Tillage and tribology

According to the World Bank, agricultural development is a dominant tool to come out of extreme poverty. A country’s economic growth is also influenced by agriculture: in 2018, it accounted for 4 percent of global gross domestic product (GDP) and in some developing countries, it can account for more than 25% of GDP. [1]

Agriculture is the practice of cultivating plants. Cropping systems vary among farms depending on the available natural resources; geography and climate; government policy; economic, social, and political scenarios of the area; and the philosophy and culture of the farmer. There are various agricultural practices involved in crop production as given in below flow chart. [1]

Tillage

Preparation of soil involves plowing/tilling. Tillage is the mechanical modification of soil structure. Tillage tools modify soil structure through a wide range of soil–tool interactions, including cutting, milling, crushing, beating, and rebound. Tillage practices can be distinguished in three methods: conventional tillage, conservation tillage, and zero tillage. Conventional tillage involves intensive plowing and harrowing with a tractor, which leads to a total inversion of the soil. Conservation tillage, on the other hand, tries to minimize soil disturbance and leave most of the crop residues on the surface. Zero tillage means that the soil is not tilled at all. [2][3]

According to a 2016 report published in Eurostat on tillage practices in the EU, Conventional tillage was the most widespread tillage practice applied on two-thirds of the total arable area, implying intensive plowing and harrowing which can have negative impacts on the environment while almost a fifth was tilled with conservation practices, and zero tillage was rarely applied. [2][3]

The type of tillage being used is a matter of argument and choice and won’t discuss further as it is out of our scope.

Tribology

From the above-mentioned paragraphs, it is clear that tillage plays an important role in soil preparation for all crops. Tillage brings in the interaction between surface and tillage tools. Many factors contribute towards the wear of these tools due to soil conditions, some outlined by Jagseer Singh & team [4] in their paper are given below,

1. Moisture content: While wear of tillage equipment’s decreased with an increasing moisture content of clay soil, it increased with an increase in moisture content in sandy soils.
2. Soil texture and its particle size: Tillage equipment showed higher wear with sandy soils.
3. The amount of stones present in the soil and their size may also impact tool wear.

Premature failure or reduction in life of tillage tools can lead to a financial burden to farmers in developing countries and can also impact the quality of soil being prepared. To reduce the wear of tillage tools various research work has been conducted in different parts of the world.

Chunsong Guan and his team [5] worked with various coatings to improve the wear resistance and anti-adhesive properties of rotary tillage blades. Selected coating materials included TiAlN, CrN, PTFE, and Ni-P-PTFE. Out of the four coatings, Ni-P-PTFE came out as a winner presenting improved wear resistance and anti-adhesive properties. In the 14-day field trial being conducted, Ni-P-PTFE coated blades had the lowest average friction coefficient (0.32) and the lowest weight loss rate (0.4 g/ha). Also, Ni-P-PTFE coated blade had the lowest soil cutting resistance. Here the self-lubricating property of PTFE material and enhancing of this property by co-deposition of Ni-P played a crucial role in enhancing the wear performance. On the economic front, PTFE coating has a lower cost in comparison to Ni-P-PTFE which makes it more suitable for practical use, and its wear performance is only second to Ni-P-PTFE coatings.

Titanium-based composites are a popular choice in the manufacturing of hard coatings mainly due to their high thermal stability and wear resistance.

In a research work involving titanium-based coatings done by Shahab Sharifi Malvajerdi and his team [6], TiCrN-TiAlN-TiAlSiN-TiAlSiCN multi-layer coating, deposited using an arc-PVD method, was used to increase the life of sweep duck blade tillage tools. The multilayer coatings demonstrated an increase in the lifetime of the tool in comparison to single-layer coatings.

Muammer Nalbant and his team [7] in their research work, coated; steel plowshare specimens with hard chromium, electroless nickel, and titanium nitride. Wear behavior was checked against uncoated specimens and amongst other coatings. Tests were carried out in sandy clay loam soil using a one-furrow plow. TiN coating showed higher wear resistance than its counterparts.

Hardfacing refers to the application of hard, wear-resistant material to the surface of a component by welding, thermal spraying, or a similar process for wear reduction.

In a research work conducted by Z. Horvat and team [8], the wear of mouldboard plow, a popular tillage tool, is brought into control by hardfacing involving a combination of two welding processes, namely shielded metal arc welding (SMAW) and high-frequency induction welding (HFIW). The hardfaced plows showed better protection against wear in comparison to regular plows through a series of experiments conducted in clay soil.

A combination of surface hardening techniques can also prove to be beneficial for improving wear resistance. Work done by Andrey Novikov and his team [9] suggests that carburizing of surface layers of the cutting blades of tillage machines manufactured from low-carbon 20 steel in combination with heat treatment followed by laser processing allows high tribological properties to be achieved.

Agricultural tine is a part of a cultivator and is fitted with a plow on it. A cultivator has usually 7-11 tines depending upon the make of the tractor with which it is used. Multiple research involving understanding wear mechanisms and wear reduction of cultivator tines are available. [10]

Jacob SUKUMARAN and his team [11] through their research work on the wear mechanism on tines pointed out that mass loss of the tine follows a linear trend as a function of plowing distance. Also, micro-cutting and micro plowing mechanisms were found dominant in the cutting edge area.

Again, coating proves to be an obvious solution for minimizing wear in agricultural tines as well. V.M Salokhe and his team [12] used enamel coating for tines in their research work. Results showed that the rate of wear of enamel-coated tines was lesser than that of the uncoated tines, which were equipped on a rotavator.

The method of deposition of coating may also impact wear resistance. Research work done by Niloofar Abed and her team [13] on abrasive wear of tillage tine included coating of nickel compounds on pieces carved from high carbon steel material via different coating methods. The coatings made by DC electroplating improved abrasion resistance by 30.41% whereas pulse electroplating with 55.83% outperformed the former. Their research also indicated that grain size in the coating also plays a vital role in wear resistance and hardness increase.

In conclusion, the interaction between tillage equipments and soil presents a complex tribological scenario. Present and future research work in this direction can minimize the wearing of tools resulting in enriching seeding efficiency, enhanced weed control, and lower fuel penalties. [14]

References

1. Agriculture and Food
2. Tillage
3. Agri-environmental indicator – tillage practices
4. Influence of soil conditions on abrasion wear behaviour of tillage implements
5. Evaluation of the tribological and anti-adhesive properties of different materials coated rotary tillage blades
6. TiCrN-TiAlN-TiAlSiN-TiAlSiCN multi-layers utilized to increase tillage tools useful lifetime, https://doi.org/10.1038/s41598-019-55677-8
7. Effects of different material coatings on the wearing of plowshares in soil tillage
8. Reduction of mouldboard plough share wear by a combination technique of hardfacing
9. Composition and Tribological Properties of Hardened Cutting Blades of Tillage Machines under Abrasive Deterioration
10. Case study on agricultural tines
11. Wear mechanisms prevalent in agricultural tines
12. Effect of enamel coating on the performance of a tractor drawn rotavator
13. The Effect of Nano-Structured Nickel Coating on Reducing Abrasive Wear of Tillage Tine
14. Tribological aspects of agricultural equipment: a review