CONVOLUTED HEAT SHIELD

Abstract

A heat shield comprises a convoluted tube preferably formed from two layers of aluminum. The convoluted tube may have an inside minor diameter ranging from 0.5 inches to 3.0 inches and preferably includes convolutions of greater than 0.070 inches and a pitch of at least 0.787 inches. Optionally, the tube is coated with a dark colored or black material to further enhance the heat shielding and dispersing properties. The present invention also includes a method of manufacturing the convoluted tube, and a method of shielding heat from an automobile EGR utilizing an aluminum convoluted tube having convolutions of at least 0.070 inches.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. application Ser. No. 60/594,799, filed May 6, 2005, which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to reflective convoluted tubing that is used to protect components from radiant heat sources and methods of forming the tubing thereof.

BACKGROUND OF THE INVENTION

There are several different ways in which to insulate a radiant heat source so that it does not emit heat to effect surrounding components. In many applications, a flexible sleeve is used, as it is easily installed over the heat source-typically an exhaust system, manifold, or exhaust gas recirculation (EGR) system. There are companies worldwide that manufacture convoluted tubing for many different applications, including insulating a radiant heat source.

Other products that serve a similar purpose are sold by Federal-Mogul Systems Protection group under the name Thermflex Spiral. This product is formed from a braided fiberglass tube or sock that is then coated with an anti-fray coating and dipped on both ends to help keep the product from splitting. A similar product is sold by Vitrica S.A. de C.V but uses a different weave pattern in the braided fiberglass tube and coating to help bond the tube.

The prior art devices discussed above all utilize fiberglass in the construction of the heat shield. Some of the disadvantages with fiberglass include the fact that fiberglass is relatively expensive, and fiberglass tends to retain heat. The present invention attempts to overcome one or more problems associated with the prior art heat shield devices. Accordingly, the present invention is hereby submitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a convoluted tube in accordance with a preferred embodiment of the present invention.

FIG. 2 is an end view of a convoluted tube of FIG. 1.

FIG. 3 is a side view of a worm inner die member.

FIG. 4 is an end view of the worm die member of FIG. 3.

FIG. 5 is an end view of an outer nut die member.

FIG. 6 is a cross-sectional view of the nut die member of FIG. 5.

FIG. 7 is a cross-sectional view of a convoluted tube.

FIG. 8 is a side view of a convoluted tube, illustrated with end cap.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

One embodiment of the present invention provides a flexible convoluted tube 10 made from layers of material that are wrapped on a mandrel, and then pass though a set of dies 20, 30 to convolute the material. Once the material is convoluted, it then passes through a heat zone that thermally sets a layer of adhesive that is previously applied to one of the material layers.

At present, the standard product manufactured on this equipment to produce a heat insulator has included using thin woven fiberglass blanketing that is placed on the inside of the convoluted tubing, and applying a layer of stainless steel to the outside, or placing the fiberglass between two layers of aluminum.

One limitation to the standard die design and resulting finished convoluted tube is that there is a limited amount of material on the dies to manufacture a deeper groove to produce a taller thread, which in turn produces a taller or bigger wall thickness of the convoluted tube. In the traditional process of manufacturing the die threads, the leading edge of one thread will cut or erode into the trailing edge of the next thread, which will limit the total thread height of the die. Additionally, if the threads are too tall on a die, the current design will not allow for the material to flow through the dies and will cause the material to either be cut or perforated once leaving the die, or the material will not pass through the die at all.

Through testing of various material combinations, it was determined that if merely two layers of aluminum were utilized without a layer of fiberglass, the resultant combination worked as well as or better than a product that includes fiberglass. As such, in one embodiment of the present invention may comprise a convoluted tube 10 consisting of two layers of aluminum and convolutions 12. The thermal conductive properties of aluminum are superior to that of fiberglass in some applications. Fiberglass acts as an insulator/absorber of heat, while aluminum tends to dissipate heat. The significance of removing the fiberglass is that the final product costs less, allows for better dissipation of heat, and does not use a material that causes health and safety issues when being formed or installed.

To further improve the performance of this new product, experimentation was done to the design of the winder dies that actually form the finished product. The die design may include a worm die member 20 that comprises a shaft 24 and threads 22. As illustrated in FIGS. 3-6, for a standard die design typically uses a thread height of 0.047″ to 0.055″ , the difference of the Major Outside Diameter (OD) and the Minor Inside Diameter (ID) divided by two of either the worm or nut die, for tube sizes ranging from 0.50″ to 3.00″ diameter. Also, the standard pitch is 0.394″ to 0.787,″ the pitch being the longitudinal distance that it takes one thread to make a full circumference of the die. Additionally, this die design uses a multi-lead thread, ranging from 4 to 6 leads, increasing the design complexity. A standard Acme Thread design uses only one lead.

The nut die member 30 comprises an aperture that receives the worm die member 20. The perimeter of the aperture may comprise threads 32. Via the cooperation between threads 22 on worm die member and threads 32 on nut die member, the tube is convoluted as it passes between the two die members 20, 30.

An exemplary embodiment of an improved die design 20, 30, uses a range of 0.063″ to 0.079″ for the thread height for the same size range of dies, and increases the pitch to 0.787″ to 1.38.″ This is roughly a 33% to 43% increase in the thread height, and a 100% increase in pitch for a 0.5 inch tube and a 75% increase for a 3.0 inch tube from the standard design. The end result creates a taller distance between the peaks and valleys of the convoluted tube. If we assume a 0.75″ ID Aluminum-Fiberglass-Aluminum tube that is currently sold today has a total material thickness of 0.013″ and a wall height of 0.067″, then you can extrapolate the straight part of the convolution to be approximately the wall height less two times the thickness or 0.067-(2*0.013)=0.041.″

The following table provides an exemplary configuration for different sized tubes according to an exemplary embodiment of the present invention, compared to prior art tubes.

Prior Art	Exemplary Embodiments
Tube	Thread		Convolution	Thread		Convolution
ID	Height	Pitch	Height	Height	Pitch	Height
0.492	0.047	0.394	0.059	0.063	0.787	0.071
0.787	0.055	0.787	0.067	0.079	1.181	0.094
1.024	0.055	0.787	0.071	0.079	1.181	0.098
1.969	0.055	0.787	0.071	0.079	1.181	0.110
2.992	0.055	0.787	0.079	0.079	1.378	0.118

An embodiment of the present invention provides a 0.75″ ID Aluminum-Aluminum tube, FIG. 5, that has a total material thickness of 0.005,″ and a convolution height CH of 0.079″ or greater. This translates to a straight part of the convolutions of approximately 0.069.″ This is roughly a 67% increase in the straight section of the convolution, and a 67% increase in the surface area where the greatest amount thermal conductivity occurs. A convolution height ranging to at least 0.118″ is also contemplated.

Additionally, it has been found that by coating the exterior surface of the new tubing design with a dark color or black outer surface further enhances the heat dissipation properties of the convoluted tubing. For example, the tubing may comprise a black epoxy coating, which may be baked-on or air-dried. Alternatively, the outer surface may be anodized, powder coated, or painted, or may have any of a plurality of dark or black coatings as are known in the art.

Optionally, an end cap 16 may be added to one or more ends of the tube to provide a smoother end surface and to help in preventing the ends of the tube from fraying or coming apart. It is contemplated that the end caps may be attached to the tube via any means as are known in the art without deviating from the scope of the present invention.

This new design has allowed for a lower cost product that performs better and is easy to install as it is more flexible, and removes any additional worker health and safety issues. This design also allows for the potential to use other thicknesses of material to increase or decrease the flexibility of the end product without sacrificing cost or performance.

Claims

1. A heat shield, comprising:

an elongated convoluted tubing having a plurality of convolutions, the elongated tubing consisting essentially of a first layer of aluminum and a second layer of aluminum.

2. The heat shield as recited in claim 1, wherein,

the convolutions comprise a height equal to a difference between a major outside diameter of the heat shield and a minor inside diameter of the heat shield,

the height of the convolutions is at least 0.070 inches; and,

the minor inside diameter is approximately 0.50 inches.

3. The heat shield as recited in claim 2, wherein the pitch of the convolutions is at least 0.787 inches.

4. The heat shield as recited in claim 1, wherein,

the convolutions comprise a height equal to a difference between a major outside diameter of the heat shield and a minor inside diameter of the heat shield,

the height of the convolutions is at least 0.090 inches; and,

the minor inside diameter is between 0.75 inches and 3.0 inches.

5. The beat shield as recited in claim 4, wherein a pitch of the convolutions is at least 0.118 inches.

6. The heat shield as recited in claim 4, wherein the minor inside diameter is about 0.75 inches, and the convolution height is about 0.094 inches.

7. The heat shield as recited in claim 6, wherein a pitch of the convolutions is at least about 1.18 inches.

8. The heat shield as recited in claim 4, wherein the minor inside diameter is about 1.0 inches and the convolution height is about 0.098 inches.

9. The heat shield as recited in claim 8, wherein a pitch of the convolutions is at least about 1.18 inches.

10. The heat shield as recited in claim 4, wherein the minor inside diameter is about 2.0 inches and the convolution height is about 0.110 inches.

11. The heat shield as recited in claim 10, wherein a pitch of the convolutions is at least about 1.18 inches.

12. The heat shield as recited in claim 4, wherein the minor inside diameter is about 3.0 inches and the convolution height is about 0.118 inches.

13. The heat shield as recited in claim 12, wherein a pitch of the convolutions is at least about 1.37 inches.

14. The heat shield as recited in claim 4, wherein the heat shield further consists of a black outer coating.

15. The heat shield as recited in claim 4, further comprising an end cap attached to at least one end of the tubing.

16. A method of shielding heat generated from an automobile exhaust gas recirculation system (EGR), the EGR having a conduit for diverting exhaust gas, the method comprising:

at least partially surrounding the conduit with a convoluted tube, wherein the convoluted tube consists essentially of two layers of aluminum, the convoluted tube including convolutions comprising a height equal to a difference between a major outside diameter of the convoluted tube and a minor inside diameter of the convoluted tube, wherein,

the height of the convolutions is at least 0.090 inches; and, the minor inside diameter is between about 0.75 inches and about 3.0 inches.

17. The method as recited in claim 16, wherein the pitch of the convolutions are at least about 1.18 inches.

18. The method as recited in claim 17, wherein the tube further comprises a dark-colored coating.

19. A method of forming a convoluted tube, comprising:

wrapping layers of aluminum around a mandrel having a diameter of 0.5 inches to 3.0 inches, wherein at least one of the layers includes an adhesive;

passing the wrapped layers between a worm and nut die to convolute the material, wherein the worm and the nut each have a thread height of at least 0.063 inches and a pitch of at least 0.787 inches; and,

passing the convoluted layers through a heat zone to thermally set the adhesive and substantially bond the layers together.

20. The method as recited in claim 19, wherein the diameter of the convoluted tube is between 0.75 inches and 3.0 inches, the thread height is at least 0.075 inches, and the pitch is at least about 1.18 inches.