Patent Application
20210095366
During galvanizing, metal parts are coated with a molten metal to protect the parts against corrosion. However, the presence of dross in the molten metal galvanizing bath can lead to defects and inferior properties of the galvanized part. In an attempt to work around dross problems, the dross can be mechanically removed from the molten metal bath or limited in formation but these are costly approaches.
A typical galvanizing process has multiple steps including submerging a part (e.g., a part made of steel), into a degreasing tank then rinsing. Next the part is submerged in a picking bath containing an acidic solution and then rinsed. Next the part is submerged in a fluxing bath and then dried. One example of a flux is zinc ammonium chloride. The flux aids in the process of the liquid zinc wetting and adhering to the steel of the part. The next step is galvanizing by submerging the part in a galvanizing bath of molten metal. The galvanizing bath can be predominantly zinc but may include other metals including lead and aluminum. Optional quenching to reduce the temperature of the coated part may be carried out. Once the part has been immersed in the molten metal and galvanized it is moved out of the bath to another location for cooling and quality inspection.
The molten zinc in the galvanizing bath rapidly oxidizes on the surface of the bath of molten metal. When the steel part is introduced into the melt, a layer of oxidized zinc will attach itself to the leading surfaces of the steel. Since this zinc oxide is the first material the steel touches, this creates an oxide layer against the steel, weakening the coating of zinc on steel and allowing it to more easily chip or flake due to a weak bond with the steel. Even if pure zinc bonds directly with the steel, the addition of the dross creates a brittle section of the coating, causing the material to chip if flexed. If a section of the coating does not remain adhered to the steel part, the benefits of galvanizing are reduced significantly, since the steel will begin to oxidize.
This creates the need for reducing an amount of dross in the galvanizing process. The conventional approaches for avoiding or removing dross are both complicated and expensive. These approaches envelop the entire molten zinc bath in an inert atmosphere or use a robot such as an auto-skimmer to relocate the dross. Another approach, raking the dross away by hand, is extremely dangerous due to risk of severe injuries and is a labor intensive approach to dross removal.
Therefore, there is a need in the industry when performing galvanizing to avoid dross adhering to metal parts. This would increase the final product's coating strength and malleability, due to the removal of impurities, as well as avoiding corrosion in the case of parts that were not completely galvanized with zinc metal.
In general, a first aspect of the disclosure features a tube pump including a tube comprised of refractory material and having a closed off lower end portion and an open upper end portion. The lower end portion is adapted to be submerged in a bath of molten metal. The tube includes an inlet opening and an outlet opening. The upper end portion of the tube is adapted to be connected to support structure. The upper end portion of the pump shaft is adapted to be connected to a drive shaft of the motor as known in the art. The pump shaft extends inside the tube. An impeller is fastened to the lower end portion of the pump shaft and disposed near a lower end portion of the tube. Inlet and outlet conduits are connected to the tube extending from the tube inlet opening and the tube outlet opening, adjacent to a top or bottom of the impeller, so that an inlet conduit opening is near the surface of the bath and an outlet conduit opening is disposed remote from the inlet conduit opening.
Referring to specific features of the first aspect, the impeller has an auger or screw shape.
Another feature is that the inlet conduit is disposed above the impeller and the outlet conduit is disposed below the impeller. The pump shaft is rotated and its screw threads have a twist direction such that molten metal travels downward upon rotation of the impeller in the refractory tube, which causes molten metal to be drawn from the inlet opening into the impeller and down to the outlet conduit and transferred to the conduit outlet opening, thereby causing the molten metal to have lesser surface dross in a region near the inlet conduit opening.
The system could have another design in which the inlet conduit is disposed below the impeller and the outlet conduit is disposed above the impeller by changing the screw thread twist direction and/or impeller rotation direction to move molten metal upward from the lower inlet conduit, past the impeller and into the upper outlet conduit.
In another feature the inlet conduit, outlet conduit and impeller are comprised of graphite or a ceramic material.
In another feature the outlet conduit extends out of the bath into another vessel for removal of the dross from the molten metal bath.
Another aspect of the disclosure features a tube pump of the first aspect combined with all of the above specific features.
A second aspect of the disclosure is a system for galvanizing metal parts comprising:
The tube pump has various advantages. One advantage is that it presents an economical and efficient way to produce cleaner galvanized parts. No costly dross removing robot or inert gas enclosure are required. Another advantage is that fewer parts are used in that a submergeable base containing a volute chamber is not needed, nor are posts for securing the base to the motor mount. A tube pump is susceptible to the influences of torque since it contains a rapidly rotating impeller that can pump in different directions. Since in the device of this disclosure flow is directed downwards into the inlet conduit, lateral torque on the tube is reduced such that the single tube can contain the forces of the pump, reducing complexity and component material to successfully create this pump. The locations of the inlet and outlet conduits can also be adjusted so as to minimize the torque on the tube pump.
The unique impeller design as a screw or auger shape allows pumping predominantly vertically instead of to the side, unlike a traditional impeller that pumps to the side. This gives two benefits. The downwards pumping direction allows a “zero-head” scenario, where the inlet and outlet of the pump are essentially level, or the outlet is slightly below the inlet. This means there is no pressure barrier to overcome in order to pump, increasing overall flow rate.
A tube pump 10 is suitable for use in removing dross during galvanizing and includes a tube 1212 comprised of refractory having a closed off lower end portion 14 and an open upper end portion 16. The lower end portion 14 of the tube 12 is adapted to be submerged in a bath of molten metal M. The galvanizing bath and the other baths are contained by enclosures, for example, the galvanizing bath is surrounded by refractory brick as known in the art. Support structure 18 is disposed outside of the molten metal bath for securing the upper end portion of the tube 12. The tube includes an inlet opening and an outlet opening (shown by 20, 22 in either upper or lower position). The position of the inlet and outlet openings can be reversed. A motor (not shown) is mounted to the support structure and includes a drive shaft (not shown). A pump shaft 24 is comprised of refractory material having upper and lower end portions 26, 28, respectively. The upper end portion 26 of the pump shaft 24 is connected to the motor's drive shaft in a manner known in the art. The pump shaft 24 extends centered inside the tube 12. An impeller 30 is fastened to the lower end portion 28 of the pump shaft 24 and is disposed near the lower end portion 14 of the tube 12. An inlet conduit 32 has one end portion 34 connected to the inlet opening 20 of the tube 12 adjacent to a top of the impeller 30 and an inlet end portion 36 with an inlet opening 38 disposed near and below a surface of the bath of molten metal M. An outlet conduit 40 has one end portion 42 connected to the outlet opening 22 of the tube 12 adjacent to bottom of the impeller and another end portion 44 including an outlet opening 46 remote from the inlet opening 38.
The impeller 30 has an auger or screw shape. In one aspect, the inlet conduit 32 is disposed above the impeller. The outlet conduit 40 is disposed below the impeller. The pump shaft rotates in a direction such as shown by the arrows and the impeller screw has a screw direction as seen in
The inlet conduit 32 above the impeller extends to near the surface of the molten metal, drawing the top portion of the molten metal bath into the pump. The outlet conduit 40 below the impeller can be located below the surface of the metal, allowing the dross to float back to the top and to be manually skimmed in a deposit region D (e.g., as shown by dotted lines in
Referring more specifically to the impeller and to
Referring to
