阅读说明：本技术 一种提高气凝胶隔热材料卷材干燥效率的工艺方法 (Process method for improving drying efficiency of aerogel heat-insulating material coiled material ) 是由 王立东 沈亚东 许剑 杨铭 郑张宜 路爱梅 孙立君 于 2021-06-24 设计创作，主要内容包括：本发明属于气凝胶制备技术领域,具体涉及一种提高气凝胶隔热材料卷材干燥效率的方法,所述工艺方法包括下列步骤：将溶胶与纤维毡通过浸胶进行复合、收卷,所述收卷过程中,向所述复合纤维毡层间加入隔离层板,或者将所述纤维毡与所述隔离层板贴合、收卷、浸胶获得含隔离层板纤维毡；将所述含隔离层板纤维毡后沿卷绕方向收紧,制得毡卷；将所述毡卷进行凝胶、干燥,制得气凝胶隔热材料。通过隔离层板的导热性进行对卷好的气凝胶隔热材料进行干燥,干燥时由于隔离层板的良好的热传导性质能够快速将热量传导到毡卷的内部层间,而且松卷工艺产生的层间间隙增加了干燥介质的热对流效果,能够有效地提高了气凝胶隔热材料卷制品的生产干燥效率。(The invention belongs to the technical field of aerogel preparation, and particularly relates to a method for improving the drying efficiency of an aerogel heat-insulating material coiled material, which comprises the following steps: compounding and rolling the sol and the fiber felt through gum dipping, wherein in the rolling process, an isolation layer plate is added between the layers of the composite fiber felt, or the fiber felt and the isolation layer plate are attached, rolled and gum dipped to obtain the fiber felt containing the isolation layer plate; tightening the fiber felt containing the isolation laminate along the winding direction to prepare a felt roll; and gelling and drying the felt roll to obtain the aerogel heat insulation material. The thermal conductivity through the isolation plywood carries out the aerogel thermal insulation material that rolls up to be dry, because the good heat-conducting property of isolation plywood can be fast with heat conduction between the inside layer of felt book during the drying, the interlaminar clearance that the process of unreeling produced has increased the thermal convection effect of dry medium moreover, can improve the production drying efficiency of aerogel thermal insulation material book product effectively.)

1. A process for increasing the drying efficiency of a roll of aerogel insulation material, the process comprising:

compounding sol and a fibrofelt by gum dipping, and then rolling, wherein in the rolling process, an isolation laminate is added between the composite fibrofelt layers, or the fibrofelt is firstly attached to the isolation laminate and then rolled and gum dipped to obtain a fibrofelt containing the isolation laminate;

the fiber felt containing the isolation laminate is tightened along the winding direction to prepare a felt roll,

carrying out gel on the felt roll, loosening the felt roll, and reserving a gap to obtain a loosened felt roll;

and drying the felt roll after the felt roll is unwound to obtain the aerogel heat insulation material.

2. The process of improving the drying efficiency of aerogel insulation blanket rolls of claim 1, wherein the fiber material of the fiber blanket is a mixed fiber of any two or more of alkali-free fibers, aluminum silicate fibers, rock wool, high silica fibers, quartz fibers, mullite fibers, and alumina fibers.

3. The process method for improving the drying efficiency of the aerogel thermal insulation material roll according to claim 1, wherein the thickness of the fiber felt layer is 2-30 mm.

4. The process of improving the drying efficiency of a roll of aerogel insulation material as claimed in claim 1, wherein the rolling comprises fixing an end of the blanket of insulation-containing blanket fibers to a mandrel and then tightening in the direction of the rolling.

5. The process method for improving the drying efficiency of the aerogel thermal insulation material coil is characterized in that the drying method comprises any one or more of alcohol supercritical drying, carbon dioxide supercritical drying and atmospheric drying.

6. The process for improving the drying efficiency of an aerogel thermal insulation material coil according to claim 1, wherein the insulation layer plate is made of stainless steel or titanium alloy.

7. The process method for improving the drying efficiency of the aerogel thermal insulation material coiled material is characterized in that the insulation layer plate is any one of a plate with the thickness of 0.1-0.3 mm, a hole plate and a net with the thickness of 0.5-3 mm.

8. The process of improving the drying efficiency of aerogel insulation coil as claimed in claim 1, wherein the container used for drying comprises a perforated plate or fence structure, and the material of the container is stainless steel or titanium alloy.

9. The process of increasing the drying efficiency of a roll of aerogel insulation material as claimed in claim 1, wherein the unrolling process comprises securing the container and rotating the mandrel in a reverse direction of the unrolling.

10. A process for improving the drying efficiency of a web of aerogel insulation material as claimed in claim 1, wherein the method of unrolling comprises fixing a mandrel and rotating the container in a reverse direction of the unrolling direction.

Technical Field

The invention belongs to the technical field of aerogel preparation, and particularly relates to a method for improving drying efficiency of an aerogel heat-insulating material coiled material.

Background

The aerogel is a nano porous light material and has excellent heat insulation performance. Compared with the traditional heat-insulating material, the aerogel heat-insulating material has the characteristics of small density, low heat conductivity coefficient, good heat resistance and flame retardance, good hydrophobic property, long service life, convenience in construction and maintenance and the like. The preparation process flow of the aerogel heat insulation material comprises the following steps: firstly preparing sol, then compounding the sol and a fiber felt layer, then gelling, and finally drying to obtain the composite material. With the increasing use of aerogel insulation, the roll product has become the first choice of production process due to the small space occupation and high productivity when drying. However, when the rolled products are produced, the layers behind the gel are tightly combined, and heat and air flow are difficult to reach the inside of the felt roll during drying, so that the drying time is long, the drying efficiency is low, and the aerogel heat insulation material is inconvenient to dry.

Therefore, a process method for improving the drying efficiency of the aerogel thermal insulation material coiled material is urgently needed.

Disclosure of Invention

The application provides a method for improving drying efficiency of aerogel thermal insulation material coiled materials, and aims to solve the technical problem of low drying efficiency caused by tight combination of gel rear layers of aerogel products.

The embodiment of the application provides a process method for improving drying efficiency of aerogel thermal insulation material coiled materials, and the method comprises the following steps:

compounding sol and a fibrofelt by gum dipping, and then rolling, wherein in the rolling process, an isolation laminate is added between the composite fibrofelt layers, or the fibrofelt is firstly attached to the isolation laminate and then rolled and gum dipped to obtain a fibrofelt containing the isolation laminate;

the fiber felt containing the isolation laminate is tightened along the winding direction to prepare a felt roll,

carrying out gel on the felt roll, loosening the felt roll, and reserving a gap to obtain a loosened felt roll;

and drying the felt roll after the felt roll is unwound to obtain the aerogel heat insulation material.

Optionally, the fiber material of the fiber felt layer is a mixed fiber of any two or more of alkali-free fiber, aluminum silicate fiber, rock wool, high silica fiber, quartz fiber, mullite fiber and alumina fiber.

Optionally, the thickness of the fiber felt layer is 2-30 mm.

Optionally, the rolling includes fixing one end of the fiber mat containing the insulation laminate on the mandrel, and then tightening in the winding direction.

Optionally, the drying method includes one or more of alcohol supercritical drying, carbon dioxide supercritical drying and normal pressure drying.

Optionally, the isolation layer plate is made of stainless steel or titanium alloy.

Optionally, the isolation layer plate is any one of a plate with the thickness of 0.1-0.3 mm, a pore plate and a net with the thickness of 0.5-3 mm.

Optionally, the container for drying comprises a perforated plate-like or fence-like structure, and the material of the container is stainless steel or titanium alloy.

Optionally, the method of unrolling comprises fixing the container and rotating the mandrel in a reverse rolling direction.

Optionally, the method of unrolling comprises fixing the mandrel and rotating the container in a reverse rolling direction.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

according to the process method for improving the drying efficiency of the aerogel heat-insulating material coiled material, provided by the embodiment of the invention, the insulation layer plate is added when the aerogel heat-insulating material is prepared, the coiled aerogel heat-insulating material is dried through the heat conductivity of the insulation layer plate, and the good heat conduction property of the insulation layer plate can quickly conduct heat to the inner layers of the felt coil during drying, so that the production drying efficiency of aerogel heat-insulating material coiled products can be effectively improved, the drying efficiency is more than 4 times of the conventional drying efficiency, the space and the energy consumption are saved, and the production cost is reduced. In addition, due to the existence of the isolation layer plate, the interlayer adhesion of the felt roll is effectively avoided, the surface flatness of the product is improved, and the apparent quality of the product is improved.

The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a schematic view of an aerogel insulation material after rolling in accordance with an embodiment of the present invention;

FIG. 2 is a schematic view of an aerogel insulation having voids after unrolling in an embodiment of the present invention;

FIG. 3 is a schematic flow chart of a process for increasing the drying efficiency of a web of aerogel insulation material as provided in an embodiment of the present application.

In the figure: 1. a fiber felt layer, 2, an isolation layer plate, 3, a shaft core, 4 and a container.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In order to solve the technical problems, the general idea of the embodiment of the application is as follows:

in an embodiment of the present application, a process for increasing the drying efficiency of a web of aerogel insulation material, as shown in FIG. 3, comprises:

s1, compounding sol and a fiber felt through gum dipping, and then rolling, wherein in the rolling process, an isolation layer plate is added between layers of the composite fiber felt, or the fiber felt is firstly attached to the isolation layer plate and then rolled and gum dipped to obtain the fiber felt containing the isolation layer plate;

s2, tightening the fiber felt containing the isolation laminate along the winding direction to prepare a felt roll,

s3, carrying out gel on the felt roll, loosening the felt roll, and reserving a gap to obtain a loosened felt roll;

and S4, drying the felt roll after the felt roll is loosened to obtain the aerogel heat insulation material.

In the embodiment of the application, when the rolled product of the traditional aerogel material is produced, the interlayer is tightly combined after the gel, and the felt roll is loosened to leave a gap, so that the interlayer bonding of the felt roll is avoided, and the product drying efficiency is improved.

In the embodiment of the application, the isolation layer plate is added during compounding of the felt rolls, and the separation of the gel roll layers along the isolation layer plate is realized by a reverse roll loosening method after gelation, so that the interlayer gap is generated, heat and air flow can reach the space between the felt rolls during drying, meanwhile, the interlayer gap increases the heat convection effect of a drying medium, and the drying efficiency is improved.

As an alternative embodiment, the aerogel thermal insulation material includes any one of silicon-based, aluminum-based, zirconium-based, and other metal oxide-based materials.

In the embodiment of the application, the aerogel thermal insulation material is wide in material selection, and any material can be suitable for the drying method provided by the invention and can achieve the purpose of improving the drying efficiency.

In an optional embodiment, the fiber material of the fiber felt layer is a mixed fiber of any two or more of alkali-free fibers, aluminum silicate fibers, rock wool, high silica fibers, quartz fibers, mullite fibers and alumina fibers, and the thickness of the fiber felt layer is 2-30 mm.

In the embodiment of the application, the fiber felt layer has wide source and wide application range, and the reason why the thickness of the fiber felt layer is 2-30 mm is as follows: at present, the common thickness range has the following adverse effects: after the thickness exceeds 30mm, the felt roll has larger folds due to the larger size difference of the upper surface and the lower surface of each layer; or too small a respective adverse effect is: the thickness is too small, the stretching resistance is small, the coil is easy to break and the deformation is large.

In an alternative embodiment, the rolling comprises fixing one end of the fiber felt containing the insulation laminate on a mandrel, and then tightening in the winding direction to obtain the felt roll.

In the embodiment of the application, the sequence of gum dipping and winding of the raw materials is not limited, and the purpose of improving the drying efficiency can be realized as long as the isolation layer plate is added and/or the gap is reserved by loosening.

As an alternative embodiment, the drying method includes any one or more of alcohol supercritical drying, carbon dioxide supercritical drying and atmospheric drying.

In the embodiment of the application, according to the fibre felt layer the difference of the kind of sol material aerogel material, can select arbitrary one of alcohols supercritical drying, carbon dioxide supercritical drying and the dry arbitrary one of ordinary pressure as required, the fibre material is little with the drying method relation, and every material is all applicable to arbitrary one drying method.

In an alternative embodiment, the material of the insulating laminate is stainless steel or titanium alloy.

As an optional implementation mode, the thickness of the isolating layer is any one of a plate with the thickness of 0.1-0.3 mm, a pore plate and a net with the thickness of 0.5-3 mm.

In the embodiment of the application, the metal material has excellent heat-conducting property, the stainless steel material is selected to have heat-conducting property and wear-resisting property, the surface of the metal material is smooth, the felt roll is loosened along the smooth direction of the surface, the interlayer bonding of the felt roll can be effectively avoided, and the flatness of the surface of a product is improved. The thickness of the isolation layer plate or the pore plate is 0.1-0.3 mm, the thickness of the net is 0.5-3 mm, and the reason is that: the process adaptability, the adverse effect of the overlarge value is as follows: the thickness is increased, the rigidity is increased, the winding is difficult, and the material cost and the heat consumption cost are increased; or too small a respective adverse effect is: the thickness is too small, the rigidity is reduced, the isolating layer is easy to wrinkle, and the thinner the stainless steel foil is, the higher the material cost is; any one of the selection plate, the pore plate and the net is favorable for heat dissipation and convection with air, so that the heat convection effect of the drying medium is increased, and the drying efficiency is improved.

As an alternative embodiment, the container used for drying comprises a perforated plate-like or fence-like structure, and the material of the container is stainless steel or titanium alloy.

In the embodiment of the application, the dry container comprises a plate-shaped or fence-shaped structure with holes, so that heat dissipation and convection with air are facilitated, the heat convection effect of the drying medium is increased, and the drying efficiency is improved.

In the embodiment of the application, stainless steel or titanium alloy has excellent heat conductivity, and stainless steel materials are selected to have heat conductivity and corrosion resistance. The stainless steel or titanium alloy, including but not limited to stainless steel or titanium alloy, can be used as long as it has excellent thermal conductivity and certain corrosion resistance to resist the erosion of the sol. In addition, for the alcohol supercritical drying process, the alcohol supercritical fluid with the temperature of more than 260 ℃ has strong etching on metals, low-melting-point nonferrous metals such as aluminum, magnesium, copper and the like are found to be easy to corrode at present, and the corrosion on the surfaces of common steel and iron is serious, so that the materials mainly used at present are stainless steel and titanium alloy.

In an alternative embodiment, the method of unrolling comprises holding the container, rotating the mandrel in a reverse rolling direction;

in an alternative embodiment, the method of unrolling comprises fixing the mandrel and rotating the container in a reverse rolling direction.

In the embodiment of the application, the mode of unwinding is not limited, the method of unwinding can directly rotate the shaft core or the container in the opposite direction, and only the mode of leaving a gap between felt rolls can achieve the aim of the invention.

The following describes a process method for improving the drying efficiency of an aerogel thermal insulation material coil in detail by combining examples, comparative examples and experimental data.

Example 1

The method comprises the steps of adopting a mode of dipping firstly and then rolling, compounding silica sol with alkali-free fiber felts with the thickness of 12mm and the length of 15m in a spraying mode, adding a stainless steel pore plate with the thickness of 0.25mm between fiber felt layers as an isolation layer plate during rolling, fixing the fiber felts and the end of the stainless steel isolation layer plate on a mandrel simultaneously, and then tightening a felt roll along the rolling direction. After the silica sol gel in the fiber pores, the felt rolls were placed in a dry stock cage. Then fixing a drying cage, and rotating the mandrel along the winding reverse direction to separate the jelly roll layers along the stainless steel isolation layer plate so as to generate an interlayer gap. And hoisting the dried material into an ethanol supercritical drying kettle in a cage manner, raising the temperature and the pressure to 260 ℃ and 6.5MPa, preserving heat and pressure for 60min to obtain a completely dried and thorough aerogel heat insulation material felt roll product, and sampling to measure the bulk density to be 190-200 kg/m 3.

Example 2

A mode of rolling first and then dipping is adopted, a stainless steel plate with the thickness of 0.15mm is added between aluminum silicate fiber felt layers with the thickness of 20mm and the length of 10m, the fiber felt and the end of a stainless steel isolation layer plate are simultaneously fixed on a mandrel, and then the fiber felt and the stainless steel isolation layer plate are rolled along the rolling direction and coiled. And then adding the aluminum-silicon mixed sol into a dipping tank for dipping, and taking out the felt roll and placing the felt roll into a dry material cage after the silica sol in the fiber pores is gelled. Then fixing the mandrel, and rotating the dry material cage along the winding reverse direction to separate the jelly roll layers along the stainless steel isolation layer plate to generate an interlayer gap. And hoisting the dried material into an ethanol supercritical drying kettle in a cage, raising the temperature and the pressure to 260 ℃ and 6.5MPa, and keeping the temperature and the pressure for 60min to obtain a completely dried and thorough aerogel heat insulation material felt roll product. The sampled samples have a measured bulk density of 190 to 200kg/m 3.

Example 3

A process for increasing the drying efficiency of a roll of aerogel insulation material, said process comprising the steps of:

attaching, rolling and dipping the fiber felt and the isolation laminate to obtain the fiber felt containing the isolation laminate;

fixing one end of the fiber felt containing the isolation laminate on a mandrel, and then tightening along the winding direction to prepare a felt roll;

and gelling and drying the felt roll to obtain the aerogel heat insulation material.

Carrying out gel on the felt roll, loosening the felt roll, and reserving a gap to obtain a loosened felt roll; and drying the felt roll after the felt roll is unwound to obtain the aerogel heat insulation material.

The aerogel insulation comprises alumina. The fiber material of the fiber felt layer is aluminum silicate fiber, and the thickness of the fiber felt layer is 30 mm. The preparation method of the felt roll comprises the steps of rolling the fiber material laminating compound and then mixing the fiber material laminating compound with the sol. The drying method comprises carbon dioxide supercritical drying. The isolation layer plate is made of a metal material and is a pore plate with the thickness of 0.2 mm. The container for drying comprises a fence-like structure, and the container is made of heat conducting materials. The heat conduction material is a metal material. The metal material is copper. The method of unrolling comprises fixing the container and rotating the mandrel in the opposite direction of rolling.

Example 4

A process for increasing the drying efficiency of a roll of aerogel insulation material, said process comprising the steps of:

attaching, rolling and dipping the fiber felt and the isolation laminate to obtain the fiber felt containing the isolation laminate;

fixing one end of the fiber felt containing the isolation laminate on a mandrel, and then tightening along the winding direction to prepare a felt roll;

carrying out gel on the felt roll, loosening the felt roll, and reserving a gap to obtain a loosened felt roll; and drying the felt roll after the felt roll is unwound to obtain the aerogel heat insulation material.

The aerogel thermal insulation material is silicon dioxide.

The fiber material of the fiber felt layer is high silica fiber, and the thickness of the fiber felt layer is 15 mm.

The preparation method of the felt roll comprises the steps of mixing the fiber felt layer with the sol and then rolling.

The drying method comprises normal-pressure normal-temperature drying. The isolation layer plate is made of a metal material and is a stainless steel plate with the thickness of 0.2 mm.

The container for drying comprises a plate shape with holes, and the material of the container is heat conduction material. The heat conduction material is made of metal materials and is a stainless steel plate.

Comparative example 1

The same manner as that of example 1, namely dipping glue firstly and then rolling, is adopted, the silica sol is compounded with the alkali-free fiber felt with the thickness of 12mm and the length of 15m by adopting a process injection manner, no stainless steel isolation layer plate is added between fiber felt layers during rolling, the end of the fiber felt is fixed on a mandrel, and then the fiber felt is rolled along the rolling direction and then coiled. After the silica sol gel in the fiber pores, the felt rolls were placed in a dry stock cage, but were not unwound. And hoisting the dried material into an ethanol supercritical drying kettle, raising the temperature and the pressure to 260 ℃ and 6.5MPa in the same way, keeping the temperature and the pressure for 60min, unfolding the obtained aerogel heat-insulating material felt roll product to find that the inside of the product is completely not dried, prolonging the heat-preservation and pressure-keeping time to 240min, unfolding the obtained aerogel heat-insulating material felt roll product to find that the inside of the product is still partially not dried, sampling the inside of the product, and measuring the bulk density to be 350-500 kg/m 3. By comparison, it can be found that the drying efficiency of example 4 is improved by more than 4 times than that of comparative example 1.

Comparative example 2

The same manner of rolling first and dipping later as in example 2 was adopted, the end of the aluminum silicate fiber felt with a thickness of 20mm and a length of 10m was fixed on a mandrel, and then rolled in the rolling direction and rolled, but no stainless steel insulation laminate was added between the fiber felt layers during rolling. And (3) similarly placing the felt roll into a dipping tank, adding the aluminum-silicon mixed sol for dipping, and taking out the felt roll and placing the felt roll into a dry material cage without unwinding after the silica sol in fiber pores is gelled. And hoisting the dried material into an ethanol supercritical drying kettle in a cage, raising the temperature and the pressure to 260 ℃ and 6.5MPa, keeping the temperature and the pressure for 60min, unfolding the obtained aerogel heat-insulating material felt roll product to find that the inside of the obtained aerogel heat-insulating material felt roll product is completely not dried, prolonging the temperature and the pressure keeping time to 240min, unfolding the obtained aerogel heat-insulating material felt roll product to find that the inside of the obtained aerogel heat-insulating material felt roll product is still partially not dried, and sampling the inside of the obtained aerogel heat-insulating material felt roll product to measure that the bulk density is 350-500 kg/m 3. By comparison, example 5 can be found to have a drying efficiency improved by more than 4 times than comparative example 2.

Add the isolation layer and go on simultaneously with the pine book, because only add the isolation layer and do not carry out the pine book, drying efficiency improves and can not be too obvious, and the effect of isolation layer plays certain heat-conduction effect on the one hand, but the primary function plays the effect that the gel was rolled up along the isolation layer pine.

The aerogel insulation materials prepared in examples 1 to 4 and comparative examples 1 to 2 were dried, and the test results are shown in Table 1.

Table 1, comparative example and comparative example drying comparative table.

From the data in table 1, it can be seen that: compared with the comparative proportion, the drying efficiency is improved by 4 times by carrying out the same ethanol supercritical drying. The invention can meet different drying modes to achieve the aim of drying, such as examples 3 and 4.

From the data in comparative examples 1-2, it can be seen that:

from the data of comparative examples 1 and 2, it can be seen that the drying efficiency is reduced by only one fourth of those of examples 1 and 2 without any stainless steel insulation laminate between the fiber felt layers during rolling, and the inside of the felt roll is still not dried completely and has a density significantly higher than that of the ideal dried product, indicating that the inside contains a part of gel which is not dried into aerogel.

Detailed description of the drawings 1-2:

as shown in FIG. 1, the schematic diagram of the rolled aerogel thermal insulation material provided by the present invention comprises a fiber felt layer, an insulation layer plate, a core, and a container, wherein the insulation layer plate can be added to shorten the drying time, so as to achieve the purpose of transferring heat to the inside of the felt roll.

As shown in fig. 2, the schematic diagram of the aerogel thermal insulation material after being unwound according to the present invention shows that the aerogel thermal insulation material is separated along the insulation layer plates to form an interlayer gap, which is beneficial for heat and airflow to reach between felt rolls during drying, and the interlayer gap increases the heat convection effect of the drying medium, thereby improving the drying efficiency.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.