Sand mold casting refers to the casting method of producing castings in sand mold.Steel, iron and most nonferrous alloy castings can be obtained by sand casting.Because the molding materials used in sand mold casting are cheap and easy to obtain, and the casting mold manufacturing is simple, it can adapt to the single casting production, batch production and mass production, and has been the basic process in casting production for a long time.
The basic raw materials for making sand mold are casting sand and sand binder.The most commonly used foundry sand is siliceous sand.When the high temperature performance of silica sand can not meet the requirements of the use of zirconium sand, ferrochrome sand, corundum sand and other special sand.In order to make the sand mold and core has a certain strength, in handling, fit and pouring liquid metal without deformation or damage, generally in the casting to join sand binder, the loose sand bond to become sand.The most widely used sand binder is clay, also can use a variety of dry oil or semi-dry oil, water-soluble silicate or phosphate and a variety of synthetic resin as sand binder.The external sand mold used in sand mold casting can be divided into three types according to the binder used in sand molding and the way of strength establishment: wet clay sand mold, dry clay sand mold and chemically hardened sand mold.
Wet sand clay
With clay and proper amount of water as the main binder of molding sand, the sand mold is made and then directly combined and poured in the wet state.Wet casting has a long history and wide application.The strength of wet sand depends on the proportion of clay and water in the clay slurry.Once the molding sand is mixed, it has a certain strength. After being made into a sand mold through the compaction, it can meet the requirements of combing and pouring.Therefore, the amount of clay and water in molding sand are very important process factors.
A casting method in which molding materials such as molding sand and core sand are used to make casting molds and liquid metal is filled and cast under gravity to produce castings.Steel, iron and most nonferrous alloy castings can be obtained by sand casting.Because the molding materials used in sand mold casting are cheap and easy to obtain, and the casting mold manufacturing is simple, it can adapt to the single casting production, batch production and mass production, and has been the basic process in casting production for a long time.
The mold used for sand mold casting is generally composed of outer sand mold and core.In order to improve the surface quality of casting, a layer of coating is often applied on the surface of sand mold and core.The main component of coating is fireproof degree tall, high temperature is good powdery material with good chemical stability and binder, still add the carrier that has to facilitate besmelling additionally (water or other solvent) with all sorts of additional content.
Clay wet sand casting advantages are: (1) rich in clay resources, cheap price.(2) the use of wet clay sand by the appropriate sand treatment, the vast majority can be recycled for reuse.(3) manufacturing mold cycle is short, high efficiency.(4) mix good molding sand can be used for a long time.(5) sand after the compaction can still allow a small amount of deformation and damage, is very beneficial to the mold and the core.The disadvantage is: (1) when mixing sand to viscous clay slurry coating on the sand surface, need to use a high power sand mixing equipment with rubbing effect, otherwise it is impossible to get good quality sand.(2) because the sand mix is quite high strength, molding sand is not easy to flow, hard to make solid, manual modeling both laborious and need a certain skill, with the machine modeling equipment is complex and huge.The rigidity of the casting mold is not high, the dimensional accuracy of the casting is poor.(4) casting is easy to produce sand, sand, air holes and other defects.
The wet water content of molding sand used for the dry clay mold is slightly higher than that used for the wet mold.
A simple core made from clay sand.
Clay dry sand
The wet water content of the molding sand used for this mold is slightly higher than that of the molding sand used for the wet mold.After the sand mold is made, the surface of the cavity shall be coated with fire-resistant coating, and then placed in the oven to dry, and the mold can be closed and poured after cooling.It takes a long time and a lot of fuel to dry the clay sand mold, and the sand mold is easy to deform during the drying process, which affects the casting precision.Clay dry sand molds are generally used in the manufacture of steel castings and larger cast iron castings.Since chemical hardened sand has been widely used, dry sand has tended to be eliminated.
Chemically hardened sand mold
The sand used in this mold is called chemically hardened sand.Its binder is generally in the role of hardener can occur molecular polymerization and then become three-dimensional structure of the material, commonly used in a variety of synthetic resin and sodium silicate.There are basically three types of chemical hardening.
1. Self-hardening: binder and hardener are added in sand mixing.After the sand or core is made, the binder reacts with the hardener and causes the sand or core to self-harden.Self-hardening method is mainly used for molding, but also for the manufacture of large core or the production of small batch core.
(2) air fog hardening: mix sand when adding binder and other additives, first without hardener.After molding or core-making, the gas hardener or the liquid hardener atomized in the gas carrier is blown into the sand mold or the core, resulting in the hardening of the sand mold.Aerosol hardening is used mainly for core making and sometimes for making small sand molds.
(3) heating hardening: mixing sand when adding binder and room temperature does not work latent hardener.When the sand mold or core is made and heated, the latent hardener reacts with some components of the binder to produce an effective hardener that hardens the binder, thus hardening the sand mold or core.The heating hardening method is mainly used for core making except for making small thin shell sand mold.