New energy mining truck tire tread compound with anti-wet slip and wear resistance during rainy season and its preparation method

Abstract

This invention discloses a tread compound for new energy mining truck tires that is resistant to wet skids and wear during the rainy season, and its preparation method, relating to the field of tire technology. This invention innovatively introduces a ternary compound of ATT-KF aramid micropowder, ATT-R85 anti-slip resin, and hydrogenated fish oil fatty acids into the tread compound system, constructing a three-in-one synergistic reinforcement network of "anti-slip, wear-resistant, and toughening." The synergistic effect of these three components solves the technical challenge of simultaneously achieving wet skid resistance, wear resistance, and processability in tread compounds under rainy mining conditions without sacrificing processing performance and mechanical strength. This invention is particularly suitable for the high-performance requirements of new energy mining truck tires under wet, slippery, and complex road conditions.

Description

Technical Field

[0001] This invention relates to the field of tire technology, specifically to a new energy mining truck tire tread compound that is resistant to wet skids and wear during the rainy season, and its preparation method. Background Technology

[0002] New energy engineering equipment has become the mainstream development direction in the mining operation field due to its energy-saving and environmental protection technological advantages. The matching new energy mining truck tires need to be adapted to the harsh working conditions of mining, such as high load, strong impact and many sharp ores. Moreover, during the rainy season, the road surface is wet and slippery due to water accumulation and mud, which puts forward more stringent requirements on the anti-slip properties, wear resistance and tear resistance of the tire tread. At the same time, the tread rubber also needs to take into account good processing performance and mechanical strength in order to meet the industrial production and actual use needs of new energy mining truck tires.

[0003] As the core component in contact with the ground, the performance of the tread compound of new energy mining truck tires directly determines the tire's service life, operational safety, and the production efficiency of new energy mining truck equipment. Traditional mining truck tire tread compounds often use high-filler carbon black or the addition of hard inorganic particles to improve wear resistance. While this can enhance wear resistance to some extent, it easily leads to decreased elasticity of the compound, increased dynamic heat generation, and a significant reduction in the coefficient of friction on wet and slippery surfaces. This makes the tires prone to slippage, seriously affecting the safety of mining operations during the rainy season. At the same time, high-filler systems increase the Mooney viscosity of the compound, reduce processing fluidity, and increase production energy consumption and process difficulty.

[0004] Due to their high strength and high modulus, aramid fibers have been explored for inclusion in tire tread compounds to improve tear and cut resistance. For example, Chinese invention patent CN103642083A discloses an environmentally friendly, cut-resistant engineering machinery tire sidewall compound that utilizes a reinforcing system of N115 and N330 carbon black combined with short aramid fibers, effectively enhancing the cut resistance of the compound. However, aramid fibers exhibit strong surface chemical inertness and poor compatibility with the rubber matrix, leading to agglomeration in the compound and difficulty in achieving uniform dispersion. Furthermore, the weak interfacial bonding between the fibers and the rubber matrix makes them prone to interfacial debonding under dynamic stress in mining conditions, becoming a source of crack initiation. This not only fails to fully utilize the reinforcing effect of aramid fibers but also results in a decline in the overall mechanical properties of the tread compound.

[0005] In existing technologies, researchers have improved the dispersibility of aramid fillers or the processability of rubber compounds by adding single processing aids. However, conventional processing aids have limited functions and can only achieve a single function in dispersion improvement, interface modification, or vulcanization activation. They cannot simultaneously meet the multiple requirements of uniform dispersion of aramid fillers, fiber-rubber interface enhancement, crosslinking optimization of vulcanization system, and surface functionalization of tread rubber. They cannot solve the technical problem of simultaneously achieving wet skid resistance, wear resistance, processability, and mechanical strength of new energy mining truck tire tread rubber under rainy mining conditions.

[0006] Furthermore, considering the usage characteristics of new energy mining truck tires, their tread compounds also need to have low dynamic heat generation properties to avoid thermal-oxidative aging of the rubber compound due to heat accumulation, which would affect the tire's aging resistance and service life. However, traditional tread compound formulations, when optimizing wet skid resistance and wear resistance, often neglect the synergistic improvement of dynamic heat generation and aging resistance, further limiting their application in new energy mining equipment during the rainy season.

[0007] Therefore, developing a new energy mining truck tire tread compound that combines anti-slip properties, high wear resistance, excellent mechanical properties, good processability, low heat generation, and high aging resistance has become a key technological requirement for adapting to the development of new energy engineering equipment in mines during the rainy season. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings of existing technologies in which the anti-slip, wear resistance and processability of new energy mining truck tire treads under rainy mining conditions are difficult to balance. The invention provides a new energy mining truck tire tread compound with anti-slip and wear resistance in rainy seasons, which is synergistically enhanced by ATT-KF aramid micro powder, ATT-R85 anti-slip resin and hydrogenated fish oil fatty acid, and its preparation method, thereby achieving a balance between high friction coefficient, excellent wear resistance and good processability of the tread compound on wet and slippery roads.

[0009] The technical solution of this invention is as follows: On the one hand, the present invention provides a new energy mining truck tire tread compound that is resistant to wet slip and wear in the rainy season, comprising the following components by weight: 100 parts of rubber matrix, 40-55 parts of carbon black, 5-15 parts of silica, 1-3 parts of silane coupling agent, 3-10 parts of ATT-KF aramid micro powder, 5-12 parts of ATT-R85 anti-slip resin, 2-6 parts of hydrogenated fish oil fatty acid, 3-5 parts of zinc oxide, 1-3 parts of stearic acid, 3-6 parts of antioxidant, 1-2 parts of microcrystalline wax, 1.5-2.5 parts of sulfur, and 1.4-2.1 parts of accelerator; wherein the rubber matrix is ​​composed of natural rubber and styrene-butadiene rubber in a weight ratio of (50-70):(30-50).

[0010] Preferably, the carbon black is N220.

[0011] Preferably, the silane coupling agent is bis-[γ-(triethoxysilane)propyl]tetrasulfide (TESPT).

[0012] Preferably, the accelerator is composed of accelerator CZ and accelerator DM in a weight ratio of (1-1.5):(0.4-0.6).

[0013] On the other hand, the present invention provides a method for preparing the above-mentioned wet-slip and wear-resistant tread compound for new energy mining truck tires, comprising the following steps: S1 First stage mixing: Rubber matrix, carbon black, ATT-KF aramid micro powder, hydrogenated fish oil fatty acid, zinc oxide, stearic acid, antioxidant, and microcrystalline wax are put into an internal mixer and mixed at a speed of 40-45 rpm. The mixture is lifted and pressed every 30-35 seconds, and the discharge temperature is controlled at 150-155℃ to obtain the first stage masterbatch. It is then cooled and left to stand for 4-8 hours. S2 Two-Stage Mixing: The first-stage masterbatch, silica, silane coupling agent, and ATT-R85 anti-slip resin are put into a mixer and mixed at a speed of 35-40 rpm. The mixture is lifted and pressed every 30-35 seconds. The temperature is raised to 140-145℃ and held for 60-90 seconds to carry out the silanization reaction. The discharge temperature is controlled at 145-150℃ to obtain the second-stage masterbatch. The mixture is then cooled and left to stand for 4-8 hours. S3 Final Mixing: The second-stage masterbatch, sulfur, and accelerator are put into an internal mixer and mixed at a speed of 25-30 rpm for 100-120 seconds. The discharge temperature is controlled to be ≤100℃. After discharge, the new energy mining truck tire tread rubber with anti-wet slip and wear resistance in the rainy season is obtained.

[0014] Compared with the prior art, the present invention has the following advantages: The hydrogenated fish oil fatty acid used in the tread compound of this invention, with its unique saturated long-chain fatty acid structure, simultaneously functions as a activator, plasticizer, dispersant, and interface modifier. As a "multifunctional bridge," it improves the dispersibility of ATT-KF aramid micropowder through melt coating and interfacial bonding, fully leveraging the reinforcing effect of ATT-KF aramid micropowder and significantly enhancing tear and cut resistance. Furthermore, by reducing system viscosity, it promotes the migration and enrichment of ATT-R85 anti-slip resin on the surface, forming a micro-rough structure and significantly improving the coefficient of friction on wet roads. Its active carboxyl groups also activate the vulcanization system, increasing crosslinking density and uniformity. Ultimately, the tread compound of this invention achieves comprehensive optimization of wet skid resistance and wear resistance, resolving the multiple performance contradictions that traditional technologies struggle to balance. It is particularly suitable for engineering tires operating in complex conditions such as rainy seasons and mining, significantly improving tire safety and service life on wet roads while improving processing efficiency and reducing energy consumption, demonstrating broad industrial application prospects and economic benefits. Detailed Implementation

[0015] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0016] The ATT-KF aramid micro powder and ATT-R85 anti-slip resin used in the following examples were provided by Nanjing Tengyi New Material Technology Co., Ltd.; the hydrogenated fish oil fatty acid was provided by Wilmar Oils Technology Co., Ltd., with an acid value of 196, an iodine value of 7, a saponification value of 198, and a melting point of 53°C; other raw materials were all commercially available industrial-grade products.

[0017] Examples 1-8 The tread compound formulations for new energy mining truck tires in Examples 1-8 and Comparative Examples 1-8 are shown in Table 1-2: Table 1. Formulations (parts by weight) of tread rubber for new energy mining truck tires in Examples 1-8

[0018] Table 2. Tread compound formulations (parts by weight) for new energy mining truck tires in Comparative Examples 1-8

[0019] The preparation methods of the new energy mining truck tire tread compound in Examples 1-8 and Comparative Examples 1-8 include the following steps: S1 First stage mixing: According to the formula in Table 1, natural rubber, styrene-butadiene rubber, carbon black N220, ATT-KF aramid micro powder, hydrogenated fish oil fatty acid, zinc oxide, stearic acid, antioxidant 4020, antioxidant RD, and microcrystalline wax are put into an internal mixer at a speed of 42 rpm. The mixture is lifted and pressed every 32 seconds, and the discharge temperature is controlled at 152℃ to obtain the first stage masterbatch. Cool for 6 hours. S2 Two-stage mixing: The first-stage masterbatch, silica, silane coupling agent TESPT, and ATT-R85 anti-slip resin are put into a mixer at a speed of 37 rpm. The mixture is lifted and pressed every 32 seconds. The temperature is raised to 143℃ and held for 75 seconds to carry out the silanization reaction. The discharge temperature is controlled at 148℃ to obtain the second-stage masterbatch, which is then cooled for 6 hours. S3 Final Mixing: The second-stage masterbatch, sulfur, accelerator CZ, and accelerator DM are put into an internal mixer at a speed of 28 rpm and mixed for 115 seconds. The discharge temperature is controlled to be ≤100℃ to obtain the tread rubber for new energy mining truck tires.

[0020] The tread rubbers prepared in Examples 1-8 and Comparative Examples 1-8 were subjected to high-temperature vulcanization (145℃ × 40 min) and their properties were tested using the following methods: Mooney viscosity was tested according to GB / T 1232.1-2016 "Determination of Unvulcanized Rubber by Disk Shear Viscometer - Part 1: Determination of Mooney Viscosity"; tensile strength and elongation at break were tested according to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber"; tear strength was tested according to GB / T 529-2008 "Determination of Tear Strength of Vulcanized Rubber or Thermoplastic Rubber (Pants-shaped, Right-angled and Crescent-shaped Specimens)"; Akron abrasion was tested according to GB / T 1689-2014 "Determination of Abrasion Resistance of Vulcanized Rubber (Using Akron Abrasion Tester)"; wet friction coefficient was tested using a BM-type pendulum friction coefficient tester under wet conditions, according to GB / T The abrasion resistance of vulcanized rubber or thermoplastic rubber was determined according to GB / T1687.3-2016 "Determination of temperature rise and fatigue resistance of vulcanized rubber in flexural test - Part 3: Compression flexural test (constant strain type)"; the aging retention rate was calculated as follows: after 100℃×48h thermo-oxidative aging, the aging retention rate = (tensile strength after aging×elongation at break after aging) / (tensile strength before aging×elongation at break before aging)×100%.

[0021] The test results are shown in Table 3-4: Table 3. Performance test results of tread rubber after high-temperature vulcanization in Examples 1-8

[0022] Table 4. Performance test results of tread rubber after high-temperature vulcanization of Comparative Examples 1-8

[0023] As shown in Tables 3-4, compared with Comparative Example 1, the tear strength of Example 2 increased from 68 kN / m to 86 kN / m, indicating a significant enhancement in the rubber compound's resistance to crack propagation; the Akron abrasion loss decreased from 0.088 cm⁻¹. 3 Reduced to 0.058cm 3The wear resistance is significantly improved, extending tire lifespan; the wet friction coefficient increases from 0.62 to 0.88, achieving a leap in anti-slip performance and greatly enhancing safety in mining operations during the rainy season; the compression temperature rise decreases from 40℃ to 32℃, significantly reducing dynamic heat generation and mitigating the risk of aging and damage caused by heat accumulation; the aging retention rate increases from 78% to 88%, demonstrating significantly enhanced resistance to heat and oxygen aging. The reasons for this are: ATT-KF aramid micropowder forms a three-dimensional rigid reinforcing skeleton, significantly improving tear and cut resistance; ATT-R85 anti-slip resin migrates to the surface during vulcanization, forming a micro-rough structure that significantly improves the friction coefficient of wet surfaces; hydrogenated fish oil fatty acids act as a multifunctional bridge, improving the dispersibility of ATT-KF aramid micropowder, activating the vulcanization system, and promoting the migration of ATT-R85 anti-slip resin. These three elements synergistically construct a three-dimensional reinforcing network of "bulk reinforcement - surface function - interface optimization - cross-linking density," achieving a comprehensive upgrade from basic to high-performance.

[0024] Compared to Example 2, Comparative Example 2 only added ATT-KF aramid micropowder, increasing the tear strength from 68 kN / m in Comparative Example 1 to 80 kN / m, but the wet slip friction coefficient was only 0.64, and the Mooney viscosity was as high as 76, exhibiting the problem of "enhanced but poor wet slip and poor processability"; Comparative Example 3 only added ATT-R85 anti-slip resin, increasing the wet slip friction coefficient from 0.62 in Comparative Example 1 to 0.80, but the tear strength was only 70 kN / m, and the Akron abrasion loss was 0.085 cm. 3 The first example exhibits the problem of "good wet slip but low strength and poor wear resistance." Comparative Example 4 only added hydrogenated fish oil fatty acids, reducing the Mooney viscosity from 78 to 71 (comparative Example 1) and increasing the aging retention rate from 78% to 84%, but the tear strength was only 72 kN / m, and the wet slip friction coefficient was only 0.65, indicating a problem of "improved processing and aging but insufficient reinforcement and slip resistance." Example 2, on the other hand, simultaneously added ATT-KF aramid micropowder, ATT-R85 anti-slip resin, and hydrogenated fish oil fatty acids, achieving a tear strength of 86 kN / m, a wet slip friction coefficient of 0.88, and an abrasion loss of 0.058 cm⁻¹. 3 It exhibits excellent overall performance with an 88% aging retention rate. This demonstrates that adding just one of ATT-KF aramid micropowder, ATT-R85 anti-slip resin, or hydrogenated fish oil fatty acids fails to achieve optimal results because each material has a limited function: ATT-KF aramid micropowder provides bulk reinforcement but lacks anti-slip properties; ATT-R85 anti-slip resin provides surface anti-slip properties but lacks reinforcement capabilities; and hydrogenated fish oil fatty acids are responsible for processing and interface optimization but lack direct reinforcement and anti-slip functions.

[0025] Example 2, compared to Comparative Examples 5-7, further verifies the irreplaceable nature of ternary synergy. Comparative Example 5, while possessing better mechanical properties (tear strength 78 kN / m, abrasion 0.068 cm),... 3 However, the wet friction coefficient was only 0.68, the compression temperature rise was 35℃, and the aging retention rate was 83%, exhibiting problems of "insufficient wet slip, high heat generation, and average aging." This is attributed to the lack of "bridging effect" from hydrogenated fish oil fatty acids, insufficient dispersion of ATT-KF aramid micropowder, incomplete migration of ATT-R85 anti-slip resin, and an unoptimized cross-linking network. Comparative Example 6 showed a tear strength of 84 kN / m and an abrasion loss of 0.062 cm. 3 The aging retention rate is 86%, indicating excellent performance. However, its wet friction coefficient is only 0.70, exhibiting the problem of "sufficient reinforcement but insufficient anti-slip properties," due to the lack of surface anti-slip function from ATT-R85 anti-slip resin. Comparative Example 7 has a wet friction coefficient of 0.82 and a Mooney viscosity of 72, demonstrating good processing and anti-slip properties, but its tear strength is only 74 kN / m and its abrasion wear is 0.077 cm. 3 The problem of "sufficient anti-slip properties but insufficient reinforcement" exists because of the lack of bulk reinforcement from ATT-KF aramid micropowder. The binary system cannot achieve optimal results because the absence of any key component will lead to functional chain breakage: without hydrogenated fish oil fatty acids, dispersion and cross-linking are not optimized; without ATT-R85 anti-slip resin, surface function is lost; and without ATT-KF aramid micropowder, bulk reinforcement is insufficient.

[0026] Compared with Comparative Example 8, Example 2 showed an increase in tear strength from 76 kN / m to 86 kN / m, indicating enhanced tear resistance; Akron abrasion loss decreased from 0.071 cm. 3 It dropped to 0.058cm 3 The wear resistance is significantly improved; the wet friction coefficient increases from 0.68 to 0.88, demonstrating a significant improvement in wet skid resistance; and the aging retention rate increases from 82% to 88%, indicating superior aging resistance. The reason for this improvement lies in the fact that the conventional stearic acid used in Comparative Example 8 only provides basic vulcanization activation, with a simple molecular structure and limited function; while the hydrogenated fish oil fatty acid used in Example 2 has a unique saturated long-chain fatty acid structure, high acid value, and low iodine value. In the rubber compound, it simultaneously functions as an activator (carboxyl groups react with zinc oxide to form zinc soap, activating the vulcanization system), a plasticizer (long chains insert between rubber molecular chains, reducing viscosity), a dispersant (melt-coating the filler surface, reducing interfacial energy), and an interface modifier (carboxyl groups bond with functional groups on the filler surface, improving interfacial bonding). This "one agent, multiple functions" characteristic is irreplaceable by conventional stearic acid and is the key to the ternary synergistic system of this invention.

[0027] The three materials—ATT-KF aramid micropowder, ATT-R85 anti-slip resin, and hydrogenated fish oil fatty acids—each possess unique performance characteristics: ATT-KF aramid micropowder is a micronized aramid product with special surface treatment, exhibiting a high aspect ratio and excellent high-temperature resistance. It can form a three-dimensional rigid skeleton in the rubber matrix, effectively inhibiting crack initiation and propagation through physical entanglement and mechanical interlocking, significantly improving the tear and cut resistance of the tread rubber. Its surface-active functional groups can also form physical entanglement and chemical bonding with the rubber matrix; ATT-R85 anti-slip resin is a modified hydrocarbon resin with good affinity to the rubber matrix. The compatibility of the compound allows it to migrate to the surface of the rubber compound during vulcanization, forming a micro-scale rough structure. This increases the mechanical interlocking force when in contact with wet and slippery surfaces and disrupts the continuity of the water film, thereby significantly improving the friction coefficient of wet and slippery surfaces. Furthermore, it can continuously replenish the surface friction layer during dynamic use, maintaining long-term anti-slip performance. Hydrogenated fish oil fatty acids are products obtained by hydrogenating and saturating fish oil fatty acids. They have a unique saturated long-chain fatty acid structure (C16-C22), a moderate melting point, high acid value, and low iodine value. In rubber compounds, they simultaneously function as activators, plasticizers, dispersants, and interface modifiers.

[0028] The synergistic effect among the three materials forms a three-dimensional reinforcing network of "bulk reinforcement - surface function - interface optimization - cross-linking density," achieving a 1+1>2 effect: First, hydrogenated fish oil fatty acids, acting as a "multifunctional bridge," melt-coat the surface of ATT-KF aramid micropowder during the mixing process, reducing its interfacial energy and promoting the uniform dispersion of ATT-KF aramid micropowder in the rubber matrix. Its active carboxyl groups form hydrogen bonds or chemical bonds with the functional groups on the surface of ATT-KF aramid micropowder. Simultaneously, the long-chain aliphatic hydrocarbon structure is compatible with the rubber molecular chains, forming a strong interfacial bond, enabling stress to be efficiently transferred from the rubber matrix to ATT-KF. Aramid micropowder fully utilizes its three-dimensional rigid skeleton to enhance its reinforcing effect. Secondly, the plasticizing effect of hydrogenated fish oil fatty acids reduces the viscosity of the system, forms lubrication channels, and promotes the migration and enrichment of ATT-R85 anti-slip resin to the surface during vulcanization, forming a uniform and stable micro-rough structure on the rubber surface, significantly improving the wet friction coefficient. At the same time, the active carboxyl groups of hydrogenated fish oil fatty acids react with zinc oxide to generate zinc soap, which activates the vulcanization system, increases the crosslinking density and crosslinking uniformity, and forms a denser vulcanization network, providing a stable load-bearing skeleton for ATT-KF aramid micropowder and a uniform migration channel for ATT-R85 anti-slip resin. In summary, the synergistic effect of the three components is as follows: ATT-KF aramid micropowder fully exerts its reinforcing effect in the interface and cross-linking network optimized by hydrogenated fish oil fatty acids; ATT-R85 anti-slip resin fully exerts its anti-slip function under the migration promoted by hydrogenated fish oil fatty acids; and hydrogenated fish oil fatty acids maximize the functions of both components by improving dispersion, activating cross-linking, and optimizing the interface. Ultimately, this achieves comprehensive optimization of processability, mechanical properties, wear resistance, wet slip resistance, and aging resistance, a balance of comprehensive performance that cannot be achieved by any single or binary system.

Claims

1. A new energy mining truck tire tread compound that is resistant to wet slippage and wear during the rainy season, characterized in that: By weight, it comprises the following components: 100 parts rubber matrix, 40-55 parts carbon black, 5-15 parts silica, 1-3 parts silane coupling agent, 3-10 parts ATT-KF aramid micro powder, 5-12 parts ATT-R85 anti-slip resin, 2-6 parts hydrogenated fish oil fatty acid, 3-5 parts zinc oxide, 1-3 parts stearic acid, 3-6 parts antioxidant, 1-2 parts microcrystalline wax, 1.5-2.5 parts sulfur, and 1.4-2.1 parts accelerator; the rubber matrix is ​​composed of natural rubber and styrene-butadiene rubber in a weight ratio of (50-70):(30-50).

2. The new energy mining truck tire tread compound with anti-wet slip and wear resistance as described in claim 1, characterized in that, The carbon black is N220.

3. The new energy mining truck tire tread compound with anti-wet slip and wear resistance as described in claim 1, characterized in that, The silane coupling agent is bis-[γ-(triethoxysilane)propyl]tetrasulfide.

4. The new energy mining truck tire tread compound with anti-wet slip and wear resistance as described in claim 1, characterized in that, The accelerator is composed of accelerator CZ and accelerator DM in a weight ratio of (1-1.5):(0.4-0.6).

5. The preparation method of the new energy mining truck tire tread compound with anti-wet slip and wear resistance as described in any one of claims 1-4, characterized in that, Includes the following steps: S1 First stage mixing: Rubber matrix, carbon black, ATT-KF aramid micro powder, hydrogenated fish oil fatty acid, zinc oxide, stearic acid, antioxidant, and microcrystalline wax are put into an internal mixer and mixed at a speed of 40-45 rpm. The mixture is lifted and pressed every 30-35 seconds, and the discharge temperature is controlled at 150-155℃ to obtain the first stage masterbatch. It is then cooled and left to stand for 4-8 hours. S2 Two-Stage Mixing: The first-stage masterbatch, silica, silane coupling agent, and ATT-R85 anti-slip resin are put into a mixer and mixed at a speed of 35-40 rpm. The mixture is lifted and pressed every 30-35 seconds. The temperature is raised to 140-145℃ and held for 60-90 seconds to carry out the silanization reaction. The discharge temperature is controlled at 145-150℃ to obtain the second-stage masterbatch. The mixture is then cooled and left to stand for 4-8 hours. S3 Final Mixing: The second-stage masterbatch, sulfur, and accelerator are put into an internal mixer and mixed at a speed of 25-30 rpm for 100-120 seconds. The discharge temperature is controlled to be ≤100℃. After discharge, the new energy mining truck tire tread rubber with anti-wet slip and wear resistance in the rainy season is obtained.

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