Patent Application
20190338404
Not applicable.
The present invention relates generally to the field of localized heat treatment of sensitized metallic compounds and, in particular, to the in-situ de-sensitization heat treatment of sensitized aluminum-magnesium alloys in naval vessels. The present invention also relates to a method for maximizing the absorption of infrared energy on a target. The present invention also relates to an apparatus for heat treating a substrate having an irregular surface.
Aluminum has been used in the construction of naval vessels for more than a century. Experimental small craft were constructed of aluminum as long ago as the 1890's and, at that time, further use seemed promising. The first sizable craft constructed of aluminum was the sloop-rigged yacht Vendenesse, built at St. Denis in France in 1892. Aluminum plate was used for the shell plating, decks and bulkheads, although the frames, keel and stringers were steel. Within four months after launch, corrosion was observed over 20 square meters (˜200 square feet) of her bottom, where the bottom paint had failed. Corrosion was a continuing problem for the Vendenesse. The first use of aluminum in the United States for a sizable craft occurred in 1895 when Herrshoff designed and built the America's Cup yacht Defender which was to be the pride of American technology. The side shell plating and some of the frames were of an aluminum-nickel alloy. The portion of the Defender below the waterline was bronze, as were the rivets for the aluminum portions. This combination of aluminum with bronze led to rapid corrosion of the aluminum but not before the Cup was won by Defender. The experience with these vessels was not promising, leading Scientific American in an article published in 1894 to state that this experience “does not present a very encouraging prospect for the introduction of aluminum boats.”1 1NTIS-PB2009101032; Aluminum Structure Design and Fabrication Guide; Sielski, R. A.; 796 pages; 2007
Aluminum was first used in the U.S. Navy for some topside fittings for the torpedo boats intended for the battleship USS Maine. These stanchions, sockets and decklight frames quickly corroded and were replaced with steel. A similar experiment with the same results was made with the torpedo boats Foote, Rodgers, and Winslow, which were built in Baltimore between 1895 and 1898. The first aluminum deckhouses for U.S. Navy ships were for the torpedo boats Dahlgren and Craven, which were designed and built by Bath Iron Works in 1898. Possibly, the use of aluminum for the hulls by French yards interested the Bath Iron Works, and they used this new technology. However, the aluminum in these boats evidently fared no better than it had in other applications, for aluminum was not used again in structural applications for forty years.
In the 1930s, lightweight topside structure was becoming important for destroyers. In 1935, aluminum was reintroduced to deckhouse and was used extensively for many other nonstructural purposes, including furniture and joiner bulkheads. With the DD-409 class, designed in 1936, came the greatest use of aluminum for exposed deckhouse structure. Plating was mixed, some of aluminum, some of mild steel, with the framing of mild steel. This application of aluminum plate was apparently successful, because the next class designed, the DD-423, used aluminum for plating throughout the entire deckhouse, except where thick steel was used for fragment protection.
Design of deckhouse structure became rather standardized with mild steel transverse frames spaced 21 inches supporting aluminum plating that was 4.8 mm ( 3/16 inches) thick everywhere except in way of gun blast, where it was 6.3 mm (¼ inches) thick. The next major design, the Fletcher (DD-445) class destroyers, used this configuration from the beginning of the class in 1940. However, with the onset of World War II, all uses of aluminum except for aircraft came under careful scrutiny because of shortages, and the use of aluminum in Navy ships was temporarily discontinued. The DD-445 class was thus a mixture of steel and aluminum.
With the USS Gearing (DD-692) and USS Sommer (DD-710) class destroyers, riveted aluminum came back, being used for about half of the deckhouse sides and decks, although the transversely framed stiffeners were welded steel. Following the war, the development of aluminum welding had an effect, and in 1948 the new destroyer leaders, the USS Mitcher (DL-2) class had aluminum deckhouses that were entirely welded, including the transversely oriented frames. From about 1953 on, all new U.S. Navy combatants (destroyers, destroyer escorts, frigates and cruisers) had aluminum for the majority of their deckhouses. In addition, aluminum is used for the deckhouse in landing ships, and for the islands of aircraft carriers and amphibious assault ships.
The use of aluminum for the hulls of high-speed merchant vessels began in the 1990s with increased construction of high-speed ferries. These vessels have become so technologically advanced that they have surpassed the capabilities of many naval vessels; many navies today are adapting derivatives of these high speed vessels to combatant craft.
The U.S. Navy is using 5XXX aluminum alloys as a critical construction material in the design and construction of state-of-the-art Navy ships. As noted above, aluminum had long been used in the construction of naval vessels. In order to maximize the stability and, in some cases, speed of naval vessels, aluminum-magnesium [5XXX] alloys have been used to construct ship superstructures. More recently, the current U.S. Navy shipbuilding plan is to grow the size of the fleet with significant aluminum structural components to approximately 170 vessels by 2040, including 32 Littoral Combat Ships [LCS], 20 Future Frigates [FF], 22 Guided Missile Cruisers [CG], 12 Aircraft Carriers [CVN], 11 Joint High Speed Vessels [JHSV], and 73 Ship to Shore Connectors [SSC] to replace the 91 Landing Craft Air Cushion [LCAC] Vehicles.2 2“Quantitative Nondestructive 5XXX Aluminum Material Assessments to Reduce Total Ownership Costs,” Dunn, Ryan, Naval Engineering Journal, March 2016, Vol. 128, No. 1, pp 23-34
The primary alloying element in 5XXX series aluminum alloys is magnesium. During production, highly controlled heat treatments are used to evenly distribute magnesium in the aluminum matrix. Different alloys in the 5XXX series contain different amounts of magnesium ranging from ˜3.5% in 5086 to ˜4% in 5083 and up to ˜5% in 5046. These alloys are popular for marine applications because they combine a wide range of strength, good forming and welding characteristics, and high resistance to general corrosion. 5XXX alloys with greater than 3.0% magnesium content may be susceptible to stress corrosion cracking [SCC]. In service, limitations should be placed on the amount of cold work and maximum permissible operating temperature for the higher magnesium content alloys to avoid increased susceptibility to stress corrosion cracking and intergranular corrosion [IGC]. For these reasons, such alloys should not be used at operating temperatures greater than approximately 65° C. [149° F.].
Ships and vessels constructed of 5XXX aluminum alloys are susceptible to a metallurgical phenomenon known as sensitization. The evenly distributed state of the magnesium within the Aluminum matrix is thermodynamically metastable and exposure to even mildly elevated temperatures for extended periods of time can cause the magnesium to form beta-phase [Mg2Al3] precipitates. The formation of these beta-phase precipitates along the grain boundaries as a connected network is called sensitization. Welding on existing 5XXX aluminum structures that have become sensitized in support of repair, maintenance and/or modification may require specific critical welding procedures and, in some cases, the application of cold working technologies or wholesale material replacement depending on the degree of sensitization (DoS).
As noted above, sensitization is the formation of magnesium rich beta-phase precipitates at material grain boundaries as the result of exposure to elevated temperatures for extended periods of time. These beta-phase precipitates are anodic to the surrounding aluminum matrix, and when exposed to a corrosive environment, sensitized material will experience intergranular corrosion [IGC]. When tensile stress is applied to material that has experienced IGC, stress corrosion cracking [SCC] can result.
At a high level, the rate of sensitization is primarily a function of four factors: thermal exposure, alloy composition (% magnesium), material temper and the material grain size and microstructure. Assuming equivalent thermal exposures, tempers, grain sizes, and microstructures, 5XXX aluminum alloys containing higher amounts of magnesium will sensitize faster than 5XXX aluminum alloys with lesser amounts of magnesium. For example, 5046 (˜5% magnesium) will sensitize faster than an equivalent 5083 (˜4% magnesium) sample, and 5083 will sensitize faster than an equivalent 5086 (˜3.5% magnesium) sample when exposed to the same thermal conditions.
The beta-phase [Mg2Al3] precipitates contain approximately 38% magnesium which is significantly higher than the aluminum matrix, which for 5456 Aluminum alloy is approximately 5% magnesium. Elemental magnesium is thermodynamically less stable and kinetically more active than elemental aluminum. These characteristics make magnesium more susceptible to dissolution in low and neutral pH environments. The beta-phase [Mg2Al3] behaves more like magnesium than aluminum and will dissolve rapidly in seawater environments. This difference in dissolution behavior, combined with the fact that beta-phase forms preferentially on grain boundaries during service, leads to the preferred corrosion of those grain boundaries. In other words, these beta-phase preferential grain boundaries are susceptible to intergranular corrosion [IGC].
Stress Corrosion Cracking [SCC] will occur if a specific set of material properties and environmental conditions are present. As illustrated in
Aluminum-magnesium alloys can become sensitized in different ways. Heating and holding the alloy for even a relatively short period of time at an elevated temperature may produce the sensitized condition. However, it is not always necessary to heat to elevated temperatures to produce the condition.
The Naval Surface Warfare Center Carderock Division [NSWCCD] has an ongoing effort to predict sensitization rates of various 5XXX aluminum alloys in the fleet. As part of this effort, two sample racks holding six samples each were mounted on a deployed Navy vessel. The temperature of each test specimen was measured and recorded by an attached thermocouple every 20 minutes. The collected temperature data was fed into a predictive model developed by NSWCCD to predict sensitization rates for different 5XXX aluminum alloys based on the recorded thermal exposures. Based on this data it is estimated that recrystallized 5083 aluminum alloy will reach sensitization levels above 25 mg/cm2 after approximately 7 to 10 years of normal operating fleet exposure and 5456 aluminum alloy is estimated to become sensitized after approximately 4 years of normal operating fleet exposure. The 25 mg/cm2 test result quoted above was obtained using the industry standard Nitric Acid Mass Loss Test (hereinafter “NAMLT”). The U.S. Navy considers 5XXX alloys which have a NAMLT test result above 25 mg/cm2 to be sensitized.
Ships and vessels with aluminum superstructures made from 5XXX aluminum alloys have experienced cracking due to the effects of corrosion. Surface ship structures made of 5456 and/or 5083 aluminum will become sensitized from long-term [4-10 years] exposure to normal fleet operating conditions. In addition, heat from welding processes, for example Friction welding or Gas Metal Arc [GMA welding], used in ship fabrication and repair may also contribute to the sensitization of these ship structures. Once the ship superstructure has become sensitized, it is more prone to intergranular corrosion [IGC] and also to stress corrosion cracking [SCC].
The importance of implementing innovative approaches to reduce total ownership costs associated with the repair, maintenance, and modernization of vessels constructed using 5XXX aluminum alloys is best exemplified by the problems and significant increases in total ownership costs associated with the repair of a significant number of sensitization and fatigue related superstructure cracks across the 22-ship Ticonderoga class guided missile cruisers. The high cost of aluminum crack repair and significant number of CG superstructure cracks in addition to the difficulties associated with working on sensitized aluminum has added several hundred million dollars to the total ownership costs of the CG class ships. With an additional 20 years of service life remaining for many of the CG class ships, it is conservative to estimate that stress corrosion cracking and the difficulties associated with performing work on sensitized aluminum will continue to significantly increase total ownership costs.
Once portions of ship structure made from 5XXX alloys have become sensitized it was not thought that this condition was easily reversible. The normal practice to deal with this situation was, often, wholesale replacement of the sensitized aluminum. However, it has been discovered that it is possible to de-sensitize these portions of ship structure in-situ by re-dissolving the beta-phase into the alloy matrix via the proper type of anneal heat treatment. Note the teachings of Kramer et al., in U.S. Pat. No. 9,394,596. This de-sensitization process is similar to the types of mill stabilization heat treatments used for many years in aluminum production. Once an area of the ship structure has been determined to be sensitized, an in-situ heat treatment using a portable heater is applied to de-sensitize the affected area. One of the disadvantages of this type of treatment is that it tends to anneal the structure. Because the 5456 aluminum-magnesium alloy commonly used in naval ship construction derives its strength from work hardening, the treated, annealed plate is softer than, for example, the H116 or H321 marine grade plate. Thus, close control of the anneal heat treatment is critical.
This invention is a method for in-situ de-Sensitization of a 5XXX alloy structure by applying a localized heat treatment. The heat treatment is similar to a mill stabilization treatment used to reverse sensitization and to restore corrosion resistance and shape fixability in existing Aluminum-magnesium products. Such a treatment is disclosed in Zhao et al. U.S. Pat. No. 6,248,193 B1 which reference teaches heating a continuously cast and rolled aluminum-magnesium alloy sheet with from 3%-6% magnesium to a temperature of 240° C. to 340° C. and holding that temperature for one hour or more. As taught in Zhao et al. this heat and hold treatment followed by a slow cooling ensures that magnesium segregated through continuous casting may be reliably precipitated in the form of particles along the grain boundaries. Of course, in a mill setting, such heat treatments are fairly easily carried out. Doing a desensitization heat treatment on an existing structure such as a ship is another matter entirely.
Another portion of the invention is a new method for more efficient heat transfer during the in-situ heat treatment process for aluminum, other metals and of non-metallic compounds. One of the heat sources envisioned for use in providing heat to the sensitized aluminum substrate is an infrared emitter. This heat source is well-known in the art. What is new is the concept of tuning the frequency of the infrared emitter to match the absorption spectrum of the material being heated. For example, with the sensitized aluminum of the current invention, the aluminum reflects over 90% of the infrared energy impacting it over a wide range of impacting energy wavelengths. Except if the frequency of the impacting radiation is in the 600-900 nm range, there is a pronounced dip in the energy reflected. At approximately 825 nm wavelength of impacting infrared radiation, the aluminum only reflects about 86% of the energy impacting it. In other words, the aluminum absorbs more of the impacted energy if the energy is coming in at these frequencies. This means that the in-situ heat treatment may be performed more efficiently.
Another way to achieve a more efficient heat transfer during the in-situ heat treatment process for sensitized aluminum, other metals and of non-metallic compounds is to coat the sensitized aluminum, other metal or non-metallic compound with a coating which will absorb more of the infrared energy than the bare substrate would absorb. It is envisaged that this coating would either be able to withstand the temperatures involved and be removed at a later time, or be a sacrificial coating and designed to burn off during the treatment.
Another portion of the invention involves the provision of a heat treatment apparatus which is capable of applying a closely controlled heat treatment to a substrate of interest which substrate may have an irregular surface. The apparatus comprises a support device and a heating unit. The support device supports the heating unit directly over the substrate of interest and permits the system to be secured to one surface of the substrate of interest in a removable and non-destructive manner. The support device has legs which have securing means on the bottom thereof to secure the system to one surface of the substrate of interest in a releasable and non-destructible way. Normally the support device will have at least three (3) legs [although there may be more or less as desired and/or necessary]. Typically, these securing means comprise powerful suction cups, but they may be magnetic if the substrate is ferrous or they could be any other suitable means to secure the device to a substrate in a releasable and non-destructible way. The support device also permits the heating unit to be biased towards the substrate of interest. Removable, as used herein, means that the system may be placed upon a surface of the substrate of interest and then removed. The idea is that the legs permit the device to be secured to and removed from a substrate in a manner that does not damage the substrate. It is to be understood that not damaging the substrate may still permit a cleaning or light abrasion of the substrate to remove a protective coating in the area where the treatment is desired. The support device also has an adjustment means that permits each leg to independently extend/retract as necessary to accommodate a substrate of interest with an irregular [non-planar] surface. The legs permit the device to be biased against the surface and the design of the heater assures that the surface directly under the heater will receive the correct treatment and the area even immediately outside the heater will receive minimal heat. In certain applications, the heating unit will be thermally sealed against the surface.
The substrate will most often be a metal, often aluminum, and may have an irregular surface. To provide the best contact possible with such an irregular substrate, each leg of the device is independently adjustable [as noted above] in order to move the heater body closer or farther away from the substrate surface. Each leg has a two stage adjustment system, a coarse adjustment and a fine adjustment. As mentioned above, the support device comprises means to secure the device to the substrate of interest and permits the device to be biased against the substrate. This feature, in combination with the above mentioned independently adjustable legs permits the device to be used on substrates with irregular surfaces. If the means to adhere is a suction cup, it is even possible to removably secure the device to an vertical surface using vacuum-powered suction cups. These are suction cups powered by air being forced through a vacuum producing venturi closely associated with the suction cup. Using this type of design, it has been found that the device can be used successfully on substrates that actually are inclined slightly beyond the vertical.
There are several significant problems inherent in performing such a heat treatment on an existing aluminum-magnesium structure. First of all is the problem of detecting just exactly which portions of the existing structure are sensitized and would thus need to be de-sensitized. Secondly, it is important when working on the sensitized portion of an existing structure that the surrounding, non-sensitized areas not become sensitized by the heat treatment applied to the sensitized areas. This situation can occur if the surrounding, non-sensitized areas receive too much heat from the de-sensitization process. Thirdly, it is important to make sure that the de-sensitizing treatment not reduce the strength of the existing, sensitized structure below acceptable levels. Lastly, it is important to make sure that the structure being treated [and surrounding structures] have the absolute minimum deformation as a result of the de-sensitization heat treatment.
The industry standard test for determining the degree of sensitization of aluminum-magnesium alloy structures is the NAMLT test [Nitric Acid Mass Loss Test]. The NAMLT test requires cutting sample coupons from areas of the structure that are suspected of being sensitized and then performing the NAMLT test on them. This test essentially destroys the sample coupons and harvesting the sample coupons leaves holes in the aluminum structure. Cutting numerous holes in the structure of a billion dollar ship is not going to win anyone a popularity contest. Since it is extremely difficult, if not outright impossible, to determine sensitization by merely looking at a suspect area, harvesting sample coupons is definitely a hit-or-miss affair. Experience with repair of previous cracks on similar ships in the fleet might at least suggest which portions of the structure are likely to be sensitized—but this is still a less than satisfactory method for directing sample coupon harvesting. Fortunately, the recent development of the DoS-Probe [note the article by Ryan C. Dunn (one of the inventors of this application) “Quantitative Nondestructive 5XXX Aluminum Material Assessments to Reduce Total Ownership Costs,” Dunn, Ryan, Naval Engineering Journal, March 2016, Vol. 128, No. 1, pp 23-34] makes this detecting step vastly easier. Using a DoS-Probe to perform a non-destructive sensitization test of various portions of the existing structure permits a rapid determination of exactly which portions of the structure are sensitized. There are also other sensors which can be used to determine the degree of sensitization [DoS] of an aluminum-magnesium structure, for example the microwave sensor developed by AlphaSense, Inc.
3 illustrates the effect of temperature on susceptibility of various aluminum-magnesium alloys to stress corrosion cracking. The x-axis represents the weight % of magnesium in the aluminum-magnesium alloy. The y-axis represents temperature in °C. Area 1 is the boundary of the sensitized range. Area 3 is the β-phase solid stability limit or the annealed range. Area 2 is the stabilization range. A sensitized structure made of aluminum-magnesium alloy with ˜4 wt % magnesium [say 5083 alloy] can be de-sensitized by a heat treatment which heats the structure to a temperature of about 190° C. 3E. H. Dix, Jr., W. A. Anderson, M. B. Shumaker, “Influence of Service Temperature on the Resistance of Wrought Aluminum-Magnesium Alloys to Corrosion,” CORROSION, Vol. 15, No. 2, pp. 55t-62t, February, 1959.
It is important to control the heat treatment closely to prevent surrounding non-sensitized areas from becoming sensitized by the de-sensitization treatment. This could occur, for example, if a non-sensitized area of the 4% wt magnesium structure close to the sensitized area was heated to a temperature ˜160° C. by waste heat from the de-sensitization treatment.
It should be noted that it generally takes more time to have aluminum-magnesium alloys become sensitized than it does to desensitize them—thus heating an area of an unsensitized or moderately sensitized aluminum-magnesium alloy to the sensitization range [for example, Area 1 in
It is also important to prevent the structure being de-sensitized [and surrounding areas as well] from losing too much strength through annealing. It is obvious that the use of thermal dams could be an important tool in controlling this undesirable side effect.
Of course, it is also important to prevent the structure being de-sensitized [and surrounding areas as well] from undesirable deformation during a de-sensitization treatment. The use of thermal dams could also be an important tool in controlling deformation.
The heat treatment method of this invention involves an in-situ heat treatment of a sensitized area of an existing structure using a portable heating device. The gist of the invention is to use the minimum amount of heat effective to achieve the desired result for the minimum amount of time. Once the desired heat has been applied for the desired time, the heat source is turned off and the affected area is allowed to air-cool. This reduces unwanted sensitization of surrounding material, reduces unwanted annealing and undesirable deformation of the structure. Having stated these principles, minimum heat for the minimum time, it should be recognized that there might be times where more heat than the bare minimum necessary may be desirable in order to avoid undesirable collateral damage as will be further explained below in § [0037].
In order to achieve this treatment, a protocol is determined for the specific aluminum-magnesium alloy comprising the sensitized structure. This protocol is determined using the relationships shown in
A heat treatment protocol with very short hold times is used to de-sensitize a sensitized structure. Once the structure has reached the desired temperature, it is not maintained at that desired temperature for long periods of time. For example temperature maintenance time periods of 5 to 60 minutes [as stated in the aforementioned Kramer et al. patent [U.S. Pat. No. 9,394,596] are not used. This method uses temperature maintenance times in the order of 0 to 4 minutes. For example, it might be determined that for a particular sensitized 5XXX structure with that the minimum temperature—minimum hold time protocol to de-sensitize the structure is 230° C., with a hold time of zero [0] minutes. The structure could then be heated to 230° C. and allowed to immediately air-cool with essentially zero [0] minutes hold time. This process is illustrated in
Since
A heating apparatus 100 suitable for performing these processes is shown in
It is possible to construct thermal dam 104 with types of cooling devices other than internal water pipes. For example air vortex tube coolers may be used. The vortex tube was discovered in 1928 by George Ranque. The device uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of these two airstreams are adjustable with a valve built into the hot air exhaust. Temperatures as low as −50° F. (−46° C.) and as high as +260° F. (127° C.) are possible.
A generally accepted explanation of how a vortex tube works is as follows. Compressed air is supplied to the vortex tube and passes through nozzles that are tangent to an internal counterbore. These nozzles set the air in a vortex motion. The air may well be spinning at up to 1,000,000 rpm in this vortex. This spinning stream of air turns 90° and passes down the hot tube in the form of a spinning shell, similar to a tornado. A valve at one end of the tube allows some of the hot air to escape. What does not escape, heads back down the tube as a second vortex inside the low-pressure area of the larger vortex. This inner vortex loses heat to the larger vortex and exhausts through the other end as cold air.
With proper selection of the cycling of the intermittent heat source 136, this situation can be maintained as long as desired with no thermal dam or other structure being necessary to keep the temperature of area G of plate 160 between 250° C. and 300° C. and still maintain the portion of plate 160 outside of circular area H at or below 100° C. The advantages of this system are obvious, the pulsed or intermittent heat source is cheaper to operate than one which is on all of the time, and doing away with the necessity of a thermal dam eliminates most of the structure [shroud, etc.] of the heat treatment device. This is clearly a great simplification of the heat treatment process.
As noted above in § [0032] it generally takes more time to have aluminum-magnesium alloys become sensitized than it does to desensitize them—thus heating an area of a unsensitized or moderately sensitized aluminum-magnesium alloy to the sensitization range [for example, Area 1 in
Base mount 312 is securely mounted to thermal dam 305 or such other portion of heating shroud 302 as is desired in order to orient the independently adjustable mounting means 200 as is shown in
This fine height adjustment is achieved by means of adjustment nut 306 which is captured in the fork 309 of adjustment screw mount 310. Adjustment nut 306 is threaded onto adjustment screw 304 [the threads on adjustment screw 304 are not shown in the drawings for clarity] but is captured in fork 309 of adjustment screw mount 310. Using this construction, rotation of adjustment nut 306 moves adjustment screw 304 upwardly or downwardly and thus moves suction cup 303, which is attached to the lower end of screw 304, upwardly or downwardly as shown by the double-headed arrow next to suction cup 303. Thus suction cup 303 can be moved up or down.
Adjustment screw mount 310 is attached to heating device 300 by leg base mount 312. The means attaching the adjustment screw mount to the leg base mount permits a coarse height adjustment of adjustment screw mount 310 with respect to leg base mount 312 as will be further described below in regard to
When the suction cups are all properly positioned, and heating device 300 secured to the sensitized portion of the structure, the air is turned on and a sizable suction drawn in each suction cup. By these means the heat treatment device 300 may be held on just about any type of surface, including a more than vertical wall, to accomplish a de-sensitization heat treatment.
Since the in situ heat treatment process of the instant invention is intended to be performed upon large structures such as portions of a Ticonderoga class CG cruiser or any other vessel comprising sensitized aluminum. With this in mind, it is clear that when performing the in situ heat treatment processes described above, a considerable amount of heat energy must be generated by the heat-treatment apparatus, transmitted to the substrate material and then absorbed by the substrate material—usually 5XXX aluminum. Obviously, if there is any way to improve the heat transfer efficiency of this process, it would be a very desirable addition to the processes described above.
When radiant energy is directed onto an aluminum surface, the aluminum surface tends to reflect over 90% of the radiant energy impacting it over a wide range of impacting radiant energy wavelengths. This is illustrated in
As shown in
In view of the discussion above in paragraph [0101], it should be possible to have a more efficient radiant energy transfer to an aluminum substrate if the impacting radiant energy has a wavelength in the 600 to 900 nm range and even more efficiency is obtained when the impacting energy has a wavelength of approximately 825 nm. To this end, the heat treatment apparatus used in performing the in situ heat treatment processes of the instant invention would be tuned to generate radiant energy in the wavelengths which would insure the maximum absorption of energy depending upon the substrate being treated. If the substrate was aluminum, the emitter wavelength would be in the 600 to 900 nm range and most particularly, approximately 825 nm. For other materials, the emitter wavelength would be tuned to the most favorable absorption range for the particular target material.
Another way to achieve more efficient energy transmission would be to adjust the radiant energy absorption of the substrate in a pre-determined wavelength range of the emitter instead of fine-tuning the emitter wavelength. For example, the substrate surface could be treated to absorb more energy in the pre-determined wavelength range of the emitter. One method of treatment for the substrate might be to sand or abrade the surface of the substrate. Another acceptable method for treating might be polishing the surface of the substrate. Or, a coating which has a high degree of radiant energy absorption in the pre-determined wavelength range could be applied to the substrate surface. The coating might be sacrificed during the heat treatment or it might be selected such that it could survive the heat treatment.
Device 700 comprises a base 726 which is shown with the shape of an irregular hexagon. Obviously, other shapes than an irregular hexagon could be used, as desired and/or necessary. Base cover 732 is mounted to the upper portion of base 726. Also mounted to base 726 are leg base mounts 712, 712′ and 712″. These leg base mounts provide the mounting means for the suction cup assemblies 701, 701′ and 701″. Heater mount 750 is mounted to the lower portion of base 726 by multiple dowels which are fixed to base 726 and slidably secured in heater mount 750. Three of these dowels 752, 754 and 756 are shown in
Each suction cup assembly comprises a large bellows-type pneumatic suction cup 703, 703′ and 703″ with a coaxial venturi 702, 702′ and 702″ mounted to the upper portion thereof. Venturi mount assemblies 708 [not shown in the drawings], 708′ and 708″ attach coaxial venturis 702, 702′ and 702″ to adjustment screws 704 [not shown in the drawings], 704′ and 704″. Elongated, threaded adjustment screws 704, 704′ and 704″ are loosely carried in a through-bore [not shown in the drawings] which runs vertically through adjustment screw mounts 710, 710′ and 710″.
Adjustment screw mounts 710, 710′ and 710″—as can be seen from
Adjustment screw mounts 710, 710′ and 710″ are attached to base 726 by leg base mounts 712, 712′ and 712″. The means attaching the adjustment screw mounts to the leg base mounts permits a coarse height adjustment of adjustment screw mounts 710, 710′ and 710″ with respect to the leg base mounts 712, 712′ and 712″ as will be further described below. Electrical connections 734 and 736 are provided to furnish power to device 700 to power the heating unit 600 as described below.
The device of the invention has a means to control the temperature of the substrate of interest in the area in the area immediately underneath the device. It is noted that the embodiments disclosed herein all use heating means to control the temperature of the local substrate area immediately beneath the device; however, it is recognized that some situations might call for a cooling means to control these temperatures.
The temperature control features of the instant invention involve the use of heating elements in thermal contact with the substrate of interest in the area directly underneath the device. The temperature control feature will be further discussed below. In addition, this embodiment requires compressed air to power the coaxial venturi assemblies 702, 702′ and 702″ in order to provide a vacuum in suction cup assemblies 701, 701′, 701′″.
The temperature control means for the substrate of interest is heating unit 600. This is shown in some detail in
A cross-section of heating unit 600 and hollow shell 601 is shown in
In
Generally horizontal rods 801, 801′ are movably mounted toleg base mounts 812, 812′. As shown by the arrows in
Although not shown in
Once the device 800 has been secured to substrate 810, heating means 900 can be adjusted as described above such that it is thermally sealed to substrate 810. This is achieved by moving heater mount 850 by means of hex adjustment screws 822, 822′ such that the attached heating means 900 is biased towards surface 810. The heating means 900 is lowered towards substrate 810 until flexible heat shields 951, 952, 953 and 954 [heat shield 954 is not shown in
No timer or control means is shown for device 700 or for device 800 but it is noted that the art is replete with such control means which are small enough to be mounted on either device 700 or device 800. Either an open loop or closed loop type of heater control means could be utilized to control heating means 600 or 900. It is also possible to simply use an external timer in conjunction with a power on/off switch to control the heat application based upon calibration testing for the particular substrate being treated.
The above-described embodiments are merely illustrative of the principles of the invention. Those skilled in the art may make various modifications and changes, which will embody the principles of the invention and fall within the spirit and scope thereof.
Obviously, this invention is primarily concerned with the treatment of 5XXX aluminum alloy structures. However, the equipment described above could be used to heat most any type of substrate where heat treatment was desired. For example, other metals could be treated; Gold [Au] or Silver [Ag] for example. Other metals and even non-metallic materials can also be treated with the processes and apparatus of the invention.
The above-described embodiments are merely illustrative of the principles of the invention. Those skilled in the art may make various modifications and changes, which will embody the principles of the invention and fall within the spirit and scope thereof.
This application claims the benefit of commonly owned U.S. Provisional patent application 62/418,150 filed on 4 Nov. 2016, and commonly owned U.S. Provisional patent application 62/451,662, filed on 28 Jan. 2017. This application is related to commonly owned U.S. Provisional patent application 62/360,372, filed 9 Jul. 2016. The heater support device of this invention is similar to the support device in commonly owned U.S. patent application Ser. No. 13/561,032, filed on 28 Jul. 2012. This application incorporates by reference the disclosure of the following commonly US patent applications: 62/418,150 filed on 4 Nov. 2016, 62/451,662, filed on 28 Jan. 2017, 62/360,372, filed on 9 Jul. 2016 and 13/561,032, filed on 28 Jul. 2012.
Not applicable.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/060073 | 11/6/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62418150 | Nov 2016 | US | |
| 62451662 | Jan 2017 | US |
