What is the sand casting and its classification?
With sand and core sand mold for the molding material, the liquid metal filling the mold in the gravity casting method to produce castings. Steel, iron, and most non-ferrous alloy castings are available in sand casting methods. As used in sand casting molding material is cheap, easy to mold manufacturing, casting a single piece on the production, mass production and mass production can meet for a long time, has been casting the basic process.
Generally used in sand casting mold and core sand from the outside combination. In order to improve the surface quality of casting, often in the sand mold and core surface layer of paint brushes. The main components of coatings of high refractoriness, good chemical stability, high temperature powder material and binder, plus there is also easy to apply a defined carrier (water or other solvent), and various attachments. The basic raw materials, manufactured sand is sand casting sand and sand binder. The most commonly used casting sand is silica sand. Silica sand can not meet the requirements of high temperature performance when used zircon sand, chromite sand, sand and other special corundum sand. To make the sand mold and core made of a certain intensity, in the handling, combined type and pouring liquid metal without deformation or damage when, generally speaking, to add sand in the foundry binder, loose sand will bond together to form the sand. Most widely used molding sand binders is clay, it can use a variety of dry oil or semi-dry oil, water-soluble silicates or phosphates, and various synthetic resin for molding sand binder. Sand casting used in the sand by the sand outside the binder used in different ways and build strength into the wet clay, sand, clay, sand and dry chemical hardening sand 3. Clay to clay and wet sand as the sand right amount of water the main binder, made of sand in the wet state directly after the joint type and casting. Wet casting a long history of application is more extensive. Intensity depends on the clay, wet sand and water made by mixing the clay slurry. Once the sand is mixed well with a certain strength, actually made of sand by Chung, you can meet the requirements of joint type and casting.
Therefore, the clay content in sand and water is very important process factors. Clay has the advantage of wet sand casting: ① clay-rich and cheap. ② used clay sand wet sand after appropriate treatment, most can be recycled. ③ create casts of short cycle, high efficiency. ④ sand mixed with a good long time to be used. ⑤ sand beyond, Chung actually suffer a small amount of deformation without damage, on the pull mode and under the core are very beneficial. Drawback is: ① When sand to thick clay slurry coating the surface of the sand, the need to use a rubbing effect of high-power mixer devices, or can not get good quality sand. ② As the sand after mixing well with a very high strength, style is not easy when the flow of sand is difficult to Chung fact, when the labor-intensive and manual modeling techniques must be using the machine when the device modeling huge complex. ③ mold of stiffness is not high, the size of less precision casting. ④ easy to produce sand casting, sand inclusion, porosity and other defects. 20th century casting industry began using rolling wheel sand mixer sand, green sand to make the quality much improved. New high-power mixer mixer can work to achieve high efficiency and high quality. Real dominated by shock-type molding machine Shock compaction appearance, but also significantly improve the casts of compactness and uniformity. With casting dimensional accuracy and surface quality requirements to improve, but also appeared to compaction-based high-pressure molding machine. High-pressure molding machine manufacturing clay wet sand, not only can improve the precision casting size, surface quality improvement, but also simplify the compaction mold action, cycles, so that shape, combined high-speed type all processes and automation.
The impact of the new gas pressure molding machine, using clay slurry thixotropy, imposed by the instantaneous pressure of 0.5 MPa are very close to the mold. These developments are clay wet sand casting can meet the requirements of modern industry essential. This traditional craft method which has been used to produce large amounts of high-quality castings. Dry sand clay manufacture the sand wet sand with the water slightly higher than the wet sand used. Sand system well after the cavity surface to be coated with fire-resistant paint, and then placed in drying oven, let it cool you can type and casting co. Sand drying clay take longer to consume large amounts of fuel, and the sand is easy to produce in the drying process of deformation, so casting accuracy affected. Generally used in the manufacture of dry clay, sand and larger steel casting iron casting. Since the widespread adoption of chemical hardening sand, the dry sand has become eliminated.
This chemical hardening sand sand sand used as chemical hardening sand. The binder is generally in the hardening agent can occur under a three-dimensional molecular structure of polymer material and then, a variety of commonly used synthetic resin and sodium silicate. There are basically three kinds of chemical hardening method. ① bake: binder and hardening agent are added in sand. Cores made of sand, or after the binder under the action of the hardening agent react resulting self-hardening sand mold or cores. Since the hard law is mainly used for modeling, but also for the manufacture of large cores or small batch production of cores. ② aerosol sclerosis: sand binder and other auxiliary when added material, without first hardening agent. After molding or core making, blowing gaseous hardening agent or blowing spray in a gaseous carrier in the liquid hardening agent to diffuse in the sand, or cores, resulting in hardening sand. Aerosol hardening law used primarily in the core, sometimes also used in the manufacture of small sand. ③ heat hardening: sand binder, and room temperature, when the potential does not work sclerosant.
Cores made of sand or, after its heating, when latent hardening agent and binder in the reaction of certain elements, can generate an effective hardener hardening binder, so that sand or Core hardening. In addition to heat curing method for the manufacture of small shell sand, the main core for the system. Chemical hardening is characterized by sand casting process: ① the strength of the chemical hardening sand is much higher than the clay sand and made sand mold after hardening to strength with very high after the stripping, no Modification. Thus, the mold can more accurately reflect the size appearance and profile shapes, in a later process is also not easy to distort. Obtained a high dimensional accuracy of castings. ② As the binder and hardening agent used in the viscosity is not high, it is easy to mix with sand, sand equipment, compact structure, small power and high productivity, simplify the working part of sand. ③ good sand mixed in the hardening of good mobility before, when the sand is very easy to Chung shape reality, and therefore does not require large, complex molding machine. ④ chemically hardened sand molding, they can choose according to production requirements look like materials such as wood, plastic and metal. ⑤ chemical hardening sand binder sand content is much lower than the clay, of which there is not powder accessories, such as the use of the same size of the original sand, sand sand between the clay is much greater than the gap.
In order to prevent infiltration of sand between the metal casting, sand mold or core surface should be coated type coating with excellent quality. ⑥ water glass as binder for chemical hardening sand, low cost, the use of the work environment odorless. But after the sand mold casting metal is not easy to collapse; used sand can not be directly recycled, renewable subject to processing, and recycled water glass sand it more difficult. ⑦ binder resin for high cost of chemical hardening sand, but after casting and sand casting easy to separate, to reduce the workload of cleaning up castings, and spent most of the sand can be recycled recycling. Core To ensure the quality of the casting, sand casting used in the cores is generally dry core. Core based adhesive used in different cores into clay sand core, oil sand core and the resin sand core few. Clay Clay Sand sand core made simple cores.
Oil sand core with a dry oil or semi-dry oil for core sand binder produced by core, wider application. Low viscosity oil, mix well and good core sand flow, when the system is very easy to tighten the core. But just made of very low intensity cores are generally required to undertake core board with a profile of child care, and then in the oven 200 ~ 300 ℃ drying within a few hours by air oxidation and to harden the oil. The disadvantage of making the core of this are: Core in stripping, handling and curing process is easy to deformation, resulting in reduced size precision casting; baking a long time, energy and more. Resin sand core manufacturing all kinds of resin sand cores. Core hardening in the core box and then remove it, can guarantee Core shape and size are correct. According to hardening methods, resin sand core manufacturing is generally divided into hot box core making and cold box core making two methods. ① hot box core legal system: the late 50s. Usually furan resin core sand binder, which also joined the latent hardening agent (such as ammonium chloride). Core system, the so-box kept at 200 ~ 300 ℃, core sand core box after injection, ammonium chloride at higher temperatures and resin acid reaction of free formaldehyde, so that soon hardened cores. Stripping strength to establish about 10 to 100 seconds. The legal system with hot-box core, core of a high dimensional accuracy, but the process complicated and expensive devices, energy consumption and emission of irritant gas, is also very poor working conditions of workers. ② cold box core legal system: the late 60s.
With a urethane resin as a core sand binder. Method has been applied when the system core, core box is not heated, the amine blowing steam which could be a few seconds to make Core sclerosis. This approach to energy, environment, production efficiency are superior to hot-box method. Mid-70s blowing sulfur dioxide appeared hardened furan resin cold box method. The hardening mechanism completely different from the urethane cold box method, but the process on the characteristics, such as hardening fast, core strength higher, then with urethane cold box method are similar.