Method and apparatus for hardening of foundry cores

It is known to harden foundry cores by admixing a polymerizable material therewith and then curing by addition of a catalyst. Means are provided for injecting gaseous catalysts and compressed air, sequentially, into the die which contains the admixture of polymerizable material and foundry core material. In accordance with the invention, the gaseous catalyst and compressed air respectively, are injected into the die containing the mixture of foundry material in measured desired amounts and very rapidly.

The present invention relates to a method to harden foundry cores made of a 
mixture which includes sand, and an apparatus to carry out the method. 
More particularly, it relates to such a method and apparatus in which the 
core is exposed to a mixture of a gaseous catalyst and a carrier gas in a 
mold or die, and thereafter is exposed to compressed air, in which the 
volume, pressure and temperature of the mixture and compressed air are 
controlled. 
It has previously been proposed to harden a core made of sand saturated 
with waterglass, and located in a die, by exposing the core to a stream of 
CO.sub.2 gas. In another method of this type, referred to as the cold box 
method, two components of an artificial resin system are added to the core 
sand, the components then hardening in the sand when an alkylamine 
catalyst is added. One component may, for example, by a polyester resin, a 
polyether resin, or any suitable liquid resin with a reactive hydroxyl 
group. The second component, in any event, is an organic isocyanate. Both 
components are thoroughly mixed with the mold sand and are then shaped. 
Efforts have been made to catalyze the reaction and to render the use and 
handling of the alkylamines more reliable. 
It has been known for some time that a mixture of tertiary alkylamine and 
air can be pressed through the isocyanate-sand mixture, while heating the 
amine-air mixture to a temperature of 30.degree. C. to 50.degree. C. in 
order to vaporize all the liquid amine. It has also been proposed to use 
carbon dioxide or nitrogen instead of air as a carrier for the amines. The 
mold parts to be hardened, in accordance with one apparatus, were placed 
during any one working step for several times in a closed apparatus, under 
vacuum, in order to reliably pass the catalyst vapor through all spaces in 
the die, or form or mold. 
All the known processes have a common disadvantage, namely that the 
hardening process requires a substantial period of time with respect to 
other working steps. For example, shaping the mixture of molding sand in a 
die using a core injection machine requires frequently only fractions of a 
second; the subsequent gas treatment to harden the core, however, requires 
several seconds. The gas treatment, therefore, is an expensive step. In 
order to decrease the gas treatment time or, respectively, the hardening 
time, it has been proposed to apply an excess quantity of amine. This, 
however, brought the danger that the binder could go back into the 
solution, thus decreasing the possible final strength of the core to about 
80-85%. A decreased final strength of the molded core reduces its 
resistance against break-up. Cores which have not been completely hardened 
also cause formation of leafing ribs at the cast element upon subsequent 
casting thereof. 
It has also been proposed to provide measuring pumps between a source of 
catalyst and the mixing station of carrier gas and catalyst (see German 
Disclosure Document No. 2,162,137) in order to permit better measured 
application of the catalyst. The overall solution, however, still was not 
satisfactory. In other processes, the gaseous catalyst was applied by 
timed opening and closing of the outlet valves from the source for the 
gaseous catalyst. In the system proposed in the aforementioned German 
Disclosure Document, the suction stroke of the pump replaced the previous 
opening and closing of the outlet valve from the source of the gaseous 
catalyst. The measured gaseous catalyst, sucked in by the pump, is mixed 
with the carrier gas immediately before being injected towards the core. 
The carrier gas was also derived directly from a compressed air source. 
Using pumps increases the cycling time of the apparatus. Accurate 
measurements depend on constant temperature conditions as well as on the 
pressure of the sources for the gaseous catalyst and of the carrier gas. 
Even if highly accurate valves and valve seats are used, more gaseous 
catalyst usually was supplied to the core than necessary, since it is 
practically impossible to maintain the pressure of the sources for gaseous 
catalyst and compressed air at a uniform, constant level. Again, an excess 
had to be contended with. 
Any structure which requires control elements, pumps, heaters, and the 
like, in the lines between the sources and the cores, increase the length 
of the flow paths and thus the injection flow speed of the gaseous 
catalyst-carrier gas mixture, as well as of subsequent flushing or 
scavenging air in and to the core. This increases the hardening or curing 
time, rather than decreasing it. 
It is an object of the present invention to provide a method, and an 
apparatus to carry out the method, in which the above referred-to 
disadvantages and time delays are decreased or, preferably, entirely 
eliminated, and which is particularly suitable for decreasing the cycling 
time of the hardening step. 
Subject matter of the present invention: Briefly, temporary measuring 
vessels are provided for the gaseous catalyst-carrier gas mixture and for 
compressed air to store the mixture and air, respectively, temporarily; 
the respective mixture and compressed air are then sequentially injected 
rapidly, abruptly, suddenly, and explosive like into the core in form of a 
sudden pulse or blast. The compressed air is stored in a vessel of greater 
volume and is heated to a higher temperature than the gaseous 
catalyst-carrier gas mixture.

The apparatus shown in the drawing is intended for cooperation with a core 
injection machine, and is part thereof. The apparatus is associated with 
the die 1 of the core injection machine. Apparatus assembly 2 is used to 
prepare and supply a gaseous catalyst mixture; apparatus assembly 3 is 
used to prepare and supply heated, compressed air. 
The gaseous catalyst mixture prepared in apparatus 2 includes a preparation 
vessel 4 to which carbonic acid or carbon dioxide is supplied at 
approximately 2 atm. gauge. Supply to vessel 4 can be derived from a 
storage container 5 through valve 6. Vessel 4 has placed therein, as 
known, an amine in liquid form. The amines in the gaseous state will form 
above its surfaces. The gaseous amine is conducted through valve 7 to a 
pressure vessel 8. The volume of pressure vessel 8 may be, approximately, 
1 liter, or any other suitable quantity in accordance with process control 
standards or legal requirements. For Germany, the presently legal 
requirements are that the volume should be such that the gaseous 
catalyst-carrier gas mixture is capable of accepting a maximum of 25 g 
tert. alkylamine in vapor form. The medium in vessel 8 is preferably held 
at about 30.degree. C. The pressure within the vessel 8 can be increased 
by addition of further gases from a gas supply vessel 9, controlled by a 
valve 10, in accordance with requirements. This further gas may be a 
carrier gas, or the carbon dioxide is itself the carrier gas. 
The assembly 3 to prepare heated, compressed air has a compressed air 
vessel 11 of about 10 liters volume including heating means (not shown) to 
generate compressed air at a temperature of between about 100.degree. C. 
to 115.degree. C. These heating means may, for example, be electrical 
heating resistance coils. The air is supplied from a compressed air source 
12 over valves 13 and conducted into compressed air vessel 11. 
The contents of vessel 8 and of the vessel 11, respectively, can be 
conducted through respective valves 21, 21', and check valves 22, 22' into 
the die 1. An interposed distribution or spray head 23 may be used, if 
necessary. The introduction of the contents from vessel 8 and vessel 11 
through the respective valves and spray or distribution head 23 should 
occur similarly to an explosion, that is, as a sharp, sudden injection 
pulse. 
After forming and shaping of the core in the die 1, for example by 
injection of the foundry sand mixture into the die, in accordance with 
well-known and standard practices, valve 21 is opened. Gaseous catalyst 
from the pressure vessel 8 can then expand through the core sand mixture, 
as shaped. Immediately thereafter, a shot of hot, compressed air is 
injected by opening of the valve 21'. 
The shot of hot air, in a quantity which is high with respect to that of 
the catalyst gas mixture, and at a temperature which is substantially 
higher than that of the catalyst gas mixture, will abruptly increase the 
temperature of the body of the sand core and thus increase the reaction 
speed of the curing or hardening process. 
It is a simple matter to automate the apparatus for manufacture of cores. A 
program control unit S, for example of the well-known numerical machine 
tool control type, controlled by magnetic tape, punch tape, or the like, 
has control lines 30, 30', 301, 302, 303, 304 extend from the control unit 
to the valves 21, 21', 13, 7, 6 and 10, respectively, to control in 
sequential steps the introduction of the respective components from 
supplies 5, 9 into the vessels 4 and 8 for the catalyst-carrier gas 
mixture and from supply 12 to vessel 11 for compressed air. A further 
control line (not shown) or a separate thermostatic control of well known 
and customary type can be connected to the heating supply for compressed 
air vessel 11 to maintain the temperature of the compressed air at the 
desired level. 
After the injection of the gaseous catalyst-carrier gas derived from the 
metering vessel 8, and subsequent curing by injection of heated, 
compressed air from the compressed air metering vessel 11, the vessels 8 
and 11 are re-filled from the respective supplies 4, 12 and, if necessary, 
auxiliary carrier gas supply 9, to their holding or storage volume at the 
respective storage conditions. 
The method, as well as the apparatus, therefore provided, alternately, a 
shot of gaseous catalyst-carrier gas mixture and then a shot of heated, 
compressed air. The quantities of the respective injected gases can be 
accurately determined by determining the metering volumes of the vessels 
8, 11, respectively, so that the respective gases will abruptly expand, as 
desired, in the core. The closing time of the opening valve 21, 21' thus 
can be delayed, since only that quantity of the respective gas can reach 
the core which was previously available from the respective vessel 8, 11 
which, as noted, contains an accurately metered quantity. 
The respective vessels 8, 11 can be maintained at respective temperatures 
with great precision and a minimum expenditure of material as well as 
control elements and control functions. Separating the flow paths for the 
gaseous catalyst-carrier gas mixture and that for compressed air, and 
using separate metering holding or storage vessels for each, permits 
independent temperature control of the respective gases and, specifically, 
heating of the shot of compressed air to a temperature which is higher by 
several orders of magnitude than that of the catalyst vapor-carrier gas 
mixture. 
The shot of hot, compressed air permits decreasing the time of the reaction 
for the curing or hardening process to one-quarter of that previously 
obtained. Actual practical experience has shown that this substantial 
reduction in curing time is readily obtainable; the overall timing of the 
process thus does not throw an entire production schedule out-of-rhythm. 
This is of primary importancei the manufacture of foundry cores. It 
appears that this reduction in reaction time is due to the abrupt, sudden 
increase of the body temperature of the sand core. The extremely high 
reaction speed permits using a catalyst mixture with very low amine 
proportion, which is then distributed uniformly about the core form by the 
shot of hot, compressed air. Subsequently thereto, displacement of the 
excess catalyst from the core is effected. Entirely apart from the much 
lower generation of odors, the method results in cores having a 
practically 100% final strength so that, during the casting process, 
subsequent hardening will no longer occur and the characteristics of the 
core, with respect to crumbling after casting, are substantially improved. 
The respective vessels 8, 11 temporarily store a predetermined mixture of 
the respective gases introduced thereto, the storage vessel for the 
compressed air being substantially larger than that for the gaseous 
catalyst-carrier gas mixture and also being heated by standard heating 
means, such as resistance coils, hot-air or steam coils, or the like, so 
that the compressed air therein will be maintained at a predetermined and 
elevated temperature, as required by the process. 
Various changes and modifications may be made within the scope of the 
invention concept. 
A mold core of 25,000 cm.sup.3 volume was to be hardened. Vessel 8, with a 
volume of 2 liter was filled with gaseous amine, at the temperature of 
30.degree. C. and at a pressure of 2 atm gauge. Vessel 11, with a volume 
of 30 liter was filled with compressed air at a pressure of 8 atm gauge 
which was heated so that, within the vessel, it had a temperature of 
110.degree. C. To cure the mold, which was at ambient air pressure and 
normal "room" temperature, valve 21 was opened to rapidly inject the 
gaseous catalyst-and-carrier gas mixture in vessel 8 into the mold; 
immediately thereafter, valve 21' was opened to inject most suddenly and 
abruptly the compressed air from vessel 11 into the mold die. 
Total time elapsed from first filling the vessels 8, 11, until curing time 
of the mold: 
The relative quantities, pressures, and temperatures of the gasses in the 
vessels 8, and 11 can readily be determined from operating data well known 
in the foundry field. 
The present invention is specifically directed to optimizing the cure 
conditions of the mold core under all circumstances, so that, in a 
repetitive and preferably automated system the cores will all be uniformly 
and identically cured by introducing thereto, at all times, the optimum 
quantities, under optimum temperature and pressure conditions of the 
respective gaseous catalyst mixture and compressed air. Preferably, the 
pressure of the compressed air should be in excess of that of the gaseous 
catalyst-carrier gas mixture by 2 to 4 times to insure reliable, and 
effective flushing, and to provide for rapid curing by thermal shock. 
The pressure of the compressed air in Source 12 is preferably in the range 
of 2 to 4 atm (gauge); the pressure in vessel 11, after the compressed air 
has been raised to the temperature in the range of about 
100.degree.-115.degree. C. is about 10 atm (gauge) at a pressure in the 
gaseous catalyst-carrier gas mixture in vessel 8 of about 2 atm (gauge). 
This is an approximate generally suitable pressure relationship valid for 
customary injection gases. The temperature of the gaseous catalyst-carrier 
gas mixture in vessel 8 can be at ambient, or "room" temperature, that is, 
approximately in the order of