Method for making sand molds in a blow-and-squeeze-type apparatus

Abstract: A new method for making a sand mold in a blow-and-squeeze-type apparatus is provided. The apparatus comprises a pattern plate (1), a flask (2,3), a squeeze plate (6,7), and a blow head (8). This method is characterized in that the compactability of the molding sand of the obtained mold can be easily calculated, and in that when the molding sand of the obtained mold has a compactability that is outside the permissible range, before the next mold is made the molding condition(s) of the apparatus for making a mold and/or the mixing condition(s) of the mixer is modified. Thus, even though the properties and conditions of the molding sand change, molds having desired and suitable properties and conditions can be made.

Description: Field of Invention This invention relates to a method for making a mold in an apparatus of a blow-and-squeeze-type for making said mold, which apparatus comprises a pattern plate, a flask, a squeeze plate, and a blow head. Prior Art Japanese Patent Publication-A No. Hei. 6-277800, whose applicant is the same as the assignee of this invention, and U. S. Patent No. 5,409,052, whose assignee is the same as that of this invention, disclose blow-and-squeeze-type apparatuses for making a mold. In these apparatuses, molding sand in a blow head is supplied into a space, which is made by a flask, a pattern plate, and a squeeze plate, and then the molding sand in that space is compacted by the squeeze plate to make the mold. When a mold is made by using a blow-and-squeeze-type apparatus for making said mold, there are the following problems: That is, the bulk density of the molding sand that was supplied by being blown-in changes, as the properties and/or conditions of the molding sand change. Therefore, the height of the mold after the molding sand has been squeezed changes. Also, the bulk density of the molding sand after it has been squeezed may change. The reason by which the properties and/or conditions of the molding sand change is that its moisture evaporates when it is carried from a mixer to a blow head by a belt conveyor. Thus, in supplying molding sand by blowing it into a flask, it is difficult to obtain and use molding sand having stable properties and having conditions that are optimal for making a mold. To solve the above problems, in the invention disclosed in U. S. Patent No. 5,409,052, a height (or thickness) of a mold after it has been squeezed is calculated from the distance that the squeeze plate has moved, the moisture of the molding sand is calculated from the electrical resistance, which is measured by using an electrode that is attached to the squeeze plate, and the height (or thickness) of the mold and the moisture of the molding sand are used as data for controlling the properties and conditions of the molding sand before it is supplied to the blow head and for controlling the conditions of the apparatus for making a mold. However, the properties and conditions of the mold and the molding sand of that mold, which are obtained by practicing that invention, are not necessarily satisfactory. Thus, the object of this invention is to provide a method for making a mold in a blow-and-squeeze-type apparatus for making said mold, by which method a mold can be made under conditions suitable for making it. The object can be attained for the reason that in this invention even if any property or condition of the molding sand before it is supplied to the blow head changes, the effects caused by such change can be rectified, and thus molds having desired and suitable properties can be obtained. Brief Description of the Drawings Fig. 1 is an elevation partly in section of a blow-and-squeeze-type apparatus for making molds, to which apparatus this invention can be applied. Fig. 2 is a flowchart that explains this invention. Fig. 3 is a graph showing the relation between the percentage of the reduction of the height of molding sand in a flask, ΔL/L, and the compactability, α, of the molding sand in the obtained mold. Fig. 4 is a graph showing the relation between the compactability and the moisture content of molding sand when it is discharged from a mixer. Fig. 5 is a schematic view of a blow-and-squeeze-type apparatus for making molds, to which apparatus this invention can be applied. Summary of the Invention The inventors of this invention have extensively investigated, and tested for solving, the above problems by a different angle from that of the invention disclosed in U. S. Patent No. 5,409,052. As a result, they have found that in a blow-and-squeeze-type apparatus for making a mold, as shown in Figure 3 the percentage of the reduction of the distance between a pattern plate and a squeeze plate caused by squeezing molding sand, ΔL/L, which is calculated by dividing the reduced amount of that distance by the molding sand being squeezed, ΔL[ = L (the distance between a pattern plate and a squeeze plate before the molding sand is squeezed) - L' (that distance after the molding sand has been squeezed)], by the distance before the molding sand is squeezed, L, correlates with the compactability. Based on the above fact, the inventors of this invention have accomplished this invention. Thus, this invention provides a method for making a mold in a blow-and-squeeze-type apparatus for making said mold, which apparatus comprises a pattern plate, a flask, a squeeze plate, and a blow head. The method comprises the steps of: a) making a mold by supplying molding sand into a space for molding which is defined by the pattern plate, the flask, and the squeeze plate by blowing the molding sand into that space, and then squeezing the molding sand by using the squeeze plate under conditions such that the following conditions are previously set: an optimal sand compactability, α0, a permissible range, ±ε, of the difference between the α0 and the actual sand compactability, α, a number, n, of molds to be made, and a relational formula that represents a correlation between a ratio of a reduced amount, ΔL, which is obtained by subtracting a distance, L', between the pattern plate and the squeeze plate after the molding sand has been squeezed from a distance, L, between them before the molding sand is squeezed, to that distance, L, (that is, a percentage of the reduction of the distance: ΔL/L), and sand compactability; b) obtaining said percentage of the reduction of the distance, ΔL/L, and substituting said percentage for said relational formula to calculate the compactability, α, of the molding sand of the obtained mold; c) judging whether the difference between said compactability, α, and said optimal compactability, α0, is within said permissible range, ± ε; and d) making the next mold when said difference is within said permissible range, or when said difference is outside said permissible range, modifying any condition by transmitting a command to modify a molding condition(s) of the apparatus for making a mold and/or a mixing condition(s) of the mixer and then making the next mold, thereby making molds of a previously set number, n. The modification(s) of a molding condition(s) of the apparatus for making a mold can be, e.g., 1) that of the pressure and/or time when the molding sand is blown into that space, or 2) that of the position of the squeeze plate before the squeeze of the molding sand is conducted. The modification(s) of the mixing condition(s) of the mixer can be that of the set compactability of the molding sand when it is discharged from said mixer, and that of any other condition(s) necessary to realize the modification of the set compactability. The condition(s) to realize the modification of the set compactability comprises, e.g., the amount of water that is mixed with molding sand, since it has been well known that (as in Figure 4) the compactability of molding sand correlates with its moisture content. The condition(s) to realize the modification of the set compactability also comprises the temperature and humidity in the plant, and the temperature of the sand. The relational formula that represents the correlation between the percentage of the reduction of the distance: ΔL/L) and compactability is, e.g., y (compactability, %) = 2.75x (ΔL/L, %) - 30.4. When the set compactability of the molding sand when it is discharged from said mixer is modified, the amount of water that is mixed with molding sand in the mixer can be calculated using, e.g., the formula: y (moisture content, %) = 0.027x (compactability, %) + 1.67. This formula represents the relational line shown in Figure 4. Detailed Description of Invention Below some of the preferable embodiments of this invention will be explained in detail. Figure 1 shows a blow-and-squeeze-type apparatus for making molds, to which apparatus this invention can be applied. This apparatus comprises a pattern plate 1, a flask 2, a flask 3, a squeeze plate 6, a squeeze plate 7, and a blow head 8. The pattern plate 1 is also called a match plate. This pattern plate 1 has two patterns, one on its front surface and one on its back surface. The flasks 2 and 3 can be set to match the pattern plate 1. The squeeze plates 6 and 7 can be moved by the functions of cylinders 4 and 5, respectively. The squeeze plates 6 and 7 slide along the inner surfaces of the flasks 2 and 3. To a space which is defined by the pattern plate 1, the flask 2, and the squeeze plate 6, the molding sand S in the blow head 8 is supplied through a blow nozzle 11. Simultaneously, to a space which is defined by the pattern plate 1, the flask 3, and the squeeze plate 7, the molding sand S in the blow head 8 is supplied through a blow nozzle 12. The blow nozzle 11, which is positioned under the blow head 8 and communicates with it, can be connected to the flask 2 at an opening 9 in the upper wall of the flask 2. The blow nozzle 12, which is positioned under the blow head 8 and communicates with it, can be connected to the flask 3 at an opening 10 in the upper wall of the flask 3. The blow nozzles 11 and 12 can be inserted into openings 9 and 10, respectively, by causing the blow head 8 to go downward. In Figure 1, the blow head 8 is at its lowest position. To the upper part of the blow head 8, a communication pipe 14 is connected. To this pipe 14, a valve is attached for controlling the pressure 13. The pipe 14 is connected to a compressed air source (not shown). To the squeeze plate 6, the top of a movement sensor 15 that is attached to the frame, to which frame the cylinder 4 is fixed, is connected. The sensor 15 is used to measure the distance that the squeeze plate 6 moves. The sensor 15 outputs data on the distance value to a microcomputer (not shown). This microcomputer is set to transmit at least one command selected from the group consisting of 1) the modification of pressure when the molding sand S is blown into the spaces by the pressure-control valve 13, 2) that of the time for blowing the molding sand S into the spaces, 3) that of the positions of the squeeze plates 6, 7 before the molding sand S is squeezed, 4) that of the pressure to squeeze the molding sand S in those spaces, and 5) that of the set compactability of the molding sand S when the molding sand S is discharged from a mixer for making the molding sand S (not shown). When the set compactability is to be modified, to realize the modification any other condition(s) that relates to the set compactability, e.g., the amount of water, is simultaneously modified. Next, the method for making molds by using the above-explained apparatus will be explained by reference to Figures 1 and 2. To the microcomputer, 1) the compactability, αo, that is optimal for making a mold, 2) the permissible range, ± ε, of the difference between the α0 and the actual compactability, α, 3) the number, n, of molds to be made, and 4) the relational formula that represents the correlation between the ratio of the reduced amount, ΔL, and the compactability, are input. Here, ΔL is obtained by subtracting the distance, L', between the pattern plate 1 and the squeeze plate 6 (7) after the molding sand S has been squeezed from the distance, L, between them before the molding sand S is squeezed, to that distance, L, (that is, a percentage of the reduction of the distance: ΔL/L). Then, compressed air of a predetermined pressure is supplied to the blow head 8 for a predetermined time through the communication pipe 14. During this period, the blow head 8 is positioned at the position shown in Figure 1. By supplying the compressed air to the blow head 8, the molding sand S is blown into the space that is defined by the pattern plate 1, the flask 2, and the squeeze plate 6, through the blow nozzle 11 that is connected to the opening 9, and into the space that is defined by the pattern plate 1, the flask 3, and the squeeze plate 7, through the blow nozzle 12 that is connected to the opening 10. Next, the cylinders 4, 5 simultaneously move the squeeze plates 6, 7 at a predetermined pressure to compress or squeeze the molding sand S that has been supplied. Thus, two molds are made. Then, the molds are detached from the pattern plate 1 and flasks 2, 3. The molds are treated as usual. By the microcomputer, the compactability of the mold that was made in the flask 2 is calculated. That is, by subtracting the distance, L', between the pattern plate 1 and the squeeze plate 6 after the molding sand S has been squeezed from the distance, L, between them before the molding sand S is squeezed, the reduced amount, ΔL, is given. Then, from the relational formula that represents the correlation between the percentage of the reduction of the distance, Δ L/L, and the compactability, the actual compactability, α, of the molding sand S constituting the mold thus obtained is calculated. The relational formula is, for example, "y (compactability, %) = 2.75x (ΔL/L, %) - 30.4," as shown in Figure 3. Next, by the microcomputer, whether the difference between the actual compactability, α, and the optimal compactability, α0, is within the permissible range, ±ε, is judged. When the difference is within the permissible range, ±ε, the next molds are made without changing any condition. When the difference is outside the permissible range, ±ε, depending on the conditions of the obtained mold, the microcomputer transmits a command that the condition(s) for making mold be modified. The conditions to be modified include 1) a modification of the pressure when the molding sand S is blown into the spaces, 2) that of the time during which the molding sand S shall be blown into the spaces, 3) that of positions (i.e., the original positions) of the squeeze plates 6, 7 before the molding sand S is squeezed, and 4) that of the pressure to squeeze the molding sand S in those spaces. Or, the microcomputer transmits a command to modify a condition(s) of making the molding sand S in the mixer. Specifically, to modify the set compactability of the molding sand S when it is discharged from the mixer, at least one of the mixing conditions, e.g., the amount of water, or the temperature of the sand as the raw material, or the formula of the raw materials, or the temperature and humidity in the room where the mixer is set, is modified. However, the compactability of the molding sand S when it is discharged from the mixer is most affected by the amount of water. Further, as shown in Figure 4, the correlation between the compactability (which may be calculated as explained above or which may be obtained by the standard method) and the moisture content is known. Thus, the modification of the set compactability is usually realized by the modification of the amount of water. In the mixer, the molding sand S is prepared so as to have a compactability that is higher than the optimal compactability, α0, because during the period the molding sand S is being carried from the mixer to the blow head, the molding sand S is dried, and thus its compactability is reduced. The intended compactability of the molding sand S that is prepared in the mixer is the set compactability. The mixing conditions can be modified only when a new batch of the molding sand S is prepared. Thus, usually, the condition(s) for making the mold is modified. For each set of molds made, the actual compactability, α, is calculated and is compared to the optimal compactability, αo. As previously explained, if necessary, that is, if the actual compactability, α, is outside the permissible range, ± ε, any condition that needs to be modified should be so modified before the next set of molds is made. Thus, a previously set number, n, of molds are made. In the apparatus shown in Figure 1, two molds are simultaneously made. However, the number of molds that can be simultaneously made is not limited. This invention can also be applied to, e.g., an apparatus by which at one time only one mold, or three or more molds, are made. The direction of the pattern plate 1 is also not limited. This invention can also be applied to, e.g., the apparatus shown in Figure 5, in which the pattern plate 1 has two patterns, one on the upper surface and one on lower surface of it. Effects of Invention In this invention, from the values that are obtained by measuring the height (or thickness) of the molding sand in a flask, the compactability of the molding sand of the obtained mold is easily calculated. Therefore, whether the compactability is within the permissible range can be promptly judged. Further, if the compactability is outside the permissible range, the next mold can be made after the molding condition(s) of the apparatus for making a mold and/or a mixing condition(s) of the mixer has been modified. Thus, even though the properties and conditions of the molding sand change, molds having desired and suitable properties and conditions can be steadily made.

Claims: A method for making a mold in a blow-and-squeeze-type apparatus for making said mold, which apparatus comprises a pattern plate, a flask, a squeeze plate, and a blow head, comprising the steps of: a) making a mold by supplying molding sand into a space for molding which is defined by the pattern plate, the flask, and the squeeze plate by blowing the molding sand into that space, and then squeezing the molding sand by using the squeeze plate under conditions such that the following conditions are previously set: an optimal sand compactability, α0, a permissible range, ±ε, of the difference between the α0 and the actual sand compactability, α, a number, n, of molds to be made, and a relational formula that represents a correlation between a ratio of a reduced amount, ΔL, which is obtained by subtracting a distance, L', between the pattern plate and the squeeze plate after the molding sand is squeezed from a distance, L, between them before the molding sand is squeezed, to that distance, L, (that is, a percentage of the reduction of the distance: ΔL/L), and sand compactability; b) obtaining said percentage of the reduction of the distance, Δ L/L, and substituting said percentage for said relational formula to calculate the compactability, α, of the molding sand of the obtained mold; c) judging whether the difference between said compactability, α, and said optimal compactability, α0, is within said permissible range, ±ε; and d) making the next mold when said difference is within said permissible range, or when said difference is outside said permissible range, modifying any condition by transmitting a command to modify a molding condition(s) of the apparatus for making a mold and/or a mixing condition(s) of the mixer and then making the next mold, thereby making molds of a previously set number, n. The method of claim 1, in which the modification(s) of a molding condition(s) of the apparatus for making a mold is that of the pressure and/or time when the molding sand is blown into that space. The method of claim 1, in which the modification(s) of a molding condition(s) of the apparatus for making a mold is that of the position of the squeeze plate before the molding sand is squeezed. The method of claim 1, in which the modification(s) of the mixing condition(s) of the mixer is that of the set compactability of the molding sand when said molding sand is discharged from said mixer, and that of any other condition(s) necessary to realize the modification of the set compactability.

Inventors: KOMIYAMA TAKAYUKI, MAKINO HIROYASU, MATSUSHITA MASATOSHI, MATSUZAWA SHIN, NARUSE EIJI, KOMIYAMA, TAKAYUKI, MAKINO, HIROYASU, MATSUSHITA, MASATOSHI, MATSUZAWA, SHIN, NARUSE, EIJI, Komiyama, Takayuki, c/o Sintokogio, Ltd., Makino, Hiroyasu, c/o Sintokogio, Ltd., Matsushita, Masatoshi, c/o Sintokogio, Ltd., Matsuzawa, Shin, c/o Sintokogio, Ltd., Naruse, Eiji, c/o Sintokogio, Ltd.
Applicants: SINTOKOGIO LTD, SINTOKOGIO, LTD.
Application year: 2000
Main classification: B22C19
IPC codes: B22C19, B22C15