This invention relates to electrocoating or electroplating conductor rolls. Specifically, this invention relates to a crown that is designed to compensate for the deflection of the conductor roll when the conductor roll is subjected to a mechanical load.
In a typical electrocoating process, a metal substrate is coated by utilizing an electric current to deposit a coating onto the substrate. The metal substrate, which may be either anodic or cathodic, carries the electrical current that is used by the chemical reactions that deposit the coating onto the surface of the substrate. In processes commonly referred to as electroplating (e.g. electrogalvanizing and electrotinning) the metal substrate is cathodic. In contrast, the metal substrate is anodic in processes often referred to as anodizing. In other electrocoating processes, the metal substrate may be either cathodic or anodic depending upon the desired chemistry of the end product.
An electrocoating process usually refers to processes in which the substrate is coated with an organic or polymeric coating often referred to as paint. The painted substrate is then cured for a predetermined amount of time to ensure that the components of the paint (i.e. pigment and resin) are sufficiently cross-linked and adhered to the surface of the substrate. Electrocoating presents a number of advantages over traditional painting processes. For instance, the amount of volatile organic compounds (VOCs), hazardous air pollutants (HAPs), and hazardous wastes are dramatically reduced or are completely eliminated when electrocoating is used in place of traditional painting processes. Additionally, electrocoating yields a more uniform coating on the surface of the metal substrate when compared to the traditional techniques of spraying, dipping, or roll coating thereby leading to a more superior end product.
When the substrate that is to be coated is a metallic sheet, one or more conductor rolls are typically used in the electrocoating or electroplating process. As the metallic sheet travels over a rotating conductor roll, an electrical current passes between the contacting surfaces of the metallic sheet and the conductor roll. The continuous integrity of the electrical contact between the metallic sheet and the conductor roll, however, is critical in avoiding a metallic sheet defect commonly known in the art as arc spots or arc pits (i.e. holes in the sheet). In the electrocoating process, arc pits form when the contact between the metallic sheet and the conductor roll is reduced to such a degree that the resulting electrical current density at the remaining contact points or contact areas causes through thickness melting of the metallic sheet. The actual holes in the metallic sheet are formed as melted material is expelled from the sheet as the temperature and pressure of the air or other gases and vapors between the metallic sheet and the conductor roll rises. The electrical contact between the metallic sheet and the conductor roll is typically reduced by the introduction of air or other insulating substances between the contacting surfaces of the metallic sheet and the conductor roll.
Two counter measures have been used to reduce the occurrence of arc pits. First, the total amount of electrical current that is used in the electrocoating system can be significantly reduced. This, however, can have a negative impact on the rate of production since the amount of time needed to coat the metal substrate would increase thereby adding to the total amount of time needed to produce an end product. Second, a hold down roll can be used to minimize or prevent air or other fluids, gaseous or liquid, from being introduced between the contacting surfaces of the metallic sheet and the conductor roll by providing a force that constantly pushes the metallic sheet against the conductor roll. When used in tandem, these counter measures have had some success at reducing the occurrence of arc pits in an electrocoated metal substrate.
In this invention, it has been found that matching the conductor roll design to sheet tension, especially when used in combination with a hold down roll, has further reduced the occurrence of arc pits during the electrocoating process. Generally, the mechanical load on a conductor roll increases as the wrap angle of a sheet that is wrapped around the conductor roll increases. As can be seen in
Therefore, there exists a need for reducing or eliminating the deflection of the conductor roll during an electrocoating process.
This invention is a response to this need by disclosing a conductor roll with a crown profile that compensates for the deflection of the conductor roll, which is caused by a mechanical load, during the electrocoating process.
This invention discloses an apparatus for reducing or eliminating the occurrence of arc pits in a metallic sheet during an electrocoating process. The apparatus includes a conductor roll that is surrounded by a crown, which extends along a substantial length of the conductor roll. The crown is designed to compensate for the deflection of the conductor roll when the conductor roll is placed under a load. The apparatus also includes a hold down roll that is positioned adjacent to the conductor roll thereby applying pressure to the metallic sheet that passes between the opposing surfaces of the conductor roll and the hold down roll.
This invention also discloses a conductor roll that is surrounded by a crown, which extends along a substantial length of the conductor roll. The crown is designed to compensate for the deflection of the conductor roll when the conductor roll is placed under a load.
This invention also discloses a method for reducing or eliminating the occurrence of arc pits in a metallic sheet during an electrocoating process including providing a metallic sheet, feeding the metallic sheet between the opposing surfaces of a crowned conductor roll and a hold down roll, wrapping the metallic sheet around the crowned conductor roll wherein the crowned conductor roll is deformed by the mechanical forces resulting from the sheet tension, and applying an electrical current through the crowned conductor roll to electrochemically deposit a coating onto a surface of the metallic sheet.
This invention also discloses a metallic sheet manufactured by the process including providing a metallic sheet, feeding the metallic sheet between the opposing surfaces of a crowned conductor roll and a hold down roll, wrapping the metallic sheet around the crowned conductor roll wherein the crowned conductor roll is deformed by the mechanical forces resulting from the sheet tension, and applying an electrical current through the crowned conductor roll to electrochemically deposit a coating onto a surface of the metallic sheet.
This invention also discloses a method for making a conductor roll for use in an electrocoating line process including providing a conductor roll, measuring or predicting the amount of deflection of the conductor roll when a metallic sheet is wrapped around the conductor roll, and fabricating a crown that surrounds and extends along a substantial length of the conductor roll. The crown is designed to compensate for the deflection of the conductor roll when the conductor roll is placed under a load.
One aspect of this invention is to reduce or eliminate the occurrence of arc pits in a metallic sheet during an electrocoating process.
Another aspect of this invention is to fabricate a crown that can compensate for the deflection of a conductor roll when the conductor roll is under a load.
The accompanying figures and the description that follow set forth this invention in its preferred embodiments. However, it is contemplated that persons generally familiar with electroplating conductor rolls will be able to apply the novel characteristics of the structures and methods illustrated and described herein in other contexts by modification of certain details. Accordingly, the figures and description are not to be taken as restrictive on the scope of this invention, but are to be understood as broad and general teachings. When referring to any numerical range of values, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum. For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shall relate to the invention as it is oriented in the drawing figures.
The term “crown” is generally understood in several industries, which use rolls or rollers, to mean a general barrel-shape. In other words, the mid section of the roll has a larger diameter than the ends of the roll.
This invention discloses a crowned conductor roll that is designed to compensate for the deflection of the conductor roll when the conductor roll is subjected to mechanical forces, e.g. sheet tension, gravity, brush assemblies, and hold down rolls, during an electrocoating process thereby reducing or eliminating the occurrence of arc pits in the coated metallic sheet. In addition, by utilizing a crown to compensate for the conductor roll's deflection, a lighter and smaller diameter conductor roll can be used in the electrocoating process since the roll itself would not have to be so strong as not to deflect or bend when subjected to the mechanical forces that occur during the electrocoating process. Yet another advantage of using a crowned conductor roll is that when it is determined that the deflection of a standard cylindrical or non-crowned conductor roll is detrimental, modification of the super structure of the electrocoating or electroplating line is most often not necessary. This is due to crowned rolls being substantially the same size (i.e. length, weight, and diameter) as the standard cylindrical roll that they will replace.
Referring to
By knowing the amount of deflection λ across the length of the conductor roll 4, a crown 22 can be incorporated into the shape of the conductor roll 4 or positioned around the conductor roll 4 in a form of a jacket to fully compensate for the deflection λ of the conductor roll 4 thereby ensuring that the top of the crowned conductor roll 24 is oriented as if the crowned conductor roll 24 was under no load. As shown in
It is contemplated that when the crowned conductor roll 24 rotates about its axis 28 the design of the crowned conductor roll 24 is symmetric about the axis 28 when the crowned conductor roll 24 is under no load. It is also contemplated that the deflecting forces acting on the crowned conductor roll 24 may not be symmetric about the center line 26 of the crowned conductor roll 24. When the deflecting forces are not symmetric about the center line 26, the maximum value of α will correspondingly not be located about the centerline 26. It is additionally contemplated that the magnitude of α, the location of α, and the detailed shape of the crown 22 will be sufficiently specific to the loads causing the deflection λ. When the crowned conductor roll 24 is in use, however, the top 23 of the crown 22, which is located at or near the midpoint B or B′ of the wrap angle A as shown in
The crown 22 is formed in the following manner. First, the amount of deflection of the conductor roll 4 is measured or modeled using techniques that are well known in the art. For instance, the computer method of Finite Element Modeling (FEM) or a similar method can be used to measure, predict, or model the amount of deflection λ. Once the deflection λ has been measured or predicted, the exact dimensions of the crown 22 are calculated to compensate for the deflection λ. A layer is then deposited over the outer surface 12 of the conductor roll 4 using methods that are commonly known in the art such as electroplating, thermal spraying, and cold spraying. It is noted that thermal spraying also includes, but is not limited to, plasma spraying, high velocity powder combustion, high velocity wire combustion, and wire arc. The crown 22 is then formed by machining the layer to the dimensions required to compensate for the deflection λ. As described in the preceding paragraphs, the diameter of the crown 22 is designed to increase and to decrease monotonously along the length of the conductor roll 4 by a distance of α, which is substantially equal to the deflection λ, thereby fully compensating for the deflection λ that is caused by the mechanical load. The deposited layer is shaped using methods that are commonly known in the art including but not limited to, grinding, polishing, and electron discharge machining (EDM).
In one embodiment, the deposited layer has a maximum thickness of about 0.254 cm (0.1 in).
In another embodiment, the deposited layer can be chromium, inconel, or alloys based on iron, nickel, or chromium. This, however, is not meant to be limiting since any material that exhibits wear resistance, adequate electrical conductivity, and adherence to the roll substrate may be used without departing from the teachings of this invention.
In another embodiment, the metal that was used to fabricate the conductor roll 4 was steel. However, the conductor roll 4 may also be fabricated from other metals or metal alloys.
In another embodiment, the maximum dimension of the crown 22 is at most about 0.025 cm (0.01 in) higher than either the first or second end 8 and 10.
In yet another embodiment, the crown 22 is able to conduct an electrical current up to about 70,000 amperes.
In another embodiment, the crown 22 is able to conduct an electrical current ranging from about 3,000 amperes to about 70,000 amperes. This is not meant to be limiting, however, since the crown 22 would also be able to conduct an electric current that is less than 3000 amperes.
In another embodiment, the surface of the crown 22 has a maximum Ra surface roughness of about 0.127 μm (5 μin). It is noted that one having ordinary skill in the art would understand what is meant by a Ra surface roughness.
In another embodiment, the surface of the crown 22 has a maximum Ra surface roughness of about 0.508 μm (2 μin).
In another embodiment, the surface of the crown 22 has a maximum Ra surface roughness of about 0.0254 μm (1 μin).
In another embodiment, the crown 22 is fabricated as a jacket from a metal or a metal alloy. The conductor roll 4 is than inserted into the jacket so that the conductor roll 4 is substantially surrounded by the crown 22. Once the crown 22 is positioned around the conductor roll 4 they are joined or affixed using techniques that are commonly known in the art such as welding, brazing or soldering thereby forming a crowned conductor roll 24.
In yet another embodiment, the metallic sheet has a thickness ranging from about 0.0127 cm (0.0050) to about 0.254 cm (0.1 in)
In another embodiment, the line speed is at least about 91 meters/minute (300 feet/minute).
In another embodiment, the crown extends substantially along the entire length of the conductor roll.
In another embodiment, the crown extends substantially along more than half of the length of the conductor roll.
Referring to
Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied within the scope of the appended claims.