Gravity casting process of bearing Babbitt alloy

Babbitt alloy casting process route of bearing bush: preparation → tile body preheating → tile blank tin lining → mold installation → Babbitt alloy pouring → water cooling → mold opening.

1. Preparation

First of all, the pouring fixture shall be kept clean and dry and placed on the tool rack; Preheat before use, keep the work site clean and tidy after each pouring, clean the assembly platform, pour the remaining alloy into the spindle mold for reuse, and remove the slag in the crucible and pouring spoon; Chemicals shall be placed in a dry cabinet and the bottle stopper shall be covered to prevent moisture absorption; First, prepare the solder flux, place it in a dry place and store it for use; The mould shall be trial assembled with the bearing bush before use, so as to check the service performance of the mould. The bearing bush shall pass the inspection before hanging the bearing alloy, the process size shall comply with the regulations, and the surface shall be free of defects such as air hole, sand hole and black skin. Protect the alloy surface and hole of non hanging bearing with asbestos; Secondly, according to the different environmental humidity, the bearing alloy surface of the tile must enter the tile preheating sequence of bearing alloy hanging casting within the specified time after machining; And check whether the equipment used in production operates normally, and preheat the molds and pouring tools used in production in advance. Pouring tools include: pouring spoon, large and small end packages, large and small lifting packages, soldering iron, metal stirring rod, bearing alloy ingot mold, slag skimming spoon, etc.

2. Tile body preheating

The bearing bush is called bearing bush for short. The bearing is composed of bearing bush and bearing seat. The tile blank is the blank part of the bearing bush. Before pouring, the tile blank needs to be heated in the trolley resistance furnace, and the heating temperature is controlled between 140 ℃ and 240 ℃. The heating temperature of tile shall not be higher than 240 ℃, so as to prevent the oxidation of tile surface, which is not conducive to the combination of Babbitt alloy and matrix.

3. Tin lining of tile blank

First, place the preheated tile blank (see Figure 1) in the tin bath for soaking and heating, and the temperature shall not be lower than 280 ℃. Then, brush the preheated tile blank with tin lining agent and put it into the tin bath for soaking and heating. The temperature of the molten tin in the tin bath shall be controlled between 280 ℃ ~ 300 ℃, and the temperature shall not be higher than 300 ℃ to prevent the oxidation of the molten tin. Brush the tin liquid on the joint surface of tile blank and bearing alloy to form a uniform tin film. The tin lining process should be carried out three times or more according to the effect. If local quality is found to be poor during tin lining, measures shall be taken immediately. Tin lining can be continued only after the problem is eliminated. It is the key process of Babbitt alloy casting to ensure the quality of tin lining and make the matrix fully react with tin liquid to form an intermediate transition layer with certain strength, which is conducive to improving the bonding strength.

4. Mold installation

All gravity casting molds shall be preheated to 450 ℃± 10 ℃ before assembly, and the temperature during pouring shall not be lower than 430 ℃. According to the principle of Babbitt liquid sequential solidification, the solidification direction is from the tile joint surface to the mold, so the heating temperature of the mold shall not be lower than the Babbitt liquid pouring temperature. Then, the preheated mould and the tin lined tile blank shall be quickly assembled on the platform. The shorter the time, the better. The large tile blank shall be controlled within 20 min. the place where the bearing alloy is easy to leak shall be blocked with asbestos mud to avoid fire and the inner diameter φ The casting method of half pair clamp is adopted for tile blank above 350 mm, as shown in Fig. 2.

5. Babbitt casting

The melted bearing alloy is refined with dehydrated NH4Cl as refining agent, and the mass fraction is 0.02%. The purpose is to remove the gas and impurities in the Babbitt liquid, and clean the scum on the surface of the Babbitt liquid at the same time, so as to avoid defects of Babbitt alloy after pouring. The refined bearing alloy can only be used for pouring after standing for 15 min. the bearing alloy melts to the specified temperature of 440 ℃ ~ 460 ℃, and the temperature of the liquid bearing alloy during pouring shall not be lower than 430 ℃. New materials and slag are not allowed to be added to the refined liquid bearing alloy. If the bearing alloy needs to be inspected, the test block can be poured at this time.

The fixed electric furnace with a capacity of 500 kg is used for smelting the bearing alloy. Before pouring, the alloy liquid in the furnace shall be fully stirred, the slag shall be removed, and the mold shall be filled at one time. During pouring, the slag shall be beaten to prevent the slag and oxide film from entering the mold. The pouring shall be towards the direction of the mold, the pouring spoon shall be close to the mold, the pouring speed shall be fast first and then slow, so as to facilitate feeding. At the same time, the sampling shall be carried out for chemical analysis, and the pouring alloy flow shall be as short and thick as possible, The flow shall not be cut off to avoid being involved in gas. In order to accurately control the temperature of Babbitt liquid, a thermocouple with a maximum range of 1100 ℃ is immersed in Babbitt liquid for temperature measurement.

6. Water cooling and mold opening

When the bearing alloy liquid is poured to 1 / 3 of the height of the tile blank, use running water to evenly cool the tile back from bottom to top (with the solidification of the bearing alloy liquid below, the water cooling position shall gradually move upward until all the bearing alloys are solidified). While cooling the bearing Bush, preheat the upper bearing alloy and use the preheated tamping rod( φ 5 mm~ φ 10 mm iron circle) vertically vibrate the bearing alloy, and the tamping rod shall not take out the liquid level to prevent molten slag from being brought into the mold or other defects. At the same time, continuously heat the upper bearing alloy surface, especially the edges and corners with blowtorch and soldering iron, so as to prolong the cooling time of the upper bearing alloy liquid and ensure feeding. After casting, it shall be poured for 2 ~ 4 times, After casting, it is not allowed to hammer the bearing bush that is still hot, let alone make the bearing bush fall to the ground. Generally, it needs to be cooled for about 30 min, and the large bearing bush can be removed after cooling for 2 ~ 3 h.