Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz.
The second most common type of sand is calcium carbonate, for example aragonite, which has mostly been created, over the past half billion years, by various forms of life, like coral and shellfish. It is, for example, the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean.
In terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm (or mm) to 2 mm. An individual particle in this range size is termed a sand grain. Sand grains are between gravel (with particles ranging from 2 mm up to 64 mm) and silt (particles smaller than 0.0625 mm down to 0.004 mm). The size specification between sand and gravel has remained constant for more than a century, but particle diameters as small as 0.02 mm were considered sand under the Albert Atterberg standard in use during the early 20th century. A 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A 1938 specification of the United States Department of Agriculture was 0.05 mm. Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour).
ISO 14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size: very fine sand ( – mm diameter), fine sand ( mm – mm), medium sand ( mm – mm), coarse sand ( mm – 1 mm), and very coarse sand (1 mm – 2 mm). These sizes are based on the Krumbein phi scale, where size in Φ = -log2D; D being the particle size in mm. On this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers.
The most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica (silicon dioxide, or SiO2), usually in the form of quartz, which, because of its chemical inertness and considerable hardness, is the most common mineral resistant to weathering.
The composition of mineral sand is highly variable, depending on the local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are eroded limestone and may contain coral and shell fragments in addition to other organic or organically derived fragmental material, suggesting sand formation depends on living organisms, too. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a (usually nearby) granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic (lava) with a high olivine content. Many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones.
Sand is transported by wind and water and deposited in the form of beaches, dunes, sand spits, sand bars and related features. In environments such as gravel-bed rivers and glacial moraines it often occurs as one of the many grain sizes that are represented. Sand-bed rivers, such as the Platte River in Nebraska, USA, have sandy beds largely because there is no larger source material that they can transport. Dunes, a distinctive geographical feature of desert environments, are on the other hand sandy because larger material is generally immobile in wind. Sand is a component of soil.
The study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is recently weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the building trade where it is preferred for concrete, and in gardening where it is used as a soil amendment to loosen clay soils. Sand that is transported long distances by water or wind will be rounded, with characteristic abrasion patterns on the grain surface. Desert sand is typically rounded.
People who collect sand as a hobby are known as arenophiles. Organisms that thrive in sandy environments are psammophiles.
While sand is generally non-toxic, sand-using activities such as sandblasting require precautions. Bags of silica sand used for sandblasting now carry labels warning the user to wear respiratory protection to avoid breathing the resulting fine silica dust. Material safety data sheets (MSDS) for silica sand state that "excessive inhalation of crystalline silica is a serious health concern".
In areas of high pore water pressure sand and salt water can form quicksand, which is a colloid hydrogel that behaves like a liquid. Quicksand produces a considerable barrier to escape for creatures caught within, who often die from exposure (not from submersion) as a result.
Sand's many uses require a significant dredging industry, raising environmental concerns over fish depletion, landslides, and flooding. Countries such as China, Indonesia, Malaysia and Cambodia ban sand exports, citing these issues as a major factor.
Sand mining is a practice that is used to extract sand, mainly through an open pit. However, sand is also mined from beaches, inland dunes and dredged from ocean beds and river beds. It is often used in manufacturing as an abrasive, for example, and it is used to make concrete. As communities grow, construction requires less wood and more concrete, leading to a demand for low-cost sand. Sand is also used to replace eroded coastline.
Another reason for sand mining is for the extraction of minerals such as rutile, ilmenite and zircon, which contain the industrially useful elements titanium and zirconium. These minerals typically occur combined with ordinary sand, which is dug up, the valuable minerals being separated in water by virtue of their different densities, and the remaining ordinary sand re-deposited.
Sand mining is a direct cause of erosion, and also impacts the local wildlife. For example, sea turtles depend on sandy beaches for their nesting, and sand mining has led to the near extinction of gharials (a species of crocodiles) in India. Disturbance of underwater and coastal sand causes turbidity in the water, which is harmful for such organisms as corals that need sunlight. It also destroys fisheries, causing problems for people who rely on fishing for their livelihoods.
Removal of physical coastal barriers such as dunes leads to flooding of beachside communities, and the destruction of picturesque beaches causes tourism to dissipate. Sand mining is regulated by law in many places, but is still often done illegally.
In the 1930s mining operations began on the Kurnell Peninsula (Captain Cook's landing place in Australia) to supply the expanding Sydney building market. It continued until 1990 with an estimate of over 70 million tonnes of sand having been removed. The sand has been valued for many decades by the building industry, mainly because of its high crushed shell content and lack of organic matter, it has provided a cheap source of sand for most of Sydney since sand mining operations began. The site has now been reduced to a few remnant dunes and deep water-filled pits which are now being filled with demolition waste from Sydney's building sites. Removal of the sand has significantly weakened the peninsula's capacity to resist storms. Ocean waves pounding against the reduced Kurnell dune system have threatened to break through to Botany Bay, especially during the storms of May and June back in 1974 and of August 1998. Sand Mining also takes place in the Stockton sand dunes north of Newcastle and in the Broken Hill region in the far west of the state.
A large and long running sand mine in Queensland, Australia (on North Stradbroke Island) provides a case study in the (disastrous) environmental consequences on a fragile sandy-soil based ecosystem, justified by the provision of low wage casual labor on an island with few other work options.
Sand mining contributes to the construction of buildings and development. However, the negative effects of sand mining include the permanent loss of sand in areas, as well as major habitat destruction.
Sand mining is a practice that is becoming an environmental issue in India. Environmentalists have raised public awareness of illegal sand mining in the state of Maharashtra and Goa of India. Conservation and environmental NGO Awaaz Foundation filed a public interest litigation in the Bombay High Court seeking a ban on mining activities along the Konkan coast. Awaaz Foundation, in partnership with the Bombay Natural History Society also presented the issue of sand mining as a major international threat to coastal biodiversity at the Conference of Parties 11, Convention on Biological Diversity, Hyderabad in October 2012.
Sand mining occurs in the Kaipara Harbour, off the coast at Pakiri and offshore from Little Barrier Island. A sand mine had operated at Whiritoa on the east coast of the North Island for 50 years extracting 180,000m3 of sand. Coastal sand mines currently operate at Maioro and Taharoa to recover iron sand. When an application was lodged in 2005 to mine iron sands on the seabed of the coast of Raglan local residents organised in opposition to the scheme. The application for the mining was turned down by Crown Minerals due to a lack of technical detail.
Recently, activists and local villagers have protested against sand mining on Sierra Leone's Western Area Peninsular. The activity is providing informal work for people who would otherwise be unemployed, but is also destroying the natural beauty of the area, driving away tourists, business owners and residents, and contributing to Sierra Leone's coastal erosion, which is proceeding at up to 6 meters a year.
The current size of the sand mining market in the United States is slightly over a billion dollars per year. The industry has been growing by nearly 10% annually since 2005. The majority of the market size for mining is held by Texas and Illinois.
Silica sand mining business has more than doubled since 2009 because of the need for this particular type of sand, which is used in a process known as hydraulic fracturing. Wisconsin is one of the five states that produce nearly 2/3 of the nation’s silica. As of 2009, Wisconsin, along with other northern states, is facing an industrial mining boom, being dubbed the "sand rush" because of the new demand from large oil companies for silica sand. According to Minnesota Public Radio, "One of the industry's major players, U.S. Silica, says its fracking sand sales nearly doubled from 2009 to 2010, from $36 million to $70 million in 2010 and brought in nearly $70 million in just the first nine months of 2011." According to the Wisconsin Department of Natural Resources (WDNR), there are currently 34 active mines and 25 mines in development in Wisconsin. In 2012, the WDNR released a final report on the silica sand mining in Wisconsin titled Silica Sand Mining in Wisconsin. The recent boom in silica sand mining has caused concern from residents in Wisconsin that include quality of life issues and the threat of silicosis. However, these are issues that the state has no authority to regulate. According to the WDNR (2012) these issues include noise, lights, hours of operation, damage and excessive wear to roads from trucking traffic, public safety concerns from the volume of truck traffic, possible damage and annoyance resulting from blasting, and concerns regarding aesthetics and land use changes.
As of 2013, industrial frack sand mining has become a cause for activism, especially in the [Area] of southeast Minnesota, northeast Iowa and southwest Wisconsin.
An open faced club, sand wedge, or sand iron, is a wedge primarily designed for use out of sand bunkers. It has the widest sole of any wedge, which provides the greatest amount of bounce, allowing the club head to glide through sand and avoid digging in.
Gene Sarazen began to win tournaments in 1935 with a new club he had invented that was specialized for sand play. He is hailed as the inventor of the sand wedge. However, history goes about 3 years further back than that. Spoon clubs offered varying degrees of loft and allowed players to scoop their ball out of sand traps and deep rough. As manufacturers became more and more innovative with club design, new types of wedges appeared. Some had concave faces, others featured deeply grooved faces, but not all of these designs conformed to USGA and R&A regulations, and many were banned. With the concave-faced wedge having been outlawed in 1931, Sarazen designed his sand wedge with a straight face. Another modification that he made was to add extra lead to the front edge of the club face, allowing it to cut through the sand more smoothly. After he won the 1932 British and U.S. Opens with the help of his new club, its popularity quickly grew.
The modern sand wedge is often the heaviest iron in a player's bag, with most weighing nearly 40 ounces (1.1 kg). Traditionally it also had the highest loft at 56 degrees (55–56 being most common), although that distinction now goes to the lob wedge, which often has a loft of 60 degrees or more. It usually has one of the shortest shafts, between 33 inches (84 cm) and 36 inches (91 cm), though in some sets the sand wedge has a longer shaft than the pitching wedge.
The main distinguishing difference of the club from most others, however, is a feature called bounce. On most other irons, the sole of the club is perpendicular to the shaft, meaning it is roughly parallel to the ground when the club is at rest allowing the leading edge to get between the ball and the ground more easily. A sand wedge however is designed with the sole of the club at an angle to the ground in the same position, lifting the leading edge of the club off the ground.
This accomplishes three things; first, this design generally requires more material, which increases the weight of the club head for more momentum and places that weight low and forward in the club head for higher launches.
Second, the angled sole lifts the leading edge off the ground at the bottom of the swing, preventing the club from digging in to softer lies such as muddy ground, thick grass and of course sand, instead tending to skim over the surface. This in turn allows players more flexibility when addressing the ball; the player can line the ball up in the centre of their stance and take a normal swing in which the club will skim over the turf before contact with the ball, or alternatively they can move the ball rearward in their stance (towards the right foot for a right-handed player) and strike the ball earlier in the swing. The natural consequence of such a shot, executed correctly, is that the club face has less loft at contact, so the ball is launched at a lower angle for more distance. Without bounce, such a shot even if executed correctly will generally cause the club to dig into the ground after it contacts the ball which, with such a high-lofted club, prevents the player from following through on their swing and can cause injury.
Lastly, when playing from a bunker, the ball may have buried itself deeply into the sand (depending on the sand's consistency and the degree of impact, the ball may be completely submerged). To lift it out, the club head must contact the ball from underneath, meaning the leading edge of the club must sometimes be an inch or two (2-4 cm) under the surface of the sand at contact. The angle of the sole counteracts the natural downward pressure of the club face digging itself ever deeper into the sand, making it easier to swing the club down under the surface of the sand and then lift the club, and the ball, back out again.
Other clubs, especially short irons and other wedges, now incorporate a small degree of bounce to assist in plays from the rough or other soft lies, but the sand wedge will typically have the highest amount of bounce of any club in a player's bag. There are however exceptions; Callaway Golf for instance markets a "Big Bertha" line of irons in which the lob wedge has significantly higher bounce than the sand wedge.
As its name suggests, a sand wedge is used most often to extract the ball from a sand bunker. However, the features which make it useful for this purpose are advantageous in other soft lies such as thick rough, soggy ground or mud. It's also used from firmer grass lies for lobs or chips, generally onto the green. It can also be used as any other short iron would; with a full swing, a skilled golfer can typically hit a sand wedge between 80–100 yards (70–90 m). Tour players often use a lob wedge (60° wedge) to get out of bunkers with controlled trajectory and lots of spin.
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a sand casting process.
Sand casting is relatively cheap and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or mold boxes known as a flask. The mold cavities and gate system are created by compacting the sand around models, or patterns, or carved directly into the sand.
There are six steps in this process:
From the design, provided by an engineer or designer, a skilled pattern maker builds a pattern of the object to be produced, using wood, metal, or a plastic such as expanded polystyrene. Sand can be ground, swept or strickled into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as contraction allowance. Pattern-makers are able to produce suitable patterns using "Contraction rules" (these are sometimes called "shrink allowance rulers" where the ruled markings are deliberately made to a larger spacing according to the percentage of extra length needed). Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others. Patterns also have core prints that create registers within the molds into which are placed sand cores. Such cores, sometimes reinforced by wires, are used to create under-cut profiles and cavities which cannot be molded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks.
Paths for the entrance of metal into the mold cavity constitute the runner system and include the sprue, various feeders which maintain a good metal 'feed', and in-gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via risers, which are added either in the pattern itself, or as separate pieces.
A multi-part molding box (known as a casting flask, the top and bottom halves of which are known respectively as the cope and drag) is prepared to receive the pattern. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object—flat on one side—the lower portion of the box, closed at the bottom, will be filled with a molding sand. The sand is packed in through a vibratory process called ramming, and in this case, periodically screeded level. The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added. Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed. Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a "green" mold which must be dried to receive the hot metal. If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about. In some cases, the sand may be oiled instead of moistened, which makes possible casting without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine-hardened resins.
To control the solidification structure of the metal, it is possible to place metal plates, chills, in the mold. The associated rapid local cooling will form a finer-grained structure and may form a somewhat harder metal at these locations. In ferrous castings, the effect is similar to quenching metals in forge work. The inner diameter of an engine cylinder is made hard by a chilling core. In other metals, chills may be used to promote directional solidification of the casting. In controlling the way a casting freezes, it is possible to prevent internal voids or porosity inside castings.
To produce cavities within the casting—such as for liquid cooling in engine blocks and cylinder heads—negative forms are used to produce cores. Usually sand-molded, cores are inserted into the casting box after removal of the pattern. Whenever possible, designs are made that avoid the use of cores, due to the additional set-up time and thus greater cost.
With a completed mold at the appropriate moisture content, the box containing the sand mold is then positioned for filling with molten metal—typically iron, steel, bronze, brass, aluminium, magnesium alloys, or various pot metal alloys, which often include lead, tin, and zinc. After filling with liquid metal the box is set aside until the metal is sufficiently cool to be strong. The sand is then removed revealing a rough casting that, in the case of iron or steel, may still be glowing red. When casting with metals like iron or lead, which are significantly heavier than the casting sand, the casting flask is often covered with a heavy plate to prevent a problem known as floating the mold. Floating the mold occurs when the pressure of the metal pushes the sand above the mold cavity out of shape, causing the casting to fail.
After casting, the cores are broken up by rods or shot and removed from the casting. The metal from the sprue and risers is cut from the rough casting. Various heat treatments may be applied to relieve stresses from the initial cooling and to add hardness—in the case of steel or iron, by quenching in water or oil. The casting may be further strengthened by surface compression treatment—like shot peening—that adds resistance to tensile cracking and smooths the rough surface.
The part to be made and its pattern must be designed to accommodate each stage of the process, as it must be possible to remove the pattern without disturbing the molding sand and to have proper locations to receive and position the cores. A slight taper, known as draft, must be used on surfaces perpendicular to the parting line, in order to be able to remove the pattern from the mold. This requirement also applies to cores, as they must be removed from the core box in which they are formed. The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mold in order to avoid an incomplete casting. Should a piece of core or mold become dislodged it may be embedded in the final casting, forming a sand pit, which may render the casting unusable. Gas pockets can cause internal voids. These may be immediately visible or may only be revealed after extensive machining has been performed. For critical applications, or where the cost of wasted effort is a factor, non-destructive testing methods may be applied before further work is performed.
In general, we can distinguish between two methods of sand casting; the first one using green sand and the second being the air set method.
These expendable molds are made of wet sands that are used to make the mold's shape. The name comes from the fact that wet sands are used in the molding process. Green sand is not green in color, but "green" in the sense that it is used in a wet state (akin to green wood). Unlike the name suggests, "green sand" is not a type of sand on its own, but is rather a mixture of:
There are many recipes for the proportion of clay, but they all strike different balances between moldability, surface finish, and ability of the hot molten metal to degas. The coal, typically referred to in foundries as sea-coal, which is present at a ratio of less than 5%, partially combusts in the presence of the molten metal leading to offgassing of organic vapors. Green Sand for non-ferrous metals do not use coal additives since the CO created is not effective to prevent oxidation. Green Sand for aluminum typically uses olivine sand (a mixture of the minerals forsterite and fayalite which are made by crushing dunite rock). The choice of sand has a lot to do with the temperature that the metal is poured. At the temperatures that copper and iron are poured, the clay gets inactivated by the heat in that the montmorillonite is converted to illite, which is a non-expanding clay. Most foundries do not have the very expensive equipment to remove the burned out clay and substitute new clay, so instead, those that pour iron typically work with silica sand that is inexpensive compared to the other sands. As the clay is burned out, newly mixed sand is added and some of the old sand is discarded or recycled into other uses. Silica is the least desirable of the sands since metamorphic grains of silica sand have a tendency to explode to form sub-micron sized particles when thermally shocked during pouring of the molds. These particles enter the air of the work area and can lead to silicosis in the workers. Iron foundries spend a considerable effort on aggressive dust collection to capture this fine silica. The sand also has the dimensional instability associated with the conversion of quartz from alpha quartz to beta quartz at 1250 degrees F. Often additives such as wood flour are added to create a space for the grains to expand without deforming the mold. Olivine, Chromite, etc. are used because they do not have a phase conversion that causes rapid expansion of the grains, as well as offering greater density, which cools the metal faster and produces finer grain structures in the metal. Since they are not metamorphic minerals, they do not have the polycrystals found in silica, and subsequently do not form hazardous sub-micron sized particles.
The air set method uses dry sand bonded with materials other than clay, using a fast curing adhesive. The latter may also be referred to as no bake mold casting. When these are used, they are collectively called "air set" sand castings to distinguish them from "green sand" castings. Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand); the latter is generally preferred due to its more consistent composition.
With both methods, the sand mixture is packed around a pattern, forming a mold cavity. If necessary, a temporary plug is placed in the sand and touching the pattern in order to later form a channel into which the casting fluid can be poured. Air-set molds are often formed with the help of a casting flask having a top and bottom part, termed the cope and drag. The sand mixture is tamped down as it is added around the pattern, and the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. Then the pattern is removed along with the channel plug, leaving the mold cavity. The casting liquid (typically molten metal) is then poured into the mold cavity. After the metal has solidified and cooled, the casting is separated from the sand mold. There is typically no mold release agent, and the mold is generally destroyed in the removal process.
The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture to the surface, and this makes them easy to identify. Castings made from fine green sand can shine as cast but are limited by the depth to width ratio of pockets in the pattern. Air-set molds can produce castings with smoother surfaces than coarse green sand but this method is primarily chosen when deep narrow pockets in the pattern are necessary, due to the expense of the plastic used in the process. Air-set castings can typically be easily identified by the burnt color on the surface. The castings are typically shot blasted to remove that burnt color. Surfaces can also be later ground and polished, for example when making a large bell. After molding, the casting is covered with a residue of oxides, silicates and other compounds. This residue can be removed by various means, such as grinding, or shot blasting.
During casting, some of the components of the sand mixture are lost in the thermal casting process. Green sand can be reused after adjusting its composition to replenish the lost moisture and additives. The pattern itself can be reused indefinitely to produce new sand molds. The sand molding process has been used for many centuries to produce castings manually. Since 1950, partially automated casting processes have been developed for production lines.
Uses organic and inorganic binders that strengthen the mold by chemically adhering to the sand. This type of mold gets its name from not being baked in an oven like other sand mold types. This type of mold is more accurate dimensionally than green-sand molds but is more expensive. Thus it is used only in applications that necessitate it.
No bake molds are expendable sand molds, similar to typical sand molds, except they also contain a quick-setting liquid resin and catalyst. Rather than being rammed, the molding sand is poured into the flask and held until the resin solidifies, which occurs at room temperature. This type of molding also produces a better surface finish than other types of sand molds. Because no heat is involved it is called a cold-setting process. Common flask materials that are used are wood, metal, and plastic. Common metals cast into no bake molds are brass, iron ferrous, and aluminum alloys.
Vacuum molding (V-process) is a variation of the sand casting process for most ferrous and non-ferrous metals, in which unbonded sand is held in the flask with a vacuum. The pattern is specially vented so that a vacuum can be pulled through it. A heat-softened thin sheet (0.003 to 0.008 in (0.076 to 0.20 mm)) of plastic film is draped over the pattern and a vacuum is drawn (200 to 400 mmHg (27 to 53 kPa)). A special vacuum forming flask is placed over the plastic pattern and is filled with a free-flowing sand. The sand is vibrated to compact the sand and a sprue and pouring cup are formed in the cope. Another sheet of plastic is placed over the top of the sand in the flask and a vacuum is drawn through the special flask; this hardens and strengthens the unbonded sand. The vacuum is then released on the pattern and the cope is removed. The drag is made in the same way (without the sprue and pouring cup). Any cores are set in place and the mold is closed. The molten metal is poured while the cope and drag are still under a vacuum, because the plastic vaporizes but the vacuum keeps the shape of the sand while the metal solidifies. When the metal has solidified, the vacuum is turned off and the sand runs out freely, releasing the casting.
The V-process is known for not requiring a draft because the plastic film has a certain degree of lubricity and it expands slightly when the vacuum is drawn in the flask. The process has high dimensional accuracy, with a tolerance of ±0.010 in for the first inch and ±0.002 in/in thereafter. Cross-sections as small as 0.090 in (2.3 mm) are possible. The surface finish is very good, usually between 150 to 125 rms. Other advantages include no moisture related defects, no cost for binders, excellent sand permeability, and no toxic fumes from burning the binders. Finally, the pattern does not wear out because the sand does not touch it. The main disadvantage is that the process is slower than traditional sand casting so it is only suitable for low to medium production volumes; approximately 10 to 15,000 pieces a year. However, this makes it perfect for prototype work, because the pattern can be easily modified as it is made from plastic.
With the fast development of the car and machine building industry the casting consuming areas called for steady higher productivity. The basic process stages of the mechanical molding and casting process are similar to those described under the manual sand casting process. The technical and mental development however was so rapid and profound that the character of the sand casting process changed radically.
The first mechanized molding lines consisted of sand slingers and/or jolt-squeeze devices that compacted the sand in the flasks. Subsequent mold handling was mechanical using cranes, hoists and straps. After core setting the copes and drags were coupled using guide pins and clamped for closer accuracy. The molds were manually pushed off on a roller conveyor for casting and cooling.
Increasing quality requirements made it necessary to increase the mold stability by applying steadily higher squeeze pressure and modern compaction methods for the sand in the flasks. In early fifties the high pressure molding was developed and applied in mechanical and later automatic flask lines. The first lines were using jolting and vibrations to pre-compact the sand in the flasks and compressed air powered pistons to compact the molds.
In the first automatic horizontal flask lines the sand was shot or slung down on the pattern in a flask and squeezed with hydraulic pressure of up to 140 bars. The subsequent mold handling including turn-over, assembling, pushing-out on a conveyor were accomplished either manually or automatically. In the late fifties hydraulically powered pistons or multi-piston systems were used for the sand compaction in the flasks. This method produced much more stable and accurate molds than it was possible manually or pneumatically. In the late sixties mold compaction by fast air pressure or gas pressure drop over the pre-compacted sand mold was developed (sand-impulse and gas-impact). The general working principle for most of the horizontal flask line systems is shown on the sketch below.
Today there are many manufacturers of the automatic horizontal flask molding lines. The major disadvantages of these systems is high spare parts consumption due to multitude of movable parts, need of storing, transporting and maintaining the flasks and productivity limited to approximately 90–120 molds per hour.
In 1962, Dansk Industri Syndikat A/S (DISA-DISAMATIC) invented a flask-less molding process by using vertically parted and poured molds. The first line could produce up to 240 complete sand molds per hour. Today molding lines can achieve a molding rate of 550 sand molds per hour and requires only one monitoring operator. Maximum mismatch of two mold halves is 0.1 mm (0.0039 in). Although very fast, vertically parted molds are not typically used by jobbing foundries due to the specialized tooling needed to run on these machines. Cores need to be set with a core mask as opposed to by hand and must hang in the mold as opposed to being set on parting surface.
The principle of the matchplate, meaning pattern plates with two patterns on each side of the same plate, was developed and patented in 1910, fostering the perspectives for future sand molding improvements. However, first in the early sixties the American company Hunter Automated Machinery Corporation launched its first automatic flaskless, horizontal molding line applying the matchplate technology.
The method alike to the DISA's (DISAMATIC) vertical moulding is flaskless, however horizontal. The matchplate molding technology is today used widely. Its great advantage is inexpensive pattern tooling, easiness of changing the molding tooling, thus suitability for manufacturing castings in short series so typical for the jobbing foundries. Modern matchplate molding machine is capable of high molding quality, less casting shift due to machine-mold mismatch (in some cases less than 0.15 mm (0.0059 in)), consistently stable molds for less grinding and improved parting line definition. In addition, the machines are enclosed for a cleaner, quieter working environment with reduced operator exposure to safety risks or service-related problems.
There are four main components for making a sand casting mold: base sand, a binder, additives, and a parting compound.
Molding sands, also known as foundry sands, are defined by eight characteristics: refractoriness, chemical inertness, permeability, surface finish, cohesiveness, flowability, collapsibility, and availability/cost.
Refractoriness — This refers to the sand's ability to withstand the temperature of the liquid metal being cast without breaking down. For example some sands only need to withstand if casting aluminum alloys, whereas steel needs a sand that will withstand . Sand with too low a refractoriness will melt and fuse to the casting.
Chemical inertness — The sand must not react with the metal being cast. This is especially important with highly reactive metals, such as magnesium and titanium.
Permeability — This refers to the sand's ability to exhaust gases. This is important because during the pouring process many gases are produced, such as hydrogen, nitrogen, carbon dioxide, and steam, which must leave the mold otherwise casting defects, such as blow holes and gas holes, occur in the casting. Note that for each cubic centimeter (cc) of water added to the mold 16,000 cc of steam is produced.
Surface finish — The size and shape of the sand particles defines the best surface finish achievable, with finer particles producing a better finish. However, as the particles become finer (and surface finish improves) the permeability becomes worse.
Cohesiveness (or bond) — This is the ability of the sand to retain a given shape after the pattern is removed.
Flowability – The ability for the sand to flow into intricate details and tight corners without special processes or equipment.
Collapsibility — This is the ability of the sand to be easily stripped off the casting after it has solidified. Sands with poor collapsibility will adhere strongly to the casting. When casting metals that contract a lot during cooling or with long freezing temperature ranges a sand with poor collapsibility will cause cracking and hot tears in the casting. Special additives can be used to improve collapsibility.
Availability/cost — The availability and cost of the sand is very important because for every ton of metal poured, three to six tons of sand is required. Although sand can be screened and reused, the particles eventually become too fine and require periodic replacement with fresh sand.
In large castings it is economical to use two different sands, because the majority of the sand will not be in contact with the casting, so it does not need any special properties. The sand that is in contact with the casting is called facing sand, and is designed for the casting on hand. This sand will be built up around the pattern to a thickness of 30 to 100 mm (1.2 to 3.9 in). The sand that fills in around the facing sand is called backing sand. This sand is simply silica sand with only a small amount of binder and no special additives.
Base sand is the type used to make the mold or core without any binder. Because it does not have a binder it will not bond together and is not usable in this state.
Silica (SiO2) sand is the sand found on a beach and is also the most commonly used sand. It is made by either crushing sandstone or taken from natural occurring locations, such as beaches and river beds. The fusion point of pure silica is , however the sands used have a lower melting point due to impurities. For high melting point casting, such as steels, a minimum of 98% pure silica sand must be used; however for lower melting point metals, such as cast iron and non-ferrous metals, a lower purity sand can be used (between 94 and 98% pure).
Silica sand is the most commonly used sand because of its great abundance, and, thus, low cost (therein being its greatest advantage). Its disadvantages are high thermal expansion, which can cause casting defects with high melting point metals, and low thermal conductivity, which can lead to unsound casting. It also cannot be used with certain basic metal because it will chemically interact with the metal forming surface defect. Finally, it causes silicosis in foundry workers.
Olivine is a mixture of orthosilicates of iron and magnesium from the mineral dunite. Its main advantage is that it is free from silica, therefore it can be used with basic metals, such as manganese steels. Other advantages include a low thermal expansion, high thermal conductivity, and high fusion point. Finally, it is safer to use than silica, therefore it is popular in Europe.
Chromite sand is a solid solution of spinels. Its advantages are a low percentage of silica, a very high fusion point ( ), and a very high thermal conductivity. Its disadvantage is its costliness, therefore its only used with expensive alloy steel casting and to make cores.
Zircon sand is a compound of approximately two-thirds zircon oxide (Zr2O) and one-third silica. It has the highest fusion point of all the base sands at , a very low thermal expansion, and a high thermal conductivity. Because of these good properties it is commonly used when casting alloy steels and other expensive alloys. It is also used as a mold wash (a coating applied to the molding cavity) to improve surface finish. However, it is expensive and not readily available.
Chamotte is made by calcining fire clay (Al2O3-SiO2) above . Its fusion point is and has low thermal expansion. It is the second cheapest sand, however it is still twice as expensive as silica. Its disadvantages are very coarse grains, which result in a poor surface finish, and it is limited to dry sand molding. Mold washes are used to overcome the surface finish problem. This sand is usually used when casting large steel workpieces.
Modern casting production methods can manufacture thin and accurate molds—of a material superficially resembling papier-mâché, such as is used in egg cartons, but that is refractory in nature—that are then supported by some means, such as dry sand surrounded by a box, during the casting process. Due to the higher accuracy it is possible to make thinner and hence lighter castings, because extra metal need not be present to allow for variations in the molds. These thin-mold casting methods have been used since the 1960s in the manufacture of cast-iron engine blocks and cylinder heads for automotive applications.][
Binders are added to a base sand to bond the sand particles together (i.e. it is the glue that holds the mold together).
A mixture of clay and water is the most commonly used binder. There are two types of clay commonly used: bentonite and kaolinite, with the former being the most common.
Oils, such as linseed oil, other vegetable oils and marine oils, used to be used as a binder, however due to their increasing cost, they have been mostly phased out. The oil also required careful baking at 100 to 200 °C (212 to 392 °F) to cure (if overheated the oil becomes brittle, wasting the mold).
Resin binders are natural or synthetic high melting point gums. The two common types used are urea formaldehyde (UF) and phenol formaldehyde (PF) resins. PF resins have a higher heat resistance than UF resins and cost less. There are also cold-set resins, which use a catalyst instead of a heat to cure the binder. Resin binders are quite popular because different properties can be achieved by mixing with various additives. Other advantages include good collapsibility, low gassing, and they leave a good surface finish on the casting.
MDI (methylene diphenyl diisocyanate) is also a commonly used binder resin in the foundry core process.
Sodium silicate [Na2SiO3 or (Na2O)(SiO2)] is a high strength binder used with silica molding sand. To cure the binder carbon dioxide gas is used, which creates the following reaction:
The advantage to this binder is that it can be used at room temperature and it's fast. The disadvantage is that its high strength leads to shakeout difficulties and possibly hot tears in the casting.
Additives are added to the molding components to improve: surface finish, dry strength, refractoriness, and "cushioning properties".
Up to 5% of reducing agents, such as coal powder, pitch, creosote, and fuel oil, may be added to the molding material to prevent wetting (prevention of liquid metal sticking to sand particles, thus leaving them on the casting surface), improve surface finish, decrease metal penetration, and burn-on defects. These additives achieve this by creating gases at the surface of the mold cavity, which prevent the liquid metal from adhering to the sand. Reducing agents are not used with steel casting, because they can carburize the metal during casting.
Up to 3% of "cushioning material", such as wood flour, saw dust, powdered husks, peat, and straw, can be added to reduce scabbing, hot tear, and hot crack casting defects when casting high temperature metals. These materials are beneficial because burn-off when the metal is poured creating voids in the mold, which allow it to expand. They also increase collapsibility and reduce shakeout time.
Up to 2% of cereal binders, such as dextrin, starch, sulphite lye, and molasses, can be used to increase dry strength (the strength of the mold after curing) and improve surface finish. Cereal binders also improve collapsibility and reduce shakeout time because they burn-off when the metal is poured. The disadvantage to cereal binders is that they are expensive.
Up to 2% of iron oxide powder can be used to prevent mold cracking and metal penetration, essentially improving refractoriness. Silica flour (fine silica) and zircon flour also improve refractoriness, especially in ferrous castings. The disadvantages to these additives is that they greatly reduce permeability.
To get the pattern out of the mold, prior to casting, a parting compound is applied to the pattern to ease removal. They can be a liquid or a fine powder (particle diameters between 75 and 150 micrometres (0.0030 and 0.0059 in)). Common powders include talc, graphite, and dry silica; common liquids include mineral oil and water-based silicon solutions. The latter are more commonly used with metal and large wooden patterns.
The Assyrian king Sennacherib (704-681BC) cast massive bronzes of up to 30 tonnes, and claims to have been the first to have used clay moulds rather than the 'lost-wax' method:
"Whereas in former times the kings my forefathers had created bronze statues imitating real-life forms to put on display inside their temples, but in their method of work they had exhausted all the craftsmen, for lack of skill and failure to understand the principles they needed so much oil, wax and tallow for the work that they caused a shortage in their own countries - I, Sennacherib, leader of all princes, knowledgeable in all kinds of work, took much advice and deep thought over doing that work. Great pillars of bronze, colossal striding lions, such as no previous king nhad ever constructed before me, with the technical skill that Ninushki brought to perfection in me, and at the prompting of my intelligence and the desire of my heart I invented a technique for bronze and made it skillfully. I created clay moulds as if by divine intelligence....twelve fierce lion-colossi together with twelve mighty bull-colossi which were perfect castings... I poured copper into them over and over again; I made the castings as skillfully as if they had only weighed half a shekel each"
In 1924, the Ford automobile company set a record by producing 1 million cars, in the process consuming one-third of the total casting production in the U.S. As the automobile industry grew the need for increased casting efficiency grew. The increasing demand for castings in the growing car and machine building industry during and after World War I and World War II, stimulated new inventions in mechanization and later automation of the sand casting process technology.
There was not one bottleneck to faster casting production but rather several. Improvements were made in molding speed, molding sand preparation, sand mixing, core manufacturing processes, and the slow metal melting rate in cupola furnaces. In 1912, the sand slinger was invented by the American company Beardsley & Piper. In 1912, the first sand mixer with individually mounted revolving plows was marketed by the Simpson Company. In 1915, the first experiments started with bentonite clay instead of simple fire clay as the bonding additive to the molding sand. This increased tremendously the green and dry strength of the molds. In 1918, the first fully automated foundry for fabricating hand grenades for the U.S. Army went into production. In the 1930s the first high-frequency coreless electric furnace was installed in the U.S. In 1943, ductile iron was invented by adding magnesium to the widely used grey iron. In 1940, thermal sand reclamation was applied for molding and core sands. In 1952, the "D-process" was developed for making shell molds with fine, pre-coated sand. In 1953, the hotbox core sand process in which the cores are thermally cured was invented. In 1954, a new core binder - water glass (sodium silicate) hardened with CO2 from the ambient air, came into use.
Sand-based athletic fields are sporting grounds constructed on sand. They can have certain advantages over those built on native soils.
Highly maintained areas of turf, such as those on an athletic field or on golf greens and tees, can be grown in native soil or sand-based systems. There are advantages and disadvantages to both that need to be considered before deciding what type of soil to grow turf in. Native soils offer many positive qualities, such as high nutrient holding capacity, water holding capacity, and sure footing. However, native soil fields are typically very poorly drained. This causes problems with growing turf and maintaining a safe surface for players. Sand-based systems provide all of the above qualities, and also improved drainage. They allow the turf manager better control over moisture management and resist soil compaction.
Sand-based systems are composed of a sand-based root zone, a gravel layer, and a drainage system. Although the root zone of a sand-based system is mostly sand, amendments are often added to increase the organic matter content and add stability to the root zone. Peat moss is the most common root zone amendment used, but other inorganic amendments can also be used. Peat moss is used because it increases water and nutrient holding capacity and decreases bulk density. The most common ratio of sand to peat moss is 8:2. This ratio will allow a water holding capacity of 15 to 26% and increase nutrient holding capacity greatly.
100% sand root zones are used often and are more cost effective. Selection of the type of sand is very crucial. Sand suitable for a root zone should be a medium to coarse (0.15-1.0 mm) particle size and should have sub-angular or sub-rounded shape. If sub-angular sand is chosen, it can deter some insects from making their homes in the soil. The shape makes it harder for them to move around in the soil. Rounded sands are not suitable because they do not pack and cannot provide a firm enough seedbed. Angular sands are not suitable because they become too firm and can potentially cut into roots. Once a sand is selected and it is determined if an amendment will be used, the layout of the root zone profile must be determined.
In the United States, the most common specifications for constructing a sand-based system are laid out by the United States Golf Association (USGA). The specifications for a sand-based athletic field are the same as what is typically used for USGA golf greens. These specifications consist of a 12 to 16 inch sand root zone. The choice of sand type and the addition of an amendment depend on the designer. When an amendment is used, it must be thoroughly incorporated with the sand. The sand overlays a 4-inch gravel layer. This creates a perched water table above the gravel that helps keep the root zone moist during dry conditions. A drainage system should be installed below the gravel to carry excess water away from the field.
Aeration on a sand-based system is used more to control the thickness of the thatch layer than to relieve compaction. A thick thatch layer on a sand-based athletic field can be detrimental. These layers prevent essential nutrients and water from reaching the plant. Further, fertilizers, fungicides, and insecticides can not penetrate the surface and reach the soil. This can obviously be devastating if a field is consumed by a soil borne disease or insect. Water penetration can also be deterred by a thick thatch layer. When there is a thick mat of organic matter near the surface of a field a second perched water table will form. This will cause roots to stay in the top couple of inches of soil because they do not need to search for water at greater depths. Without a deep root system, a field can become unsafe due to footing issues.
Core aerification is the most conventional way to control thatch. Taking up plugs and removing them from the surface eliminates much of the organic matter that is in the soil. The most common aerificaiton tines used are usually a half inch in diameter, normally penetrate about four inches, and are hollow. If the holes are on 2 inch center, 36 holes will be punch per square foot. After a field is aerified, the cores can either be raked up and removed, or left on the surface to break down. Solid tines will punch holes into surface but are only a temporary solution. This is because they do not reduce the organic layer, but merely displace it. Another common method of reducing thatch is vertical mowing. This consists of vertical blades tearing into the soil and pulling out organic matter. It is very effective at reducing thatch, but is also very disruptive. This can lead to a long recovery time for the turf. Reducing the amount of thatch at the surface allows nutrients and pesticides to penetrate into the soil more effectively. Collecting grass clippings will not reduce the formation of a thatch layer. Thatch layers are made up of decomposed vegetative parts of grass plants like stolons and rhizomes.
Once a field is aerified, and there are holes in the surface, a field should be topdressed with the same sand that was used in the construction of the field. Refilling the aerification holes with sand improves the macroporosity of the soil and allows better penetration of water. This will allow the turf manager to water deeper and therefore improve the root system. Introducing sand into the thatch layer allows the growth media to be suitable for play. Without sand mixed with the thatch layer, divots would readily kick out and the field would not be safe for any type of sport.
Nutrient management is essential in maintaining a healthy stand of turfgrass, and is much more difficult to achieve effectively in a sand-based system. Unlike with native soil fields, leaching of nutrients is a major concern when managing a sand-based turf system.
Nutrient leaching occurs more readily in a sand-based system because sand has a relatively low cation exchange capacity (CEC). This refers to the sand's ability to retain nutrient particles. Soil particle "hold on" to positively charged nutrient particles because they are negatively charged. The opposite charges cause the nutrients to adhere to soil particles which can then be taken up by plants. Sand has virtually no CEC, whereas clay and organic matter have relatively high CEC. This means that the higher the clay and organic matter of a soil, the more nutrients it will hold.
Low CEC is a major concern when an athletic field is constructed with 100% sand because substantial amounts of nutrients will be unavailable to the turf. The pure sand base will not hold on to nutrients until there is substantial organic matter incorporated into the soil to keep nutrients from leaching. Eventually, organic matter levels will rise as the plants begin to mature and dead vegetative matter decomposes.
The best way to avoid this problem is to incorporate some type of organic matter into the root zone mix during construction. The most common, as noted above, is peat moss. Mixing peat moss into the root zone mixture greatly increases nutrient holding capacity. This will greatly increase the chances of establishing a healthy stand of turfgrass because the soil will be able to retain both nutrients and water.
Because the nutrient holding capacity is low, soil tests are crucial for sand-based athletic fields. Soil tests should be taken frequently to measure what nutrients are lacking. Fertility programs should then be based on the soil tests. Unlike a native soil field, where most nutrients that are applied stay in the soil, sand-based fields nutrient status fluctuates. That is why a yearly fertilizer program can not be followed. It is more important to obtain soil tests during the establishment of a new field because organic matter will be low and amounts of nutrients will fluctuate even more.
One of the many advantages of sand-based systems is extremely good drainage. A well constructed sand-based system can drain excessive amounts of rainfall very quickly. The good drainage that sand-based systems exhibit also offer the turf manager better control over soil water content.
The large size of sand particles allow water to flow freely which, in turn, allows sand-based system to drain extremely well. This is beneficial because it allows fields to be used during inclement weather. Sand-based systems will drain multiple inches of water within a short period of time. This allows a sporting event to be played through a rain or after a short delay. Native soil fields, on the other hand, do not drain well and many games have to be cancelled or postponed due to puddling on the field.
The good drainage of a sand-based system allows turf managers better control over their irrigation. Once the turf manager learns how his/her field drains, they will know, fairly accurately, when the field will need water. This allows them to make an irrigation plan that provides the turf with just enough water to maintain its health.
Localized dry spots, more commonly known as hot spots, are a common occurrence on sand-based turf systems. Hot spots are small areas of turf that are dry and often become hydrophobic. They can be first seen when the grass plants in the area begin to wilt. If the hot spot is not taken care of, the turf in that area will eventually die. Once the soil becomes hydrophobic, it is very hard to get water to penetrate. The best way to alleviate a hot spot is through long, light irrigation or rainfall. It may also help to use a pitchfork to poke holes into the soil to increase percolation.