Nozzle assembly and surface treatment method with nozzle assembly

1. A nozzle assembly for processing a surface of a workpiece by ejecting a solid-gas two phase flow in which ejection materials are mixed with compressed air flow, the nozzle assembly comprising:

a nozzle main body including an ejection material suction port configured to suction the ejection materials into the nozzle main body, and an ejection port configured to eject the suctioned ejection materials with the compressed air flow from the nozzle main body; and

an air nozzle configured to jet the compressed air flow into the nozzle main body;

wherein the nozzle main body includes a mixing chamber forming a space for mixing the ejection materials suctioned into the nozzle main body from the ejection material suction port with the compressed air flow jetted from the air nozzle, a first pathway configured to direct a flow of the ejection materials from the ejection material suction port toward the mixing chamber, and a second pathway configured to direct the compressed air flow containing the ejection materials from the mixing chamber toward the ejection port;

wherein the air nozzle includes a compressed air jet portion formed at a tip thereof and a third pathway configured to direct the compressed air flow toward the compressed air jet portion, and the air nozzle is inserted into the nozzle main body so that the third pathway is as aligned with the second pathway of the nozzle main body, and the compressed air jet portion is positioned in the mixing chamber of the nozzle main body;

wherein the compressed air jet portion of the air nozzle is provided with a cylindrical flow contracting portion having an opening whose cross section is smaller than a cross section of the third pathway;

wherein the third pathway of the air nozzle includes a flow straightening portion having a uniform cross sectional area along its length, and wherein the flow contracting portion communicates with the flow straightening portion, and a cross sectional area ratio (S2/S1) of an opening area (S2) of the opening of the flow contracting portion with respect to a cross sectional area (S1) of the flow straightening portion is set at 0.3 to 0.8; and

wherein a flow contracting portion ratio (L2/D2) of an axial length (L2) of the opening of the flow contracting portion with respect to a diameter (D2) of the opening of the flow contracting portion of the air nozzle is set at 0.1 to 0.5.

2. The nozzle assembly according to claim 1 , wherein a flow straightening portion ratio (L1/D1) of an axial length (L1) of the flow straightening portion with respect to a diameter (D1) of the flow straightening portion is set at 2 to 50.

3. The nozzle assembly according to claim 1 , wherein the nozzle assembly ejects abrasive grains which are used as the ejection materials in a blast processing apparatus.

4. A surface processing method for processing the surface of a workpiece by using the nozzle assembly according to claim 1 , comprising the steps of:

jetting the compressed air flow into the mixing chamber in the nozzle main body from the air nozzle, and negatively pressurizing the mixing chamber;

suctioning the ejection materials into the mixing chamber from the ejection material suction port of the nozzle main body by using a negative pressure in the mixing chamber of the nozzle main body, and mixing the ejection materials with the compressed air flow jetted from the air nozzle in the mixing chamber;

ejecting the solid-gas two phase flow from an ejection port of the nozzle main body; and

processing the surface of the workpiece by a collision of the ejected ejection materials with the surface of the workpiece;

wherein jetting the compressed air flow from the air nozzle suppresses an expansion of the jetted compressed air flow by the flow contracting portion of the air nozzle.

5. The surface processing method according to claim 4 , wherein the compressed air flow jetted from the air nozzle has a higher velocity in an outer peripheral of the jetted compressed air flow than an interior thereof.