Abstract:
A method and article of manufacture for providing a mechanical bond and an improved water vapor seal between a lens ( 11, 41 ) and a base ( 17, 47 ) in an instrument housing ( 10, 40 ), includes heating the components and a hot butyl rubber sealant ( 18, 58 ) prior to assembly, maintaining a level of heating for the assembly during assembly, dispensing the heated sealant ( 18, 58 ) into a channel ( 25, 65 ) to form a ring-shaped body of sealant ( 18, 58 ), assembling the lens ( 11, 41 ) to the base ( 17, 47 ) and pressing a lower edge ( 11   a   , 41   a ) of the lens ( 11, 41 ) into the ring of sealant ( 18, 48 ) and bending an upper edge ( 17   b   , 47   b ) of the side wall ( 17   a   , 47   a ) over a portion ( 11   b   , 41   b ) of the lens ( 11, 41 ). The method is applied in a second embodiment to an instrument having at least two signal conductors ( 55 ) entering the base ( 47 ) at two entry points. Apparatuses manufactured with the method are also disclosed.

Description:
TECHNICAL FIELD 
   The present invention relates to utility meter registers used in moist environments. 
   DESCRIPTION OF THE BACKGROUND ART 
   In the field of utility metering, the actual metering device (the “meter”) is a different mechanism than the counting and display device which shows a total to the user or customer. This counting and display device is called a “meter register.” Traditionally, these meter registers have been mechanical devices, with a tabulating mechanism and with a dial or an odometer for displaying units of consumption for a utility, such as water, electric or gas. The meter register is mounted on or in close proximity to the meter to provide a local display of a consumption total. 
   Today, there are at least two types of water meter registers, a basic stand-alone type that is designed to be viewed directly, and a pulse-generating type, which in addition to providing a local visual display, also transmits pulses representing units of consumption to other remote displays and to data collection and monitoring devices. 
   In the basic type of meter register, an ethylene propylene gasket is assembled between a glass portion and a metal base portion to form a seal. In Walding et al., U.S. Pat. No. 5,734,103, an improvement is disclosed for the pulse-type meter register which uses an epoxy-based adhesive to join a glass lens portion to a metal base portion. The pulse-type register includes wires which exit the unit for connection to a remote display or monitoring unit, whereas the basic register does not include such wires and presents a simpler case for sealing. 
   In the southern United States, utility meters are often located outside of residential buildings, sometimes in subsurface enclosures. During rainy periods, these units may be subjected to extreme moisture conditions, and even submersion under water. There remains a need to provide a suitable seal in these conditions, such as offered by the epoxy sealing system described above, but at a lower cost of manufacture. 
   Therefore, there remains a need for better sealing methods and structures for meter registers and better methods of manufacture and assembly of these units. 
   SUMMARY OF THE INVENTION 
   The invention is incorporated in an instrument assembly comprising a base and a lens which is at least transparent in part, to enclose an instrument works, while allowing a view to the interior. An annular body forms a seal between the base and lens. The sealant is flowed into position in a channel formed by the base around the perimeter of the instrument works. The lens has a lower edge pressed into the body of sealant, which is a hot melt butyl rubber that has been cured within the channel 
   The flowed body of butyl rubber has been found to provide a better vapor seal than the gasket and a lower cost of manufacture than the epoxy-based system of the prior art. 
   The invention is further practiced in a method of providing a water vapor seal and mechanical bond between a lens and a base comprising: heating the lens and the base to at least approximately 180 degrees F.; heating an instrument works to a temperature of at least approximately 140 degrees F.; assembling the instrument works and the base, such that a groove is formed around the instrument works; maintaining a level of heating for the assembly of the instrument works and the base, such that the base is at a temperature of at least approximately 250 degrees F. in the channel; dispensing a heated body of sealant into the channel to form a ring of sealant; assembling the lens to the base and pressing a lower edge of the lens into the ring of sealant; and allowing the sealant to cure. 
   In contrast to the prior art, the above method provides for preliminary heating of the components to provide better results in forming the lens-to-base seal. 
   As a further aspect of the invention, it is advantageous to bend over a portion of an edge of the base to form a lip which helps hold the sealant in place and helps hold the assembly together. 
   The invention can be applied to a local utility meter register and to a pulse-generating meter register in which at least two signal conductors penetrate the housing. In the second case, an overlap point for the bead of sealant is spaced from the entry points to isolate possible causes of leakage. 
   Other objects and advantages of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiments which follows. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a basic meter register incorporating the present invention; 
       FIG. 2  is a longitudinal section view taken in the plane indicated by line  2 — 2  in  FIG. 1 ; 
       FIG. 3  is perspective view of a step in manufacturing the basic meter register of  FIG. 1 ; 
       FIG. 4  is a top plan view of  FIG. 3  rotated by 90 degrees; 
       FIG. 4   a  is a sectional detail view taken in the plane indicated by line  4   a — 4   a  in  FIG. 4 ; 
       FIG. 4   b  is a sectional detail view taken in the same plane as  FIG. 4   a;    
       FIG. 5  is a bottom plan view of a forming head used in manufacturing the meter register of  FIG. 1 ; 
       FIG. 6  is a side view in elevation of the forming head of  FIG. 5 ; 
       FIG. 6   a  is a detail sectional view taken in the location indicated by line  6   a — 6   a  in  FIG. 6 ; 
       FIG. 7  is a second embodiment of a meter register of the present invention; 
       FIG. 8  is a longitudinal section view taken in the plane indicated by line  8 — 8  in  FIG. 7 ; 
       FIG. 9  is a detail sectional view from the bottom of a grommet area in the embodiment of  FIG. 8 ; and 
       FIG. 10  is a flow chart of the manufacturing process for making the embodiments of FIGS.  1  and  7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a first embodiment of a local meter register assembly  10  that incorporates the present invention. The device is called “local” because it provides a view of consumption units only at the location of the device. The register  10  includes a transparent, dome-shaped lens  11  for viewing an instrument face  12 . Preferably this lens is made of glass, but plastic and other materials could be used as long as a transparent portion or window is provided. A dial hand  13  is pivotally connected at the center of the instrument face  12 , and indicia  14  are provided around a periphery of the instrument face  12 . An odometer  15  is positioned below the dial pivot point. The odometer  15  includes a plurality of number wheels  16  for respective digits. The odometer  15  is viewed through an aperture  28  in the instrument face  12  as seen best in FIG.  2 . 
     FIG. 2  illustrates that the lens  11  is joined to a base  17  by a body of sealant  18  to form an enclosure for the assembly  10 . The base is made of metal, with materials such as copper, a brass or a copper alloy being preferred, but other metals, such as tin alloys or aluminum alloys could be used and other materials such as resinous synthetic materials, glass or ceramics could be used. Inside the enclosure formed by the lens  11  and the base  17  is an instrument works assembly  19 , which is supported by a plastic base  20  and a chassis  21 . The instrument works  19  provides a mechanical counting mechanism. Also seen is a magnetic pickup wheel  22  which rotates in response to movement of a water turbine in a meter housing (not shown). The rotations are coupled through a mechanical drive train  23  in the instruments works  19  to drive the dial hand  13  and the odometer  15 . 
   The sealant  18  ( FIG. 2 ) to be used for providing a seal between the glass lens  11  and the metal base  17  is a butyl rubber sealant, such as Delchem D-2000. This sealant has an approximate viscosity of 300,000 Centipoise (CPS) at 400 degrees F. The sealant is thick and sticky, thicker than peanut butter at room temperature. The metal base  17  is made of “red brass” which has a relatively high copper content. A base  17  of this material has a tendency to draw heat out of the butyl rubber after it is applied to the base  17 . As the sealant cools, the viscosity increases, making it thicker. For proper flow, adhesion and curing, the sealant should be applied after being heated to approximately 380 degrees F. 
   In assembling the meter register  10  seen in  FIG. 2 , there are three main subassemblies, the lens  11 , the base  17  and the instrument works  19 .  FIG. 10  shows the steps in assembling and sealing the assembly  10 . After the start of the process, represented by start block  80 , the components  11 ,  17  and  19  are preheated, as represented by process block  81 . This helps in preserving the heat of the dispensed bead of sealant  18 . The dispensing equipment is also set up to transfer heat into the sealant, all the way through the system, and into a channel formed to receive the sealant. 
   The glass lens  11  is preheated in an oven to 300 degrees F. to get adhesion strength, to promote a homogeneous overlap point, and cause the butyl rubber to flow into a channel in the register assembly. The base  17  is preheated in the same oven as the glass to a temperature of 300 degrees F. The register works assembly  19  is preheated in a separate oven to 140 degrees F. 
   After preheating for a suitable time, the base  17  and register works assembly  19  are removed from the ovens, and assembled as represented by process block  82  in  FIG. 10. A  heated metal base  17  and a heated register works  19  are manually brought together and assembled outside of the ovens to form the assembly seen in  FIGS. 3 and 4 . During this time, the temperature of the base  17  may drop below 200 degrees F. 
   The assembly seen in  FIGS. 3 and 4  is placed in a heated holder as represented by process block  83  in FIG.  10 . In the preferred embodiment, the holder is heated by induction heating. Because the works assembly  19  includes plastic parts, and heat can be transferred from the base  17  during assembly, the metal base  17  is maintained at only approximately 250 degrees F. during its time in this holder. This is sufficient to preserve the integrity of the butyl sealant, keeping it soft and pliable for the hot glass to make a homogeneous interface, particularly at the overlap point where the two ends of the bead of sealant meet. 
   Before dispensing a bead of sealant  18 , as seen in  FIGS. 3 and 4 , the butyl rubber material is heated in zones to 380 degrees F. as represented by process block  84  in FIG.  10 . Next, a bead of sealant  18  is applied to a channel  25  ( FIG. 3 ) formed between the base  20  and side wall  17   a , while the sealant is heated, as represented by process block  85  in FIG.  10 . It should be noted that while the cross section of the channel is generally rectangular, the use of the term “channel” herein encompasses grooves and channels of various available cross sections, and is not limited to rectangular cross sections. In dispensing the bead in  FIG. 3 , the dispensing nozzle  24  is fixed in its position and the assembly  17 ,  19  is rotated (in the direction of the arrow) to create the bead  18 . 
   The nozzle  24  utilizes a heavy-wall, high mass, beryllium copper material for maintaining the sealant  18  at the temperature of 380 degrees F. as it is laid down in a circular bead as seen in FIG.  3 . The bead is dispensed into a channel  25  formed between base  20  of the instrument works  19  and a side wall  17   a  of the metal base  17 . The sealant  18  is pumped through a nozzle  24  using a gear pump driven by a servomotor. A shot size is programmed to correspond the volume of sealant  18  necessary to make the ring-shaped bead of sealant  18 . The dispensing of sealant  18  will be turned off when the nozzle  24  reaches an end point. 
   Backpressure is created by dispensing a large bead  18  with the tip  24   a  as close to the channel  25  as possible without bottoming the tip  24   a . Clearances are held as close as 0.020 inch from tip  24   a  to the side wall  17   a  and to the edge of the base  20 . Backpressure causes the dispensed bead to have a bulb  26  ( FIG. 4A ) that travels in front of the nozzle tip  24   a  as the assembly is rotated to create the bead  18 . It is this bulb  26  that makes the start and stop interface overlap and a homogeneous blend of the start and stop points for the nozzle. The bulb  26  at the stop end is able to push its way under, into and over the start end  27  of the bead  18 , when the bead is finished at the end of the dispensing cycle (FIG.  4 B). The formation of a homogenous overlap point is critical to successful sealing. 
   After the sealant  18  has been dispensed into the assembly  17 ,  19 , as a ring-shaped body, the glass lens  11  is assembled as represented by process block  86  in FIG.  10 . The glass lens  11  is inserted, such that a bottom edge  11   a  of the glass lens  11  contacts the overlap point first. The glass lens  11  is angled into the sealant  18  at the overlap point, and then the angle is reduced to zero as the glass lens  11  is brought into contact with the body of sealant over 360 degrees. In this way, the overlap point is made homogeneous due to the heat and pressure transferred to the overlap point through the glass lens  11 . 
   Next, as represented by process block  87  in  FIG. 10 , the assembly is removed from the heated fixture and placed in a forming machine. The forming machine has a rotating head  30 , seen in  FIGS. 5 and 6 . The head  30  rotates around an axis of rotation  32  and supports three forming wheels  31   a ,  31   b  and  31   c . The wheels  31   a - 31   c  each have a niche  33  that receives the top edge  17   b  of the side wall  17   a  and rolls the edge over the lip  11   b  of the glass lens  11  as the wheels  31   a - 31   c  roll around the top edge  17   b  of the base  17 . During this operation, the forming head  30  also presses the glass lens  11  further into the body of sealant  18 . 
   Next, as represented by process block  88  in  FIG. 10 , the assembly is removed from the forming machine and set aside for cooling. Cooling takes approximately thirty minutes. When the sealant  18  reaches room temperature, the hot melt properties of the sealant have been cured. In approximately three to five months, the reactive components of this material are fully cured by way of reactions with moisture. In three to five months, the material has reached ultimate properties and no further curing can occur. This completes the process for the local register as represented by end block  89 . 
   Referring to  FIGS. 7 and 8 , a meter register assembly  40  of the pulse-transmitting type is shown. This register  40  has a glass lens  41 , dial face  42 , dial hand  43 , indicia  44 , odometer  45 , number wheels  46 , a metal base  47 , an instrument works  49  and other parts similar to the local meter register  10 , except for additional parts to be described. In this register  40 , a magnetic pickup  52  drives a cam which operates a piezoelectric-based pulse-generating element of a type known in the art. The electrical pulses represent units of consumption. These are transmitted through two insulated wires  55  to remote displays and to remote data collection and utility usage monitoring equipment. The wires  55  have portions  57  inside the base side wall  47   a  ( FIG. 9 ) which are stripped of insulation where the sealant  58  will contact them, to provide a better vapor seal around the wire entry points to the assembly  40  than would be provided by the wire insulation. 
   A grommet  54  ( FIG. 9 ) supports the wires  55  as they enter the register  40 . The grommet  54  has a flange and groove portion  56  for anchoring the grommet  54  in a side wall  47   a  of the metal base  47 . The grommet  54  has holes  62  through its body from the inside to the outside of the register  40  with a spacing of at least 0.164 inches to receive the two wires  55 . This spacing is greater than in the prior art and is necessary to allow enough space for the sealant  58  to flow in and around the wires  55 . No other holes or vents in the grommet are necessary. The process of assembling and sealing this assembly follows the process of  FIG. 10 , with the following differences. Because the wires  55  must exit the assembly through side wall  47   a  of the base  47 , the register works assembly  49 , the plastic instrument base  50  and the metal register base  47  are assembled as represented by process block  82  before being heated as represented by process block  81  in FIG.  10 . 
   Another difference is that the start point  59  for the sealant bead  58  is approximately three-eighths of an inch away from the stripped portions  57  of the wires  55 . The assembly  47 ,  49  is rotated such that the stripped portions  57  of the wires  55  are rotated away from the stationary dispensing nozzle tip  24   a  (in the direction of the arrow in FIG.  9 ). The stripped portions  57  of the wires  55  are covered near the end of the rotation with the overlap point being reached after crossing the wires  55 . This allows the base  47  to build-up heat as a result of time in the heated fixture and exposure to the hot sealant bead. This also places the overlap point at a different point than the wire entry points. This isolates the wire entry point from the overlap point so that these can be checked individually for leakage. If the bead is started and stopped over the wires, two possible leakage causes would be present in one location, which would make leakage problems more difficult to diagnose. 
   The heated glass lens  41  is pressed into the overlap point and wire entry points first, to create the best possible seal in those regions. Then, the glass lens  41  is angled into the remaining portion of the sealant  58 , as described previously. 
   All other operations were the same as described previously for FIG.  10 . By using a common process as described above, one dispensing machine system can accommodate two different assemblies, the local register and remote pulse-transmitter register, thus reducing set-up time, tooling and machine complexity. 
   This has been a description of the preferred embodiments of the invention. For embodiments falling within the spirit and scope of the present invention, reference is made to the claims which follow.