In many regions of the country hailstorms are an annual occurrence that causes great financial loss to farmers. Summer days are very hot and the heavy rainfall combined with strong winds during active plant vegetation is a common occurrence. Building a hail system will effectively protect fruit plantations not only from hail, but also from torrential rains, high winds, birds, insects and sunburn.
The hail protection structure for the orchard planting consists of nearly 30 different individual elements, interconnected and forming a complete system.
The system consists of two main parts – a supporting structure and a roof structure.
The reinforced concrete poles are made of high quality reinforced fittings and concrete grade B60 with additives, which guarantees high mechanical strength. Their quality is ensured by appropriate product certification – a document specifying the maximum and minimum values for poles, with respect to the following criteria: bending strength of the finished product; strength of concrete; frost resistance; product linearity.
They can be up to 7.00 meters long and are piled into the soil at a depth of 60-90 centimeters. The piling is done by means of an excavator, on which a vibrating head is mounted with rubber nozzles, preserving the integrity of the material. The vertical pressure exerted by the machine, combined with the vibrations, allows the pole to dig into to the required depth. The reinforced concrete poles are of two sizes. The first is 7-8 cm, which is used for the internal supports of the structure.
The outer poles are 9-9.5 cm in size and are only installed at the beginning, the end of rows and ends laterally of rows, i.e. encircle the covered plot of land around. Another specific feature is that they need to be mounted at an angle of 8° for better and maximum stability after system loading. The point where the structure forms a 90-degree angle, two poles are mounted on an “X” link, each holding a rope or wire perpendicular to the other. It is also important to orient them, with the wide part of the pole facing the rows and the narrow one facing outwards for maximum flexural strength.
At the base of the outer poles, measuring 9-9.5 cm, anti-slip plates are fitted, which do not allow the poles to sink in the event of soil settling. The anti-slip plates consist of two D-shaped parts connected by bolts, between which is the pole.
The clamping steel cable Ø7 is connected to the concrete pole by a U-shaped clamp and to the anchor by another U-shaped clamp. It is also coiled at one end, forming an ear through which the reinforced concrete pole 9-9.5 cm is passed. The other end is made of PVC tape, which prevents the cable from being untangled.
The anchors consist of two parts – straight iron – A3 steel with an ear made at the end and a disk welded to its base. Dimensions are 1500/26/300 mm (anchor height/steel diameter/disc diameter). They are piled at a distance of 1.50 meters from the base of the poles 9-9.5 cm. This distance may vary according to the location and specificity of the individual soil locations, but should not be less than 1.00 meter from the base of the pole. Mounting is done with a rotary head excavator that screws the anchor in a helical manner until it fully penetrates the ground and only the anchor’s ear remains above it. In the case of “X” connection of a pair of stakes 9-9.5 cm, 3 anchors are placed, with the rope tighten around the middle one and holding the poles at the point where they meet.
The U-shaped double clamp is the connection of the supporting ropes and the wire with the anchor. It consists of a body, two hexagon bolts on which the cable Ø5 and wire Ø4 are tightened and wound, and keys with which the tensioned hexagons are locked to the body of the clamp.
When the length of the poles is more than 4.00 meters, it is necessary to further strengthen the outer poles 9-9.5 cm with a crimped cable Ø5. It is made in the same way as the Ø7 crimped cable, but is shorter and mounted in the middle of the visible part of the pole with its ear attached to a wire clamp and tightened in the lower part by a small U-shaped clamp (single).
The transverse row of reinforced concrete poles 9-9.5 cm is strengthened by a rope Ø7, which is secured to the poles by a rope clamp Ø10, passing through the U-shaped clamp. The U-shaped clamp is mounted 50 cm from the top of the pole.
Plastic caps are attached to the top of all poles, which sticks tight to them. As a further measure, a screw is inserted into the cap for additional stick to the pole. Pole caps are required to secure the longitudinal and transverse cables and wires. They are also necessary to protect the net from possible damage due to the uneven surface of the poles. They are made of high quality polypropylene, which guarantees the durability and long life of the product. They consist of a housing, PPR washers, PPR cap and galvanized fasteners, which tighten the rope and wire intersecting at 90° in the grooves of the cap.
The steel cable Ø5 is mounted perpendicular to the rows of plantations through the caps, and is tightened at both ends by a double U-shaped clamp.
The net is supported by galvanized highly carbon wire that runs through the lower channel of the polypropylene cap. Its cross-section is 4 mm and in addition to its high chemical properties, which guarantee a long life, it also has certain physical properties, necessary for its correct stretching in the order of plantations. At both ends of the row, the wire is stretched and locked in tension by the double U-shaped clamp.
The net is attached to the wire by means of plastic clips and plates. The clamps tighten the net to the wire Ø4 and the distance between them should be 1.50 meters.
Plates are the connecting accessory of the individual nets. They are made of high quality polyethylene and consist of four elements in a special assembly, so they can be easily removed when retracting the net.
Polyethylene nets and foils are widely used in Europe to solve various problems in the agriculture: protection from hail, wind, snow or heavy rainfall in horticulture, viticulture, greenhouses, etc. Their application is wide-ranging, thanks to the versatility of the materials. Thanks to them, a microenvironment for plants is maintained and controlled, which also helps fight viral influences.
The net is a product made of polyethylene fibers, bonded and woven into each other in a way that creates a porous geometric structure that allows the fluids (gases and liquids) to pass through it.
The most widely used raw material in the nets for agriculture is high density polyethylene (HDPE). Polypropylene (PP) is also used as a staple for nets, mainly for the production of nonwovens.
In a detailed review of the current state of polymeric materials used in agriculture shows that they are the most modern and have been developed with the help of state-of-the-art technical studies that meet ISO standards and EU quality requirements.
Species are characterized by various structural functions such as the type of filaments, tissues, shape and size of the fibers and their combination with physical properties such as weight, color, shading factor, durability, porosity, breathability and mechanical characteristics such as stress, tear strength, and stretchability.
The raw material used for agricultural nets is high density polyethylene (γHDPE = 0.94-0.96 g/cm3). It is a non-toxic material that can be used in direct contact with plants. It is fully recyclable, easily convertible, waterproof, durable, stabilized with ultraviolet (UV) resistance additives and has good mechanical characteristics (Tensile strength σ = 20 ÷ 37MPa, break elongation ε = 200 ÷ 600 %).
The cover film is made of LDPE polyethylene, UV stabilized. Thanks to the treatment and its improvements, caps are built into it, which allows considerable stability after its attachment.
Its thickness is 160μm and is reinforced at the end by 700μm and in the middle by 400μm. Conformity with the main component of the polyethylene film product is indicated and complies with EN 13206:2001.
The cover film has the following strength characteristics: