Based on the use of Babbitt alloy in the production and maintenance of oil film bearings, this article studies and discusses the feasibility and strategy of recycling Babbitt alloy to reduce costs, and calculates the rate at which Babbitt alloy can be recycled and reduced in each production link. Using the powerful calculation function of Excel spreadsheets and combined with actual production experience data, a Babbitt alloy usage calculator and a Babbitt alloy recovery calculator are compiled to facilitate the use of production and business people. According to the cost reduction strategy introduced in the article, production costs can be significantly reduced, and users can gain advantages in the increasingly fierce market competition.
Oil film bearings are a type of sliding bearings. They can meet the requirements of high-speed and heavy-load working conditions and are widely used in modern large-scale rolling mills, especially plate and strip continuous rolling mills with automatic control of plate thickness and plate shape. They are also widely used in high-speed wire rolling mills. Oil film bearings are composed of tapered sleeves and bushings. The two slide relative to each other and reduce the friction between the friction pairs through lubricating media. The contact surfaces of the two need to be welded with a material called Babbitt alloy. Babbitt alloy materials can further reduce friction and extend the service life of oil film bearings. This is because Babbitt alloy belongs to the organization of hard points in soft matrix. The soft matrix can withstand impact and vibration, and has good running-in performance. The hard points can reduce the contact surface, friction coefficient and wear, and have good wear resistance. The concave-convex gap between the soft matrix and the hard points is also conducive to the storage of lubricating oil.
The oil film bearings used in various rolling mills need regular inspection and maintenance. Replacement and maintenance are determined by the working environment of the rolling mill. During the use of oil film bearings, the bushing Babbitt alloy often peels off and wears due to serious emulsification of lubricating oil, impurities entering, water entering the bearing, and rolling rollers. In addition, under non-abnormal conditions, after long-term use, the Babbitt alloy cladding layer is worn to a certain extent and can no longer be used. These all require the worn Babbitt alloy layer to be removed and then cast or welded.
As a non-ferrous metal, Babbitt alloy is expensive, with a market price of up to 160 yuan/kg. It accounts for a large proportion of the manufacturing and maintenance costs of oil film bearings. Therefore, it is crucial to achieve cost reduction by recycling Babbitt alloy. This article proposes some discussions and analyses on the recycling and cost reduction of Babbitt alloy in the maintenance of oil film bearing bushings and the production of spare parts, hoping to bring advantages to enterprises in market bidding.
1 Recyclable links of Babbitt alloy in production
1.1 Recycling of Babbitt alloy chips in new oil film bearings
In the processing technology design of taper sleeves and bushings, in order to avoid production defects, a part of the processing allowance will be left in the welding process of Babbitt alloy linings, and the maximum allowance can reach 50% of the total welding amount. After the surfacing is completed, it is removed by cutting. This part of the Babbitt alloy cut out can be completely recycled, but it needs to meet certain requirements. The following standards are usually used to judge whether the composition of the recycled Babbitt alloy meets the relevant requirements: ① The impurity content is lower than the specified range; ② The alloy composition is within the specified range.
The recycled Babbitt alloy chips will be mixed with impurities in the machining process. In the machining process, due to the wide variety of materials processed by the machine tool, chips of different types of materials will be stored around the machine tool. At this time, the processing plant should be required to formulate a strict operation management system. For example, before processing the babbitt alloy lining, it is necessary to clean up the steel, cast iron and other fine debris around the machine tool. This ensures that the recycled chips will only contain a very small amount of cast iron and steel debris. However, these very small amounts of impurity debris still need to be processed. Since steel and cast iron are magnetic materials, they can be strongly attracted by magnets, while babbitt alloys are antimagnetic materials and are weakly repelled by magnetic fields. Therefore, this small amount of debris can be cleaned up by magnetic separation to obtain babbitt alloy chips with almost no impurities.
At the same time, babbitt alloy is not easily oxidized by air at room temperature, and because its mechanical properties are much lower than those of steel, during the processing, even if a high-speed and large-scale cutting method is used, the local instantaneous temperature will not be higher than 100°C, and the cutting material will be bright white and will not be oxidized (generally the color after oxidation is gray-blue). From this characteristic, it can be seen that the alloy composition of the babbitt alloy chips is not contaminated during the cold processing process, and the composition can be guaranteed.
In summary, after taking certain measures during the processing, pure Babbitt alloy chips can be obtained and can be recycled and reused.
1.2 Recycling of Babbitt alloy for repair bushings
The recycling of Babbitt alloy for repair bushings mainly refers to the recycling of the Babbitt alloy layer still attached to the bushing after wear and peeling. Depending on the degree of wear, 30%~70% of residual Babbitt alloy will remain. This part of Babbitt alloy is usually recycled by two methods: melting and cold working cutting.
(1) The melting method is to utilize the low melting point characteristics of Babbitt alloy. Specific operation process: First, heat and melt the original Babbitt alloy. If heated directly, Babbitt alloy is easily oxidized, which greatly reduces the recycling amount and causes unnecessary waste. Choose a special crucible with a size suitable for the size of conventional bushings. Pre-melt some Babbitt alloys with similar composition in the crucible. The heating temperature should not be too high. The temperature should be controlled at 410~420℃ to prevent deformation of the body. Cover the liquid surface with a layer of roasted charcoal powder (about 10~15mm in size) to prevent the oxidation problem mentioned in “1.1”. Then sink the bushing completely into the crucible and keep it warm for 3 minutes. After it is completely melted, take it out quickly and clean the surface with compressed air. After cooling, use a scraper or wire brush to remove other rust and dirt, and the residual alloy on the inner ring of the bushing should be cleaned. Use a metal cleaning agent to carefully clean the oxide film and oil on the surface to prevent obstruction of metal fusion and ensure a clean surface.
As can be seen from the above, when recycling Babbitt alloy by melting, measures need to be taken to separate the liquid Babbitt alloy from the air to avoid oxygenation, so as to ensure that its alloy composition meets the standard requirements.
(2) The basic operation requirements of cold machining are the same as those of the above machining allowances. It is necessary to control the machining accuracy to avoid damaging the main body and prevent the main body chips from mixing into the recyclable Babbitt alloy in the form of “impurities”.
1.3 Statistics and calculation based on the empirical data of the recyclable utilization rate of Babbitt alloy
In order to avoid the cladding defects of bushing Babbitt alloy, the welding thickness is usually 2 to 3 times thicker than the theoretical thickness during the welding process. Taking the single-side thickness of the new bushing of 1.2 to 1.3 mm as an example, the actual welding thickness must reach 2.85 mm. According to the Babbitt alloy density of 7380 kg/m3, the theoretical calculation is carried out, considering the 8% increment to compensate for the loss during the welding process, then the theoretical amount of cladding required is: 0.00285×7380×1.08=22.716 kg/m2. After machining, turning, boring and milling, the thickness of the Babbitt alloy left on the bushing is about 1.25mm. At this time, it can be calculated that the theoretical remaining amount of Babbitt alloy is 0.00125×7380=9.225kg/m2. Assuming that all the scraps cut off can be recycled, the price of recycled iron scraps is calculated as half the price of welding wire cost, (22.716-9.225)×0.5/22.716 ≈ 30%. In the end, about 30% of the cost is recovered. Therefore, before production preparation, the material preparation of Babbitt alloy is carried out according to the required welding wire weight. In terms of cost, 30% is recycled, that is, 70% is effectively utilized.
In the recycling process of Babbitt alloy in the production process, in addition to recycling the scraps, another link is the Babbitt alloy remaining on the repaired bushing. Usually, 60% of the Babbitt alloy remaining on the bushing can be retained.
If the thickness of the above bushing babbitt alloy is 1.25mm, the babbitt alloy remaining on the bushing is 0.00125×7380×60%=5.535kg/㎡. According to the half price after recycling, it accounts for about 5.535÷22.716×50%≈13% of the total welding amount required.
Because some bushings are severely worn, a thicker welding layer may be required. Therefore, according to different welding thicknesses, the weight of welding wire required per square meter of different welding thicknesses can be calculated. According to the above method, according to different welding thicknesses and combined with production practice, it can be concluded that the weight of welding wire required per unit area under different welding thicknesses. The practical experience data of the amount of babbitt alloy welding wire for oil film bearing bushings is shown in Table 1, where “1” and “一” both indicate that the number of welding layers is 1, but the welding parameters are set differently due to different thicknesses to distinguish them.
2 Use Excel to prepare a Babbitt alloy welding wire consumption calculator
Table 1 is based on the theoretical calculation data of Babbitt alloy consumption per square meter under different welding thicknesses, combined with actual operation experience, and provides empirical data on Babbitt alloy consumption per square meter under different welding thicknesses. And the number of welding layers is distinguished according to the welding process thickness. Based on these empirical data, Excel is used to prepare a parameterized calculator for bushing Babbitt alloy consumption. The consumption of Babbitt alloy is closely related to the welding thickness and the inner lining area of the bushing. Therefore, the key to the design of this calculator is to be able to input parameters that affect the Babbitt alloy area, select the Babbitt alloy welding thickness, and quickly calculate the use area to achieve the desired function.
According to the bushing drawing, the Babbitt alloy welding surface is a regular cylindrical surface, so the parameters that affect the bushing welding area are the diameter and the height of the cylinder. Using the powerful computing power of Excel tables, the Babbitt alloy consumption calculation formula is compiled through calculation formulas, functions (ifs, etc.), drop-down menus, data selection and other functions. The user can calculate the amount of babbitt alloy used in the bushing and the amount of recycling saved by inputting the effective length of the bushing welding surface (mm), the size of the bushing inner hole shell D (mm), and selecting the number of welding layers according to the babbitt alloy welding thickness through the drop-down button.
2.1 Make a single-select drop-down box
In this calculator, in addition to using formulas and functions, which are commonly used in statistical calculations, the production of a single-select drop-down box is mainly used. By selecting data in the Excel table – validity – sequence – select data source – generate a single-select drop-down box, the operation interface is shown in Figure 1.
2.2 Matching of drop-down box data source
After the drop-down box is completed, the function of selecting the number of welding layers can be realized. At this time, what needs to be considered is the matching of the acquisition of the welding wire demand per unit area, so that the drop-down box of the number of welding layers is completed, as shown in Figure 2. At this time, you can use the if conditional sentence. If it is one layer, then the unit area
weight is 25kg/m2. However, there are multiple layer selection distinctions here, so the multi-conditional selection statement ifs is used. Here, the statement ifs (L11=K15; L15; L11=K16; L16; L11=K17; L17; L11=K18; L18; L11=K19; L19) is used to obtain the data of welding wire quantity per unit area.
Below the calculation of the bushing babbitt alloy calculator is the recycling quantity calculator, which calculates the recycling quantity of babbitt alloy by referring to the babbitt alloy quantity obtained above and the recycling rate of babbitt alloy on new and old products calculated above.
So far, the new and recycled quantity of babbitt alloy, the repaired quantity and the recycled quantity can be directly obtained by entering the bushing size parameters. After the calculator design is completed, the basic operation interface is shown in Figure 3.
Here, the experience data for production is summarized and collected, which provides strong data support for the preparation of production materials for planners, and also greatly saves the cost calculation time for business personnel, and can quickly and accurately provide users with price basis, providing strong support for winning orders.
Babbitt alloy is widely used in oil film bearing bushings, and the cost accounts for a high proportion. If recycling is not considered, the cost of babbitt alloy is almost the same as the price of the bushing itself, accounting for 38% to 42% of the entire set cost. In the case of fierce market competition, recycling and cost reduction measures are taken to improve the competitiveness of enterprises.
