Dredging pumps are professional pumps for the dredging […]
Dredging pumps are professional pumps for the dredging industry a few days ago. The materials of the flow parts mainly need to use wear-resistant steel and Hangzhou mill white cast iron. The pump casing is the main required part of the dredging pump, and it is also its largest wear-resistant material casting. It has certain difficulties in casting production and is prone to defects such as shrinkage, shrinkage, porosity and cracks. This article explains the process characteristics of this type of casting, and adopts a series of process measures, which have received good results.
1. Structural characteristics of castings
The pump body castings of the dredger are thick-walled castings, the outline dimensions are above 2000mm × 2000mm, the total height is 600 ~ 1000mm, and the wall thickness is 60 ~ 120mrn. The operating material is mostly anti-wear white cast iron to adapt to the large size of industrial and mining media. abrasion.
2. Casting process description
The body shrinkage and line shrinkage of the anti-wear white cast iron are very large, and the casting process is similar to that of cast steel. At the same time, the thicker wall thickness of the casting is used to enhance the shrinkage effect, and the top riser is usually preferred. And appropriate measures such as increasing the runner
(1) Establishment of pouring system
The pouring system is made of gate cups, flowing steel bricks, four-hole hexagonal bricks and shaped ceramic tubes. The double pouring system is adopted. 1. The upper and lower layers are symmetrically separated from each other. The sprue cup is used to form Φ270 / Φ90mm ceramics, the straight runner is used to flow steel bricks of different diameter series, and the inner runner is formed of ceramic nozzle pipes of different diameter series. The size of each runner unit is determined according to (1 ~ 1.5), and the blocking area is usually 1.2 ~ 2 times that of gray cast iron.
(2) Riser settings
According to the established filling rules, combined with the volute shape of the pump body, a mixing process using a side riser at a small cross section and a top riser at the rest is required. The side riser needs to be raised to the same height as the top riser. The riser is determined by the modulus method and the proportional method.
(3) Decoration of cold iron
Place a ring of cold iron on the bottom of the lower box, usually giving multiple pieces a spaced apart way. The tongue (the interface between the water outlet and the main body) is the typical hot joint of this type of casting, and it is not easy to use the riser to shrink. Usually, sand-covered conformal cold iron is used to cool, to reduce the occurrence of shrinkage defects .
(4) Other process parameters
Can be selected as appropriate according to the manual. Typical casting process
3. Production process measures and implementation
(1) Coating and painting
For ordinary pump body sand mold (core), alcohol-based zircon powder coating for steel castings is used; for large dredging pump body sand mold (cores are alcohol-based zircon powder or water-based zircon powder coating for steel castings).
① For the sand-type (core) painted with water-based paint, after the core is required, first brush it with a thicker coating, then flatten and compact it with a pressure spoon, and use it repeatedly to ensure that the thickness of the paint is between 1.5 and 2 mm. And then let it dry naturally (Public number: Pump housekeeper). Brush it again the next day and dry it in the kiln. The kiln temperature (250 ± 10) ℃ should be required, the temperature should be kept for 2 hours, and the heating rate should be controlled at about 1000 ℃ / h.
②Alcohol-based zircon powder coatings for steel castings are similar to water-based methods. First, brush with a higher concentration of paint, and then press and brush for 3 minutes to ignite. The thickness of the coating is 1.5 ~ 2mm without bubbles. Layering gives rules.
(2) Handling of cast marks
To ensure that the inscriptions are clear and beautiful, it is better to use zircon sand to cover the ingots by hand mixing zircon sand, or to use professionally manufactured ingots sand cores. After the lifting process, it should be painted with a less concentrated paint, and it is necessary to prevent dead spots from "accumulating ash."
(3) Exhaust measures
① Tie the straw rope on the core iron to form an airway, no less than 6 strands of straw rope, and straight out from the core head. Use a Φ60mm hole outside the core head to lead the air out. ② At the center of the core of the sand-shaped upper box, a hole of Φ60mm is used to form 2 ~ 3 air channels.
(4) Other related measures
① When making the core, if the straw rope is placed in the core dry, the exhaust and core concession can be enhanced. ② The riser neck is made of refined quartz sand or special sand with high fire resistance. ③ For the lifting core of the pump body, use zircon sand.
(5) Smelting and pouring
① Before the furnace, 0.6% Al + 0.2% CaSi is added to the molten iron bag to degas. The iron is slag mixed out. ② Ladle of refractory lining must be fully dried and baked to dark red or red. The plug and seat bricks used for the ladle should be carefully screened, and the shaped bricks with compact contact surface and uniform clay quality should be selected to prevent the package from opening when pouring. ③ The baking temperature is 1450 ~ 1480 ℃, and the pouring temperature is 1400-1430 ℃. Depending on the specific structure of the casting, appropriate adjustments can be made. ④After the molten iron is out of the furnace, it is left to stand in the ladle for a while and then starts pouring.
(6) Casting pressure box
The pressing time depends on the condition of the casting, and it is guaranteed that the falling sand temperature of the casting is within 200 ° C.
(7) Clean up
Cleaning procedure: falling sand. Riser removal, batch seam removal, heat treatment, grinding riser repair, grinding, painting, storage.
(8) Heat treatment
Quenching and tempering.
This type of casting includes the pump body of the single pump casing of the dredging pump, and the jacket of the double pump casing (also known as the inner liner, gall cover, inner casing), etc., which accounts for a large proportion in the dredging pump casting, and it is difficult to handle the process. After mass production, good economic benefits can be obtained. We can start by explaining its structural characteristics and material craftsmanship, and put forward mature casting and field process 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 to occupy the company for dredging. The market provides a strong technological guarantee.