Background Art As well known to those skilled in the art, in shot peening systems, a plurality of small steel balls are blasted against a surface of an objective material to allow residual compressive stress to remain in the surface of the objective material, thus increasing the strength and elongation of the objective material, and reducing the fatigue crack of the objective.

The shot peening systems are classified into two types, which are impeller-type shot peening systems and air nozzle-type shot peening systems, according to the types of apparatuses to blast the plurality of small steel balls.

The operation of a conventional impeller-type shot peening system will be described herein below, with reference to FIGS. la and lb.

First, in a state in that a door 420 of a cabinet 400 of the system is opened by a door control unit 430, a jig 10 holding a plurality of objective materials 20 thereon is carried by a carrying unit 1100 to be seated on a rotating base 410 which is installed in the cabinet 400. Thereafter, the door 420 of the cabinet

400 is closed by the door control unit 430. At this time, a robot arm, which is possible to hold and carry the jig 10 or the objective material 20, is generally used as the carrying unit 1100. The operation of the conventional impeller-type shot peening system will be described herein below on the supposition that the carrying unit 1100, such as the robot arm, carries the jig 10. The objective materials 20, held on the jig 10, are compressed downward by a motion of a compression unit 920 which is operated by a reciprocating drive unit 910 of a locking unit 900. Thereafter, the rotating base 410 with the jig 10 holding the objective materials 20 thereon is rotated by an operation of a rotating drive unit 500. At this time, any means, which is possible to vertically reciprocate the compression unit 920, may be used as the reciprocating drive unit 910, but, generally, an air cylinder is preferably used as the reciprocating drive unit 910.

The compression unit 920 is rotatably coupled to a drive shaft of the reciprocating drive unit 910. In the above state, a steel ball control valve 210 is opened, so that a plurality of small steel balls S, temporarily stored in a steel ball storage chamber 110, are continuously fed into a center portion of an impeller 312 of an impeller unit 310 through a steel ball input line L2. The impeller 312 is rotatably coupled to a rotating shaft 311 a of a drive motor 311. Thus, the plurality of small steel balls S, which have been fed into the center portion of the impeller 312, move outward along the wings of the impeller 312, and, thereafter, the plurality of small steel balls S are blasted from predetermined positions of the wings of the impeller 312 against the surface of the objective materials 20. The blasted positions of the small steel balls S are varied according to a rotating speed of the impeller 312, input positions and input angles of the small steel balls S which are fed into the center portion of the impeller 312. In the drawings, the reference numeral 1000 denotes an input line position changing unit which varies the input positions and the input angles of the small steel balls S. The plurality

of small steel balls S, which have been blasted from the impeller 312 against the surfaces of the objective materials 20, fall downward in the cabinet 400, after being in collision with the surface of the objective materials 20. Thereafter, the plurality of small steel balls S are collected by a steel ball collecting unit 600.

At this time, any means, which is possible to carry the small steel balls S collected from the cabinet 400 to a return line LI, may be used as the steel ball collecting unit 600, but, in the conventional impeller-type shot peening system, as shown in FIGS. la and lb, both a screw conveyer 610 and a bucket elevator 620 are used as the steel ball collecting unit 600. Thereafter, the plurality of small steel balls S, which are collected by the steel ball collecting unit 600, are carried to the return line Ll by both the screw conveyer 610 and the bucket elevator 620. The plurality of small steel balls S are thereafter fed to the steel ball storage chamber 110 along the return line L 1 after passing through a foreign material screening unit 700. Thereafter, the plurality of small steel balls S repeatedly circulate along the above-mentioned cycle. The foreign material screening unit 700 is to remove foreign materials from the plurality of small steel balls S. In the conventional impeller-type shot peening system, a drum-type foreign material screening unit or a screen-type foreign material screening unit may be used as the foreign material screening unit 700. The foreign materials, screened by the foreign material screening unit 700, are drained through a foreign material drain line L3 to the outside of the system. After the shot peening treatment for the objective materials 20 is finished, the steel ball control valve 210 is closed to stop the feeding of the plurality of small steel balls S into the impeller 312. Furthermore, the operation of the rotating drive unit 500 is stopped, thus the rotating motion of the rotating base 410 is stopped.

Thereafter, the reciprocating drive unit 910 of the locking unit 900 is oppositely operated, so that the compression unit 920 is returned to the initial position

thereof. At this time, the plurality of small steel balls S, which were blasted against the surfaces of the objective materials 20 in the cabinet 400, are carried to the return line LI by the steel ball collecting unit 600, and, thereafter, the plurality of small steel balls S are temporarily stored in the steel ball storage chamber 110 after passing through the foreign material screening unit 700 along the return line LI. After the rotating motion of the rotating base 410 is stopped, the door 420 of the cabinet 400 is opened by the door control unit 430. The jig 10, holding the objective materials 20 treated by the shot peening treatment, is carried to the outside of the cabinet 400 by the carrying unit 1100. Thereafter, the conventional impeller-type shot peening system sequentially and repeatedly executes the above-mentioned shot peening processes for next objective materials. The operations of the variety of units of the conventional impeller- type shot peening system are controlled by a control unit (not shown). In the meantime, the cabinet 400 further includes a dust collector 800 to collect dust from the interior of the cabinet 400.

In the conventional impeller-type shot peening system using the impeller 310 as the steel ball blasting means, the plurality of small steel balls are dispersedly blasted upward, downward, leftward and rightward against the surfaces of the objective materials 20, so that the conventional impeller-type shot peening system is possible to treat the plurality of objective materials 20, simultaneously.

However, in the conventional impeller-type shot peening system, some of the plurality of blasted small steel balls S are not in collision with the objective materials 20, thus reducing the operational efficiency of the shot peening system.

Furthermore, the plurality of small steel balls S are unevenly blasted upward, downward, leftward and rightward from the impeller 312, so that the improved physical properties of the objective materials 20 treated by the shot peening

treatment may be not uniform.

In addition, the conventional impeller-type shot peening system does not have any cooling means which reduces temperatures of the surfaces of the objective materials 20 increased due to the shot blasting with the small steel balls S during the shot peening process. Therefore, the conventional impeller-type shot peening system may not accomplish the desired improvement in the physical properties of the objective materials 20.

The above-mentioned problems experienced in the conventional impeller-type shot peening system will be explained below in further detailed, with reference to FIGS. 3a and 3b. As shown in FIG. 3a, the temperature of the surface of an objective material 20 increases due to the shot blasting with the small steel balls S during the shot peening process, so that a temperature difference is caused between the interior and the surface of the objective material 20. Therefore, the surface of the objective material 20 having a relatively higher temperature thermally expands, thus tensile stress is generated in the interior of the objective material 20 contiguous to the surface of the objective material 20, and compressive stress corresponding to the tensile stress is generated in the surface of the objective material 20. In the above state, when the plurality of small steel balls S are further blasted against the surface of the objective material 20, residual compressive stress remains in the surface of the objective material 20 while the surface of the objective material 20 is further compressed by the plurality of small steel balls S. However, because the compressive stress was already generated in the surface of the objective material 20 by the temperature difference between the interior and the surface of the objective material 20, the residual compressive stress, remaining in the surface of the objective material 20, is reduced. As shown in FIG. 3b, while the surface of the objective material 20 is cooled after the shot peening process, the surface of

the objective material 20 is contracted. Therefore, the compressive stress, generated in the surface of the objective material 20, is reduced, and residual tensile stress, corresponding to the residual compressive stress remaining in the surface of the objective material 20, remains in the interior of the objective material 20 contiguous to the surface of the objective material 20. As shown in FIG. 4, in case of the objective material 20 treated by the shot peening treatment in the conventional impeller-type shot peening system, the residual compressive stress remaining in the surface of the objective material 20 is greatly reduced by an increase in the temperature of the surface of the objective material 20 due to the shot blasting with the small steel balls S. FIG. 5 is a graph comparatively showing physical properties of a material without being processed by the shot peening treatment, the objective material processed by the shot peening treatment in the conventional impeller-type shot peening system, and an objective material processed by a shot peening treatment in a conventional air nozzle-type shot peening system. As shown in FIG. 5, elongations of the three materials are respectively increased in proportion to the residual compressive stresses of the materials. Furthermore, it is noted that the effective tensile stress of the objective material processed by the shot peening treatment in the conventional impeller-type shot peening system is lower than the objective material processed by the shot peening treatment in the conventional air nozzle-type shot peening system.

As shown in FIG. 2, the conventional air nozzle-type shot peening system includes an air nozzle unit 320 which is used as a steel ball blasting means. The operation of the conventional air nozzle-type shot peening system will be described herein below.

First, a jig 10, holding an objective material 20, is seated on a rotating base 410. Thereafter, the objective material 20 is compressed downward by a

compression unit 920, before the rotating base 410 is rotated by a rotating drive unit 500. In the above state, when an air control valve 323 and a steel ball control valve 210 are opened, a plurality of small steel balls S, which have been temporarily stored in a steel ball storage chamber 110, are drawn into an air ejecting line L5 through a steel ball input line L2. Thereafter, the plurality of small steel balls S are rapidly moved along with compressed air through the air ejecting line L5 to an air nozzle N1, prior to being blasted against the surface of an objective material 20 through the air nozzle N1. In the above-mention process, to prevent the compressed air from being drawn into a return line LI through the steel ball input line L2, a pressure shutoff valve 250 is closed in response to an opening action of the steel ball input valve 210. The plurality of small steel balls S, which have been blasted from the air nozzle N1, fall downward in a cabinet 400, after being in collision with the surface of the objective material 20. Thereafter, the plurality of small steel balls S are collected by a steel ball collecting unit 600. The plurality of small steel balls S, which are collected by the steel ball collecting unit 600, are carried to the return line LI along the steel ball collecting unit 600, prior to being temporarily stored in the steel ball storage chamber 110. After the shot peening treatment for the objective material 20 is finished, the steel ball control valve 210 and the air control valve 323 are closed to stop the blasting of the plurality of small steel balls S from the air nozzle N1. Thereafter, the objective material 20 processed by the shot peening treatment (with the jig 10) is removed from the shot peening system, and a new one which is not yet treated by the shot peening system is installed on the rotating base 410. The conventional air nozzle-type shot peening system sequentially and repeatedly executes the above-mentioned shot peening process to treat the now objective material. The operations of the variety of units of the conventional air nozzle-type shot peening system are

controlled by a control unit (not shown).

In the conventional air nozzle-type shot peening system using the air nozzle unit 320 as the steel ball blasting means, the surface of the objective material 20 is cooled by the compressed air which is ejected from the air nozzle N1, while the plurality of small steel balls S are blasted from the air nozzle N1 against the surface of the objective material 20. Thus, the temperature of the surface of the objective material 20 is prevented from being increased.

Therefore, the conventional air nozzle-type shot peening system is advantageous in that a reduction in residual compressive stress of the surface of the objective material 20 is prevented while the surface of the objective material 20 is cooled by the compressed air. As shown in FIG. 4, the reduction in the residual compressive stress remaining in the surface of the objective material 20 processed by the shot peening treatment in the conventional air nozzle-type shot peening system, is lower than the reduction in the residual compressive stress remaining in the objective material which is processed by the shot peening treatment in the conventional impeller-type shot peening system. This results from the compressed air, ejected from the air nozzle N1 of the air nozzle-type peening system to the surface of the objective material 20, reducing the temperature of the surface of the objective material 20. Therefore, the effective tensile stress of the objective material 20, processed by the shot peening treatment in the conventional air nozzle-type shot peening system, is higher than the effective tensile stress of the objective material which is processed by the shot peening treatment in the conventional impeller-type shot peening system, as shown in FIG. 5.

However, in the conventional air nozzle-type shot peening system, the plurality small steel balls S are blasted along an almost straight line from the air nozzle N1 against the surface of the objective material 20. In addition, the size

of the air nozzle N1 must be limited to produce a desired pressure for blasting the plurality of small steel balls S against the surface of the objective material 20.

Therefore, the number of the objective materials 20, which can be treated by the conventional air nozzle-type shot peening system in one process, is limited.

Therefore, in case of treatment of a plurality of objective materials 20, the conventional air nozzle-type shot peening system is disadvantageous in that its operating time increases.

Disclosure of the Invention Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an impeller-type shot peening system which has a cooling unit to prevent a temperature of a surface of an objective material from being increased during a shot peening process, and thus to simultaneously treat a plurality of objective materials in one process.

In order to accomplish the above object, the present invention provides an impeller-type shot peening system, in which a plurality of small steel balls are blasted from an impeller rotating at a high speed against a surface of a rotating objective material to allow residual compressive stress to remain in the surface of the objective material. The shot peening system includes a cooling unit to reduce a temperature of the surface of the objective material increased due to a shot blasting with the small steel balls. The cooling unit includes an air compressor to produce compressed air, a pressure regulator to regulate a pressure of the compressed air fed from the air compressor, an air control valve to control a feeding of the compressed air from the pressure regulator, and an air nozzle to eject the compressed air fed from the air control valve to the surface of the

objective material.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. la is a view showing a construction of a conventional impeller-type shot peening system; FIG. lb is a partially enlarged plan view showing an arrangement of important parts of the shot peening system of FIG. la ; FIG. 2 is a view showing a construction of a conventional air nozzle-type shot peening system; FIGS. 3a and 3b are views showing changes of stress in the interior of an objective material while the objective material is treated by the conventional impeller-type shot peening system; FIG. 4 is a graph comparatively showing stresses of the interiors of objective materials which are respectively treated by the conventional impeller- type shot peening system and the conventional air nozzle-type shot peening system; FIG. 5 is a graph comparatively showing physical properties of a material without being processed by a shot peening treatment, the objective material processed by a shot peening treatment in the conventional impeller-type shot peening system, and the objective material processed by a shot peening treatment in the conventional air nozzle-type shot peening system; FIG. 6a is a view showing a construction of an impeller-type shot peening system, according to a first embodiment of the present invention;

FIG. 6b is a partially enlarged plan view showing an arrangement of important parts of the shot peening system of FIG. 6a; FIG. 7a is a view showing a construction of an impeller-type shot peening system, according to a second embodiment of the present invention ; FIG. 7b is a view showing a construction of an impeller-type shot peening system, according to a modification of the second embodiment of FIG.

7a ; FIG. 8a is a view showing a construction of an impeller-type shot peening system, according to a third embodiment of the present invention; and FIG. 8b is a partially enlarged plan view showing an arrangement of important parts of the shot peening system of FIG. 8a.

Best Mode for Carrying Out the Invention Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Reference should now be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. FIG. 6a is a view showing a construction of an impeller-type shot peening system, according to a first embodiment of the present invention. FIG. 6b is a partially enlarged plan view showing an arrangement of important parts of the shot peening system of FIG. 6a.

The impeller-type shot peening system according to the first embodiment of the present invention includes an air-cooled type cooling unit 1200 to reduce temperatures of surfaces of objective materials 20 increased due to a shot blasting with small steel balls S, thus preventing the temperatures of the surfaces of the objective materials 20 from being increased during a shot peening process.

The air-cooled type cooling unit 1200 includes an air compressor 1210 to produce compressed air, and a pressure regulator 1220 to regulate a pressure of the compressed air fed from the air compressor 1210. The air-cooled type cooling unit 1200 further includes an air control valve 1230 to control a feeding of the compressed air from the pressure regulator 1220, and two air nozzles N2 to eject the compressed air fed from the air control valve 1230 to the surfaces of the objective materials 20.

The operation and effect of the impeller-type shot peening system according to the first embodiment of the present invention will be described herein below.

First, a jig 10, holding the objective materials 20 thereon, is seated on a rotating base 410. Thereafter, the objective materials 20 are compressed downward by a compression unit 920, before the rotating base 410, seating the jig 10 and the objective materials 20 thereon, is rotated by an operation of a rotating drive unit 500. In the above state, when a first steel ball control valve 210 is opened, the plurality of small steel balls S are fed into an impeller 312, rotating at a high speed, through a first steel ball input line L2. Thus, the plurality of small steel balls S are blasted from the impeller 312 against the surfaces of the objective materials 20. Simultaneously, the air control valve 1230 is opened, so that the compressed air, produced by the air compressor 1210, is guided to the two air nozzles N2 along two air ejecting lines L6, and, thereafter, the compressed air is ejected from the two air nozzles N2 to the surfaces of the objective materials 20. Each of the two air nozzles N2 may have various shapes, but, preferably, each of the two air nozzles N2 comprise a nozzle which is enlarged in the diameter at an outlet end thereof to meet the sequential arrangement of the plurality of objective materials 20. After the shot peening treatment for the objective materials 20 is finished, the first steel ball control

valve 210 is closed to stop the feeding of the plurality of small steel balls S into the impeller 312, and the air control valve 1230 is closed to stop the ejection of the compressed air to the surfaces of the objective materials 20. The operations of the variety of units of the impeller-type shot peening system according to the first embodiment of the present invention are controlled by a control unit (not shown).

In the impeller-type shot peening system according to the first embodiment, the air-cooled type cooling unit 1200 prevents the temperature of the surface of each of the objective materials 20 from being increased during the shot peening process, thus preventing residual compressive stress remaining in the surface of each of the objective materials 20 from being reduced due to an increase in the temperature of the surface of each of the objective materials 20.

In the impeller-type shot peening system according to the first embodiment, the two air nozzles N2, which eject the compressed air to the surfaces of the objective materials 20, are respectively arranged around both sides of the impeller 312, thus preventing the plurality of small steel balls S blasted from the impeller 312 from being undesirably dispersed leftward or rightward. Therefore, most small steel balls S, blasted from the impeller 312, are in collision with the surfaces of the objective materials 20, thus increasing operational efficiency of the impeller-type shot peening system of the present invention.

FIG. 7a is a view showing a construction of an impeller-type shot peening system, according to a second embodiment of the present invention.

FIG. 7b is a view showing a construction of an impeller-type shot peening system, according to a modification of the second embodiment of FIG. 7a.

As show in FIGS. 7a and 7b, the impeller-type shot peening system according the second embodiment of the present invention includes a second

steel ball input line L7 communicating with predetermined portions of the air ejecting lines L6 which couple the air control valve 1230 to air nozzles N2 or N1, a foreign material screening unit 700 which is coupled to the second steel ball input line L7, and a steel ball storage chamber 120 which is provided on a predetermined portion of the second steel ball input line L7 to temporarily store therein the plurality of small steel balls S which are collected from the foreign material screening unit 700. The shot peening system further includes a second steel ball control valve 220 which is provided on a predetermined portion of the second steel ball input line L7 to control a feeding of the small steel balls S from the steel ball storage chamber 120 to the second steel ball input line L7, and a pressure shutoff valve 250 which is provided on a predetermined portion of the second steel ball input line L7 to prevent the compressed air from being drawn into the second steel ball input line L7. In the impeller-type shot peening system according to the second embodiment of the present invention, an air- cooled type cooling unit 1200 may execute the role as the air nozzle unit 320 (see. FIG. 2) of the conventional air nozzle-type shot peening system.

The operation and effect of each of the impeller-type shot peening systems according the second embodiment of the present invention will be described herein below.

Usually, the second steel ball input valve 220, associated with the air ejecting lines L6, has been closed, as shown in FIG. 7a. When the first steel ball input valve 210, associated with the impeller 312, is opened, the plurality of small steel balls S are blasted from the impeller 312 against the surfaces of the objective materials 20, and, simultaneously, the surfaces of the objective materials 20 are cooled by the compressed air ejected from the air nozzles N2.

As shown in FIG. 7b, in the impeller-type shot peening system according to the modification of the second embodiment of the present invention, the shot

peening system is used in the same manner as that described for the conventional air nozzle-type shot peening system (see. FIG. 2). That is, the first steel ball input valve 210, associated with the impeller 312, is closed, and the second steel ball input valve 220, associated with the air ejecting lines L6, is opened.

Therefore, the plurality of small steel balls S are blasted from the air nozzles N1 through the air ejecting lines L6. In the above case, when the air nozzles N2, enlarged in the diameter at the outlet end thereof, are used as the blasting means for blasting the plurality of small steel balls S, the blasted speed of the plurality of small steel balls S may be reduced, so that the air nozzles N1 may be preferably used as the blasting means for blasting the plurality of small steel balls S. In the meantime, when the steel ball input valve 220 is opened, the pressure shutoff valve 250 is closed to prevent the compressed air from being drawn into the second steel ball input line L7.

FIG. 8a is a view showing a construction of an impeller-type shot peening system, according to a third embodiment of the present invention. FIG.

8b is a partially enlarged plan view showing an arrangement of important parts of the shot peening system of FIG. 8a. As shown in FIGS. 8a and 8b, in the impeller-type shot peening system according to the third embodiment of the present invention, a plurality of objective materials 20'are preheated in a preheating chamber 1300 which is provided with a heater 1400, before the objective materials 20 are treated by a shot peening process while being cooled by an air-cooled type cooling unit 1200. Therefore, residual compressive stress, remaining in the surfaces of the objective materials 20, is increased, thus greatly improving the physical properties of the objective materials 20. That is, when the surfaces of the objective materials 20 are treated by the shot peening process while being cooled by the compressed air, after the objective materials 20 are preheated to a predetermined temperature higher than room temperature, the

compressive stress in the surface and the tensile stress in the interior of each of the objective materials 20 are changed in a manner opposite to the state of FIGS.

3a and 3b. Therefore, the residual compressive stress, remaining in the surfaces of the objective materials 20, is increased. In the drawings, the reference numeral 1310 denotes a door of the preheating chamber 1300, and 1320 denotes a door control unit which controls the door 1310 of the preheating chamber 1300.

Industrial Applicability As described above, the present invention provides an impeller-type shot peening system which has a cooling unit to prevent a temperature of a surface of an objective material from being increased during a shot peening process, so that a reduction in residual compressive stress remaining in the surface of the objective material is prevented, thus increasing the physical properties of the objective material.

Furthermore, in the impeller-type shot peening system of the present invention, an air nozzle of the cooling unit, which ejects compressed air to the surface of the objective material, may comprise two air nozzles which are respectively arranged around both sides of an impeller, so that the compressed air is ejected from the two air nozzles to the surface of the objective material, thus preventing a plurality of small steel balls, blasted from the impeller, from being undesirably dispersed leftward or rightward. Therefore, most small steel balls, blasted from the impeller, are in collision with the surface of the objective material, thus increasing operational efficiency of the impeller-type shot peening system of the present invention.

In addition, the impeller-type shot peening system of the present invention may include a preheating chamber which is provided with a heater.

Therefore, when the objective material is preheated in the preheating chamber to a predetermined temperature higher than the room temperature, prior to being treated by the shot peening process, the shot peening system of the present invention is advantageous in that the physical properties of the objective material are greatly improved.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.