Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Sand casting
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
==Processes== In general, we can distinguish between two methods of sand casting; the first one using ''[[Molding sand#Green sand|green sand]]'' and the second being the ''air set'' method. ===Green sand=== {{further|Molding sand#Green sand}} These castings are made using sand molds formed from "wet" sand which contains water and organic bonding compounds, typically referred to as clay. The name "green sand" comes from the fact that the sand mold is not "set", it is still in the "green" or uncured state even when the metal is poured in the mold. Green sand is not green in color, but "green" in the sense that it is used in a wet state (akin to green wood). [[Misnomer|Contrary to what the name suggests]], "green sand" is not a type of sand on its own (that is, not [[greensand]] in the geologic sense), but is rather a mixture of: * [[silica]] sand (SiO<sub>2</sub>), [[chromite]] sand (FeCr<sub>2</sub>O<sub>4</sub>), or [[zircon]] sand (ZrSiO<sub>4</sub>), 75 to 85%, sometimes with a proportion of [[olivine]], [[staurolite]], or [[graphite]]. * [[bentonite]] ([[clay]]), 5 to 11% * water, 2 to 4% * inert [[sludge]] 3 to 5% * [[anthracite]] (0 to 1%) 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 [[degasification|degas]]. Coal, typically referred to in [[foundry|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 casting for non-ferrous metals does not use coal additives, since the [[carbon monoxide|CO]] created does not prevent oxidation. Green sand for aluminum typically uses [[olivine]] sand (a mixture of the minerals [[forsterite]] and [[fayalite]], which is made by crushing [[dunite]] rock). The choice of sand has a lot to do with the temperature at which the metal is poured. At the temperatures that copper and iron are poured, the clay is 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 expend considerable effort on aggressive dust collection to capture this fine silica. Various types of respiratory-protective equipment are also used in foundries.<ref>{{Cite journal|title=Respiratory Health and Cross-Shift Changes of Foundry Workers in Iran|author1=Mayam Saraei |author2=Habibbolah Masoudi |author3=Omid Aminian |author4=Nazanin Izadi |journal=Tanaffos Journal of Respiratory Diseases, Thoracic Surgery, Intensive Care and Tuberculosis|year=2018|volume=17|issue=4|pages=285β290|pmid=31143220|pmc=6534795}}</ref><ref>{{Cite journal|url=https://www.foundrymag.com/opinion/article/21926109/respirator-use-and-practices-in-primary-metal-operations|title=Respirator Use and Practices in Primary Metal Operations|journal=Foundry Management and Technology|access-date=2021-04-05}}</ref> The sand also has the dimensional instability associated with the conversion of [[quartz]] from alpha quartz to beta quartz at 680 Β°C (1250 Β°F). Often, combustible additives such as wood flour are added to create spaces for the grains to expand without deforming the mold. [[Olivine]], [[chromite]], etc. are therefore used because they do not have a [[phase transition]] that causes rapid expansion of the grains. Olivine and chromite also offer greater density, which cools the metal faster, thereby producing finer grain structures in the metal. Since they are not [[metamorphic minerals]], they do not have the [[polycrystals]] found in [[silica]], and subsequently they do not form hazardous sub-micron sized particles. ==="Air set" method=== 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.<ref>[http://www.custompartnet.com/wu/SandCasting Sand Casting Process Description]</ref> 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 (instrument)|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. ===Cold box=== Cold box 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===<!-- [[No bake mold casting]] redirects here --> 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.<ref>{{harvnb|Todd|Allen|Alting|1994|pp=256β257}}.</ref> 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]], [[vacuum molding (casting)]] & [[V process]] redirect here --> ''Vacuum molding'' (''V-process'') is a variation of the sand casting process for most ferrous and non-ferrous metals,<ref>{{Citation | title = Metal Casting Techniques - Vacuum ("V") Process Molding | url = http://www.engineershandbook.com/MfgMethods/vacuumprocessmolding.htm | access-date = 2009-11-09 | postscript =.}}</ref> 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 ({{convert|0.003|to|0.008|in|abbr=on}}) of [[plastic]] [[film]] is draped over the pattern and a vacuum is drawn ({{convert|200|to|400|mmHg|abbr=on}}). 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.<ref name="degarmo310">{{harvnb|Degarmo|Black|Kohser|2003|p=310}}.</ref><ref name="vprocess">{{Citation | title = The V-Process | url = http://www.mccannsales.com/book/vprocess.pdf | access-date = 2009-11-09 | postscript = . | archive-date = 2012-03-01 | archive-url = https://web.archive.org/web/20120301040048/http://www.mccannsales.com/book/vprocess.pdf | url-status = dead }}</ref> 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 Β±0.010 in for the first inch and Β±0.002 in/in thereafter. Cross-sections as small as {{convert|0.090|in|abbr=on}} are possible. The surface finish is very good, usually between 150 and 125 [[root mean square|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.<ref name="degarmo310"/><ref name="vprocess"/><ref>{{harvnb|Degarmo|Black|Kohser|2003|p=311}}.</ref> ===Fast mold making processes=== 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. ====Mechanized sand molding==== The first mechanized molding lines consisted of [[Sand slinger|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. ====Automatic high pressure sand molding lines==== 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. =====Horizontal sand flask molding===== 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 [[Bar (unit)|bars]]. The subsequent mold handling including turn-over, assembling, pushing-out on a conveyor were accomplished either manually or automatically. In the late fifties [[hydraulics|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 [[pneumatics|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 90β120 molds per hour. {{wide image|Horizflask.png|600px}} =====Vertical sand flaskless molding===== 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 {{convert|0.1|mm|in|abbr=on}}. 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. {{wide image|disa.jpg|600px}} =====Matchplate sand molding===== 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 molding 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 {{convert|0.15|mm|in|abbr=on}}), 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. [[File:match-de.png|center|700px]] =====Safety standards===== With automated mold manufacturing came additional workplace safety requirements. Different [[Technical standard|voluntary technical standards]] apply depending on the geopolitical jurisdiction where the machinery is to be used. ======Canada====== Canada does not have a machine-specific voluntary technical standard for sand-mold making machinery. This type of machinery is covered by: [https://store.csagroup.org/ccrz__ProductDetails?viewState=DetailView&cartID=&portalUser=&store=&cclcl=en_US&sku=Z432-16 Safeguarding of machinery, CSA Z432. Canadian Standards Association. 2016.] In addition, the electrical safety requirements are covered by: [https://store.csagroup.org/ccrz__ProductDetails?viewState=DetailView&cartID=&portalUser=&store=&cclcl=en_US&sku=C22.2%20NO.%20301-16 Industrial Electrical Machinery, CSA C22.2 No. 301. 2016.] ======European Union====== The primary standard for sand-mold manufacturing equipment in the EU is: [https://standards.cen.eu/dyn/www/f?p=204:110:0::::FSP_PROJECT,FSP_ORG_ID:38822,6183&cs=187F082E35537138F42BC892EB6E6F41B Safety requirements for foundry moulding and coremaking machinery and plant associated equipment, EN 710. European Committee for Standardization (CEN).] EN 710 will need to be used in conjunction with [https://www.cenelec.eu/dyn/www/f?p=104:110:1254549426375101::::FSP_ORG_ID,FSP_PROJECT,FSP_LANG_ID:1257239,58483,25 EN 60204-1] for electrical safety, and [https://standards.cen.eu/dyn/www/f?p=204:110:0::::FSP_PROJECT,FSP_ORG_ID:39285,6096&cs=1269268F03116BF7319D76D5A120E771A EN ISO 13849-1] and [https://standards.cen.eu/dyn/www/f?p=204:110:0::::FSP_PROJECT,FSP_ORG_ID:32684,6096&cs=14A2AF9B02A956FEEFFE273E56BFE6C04 EN ISO 13849-2] or [https://www.cenelec.eu/dyn/www/f?p=104:110:476494116260901::::FSP_ORG_ID,FSP_PROJECT,FSP_LANG_ID:1257239,58972,25 EN 62061] for functional safety. Additional type C standards may also be necessary for conveyors, robotics or other equipment that may be needed to support the operation of the mold-making equipment. ======United States====== There is no machine-specific standard for sand-mold manufacturing equipment. The ANSI B11 family of standards includes some generic machine-tool standards that could be applied to this type of machinery, including: * Safety of Machinery, ANSI B11.0. American National Standards Institute (ANSI). 2020.<ref>[https://www.b11standards.org/standards B11 Standards]</ref> * Performance Requirements for Risk Reduction Measures: Safeguarding and other Means of Reducing Risk, ANSI B11.19. American National Standards Institute (ANSI). 2019. * Safety Requirements for the Integration of Machinery into a System, ANSI B11.20. American National Standards Institute (ANSI). 2017. * Safety Requirements for Transfer Machines, ANSI B11.24. American National Standards Institute (ANSI). 2002 (R2020). * Functional Safety for Equipment (Electrical/Fluid Power Control Systems) General Principles for the Design of Safety Control Systems Using ISO 13849-1, ANSI B11.26. American National Standards Institute (ANSI). 2018. * Sound Level Measurement Guidelines, ANSI B11.TR5. American National Standards Institute (ANSI). 2006 (R2017).
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)