Abstract:
A direct tension indicating washer including a first surface having a protuberance formed thereon; a second surface having an indentation formed opposite the protuberance; an indicating material positioned in the indentation; and a channel leading from the indentation to an outer diameter of the direct tension indicating washer; wherein the protuberance has four walls, each of the walls being substantially perpendicular to the first surface.

Description:
BACKGROUND 
       [0001]    The invention relates in general to direct tension indicating washers and in particular to direct tension indicating washers that indicate when the proper bolt tension has been achieved. 
         [0002]    Direct tension indicating (DTI) washers are used in the art to indicate when proper bolt tension has been reached. U.S. Pat. No. 5,931,618, the entire contents of which are incorporated herein by reference, discloses an exemplary DTI. FIG. 1 is a top view of the DTI from U.S. Pat. No. 5,931,618. A direct tension indicating washer  60  includes protuberances  12  formed on a first surface  14  and corresponding indentations  16  formed on a second surface  18 . The direct tension indicating washer  60  also includes channels  62  that lead from each indentation  16  to the outer diameter of the direct tension indicating washer  60 . The indentation  16  is filled with an indicating material  64 . The direct tension indicating washer  60  is manufactured using a tool and die to stamp the protuberances  12 , indentations  16  and channels  62  into a blank washer. Other processes, such as metal machining or metal casting may be used to form the direct tension indicating washer  60 . Direct tension indicating washer  60  is made from carbon steel, but stainless steel, nonferrous metals, and other alloy products may also be used. The indicating material  64  is an extrudable, elastomeric solid material such as colored silicone.  FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 .  FIG. 3  illustrates the protuberances before installation and after installation illustrating the compression of a protuberance  12 , which forces indicating material  64  out channel  62  to the periphery of the direct tension indicating washer  60 . 
         [0003]    While the direct tension indicating washer of  FIGS. 1-3  is well suited for its intended purposes, it has been discovered that a more prominent exodus of indicating material  64  from channel  62  is desirable. Pending U.S. patent application Ser. No. 11/875,224, the entire contents of which are incorporated herein by reference, discloses a direct tension indicating washer having a modified indicating material to provide a more prominent exodus of indicating material (also referred to as a “squirt event”). While this design is well suited for its intended purpose, there is a need to further improve the exodus of indicating material from the channel. 
       SUMMARY 
       [0004]    Embodiments of the invention include a direct tension indicating washer including a first surface having a protuberance formed thereon; a second surface having an indentation formed opposite the protuberance; an indicating material positioned in the indentation; and a channel leading from the indentation to an outer diameter of the direct tension indicating washer; wherein the protuberance has four walls, each of the walls being substantially perpendicular to the first surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0006]      FIG. 1  is a top view of a conventional direct tension indicating washer; 
           [0007]      FIG. 2  is a cross-sectional view of the direct tension indicating washer shown in  FIG. 1  taken along line  2 - 2 ; 
           [0008]      FIG. 3  illustrates compression of convention protuberances during installation of the direct tension indicating washer; 
           [0009]      FIG. 4  is a perspective view of a conventional protuberance; 
           [0010]      FIG. 5  is a perspective view of a protuberance in embodiments of the invention; and 
           [0011]      FIG. 6  illustrates the formation of the protuberance of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    One issue with direct tension indicating (DTI) washers loaded with indicating material is that when the DTI protuberances  12  get too small, or low, relative to the indentation  16  depth under them, when used to expel indicating material  64 , the compression of the small protuberances  12  sometimes does not result in sufficient deformation of the indentation  16  cavity to eject indicating material  64  in a reliable manner. 
         [0013]      FIG. 4  illustrates a conventional protuberance  12 . The protuberance  12  is formed using a punch driven into the bottom surface of the DTI  60  and a die on the top surface of the DTI. The die has two walls, which results in protuberance  12  having two sides  70  that are substantially planar and substantially perpendicular to the top surface of the DTI. The remaining sides  72  of the protuberance are arcuate and meet at an apex of the protuberance. 
         [0014]    To improve the ability to expel the indicating material  64 , a protuberance  110  as shown in  FIG. 5  is formed.  FIG. 5  illustrates a portion of a direct tension indicating washer  100 . Direct tension indicating washer  100  is similar to that shown in  FIG. 1 , with the exception of the protuberances used. Two aspects of the protuberance  110  are improved in embodiments of the invention. The protuberance  110  is formed using a die having four sides such that all four sides  112  of protuberance  110  have walls that are substantially planar and substantially perpendicular to a top surface  114  of the DTI  100 . 
         [0015]    Formation of the protuberance  110  is also improved.  FIG. 6  illustrates the formation of protuberance  110 . The protuberance  110  is formed by a punch  120  which is much wider than the standard punches, so that when the wide punch  120  enters the base metal it causes the metal to flow into a die  122  cavity which constrains the protuberance  110  on four sides. Being thus constrained, the protuberance  110  produced is relatively higher and weaker compared to protuberance  12  of the same volume made with narrower punches. Upon use of the DTI, as the higher and weaker protuberance  110  is compressed, it deflects more easily, and coincidentally causes more interior deformation of the indentation  116 . In a sense, protuberance  110  acts more like a piston with a longer stroke, and is therefore capable of ejecting much more indicating material to the outer diameter of the direct tension indicating washer  100 . Also, ejection of the indicating material is more predictable as ejection relates to the compression strength of the protuberance. 
         [0016]    The indentation  116  is longer than the protuberance  110  as measured in a direction (shown as axis Y) that is transverse to a line running radially from the centroid or center of the direct tension indicating washer  100  to the middle of the protuberance  110 . By making the indentation  116  much longer relative to the protuberance  110  length, the protuberance  110  is weaker as it deforms into the indentation  116 , which allows for deformation of the upper portion  118  of the indentation  116 . The deformation of indentation  116  is primarily at the center of the indentation  116 , which has the effect of displacing indicating material precisely where intended as the center of indentation  116  is immediately adjacent to the channel  62  resulting in a very predictable emission of indicating material. 
         [0017]    The size of the protuberance  110  is also a factor in generating a predictable squirt event. The protuberance  110  has approximately the same metal volume as that displaced by the punch  120  in forming indentation  116 . As shown in  FIGS. 5 and 4 , the height, c, of protuberance  110  is greater than height, b, of protuberance  12 . Further, the volume, V 2 , of protuberance  110  is greater than the volume, V 1 , of protuberance  12 . This gives protuberance  110  a more piston-like compression when used to more forcefully expel indicating material  64 . The volume of indicating material  64  should be approximately equal to the indentation volume. If there is an excess of indicating material  64 , the direct tension indicating washer  100  will rotate about the indicating material and not function correctly. 
         [0018]    The compression resistance of the protuberance  110  is determined by structural steel application specifications, and must be met by each and every direct tension indicating washer  100 . If the protuberances  110  are too small, or low, relative to the indentation volume under them, the compression of the small or low protuberances and the small volume of indicating material  64  affected by protuberance compression sometimes does not result in sufficient deformation of the indentation  116  to eject indicating material in a reliable manner. 
         [0019]    Each protuberance  110  on direct tension indicating washer  100  should resist a certain load, or compression resistance, before the indicating material is ejected, and this characteristic is expressed in terms of volume of indicating material/desired compression resistance, expressed as a ratio of cc (volume) per unit of compression resistance (load, or lb). If the volume of indicating material/desired compression resistance is in the range of about 0.7×10 −6  cc per lb to about 0.9×10 −6  cc per lb, there is sufficient indicating material affected by protuberance deflection to make the squirt event predictable and reliable. Conversely, if the volume of indicating material/desired compression resistance is in the range of about 0.4×10 −6  cc per lb to about 0.6×10 −6  cc per lb, there is not sufficient indicating material affected by the protuberance deflection to make the squirt event predictable and reliable. 
         [0020]    The shape of protuberances  110  (i.e., having four planar walls) and using a punch  120  which is much wider than the standard punches, so that when the wide punch enters the base metal to the same depth as convention punches it causes the metal to flow into a die  122  cavity which, being constrained on four sides, causes the protuberance  110  to become relatively higher. Being constrained on four sides by the die cavity, the protuberance  110  is relatively higher and yet the indention  116  allows sufficient indicating material to be deposited in the indentation  116  to bring into the volume of indicating material/desired compression resistance of between about 0.7×10 −6  cc per lb and about 0.9×10 −6  cc per lb. 
         [0021]    In this process, the compression strength of protuberance  110  is also kept in the necessary range as determined by application specifications. Consequently, when the protuberance  110  is compressed, it deflects in such a way that it affects a greater volume of indicating material, and causes more interior deformation of the indentation which is the primary mechanism of indicating material ejection. As noted above, protuberance  110  acts more like a piston with a longer stroke, and is therefore capable of ejecting much more indicating material to the outer diameter of the direct tension indicating washer. 
         [0022]    The direct tension indicating washer  100  also provides for execution of a unique method for determining if a bolt has lost tension. After initial installation, a user may subsequently re-tighten the nut in contact with the direct tension indicating washer  100  to detect the degree to which bolt tension has decreased since initial installation. When the user re-tightens the nut, indicating material will be expelled from channel  62  due to the nut compressing protuberance  110 . This is due to the fact that some indicating material remains beneath the protuberance and in the channel after initial installation. If the user turns the nut a small amount (e.g., 3-4 degrees) before the indicating material is expelled on the outer periphery of the direct tension indicating washer  100 , this indicates that the bolt has lost a small amount of tension since initial installation. If the user turns the nut a larger amount (e.g., 30-40 degrees) before the indicating material is expelled on the outer periphery of the direct tension indicating washer  100 , this indicates that the bolt has lost a larger amount of tension since initial installation. 
         [0023]    While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.