JPS61182845A - Method for reconditioning molding sand for cold box method - Google Patents

Abstract

PURPOSE:To eliminate replenishment of new sand by allowing reconditioned sand to contact with flowing air mixing prescribed time, and converting CaO on the surface 8 the sand to CaCo3, in the process of fluidizing classification removal of fine grains in the sand. CONSTITUTION:The sands containing CaO in their superficial layer recovered in the shaking-out stage are once stored in the recovery hopper 1, and then sent to a calcination oven 2 at a constant flow rate, where coal powder contained in the sand and resin film on the surface are burnt. Calcination, after being cooled, is sent to the superficial layer removing device 3 in which mechanical impacts using the centrifugal force is applied to deposit of binder such as bentonite stuck on the surface of sands as a result of calcination to grind the surface of sands and remove the deposit material. Then, the sand is introduced in the fluidization classification device 4 where the sand comes in contact with the flowing air containing more than 0.5%, preferably 2-3% Co2 for 5min or more. Fine powder classified is collected by the dust collector 5, and reconditioned sand is stored in the hopper 6. CaO on the surface of the sand is changed into CaCO3 being an inert compound against resins, giving reconditioned sand capable of forming casting molds stronger than normally reconditioned sand.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for regenerating foundry sand for cold box molds.

[Prior art]

The cold box method, which is one of the methods for making molds used in casting, allows the mold to harden at room temperature, so resins such as epoxy resin or wooden models can be used.
It has an excellent 1R property of fast hardening and very good heat disintegration properties, and is also excellent in terms of energy saving and labor saving, so it is suitable for high-mix, low-volume production and is used for various parts. It is used for casting.

The Ashland method is a typical method, in which resins with isocyanate groups and phenolic resins are mixed into sand grains as binders, and the mixed sand is blown into the core at room temperature using the blow ink method. This is a method of curing by supplying amine gas, and is said to be the most suitable method for cores.

In this cold box method, as in general mold making, sand resources are recovered and recycled in order to make effective use of them, but they are mixed into the main mold sand at a desired ratio during the recovery stage. . In other words, a foundry sand mold consists of a main mold and a core mold, which are taken apart at the same time after casting, so when the sand is removed, the main mold is recovered mixed with the core mold, and the recovered sand is generally mixed with the base sand. Caking materials such as silica sand and bentonite,
Consists of coal powder and other binding materials.

Therefore, the recovered sand is usually processed in a dry or wet regeneration device, and the dry regeneration device consists of a hopper that stores and sends out the recovered sand, a roasting furnace that removes resin and coal powder from the coated sand, and a roasting furnace that removes resin and coal powder from the coated sand. It consists of a surface stripping device that removes welded substances such as atomized bentonite, a fluid classifier that removes fine powder, a blower, a dust collector that collects the removed fine powder, and a hopper that stores recycled sand.

[Problem that the invention seeks to solve]

However, the problem with the above-mentioned recycling equipment is that if sand treated by the recycling method is used alone, the strength of the mold will decrease for reasons that will be explained later, making it particularly unsuitable for molding cores, and a large amount of fresh sand must be used. Therefore, a large amount of recovered sand is discharged as waste, which poses a problem in terms of pollution control.

The coal powder in the resin-encrusted sand used as core sand is removed in the high-temperature roasting process, but in the recycled sand, an roe-like (oldic) layer is formed on the sand surface. Bentonite and CaO remain on the sand surface, which is firmly welded and cannot be completely removed by the surface stripping device. Therefore, during humid summer months, CaO on the sand surface reacts with moisture and changes into active substances such as CaC0H)z, and it is thought that residual bentonite is involved in this reaction. Next, when a resin is added to such recycled sand and kneaded, the Ca(OH)t described above will harden the resin, making it difficult to obtain a mold with sufficient strength even if it is subsequently molded.

For the reasons mentioned above, the presence of CaO shortens the life (pot life) of the kneading sand, so in order to obtain a good mold, it is necessary to use a large amount of fresh sand with less dirt. CaO in the new sand has already been changed to CaC0 by Cot in the atmosphere, so it does not affect the molding, but due to an imbalance in the sand balance, the amount of sand to be discarded increases, resulting in an increase in the purchase cost of new sand, the occurrence of pollution, etc. 0 Problems Occurrence The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method for regenerating recovered sand that can obtain recycled sand that does not adversely affect the strength of the mold.

[Means to solve all problems]

The foundry sand regeneration method for the cold box method of the present invention involves mixing Cot gas of 0.5 IF or more with fluidized air when removing fine particles in the recovered foundry sand by fluid classification. The method is characterized in that calcium oxide (CaQ) on the surface of the foundry sand is changed into calcium carbonate (CaCO3)K by contacting the molding sand for 5 minutes or more.

[Effect]

The method of the present invention can be easily implemented by simply adding some equipment to the conventional sand reclamation apparatus. That is, liquefaction c
o, '6 Heating and vaporizing a certain amount of CO2 just before the blower
The mixing method is not particularly limited, as long as the gas gold is mixed and fed into a fluid classifier. At this time, while the sand is staying in the above device, the CaO on the sand surface is sufficiently
o.

It is only necessary to adjust the sand supply ti or adjust the capacity f of the device so as to change the value.

The mixing ratio of Cot gas to fluidized air is determined by the Ca in the recovered sand.
It is related to the O content, but according to the test results of the present inventors, it is 0.5
The residence time of the sand in the fluidized fluid classifier is preferably 5 minutes or more. Furthermore, it has become clear that even greater effects can be obtained by dehumidifying the flowing air beforehand.

〔Example〕

The present invention will be explained by way of examples with reference to the drawings.Example 1 Figure 1 shows a process diagram of sand regeneration to carry out the present invention, 1 is a recovery sand hopper mouth, 2 is a roasting furnace. , 3 is a surface stripping device, 4 is a fluid classifier, 5 is a dust collector, 6μ recycled sand hopper, 7 is a blower, 8 is a liquefaction tank, and 9 is an evaporator.

0.0002 to 0.0.
The sand containing 4% CaO is once stored in a recovery sand hopper 1, and then sent in a fixed amount to a roasting furnace 2, where the resin of the coating sand and coal powder etc. in the sand are incinerated. After cooling, the sand is sent to a surface peeling device 3, where a mechanical shock is applied to the welded material (alltic layer) of a binder such as bentonite generated on the surface of the sand by the roasting process, making full use of centrifugal force to remove the surface of the sand. Polish to remove deposits. The sand is then introduced into a fluid classifier 4 and brought into fluid contact with fluidized air containing 2 to 3% CO for 5 minutes. Note that Cot gas is liquefied CO1 in evaporator 9.
It can be easily obtained by heating and vaporizing with a heater lo. The fine powder classified by the fluid classifier 4 is collected in a dust collector 5, and the regenerated sand is stored in a regeneration hopper 6.

The CaO on the surface of the hard surface regenerated in this way changes to CaCO, which is inert to the resin, and therefore, even under humid summer conditions, substances that promote the chemical reaction of the resin are not generated, resulting in increased strength. It is possible to make a high mold.

In other words, recycled sand has 3 odor, polyisocyanate resin as a binder has 37.5F, and phenolic resin has 37.5? was added and kneaded for 1 minute with a speed muller (mixing device), and after 30 minutes of kneading, it was blown into a mold of 1 OwX 30 wX 85■, and triethylamine was aerated to harden it to make a test piece, and the bending strength was measured. .

As a result, recycled sand treated without CO or gas mixed with fluidized air cannot produce a mold with practical strength unless 80% by weight of new sand is added, whereas with the recycled sand in this example, only 20% of new sand is added. A mold with comparable strength was obtained. In addition! Figure 3 shows the strength ratio (strength ratio) of a mold made of 100% recycled sand to a mold made of 100 cm new sand.
It is shown that a strength ratio of about 70% can be obtained by using recycled sand that has been fluidized and classified using telefluidized air to which 100% of CO8 has been added.

Embodiment 2 In this example, as shown in FIG. 2, a dehumidifier 11 is provided on the suction side of the blower 7 to dehumidify and dry air (absolute humidity 15 to 9H!).
0/Kf dry air) was used, and the other conditions were the same as in Example 1. Furthermore, by combining dehumidification with CO and gas mixing, it is possible to add new sand.

Figure 4 is a graphical representation of the combined effect of dehumidification and COl, divided into the periods of high atmospheric humidity from the end of July to the end of September and the periods of low atmospheric humidity from October onwards. This shows that a mold with high flexural strength can be obtained regardless of the size. Next, the six curves will be explained. A represents the atmospheric humidity, and B represents the humidity after dehumidification. C indicates the bending strength of the gold molded immediately after kneading, and shows the highest value regardless of whether the gold is treated with flowing air or not.

D, E, F, and G indicate the bending strength when molded 30 minutes after kneading, and curves D and E respectively.

The processing conditions for F and G are as follows, and the effect of the present invention appears when the molding is carried out approximately 5 hours after the crosstalk.

D: Dehumidification only, CO, none, E: Mixing CO without dehumidification, F: untreated, G: Dehumidification and CO! Used together.

〔Effect of the invention〕

As described above, even if only the sand recycled by the method of the present invention is used, molds with sufficient strength can be stably made under humid summer conditions, so there is no need to use new sand, and sand resources can be used effectively. Can be used. Therefore, the cost of purchasing new sand, the cost of dealing with waste, and the cost of energy for mixing new sand and recycled sand are reduced, operational management becomes easier, and casting costs are reduced.

Furthermore, since the quality of the sand used is stable, the amount of resin added can be reduced, resulting in fewer gas defects during casting and a lower incidence of defective products.

[Brief explanation of drawings]

FIG. 1 shows a process diagram of Example 1, FIG. 2 shows a process diagram of Example 2, FIG. 3 shows a graph showing the relationship between COt mixing ratio and mold strength rate, and FIG. Figure 3 represents a graph regarding the dehumidification and CO2 mixing effect of flowing air. In the figure, l......Recovered sand hopper 2...Roasting furnace 3...Surface peeling device 4... - Fluid classifier 5... Dust collector 6... Recycled sand hopper 7... Blower 8... ...Liquefied CO2 tank 9...Evaporator IO...Heater 11...Dehumidifier (1 other person) Fig. 1 5 Fig. 2

Claims (1)

[Claims] When removing fine particles in recovered foundry sand by fluid classification, CO_2 gas of 0.5% by weight or more is mixed with fluidized air and brought into contact with the recovered foundry sand for 5 minutes or more to remove calcium oxide ( CaO) to calcium carbonate (CaCO_3
) A method for regenerating foundry sand for cold box method.