engleski

New technical and technological solutions in thinning operations of lowland forests

The transportation of so-called smallwood, which is produced in thinnings of natural regenerated oak forest in eastern lowland part of Croatia, is very significant because of large amount of timber assortments (approximately about 50 % of total annual felling), ecological sensitivity and economic efficiency. Application of forest machines in thinnings has been started at the begining of 70s of last century with tractor assemblies: adapted farming tractor and forest semi-trailer. The first tractor assembly of that kind was so-called "Pionir" which was equipped with mechanical crane and forest winch. Ecological issues demanded winching of processed assortments (logs) from stand (place of processing of logs) to the one of parallel strip roads (75 m distance between parallel strip roads). Such organization of work was very hard to perform due to technical disadvantages of tractor assembly "Pionir". Tractor assemblies were moved through stand damaging forest soil and disturbed ecological features of stand as well as stand economic aspects. There were no significant improvement with better oppening of forest with 37, 5 m distance between parallel strip roads At the begining of 90s of last century, intensive searching for optimal tractor assembly has been started. The next solution was parallel work of "Pionir" and adapted farming tractor equipped with crane and grapple which collected timber assortments in the stand and skidded assortments to the strip road. From ecological and primarly from economic point of view (two machines for one work and great time consumption for loading and unloading with unsuitable mechanical crane) that organization of work didn`t exist for a long time. After that, following tractors assemblies were used: 1. Farming tractor Torpedo 55A, semi-trailer Moheda 6t and hydraulic crane FMV 230 with hydraulic winch on the crane (1993.) 2. Thinning skidder with semi-trailer and hydraulic crane instead forest winch (1996.) 3. Farming tractor Steyr 860, semi-trailer Kronos 6t and hydraulic crane Kronos 250 with hydraulic winch on the crane (1997.) 4. Farming tractor Steyr 8090 with narrow track, semi-trailer Igland Swingtrac 480 and hydraulic crane Igland 43-65 without winch (2003.) Based on experiencies with application of mentioned tractor assemblies, some reccomendations for basic technical characteristics of tractor assemblies were suggested, such as: &#61485; loading capacity of semi-trailer 6 t &#61485; engine power of tractor about 60 kW &#61485; lifting capacity (netto) of hydraulic crane > 40 kNm &#61485; the same track width of tractor and semi-trailer < 1, 7 m &#61485; total length of tractor assembly < 9 m &#61485; clearance > 300 mm &#61485; double-drum winch with line pull > 50 kN &#61485; decreasing of turning radius with articulated shaft or swinging bogie wheels In the year 2004., a new tractor assembly is produced which is consist of: silvicultural tractor Steyr 8090 with narow track, double-drum winch Igland 6002 Pronto TL, hydraulic crane Igland 43-65, semitrailer Metalac S-6 with loading capacity of 6 t.

tractor assembly; semi-trailer; thinnings; technical characteristics; lowland forest

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