U.S. patent number RE32,720 [Application Number 06/900,618] was granted by the patent office on 1988-07-26 for foundry moulds and cores.
This patent grant is currently assigned to Borden (UK) Limited. Invention is credited to Peter H. R. B. Lemon, Peter R. Ludlam, Jeffrey D. Railton, Timothy J. Reynolds.
United States Patent |
RE32,720 |
Lemon , et al. |
July 26, 1988 |
**Please see images for:
( Certificate of Correction ) ** |
Foundry moulds and cores
Abstract
A foundry moulding composition comprising (a) a granular
refractory material, and (b) from 0.5% to 8% based on the weight of
the refractory material of a binder comprising (i) an aqueous
solution of a potassium alkali phenol-formaldehyde resin, said
aqueous solution having a solids content of from 50% to 75% and
said resin having a weight average molecular weight (M.sub.w) of
from 600 to 1500, a formaldehyde:phenol molar ratio of from 1.2:1
to 2.6:1 and a potassium hydroxide:phenol molar ratio of from 0.2:1
to 1.2:1 and (ii) at least one silane in an amount of from 0.05% to
3% based on the weight of said aqueous solution, said binder being
curable by contact therewith of from 5% to 60% based on the weight
of said aqueous solution of a C.sub.1-3 alkyl formate.
Inventors: |
Lemon; Peter H. R. B.
(Sherfield, GB2), Railton; Jeffrey D. (Shirley,
GB2), Ludlam; Peter R. (Shootash, GB2),
Reynolds; Timothy J. (North Baddesley, GB2) |
Assignee: |
Borden (UK) Limited
(Southampton, GB2)
|
Family
ID: |
27032365 |
Appl.
No.: |
06/900,618 |
Filed: |
August 26, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
440278 |
Nov 9, 1982 |
04468359 |
Aug 28, 1984 |
|
|
Current U.S.
Class: |
523/145; 264/82;
524/596 |
Current CPC
Class: |
B22C
1/2253 (20130101); C08G 8/28 (20130101); C08G
16/0218 (20130101); C08K 5/54 (20130101); C08K
5/54 (20130101); C08L 61/06 (20130101) |
Current International
Class: |
B22C
1/16 (20060101); B22C 1/22 (20060101); C08G
16/00 (20060101); C08K 5/00 (20060101); C08G
8/00 (20060101); C08G 8/28 (20060101); C08K
5/54 (20060101); C08G 16/02 (20060101); C08K
003/36 (); C08K 003/34 () |
Field of
Search: |
;523/145 ;524/401,596
;264/82,221 ;164/12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0027333 |
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Apr 1981 |
|
EP |
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0085512 |
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Aug 1983 |
|
EP |
|
1065605 |
|
Sep 1959 |
|
DE |
|
50-130627 |
|
Oct 1975 |
|
JP |
|
1190644 |
|
May 1970 |
|
GB |
|
1411975 |
|
Oct 1975 |
|
GB |
|
2059972A |
|
Sep 1980 |
|
GB |
|
2059972B |
|
Sep 1980 |
|
GB |
|
2154594A |
|
Feb 1985 |
|
GB |
|
Other References
"FENOTEC: A Sand Binder System for the Production of All Ferrous
and Non-Ferrous Metals", Foseco Brochure. .
"FENOTEC 100 Sand Binding System, FENOTEC 100 Resin, FENOTEC
Hardeners", Eoseco Product Data Sheet. .
"Betaset: The Revolutionary Cold Box System", Borden Technical
Information Brochure, Apr. 1984. .
Lemon et al., "The Betaset Process for the Rapid Production of
Moulds and Cores", Proc. of 1984 Annual Conference. .
"The ECOLOTEC Bonding System", Foseco Product Data Sheet. .
Gardikes et al., "Molecular Weight Distribution of Phenolic
Resins", May 4, 1966. .
Ishida, "Molecular Weight of Phenolic Resins", Nov. 21, 1982. .
Tobiason et al., "Molecular Weight Characterization of Resole
Phenol-Formaldehyde Resins", Polymer Molecular Weight Methods
(1975). .
English Translation of previously submitted German Patent No.
1,065,605 dated 9/59. .
Chem. Abst. 84, 125183c, (1976)..
|
Primary Examiner: Jacobs; Lewis T.
Attorney, Agent or Firm: Robbins; Frank E. Laramie; James R.
Maskas; George P.
Claims
What is claimed is:
1. A process for the production of foundry moulds or cores which
comprises;
mixing a granular refractory material with from 0.5% to 8% based on
the weight of the refractory material of a binder solution, said
binder solution comprising (i) an aqueous solution of a potassium
alkali phenol-formaldehyde resin, said aqueous solution having a
solids content of from 50% to 75% and said resin having a weight
average molecular weight (M.sub.w) of from 600 to 1500, a
formaldehyde:phenol molar ratio of from 1.2:1 to 2.6:1 and a
potassium hydroxide:phenol molar ratio of from 0.2:1 to 1.2:1 and
(ii) at least one silane in an amount of from 0.05% to 3% based on
the weight of said aqueous solution,
discharging the mixture into a vented core or mould box, and
gassing the formed mixture with at least one C.sub.1-3 alkyl
formate to cure the binder.
2. The process of claim 1 wherein the refractory material is
selected from the group comprising silica sand, quartz, chromite
sand, zircon, olivine sand or beach sands containing shell
fragments.
3. The process of claim 2 wherein the refractory material is
chromite sand, olivine sand or beach sands containing shell
fragments.
4. The process of claim 1 wherein the M.sub.w of said resin is from
700 to 1100.
5. The process of claim 1 wherein the potassium hydroxide:phenol
molar ratio is from 0.3:1 to 1:1.
6. The process of claim 4 or 5 wherein the potassium
hydroxide:phenol molar ratio is from 0.4:1 to 0.6:1.
7. The process of claim 1 wherein the formaldehyde:phenol molar
ratio is from 1.5:1 to 2.2:1.
8. The process of claim 6 wherein the formaldehyde:phenol molar
ratio is from 1.5:1 to 2.2:1.
9. The process of claim 1 wherein said refractory material is mixed
with from 1% to 3% based on the weight of the refractory material
of said binder solution.
10. Th process of claim 1 wherein the mixture is gassed with from
5% to 60% based on the weight of the aqueous solution of said alkyl
formate.
11. The process of claim 10 wherein the mixture is gassed with from
15% to 35% based on the weight of the aqueous solution of said
alkyl formate.
12. The process of claim 11 wherein said alkyl formate is methyl
formate.
13. The process of claim 1 or 12 wherein said alkyl formate is
dispersed in a carrier gas.
14. The process of claim 13 wherein the concentration of said
formate in the carrier gas is from 0.5% to 5% by volume. .Iadd.
15. A process for the production of foundry moulds or cores from a
mixture of sand with a curable binder, which comprises:
mixing sand with from 0.5% to 8% based on the weight of the sand of
a binder solution, said binder solution comprising (i) an aqueous
solution of a potassium alkali phenol-formaldehyde resin, said
aqueous solution having a solids content of from 50% to 75% and
said resin having a weight average molecular weight (M.sub.w) of
from 600 to 1500, a formalehyde-phenol molar ratio of from 1.2:1 to
2.6:1 and a potassium hydroxide:phenol molar ratio of from 0.2:1 to
1.2:1, and (ii) at least one silane in an amount that provides a
significant improvement in strength,
discharging the mixture into a vented core or mould box, and
gassing the formed mixture with at least one C.sub.1-3 alkyl
formate to cure the binder..Iaddend. .Iadd.16. The process of claim
15 wherein the weight average molecular weight of said resin is
from 700 to 1100..Iaddend. .Iadd.17. The process of claim 15
wherein the potassium hydroxide:phenol molar ratio is from 0.3:1 to
1:1..Iaddend. .Iadd.18. The process of claim 15 wherein the
formaldehyde-phenol molar ratio is from 1.5:1 to 2.2:1..Iaddend.
.Iadd.19. The process of claim 15 wherein the mixture is gassed
with from 5% to 60% of said alkyl formate, based on the weight of
the aqueous solution of binder resin..Iaddend. .Iadd.20. A process
for the production of foundry moulds or cores from a mixture of
sand with a curable binder, which comprises:
mixing sand with from 0.5% to 8% by weight of a binder solution
based on the weight of the sand, said binder solution comprising
(i) an aqueous solution of a potassium alkali phenol-formaldehyde
resin, said aqueous solution having a solids content of from 50% to
75% and said resin having a weight average molecular weight of from
700 to 1100, a formaldehyde-phenol molar ratio of from 1.5:1 to
2.2:1, and a potassium hydroxide:phenol molar ratio of from 0.3:1
to 1:1, and (ii) at least one silane in an amount that provides a
significant improvement in strength,
discharging said mixture into a vented core or mould box, and
gassing the formed mixture with from 5% to 60% of at least one
C.sub.1-3 alkyl formate, based on the weight of the aqueous resin
binder solution, to cure said binder..Iaddend. .Iadd.21. The
process of claim 20 wherein the potassium hydroxide:phenol molar
ratio is from 0.4:1 to 0.6:1..Iaddend. .Iadd.22. The process of
claim 20 wherein the alkyl formate is methyl formate..Iaddend.
.Iadd.23. A cold set system for the production of foundry moulds or
cores utilizing vented core boxes or vented mould boxes, during
which production foundry sand is mixed with a phenolic resin
binder, the sand is shaped, and a curing agent is applied, to cure
the binder, comprising:
a phenolic binder comprising an aqueous solution of a potassium
alkali phenol-formaldehyde resin, said aqueous solution having a
solids content of from 50% to 75% and said resin having a weight
average molecular weight of from 600 to 1500, a formaldehyde:phenol
molar ratio of from 1.2:1 to 2.65:1 and a potassium
hydroxide:phenol molar ratio of from 0.2:1 to 1.2:1, and,
for curing said binder upon contact therewith, after said binder
has been applied to said sand and said sand has been shaped in a
vented core box or a vented mould box, at least one C.sub.1 to
C.sub.3 alkyl formate dispersed in a carrier gas as a vapor or as
an aerosol..Iaddend. .Iadd.24. The system of claim 23 wherein the
weight average molecular weight of said
resin is from 700 to 1100..Iaddend. .Iadd.25. The system of claim
23 wherein the potassium hydroxide:phenol molar ratio is from 0.3:1
to 1:1..Iaddend. .Iadd.26. The system of claim 23 wherein the
formaldehyde:phenol molar ratio is from 1.5:1 to 2.2:1..Iaddend.
.Iadd.27. The system of claim 23 wherein said binder comprises at
least one silane in an amount that provides a significant
improvement in strength..Iaddend. .Iadd.28. A cold-set system for
the production of foundry moulds or cores utilizing vented core
boxes or vented mould boxes, during which production foundry sand
is mixed with a phenolic resin binder, the sand is shaped, and a
curing agent is applied to cure the binder, comprising:
a phenolic binder comprising an aqueous solution of a potassium
alkali phenol:formaldehyde resin, said aqueous solution having a
solids content of from 50% to 75%, and said resin having a weight
average molecular weight of from 700 to 1100, a formaldehyde:phenol
molar ratio of from 1.5:1 to 2.2:1, and a potassium
hydroxide:phenol molar ratio of from 0.3:1 to 1:1, and said binder
comprising at least one silane in an amount that provides a
significant improvement in strength upon curing, and
for curing said binder upon contact therewith after said binder has
been applied to said sand and said sand has been shaped in a vented
core box or a vented mould box, at least one C.sub.1 to C.sub.3
alkyl formate dispersed in a carrier gas as a vapor or as an
aerosol..Iaddend. .Iadd.29. The system of claim 28 wherein said
potassium hydroxide:phenol molar ratio is from 0.4:1 to
0.6:1..Iaddend. .Iadd.30. The system of claim 28 wherein said alkyl
formate comprises methyl formate..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to the manufacture of foundry moulds and
cores which do not evolve pungent acid gases on thermal
decomposition. More particularly it refers to a method of making
moulds and cores of this type rapidly at ambient temperature.
Phenol formaldehyde and phenol formaldehyde/furfuryl alcohol
condensation products catalyzed with strong acids such as sulphuric
acid, paratoluene sulphonic acid, are well known as binders for
sand in the production of foundry moulds and cores. However, they
have the disadvantage that pungent fumes of sulphur dioxide are
evolved on thermal decomposition.
The use of alkaline phenolic resins catalyzed with esters has been
suggested in Japanese Patent Publication No. 130627/1975 and is the
subject of co-pending U.S. Application Ser. No. 224,131, filed Jan.
12, 1981, now U.S. Pat. No. 4,426,467, issued Jan. 17, 1984 and
U.S. Ser. No. 434,462 filed Oct. 14, 1982, now abandoned. The use
of such binder systems enables the manufacture of foundry moulds
and cores which do not evolve pungent acid gases on mixing or
during casting. Further, by suitable selection of resins and ester
catalysts rapid hardening at ambient temperature can be achieved.
However, to obtain such results on a large scale it is necessary to
use specialized rapid mixing equipment such as that described in
British patent specification Nos. 1257181 and 1369445 of Baker
Perkins.
The present invention is based on the discovery that the use of
esters as catalysts for alkaline phenolic resins in the manufacture
of foundry moulds and cores can be adapted to a gassing system
which is capable of rapid cure at ambient temperature. The use of
gassing to promote curing of binders for foundry moulds and cores
is known. The major systems which are or have been industrially
used are as follows:
(a) The "Carbon Dioxide Process" in which CO.sub.2 is passed
through a mixture of sand and sodium silicate. However, the
resultant cores or moulds are very sensitive to water and lose
strength "damp back" on storage, will not accept aqueous washes and
show very poor breakdown on casting. It is necessary to add
breakdown agents such as sucrose to promote better breakdown.
Over-gassing produces very poor strengths.
(b) The "Sulphur Dioxide Process" disclosed by SAPIC in British
Pat. No. 1,411,975 which uses (1) a peroxide which is dangerous to
store and dispense, particularly in a foundry environment, and (2)
pungent SO.sub.2 which has a low Threshold Limit Value (TLV) and is
unpleasant to handle.
(c) The "Isocure" process disclosed by Ashland in British Pat. No.
1,190,644 which uses a benzilic ether phenolic polyol and methylene
diphenyl diisocyanate. The reaction between the polyol and
diisocyanate is accelerated by gassing with triethylamine or
dimethyl ethylamine. The diisocyanates have very low TLV's and
react with water preferentially over the polyol so that it is
necessary to use dry sand and dry air to convey the sand/binder mix
into core box or mould. The amines have relatively low TLV's and
their toxicology is not well understood. Cured cores tend to absorb
water and lose some strength on storage. Certain casting defects
are observed with "Isocure" cores/moulds, e.g. "pinholing" caused
by the nitrogen content of the binder which reduces to ammonia in
the casting environment, dissolves in the molten metal, and is
evolved as small blow holes on cooling; "graphitic defect" which is
a deposit of graphite carbon which collects in flakes on the
surface of the casting; and "finning" or "veining" caused by the
mould or core cracking under the expansion stresses during casting
and molten metal running into the cracks.
The present invention enables the rapid and efficient production of
foundry moulds and cores without the disadvantages of the prior art
as described above.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method of making a
foundry mould or core which method comprises mixing a granular
refractory material with from 0.5 to 8% of a binder which comprises
an aqueous solution, having a solids content of from 50 to 75% by
weight, of a potassium alkali phenol-formaldehyde resin having the
following characteristics:
(a) a weight average molecular weight (M.sub.w) of from 600 to
1500;
(b) a formaldehyde: phenol molar ratio of from 1.2:1 to 2.6:1;
and
(c) a KOH: phenol molar ratio of from 0.2:1 to 1.2:1, the binder
including from 0.05 to 3% by weight based on the weight of the
resin solution of at least one silane, forming the mixture in a
vented core or mould box and gassing the formed mixture with at
least one C.sub.1 to C.sub.3 alkyl formate to cure the binder.
DETAILED DESCRIPTION OF THE INVENTION
The granular refractory materials used in the present invention may
be of any of the refractory materials employed in the foundry
industry for the production of moulds and cores, such as silica
sand, chromite sand, zircon or olivine sand. The compositions of
the invention have the particular advantage that the difficulties
commonly associated with the bonding of sands of alkaline reaction
such as olivine and chromite or beach sands containing shell
fragments and which arise from the neutralization or partial
neutralization of the acid catalyst used, are completely overcome
since in the invention the binder is cured under alkaline
conditions. The invention is, therefore, of particular utility
where it is necessary or desirable to employ alkaline sands.
The nature of the phenol-formaldehyde resin used is an important
feature of the present invention. There are several features of the
resin which are important. Since the present invention is directed
to cold set techniques, the resin binder will be used as an aqueous
solution of the resin. The solids content of the aqueous solution
is in the range 50 to 75% by weight. Solids contents below 50% are
not used because they contain too much water which reduces the
effectiveness of the binder. Solids contents above 75%, are not
used because the viscosity becomes too high.
The phenol-formaldehyde resins used in this invention have a weight
average molecular weight (M.sub.w) of from 600 to 1500. Resins with
M.sub.w outside this range give products which are relatively weak
or build up strength more slowly. We have, to date, obtained best
results using resins having M.sub.w in the range 700 to 1100.
The resins used in this invention are potassium alkaline
phenol-formaldehyde resins by which is meant that the alkali in the
resin is potassium alkali. This alkali will usually be present in
the resin during manufacture but can be added to the resin
subsequently as KOH, preferably in aqueous solution of suitable
strength. The alkalinity of the resin is expressed in terms of its
KOH content and specifically by the molar ratio of KOH to the
phenol in the resin. Other alkalis are not expressly excluded and
may be present in minor amounts but will not be specifically added
because they give products having lower strength.
The molar ratio of KOH: phenol in the resin solution is in the
range 0.2:1 to 1.2:1 preferably 0.3:1 to 1:1. Outside this range
the products have relatively poor strength and, above the top range
limit, the resin is hazardously alkaline. We have obtained best
results using resin solutions having a KOH: phenol molar ratio in
the range of 0.4 to 0.6.
The resins used have a formaldehyde to phenol molar ratio of from
1.2:1 to 2.6:1, preferably 1.5:1 to 2.2:1. Lower ratios are not
used because the resins are relatively unreactive. Higher ratios
are not used because the resins produced contain undesirably high
levels of unreacted formaldehyde and give products having lower
strength.
It is a subsidiary aspect of this invention that the resin used
satisfies the following criteria:
(a) M.sub.w from 700 to 1100;
(b) KOH: phenol molar ratio 0.4:1 to 0.6:1 and
(c) formaldehyde: phenol molar ratio 1.5:1 to 2.2:1
A silane is included in the binder to improve strength. Amounts as
low as 0.05% by weight on the weight of resin solution provide a
significant improvement in strength.
Increasing the amount of silane gives greater improvements in
strength up to about 0.6% by weight on the resin solution. Higher
silane concentrations are not preferred because of added cost.
Further, because the silane typically used is
.gamma.-aminopropyltriethoxy silane which contains nitrogen, use of
excess silane may increase the risk of pinholing defects and for
these reasons amounts in excess of 3% by weight on the resin
solution are not used.
The binder and particulate refractory material can be mixed and
formed by conventional techniques. The vented core and mould boxes
used can also be of conventional type as are used in prior art
gassing systems. The binder is cured, according to the present
invention, by gassing with a C.sub.1 to C.sub.3 alkyl formate, very
preferably methyl formate. The alkyl formate curing catalyst will
not usually be used as a pure gas but as a vapour or aerosol in an
inert carrier gas. By inert carrier gas we mean a gas which does
not react with the formate catalyst or have an adverse effect on
the curing reaction or the properties of the product. Suitable
examples include air, nitrogen or carbon dioxide.
The gassing catalyst is a C.sub.1 to C.sub.3 alkyl formate
preferably dispersed in a carrier gas as vapour or an aerosol.
Other esters e.g. formate esters of higher alcohols such as butyl
formate, and esters of C.sub.1 to C.sub.3 alcohols with higher
carboxylic acids such as methyl and ethyl acetates, are not
effective as gassing catalysts. Methyl formate is significantly
more active as a catalyst than ethyl formate which is better than
the propyl formates. The reasons for the catalytic activity of the
C.sub.1 to C.sub.3 alkyl formates and, within this group, the
marked superiority of methyl formate, are not clear. The relative
volatility of these compounds enables their use as gassing
catalysts. This is especially true of methyl formate which is a
volatile liquid having a boiling point at atmospheric pressure of
31.5.degree. C. At ambient temperatures (below 31.5.degree. C.),
typically 15.degree. to 25.degree. C., it is sufficiently volatile
that passing carrier gas through liquid methyl formate (maintained
at ambient temperature) gives a concentration of methyl formate
vapour in the carrier gas sufficient to act as catalyst to cure the
binder. Ethyl and the propyl formates are less volatile than the
methyl ester, having boiling points in the range 54.degree. to
82.degree. C. at atmospheric pressure.
In order to entrain sufficient of these esters in the gas phase to
enable effective catalysis, we have found it appropriate to heat
the esters to near their boiling point and use a stream of carrier
gas preheated to e.g. 100.degree. C.
An alternative to true vaporization is to form an aerosol in the
carrier gas. Methyl formate is so volatile as to make this
impractical. Using ethyl and propyl formates it is desirable to
pre-heat them to enhance even distribution in the core or mould
during gassing.
As is indicated above, methyl formate is the most active catalyst
and, by virtue of its volatility, is the easiest to use.
Accordingly, the use of methyl formate in a stream of inert carrier
gas as the gassing catalyst forms a particular aspect of this
invention. A further practical advantage of these formate esters,
especially methyl formate is their relative low toxicity and the
fact that their toxicity is well understood.
The concentration of the formate catalyst in the carrier gas is
preferably at least 0.2% by volume and typically from 0.5 to 5% by
volume. The total amount of catalyst used will typically be from 5
to 60% preferably from 15 to 35%, by weight on the weight of the
resin solution. The time required for adequate gassing depends on
the size and complexity of the core or mould and on the particular
resin used. It can be as short as 0.1 secs but more usually is in
the range 1 sec to 1 min. Longer times e.g. up to 5 mins can be
used if desired or for large moulds or cores. After gassing the
core or mould is stripped from the box. Sufficient time must elapse
to permit the strength of the mould or core to build up to enable
stripping without damage. Production speed can be enhanced by
purging the mould or core box with a suitable inert gas such as air
which removes residual catalyst vapour and water and other
by-products of the curing reaction.
The amount of resin solution used as binder is from 0.5 to 8%,
preferably 1 to 3%, by weight on the weight of the refractory
particulate material. Use of lower amounts of binder gives cores of
poor strength. Higher amounts of binder give no significant
advantage and give generally poorer breakdown on casting and
increase the difficulty of sand recovery.
The following Examples illustrate the invention.
The techniques used in the Examples are described below:
Manufacture of phenol formaldehyde resin solutions
100% phenol was dissolved in 50% aqueous KOH in an amount
corresponding to the desired KOH:phenol molar ratio (from 0.2 to
1.2). The solution was heated to reflux and 50% aqueous
formaldehyde was added slowly, whilst maintaining reflux, in an
amount corresponding to the desired formaldehyde:phenol molar ratio
(1.6, 1.8 or 2.0). The reaction mixture was maintained under reflux
until it attained a pre-determined viscosity corresponding to the
desired value of M.sub.w. (If desired the solids content can be
adjusted by distillation, but this is not usually necessary, a
further advantage of the invention. In some cases minor amounts of
KOH solution were added to adjust the KOH:phenol ratio, but this
would not be necessary in full scale production.) The resin
solution was cooled to 40.degree. C. and 0.4% by weight on the
weight of the resin solution of .gamma.-aminopropyl triethoxy
silane was added.
Testing of resins
(a) viscosity--measured using an Ostwald (U-tube) viscometer at
25.degree. C.
(b) solids content--measured by heating a weighed sample
(2.0.+-.0.1 g) in an air circulating oven for 3 hrs at 100.degree.
C.
(c) Molecular weight M.sub.w)--measured using gel permeation
chromatography. Samples were prepared by precipating resin from the
resin solution by adding H.sub.2 SO.sub.4 ; separating, washing and
drying the precipitate and dissolving it in tetrahydrofuran.
Preparation of foundry sand core mix
1 kg of the selected sand was charged into a Fordath laboratory
core mixer and mixed for 2 mins, with 20 g phenol-formaldehyde
resin prepared as described above. The mix was discharged into a
tin and sealed immediately to prevent evaporation of water.
Preparation of test foundry cores
5.times.5 cm cylinder compression test pieces were prepared by the
standard procedure recommended by I.B.F. working party P but using
a perforated bottom plate of the cylinder with a recess which could
be connected to a source of negative pressure. The top of the
cylinder was sealed with another perforated plate connected to a
bubbler containing liquid methyl formate at ambient temperature.
When vacuum was applied to the bottom plate air was bubbled through
the methyl formate and the ester vapour conveyed in the air stream
through the sand resin mix in the cylinder core box. Compression
strength was determined on the resultant cores after storing at
20.degree. C., 50% relative humidity for 1 min, 5 mins, 1 hr. 2
hrs. 3 hrs. and 24 hrs. Initial tests indicated that 30 secs. was
sufficient time to produce the optimum strength and this was used
as a standard in the Examples below.
EXAMPLE 1
Test cores were made using solutions of resins having the following
properties:
formaldehyde:phenol molar ratio--2.0
KOH:phenol molar ratio from--0.4 to 0.8.
M.sub.w --960 or 1000
Solids content--63.5%
0.4% by weight on the resin solution of
.gamma.-aminopropyltriethoxy silane was added. The sand used was
Chelford 50 and the amount of resin was 2% by weight resin solution
on the sand. The results are set out in Tables 1 and 2. Table 1
gives the results for resins with M.sub.w =960 and Table 2 for
resins with M.sub.w =1000.
The data in the table show that cores of adequate strength can be
made but that the strength falls of somewhat at KOH:phenol ratios
greater than 0.6.
TABLE 1 ______________________________________ Test No. 1 2 3 4 5
______________________________________ KOH:Phenol 0.4 0.5 0.6 0.7
0.8 Viscosity (cP) 500 390 313 250 -- Compression Strength (MPa) 1
min 1.2 2.2 2.6 2.6 2.9 5 min 1.9 3.6 3.1 3.0 3.0 1 hr 2.2 3.4 3.5
3.2 3.0 3 hr 2.1 3.9 4.0 3.5 3.1 24 hr 3.0 4.3 4.8 3.2 2.2
______________________________________
TABLE 2 ______________________________________ Test No. 6 7 8 9
______________________________________ KOH:Phenol 0.4 0.5 0.6 0.7
Viscosity (cP) 688 500 375 -- Compression Strength (MPa) 1 min 1.7
2.4 2.9 2.9 5 min 2.4 3.2 3.2 3.3 1 hr 2.4 3.4 3.7 3.6 3 hr 3.2 4.1
3.2 3.4 24 hr 4.4 4.8 3.9 2.9
______________________________________
EXAMPLE 2
Test cores were made using solutions of resins having the following
properties:
formaldehyde:phenol molar ratio--2.0
KOH:phenol molar ratio--0.65
M.sub.w from--718 to 1050
Solids content--66%
0.4% by weight .gamma.-aminopropyltriethoxy silane was added to the
resin solution. The sand used was Chelford 50 and the amount of
resin solution used was 2% by weight on the sand. The experiment
was reported using similar solutions to which 50% KOH solution was
added to increase the KOH:phenol ratio to 0.85. The solids contents
of these resin solutions were 64%. The results are set out in Table
3. The data for the resins with KOH:phenol=0.65 is in the (a)
columns and for resins with KOH:phenol=0.85 in the (b) columns. As
in Example 1 the use of higher KOH:phenol ratios gives inferior
results especially at the higher values of M.sub.w.
TABLE 3 ______________________________________ Test No. 10 11 12 13
--M.sub.w 718 849 966 1050 a b a b a b a b
______________________________________ KOH:Phenol 0.65 0.85 0.65
0.85 0.65 0.85 0.65 0.85 Solids (%) 66 64 66 64 66 64 66 64
Viscosity 107 81 220 111 320 144 405 167 (cP) Compression Str.
(MPa) 1 min 2.7 2.3 2.9 2.2 2.6 2.0 1.9 2.0 5 min 3.4 2.7 3.3 2.6
3.0 1.1 2.2 2.0 1 hr 3.0 2.7 3.5 2.7 2.7 2.2 2.2 2.0 3 hr 3.6 3.2
3.5 2.6 2.9 1.7 1.9 2.0 24 hr 4.5 2.9 3.5 1.1 1.8 0.8 1.2 0.9
______________________________________
EXAMPLE 3
Resins with varying properties were used to make test cores as
described above. The sand used was Chelford 50, the amount of resin
solutions was 2% by weight on the sand and all the resin solutions
contained 0.4% by weight .gamma.-aminotreithoxy silane. The results
are set out in Table 4.
TABLE 4 ______________________________________ Test No. 14 15 16 17
18 19 20 21 ______________________________________ --M.sub.w 850
850 850 1000 1000 1000 1000 1000 KOH:Phenol 0.72 0.72 0.45 0.34
0.57 0.68 0.85 1.02 formalde- 1.6 1.6 1.6 2.0 2.0 2.0 2.0 2.0
hyde:phenol Solids (%) 60.2 66.2 65.4 64.0 64.0 64.0 64.0 64.0
Viscosity 277 414 600 -- -- -- 150 -- (cP) Compression Strength
(MPa) 1 min 2.4 2.3 1.8 0.9 2.7 2.5 2.3 1.6 5 min 2.5 2.4 2.5 2.7
2.8 2.7 2.4 1.8 1 hr 2.5 2.7 2.0 2.3 2.8 2.8 2.4 2.0 3 hr 2.5 3.2
2.1 2.2 3.9 3.2 2.3 -- 24 hr 1.2 3.0 3.5 3.1 4.5 2.2 1.8 1.9
______________________________________
While the invention has been disclosed in this patent application
by reference to the details of preferred embodiments of the
invention, it is to be understood that this disclosure is intended
in an illustrative rather than in a limiting sense, as it is
contemplated that modifications will readily occur to those skilled
in the art, within the spirit of the invention and the scope of the
appended claims.
* * * * *