Note: Descriptions are shown in the official language in which they were submitted.
I',ACKGROUI~D Ol: TIIE INVENTION
The present invention relates to an improved phenolic
resin ~in~er and resin coated sand obtained therefrom to be used
in a shell-molding process~ In conventional shell-molding
operations, ~oundry sand is mixed or coated with a resin and
placed in a mold to obtain the configuration desired, followed
by a heating cycle to allow the resin to polymerize and bind the
sand particle~ into a firm structure. After the introduction of
the molten metal into the cavity, the heat of the metal during
the cooling cycle is transferred to the sand-binder mixture
causing the binder to be destroyed to a degree that will allow
the casting to be removed ~nd cleaned of sand in an efficient
manner~
Conventional resin coated sand compositions have been
typically prepared by mixing heated sand with a phenolic resin
to obtain a coated sand~ Catalysts are mixed with the sand prior
to the placing of the resin coated sand into the mold. However,
there is a drawback in the conventional phenolic binders when
used in shell-molding operations, namely the shell molds often
crack. This is caused by abrupt thermal expansion of the mold
of resin-coated sand exposed to high temperatures at pouring.
In order to eliminate this problem, cushioning sub-
stances are usuall~ incorporated into the resin binder or resin-
coated sand, to enable the shell-molds to have a degree of
flexibility as well as reducing thermal expansion. Materials
known to be cushioning substances are bisphenol A, "Vinsol",
petroleum resins and rosins. These materials lower the thermal
expansion o~ molds and are partially effective in the prevention
of cracks that occur at pouring. Howe~er, they also present un-
wanted problems, such as the emission of disagreeable odors due
A~9P~
o decomp~sLtion and evaporation of disassociation products and
hindering the shake-out property.
It is an object of this invention to provide a binder
formulation that will prevent cracks in the mold due to the
thermal shock created by casting hot metal into the shell-mold.
I~ is a fur~her object of this invention to improve the
shake-out proper~y of the sand grains by utilizing the resin
coated sand of this invention.
SUMMARY OE' THE INVENTION
This invention relates to a phenolic resin binder and
resin-coated sand obtained therefrom for sand shell-molding
operations. The phenolic resin binder, disclosed herein, is
prepared by reacting the phenol component with a sugar, such as
cane or beet sugar or the syrupy residue of refined sugar,
molasses. The reaction between the sugar and phenol is con-
ducted in the presence of an acid catalyst. This product is
then reacted with formaldehyde under basic or acidic conditions
to form a resole or novolac phenolic resin. The phenolic resin
is mixed with foundry sand and catalysts to form a resin-coated
sand for use in shell-molding operations. The incorporation of
a lubricant to the phenolic resin will improve the curing
characteristics of the binder, and will assist in the preparation
of the resin-sand mixture.
~ ~4'3~
DESCRIPTION OF THE PREE'ERRED EMBI~DIMENT
_ . __ _
After investigation to overcome the above mentioned
drawbacks, the inventors hereof have found that both prevention
of cracks in molds and improvement of shake-out property are
attained by using resin-coated sand wherein foundry sand grains
are coated with sugar-modified phenolic resins. A phenolic resin
of the novolac type, that is, one obtained by reacting sugars and
phenols with an acid catalyst, and successively reacting the
product with formaldehyde with an acidic catalyst; or a resole
type resin obtained by reacting sugars and phenols with an acid
catalyst, and successively reacting the product with formaldehyde
with a basic catalyst may be used.
Generally speaking, the major portion of commerclal
sugar is saccharose, which is called cane or beet sugar according
to its source, graded as syrup-containing and syrup-free at stages
of processing, as crude and refined, and at refining steps as
white, brown and black according to its color, or as powder,
cube and crystal according to its available form. Also molasses
is the syrupy residue of refined sugar. Any of said grades there-
of is usable in the present invention.
~ hen phenols and sugars are mixed and heated with an
acid catalyst, they react with each other and form a chemical
bond. ~hPy scarcely react in a neutral state or with a basic
catalyst. Acid catalysts used for the reaction between sugars
and phenols, or successively with formaldehyde are inorganic
acids such as sulfuric acid, hydrochloric acid, nitric acid, boric
acid and phosphoric acid, and organic acids such as para-toluene
sulfonic acid, benzene sulfonic acid, xylene sulfonic acid, oxalic
acid, maleic acid, formic acid, acetic acid and succinic acid.
After reacting su~ars and phenols with an acidic catalyst ,
he reaction mixture is :uccessively reacted in acidic ccndition
3~
with formaldehyde, followed by dehydration under vacuum producing
a s~gar-modified novolac type phenolic resin of reddish-brown
to brownish-black in color. This resln, resembles ordinary
novolac type phenolic resin obtained by reacting phenols and
formaldehyae ~ith ar. acid catalyst and cures by heating with
addition of a formaldehyde donor such as hexamethylenetetramine
or para-formaldehyde forming a three-dimensional cross-linked
structure.
After reacting sugars and phenols with an acid catalyst,
the reaction mixture is successively reacted by adding a basic
catalyst thereto, such as sodium hydroxide, potassium hydroxide,
aqueous ammonia, aminesl calcium hydroxide, magnesium hydroxide,
or quick lime, with formaldehyde,followed by dehydration under
vacuum to produce a sugar-modified resole type phenolic resin of
yellowish-brown to brownish-black in color. This resin, resembles
ordinary resole type phenolic resin obtained by reacting phenols
and formaldehyde with a basic catalyst and cures by heating
forming a three-dimensional cross-linked structure~
In preparing sugar-modified phenolic resins, phenols
herein are phenol, cresol, xylenol, catechol, resorcine, and a
mixture thereof, however, a portion thereof may be substituted
with hydroquinone, aniline, urea, melamine, cashew nut shell oil,
etc. Formaldehyde herein is selected from aldehyde donors such
as formalin, parafo~naldehyde, and trioxane.
The ratio of sugar to phenol should range from 70-10 to
30-90 parts, by weight. When khe sugar is less than 10 parts
relative to the phenol, there is present insufficient sugar
modified phenol to prevent crac~ing of the mold and the shake out
property of the resin is not improved. ~hen the sugar is greater
than 70 parts relative to the phenol, the mechanical strength of
l~C3~45~
the shell molds is lowered due to a chemically loose three-
dimensional structure of the cured ~esin.
In preparing a suitable novolac type phenolic resin,
the molar ratio o~ formaldehyde to 1 mole of phenols is 0.3 - 0.9.
When said ratio is less than 0.3, the chemical three-dimensional
structure after curing said resin binder is loose, and it results
in lowering the physical properties of shell-molds. When said
ratio is more than 0.9, mold cracks are inevitable at pouring
and the resin binder thus obtained is ineffective for a better
shake-out property of shell-molds.
In preparing a resole type phenolic resin, a suitable
resin is obtained by selecting the molar ratio of formaldehyde to
1 mole of phenols at 1 - 3. When said ratio is less than 1, it
results in lowering the rate of cure of the resin binder, and a
chemically loose three-dimensional structure after curing results,
thus it leads to lowering the physical properties of shel]-molds.
When said ratio is more than 3, mold cracks are inevitable at
pouring, and no improvement in shake-out property can be obtained.
A preferable embodiment o~ the present invention is to
add lubricants into phenolic resins. Said lubricants are not
only useful in improving shell properties but also prevent the
powder resin from agglomerating or improve the curing
characteristics of xesin binders. Ordinary lubricants are usable
in the present invention, however, preferable are ethylene bis-
stearic amide, methylene bis-stearic amide, oxy-stearic amide,
and methyol stearic amide.
Methods for producing coated sand adopted in the present
invention may be any of the commercial hot coatiny, semi-hot
coating, cold coating, and powder solv nt coating processes. The
respective embodiments are as follo~s.
_5_
(1~ ~t coating process: A method for coating hot
sand (130 - 140C) ~y adding a solid resin thereto.
(2) Cold coating process: A method for coating sand
with a resin dissolved in a solvent such as methanol.
(3) Semi-hot coating process: A method fox coating
hot sand (80 - 100C) by adding said liquid resin thereto.
~ 4~ Powder-sol~ent process: ~ method for coating sand
by adding a solvent such as methanol, after adding a powdered
resin to the sand.
Among them, the hot coating process is more preferable
in caxrying out the present invention.
The inventors hereof will explain the present invention
with the following nonlimitative Examples and Comparative Examples
wherein both "parts" and "percent" indicate "part by weight" and
"percent by weight", respectively.
EXAMPLE 1
To a reaction kettle with a reflux cooler and stirrer,
1000 parts of phenol, 429 parts of sugar and 7 parts of con-
centrated sulfuric acid were charged, and the temperature of the
kettle was gradually ele~ated. After reacting sugar with phenol
at 100C for 180 ~sinutes, the pH value of the reaction mixture
was found to be 0~8. To the reaction mixture, 431 parts of 37~
formalin was added and reacted for additional 120 minutes at 96C.
Successively it was neutralized by adding 9 parts of slaked lime
thereto. After adding 10 parts of methylene bis-stearic amide
thereto with mixing~ followed by dehydration under vacuum, 1320
parts of a sugar-modified nvvolac type phenolic resin were ob-
tained.
EXAMPLE_2
To a reaction kettle with a reflux cooler and a stirrer,
1000 parts of phenol,1000 parts of sugar and 15 parts of para-
toluene sulfonic acid were charged and the temperature of the
kettle was gradually elevated. After reacting sugar with phenol
at 100C for ~40 minutes, the pH value of the reaction mixture
was found to be 1 2. To the reaction mixture, 518 parts of 3~%
formalin were added and reacted for additional 90 minutes at 96C.
Successively, 80 parts of 50% sodium hydroxide solution, 200 parts
of 28~ a~ueous ammonia and 1206 parts of 37% formalin werP added
thereto, then, reacted for 30 minutes at 96C. After adding 15
parts of ethylene bis-stearic amide thereto with mixing, followed
by dehydration under Yacuum, 2350 parts of a sugar modified resole
type phenolic resin were ohtained.
EXAMPLE 3
To a reaction kettle with a reflux cooler and a stirrer,
900 parts of phenol, 100 parts of cashew nut shell oil, 429 parts
of sugar and 10 parts of concentrated sulfuric acid were charged,
and the temperature of the kettle was gradually elevated. After
reacting sugar, phenol and cashew nut shell oil for 240 minutes
at lOO~C, the pH value was ound to be 0.5. To the reaction
mixture, 431 parts of 37% formalin were added and reacted for
additional 120 minutes at 96C. Successively it was neutralized
by adding 12 parts o~ slaXed lime thereto. After adding 10 parts
of methylene bis-stearic amide thereto with mixing, followed by
dehydra~iDn under ~acuum, 1350 parts of a sugar-modified novolac
type phenolic resin were obtained.
EX~MPLE 4
To a reaction kett1e with a reflux cooler and a stirrer,
~ ~ 51~
50 par~s of phenol, 250 parts of meta-cresol, 429 parts of sugar
and 6 par~s of concentrated sulfuric acid were charged, and the
temperature of the kettle was gradually elevated. After reacting
sugar,phenol and metal-cresol, the pH value was found to be 0.9.
To the reaction mixture, 431 parts of 37~ formalin were added and
reacted for additional 90 minutes at 96%C. Successively it was
neutralized by adding 8 parts of slaked lime. After adding 10
parts of methylene bis-stearic amide thereto with mixing, followed
by dehydration under vacuum, 1330 parts of a sugar-modified
novolac type phenolic resin were obtained.
COMPARATIVE EXAMPLE I
To a reaction kettle with a reflux cooler and a stirrer,
1000 parts of phenol, 650 parts of 47% formalin and 10 parts of
oxalic acid were charged, and the temperature of the kettle was
gradually elevated. After the tempexature reached 96C, and 120
minutes' reaction thexeafter, 10 parts of ethylene bis-stearic
amide was added thereto with mixing, followed by dehydration under
vacuum, 970 parts of a novolac type phenolic resin were obtained.
COMPARATIVE EX~MPLE II
To a reaction kettle with a reflux cooler and a stirrer,
1000 parts of phenol, 1553 parts of 37% foxmalin, 60 parts of 50%
sodium hydroxide solution, and 160 parts of 28% aqueous ammonia
were charged, and the temperature of the kettle was gradually
eleva~ed. After the temperat~re reached 96C, and 30 minutes
reaction thereafter, 40 parts of ethylene bis-stearic amide was
added thereto with mixing, followed by dehydration under vacuum,
1060 parts of a resole type phenolic resin were obtained.
Table I indicates the characteristics of the four
examples of sugar-modified phenolic resins and two comparative
x~nple~ of non sugar-m~dified phenolic resins.
TABLE I
Reaction Conditions
and ~omparative
Resin Properties Examples Examples
1 2 3 4 I II
...... , ~ ~
Weight proportion: 0 43 1 0.43 0.43 0 0
Sugars/Phenols _ _
Molar ratio:
Formaldehyde/Phenols 0.5 2 0.54 0.5~ 0.75 1.8
Melting point (C) 83 80 81 ~ 84 80 _ 78
Free phenol content
~ 3.7 4 1 3.2 3.5 5.5 5 9
The resin prepared in Examples 1-4 and Comparative
Examples I and II were coated onto foundry sand and subjected to
testing.
EXAMPLE 5
After heating to 130 ~ 140~C, 7000 parts of Sanei No. ~
shell sand was charged into a whirl-mixer and 210 pa~ts of sugar-
modified novolac type phenolic resin obtained according to
Example 1 was added thereto. After mixing for 30 seconds, 30 part s
of hexamethylenetetramine dissolved in 80 parts of water was
added thereto. The mixture was further mixed until it crumbled.
7 parts of calcium stearate was added thereto, followed by 30
seconds mixing, the mixture was discharged and aerated to obtain
the resin-coated sand.
EXAMPLE 6
The proc~dure ~f Ex~mple 5 was followed except the sugar~
modified resole type phenolic resin obtained according to
Example 2 was substituted, and the hexamethylenete~ramine was
_g_
I
omitted to produce ~he resin-coated sand.
EXAMPX.E ?
The procedure of Example 5 was followed except the
sugar-modified novolac resin prepared according to Example 3
was substituted, and resin coated sand was produced.
EXAMP~E 8
The procedure of Example 5 was followed except the
sugar-modified novolac resin prepared according to Example 4
was substituted to produce the resin coated sand.
COMPARATIVE EXAM2LE III
The procedure of Example 5 was followed except the
novolac resin prepared according to Comparati~e Example I
was substituted to produce the resin coated sand.
- COMPARATIVE EXAMæLE IV
The procedure of Example 6 was followed except the
resole resin prepared according to Comparative Example II
was substituted to produce the coated sand.
Table Il indicates the characteristics of the resin
coated sand and the shake out property of shell-molds therefrom.
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Test Methods:
Bending strength~ according to JACT Method SM-l
stick point. ~cc~r~ing to JACT Method C-l
Tensile strength under elevated temperature:
according to JACT Method SM-10
Abrupt thermal expansion rate:
according to JACT Method SM-7 at 1000C
Shake-out property:
Preparation of specimen:
Coated sand is fed into an iron pipe of 29mm in
diameter and 150mm in length. After 30 minutes
baking, it is covered with aluminium foil and
~urther heated for 3 hours at 370C. After
cooling, the sand molded pipe is taken out.
Test method:
The specimen is struck by the impact arm of the
apparatus illustrated in Fig. 1. Crumbled sand is
removed from the pipe after each flogginy~
Weighing the residual molded sand of the specimen
until it becomes zero, the shake-out property is
defined by the number of floggings required.
Test apparatus:
A molded sand specimen is disposed below an
arm which revolves around a pivot set at 30cm
high. Said arm is at first set horizontally, and
then allowed to drop so as to flog said specimen.
