Abstract:
A metallic tape blade may be substantially coated with a powder and then passed through an induction unit to heat the powder and form a coating on the blade, with the blade having a concavo-convex cross-section when passing through the induction unit. Alternatively, the metallic tape blade is substantially covered with a powder consisting essentially of nylon having a particle size of 20 microns or less and then passed through an induction unit to heat the blade and form a nylon coating derived from the powder thereon. Alternatively, a nylon coating is applied to the metallic tape blade, with the coating having a thickness of not more than 0.0015 inches and an abrasion resistance according to ASTM D968-81 of at least 30 liters of sand. One or more of these aspects may be combined to form a tape blade having a protective coating thereon.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed generally to tape measures and, more particularly, to a coated tape measure blade and a method of making the same.  
         BACKGROUND OF THE INVENTION  
         [0002]    Modern power return tape measures (or “tape rules”) typically include a coiled tape that is spring-biased towards a retracted position. A housing generally surrounds protects the tape and biasing spring and includes an opening through which a distal end of the tape extends. The distal end of the tape is pulled away from the housing during use, and when released, the spring pulls the tape back into the housing so that the tape returns to the retracted position.  
           [0003]    The tape blades for such devices are typically formed from a metal ribbon that assumes a concavo-convex configuration when outside the housing, but that is wound into a revolute coil inside the housing with each layer of the coil having a flat cross-section. While the base material of the blade is typically metal, the surface of the blade material is rarely bare metal. Instead, the blade material is typically painted, printed with length indicia, and then coated with a polymer coating to improve abrasion resistance and/or reduce friction. This polymer coating is typically applied by passing the ribbon material over a coating roller and then through an oven to cure the coating.  
           [0004]    Obviously, increasing the blade coating thickness has the beneficial effect of increasing the abrasion resistance; however, increasing the coating thickness increases also the space consumed by the coiled blade, thereby deleteriously increasing the overall size of the tape measure.  
           [0005]    Separately, the conventional technique of applying the polymer coating to the blade material—using a coating roller—has proved somewhat problematic, particularly in forming a coating of a relatively uniform thickness without undesirable voids.  
           [0006]    As such, there remains a need for alternative methods of coating a tape measure blade. While it is not required, it is preferred that the alternative methods address one or more of the problems discussed above.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed to a coated tape measure blade and a novel method of making the same. In one embodiment of the invention, a metallic tape blade is substantially coated with a powder and then passed through an induction unit to heat the powder and form a coating on the blade, with the blade having a concavo-convex cross-section when passing through the induction unit. In another embodiment, the metallic tape blade is substantially covered with a powder consisting essentially of nylon having a particle size of 10-20 microns or less and then passed through an induction unit to heat the blade and form a nylon coating derived from the powder thereon. In yet another embodiment, a nylon coating is applied to the metallic tape blade, with the coating having a thickness of not more than about 0.001 inches or less per side and an abrasion resistance according to ASTM D968-81 of at least 30 liters, and more preferably at least 40 liters, of sand. In still other embodiments, one or more of these aspects are combined to form a tape blade having a protective coating thereon.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 shows a power return tape measure that may employ a tape blade constructed in accordance with the present invention.  
         [0009]    [0009]FIG. 2 is a perspective view of a concavo-convex tape blade.  
         [0010]    [0010]FIG. 3 is a cross-sectional view of the tape blade of FIG. 2.  
         [0011]    [0011]FIG. 4 shows a process line for forming a coating on the tape blade of FIG. 2.  
         [0012]    [0012]FIG. 5A shows a top view of a coil having a non-circular shape suitable for the induction unit of the process line of FIG. 4.  
         [0013]    [0013]FIG. 5B shows a side view the coil of FIG. 5A. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    As the present invention relates to a coated tape measure blade, particularly for so-called power return tape measures, a brief discussion of such devices may be helpful in understanding the present invention. As illustrated in FIG. 1, a power return tape measure, generally designated  10 , typically includes a coilable measuring tape or blade  12  and an associated housing  20 . The distal end of the tape  12  may include an end hook  14  to prevent it from being retracted into the housing  20 . A tape-biasing device (not shown), such as a spring, is operatively connected to the tape  12  to bias it towards a retracted orientation. A locking mechanism, including a toggle  16  or similar actuator is provided to aid in controlling the movement of the tape  12  into and out of the housing  20 . One or both sides of the housing  20  may include a clip  18 , as desired. The housing  20  may include a main case or shell  22  and a grip element  24  mounted on the shell  22 . Shell  22  is preferably made from a durable material such as a hardened plastic (e.g., ABS, polycarbonate, or the like) and may be constructed from two portions joined together by suitable screws  26 , as is known in the art. The housing  20  is preferably sized to fit within a user&#39;s hand, and also conveniently stored on a work belt or in a toolbox. As the present invention primarily relates to the tape blade  12 , additional details of the construction of the tape measure  10  are not necessary for one of ordinary skill in the art to understand the present invention. If additional details are desired, see U.S. Pat. Nos. 4,527,334; 4,976,048; 6,349,482, and U.S. patent application Ser. No. 10/174,629, filed Jun. 19, 2002, which are incorporated herein by reference.  
         [0015]    The tape blade  12  is typically formed from a relatively thin metal ribbon  32  shaped to form the desired concavo-convex cross-sectional shape (as shown in FIGS.  2 - 3 ) when extended from the housing  20 , and the desired flat cross-section when coiled inside the housing  20 . The underlying metal ribbon  32  is typically a steel alloy, such as medium to high carbon steel (e.g., 1095 steel or 1050 steel), with a thickness in the general range of 0.004 to 0.0055 inches. While not required, the ribbon  32  forming the core of the tape blade  12  preferably has a uniform thickness across its width and along its length. The ribbon material itself may be formed into the desired shape using any one of a variety of known techniques, such as roll forming. The metal ribbon  32  is typically painted and then printed with appropriate length indicating indicia  36  using known techniques. Thereafter, the printed tape blade  12  is coated with a suitable protective coating  34 . The purpose of the coating  34  is to increase abrasion resistance and/or to provide a low friction surface to aid in coiling the blade  12 .  
         [0016]    The present invention relates to one or more methods of coating the tape blade  12 , and preferably the painted and printed tape blade  12 . As such, the discussion will assume that the tape blade  12  is painted and printed with the length indicating indicia  36  prior to the coating process, but this is not strictly required for all embodiments.  
         [0017]    The coating process may take place at a coating process line  50 , such as that shown in FIGS.  4 - 5 . The coating process line  50  typically includes a let-off station  52 , a coating station  60 , and a take-up station  56 . The let-off station  52  operates in a  10  conventional fashion to supply the painted and printed tape blade material  12  to the coating station  60 , and the take-up station  56  operates in a conventional fashion to receive the coated tape blade  12  from the coating station  60 . Further, it may be advantageous to include suitable accumulators  54 , 58  on the input and/or output portions of the process line  50  so that the tape blades  12  may be supplied to the coating station  60 , and output therefrom, in the form of rolls of concatenated blades (e.g., multiple blades  12  riveted end to end), as is known in the art.  
         [0018]    For the preferred embodiments of the invention, one primary difference with the prior art coating processes lies in the use of a novel process within the coating station  60 . As shown in FIG. 4, the coating station  60  has two principle components—the powder unit  62  and the fusing unit  66 . The powder unit  62  applies a polymer based powder  64  to the ribbon  32 ; this powder  64  is subsequently fused into a coating  34  in the fusing unit  66 . In the powder unit  62 , the ribbon  32  is routed through a vortex of polymer particles  64  that have been triboelectically charged. The particles themselves are preferably nylon, more particularly nylon  11  with a particle size of 10-20 microns or less, and preferably 15 microns or less. Such nylon should be commercially available from Atofina Chemicals of Philadelphia, Pa. The triboelectric charge is applied by agitating the powder  64  using one or more blowers (not shown), such as the triboelectric powder spray gun of the type generally described in U.S. Pat. No. 5,402,940, which is incorporated herein by reference. The mixing action of the powder  64  causes a positive static electricity charge (sometimes referred to as a triboelectric charge) to build up. The tape blade  12  is grounded, such as by grounding a feed roller immediately upstream of the powder unit  62 , giving the tape blade  12  a relatively negative charge (with respect to the powder  64 ) so that the powder particles  64  are attracted to the blade  12 . The combination of the very small particle size of the powder  64  and the triboelectric charging is believed to help form a uniform layer of powder  64  on the ribbon  32 . In addition, because a vortex of powder  64  is used, rather than a roller, the ribbon  32  may optionally have its “normal” concavo-convex cross-sectional shape while passing through the powder unit  62 .  
         [0019]    A powder unit  62  for use with the present invention may be formed using a number of off-the shelf components supplied by Nordson Corp. of Amherst Ohio. For instance, a triboelectric powder spray gun of part numbers 631201, 631271, 630008, and 133403 may be used in conjunction with a model 163567 hopper having a model 631401/163555 “tribo pump” and a model 631152 control unit. The powder  64  in the hopper is preferably in the form of a fluidized bed of powder that is pumped to the triboelectric powder spray gun by the tribo pump. The output of the triboelectric powder spray gun is fed to a generally cylindrical vortex tower tangent to the outer wall thereof. In the vortex tower, half the input of charged powder  64  is directed along the inside of the outer wall, and half the input is deflected by an internal deflector towards a point approximately 180° away from the input point. The vortex tower may be made from PVC, be approximately eight inches in diameter and approximately eighteen inches tall. The bottom of the vortex tower may be tilted towards an exhaust port leading to filter for pulling powder laden air out of the vortex tower for recycling to the hopper. The hopper may also be vented via a hose that lead to the vortex tower, with an input port approximately 6 inches below the input from the triboelectric powder spray gun and offset by approximately 90°. The bottom of the vortex tower should have a slit cut therein to allow for the passage of the blades  12  being processed. This slit may optionally be faced with soft bristles to help prevent unwanted escape of powder  64  from the vortex tower.  
         [0020]    From the powder unit  62 , the powdered ribbon  32  proceeds, preferably directly, to and through the fusing unit  66 . While traditional coating furnaces are either electrical resistance heaters (or more rarely gas-fired ovens), the fusing unit  66  for the present invention is preferably based on the induction principle wherein a time-varying electromagnetic field is applied to the blade  12  via coil  68 . In preferred embodiments, the electromagnetic field has a frequency of approximately 450 kHz. Such an electromagnetic field causes the metallic ribbon  32  to heat up very quickly and substantially uniformly. Additionally, the use of induction heating allows the blade  12  to have its “normal” concavo-convex cross-sectional shape while passing through the fusing unit  66  at a high line speed (e.g., forty to sixty feet per minute) without adverse coating effects proximate the lateral edges of the blade  12 . The heat from blade  12  causes the powder  64  to fuse, forming the preferably transparent coating  34  on the painted and printed blade  12 . The blade  12  then passes outside the fusing unit  66  for cooling. Note that it is preferred that the blade  12  not encounter any rollers or other guides, either while passing through the fusing unit  66 , or immediately thereafter, until the coating  34  has cooled sufficiently; however, if desired, the first roller downstream from the fusing unit  66 , typically disposed ten feet or more downstream, may be so-called cooling roller to additionally cool the blade  12 . The final coating thickness should be on the order of 0.001 inches or less on a given side of the blade  12 .  
         [0021]    As described above, the preferred fusing unit  66  utilizes the induction heating principle. The relevant electromagnetic field is generated by passing electricity through a coil  68 , with the blade  12  passing through the central opening in the coil  68 . Preferably, the coil  68  has a non-circular shape, such as that shown in FIGS.  5 A- 5 B. As shown in FIGS.  5 A- 5 B, the coil  68  may include a main coil section  68   m  with spaced windings supported by stabilizer  68   s  and leads that are insulated from one another by insulator  68   i  and held together by ties  68   t . The coil  68  may be formed from ¼ inch cooper tubing, coated with suitable ceramic coatings. The coil may have a generally oval center opening with an inner dimension of approximately 3½ inches by ¾ inches, as shown in FIGS.  5 A- 5 B. Indeed, if the coil  68  is in the shape shown in FIGS.  5 A- 5 B, two or more blades  12  can be passed through the coil  68  simultaneously without adversely affecting the fusing operation. Of course, additional let-offs  52  and take-ups  56 , etc. may be required if more than one tape blade  12  is to be coated simultaneously using the same coating station  60 . Further, the required power for the induction coil  68  will vary based on process conditions, but a coil  68  of 5 KW running at about 60% is believed sufficient for operations with two blades  12  passing through the induction unit  66  simultaneously at a line speed of 40-60 feet/minute.  
         [0022]    It should be noted that the fusing unit  66  using the induction principle is capable of generating significant heat in the blade  12 , and may even entirely melt the blade  12  if the blade  12  stops while in the fusing unit  66 . Accordingly, it may be advantageous to incorporate suitable automatic systems that shutoff the coil  68  when line speed drops below a given level, such as line speed monitors and switches, etc. known in the art. In addition, other suitable safety measures known in the art may be employed, such as out-gas exhausting of the induction unit  66 , flame detectors aimed at the coil  68 , and the like.  
         [0023]    One of the purposes of applying a coating  34  to the tape blade  12  is to increase the life of the blade  12 . As known in the art, one useful predictor in estimating blade  12  life is the measured abrasion resistance when tested according to ASTM D968-81. The results of such testing are usually expressed as an amount of falling sand (e.g., X liters of sand) until failure is detected. Most, if not all, commercially available power return tape blades have a reading of less than twenty liters of sand using this test method. In contrast, tape blades  12  processed according to the process outlined above have a measured abrasion resistance of at least thirty liters of sand, with values of forty liters, fifty liters, or seventy-five liters of sand or more being more typical. Indeed some test results have exceed one hundred liters of sand. Thus, processing the tape blades  12  according to such a process is believed to lead to substantially improved blade life, even with relatively thin (e.g., approximately 0.001 inch thick) coatings  34 .  
         [0024]    The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the essential characteristics of the invention. Just by way of non-limiting example, the length indicating indicia  36  on the tape blade  12  may be embossed, rather than printed, without deviating from the scope of the present invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.