CA1092011A

CA1092011A - Thermal insulation enhancement

Info

Publication number: CA1092011A
Application number: CA263,801A
Authority: CA
Inventors: Gordon K. Lambert; Thaddeus D. Misiura
Original assignee: Parker Hannifin Corp
Current assignee: Parker Hannifin Corp
Priority date: 1976-07-27
Filing date: 1976-10-20
Publication date: 1980-12-23
Also published as: DE2655616A1

Abstract

ABSTRACT

A pipe, tube, hose or the like, has thermal insulation applied thereto in the form of a plurality of layers of tape having wrinkles therein defining air spaces serving to reduce the trans-mission of heat through the insulation. The wrinkles may be introduced by wrapping the tape about the pipe at an applied angle greater or smaller than the angle required for a given effective diameter, overlap factor, and width of tape.

Description

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FIELD OF INVENTION
In the manufacture of fibrous or reinforced tubes, it is usual practice to wind paper tape or the like in a helical fashion about a core or tube to provide multiple layers of . . .
material about a central body. In the same way, electrical '~; insulation has been applied to electrical conductors. Typical patents illustrating such constructions and methods are U.S.
Nos. 3,128,216; 3,296,051 and 3,813,026. In such constructions, great care is taken to assure positioning of the adjacent turns of the tape in such a manner that the edges of the tape are not ~; spaced apart and do not overlap.
, In some types of electrical conductors, tapes formed of insulating or conducting material are wrapped about a central conductor and in some instances, the edges of the tape `~ are spaced apart or overlap as exemplified by U.S. Patent Nos.
~i 3,300,573; 3,404,050 and 3,598,691.
;~ In some constructions, thermal insulating tape is applied to pipes, tubes, hose and the like by applying a -~ plurality of layers of helically wound tape formed of material having low heat conductivity such as polyethylene, fiberglass, polyester, "Mylar" (Trade Mark) or laminated asbestos products.
~` However, as in the prior art, the angle at which the tape is -~;;i' supplied to the tube or conductor being insulated is controlled .',r~ to equal the proscribed angle calculated from mathematical ,.~., relationships among the actual tape width, fractional overlap, and effective diameter of the tube or conductor to which the tape is to be applied.
THE PRESENT INVENTION
In order to increase the thermal insulating propPrties of the layer of insulation applied to a pipe, tube, hose or the .

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like, the present invention serves to introduce a multitude of air spaces or cavities in the insulation by presenting wrinkles in the tape applied to the tube or pipe. This can be -, accomplished by supplying the tape to the pipe or tube at an angle different from that which is calculated from the parameters ~-of the product being taped such as: the overlapped portion which can be controlled by the speed which the product is moving in relation to the angular tape head speed; the effective diameter of the product which is related to the tube diameter;
tape thickness and fractional overlap; and the width of the tape being applied. The angle at which the tape is supplied -~
to the tube is preferably greater than the calculated angle with the result that the wrinkle occurs at the trailing edge ;
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' Thus the present invention provides a thermally insulated tubing product comprising: (a) a single tubular core . : - ..
element for conveying a fluid the temperature of which is to be maintained, said tubular core element having a smooth and ' uninterrupted cylindrical outer surface; (b) a spiral wrapping ~;~

of thermally insulative tape covering said core element, said , . .i .
,: tape being of substantially uniform thickness, said tape being contiguous to said core element around the entire circumfer-ential extent of said cylindrical outer surface, said tape being randomly wrinkled and defining random air spaces around ` the entire circumferential extent of said core element to enhance the insulating properties of said tape; and (c) a jacket protectively enclosing said core element and said wrap.
In another aspect the present invention provides a -thermally insulated tubing product comprising: (a) a single tubular core element for conveying a fluid the temperature of -;, -

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which is to be maintained, said tubular core element having a smooth and uninterrupted cylindrical outer surface; (b) a spiral wrapping of thermally insulative tape covering said core :: element, said tape being of substantially uniform thickness, said tape being contiguous to said core element around the . entire circumferential extent of said cylindrical outer surface, said tape having an actual helix angle that differs from the ,:
., helix angle calculated to produce a smooth and wrinkle-free .; wrap, said tape being randomly wrinkled and defining random .

air spaces around the entire circumferential extent of said core .;. ~.
. element to enhance the insulating properties of said tape; and (c) a jac]~et protectively enclosing said core element and said ~ wrap.
~ In a further aspect the present invention provides a thermally insulated tubing product comprising: (a) a single ~. tubular core element for conveying a fluid the temperature of ;~ which is to be maintained, said tubular core element having a ~: smooth and uninterrupted cylindrical outer surface; (b) a first . spiral wrapping of thermally insulative tape covering said core element, said first wrapping being immediately contiguous to said core element around the entire circumferential extent of said cylindrical outer surface, said first wrapping having an actual helix angle that differs from the helix angle calculated to produce a smooth and wrinkle-free wrap, said first wrapping being randomly wrinkled and defining random air spaces ;
. around the entire circumferential extent of said core element ;~ to enhance the insulating properties of said first wrapping;
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.`.~ (c) a second spiral wrapping of thermally insulative tape covering said core element and said first wrapping, sai~d second :` 30 wrapping having an actual helix angle that differs from the: '

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helix angle calculated to produce a smooth and wrinkle-free wrap, said second wrapping being randomly wrinkled and defining random air spaces adapted to enhance the insulating properties of said second wrapping; and (d) the difference between the , actual helix angle and the calculated helix angle being greater for said first wrapping than for said second wrapping, and; (e) a jacket protectively enclosing said core element and -;! said wrap.
, -~ In a preferred embodiment of the above product the i 10 angle calculated to assure a smooth tape wrap~i~ calculated according to ~he equation cos A = W (~ L) wherein A is said De - angle, W. is the actual tape width, L is the portion of the tape width overlapped, and De is the diameter of the core ~;~
; element and the tape already applied.
Preferably such a product is provided wherein the thermal gradient of said product is greatest in the area ~` immediately surrounding the core element and lessens progres-~ sively in a direction taken radially outwardly from the element, - said air spaces being maximized in the area wherein the thermal : 20 gradient is highest to provide a maximum decrease in thermal conductivity in said axea.
Also preferably such a product is provided, including ` a third spiral wrapping of thermally insulative tape covering said core element and said first and second wrappings, said third wrapping having an actual helix angle that differs from the helix angle calculated to produce a smooth and wrinkIe-free wrap, said third wrapping being wrinkled and defining random ., . . ~
~; air spaces adapted to enhance the insulating properties of said ; third wrapping, and the difference between the actual helix angle and the calculated helix angle being smaller for said ~

third wrapping than for said second wrapping. ~ -.,, " , , ~ 3(a) . . .

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THE DR~N~ .
F~gure 1 is a cros~.sectional v~ew o~ a typical pipe ~ or tube provided ~th thermal insulation embodying the present invention; and Figure 2 is a longitudinal view of a portion of the construction shown in Figure 1. `
Figure 3-iisea-`diagrammaticmdlllustration~oflt~-picalY~
": equipment which may be employed in the manufacture of the product of Figure 1.
, 10 In that embodiment of the invention chosen for purposes of illustration in Figure 1, a pipe, tube, hose or the like is i.`
'~ indicated at 2 and may be formed of copper, steel, brass or other ~. -metal or may be formed of plastic or the like if desired. Thermal ` insulation in the form of a plurality of layers of helically wound tape 4 surrounds the tube 2 and presents a multitude of air spaces or voids resulting from the presence of wrinkles 6 in the various .
tape layers.
-. The tape employed preferably is characterized by its , .
low heat conductivity and for this purpose may be formed of .. :

polyethylene, fiberglass, polyester, "Mylar", laminated asbestos ~. material or the like. However, the heat insulating effect of such ...................... ~`~

.. `` material is increased by the presence of a multitude of air cells ,~. ~- :
within the assembly and between the various layers of tape.
..................... The assembly may be provided with an outer smooth layer of thermal insulation as indicated at 8 which may be formed of plastic, spirally wound tape or other suitable material.
The wrinkles which serve to form the air spaces between the various layers of tape may be produced in various ways as by , increasing or wrinkling the tape prior to its application to the ;''.f^ 30 central tube 2. However, the preferred method of introducing the `
wrinkles and air spaces into the tape is represented by Figure 2 .;.
~, wherein the wrinkles are developed during the application of the *trademark 4 ., ','` ' ':

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insulatin~ tape to the central tube. ~`~
~g shown in Pigure 2, the tube 2 i~ passed through the ~ ;
center of a rotatafile taping head 10 ha~ing a tape supply drum 12 thereon. The web of tape 14 pass~ng from the drum 12 is passed over a guide 16 from which the tape strand 18 is supplied tangentially to the pipe or tube 2.
In order to develop the desired wrinkles in the tape ; as it is applied to the tube, the tape is supplied to the tube at an angle which differs from that at which it is actually applied to the tube. Thus, the angle A at which the strand 18 passes ; . :.
from the guide 16 to the tube 2 is di~ferent from, and preferably -greater than, the angle B at which the strand 18 is applied to the tube. The difference in these angles with respect to the horizontal axis of the tube 2 preferably range from about 2 to 20, However, the preferred method of introducing the .
wrinkles and air spaces is explained by Figures 2 and 3 which represent a tube that is being wrapped by a tape thickness "T"
through an angle a of application, with an approximate 50~ ;
overlap. One relationship that specifies the proper angle of application to result in a smooth non-wrinkled surface is given by the equation cos a = W (+ L ?

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De where W is the actual tape width, L is the width of tape over-lapped (and for our example is equal to 1 3/8"), and De is the average or effective diameter of the tube plus tape upon which the tape is applied.

The angle so calculated is the angle at which the tape must be applied to produce a smooth non-wrinkled surface. The angle is measured from the horizontal and is the helix angle formed by the edge of the tape with the longitudinal axis of the ~' : , . . ,' ' . . : . ~ ' , ' . . .
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tube as thR re$erence li,ne~ In practice it is found that the angle may vary~considera~ly dependi,ng upon the eIongatIon , properti~es of the tape and yet produce a smooth wrapping. For the fiberglass mat tape used in this discovery the angle may vary by ', 2 and yet provide a smooth wrinkle-free wrapping. Where the angle ,' '~
,~ differs ~y more t~an 2 a wrinkled surface will appear, producing 'J` air voids within the thermal insulation.
the angle of tape application is greater than that ' calculated by the equation referred to above, the wrinkles will ,~ 10 form at the trailing edge of the tape. Similarly, if the angle , is smaller than the calculated angle, the wrinkles will form at the leading edge of the tape.
' On a typical taping machine the tube is passed through ` a rotatable taping head having a tape supply drum and passed over ' one or more guides to fix the angle of tape application with '~
'' respect to the tube.
~, The angle of tape application different from that calculated is controlled by: the linear speed with which the tube passes through the rotatable taping head; the speed of the ''' 20 taping head; and the fractional portion of the tape width that overlaps a preceding wrap of the tape.
, For a typical thermal insulating tape such as fiberglass ' mat the range of angle deviation producing wrinkles on the surface `' '' of the product is 2 to 10.
In practice, it is found expedient to produce the -~
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''` wrinkles and hence the voids as close to the tube as possible and ~, usually this occurs in the first 3 tapes of a 6 tape construction.

'',~ The remaining tapes are applied at or near the calculated angle .. . .
,' corresponding to the actual effective diameter of the preceding ' 30 wrap, so that a relatively smooth and round product results.

' The following table is an example of a typical product produced utilizing this innovative concept on a one-half inch ~ 1~)9Z(~

.'. ""~ '~ -' copper tubP. , ng.le:~e~ui~red ~o ~raduce.~ Actual Angl~'Resulting ,, Tape ' A 5m~oth: 5ur~ace~n A ~ri~n~le'd Sur~ace ':

2 54 58 :~
3 64 , : ,

4 69Q 70 ~ ollow~ng the'application of tapes to the tube in the a ~rinkle producing manner described, it is generally desirable to ' apply an outer layer or coating of material in the form of con- :~
ventionally applied tape or a smooth plastic coating to present ' :' a finished.appearance and contour to the assembly. ~', . T~e effectiveness o~ the thermal insulation thus pro-:. duced is materially enhanced over that resulting from the appli- ;
,.' cation of insulating tape in a flat unwrinkled condition to :,': :
. a tube in a conventional manner as indicated by the following test conducted on a fiberglass tape applied to a thickness of .' -., 1/2 inch where X is the conductivity coefficient of insulation ':' 20 in units of BTU/HR FT F/FT. .
Material ~ Wrinkled Tape . ~ :
.,`.............. Fiberglass Mat K = .295 K = .0167 , . :
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~- While the method and apparatus employed in the pro- ;.
.~ duction of thermal insulation in accordance with the present "'' invention may be varied, the type of equipment disclosed herein .
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has proven effective and is intended to be illustrative of a `, preferred embodiment of the invention.
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermally insulated tubing product comprising:
(a) a single tubular core element for conveying a fluid the temperature of which is to be maintained, said tubular core element having a smooth and uninterrupted cylindrical outer surface;
(b) a spiral wrapping of thermally insulative tape covering said core element, said tape being of substantially uniform thickness, said tape being contiguous to said core element around the entire circumferential extent of said cylindrical outer surface, said tape being randomly wrinkled and defining random air spaces around the entire circumferential extent of said core element to enhance the insulating properties of said tape; and (c) a jacket protectively enclosing said core element and said wrap.

2. A thermally insulated tubing product comprising:
(a) a single tubular core element for conveying a fluid the temperature of which is to be maintained, said tubular core element having a smooth and uninterrupted cylindrical outer surface;
(b) a spiral wrapping of thermally insulative tape covering said core element, said tape being of substantially uniform thickness, said tape being contiguous to said core element around the entire circumferential extent of said cylindrical outer surface, said tape having an actual helix angle that differs from the helix angle calculated to produce a smooth and wrinkle-free wrap, said tape being randomly wrinkled and defining random air spaces around the entire circumferential extent of said core element to enhance the insulating properties of said tape; and (c) a jacket protectively enclosing said core element and said wrap.

3. A thermally insulated tubing product comprising:
(a) a single tubular core element for conveying a fluid the temperature of which is to be maintained, said tubular core element having a smooth and uninterrupted cylindrical outer surface;
(b) a first spiral wrapping of thermally insulative tape covering said core element, said first wrapping being immediately contiguous to said core element around the entire circumferential extent of said cylindrical outer surface, said first wrapping having an actual helix angle that differs from the helix angle calculated to produce a smooth and wrinkle-free wrap, said first wrapping being randomly wrinkled and defining random air spaces around the entire circumferential extent of said core element to enhance the insulating properties of said first wrapping;
(c) a second spiral wrapping of thermally insulative tape covering said core element and said first wrapping, said second wrapping having an actual helix angle that differs from the helix angle calculated to produce a smooth and wrinkle-free wrap, said second wrapping being randomly wrinkled and defining random air spaces adapted to enhance the insulating properties of said second wrapping; and (d) the difference between the actual helix angle and the calculated helix angle being greater for said first wrapping than for said second wrapping, and;

(e) a jacket protectively enclosing said core element and said wrap.

4. A tubing as defined in Claim 3 wherein a plurality of said layers of tape have wrinkles therein.

5. A tubing as defined in Claim 3 wherein most of the layers of tape making up said insulation are wrinkled.

6. A tubing as defined in Claim 3 wherein the wrinkles in said tape are randomly distributed about the circumference of the pipe.

7. A tubing as defined in Claim 3 wherein an outermost layer of tape is unwrinkled.

8. A tubing as defined in Claim 3 wherein said tape is a laminated material.

9. A tubing as defined in Claim 3 wherein said tape embodies fiberglass.

10. A tubing as defined in Claim 3 wherein said tape has preformed wrinkles therein.

11. A tubing product as in Claim 3 wherein the angle calculated to assure a smooth tape wrap is calculated according to the equation wherein A° is said angle, W. is the actual tape width, L is the portion of the tape width overlapped, and De is the diameter of the core element and the tape already applied.

12. A tubing product as in Claim 11 wherein the thermal gradient of said product is greatest in the area immediately surrounding the core element and lessens progressively in a direction taken radially outwardly from the element, said air spaces being maximized in the area wherein the thermal gradient is highest to provide a maximum decrease in thermal conductivity in said area.

13. A tubing product as in Claim 11 including a third spiral wrapping of thermally insulative tape covering said core element and said first and second wrappings, said third wrapping having an actual helix angle that differs from the helix angle calculated to produce a smooth and wrinkle-free wrap, said third wrapping being wrinkled and defining random air spaces adapted to enhance the insulating properties of said third wrapping, and the difference between the actual helix angle and the calculated helix angle being smaller for said third wrapping than for said second wrapping.