In the construction of agricultural machinery, the quality of materials is very important, and in recent years polyethylene materials have taken over machinery with fiberglass components, mainly because of the difference between the two materials.
Several factors led manufacturers to this choice, not always for regulatory reasons. In fact, in recent years the choice of polyethylene has been shown to be more suitable to meet the needs of the many agricultural entrepreneurs.
In addition, as far as the chemical industry is concerned, fiberglass is in a legislative grey area. In fact, Italian law does not exclude this material, but containers of chemical materials cannot have a roughness above 0.1mm.
The difference in strength between polyethylene and fiberglass
One of the relevant factors in the production of agricultural machinery is the strength of the materials, especially with regard to the use of products of a chemical nature. In fact, phytosanitary substances have great acidity, and if not contained in an appropriate reservoir they risk damaging it.
Because of this factor, the strength of the tank material is most important both to protect the farmer’s investment and the health of the operators.
This is precisely why polyethylene (PE) is the best material for containing chemicals because its degree of resistance is almost total. Fiberglass (GRP), on the other hand, has six times less abrasion resistance than PE (source Rototec technical area).
GRP also retains many chemical residues due to its high porosity, making it unsuitable for chemical storage. In addition, fiberglass experiences much faster wear and tear than other materials.
This behavior also makes polyethylene much more resistant to mechanical stress, which can lead to deformation but almost never to breaking.
The Soundness of Polyethylene
Another advantage of PE structures is its robustness, partly due to the manufacturing process. The rotational molding by which polyethylene is produced makes it possible to obtain a monolithic, i.e., one-piece, structure without welding, thus reducing weaknesses brought about by welds, unlike in GRP structures.
In addition, polyethylene tanks, unlike fiberglass tanks, are attached to the frames by means of external tie rods and supported by subframes that result in greater stability. In contrast, the fastening of GRP tanks is done through anchor pins properly fixed inside the tank by welding operation, resulting in higher stresses, which can lead to tank rupture and leakage over time.
Fiberglass tanks, moreover, tend to become brittle leading to two major problems: filter deposition and occlusion and deposition on the food product. In fact, fibers can settle on the filters, reducing the flow rate of the jet, and if they are ejected from the lance they risk settling on the crop product , contaminating the food.
The difference in temperature resistance between polyethylene and fiberglass
Fiberglass in high temperature environments is not the best material, as it tends to stiffen too much at high temperatures. Polyethylene, on the other hand, keeps its structure almost intact even in very wide temperature ranges from -20 to +80°C.
The polyethylene tank is more elastic and better suited to the stresses that can result from water slamming than fiberglass tanks.
The reuse of materials
Polyethylene tanks as is the case with GRP tanks, can be repaired through the use of appropriate equipment and with the right components.
In the case of integral damage, moreover, the replacement costs of tanks are much more expensive for those made of fiberglass than in those fabricated of PE.
Another factor that turns in favor of polyethylene is sustainability: in fact, PE is 100 percent recyclable, helping the environment. Fiberglass, on the other hand, cannot be melted down and reused and must be disposed of at special centers, incurring additional costs. In addition, improper disposal of this type of material is punished with heavy fines.
Legislative restrictions on the use of fiberglass for chemical material tanks
In addition to technical guidance, since 1985, the law has implicitly excluded fiberglass from the list of materials suitable for chemical containment. In fact, what is being challenged is the porosity, which must not go beyond 0.1mm roughness.
Fiberglass, even when produced with smooth, homogeneous walls, tends to wear quickly and create a porous surface that does not meet legal criteria. In fact, according to the regulations, the farmer should change the GRP tanks very often or carry out (very expensive) maintenance work such as to make the inner walls smooth in order to avoid chemical deposits, in order to avoid porosity-related penalties.
