Method of producing foamed sand and production apparatus for producing foamed sand

1. A method of producing foamed sand for forming a sand mold, the foamed sand including sand particles and foam adhering to surfaces of the sand particles, the foam containing water glass, water, and a surfactant, the method comprising:

generating froth from an aqueous surfactant solution in which the surfactant is dissolved, by frothing the aqueous surfactant solution; and

kneading the generated froth, the water glass, and the water together with the sand constituted by the sand particles.

2. The method according to claim 1 , wherein, when the froth is generated, the aqueous surfactant solution is frothed by causing the aqueous surfactant solution to pass through a plurality of pores together with air.

3. A production apparatus for producing foamed sand for forming a sand mold, the foamed sand including sand particles and foam adhering to surfaces of the sand particles, the foam containing water glass, water, and a surfactant, the production apparatus comprising:

a storage portion in which sand constituted by the sand particles is stored;

a water glass supply portion configured to supply the water glass into the storage portion;

a water supply portion configured to supply the water into the storage portion;

a froth supply portion configured to supply, into the storage portion, froth generated by frothing an aqueous surfactant solution in which the surfactant is dissolved; and

a kneader configured to knead, in the storage portion, the sand with the water glass, the water, and the froth supplied into the storage portion.

4. The production apparatus according to claim 3 , wherein

the froth supply portion includes:

a liquid supply pipe configured to supply the aqueous surfactant solution;

an air supply pipe configured to supply air;

a joining portion in which the aqueous surfactant solution supplied from the liquid supply pipe and the air supplied from the air supply pipe join together; and

a porous body having a plurality of pores, the porous body configured to allow the aqueous surfactant solution and the air that have joined in the joining portion to pass through the porous body to froth the aqueous surfactant solution.

5. The production apparatus according to claim 4 , further comprising a controller configured to control start and stop of supply of the aqueous surfactant solution from the liquid supply pipe, and control start and stop of supply of the air from the air supply pipe,

wherein the controller is configured to:

i) start the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is started;

ii) then temporarily stop the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is stopped; and

iii) then restart the supply of the air from the air supply pipe such that air having a pressure higher than a pressure of the air supplied before temporary stop of the supply is supplied for a prescribed time.

6. The production apparatus according to claim 4 , further comprising a controller configured to control start and stop of supply of the aqueous surfactant solution from the liquid supply pipe, and control start and stop of supply of the air from the air supply pipe,

wherein the controller is configured to:

i) start the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is started;

ii) then stop the supply of the aqueous surfactant solution from the liquid supply pipe; and

iii) stop the supply of the air from the air supply pipe after a lapse of a prescribed time from the stop of the supply of the aqueous surfactant solution.

7. The production apparatus according to claim 4 , further comprising:

a vacuum mechanism connected to the joining portion, the vacuum mechanism configured to operate to generate a negative pressure in an inside of the joining portion; and

a controller configured to control start and stop of supply of the aqueous surfactant solution from the liquid supply pipe, control start and stop of supply of the air from the air supply pipe, and control an operation of the vacuum mechanism and stop of the operation,

wherein the controller is configured to:

i) start the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is started;

ii) then stop the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is stopped; and

iii) then operate the vacuum mechanism for a prescribed time from the stop of the supply of the air and the aqueous surfactant solution.

8. The production apparatus according to claim 4 , further comprising:

an on-off valve disposed below the porous body, the on-off valve configured to allow supply of the froth from the porous body into the storage portion while the on-off valve is open, and stop the supply of the froth from the porous body into the storage portion while the on-off valve is closed; and

a controller configured to control start and stop of supply of the aqueous surfactant solution from the liquid supply pipe, control start and stop of supply of the air from the air supply pipe, and control opening and closing of the on-off valve,

wherein the controller is configured to:

i) open the on-off valve and start the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is started;

ii) then stop the supply of the air from the air supply pipe when the supply of the aqueous surfactant solution from the liquid supply pipe is stopped; and

iii) then close the on-off valve after a lapse of a prescribed time from the stop of the supply of the air and the aqueous surfactant solution.

9. The production apparatus according to claim 4 , further comprising a pressure sensor configured to measure a pressure of the air in an air flow path of the air supply pipe.