Patent Publication Number: US-2003221951-A1

Title: Two-electrode corona apparatus for plastic throttle body surface treatment

Description:
BACKGROUND OF THE INVENTION  
       [0001] Plastic structures, while lightweight, have particularly low adhesive qualities. While equivalent metal structures will easily allow coating, foams or other such materials to adhere to its surface, the low surface energy level inherent in most plastics do not afford that luxury. There are many applications in which the ability to adhere a substance to a plastic structure is highly desirable. For example, in the field of vehicle mechanics, it would be desirable to make a throttle body out of plastic.  
       [0002] The throttle body structure is particularly critical to vehicle operation. The throttle, contained in the throttle body structure, serves to regulate air flow to the engine and is coupled to the acceleration system of the vehicle. In addition, the throttle is related to the idling speed of the vehicle. For more efficiency, a vehicle engine should have the lowest possible idle speed while maintaining an idle speed above the stalling speed of the vehicle engine. The throttle body should therefore be as airtight as possible, as an airtight throttle body will allow the throttle to more efficiently regulate air flow. If the throttle body is not airtight, there will be air flow loss through the unsealed throttle body and the throttle will not operate properly. Metallic throttle bodies have been treated with a sealant in order to make them more airtight. Plastic throttle bodies, while more lightweight than metal throttle bodies, do not allow the sealant to adhere correctly. To allow a plastic throttle body to accept the sealant, it is necessary to treat the plastic surface to improve its adhesive qualities.  
       [0003] Standard methods of surface treatment, such as flame treatment methods, have had only marginal effectiveness. Such treatments are limited as to the shape and size of the part to be treated. For example, irregularly shaped pieces are particularly difficult to treat. Sharp corners and imperfections hamper the effectiveness of the treatment. Large pieces are more difficult to treat than smaller pieces. Further, the high cost of such a process can be prohibitive.  
       [0004] Corona methods have also been used, and are well known in the art. Corona treatment consists of creating an electric field, either between an electrode and a ground, or between two electrodes. The most common method of increasing surface energy in plastic films, the corona treatment involves applying a high frequency, high-voltage charge that ionizes the surrounding air. The ionized particles in the corona are discharged and contact the film surface, leading to an increase in surface energy as a result of surface oxidation. Increasing the surface energy of a plastic film helps inks and coatings wet the film, as opposed to forming droplets on the surface. Corona treatment also enhances adhesion when thermally applying film to another substrate.  
       [0005] A single electrode can be used to create the corona in combination with a ground, such as a grounded table. Such a system is disclosed is U.S. Pat. No. 5,466,423. However, a single electrode system creates a difficult to control corona. Most specifically, any metal piece, such as a screw or stud, in an otherwise plastic throttle body will attract and misdirect the corona. Throttle bodies must therefore be fully disassembled before treatment, with all metallic parts removed, wasting assembly time.  
       [0006] A double electrode corona system aids the problem of corona control. The two electrodes form a completed electrical circuit and the corona is not misdirected by metallic substances. However, such systems are extremely large, and require a large amount of manpower to control. Such a system may take up over 80 square feet of valuable factory space. It also includes assembly-line-style conveyor belts as well as requiring significant supervision. Such a system would be inappropriate for a lean manufacturing operation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] According to one embodiment of the present invention, there is provided an apparatus for surface treatment of a throttle body structure, having a first and a second electrode electrically connected to a transformer configured to generate voltage between the electrodes. A housing surrounds the electrodes and transformer, and also houses a rotating fixture base.  
       [0008] According to another embodiment of the present invention, there is provided a method for surface treatment of a throttle body structure. The apparatus provided includes a housing containing first and second electrode connected to a discharge head, a transformer electrically connected to the discharge head, an air blower attached to the discharge head via an air pipe, a pneumatic slide attached to the housing and the discharge head, and a fixture base. A control panel is connected to the pneumatic slide and the transformer. A throttle body structure is provided and secured to said fixture base. The control panel is operated such that the discharge head and the two electrodes are lowered into an engaged position in the center of the throttle body via the pneumatic slide. Air is pumped through the air blower and air pipe towards the electrodes. Voltage from the transformer is applied to the electrodes, and the fixture base and throttle body are rotated. The discharge head and electrodes are then returned to the home position.  
       [0009] Other aspects of the present invention will become apparent in connection with the following description of the present invention. 
     
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
     [0010]FIG. 1A is a front-view of the double corona surface treatment apparatus according to the present invention;  
     [0011]FIG. 1B is a side view of the double corona surface treatment apparatus according to the present invention;  
     [0012]FIG. 2 is a flow diagram of a preferred embodiment of the present method; and  
     [0013]FIG. 3 is a magnified view of the “home” and “engaged” positions of the apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0014]FIG. 1A depicts a two dimensional, front-view diagram of a first embodiment of double corona treatment apparatus in accordance with the present invention. FIG. 1B shows the same apparatus from a side view. Two electrodes  10  are held in a discharge head  12 . The electrodes are made of tungsten, aluminum, stainless steel, or another electrically conductive metal able to withstand high temperatures. In FIG. 1A, the electrodes  10  are depicted as cylindrical bars. However, the electrodes  10  may have other geometries, such as cylindrical bars with a pointed end, cylindrical bars with a rounded end, spikes, or hooks. The choice of geometry is dependent on the application for which the apparatus is to be used, as is well known in the art.  
     [0015] In a preferred embodiment, cylindrical bars or hooks are used. The electrodes  10  are inserted into the discharge head  12 . The electrodes  10  are spaced apart at a predetermined distance from each other, as known to one of skill in the art. In a preferred embodiment, the discharge head  12  may be designed to allow the spacing between the electrodes  10  to be modified. The discharge head  12  is made of an insulating material, such as a rubber material, so that any voltage that runs through the electrodes  10  remains in the electrode  10  and does not leak into the discharge head  12 .  
     [0016] The discharge head  12  is further connected to a transformer  14  through a high voltage line  16 . The transformer  14  typically in this embodiment produces a line voltage of between about 8 kV to about 200 kV, preferably about 12 kV. Of course, other voltages may be used. The voltage created by the transformer  14  is discharged to the electrode  10  through the discharge head. Preferably, this is done by connecting the high voltage line  16  to one electrode  10  through the discharge head  12 . The other electrode  10  is connected to the high voltage line  16  to return the voltage to the transformer  14 . A complete circuit is therefore made, with a gap defined between the two electrodes  10 . When voltage is applied to the circuit from the transformer  14 , the electricity bridges the gap between the electrodes  10  by forming a corona.  
     [0017] The discharge head  12  is also attached to an air blowing unit  18  via an air pipe  20 . The air pipe  20  is preferably made of a flexible rubber tubing material. The air pipe  20  is connected to and passes through the discharge head  12  such that air is preferably blown out between the two electrodes  10 , and directed to blow through the corona.  
     [0018] The discharge head  12  is in turn connected to a pneumatic slide  22 . The pneumatic slide  22  is configured to move in a vertical direction, moving the discharge head  12  with it. Such a pneumatic slide is well known in the art.  
     [0019] Underneath the electrodes  10  and discharge head  12  is a fixture base  24  for holding a throttle body  26  during the double-corona treatment. Preferably, the fixture base  24  comprises a clamp or other type of positioning lock, as is well known in the art, to hold the throttle body structure  26  to the fixture base  24  while the treatment is progressing. The fixture base  24  is further configured to be able to rotate around its center axis. This fixture base  24  preferably has a maximum rotational speed of at least about 72 degrees/second, so that the fixture base  24  can make a complete rotation in about 5 seconds. Further, the fixture base  24  should be made of an insulating material, such as a rubber material. This will assure that the base fixture  24  does not provide a grounding conduit to affect the corona treatment The entire apparatus, except for the transformer  14  and the air blowing unit  18 , is preferably positioned inside a housing  28 . Because of the compact design of the treatment apparatus, the housing can be designed to take up as little as  4  square feet of floor space. The housing has on a front surface a safety door  30 . The safety door  30  can be better seen in the side view of FIG. 1B, where it is shown open. The safety door  30  can be configured to slide up, as shown in FIG. 1B, or it can be configured to open from the side or bottom. A safety door sensor is also installed in the housing  28 . In a preferred embodiment, the safety door sensor is an electrical, a mechanical or an optical sensor, and is configured to recognize whether the safety door  30  is open. The transformer  14  is also preferably connected electronically to the safety door sensor, and is configured to not generate voltage while the safety door  30  is still open. In one preferred embodiment, a two-handed safety switch acts as the mechanical sensor, and the transformer is configured to only generate voltage when the safety switch has been activated, locking the safety door  30  in the process.  
     [0020] In a preferred embodiment, most of the surface treatment technique is controlled via a control panel  32 . Parameters such as the voltage applied by the transformer  14 , the air velocity of the air blown by the air blower  18 , the electrode  10  geometry, the distance between the electrodes  10 , and the rotational speed of the fixture base  24  would preferably be controlled by an operator from the outside of the apparatus, or at a remote location. These parameters are variable based on the specific geometry and chemical makeup of the throttle body structure  26 . Specific values are well-known in the art. Further, other mechanical aspects of the apparatus may be controlled via the control panel  32 , such as the position of the safety door  30  or movement of the pneumatic slide  22 .  
     [0021] With the apparatus as described above, the surface of a throttle body structure can be treated. A preferred method according to the present invention is shown in FIG. 2. The apparatus according to the present invention is provided at Box  100 . The throttle body structure  26  is placed on the fixture base  24  inside the housing  28  at Box  110 . Clamps, positioning locks, or other means of securing the throttle body structure  26  to the fixture base  24  are employed. The safety door  30  of the housing  28  should preferably be closed before proceeding, to protect the operator from the voltage used in the treatment process. Preferably, the safety door sensor prevents the treatment from going further unless the safety door  30  is closed.  
     [0022] When the treatment is ready to begin, the electrodes  10  are lowered via the pneumatic slide  28  and the discharge head  12  at Box  120 . The electrodes  10  and the discharge head  12 , starting in a home position, should be lowered into an engaged position in the center of the throttle body structure  26 . This is shown in FIG. 3, where the electrodes  10  are depicted in the home position and in the engaged position (at  10 ′). After the electrodes  10  are lowered into the throttle body structure  26 , the air blower  18  blows air through the air pipe  20  and between the electrodes  10  at Box  130 . The transformer  14  applies voltage to the electrodes  10  at Box  140  to create the corona. The air blown between the electrodes  10  at Box  130  is directed towards the corona. This air stream blows the electrical arcs of the corona out towards the throttle body structure  26 . The fixture base  24  and throttle body structure  26  are rotated at Box  150  to give equal treatment to all areas of the throttle body structure  26 . Preferably, the throttle body is rotated once during treatment, one revolution preferably occurring within about 5 seconds.  
     [0023] Once the treatment is complete, the electrodes  10  and the discharge head  12  are preferably returned to their home position at Box  160 . The throttle body structure  26  can then be removed from the fixture base  24 .  
     [0024] The embodiments shown in the present invention are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the following claims.