Abstract:
A direct tension indicating washer includes 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 indicating material is weather-resistant.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional patent application Ser. No. 61/994,242, filed May 16, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Embodiments relate in general to direct tension indicating washers and in particular to a direct tension indicating washer with enhanced indicating material and a method of manufacturing. 
         [0003]    Direct tension indicating washers are used 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 direct tension indicating washer.  FIG. 1  is a top view of the direct tension indicating washer from U.S. Pat. No. 5,931,618.  FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 . 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  includes channels  62  in bottom surface  18  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 . When direct tension indicating washer  60  is used with a bolt, protuberances  12  are compressed as the bolt is tensioned. When the desired bolt tension is achieved, indicating material  64  emerges from channel  62  at the outer diameter of direct tension indicating washer  60 . The emission of the indicating material provides a visual indicator that the bolt has been properly tensioned. 
         [0004]    One issue with existing direct tension indicating washers is that the indicating material can become granulated and wear away in the presence of environmental conditions, such as wind, rain, etc. An installer may visually confirm proper bolt tension upon installation, but a subsequent visitor (e.g., an inspector) will not see the indicating material. The inspector must use a feeler gauge to confirm proper bolt tension, which is a more laborious process than a visual inspection. 
     
    
     
       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 ; and 
           [0008]      FIG. 3  depicts manufacturing in an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Exemplary embodiments employ a weather-resistant indicating material  64 . The weather-resistant indicating material remains visible (e.g., on the supporting structure and/or in the distal end of channel  62 ) for a longer period of time and thereby allows visual confirmation that proper bolt tension was achieved at installation. The indicating material may be selected to have a rheology and a tear resistance, which allows the indicating material  64  to extrude smoothly from channel  62  without crumbling. This results in less damage to the indicating material  64  when it is emitted through channel  62 , giving the indicating material  64  better strength to resist dislodging from the supporting structure and/or channel  62  in the presence of wind, rain, etc. 
         [0010]    Any suitable thermoplastic or thermoset may be used for the indicating material  64 , so long as it has suitable weather-resistant properties. Representative thermoset materials include one or more epoxides, phenolics, melamines, ureas, polyurethanes, polysiloxanes, or polymers including a suitable crosslinkable functional moiety. 
         [0011]    Illustrative examples of thermoplastic polymeric materials include one or more of olefin-derived polymers, for example, polyethylene, polypropylene, and their copolymers; polymethylpentane-derived polymers, for example, polybutadiene, polyisoprene, and their copolymers; polymers of unsaturated carboxylic acids and their functional derivatives, for example, acrylic polymers such as poly (alkyl acrylates), poly (alkyl methacrylate), polyacrylamides, polyacrylonitrile, and polyacrylic acid; alkenylaromatic polymers, for example polystyrene, poly-alpha-methylstyrene, polyvinyltoluene, and rubber-modified polystyrenes; polyamides, for example, nylon-6, nylon-66, nylon-11, and nylon-12; polyesters, such as, poly(alkylene dicarboxylates), especially poly(ethylene terephthalate) (hereinafter sometimes designated “PET”), poly(1,4-butylene terephthalate) (hereinafter sometimes designated “PBT”), poly(trimethylene terephthalate) (hereinafter sometimes designated “PTT”), poly(ethylene naphthalate) (hereinafter sometimes designated “PEN”), poly(butylene naphthalate) (hereinafter sometimes designated “PBN”), poly(cyclohexanedimethanol terephthalate), poly(cyclohexanedimethanol-co-ethylene terephthalate) (hereinafter sometimes designated “PETG”), and poly(1,4-cyclohexanedimethyl-1,4-cyclohexanedicarboxylate) (hereinafter sometimes designated “PCCD”), and poly(alkylene arenedioates); polycarbonates; co-polycarbonates; co-polyestercarbonates; polysulfones; polyimides; polyarylene sulfides; polysulfide sulfones; and polyethers such as polyarylene ethers, polyphenylene ethers, polyethersulfones, polyetherimides, polyetherketones, polyetheretherketones; or blends or copolymers thereof. 
         [0012]    Silane end-capped polyether compositions, specifically methoxy silane end-capped polyether compositions, are specifically mentioned. Such materials can provide a desirable combination of weather-resistance, rheology, and tear resistance. For example, reacting terminal isocyanate groups of a polyurethane with a silane monomer having at least one dialkoxy silane group and an organofunctional group can provide a material having improved elongation, flexibility, and modulus. Such materials are disclosed in U.S. Pat. No. 4,65,816, the content of which is incorporated herein by reference in its entirety. 
         [0013]    In other embodiments, the indicating material  64  may be implemented using urethane and other polyurethane based adhesives, methacrylate adhesives, ethylene-vinyl acetate copolymers including ethylene-acrylates, other polyolefins including polybutene and amorphous polyolefin, polyamides and polyesters, styrene block copolymers, polycarbonates, silicone rubbers as well as other thermoplastic elastomers. 
         [0014]    The weather resistance of the indicating material can be evaluated by measurement of the impact strength, either by notched charpy impact strength in accordance with ASTM A370, or by Izod impact strength according to ASTM D256 before and after QUV treatment in accordance with ASTM G154, the contents of which are incorporated herein by reference in their entirety. To evaluate weather resistance, 10 mm×10 mm×55 mm samples of the indicating material are treated by QUV for 500 hours using a cycle of 8 hours UV exposure at 70° C. followed by 4 hours of condensation at 50° C. Suitable indicating materials include those having a change in impact strength after weathering by QUV for 500 hours of less than 50%, specifically less than 25%, more specifically less than 10%, or 0.001 to 50%, or 0.001 to 25%. In an embodiment the indicating material has a change in impact strength after treatment by QUV for 500 hours using a cycle of 8 hours UV exposure at 70° C. followed by 4 hours of condensation at 50° C. of less than 50% when impact strength is determined as Izod impact strength according to ASTM D256. 
         [0015]    In addition to enhanced indicating material, embodiments include methods for manufacturing direct tension indicating washer  60 .  FIG. 3  depicts portions of an exemplary manufacturing process. It is understood that the entire manufacturing process is not illustrated. 
         [0016]    Once the protuberances  12 , indentations  16  and channels  62  are formed in the direct tension indicating washer  60  (e.g., by stamping), the indication material is placed in the indentations  16 . Prior machinery for applying the indicating material did not provide precise control of the amount of indicating material applied to each indentation  16 . Also, the prior applicator would allow indicating material to drip from the applicator, causing variation in the amount of indicating material dispensed in the indentation. 
         [0017]    The system of  FIG. 3  uses a positive pressure, volumetric dispensing system that imparts a mechanical shock to the indicating material, causing a shearing or rupturing within the indicating material upon dispensing. The dispensing system eliminates dripping by firing the indicating material droplet aggressively from a dispense needle with increased velocity. As shown in  FIG. 3 , a source  100  of indicating material may be in the form of a cartridge, hopper, vat, etc. Indicating material in source  100  is uncured. A dispenser  102  is coupled to the source  100  and emits a drop of indicating material  64  into indentation  16 . Dispenser  102  may use a pump or other positive pressure source to eject the indicating material  64 . A needle  104  is coupled to the dispenser  102  to direct the indicating material  64  into the indention  16 . A controller  106  controls operation of dispenser  102 , to ensure that indicating material is ejected at proper times. 
         [0018]    The increased dispense velocity of the indicating material causes the indicating material to impact into the indentation and lay out. This prevents mounding due to surface tension and viscosity of the indicating material. Additionally, without dripping of indicating material from the needle  104 , the production rate is increased by decreasing the time the dispenser  102  needs to wait until it can move to the next location. Another benefit correlates to the volumetric nature of the dispensing system. The amount of indicating material  64  in each indentation  16  is controlled more precisely. This results in better performing direct tension indicating washers due to increased consistency and/or reduced scatter of the indicated tension across many direct tension indicating washers. This allows the tension at which the indicating material is emitted to be closer to the targeted bolt tension without the risk of the indicating material being emitted after the desired bolt tension has been achieved. 
         [0019]    Another feature of the dispensing system of  FIG. 3  is the use of a heater  108  to control the viscosity of the indicating material in its un-cured and un-dispensed state in source  100 . Heater  108  may be positioned inside or outside of source  100 . Controlling the viscosity of the uncured indicating material allows the dispensing system to use indicating materials that would be impractical to pump or dispense with at the required volumes and tolerances (e.g. microgram). Controller  106  controls heater  108  to maintain the indicating material in source  100  at a desired temperature to achieve a desired viscosity. Controlling the viscosity of the indicating material in source  100  also reduces the time it takes to manufacture a part as well as extending the flow and settling within the indentation  16 . 
         [0020]    Another feature of the dispensing system of  FIG. 3  is the use of accelerated curing techniques (e.g., heat, humidity and/or UV exposure) after the indicating material  64  is dispensed in the indentations  16 . As shown in  FIG. 3 , a curing station  110  is used to cure the indicating material  64 . This reduces the natural curing time of the indicating material  64 . This is particularly helpful for more durable indicating materials where the exterior skin formed will naturally protect the core of uncured squirt media. The acceleration of curing reduces the time delay in process control feedback and reduces out of control production. Accelerated curing also enables faster packaging and delivery of product than what would be possible using air curing of the indicating material. 
         [0021]    While exemplary 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.