Harrows, a big family

Working with free wheeling components or those powered by the tractor PTO harrows operate to pulverize the soil on rough terrain to prepare the best bed for a successive seeding. For always producing the optimum results there are a large number of differentiated types available on the market. To cite among the features likely to come up for further development are the quality of materials for their

One of the most compelling challenges faced by modern farming enterprises is taking efficiency to the maximum as well as profit margins in spite of continuous increases of production costs, the volatility of commodity prices and ongoing environment problems and uncertain weather. 

This challenge can be overcome through careful application of the principals of agronomic management, seeding, fertilizing, plant treatment products and the like, while deploying the best agronomic techniques, beginning with soil preparation. In this connection, there are two phases in traditional technical work, plowing followed by complementary operations for the preparation of a well refined seedbed. For this, the use of harrows is essential. These make up a highly varied family of a multitude of machines, very different one from another but having as their single shared feature the result of their work. In fact, every harrow is suitable for a determined type of terrain and not another. The various types are clearly distinguished by their structure which means that there are variable demands of energy and capability power for lifting the drive wheel.

 

Harrows and free-wheeling components

In general, what are called rotary harrows, with worktools powered off the tractor PTO, a single pass is often sufficient for completing the operation at moderate speed. On the other hand, this is not the case for harrows with free-wheeling tools which require work on fairly dry soil at sustained speed and almost always repeated passes. In any case, there is no doubt that the configuration of the tools, their number and the way the operation is performed are the most important criteria for distinguishing them.

Starting with the now obsolete chain mesh harrow, now used only for beautifying the walls of farmhouses, the first step in the evolution of this machine was the present day weeding harrow equipped with a variable number of knotted grids on which more or less flexible steel teeth are mounted. These are suitable for aerating the top layer of soil under grass by breaking the crust but also for weeding in the first phase of weed growth. There are many ∅ 6-8 mm flexible teeth with average lengths of 30-40 cm mounted in an offset array on a chain grid frame. Some models for post-emergence weeding can be regulated for various working widths. Along the same line but one step ahead is the spike tooth harrow in mounted or trailed versions with a rigid tubular frame, and rarely articulated, equipped with ranks of round or square profile spike teeth of various types, direct or blade teeth or slanted in the direction of advance. The teeth are normally equidistant from one another and work to the depth of 10-15 cm. Work on the soil requires little power on superficial layers with no bounce on disturbed terrain. If equipped with large teeth with pointed anchor tips, direct or with other configuration, the machine has evolved to a grupper harrow type put to use mainly on terrain covered with abundant crop residues.

On the other hand, there is the tine harrow with flexible or curved teeth which provide a spring function to help break up clods. The teeth can be simple or curved to a spiral shape, called Canadian, differing mainly in their degree of work on raising heavy clods to the surface. As it is, the tine harrow with elastic teeth works to the depth of 10-15 cm for pulverizing the soil to a degree similar to that of the other types reported above but with less power needed. Coming along more recently was the disc harrow equipped with tools set in motion by reacting to their cutting into the terrain. These are spherical caps or truncated cones with thin edges normally connected to the main frame or towed by a tractor. Because the discs are inclined to the forward direction, their rotation cuts, lifts and remixes and pulverizes the soil. These discs, often offset, work down to the depths of 15-20 cm. The combination of rigid discs with anchor points and discs is defined as a disc harrow combined with grubber, a machine capable of breaking up two layers of soil. The teeth break up the terrain down to 30 cm without turning it and the discs turn up the top 5-10 cm. 

 

Harrows powered by tractor PTO

Harrows with oscillating teeth are provided with a transverse reciprocating motion with respect to the advancing direction of the working tools. These are mounted in ranks and each tooth bar has a transverse reciprocating motion in phase opposition with respect to the adjacent one. Compared to free-wheeling tools, in this case, the degree of soil pulverization to the depth of 10-12 cm is undoubtedly better but at the price of much greater power absorption. Rotating harrows differ from the others in the drive of the rotary motion of the blades. These, of various shapes and sizes, can work to depths of 5 to 30 cm. These harrows undoubtedly consume the most power but achieve the highest level of pulverizing the terrain.  

 

The rollers

Rollers are accessories which can be connected with a harrow rear air ventilation function for aeration, further crushing or the surface leveling of the ground. They are usually run by dragging them over the ground and are sometimes used to regulate the depth of work. In relation to the characteristics of the terrain superficial soil layers the types of roller suitable for use can be the cage roller, roller struts, packer roller or spiral roller. Such accessories derive the movement from dragging on the ground. The cage roller is advised for somewhat humid terrain and the packer for wet ground for getting optimum drainage. For increasing efficiency, roller struts can be combined with a scraper bar to remove soil which might stick to it. The packer roller, on the other hand, is the universal component suitable for all soil types. For the special function of compacting very light soil, within this work parameter is the spiral roller to use when it is not necessary to perform surface compacting.

 

Materiali for reliability and durability

The leading challenge for manufacturers is the durability of their harrows, especially, the workingtools when the machines must operate in flinty terrain. The thinking is that using common steel for teeth makes them unusable after only a few dozen hours of operations.  This means that it essential to have recourse to extremely high quality steel with great resistance to superficial wear. For this purpose there are alloys used in small quantities for hard-facing steel such as chromium, molybdenum, cobalt, nickel, vanadium and titanium carbide. These alloy steels must be industrial heat treatment to ensure that these components are able to resist the shocks they are subjected to. These procedures provide excellent results to ensure durability 8-10 times greater compared to average quality steel, the Fe430 type for example. Moreover, the high durability of the cutting profiles drastically reduces the consumption of energy in soil preparation operations.  Though the leading manufacturers in number of units produced are those in North Europe, a considerable number of harrows are also turned out by the Italian industry made up of big multinationals down to small crafts enterprises capable out building tailor-made machines to meet each single requirement requested. At the national level, there are highly competitive companies which export 90% of their production thanks to the winning combination of manpower at reasonable cost, compared to the North European standard, and especially to the excellent quality of their machines and their great efficiency at work.