Patent Abstract:
A core for creating an airfoil has a ceramic material that forms a body. The body has an outer dimension, a slot extending through the outer dimension and into the body for receiving an insert, the slot disposed at an angle to the outer dimension, and a trip strip having a first portion disposed in the outer dimension. The first portion is in register with the slot wherein a constant dimension such as minimum thickness is maintained between the trip strip and the slot along a length of the slot and wherein said first portion tapers towards said outer dimension.

Full Description:
GOVERNMENT RIGHTS 
     This invention was made with government support under Contract No. F33615-03-D-2354-0009 awarded by the United States Air Force. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Materials used in the turbine section of a gas turbine engine may be subjected to temperatures that are above the melting point of those materials. To operate under such high temperatures, the parts using those materials must be internally cooled. Turbine airfoils, for example, use internal cores that form hollow passages within the airfoils. In high heat load applications, trip strips may be used within these passages to further enhance convective cooling. 
     It is typical in the art, for a ceramic material to be injected into a metal die and then fired to form desired core passages of a turbine airfoil. Slots are built into the die into which a RMC (Refractory Metal Core) is inserted. The RMC is stamped or cut out and then put into form dies to achieve the desired 3D shapes. The RMC is then attached into the slots in the ceramic core. At this point, the sacrificial die is prepared for further processing such as a lost wax process, investment casting or the like. 
     SUMMARY OF THE INVENTION 
     According to an exemplar, a core for creating an airfoil has body made from a ceramic material. The body has an outer dimension, a slot extending through the outer dimension and into the body for receiving an insert, the slot disposed at an angle to the outer dimension, and a trip strip having a first portion disposed in the outer dimension. The first portion is in register with the slot wherein a constant dimension is maintained between the first portion and the slot along a length of the slot and wherein said first portion tapers towards said outer dimension to facilitate the manufacturability of the ceramic core. 
     According to a further exemplar, a core die for creating a core has a first section, a second section mating with the first section, and an insert for creating a slot. The first section and the second section define a body having an outer dimension, the insert disposed at an angle to the outer dimension, and trip strips having a first portion disposed in the second section, the first portion in register with the insert wherein a constant dimension such as minimum thickness is maintained between the first portion and the insert along a length of the insert and wherein said first portion tapers towards said outer dimension. 
     According to a further exemplar, an airfoil has a body having an inner passageway for cooling the body, trip strips disposed within the inner passageway, the trip strips tapering into an area requiring increased cooling. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side, perspective view of a ceramic core including an RMC insert. 
         FIG. 2  is a cut-away view of the core of  FIG. 1 , taken along the line  2 - 2 , shown in a ceramic core mold. 
         FIG. 3  is a cut-away view of the core of  FIG. 1  taken along the line  3 - 3 . 
         FIG. 4  is a partial view of the core die, which is a negative of the core. 
         FIG. 5  is a partial, cross-sectional view of a turbine blade made from the ceramic core and RMC insert of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a sacrificial core assembly  10  used in making a turbine blade  130  (see  FIG. 5 ). The sacrificial core assembly  10  has a ceramic core  15  and an RMC  20 , also known as a Refractory Metal Core, that acts as an insert and is attached into a slot  25  (see the ceramic core  15  shown in die  90  in  FIG. 2  and isolated in  FIG. 3 ) in the ceramic core  15 . The ceramic core  15  has a plurality of trip strips  65  that provide enhanced heat transfer to cool a turbine blade  130  (see  FIG. 5 ). The ceramic core  15  has an outer dimension including a suction side  35 , a pressure side  40 , a trailing edge  45 , a leading edge  50  and slot  25  (see  FIGS. 2 and 3 ) for RMC  20  to be inserted. The RMC may be secured in the slot in several ways including gluing or mechanical means, such as clips or the like (not shown). 
     Referring to  FIGS. 2 and 3 , a plurality of trip strips  65  extend along a length of the suction side  35  of the ceramic core  15 . The trip strips  65  are shown adjacent the trailing edge  45  of the suction side  35  but may be placed anywhere heating loads in or on the turbine blade  130  make additional cooling desirable. 
     This description shows trip strips  65  placed towards the trailing edge  45  of the ceramic core  15 , while still allowing for adequate dimension D, such as thickness or depth or the like, from the slot  25  to maintain manufacturability as will be discussed herein. Without the placement of the tapered trip strip portion  70 , trip strip coverage is reduced to accommodate minimum ceramic core thickness requirements for manufacturing and required cooling may not be provided. Trip strips  65  may be of any size, shape and configuration (straight, chevron—see  FIG. 4 , etc.) as may be required to provide cooling. Although this disclosure shows the trip strips  65  on the suction side  35 , all the same concepts could be used with trip strips on either the suction side  35  or pressure side  40 , depending on the cooling requirements of the particular part. 
     Referring now to  FIG. 4 , the negative features to produce trips strips  65  of a core die  90  are shown. Each trip strip  65  has a portion  75 , which is elongated and has a rectangular cross-section. The portion  75 , which may have an angled part  75 A attached thereto to form a chevron, is attached to a tapered portion  70 . Both the portion  75  and tapered portion  70  are disposed on a wall  80 , which is the same surface on a finished blade (see  FIG. 5 ). Each tapered portion  70  tapers towards the wall portion  80  from the portion  75 A. The tops  81  and  81 A are in plane but the top  70 A of portion  70  tapers downwardly out of plane with tops  81  and  81 A of portions  75  and  75 A thereby creating taper portion  70 . One of ordinary skill in the art will recognize that the tapered portion  70  may disposed on any portion of the trip strip  65  to accommodate an area  125  between the slot  25  and the wall  70 A (see  FIG. 2 ) as will be discussed hereinbelow and as may be required by a particular design. Taper portion  70  also need not be attached to a portion  75  to be functional herein. Similarly, both the taper portion  70  and the portion  75  may have other cross-sectional dimensions and such other shapes are contemplated herein. 
     Referring now to  FIG. 2  and the core die  90  shown in  FIG. 4 , the ceramic core  15  is shown along lines  2 - 2 . The ceramic core  15  is formed in a core die  90  having a first half  95 , a second half  100  and a manufacturing insert  105  that is removably attached to the respective core die  90  halves  95  and  100  or sections, as is known in the art. The ceramic core  15  shows portions  75 A of the trip strips  65  and the tapered portions  70  of the trip strips  65 . The trip strips  65  come out of the core die  90  as shown in  FIG. 3 . 
     Referring now to  FIG. 2 , the core die  90  includes the insert  105  and ceramic material  120  is inserted into the core die  90 . The ceramic material flows to all areas of the core die  90 , however, areas in which the ceramic material  120  flows must have a dimension such as minimum thickness to allow the material to fill the core die  90  as well as provide strength in the finished ceramic core. For instance the area  125  between the tapered portion  70  of the trip strip  65  and the slot  105  has a thickness D, which is dependent on the type of ceramic material used, to allow the ceramic material  120  to fill the area  125  to the trailing edge  45 . It should be noted that the dimension D may vary for given ceramic materials. 
     By recognizing the need for a thickness D, the trip strip portion  70  may be tapered while maintaining the thickness D to allow for the tapered portion  70  to extend closer to trailing edges of the ceramic core  15 . If the thickness D is not maintained, the ceramic material  120  may not flow to the trailing edge  45  or breakage in the finished ceramic core may be experienced. The trip strip portion  70  tapers in register with the shape of the slot  25  so that the thickness D is maintained in area  125 . 
     Referring to  FIGS. 2 ,  3  and  5 , the ceramic core  15  is removed from the core die  90  and the insert  105  is removed from the ceramic core  15 . The RMC  20  is attached into slot  25 . The ceramic core  15  and the RMC are sacrificed, as is known in the art, to make the turbine blade  130  shown partially in  FIG. 5 . The RMC  20  and ceramic core  15  become shaped opening  135  (of the finished part—see  FIG. 5 ) and the trip strips  65 , including the tapered portion  70  and portions  75  are distributed along the outer edges of the opening  135 . Because of the tapered portions  70  of surface the trip strips  65 , the trip strips  65  can now be distributed to a greater area of the shaped opening  135 . 
     Typically, trip strips  65  can be placed anywhere within the turbine blade  130 . However, when forming the ceramic core  15 , there must be enough room in the core die  90  to allow for the manufacturability of the ceramic core  15  and a certain dimension such as minimum thickness D must be allowed. Prior art cores have not been designed to accommodate trip strips  65  where they would be most useful. This disclosure allows for the additional of trip strips  65  in areas  135  not previous thought as suitable for trip strips. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Technology Classification (CPC): 1