Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE IN~7ENTION
1. Field of the Invention:
This invention relates to a powdered facing agent
for use in forminy a shell mold, and more particularly to
a powdered facing agent composed of a powdered refractory,
such as silica, alumina, zircon, silex, magnesia, etc., a
novolak type phenol resin, a resol type phenol resin and/or
vinyl acetate resin.
2. Description of the Prior Art:
In forming a shell mold, it is a usual practice to
coat a facing agent on the surface of a metal die for the
purpose of obtaining a fine casting surface. Therefore,
this facing agent is required to have properties that it is
softened by heating, that it well adheres to a ~etal die
when it is coated thereon, and that it loses its adhering
force to the metal die when resin coated sand is brought to
back up, while it well adheres to a shell mold made of the
resin coated sand backed up, particularly in case that it
is parted away from the metal die.
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The facing agent widely used at present is of the
type which is composed of a powdered silica mixed with, for
instance, a novolak type phenol resin used as a thermosett-
ing agent and hexamethylenetetramine used as a hardening
agent. The facing agent of this type has a good adherence
property to the metal die. However, it has disadvantages
that the adherence thereof to the shell mold is ~oor when
it is parted away from the metal die, and accordingly a
coated film formed by coating the facing agent onto the
metal die tends to remain on the metal die. In addition,
even when it has adhered to the shell mold, the coated film
tends to peel off from the shell mold during pouring.
In order to eliminate the above-described dis-
advantages of the conventional facing agent, we heretofore
proposed a novel facing agent composed of a powdered
refractory, such as silica, alumina, zircon, silex, magnesia,
etc., a novolak type phenol resin, and a small amount of
vinyl acetate resin, which has a good adherence property
to resin coated sand as a back-up material and has a good
parting property from the metal die. However, through our
further careful study, we found that the facing agent of
this type also has the following disadvantages:
At the portions where the coated film is too thick,
unhardened portions tends to occur, thereby weakening the
adhering force of the coated film to the backed up resin
coated sand, with a result that, the coated film is partial-
ly left on the metal die. On the other hand, at the portions
where the temperature of the metal die is too low, unhardened
coated film also tends to occur, with a result that, the
coated film tends to be left on the metal die. Accordingly
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a temperature control must be carried out so that the difference
of the temperature of the metal die may be minimized.
In the case of the facing agent containing a novolak
type phenol resin, a hardening rate control for the coated film
is difficu1t even if vinyl acetate resin is admixed therewith.
When hexamine is admixed with the facing agent in order to
control the hardening rate of the coated film, its reaction
becomes too rapid. As a result, veining tends to occur and the
adhesion of the coated film to the backed up resin coated sand
tends to be deteriorated.
SUMMA~Y OF THE INVENTION
The present invention is intended to eliminate the
aforementioned disadvantages of the conventional facing agent
for use in forming a shell mold, and to provide a novel and
improved facing agent used therefor.
It is, therefore, an object of an aspect of the
present invention to provide a facing agent for use in forming
a shell mold, wherein a hardening rate thereof can be controlled
freely.
It is an object of an aspect of the present invention
to provide a facing agent for use in forming a shell mold, which
has an excellent adherence property to a shell mold when resin
coated sand is brought to back up.
It is an object of an aspect of the present invention
to provide a facing agent for use in forming a shell mold, which
has an excellent parting property from a metal die after resin
j coated sand is brought to back up.
In accordance with one aspect of this invention there
is provided a powdered facing agent for use in forming a shell
mold which comprises a powdered refractory, a novolak type
phenol resin and a resol type phenol resin; the ratio of said
novolak type phenol resin to said resol type phenol resin being
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in the range of 90 to 40 parts, by weight, of novolak type
phenol resin to 10 to 60 parts, by weight, of resol type
phenol resin; and the total parts by weight of said novolak
type phenol resin and resol type phenol resin in said facing
agent being 20 to 30 parts per 100 parts of said powdery
refractory.
In order to achieve the foregoing objects, there is
provided in accordance with another aspect of the present
invention a facing agent for use in
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forming a shell mold, which is composed of a powdered
reractory comprising at least one member selected from
the group consisting of silica, alumina, zircon, silex,
magnesia, etc., a novolak type phenol resin, a resol type
phenol resin and/or vinyl acetate resin.
DETAILED DESCRIPTION OF THE INVENTION
-
Our studies prove that a powdered facing agent con-
taining a novolak type phenol resin admixed with a suitable
amount of a resol type phenol resin can improve the adherence
property thereof to a back-up material and the parting pro-
perty from a metal die on which it is coated in a thic~ness
of about 0.1 to 1.0 mm, preferably about 0.2 to 0.5 mm and
and can form a coated film on the metal die even when the
metal die is heated at a temperature lower than that hereto-
fore adopted, and therefore can be applied over a wider'
range of temperature of the metal die.
More particularly, if a shell mold is formed by using
the facing agent according to the present invention,the most
optimum hardening time thereof is selected so as to meet the
working conditions of the shell mold, and a novolak type
phenol resin and a resol type phenol resin are properly
combined with each other so as to meet this hardening time,
and the combination of both resin strengthens the bindins
force between the coated film and resin coated sand as a
back-up material.
For example, if the temperature of the metal die
is relatively low, or if the molding speed is fast, a large
amount of resol type phenol resin is combined, while if the
temperature of the metal die is high, or if the molding
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speed is slow, a small amount of resol type phenol resin is
combined, and therefore a large amount of nobolak type phenol
resin is combined.
The operation by the variation of the combining
ratio of the resol type phenol resin and novolak type phenol
resin in the facing agent according to the present invention
will now be described in detail in the following.
The facing agent made only of a novolak type phenol
resin without combining with a resol type phenol resin at
all introduces the fact that, when the temperature of rnetal
die is below 240C, the coated film remains on the metal die
in adherence thereto.
However, when 85 parts, by weight, of novolak type
phenol resin is combined with 15 parts, by weight, of resol
! 15 type phenol resin, the coated film may be formed in the range
of the temperature of the metal die of 230C to 290C, and
when the resol type phenol resin is increased to 30 parts
and the novolak type phenol resin is decreased to 70 parts,
by weight,the temperature of the metal die may be used in
the range of 220 to 285C. In this case if a sr,~all amount
of vinyl acetate resin is added thereto, the parting pro-
perty of the coated film from the metal die is further
improved, and the adherence between the coated film and the
back-up material becomes superior.
When 55 parts of novolak type phenol resin is com-
bined with 45 parts of resol type phenol resin, the coated
filr.l may be forrmed on the metal die in the range of the
temperature of the metal die of 280 to 210C even if vinyl
acetate resin is not combined therewith.
However, if contents of resol type phenol resin are
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excessively increased, the formation of the coated film on
the surface of the metal die becomes difficult, and the
adherence property of the coated film to the back-up material
and the coated film itself become worse, which is not pre-
ferable.
For example, if 30 parts of novolak type phenol
resin is combined with 70 parts of resol type phenol resin,
it may be used in the range of the temperature of the metal
die of 280 to 210C without difficulty, but in such combin-
ing ratio of the novolak type phenol resin and the resol
type phenol resin, that is, when the content of resol type
phenol resin is increased, the hardening rate of the coated
film becomes lightly faster, and when it is coated onto the
metal die, the coated film tends to be spatterred by the air
pressure of injection of the coated film, and the coated
film thus formed becomes roush. Therefore it tends to become
a worse coated film.
If the resol type phenol resin is further increased,
such as, for example, when 25 parts of novolak type phenol
resin is combined with 75 parts of resol type phenol resin,
the range of the applying temperature of the facing agent
becomes remarkably narrow, and yet the formation of the
coated film onto the surface of the metal die becomes extremely
difficult. In addition, the adhesion thereof to the back-up
material becomes worse, and further cracks occur in the coated
filrn.
It may be seen from the foregoing description that
it is not preferable that an excessive amount of resol type
phenol resin is combined, and accordingly it is proper in the
present invention that the combining ratio of the novolak
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type phenol resin to the resol type phenol resin is 90 to
40 to 10 to 60, and particularly the facing agent made by
using the phenol resin consisting of 85 to 55 parts of novolak
type phenol resin and 15 to 45 parts of resol type phenol
resin is most preferable.
The refractory powder as a basic powder of the facing
agent according to the present invention may be silica, alumina,
zircon, silex, magnesia, etc., as described above.
The agent for forming the coated film to be combined
with the base powder is admixed normally in the range of 20
to 30 parts by weight, to 100 parts, by weight, of the base
powder. Said agent for forming the coated film is not only
the mixture of novolak type phenol resin and resol type phenol
resin, but also 3 to 5 ~, by weight, of vinyl acetate resin
may be further added to the base powder for the purpose of
improving the adhering property of the coated film to the
back-up material.
The hardening rate of the facing agent of the present
invention may be freely controlled by selecting a proper com-
bining ratio of the resol type phenol resin to the novolak
type phenol resin, and at the same time, by combining resol
type and novolak type phenol resins with each other in a
hardened state, the parting property of the coated film from
the metal die after resin coated sand as a back-up material
is brought to back up may be enhanced. This results from
the fact that the resins existing in the resin coated sand
and the novolak type phenol resin contained within the un-
hardened facing agent applied onto the metal die combine
with each other and become hard at the contacting boundary
therebetween, which is simultaneous with the hardening of
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the resin coated sand, so as to enhance the adhesion of
the coated film to the resin coated sand, at the same time,
to improve the parting property of the coated film fro~. the
metal die.
Further, the addition of iron sand to the powdered
facing agent having a composition as described above may
provide a good casting surface with cast products made parti-
cularly of SC materials according to ~apanese Industrial
Standards, and it prevents an occurrence of veining.
The following Examples are construed by way of illust-
ration only, but the present invention is not limited to
these.
Example 1.
Powdered facing agent composed, by weight, of;
powdered silica: 100 parts,
Pkenol resin : 25 parts, which is
composed of 60 parts by weight of novolak type phenol resin
and 40 parts by weight of resol type phenol resin,
vinyl acetate resin: 3 parts, and
iron sand : 15 parts;
was made up in the following manner:
30~, by weight based on the weight of the phenol
resin composed of 60 parts by weight of novolak type phenol
resin and 40 parts by weight of resol type phenol resin, of
methanol was added to the phenol resin and the mixture thus
obtained was liquefied. On the other hand, to the vinyl
acetate resin was added 30~, by weight, based on the vinyl
acetate resin, of acetone. Then, the above powdered silica,
liquefied phenol resin containing methanol, vinyl acetate
resin containing acetone and iron sand were mixed and kneaded
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for 30 minutes. In this case, a wall temperature of mixer
was held at 70C so that solvent tends to be evaporated easy.
The mixture thus obtained jellied, and as the temper-
ature thereof was decreased, it was slightly hardened. Then,
it was introduced to a granulator to form it in noodle state,
and thereafter it was introduced into a screening machine to
form it in particles having diameters of 2 mm to 4 mm. ~fter
these particles were dried, they were pulverized so as to
obtain a powdered facing agent of approximately 300 meshes.
The powdered faci~g agent thus obtained was coated
on an annular casting metal die heated at a temperature of
210C.
In case of a conventional facing agent containing only
novolak type phenol resin, the coated film sometimes adhered
to the metal die when the metal die was heated to such a low
temperature, but in case of the facing agent according to
the present invention, such unfavorable phenomenon did not
occur, on the contrary, a preferable coated film was formed
on the back-up material as a shell mold, and yet the work-
ability was extremely good.
Fxample 2.
A powdered facing agent composed, by weight, of;
powdered silica: 100 parts,
phenol resin : 20 parts, which is
composed of 70 parts by weight, based on the phenol resin,
of novolak type phenol resin and 30 parts by weight, based
on the phenol resin, of resol type phenol resin;
was mae up in the following manner:
Firstly, 6 parts by weight, based on the weight of
the powdered silica, of powdered resol type phenol resin and
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100 parts by weight of the powdered silica were uniformly
mixed by using a mixer. Then, to the powdered mixture thus
obtained was added 14 parts by weight, based on the weight
of the powdered silica, of li~uefied novolak type phenol resin
obtained by adding 40%, by weight based on the novolak type
phenol resin, of methanol to the powdered novola~ type phenol
resin, and the resulting mixture was mixed and ~neaded for
20 minutes.
The jellied mixture thus obtained was formed in powdery
form by the same manner as described in the Example 1~
Using the powdered facing agent thus obtainea, a
plate metal die having a thickness of 10 mm, a length of 150mm
and a width of 50 mm and heated at a temperature of 280C
was coated. The coated film thus obtained was extremely good.
! 15 When aluminium alloy was casted by using a shell mold of
which its peripheral surface was coated with the coated film,
a preferable casting having a fine casting surface of 12.5
to 25S according to Japanese Industrial Standards was obtained,
and yet there occurred no veining and exfoliation of the
coated film.
Example 3.
A powdered facing agent composed, by weight, of;
powdered silica: 100 parts,
phenol resin : 25 parts, which is
composed of 50 parts, by weight based on the phenol resin, of
novolak type phenol resin and 50 parts, by weight based on
the same, of resol type phenol resin;
was made up in the following manner:
12.5 parts, by weight based on the powdered silica,
of powdered re~ol type phenol resin and 100 parts by weight
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of the powdered silica was uniformly mixed by using a mixer.
Then, 12.5 parts, by weight based on the powdered silica, of
liquefied novolak type phenol resin obtained by adding 5~%,
by weight, based on the novolak type phenol resin, of methanol
thereto was added to the powdered mixture as obtained above,
and the resulting mixture was mixed and kneaded for 25 minutes.
The jellied mixture thus obtained was formed in powdery
form by the same manner as described in the foregoing Example
1.
By using the above powdered facing agent, a name plate
metal die having the size of 150 mm x 100 mm x 7 mm and heated
at a temperature of 250C was coated. When FC material accord-
ing to Japanese Industrial Standards was casted by u~ing a
shell mold of which its peripheral surface was coated with
the coated film thus obtained, an extremely good casting
could be obtained. Further, the parting property of the
coated film frorn the metal die was good, and yet the adherence
property of that to the back-up material was also good.
