Dredging pump is a professional pump used in dredging industry recently. The material of flow passage parts is mainly made of wear-resistant steel and Hangzhou grinding white cast iron. Pump shell is the main part of dredging pump, and also the largest wear-resistant material casting. It is difficult in casting production. It is prone to shrinkage, porosity and cracks. In this paper, the technological characteristics of this kind of castings are analyzed, and a series of technological measures are adopted, and good results are obtained.
1.Structural characteristics of castings
Dredger pump body castings are thick-walled castings with outline sizes of more than 2000 mm * 2000 mm, total height of 600-1000 mm and wall thickness of 60-120 mrn. Most of them are made of wear-resistant white cast iron to adapt to the greater wear of industrial and mining media.
2. Analysis of Foundry Technology
The body shrinkage and linear shrinkage of wear-resistant white cast iron are very large, and the casting process similar to that of cast steel is adopted in principle. At the same time, in order to improve the feeding effect, top riser feeding and proper increase of runner are generally preferred in combination with the characteristics of thicker wall castings.
(1) setting up of gating system
The gating system is made of gate cup, flow steel brick, four-hole hexagonal brick and forming ceramic pipe. The double gating system is adopted. 1. The upper and lower layers are symmetrically separated from each other;s upper and lower mouth rings. The gate cup is made of 270/90mm ceramics, the direct gate is made of flowing steel bricks with different diameters, and the inner gate is made of ceramic gate tubes with different diameters.
(2) Riser setting
According to the established feeding principle, combined with the shape of the volute shell of the pump body, the mixing technology of side riser at small section and top riser at other parts is adopted. The side riser should be raised to the same height as the top riser. Riser size is determined by modulus method combined with proportional method.
(3) Arrangement of chill
Place a circle of chilled iron on the bottom of the lower box, usually in the form of multiple blocks separated. The tongue (the junction between the outlet and the main body) is a typical hot spot of this kind of castings, and it is not easy to use riser to compensate. Generally, cold iron with sand coating is used to quench, so as to reduce the shrinkage defect.
3. Measures of Production process and its Implementation
(1) Coatings and brushing
Alcohol-based zircon powder coatings for steel castings are used for general pump sand moulds (cores), and alcohol-based zircon powder or water-based zircon powder coatings for large dredging pump sand moulds (cores).
Brushing process: 1. After the core of sand mould (core) which is coated with water-based paint is required to be removed, the core is first brushed with a thicker coating, then pressed and compacted with a spoon, and repeatedly operated to ensure that the thickness of the coating is between 1.5 and 2 mm, and then dried naturally (Public No. Pump Manager). The next day, brush again, enter the kiln to dry, requiring the kiln temperature (250 +10) C, holding for 2 hours, and the heating rate to be controlled at about 1000 /h. (2) For alcohol-based zircon powder coatings for steel castings, a similar method is adopted to water-based coatings. First, the coatings with high concentration are brushed, then pressed and brushed for 3 minutes before ignition. The principle is that the coating thickness is 1.5-2 mm and there is no bubble delamination.
(2) Processing of Character Marking
In order to ensure the clear and beautiful identification of the casting characters, zirconium sand is used to make, zirconium sand is manually mixed and coated on the casting characters, or the core made by professionals is better. After shaping, it should be brushed with a low concentration of paint to prevent ash accumulation in dead corners.
(3) measures of venting
(1) Tie straw rope on core iron to form airway, not less than 6 strands of straw rope, and go out from core head. Outside core, use hole of 60mm to draw out air. (2) 2-3 airways are formed at the core head of the upper box of sand moulds with holes of 60mm.
(4) Other relevant measures
When making cores, straw rope bundles are placed in cores to enhance exhaust and core concession. (2) Riser neck is made of refined quartz sand or special sand with high refractory. (3) Zircon sand is used to make the core of the lifting hole of the pump body.
(5) Melting and pouring
(1) Before discharging, 0.6% Al + 0.2% CaSi is added to the ladle for degassing. Iron is produced by mixing iron slag. The refractory lining of pouring ladle must be fully dried and baked to dark red or red. The plug and seat bricks for ladle casting should be carefully selected. Formed bricks with compact contact surface and uniform clay should be selected to prevent the blindfold opening during pouring. (3) The tapping temperature is 1450-1480 C and the pouring temperature is 1400-1430 C. Appropriate adjustments can be made depending on the specific structure of the castings. (4) After the molten iron is discharged from the furnace, it is placed in the ladle for a moment before pouring.
(6) Casting pressure box
The pressing time depends on the casting condition, and the sand drop temperature of the castings is guaranteed to be less than 200 C.
Cleaning procedure: sand fall. Riser removal, batch seam removal, heat treatment, one repair of grinding riser, grinding, painting, storage.
(8) Heat treatment
Quenching + tempering treatment.
4. Concluding remarks
Such castings include pump body of single pump case of dredging pump, sheath of double pump case (also known as inner tank, protecting tank, inner shell) and so on. They account for a large proportion of dredging pump castings. After solving the technical problems, batch production can obtain better economic benefits. Starting from the analysis of its structural characteristics and material and technological properties, we put forward mature foundry technology and on-site technological measures. The castings produced have a smooth surface and good internal quality. They have been successfully applied to dredgers of major waterway bureaus in China, providing a strong technological guarantee for enterprises to occupy the dredging market.