Shredders and milling machines, technology for forests
Designed to carry out operations of arrangement and maintenance of the wooded areas, the shredders and milling machinery represent a particularly interesting segment in the field of agricultural mechanics. The difference between a forest shredder and a forest milling machinery is that, while the former is used for shredding trees, bushes, cutting waste and piles of branches, with the latter it is also possible deeply mill and crush roots and stumps
When the materials to be chopped are so hard that they would not be processed, even by the heavier hammer shredders among those commonly used in agriculture, it is necessary to use machinery expressly designed to operate when it is likely to find stones and stumps.
This result can be achieved with machinery similar to those commonly used in agriculture but equipped with particularly strong and resistant working parts, which moreover in most cases are fixed, and not mounted on pins.
Often these machines allow to operate simultaneously on the surface layer of the ground, and this allows to promote a certain mixing between ground and shredded material, which is then very useful for the transformation of the shredded plant material into fertile humus.
Forestry shredders and milling machinery are designed to adapt to many and different uses or applications, which can be traced to the following situations: create passages or corridors in the vegetation to install oil pipelines, water mains or power lines; create hiking trails and white roads; maintain agricultural soil usually by grinding of waste wood; change into arable land, where it is necessary chop up shrubs, small trees, stumps, crush rocks and work the ground also deeply; improve accessibility in hunting areas; clean the rivers or canals’banks; carry out maintenance work of green areas and undergrowth; open new access routes in the woods; maintain natural areas, parks and pastures; clean up the forest soil from flammable plant material and create forest corridors and firebreak ways; take care of and clean the road docks; grind pruning and green waste or grind logs and roots to be mixed with the soil after the hauling operations.
As for the specific of the aspects of construction, the machinery can be divided into the following main components: frame and supporting structure, power transmission, shredder roller and auxiliary components.
The difference between a forest shredder and a forest milling machinery is that, while the former are used for shredding trees, bushes, cutting waste and piles of branches, with the latter it is also possible to mill and crush roots and stumps in depth (up to 50 cm).
Based on the type of application to be carried out, the structure and working parts are adequately sized to stand the different stress sustained while working; in addition, some models combine features of both types for maximum versatility.
Chassis and machinery structure
The machinery is made up of the main steel machinery to which the three-point hitch is connected at the front, a gearbox for transmission is located at the top and the rotor bearers are at the sides, the rotor itself is inside the machinery, that is to say, in the cutting room and behind, a bonnet with a hydraulic opening.
While the machinery is working, it is supported by two sleds, fitted with a wear resistant base, that allow adjusting the working height.
To improve the machinery operation, a hydraulic translation device, usually mounted on a slide between the three-point attachment and the operating part can be installed on some models specifically made for lighter jobs.
Alternatively, the hydraulic side tilt function of the machinery is available for a better adjustment to the terrain profile.
The pattern of the support ledge of the machinery housing helps to improve the operating efficiency by optimizing the material processing capacity by avoiding dragging and, at the same time, offering a better protection of the mechanical working parts and more protected hydraulic lines.
Transmission
The motion, derived from the tractor through a cardan shaft, triggers a gearbox (usually available both with clockwise and anticlockwise rotation) provided with a free-wheel and a bevel gearbox, which is in turn connected to the shredding shaft through an additional shaft and a belt transmission (up to 12 units).
In models with a hydraulic transmission, usually designed for connecting with an earth-moving machinery, a hydraulic engine acting directly on the final driving belt pulley is flanged instead of the angular transmission box.
On the machinery equipped as a milling cutter, a cascade gear lateral transmission is also available instead of the belts.
If the conditions are particularly severe with high load and power peaks, a double transmission is used to operate the rotor.
On the models with the highest performances, the mechanical transmission foresees the oil cooling and some hydrodynamic protection joints.
Shredding roller and auxiliary components
The shredding roller is of tubular shape, pivoted to the sides by bearing supports fitted on the body machine and directly connected to the transmission.
On millers and shredders for heavy work, a larger and heavier rotor is usually installed to offer more inertia as well as strength.
Depending on the type of work and the result to be obtained, the work tools have a specially adapted profile (straight, double-blade, single-tooth or multi-tooth profile, etc.) while the material consists of high-strength steel as hardox or tungsten carbide.
The equipment is completed by screwed or soldered counter knives, which improve the efficiency of the tools, from conveyor fins, rear rakes, grilles for adjusting the grain size of the material coming out on the rear hood (on drills).
To contain the throwing of splinters and pebbles, in the rear part and possibly also on the front of the machine body a barrier formed by segments of chains and/or vanes is connected.
The summary of the models’ characteristics available on the market can be summarized as listed below, with the ranges of the main parameters of use of the vehicles marketed (NB: each parameter is independent of the others): Operating mass: from 750 to 6320 kg; Dimensions (width x depth x total height): from 1580 x 1150 x 960 mm to 3450 x 1600 x 1080 mm; Working width: from 1290 to 3100 mm; Power consumption: from 44 to 368 kW; Type of PDP: central connection 540/1000 or only 1000 rpm; Number of elements: from 22 to 108 units (depending on the size of the element and the working width of the machine); Wood material diameter: from 180 to 600 mm; Rotor diameter: up to 520 mm; Feed speed: up to 5 km / h; Three point connection: cat I, II, III and IV, (depending on the power level).
The currently available combination of models is high, and includes both high-performance compact models and mod elli of great work capacity but for lighter work.
