The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. D.O.E. DE-PS07-011D14026 awarded by the Department of Energy.
This invention relates to a method for preparing metal parts to affect and control the reflectivity of the surfaces of the parts so as to allow consistent and uniform heating of the metal parts when exposed to infrared radiance.
In processing metal parts, the metal or alloy is typically first formed into rods, bars, billets, sheets or plates to be used as a starting material for subsequent processing. Preformed shapes produced by different production methods may also be used for raw material input to subsequent processing. The input material may then be subjected to manufacturing processes such as forging, pressing, stamping, impact forming, spinning, flow turning and/or heat treating. As a preliminary and necessary step to these manufacturing processes, the input material typically must first be heated. Convection ovens are one known method for heating the metal parts for subsequent processing. However, oven heating has disadvantages, such as high net energy input.
Recently, infrared (IR) heating has been proposed as a means for heating parts for subsequent manufacturing operations. Infrared is an “instant on” heat source that uses energy only when needed, resulting in a significantly lower net energy input than convection ovens. Improvements in the microstructure and physical properties of metal parts may also be achieved by the use of IR rapid heating. However, variations in the surface finish on the various surfaces of a metal part or between the surfaces of different metal parts in a batch process will cause the parts or the surfaces thereof to achieve different temperatures at different rates. Such temperature differences will have deleterious metallurgical affects and potentially render the products unacceptable for use.
Dip and spray coatings have been used as a means for applying material to act as a lubricant in subsequent aluminum manufacturing processes. However, these treated aluminum parts will have non-uniform coatings that are not intended to address the surface finish of the part when subsequent processing involves IR radiance as the means for heating the part. Thus, previous attempts to utilize IR heating of aluminum and other metal parts have been unsuccessful due to the lack of control of the surface finish, such as surface reflectivity. Insufficient consideration has been given to the reflection of energy from the metal surface, and the resulting variable heating rates that cause under-temperature and over-temperature conditions in the IR heated parts.
There is thus a need for a method of preparing metal parts for heating by IR radiance that addresses the importance of the surface finish of the metal parts during subsequent metal heating.
The present invention provides a method for preparing metal for heating by infrared radiance to enable uniform and consistent heating. To that end, the method of the present invention includes treating the surface of a metal part to alter the surface finish to affect the reflectivity of the surface. The surface reflectivity is evaluated at one or more points on the surface to determine if a desired reflectivity has been achieved. The treating and evaluating are performed until the evaluation indicates that the desired reflectivity has been achieved. Once the treating has altered the surface finish to achieve the desired reflectivity, the metal part may then be exposed to infrared radiance to heat the metal part to a desired temperature, and that heating will be substantially consistent throughout by virtue of the desired reflectivity. In embodiments of the present invention, a single metal part may be treated or a batch of metal parts may be treated. In further embodiments of the present invention, evaluation may be by taking measurements at a single point on a single part, at a single point of each of multiple parts, at multiple points on a single part, or at multiple points on each of multiple parts. In an exemplary embodiment of the present invention, one or more aluminum or aluminum alloy parts are treated. In another exemplary embodiment of the present invention, the orientation of the metal part or batch of metal parts are changed during the treatment so as to expose the entire surfaces thereof to the surface treatment. Alternatively, the treatment medium may be reoriented during the treatment so as to expose all surfaces to the treatment. Similarly, the orientation of one or more metal parts may be changed during measuring to accommodate measurements from differing surface points, or the measuring devices may be reoriented during the measuring to achieve the same affect.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.
The present invention provides a method for preparing metal parts for subsequent heat treatment by infrared (IR) radiance to provide consistent and reliable heating of the parts. To that end, the surface of one or more metal parts is treated to alter the surface finish to affect the reflectivity of the surface, and the reflectivity is evaluated, for example measured, at one or more points to determine if a desired reflectivity has been achieved. The treatment of the surface may be repeated as many times as necessary until the measurements or other evaluation indicate that the desired reflectivity is achieved. The metal part(s) may then be exposed to IR radiance as a means of heating the part(s). The heating will be uniform by virtue of the desired reflectivity having been achieved and verified. The present invention recognizes that control of the reflectivity of the surface of metal parts is necessary for subsequent infrared heating of the metal parts. Depending on the surface reflectivity, IR radiation may be absorbed or reflected from the surface, and may be absorbed or reflected at different intensities. Therefore, the present invention recognizes that an inconsistent surface finish on a single metal part or an inconsistent surface finish from one part to another within a batch of metal parts may cause variations in the rate and/or extent of heating within each metal part or among the different parts in a batch. Thus, not only must the surface of the metal part be treated to affect a change in the surface reflectivity, but the surface reflectivity must be measured or otherwise evaluated to determine if a desired surface reflectivity has been achieved so as to provide subsequent consistent and reliable IR heating. The method of the present invention may be utilized any time IR heating is deemed to be desirable as a preliminary and necessary step to a subsequent manufacturing process, such as forging, pressing, stamping, impact forming, spinning, flow turning or heat treatment. The surface conditions created by the method of the present invention are uniform and consistent, and are not removed or significantly altered by typical handling processes.
The method of the present invention may be applied to any metal part or surface where reflectivity must be controlled for subsequent heating utilizing IR radiation. The term “metal” is understood to refer to any metallic part, whether it be pure metal or a metal alloy. The present invention may find particular applicability in the treatment of aluminum parts. For example, the method of the present invention may be applied to all aluminum alloy systems, including the wrought alloy systems, the cast alloy systems, and other grades and alloys where aluminum is the primary alloying element. The wrought aluminum alloy systems are generally designated as 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, 7XXX, 8XXX and 9XXX, in accordance with the Aluminum Association (AA) classification system. The cast aluminum alloy systems are generally designated as 1XX.X, 2XX.X, 3XX.X, 4XX.X, 5XX.X, 6XX.X, 7XX.X, 8XX.X and 9XX.X, in accordance with the AA classification system. By way of further example and not limitation, the method of the present invention may also be applied to titanium, titanium alloy systems, copper, copper alloy systems, and other titanium and copper grades and alloys where titanium or copper is the primary alloying element.
The metal parts to be treated by the method of the present invention may be in any desired starting form, for example, rod, bar, billet, sheet, plate, or preformed shapes. Alternatively, the starting material may be the product of pressing, forming, forging, casting, or powder or liquid metal molding, or the products of other methods of producing shape-specific metal parts. Non-uniform shapes may be especially suited for heating with IR radiance, and thus may be especially suited for treatment by the present invention.
The method of the present invention will be further described with reference to the schematic depictions of
Referring to
In addition to abrasive blasting, as depicted in
After treating the surface of the metal part(s), the reflectivity of the surface is evaluated to determine if the desired reflectivity has been achieved. In an exemplary embodiment, the evaluation is by means of measuring the surface reflectivity with an appropriate measuring device. The treating and measuring are performed until the measuring indicates that that desired reflectivity has been achieved. The surface treatment and the measurements of the surface reflectivity may only need to be performed once if the first measurements indicate that the first treatment was sufficient to achieve the desired reflectivity. Alternatively, the surface treatment and measurements may be repeated as many times as necessary to achieve the desired reflectivity. It may be appreciated that most surface treatment techniques are destructive in nature, rendering measurement of the surface reflectivity during the treating to be impractical, if not impossible. Thus, the method of the present invention contemplates performing the surface treatment and then stopping the treatment to perform the measurements, and then repeating these two sequential steps, if necessary, and as many times as necessary until the measurements indicate that the desired surface reflectivity has been achieved. In batch processing, it may be appreciated that the measurements may be performed on the entire batch, or on a sample of metal parts taken from the batch, which sampling is expected to be indicative of the surface finish for the entire batch. The present invention further contemplates that measurement devices may now or hereafter exist that are capable of taking in situ measurements of the surface reflectivity during treatment, such that the treating and measuring may occur concurrently, and the treating is stopped when the concurrent measurements indicate that the treatment has achieved the desired reflectivity.
In another embodiment of the present invention, the surface reflectivity is evaluated by other means, such as visual inspection of the surface finish. The present invention contemplates that there are persons skilled in the art of metal surface finishing that possess the ability to visually compare the surface of a treated part to the surface of a known acceptable part (a standard part) and accurately assess whether the desired reflectivity has been achieved. Thus, the method of the present invention is not limited to physical measurement techniques for evaluating the surface reflectivity.
In one embodiment of the present invention, the measuring includes taking measurements from a plurality of points 37 on the surface of the treated metal part 16′ and the values are compared to determine if the surface reflectivity is substantially uniform among the plurality of points 37. For example, the desired surface reflectivity may be achieved when all measurements indicate that the surface reflectivity is within +/−5% of a specified surface finish ideal for IR heating for the particular part being treated. It may be understood that the desired surface reflectivity may vary depending on the type of metal or metal alloy system, the number of parts, the shape of the parts, etc. In another embodiment, the measuring may be at a single point 37 that is on a surface of the metal part 16 that is particularly difficult to treat, such that when a measurement taken at that point 37 indicates that a desired reflectivity has been achieved, it may be assumed that the surface finish has a desired reflectivity on the remainder of the surfaces that are not difficult to treat. In other words, the metal part may have a surface that is oriented so to present a difficulty of alteration of the finish thereof that represents a maximum difficulty of alteration for the part. The measuring may then include a point on that surface, and the desired reflectivity is achieved when the measurement indicates that a minimum threshold reflectivity has been reached on that surface. It may be appreciated that in some instances, once a threshold value has been reached, additional surface treatment may have no further affect on the reflectivity and consequently on the uniformity of the IR heating. Thus, measuring at a point on the surface that is likely to be the last place that the threshold reflectivity will be achieved may be indicative of the desired reflectivity for the entire surface of the part.
In an alternative embodiment of the present invention depicted in
In yet another alternative embodiment of the present invention depicted in
It may be appreciated that the orientation of the emitting devices 32 and detection devices 34 as well as the energy intensity for the emitting devices 32 will vary based upon the geometry of the part being measured and the sensitivity of the detector being used. By way of example and not limitation, the emitting devices may be positioned approximately 10-100 mm away from the surface of the part. In a further example, a high intensity visible wavelength emitter (a bright light) may be directed through a fiber optic conductor to a focusing device positioned 25 mm from the surface to be measured and positioned such that the radiation emitted will be reflected at an angle matched by a photodetector receiver similarly positioned to receive the reflected radiation.
One embodiment of the method of the present invention will be further described with reference to the flow chart in
While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.
Pursuant to 37 C.F.R. § 1.78(a)(4), this application claims the benefit of and priority to prior filed co-pending Provisional Application Ser. No. 60/488,004, filed Jul. 17, 2003, which is expressly incorporated herein by reference.
Number | Date | Country | |
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60488004 | Jul 2003 | US |