High-speed injection valve for expanding-gas molding machines

Abstract: An injection valve for expanding-gas molding machines for molding-sand molds, includes a valve body (2) that encloses a main chamber with an intake port (6) that is connected to an external pneumatic system (R) and a discharge port (7) that is connected to an injection chamber (C) of a molding machine, a secondary chamber (4) provided with a first opening (8) that is selectively connected to the pneumatic system (R) or to the outside and at least one passage (9) that is connected to the main chamber (3). A piston (10) is slidingly inserted in the secondary chamber (4) and is operatively coupled to a shutter (12) that is accommodated in the main chamber (3) and is meant to interact with the discharge port (7) to open it when the first opening (8) of the secondary chamber (4) is connected to the outside. The valve thus configured has very short activation response times and allows high discharge pressure gradients.

Description: The present invention relates to an injection valve of the type applied to expanding-gas molding machines used to produce molding-sand casting molds by means of pressure waves of compressible gases. In the injection chambers of molding machines, the compressed gas is accumulated in tanks upstream of the injection valve. By activating the injection valve, the gas suddenly expands into the molding chamber, generating a pressure wave that strikes the sand and compacts it against the pattern. In order to achieve good results, the pressure gradient must be very high, on the order of hundreds of bars per second, and the expansion time must be minimal, on the order of ten-thousandths of a second. A drawback of conventional injection valves is their relatively long intervention time, which can limit the expansion rate of the gas and thus limit the pressure on the molding sand, consequently reducing the compaction of the sand and the quality of the molding. Another drawback of conventional valves is their limited flow-rate, which forces the use of considerably bulky valves in order to achieve satisfactory results. Another drawback of conventional valves is the high consumption of working fluid for operating the valve and the molding section. The aim of the present invention is to eliminate the drawbacks described above, providing an injection valve that has very short activation response times, so as to maximize the pressure gradient and therefore the compression of the sand during molding. An object of the invention is to provide a high-efficiency valve that minimizes energy losses and consumption of the working fluid. Another object of the invention is to provide an injection valve that has a high flow-rate, is strong and reliable, and is suitable for use in heavy-duty conditions. This aim and these objects are achieved by an injection valve for expanding-gas molding machines for molding-sand molds, which includes a valve body that encloses a main chamber with an intake port that is connected to an external pneumatic system and a discharge port that is connected to an injection chamber of a molding machine, characterized in that the valve body includes a secondary chamber, which has a first opening that is selectively connected to the pneumatic system or to the outside and at least one passage that is connected to the main chamber, and a piston that can slide in the secondary chamber and is operatively coupled to a shutter arranged in the main chamber and adapted to interact with the discharge port to open said port when the first opening of the secondary chamber is connected to the outside. The injection valve according to the invention has an extremely short activation response time that allows a high pressure gradient. This is decisive in expanding-gas forming for the optimum compaction of the sand around the pattern. Furthermore, the valve thus configured has a high efficiency and a low consumption of working fluid. An embodiment of the injection valve according to the invention and of the corresponding operating method is described hereinafter and illustrated by way of non-limitative example with the aid of the accompanying drawings, wherein: Figure 1 is a reduced-scale sectional view of an injection valve according to the prior art; Figure 2 is a partially sectional schematic front view of the injection valve according to the invention; Figure 3 is a general view of the valve of Figure 2, installed on a molding machine. With reference to the above figures, the injection valve according to the invention, generally designated by the reference numeral 1, includes a valve body 2 that encloses a main chamber 3 and a secondary chamber 4 that are separated by an intermediate wall 5. Main chamber 3 has an intake port 6 connected to a pneumatic system R and a discharge port 7 connected to an injection chamber C of a molding machine. Secondary chamber 4 has a first opening 8, that can be connected to an external pipe 8', and a passage 9 connected to main chamber 3 and constituted by at least one hole provided on intermediate wall 5. A piston 10 is slidingly inserted in secondary chamber 4 and is operatively coupled, by an axial stem 11, to a shutter 12 arranged in main chamber 3 and interacting with discharge port 7. Piston 10 has a first surface 10', directed toward first opening 8, and a second surface 10'' opposite to first surface 10' and orientated toward passage 9. The diameter of piston 10 is greater than the diameter of shutter 12, so that the sum of the forces applied by the pressures that act on the opposite surfaces 10' and 10'' of the piston and on shutter 12 helps to keep the shutter normally closed against discharge port 7. A central sleeve 13 is fixed to intermediate wall 5 and has a through hole 14 in which axial stem 11 is slidingly inserted. According to the invention, an external valve means is provided for actuating and repositioning the injection valve, connecting first opening 8 of secondary chamber 4 selectively and alternately to the pneumatic system R or to the outside. The valve means can be constituted, for example, by an electrically or pneumatically-driven, normally-open, three-way pneumatic valve of a per se known and commonly commercially available type. The actuation of valve V can be controlled by an automatic control unit U of the molding machine. During use, by actuating valve V, the portion of secondary chamber 4 that lies above piston 10 is connected to the discharge. Accordingly, the pressure that acts on second surface 10'' of piston 10 pushes piston 10 toward first opening 8, causing the rapid rise of shutter 12 from discharge port 7 and thus allowing the instantaneous discharge of the pressurized fluid into injection chamber C. Conveniently, the maximum stroke of piston 10 is shorter than the minimum distance between shutter 12 and intermediate wall 5, so as to avoid the collision of the latter two parts 12 and 5. Furthermore, piston 10 is provided with a stroke-limiting, shock-absorbing means 15 that is fixed to its upper surface 10' and is adapted to cushion the impact against the facing wall of secondary chamber 4. In order to ensure the perfect gas-tightness of the valve according to the invention, there is a first pneumatic sealing means 16 that is associated with shutter 12 and is constituted by an annular gasket that cooperates frontally with the edges of discharge port 7. Likewise, there is a second sealing means 17 that is associated with piston 10 and is constituted by two annular lip-shaped gaskets that are fitted at the opposite ends of piston 10 and cooperate with the inner wall of secondary chamber 4. The injection valve according to the invention minimizes working fluid losses and therefore has a high efficiency; moreover, it is sturdy, suitable for heavy-duty uses, and constructively simple. Experimental tests have shown that the activation response time of the valve according to the invention is markedly lower than that of similar valves of the prior art. This allows to achieve very high pressure gradients in the injection chamber of the molding machine, improving the productivity and quality of expanding-gas forming with respect to known similar valves used in this field of production. The injection valve according to the invention is susceptible of modifications and variations, all of which are within the scope of the inventive concept expressed by the claims. All the details may be replaced with technical equivalents. The materials, the shapes, and the dimensions may be any without thereby abandoning the scope of the invention. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: Injection valve for expanding-gas molding machines for molding-sand molds, comprising a valve body (2) enclosing a main chamber (3) with an intake port (6) connected to an external pneumatic system (R) and a discharge port (7) connected to an injection chamber (C) of a molding machine, characterized in that said valve body comprises a secondary chamber (4), which has a first opening (8) that is selectively connected to said pneumatic system (R), or to the outside, and at least one passage (9) connected to said main chamber (3), and a piston (10) that can slide in said secondary chamber (4) and is operatively coupled to a shutter (12) arranged in said main chamber (3) and adapted to interact with said discharge port (7) to open said port when said first opening (8) of the secondary chamber (4) is connected to the outside. Injection valve according to claim 1, characterized in that said piston (10) and said shutter (12) are operatively coupled by means of a rigid axial stem (11). Injection valve according to claim 2, characterized in that said main chamber (3) and said secondary chamber (4) are separated by an intermediate wall (5) supporting a central sleeve (13) provided with a hole (14) for the sliding of said axial stem (11). Injection valve according to claims 2 and 3, characterized in that said passage (9) of said secondary chamber (4) comprises at least one hole formed on said intermediate wall (5). Injection valve according to claim 1, characterized in that said piston (10) has a larger diameter than said shutter (12). Injection valve according to claim 1, characterized in that the maximum stroke of said piston (10) is shorter than the minimum distance between said shutter (12) and said intermediate wall (5). Injection valve according to claim 1, characterized in that said piston (10) has a first surface (10') that is directed toward said first opening (8) and a second surface (10'') that lies opposite to the first one (10') and is orientated toward said passage (9). Injection valve according to claim 1, characterized in that it has a stroke-limiting shock-absorbing means (15) that is fixed to the upper surface (10') of said piston (10). Injection valve according to claim 1, characterized in that it has a first pneumatic sealing means (16) that is associated with said shutter (12) to frontally interact with said discharge port (7) and a second pneumatic sealing means (17) that is anchored to said piston (10) to cooperate with the inner wall of said secondary chamber (4). Injection valve according to claim 1, characterized in that it has a controlled external valve means (V) that is suitable to connect said first opening (8) of said secondary chamber (4) selectively and alternately to said pneumatic system (R) or to the outside.

Inventors: MANTELLATO GIOVANNI, MANTELLATO, GIOVANNI
Applicants: FOUNDRY AUTOMATION S A S DI VI, FOUNDRY AUTOMATION S.A.S. DI VISENTIN ALDO & C.
Application year: 1996
Main classification: B22C15
IPC codes: B22C15