A breathable salt core is provided that is placed in a cavity of a casting mold in order to mold a hollow part of a cast product and that is dissolved and removed after casting, the breathable salt core being formed by powder molding innumerable salt particles into a predetermined shape corresponding to the hollow part, wherein a gap that can retain a gas remaining in the cavity in a casting process is formed between the innumerable salt particles that have been powder molded. The breathable salt core thus manufactured assures that residual gas within the cavity pushed by the molten metal to enter the gap formed between salt particles of the salt core, thereby avoiding any incomplete filling of the molten metal, and which can be formed with a simple production process at a low cost.

Provided is a multicore. The multicore includes a first core, being made of a water-insoluble material, having a hollow formed in the first core and, having an opening formed at both ends of the first core and connected to the hollow, a second core, being made of a water-soluble material and disposed inside the hollow, and a coating layer, being configured to surround the first core to prevent at least a portion of the first core and the second core from being exposed to an outside. Further, the first core includes a plurality of spaces to allow a fluid supplied to an interior of the first core to flow toward the second core.

Provided is a piston for an internal combustion engine, the piston including a body having a piston pin boss for inserting a piston pin thereinto, and a skirt corresponding to a cylinder wall, and a cooling channel provided in the body to allow a refrigerant for cooling the body, to flow therethrough, and having a ring shape including a first channel provided from a refrigerant inlet to a refrigerant outlet along a first outer circumferential direction of the body, and a second channel provided from the refrigerant inlet to the refrigerant outlet along a second outer circumferential direction of the body.

Provided is a piston for an internal combustion engine, the piston including a body having a piston pin boss for inserting a piston pin thereinto, and a skirt corresponding to a cylinder wall, and a cooling channel provided in the body to allow a refrigerant for cooling the body, to flow therethrough, and having a ring shape including a first channel provided from a refrigerant inlet to a refrigerant outlet along a first outer circumferential direction of the body, and a second channel provided from the refrigerant inlet to the refrigerant outlet along a second outer circumferential direction of the body.

A method for producing a salt core includes a step A of adding a saturated sodium chloride aqueous solution to a sodium chloride crystal that is granular, to prepare a slurry mixed material of sodium chloride and water, a step B of subjecting the slurry mixed material to pressure molding to obtain a molded article, and a step C of drying the molded article to remove moisture.

A method for producing a cooling channel piston may include producing a salt core blank by pressing and sintering a pure salt material having a surface roughness R.sub.z of at most 60 μm. The method may also include one of immersing the salt core blank into a saturated solution of the salt material, or spraying the salt core blank with a saturated solution of the salt material. The method may also include drying the salt core blank to form a salt core having a surface roughness R.sub.z of at least 200 μm. The method may further include placing the salt core in a casting mold, and casting the cooling channel piston from a metallic casting material.

Provided are a multicore and a method of manufacturing a hollow product using the multicore enabling a hollow of a molded product to be molded more easily by casting and a quality problem to be addressed. The multicore includes a first core, being made of a water-insoluble material, having a hollow formed in the first core and, having an opening formed at both ends of the first core so that the hollow is exposed to the outside through the opening, a second core, being made of a water-soluble material and disposed inside the hollow, and a coating layer, being configured to surround the first core to prevent the first core and the second core from being exposed to an outside. Further, the first core includes a plurality of spaces to allow a fluid supplied to an interior of the first core to flow toward the second core.

Provided is a multicore. The multicore includes a first core, being made of a water-insoluble material, having a hollow formed in the first core and, having an opening formed at both ends of the first core and connected to the hollow, a second core, being made of a water-soluble material and disposed inside the hollow, and a coating layer, being configured to surround the first core to prevent at least a portion of the first core and the second core from being exposed to an outside. Further, the first core includes a plurality of spaces to allow a fluid supplied to an interior of the first core to flow toward the second core.

A slide for the high pressure die casting of at least one closed deck engine block having at least one cylinder is disclosed. The slide includes a tool steel portion with reliefs for forming a water jacket surrounding each cylinder. At least one expendable core is located in each relief, the expendable core having an inner surface and an outer surface with an aperture extending therethrough. The outer surface and inner surface of the expendable core is coextensive with an inner surface and outer surface of the tool steel portion. A method for high pressure die casting a closed deck engine block using the disclosed slide and expendable cores is also disclosed. The expendable cores are separable from the reliefs in the slide, and form bridges or supports across a water jacket to add stiffness and rigidity to the cast engine cylinders.

A manufacturing method of a cooling member to be used for a rotary electric machine. The manufacturing method includes a preparation step for preparing a plurality of annular collapsible cores having radial projections and recesses, a stacking step for concentrically stacking the plurality of collapsible cores along a direction of extension of a rotational axis of the rotary electric machine, a casting step for pouring a material of the cooling member into a die with the plurality of collapsible cores stacked in the die so that the material covers outer peripheral surfaces and inner peripheral surfaces of the plurality of collapsible cores, and a removal step for removing the plurality of collapsible cores after the casting step.