Patent Publication Number: US-2021162674-A1

Title: Apparatus for supplying pellet and method for supplying pellet

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 of Korean Patent Application Nos. 10-2019-0159124, filed on Dec. 3, 2019, and 10-2020-0042192, filed on Apr. 7, 2020, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The present disclosure herein relates to an apparatus for supplying a pellet and a method for supplying a pellet, and more particularly, to an apparatus for supplying a pellet, which is capable of uniformly extruding a pellet, and a method for supplying a pellet 
     Three-dimensional (3-D) printing is a method of processing a 3-dimensional shape by laminating materials, and there are various methods for the 3-D printing. For example, fused deposition modeling (FDM) refers to a method of processing a 3-dimensional shape by melting a filament-shaped material and laminating a 2-dimensional cross-sectional shape. Before performing the FDM, a thermoplastic polymer is melted at a high temperature, and then a wire-shaped filament is manufactured by using an extruder in advance. In order to process the polymer material into the filament shape, viscosity, extruding speed, and cooling speed have to be property adjusted. A material such as an inorganic material may be additionally mixed to improve strength and thermal stability of the material. As another method for the 3-D printing, the thermoplastic polymer may be processed into a pellet shape. When the material having the pellet shape is used, a large amount of small pellets may be inserted to a small-sized precision extruder for the 3-D printing by using a chamber. 
     SUMMARY 
     The present disclosure provides an apparatus for supplying a pellet, which is capable of uniformly extruding a pellet, and a method for supplying a pellet. 
     The present disclosure also provides an apparatus for supplying a pellet, which is capable of preventing a bottleneck phenomenon of a pellet at an inlet of a supply unit, and a method for supplying a pellet. 
     The present disclosure also provides an apparatus for supplying a pellet, which is capable of removing a pore in the supply unit, and a method for supplying a pellet. 
     The present disclosure also provides an apparatus for supplying a pellet, which is capable of preventing a pellet from being melted in advance, and a method for supplying a pellet. 
     The present disclosure also provides an apparatus for supplying a pellet, which is capable of preventing a pellet from being clogged by melting of the pellet, and a method for supplying a pellet. 
     The present disclosure also provides an apparatus for supplying a pellet, which is capable of using various materials in 3-D printing, and a method for supplying a pellet. 
     The present disclosure also provides an apparatus for supplying a pellet, which is capable of simplifying a process, and a method for supplying a pellet. 
     The object of the present invention is not limited to the aforesaid, but other objects not described herein will be clearly understood by those skilled in the art from descriptions below. 
     An embodiment of the inventive concept provides an apparatus for supplying a pellet, including: a supply chamber configured to accommodate a pellet; a rotation unit connected to a driving unit; and a supply unit coupled to the supply chamber. Here, the rotation unit includes: a rotation shaft extending in a first direction; a screw coupled to an outer surface of the rotation shaft and configured to progress in the first direction; and a scraper extending from the outer surface of the rotation shaft in a direction crossing the first direction. Also, the supply unit surrounds the screw, and the scraper is disposed in the supply chamber while being positioned higher than the screw. 
     In an embodiment, the scraper may have an extension direction perpendicular to the first direction. 
     In an embodiment, the scraper may have a bar shape. 
     In an embodiment, the scraper may be spaced upward by about 0.5 mm to about 2 mm from an upper boundary of the supply unit. 
     In an embodiment, the scraper may have a length in the extension direction, which is greater than a length of the screw in the extension direction of the scraper. 
     In an embodiment, the supply chamber may provide a pellet accommodation space having a diameter that gradually decreases in the first direction, the pellet accommodation space may be connected with an inner space of the supply unit, and a supply chamber body configured to define the pellet accommodation space may provide a coolant accommodation space therein. 
     In an embodiment, the apparatus may further include a heating unit coupled to an outer surface of the supply unit, and the heating unit may heat the pellet supplied to the inner space of the supply unit. 
     In an embodiment of the inventive concept, an apparatus for supplying a pellet includes: a supply chamber configured to accommodate a pellet; a rotation unit connected to a driving unit; and a supply unit coupled to the supply chamber. Here, the rotation unit includes: a rotation shaft extending in a first direction; and a screw coupled to an outer surface of the rotation shaft and configured to progress in the first direction. Also, the supply unit surrounds the screw, the supply chamber includes a supply chamber body and a pellet accommodation space defined by the supply chamber body, the pellet accommodation space has a diameter that gradually decreases in the first direction and is connected with an inner space of the supply unit, and the supply chamber body provides a coolant accommodation space therein. 
     In an embodiment, the coolant accommodation space may surround a portion of the supply unit and the pellet accommodation space. 
     In an embodiment, the apparatus may further include a coolant inlet and a coolant outlet, which are coupled to an outer surface of the supply chamber, and each of the coolant inlet and the coolant outlet may be connected to the coolant accommodation space. 
     In an embodiment, the coolant outlet may be positioned higher than the coolant inlet. 
     In an embodiment, the apparatus may further include a coolant pump connected to the coolant outlet or the coolant inlet. 
     In an embodiment of the inventive concept, a method for supplying a pellet includes: supplying a pellet to a supply chamber; pushing the pellet from the supply chamber to a supply unit by a scraper; and pushing the pellet downward while a screw disposed in the supply unit rotates forward. Here, the scraper is disposed in the supply chamber while being coupled to an upper side of a rotation shaft coupled with the screw. 
     In an embodiment, the method may further include pushing the pellet upward while the screw rotates reversely after the screw rotates forward to push the pellet downward. 
     In an embodiment, a ratio of the forward rotation and the reverse rotation may be about 5:1 to about 15:1. 
     In an embodiment, the method may further include supplying a coolant to a coolant accommodation space in the supply chamber. 
     Particularities of other embodiments are included in the detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings: 
         FIG. 1  is a cross-sectional view illustrating an apparatus for supplying a pellet according to an embodiment of the inventive concept; 
         FIG. 2  is an enlarged cross-sectional view illustrating portion X of  FIG. 1 ; 
         FIG. 3  is a flowchart representing a method for supplying a pellet according to an embodiment of the inventive concept; and 
         FIGS. 4 to 8  are cross-sectional views sequentially illustrating the method for supplying the pellet in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will be described with reference to the accompanying drawings so as to sufficiently understand constitutions and effects of the present invention. The technical ideas of the inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Further, the present invention is only defined by scopes of claims. 
     Like reference numerals refer to like elements throughout. The embodiment in the detailed description will be described with cross-sectional views and/or plan views as ideal exemplary views of the inventive concept. Also, in the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Areas exemplified in the drawings have general properties, and are used to illustrate a specific shape of a semiconductor package region. Thus, this should not be construed as limited to the scope of the present invention. 
     Also, although various terms are used to describe various components in various embodiments of the inventive concept, the component are not limited to these terms. These terms are only used to distinguish one component from another component. Embodiments described and exemplified herein include complementary embodiments thereof. 
     In the specification, the technical terms are used only for explaining a specific exemplary embodiment while not limiting the present invention. The terms of a singular form may include plural forms unless referred to the contrary. The meaning of “include,” “comprise,” “including,” or “comprising,” specifies a property, a region, a fixed number, a step, a process, an element and/or a component but does not exclude other properties, regions, fixed numbers, steps, processes, elements and/or components. 
     Hereinafter, the present invention will be described in detail by explaining preferred embodiments of the invention with reference to the attached drawings. 
       FIG. 1  is a cross-sectional view illustrating an apparatus for supplying a pellet according to an embodiment of the inventive concept. 
     Hereinafter, in  FIG. 1 , D 1  may be referred to as a first direction, D 2  may be referred to as a second direction, and D 3  that is substantially perpendicular to the first direction D 1  and the second direction D 2  may be referred to as a third direction. 
     Referring to  FIG. 1 , an apparatus for supplying a pellet (hereinafter, referred to as a pellet supply apparatus) may be provided. The pellet supply apparatus may be used in three-dimensional (3-D) printing. That is, the pellet supply apparatus may be a portion of a 3-D printer. The pellet supply apparatus may serve to extrude a printing material in a 3-D printing process. The pellet supply apparatus may include a supply chamber  1 , a supply unit  3 , a rotation unit  5 , a heating unit  7 , a driving unit m, a pellet supplier U, and a coolant pump P. 
     The supply chamber  1  may accommodate a pellet a (refer to  FIG. 4 ). The supply chamber  1  may supply the pellet a to the supply unit  3 . The supply chamber  1  may be connected to the pellet supplier U. The supply chamber  1  may receive the pellet from the pellet supplier U. The supply chamber  1  may receive the pellet from the pellet supplier U and supply the received pellet to the supply unit  3 . The chamber  1  may include a supply chamber body  11 , an extended body  15 , an insertion part  13 , a coolant inlet  11   i , and a coolant outlet  11   e.    
     The supply chamber body  11  may define a pellet accommodation space  11   h.    
     That is, the supply chamber body  11  may surround the pellet accommodation space  11   h . In embodiments, the supply chamber body  11  may have an appearance of a cylindrical shape. However, the embodiment of the inventive concept is not limited thereto. The pellet a may be accommodated in the pellet accommodation space  11   h . The pellet accommodation space  11   h  may have a diameter that gradually decreases in the first direction D 1 . That is, an inner surface  11   s  of the pellet accommodation space  11   h  may have a diameter that decreases in a downward direction. The pellet accommodation space  11   h  may be connected to an inner space  31   h  of the supply unit  3 . The pellet a accommodated in the pellet accommodation space  11   h  may be supplied to an inner space  31   h  of the supply unit  3 . The supply chamber body  11  may provide a coolant accommodation space  11   hi . More specifically, the coolant accommodation space  11   hi  may be provided in the supply chamber body  11 . The coolant accommodation space  11   hi  may not be connected to the pellet accommodation space  11   h.    
     That is, the coolant accommodation space  11   hi  may be separated from the pellet accommodation space  11   h  by the supply chamber body  11 . The coolant accommodation space  11   hi  may surround the pellet accommodation space  11   h . More specifically, the coolant accommodation space  11   hi  may surround an outside of the pellet accommodation space  11   h . The coolant accommodation space  11   hi  may surround a portion of the supply unit  3 . More specifically, the coolant accommodation space  11   hi  may surround an outside of an upper portion of the supply unit  3 . The supply chamber body  11  may be coupled with the coolant inlet  11   i  and the coolant outlet  11   e . The coolant inlet  11   i  may be defined in an outer surface of the supply chamber body  11 . The coolant outlet  11   e  may be defined in the outer surface of the supply chamber body  11 . The coolant outlet  11   e  may be disposed higher than the coolant inlet  11   i . The coolant accommodation space  11   hi  may be connected with the coolant inlet  11   i . The coolant accommodation space  11   hi  may be connected with the coolant outlet  11   e . A coolant may be disposed in the coolant accommodation space  11   hi . The coolant may be supplied to the coolant accommodation space  11   hi  through the coolant inlet  11   i . The coolant may be discharged from the coolant accommodation space  11   hi  through the coolant outlet  11   e . Detailed description thereof will be described later. 
     The extended body  15  may be coupled to the supply chamber body  11 . The extended body  15  may extend upward from the supply chamber body  11 . The extended body  15  may have a cylindrical shape. However, the embodiment of the inventive concept is not limited thereto. The extended body  15  may define an extended accommodation space  15   h . That is, the extended accommodation space  15   h  may be defined inside the extended body  15 . 
     The extended accommodation space  15   h  may not be connected with the pellet accommodation space  11   h.    
     The insertion part  13  may be coupled to the extended body  15  and/or the supply chamber body  11 . Hereinafter, it is illustrated for convenience of description that the insertion part  13  is coupled to the extended body  15 . In the embodiments, the insertion part  13  may have a predetermined angle with the first direction D 1 . The insertion part  13  may provide an insertion passage  13   h . The insertion passage  13   h  may be connected to the extended accommodation space  15   h  and/or the pellet accommodation space  11   h . The pellet a may be supplied to the extended accommodation space  15   h  and/or the pellet accommodation space  11   h  through the insertion passage  13   h . The insertion passage  13   h  may be connected to the pellet supplier U. The insertion passage  13   h  may receive the pellet a from the pellet supplier U. The pellet a supplied from the pellet supplier U may be supplied to the extended accommodation space  15   h  and/or the pellet accommodation space  11   h  along the insertion passage  13   h.    
     The coolant inlet  11   i  may be coupled to the outer surface of the supply chamber body  11 . The coolant inlet  11   i  may be connected with an inlet pipe Pi or the like. The coolant inlet  11   i  may receive the coolant from the inlet pipe Pi. The coolant inlet  11   i  may transfer the coolant received from the inlet pipe Pi to the pellet accommodation space  11   h.    
     The coolant outlet  11   e  may be coupled to the outer surface of the supply chamber body  11 . The coolant outlet  11   e  may be connected with an outlet pipe Pi or the like. The coolant outlet  11   e  may discharge the coolant to the outlet pipe Pi or the like. The coolant outlet  11   e  may be disposed higher than the coolant inlet  11   i . More specifically, the coolant inlet  11   i  may be disposed at the first direction D 1  more than the coolant outlet  11   e.    
     The supply unit  3  may be connected to the supply chamber  1 . The supply unit  3  may include a supply pipe  31  and a nozzle  33 . 
     The supply pipe  31  may be connected to the supply chamber body  11 . More specifically, the supply pipe  31  may be connected to a central portion of the supply chamber body  11 . The supply pipe  31  may extend in the first direction D 1 . The supply pipe  31  may extend from the supply chamber body  11  in the first direction D 1 . The supply pipe  31  may provide the inner space  31   h . The inner space  31   h  may extend along the supply pipe  31  in the first direction D 1 . The inner space  31   h  may be connected with the pellet accommodation space  11   h . The pellet a (refer to  FIG. 4 ) may move from the pellet accommodation space  11   h  to the inner space  31   h.    
     The nozzle  33  may be coupled to the supply pipe  31 . More specifically, the nozzle  33  may be coupled to a lower end of the supply pipe  31 . The nozzle  33  may have a diameter that gradually decreases in the first direction D 1 . The nozzle  33  may include a connection space  33   h  and a discharge hole  33   e . The connection space  33   h  may be connected to the inner space  31   h  of the supply pipe  31 . The connection space  33   h  may have a diameter that gradually decreases in the first direction D 1 . The discharge hole  33   e  may be connected to the connection space  33   h . The discharge hole  33   e  may be connected to the outside. The connection space  33   h  may be connected to the outside through the discharge hole  33   e.    
     The rotation unit  5  may include a rotation shaft  51 , a screw  53 , a connection shaft  55 , and a scraper  57 . 
     The rotation shaft  51  may extend in the first direction D 1 . The rotation shaft  51  may be disposed in the supply pipe  31 . The rotation shaft  51  may be connected to the connection shaft  55 . The rotation shaft  51  may rotate by the connection shaft  55 . More specifically, the rotation shaft  51  may receive torque from the driving unit m through the connection shaft  55  to rotate in clockwise and counterclockwise directions. Detailed description thereof will be described later with reference to  FIGS. 4 to 8 . 
     The screw  53  may be coupled to the rotation shaft  51 . More specifically, the screw  53  may be coupled to an outer surface of the rotation shaft  51 . The screw  53  may be coupled to the outer surface of the rotation shaft  51  to progress in the first direction D 1 . Detailed description of the screw  53  will be described later. 
     The connection shaft  55  may be coupled to an upper side of the rotation shaft  51 . The connection shaft  55  may extend in the first direction D 1 . At least a portion of the connection shaft  55  may be disposed in the supply chamber  1 . The connection shaft  55  may be connected to the driving unit m. The connection shaft  55  may transmit a rotation force of the driving unit m to the rotation shaft  51 . 
     The scraper  57  may be connected to the rotation shaft  51  or the connection shaft  55 . When the scraper  57  is coupled to the rotation shaft  51 , the scraper  57  may be coupled to the upper side of the rotation shaft  51 . The scraper  57  may be disposed higher than the screw  53 . The scraper  57  may have a bar shape. The scraper  57  may have an extension direction crossing the first direction D 1 . For example, the extension direction of the scraper  57  may be substantially perpendicular to the first direction D 1 . More specifically, the extension direction of the scraper  57  may be disposed on a plane defined by the second direction D 2  and the third direction D 3 . Detailed description of the scraper  57  will be described later with reference to  FIG. 2 . 
     The heating unit  7  may heat the supply part  3 . The heating unit  7  may be coupled to the supply part  3 . For example, the heating unit  7  may be coupled to the lower end of the supply pipe  31 . The heating unit  7  may heat the pellet a in the inner space  31   h  of the supply pipe  31 . The heating unit  7  may include a hot wire  73  and a support member  71 . The hot wire  73  may receive electrical energy from an external power (not shown). When the hot wire  73  receives the electrical energy, joule heat may be generated. The hot wire  73  may transfer heat to the inner space  31   h  of the supply pipe  31 . A portion or all of the pellet a may be melted when receives the heat. The support member  71  may fix the hot wire  73 . 
     The driving unit m may be connected to the connection shaft  55 . The driving unit m may provide torque to the connection shaft  55 . The driving unit m may include various units providing a rotation force. For example, the driving unit m may include a motor. However, the embodiment of the inventive concept is not limited thereto. 
     The pellet supplier U may be connected to the insertion part  13 . The pellet supplier U may supply the pellet a. The pellet supplier U may supply the pellet a to the insertion part  13 . 
     The coolant pump P may supply a coolant to the coolant accommodation space  11   hi . The coolant pump P may be connected to the coolant inlet  11   i  and/or the coolant outlet  11   e . More specifically, the coolant pump P may be connected to the coolant inlet  11   i  through the inlet pipe Pi or connected to the coolant outlet  11   e  through the outlet pipe Pe. 
       FIG. 2  is an enlarged cross-sectional view illustrating portion X of  FIG. 1 . 
     Referring to  FIG. 2 , the scraper  57  may be disposed above the screw  53 . The scraper  57  may be disposed higher than the supply unit  3 . That is, the scraper  57  may be disposed in the supply chamber  1 . More specifically, the scraper  57  may be disposed inside the supply chamber body  11 . In other words, the scraper  57  may be disposed in the pellet accommodation space  11   h . The scraper  57  may be spaced apart from the supply unit  3  in a direction opposite to the first direction D 1 . That is, the scraper  57  may be spaced upward from an upper boundary of the supply unit  3 . That is, the scraper  57  may be spaced by h from the upper boundary of the supply unit  31 . In the embodiments, the h is about 0.5 mm or more and about 2 mm or less. 
     The scraper  57  may have a length L in the extension direction thereof, and the length L may be greater than L′ in the extension direction of the scraper  57 . That is, the scraper  57  may extend outward from the rotation shaft  51  more than the screw  53 . For example, the scraper  57  may extend outward from the rotation shaft  51 , and a portion of an outer side of the scraper  57  may be disposed above the supply pipe  31 . 
     The coolant accommodation space  11   hi  may surround a portion of an upper portion of the supply pipe  31  and/or a portion or all of the pellet accommodation space  11   h . The coolant disposed in the coolant accommodation space  11   hi  may absorb heat from each of a portion of the upper portion of the supply pipe  31  and/or a portion or all of the pellet accommodation space  11   h . Detailed description regarding this will be described later. 
       FIG. 3  is a flowchart representing a method for supplying a pellet according to an embodiment of the inventive concept. 
     Referring to  FIG. 3 , a method S for supplying a pellet may include a process S 1  of supplying a pellet to a supply chamber, a process S 2  of pushing the pellet by a scraper, a process S 3  of pushing the pellet downward while a screw rotates forward, and a process S 4  of pushing the pellet upward while the screw rotates reversely. 
     Hereinafter, each of the processes of the method S for supplying the pellet will be described in detail with reference to  FIGS. 4 to 8 . 
       FIGS. 4 to 8  are cross-sectional views sequentially illustrating the method for supplying the pellet in  FIG. 3 . 
     Referring to  FIGS. 3 and 4 , the process S 1  of supplying a pellet to the supply chamber may include a process of supplying a pellet a from the pellet supplier U to the insertion part  13 . The pellet a may include a 3-D printing material. For example, the pellet a may include a polymer material. More specifically, the pellet a may include a thermoplastic polymer. The pellet a may further include another material for strength increase and/or thermal stability. For example, the pellet a may further include various inorganic materials. In addition, the pellet a may include various materials for the 3-D printing. The pellet a may have a granule shape. The pellet a inserted to the insertion passage  13   h  of the insertion part  13  may move downward by the gravity. That is, the pellet a may move from the insertion passage  13   h  to the pellet accommodation space  11   h . The pellet for the 3-D printing may be stacked in the pellet accommodation space  11   h.    
     Referring to  FIGS. 3 and 5 , the process S 2  of pushing the pellet by the scraper may include a process in which the rotation part  5  rotates by the driving unit m. More specifically, the connection shaft  55  may rotate by being driven by the driving unit m. Along a progress direction of the screw  53 , a forward rotation direction of the connection shaft  55  may be determined. For example, when the screw  53  progresses clockwise, clockwise rotation may be the forward rotation of the connection shaft  55 . On the contrary, when the screw  53  progresses counterclockwise, counterclockwise rotation may be the forward rotation of the connection shaft  55 . When the connection shaft  55  rotates forward, the rotation shaft  51  also may rotate forward. Each of the scraper  57  and the screw  53  may rotate forward by the forward rotation of the rotation shaft  51 . The scraper  57  may push the pellet a in the pellet accommodation space  11   h  while rotating. More specifically, the scraper  57  may push the pellet a upward and/or downward while rotating. As the scraper  57  pushes the pellet a, a feature in which the pellet a does not move downward because the pellets a collide each other may be prevented. Thus, a bottleneck phenomenon of the pellet a at an inlet of the supply unit  3  may be prevented. 
     In the pellet supply apparatus and the method for supplying the pellet according to the embodiments of the inventive concept, the pellet may be transferred from the supply chamber to the supply pipe by using the scraper. That is, the scraper stirs the pellets gathered in a lower end of the supply chamber to prevent the pellet from being clogged by the bottleneck phenomenon. Thus, the pellet may be smoothly supplied to the supply pipe. Thus, the pellet may be uniformly extruded. Also, uniformity of the 3-D printing may improve. 
     In the pellet supply apparatus and the method for supplying the pellet according to the embodiments of the inventive concept, a material having a pellet shape instead of a filament shape may be uniformly extruded. Thus, a material is unnecessarily manufactured into the filament shape. Thus, a process may be simplified, and a manufacturing cost may be saved. Also, various materials in which a content of an inorganic material is high may be used. Thus, strength and thermal stability of a material may improve. 
     Referring to  FIG. 6 , the pellet a may be pushed by the scraper  57  to move in the first direction D 1 . As the bottleneck phenomenon caused by collision between the pellets s is prevented, the pellet a may be uniformly supplied to the supply pipe  31 . 
     Referring to  FIGS. 2, 5, and 6 , the process S 3  of pushing the pellet downward while the screw rotates forward may include a process of pushing the pellet a downward, which is supplied to the supply pipe  31  by the scraper  57 , by the screw  53 . The screw  53  may push the pellet a along the supply pipe  31  in the first direction D 1  while rotating. Thus, the pellet a may be continuously pushed downward. 
     Referring to  FIGS. 2 and 7 , the process S 4  of pushing the pellet upward while the screw rotates reversely may include a process in which the screw  53  rotates forward a predetermined number repeatedly, and then reversely rotates. In the embodiments, a ration between the forward rotation and the reverse rotation may be about 5:1 to about 15:1. The ration between the forward rotation and the reverse rotation of the screw  53  may be determined in various methods. In the embodiments, the ratio between the forward rotation and the reverse rotation of the screw  53  may be determined according to the diameter of the nozzle  33  and/or a printing speed of a 3-D printer. For example, when the nozzle  33  has a diameter of about 400 μm to about 600 μm, and the printing speed is about 30 mm/sec, the ratio between the forward rotation and the reverse rotation of the screw  53  may be about 10:1. That is, the screw  53  rotates forward about 5 turns and then rotates reversely about 0.5 turn. When the diameter of the nozzle  33  increases, the ratio of the forward rotation may increase. On the contrary, when the diameter of the nozzle  33  decreases, the ratio of the forward rotation may decrease. Also, the ratio of the forward rotation may be changed according to the constituents and/or kind of the pellet a. 
     Referring to  FIG. 8 , when the screw  53  reversely rotates, the pellet a moves upward. That is, the pellet a moving downward in the first direction D 1  may move back in an upward direction. A portion of the pellet a, which is disposed at an upper side of the supply pipe  31  may move out of the supply pipe  31 . The pellet a may return to the supply chamber  1 . That is, the pellet a may return to the pellet accommodation space  11   h.    
     Referring to  FIG. 2  again, when the reverse rotation of the screw  53  is finished, the screw  53  may rotate forward again. The forward rotation and the reverse rotation of the screw  53  may be repeated according to a predetermined ratio. 
     In the pellet supply apparatus and the method for supplying the pellet according to the embodiments of the inventive concept, the forward rotation and the reverse rotation of the screw may be repeated. Thus, pores or the like disposed between the pellet in the supply pipe may be discharged to the supply chamber. Thus, the pellet may be uniformly extruded through the nozzle. 
     In the embodiments, the method S for supplying the pellet may further include a process of supplying the coolant to the coolant accommodation space in the supply chamber. That is, the coolant pump P may supply the coolant to the coolant accommodation space  11   hi . The coolant may be supplied to the coolant accommodation space  11   hi  through the coolant inlet  11   i . The coolant may include various materials capable of absorbing heat. In the embodiments, the coolant may include a secondary coolant having no phase change. For example, the coolant may include water. However, the embodiment of the inventive concept is not limited thereto. For example, the coolant may include various materials. The coolant may be disposed in the coolant accommodation space  11   hi  to absorb heat from a portion of the supply pipe  31  and/or the pellet accommodation space  11   h . The coolant may be supplied at various times. For example, the coolant may be supplied to the coolant accommodation space  11   hi  in advance before the pellet a is inserted to the pellet accommodation space  11   h . Alternatively, the coolant may move downward along the supply pipe  31  and be supplied to the coolant accommodation space  11   hi  after heated by the heating unit  7 . 
     In the pellet supply apparatus and the method for supplying the pellet according to the embodiments of the inventive concept, a portion of the supply pipe and/or the pellet accommodation space may be cooled by using the coolant. That is, the coolant may absorb the heat from pellet disposed in a portion of the supply pipe and/or in the pellet accommodation space. Thus, the pellet disposed in a portion of the supply pipe and/or in the pellet accommodation space may be prevented from being melted early by heat conducted from the heating unit. Thus, a phenomenon in which the pellet is melted early and attached to a wall surface of the supply pipe and/or a surface of the screw may be prevented. Due to this, the pellet may be uniformly extruded. 
     In the pellet supply apparatus and the method for supplying the pellet according to the embodiments of the inventive concept, the coolant outlet may be disposed higher than the coolant inlet. Thus, the coolant having a lower temperature may absorb heat from the pellet disposed more adjacent to the heating unit. Thus, the pellet may be effectively cooled. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, the pellet may be uniformly extruded. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, the bottleneck phenomenon of the pellet at the inlet of the supply unit may be prevented. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, the pore in the supply unit may be removed. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, the early melting of the pellet may be prevented. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, the clogging of the pellet due to the melting of the pellet may be prevented. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, various materials may be used in the 3-D printing. 
     In the apparatus for supplying the pellet and the method for supplying the pellet according to the embodiments of the inventive concept, the process may be simplified. 
     The object of the present invention is not limited to the aforesaid, but other objects not described herein will be clearly understood by those skilled in the art from descriptions below. 
     Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed. Thus, the above-disclosed embodiments are to be considered illustrative and not restrictive.