阅读说明：本技术 一种防热套及其制备方法和成型装置 (Heat-proof sleeve and preparation method and forming device thereof ) 是由 艾进 张天胤 张权 谢道成 于 2020-12-31 设计创作，主要内容包括：本发明提供了一种防热套及其制备方法和成型装置,所述防热套为环形且沿直径方向呈波浪形,所述防热套沿垂直于环形方向依次包括柔性层、力学增强层和耐烧蚀层；所述耐烧蚀层由粒径≤1μm的陶瓷粒子在硅橡胶中瓷化后获得。本发明提供的防热套,其柔性层侧温度为64-70℃,具有良好的耐烧蚀性,断裂延长率为358-413％,柔性好。(The invention provides a heat-proof sleeve, a preparation method and a forming device thereof, wherein the heat-proof sleeve is annular and waved along the diameter direction, and the heat-proof sleeve sequentially comprises a flexible layer, a mechanical enhancement layer and an ablation-resistant layer along the direction vertical to the annular direction; the ablation-resistant layer is obtained by vitrifying ceramic particles with the particle size less than or equal to 1 mu m in silicon rubber. The heat-proof sleeve provided by the invention has the advantages that the temperature of the flexible layer side is 64-70 ℃, the ablation resistance is good, the fracture elongation is 358-413%, and the flexibility is good.)

1. The heat-proof sleeve is characterized in that the heat-proof sleeve is annular and wavy along the diameter direction, and the heat-proof sleeve sequentially comprises a flexible layer, a mechanical enhancement layer and an ablation-resistant layer along the direction perpendicular to the annular direction; the ablation-resistant layer is obtained by vitrifying ceramic particles with the particle size less than or equal to 1 mu m in silicon rubber.

2. The heat shroud as claimed in claim 1, wherein said ceramic particles are at least one of: zirconium boride, zirconium oxide.

3. The heat shroud as claimed in claim 1, wherein said ablation resistant layer has a thickness of 0.7 to 0.8 mm.

4. The heat shroud as claimed in claim 1, wherein the flexible layer is made of silicone rubber, and the thickness of the flexible layer is 0.7-0.8 mm.

5. The heat shield sleeve as claimed in claim 1, wherein the mechanical enhancement layer is made of any one of the following materials: quartz glass fiber, high silica fiber reinforced glue, the thickness of mechanics enhancement layer is 2.1-2.3 mm.

6. The method of manufacturing a heat shroud as claimed in any one of claims 1 to 5, wherein said method comprises,

spraying a film coating agent on the surfaces of the upper die and the lower die;

sequentially laying a flexible material, a mechanical reinforcing material and an ablation-resistant material on the surface of the lower film coated with the coating agent, then closing an upper die, heating to the temperature of 170-180 ℃ and curing at the pressure of 200-220T, and demoulding to obtain the heat-proof sleeve; the ablation-resistant layer material consists of ceramic particles and silicon rubber.

7. The heat shield sleeve as claimed in claim 6, wherein during the layering process, the layers are layered clockwise along the circumferential direction of the lower die, the flexible material and the mechanical reinforcing material are overlapped, and the overlapping width is 60-100 mm; the mechanical reinforcing material and the ablation-resistant material are overlapped, and the overlapping width is 60-100 mm.

8. The method for preparing the heat-proof jacket as claimed in claim 6, wherein in the heating process, the heating rate is 1.5-2 ℃ for min, the temperature rise time is 1.5-2.5h, and the heat preservation time is 0.5-1.5 h.

9. The method for preparing the heat-proof jacket as claimed in claim 5, wherein in the spraying process, the spraying times are 2-3 times, the time interval between two adjacent spraying times is 15-20min, and the total spraying amount is 45-55g/m²。

10. A device for preparing a heat-proof sleeve, which is used for preparing the heat-proof sleeve as claimed in any one of claims 1 to 4, and is characterized by comprising an upper die and a lower die, wherein the upper die is arranged on the lower die, and an annular wavy cavity is formed after the upper die and the lower die are closed; the cavity is used for molding flexible materials, mechanical reinforcing materials and ablation-resistant materials, so that the heat-proof sleeve is obtained.

Technical Field

The invention belongs to the technical field of composite materials, and particularly relates to a heat-proof sleeve, and a preparation method and a preparation device thereof.

Background

The heat-proof sleeve can be used for an annular gap part between the tail section and the engine spray pipe to prevent high-temperature combustion flow at the outlet of the spray pipe from reversely flowing into the tail section cabin and prevent the bottom of the tail section from being heated in the flying process.

At present, the heat-proof sleeve is made of glass fiber reinforced plastic materials and is made of rigid materials, the spray pipe needs to swing when an engine works, the rigid materials cannot enable the spray pipe to work normally, meanwhile, the flame temperature sprayed out by the spray pipe is high, and common glass fiber reinforced plastic materials cannot meet the requirement of ablation resistance.

Disclosure of Invention

The invention provides a heat-proof sleeve and a preparation method and a preparation device thereof, and aims to solve the technical problems of poor flexibility and poor ablation resistance of a glass fiber reinforced plastic heat-proof sleeve in the prior art.

The invention provides a heat-proof sleeve which is annular and wavy along the diameter direction, and sequentially comprises a flexible layer, a mechanical enhancement layer and an ablation-resistant layer along the direction vertical to the annular direction; the ablation-resistant layer is obtained by vitrifying ceramic particles with the particle size less than or equal to 1 mu m in silicon rubber.

Further, the ceramic particles are at least one of: zirconium boride, zirconium oxide.

Further, the thickness of the ablation-resistant layer is 0.7-0.8 mm.

Further, the flexible layer is composed of silicon rubber, and the thickness of the flexible layer is 0.7-0.8 mm.

Further, the raw material of the mechanical enhancement layer is any one of the following materials: quartz glass fiber, high silica fiber reinforced glue, the thickness of mechanics enhancement layer is 2.1-2.3 mm.

In another aspect, the present invention provides a method for preparing the above heat-proof jacket, the method comprising,

spraying a film coating agent on the surfaces of the upper die and the lower die;

sequentially laying a flexible material, a mechanical reinforcing material and an ablation-resistant layer material on the surface of the lower film coated with the coating agent, then closing an upper die, heating to the temperature of 170-180 ℃ and curing at the pressure of 200-220T, and demoulding to obtain the heat-proof sleeve; the ablation-resistant layer material consists of ceramic particles and silicon rubber.

Further, in the layering process, clockwise layering is carried out along the circumferential direction of the lower die, the flexible material and the mechanical reinforcing material are in lap joint, and the lap joint width is 60-100 mm; the mechanical reinforcing material and the ablation-resistant material are overlapped, and the overlapping width is 60-100 mm.

Furthermore, in the heating process, the heating rate is 1.5-2 ℃ for min, the temperature rise time is 1.5-2.5h, and the heat preservation time is 0.5-1.5 h.

Furthermore, in the spraying process, the spraying frequency is 2-3 times, the time interval of two adjacent spraying is 15-20min, and the total spraying amount is 45-55g/m²。

On the other hand, the invention also provides a device for preparing the heat-proof sleeve, which is used for preparing the heat-proof sleeve and comprises an upper die and a lower die, wherein the upper die is arranged on the lower die, and an annular wavy cavity is formed after die assembly; the cavity is used for molding flexible materials, mechanical reinforcing materials and ablation-resistant materials, so that the heat-proof sleeve is obtained.

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

the invention provides a heat-proof sleeve and a preparation method thereof, wherein the heat-proof sleeve is made of three layers of materials, wherein the flexible layer can enable the heat-proof sleeve to have certain flexibility, so that a spray pipe is protected from swinging; the mechanical enhancement layer can improve the strength of the heat-proof sleeve so as to meet the requirement that the heat-proof sleeve bears violent swing during working; the silicon rubber in the ablation-resistant layer is subjected to polymer cracking under the action of high temperature, and simultaneously, the cracked product reacts with ceramic particles to form a ceramic phase with a three-dimensional net structure, so that a continuous fiber and ceramic two-phase reinforced resin-based composite material is finally formed, the size ablation amount of the composite material is reduced, and the ablation-resistant layer has good ablation resistance. The heat-proof sleeve provided by the invention has the advantages that the temperature of the flexible layer side is 64-70 ℃, the ablation resistance is good, the fracture elongation is 358-413%, and the flexibility is good.

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 structural view of a device for manufacturing a heat-proof jacket according to an embodiment of the present invention.

Fig. 2 is a heating curve of a thermal sleeve ablation performance test provided by an embodiment of the invention.

In fig. 1, 1-upper mold, 2-lower mold, 3-flexible layer, 4-mechanical enhancement layer, 5-ablation-resistant layer.

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.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

In order to solve the technical problems, the embodiment of the invention provides the following general ideas:

on one hand, the embodiment of the invention provides an annular heat-proof sleeve which is wavy along the diameter direction and sequentially comprises a flexible layer, a mechanical enhancement layer and an ablation-resistant layer along the direction vertical to the annular direction; the ablation-resistant layer is obtained by vitrifying ceramic particles with the particle size less than or equal to 1 mu m in silicon rubber.

The flexible layer can enable the heat-proof sleeve to have certain flexibility, so that the spray pipe is protected from swinging; the mechanical enhancement layer can improve the strength of the heat-proof sleeve so as to meet the requirement that the heat-proof sleeve bears violent swing during working; the ceramic particles in the ablation-resistant layer react to form a ceramic phase with a three-dimensional net structure while the polymer is cracked under the action of high temperature, and finally the continuous fiber and ceramic two-phase reinforced resin-based composite material is formed, so that the size ablation amount of the composite material is reduced, and the ablation-resistant layer has good ablation resistance.

The distance between the wave crests of two adjacent waves of the heat-proof sleeve can be 30-35mm, the distance between two connected wave troughs can be 40-50mm, and the number of the waves can be 2; the difference between the inner diameter and the outer diameter of the heat-proof sleeve can be 240 mm and 260 mm.

As an embodiment of the present invention, the ceramic particles are at least one of: zirconium boride, zirconium oxide. The particles in the zirconium boride and the zirconium oxide can react at high temperature to form a ceramic phase with a three-dimensional net structure, so that the continuous fiber and ceramic two-phase reinforced resin-based composite material is formed.

As an implementation of the inventive example, the thickness of the ablation-resistant layer is 0.7-0.8 mm. The thickness of the ablation-resistant layer is too small, the ablation-resistant effect is poor, the thickness of the ablation-resistant layer is too large, and the cost is high.

As an implementation manner of the embodiment of the invention, the raw material of the flexible layer is silicon rubber, and the thickness of the flexible layer is 0.7-0.8 mm.

Silicone rubber is a rubber having a backbone composed of alternating silicon and oxygen atoms, with the silicon atoms typically having two organic groups attached to them. The phenyl group can improve the high and low temperature resistance of the silicon rubber, can work at the low temperature of-73 ℃, can work for a long time at the high temperature of 180 ℃, can still bear elasticity for a plurality of weeks or more even at the temperature slightly higher than 200 ℃, and can instantly resist the high temperature of more than 300 ℃. The thickness of the flexible layer is too small, the heat insulation performance and the high temperature resistance of the heat-proof sleeve are poor, the thickness of the flexible layer is too large, and the cost is high.

As an implementation manner of the embodiment of the present invention, the raw material of the mechanical enhancement layer includes, but is not limited to, any one of the following: quartz glass fiber, high silica fiber reinforced glue, the thickness of mechanics enhancement layer is 2.1-2.3 mm.

The quartz glass fiber reinforced glue is made of crystal or pure SiO₂Is a quartz glass fiber reinforced material prepared by melting and drawing or rod drawing and other methods, and SiO thereof₂The content reaches 99.9 percent. The mechanical enhancement layer has too small thickness, poor strength of the heat-proof sleeve, too large thickness and high cost.

On the other hand, the embodiment of the invention also provides a preparation method of the heat-proof jacket, which comprises the following steps,

s1, spraying the film coating agent on the surfaces of the upper die and the lower die;

s2, sequentially paving a flexible material, a mechanical reinforcing material and an ablation-resistant material on the surface of the lower film coated with the film coating agent, then closing the upper die, heating to the temperature of 170-; the ablation-resistant layer material consists of ceramic particles and silicon rubber.

And (3) carrying out vulcanization reaction on the silicon rubber through heating and curing, and forming a cross-linked network structure among molecular chains to form the composite material. If the heating temperature is lower than 170 ℃, the adverse effect of insufficient vulcanization of the silicon rubber exists; if the heating temperature is higher than 180 ℃, the adverse effect of material hardening is caused by the excessive vulcanization of the silicon rubber. The low pressure can lead to insufficient material crosslinking, the flexible layer, the mechanical enhancement layer and the ablation-resistant layer are separated and layered, the high pressure can lead to overflow loss of silicon rubber and reduction of material performance.

As an implementation mode of the embodiment of the invention, in the layering process, clockwise layering is carried out along the circumferential direction of the lower die, the flexible material and the mechanical reinforcing material are in lap joint, and the lap joint width is 60-100 mm; the mechanical reinforcing material and the ablation-resistant material are overlapped, and the overlapping width is 60-100 mm. More specifically, the paving layer is a heat-resistant layer paved clockwise along the circumferential direction of the mould, and the lapping width of each heat-resistant layer glue film is 60-100 mm; after finishing, performing mechanical reinforcement layer laying, wherein the lapping positions of the mechanical reinforcement layer laying and the heat-resistant layer are required to be staggered, namely the lapping positions between the layers are not allowed to be overlapped; after the completion, the ablation-resistant layer laying is carried out, and the lapping position of the ablation-resistant layer laying and the mechanical enhancement layer is required to be staggered, namely the lapping position between the layers is not allowed to be overlapped.

As an implementation manner of the embodiment of the invention, in the heating process, the heating rate is 1.5-2 ℃ for min, the temperature rise time is 1.5-2.5h, and the heat preservation time is 0.5-1.5 h. Too high or too low heating rate leads to insufficient vulcanization reaction and reduced mechanical properties. The heat preservation time is less than 0.5h, and the adverse effect of insufficient vulcanization of the silicon rubber is caused; the heat preservation time is more than 1.5h, and the adverse effects of silicone rubber transition vulcanization and material hardening exist.

As an implementation mode of the embodiment of the invention, in the spraying process, the spraying times are 2-3 times, the time interval between two adjacent spraying times is 15-20min, and the total spraying amount is 45-55g/m². The release agent can be silicone oil and stearic acid, and the spraying is uniform. The spraying time interval is 15-20min, so that the demoulding is convenient, the efficiency is improved, the service life of the mould is prolonged, and meanwhile, the surface of the product is smooth, the size is qualified, and waste products are reduced; too long spraying time interval affects production efficiency, and too short spraying time interval is not beneficial to forming uniform thin films. Too much release agent affects the appearance quality of the product, and too little release agent is difficult to release.

On the other hand, the embodiment of the invention also provides a device for preparing the heat-proof sleeve, which is used for preparing the heat-proof sleeve, and with reference to fig. 1, the device comprises an upper die 2 and a lower die 3, wherein the upper die 2 is arranged on the lower die 3, and an annular wavy cavity is formed after die assembly; the cavity is used for forming a flexible material, a mechanical reinforcing material and an ablation-resistant material into a flexible layer 4, a mechanical reinforcing layer 5 and an ablation-resistant layer 6 respectively, so that the heat-proof sleeve is obtained.

The heat shroud of the present invention, a method for manufacturing the same, and an apparatus for manufacturing the same will be described in detail with reference to examples, comparative examples, and experimental data.

Example 1

Embodiment 1 provides a method for preparing a heat-proof jacket, which comprises the following steps:

1. spraying a release agent:

spraying the coating agent on the surface of the upper mold 2 and the surface of the lower mold 3 by a low-pressure spray gun for 2 times at an interval of 15min, wherein the total spraying amount of the upper mold is 50g/m²The total spraying amount of the lower die is 50g/m²。

2. Layering:

silicon rubber, quartz glass fiber reinforced silicon rubber and zirconium boride particle doped silicon rubber with the particle size of less than or equal to 1 mu m are sequentially paved on the surface of a cavity of a lower die 3, and the layers are lapped to form a heat-resistant layer 4, a mechanical enhancement layer 5 and an ablation-resistant layer 6, wherein the lapping width is 60mm, and the interlayer lapping strength is staggered.

3. Die assembly:

the upper die 2 and the lower die 3 are clamped.

4. And (3) vulcanization:

the curing system is as follows: heating the mixture to 175 ℃ at room temperature, keeping the temperature for 1h, heating the mixture for 2h, and heating the mixture at a rate of 1.3 ℃/min; the pressure was 200T.

5. Demolding:

and (4) opening the mold after vulcanization is finished, and cutting the flash to obtain the heat-proof sleeve.

Example 2

Embodiment 2 provides a method for preparing a heat-proof jacket, which comprises the following steps:

1. spraying a release agent:

spraying the coating agent on the surface of the upper mold 2 and the surface of the lower mold 3 by a low-pressure spray gun for 3 times at an interval of 16min, wherein the total spraying amount of the upper mold is 50g/m²The total spraying amount of the lower die is 50g/m²。

2. Layering:

silicon rubber, quartz glass fiber reinforced rubber and zirconium oxide particle doped silicon rubber with the particle size of less than or equal to 1 mu m are sequentially paved on the surface of a cavity of a lower die 3, and the layers are lapped to form a heat-resistant layer 4, a mechanical enhancement layer 5 and an ablation-resistant layer 6, wherein the lapping width is 80mm, and the interlayer lapping strength is staggered.

3. Die assembly:

the upper die 2 and the lower die 3 are clamped.

4. And (3) vulcanization:

the curing system is as follows: heating to 180 ℃ at room temperature, keeping the temperature for 1.5h, heating for 2.5h, and heating at a rate of 1 ℃/min; the pressure was 205T.

5. Demolding:

and (4) opening the mold after vulcanization is finished, and cutting the flash to obtain the heat-proof sleeve.

Example 3

Embodiment 3 provides a method for preparing a heat-proof jacket, which comprises the following steps:

1. spraying a release agent:

spraying the coating agent on the surface of the upper mold 2 and the surface of the lower mold 3 by a low-pressure spray gun for 3 times at an interval of 16min, wherein the total spraying amount of the upper mold is 45g/m²The total spraying amount of the lower die is 45g/m²。

2. Layering:

silicon rubber, quartz glass fiber reinforced rubber, zirconium boride particles with the particle size of less than or equal to 1 mu m and zirconium oxide particles are mixed with the silicon rubber and sequentially paved on the surface of a cavity of a lower die 3, and the layers are lapped to form a heat-resistant layer 4, a mechanical enhancement layer 5 and an ablation-resistant layer 6, wherein the lapping width is 80mm, and the interlayer lapping strength is staggered. Wherein the mass ratio of the zirconium boride particles to the zirconium oxide particles is 1: 1.

3. Die assembly:

the upper die 2 and the lower die 3 are clamped.

4. And (3) vulcanization:

the curing system is as follows: heating to 170 ℃ at room temperature, keeping the temperature for 1.5h, heating for 2.5h, and heating at a rate of 1 ℃/min; the pressure was 205T.

5. Demolding:

and (4) opening the mold after vulcanization is finished, and cutting the flash to obtain the heat-proof sleeve.

Comparative example 1

1. Spraying a release agent:

spraying the coating agent on the surface of the upper die 2 and the surface of the lower die 3 by a low-pressure spray gun for 3 times at intervals16min, the total spraying amount of the upper die is 45g/m²The total spraying amount of the lower die is 45g/m²。

2. Layering:

silicon rubber and quartz glass fiber reinforced rubber are sequentially paved on the surface of a cavity of the lower die 3, and the layers are lapped to form a heat-resistant layer 4 and a mechanical enhancement layer 5, wherein the lapping width is 80mm, and the interlayer lapping strength is staggered.

3. Die assembly:

the upper die 2 and the lower die 3 are clamped.

4. And (3) vulcanization:

the curing system is as follows: heating to 170 ℃ at room temperature, keeping the temperature for 1.5h, heating for 2.5h, and heating at a rate of 1 ℃/min; the pressure was 205T.

5. Demolding:

and (4) opening the mold after vulcanization is finished, and cutting the flash to obtain the heat-proof sleeve.

Comparative example 2

Comparative example 2 provides a heat shroud, which is the same as example 1 except that comparative example 2 is different from example 1 in that a mixture of a titanium dioxide material and a silicone rubber material is used as a raw material for an ablation-resistant layer.

Comparative example 3

Comparative example 2 provides a heat shield case, which is the same as example 1 except that comparative example 2 is different from example 1 in that a mixture of silica and a silicone rubber material is used as a raw material for an ablation-resistant layer.

The heat shield sleeves provided in examples 1 to 3 and comparative examples 1 to 2 were subjected to ablation performance tests, specifically, the ablation-resistant layer side of the heat shield sleeve was heated with the temperature profile shown in fig. 2, and at the test end point of 60s, the temperature and ablation depth on the flexible layer side were measured, and the test results are shown in table 1; detecting the Shore hardness of the heat-proof sleeve; and the tensile strength and the elongation at break of the heat-proof sleeve are detected according to GB/T528-one 2009 determination of tensile stress-strain performance of vulcanized rubber and thermoplastic rubber, as shown in Table 1.

TABLE 1

As can be seen from Table 1, the heat shroud provided in examples 1 to 3 had a hardness of 54 to 57HA, a tensile strength of 3.10 to 4.2MPa, an ablation depth of 0, a side temperature of the flexible layer of 64 to 70 ℃, a good ablation resistance, a fracture elongation of 358-. The thermal protective sleeve provided by the comparative example 1 HAs the hardness of 50HA, the tensile strength of 2.5MPa, the ablation depth of 1.2mm, the temperature of the flexible layer of 145 ℃, the ablation resistance far lower than that of the examples 1-3 of the invention, the elongation at break of 276% and the flexibility lower than that of the examples 1-3 of the invention. Comparative example 2 provides a thermal shroud having a hardness of 52HA, a tensile strength of 2.7MPa, an ablation depth of 0.3mm, a flexible layer temperature of 96 ℃, an ablation resistance lower than that of examples 1-3 of the present invention, an elongation at break of 276%, and a flexibility lower than that of examples 1-3 of the present invention. Comparative example 3 provides a heat shroud having a hardness of 48HA, a tensile strength of 2.95MPa, an ablation depth of 0.51mm, a flexible layer temperature of 103 deg.C, an ablation resistance lower than that of examples 1-3 of the present invention, an elongation at break of 264%, and a flexibility lower than that of examples 1-3 of the present invention. .

The invention provides a heat-proof sleeve and a preparation method thereof, wherein the heat-proof sleeve is made of three layers of materials, wherein the flexible layer can enable the heat-proof sleeve to have certain flexibility, so that a spray pipe is protected from swinging; the mechanical enhancement layer can improve the strength of the heat-proof sleeve so as to meet the requirement that the heat-proof sleeve bears violent swing during working; the silicon rubber in the ablation-resistant layer is subjected to polymer cracking under the action of high temperature, and simultaneously, the cracked product reacts with ceramic particles to form a ceramic phase with a three-dimensional net structure, so that a continuous fiber and ceramic two-phase reinforced resin-based composite material is finally formed, the size ablation amount of the composite material is reduced, and the ablation-resistant layer has good ablation resistance. The heat-proof sleeve provided by the invention has the advantages that the temperature of the flexible layer side is 64-70 ℃, the ablation resistance is good, the fracture elongation is 358-413%, and the flexibility is good.

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.