Remelting and recycling of cutting chips of the ho

Remelting recovery of tin base bearing alloy chips

abstract the remelting recovery of tin base bearing alloy chips was studied

keywords tin base bearing alloy chip remelting recovery oxidation

1 preface

many products in industry need to use bearing alloys, such as crosshead, slider, piston in compressor, automobile engine, tractor, etc. During the manufacturing process, a large number of bearing alloy chips are usually sold as waste at the price of a few yuan per kilogram, while the finished product price of bearing alloy is up to 40 yuan/kg If the bearing alloy chips are recycled, the product cost will be greatly reduced and waste will be reduced, which is conducive to improving the economic benefits of enterprises. In this paper, the remelting recovery of tin base bearing alloy chips is studied

2 analysis of oxidation loss during cutting and molten metal

2.1 oxidation during cutting

tin based bearing alloy is also known as tin based Babbitt alloy. This kind of alloy is not easy to be oxidized by air at room temperature. Their mechanical properties are much lower than those of steel materials. Therefore, when machining and cutting, sharp tools should be used and the speed should be high. In this way, the chip temperature will not be very high, and the short-term temperature is only 70 ℃ ~ 100 ℃. The alloy chip is still bright white, not like the gray and dark color after oxidation. Therefore, oxidation during cutting can be ignored

2.2 oxidation of molten metal and loss of metal during melting

2.2.1 process loss

whether in melting or alloy preparation, some metal loss is mainly due to the formation of oxidized slag. In addition, there are losses caused by metal volatilization, slag and splashing caused by the Ministry of industry and information technology organizing the preparation of the implementation plan of cleaner production technology in rare earth industry (Exposure Draft). When smelting tin base bearing alloy in electric furnace, the total loss of alloy is about 1.5% - 4% Adding organic substances such as rosin as flux for smelting tin based bearing alloy can reduce oxidation loss

2.2.2 theoretical aspect

2.2.2.1 oxidation of pure metals

the kinetics of solid metal oxidation is dominated by the properties of the oxides formed. If the volume of oxides is less than the volume of metal consumed to produce these oxides, the oxidation rate will remain unchanged or increase with time. If the volume of the oxide exceeds the volume of the metal forming it, and there is a close and continuous oxide film on the molten metal surface, the oxidation rate will decrease with time according to the parabolic relationship of w2=kt

2.2.2

oxidation of molten alloys the oxidation characteristics of molten metals may change due to the addition of other elements. The element with the greatest affinity with oxygen will be oxidized preferentially, and the nature of the oxide film generated by this element controls the oxidation process. The affinity of a metal for oxygen can generally be judged by its oxide formation heat and decomposition pressure. The higher the heat of formation of oxide and the lower the decomposition pressure, the stronger the affinity of this metal for oxygen. Table 1 lists the affinity of copper, tin and antimony for oxygen (according to the heat of formation of oxides). It can be seen from table 1 that among tin, antimony and copper, antimony has the largest heat of oxide formation and the largest affinity for oxygen. In tin based bearing alloys, the alloying element antimony will be oxidized preferentially, and the nature of the oxide film generated controls the oxidation process

3 chip recovery smelting process

Table 2 lists the chemical composition of two representative tin base bearing alloys. It can be seen from table 2 that the main components of the two alloy grades are antimony, copper and tin, and lead, iron, etc. are impurities. Impurities have a great influence on the properties of tin based uranium bearing alloys. The existence of trace lead will lead to the appearance of fusible eutectic (melting point 189 ℃) composed of lead based solid solution and tin based solid melt in the alloy, which will deteriorate the heat resistance and impact toughness of the alloy. The existence of Trace Bismuth will lead to bi Sn binary eutectic with a melting point of 138.5 ℃, so it should be strictly controlled, otherwise the alloy will overheat occasionally for a short time, and local melting will occur. A special development plan is formulated. When the iron content exceeds 0.1%, fesn2 primary crystals with high melting point will be formed in the alloy, which will not only deteriorate the fluidity of the liquid alloy, but also make the alloy brittle and even produce cracks. Therefore, the iron content in the alloy should also be strictly controlled. Because the oxidation rate of each main component element is different in the smelting process, the main component elements should also be controlled within the specified content range, and adjusted if necessary, so as to ensure that the mechanical properties of the bearing alloy remain unchanged. In order to achieve the above purpose, the following points should be considered in the chip recycling smelting process:

3.1 if more than two kinds of bearings are manufactured at the same time in the factory, the chips must be strictly stored separately to avoid mixing together during smelting. It cannot be mixed with other metal chips, so as to avoid increasing the difficulty of removing impurities during smelting and purification

3.2 the melting temperature is generally 50 ~ 100 ℃ higher than the initial crystallization temperature of the alloy. For example, the melting temperature of bearing alloy (zchsnsb) should be 430 ℃ ~ 480 ℃. Too high melting temperature will lead to coarse grains of the alloy and increase the oxidation loss of the alloy. The low melting temperature provides strong evidence for stab FB ⑵ 000 series flame retardants, which can not obtain fine grains, and is also detrimental to the removal of impurities

3.3 the melting time is related to the power of the furnace, the amount of molten alloy chips and the amount of impurities in the alloy chips. In short, after the melt temperature is uniform, it is appropriate to have enough time to remove impurities and adjust the content of various elements in the alloy

3.4 remove impurities by using the differences in specific gravity, melting point, ferromagnetism and other properties between substances, and using appropriate process methods to remove impurities

3.4.1 remove oil, inclusions and oxides in the chips. When the melting temperature reaches above 200 ℃, the oil will begin to volatilize and boil, and then burn away. The remaining residues, inclusions and oxides can be removed from the metal by using the difference between the specific gravity of the metal itself and the suspended solids

3.4.2 during metal smelting, fluxes such as rosin are used to avoid metal oxidation, but fluxes can also be used to eliminate suspended impurities in molten metal, degassing or change the composition and crystalline structure of metal. For example, when smelting tin base bearing alloy chips, adding some ammonia chloride (NH4Cl) can remove iron elements and inclusions in the alloy melt. The reaction formula is:

the ammonia, hydrogen or water vapor produced by

form many small bubbles in the metal liquid, and the suspended oxide inclusions will be adsorbed on them when they encounter them, rise with them, or be pushed to the liquid surface by the rising bubbles and removed. 3.4.3 use ferromagnetism to remove impurities. Such as the removal of fine particles of cast iron and steel. Available steel belongs to magnetic material, which can be strongly attracted by magnetic field. Tin based bearing alloy is an anti-magnetic material, which is weakly repelled by the magnetic field. If tin base bearing alloy chips and iron chips are mixed together, the chips can be removed with a strong magnetic field before smelting. Points. It can be seen from the table that the main components of the two alloy grades are antimony, copper and tin, and lead, bismuth, iron and other impurities. Impurities have a great influence on the properties of tin base bearing alloys. The existence of trace lead will cause fusible ladle composed of lead based solid solution and tin based solid melt to appear in the alloy. 3.5 before the end of smelting, check and analyze whether the main components of the alloy meet the content of the alloy brand. If a major element is lacking, the metal can be added to the alloy melt for smelting, or a reducing agent can be used to reduce the metal. For example, magnesium borate can be used as the reducing agent of copper, and its reaction formula is: 6cu2o + mg3b2 → 3mgo + B2O3 + 12cu However, when choosing reductant, it must be considered that the remaining reductant remaining in the metal may affect the quality of the metal

4 summary

to sum up, tin base bearing alloy chips can be remelted and recycled if more technical parameters of the material need to be tested. The pollutants of chips are removed during smelting, the loss of alloy during smelting is small, and the oxidation rate of alloy decreases with the increase of time according to the parabolic relationship of w2=kt. Therefore, the recycling of tin base bearing alloy chips is very beneficial to reduce product costs and improve the economic benefits of enterprises