JPH0318449A - Casting method for using organic self-hardening mold - Google Patents

Abstract

PURPOSE:To control hardening velocity of molding sand by preheating heat resistant volume increasing material to the prescribed temp. after forming the prescribed thickness of facing sand layer on surface of a pattern set in a flask of the organic self-hardening molding sand, charging, packing and molding the mold. CONSTITUTION:A cope 2 and drag 4 constituting a product cavity 10 is formed by packing the flask 6 with the molding sand 8. In the part except the facing sand layer constituting the cavity face in both molds of the cope 2 and drag 4, the volume increasing material 18 composed of the material having heat resistance except the molding sand 8, such as brick pieces, metal pieces, ceramic pieces, is packed. By the above mold structure, the using quantity of the molding sand 8 is effectively reduced and the hardening velocity of the molds 2, 4 is accelerated. The volume increasing material 18 used in there, is preheated to the prescribed temp. prior to packing into the flask 6. After waiting for hardening the surface layer of the mold, the pattern is released, and uneven time required for hardening caused by dispersion of various kinds of temp. conditions can be effectively avoided with the heat of the volume increasing material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a casting method using an organic self-hardening mold, and particularly to a method of controlling the hardening rate of foundry sand in the mold making process.

(Background Art) Conventionally, among cast products, so-called medium and large products weighing 50 kg or more, such as machine tool parts, are often manufactured by a casting method using an organic self-hardening mold. This method of using an organic self-hardening mold is also called the no-bake method, and it allows the desired mold to be obtained by curing without applying heat.For this reason, it is often used as an organic binder. Molds are often made using resins such as furan-based resins, but in general, liquid condensate resins whose molecular weight is not too large are used, and an acidic curing catalyst (curing agent) is mixed with this to perform condensation. start the reaction,
The activity is gradually increased, and finally the binding strength is maximized through three-dimensional crosslinking, making it a perfect template for the intended purpose. When casting using such an organic self-hardening mold, after forming such a mold, a predetermined amount of molten metal is poured into the obtained organic self-hardening mold, and then casting is performed. After that, by breaking the mold,
While the formed casting product is taken out, the casting sand contains foreign matter (inclusions) such as cast iron, iron pieces, and iron powder mixed into it.
It will be subjected to magnetic separation, recovered and reused.

By the way, the casting method using such an organic self-hardening mold has two advantages: (a) it completely hardens at room temperature, so there is no need for the labor and time required for firing, reducing the number of molding steps; and (b) the mold strength is improved. It is possible to produce high-quality castings with high dimensional accuracy and high dimensional accuracy.
C) It can contribute to the resource saving of silica sand, industrial waste, and pollution prevention. (d) The sand has excellent disintegration properties after pouring, and 90 to 95% of the used sand can be recovered, and it can be used repeatedly. Done,
It has the following characteristics, such as enabling a closed system for molding sand, and for these reasons, it is used in many foundries today for casting general industrial machinery and machine tool parts.

Therefore, in the case of organic self-hardening molds that have many advantages, the strength of the mold depends on the bonding strength of the three-dimensional crosslinks brought about by the condensation reaction between the resin added to the foundry sand and the hardening agent. Since the reaction rate of the condensation reaction is greatly influenced by temperature, the hardening rate of the foundry sand, or in other words, the time required to make the mold, can be affected by fluctuations in the environmental temperature during mold making. There was a problem that caused a considerable difference.

In fact, in foundries, it is difficult to keep the temperature inside the factory and the temperature of models, casting flasks, etc. constant throughout the year, and it is not uncommon for the temperature difference between summer and winter to be more than 30°C. In addition, during casting operations, in non-mass production molds, the mold and flask are different for each product, so there is little temperature variation, whereas in the case of medium-mass production molds, the molds are removed in a short period of time, and the same model can be immediately replaced.・When molding is performed using a flask, the temperature of the model and flask gradually rises. Therefore, due to such various temperature changes, variations occur in the curing time of the mold, and such disturbances in the molding cycle eventually cause disturbances in the entire production cycle. Therefore, it is necessary to control variations in the curing time of such molds, and even for products that use the same organic self-hardening process, the number of molds made per day is determined by the production quantity and delivery date. It is also necessary to control the curing time of the mold in accordance with the mold making cycle specified by the speed, so conventionally several types of curing agents (for example, a mixture of sulfonic acid and additives) are prepared. Then, the curing agent to be used was appropriately selected and the amount added was adjusted according to the set curing time of the mold.

For example, assuming that the type and temperature of the model, the size and temperature of the frame, the temperature of the sand, the added resin and hardening agent are set constant, a mold that can be removed in 10 to 15 minutes in the summer will take 20 minutes to be removed in the winter. It may take more than a minute, but in such case,
The amount of hardening agent added was increased, and if the curing time was still slow even with the maximum amount added, the type of hardening agent was changed so that mold cutting could be done in approximately the same amount of time as in summer. It is.

However, in such conventional methods, controlling the curing time is complicated because multiple curing agents are used, and if a mistake is made, there is a risk that not only the molding process but the entire production process will be disrupted. was there. In addition, it was necessary to manage many types of curing agents, which made management complicated and required equipment such as multiple tanks. Furthermore, when molding large objects, it may take about 10 minutes to fill the molding sand because it is necessary to form a uniform sand layer. There was also a concern that curing would begin, resulting in decreased workability and defective molds.

On the other hand, when trying to directly control the temperature, it is necessary to heat the molding sand, model, mold, etc., which requires a large-scale process, and the molding sand is exposed to heat from the beginning of filling. As a result, there is a high possibility that hardening will begin during filling, making it difficult to use in practice.

(Problem to be solved) Under such circumstances, the problem to be solved by the present invention is to
In a casting method using an organic self-hardening mold, a method for easily and stably controlling the hardening time of the mold is provided, and the type and amount of hardening agent used is reduced to simplify its management. There is a particular thing.

(Solution Means) In order to solve this problem, the present invention uses organic self-hardening molding sand to mold a target mold, and then applies a predetermined method to the obtained organic self-hardening mold. In a casting method using an organic self-hardening mold, which involves pouring molten metal and performing casting, the mold is formed by forming a surface sand layer of a predetermined thickness with the molding sand on the surface of the model placed in a casting flask. After the formation, a heat-resistant volume increasing material is added and filled, and if necessary, the above-mentioned foundry sand is added as backing sand, and the volume increasing material is heated to a predetermined temperature. By heating the molding sand in advance, the heat of the volume increasing material controls the hardening speed of the molding sand forming the mold.

(Specific structure e.) In short, in the present invention, the curing speed of the organic self-hardening mold is controlled not by the curing agent added, but by the heat added to the volume increasing material. By the way, this volume increasing material is used for the purpose of reducing the sand/metal ratio of organic self-hardening molds, and is used instead of self-hardening foundry sand in the part of the mold excluding the surface sand layer. It is something that can be done. FIG. 1 shows an example of an organic self-hardening mold used in the casting method of the present invention, in which an upper mold 2 and a lower mold 4, which constitute a product cavity 10, each contain a mold to be cast in a flask 6. It is formed by being filled with sand 8. The parts of both the upper and lower molds 2 and 4, excluding the skin sand layer constituting the cavity surface, are volumes made of heat-resistant materials other than the molding sand 8, such as brick pieces, metal pieces, ceramic pieces, etc. It is filled with the increasing material 18. By adopting such a mold structure, the amount of molding sand 8 used can be effectively reduced, the curing speed of the molds (2, 4) can be increased, and costs can be reduced.

In addition, in the figure, 12 is a core, . 14 is the sprue, and 16 is the top.

The volume increasing material 18 used in the present invention is
Before being filled into a predetermined flask 6, it is heated to a predetermined temperature in advance.

For example, FIG. 2 shows an example of a molding line in which the temperature of the volume increasing material is controlled. In such a line, the molded organic self-hardening mold is demolded after casting, and inclusions such as mold particles are removed from the molding sand by a predetermined magnetic separation device, and
The volume increasing material is separated by a predetermined recovery device, and the remaining molding sand is sent to a sand regeneration device, while the volume increasing material is transferred to a temperature adjustment device and adjusted to a predetermined temperature. It is stored for the next molding cycle.

More specifically, the temperature of the separated volume increasing material is first measured when it comes out of the recovery hopper 22, and while it is moving through the rotating drum 28, it is exposed to burners, etc. The heating and cooling device 30 is composed of a heating means and a cooling means such as a cooling air blower.
The temperature is raised or lowered to reach a predetermined set temperature. After the temperature adjustment is completed, the liquid is transferred to the filling supply device 26 through the stock hopper 24 and stocked. In addition, as a heat source for heating,
It is also possible to utilize the residual heat of the foundry sand immediately after separation.

Various conditions for temperature adjustment, such as the temperature setting of the heating means/cooling means (30) and the moving speed of the volume increasing material 18 in the drum 28, are determined by the above-mentioned measured temperature and processing amount of the volume increasing material 18, and further settings. It is determined by temperature, etc., and feedback control by measurement at intermediate points is also possible.

By the way, the specific temperature setting range for the volume increase material is as follows:
It is determined by the temperature of the molding sand, mold, and flask, and the setting cycle of the line. For example, if the overall temperature is low and the molding cycle is short, the temperature may be set to a high temperature of about 100°C. On the other hand, if the molding cycle is long despite the overall temperature being high, the temperature will be set at a low temperature of about 50''C.

Then, once a specific set temperature is determined, temperature control of the volume increasing material is executed by operations as shown in FIG. In general, the volume increasing material immediately after separation is
The measured temperature of this volume increasing material is compared with the temperature value set by various condition setting factors (individual temperature, setting cycle, etc.).
When the temperature of the volume increasing material is high, a cooling process is performed, and when it is low, a heating process is performed, and the temperature is controlled to a predetermined temperature by checking and adjusting the temperature again.

Incidentally, the temperature of the volume increasing material is generally controlled within a temperature range of 30 to 100°C. and,
The volume increasing material is not particularly limited in its size or shape, but since it is used as a heat storage material, it is desirable to have a predetermined capacity, and it is generally about 20 mm to 40 mm in diameter. Of course, it is also possible to use a combination of different sizes.

In addition, as a method for adjusting the temperature of the volume increasing material, batch processing as mentioned in the above specific example is possible because it can be stocked in a tank. On the other hand, sequential processing type line processing is suitable for lines where small items are passed in short cycles. In this line processing, a predetermined heating/cooling device is installed on the transfer pipe that transfers the volume increasing material from the separation device to the molding process, and the temperature is adjusted when the volume increasing material passes through the transfer pipe. This can be effectively carried out by making the transfer tube, for example, in the shape of a screw. These two processing methods are appropriately selected depending on the type of product to be processed in the molding line, the size of the flask, the molding cycle, etc.

In the casting method according to the present invention, the volume increasing material, which has been preheated to a predetermined temperature in this way, is placed in a casting flask, and a surface sand layer of a predetermined thickness is formed with molding sand on the surface of the model. After that, it is fed into the flask. The molding sand used in this process is the same as conventional molding sand, and contains resins such as furan resin, phenol resin, and acrylic resin as an organic binder, and also hardens such resins. It is made by adding a hardening agent for this purpose. however,. Since the purpose of the present invention is to control the hardening speed of the foundry sand using the heat of the volume increasing material, the amount of the hardening agent to be blended can be kept lower than in the past. Therefore, hardening can be prevented from starting during the formation of the sand layer, while after the formation of the sand layer,
By adding the temperature-controlled volume increasing material, the molding sand immediately begins to harden, regardless of the outside temperature or the temperature of the model or flask. and,
After filling with the volume increasing material, backing sand is formed to a predetermined thickness as necessary to strengthen the mold.Of course, these sand, volume increasing material, and backing sand are When charging the molding sand, as in conventional sand filling work, vibration is applied using a vibration generator or the like to improve the filling properties of the foundry sand and the volume increasing material. In addition, the ratio of the foundry sand and the volume increasing material in the mold is not constant depending on the shape, size, weight of the product, and the structure of the flask, but the ratio is approximately 30 to 40% of the volume in the flask. It can be replaced with a volume increasing material, which reduces the overall strength of the mold.

After filling as described above, wait until the surface layer of the mold hardens and then remove the mold.At this time, in the present invention, the volume increasing material is hardened by heat. Since the time can be freely controlled, curing delays in winter can be prevented, and variations in curing time due to variations in various temperature conditions can be effectively avoided.

Then, the removed flask and model are immediately returned to the filling process so that they can be used for the next mold, while the obtained mold is transferred to the mold coating process as necessary. . Note that at this point, the condensation reaction has not completely completed to the inside, so it is necessary to allow a certain amount of time before the subsequent mold coating process, but in order to shorten the time until the mold coating starts, the mold removal time is By delaying and sufficiently transmitting heat to the inside, it is also possible to shorten the overall time from the start of molding to mold coating and mold matching.

In the casting method according to the present invention, after waiting for the inside to completely harden, coating the mold as necessary and performing mold matching, a predetermined molten metal, such as cast iron, is poured in accordance with a conventional method. Molten metal, molten steel, etc. are poured into the mold to form the desired cast product. Thereafter, when cooling is completed, the mold is demolded and the cast product formed in the mold is taken out.
After further shot blasting and deburring, the material is made into a finished product. On the other hand, from the molding sand that has been demolded, a magnetic separator is used to magnetically separate inclusions such as mold particles, iron pieces, and iron powder that have been mixed into the molding sand, as in the conventional method. The volume-enhancing material is separated by means of a predetermined suction device, such as a screen. The foundry sand is recycled and then stored for reuse, and the volume increasing material is temperature-adjusted and then stored.

Incidentally, the volume increasing materials that have been proposed in the past have had the problem of being difficult to separate from the foundry sand and difficult to recover. By applying this material, the volume increasing material can be easily recovered using a magnetic separator or the like that removes casting debris, etc., and casting can be automated and a special suction device is not required. This results in an excellent effect. For example, such volume increasing materials include:
In addition to metal materials, various heat-resistant materials containing magnetic materials can be considered, such as those described in detail in Japanese Patent Application No. 1-40948 previously filed by the inventors of the present application. Ceramic poles containing magnetic material are particularly suitable. Such materials have excellent strength, heat resistance,
Because it has wear resistance, it can withstand thermal shock during casting, and because it is lightweight, it has excellent filling workability, and is also good as a heat storage material. Therefore, such ceramic poles can be used as a volume increasing material that is very suitable for the casting method of the present invention, and can effectively control the hardening rate of the mold, and can also be used as an intervening material after casting and demolding. The "magnetic separator" installed to remove the molding sand can easily separate it from the foundry sand, making it easy to recover it.

(Effects of the Invention) As is clear from the above explanation, in the casting method using the organic self-hardening mold according to the present invention, it is possible to replace the conventional method of increasing/decreasing the amount of hardening agent added and changing the type thereof. ,
Since the curing time of the mold is controlled by the heat of the volume increasing material that has been heated to the required temperature in advance, the curing time of the mold can be easily and stably controlled only by adjusting the temperature of the volume increasing material. It is possible to do so. Therefore, it is possible to prevent the prolongation of mold curing time in winter, and also to effectively prevent variations in mold curing time that change due to various temperature conditions, making it possible to stably control the production cycle. It became. In addition, it becomes possible to limit the curing agent to a single type, making it easier to manage the molding line and to manage inventory significantly.

(Example) Below, typical examples of the present invention will be shown to clarify the present invention more specifically. However, the present invention is not limited in any way by the description of such examples. Needless to say, it is not something that can be accepted.

In addition to the following examples and the above-mentioned specific description, the present invention includes various changes and modifications based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. It should be understood that improvements and modifications may be made.

Example 1 The target cast product has an outer diameter of 1200mmφ, a thickness of 50=120InIm, and a weight of 550
kg, the metal frame size is 1600mmXl800mmX300mm in order to cast the Gya material made of FC30.
(upper mold) or 250 mm (lower mold) casting flask is used, and the molding sand is AFS40, strangely furan resin 0.
A uniform mixture of 8% by weight and 24% by weight of curing agent (based on the amount added to the resin) was used, and the volume increasing agent was
Kogelai} (2Mg0・2A/!.0, ・5
SiO4) and magnetic material Ni-Zn based film
2 having a core of 10mmφ made of light.
A mold having the structure shown in FIG. 1 was molded using a ceramic pole having a size of 5lTIIIφ. The outside temperature was 4°C, the sand temperature was io'c, and ceramic poles heated to 90°C were used. Moreover, the S/M ratio was 1.63.

Such a mold can be prepared by i. o-1 It cured in 5 minutes and was able to be removed from the mold. Comparative Example 1 In order to cast the same material as in the example, multiple castings were made using the same flask as in the example without using a volume increasing material under the temperature conditions of an outside temperature of 4°C and a sand temperature of kO'C. The mold was made. The molding sand used was AFS40 sand mixed with 0.8% furan resin, and for each molding,
The amount of curing agent added was varied. In order to obtain a curing time comparable to that of the example, it was necessary to add 38% by weight of curing agent (based on the amount added to the resin).

From the above results, in the casting method according to the present invention, the curing speed is well controlled by the heat of the volume increasing material, and a good curing speed is obtained with a very small amount of curing agent added. It turns out that.

[Brief explanation of drawings]

FIG. 1 is an explanatory longitudinal cross-sectional view showing an example of the mold structure of an organic self-hardening mold used in the present invention, and FIG. 2 is a diagram showing a specific example of a molding line implementing the casting method according to the present invention. FIG. 3 is an explanatory diagram, and FIG. 3 is a flowchart showing a procedure for adjusting the temperature of the volume increasing material. 2: Upper mold 6: Casting flask 18: Volume increasing material 26: Filling supply device 28: Drum 30: Heating and cooling device 4: Lower mold 8: Molding sand Fig. 1 14

Claims (1)

[Claims] An organic self-hardening mold is created by molding a desired mold using organic self-hardening foundry sand, and then pouring a specified amount of molten metal into the obtained organic self-hardening mold. Using the casting method used, the mold is formed by forming a surface sand layer of a predetermined thickness with the molding sand on the surface of the model placed in the casting flask, and then filling it with a heat-resistant volume increasing material; Further, if necessary, the above-mentioned foundry sand is thrown in as backing sand, and the above-mentioned molding sand is carried out by heating the volume-increasing material to a predetermined temperature in advance. A method characterized in that the hardening speed of foundry sand forming a mold is controlled.