Process and apparatus for automatic and continuous measurement of the shearing resistance of green sand used in modern molding machines

Process for automatically measuring the shearing resistance of green sand used in a repetitive sand molding process using pattern plates, and for using the measurements in such a way as to modulate the various parameters of the process in which a measuring ring is placed upon one of the pattern plates. The measuring ring has an opening and stress gauges fastened within narrowed sections of said measuring ring on either side of said opening. The gauges are connected electrically through the pattern plate to an electronic measurement and operation device within which various physical measurements are computed, including the shearing resistance of the test sample of sand compressed within said opening. The result of said measurements is processed by a computer to determine the magnitude of modulations to be made, particularly that pertaining to the replenishment of agglomerating agents for the recycled sand.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to sand molding, and more particularly to modern, 
automatic, repetitive, high-speed molding processes. 
2. Description of the Prior Art 
A well known sand molding process consists of forming essentially 
parallelopiped blocks by compressing sand in a horizontal press between a 
front pattern plate which opens and a back pattern plate which exerts 
pressure. In this process, the blocks are assembled into a continuous 
horizontal column as they leave the press, forming a complete mold 
impression at each joint between blocks, which will then enable metal to 
be poured repeatedly into the various impressions. The blocks continue to 
advance, while the pieces cool, up to an end station where the sand is 
removed. In each operating cycle, sand is projected vertically and at high 
speed into the press between the closed front plate and the withdrawn back 
plate before the pressure is applied. 
The sand used is molding sand called green sand, a material composed of 
silica grains mixed with a clay called bentonite, powdered charcoal, and 
water. By appropriate mixing, each solid grain is coated with a thin film 
of suitably hydrated clay in order to impart the necessary adhesive power 
under a high forming pressure, generally on the order of 10 kg/cm.sup.2. 
Like any molding sand, this sand must meet conflicting requirements, since 
it must be sufficiently fluid to be able to be easily packed around all of 
the details of the pattern plates, while at the same time being 
sufficiently stiff not to collapse after packing nor to lose shape after 
separation from the pattern plates. It must also exhibit good cohesion, 
particularly a shearing resistance high enough to resist the stresses of 
molding, such as the hydrostatic pressure of molten metal, the thermic 
shocks at the moment of pouring, and the stresses due to the contraction 
of the metal in the process of solidification. Moreover, it must be able 
to be broken for the extraction of the pieces without too much difficulty. 
Modern molding processes such as the one described above are even more 
demanding on the quality of the sand due to the absence of any frame, 
which thus necessitates a greater self-cohesion of the blocks, the high 
pressure exerted on the sand in the joint planes of the lead blocks, which 
must push back the whole column and, finally the fact that the sand 
removal operation itself must be automatic and take place at high speed. 
In each case, an optimal quality of sand must be set and it is necessary 
to monitor this quality to ensure that it remains within the narrow and 
precise limits thus defined. 
The usual methods for monitoring the quality of the sand consist of drawing 
off a sample of non-packed sand, i.e., from the hopper of the machine, 
forming a test cylinder (5 cm.times.5 cm) in an outside laboratory 
apparatus, compressing it at 10 kg/cm.sup.2, and shearing it on a special 
machine. Depending on the result of this measurement, the replenishment of 
agglomerating agents, or bentonite clay, is adjusted as a function of the 
observed fluctuations from the set limits. These measurements are 
repetitive, but as a result of the process used the measurement speed is 
always slow and rarely exceeds more than two measurements per hour, which 
nevertheless requires a full-time operator and imposes a great lag between 
the moment of sampling and the moment at which the result of the 
measurement is finally known. 
This known process permits the above demand for constancy of sand quality 
to be met only in a way that is approximate. In addition, the check covers 
only the quality of the sand per se, prior to packing, and not the real 
conditions in which it is found inside the block. 
SUMMARY OF THE INVENTION 
The object of the invention is to eliminate the foregoing drawbacks by 
providing a process and apparatus for measuring, as rapidly and 
automatically as possible, the quality of the sand per se as well as the 
quality of its packing within each block. 
The invention consists of fastening onto one of the pattern plates, 
preferably the back one, a measuring ring having a central hole, 
preferably one whose axis is parallel to the pattern plate and preferably 
parallel to the direction from which the sand is blown (i.e., generally 
vertically) with a narrowed section along its two lateral edges containing 
a stress gauge electrically connected across the support and the pattern 
plate to an outside measuring apparatus. This ring is defined by two 
planes, either parallel or preferably, slightly tapered in the direction 
of withdrawal of the mold, so that when the pattern plate is drawn away 
from the block, the ring performs a double shearing of the cylinder of 
sand contained inside its hole, said sand having been compacted by the 
normal process of producing the block under the normal conditions 
prevailing within. The signals provided by the stress gauges are analyzed 
electronically to give the shearing resistance and processed by computer 
to govern various parameters, particularly instructions for adjustment of 
the replenishment of agglomerating agents and for adjustment of the 
pressure exerted by the press.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 can be seen press 1 having back pattern plate 2 borne by plate 3 
of the press, plate 3 being integral with shank 4. Sand is blown through 
opening 5 in the direction of arrow 6. One end of the column of blocks 7 
can also be seen. 
In a known fashion, pattern plate 2 comprises protrusions 8 corresponding 
to the shape of the piece to be molded, up to the joint plane (shapes 
beyond this plane are carried on the other pattern plate, which is not 
shown), as well as protrusion 9 intended to form the pouring hole and 
pouring channel (direct or from a source). 
In accordance with the invention, a measurement ring 10, shown in detail in 
FIGS. 2 and 3, is fastened onto pattern plate 2 in an appropriate spot 
between the protrusions 8 and 9, preferably in the core of the block. 
This ring is advantageously in the shape of a journal bearing having a base 
so as to enable it to be conveniently fastened to pattern plate 2 using 
screws passing through holes 11 in its base. The ring includes a hole 12 
(e.g., 50 mm diameter) the axis of which is parallel to the direction of 
arrow 6 (e.g., generally vertical). The body of the ring, made of wear 
resistant steel, preferably 35CD4T4 steel, is defined by two planes 13 
essentially perpendicular to pattern plate 2 but preferably tapered 
slightly in the direction of withdrawal, as shown in FIG. 3. Two lateral 
millings 14 (e.g., cylindrical, as shown in the figures) have the effect 
of reducing the section of the lateral branches of the ring--which extend 
in the direction in which the pattern plate is extracted--down to a small 
section 15 (e.g., on the order of 1.5 mm in thickness). At the point of 
maximum reduction, which corresponds to the point at which tangents to 
hole 12 are parallel to the direction of shank 4 of the press, stress 
gauges (not shown) are fastened in the bottom of millings 14 and are 
coupled by a Wheatstone bridge with thermic compensation gauges in the 
usual manner and connected electrically by cables passing through ring 10, 
via holes 16, and through pattern plate 2 and plate 3, via appropriate 
holes, so as to reach the measuring and operating apparatus 17 by means of 
flexible connections (not shown). 
When sand is compacted between the two pattern plates, sand also fills hole 
12 of ring 10 and is there compacted at the pressure existing at that 
spot. When the pattern plate is withdrawn by retraction of shank 4, the 
ring draws with it the cylinder of sand it contains, separating said sand 
cylinder from the rest of the block by a double shearing along planes 13. 
The tapering of these two planes facilitates this separation by avoiding 
the imposition of parasitic stresses which would affect the measurement. 
The two millings 14 are preferentially filled with a filler material 
designed to protect the stress gauges from the sand while at the same time 
eliminating any counter-taper. 
The shearing resistance of the cylinder of sand along the two shearing 
planes 13 is thus measured precisely by the sum of the tensions of the two 
sections 15, which are measured by the stress gauges, and which are 
related to the sum of the two sections and of the cylinder of sand. 
The indentation made by the ring in the block is not important since it 
does not communicate with the other impressions or with the pouring hole. 
On the other hand, by virtue of the orientation selected for the ring, the 
cylinder of sand which remains in hole 12 of the ring is removed in the 
next molding cycle by the projection of sand blown into the press in 
direction 6. The sand thus flushed downward by blowing pressure mixes with 
and adheres to the rest of the sand in the following pressing cycle. 
With each cycle of formation of blocks 7, the invention thus provides a 
precise and instantaneous measurement of the shearing resistance of the 
cylinder of sand under the compacting pressure actually present within the 
block. 
These various measurements, succeeding each other at the speed of the 
press, may advantageously be monitored by an electronic computer, which 
computes the shearing resistance in the appropriate units as well as 
various required data and stores this data in memory in order to carry out 
a periodic computation (e.g., every 100 samplings) of statistical 
parameters, such as average and scattering, which are compared with the 
preset tolerances, and to provide the necessary instructions for manual or 
automatic correction of the replenishment of agglomerating agents to 
successive loads of sand sent to the hopper of the press. As long as the 
press works at constant pressure, variations in the measurements can only 
be ascribed to variations in the composition of the sand. 
Moreover, if the properties of the sand used are known, the process of the 
invention further enables one to monitor the quality and development of 
packing in the core of the mold, and to regulate accordingly the pressure 
exerted by the press. It also enables individual monitoring to check that 
each mold actually receives the correct pressure, with an instantaneous 
warning in the event of any lapse. 
The invention thus eliminates the need for employment of a monitor while 
furnishing instantaneous indications concerning the various adjustments to 
be made, either manually or automatically, in order to achieve perfect 
manufacturing uniformity enabling production of quality castings with a 
minimum of rejects. 
Finally, the invention clearly can be very simply adapted to existing 
equipment. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.