The cast valve is the valve made by casting. General cast valves have low pressure rating (such as PN16. PN25. PN40, but also high pressure, up to 1500LB. 2500LB), and most of the diameters are above DN50. Forged valves are forged, generally used for high grade pipes, with small diameter, generally lower than DN50.
1、 Casting
1. Casting: melt the metal into a liquid that meets certain requirements, and pour it into the casting shape to cool and solidify. After cleaning, castings (parts or blanks) with predetermined shape, size and performance are obtained. Basic technology of modern machinery manufacturing industry.
2. The blank production cost is low and the shape is complex. Especially the parts with complex inner cavity can better reflect its economy; At the same time, it has wide adaptability and good comprehensive mechanical performance.
3. However, there are many materials (such as metal, wood, fuel, molding materials, etc.) and equipment (such as metallurgical furnace, sand mixer, molding machine, core-making machine, shakeout machine, shot blasting machine, cast iron plate, etc.) required for casting production, which will produce dust, harmful gas and noise, and pollute the environment.
4. Casting is a metal hot working process that human beings mastered in the early stage, with a history of about 6000 years. In 200 AD, copper frog castings appeared in Mesopotamia. From the 13th century BC to the 20th century AD, China has entered the heyday of bronze casting, and the technology level is quite high, such as the Simu Wufang tripod weighing 875 kg in the Shang Dynasty. During the Warring States Period, the Zun Pan of Marquis Yi of Zeng and the translucent mirror of the Western Han Dynasty were representative products of ancient casting. Early casting was greatly influenced by pottery. Most castings are produced in agriculture. Tools or instruments such as religion and life have strong artistic color. In 513 BC, China forged the world's first recorded iron casting, the Guozhu Ding (about 270 kg). Around the 8th century, Europe began to produce iron castings. After the industrial revolution in the 18th century, castings entered a new era of service for large-scale industries. In the 20th century, casting developed rapidly and invented nodular cast iron, malleable cast iron, carbon stainless steel, aluminum magnesium alloy and other new technologies. After the 1950s, new technologies such as wet sand high pressure shape, chemical hardened sand shape, core shape and negative pressure shape appeared.
5. There are many kinds of casting, which can be divided into:
① Ordinary sand mold casting, including wet sand mold, dry sand mold and chemical hardening sand mold.
② According to the molding materials, special casting can be divided into special casting with natural mineral sand as the main molding material and special casting with metal as the main molding material.
6. The casting process usually includes: ① preparation of casting mold (making liquid metal become solid casting container). The casting mold can be divided into sand mold, metal mold, ceramic mold, clay mold, graphite mold, etc. according to the materials used, and can be divided into disposable mold according to the times of use. The advantages and disadvantages of casting preparation are the main factors affecting the casting quality; ② Cast metals (cast alloys) mainly include cast iron, cast steel and cast non-ferrous alloys; ③ Casting treatment and inspection. The casting treatment includes the removal of foreign matters on the core and casting surface. Cut off the casting outlet. Remove burrs, seams and other protrusions and heat treatment. plastic operation. Rust-proof treatment and rough machining. Inlet pump valve.
2、 Forging
1. Forging: use forging machinery to exert pressure on the metal blank to make it plastic deformation, so as to obtain certain mechanical properties. The processing method of forgings has certain shape and size.
2. One of the two components of forging pressure. The mechanical properties of forgings are generally better than those of castings of the same material. Loose metal castings and weld holes can be eliminated by forging. High mechanical load. In addition to simple rolling shape, important parts with severe working conditions. Forgings are mainly used for profiles or welded parts.
3. Forging can be divided into:
① Open forging (free forging). Use impact or pressure to deform metal between iron (anvil) to obtain required forgings, mainly including manual forging and mechanical forging.
② Closed die forging. The metal blank is deformed under pressure in a certain shape of forging die, which can be divided into die forging, cold heading, rotary forging, extrusion, etc. According to the deformation temperature, forging can be divided into hot forging (the processing temperature is higher than the recrystallization temperature of the billet metal). Temperature forging (below recrystallization temperature) and cold forging (room temperature).
4. Forging materials are mainly carbon steel and alloy steel with various components, followed by aluminum, magnesium, titanium, copper and their alloys. The original state of the material includes rod, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area of the die after deformation is called the forging ratio. Correctly select forging comparison to improve product quality. Cost reduction is of great importance.
3、 Castings and forgings
1. The fine density of the surface structure of the forging, the casting surface should be thicker, and the machined surface of the forging should be brighter.
2. The cast iron section is gray, and the forged steel section is silver.
3. Listen to the sound, the forging is dense, the sound is crisp after striking, and the casting sound is dull.
4. Grind with a grinder to see if the sparks of the two are different (the forging is bright), etc.