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The GrindStar is described by Saphir as a rotary grinder. This type of machine is new. The manufacturer offers it in working widths of 3 and 6 meters.
This test protocol is part of the system comparison "Going for Rapeseed Stubble: five devices compared". The additional protocols are also available as individual articles on www.topagrar.com/technik.
In terms of operation, the GrindStar can be placed between the classic soil cultivation devices in the test - disc harrow and heavy tine harrow - and the superficial working machines - harrow and knife roller. It combines the working methods of both categories to some extent. Rotors equipped with knives cut the soil horizontally. This is intended to cut rapeseed stubble or frozen catch crops just below the soil surface from the root and provide good conditions for emergence of volunteer grains during stubble cultivation.
One to the left, one to the right
The rotors each have a diameter of 75 cm. Their angle of attack can be adjusted in three steps between 6 and 10 degrees.
The 6-meter wide GrindStar has a total of 16 rotors. These rotors consist mainly of three elements. Around each rotor, there are seven knife holders, to which angled cutting edges made of a special steel are attached. These cutting edges are parallel to the ground. The knife holders are designed to be movable. For this purpose, a rubber element is clamped between a metal upper shell and a plastic lower skid. Unlike other models, the manufacturer saves additional springs. This allows the cutting edges to move upwards in the field when encountering obstacles.
The rotors spin solely through forward movement. They each measure 75 cm in diameter and are clamped onto the beam with a distance of 75 cm from each other. Behind the first row of rotors, a second row works at a distance of 94 cm. These rotate in the opposite direction. Parallelograms ensure good ground adaptation, pulling the tools down onto the ground with springs but allowing the rotating elements to move upwards when encountering obstacles. The vertical travel of the working elements is 20 cm.
Furthermore, the rotors are not horizontally placed on the ground. They are laterally twisted so that three knives are always parallel to the ground and thus engaged. Depending on the conditions, the rotor inclination can be set to 6, 8, or 10 degrees. In the test, we operated with a 10-degree inclination, making the knives act most aggressively.
Additional Tools
Mounted in front of the rotors is an impulse rail, which is optional.
Additionally, an impulse rail was also mounted on our GrindStar in front of the rotors. This rail, known from harrows and knife rollers, can be hung up and removed from the working area by bolts. Behind the rotors, an optional double-row harrow works. However, this is not for height guidance but for leveling the soil surface and providing a proper finish to the work. For good height guidance on the 6-meter machine, each side element has a leading gauge wheel. The frame of the GrindStar must be horizontal to the ground during operation.
Cutting, shredding, and crumbling
A double-row harrow behind the rotors takes care of the finishing touches. It partially smoothes the soil surface.
Weighing 2.34 tons, the GrindStar falls into the middle range of the test candidates in terms of machine weight. The diesel consumption of 2.6 l/ha also falls within the middle of the test group. A good operational performance with the rotary grinder requires relatively high driving speeds. In the test, we operated the machine at 18 km/h, resulting in a theoretical area output of 10.8 ha/h.
The machine generates a lot of fine soil on the surface. The crop residues or rapeseed stubble did not pose any problems for the machine. The shredding was effective, and the roots were cut directly at the root neck - excellent. Despite the fine soil, the crop residues remain as mulch on the surface, protecting the soil from erosion and reducing evaporation.
During operation, we noticed some slight ridge formation; the machine did not leave a perfectly flat field. For the current season, Saphir has reportedly revised the arrangement of the rotors to prevent these ridges.
The heavy weed infestation in the test area posed some challenges for the rotors. Due to prolonged waterlogging in the spring, a lot of bindweed had grown. In such cases, the use of a leading knife roller ahead of the rotors is advisable.
A strong weed infestation can cause issues for the machine. In the test, bindweed occasionally wrapped around the rotors. The optional single-row knife roller ahead of the rotors can help in such situations. It was noted positively that the knives were able to uproot weeds, a task that the knife roller and straw harrow were unable to accomplish. The soil is uniformly cut, with the working depth ranging from about 1 to 2 cm.