Patent Application
20120038346
The present disclosure relates generally to the art of applying powder coating material to a work piece using electrostatic spraying technology. More particularly, the disclosure and inventions herein relate to methods and apparatus for monitoring or detecting flow of powder coating material during a powder coating operation.
In many industries, it has become common practice to apply paints and other coatings to products in the form of dry particulate powder. Powder coatings offer a number of advantages over traditional liquid coatings and paints, among them are lower cost, reduced pollution, shorter curing times and improved physical properties.
Powder coating materials are applied to workpieces by spraying. The powder is drawn from a container or hopper by a pump that feeds the powder through hoses to one or more spray guns from which it is sprayed towards the workpiece by means of the pneumatic force supplied by the pump. Powder coating application is also commonly although not exclusively done with electrostatic spray guns in which the workpiece is held at ground and the powder is electrostatically charged. The electrostatic charge is applied to the powder coating particles by an electrode supported by the spray gun. Electrostatic charge may alternatively be applied to the powder coating particles using tribo-charging within the spray gun.
From the simplest powder coating system that may use only one spray gun and one powder supply, to more complex powder coating systems that may use forty or more spray guns supplied from a plurality of pumps and supply hoppers (for example, hoses that convey about 5 to about 60 or more pounds of powder coating material per hour), it can be advantageous to be able to confirm or verify that powder coating material is in fact flowing through the hoses to the spray guns. By providing an automatic way to detect powder flow, an operator need not spend time manually checking all the spray guns, pumps and hoses. U.S. Pat. No. 5,739,429 (the ‘429 patent), the entire disclosure of which is fully incorporated herein by reference, discloses flow monitoring apparatus using a flow meter and hopper weight change characteristics. U.S. Pat. No. 6,734,679 (the ‘679 patent), the entire disclosure of which is fully incorporated herein by reference, discloses detecting flow of powder particles using a powder transportation line that includes a portion provided with a electrostatically friction charging material that is located upstream or downstream of a powder pump, or within a powder pump. The powder particles flowing through the portion of the transportation line generate an electric charge as a result of friction between the powder and the friction charging material. The electrical charge that is generated is detected in the form of a current by a sensing unit.
In accordance with an embodiment of one or more of the inventions presented in this disclosure, an apparatus for monitoring or detecting the flow of powder coating material entrained in an air stream utilizes an electrically conductive material that extends along a portion or length of an electrically non-conductive powder hose or tubing that connects a source of powder coating material to a spray gun. The hose exhibits tribo-charge transfer caused by friction between the powder coating material flowing through the hose and the inside wall of the hose. The electrically conductive material may be connected or coupled to a circuit that detects current produced in the electrically conductive material by the tribo-charge transfer. In a particular embodiment, the electrically conductive material comprises an electrical conductor such as a wire.
In various alternative exemplary embodiments, the wire may be embedded in the hose, wrapped around the hose, disposed adjacent the hose, supported on a member that is outside the hose, and disposed as part of a second tube or hose that surrounds at least a portion of the hose, to name a few examples.
The use of an electrically conductive material that extends along at least a portion of the length of the hose significantly increases the signal strength of the current produced by the tribo-charge transfer, thus providing an excellent signal that indicates whether powder coating material is flowing through the hose. The inventions herein also include methods for monitoring or detecting powder flow embodied in the use of such apparatus.
These and other embodiments of the various inventions disclosed herein will be understood and readily apparent to those skilled in the art based on a reading of the following detailed description of the exemplary embodiments in view of the accompanying drawings.
Although the exemplary embodiments herein are presented in the context of a powder coating material application system for applying powder coating material to a workpiece, the inventions are not limited to powder coating materials but rather will find application for transport or conveyance of any dry particulate material that can exhibit a tribo-charging effect with a portion of the flow path of the material, for example, a hose. The present inventions may be used with dense phase systems utilizing dense phase pumps for transporting particulate material such as the pumps shown in United States Patent Application publication number 2005/0158187 A1, and may also be used with dilute phase systems utilizing Venturi pumps such as the pumps 308 shown in U.S. Pat. No. 7,325,750, the entire disclosures of which are both fully incorporated herein by reference. The inventions are not limited to any particular type of process media or dry particulate material, although the inventions are especially suited for powder coating material as the process media. Still further, while the exemplary embodiments herein illustrate and refer to specific design and configuration features of a powder coating material application system including examples of pumps, hoses and spray guns, those skilled in the art will readily appreciate that the inventions herein will find application beyond just the exemplary embodiments and may be used with application systems having various modifications and components such as pumps and spray guns of many different designs. Although the exemplary embodiments illustrate use of the inventions in corona-type electrostatic charging systems, the inventions may be used with other electrostatic technologies such as, for example, tribo-charging systems.
While various inventive aspects, concepts and features of the inventions may be described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects, concepts and features may be used in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein, all such combinations and sub-combinations are intended to be within the scope of the present inventions. Still further, while various alternative embodiments as to the various aspects, concepts and features of the inventions—such as alternative materials, structures, configurations, methods, circuits, devices and components, software, hardware, control logic, alternatives as to form, fit and function, and so on--may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the inventive aspects, concepts or features into additional embodiments and uses within the scope of the present inventions even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the inventions may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present disclosure, however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. Moreover, while various aspects, features and concepts may be expressly identified herein as being inventive or forming part of an invention, such identification is not intended to be exclusive, but rather there may be inventive aspects, concepts and features that are fully described herein without being expressly identified as such or as part of a specific invention, the inventions instead being set forth in the appended claims. Descriptions of exemplary methods or processes are not limited to inclusion of all steps as being required in all cases, nor is the order that the steps are presented to be construed as required or necessary unless expressly so stated.
As used herein, we define an “exterior surface” of a hose to mean a radially outermost surface that defines the outside diameter of the hose at least along a portion of the hose, meaning that a hose may have more than one outside diameter although typically hoses are uniform in diameter. We use the terms “outside” and/or “outward” an exterior surface to mean any position or location that is other than embedded in the exterior surface. For example, outside or outward of an exterior surface may mean lying adjacent to or in contact with or attached to or spaced from the exterior surface. We use the term “embedded” in a surface to refer to disposing a member or component sub-surface such as, for example, at least partially below a surface or completely within a body of material. We use the TERM “non-conductive material” when referring to a hose to mean that in normal use the hose material is electrically insulating and does not conduct current. We use the term “electrically conductive” to mean a material, for example a metal wire or composite material, that has a low resistance to current in normal use.
With reference to
The inventions herein provide a way to verify that powder coating material is indeed flowing through the one or more hoses or tubing 18 (we use the terms tubing and hose interchangeably herein), as distinguished from the prior known systems that primarily try to verify flow through the pump or the spray gun. It is not uncommon for the hoses 18 to become kinked or blocked during use, and when there are many hoses it can take a long time to confirm which hose or hoses are blocked. A blocked hose during a powder coating operation can produce a poor finish or no coating on the end product or workpiece.
The spray gun 20 may be any suitable corona-type spray gun that uses a high voltage supply (not shown) to produce ionization at an electrode 22, which applies an electrostatic charge to the powder coating material particles. An example of a spray gun is shown in International Patent Application publication no. 2005/018823 A2, the entire disclosure of which is fully incorporated herein by reference. The workpiece (not shown) is typically maintained at ground potential so that the charged particles are attracted to and adhere to the workpiece. Many different types of corona spray guns are known and commonly used today, and the inventions may also be used with corona type spray guns later developed. The inventions may also be used with other electrostatic spray technologies such as, for example, tribo-charging spray guns, and moreover may find application in systems that are not electrostatic. The inventions herein utilize the powder coating material exhibiting a tribo-charge effect for charge transfer with the hose 18 when the flowing powder coating material contacts the hose interior surface. Whether the hose and powder combination exhibits a stronger or weaker tribo-charge effect is not critical to the present inventions, although a stronger tribo-charging effect may produce a better signal related to flow of powder coating material 16 in the hose 18.
In the embodiment of
A signal wire 26 may be used to form an electrical circuit that includes the electrically conductive material 24. In the exemplary embodiments herein, the signal wire 26 is electrically coupled or connected at one end to the electrically conductive material 24, and at another end to a control circuit 27. The signal wire 26 may be connected at any location to the electrically conductive material 24, but we have had particularly good success if the signal wire 26 is connected near the outlet of the pump 14, but such is not required.
The control circuit 27 may include a current detection circuit 28. The control circuit 27 may be an overall control circuit or system for the powder coating material application system 10, for example, a model i-Control® system available from Nordson Corporation, Westlake, Ohio. However, the inventions may be used with any control system, or may be used as a standalone circuit or a standalone circuit that interfaces with a control system. All that is needed is a current detection circuit 28 or other current detection technique (for example, magnetic coupling induced by the current in the electrically conductive material 24) that can detect current in the electrically conductive material 24, for example via the signal wire 26, which current is produced by tribo-charge transfer between the powder coating material 16 and the interior surface of the hose 18. The tribo-charge transfer produces electrical charges that are collected by the electrically conductive material 24. The circuit 28 may be a standalone circuit that produces a signal 30 that indicates whether powder coating material is flowing through the hose 18. This signal 30 may be used by a control circuit 27 to decide whether to interrupt a coating operation or at least operation of the associated spray gun. Alternatively, the signal 30 may simply be used to produce a visual or audible warning or alert that there is a problem with powder flow through the associated hose 18.
The current detection circuit 28 may be any circuit that can detect current. For example, the circuit 28 may be an ammeter, a multi-meter, a circuit that converts current to voltage and detects voltage levels, a voltmeter, and so on. Typically, a threshold current level will be selected or predetermined to indicate whether powder coating material is flowing through the hose 18. The current level may be automatically determined by the circuit 28, for example using a simple comparator, or an operator might visually confirm current level with an ammeter or other device. The output signal 30 may be used, for example, as a go/no-go signal to indicate whether powder coating material is flowing through the hose 18. The current produced in the electrically conducive material may be on the order of nanoamps to milliamps but other signal levels, higher or lower, may be used as needed.
It will be noted that in all the embodiments herein, preferably the electrically conductive material 24, wherever it is disposed, is isolated from contact with electrical ground. For example, the electrically conductive material 24 is preferably not exposed to human contact or contact with a grounded surface or object.
In the
Alternatively, the hose 18 may include an embedded wire mesh or braided wire jacket 60 that functions like the conductor 56. The signal wire 26 (
One of the improvements we note in our inventions is that the longer the length that the electrically conductive material 24 extends along the length of the hose 18, or stated another way the greater the amount of electrically conductive material 24 provided along the length of the hose 18, the more tribo-charge transfer is collected in the electrically conductive material 24. The more tribo-charge transfer that is collected in the electrically conductive material 24 increases the signal level of the electrical current that can be produced in the electrically conductive material 24 when the electrically conductive material is coupled to a current detection circuit 28. However, other factors may be taken into account in determining the length that the electrically conductive material 24 should extend along the length of the hose 18 for any particular application, as well as for selecting the threshold current level that will be used to indicate whether powder coating material is flowing through the hose 18. These factors may include, but are not necessarily limited to nor required in all cases: the length of the hose 18, the location of the electrically conductive material relative to the hose 18, type of powder coating material, material from which the annular wall of the hose 18 is constructed, velocity of the powder flow through the hose, flow rates of the powder coating material through the hose, and inside diameter of the hose 18.
The inventive aspects have been described with reference to the exemplary embodiments. Modification and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
