Process for producing foundry exothermic body

Abstract: A process for producing a foundry exothermic body such as an foundry exothermic riser sleeve includes the steps of preparing a raw material mixture whose components include one or more powdered/granular refractories, one or more powdered/granular exothermic materials, one or more powdered/granular oxidants and one or more powdered pro-oxidants, mixing thermosetting phenol resin with the raw material mixture to coat grain surfaces of the raw material mixture with thermosetting phenol resin and obtain a thermosetting phenol resin coated raw material mixture, and using the shell molding process to form and cure the thermosetting phenol resin coated raw material mixture into a foundry exothermic body of prescribed shape.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a process for producing a foundry exothermic body. Description of the Prior Art A number of processes are available for making shaped foundry exothermic bodies from a raw material consisting of a mixture of an exothermic material, typically aluminum, an oxidant, typically manganese dioxide, a pro-oxidant, typically powdered cryolite, and a refractory as an aggregate. These include the commonly used hand ramming process, CO 2 process and cold box process. For reasons explained below, however, the shell molding process is not used to produce shaped foundry exothermic bodies. Among processes for making molds for metal casting, the shell molding process is the one that uses a foundry sand such as silica sand as the mold material. For example, a mold material referred to as "resin coated sand" is used which consists of silica sand coated with a thermosetting resin such as phenol resin as a binder. However, the raw material of a foundry exothermic body does not consist solely of refractory materials. It is a mixture also including materials with properties different from those of a refractory, such as the aforesaid exothermic material, typically aluminum, oxidant, typically manganese dioxide, pro-oxidant, typically powdered cryolite, and the like. When the shell molding process is applied to form a foundry exothermic body using such a mixture as the forming material, the thermosetting resin added as binder must be coated on the forming material in order to minimize the amount thereof added and prevent its segregation. French Patent 2 010 247 discloses a spherical foundry exothermic body comprised of mixture of different ingredients including refractories, agglomerating agents, termic shook adsorbers, exothermic materials, demoulding agents, and catalysts. For forming the exothermic foundry body, the raw material mixture is coated with a resin such as calcium stearate. The coated mixture is then transformed into a foundry body by hardening the thermoretting resin. Since the properties of the components making up the mixture are extremely different, however, it is difficult to uniformly disperse the thermosetting resin used as binder in the raw material, In addition, when the coating with the thermosetting resin is effected by the hot process, which involves heating to around 130-160°C, the raw material mixture may ignite and burn during the heating owing to reactions among the exothermic material, the oxidant and the pro-oxidant. This makes it difficult to supply a raw material mixture of constant composition on an industrial basis. Stable production of foundry exothermic bodies having prescribed uniform strength and exothermic property has therefore been difficult. SUMMARY OF THE INVENTION This invention is directed to providing a process for producing a foundry exothermic body by the shell molding process that do not have the foregoing problems of the prior art. To achieve this object the invention provides a process for producing a foundry exothermic body comprising the steps of: preparing a raw material mixture whose components include one or more powdered/granular refractories, one or more powdered/granular exothermic materials, one or more powdered/granular oxidants and one or more powdered pro-oxidants, said raw material mixture being obtained by mixing those components of the raw material mixture into a primary raw material inixture that do not undergo exothermic or combustion reaction when heatad to a temperature of 130-300°C and mixing all components of the raw material mixture other than the primary raw material mixture components into a secondary raw material mixture components, to obtain a primary and a secondary raw material mixture, mixing thermosetting phenol resin with the primary raw material mixture components at a temperature of 130-160°C to coat grain surfaces of the primary raw material mixture components with a molten thermosetting phenol resin layer, mixing liquid thermosetting phenol resin with the secondary raw material mixture components at room temperature or a temperature exceeding room temperature but not exceeding 130°C to coat grain surfaces of the secondary raw material mixture components with thermosetting phenol resin, and mixing the thermosetting phenol resin coated primary and secondary raw material mixtures to obtain the raw material mixture, and using the shell molding process to form and cure the obtained thermosetting phenol resin coated raw material mixture into a foundry exothermic body of prescribed shape. The above process for producing a foundry exothermic body may comprise the steps of: preparing a primary raw materiel mixture composed 60-70 wt% of one or more powdered/granular refractories, 15-30 wt% of one or more powdered/granular exothermic materials and 5-15 wt% of one or more powdered/granular oxidants, adding to 100 parts of the mixture 1-5 parus of thermosetting phenol resin together with resin curing agent followed by mixing at 130-160°C to coat grain surfaces of the mixture with a molten thermosetting phenol resin layer and obtain a thermosetting phenol resin coated primary raw material mixture, adding to 100 parts of the thermosetting phenol resin coated primary mixture 10-20 parts of a thermosetting phenol resin coated secondary raw material mixture obtained by mixing at room temperature or at a temperature exceeding room temperature but not exceeding 130°C 1-6 wt% of liquid or powdered phenol resin, 10-30 wt% of one or more powdered oxidants, 60-75 wt% of one or more finely powdered pro-oxidants and 8-15 wt% of one or more finely powdered exothermic agents, to form a raw material mixture and using the shell molding process to form and cure the resulting mixture into a foundry exothermic body of prescribed shape. In any of the foregoing processes, the foundry exothermic body can be an exothermic riser sleeve, an exothermic core, an exothermic neckdown core, an exothermic mold, an exothermic pad or a body similar to any of these. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention relates to a process for forming a foundry exothermic body such as an exothermic riser, an exothermic core, an exothermic sleeve, an exothermic neckdown core, an exothermic mold or an exothermic pad by the shell molding process. Raw materials of the thermosetting resin coated powdered/granular composition according to this invention include refractories such as silica sand, zircon sand, alumina sand and dolomite, exothermic materials such as aluminum, ferrosilicon, calcium silicon, magnesium and aluminum-magnesium alloy, oxidants such as manganese dioxide, potassium nitrate, sodium nitrate, potassium chlorate, iron oxide and red iron oxide, and pro-oxidants such as cryolite, calcium fluoride and sodium silicofluoride. The refractories can be used as granules of around 0.10-0.15 mm (100-150 mesh), and the exothermic materials, oxidants and pro-oxidants as granules, powders of under 0.10 mm (100 mesh) or mixtures of powders and granules. The thermosetting resin used to coat the grain surfaces of the components of the powdered, granular or mixed powdered and granular raw materials can be a novolak-type or resol-type phenol resin. The setting agent can be hexamine (hexamethylene tetramine). Coating of the powdered/granular primary raw material mixture components with thermosetting resin can be conducted, for example, by the method of preheating the primary raw material mixture components to around 130-160°C and charging them into a mixer, adding hexamethylene tetramine (resin setting agent) and 2-4 wt% of 85-100°C softening point powdered thermosetting resin thereto, and mixing the result to coat the surfaces of the primary raw material mixture component grains with molten thermosetting resin. Another method that can be adopted is to mix powdered thermosetting resin dissolved in a solvent or liquid thermosetting resin with the raw material mixture components. Still another is to mix liquid thermosetting resin with the raw material mixture components at a temperature exceeding room temperature, e.g., at 40-70°C. The invention will be explained with reference to specific examples. Example 1 (comparison) To 100 parts of a primary raw material mixture composed of Foundry silica sand 40 wt% Zircon sand 25 wt% Aluminum powder 25 wt% Iron oxide (Fe 3 O 4 ) 8 wt% Potassium nitrate 2 wt% was added 3 parts of novolak-type thermosetting phenol resin. The result was mixed at 130-160°C to coat the grain surfaces of the primary raw material mixture with the resin. The obtained resin coated primary raw material mixture was used to form a foundry exothermic riser by the shell molding process. The granularity of the silica sand, zircon sand, aluminum powder and iron oxide in the resin coated primary raw material mixture was made not less than 0.10 mm (100 mesh) to reduce the amount of fine powder contained in the mixture. As this' prevented any loss of the raw material by dust collection/removal owing to heat generation and dust collection during the heating step, there could be obtained a foundry exothermic riser exhibiting a strength of 30-35kgf/cm 2 . The foundry exothermic riser thus entailed no problem regarding practical utility from the aspect of strength, despite being formed by the shell molding process, Example 2 To 100 parts of a primary raw material mixture composed of Foundry silica sand 40 wt% Zircon sand 25 wt% Aluminum powder 25 wt% Iron oxide (Fe 3 O 4 ) 10 wt%, all of a granularity of not less than 0.10 mm (100 mesh), was added 3 parts of novolak-type thermosetting phenol resin. The result was mixed and kneaded at 130-160°C to coat the grain surfaces of the primary raw material mixture with the resin and obtain a thermosetting phenol resin coated primary raw material mixture. To 100 parts of the obtained thermosetting phenol resin coated primary raw material mixture was added 10-15 parts of a secondary raw material powder composed of Phenol resin 5 wt% Potassium nitrate 20 wt% Cryolite of under 0.10 mm (100 mesh) 40 wt% Iron oxide (Fe 3 O 4 ) of under 0.10 mm (100 mesh) 25 wt% Aluminum fine powder of under 0.10 mm (100 mesh) 10 wt% Aluminum fine powder of under 0.10 mm (100 mesh) 10 wt% and the result was mixed. The obtained mixture was used to form an exothermic neckdown core by the shell molding process. The shaped body exhibited a strength of 20-30kgf/cm 2 , which is near the 30-40kgf/cm 2 strength of ordinary shell molds and superior to the 20kgf/cm 2 strength of an exothermic body formed by the CO 2 process. The strength was sufficient for practical use. The inclusion of nitrate and finely powdered aluminum, cryolite and iron oxide in accordance with Example 2 enhances the uniformity of the raw material mixture composition, lowers the ignition temperature of the shaped body and increases its combustion rate compared with the case of comparative Example 1. Like the foundry exothermic bodies in common use, therefore, an exothermic pad, exothermic core, exothermic mold, exothermic neckdown core, exothermic riser sleeve or the like formed using raw material mixture is completely adequate for use as part of a foundry mold. Example 3 To 100 parts of a primary raw material mixture composed of Foundry silica sand 35 wt% Zircon sand 25 wt% Granular aluminum 25 wt% Iron oxide (Fe 3 O 4 ) 15 wt%, all of not less than 0.10 mm (100 mesh), was added 1 part hexamine as resin setting agent and 3 parts of phenol resin. The result was mixed at 130-160°C to obtain a thermosetting phenol resin coated primary raw material mixture. Separately from this process, liquid thermosetting resin was added to a mixture of finely powdered aluminum and cryolite of under 0.10 mm (100 mesh). The result was mixed to obtain a thermosetting resin coated secondary raw material powder. The thermosetting resin coated secondary raw material powder was added to the thermosetting resin coated primary raw material mixture to obtain a thermosetting resin coated raw material mixture that was used to form an exothermic sleeve by the shell molding process. The exothermic sleeve exhibited a strength of about 35-45kgf/cm 2 , which is comparable with the strength of an ordinary shell mold and sufficient for practical use. In accordance with this example, mixture components such as finely powdered aluminum, nitrate, red iron oxide and cryolite, which are liable to undergo exothermic reaction and combustion if present in the primary raw material mixture at the time of effecting resin coating of the primary raw material mixture at 130-160°C (hot process), can be processed separately of the primary raw material mixture by a resin coating process effected at room temperature or, for example, at 40-70°C (cold process or warm process) and the obtained thermosetting resin coated mixture can thereafter be mixed with the primary raw material mixture. This improves the safety of the work while enabling production of a foundry exothermic body with a low ignition temperature like that of an ordinary exothermic material. When a foundry exothermic body such as an exothermic neckdown core or an exothermic pad produced by the shell molding process in accordance with this invention is used in iron or steel casting, no gas induced defects occur in the casting surface in contact therewith. The invention therefore provides an outstanding effect of enabling securement of an excellent casting surface of superb appearance. Further, when an exothermic neckdown core according to the invention is used, productivity is markedly increased because the opening of the core can be made smaller to facilitate break-off of the riser. Moreover, since the invention enables the shell molding process to use a thermosetting resin coated raw material containing exothermic components for high-volume production of high-strength foundry exothermic bodies of desired shape capable of manifesting uniform and excellent exothermic effect, it reduces casting production cost and, as such, has very great industrial utility.

Claims: A process for producing a foundry exothermic body comprising the steps of: preparing a raw material mixture whose components include one or more powdered/granular refractories, one or more powdered/granular exothermic materials, one or more powdered/granular oxidants and one or more powdered pro-oxidants, said raw material mixture being obtained by mixing those components of the raw material mixture into a primary raw material mixture that do not undergo exothermic or combustion reaction when heated to a temperature of 130-300°C and mixing all components of the raw material mixture other than the primary raw material mixture components into a secondary raw material mixture components, to obtain a primary and a secondary raw material mixture, mixing thermosetting phenol resin with the primary raw material mixture components at a temperature of 130-160°C to coat grain surfaces of the primary raw material mixture components with a molten thermosetting phenol resin layer, mixing liquid thermosetting phenol resin with the secondary raw material mixture components at room temperature or a temperature exceeding room temparature but not exceeding 130°C to coat grain surfaces of the secondary raw material mixture components with thermosetting phenol resin, and mixing the thermosetting phenol resin coated primary and secondary raw material mixtures to obtain the raw material mixture, and using the shell molding process to form and cure the obtained thermosetting phenol resin coated raw material mixture into a foundry exothermic bcdy of prescribed shape. A process for producing a foundry exothermic body according to claim 1 comprising the steps of: preparing a primary raw material mixture composed 60-70 wt% of one or more powdered/granular refractories, 15-30 wt% of one or more powdered/granular exothermic materials and 5-15 wt% of one or more powdered/granular oxidants, adding to 100 parts of the mixture 1-5 parts of thermosetting phenol resin together with resin curing agent followed by mixing at 130-160°C to coat grain surfaces of the mixture with a molten thermosetting phenol resin layer and obtain a thermosetting phenol resin coated primary raw material mixture, adding to 100 parts of the thermosetting phenol resin coated primary mixture 10-20 parts of a thermosetting phenol resin coated secondary raw material mixture obtained by mixing at room temperature or at a temperature exceeding room temperature but not exceeding 130°C 1-6 wt% of liquid or powdered phenol resin, 10-30 wt% of one or more powdered oxidants, 60-75 wt% of one or more finely powdered pro-oxidants and 8-15 wt% of one or more finely powdered exothermic agents, to form a raw material mixture and using the shell molding process to form and cure the resulting mixture into a foundry exothermic body of prescribed shape. A process according to any of claims 1 to 2 wherein the foundry exothermic body is an exothermic riser sleeve, an exothermic core, an exothermic neckdown core, an exothermic mold, an exothermic pad or a body similar to any of these.

Inventors: MIKI MASAMITSU, TUNEMOTO ISAMU, MIKI, MASAMITSU, TUNEMOTO, ISAMU
Applicants: HATSUNEN CO LTD, HATSUNEN CO., LTD.
Application year: 1998
Main classification: B22C13
IPC codes: B22C13, B22D7, B22C9