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Anno 2020 Numero 3

Technology
March 2020

Ballasting, to increase grip and stability

It is a widespread practice in agriculture which, if applied correctly, allows the optimization of many processes. Ballasting, which involves the use of several materials, can also be performed on the wheel rims. In recent years, innovative technical solutions made by manufacturers have attracted attention, also winning awards in competitions rewarding technical innovations

Ballasting is a very popular, economical and practical method to maximize traction and stability. These two parameters are both essential to optimize production. They require a careful distribution of the masses (and therefore a different location of the ballast) concerning the overall balance of the tractor-machinery assembly.

Adherence, technically understood as the traction capacity of the tractor, substantially depends on two factors: the adhesive weight (therefore the part of the weight of the machinery weighing on the axle or driving axles) and the effectiveness of the contact between the ground and the propulsion organs (tires or tracks).

The stability of the tractor-equipment combination is the most important condition required for fieldwork, even more, transfers would be made safely.

In this case, stability depends on the masses' distribution and the moments of the generated forces. In particular, according to the Italian Highway Code, in order to ensure safe public traffic, at least 20% of the total mass acting on the tractor must be guaranteed on the steering axle, therefore including the mass of a possible operator carried on the 3-point hitch or any component that is discharged onto the coupling device of a towed machinery.

To meet these needs, different types of ballast have been developed over time, to achieve the most efficient mass distribution, to improve grip and stability.

 

Front overhang ballast

As the definition suggests, these ballasts are positioned in front of the body of the tractor: on special ballast, holder supports (often in cast iron, to increase the size of the ballast), in the case of small-medium power tractors, or on the front three-point hitch, on tractors with a higher power.

They can be either in case or monolithic shapes and differ in the way they are assembled. To allow manual application, the case ballasts have a relatively limited mass and a handle on the top. They are commonly made of cast iron and have holes for inserting anchor pins.

The mass of each individual case usually varies between 15 and 40 kg, which makes them manageable by a single employee, without the aid of mechanical means. Monolithic, metal or concrete ballasts are instead of much larger dimensions and masses. They must be positioned on dedicated supports or, more modernly, directly on the front of the tractor (or rear in the case of simultaneous front loader mounting), using pins and arms of appropriate sturdiness. Sometimes they can also be coupled together, always through safety pins.

 

Ballasting on the wheel rims

A solution that has the purpose of increasing the tractor's only adherent weight (i.e. that which increases the traction capacity) consists of applying sturdy cast iron rings on the tractor's drive wheels, in single or multiple configurations, fastened with bolts to the rim flanges.

Usually, this ballast utilizes the front overhang to obtain a more balanced distribution of high global quantities (however usually not more than 30% of the total mass of the tractor as such).

In this case, usually, 2/3 of the ballast is mounted on the front overhang, and the rest on the rear rims. This division has also the purpose of not putting too much stress on the tractor structure.

 

John Deere's EZ Ballast

It is a system to facilitate the management of a dedicated ballast, developed in two different versions and for different purposes.

The first involves the application of the ballast in the ventral part of the tractor, in order to maximize the adhesive weight of the machinery and therefore increase its traction capacity, while the second consists, instead, of a mechanism to easily apply ring ballasts to the wheel rims.

The first solution, awarded with the silver medal at Agritechnica 2015, consists of a 1700 kg monolithic ballast moved by a special hydraulic arm (placed under the tractor) and an automatic coupling and release mechanism. Ballast management is managed from the driver's seat through dedicated controls, including locking with appropriate fixing pins.

Instead, the EZ Ballast Wheel System was awarded the silver medal at Agritechnica 2017, a facilitating system for ballasting the tractor wheels, the front ones up to 250 kg per rim and the rear ones up to 500 kg per rim.

The EZ Ballast Wheel System is implemented by the Ballast Assist System which detects the assembly of equipment at the three-point hitch (front or rear) and consequently determines the optimal distribution of the ballast.


Ballast materials

The ballasts for agricultural tractors are dif­ferent in shape, size and above all for the materials used. Among the­se, the most common are cast iron, magnetite, and concrete. Cast iron and magnetite are the material of choice for "case" ballast (or in any case modular); the density is high, about 5,200 kg/m3 for magnetite and even 7,900 kg/m3 for cast iron, 2-3 -fold that of concrete. With the sa­me mass, these are smal­ler ballasts, therefore of limited size. Concrete is used to build medium-large mo­nolithic ballast and has the advantage of being cheap and easy to shape, even if it is, perhaps, a little less impact-resistant than metal ballast.


The ALI “ballast multiplier”

The Ali firm, from Anghiari (AR), produced a device in 2016, that was defined (albeit improperly) a "ballast multiplier".  It was awarded as a technical novelty at EIMA 2016, it is a mechanism consisting of 3 fundamental elements, namely:  1) an anchoring module positioned on the front of the tractor; 2) two hydraulically operated arms which, employing a dedicated control in the cab, move the ballast away from the body of the tractor; 3) the actual ballast holder.

In fact, this device does not significantly increase the overall size of the ballast (except for the newly installed mechanism, which has a variable mass between 450 and 650 kg, depending on the version), however, it improves its effectiveness, acting on the moment of the weight force exerted by the ballast.

In physics, the moment of a force defines the rotational motion imparted to a body due to the application of a force at a certain point, at a known distance from the center of rotation (the fulcrum).    The formula of the moment of a force is: M=F*b*sinα, or the product of the force vector module, multiplied by the length of the arm, considering its component orthogonal to the direction of the force, therefore the sine of the angle between the arm and the direction of the force. 

The principle used by this device consists of varying the length of the arm (b), i.e. the distance between the ballast and the front axle of the tractor, to increase the moment (M).  The key purpose is to create a stabilizing moment, to counteract the overturning moment generated by the equipment carried or towed behind.

Assembly of both monolithic and case ballasts is foreseen, up to 2000 kg. Basically, by doubling the length of the arm, both moments being equal, it is possible to adopt a halved mass ballast (Ma eMb), while, on the contrary, for the same ballast doubling the distance will have a 2-fold greater moment (Mc).  Applying the equation, it is gotten:

 

Ma=F*b*sinα= [(2000 kg*9,81 N/kg)*0,5 m*1] = 9810 Nm

Mb=F*b*sinα= [(1000 kg*9,81 N/kg)*1 m*1] = 9810 Nm

Mc=F*b*sinα= [(2000kg*9.81N/kg)*1 m*1] = 19620 Nm


Water ballasting

It is a solution, now little practiced, which provides for the partial filling of tires with water (to which is added a substance to lower the freezing point) up to about 75% of their internal volume, inflating the remaining 25% at standard pressure.

The reasons for the low diffusion of this type of ballast are both legal and practical.

It is not, in fact, allowed to circulate on a public road with water ballasted tires, because they create a greater difficulty in controlling the vehicle, especially in the event of emergency maneuvers, while from a practical point of view there are critical issues when emptying the liquid. Water ballasting is, obviously, more sensitive to temperature changes than traditional inflation.

During the harshest seasons, maintaining the water ballast without proper precautions inside the tires can seriously compromise the tire. In this case, it is essential to adopt a suitable anti-freeze: the best option is calcium chloride, which must be added in proportionally increasing quantities according to the minimum temperature at which the water must not solidify.

by Lavinia Eleonora Galli

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