A strong solar energy automatic tracker middle axle and its preparation method

Abstract

The present application relates to a kind of tough solar automatic tracker middle shaft and its preparation method, belong to the technical field of austempered ductile iron castings.The present application is cooled to eutectoid transformation temperature range before austempering process, make it produce pearlite, then reheated to 860~880 DEG C and insulate, make pearlite completely convert into carbon-rich austenite, after the above operation, austenite organization is obviously refined and homogenized;Refined austenite organization has significant promoting effect for ADI austempering process relative to coarse austenite organization;Solar automatic tracker middle shaft prepared by the method has the characteristics of high graphite spheroidization rate and sphericity, and excellent mechanical properties of cast iron material.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of strong and tough solar automatic tracker middle shaft and its preparation method, belong to the technical field of austenite cast iron casting. BACKGROUND

[0002] Solar automatic tracker is used to track the sun, so that the light main shaft of collector is always parallel to sunlight.The sun is usually tracked in azimuth and elevation, so that the collector plane is always perpendicular to the incident light of the sun.Solar automatic tracker middle shaft assembly is an important force piece, and its safety is particularly important.

[0003] At present, the various performance requirements of solar automatic tracker middle shaft proposed by people are basically as follows:

[0004] Tensile strength ≥700MPa;

[0005] 0.2% yield strength ≥600MPa;

[0006] Hardness 310~450HB.

[0007] And the conventional casting method is difficult to fully meet the various performance requirements described above.It is necessary for us to optimize the formula and process to further improve the product quality. SUMMARY

[0008] The purpose of the present application is to propose a kind of strong and tough solar automatic tracker middle shaft, which has optimized mechanical properties.

[0009] The technical solution of the present application to solve the problem is as follows:

[0010] A kind of strong and tough solar automatic tracker middle shaft is made of ductile cast iron, and the ductile cast iron includes the following components by mass fraction: C 3.4~3.9%, Si 2.5~2.7%, Mn 0.1~0.3%;The remaining part is iron (Fe) and unavoidable residual elements with content less than 0.1%.

[0011] In the above technical solution of the present application, the following effects of each element are considered in the formula design:

[0012] -Carbon

[0013] Beneficial to graphitization and spheroidization, increasing carbon content is beneficial to the toughness of the material.

[0014] -Silicon

[0015] Silicon is an element strongly promoting graphitization and is beneficial to increase toughness. The inoculation of silicon can refine eutectic cells and disperse phosphorus eutectic. The final silicon content of the tough ferrite spheroidal graphite iron is generally controlled below 2.7%. If the content of manganese in the pig iron is less than or equal to 0.5% and the content of phosphorus is less than or equal to 0.7%, the final silicon content can be relaxed to about 3.0%.

[0016] Manganese

[0017] Manganese hinders the decomposition of cementite and pearlite. The chilling tendency of spheroidal graphite iron is already quite high, so the content of manganese should be controlled, which is generally less than 0.4%. In the present application, it is limited to 0.3%.

[0018] Phosphorus

[0019] Phosphorus can form brittle phases in cast iron, especially ternary phosphorus eutectic or compound phosphorus eutectic, which is extremely harmful to toughness. The following measures are usually taken to weaken the harmful effects of phosphorus: increasing the carbon content, adopting a high-carbon and low-silicon composition scheme to hinder the precipitation of ternary phosphorus eutectic; strengthening inoculation to refine eutectic cells and disperse phosphorus eutectic; annealing at 920-980°C to convert ternary phosphorus eutectic or compound phosphorus eutectic into binary phosphorus eutectic, reduce the amount of phosphorus eutectic, and improve the spheroidal graphite shape. Using metal mold casting to form a honeycomb structure, i.e., spheroidal graphite, ledeburite, and cementite structure, and then annealing at high temperature can avoid the generation of phosphorus eutectic.

[0020] Sulfur

[0021] Too high content of sulfur can make spheroidization unstable and produce too many sulfide inclusions, which seriously affect toughness, so the sulfur content of the original molten iron should be as low as possible, and preferably the molten iron is subjected to desulfurization measures.

[0022] As a preference, the spheroidal graphite cast iron has a carbon equivalent C EQ = C(%) + 1 / 3 Si(%) + 1 / 3 P(%) of 4.30-4.70. Preferably, between 4.40 and 4.60, in particular between 4.50% and 4.60%.

[0023] As a preference, the spheroidal graphite cast iron has a tensile strength greater than 700 MPa. Preferably, a tensile strength greater than 1000 MPa, in particular between 1200 MPa and 1400 MPa.

[0024] As a preference, the spheroidal graphite cast iron has a 0.2% yield strength greater than 700 MPa. Preferably, a 0.2% yield strength greater than 750 MPa, in particular between 800 MPa and 850 MPa.

[0025] As a preference, the spheroidal graphite cast iron has an elongation greater than 1%. In particular, between 3.0% and 7.0%.

[0026] As a preference, the ductile cast iron has a Brinell hardness between 310 HB and 450 HB. In particular between 380 and 420.

[0027] As a preference, the ductile cast iron has a spherulitic grade ≤ 3. In particular the spherulitic grade is 1 or 2.

[0028] As a preference, the ductile cast iron has a number of graphite spheres ≥ 100 / mm^2; a spheroidization rate ≥ 85%.

[0029] Another object of the present application is to provide a method for manufacturing the above-mentioned central shaft of the strong and tough solar automatic tracker.

[0030] A method for manufacturing a central shaft of a solar automatic tracker, comprising the following steps:

[0031] S1, heating ingredients to a molten state to form a molten material;

[0032] S2, injecting the molten material into a mold to form a casting after solidification;

[0033] S3, keeping the casting at a graphitization temperature of 850-1000℃ for 10-30min;

[0034] S4, then slowly cooling the casting to 725-730℃ at a rate of less than 50℃ / min;

[0035] S5, then re-heating the casting to 880-920℃ and keeping it for 1-2h to make it completely transform into carbon-rich austenite, and then quickly quenching it into a salt bath at an austenite isothermal transformation temperature of 320-350℃ for 1-2h;

[0036] S6, then air cooling to room temperature.

[0037] In the above technical solution of the present application, in step S4, the casting is slowly cooled at a rate of less than 50℃ / min until less than the eutectoid transformation temperature. This process is to make the casting enter the critical state, so that the casting occurs between pearlite and austenite.

[0038] As a preference, the mold is a mold suitable for the iron mold sand coating process. After the casting is formed in the mold and solidified, it is taken out after being lowered to a suitable temperature and then heat treated.

[0039] As a preference, the ingredients include the following components by mass fraction: scrap steel 480-520, pig iron 180-220, recycled material 330-370, manganese iron 0.8-1.2, silicon iron 4-5, silicon carbide 8-12, copper 2-4, spheroidizing agent 12-18, inoculant 3-5, and carbon additive 18-19.

[0040] In the technical scheme, the spheroidizing agent is a molten iron additive for making graphite in cast iron spheroidize.

[0041] In the technical scheme, the inoculant is a molten iron additive for forming local concentration difference in the molten iron, and becoming the core of graphite, thereby refining the graphite; and the inoculant is specifically 75 ferrosilicon.

[0042] When casting, the castings have requirements for carbon.

[0043] As a further preferred aspect of the technical scheme, the ingredients include the following components by mass: scrap steel 500, pig iron 200, return material 350, manganese iron 1, ferrosilicon 4.5, silicon carbide 10, copper 3, spheroidizing agent 15, inoculant 4, and carbonizing agent 18.5.

[0044] In summary, the present application has the following advantages:

[0045] 1. The present application screens the suitable composition of the molten iron through high-throughput component material thermodynamic calculation, actual casting cooling conditions, and the constructed solidification characteristic discrimination criterion of high-quality spheroidal graphite castings, thereby forming the molten iron composition window.

[0046] 2、The present application adopts the sand coated iron mold process to replace the traditional clay sand or resin sand molding process, so that the casting has high strength, good yield, small machining allowance, the yield is improved from 80% to 95%, and the molten iron utilization rate is increased by 15%;

[0047] 3、The present application cools the casting to the eutectoid transformation temperature range before the isothermal quenching process, the transformation between austenite and pearlite occurs, then the temperature is reheated to 880-920 DEG C for insulation, and then the pearlite is completely converted into carbon-rich austenite (and the reheating temperature cannot be too high, otherwise the austenite organization is easy to grow, which is not conducive to isothermal quenching), after the above operation, the austenite organization is obviously refined and homogenized (the refinement and homogenization of austenite organization before isothermal quenching process); the refined and homogenized austenite organization has a significant promoting effect on the ADI isothermal quenching process; then the ADI isothermal quenching process is adopted, and the isothermal quenching is carried out at 320-350 DEG C, so that the mixed organization of acicular ferrite + austenite + residual pearlite + residual bainite is obtained; the mechanical property is improved from QT600-3 to QTD1050-6. DETAILED DESCRIPTION

[0048] The present application will be further explained and described below.

[0049] The present embodiment is only an explanation of the present application, and is not a limitation of the present application, any change made by the person skilled in the art after reading the specification of the present application will be protected by the patent law as long as it is within the scope of the claims.

[0050] Example 1

[0051] A strong and tough solar automatic tracker middle shaft is made of nodular cast iron, which comprises the following components in mass fraction.

[0052] Carbon C % Silicon Si % Manganese Mn % Phosphorus P % Sulfur S % 3.68 2.65 0.138 0.017 0.0105

[0053] The preparation method of the above-mentioned strong and tough solar automatic tracker middle shaft is as follows:

[0054] S1, heating the ingredients to a molten state to form a molten material;

[0055] S2, pouring the molten material into a casting mold to form a casting after solidification;

[0056] S3, keeping the casting at a graphitization temperature of 950 DEG C for 25 min;

[0057] S4, then slowly cooling the casting to 725 DEG C at a rate of less than 50 DEG C / min (about 50 DEG C / min in this embodiment);

[0058] S5, then the casting is reheated to 890℃, and kept for 1h, so that it is completely transformed into carbon-rich austenite, and then it is rapidly quenched into a salt bath at the austenite isothermal transformation temperature of 350℃, and kept for 1h;

[0059] S6, then it is discharged and air-cooled to room temperature to obtain a rough product;

[0060] S7, the rough product is trimmed, and after testing, a finished product is obtained.

[0061] In the above technical solution, 890℃ is the best temperature (close to the inflection point value) obtained through orthogonal test, when the temperature is higher, the uniformity and refinement of austenite change obviously, and when the temperature is lower, more time is needed for keeping, and the efficiency is reduced.

[0062] The ingredients are as follows:

[0063] Material name Addition weight (Kg) Scrap 500 Pig iron 200 Reverberatory material 350 Manganese iron 1 Silicon iron 4.5 Silicon carbide 10 Copper 3 Spheroidizing agent 15 Inoculant 4 Recarburizer 18.5

[0064] The inoculant is 75 ferrosilicon, the spherulitic agent is magnesium ferrosilicon alloy containing 6%-7% of magnesium and 35%-50% of silicon, and the carburant is artificial graphite.

[0065] In particular, the above preparation method adopts the iron mold coated sand process, specifically, the mold temperature is controlled to be 220-250℃ (in this example, 220℃), and the sand coating air pressure is 0.35-0.4MPa (in this example, 0.35MPa).

[0066] The above casting (solar automatic tracker central shaft) is detected (the test standard is GB / T 24733-2009), and the results are as follows:

[0067]

[0068] Comparative Example 1

[0069] A solar automatic tracker central shaft is made of nodular cast iron, and the nodular cast iron comprises the following components in mass fraction.

[0070] Carbon C % Silicon Si % Manganese Mn % Phosphorus P % Sulfur S % 3.68 2.65 0.138 0.017 0.0105

[0071] The preparation method of the above solar automatic tracker central shaft is as follows:

[0072] S1, the ingredients are heated to a molten state to form a molten material;

[0073] S2, the molten material is injected into a mold to form a casting after solidification;

[0074] S3, heat the casting to 920℃, keep for 1h, make it completely transform into carbon-rich austenite, then quickly quench it into a salt bath with austenite isothermal transformation temperature 350℃, keep for 1h;

[0075] S4, then air cool to room temperature after discharging, to obtain a rough finished product;

[0076] S5, trim the rough finished product, and obtain a finished product after testing.

[0077] The ingredients are as follows:

[0078]

[0079]

[0080] The inoculant is 75 ferrosilicon; the spheroidizing agent is magnesium ferrosilicon alloy with magnesium content of 6% to 7% and silicon content of 35% to 50%; and the carburant is artificial graphite.

[0081] In particular, the above preparation method adopts the iron mold coated sand process, specifically, the mold temperature is controlled to be 220 to 250℃ (in this example, 220℃), and the sand coating air pressure is 0.35 to 0.4MPa (in this example, 0.35MPa).

[0082] The above casting (solar automatic tracker central shaft) is detected (the test standard is GB / T 24733-2009), and the results are as follows:

[0083]

[0084] Comparative Example 2

[0085] The difference from Comparative Example 1 is that in step S3, the heat treatment temperature is 890℃, and the holding time is 1h.

[0086] The casting (solar automatic tracker central shaft) in this example is detected (the test standard is GB / T 24733-2009), and the results are as follows:

[0087]

Claims

1. A method for manufacturing a robust solar automatic tracker central shaft, wherein the central shaft is made of ductile iron, and the ductile iron comprises the following components by mass fraction: C 3.4~3.9%, Si 2.5~2.7%, Mn 0.1~0.3%; The remainder consists of iron and unavoidable residual elements, with a content of less than 0.1%. The preparation method includes the following steps: S1. Heat the ingredients to a molten state to form a melt; S2. Pour the molten material into the mold, and after solidification, a casting is formed; S3. Hold the casting at a graphitization temperature of 850~1000℃ for 10~30 minutes; S4. The casting is then slowly cooled to 725-730°C at a rate of less than 50°C / min. S5. Then, the casting is reheated to 860~880℃ and held for 1~2 hours to completely transform it into carbon-rich austenite. Then, it is quickly quenched into a salt bath with an austenite isothermal transformation temperature of 325~350℃ and held for 1~2 hours. S6. Then remove from the oven and air cool to room temperature.

2. The method for preparing a robust solar automatic tracker central shaft according to claim 1, characterized in that: The ingredients include the following components in parts by weight: scrap steel 480~520, pig iron 180~220, recycled material 330~370, ferromanganese 0.8~1.2, ferrosilicon 4~5, silicon carbide 8~12, copper 2~4, spheroidizing agent 12~18, inoculant 3~5, and carbon raiser 18~19.

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