The present invention relates to an improved gas dynamic cold spray device, a system and method of coating by depositing wide variety of materials on substrates of different shapes and types. Here deposition takes place by means of solid particles impacting the metallic as well as non-metallic substrates at very high velocities that is accomplished via a supersonic jet of process/ carrier gas such as air or nitrogen or helium. This method is free from majority of disadvantages common to other metal deposition methods. This method also possesses a number of additional technological, economic, and ecological advantages such as reduced thermal energy input, ability to deposit free forms and options of portability, using clean air or nitrogen or helium as process gas unlike other combustible gases. This makes this method unique and more attractive for depositing wide spectrum of material on substrates. BACKGROUND OF THE INVENTION

Coatings are applied on substrate requiring a shiny or glossy appearance and protection from sunlight, corrosion and oxidation. Metallic or non- metallic coatings can be applied by using a spray, electrochemically, chemically or mechanically. These coatings modify the surface of the component and increase its lifetime in service. One of such coating technology is thermal spraying. In this family of techniques, coatings are obtained by spraying material in a molten or semi-molten condition. The starting feedstock coating material may be in the form of powder, rod, and wire. PRIOR ART

However, gas dynamic cold spray according to our invention is a thermal spraying process yielding thick coating owing majorly to the kinetic energy of the powders than the thermal energy. The thermal energy input to the powders in this technique is negligible. Solid metal powders are accelerated to very high velocities on to the surfaces of the substrate to be coated or repaired by a pressurized process/ carrier gas such as air or nitrogen or helium at a pressure in the range of 0.7 to 5 MPa and at gas temperatures ranging from 298 K to 1273 K. During the impact of the powder particles on the substrates they undergo severe plastic deformation and adhere to the surface, ensuring the effective coating.

The existing systems and methodologies adopted by prior art to obtain coatings of some of the materials mentioned in the present invention rely on attaining higher gas velocities or kinetic energies. This can be obtained by two ways 1 ) increasing the design mach number of the nozzle and 2) increase process gas pressure and process gas preheat temperatures for a given nozzle. By doing the above the power consumption, gas consumption, size and weight of the system becomes very high and result in the increase in overall cost and diluting the portability aspect of such a technique. Also, existing systems relay on additional accessories such as a powder preheater (electrical or electromagnetic) other than Gun, Gas Heater, Powder Feeder and nozzle to accomplish the above which will again add to the weight and size of the total system and increase overall cost. In this connection reference is made to the following prior art documents. EP2175050A1 , US200627687, US20070137560, WO05061 1 16A1 , G. Bae et al., Acta Materialia 60 (2012) 3524-3535. One of the prior art, IN198651 , discloses a device that does not claim the deposition spectrum claimed by the present invention especially deposition of refractory materials (Ta,Ti, Nb and their alloys) and especially materials that have a strong temperature sensitivity to flow stress such as Ni, Ni-Cr, Inconel, Cu and Steel to name a few. The present invention is capable of depositing all the above materials.

As per prior art US20070137560, a separate powder preheating device is claimed by virtue of which powders are preheated prior to entry in to the nozzle. The prior art explains how deposition of materials such as Ni, WC- Co can be enhanced by using such preheating devices. However, in addition to the fact that this prior art adds a separate device to the list of accessories, the probability of heating the powders for long enough time to promote grain growth, decarburization, crystallization and oxidation is increased. Another disadvantage is the increase in power consumption in comparison to normal cold spray process. The process described is more warm spray than cold spray. In the present invention, no additional heating set up is required in this invention and materials that have temperature sensitivity to flow stress and critical velocity can be deposited at an overall lower power and gas consumption.

As per one of the prior art, Fukanuma et al (EP2175050A1 ) intended to deposit materials by having a preheating zone (50 mm- 1000 mm) before the convergent portion of the nozzle. The objective was to preheat the gas-powder mixture and increase the deformability of the powder particles and deposit thicker coatings at higher efficiencies. However, it also utilizes a separate heater(s) to heat the preheat zone which is 50 mm to 1000 mm long based on several factors such as length of preheat zone, gas type, gas density, raw material chemistry, raw material shape and size, nozzle material type and wall thickness. All the above factors not only increase the number of accessories/spares but also increases the total energy consumption in the coating process and for longer preheat zones it is akin to having a separate powder preheater. Addressing this issue, no additional heating set up is required in this invention and materials that have temperature sensitivity to flow stress and critical velocity can be deposited at an overall lower power and gas consumption.

Another prior art US7244466, discloses a nozzle design that incorporates biconical flow regulator or concentrator to produce coating of fine dimensions or spot size. The above invention also uses two types of flow regulators to adjust the dimensions of coating obtained thereof. The present invention performs the same at a lower energy input without using complicated flow regulators that call for additional fabrication steps and adds cost to the entire system.

Hence, a state of the art improved gas dynamic cold spray device and method of coating by depositing a wide variety of materials on substrates of different shapes which is devoid of the above drawbacks. We change the configuration of the gas and powder delivery system to tailor the particle velocity, particle temperature and dispersion to cater to various material requirements. We obtain this at lower power and gas consumption and improved deposition efficiency that has resulted in successful deposition of not only the regular materials such as Cu, Cu Alloys, Sn, Sn Alloys, Ag, Ag Alloys, Zn, Zn Alloys but also deposition of difficult to coat materials such as Ta, Ta Alloys, Nb, Nb Alloys, Ti, Ti Alloys, Ni, Ni-Cr, Ni super alloys, Stainless Steels, Powder Blends, Nano structured Agglomerated powders, High Entropy Alloys, bio glasses, metal matrix composite powders (with ceramic reinforcements) at much lower input energy than currently being used by other systems. The details are disclosed in the detailed description of the present invention.

OBJECTIVES OF THE PRESENT INVENTION

The main objective of the present invention is to provide an improved gas dynamic cold spray device with an enhanced ability to deposit better coatings of materials such as Ta, Ta Alloys, Nb, Nb Alloys, Ti, Ti Alloys, Ni, Ni-Cr, Ni super alloys, Stainless Steels, Powder Blends, Nano structured Agglomerated powders, High Entropy Alloys, bio glasses, metal matrix composite powders (with ceramic reinforcements) other than the regular materials such as Cu, Cu Alloys, Sn, Sn Alloys, Ag, Ag Alloys, Zn, Zn Alloys at lower input power and gas consumption. The additional list of materials is useful in various engineering and non-engineering applications. Another objective of the invention is to provide a device and a methodology that is capable of depositing phase pure coatings with high electrical and thermal conductivities for application in electrical industry.

Another objective of the invention is to provide a device and a methodology that is capable of depositing phase pure coatings with excellent resistance to cavitation corrosion damage.

Another objective of the invention is to provide a device and a methodology that is capable of depositing metallic coating on boiler tubes for high temperature electrical conductivity, oxidation resistance and thermal cycling resistance.

Another objective of the invention is to provide a device and a methodology that is capable of depositing metallic coating on non-metallic substrates for power electronics applications.

Another objective of the invention is to provide a device and a methodology that is capable of depositing metallic/alloy/cermet coatings on electrical bus bars for joining purpose.

Another objective of the invention is to provide a device and a methodology capable of depositing corrosion resistant coatings for sacrificial protection/barrier protection and anodic protection. Another objective of the proposed invention is to provide a device and a methodology capable of depositing refractory metals for high temperature applications (oxidation and corrosion resistance), bio-medical applications, superconductivity applications, for sputter target repair, high temperature wear resistant applications. Another objective is to provide a device and a methodology to deposit nanostructured agglomerated powders and blends for high conductivity and wear resistant applications, bulk metallic glasses for erosion corrosion resistant applications, high entropy alloys for high temperature applications and bio-glass for biomedical applications.

Another objective of the present invention is to provide a device and a methodology to obtain very thick coatings or free forms or free-standing coatings akin to additive manufacturing.

All the above objectives are achieved by providing a system as explained in details in the forthcoming paragraphs.

SUMMARY

An improved gas dynamic cold spray device that can deposit a wide variety of materials viz., Cu, Cu Alloys, Sn, Sn Alloys, Ag, Ag Alloys, Zn, Zn Alloys, Stainless Steels, Ni, Ni-Cr, other Ni super alloys, Ta, Ta Alloys, Nb, Nb Alloys, Ti, Ti Alloys, Powder Blends, Nano structured Agglomerated powders, High Entropy Alloys, Bulk Metallic Glasses, bio glass, metal matrix composite powders (with ceramic reinforcements) for a wide range of applications at lower overall power and gas consumption. The process and carrier gas used for all the above is compressed air. Other gases like helium and nitrogen can also be used if the application demands. In addition to depositing metallic powders on metallic objects, the device can deposit metallic powder on non-metallic objects as well. Very thick free standing coatings or free forms of one or many of the above mentioned materials can also be accomplished by the present invention. This improved version also includes improved air tight gun design, improved nozzle designs (and nozzle material), improved powder delivery system with an option of depositing material at different deposition rates without compromising the deposition efficiency. Improved design of the device also permits coating deposition on non - flat objects, inaccessible areas useful in real application. The process control side is also equipped with automatic temperature controller, powder feeding by making use of the state of the art electronics. The device is portable and can be carried to outdoor sites for onsite application of coatings.

According to the invention there is provided an improved gas dynamic cold spray device system for coating materials to be deposited on the substrates comprising of three major components viz. a) a control panel (1 ), b) a spray gun (2) and c) a powder feeder (3).

The control panel (1 ), is an automated one provided with automatic heating and powder feed controls using PLC control panel. It is connected to i) a pneumatic flexible hose (5) for providing compressed carrier/ process gas supply (4); ii) other pneumatic flexible hoses (6 and 7) are connected to the spray gun (2) and powder feeder (3) respectively; iii) electric cable (12, 13, and 8) for powering gas heater (1 1 ), powder feeder (3); and thermocouple (14) of the spray gun (2) respectively.

The spray gun (2) houses a nozzle (9) which is of converging and diverging type by virtue of which supersonic velocities are realized. It is connected to i) pneumatic flexible hoses (6) coming from the control panel (1 ); ii) powder feeding tube (15) to which pneumatic flexible hose (7a) carrying powder and carrier gas coming from the powder feeder (3) is merged; iii) thermocouple (14) that is electrically connected to the control panel (1 ) by means of electric cable (8) and iv) gas heater (1 1 ) of the spray gun (2) to which electric cable (12) coming from the control panel (1 ) is connected; and

The powder feeder (3) is connected to i) control panel (1 ) by means of pneumatic flexible hose (7) that carries the carrier gas from the control panel (1 ); ii) pneumatic flexible hose (7a) containing carrier gas and powder which merges with powder feeding tube (15) of the spray gun (2); iii) the electric cable (13), connected to the control panel (1 ); and iv) a variable speed motor with light weight "motor-gear box assembly" drives a rotating drum which is a shaft with conical grooves on the surface that delivers the powder.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention should become apparent from the following description of the preferred process, and read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

Figure 1 : Schematic of the system in block diagram

Figure 2: Sketch of the improved spray gun Figure 3: Sketch of the improved nozzle-1

Figure 4: Sketch of the improved nozzle-2

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, there is provided an improved gas dynamic cold spray device, a system and method of coating on substrates by depositing with wide variety of materials viz., Cu, Cu Alloys, Sn, Sn Alloys, Ag, Ag Alloys, Zn, Zn Alloys, Stainless Steels, Ni, Ni-Cr, other Ni super alloys, Ta, Ta Alloys, Nb, Nb Alloys, Ti, Ti Alloys, Powder Blends, Nano structured Agglomerated powders, High Entropy Alloys, bio glass, metal matrix composite powders (with ceramic reinforcements) for a wide range of applications at an overall lower power and gas consumption by choosing the appropriate combination of nozzle dimensions. Here deposition takes place by means of solid particles impacting the metallic as well as non-metallic substrates at very high velocities that is accomplished via a supersonic jet of process/ carrier gas and process gas as compressed air. Nitrogen or helium can also be used based on the requirement with the present system. In addition to coating on the substrates it is also used for repairing the damaged parts. Referring to the schematic Figure.1 , the system has three major components. They are the control panel (1 ), spray gun (2) and the Powder feeder (3). The automated control panel (1 ) with automatic heating and powder feed controls is using PLC control panel. Further, the control panel is portable and built to withstand usual loads on the shop floor or onsite. The control panel is connected to the incoming compressed carrier gas (4) selected from air, Nitrogen or Helium, preferably air supply through the pneumatic flexible hose (5) through which process/ carrier gas enters the control panel. Further two more pneumatic flexible hoses (6,7) are also connected to the control panel (1 ). Out of which one pneumatic flexible hose (6) is connected to the improved spray gun (2) for feeding the process to the spray gun (2). The other pneumatic flexible hose (7) connected to the improved powder feeder (3) is used for supplying carrier gas from the control panel (1 ) to the powder feeder (3). Then the pneumatic flexible hose (7a) which carries carrier gas and the powder that is coming out of the powder feeder (3) is connected to the spray gun (2) after merging with the feeder tube (15) near to the process gas entry coming through the pneumatic flexible tube (6).

The control panel (1 ) is also connected to the improved spray gun (2) by a thermocouple (14) by way of cable (8). In addition, the control panel (1 ) is connected to the spray gun electrically by means of cable (12) to power the gas heater (1 1 ) in the spray gun (2). An improved spray gun is shown in Figure 2, which effectively heats the process gas and increases the longevity of heating element by using a copper check nut and seals and/or gaskets (16) and a higher wall thickness (17) at the rear end compared to the front end. This in turn ensures minimal damage to the gun during maintenance and aids in efficient sealing of the gun in addition to increasing the efficiency of heat transfer and increased life of spray gun by minimizing wear of gun inner walls by way of their sacrificial nature. These seals are made of flouro polymer based materials such as but not limited to Teflon and Viton. This feature is critical because the spray gun (2) houses the gas heater (1 1 ). Additionally, the spray gun housing can accommodate heaters with varying wattage without changing the basic design. This will further result in capability to reach increased gas preheat temperatures thereby resulting in higher gas velocities and in turn resulting in higher particle velocities and thereby resulting in wider deposition spectrum and better coating quality. The spray gun is portable and light weight and robust. This further helps during the operation, handling and maintenance. The spray gun is also provided with an optional switch (10) to control power supply to the powder feeder (3) especially while it is being operated manually. This makes the device portable and capable of depositing all the materials mentioned in the present invention at lower overall power and gas consumption on site.

The spray gun (2) further is connected to pneumatic hoses (6, 7), Powder feeding tube (15), thermocouple (14) and improved nozzle(s) (9). The control panel (1 ) automatically controls current input to the gas heater (1 1 ) within the improved spray gun (2) based on the temperature desired as soon as the gas pressure reaches beyond a set initial pressure. In the case of fall in gas pressure to a value lower than set initial pressure the control panel shuts off current supply to heater to avoid damage to the heater.

The powder feeder (3) is shown in Figure 1 . It consists of a variable speed motor with light weight "motor-gear box assembly" that drives a rotating drum which is a shaft with conical grooves on the surface. The dimensions of these grooves are modified to accommodate more powder and deliver efficiently. Powder feeder (3) also has an improved lightweight and efficient "motor-gear box-assembly" enabling upgrading the ratings of the motor-gear box assembly if required." It can be made of light weight material like aluminium. The control panel (1 ) and powder feeder (3) are connected with pneumatic flexible hose (7) and electrical cable (13). The powder feeder (3) is prompted to be switched ON by the control panel (1 ) as soon as the process gas temperature rises to the desired value fed to the control panel (1 ) by passage of current through the gas heater (1 1 ) provided in the spray gun (2).

The pneumatic hose carrying powder and carrier/ process gas (7a) from the powder feeder (3) merges with powder feeding tube (15) prior to entering in the spray gun (2). Process gas line (6) is connected to the spray gun (2) as shown in Figure 2. The spray gun (2) also houses a nozzle (9) by virtue of which supersonic velocities are realized. The basic design of the nozzle is converging diverging type. The sketches of two nozzles are shown in Figure 3 and 4. The nozzles have a converging portion (20,25), a throat portion (22,27) and diverging portion (21 ,26) and inner (19, 24) and outer walls (18, 23). Improved nozzle in Figure 3 in the present invention is capable of depositing coatings at (i) varying deposition rates (50-500 μιτι/s) (ii) varying spot width or diameter (0.9- 4 mm) (iii) varying spot length or diameter (0.9-12 mm) without compromising the deposition efficiency of the process and without use of any mask or stencil or any additional flow regulators inside the nozzle. Areas requiring thick coatings as in repair applications and areas requiring controlled deposition rates as in electrical and electronic applications can be deposited with equal ease. Improved nozzles in the present invention are power efficient as they dictate the flow and the power requirements to achieve the desired process parameters and hence for different deposition rates and deposition area similar coatings can be obtained at optimal power and gas consumption. This is achieved by reducing or increasing the throat (0.2 mm ² to 16 mm ² ) and exit areas (0.6 mm ² to 50 mm ² ) by maintaining a constant exit to throat area ratio or constant mach number or varying them. The mach number can be selected from 2 to 3.5, if required. Based on the actual requirement the throat and exit areas are tailored to yield the best coatings at the optimal power and gas consumption. Another example of the improved nozzle is shown in Figure 4. The present invention enables successful deposition of materials that have a strong temperature dependence of critical velocity and/or flow stress (Ni, Ni-Cr,IN625 and Cu etc.,) and obviate the need for powder preheater(s) and/or higher gas pressures and gas preheat temperature or monatomic gases such as helium. This is achieved by extending the length of the convergent portion (cylindrical extension if required) with respect to the diverging portion of the nozzle. It can be seen that length of the convergent portion is different for the nozzle given in the Figure 3 and Figure 4.The divergent portion length also can be varied if required. While the current device deposits these materials without powder preheating, a powder preheater can be used with the current device, if required. The present invention also includes a gas-powder mixing chamber before the converging portion of the nozzle. Additionally, by changing the location of powder injection along the nozzle, particle velocity, particle temperature, particle spread can be controlled to yield the best coatings at optimal power and air consumption. The current invention can utilize one or more or all of the above modifications depending on the application requirements.

EXAMPLE 1

Deposition of highly electrically conductive coatings

Highly electrically conductive coatings of silver, copper and tin and composites (CU-AI2O3 or Cu-ZrO2 or Cu-SiC) were applied on metal substrates using the improved gas dynamic cold spray device to demonstrate the efficacy of our system of the instant invention. The metal substrates chosen in this experiment were stainless steel and aluminium as examples and nonmetallic substrates such as ceramics (AI2O3 as an example) and polymers or layered composites can also be chosen to deposit the above mentioned coatings with high electrical conductivity. Water atomized silver powder, spherical tin powder, agglomerated nano Cu-1 % AI2O3 in the size range of 10-45 μιη was used as the feedstock powder in each case. The powders had purity close to 99.9%. Stainless steel, aluminium, copper and AI ₂ O ₃ substrates were grit blasted to induce surface roughness to enable coating deposition. Alumina grit in the size cut of 240 μιη was employed at a pressure of 2.5 bar to blast stainless steel whereas a pressure of 1 .5 bar was used to blast aluminium and copper substrates. AI2O3 substrates was grit blasted using micro blasting technique with much finer grit size in the range of 50-60 μιη. Post grit blasting the substrates were cleaned thoroughly in an ultrasonic cleaner in acetone medium. The substrates were fixed firmly in a vice. The powder feeder (3) was filled with feedstock powder. The standoff distance between nozzle and the substrate surface was fixed at 15 mm. A nozzle (9) with circular inlet, square throat and rectangular exit was employed in this example. Coating process parameters employed were 8 bar, 100°C for tin and 20 bar, 450°C for silver, Cu-AI ₂ O ₃ .A total of two passes for silver, 4 passes for Cu- AI2O3 and single pass for tin was used to generate coating of desired thickness and conductivity. A coating thickness of around ~ 500 μιη was obtained in case of silver at a powder feed rate of 34 g/min and a coating thickness of- 100 μιη was obtained in case of tin at a feed rate of 12 g/min. The robot raster speed was 10 mm/s for silver coating and 30 mm/s for tin coating. Since both the coatings were meant for different applications the thickness desired per pass was different and hence the difference in coating built up per pass. In case of Cu- AI2O3 the coating thickness developed was 750-800 μιη and the feed rate was maintained at 10 g/min and similar standoff distance and robot speeds were used as in case of silver and tin. The copper coating on Alumina AI2O3 was performed at 10 bar 400°C and standoff distance, robot raster speed was maintained similar to silver and tin coatings. The electrical conductivity of close to -75-85% of bulk silver was obtained (i.e., 46-51 MS/m) and nearly 90% of bulk tin (8-8.2 MS/m) in tin coatings was obtained. The silver coating and tin coating are potential candidates in power and electrical industries respectively. The electrical conductivity of nano Cu-AI ₂ O ₃ coatings was around 28-32 MS/m and hardness was around 1 .9-2.1 GPa which qualifies it as spot welding electrode material by virtue of favorable combination of electrical conductivity and hardness.

The copper coating obtained on Alumina exhibited electrical conductivity in the range of 25-35 MS/m and the dense coating finds use in power electronics application as an electrically and thermally conductive coating on insulating ceramics.

The electrical conductivity was measured using an eddy current probe (FOERSTER, USA). EXAMPLE 2

Development of coatings of materials with high temperature

sensitivity to flow stress and critical velocity

Under cold spray conditions, coating deposition takes place based on the critical velocity of the powder being sprayed. Beyond the critical velocity, at localized interfacial zones, the material strength breaks down and there is a drastic jump in strain and localized temperature leading to bonding between particles and substrate. The governing constitutive equation called Johnson-Cook lasticity model is written as follows where

STRAIN AND STRAIN RATE TEMPERATURE

Where σ is flow stress, A is yield stress in quasi static tension or compression, B is Strain hardening parameter, C is strain rate hardening parameter, n is strain hardening exponent and m- thermal softening exponent.

TABLE-1

value of copper - 1 .09

value of Nickel - 1 .44

value of IN625 - 1 .90

Utilizing the concept above, improved nozzle (9) shown in fig.4. was utilized and coatings were performed as per the parameters given in table.1 . along with the thickness built up.

In cold spray, the main process parameters are the gas pressure and gas temperature which will ultimately decide the resultant gas and particle velocity for a given gas, particle combination. However, careful design and selection of nozzle can result in reducing the overall energy consumption by reducing the overall gas consumption (reduced gas pressure or reduced gas flow rates) and power consumption (necessary to heat the gas to a desired temperature). In the present example, in comparison to the prior art, the product of "P ^* T" (gas pressure and gas temperature) is much lower to obtain the similar range of coating thicknesses. If the product of P and T in the present case is assumed as "1 ", the ratio (P ^* T) _prior an / (P ^* T) _pre sent invention will always be greater than "1 ". This substantiates that the present invention utilizes lower energy to deposit the same materials in the similar thickness range.

EXAMPLE 3 Development of refractory metal coatings

In the present example, development of coatings of refractory metals viz., tantalum, titanium and niobium are disclosed. All the above metals and their alloys are refractory (high melting point) in nature and find applications in high temperature applications. Highly dense coatings were obtained at a process parameter combination of 2 MPa or 20 bar and 450°C for all the materials using air as the process and process/ carrier gas. The starting feedstock used in all the above powders was in the size range of 10-45 μιη. Tantalum powder used was chemically derived, titanium and niobium were crushed powders. The thickness deposited per pass was around 200-300 μιη for Ta and Nb whereas it was around 500- 600 μιη in case of titanium. The porosity in the coatings was under 0.8% in case of Ta and Nb and around 3-5% in titanium (which is beneficial from the point of view of biomedical applications).

Tantalum and niobium can be used for high temperature applications and also to repair sputter targets in PVD industry. Titanium on the other hand has huge potential in biomedical applications and aerospace applications. Conclusion:

Similarly, we can deposit solid powder materials like Cu, Cu Alloys, Sn, Sn Alloys, Ag, Ag Alloys, Zn, Zn Alloys, Stainless Steels, Ni, Ni-Cr, other Ni super alloys, Ta, Ta Alloys, Nb, Nb Alloys, Ti, Ti Alloys, Powder Blends, Nano structured Agglomerated powders, High Entropy Alloys, Bulk Metallic Glasses, bio glass, metal matrix composite powders can be applied on metallic/ nonmetallic substrates at an overall optimal power and gas consumption by using the appropriate combination of throat and exit area and divergent and convergent length and without the use of any mask or stencil or any other flow regulator(s) inside the nozzle and without the use of powder preheater(s) and without resorting to higher pressures and temperatures.

We have brought out the novel features of the invention by explaining some of the preferred embodiments under the invention, enabling those skilled in the art to understand and visualize our invention. It is also to be understood that the invention is not limited in its application to the details set forth in the above description. Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, various modifications can be made without departing from the spirit and scope of the invention as described herein above and as defined in the following claims.