Abstract:
A linecutter article, apparatus and method wherein the linecutter is mounted adjacent a shaft seal cutting line to protect the shaft seal(s). The linecutter includes an annular ring of tough, low coefficient of fricton, abrasion-resistant, ultra-high molecular weight polyethylene or its equivalent in contact with the shaft and having a sharp linecutter edge facing outwardly. The ring is tough enough to cut monofilament fishing line but flexible enough to follow shaft runout and provides an additional seal.

Description:
TECHNICAL FIELD 
     This invention relates to linecutters and in one embodiment to linecutters mounted adjacent propshaft seals of small marine engines for cutting nylon fishing line to protect the propshaft seal(s). 
     BACKGROUND 
     It is current practice to use a formed metal linecutter adjacent the propshaft of small marine engines such as outboards, inboards and inboard-outboards, used for fishing. The purpose of the linecutter is to protect the propshaft seal(s) from nylon fishing line which may wrap around the propshaft. The inner diameter of the linecutter must be ground for two reasons: (1) to produce a sharp outward-facing edge to cut fishing line, and (2) to achieve a minimal shaft clearance with an exceptionally tight tolerance (±0.0005-0.0010 inches). 
     The linecutter shell is usually cup-shaped and the outer propshaft seal is pressed into it to form a seal-linecutter assembly. Therefore, the inside diameter-outside diameter concentricity of the metal linecutter must be held to 0.005 inch TIR (total indicator reading) or less. The major disadvantages of such known linecutters are cost, grooving of the shaft due to shaft runout, and generation of heat near the seal. 
     SUMMARY OF THE INVENTION 
     A linecutter seal, apparatus and method including an annular ring of tough, abrasion resistant, ultra-high molecular weight polyethylene or its equivalent, having an annular inside diameter shaft-contacting surface and an axially outer radial surface that meets the shaft-contacting surface at an acute angle forming a sharp linecutter edge riding on the shaft. The polyethylene ring is tough enough to cut nylon monofilament fishline, yet is preferably flexible enough to follow shaft runout and is non-abrasive thus virtually eliminating grooving of the shaft. Because of its flexibility and low abrasiveness, the polyethylene ring is designed with shaft interference eliminating the need for the tight tolerances needed on the prior art ground metal linecutter, and also producing an additional sealing effect on the shaft axially outside of the primary seal(s). 
     The polyethylene ring is preferably part of a molded unit including a metal shell and an elastomeric body with the ring being a liner on the inside diameter of the elastomeric body. 
     It is an object of the present invention to provide a linecutter seal, apparatus, and method that eliminates the above-mentioned problems in the prior art. 
     It is another object of the invention to provide a linecutter that eliminates shaft grooving, that does not overheat adjacent the propshaft seal(s), that is less expensive in eliminating a grinding operation and the need for tight tolerances and concentricity, and that, at the same time, provides an additional sealing effect on the shaft outside of the primary seal(s). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood by reference to the following detailed description thereof, when read in conjunction with the attached drawings, wherein like reference numerals refer to like elements and wherein: 
     FIG. 1 is a partial cross-sectional view through a prior art linecutter; 
     FIG. 2 is a partial cross-sectional view showing the linecutter of the present invention in combination with a marine engine housing, shaft and primary seals; and 
     FIG. 3 is an enlarged partial cross-sectional view of the linecutter of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to the drawings, FIG. 1 shows a known linecutter and seal arrangement including a marine engine housing 10, a shaft 12, a bearing 14, a propshaft seal 16, and a metal linecutter 18 having a cutting edge 20. The linecutter 18 is cup-shaped and the propshaft seal 16 is pressed into the linecutter and held by a crimped edge 22. The inside diameter surface 24 of the linecutter is ground to produce the sharp edge 20 and to achieve a minimal shaft clearance with an exceptionally tight tolerance of about ±0.0005-0.0010 inch. 
     FIG. 2 shows a linecutter 30 according to the present invention, installed in a marine engine housing 32 having a bore 34, defined by a bore wall 36, through which bore a propshaft 38 extends, a bearing 40, a propshaft seal 42 and the linecutter 30. 
     The linecutter 30 has an inside diameter shaft-contacting surface 44 and a cutting edge 46 in contact with the shaft. FIG. 2 also shows, in dotted lines, the as-molded shape of the linecutter 30, showing that the linecutter is designed with a certain amount of interference with the shaft. As shown in FIG. 2, both the seal 42 and the linecutter 30 form a press-fit with the bore wall 36. 
     For purposes of the present specification and claims, the term &#34;axially inner&#34; means the oil side, or to the left in FIGS. 1-3, and &#34;axially outer&#34; means the water side or to the right in FIGS 1-3. 
     Referring now to FIG. 3, the linecutter 30 includes an annular metal shell 48, a molded elastomeric body 50 and a liner or ring 52 of ultra high molecular weight polyethylene. The linecutter 30 is preferably made by a known molding process (as will be understood by anyone skilled in the art) in which all three of the shell, elastomeric preform, and ring are placed in a mold cavity; the mold is then closed molding the body to the desired shape from the preform, forming the ring to the desired shape from a flat ring tube or washer, and bonding the three parts together. 
     The shell 48 includes a cylindrical portion 54 and a radial flange 56 extending radially inwardly from the axially inner end of the cylindrical portion. The outside diameter surface of the cylindrical portion 54 is designed and adapted to form a press-fit in the bore wall 36. The shell is preferably type 302/304 stainless, and in one embodiment is 0.030 inches thick (#22 gauge), having a pierce of about 0.655 inches and a width of 0.128 inches. 
     The molded elastomeric body 50 is bonded to the cylindrical portion 54 and to the radial flange 56 and is located radially inwardly of the cylindrical portion and axially outwardly of the radial flange. The body 50 has an axially outer radial surface 58 including a radially outer radial portion 60, a radially inner tapered portion 62, and a cylindrical portion 64. The radial surface 58 thus has an outwardly facing groove 59 which provides a desired amount of flexibility to the ring 52. The radial surface 58 is located axially outwardly of the edge 46 in their as-molded shape. The preferred elastomer is nitrile. 
     The liner or ring 52 is bonded to the radially inner, generally cylindrical surface of the elastomeric body. The ring 52 includes an axially outer radial surface 66 that forms an acute angle with the annular inside diameter shaft-contacting surface 44 thus forming the sharp linecutter edge 46. The sharp cutting edge 46 can be formed during molding via pinchoff, or it can be trimmed after molded. Preferably it is formed by pinchoff during molding. The ring 52 is formed to its desired shape during molding. The acute angle is most preferably about 50°, however, it can be any acute angle less than 90°, but preferably is in the range of from about 30°-70°. The ring 52 is preferably made of an ultra-high molecular weight polyethylene. The ring 52 must be tough enough to cut nylon fishing line, abrasion resistant and is also preferably flexible enough to follow shaft runout. While ultra-high molecular weight (2,000,000 to 6,000,000) polyethylene (see pages 66-68 of &#34;Modern Plastics Encyclopedia&#34;, 1980-81 Edition (McGraw-Hill, New York, 1980) is preferred, other equivalent tough, low coefficient of friction, abrasion-resistant materials can be used including various plastics, such as glass-filled nylon. 
     In the as-molded shape of the linecutter 30, the inside diameter surface 44 makes an acute angle of about 10° to the linecutter axis, while the radial surface 66 makes an acute angle of about 60° to the linecutter axis. 
     In one preferred embodiment, the ring 52 as formed in the mold had an interference of about 0.010 inch with the shaft 38, which had a diameter of 0.6245 inch. The linecutter 30 outside diameter was 1.128 inch, the axial length of the linecutter was 0.143 inch, the radial clearance between the shaft and the axially inner end of the inside diameter surface 44 of the ring 52 was 0.005 inch, and the axially inner end of the ring 52 was cylindrical for 0.045 inches before it started to taper radially inwardly toward the shaft. The axial length of the linecutter was 0.130 inches. The radial distance from the shaft to the cylindrical portion 64 of the surface 58 was 0.100 inch. 
     The invention has been described in detail with particular reference to the preferred embodiments thereof, but it will be understood that variations and modifications can be affected within the spirit and scope of the invention as described hereinafter and as defined in the appended claims. For example, the linecutter 30 can be used in other assemblies than that shown in FIG. 2, and with other types of seals. One such example would be an apparatus in which the linecutter also performs a principal sealing function and the axially outwardly facing lip of FIG. 2 is omitted. Further, the linecutter and the seal may be united within a unitary structure. Such a unitary structure can be made with a separate unifying shell or by an extension of the shell of the seal or the shell of the linecutter to retain both members. Further, other shapes for the shell 48 and the body 50 can be used, and in fact one or both of these can be omitted with other means substituted therefore for holding the ring 52 in place. The linecutter 30, is, of course, not limited in use to cutting fishing line and is not limited to use in marine engines. For example, this invention can be applied in a disk harrow to exclude &#34;lines&#34; such as cornstalks or vines. The term &#34;line&#34; is defined for use in the present specification and claims as meaning any of various elongated materials that might tend to wrap around a shaft, such as and including fishing line, grass, cornstalks, vines and the like.