JPS6338254B2 - - Google Patents

Description

Claim 1: A method for manufacturing a foundry core or mold of granular and/or fibrous material using sodium silicate or potassium silicate as a binder, in which the sodium or potassium silicate is calculated based on the weight of the material. and at least one surfactant selected from the group consisting of silicone oils, silicone emulsions and siliconates in an amount of 1-3% to the mixture of substances, and 0.1% calculated on the weight of the substances. A method for manufacturing a foundry core or mold, which comprises adding the core or mold to a temperature of 110-180°C.

2. The method according to claim 1, characterized in that a core box is used and the core box is heated to 110-180°C.

3. The method according to any one of claims 1 to 2, characterized in that hot air at a temperature of 110 to 180° C. is blown onto the core.

4. The method according to any one of claims 1 to 2, characterized in that CO ₂ is blown into the core, and hot air may or may not be blown supplementarily.

5. Forming a core or a mold with a core and a molding agent, respectively,
The method according to any one of claims 2 to 4, characterized in that an ester curing agent is added thereto.

6 Molar ratio of sodium or potassium silicate
Process according to any of the preceding claims, characterized in that SiO ₂ /Na ₂ O is 2-3.

Description The present invention relates to a method for producing foundry cores or molds of granular and/or fibrous material using sodium or potassium silicate as a binder.

Sodium or potassium silicates, hereinafter referred to as alkali silicates, have long been used in the foundry industry, for example in the production of sand molds and cores. The mold or core is cooled at room temperature with a mixed curing agent or by blowing CO ₂ . However, such manufacturing requires a relatively high binder content to obtain sufficient strength. Moreover, the use of potassium silicate as a binder is associated with several other disadvantages, among which are mentioned the following:

Reduced fire resistance of molds and cores.

Insufficient collapse of the mold or core after casting.

Low recovery of used molds and core material (molding sand).

These disadvantages have traditionally limited the use of alkali silicates in the manufacture of molds or cores.

In the manufacture of cores using organic binders, generally resins, a substance that acts as a curing agent (for example, an acid) is mixed and the core box or core is
Heat to a temperature of 250-300 ° C.

Cores made in this manner exhibit substantial gas evolution both during core manufacture and subsequent casting, thereby rendering the environment in such foundries inhospitable. Moreover, the production of such cores requires a lot of energy.

The present invention has the aim of reducing the aforementioned disadvantages and relates to a method for producing foundry cores or molds of granular and/or fibrous material using sodium or potassium silicate as binder. The invention is essentially characterized in that the surface-active substance is added during mixing of the substances and the core or mold is heated to 110-180°C.

By adding surface-active substances to the mold material according to the invention and heating the core or mold to 110-180°C, it is possible to reduce the amount of alkali silicate added compared to the amounts used previously. , thereby not reducing the strength or surface hardness of the mold or core. This also means that the mold and core can be handled and stored more easily and that the mold and core exhibit sufficient resistance to heat and mechanical stress during casting. Due to the low alkali silicate content, the disintegration after casting is very good. Moreover, casting protects the environment, since it produces very few gases that are harmful to health. The radiant heat during core manufacturing is moderate and energy consumption is low. Due to its rapid procedure, the method particularly allows continuous production.

A relatively small amount of liquid alkali silicate with a SiO ₂ /Na ₂ O ratio (molar ratio) of 0.5 to 3.5 and a surfactant in the form of a surfactant, silicone oil, silicone emulsion or siliconate are used. Added to the mold or core material to be bound.

In order to be able to keep the amount of binder to a minimum and achieve optimal disintegration after casting, for example sodium silicate with some additives is used, the additives being: (a ) At least one surfactant selected from the group consisting of silicone oil, silicone emulsion and siliconate.

(b) Disintegrants and surfactant-forming agents in the form of sugar derivatives, which are usually treated to keep them stable in sodium silicate solutions. The sugar derivatives refer to a group of substances similar to sugars that can be derived from sugars, such as glucose phosphate, glucosan, glycosemide, glycal, thioacetal, glucofuranose, glucopyranose, gluconate, lactite, Examples include lactulose, sorbitol, xylitol, and the like.

The present invention will be described in more detail below using examples in which the invention is used. It is observed that the conventional usual amount of alkali silicate is 3-5% or more, calculated on the basis of the amount of sand.

(1) A mixture of 1.5% sodium silicate (ratio 2.7) and 0.015% silicone emulsion was made, calculated based on the amount of sand and sand. Height 50mm and diameter 50mm
A cylindrical specimen was made from this mixture. sample
It was heated to 150°C, and after cooling, a pressure test was conducted.
Compressive strengths of 500-600 N/cm ² were obtained. A zero point test without the addition of silicone (a comparative test conducted in the same manner as above except without the addition of silicone emulsion) produced a compressive strength of only 80 to 90 N/cm ² .

For a 2% sodium silicate content and 0.02% silicone emulsion, a compressive strength of about 800 N/cm ² is obtained, while in the zero point test it is about 550 N/cm ²
occurred.

(2) The core box was heated to 150°C in a core shooter of an automotive material foundry. A core mix was made of sand (average particle size 0.25 mm) and 2.5% of the binder as described above. The core mixture is filled into the machine and the pressure is such that a good degree of core filling is obtained, usually 400-700kPa (4-7Kg/cm ² ).
I shot it with The core was heat cured in the box in 20-60 seconds depending on the thickness (10-50 mm) and was then ready for casting.

(3) Core manufacturing was performed as described above. However, this time the core was thicker, so hot air (110-150°C) was also blown into the core box. In this way, a completely satisfactory core could be produced in less than 60 seconds.

(4) The core was manufactured according to (3). However, here the hot air was replaced with _CO2 gas. This method also produced completely satisfactory cores. Hitherto, this has not been possible with the above alkali silicate contents.

(5) The core was manufactured according to (3), but some of the hot air was replaced with CO ₂ . A completely satisfactory core was obtained.

(6) The core was manufactured according to (4). However, here the binder is 49°Be (where the unit "°Be" refers to the Baume hydrometer reading and the unit "Baume degrees" used as a measure of specific gravity), with a ratio of 2.7. Pure sodium silicate 3% and 1
% sugar derivative, i.e. the total amount of binder is 4%
It was hot. The core showed good surface hardness. However, the collapse after casting is due to the above (2),
It was somewhat worse than (3) and (4).

(7) The core was prepared according to (3), but with the addition of 7-10% ester hardener of the usual type. As a result, the core soaks and dries more quickly, which is valuable in the manufacture of large molds/cores.

Experiments have shown that the surfactant should not exceed 0.1%, calculated on the weight of the material, and should preferably be in the range 0.0001-0.1%.