Patent Publication Number: US-2016243513-A1

Title: System including an electrically-driven mixing device for mixing a coating

Description:
TECHNICAL FIELD 
     This invention relates to systems including driven mixing devices for mixing water or solvent-based coatings and, in particular, to systems including electrically-driven mixing devices for mixing such coatings. 
     Overview 
     The term “coating” refers to various mixes of solid components and liquid components to form a liquid mixture, either true solution where solids fully dissolve or dispersion where solids are simply mixed in liquid. Approximately 50% of these coatings are waterbase and 50% are solvent-based in the industry. These coatings are used in painting, adhesive, low friction and many more fields depending on the characteristics of their films. These coatings can be applied to a surface using several means including, dipping, atomized spray applicators, flow coated (no atomizing air) or brushed. In all cases these coatings can settle (separate) where coating solids drop to the bottom of a container and the liquid portion of the mixture remains on top. This is referred to as coating striation. 
     Coating striation results in an altered coating formulation which when applied to a surface and subsequently dried, results in an incomplete film, i.e., too much liquid or too much solids in the final applied film. Incomplete dry films result in a number of unfavorable results. Specifically:
         Too much liquid
           Low dried film solids result in lower film thickness   Incomplete dry characteristics   
           Result
           Poor physical performance (chemical resistance—poor weathering—poor salt spray—poor color control—poor adhesion   
           Too many solids in the final film exhibits the same undesirable physicals (film characteristics)       

     Thorough mixing of the coatings prior to and during application is necessary for desirable dry film characteristics. 
     Traditionally air agitator motors have been used, driven by compressor supplied pressurized air. It is convenient to use air motors since most plants have compressors and agitator air motors present no problem in flammable vapor environments created by solvent-based coatings. Air mixing motors are typically the single largest user of compressed air in any finishing operation. 
     The problem with air agitators are several:
         ‘Stall’—motor stops without warning especially at low RPM&#39;s   Inaccurate speeds and no good way of confirming actual agitation in the vessel   Compressor air is expensive and often contaminated with water and oil   Air motors must be lubricated regularly with the possibility of coating contamination   An air motor with or without an accompanied gearbox tends to stall at low speeds. Most water-based dispersions require very low RPM (say 1 RPM/second) or they will foam or aerate. This causes aerated dry films and resultant performance issues. By the same token they must be agitated at a sufficient RPM or will settle rapidly. Exact RPM control is necessary. This applies to most coatings.       

     When solvent-based coatings are used in a mixing vessel, the area around the mixing vessel is “classified”. The reason is that any sort of spark (source of ignition) can ignite the vapors around the coating vessel. All plants that use flammable coatings must adhere to safety rules which apply to these areas. It is necessary to comply to OSHA, safety and insurance rules. The classification rules are well defined by NEC (National Electronic Code) NFPA (National Fire Prevention Act) and other agencies such as FM Global. 
     Specifically the area around a mixing vessel which contains a solvent-based coating is classified as a Class I Div. I and Class I Div. II by NFPA 70. These areas are defined by arcs or radii around the mixing vessel. Class I Div. I is defined as an area where flammable vapors will be present (especially when the vessel lid is removed for refill). This area is defined in the first 3 ft. arc in all directions around the mixing vessel. No source of ignition is allowed in this area. If electric drive motors are used in this area they must be the more expensive, heavier, explosion-proof type when mounted on the vessel lid. These type of motors cause ergonomic issues for operators since they are very heavy. Also, an explosion-proof power cable must be run from the electric control panel to the electric motor. 
     Class I Div. II creates a second arc or radius 5 ft. away from the vessel in all directions where flammable vapors might be present. In this area “sealed” electric motors are allowed but not necessarily explosion-proof. Outside of the 5 ft. arc or radius any “normal” electric device is allowed. 
     All space in all directions within 2 ft. of a Division I area surrounding supply containers as well as the area extending 5 ft. beyond the Division  1  area up to a height of 1½ ft. above the floor or grade level is defined as a Class  1  Div.  2  area. 
     The following U.S. Pat. No. references are generally related to at least one aspect of the present invention: 4,401,268; 4,984,745; 5,421,218; 5,949,209; 6,835,248; 7,915,773; 8,667,926; and 2011/0315785. 
     SUMMARY OF EXAMPLE EMBODIMENTS 
     An object of at least one embodiment of the present invention is to provide a system including an electrically-driven mixing device for mixing a water or solvent-based coating without the need for an explosion-proof electric motor. 
     In carrying out the above object and other objects of at least one embodiment of the present invention, a system including an electrically-driven mixing device for mixing a water or solvent-based coating is provided. The mixing device includes a supply container, a rotary agitator shaft and an agitator disposed within the container and coupled to the agitator shaft to rotate therewith. The agitator mixes a water or solvent-based coating contained within the container upon rotation of the agitator shaft. The solvent-based coating creates a flammable vapor environment around the container wherein a source of ignition is capable of igniting flammable vapors in the environment. A drive mechanism includes an electric motor having a rotary output shaft disposed outside of the environment and a mechanical power transmission coupled to the output shaft of the motor and to the agitator shaft of the device to transfer torque from the output shaft to the agitator shaft to mix any coating in the container. 
     The system may further include a controller for supplying electrical power to the motor and for controlling the motor. The controller is disposed outside of the environment and is electrically connected to the drive mechanism to operate the motor through an electrical power cable. 
     The controller may be programmable wherein the controller controls the motor in accordance with a predetermined mixing program. 
     The electric motor may be a non-explosion proof electric motor. 
     The electrical power cable may be a non-explosion proof electrical power cable. 
     The mechanical power transmission may include an elongated transmission shaft having opposite ends. The first end may be located within the environment and may be coupled to the agitator shaft. A second end may be located outside the environment and may be coupled to the output shaft of the motor. 
     The transmission shaft may be flexible or rigid. 
     The power transmission may include a gear mechanism coupled to the transmission shaft and the agitator shaft. The rotary speed of the agitator shaft may be less than the rotary speed of the motor. 
     The supply container may include a lid wherein the agitator shaft extends through the lid. 
     The lid may be removable. 
     The system may further include a housing for housing the controller and to mount the controller and the motor on an exterior surface of a spray booth outside of the environment. 
     The controller may monitor electrical power supplied to the motor to determine an operating state of the mixing device. 
     The coating may be a water or solvent-based paint. 
     Further in carrying out the above object and other objects of at least an embodiment of the present invention, a system including an electrically-driven mixing device for mixing a water or solvent-based coating is provided. The mixing device includes a supply container, a rotary agitator shaft and an agitator disposed within the container and coupled to the agitator shaft to rotate therewith. The agitator mixes a water or solvent-based coating contained within the container upon rotation of the agitator shaft. The solvent-based coating creates a flammable vapor environment around the container wherein a source of ignition is capable of igniting flammable vapors in the environment. A drive mechanism includes an electric motor having a rotary output shaft disposed outside of the environment and a mechanical power transmission coupled to the output shaft of the motor and to the agitator shaft of the device to transfer torque from the output shaft to the agitator shaft to mix any coating in the container. The system also includes an electrical power cable and a controller for supplying electrical power to the motor and for controlling the motor. The controller is disposed outside of the environment and is electrically connected to the drive mechanism to operate the motor through the electrical power cable. 
     The controller may be programmable wherein the controller controls the motor in accordance with a predetermined mixing program. 
     The electric motor may be a non-explosion proof electric motor. 
     The electrical power cable may be a non-explosion proof electrical power cable. 
     Still further in carrying out the above object and other objects of at least one embodiment of the present invention, a system including an electrically-driven mixing device for mixing a water or solvent-based coating is provided. The mixing device includes a supply container, a rotary agitator shaft and an agitator disposed within the container and coupled to the agitator shaft to rotate therewith. The agitator mixes a water or solvent-based coating contained within the container upon rotation of the agitator shaft. The solvent-based coating creates a flammable vapor environment around the container wherein a source of ignition is capable of igniting flammable vapors in the environment. A drive mechanism includes an electric motor having a rotary output shaft disposed outside of the environment and a mechanical power transmission coupled to the output shaft of the motor and to the agitator shaft of the device to transfer torque from the output shaft to the agitator shaft to mix any coating in the container. The mechanical power transmission includes an elongated transmission shaft having opposite ends. A first end is located within the environment and is coupled to the agitator shaft and a second end is located outside the environment and is coupled to the output shaft of the motor. 
     The transmission shaft may be flexible. 
     The power transmission may include a gear mechanism coupled to the transmission shaft and the agitator shaft. The rotary speed of the agitator shaft may be less than the rotary speed of the motor. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated, various embodiments may include all, some or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and for further features and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic, perspective environmental view of a coating spray booth and an operator who is using a system constructed in accordance with at least one embodiment of the present invention; 
         FIG. 2  is a front schematic view of a control panel with a housing which houses a motor controller and which mounts an electric motor on the spray booth of  FIG. 1 ; a flexible transmission shaft, partially broken away, extends from a drive shaft of the motor; and 
         FIG. 3  is a front schematic view of a mixing device including a supply container and an agitator shaft and agitator indicated by phantom lines within the container; the flexible transmission shaft of  FIG. 2  is partially broken away and extends from a gear box. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     In general, and as described below, at least one embodiment of the present invention provides a system, generally indicated at  10 , including an electrically-driven mixing device, generally indicated at  12 , for mixing a water or solvent-based coating contained therein. 
     As shown in  FIGS. 1 and 3 , the mixing device  12  includes a supply container  14 , a rotary agitator shaft  16  and an agitator  18  disposed within the container  14  and coupled to the agitator shaft  16  to rotate therewith. The agitator  18  mixes a water or solvent-based coating contained within the container  14  upon rotation of the agitator shaft  16 . The solvent-based coating creates a flammable vapor environment around the container  14  wherein a source of ignition is capable of igniting flammable vapors in the environment.  FIG. 3  shows various areas around the container  14  as defined by NFSA 70. A first area  20  is a class A Div.  1  area which extends a first radius, (R 1 , 3 ft.) around the container  14 . A second area  22  is a class  1  Div.  2  area which extends a second radius, (R 2 , 5 ft.) around the container  14 . A third area  24  is also a class  1 , Div.  2  area which extends a radius, R 3 , (i.e. 5 ft. beyond the Div.  1  area) around the container  14  and extends a height, H, (i.e. 1½ ft.) above the floor or grade level on which the container  14  sits. 
     Referring again to  FIG. 1 , an operator is shown operating a spray gun  30  which sprays the coating in a coating spray booth, generally indicated at  32 . The coating may be a water or solvent-based paint. 
     Referring again to  FIG. 3 , the agitator shaft  16  extends through a bearing pac  34  supported on a removable lid  36  of the container  14 . The shaft  16  extends through the lid  36  and is coupled to a gear mechanism or box  38  of a drive mechanism, generally indicated at  40 . The gear box  38  typically reduces the rotary speed of the shaft  16  below the rotary speed of a shaft  44  of an electric, non-explosion-proof motor  42  disposed outside of the environment. 
     The drive mechanism  40  includes the motor  42  and a mechanical power transmission coupled to the output shaft  44  of the motor  42  and to the agitator shaft  16  of the device  12  to transfer torque from the motor shaft  42  to the agitator shaft  16  to mix any solvent-based coating in the container  14 . The mechanical power transmission comprises an elongated transmission shaft or cable  46  having opposite ends. A first end  48  is located within the environment and is coupled to the agitator shaft  16  via the gearbox  38  and a quick release coupling  50 . A second end  52  of the shaft  46  is located outside the environment and is coupled to the output shaft  44  of the motor  42  via a coupling  54 . 
     Preferably, the shaft  46  is flexible but could alternatively be a rigid drive shaft. A rigid drive shaft would typically require locating the agitator shaft  16  of the mixing vessel  12  directly in line with the electric motor shaft  44 . This might provide difficult in practice since agitator vessels are moved frequently. 
     A flexible shaft cable such as the shaft  46  typically comprises a flexible shaft assembly which transmits rotary motion much like a solid steel shaft, but it can be routed over, under, and around obstacles that would make using a solid shaft impractical. Such a flexible shaft assembly typically includes a rotating shaft (sometimes called a core) with end fittings for attachment to the driving and driven mating parts. A protective outer casing is used when necessary. This casing has its own fittings, called ferrules, which keep it stationary during use. 
     A flexible shaft or cable is an effective means or mechanism of transmitting rotary motion and is more often efficient than universal joints, gears, sprockets and chains, or belts and pulleys. It offers the added benefit of compensating for misalignments in the system  10  that can greatly reduce cost and assembly time. 
     The system  10  further includes a variable frequency drive or controller generally indicated at  60 , for supplying electrical power to the motor  42  and for controlling the motor  42 . The controller  60  is disposed outside the environment and is electrically connected to the motor  42  through an electrical power cable  62  which is a non-explosion-proof electrical power cable. A housing  64  houses the controller  60  and a graphical user interface  68  for the controller  60  and mounts the controller  60  and the motor  42  on the outer surface of a wall of the spray booth  32 . A transformer  66  for the controller  60  is typically supported on the housing  64 . 
     The controller  60  is typically programmable wherein the controller  60  controls the motor  42  in accordance with a predetermined mixing program. 
     The electric agitator drive of at least one embodiment of the present invention provides many advantages:
         Will not stall out at lower RPM&#39;s   Extremely accurate RPM control and verification   Method of confirming agitation that is actually taking place (agitator  18  itself is actually turning in the vessel  14 ). This is evident by detecting a lower amperage draw in the motor  42  if there is less resistance from the agitator or propeller  18 .   Approximately ⅓ the energy cost for electric drives versus air motor drives with associated cost of compressed air.       

     Confirming agitation
         Short of mounting a proximity switch on the vessel lid  36  pointing at the head of the agitator  18 , there has been no way to confirm that agitation is actually taking place. For example, a propeller  18  could fall off of the agitator shaft  16  or the agitator shaft  16  detaches from the drive motor  42  (i.e., the device  12  changes its operating state). A power wire and a proximity switch is cumbersome and often broken when the lid  36  is removed. Further, a proximity switch had to be explosion-proof if solvent fumes are present. Detection of amperage drop in an electric drive or mechanism  40  can be determined quite easily without a cumbersome cable and a proximity switch.   There is no good way of controlling the RPM of air motors. Further, they are not consistent due to varying coating level resistance and compressor outputs. All of these problems are eliminated with the electric drive  40  of at least one embodiment of the present invention.       

     Lower energy costs
         The KW power draw of an electric agitator motor  42  is ⅓ the KW draw of an air agitator motor. Furthermore, a plant can now shut compressors down for maintenance, weekends, holidays etc. without the worry of coating settling.       

     The remote electric motor  42  which uses the drive cable  46  which extends to the vessel agitator shaft  16  solves many of these problems. Although the flexible drive cable  46  works best, a rigid drive shaft extending from the drive motor  42  to the vessel agitator shaft  16  would work as well. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.