JPS59215242A - Reconditioning method of molding sand - Google Patents

Abstract

PURPOSE:To recondition old sand to molding sand with high thermal efficiency by treating the old sand used for casting in a fluidized roasting furnace having a specific construction thereby utilizing the combustible component of a binder sticking on the old sand. CONSTITUTION:Old sand (a) on which a binder is stuck after use for casting is charged from a hopper 15 into a fluidized roasting furnace 11 up to a prescribed level. Blasting is started from a blower 19 to form a fluidized layer 21 fo the old sand (a) in the lower part of a roasting part 13 in the furnace and thereafter a burner 16 is ignited to heat and roast the old sand (a) forming the fluidized layer 21. The old sand is taken out as reconditioned sand from a take- out port 17 upon heating of the layer 21 up to the prescribed roasting temp. The old sand (a) is then charged from the hopper 15 and after the sand is preheated by the high temp. waste gas in a preheating part 12, the sand is heated in the layer 21 and heats the air for the fluidized layer in a heat exchanger 20 of a flowing air heating part 14. Since the temp. of the layer 21 rises successively, the burner 16 is throttled and at the same time the combustible components of the binder sticking on the old sand is burned to roast the sand. The old sand is reconditioned to reconditioned sand with less fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating foundry sand, and in particular to a method for efficiently roasting foundry sand in a natural state by utilizing the thermal energy of combustibles contained in the binder of old sand. This relates to a method for recycling recycled foundry sand.

Conventionally, many mechanical methods have been proposed and widely used for regenerating this type of foundry sand 1, such as organic self-hardening sand. In the case of Shikaji green sand, it is difficult to regenerate using only mechanical methods, so the old sand is first roasted in a fluidized roasting furnace and then recycled using mechanical methods. Although relatively high-quality recycled sand can be obtained, it is generally unprofitable due to the low thermal efficiency of fluidized torrefaction furnaces, and there are few examples of this method outside of large-scale factories, and there may be no more economical method. The reality is that in most factories, old sand is simply disposed of.

Furthermore, for the purpose of reducing the recycling cost of the old sand, various proposals have been made for improving the thermal efficiency of the fluidized torrefaction furnace, and some examples will be described below.

First, Figure 1 shows the general configuration of a basic fluidized roasting furnace. That is, in this FIG. 1, there is a hopper 2 in the roasting furnace 1.
The foundry sand a introduced from the furnace is fed by a blower 3 and is blown out from an air nozzle 4 to form a fluidized bed 5 near the bottom of the furnace. The foundry sand a1 forming the fluidized bed 5 is heated into the furnace by a burner 6 provided on the furnace wall, and after being roasted, it is collected and discharged to the outside from the lower.

However, in a fluidized torrefaction furnace with a lever configuration, the characteristic of the fluidized bed is 2. It is possible to perform homogeneous torrefaction, and the retention time of the foundry sand in the fluidized bed can be extended, so it is relatively expensive. This means that high-quality recycled sand can be obtained.

However, in such a fluidized torrefaction furnace, the combustion conditions for the foundry sand in the fluidized bed are insufficient, so more thermal energy is consumed than necessary, and the amount of heat emitted as combustion exhaust gas is reduced. The thermal efficiency was extremely poor. That is, the foundry sand is heated in the upper part of the fluidized bed 5 by the flame and combustion gas of the burner 6, and the temperature is increased, but due to the lack of oxygen, the foundry sand 3 is heated.
The combustion rate of the carbon-based combustibles contained in 1 is slow, and as this foundry sand a'' descends in the fluidized bed 5 as it flows, the air nozzle 4 is also blown out into a high oxygen atmosphere by the flowing air. However, on the other hand, the fluidized air blown out lowers the temperature and suppresses its combustion.In other words, the foundry sand a' forming the fluidized bed 5 is
The heating stage in an oxygen-deficient environment and the cooling stage in an oxygen-enriched environment are repeated, and it takes a long time to sufficiently burn off the carbon-based combustibles contained therein, making it extremely inefficient. In addition to this, as mentioned above, there was a disadvantage that a large amount of thermal energy was consumed.

Therefore, in order to improve this point, conventional efforts have been made to improve thermal efficiency by recovering waste heat. An example of this is, for example, a method of providing a multi-stage grate above the fluidized bed (Jetko Sho 1).
54-28411), means for providing a vertical heat exchanger at the exhaust port (as described in Japanese Utility Model Publication No. 54-28412),
Means for introducing the roasted foundry sand into a cooling chamber and exchanging its sensible heat (published in Publication No. 1983-3126);
A means for forming a preliminary combustion zone by alternately arranging conical and inverted conical guide plates in several stages above the fluidized bed (Japanese Patent Publication No. 5
7-59015), and means using a fluidized bed heat exchanger (published in Japanese Utility Model Application Publication No. 58-4249).

Although each of these methods allows the waste heat of the fluidized roasting furnace to be recovered relatively efficiently, the temperature of the fluidized air preheated by the waste heat does not rise despite the large amount of waste heat recovered. Due to the relatively low thermal energy density of the recovered heat, it is not possible to improve the incomplete combustion conditions in the fluidized bed, which are the essential drawbacks of the fluidized torrefaction furnaces described above, and therefore, each of these examples Energy-saving measures naturally had their limits.

In view of these conventional drawbacks, the inventors thoroughly investigated the combustion action of fluidized roasting furnaces and discovered the following new technology. In other words, the disadvantage of the fluidized torrefaction furnace is that the combustion of carbon-based combustibles contained in the foundry sand is suppressed due to the synergistic effect of the cooling effect of the relatively low-temperature fluidized air in the fluidized bed and the oxygen-deficient state caused by the burner exhaust gas. It is to be done. On the other hand, when the fluidizing air temperature reaches, for example, 650°C or higher, the foundry sand self-combusts and generates thermal energy without the need for heating with a burner, and the amount of heat generated at this time is equal to the total amount of exhaust heat. Alternatively, if it is thicker than this, the temperature of the fluidized bed can be maintained at the desired high temperature, and the roasting action can be achieved without using any auxiliary fuel.

This invention focuses on the above point, and by effectively recovering waste heat and increasing the temperature of the flowing air as much as possible, it is possible to cause carbon-based combustibles contained in recycled foundry sand to self-combust. It is characterized by what it did.

In order to effectively recover waste heat in this step, it is best to recover heat directly from the maximum temperature zone of the fluidized torrefaction furnace, and foundry sand immediately after torrefaction is optimal for this maximum temperature zone. In this case, the means for moving the foundry sand from the fluidized bed to the heat exchange section and the passage of fluidized air from the heat exchange section to the air nozzle must be minimized to avoid a drop in temperature.

On the other hand, the exhaust gas directly above the fluidized bed is as high as the highest temperature zone, but the heat transfer coefficient is about % to % lower than that of foundry sand. It is inappropriate to recover heat from the exhaust gas, and on the contrary, it is more effective to use the heat of the exhaust gas for drying and preheating the molding sand that is introduced.

The minimum necessary temperature of the fluidizing air is determined by the calorific value and processing amount of the foundry sand, the furnace capacity, etc.

Next, FIGS. 2 to 4 show an embodiment of the method of this invention.
This will be explained in detail with reference to the drawings.

FIG. 2 shows a schematic configuration of a fluidized roasting furnace to which this embodiment method is applied. In FIG. 2, a preheating section]-2° roasting section 13 and a fluidized air heating section 14 are sequentially formed in the roasting furnace 1 from above. Input hopper 15. A burner 16 is installed on the furnace wall of the roasting section 13 toward the inside of the furnace. A take-out port 17 is provided at the bottom of the lower furnace of the fluidized air heating section 14, and the space between the roasting section 13 and the fluidized air heating section 4 below is partially partitioned by a fluidized air nozzle 18. Both parts 13.
There is no chute or other additional means between the fluidizing air nozzle 18 and the blower 19 outside the lower part of the furnace body.
A pipe connecting between the two is located within the fluidized air heating section 14 and forms a heat exchanger 20.

Therefore, in the first case of IW & formation, first, the molding sand 3 is charged from the bomber 15 to a predetermined level and then stopped, and the air blowing from the blower], 9 is started to air the fluidized bed 21 of the molding sand a'f. After forming the molding sand aI in the lower part of the roasting section 13 on the nozzle]-8, the burner 16 is ignited to heat and roast the foundry sand aI forming the fluidized bed 21, and this fluidized bed 2 is roasted. After waiting for the firing temperature to rise by 1", the outlet 17 is opened, and at the same time, the injection of foundry sand a is resumed.

Here, the foundry sand a is charged into the preheating section 12, dried and preheated by the exhaust gas, and then descends through the roasting section 3 to reach the fluidized bed 21. sand a'
is roasted by the burner 16 and heated to the maximum temperature in the furnace. Then, the foundry sand a+′ roasted in this way is
The sensible heat is exchanged with the flowing air that flows down inside the fluidized air heating section 14 and passes through the heat exchanger 20 with almost no temperature drop, and is eventually discharged from the outlet 7 to the outside. is discharged.

As this process is repeated, the fluidized air heating section 14
The average temperature of the air increases, and at the same time the temperature of the flowing air that undergoes heat exchange also gradually increases. The temperature of the fluidized bed 21 in which the fluidized air is blown out also shows a tendency to rise by 1, but in order to keep the roasting temperature constant, the burner 16 is gradually throttled down, and eventually the burner 16 is completely stopped. Even if the roasting temperature is maintained, the roasting temperature will be maintained, and the automatic combustion roasting operation will be automatically started. As the self-combustion roasting continues, the roasting temperature gradually changes, but when the temperature tends to rise, the amount of casting sand a is increased, and on the other hand, when the temperature tends to fall, the burner 16 is assisted. All you have to do is to control the roasting temperature by, for example, igniting the roasting material.

Incidentally, an example of a trial operation with this equipment configuration is shown in Fig. 3, but in this case, after the start of operation.

The system transitioned to full self-combustion roasting operation in about 3 hours.

Furthermore, the recycled sand obtained in this example can be used for self-hardening molds and the like by grinding without causing any problems with bamboo, but when used as shell sand, it requires further recycling treatment as in the conventional method. The recycled foundry sand obtained in this example is recycled using, for example, a mechanical recycling device described in Japanese Patent Publication No. 57-42411, and then processed according to JIS K 691.
When the bending strength of the shell sand was measured using 0, as shown in Figure 4, the recycled sand showed a bending strength higher than that of new sand after 5 treatments as shown by the symbol aiC, and compared to the conventional sand shown by the symbol aiC. Sand that was almost the same as recycled sand that was not subjected to self-combustion roasting was obtained.

Incidentally, code C is an example of recycled sand obtained only by a mechanical regeneration method.

As detailed above, according to the method of the present invention, there is a method for recycling foundry sand in which foundry sand containing a combustible binder is roasted in a fluidized roasting furnace. Foundry sand is allowed to flow down into a fluidized air heating section directly below the fluidized bed, and the fluidized air is heated to around the roasting temperature through heat exchange in this heating section, and then this heated fluidized air is blown out into the fluidized bed to form castings. Since the sand is made to undergo self-combustion roasting, it is possible to perform self-combustion roasting even for foundry sand, which has a low calorific value, such as earth and sand, thereby improving the thermal efficiency of the -C fluidized roasting furnace. Furthermore, it has the advantage of reducing the fuel consumption for re-burning the foundry sand, making it suitable not only for large-scale foundries but also for small-scale foundries where conventional technology was unprofitable. It has the advantage of being able to regenerate foundry sand at low cost and greatly contributing to resource and energy savings and pollution prevention.

[Brief explanation of drawings]

Figure 1 is a sectional view showing the general configuration of a basic fluidized roasting furnace.
Fig. 2 is a sectional view showing the general configuration of a fluidized roasting furnace to which an embodiment of the method of the present invention is applied, Fig. 3 is an illustration showing an example of the same operation, and Fig. 4 is a cross-sectional view showing the general configuration of a fluidized roasting furnace to which an embodiment of the method of the present invention is applied. It is a graph showing test results of recycled sand. 11. Roasting furnace, 12. Preheating section, ■3. Roasting section, 1
4... Fluid air heating section, 16... Nokuna, 18...
Fluidized air nozzle, 19... Blower, 20... Heat exchanger, 21... Fluidized bed. Patent Applicant Nippon Steel Pipe Fittings Co., Ltd. Agent Patent Attorney Takashi Suzu - Figure 1 Figure 3 Figure 4 - Visit to the R-Series Sales Market Tl ・1 ¥ List I < Patent Application 1982 -90519吋2, Name of the invention IIf production method of foundry sand 3, Name of amendment/Relationship with 11 cases Patent applicant 11 Wood and Steel Pipe Joint Co., Ltd. 4, Agent 5 Supplement 11 - Voluntary request for order 11 6. Specification and drawings to be amended: (1) The statement in the scope of claims column of the specification shall be supplemented as shown in the attached sheet. (2) Correct r650J in the first line of page 6 of Specification J) to r600J. (3) The following statement is added between page 9, line 20 and page 10, line 1 of specification J). [In addition, A in Fig. 3 shows the case where the amount of casting sand a is increased, and B shows the case where the air blowing by the blower 19 is stopped.
- Indicates when the Furthermore, is the dotted line in C fluid? :d
The graph shows the temperature change near the outlet where air is blown into the fluidized bed 21.According to this, the foundry sand that has been roasted to a high temperature flows into the fluidized air heating section 14 at the same time that the casting sand starts to be introduced. The temperature of the flowing air rose rapidly and reached a temperature of about 60℃.
．． It is understood that the foundry sand completely shifted to self-combustion roasting operation when the temperature exceeded 0°C. However, it goes without saying that the lower limit temperature of the fluidized air that is possible for self-combusting roasting of foundry sand varies depending on the capacity of the roasting furnace, the heat retention state, the amount of molding sand input, and the like. ” (4) Details f'-+
(') ``fs l O page 20 line 1-1 ni r roasting temperature near'' is replaced with ``temperature at which self-combustion roasting of foundry sand is possible.''
and correct it. (5) Among the drawings that we visited at the time of inspection, Figure 53 is attached in Appendix 1.
1. Supplement. Claims: A method for regenerating foundry sand in which foundry sand containing a combustible binder is subjected to JI calcining in a rotary torrefaction furnace, wherein the foundry sand roasted in a JQ fluidized bed is heated in a fluidized bed. The fluidized air is allowed to flow down to the fluidized air heating section directly below, and the fluidized air is heated to the self-combustion temperature of the foundry sand by heat exchange in this heating section, and then the heated fluidized air is blown into the fluidized bed to A method for recycling foundry sand, characterized in that the sand is self-combustible and roasted.

Claims (1)

[Claims] In a method for regenerating foundry sand in which foundry sand containing a combustible binder is roasted in a fluidized roasting furnace, the foundry sand roasted in a fluidized bed is flowed down to a fluidized air heating section directly below the fluidized bed. , the fluidized air is heated to around the roasting temperature by heat exchange in this heating section, and then the heated fluidized air is blown out into the fluidized bed to naturally roast the foundry sand. A method for recycling foundry sand.