Abstract:
A knife for heating the wax on the surface of a wax runner. The knife as a surface which is recessed in the center of the surface to permit melted wax to flow up into the recessed area and not flow away from the knife. Alternately, conformal heating surface which melts only that portion of the wax runner to which the pattern gate is affixed. Additionally an electrical circuit is provided which includes a heater and a temperature controller to limit the temperature at which wax is melted.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to the production of wax trees for casting and, more particularly, to the design of blades or knives for heating wax runners and wax pattern gates to attach the wax pattern gate to a wax runner.  
           [0003]    2. Prior Art  
           [0004]    The Lost Wax Process is a long established process for casting. In the practice of the Lost Wax Process a wax pattern of a part to be cast is molded in wax. When the wax pattern is molded, a pattern gate is molded with the wax pattern in one piece. Wax runners are also molded separately. Wax runners are usually at least one branch frequently with flat surfaces and two ends. Some wax runners have a circular cross section and thus do not have either flat surfaces or edges. At one end of the runners there is a head and the other end there is a tail. A pour cup may be located at the head. The wax pattern gates are affixed to the wax runners to form a wax tree. To do this both ends of the wax pattern gate and the surface of the wax runner need to be heated sufficiently to melt wax to permit fusion. Once the wax patterns are affixed to the wax runner, a wax tree has been formed, and then ceramic material is placed on the wax tree. Once the ceramic has hardened it is heated causing the wax to flow out of the ceramic. The ceramic thus forms a mold into which the molten metal is poured to produce the desired part.  
           [0005]    In recent times, much of the Lost Wax Art has been substantially automated. In the patent application of Ludwig, et al, entitled Process and Apparatus for the Assembly of Wax Trees, Ser. No. 10/3-4,840, assigned to the same assignee, an advanced process and apparatus is taught for automating the fusion of wax gates of wax pattens to a wax runner. A heated blade is used to heat the pattern gates and the wax runner. The heated blade, the pattern gates and the wax runner are all operated by robotics. However, the fusion of wax pattern gates to a wax runner has been traditionally a manual operation performed by heating putty knives on a Bunsen Burner to melt the surface of the wax runner and the end of the pattern gate.  
           [0006]    In the automated process, the wax runners are held by a head stock and a tail stock in a runner station. The wax runner is also heated in the automated process so that a plurality of wax patterns can be affixed to the wax runner at one time.  
           [0007]    Maintaining a wax runner in a perfectly flat position when attaching the wax patterns is a most desirable goal, but unfortunately is not readily attainable. As a result, portions of the wax runner are penetrated more deeply by the heated blade than other portions. Excess molten wax is a result of excessive melting, and should the excessive melted wax run over the side of the wax runner, the wax runner and the wax patterns attached to it are not useable resulting in lost product.  
           [0008]    In heating the wax gate and the wax runner, the temperatures of heating the wax can become sufficiently high as to exceed the flash point of the wax causing it to give off fumes which are considered to be a health hazard.  
           [0009]    Therefore, it is highly advantageous to provide a blade for heating the wax runner which prevents molten wax from running over the edge of a wax runner, and it is also highly desirable to control the temperature of melting of the wax gate and wax runner to avoid the emission of fumes.  
           [0010]    Therefore, the objects of this invention are to provide the following:  
           [0011]    a knife for melting wax on a wax runner which prevents molten excess wax from flowing over the side of the wax runner by providing space in the surface of the knife to retain molten wax.  
           [0012]    a knife which conforms the heated area to the configuration of the end of the wax gate of the wax pattern, to eliminate the melting of unnecessary wax.  
           [0013]    a knife which reduces the incidence of lost wax trees.  
           [0014]    a knife which is economical to produce and which is durable and dependable.  
           [0015]    a knife whose temperature is controlled to prevent the formation of undesirable fumes by maintaining the temperature of the knife below the flash point temperature of the wax.  
         SUMMARY OF THE INVENTION  
         [0016]    A knife is provided which has two opposite sides. The knife further includes an elongated bar of heat-conducting material that has two opposed and generally parallel surfaces. One surface is for contacting the pattern gate and the other is for contacting the wax runner. The surface for contacting the wax runner has two side edges and a center section between the two side edges. At least a portion of the center section, whether grooved or concave, is slightly closer to the opposite surface.  
           [0017]    As an alternative, in placed of the grooved or concave surface, a eries of raised conformal surfaces are located to heat only that portion of the wax runner where the pattern gate will be placed.  
           [0018]    The knife further includes a means for heating the elongated bar. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a side elevation showing wax patterns with pattern gates being held in a fixture on one side of a knife with a wax runner on the opposite side of the knife, with the knife including conformal contact areas.  
         [0020]    [0020]FIG. 2 is a plan view of the base of a knife having an elongated groove pattern.  
         [0021]    [0021]FIG. 3 is a cross sectional view along lines  3 - 3  of FIG. 2.  
         [0022]    [0022]FIG. 4 is a plan view similar to FIG. 2 but with a concave pattern.  
         [0023]    [0023]FIG. 5 is a cross-sectional view along lines  5 - 5  of FIG. 4.  
         [0024]    [0024]FIG. 6 is a plan view of the base of a knife having conformal heating surfaces.  
         [0025]    [0025]FIG. 7 is a cross-sectional view along lines  7 - 7  FIG. 6.  
         [0026]    [0026]FIG. 8 is a plan view of the base of a knife having conformal heating surfaces with grooves in the surfaces.  
         [0027]    [0027]FIG. 9 is a cross-sectional view along lines  9 - 9  of FIG. 8.  
         [0028]    [0028]FIG. 10 is a cross-sectional view of the knife shown in FIG. 1 showing the heating element and a temperature sensor in the blade.  
         [0029]    [0029]FIG. 11 is a circuit diagram for the controlled heating of the knife. 
     
    
       [0030]    [0030]                                             DESCRIPTION OF THE NUMERALS                Numeral   Description                       11   Wax Pattern           13   Wax Runner           14   Wax Pattern Gate           15   Pattern Holder           17   Pour Cup           19   Head           21   Knife           22   Surface (Contact Runner)           23   Surface (Contact Gate)           27   V-shaped Groove           29   Edge           31   Concave Surface           33   Sides           35   Conformal Surface           36   Grooves           37   Base Surface           39   Heating Element           41   Temperature Sensor           43   A-C Power Supply           45   Circuit Breaker           47   Temperature Controller           51   Solid State Relay           53   Solid State Contact                        
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    Referring now to FIG. 1, the general relationship is shown between wax patterns  11  and a wax runner  13 . The wax patterns include wax pattern gates  14 . The wax patterns  11  are held by a pattern holder  15 . The wax runner  13  with a pour cup  17  at the head  19  is located beneath the wax patterns  11 . A knife  21  having conformal surfaces in accordance with this invention as will be hereinafter explained is located between the wax patterns  11  and the wax runner  13 . After both the wax pattern gates  14  of the wax patterns  11  and the wax runner  13  are heated by the knife  21 , which is temporarily interposed between the wax patterns  11  and the wax runner  13 , the knife  21  is withdrawn and the wax pattern gates  14  are brought into contact with the wax runner  13  to create fusion.  
         [0032]    Referring now to FIGS. 2 and 3 a knife  21  in accordance with this invention is shown. The surface  22  of the knife  21 , shown in FIG. 2, heats the wax runner  13 . The surface  23  of the knife  21  contacts the wax pattern gates  14 . FIGS. 2 and 3 show the surface  22  of a knife  21  for contacting the wax runner  13  which surface  22  is formed with three v-shaped grooves  27  in it. Two of the grooves  27  are close to the edge  29  of the surface  22  which contacts the wax runners  13  and are v-shaped grooves  27  is located generally equally between the two v-shaped grooves  27  and to the edges  29 . In FIGS. 4 and 5, there is shown a variation to the configuration of FIGS. 2 and 3, namely a concave surface  31  extending across the width of the surface  22  of the knife  21  in contact with the wax runner  13 .  
         [0033]    The cross sections shown in FIGS. 3 and 5 are just two of numerous possibilities. The exact configuration is not vital. The common feature of both FIG. 3 and FIG. 5 is to provide a space in the knife  21  into which molten wax will flow when the knife  21  is pressed against the wax runner  13 . With a knife  21  having a surface  22  which is flat, the molten wax is forced outwardly which readily can result in the undesirable condition of molten wax flowing over the sides  33  of the wax runner  13 . By having at least a portion of the surface  22  between the edges  29  of the knife  21  recessed or withdrawn slightly away from the wax runner  13 , a space is provided to receive molten wax while retaining that molten wax under the knife  21 . Thus, the v-shaped grooves  27  of FIG. 2 and FIG. 3 as well as the concave surface  31  as shown in FIG. 4 and FIG. 5 provide a space where melted wax can be held to prevent that wax from flowing over the sides of the wax runner  13 .  
         [0034]    In FIGS. 6 and 7 and FIGS. 8 and 9 conformal surfaces  35  are shown. In FIGS. 6 and 7 the conformal surfaces  35  are flat while in FIGS. 8 and 9 the conformal surfaces  35  have grooves  36 . The conformal surfaces  35  protrude slightly beyond a base surface  37  of the knife  21 . The grooves  36  provide the space for molten wax to be held further to avoid wax running over the sides of the wax runner  13  as has previously been explained. With conformal surfaces  35 , the wax runner  13  is heated only in the area where the wax pattern gates  23  are to be connected the wax runner  13 . The configuration of the conformal surfaces are designed to conform to the shape of the wax pattern gate  14  to be fused to the wax runner  13 . The polygram configuration of the conformal surface  35  shown in FIGS. 6 and 8 is merely illustrative. The conformal surface  35  eliminates melting for substantially the length of the wax runner thereby melting less wax and as a result, reducing the possibility of wax running over the side of the wax runner  13  due to a reduction in the area of the wax runner  13  that is heated. As a result there is an elimination of any flow of wax where heating is not required.  
         [0035]    As can be seen in FIGS. 7, 9 and  10 , a heating element  39  is located in the knives  21 . The heating element  39  is controlled by a temperature sensor  41  (FIG. 10) also located in the knife  21 , which determines the temperature of the knife  21 . As a result, the melting temperature of the wax is controlled. The flash temperature of wax, generally speaking, is about five hundred degrees Fahrenheit. At the flash temperature volatilities, which are undesirable, are emitted into the atmosphere. By use of the electrical control system show in FIG. 11, the knife  21  is held to a temperature under the flash point and the attachment of the wax pattern gate  14  to the wax runner  13  is accomplished without undesirable volatilities being released into the atmosphere.  
         [0036]    Referring to FIG. 11, which is an electrical circuit diagram for the heating element  39  in the knife  21 . An alternating current power supply  43  is required. The power supply  43  is fed through a circuit breaker  45  into a temperature controller  47  which is activated by the temperature sensor  41 . When the temperature controller  47  detects a specified level of temperature in the knife  21 , it breaks the supply of power to the heating element  39  through a solid state relay  51  which opens and closes a solid state contact  53  in series with the heating element  39 .  
         [0037]    It is to be understood that the drawings and description matter are in all cases to be interpreted as merely illustrative of the principle of the invention, rather than as limiting the same in any way, since it is contemplated that various changes may be made in various elements to achieve like results without departing from the spirit of the invention or the scope of the appended claims.