The performance of disc trenchers needs to be further improved, in order to successfully employ an intermittent mode of operation also on technically adverse sites. A Murveln powered disc trencher was used in an experiment aiming at improved knowledge about the scarification process. The trencher was studied on three sites in Sweden on sand and till soil. Hydraulic pressure and speed of disc rotation were measured continuously during work on one of the disc motors. In addition, the process was recorded on video tape. The ground surface was surveyed before and after treatment by use of a levelling instrument. The maximum torque, that the disc motor could transfer to the trenching disc, was studied at three different levels: 3.7, 5.5 and 7.3 kNm. Pilot studies were made of the influence of travel speed.
An increase in maximum torque, applied by the disc motors, increased the volume of moved soil, the area of exposed mineral soil, and the occurrence of raised, mineral-soil micro sites. On a powered disc trencher, substantial interaction can be expected for at least five factors:
1. Resistance in the soil to disc rotation
2. Disc torque supplied by the disc motors
3. Disc torque emanating from the tractive force of the prime mover
4. Nominal speed of disc rotation
5. Travel speed
The registrations made during scarification showed that the power and mechanical work, that the disc motor could transfer to the soil, generally was limited by the maximum torque that the motor could develop. Simulations based on experimental data indicate that an insufficient disc torque most probably can not be compensated for by other factors. When a sufficient torque is provided for disc rotation, influence can be expected also of travel speed and nominal speed of disc rotation.
The method to register ground surfaces by use of a levelling instrument was feasible but laborious. Other methods should be developed for fast and accurate registration of uneven ground surfaces. The video recordings proved to be very useful and a further application of this technique can be recommended.
Key words: site preparation, soil scarification, disc trencher, disc torque and machine-related factors.
Correspondence: Bengt Gyldberg, Swedish University of Agricultural Sciences, Department of Operational Efficiency, S-776 98 Garpenberg, Sweden
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