Analysis of forged and cast valves
Forged valves are forged. They are generally used in high-grade pipelines with small caliber, generally below DN50. Of course, there are also large caliber for special use. Cast valves are cast valves. Generally, the pressure grade of cast valves is relatively low [such as PN16, PN25, PN40, but there are also high-pressure valves, which can reach 1500Lb, 2500lb], and most of them are above DN50.
★ forging
Forging: it is a processing method that applies pressure to metal blank by forging machine to make it produce plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes.
One of the two major components of forging. Through forging, the metal as cast porosity and welding holes can be eliminated, and the mechanical properties of forgings are generally better than those of castings of the same material. For the important parts with high load and severe working conditions in machinery, except for the rolled plates, profiles or weldments with simple shapes, forgings are mostly used.
Forging can be divided into: ※ open forging [free forging]. Using impact force or pressure to deform the metal between the upper and lower iron blocks [anvil blocks] to obtain the required forgings, there are mainly two types of manual forging and mechanical forging. ※ Closed mode forging. The metal blank is pressed and deformed in the forging die bore with a certain shape to obtain forgings, 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], warm forging [lower than the recrystallization temperature] and cold forging [normal temperature].
The 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 materials includes bars, ingots, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to the die cross-sectional area after deformation is called the forging ratio. Correct selection of forging ratio has a great relationship with improving product quality and reducing cost.
★ casting
Casting: it refers to the process of melting metal into a liquid that meets certain requirements and pouring it into the mold. After cooling, solidification and cleaning, the casting [parts or blanks] with predetermined shape, size and performance can be obtained. Basic technology of modern machinery manufacturing industry.
The cost of the blank produced by casting is low, and it can show its economy for the parts with complex shape, especially the parts with complex internal cavity; At the same time, it has wide adaptability and good comprehensive mechanical properties.
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, sand dropping machine, shot blasting machine, cast iron plate, etc.) required for casting production, and dust, harmful gas and noise will be generated to pollute the environment.
Casting is one of the earliest metal hot working processes mastered by human beings, with a history of about 6000 years. In 3200 BC, copper frog castings appeared in Mesopotamia. From the 13th century BC to the 10th century BC, China has entered the heyday of bronze casting, and the technology has reached a fairly high level. For example, the 875kg simu Wufang Ding of the Shang Dynasty, the zunpan of marquis Zeng of the Warring States period and the transparent mirror of the Western Han Dynasty are all representative products of ancient casting. Early casting was greatly influenced by pottery. Most of the castings were tools or utensils for agricultural production, religion, life and so on, with strong artistic color. In 513 BC, China cast the world’s earliest recorded iron casting Zui, the Jin state casting 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 period of serving the large industry. In the 20th century, the development of casting has been very fast. Ductile iron, malleable iron, ultra-low carbon stainless steel, aluminum copper, aluminum silicon, aluminum magnesium alloy, titanium base, nickel base alloy and other casting metal materials have been developed successively, and a new process for inoculation treatment of gray cast iron has been invented. After the 1950s, new technologies such as wet sand high-pressure molding, chemical hardening sand molding, core making, negative pressure molding, and other special casting and shot blasting emerged.
There are many kinds of casting, which are customarily divided into: ※ ordinary sand mold casting, including wet sand mold, dry sand mold and chemical hardening sand mold. ※ According to the molding materials, special casting can be divided into two types: special casting with natural mineral sand and stone as the main molding materials [such as investment casting, mud mold casting, shell mold casting in casting workshop, negative pressure casting, full mold casting, ceramic mold casting, etc.] and special casting with metal as the main molding materials [such as metal mold casting, pressure casting, continuous casting, low-pressure casting, centrifugal casting, etc.].
The casting process generally includes: ※ preparation of casting mold [container for making liquid metal into solid casting]. 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 one-time mold, semi * mold and * mold according to the number of times of use. The quality of the casting mold preparation is the main factor affecting the casting quality; ※ Melting and pouring of cast metal, cast metal [cast alloy] mainly includes cast iron, cast steel and cast non-ferrous alloy; ※ Casting treatment and inspection: the casting treatment includes removal of foreign matters on the core and surface of the casting, removal of sprue and riser, shoveling and grinding of burr and burr, as well as heat treatment, reshaping, rust prevention treatment and rough machining.