Foundry sand reclamation

A dry method of conditioning spent foundry sand is disclosed. After having sized the sand and removal of tramp metallic elements, the sand is subjected to a sequence of squeezing under a high-stress low kinetic energy system for a period of 5-30 minutes, and then propelled against a target with high-kenitic energy in the presence of a suction for several minutes. This sequence can be preferably repeated to increase the quality of the resulting product which should have 0.1% or less of fine particles, a pH of 6-9, a clay content and organic combustible content of substantially zero. The reclaimed sand will exhibit a density of at least 100 grams/biscuit when compacted for core making or molding.

BACKGROUND OF THE INVENTION 
Confusion has existed as to what sand reclamation means, particularly in 
the early years of sand conditioning. Some foundrymen deemed reuse of old 
used sand a form of reclamation, while others deemed rejuvenation of old 
sand heaps with new sand and clay additions to be reclamation. Yet others 
felt that the mechanical reconditioning of an old sand mass by merely 
removing lumps, foreign metal and ultra fine particles, should be accepted 
as reclamation. Only a few in the earlier years conceived reclamation to 
be a matter of treating individual grains to restore them to a physical 
state approximating that of new sand grains. It is this latter meaning 
that applies in this disclosure because it has become the accepted meaning 
of sand reclamation in modern foundry technology. One recent twist may be 
added to this definition: it should include the reclamation of new sand 
which is below ground mined; although it is new sand, it contains 
quantities of impurities which must be removed if they are to be 
equivalent to bank sand or above ground mined sand. 
Sand reclamation has been slow in being accepted by the foundry for 
commercial implementation. There has existed for some time an industrywide 
attitude that reclamation only adds to the complexities of selecting, 
preparing, testing and controlling the sand to be used to make cores or 
molds. The average foundryman is adverse to changing established 
procedures that have taken years of trial and error to arrive at the right 
binder chemistry, shape, flowability, and grain size that will give the 
right ramming pressure and carrying properties. Reclaim sand is believed, 
in accordance with this attitude, to introduce additional unknown variable 
and technical considerations that trade off new problems for solving the 
immediate problem of conserving sand. This invention is designed to 
provide a reclaim sand product that does not trade off new problems; the 
reclaim sand is defined by a number of parameters that make it 
substantially the same as new bank sand and in many cases better. 
The primary consideration that has guided the course of sand reclamation 
development heretofore has been the technical success of the particular 
process in terms of the quality of the reclaim sand; today the important 
considerations are (a) the cost of energy employed in the process, (b) the 
amount of land that is required to support the processing equipment, (c) 
governmental regulations of waste disposal, and (d) density or chemical 
variability of the reclaim sand preventing sand bonding for core making. 
The progression of the technology includes reuse of old sand, rejuvenation 
by dilution, reconditioning, wet methods, thermal methods, dry methods, 
and combination of the latter. With this in mind, a review of the 
fundamental concepts for each of these categories shall follow: 
Reuse of Old Sand 
Any initial period of success which is enjoyed by reusing old sand with no 
further reconditioning or reclamation, is followed by a progressive 
deterioration in sand workability and casting finish with the passing of 
time. Eventually, savings effected by reusing the old sand becomes 
questionable as increasing losses are suffered in production and cleaning 
operations. The progressive deterioration results from the cumulative 
effects of physical changes (a) within a sand mass as a whole, and (b) 
upon the surfaces of individual sand grains. In preparing foundry sand 
mixtures, individual grains are provided with coatings of bond. Through 
successive cycles of a system, such coatings become thicker with each 
added layer of fresh bond. Eventually, and as shown in FIG. 2, most grains 
become encased in "shells" 13 and 14 of old bond; the "shells" tend to 
become hard and brittle with the passing of time and repeated subjection 
to high temperatures. The continuous artificial enlargement of individual 
grains creates a sand mass with an increasingly greater number of grains 
being retained on the coarser sieves of a distribution analysis. At the 
same time, under mechanical and thermal stresses, the embrittled coatings 
on some grains crack and separate to produce an increase in fine 
particles. Thus, over a period of time, a progressive change in the mass 
grain distribution results in more and more fines becoming dispersed 
throughout a matrix containing more and more oversized grains. In 
addition, compound grains may result when a number of small grains become 
cemented together to create large irregular shapes possessing uncertain 
physical stability in the presence of mechanical and thermal forces. This 
change in grain distribution produces an increase in total surface area 
and forces the foundrymen to increase strength and moisture levels with 
each additional cycle through the system. Eventually this gets out of 
control. 
An important physical change with respect to individual sand grains and 
their contribution to mass deterioration is the creation of "pickled" sand 
grains; grains which have surfaces covered with wart-like projections 11 
because of small particles 12 being embedded in the old bond coatings 13 
and 14. These projections interfere with the movement of the sand grains 
and the projections decrease mass flowability and response to ramming 
energy. Increasing ramming energy or pressure also results in problems 
because more particles with their shells are broken increasing the fines 
which also causes the sand mass to suffer. 
Rejuvenation by Dilution 
It was hoped, in the earlier years, that used sand from an old system could 
be kept within control if it received daily additions of fresh sand. The 
incoming fresh sand would serve to constantly dilute the system thus 
offsetting the influence of old sand and hopefully to offset the 
accumulation effects of various physical changes of the used sand. 
However, this has not proved successful because of the stringent 
requirements that are placed upon sand selection and physical condition of 
the sand for core room use. But more importantly, dilution requires a ton 
of used sand to be removed for each ton of fresh sand added to keep the 
system at more or less constant tonnage level. This creates considerable 
disposal problems and comes in direct conflict with governmental 
regulations which inhibit the dumping and burying of used sand carrying 
various types of chemicals. 
Reconditioning 
Reconditioning merely contemplates that the used sand will be passed over 
magnetic pulleys, through lump breakers and screens, and then aerated to 
remove fines. Unfortunately, reconditioning treats a sand mass as a whole 
and fails to materially affect the physical state of individual grains. 
Nothing is done to remove the old bond coatings on individual grains and 
the breaking up of compound grain formations. Thus, reconditioned sand 
cannot perfrom similar to new sand because nothing is done to restore the 
surface condition of the old grains. 
Wet methods 
Wet reclamation installations have failed to meet expectations in the past 
because their designers assumed the solvent action of water to be 
sufficient to remove "shells" from old sand grains. In actuality, it is 
not enough to just wash an old sand mass. The individual sand grains must 
be subjected to an intense wet-scrubbing action. Such an action can be 
obtained by pumping or mechanically agitating a properly proportioned 
mixture of used sand in water. Peak efficiency in wet scrubbing is never 
obtained because the maximum impact in abrasion between colliding sand 
grains cannot be fully obtained. The "shells" possess durability and wet 
scrubbing produces a continuous abrasion that smoothes and reduces the 
thickness of old bond coating, but never entirely removes all of the 
shells from the sand grains. Only by extremely lengthy scrubbing cycles 
can increased shell coatings be removed. 
Wet methods are particularly useful in removing the clay content of used 
sand, which becomes a chammote upon being used under heat. This dead or 
used clay content of the sand is water soluble. However, the greatest 
drawback of wet reclamation, and probably its principal reason for 
rejection, is that it requires a wet separation step to remove the debris 
and fines from the water solution. Wet separation requires huge settling 
reservoirs or ponds demanding extensive land usage which must be devoted 
to this technique of settling. Because of this the cost of land 
requirements for supporting such a system are prohibitive. Due to the 
solubility of clay in water, no satisfactory method has been devised to 
separate such Bentonite clays from the water solution except by settling. 
Thermal Methods 
Thermal or ignition methods are most helpful when attempting to reclaim 
sands bonded only with carbonaceous materials such as cereals, core oils, 
and resins. They have not been successful when applied to mixtures of core 
and molding sands containing varying amounts of clay binders. Various 
types of apparatus have been employed to carry out the thermal methods of 
treatment, including a roasting furnace, a fluid bed furnace and a rotary 
kiln. The thermal calcine system subjects the sand to temperatures in the 
range of 1200.degree.-1500.degree. in the presence of excess oxygen, 
thereby hopefully removing carbonaceous costings and organic binders. 
Regardless of the type of heating apparatus employed, it is rather 
difficult to heat all individual grains within a sand mass to the same 
degree in a continuous and uniform manner. When clay-containing sands are 
being thermally reclaimed, some grains receive just enough heat units to 
dehydrate, bake, and/or embrittle their "shells". Other grains, at higher 
temperatures, have their coatings more firmly attached to their surfaces 
because traces of basic oxides become fluxing agents and promote an 
incipient fusion of coatings to the grains. This higher temperature may be 
in part due to carbonaceous materials which are combustible, and create 
their own heat units. Thus, the destruction of some carbonaceous material 
may serve to free clay from some grains, but a concentration of heat units 
also contributes to a firmer adhesion of clay on some other grains. All of 
this results in some sand grains emerging from thermal reclamation with 
their clay shells still present, maintaining the influence of enlarged and 
irregular grain surfaces. Other grains emerge with their coatings 
susceptible to cracking when they encounter mechanical or thermal forces 
during subsequent cooling and/or reuse. If the embrittled shell separates 
from its grain during the preparation of the sand for core binding, such 
dehydrated particles will be difficult to wet and possess poor 
adhesiveness with the fresh bond. 
While the appearance of a thermally treated sand may be visually pleasing 
to the eye, because the color is a fresh whitish appearance, this is not 
indicative of its ability to duplicate the casting performance of new 
sand. There is evidence to indicate that complete destruction of 
carbonaceous coatings on individual sand grains contributes little toward 
satisfactory reuse in either cores or molds. But more importantly, thermal 
methods may change the electrostatic charge of the reclaim sand so that it 
never approaches the density and flowability of new sand. This may be due 
to the discharge of water and thereby hydroxl ions from the sand grains 
when heating above 1000.degree., such hydroxl ions normally sharing bonds 
with SiO.sub.2 ions. 
Dry Methods 
Mechanical methods comprise impacting sand grains to fracture the "shells" 
of old bonds from individual grains. There are several modes that would 
fall under the category of being dry, including (a) centrifuging sand 
against an enclosure; (b) a pneumatically shooting sand against a target, 
or additionally causing two separate streams of sand to intersect for 
scrubbing; and (c) mulling at low kinetic energy levels to squeeze the 
sand grains under pressure of a wheel. The pressure of mulling may crack 
certain shell segments, but it is almost impossible to treat all grains to 
a like degree. To be more satisfactory, small batches must be mulled for 
lengthy periods of time. While mulling removes some segments of the grain 
coatings, the remaining rough irregular surfaces are just as 
unsatisfactory as the initial "pickled" surfaces on unmulled grains. 
Each of these dry impact modes create new particle fines as a result of 
fracturing of certain of the sand grains, the amounts varying from 0.1% as 
a result of pneumatic methods, to as much as 1% by the mulling method. 
Each of these dry modes suffer some disadvantage, each being unable to 
separate a significantly high percentage of the shells regardless of the 
time of use of the apparatus. 
Combination Methods 
The above has indicated to the foundrymen through the years that each of 
the different types of reclamation methods provide a separate advantage. 
For example, organic contaminants respond well to a thermal treatment, 
whereas soluble contaminants respond well to a wet treatment and insoluble 
contaminants respond to a dry mechanical treatment. With this in mind, 
several of the more recent reclamation processes have included certain 
combinations of these different types. Thermal treatments have been 
combined with a subsequent wet scrubbing treatment or vice versa; thermal 
treatments have been combined with dry mechanical treatments (either of 
the centrifuging type or of the dry scrub type) and in certain instances 
have additionally been combined with a wet treatment. What these 
combination processes have failed to appreciate is the economic and 
governmental regulation deficiencies that are associated with such types 
and more importantly failed to recognize that different mechanical energy 
imputs are necessary to obtain a full range of cleaning benefits. Thermal 
treatments suffer from high energy costs and wet treatments suffer from 
the serious requirement for extended land usage and inability to meet 
governmental regulations on disposal of waste sludge, and dry mechanical 
methods have suffered because of an unsatisfactory product. 
Superimposed upon these considerations of economics, legal disposal modes, 
and technical ability to be reused as a foundry sand, is the technical 
criteria as to what is a satisfactory reclaimed sand product. Under the 
old production methods of preparing molding sand and curing of such sand, 
the criteria for judging successful use of the reclaimed sand was markedly 
less stringent than today. Today, the requirements, for accepting a 
reclaimed sand, demand that there be almost no metallics, an absence of 
organic impurities, an absence of lime, a density equivalent to new sand, 
a substantial absence of inert friable material (such as dead clay), and a 
Ph of 7-9. These requirements are impossible to meet with the present 
state of the art and still meet the Environmental Protection Agency 
regulations as to disposal, and do so at a reduced energy cost for 
processing. 
SUMMARY OF THE INVENTION 
A general object of this invention is to be able to take any type of used 
dirty sand from a foundry operation and produce a clean sand usable again 
for core making without the penalties of high thermal energy costs and 
land disposal problems. 
Specifically the invention is to upgrade used foundry sand by a method 
which is not selective or dependent on the type of contaminants present in 
the used sand, and by a method which will not be subject to the penalties 
of high economic costs related to heat energy consumption and not subject 
to the penalties of governmental regulation related to land usage and 
disposal of wastes, and which has the capability of producing a product 
which will cure rapidly in a core making operation equivalent to new lake 
sand and which will provide a predetermined Ph and low acid demand value 
indicative of the absence of clay and lime. 
A specific object of this invention is to provide an improved method for 
reclaiming used foundry sand that may contain binder ingredients from both 
core making and molding and operations, the method being carried out 
without the expense of employing heat and without the disposal problems 
associated with wet methods. The resulting product from such improved 
method is characterized by the substantial absence of fines (0.1% or 
less), a density of at least 100 grams/biscuit, a biscuit is defined in 
the AFS Handbook, 1963, a Ph of 7-9, an acid demand value of 15 or less 
(preferably less than 10) for sand that contains heat converted oxides, 
and a capability of performing in a core curing operation to provide a 
strength of at least 300 psi in less than 20 seconds as measured in a hot 
box core process. 
Features pursuant to the above objects comprise: (a) utilizing a totally 
dry method which in sequence employs a high stress, low kinetic energy 
cleaning cycle, followed by a high kinetic energy cleaning cycle 
accompanied by negative pressure for particle separation, (b) carrying out 
the high stress, low kinetic cycle by use of a sand muller which 
repeatedly squeezed sand under a high unit pressure of a weighted wheel, 
and (c) carrying out the high kinetic energy cleaning cycle by use of a 
pneumatic attrition device which shoots sand grains against a target by 
way of a high velocity air stream in the presence of a negative air 
pressure.

DETAILED DESCRIPTION 
Spent Foundry-Sand 
The origin and use history of spent sand determines its chemical content. A 
successful reclamation process must be capable of operating with spent 
sands that have varied origins and varied use histories. The spent sand 
may be derived from relatively pure new sand or impure below-ground new 
sand. Below ground sand deposits may contain considerable quantities of 
lime and magnesium carbonate. These impurities are usually removed by the 
sand mining operation by way of mineral flotation for the lime and by way 
of fatty acid techniques for the magnesium carbonate. Since pure natural 
sand is scarce and costly, new sand will be considered for this invention 
as typically comprising below ground sand that has been treated as above. 
Thus, when the natural sand is delivered, it usually contains impurities 
in the following ranges: 
______________________________________ 
Al.sub.2 O.sub.3 
5.2% Alkalies 1.7% 
Fe.sub.2 O.sub.3 
.5 SiO.sub.2 
90.6 
CaO .7 Clay 3-6 
MgO .5 
______________________________________ 
The impurities in this delivered new sand, of course, become a part of the 
impurities after the sand is used in the foundry technique. Impurities 
added to the sand as a result of the foundry practice usually fall into 
the following classes: 
(a) Molding sands contain clay in an amount of 3-6% by volume, powdered 
coal, alkaline materials such as active lime, and if the sand was employed 
in a shell molding process, it will contain 1.5-6% phenolics or other 
organic binding substances. The clay content of such molding sands may 
consist principally of bentonite which has a high floatability 
characteristic and is difficult to eliminate from a solution which 
attempts to dissolve it. Such sand is incapable of being reused in such an 
impure condition for a core making process. The impurities form a pickled 
coating on each of the sand grains inhibiting their flowability and 
bonding characteristics in a new core making process. 
(b) Used core sand may contain resins of the cold cure type, such as 
isocyanates, core oils, cereal binders, core washes, red oxide, or of 
three general hot box resin types which respond differently to thermal, 
wet and dry reclaiming techniques. One hot box resin type contains 
phenolic resins of the class consisting of hexamethylene, tetraamines, or 
novalac, and contains no clay. This core sand responds well to ignition 
techniques for elimination of the resins. Another hot box type is that 
containing phenyl formaldehyde urea. The third type contains furan urea. 
Each of these different types of hot box resins have a different removal 
characteristic, some removable more easily than others, i.e. furan urea 
has a tendency to be removed by scrubbing easier than phenolics. The resin 
content of the spent sand may range from 5-15%. 
For purposes of sand reclamation in this invention, used sand is considered 
as having some of all of the different additives. This assumption is 
necessary because most large scale foundries, such as that of the assignee 
hereof, are core intensive industrial users of sand. This means that new 
sand is primarily added to the core making area of the foundry and 
additional sand makeup, for the molding operations, is usually taken from 
used core sand. Thus, spent sand from the molding operations, which must 
be reclaimed, contains core making additives and molding sand additives. 
Moreover, some of the sand is calcined by being burned by the hot metal 
during casting. Since the total volume of sand will eventually circulate 
through the different industrial areas of the foundry, it acquires some 
degree of all of these additives; any successful reclamation process must 
be capable of removing impurities that are added by either the core making 
or molding process. Segretation of molding and core sands becomes 
virtually impossible because in removing the castings from a sand molding, 
invariably a certain percentage of the cores are broken and drop into the 
mold to become inadvertently mixed with the molding sand in a quantity 
that must be recognized. 
As shown in FIG. 2, spent sand grains 10 are characterized by their 
surfaces being covered with wart-like projections 11 due to small 
particles 12 being embedded in the old-bond coatings 13 and 14, which may 
consist of clay, oils, resins, carbonaceous material or oxides. Such 
projections 11 not only serve to greatly increase the total surface area 
of each grain, but by interfering with the movement of one grain past 
another, the projections decrease flowability and response to ramming 
energy. When the resistance offered by one or two grains is multiplied by 
thousands of grains, one comes to understand why old used sands are so 
difficult to ram into compact uniform mold surfaces. 
The size of the grain has a pronounced effect upon the amount of work which 
a reclaiming system is called upon to do and the degree of cleanliness 
which the reclaimed product will exhibit. As sand fineness increases, the 
amount of work necessary to reclaim waste sand increases; as sand shape 
changes from round to subangular and angular, more effort and energy is 
required to remove the residual coatings. 
Moreover, the exposure of sand to elevated temperatures results in varying 
linear and volumetric increases in the quartz crystal. Such exposure takes 
place in molding or core sands during pouring of molten metal. The sand 
closest to the molten metal receiving the greatest thermal change. This 
local thermal treatment not only affects resins or clays on the sand 
grains, but the grain themselves. 
Spent or used foundry sand, for which this process has been developed 
specifically, would typically contain the following constituents: 0-15% by 
weight of combustible elements (seacoal, cereal binders, core oils, red 
oxide, hot resins, cold cure resins, etc.); 0-12% clay; 0-3% water 
moisture; 0-10% metallic elements, resulting from metal spills on scrap 
metal; minor amounts of foreign matter which may exist as tramp material 
resulting from careless handling; 5-15% resins from scrap sand cores; the 
remainder being sand. With respect to the combustible impurities, seacoal 
usually is comprised of at least 30% volatile combustible matter, at least 
50% fixed carbon, 5% maximum ash, 1% maximum sulphur and less than 5% 
moisture. Bentonite, added as a collodial clay, contains about 55-62% 
silica, 15-25% alumina, 3.2-3.7 iron oxide, 1.5-2.3 magnesia, and less 
than 1/2% each of calcium oxide, potassium oxide, and sodium oxide. Red 
iron oxide is added in a finely ground form for retarding core 
collapsibility and for retarding the effects caused by sand expansion; the 
red iron oxide usually consists of 82-88% iron oxide, 7-8% silica and 2-3% 
alumina and some minor amounts of lime, magnesia and alkali. Mold sprays 
usually consist of carbon powder applied to the mold walls. Core washes 
usually consist of silica flour modified with a carbon base powder or clay 
and may have in addition minor amounts of dispersing and wetting agents or 
binders. 
A preferred method sequence for carrying out the invention is illustrated 
in FIG. 1 and is detailed as follows: 
(1) A charge of spent foundry sand is sized to AFS 43-53 utilizing a 
screening sequence, the sized distribution will 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 35-53.0 
100 mesh 5.0-15.0 
140 mesh 4.0 max. 
200-270 mesh .3 max. 
______________________________________ 
The spent foundry sand will contain a combination of both organic 
combustible ingredients as well as dead clay (clay that has been subjected 
to a heating cycle and fails to respond to addition of moisture for 
maintaining adherency between sand grains). The combustible organic 
materials will be in the range of 0.5-10% and will typically consist of 
oils, seacoal, resins of the formaldehyde urea type, furan type or alkyd. 
The clay content will range between 0.1-12%, a lime content, 0-3% moisture 
and 0-10% metallic bodies. 
(2) Either before or after the sizing step, the spent sand charge is 
subjected to a magnetic separator whereby tramp metallic bodies are 
removed and separated. 
(3) The sized and magnetically processed sand charge is repeatedly 
subjected, while under ambient pressure and temperature conditions, and 
while dry, to a low kinetic energy squeezing action effective to apply a 
high stress to fragment and burst at least part of the shells on 
substantially each sand grain in the charge or mixture. The force exerted 
upon the sand grains should be at least 300 lbs. This squeezing action can 
be imparted preferably by a mulling device. In a muller, a relatively 
large body of sand is pressed under pressure received from a mulling wheel 
which bears down upon the quantity of sand; the sand is continuously 
plowed so as to be displaced before being resubjected to the squeezing 
pressure. Mulling should be carried out for a period of 5-30 minutes, 
depending on the size and force capabilities of the device. 
The net yield in processing sand through a muller should be very high, 
typically close to 100%; that is, for every 1000 pounds of used sand that 
is processed in a muller, 1000 pounds comes out of the muller for further 
processing. The quartz crystals, of which the spent sand is comprised, are 
very hard and do not break down relatively easy as a result of mechanical 
impacting, as earlier believed by many in the prior art. Mulling does 
crack "shell" segments from the grain, but it is almost impossible to 
treat all of the grains to a like degree and most grains will remain with 
some shell fragments still attached. Fragments of the shells which remain 
on the grain will provide a rough irregular surface just as unsatisfactory 
as the initial pickled and unbroken shell surface. 
Mulling is very effective in removing live clay which will not come off 
completely by any other operative mode of sand reclamation. Live clay is 
defined as that type of clay which will react with water to rebond sand. 
Spent or dead clay is that which has been affected by heat cycling through 
a casting procedure whereby high temperatures have affected its ability to 
respond further to the addition of water. The presence of live clay, of 
course, is of interest to the foundryman in that its presence is 
detrimental to core making. Accordingly, if reclaimed foundry sand is to 
have universal application, it must be free of such live clay. 
Mulled sand will contain a heavy proportion of fines, approximately 1% or 
more. Fines are those particles which are defined to be in a size range 
below 200 mesh. Fines are not removed by the mulling process because of 
the low kinetic energy involved which fails to suspend such particles for 
separation. Fines are unsatisfactory if retained in the reclaimed sands, 
since they affect proper core making. 
Apparatus for carrying out mulling may be of the three general types (a) 
rapid mulling in which mulling wheels are eccentrically mounted to be 
urged by centrifugal force against upright side walls, (b) slow speed 
mulling in which the mulling wheels are held stationery while a crib is 
rotated to carry plowed sand under the weight of the wheels, and (c) a 
stationery crib in which hinged mounted mulling wheels are rotated about 
an offset axis, while being free to rotate about their own wheel axis, to 
press plowed sand residing beneath the wheels. The mulling device found 
most useful to carry out the present invention is that shown in FIG. 3. 
Tandem rollers 20 and 21 are pivotally supported on arms 26 and 27 
respectively, which carry spindles 22 and 23 respectively for rotary 
movement of the wheels about their own central axes. The arms are pivotal 
about axes 28 and 29 respectively. The axes 28 and 29 are rotated as an 
assembly by a power rotated post 24 and carriage 25. Each wheel, 20 or 21, 
should weight at least 300 pounds but not more than 700 pounds. One side 
of each wheel is located adjacent the crib side wall 30 so that sand 
build-up along the outer periphery of the base is moved under the wheels. 
Plows or scrappers 31 and 32 peel up the compacted sand from the floor 33 
and reposition the grains for squeezing and kneading along a radius that 
will encounter the wheels. 
(4) The mulled sand is repeatedly subjected, while in the presence of a 
suction (negative pressure) to a shooting action against a target. The 
sand is propelled by a stream of air to impart high kinetic energy, the 
stream delivering between 1,000-10,000 lbs. of sand through a discharge 
opening having a diameter between 0.6-2 inches, whereby the remaining 
fragments of said shells are dislodged and any particles finer than 200 
mesh are separated by said suction. 
This step can be carried out by a pneumatic attrition device as shown in 
FIG. 4. Essentially, it consists of an air delivery system (40-41), a 
containing shell 44, an air nozzle 43, a bottom flared (45) center pipe or 
tube 42, a conical target 47, an expansion chamber 53, and an exhaust 
duct. 
In operation, the unit is charged with a batch of used sand at 54. Air from 
a positive-pressure type blower 41 is introduced through the high-velocity 
nozzle 43. 
The elongated portion of the containing shall 44 surrounding the 
center-pipe 42 (which has been termed the "well") is so designed for a 
purpose. By concentrating the weight of the charged sand on a small 
horizontal area, sufficient vertical "sand-pressure" is developed to 
overcome the static pressure of the air stream after it leaves the nozzle 
43 and before it enters the center-pipe. This "sand-pressure" confines the 
air-stream to passing upward through the center-pipe, and prevents 
"blow-backs" along the exterior of the center-pipe and upward through the 
"well". The "sand-pressure" also forces sand into the high-velocity air 
stream, and ensures a consistent loading of the stream at a maximum rate. 
As sand is forced into the space 46 between nozzle and center-pipe, it 
becomes entrained in the air stream, and is hurled upward through the 
pipe. It emerges at the top of the pipe with considerable velocity and 
collides with sand 50 trapped in the peak of the conical target 47. 
The conical target possesses the ability to hold an ever-changing, yet 
more-or-less constant, mass of sand within its peak. The mass is held in 
position by the upward force of the sand/air mixture emerging from the 
center-pipe. Sand grains continuously escape from around the circumference 
of the conical mass while new grains are being added to its center. The 
net result is that most of the metal target is continuously covered with a 
layer of sand; and sand grains impinge upon sand grains - not sand grains 
against metal. 
After emerging from the center pipe and colliding with the sand mass 50 
trapped in the target peak, the sand/air mixture is deflected outward and 
downward by the skirts of this target cone. The sand separates from the 
air and returns by gravity to the main sand mass lying in the bottom of 
the containing shell. The air flows outward and upward around the edges of 
the target and escapes from the shell via the exhaust ducts in the upper 
walls. The enlarged upper portion 53 of the containing shell serves as an 
expansion chamber, the mixture being permitted to suddenly expand after 
emerging from the center pipe/target cone area. The high velocity air 
stream is converted to slow moving air currents which rises outside of the 
cone. Such currents are unable to retain most sand grains in suspension; 
however, particles 51 of fragmented bond and silica that are of a fine 
size, are air floated to remain in suspension and be carried out of the 
containing shell with the escaping exhaust gas. 
In each cell the sand is deflected by the conical target 47 and piled up 
along the exterior walls 44 of the cell; the sand then flows inward and 
downward into the well surrounding the cell center pipe. Flow in this 
manner creates a steeply slopping upper sand surface 60 in the shape of an 
inverted cone or vortex, in each cell. Because of this natural feature, 
baffles are not needed in the cells to prevent sand grains moving directly 
from inlet opening 54 to outlet opening 55. As sand grains enter and fall 
into the vortex in a cell, they must be cycled one or more times in that 
cell before target deflection places them in position to escape through 
the opening 55 to the next cell. While the conical target is deflecting 
sand from all points on its circumference and the deflected sand is piling 
up along all of the exterior walls of the cells, only the sand grains that 
fall immediately onto the shelf 56 in front of the limited opening 55 
escape to the next cell during any one cycle. The sand grains that do not 
escape must, of necessity, continue to recycle until they are fortunate 
enough to fall in front of the opening. 
It is important to carry out the high kinetic energy impacting for a period 
sufficient to cleanse each particle. The yield from pneumatic dry 
scrubbing can be about 95% if a 4000 lb./hr. delivery tube is employed. 
The yield drops somewhat as the capacity of the device is lowered. The 
quality of sand affects the scrubbing period to some degree. For more 
severe applications such as coarse sands, it may be required to carry out 
the dry scrubbing for as long as 45 minutes per batch. 
The construction of a continuous pneumatic reclaiming unit would comprise 
several batch units combined in each sequence to provide at least four 
units or cells using a common expansion chamber 53, exhaust and intake 
systems 41. Through a receiving tank and the manifold 41, a single blower 
40 supplies air to all the cells 1, 2, 3 and 4. In each four cell 
sequence, continuous flow is achieved by connecting the cells together in 
a step like fashion. Openings permit sand to flow from feed hopper 54 to 
cell #1, cell #2, cell #3, and cell #4 to discharge. Sand flowing from 
feed hopper into the #1 cell raises its level beyond a set height and it 
is forced to overflow into the #2 cell. #2 cell in turn is forced to 
overflow into #3 and #3 into #4 and #4 into the discharge unit. 
The mulled and scrubbed sand is then subjected to classification to 
separate the burst shells from the sand grains and to size the sand 
grains. This may be carried out by conventional series of sieves or by air 
separation in a cyclone chamber.