trailers. The fixed positioning of the top link ensures more driving comfort and often also additional lifting height. These pendulum compensations can also be dampened, for example using rubber buffers. Some manufacturers also offer fully sprung rollers or segments. This means that the ground following can be further improved, comparable to a classic disc harrow and a short disc harrow, and driving comfort can be further increased thanks to less vibration.

Depending on the scope of use and focus, knife rollers can be equipped with additional tools for better work results. Advance smooth rollers, strips or similar push the crops in the direction of travel. This is intended to improve the quality of the cut, as the plants lie on the ground and a larger proportion of them can be caught by the blades at right angles. Plants lying across the field are cut through by the corrugated discs. A subsequent harrow can distribute the chopped stalks and leaves evenly over the field, shake out the seeds they contain and mix them with the soil. For safety and to protect against damage, additional metal sheets that hold back stones and soil are recommended. Due to the high priority speeds, stones can have great force and be thrown far away. The mudguards also prevent heavy soiling of the tractor.