Note: Descriptions are shown in the official language in which they were submitted.
i~ ~
1 3267
3 SILICAT~ TREAT~JENT OF
4 ïMPURE SILICA SA~DS
7 FIELD OF THE I~VEI~TIO~
9 This invention relates to silica~-containing foundry
sand alld to a process for t;reating silica.-contaill:LnF~:roundry
11 Salld W:i.t}l all alk,ll~. metal S~ i.C.lte to l~llprove the ~ensi~
12 strength of foundry cores or molds Inade from the sand.
13
14 BACKGROUND OF THE IhVENTION
16 In the foundry art, cores or ~nolcls for makin~ rnetal
17 castings are normally prepared frorn a r)-Lxture of an aggregate
1~ rnaterial, such as sand; and a bi.ndi.ng amoullt of a binder or
19 binder system. Typically, a.fter the ~ggregate rnateri.al and
binder have been mixed, the resulting mixture is rammed,
21 blown or otherwise ~ormed to the desired shape or pattern
22 and then cured with the use of catalysts and/or heat to a
23 solid, cured state.
24
A variety of different processes for forming molds
26 and cores have been developed in the fo~ndry industry. One
27 type of process kno~n as the shell moldin~ process, is ~ell
28 known in the art. While there are man~ variations of this
3
~1~'32
1 process, the process essentially comprises depositing a
2 corr~bination of sand and potentially thermosetting resin
3 against a heated pattern such tha~ the resin melts and
4 cures to form a rigid shell mold or core section for use
in the casting of metals. The combination of resin and
sand used in the process can be a mixture of powdered resin
7 and sand, or a free-flowing coated sand in which each grain
8 is coated with a nontacky layer of resin.
The product:ion Or a core or rnold hy the shell
11 proces'i :invo].ves t~o basic st;ep~" I}~e lnves~ arld the e~ ne
12 step. In the first step, the resin-coated sand is dulnped
13 onto or blown against the heated metal pattern. T~e
14 resin-coated sand is held against the pattern (invested)
until the shell is thick enough to hold ~netal in a given
16 application. In the second step, the resin-coated sand is
17 dumped or dropped away from the shell of bonded coated
18 particles o~ sand and the resulting shell is cured. After
19 the shell is cured, it is removed from the hot meta~ pat1;ern
and is ready for use.
21
22 Another process, known to the art as the t'no-bake"
23 process, is also used in I`orming resin cores. This process
24 requires no external heating. Instead, curing is accomplished
by means of a catalyst added just beI`ore the sand and resin
26 components are introduced into the core box. Base-cured
27 resin components used in the no-bake process are generally
28
29
3~ -2-
f
1 m tures o î poly~ls and polylsocy2nat~s. Solutions o r these
2 components are usually coated on ~he sand immediately before
4 use.
A third process for making cores and molds employs
6 sands treated with core oil mixes. These mixes contain drying
7 oils and cereal binders. Cores and molds made with such core
8 oil mixes are cured by baking them in an oven.
.In all of thec;e processes, t}l(:' bl11d~r W~ Ch }laS be~n
1l n~ ed wi1;h sand ac~s, whel1 cured, to b:ind tlle particle!~ of s,ancl
12 in the form of the pattern. The core or mold mus~ be strong
13 enough to contain the rnolten metal until it solidifies. For
14 this reason, a core or mold with high tensile strength is
required.
16
17 One factor influencing t;he tensile strength of the
lo cores and molds -is the quality of the sand usecl in the:ir
l9 preparation. When a silica sand is ernployed, it is generally
necessary to use a sand Or high purity. In the past~ when
21 silica sands of lower purity were used, it was necessary to
22 add large amounts of binder to ensure structural integrity
23 of the mold. This was not only costly but led to other
24 undesirable results when gaseous decomposition products of
the excess resin penetrated into the molten or solidifying
26 m t l resu~ting in yinholes lnd scarring of the metal shspe.
-3-
9~
_ ll Impure silic2 sands, such 2S lake and bank sands,
2 ¦ are readily available in many areas of he United States.
3 These impure sands are sometimes beneficiated by various
4 processes such as water washing. However, it is still
necessary to use excess binder with the washed sands to
6 obtain t;he desired tensile strength Or the cores and molds
7 made from them. It is therefore desirahle to develop a
8 process whereby these inexpensive sands can be used to make
9 foundry cores alld molds wi.thout the necd to use excess b:inder
1~ ~ tl~ s~ d.
:1.1
12 Bushey described a method for treating zircon--
13 containing sands, U.S. Patent 4,115,345~ and olivine sands,
lLI U.S. Patent 4,154,894, with an alkali metal silicate to
improve the tensile strengths o~ resin shell molds or
16 cores made from the sands. Hcwever, he reported that when
17 this method was used with si.lica and chromite sands, no
18 improvement in the tensi].e str7ength Or t;he cores and Inolcls
19 was observed.
21 A process has now been discovered which permits
22 the use Or impure sil.ica sands in conjunction with moderate
23 amounts of binder to form foundry cores and molds with
24 improved tensile strength. This process is less expensive
thall present beneficiation methods and gives cores and molds -
26 with improved tensile strengths.
28
29
3 -4- __
~, . ..
l A further unexpected benefi~ of ~lsing these treated
2 sands .is t~at cores prepared from t}~em by the b2se-curing
3 "no-bake" process are more readily released from the core
4 box. Easy release Or the cores is commercially important,
since sticking cores slow down i,he core-making process and
6 often become broken and useless.
8 SUMMARY OF THE INVE~TION
In accordance W:it}l thi.s :imven1.:Jon, therea is
ll provi.deA a process for th~:? prepar'.ll;i.on o:f` t~"eal;~i'd ~:Li.i.ca
12 sand which is useI`ul for formillg foundry cores and molds
13 having improved tensile strength. The ~rocess comprises
14 treating an impure silica sand with an aqueous solution of
an alkali metal silicate and heating the mixture of sand
16 and silicate.
17
18 Adclitionally,~in accordance with this invention,
19 there is provided a process for the pr~paration Or a
molding composition useful for forming foundry cores and
21 molds having improved tensile strength. The process
22 comprises treating impure silica sand with an aqueous
23 solution of` an alkali metal silicate and heati.ng t~ie
24 mixture of sand and silicate. The treated sand i.s then
mixed or coated with an effective bonding amount of a
26 binder selected from the group consisting of shell resins,
27 base-curing "no-bake" resin compounds and core oil mixes. .
28
29
3 -5-
' ... .... ..'. ~
(
1 ?urthermore, in accordance with this invention,
2 there is provided silica four!dry sand useful for making
3 foundry cores and molds with i~proved te~sile strength.
~ This is prepared by treating impure sili^a sand with an
aqueous solution of an alkali metal sili~ate and heating
6 the mix'ure of sand and silicate.
8 Finally, in accordance with th~s invent:ion,
9 there is pr~ovided a rnolding compositiorl use:ru]. for
~.n p~p~r illK r~O~,n(~ry (~ eS ~ rno~ 3 llav~ r~ vt~ ?llS~
ll strength. Th-is cornpos:i~iorl colllp~lise-s an 9rlL)u:Le sili.ca
12 sand, which has been treated by heating l~ith an aqueous
13 solution of an alkali metal silicate, and an effective
14 bonding amollnt of a binder. The binder is selected
from the group consisting o~ shell resin~ base-cur:~ng
16 "no-bake" resin components and core oil ~ixes.
17
18 DF.TAILF.,D DESCR:r.~:'T:[C)N C)~ L'III', INV:E~lr~':.l-C)
19
Any impure silica sands may be used in the practice
21 of this invention. Examples of such sands are lake and bank
22 sands which generally consist of from a~ut 85% to about 98%
23 by weight of silicon dioxide and small a~ounts of` sllch
24 impurities as aluminum oxide, iron oxide~ alkaline oxides
and alkaline earth oxides. The impure s~ica sand can be
26 a naturally--occurring silica sand or a m~ture Or various
27 silica sands. The processes of this inve~tion are useful
28
~9
3 -6-
;
¦1 ir the sand or mixture of sands contain ~ess than about
2 ¦ 99~D silicon dio~ide.
4 Commercially available lake and bank silica sands
include 20KK Sand, available from the Martin Marietta
6 Corporation, Bridgman, Michigan; Ludington Sand, available
7 from the Sargent Sand Company, Saginaw, ~qichigan; Muskegon
8 Sand No. 850 and Beneficiated Muskegon Sand W~51, available
9 ~rorn the Nugent Sarld Company, Muskegon, ~1-ichigan; and
].0 Vassclr ,',and, available from the Sar¢ent; Sa1ld ~omparly~
11 Sa.g:irla~ M:ichi.~ rl.
12
13 In the process of this invention, the impure
14 ~ silica sand is treated with an aqueous solution of an
alkali metal silicate. Treatment may be carried out ~y
16 stirring a slurry of the sand in a dilute silicate solution.
17 It is often satisractory to treat the sanA with a more
18 concerltrated silicate solution by placin~ the sand in
19 a rnixer and adding the required arnoul1t of s~ icate solution
to the sand with mi~ing. Alternatively, the silicare solution
21 may be sprayed onto a thin layer of the sand.
22
23 Any alkali metal silicate, such as sodiurn and
24 potassium silicate, can be employed in the process of this
invention. Solutions of sodium silicate are commerclally
26 available. Such solutions contain varying ratios of
27 sodium oxide to silicon dioxide. These ~eight ratios may
28
29
3 -7- __
~ ,.
. .
Ij )
1 ll vary fro~ 1 to 4 ~arts of silicon dio~ide per 1 part of
2 sodium oxide. The amount of water present in the alkali
3 ¦ metal silicate solution is not critical. However,
4 ¦ sufficient water should be present to permit adequate
dispersion of the silicate over the surface of the sand
6 grains.
8 The amount of alkali metal silicate used with a
9 given sand should be an arnount that effecti.vely imparts
the desi.red strength to the cores OI' mo].ds without .
11 i.nter~Ierintr w.i.th the f.ree I.l.ow:i.nrr properl;ies o.~ the
].2 s:i.]lcate-l;rea.~ed sarltl. l:~ :1s ~ re.t~.rl,7ed to U'iC .E'I'Oln abOllt
13 0.2 to about 1.1 g of silicate on a dry sol:i.ds basis per
14 kg of sand. .
.5
16 hfter the silica sand has been thoroughly rnixed .
17 with the silicate solution, the sand may be iso].ated from
18 the slu.rry by any conventiona]. means such as decantation
19 or filtration. However, whell the more concentrated
solutions of silicate are employed, no rnechanical separation
21 of the sand from the silicate solution is requi.red. It is
22 only necessary to heat the sand to about 100C, or above,
23 for a short period of time to evaporate a portion of the
24 water and provide a free-flowing sand for use in the coating
process. This simplifies the process by avoiding a
26 decantation or filtration step.
28
29
3 -8- _ _
~ ,, ' . .
Al-ternatively, the sand can be preheated before
the silicate solution is added to it. Mixing is -then
continued until the water is evaporated.
The silicate--treated silica sands of this i.nvention
are used to make foundry molds or cores using the procedures
practi.ced with pure silica sand. In generall these processes
involve mixincJ the sand w:ith t-~:E:Etect:ive borld~ g amoullts oE
b.Lndters. Usua:l.ly, l:ht-' components oE t.htl. b~ 5tlees aro co,lted
on the sand to insure the:ir un:i:Eorm cllstr:ibllt:i.orl,
Details of the preparation and use of resin-coated
sands in the shell molding process are given in U.S. Patent
3,833,095. Illustrative of "no-bake" processes, using
base-curing polyure-thane resin components, are U.S. Patents
3,409,579 and 3,429,848. The use of core oil m:i.xtures as
:Eoundry core b:inders is described in U.S. :Patent 2,375,073.
Suitable resins for use in the shell-moldlng process
include phenol~formaldehyde novolak resins which become
-thermosetting when hea-ted in the presence o:E a curing
agen-t. Hexame-thylene-tetramine is a satisEactory curing
agent for these resins. Single-stage phenol-
:Eormaldehyde shell resins which require no added curi.ng
5' ,. ,~
/'''~
'.;: ,~,.~
- j! agellt can also be used. ~oundr~ sanc, l~hich has been ccateu
~ I or ~rixed ~ith resin is pldced in 2 nlolc ana heeted to cause
3 ¦ the resin to haràen rormin~ a shell of resin-bonded sand.
4 ~-lhen the silicate-treated silica sand of thls invention is
used as the sand component in the mold, the resulting mold
6 shows considerably improved tensile strength over the molds
prepared using untreated impure silica sand at the same resin
8 loading.
Re;ill cornponent.s useflll in the no-ba~;e~ ~roces~ ilr~
1] polyols aorl pvlyisoc~yilna~es- A var:iety o;t ply~s c;ln i
12 used~ but resole-type phenolic resins are often employed.
13 These are usually dissolved in a solvent mixture and mixed
llJ with the sand. Polyisocyanates, either as liquids or in
solution are also added- Then a basic catalyst i;s added to
16 the mixture just before it is p~aced in the mold. It cures .
17 without heatirlg. Tertiary amines are commonly useà as the
18 basic catalysts. l~hen t;he sil:icate-treated silica sand
19 of this invention is used -in the ~ase-catalyzed "no-bake"
process, the resulting cores show better tensile strength
21 and better scratch hardness than do cores prepared from
22 untreated impure silica sand- Cores prepared ~rom the
23 treated sand are also ea5ier to remove from the core box.
~4
26
27
28
29
3 10- --~~
~ , ' . .
It is ol~en tne practice in the foundry ar~ to
~ ¦ include G varietv ol` additi~es in the resins used to
3 ¦ prep2re foundry cores and molds. These additives include
4 such ma~erials as silanes, sources of fluoride, deodorizing
agents and the like. Such additives may be used with
6 resins in the present process and do not interfere
7 with the improved tensile strength of the cores and molds
8 obtained from the sands of this invention.
The I`oll owinfr e.xa1-rlples illustrate t,he :inver]t;:i.on.
11 lt is to be understoocl that the e~:alnples are ill.ust:ratlv~
12 only alld do not intend to llrnit the invent:loll in any way.
13 In the examples, all parts and pe-rcentages are by weight
14 and the temperatures are degrees centigrade unless otherwise
indicated. All tensile strengths are given in p~unds per
16 square inch (psi).
17
18 E.XhMPL~_l
19 .
An aqueous solution contai.ning 2.8 g/l of sodium
21 silicate was prepared by mi.xing with 10 1 of water 73 g Or
22 a sodium silicate solution available from the Diamond . ..
23 Shamrock Corp., containing 9.1% by weight of Na2O and 29.2%
24 by weight of SiO2. Five kilograms ol 20KK silica sand
was added to the silicate solution a.nd the mixture was
26 stirred for 40 minutes. After stirri.ng was stopped, the
27 sand was allowed to settle for 30 minutes before the
29
3 ~ . . -- .
~, "
213~ ~
I liquid was decanted. The sand was then dried at 121C
2 11 overni~ht. A l-kg sample ol tne trea-ea sand WGS neatea
3 ~o 128~C and added to a Hobart i~i~er. After 30 g Or
comrnercial novolak roundry resin was added to the mixer,
1 5 the mixture of resin and sand ~as blended for 90 seconds
6 to melt the resin and coat it onto the sand. Then 14.4 ml
7 of a 27.6% solution o~ hexamethylenetetramine in water
8 was added to the mixer. Blending was continued until the
9 mixture broke up into free-flowing grai,ns of resin-coated
sand.
11
]2 This procedure was repeated using I,udington,
13 Beneficiated Muskegon W/51 and Wedron 7020 silica sands.
14
Cold tensile and hot tensile strengths of test
16 specimens made from each of the coated sands were measured
17 as fo]lows: ,
18
19 The hot tensile strengths were determilled by use
of a Dietert No. 365 Hot Shell Tensile Tester. Tests were
21 run at 232C with a 3-minute cure time.
22
23 , The cold tensile st:rengths were determined by
24 making 1/4-inch thick "do~-bone" test briquets in a ,
Dietert No. 363A Heated Shell Curing Accessory. The
26 test briquets were cured for 3 rninutes at,232C and
27 allowed to cool to room temperature. The cold tensile
28
29
3 -12- ~=
., , ', ..
~ ll strength of each ~riquet was determined by using a 401
2 I ~ni-~/ersal Sand Strength Tester in the rnann~r set forth
3 by the American Foundryman's Society.
Results of tests using the various silica sands
6 are given in Table I.
8 CO~TR_L TEST I
9 ~ .
The untreated sands used as starting materials
11 in Example 1 were coated with novolal{ resin according to
12 the proceclure o:~ ExalllpIe .1,. Tlle hot an~l co:l.d tensilc
13 st;rerlgths of' cores ma(1e rrc)ln thec;e res:in~-coatecl .~ r-ld~s
14 ~Jere likewi.se tes~ed by the procedure oI' that exarrlple.
. Results of these control tests are given in Table I.
16
17 CO~TROL TEST 2
18 _ __ __
19 EaGh of the sands used in Exarnple 1 was washed
aild dried using tlle same general procedure o~ Exalnple 1
21 except that no sodillln si].icate was added to the washwater.
22 The washed sand was coated with novolak resill follo'wing
23 the procedure of Example 1, and hot and cold tensile
24 strengths were determined ~or cores made from these
resin-coated sands. Results of these control tests are
26 given in Table I.
27 .
28
29
3 _1~_ .
. ' ` . .
~ ~3~3~ ,
~ hese results show that impure silica lake sands
2 1l ~ive fourdry cores and rnolds with improved tensile strengths
~ if they are treated with a silicate solution before they
4 are coated with a ~oundry resin. In contrast, cores and
molds made from resin-coated, silicate-treated pure silica
6 sand show no improvement in tensile strength over those
8 prepared from untreated pure silica sand.
23
28
29Z
T.~ 3LE
2 ..
O~re Prc)ptrties
3 Hot Cold
Tensile Tensile
~ Sand Type Treatment ~psi~
20KKa) Untreated (Control Test 1) 27~ 400
l~ater washed (Control Test 2) 363 q59
6 Silicate treated 432 525
7 Ludingtonb) Untreated (Control Test 1) -l90 230
Water washed (Control Test 2) 230 250
8 Silicate treated 335 345
9 BeneFiciated Untreated (Control Test 1) 297 353
Mllskegon W/51C) l~ater washed~Control Test 2) 2t34 3~
Silicate treatecl 377 fi50
:ll Wedron 7020~l) Untreated (Cont:rol Test 1) 352 465
~later ~ashed (Control lest 2) 304 500
12 Silicate treated 300 500
13
a) A lake sand available from the Martin Mariet~a Corp., Bridgman,
14 Michigan, containing about 94% SiO2 and smaller amounts of
A1203 plus alkaline oxides and alkaline earth oxides.
b) A lake sand available from the Sargent Sand ~n., Saginaw, Michigan,
16 containing 96.2% SiO2 and smaller amounts of Fe203 and A1203 plus
alkaline oxides and alkaline earth oxides. The untreated sand
]7 contained 7.3 ppm (parts per million) sotl;ul-n; the silica-treated
18 sand contained 94 ppm soclillrn.
c) A washed and dried lake sand available From the Nugent Sand Co.,
19 Muskegon, Michigan, containing about 95% SiQ2 and smaller amounts
of A1203 plus alkaline oxides and alkaline earth oxides.
d) A pure silica sand available from the Martin Marietta Corp.,
21 ~ We r n, Illinois, containing over 99.8% SiO2.
26
23
_lr_
2 _Y~M?L_ ~ ,
3 An a~ueous solution of sodiu~ silica~e was prepared
4 by adding 12.6 g of the co~ ercially available sodium silicate
solution used in Example 1 to 200 g of wateI. A mixture of
6 25.7 g of the silicate solution and 1100 g of 20KK sillca
7 sand (0.53 g sodium silicate per kg sand) W2S mixed in a
8 Hobart MiY.er at, room temperature for 12 minutes before it
9 was dried overnight at 232C. Gne thousalld grarns Or the
t;reated sarld was coatecl with 30 g oI' p~-lcllo]ic no~olak
:Ll rc~ in .~ L~C, ~nc~ rll o~ ,~ 27.G% }~ y:].~ J~
12 solution was added according to the procedure of Example 1.
13 Hot and cold tensile strengths were determined for cores
14 prepared using the resin-coated,sand.
16 This procedure was repeated using Muskegon 850
17 and Vassar sillca sands.
18
19 Reslllts of the tests are reported in Table II.
21 For control tests, untreated 2OKK, Muskegon 850
22 and Vassar sands were coated with phenolic novolak resin and
23 he~amethylenetetrarnine solution. Hot and cold tensile
24 strengths were then measured on cores prepared ~rom these
coated sands. The results of these control tests are also
26 reported in Table II.
27
28
29
3 ' -16-
. ' "
3~
I '
li ,
- T
_Oo~^e Pr~perties_
4 Hot Cold
Tensil eTensile
Sand Type Treatrnent 1~5~;~ (psi)
20KKa) Untreated (Control) 251 278
Silicate treated 373 381
7 Muskegon 850b) Untreated (Control) . 242 299
8 Silicate treated 303 350
9 Vassar SandC) Untreated (Control) 165 215
Silicate treated 213 257
11 a) A lake sand available from the ~artin ~arietta Corp., Bridgman,
l~ichigan, containing about 94% SiO2 arlcl slnal l~r alnounts of
12 A1~03 l~lus alkaline oxides and all;aline earl:~ oxicles~
13 b) A bank sall(l conl:ainin9 about 91% SiO~ arl~l srnall~r amOllll~.S oF
A1203, Fe203, and alkaline oxides avc;ilable frorn l:he ~uycrlt
14 Sand Co., Muskegon, Michigan.
c) A bank sand available from Sargent Sand Co., ~;agina!~l, Michigan,
containing about 90% SiO2 and smaller amounts of A1203, Fe203,
16 ~ alkaline oxides and alkaline earth oxides.
17
18
19 This experilnent demonstrates that sllica sands
can be treated wi.th a si].:i.cate solut;1.on -ko give ir~lproved
21 :~oundry sands and that i.t ls unnecessary to sepa:rate the
22 silicate solution mechanically ~rom the ~reated sand.
26
28
29
3 . -17.- _
. ,.
. .
3~
1 EXAMPLE 3
3 Sand mixtures were prepared l~sin~ various proportions
4 of Wedron 720, a pure silica sand, and 20KK~ a lake sand
containing about 94~ silicon dioxide. The mixtures, which
6 contained from 96.4 to 99.~% silicon dioxide, were trea~ed
7 with sodium silicate solutions by the procedure of Example 2.
8 Both treated and untreated sands were coated with novolak
9 resin according to the procedure of E~amp].e 1. Hot and cold
tensile strengths ~ere measured on cores prepared ~`rom these
11 coated sands. Results of these tes-ts sho~Jed that sillcate
12 treatlllent i.s er~ective ln irnprovlng terlsi.le propert.ies Or
13 cores made ~rorn sancls containinf-~ less than about 99% s~ll.con
14 dioxide.
:L6 EXAMPLE 4
17
18 The general p.rocedure of Example 2 was repeated
19 with 20KK silica sand using amounts of sodium silicate
varying from 0.11 to 1.79 ~ of sodium si]icate per kg of sand.
21 Hot and cold tensile strenet}ls were obtained .ror cores
22 prepared from silicate-treated sarlds which had been coated
23 with novolak resin. These tests showed that the impure sillca
24 lake sand gave foundry cores with improved tensile strengths
if the sand was first treated with between about 0.2 g and
26 ~ ~.1 g of s ium silicate per kg Or sand.
28
29
3
1 EXA;~I`L_ 5
3 In this e~periment, 45.5 kg of 2GKK bank sand was
4 placed in a cement mixer. To the mixing sand was added an
aqueous solution of sod-i.um silicate prepared by mixing
6 63 g of the commercially available sodium silicate solution
7 used in ~Y.ample 1 with 1000 g water. Mixing was continued
8 at room temperature for 90 seconds before a gas flarne was
9 applied to the mixture. Heating was continued unti] the
temperature of the mixture reached 166C. The hot treated
11 sand was transferred to a Mull.er Mixe:r and coatecl with
~2 phel1olic novo:l.ak resin at 1 28C u~:,i.ng the ,sarne rel.atlv~
:1.3 l~oporl;ior]s oI':resl.n, hexalnet;hyl.enetetrarlli.ne and ~;rlrld ~s
14 used in E~ample 2.
16 In a control experiment, un~reated 2 OKK ~ank sand
17 was heated to 180C, transferred to.a Muller Mixer and
18 coated with phenolic no.volak resin by the same procedure
19 used to coat the treated sand.
21 Cores were prepared frorn the t:reated c:oated sand as
22 well as from untreated coated sand which was used as a
23 control. Hot and cold tensile strengths of t~e cores were
24 measured by the standard p:rocedures. Silicate-treated
coated sand gave cores which sho~ed a hot tensile stren~;th
26 of 468 psi and a cold tensile strength of 471 psi. These
27 values compared ~ith a hot tensile strength of 336 psi and
28 a cold tensile strength of 362 psi for cores prepared from
29 the untreated coated sand~
-19- _
' '.....
: i
l,
¦ Tnis e~periment sho~^~s that the procedure of this
¦ invention is readily scaled up to a commercially acceptable
3 process without the need for rnechanical separation Or the
4 silicate solution from the treated sand.
6 EXAMPLF 6
8 An aqueous solution of sodiurn silicate was prepared
9 by di].uti.ng 17 g of a sodi.urn silicate soluti.on available :from
LO thf' D:i.alnol-ld '~hamrock Corp. corJtaini~g G. 7% N~20 al-ld 25.~3%
.1.1. Si.02 with 196 gr c~ 'lat~.?:r'. 'rh:i.S 5011.1t;:i.0n ~t:l'i li,S~.`d tC~ t;l='l~?al;
12 Vassar sand according to the procedure O:r Example 2 and test
13 cores were evaluated as described in that example.
14
Foundry cores prepared with silicate-treated sand
16 showed a hot tensile strength Or 253 psi and a cold tensile
17 strength of 270 psi. These values compared with a hot
18 tellsile strength of 165 psi. and a col.d tensi.le s~rengt}l of
19 215 psi for the control sand which had not been txeated w:i.th
silicate solution.
21
22 _XAMPLE 7 - ..
23 .
24 A mixture of 1000 g of 20KK silica sand, treated
with sodium silicate solution as in Fxample 2 and 30 g of
26 701 Liquid Shell Resin (a single-stage shell resin solution
27 available from the Acme Resin Corporation Forest Park
28
29
3 -20~ = .
.. ..
` ll Illlnois, havingr a pH of 3.5 ~o 4.5, a viscosity a~ 25~C of
2 3500-4500 cps and a solids conten~ of 72% to 75% by weight)
3 ~as mixed in a Hobart Mixer for 3 minuves at 149C. Then
4 14 ml of water was added .,o cool the coated sand and cause
the sand to break up into individually coated grains.
After the individual grains had forrned, 1.2 g of calcium
7 stearate was added and mixing ~as continued for 1 minute.
8 Hot and cold tensile strengths of test specimens prepared
9 from the sand were determined by the procedures described
in Exarllple 1. The hot tensile strerlgth of the .specirnerls
11 was 1ll0 psi and the cold tellsiLe streng~ was lllO ps~.
.1.~
13 Control tests performed using untreated 20KK sand
14 gave specimens showing 100 psi cold tenslle and 270 psi hot
tensile strengths.
16
17 These results show that co:res prepared using
18 silicate-treated sand coated with sing]e-stage shell
]9 resins have improved hot and cold tensile strerlgth over
cores prepared from untreated impure sand.
21
22 _AMPLE 8
23
24 This is an example of a "no-bake" foulldry process.
Silicate-treated 20KK bank sand was prepared as in Example 5.-
26 TQ 2500 g of the silicate-treated sand in a K-45 Kitchen
27 Aid Mixer was added 17.2 g of Acme Bond 5022 polyol, 14.1 g
2~
29
3 -21- --
.~ ,.
~ r3~
1 of ~cme ~ond 506~ polyisocyanâte and 0.63 g Or ~cme Bond 5082
2 basic catalyst. The Acme Bond componenls are available~ from
3 the Acme Resin Corporation ~orest Par~ Illinois Sand and
4 resin comDonents were mixed for 1 minute and discharge-d into
a Dietert No. 623-50 pyramid core box. The sand was jolted
6 4 times using a Dietert No. 623 core box jolter. A thermometer
7 was inserted about 6 inches into the core. The stripping
8 time is the time it takes to cure the core so hard that the
9 thermometer can no longer be pushed by hand deeper into the
core. Strip time was determined to be 5 minutes 15 seconds.
:1.1 .,
12 A s~corld ide?-lt;ical -lnd-re;:in lllix ~as prep~r-ed an~l
13 discharged i.lltO a Dietert No. 696, l2-frJlrl~ tensilc COl'e box
14 to prepare 12 standard Arnerican Foundrymen's Society l-inch
dog bone tensile briquets. The cores were cured at room
16 temperature and broken after 1 hour and 24 hours. Humidity
17 testing was carried out by placing tensile briquets in `80~1O
18 and 90% relative humidlty (r.h.) chambers for 24 hours before
]9 determining tensile strengths. The tensile strengths were
Jneasured usirlg a Detroit Testirlg Machine Co. Model SCT Te~ter,
21 and scratch hardness was determined using a Dietert; No. 674
22 scratch hardness tester. Results of the tests are summarized
2 5 , 1 n Ta D ` I I .
26
28
29
30 ~ -22- ~
3;~
.
1 .r~S a coi1trol, the above procedure ~as repeated using
2 untreated 2GKK lake sand with tne s~me a~ount of resin
3 components except that 0.75 ~ of the Acme Bond 5032 c?~talyst
4 ~1as used. In this case, a strip time of 5 minutes 30 seconds
was obtained. Results o~ the other control tests are given
6 in Table III.
8 TA~LE III
9 _ Tensile, ps~_ and IScratch_Hardness~_
lOCores Prepared 24 hrs 24 hrs
From 1 hr 24 hrs~ ~O',Or.h.~ 90% r.h.
l.l1l~ea-t,ed S~nd1~7 (64)267 (72)2l7 (71).157 (61)
12Untre~te~ Sand120 (62)183 (70)20t) (70)123 (64)
l3(Control)
14
These results show that cores prepared rrom the
16 silicate-treated sand by a base-catalyzed "no-bake" process
17 generally give irnproved tensile strength and better scratch
l8 hardness than the co:res,prepared from untreated impure sand.
].9 Cores prepared from t.reated sand also gave :i.mproved
release ~rom the core box. This property .is beneficial
21 because stickin~ to the core box slows production in a
22 foundry and can result in core or mold damage during
23 ~ remov rrom the pattern.
26
27
2~
29
-29-
i3~ 1
ll E~ PL~ 9
3 .~ mixture of 4000 g of 20KK silica sand, treated
4 with sodium silicate solution as in Example 2, and 40 g of
powdered corn cereal was mulled in a Simpson Mix-Muller
6 (18-inch model) for 1 minute. Then 80 g of water was
7 added and mulling W2S continued for an additional 4 minutes.
8 Mulling was stopped and 20 g of foundry core oil~ obtained
9 from the Archer--Daniels-Midland Cornpany, Minneapolis,
Minnesota, was added. The mixture ~as mulled for 1 mi.nute
11 and collected in a polyetllylene ba~. I'he bag was seal~d
12 :ilmnecliately t;o minimi.ze COll~;clC~ with t,he tl i.r~.
:l3
14 Green compression strength of the coated sand was
determined by placing 168 g of the material in a Dietert
16 r~etroit No. 315-9 specimen tube. The specimen was rammed
17 three times with a Dietert Detroit No. 315 sand rammer.
18 The resultin~ 2-inch x 2-inch test cylinder was compressed
19 in a Dietert Detroi.t No. 465 compression instrllmellt to
deterrn:ine the green cornpression strength.
21
22 Baked tensile strength specimens were prepared
from the coated sand by placing the sand in a tensile specimen
24 mold and ramming it four times with the Dietert Detroit No.
315 sand rammer. Specimens were placed in a tray in a
26 circulating air oven at 224~C. Specirnens were remo~Ted from
27 the oven at varying times. After the specimens had cooled
28
29
3 -24- -
g~
l, l
~ I ~o room temperature, their tensile str~ngths were measured
Z ¦ usin~ a Detroit Testing Mzchi~e, Model CST, ~ensile tester. 1,
3 ¦ Each value reported is the average of the strengths measured
4 using three specimen~.
6 For comparative tests, spec~mens were prepared from
7 coated 20KK sand that had not been trea~ed with s,ilicate
solutions.
The results given in Table IV show tha-t cores made
11 ~rom silicate-treated sand coated w:i.th a core oil mix exhibit
12 about 25% greater tensile strength tharl ~o cores rnade f'rorn
13 uncoated sand whell ~he cores a:re ba.ked S'or 30 rn.i.nu~es.
11~
TABLE IV
~6
Tests on
Specirnens From Control
18 Silicate-lreated 5and Tests
( P~
Green Compress;on 0.5 0.45
Baked Tensile Strength
21 (Baking Time, mirl)
22 30 225 l80
23 45 22l5 -l807
24
`25
26
27
28 _
-Z5- _
.~ ,.
9Z
1 Thus, it is apparent that the~e has been provided,
2 in accoraânce with the invention, a process for the
3 preparation of resin-coated silica. sanQs that fully
4 satisfies the objects, aims and advantâGes set forth
above. While the invention has been described in
6 conjunction with specific ernbodiments Ihereof, it is
7 evident that many alternatives, modifications, and
8 variations will be apparent to those skilled in the
9 art in ].ight of the foregoing description. Accordingly,
it`is intended to inc]ude all such alte~Anatives,
11 modifications, and variations as s~t ror~h ~li.th:i.rl th~
13 Spl t ~nd soope of lhe app~ ed cla:~me.
' 16
21
- 23
26
27
29
3 ~ -26- . .
