CA1050209A - Sand reclamation and purification - Google Patents
Sand reclamation and purificationInfo
- Publication number
- CA1050209A CA1050209A CA236,034A CA236034A CA1050209A CA 1050209 A CA1050209 A CA 1050209A CA 236034 A CA236034 A CA 236034A CA 1050209 A CA1050209 A CA 1050209A
- Authority
- CA
- Canada
- Prior art keywords
- sand
- charge
- grains
- product
- resin
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C5/00—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose
- B22C5/18—Plants for preparing mould materials
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method is disclosed for reclaiming clean sand from a sand mixture impregnated with resin. The method provided for a clean sand product having an acid demand of 15 or less without producing a sludge or waste water by-product to be discarded or treated.
Additionally, a method of preparing sand molds or cores from such reclaimed sand at relatively fast cure rates is disclosed; the molds or cores are characterized by high tensile strengths.
A method is disclosed for reclaiming clean sand from a sand mixture impregnated with resin. The method provided for a clean sand product having an acid demand of 15 or less without producing a sludge or waste water by-product to be discarded or treated.
Additionally, a method of preparing sand molds or cores from such reclaimed sand at relatively fast cure rates is disclosed; the molds or cores are characterized by high tensile strengths.
Description
The present invention is directed to the reclaiming of clean sand.
Sand is an indispensible raw material for the production process of the foundry. It occurs abundantly in nature, but frequently the particular sands required hy the foundry must be transported at great distances, making this basic manufactured material an expensive one.
Accordingly, an economical process for the reclaiming of used sand will alleviate the transportation expense and to some degree storage problems associated with bringing in new quantities of sand having a precise size and char-acter distribution; in addition natural raw materials will be conserved.
Early methods of reclaiming sand specifically avoided using molding sand laden with resins or other difficult to remove impurities. Only green sand and/or dry sand was put through a reclamation process which included calcining followed by washing which did in fact remove a substantial portion of any impurities. This process, however, required that the resulting sludge from the washing operation be conveniently discarded in rivers or settling ponds. With the advent of stricter envieonmental protection regulations~ the ability to dispose of a colloidal clay effluent, such as the sludge, was virtually eliminated or at least made economically prohibitive.
.
B
.
-- - . ,- . ~ . . -~ . . . . -lns(~20~
Under the older production methods ~f molding and curing sand, criteria for judging successful use of the re-claimed sand was markedly less stringent than today. Today, the requirements for accepting reclaimed sand demand that there be almost no metallics, an absence of organic impurities, absence of lime, and most importantly inert friable material must be removed to provide the reclaimed sand with an acid demand of 15 or less. These requirements are almost impossible to meet by the present state of the prior art and still meet environmental protection agency regulations.
Typical of current prior art methods, the process includes crushing the dirty sand charge to size it to a uniform mesh character, adding water and/or other suspension agents to form a wet mud, scrubbing said mud and subject-ing the mud to a vacuum filter to remove fines. The wet sand is ther. subjected to a calcining operation, sprayed with water following the calcining operation, and allowed to cool. The high solid colloidal clay effluent from the scrubbing and filtering operation had to be dumped in con-venient areas such as rivers, etc. A conceptual modificationof the above process has been suggested; the sand charge is fluidized during calcining by injection of gases. The particulate body of sand is virtually suspended allowing a vacuum system to remove certain particles based upon a variation in density. Unfortunately, the fluid bed attrition approach is highly inefficient and has not been successful ~rom a technical standpoint.
More current investigative work by the industry has used a fatty acid for mixing resin impregnated or dirty sand to form an aggregate, the fatty acid being oleic acid or an equivalent. A frothing agent is then added on a ~ - 2 -, ' ' ~
lOS(~Z09 continuous basis; t~.e mixture frot~s and boils over the sand container - 2a -:
.
: :
:, . .~ - . - :
1(~50Z0~ -carrying impurities in the frothing medium. The cost of this process is very high and efficiency is not attractive, but more importantly, the waste disposal problem of the frothing mixture still remains.
In accordance with one aspect of the present invention, there is provided a method of upgrading sand, comprising: (a) calcining a charge of sand to be up-grade~ at a temperature-pressure condition for a period of time effective to convert any clay on or in the sand charge to a friable material and to convert any dolomitic lime in the sand charge from a carbonate to an oxide, and (b) subjecting the calcined charge to severe agitation so as to burst or split any shell-like coating appearing on any sand of the charge whereby clean sand may be separated from the charge to render a statistical average acid demand of ]5 or less.
In accordance with a second aspect of the present invention, there is provided a method of reclaiming clean sand from a sand mixture impregnated with resin and containing dolomitic lime and clay or improving unused sand, the clean or improved sand being particularly charac~erized by a low level of inert friable material rendering an acid demand of 15 or less, the method com-prising: (a) sizing the grains of a charge of sand coated wi~h resin, clay or a mixture thereof to AFS 40 to 130, (b) calcining the sized charge at a temperature to substa~tially convert all clay to a friable material and convert dolomitic lime from a carbonate to an Qxide, (c) subjecting the grains of the calcined sized charge to severe agitation so as to burst or split any shell-like coatings appearing on the calcined grains, the coating : ~ :
~ ~ - 3 ~
---l~S~ Q~
being typically composed of inert friable material, cooling the calcined grains of the charge to a temper-ature of 200F either before or after agitation, and (d) collecting and separating the burst or split shell-like coatings from the grains, the latter constituting the clean sand.
In accordance with a third aspect of the present invention, there is provided a method of preparing sand molds or cores from sand previously impregnated with resin, comprising: (a) sizing the grains of a charge of resin impregnated sand to AFS 40 to 130, (b) separating metallic elements from the sand charge either before or subsequent to the sizing step, (c) calcining the sized sand charge at a temperature in the range of 1200 to 1500F for about one hour, (d) immediately following calcination, dry scrubbing the sand charge to produce a reclaimed sand product characterized by being free of injurious coatings of in-combustible oxides or inert . friable material, (e) mixing the reclaimed sand product . 20 with a resin curing agent and a catalyst, thereafter forming the sand mixture into molds or core bodies, and (f) either with or without the use of heat, curing the bodies, each body having a cure rate such that at the end of five seconds, the cured body will have a tensile strength of at least 90 psi, and at the end of 30 seconds each cure body will have a tensile strength of at least 300 psi~
In accordance with a fourth aspect of the present invention, there is provided a reclaimed sand product, comprising: (a) a collection of sand grains sized in the range of AFS 43 to 53 and substantially _ 4 _ .
~S()2~9 distributed as follows:
20 mesh 0.1 max.
30 mesh 2.0 max.
40 mesh 3.0 to 15.0 50 mesh 26.Q to 40.0 70 mesh 35.0 to 53.0 100 mesh 5.0 to 15.0 140 mesh 4.0 max 200-270 mesh 0.3 max.
(b) the collection of sand grains having a shiny clear appearance when magnified, a pH of 7.5 to 9.0, a clay ~-content no greater than 0.1, an acid demand no greater than 10, and a lime content rendering no appreciable effervecence when a 10 gram sample of the sand is placed in 30 milliliters of 1-1 HCl.
Two principal characteristics provided in the reclaimed sand product of this invention are: (a) a highly desirable and much lower acid demand capability, and (b) an ability to form densified sand bodies, cured or uncured, at higher tensile strengths not attainable by the prior art.
Acid demand is defined herein as the amount of a limited quantity of test acid consumed by a defined quantity of sand composition (the acid is principally or preferQn-tially reacted with the impurity content of the composition). The procedure followed in determining an acid demand according to that required of this invention is as follows: -~
(1) Take a 50 gram sample of a sand composition to be tested and add to it 15 cc of water and 50 cc of a 1/10 normal hydrochloric acid solution.
Sand is an indispensible raw material for the production process of the foundry. It occurs abundantly in nature, but frequently the particular sands required hy the foundry must be transported at great distances, making this basic manufactured material an expensive one.
Accordingly, an economical process for the reclaiming of used sand will alleviate the transportation expense and to some degree storage problems associated with bringing in new quantities of sand having a precise size and char-acter distribution; in addition natural raw materials will be conserved.
Early methods of reclaiming sand specifically avoided using molding sand laden with resins or other difficult to remove impurities. Only green sand and/or dry sand was put through a reclamation process which included calcining followed by washing which did in fact remove a substantial portion of any impurities. This process, however, required that the resulting sludge from the washing operation be conveniently discarded in rivers or settling ponds. With the advent of stricter envieonmental protection regulations~ the ability to dispose of a colloidal clay effluent, such as the sludge, was virtually eliminated or at least made economically prohibitive.
.
B
.
-- - . ,- . ~ . . -~ . . . . -lns(~20~
Under the older production methods ~f molding and curing sand, criteria for judging successful use of the re-claimed sand was markedly less stringent than today. Today, the requirements for accepting reclaimed sand demand that there be almost no metallics, an absence of organic impurities, absence of lime, and most importantly inert friable material must be removed to provide the reclaimed sand with an acid demand of 15 or less. These requirements are almost impossible to meet by the present state of the prior art and still meet environmental protection agency regulations.
Typical of current prior art methods, the process includes crushing the dirty sand charge to size it to a uniform mesh character, adding water and/or other suspension agents to form a wet mud, scrubbing said mud and subject-ing the mud to a vacuum filter to remove fines. The wet sand is ther. subjected to a calcining operation, sprayed with water following the calcining operation, and allowed to cool. The high solid colloidal clay effluent from the scrubbing and filtering operation had to be dumped in con-venient areas such as rivers, etc. A conceptual modificationof the above process has been suggested; the sand charge is fluidized during calcining by injection of gases. The particulate body of sand is virtually suspended allowing a vacuum system to remove certain particles based upon a variation in density. Unfortunately, the fluid bed attrition approach is highly inefficient and has not been successful ~rom a technical standpoint.
More current investigative work by the industry has used a fatty acid for mixing resin impregnated or dirty sand to form an aggregate, the fatty acid being oleic acid or an equivalent. A frothing agent is then added on a ~ - 2 -, ' ' ~
lOS(~Z09 continuous basis; t~.e mixture frot~s and boils over the sand container - 2a -:
.
: :
:, . .~ - . - :
1(~50Z0~ -carrying impurities in the frothing medium. The cost of this process is very high and efficiency is not attractive, but more importantly, the waste disposal problem of the frothing mixture still remains.
In accordance with one aspect of the present invention, there is provided a method of upgrading sand, comprising: (a) calcining a charge of sand to be up-grade~ at a temperature-pressure condition for a period of time effective to convert any clay on or in the sand charge to a friable material and to convert any dolomitic lime in the sand charge from a carbonate to an oxide, and (b) subjecting the calcined charge to severe agitation so as to burst or split any shell-like coating appearing on any sand of the charge whereby clean sand may be separated from the charge to render a statistical average acid demand of ]5 or less.
In accordance with a second aspect of the present invention, there is provided a method of reclaiming clean sand from a sand mixture impregnated with resin and containing dolomitic lime and clay or improving unused sand, the clean or improved sand being particularly charac~erized by a low level of inert friable material rendering an acid demand of 15 or less, the method com-prising: (a) sizing the grains of a charge of sand coated wi~h resin, clay or a mixture thereof to AFS 40 to 130, (b) calcining the sized charge at a temperature to substa~tially convert all clay to a friable material and convert dolomitic lime from a carbonate to an Qxide, (c) subjecting the grains of the calcined sized charge to severe agitation so as to burst or split any shell-like coatings appearing on the calcined grains, the coating : ~ :
~ ~ - 3 ~
---l~S~ Q~
being typically composed of inert friable material, cooling the calcined grains of the charge to a temper-ature of 200F either before or after agitation, and (d) collecting and separating the burst or split shell-like coatings from the grains, the latter constituting the clean sand.
In accordance with a third aspect of the present invention, there is provided a method of preparing sand molds or cores from sand previously impregnated with resin, comprising: (a) sizing the grains of a charge of resin impregnated sand to AFS 40 to 130, (b) separating metallic elements from the sand charge either before or subsequent to the sizing step, (c) calcining the sized sand charge at a temperature in the range of 1200 to 1500F for about one hour, (d) immediately following calcination, dry scrubbing the sand charge to produce a reclaimed sand product characterized by being free of injurious coatings of in-combustible oxides or inert . friable material, (e) mixing the reclaimed sand product . 20 with a resin curing agent and a catalyst, thereafter forming the sand mixture into molds or core bodies, and (f) either with or without the use of heat, curing the bodies, each body having a cure rate such that at the end of five seconds, the cured body will have a tensile strength of at least 90 psi, and at the end of 30 seconds each cure body will have a tensile strength of at least 300 psi~
In accordance with a fourth aspect of the present invention, there is provided a reclaimed sand product, comprising: (a) a collection of sand grains sized in the range of AFS 43 to 53 and substantially _ 4 _ .
~S()2~9 distributed as follows:
20 mesh 0.1 max.
30 mesh 2.0 max.
40 mesh 3.0 to 15.0 50 mesh 26.Q to 40.0 70 mesh 35.0 to 53.0 100 mesh 5.0 to 15.0 140 mesh 4.0 max 200-270 mesh 0.3 max.
(b) the collection of sand grains having a shiny clear appearance when magnified, a pH of 7.5 to 9.0, a clay ~-content no greater than 0.1, an acid demand no greater than 10, and a lime content rendering no appreciable effervecence when a 10 gram sample of the sand is placed in 30 milliliters of 1-1 HCl.
Two principal characteristics provided in the reclaimed sand product of this invention are: (a) a highly desirable and much lower acid demand capability, and (b) an ability to form densified sand bodies, cured or uncured, at higher tensile strengths not attainable by the prior art.
Acid demand is defined herein as the amount of a limited quantity of test acid consumed by a defined quantity of sand composition (the acid is principally or preferQn-tially reacted with the impurity content of the composition). The procedure followed in determining an acid demand according to that required of this invention is as follows: -~
(1) Take a 50 gram sample of a sand composition to be tested and add to it 15 cc of water and 50 cc of a 1/10 normal hydrochloric acid solution.
(2) Stir the acid, water and sand mixture by an automatic stirrer for approximately 7 minutes, such stirring being carried out by magnetic means.
; ~ ~ :
'. ..
' '1~51~209 t3) Allow the stirred mixture to set for 1 hour.
(4) Filter the mixture so as to separate the sand from the water and acid; wash the sand residue with distilled water.
(5~ Take the separated sand or filtered sand and back titrate to 7 pH utilizing a 1/10 normal sodium hydroxide solution.
(6) Substract the amount of sodium hydroxide utilized from the known amount (50 cc) of 1/10 normal ! hydrochloric acid utilized, the dividend of such sub-traction rendering an acid demand number.
According to this invention, the acid demand must be 15 or less (preferably 10 or less) indicating that the content of alkaline material, such as clay or other impurities, in the .
~ - 4b -B
.. . . . . .. . . ~
- : . .
~ns(l2~s reclaimed sand product will react with less than 15 cc of acid. The acid will be absorbed at such a low level that the later utility of the reclaimed sand in hot box core processes and other stringent uses will be enhanced.
Heretofore, processing techniques for reclaimed sand have resulted in an acid demand for the reclalmed product typically about 30. When the alkaline material occu~red as a carbonate, the high acid demand was not harm-ful in subsequent core and molding operations, since it did not affect the cure rate of the reclaimed product when mixed with resins. However, when spent sand is calcined to remove organic impurities, much of the alkaline material will convert to an oxide and this is extremely harmful to subsequent core and molding operations if simultaneously the acid demand is allowed to remain typically at about 30.
With the alkallne material in the oxide form, the acid demand must be reduced to 15 or less and preferably about 10 or less to provide the first of the principal character-istics.
Under the earliest methods, only 15 - 75% of the spent or dirty sand was reclaimable. This was helped some-what by the shell molding process which introduced a new molding techniqùe which was non-aqueous. With the shell molding type sand, all organic impurities could be burned off and the resulting sand looked very good under visual inspection. However, when dried in a hot box core process, it was not capable of meeting required cure strength re-quirements because of the presence of the oxide alkaline content and thus did not provide the second of the principal characteristics herein.
Calcining is an integral and important step in any reciaiming process because it permits a continuous type operation rendering efficient and economical cost factors.
The problem is how to make a process, utilizing a calcining step, successful in the sense that the ultimate product will work in a hot box core process as well as o-ther demand-ing molding operations. To these ends, the present in-vention is set forth.
A preferred method sequence is as follows:
(l) A charge of spent or dirty foundry sand is sized to AFS 43-53 utilizing a screening sequence, the sized distribution should preferably be about as follows:
20 mesh .1 max.
30 mesh 2.0 max.
40 mesh 3.0 - 15.0 50 mesh 26.0 - 40.0 70 mesh 35.0 - 53.0 - lO0 mesh 5.0 - 15.0 140 mesh 4.0 max.
200 - 270 mesh .3 max.
(2) Either before or after the sizlng step, the spent sand charge is subjected to a magnetic separator whereby metallic eIements may be removed and thereby separated from the charge.
`~ (3~ The sized and magnetically processed charge is subjected to a calcining operation whereby the collection of sand grains is heated to a temperature range of 1300 -1500F and for a period of time about one hour. A con-ventional calcining apparatus may be utilized and may pre- ~-ferably be of the two~stage type in which the collection of sand gralns are indexed upwardly in temperature and sub-jected to differential temperature zones for different 1~5~20g periods of time. The two-stage ~peration permits spent gases from calcination to be used to preheat the sand grains prior to entry into the calciner. The off-gases from calcination may be conveyed to a continuous rotary kiln acting as a preheater.
Another apparatus that can be used for this purpose has a vertical steel cylinder lined with fire brick and has a number of stationary brick hearths attached to~a center drive shaft with a number of arms,`two for each hearth, which carry rabble teeth that plow the sand through the furnace. A number of oil or gas burners make up the combustion system. The movement of the sand through the furnace is a slow, rolling, tumbling, cascading flow back and forth across the plurality of hearths, during which time the grains are exposed to intense heat which ignites and burns the carbonaceous materials from the grains, leaving the sand virtually carbon free upon its exit from --` the furnace.
Calcinlng is important because it converts the resin constituent of the spent sand to a gas whereby so that it may be removed. The binder resin referred to is typically a phenolic resin either of the one or two step type and may be in one of several different forms: dry powder, lump, flake, granular or liquid. Carbonaceous materials, clays and/or filler materials will form a glaze on eac~ sand grain as a result of calcination. Washing will not remove this glaze; it has been earlier determined that if the reclaimed sand was washed or utilized in the glazed condition in a subsequent molding operation, the glaze would have a detrimental effect on rebinding the sand with oils or new resins and the washing would only pose sn ' 1~50209 environmental disposal problem.
In the event the spent sand was previously used in a shell molding operation, then certain foreign material must be removed from the sand prior to reclamation, such as shot. All spent sand may contain iron fragments such as gates, risers and fins. The collecting system usually has screens and magnetic separators in abundance to separate out shot or other metallic material; manual labor may also be utilized to ca~ry out the separation.
(4) Sand leaving the last of the hearths of the calcining furnace is approximately at 1500F and preferably is sent to a sand cooler. The cooler is generally com-~, . .. .
prised of steel cylinder filled with a high number of steel tubes about which cooling air is circulated. The sand descends slowly through the cooler tubes, the rate being determined by the length of time the discharge gate~
at the bottom of the coolers are opened as well as the interval between the gate openings. It is in this slow descent, in conjunction with the large volume of cooling 20 air that reduces the sand temperature to less than 200F. ~ -In the calcining operation, all of the clay content of the spent sand is converted to a friable material which encases each grain of sand and all the dolomitic lime is converted to an oxide, (5) The most important step of the process is the subjection of the calcined sized charge to severe and/-or violent dry agitation which must ~e greater in scrubbing . . - . , . -action than that afforded by attrition systems and much greater than that provided by simple gentle agitation system. A rugged mulling machine must be utilized to achieve the kind of severe agitation contemplated by the present ~ .
.
- , - .. : . : ..
1~50Z(~9 invention, although a hurricane like blower system may be envisioned to accomplish same. The charge should be sub-jected to such severe scrubbing in a dry condition for a period of time, such as from 15 - 25 minutes, whereby all of the shell-like glaze coatings on each of the sand grains are burst or split to expose and release the encased sand grain, leaving it in a shiny condition.
(6~ Means should be utilized to separate the burst shell-like coatings from the released sand grains so that the clean sand grains may constitute the sole con-stituent of the reclaimed sand product.
(7) The clean reclaimed sand may then be further subjected to a washing operation, if desired, but it is not necessary since the product in its present condition will achieve an acid demand of 15 or less according to this invention, and preferably 10 or less.
(8) The clean reclaimed sand is then recycled into a core making or molding process by mixture with certain resins or suitable compounds.
This process also achieves utility with respect to new or raw sand, as opposed to reclaimed sand. Availability and cost factors cause raw sand supplies to typically have an acid demand of about 30. The raw or new product can be improved in physical characteristics to promote better and more eficient casting. Furthermore, continuous recycling of raw or reclaimable sand will progressively upgrade the product proportionate to the number of recycles; it is possible that acid demands of about 3 can eventually be achieved.
The reclaimed sand product resulting from the method of this invention, has achieved a new status in that ~ _ 9 _ ,:
~ . . , ' :
it is a new type of product having character~stics neverbefore achieved. The product will have a pH of between 7.5 and 10.0, an acid demand of 15 or less, and visual or microscopic inspection of the sand grains will indicate that they are clean, shiny, and free of any glazed coating and other impurities. The product has a lime content such that there will be no appreciable effervescence when a 10 gram sample is placed in a 30 milliliter solution of 1-1 hydrochloric acid. The clay content of the product is .1 or less as determined by the American Foundry Society sand test method. It is desired that the clay content be substantially 0, but a tolerance up to .1 is provided.
The moisture content of the sand product is .25% or less and has a calcium oxide and magnesium oxide content of .2 ~ax. The grain size of the product should be preferably about AFS 43-53.
- 9a -:
, , . , . , , . . . . ,, ................... - . ,
; ~ ~ :
'. ..
' '1~51~209 t3) Allow the stirred mixture to set for 1 hour.
(4) Filter the mixture so as to separate the sand from the water and acid; wash the sand residue with distilled water.
(5~ Take the separated sand or filtered sand and back titrate to 7 pH utilizing a 1/10 normal sodium hydroxide solution.
(6) Substract the amount of sodium hydroxide utilized from the known amount (50 cc) of 1/10 normal ! hydrochloric acid utilized, the dividend of such sub-traction rendering an acid demand number.
According to this invention, the acid demand must be 15 or less (preferably 10 or less) indicating that the content of alkaline material, such as clay or other impurities, in the .
~ - 4b -B
.. . . . . .. . . ~
- : . .
~ns(l2~s reclaimed sand product will react with less than 15 cc of acid. The acid will be absorbed at such a low level that the later utility of the reclaimed sand in hot box core processes and other stringent uses will be enhanced.
Heretofore, processing techniques for reclaimed sand have resulted in an acid demand for the reclalmed product typically about 30. When the alkaline material occu~red as a carbonate, the high acid demand was not harm-ful in subsequent core and molding operations, since it did not affect the cure rate of the reclaimed product when mixed with resins. However, when spent sand is calcined to remove organic impurities, much of the alkaline material will convert to an oxide and this is extremely harmful to subsequent core and molding operations if simultaneously the acid demand is allowed to remain typically at about 30.
With the alkallne material in the oxide form, the acid demand must be reduced to 15 or less and preferably about 10 or less to provide the first of the principal character-istics.
Under the earliest methods, only 15 - 75% of the spent or dirty sand was reclaimable. This was helped some-what by the shell molding process which introduced a new molding techniqùe which was non-aqueous. With the shell molding type sand, all organic impurities could be burned off and the resulting sand looked very good under visual inspection. However, when dried in a hot box core process, it was not capable of meeting required cure strength re-quirements because of the presence of the oxide alkaline content and thus did not provide the second of the principal characteristics herein.
Calcining is an integral and important step in any reciaiming process because it permits a continuous type operation rendering efficient and economical cost factors.
The problem is how to make a process, utilizing a calcining step, successful in the sense that the ultimate product will work in a hot box core process as well as o-ther demand-ing molding operations. To these ends, the present in-vention is set forth.
A preferred method sequence is as follows:
(l) A charge of spent or dirty foundry sand is sized to AFS 43-53 utilizing a screening sequence, the sized distribution should preferably be about as follows:
20 mesh .1 max.
30 mesh 2.0 max.
40 mesh 3.0 - 15.0 50 mesh 26.0 - 40.0 70 mesh 35.0 - 53.0 - lO0 mesh 5.0 - 15.0 140 mesh 4.0 max.
200 - 270 mesh .3 max.
(2) Either before or after the sizlng step, the spent sand charge is subjected to a magnetic separator whereby metallic eIements may be removed and thereby separated from the charge.
`~ (3~ The sized and magnetically processed charge is subjected to a calcining operation whereby the collection of sand grains is heated to a temperature range of 1300 -1500F and for a period of time about one hour. A con-ventional calcining apparatus may be utilized and may pre- ~-ferably be of the two~stage type in which the collection of sand gralns are indexed upwardly in temperature and sub-jected to differential temperature zones for different 1~5~20g periods of time. The two-stage ~peration permits spent gases from calcination to be used to preheat the sand grains prior to entry into the calciner. The off-gases from calcination may be conveyed to a continuous rotary kiln acting as a preheater.
Another apparatus that can be used for this purpose has a vertical steel cylinder lined with fire brick and has a number of stationary brick hearths attached to~a center drive shaft with a number of arms,`two for each hearth, which carry rabble teeth that plow the sand through the furnace. A number of oil or gas burners make up the combustion system. The movement of the sand through the furnace is a slow, rolling, tumbling, cascading flow back and forth across the plurality of hearths, during which time the grains are exposed to intense heat which ignites and burns the carbonaceous materials from the grains, leaving the sand virtually carbon free upon its exit from --` the furnace.
Calcinlng is important because it converts the resin constituent of the spent sand to a gas whereby so that it may be removed. The binder resin referred to is typically a phenolic resin either of the one or two step type and may be in one of several different forms: dry powder, lump, flake, granular or liquid. Carbonaceous materials, clays and/or filler materials will form a glaze on eac~ sand grain as a result of calcination. Washing will not remove this glaze; it has been earlier determined that if the reclaimed sand was washed or utilized in the glazed condition in a subsequent molding operation, the glaze would have a detrimental effect on rebinding the sand with oils or new resins and the washing would only pose sn ' 1~50209 environmental disposal problem.
In the event the spent sand was previously used in a shell molding operation, then certain foreign material must be removed from the sand prior to reclamation, such as shot. All spent sand may contain iron fragments such as gates, risers and fins. The collecting system usually has screens and magnetic separators in abundance to separate out shot or other metallic material; manual labor may also be utilized to ca~ry out the separation.
(4) Sand leaving the last of the hearths of the calcining furnace is approximately at 1500F and preferably is sent to a sand cooler. The cooler is generally com-~, . .. .
prised of steel cylinder filled with a high number of steel tubes about which cooling air is circulated. The sand descends slowly through the cooler tubes, the rate being determined by the length of time the discharge gate~
at the bottom of the coolers are opened as well as the interval between the gate openings. It is in this slow descent, in conjunction with the large volume of cooling 20 air that reduces the sand temperature to less than 200F. ~ -In the calcining operation, all of the clay content of the spent sand is converted to a friable material which encases each grain of sand and all the dolomitic lime is converted to an oxide, (5) The most important step of the process is the subjection of the calcined sized charge to severe and/-or violent dry agitation which must ~e greater in scrubbing . . - . , . -action than that afforded by attrition systems and much greater than that provided by simple gentle agitation system. A rugged mulling machine must be utilized to achieve the kind of severe agitation contemplated by the present ~ .
.
- , - .. : . : ..
1~50Z(~9 invention, although a hurricane like blower system may be envisioned to accomplish same. The charge should be sub-jected to such severe scrubbing in a dry condition for a period of time, such as from 15 - 25 minutes, whereby all of the shell-like glaze coatings on each of the sand grains are burst or split to expose and release the encased sand grain, leaving it in a shiny condition.
(6~ Means should be utilized to separate the burst shell-like coatings from the released sand grains so that the clean sand grains may constitute the sole con-stituent of the reclaimed sand product.
(7) The clean reclaimed sand may then be further subjected to a washing operation, if desired, but it is not necessary since the product in its present condition will achieve an acid demand of 15 or less according to this invention, and preferably 10 or less.
(8) The clean reclaimed sand is then recycled into a core making or molding process by mixture with certain resins or suitable compounds.
This process also achieves utility with respect to new or raw sand, as opposed to reclaimed sand. Availability and cost factors cause raw sand supplies to typically have an acid demand of about 30. The raw or new product can be improved in physical characteristics to promote better and more eficient casting. Furthermore, continuous recycling of raw or reclaimable sand will progressively upgrade the product proportionate to the number of recycles; it is possible that acid demands of about 3 can eventually be achieved.
The reclaimed sand product resulting from the method of this invention, has achieved a new status in that ~ _ 9 _ ,:
~ . . , ' :
it is a new type of product having character~stics neverbefore achieved. The product will have a pH of between 7.5 and 10.0, an acid demand of 15 or less, and visual or microscopic inspection of the sand grains will indicate that they are clean, shiny, and free of any glazed coating and other impurities. The product has a lime content such that there will be no appreciable effervescence when a 10 gram sample is placed in a 30 milliliter solution of 1-1 hydrochloric acid. The clay content of the product is .1 or less as determined by the American Foundry Society sand test method. It is desired that the clay content be substantially 0, but a tolerance up to .1 is provided.
The moisture content of the sand product is .25% or less and has a calcium oxide and magnesium oxide content of .2 ~ax. The grain size of the product should be preferably about AFS 43-53.
- 9a -:
, , . , . , , . . . . ,, ................... - . ,
Claims (16)
1. A method of reclaiming clean sand from a sand mixture impregnated with resin and containing dolomitic lime and clay or improving unused sand, said clean or improved sand being particularly characterized by a low level of inert friable material rendering an acid demand of 15 or less, said method comprising:
(a) sizing the grains of a charge of sand coated with resin, clay or a mixture thereof to AFS
40 to 130, (b) calcining said sized charge at a tempera-ture to substantially convert all clay to a friable material and convert dolomitic lime from a carbonate to an oxide, (c) subjecting the grains of said calcined sized charge to severe agitation so as to burst or split any shell-like coatings appearing on said calcined grains, said coating being typically composed of inert friable material, cooling said calcined grains of said charge to a temperature of 200°F either before or after agita-tion, and (d) collecting and separating said burst or split shell-like coatings from said grains, the latter constituting said clean sand.
(a) sizing the grains of a charge of sand coated with resin, clay or a mixture thereof to AFS
40 to 130, (b) calcining said sized charge at a tempera-ture to substantially convert all clay to a friable material and convert dolomitic lime from a carbonate to an oxide, (c) subjecting the grains of said calcined sized charge to severe agitation so as to burst or split any shell-like coatings appearing on said calcined grains, said coating being typically composed of inert friable material, cooling said calcined grains of said charge to a temperature of 200°F either before or after agita-tion, and (d) collecting and separating said burst or split shell-like coatings from said grains, the latter constituting said clean sand.
2. The method of claim 1, wherein the step of severe agitation is carried out by scrubbing said grains of sand one against each other in a dry condition.
3. The method of claim 1, wherein said charge of sand is subjected to a magnetic separation prior to step (a), for separating out the metallic content of said sized grains, and step (b) is carried out to additionally burn off organic impurities and reduce the lime content resulting from said method to a level of 0.2%.
4. The method of claim 1, wherein said step (c) is carried out for a period of at least 15 minutes in a dry mulling machine.
5. The method of claim 1, wherein said sized sand is subjected to a washing operation prior to step (b).
6. A method of preparing sand molds or cores from sand previously impregnated with resin, comprising:
(a) sizing the grains of a charge of a resin impregnated sand to AFS 40 to 130, (b) separating metallic elements from said sand charge either before or subsequent to said sizing step, (c) calcining said sized sand charge at a temperature in the range of 1200 to 1500°F for about one hour, (d) immediately following calcination, dry scrubbing said sand charge to produce a reclaimed sand product characterized by being free of injurious coatings of in-combustible oxides or inert friable material, (e) mixing said reclaimed sand product with a resin during agent and a catalyst, thereafter forming said sand mixture into molds or core bodies, and (f) either with or without the use of heat, curing said bodies, each body having a cure rate such that at the end of five seconds, the cured body will have a tensile strength of at least 90 psi, and at the end of 30 seconds each cure body will have a tensile strength of at least 300 psi.
(a) sizing the grains of a charge of a resin impregnated sand to AFS 40 to 130, (b) separating metallic elements from said sand charge either before or subsequent to said sizing step, (c) calcining said sized sand charge at a temperature in the range of 1200 to 1500°F for about one hour, (d) immediately following calcination, dry scrubbing said sand charge to produce a reclaimed sand product characterized by being free of injurious coatings of in-combustible oxides or inert friable material, (e) mixing said reclaimed sand product with a resin during agent and a catalyst, thereafter forming said sand mixture into molds or core bodies, and (f) either with or without the use of heat, curing said bodies, each body having a cure rate such that at the end of five seconds, the cured body will have a tensile strength of at least 90 psi, and at the end of 30 seconds each cure body will have a tensile strength of at least 300 psi.
7. The method of claim 6, wherein step (e) is carried out with about 2.9% resin, about 10% accelerator being added to the reclaimed sand product.
8. The method of claim 6, wherein said resin if of the furan urea formaldehyde, phenolic urea formaldehyde, or cold box-type gas chemically set types.
9. The method of claim 6, wherein said resin is comprised of core oil.
10. A reclaimed sand product, comprising:
(a) a collection of sand grains sized in the range of AFS 43 to 53 and substantially distributed as follows:
(b) said collection of sand grains having a shiny clear appearance when magnified, a pH of 7.5 to 9.0, a clay content no greater than 0.1, an acid demand no greater than 10, and a lime content rendering no appreciable effervecense when a 10 gram sample of said sand is placed in 30 milliliters of 1-1 HC1.
(a) a collection of sand grains sized in the range of AFS 43 to 53 and substantially distributed as follows:
(b) said collection of sand grains having a shiny clear appearance when magnified, a pH of 7.5 to 9.0, a clay content no greater than 0.1, an acid demand no greater than 10, and a lime content rendering no appreciable effervecense when a 10 gram sample of said sand is placed in 30 milliliters of 1-1 HC1.
11. The product of claim 10, wherein the moisture content of said collection is no greater than 0.25%.
12. The product of claim 10, wherein said collection contains calcium oxide and magnesium oxide together no greater than 0.2%.
13. The product of claim 10, wherein said collection provides an ignition loss of 0.1% max.
14. The product of claim 10, wherein said collection has a fusion conforming to ASTM C-24 standard.
15. A method of upgrading sand, comprising:
(a) calcining a charge of sand to be upgraded at a temperature-pressure condition for a period of time effective to convert any clay on or in said sand charge to a friable material and to convert any dolomitic lime in said sand charge from a carbonate to an oxide, and (b) subjecting said calcined charge to severe agitation so as to burst or split any shell-like coating appearing on any sand of said charge whereby clean sand may be separated from said charge to render a statistical average acid demand of 15 or less.
(a) calcining a charge of sand to be upgraded at a temperature-pressure condition for a period of time effective to convert any clay on or in said sand charge to a friable material and to convert any dolomitic lime in said sand charge from a carbonate to an oxide, and (b) subjecting said calcined charge to severe agitation so as to burst or split any shell-like coating appearing on any sand of said charge whereby clean sand may be separated from said charge to render a statistical average acid demand of 15 or less.
16. The method of claim 15 wherein said steps (a) and (b) are successively repeated a number of times, the resulting clean sand from each repetition being progressively lower in acid demand.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US53336774A | 1974-12-16 | 1974-12-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1050209A true CA1050209A (en) | 1979-03-13 |
Family
ID=24125657
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA236,034A Expired CA1050209A (en) | 1974-12-16 | 1975-09-22 | Sand reclamation and purification |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5186019A (en) |
| CA (1) | CA1050209A (en) |
| DE (1) | DE2554405A1 (en) |
| GB (1) | GB1476609A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH631643A5 (en) * | 1978-04-14 | 1982-08-31 | Fischer Ag Georg | METHOD FOR REGENERATING OLD FOUNDRY SAND AND DEVICE FOR CARRYING OUT THE METHOD AND PRODUCT OF THE METHOD. |
| US4449566A (en) * | 1979-04-09 | 1984-05-22 | Ford Motor Company | Foundry sand reclamation |
| US4487372A (en) * | 1982-04-16 | 1984-12-11 | Combustion Engineering, Inc. | Thermal sand reclamation system |
| DE4004553C1 (en) * | 1990-02-14 | 1991-10-10 | Saz Sommer Aluminium Zug Ag, Zug, Ch | |
| US5211215A (en) * | 1990-02-14 | 1993-05-18 | Sommer Hermann W | Process for neutralizing regenerated sand |
| ES2100205T3 (en) * | 1991-06-29 | 1997-06-16 | Kuettner Gmbh & Co Kg Dr | PROCEDURE FOR REGENERATING USED FOUNDRY SAND. |
| DE102016206546A1 (en) * | 2016-04-19 | 2017-10-19 | Siemens Aktiengesellschaft | Apparatus for selecting a fraction of a starting material |
| CN110510620B (en) * | 2019-09-11 | 2021-08-24 | 江苏凯达石英股份有限公司 | Purification method of high-purity quartz sand tailings |
| CN113426942B (en) * | 2021-06-24 | 2022-09-13 | 南阳仁创砂业科技有限公司 | Method for preparing precoated sand for cast steel from recycled material |
| CN117123729B (en) * | 2023-07-06 | 2024-05-24 | 江门市新会区金昌矽砂有限公司 | Regeneration preparation process of baozhu sand |
-
1975
- 1975-09-22 CA CA236,034A patent/CA1050209A/en not_active Expired
- 1975-10-17 GB GB4265375A patent/GB1476609A/en not_active Expired
- 1975-12-03 DE DE19752554405 patent/DE2554405A1/en not_active Withdrawn
- 1975-12-15 JP JP14855975A patent/JPS5186019A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB1476609A (en) | 1977-06-16 |
| DE2554405A1 (en) | 1976-06-24 |
| JPS5186019A (en) | 1976-07-28 |
| JPS5319535B2 (en) | 1978-06-21 |
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