US2755821A - Laminated tube structure - Google Patents

Description

July 24, 1956 w. F. STAHL LAMINATED TUBE smucruas Filed April 21, 1953 IN V EN TOR: fldmfib za/, B Y M, kZzfizt y w,

ATTORNEYS.

LAMINATED TUBE STRUCTURE William F. Stahl, Kenilworth, Ill. Application April 21, 1953, Serial No. 350,083

8 Claims. (Cl. 138-76) This invention relates to laminated tubes, and more particularly to laminated tubes wherein at least a portion of the laminations are formed of a material that cannot be secured together by presently-known means such as glue, adhesives, heat sealing, etc. The laminated tubes may be cylindrical, square, rectangular, or of any desired cross-sectional configuration. Such tubes have numerous uses and, for example, may be employed in numerous electrical applications. Exemplary of an electrical application is the use of the tubes as bases or forms for coil windings, transformer windings, etc.

There are two widely used methods for forming lamihated tubes. One of these methods is, spirally winding separate layers or strips of the material forming the tube one upon another to provide the laminations. This type of operation is continuous and very rapid and tubes formed by this method are frequently wound at a speed of approximately 80 feet per minute. The second method is to employ a wide band of material and coil it so that the convolutions he one upon another and form a cylindrical tube. This is not a continuous operation in that when a sufficient number of turns are taken to provide the desired wall thickness the wide band or web of material must be severed and a second winding operation must then be started before another tube may be formed. In this type of operation the length of the tube is limited by the width of the starting web or band. The rate at which tubes may be formed in the convolute winding operation is approximately 2 feet per 10 minutes. It is apparent, then, that spiral winding of tubes is the most desirable from a commercial point of view in that it is by far the less expensive and most rapid.

There are a number of materials, particularly in the plastics, that have excellent dielectric and insulating properties and could be used very desirably in the electrical field Where members having high dielectric and insulating properties are needed. A number of such needs involve the use of tubular members, as for example the forms for coil windings, etc. With such materials it is a simple matter to provide just the right dielectric strength needed by providing the number of layers of the material required to yield the specific dielectric capacity. The difificulty has been, however, that a number of these desirable materials cannot be secured to themselves by known means so that a rigid, unitary structure could be provided. It has been customary to form tubes of such materials by cylindrically winding webs of the material and then securing the laminations together by mechanical means such as by rivets or bolts, etc. The reason this method of tube formation has been employed is that it has heretofore been believed impossible to form tubular members of such material by the usual spiral winding method because spiral winding of. a number of laminations one upon another requires that each layer or lamination be rigidly joined to the one before and that it covers. Spiral winding could not, then, be used where the material forming the laminations could not be secured to each other by adhesives,

States Patent ice or by heat sealing or other known means. I have dis covered a structure that permits the formation of spirallywound laminated tubes and in which at least some of the laminations are formed of a material that cannot be secured to itself or to other materials by presentlyknown means.

My laminated tubular structure is also desirable for another reason. In spiral winding operations wherein laminated tubes are formed, stresses are frequently built up in the tube during the forming thereof that tend to distort the same, though initially the stresses are overcome by the adhesion of one spiral layer to another and the formation thereby of a rigid, integrated tube structure. However, when the tube is subsequently employed as a bobbin core and electric conductors are wound thereon to form coils, etc., the heat developed by the current flowing through the conductor tends to amplify the latent stresses and cause core distortion which is undesirable. The same distortion condition arises when the laminated tubes or cores are treated to obtain certain mechanical or electrical characteristics, as for example resin impregnation of the laminations. Impregnation treatments are generally harsh and bring out the unequal stresses within the treated core and often result in core distortion.

It is, accordingly, an object of this invention to provide a laminated tube structure in which materials that cannot be secured to themselves or to other materials may be used to form a spirally-wound laminated tube structure. Another object of the invention is to provide a laminated tube having spaced-apart inner and outer tube portions formed of strips spirally wound one upon another and secured together, and sandwiched therebetween spirally-wound strips of a material that cannot be and is not secured either to the layers forming the sandwiched tube portion or to the inner and outer tube portions. Still another object is to provide a sandwichtype spirally-wound tube in which the sandwiched tube portion is unsecured to the inner and outer tube portions and the layers or laminations thereof are spirally wound and have overlapping edge portions. A further object of the invention is to provide a laminated tube that is self-adjustable and stress-releasing so that unequal stresses developed therein in the forming or treating of the tube are eliminated. Additional objects and advantages will appear as the specification proceeds.

An embodiment of the invention is illustrated in the drawing, in which- Figure 1 is a transverse sectional view; Fig. 2 is a perspective View showing some of the strips in position to be spirally wound to form the tube; and Fig. 3 is a broken longitudinal sectional view showing a tube as used to provide a bobbin core.

The laminated tube 10 consists of an inner tube portion 11, an outer tube portion 12 spaced therefrom, and a central tube portion 13 sandwiched between the inner and outer portions 11 and 12. The inner portion 11 is formed by a plurality of spirally-wound strips 14 that are wound so that one edge of each strip abuts the opposite edge of the same strip. Any number of strips maybe wound one upon another and preferably each additional spiral strip winding is staggered so that the joint 15 formed by the abutment of the edges of the preceding strip is completely covered by the subsequent Winding. That is to say, the abutting edges 15 of each strip are not in alignment but are offset from each other. Any suitable material may be used to form the inner tube portion 11 and the particular material will depend upon the desired physical and electrical characteristics that are needed for any particular use. For example, the inner tube portion 11 may be formed by spirally Wind'- ing a plurality of strips of insulating paper one upon another and preferably the strips are coated with an adhesive so that the contiguous strips are secured together by the adhesive. A water-soluble glue or adhesive may be employed for this purpose.

' Coaxial with the inner tube portion 11 and wound tightly thereabout is the central tube portion 13. The central portion 13 is formed of a plurality of strips spirally wound one upon another to form the tube portion 13. Preferably the strips 16 that are spirally wound to provide the central tube portion 13 are wound so that one edge of the strip overlaps the opposite edge to form a lapped joint that is indicated generally by the numeral 17. In the illustration given, the edge 18 of the strip 16 overlaps the edge 19 of the strip on each successive spiralled turn of the strip.

Any material may be used to form the central tube portion 13, and any number of layers may be provided by simply increasing the number of strips 16 that are employed and spirally wrapping each strip upon the preceding one. I prefer to use a plastic material to form the strips 16, and especially desirable is a cast polyester film that is thermo-setting. Moreover, a plastic material of this sort having good dielectric and temperature characteristics and that is smooth and non-fibrous has been found to provide excellent results. The electrical properties of the tube may be varied by increasing and decreasing the number of strips 16 of plastic that are wound upon the inner tube portion 11. The strips 16 though wound one upon another in spiral form are not secured together by adhesive or otherwise and are not secured to the inner tube portion 11. Winding the strips 16 so that one edge thereof overlaps the opposite edge provides a plurality of spaced-apart lips at the joint 17 that extend laterally from the tube periphery. It is desirable that each subsequent strip 16 be staggered relative to the preceding strip so that the lapped edges 17 of each strip are not aligned but rather are oliset from each other. A plastic material having the properties set out above and that has been used advantageously for the strips 16 is sold under the trade name Mylar.

The outer tube portion 12 is formed from a plurality of spirally-wound strips 20 that are wrapped or wound in an identical manner with the strips 14 forming the inner tube portion 11. A smooth joint or seam 21 is thereby provided and preferably the initial strip 20 contiguous with the plastic strips 16 is staggered relative thereto so that the lapped seams 17 are completely covered. Similarly, each subsequent strip 2-0 is staggered relative to the preceding strip so that the smooth seams 21 of each strip are not aligned. Any material may be employed for forming the outer tube portion 12, and an adhesive-coated insulating paper may be employed.

The strips of insulating paper 20 wound one upon another are secured together by adhesive, while the initial or inner strip 20 is not secured to the central tube portion 13.

The outer strips 20 are spirally wound tightly about the central tube portion 13 made of the plastic strips 16. Since no adhesive or other means is employed to secure the outer tube portion to the central tube portion, limited shifting or movement between the tube portions may result under certain conditions, while the laterally-extending lips 17 provide a relatively sharp edge that tends to bite into the strips of paper 20 and to thereby normally hold the inner and outer tube portions in position relative to each other. In the same manner, the inner tube portion 12, since it is not secured to the central tube portion 13, may shift relative thereto, while the joint or seam 17 also provides an inwardly-extending lip having a relatively sharp edge that tends to bite into the inner tube portion and to lock the inner portion and central tube portion together.

Normally, the friction between the central tube portion 13 and the inner and outer tube portions 11 and 12 respectively that lie against the same, and the biting action of the inwardly and outwardly extending lips provided by the joints or seams 17, tend to hold the tube portions in predetermined position. Since the spirallywound strips forming the inner and outer tube portions are secured to the contiguous strips of each portion by adhesive, a rigid and stable tube structure is provided. However, when the tube 10 is cut into appropriate lengths to provide a core 22 equipped with terminal flanges 23 to provide a bobbin upon which electrical transformer windings may be mounted, the heat developed by the flow of current through the conductor turns does not cause a distortion of the core 22 by amplifying any latent stresses that may have developed in forming the tube 10. Instead, a shifting between the tube portions is permissible and a self-adjusting or self-aligning of the core portions results that is effective to reduce and substantially eliminate the stresses that normally cause core distortion. The same shifting and self-aligning characteristic results in adjustment of the tube portions relative to each other whenever the tube or core is subjected to treating operations that normally would cause the unequal tube stresses to distort the tube or core during such operation.

The tube structure I have provided is sufficiently strong and rigid to enable its use in customary applications. At the same time, the structure permits the use of materials such as certain plastics that have very desirable dielectric and insulating properties but have the disadvantages of not being susceptible to adhesives and heat sealing methods, etc., to secure layers of the material to each other or to other, different materials. Yet the tube structure may be formed in a spiral winding operation wherein the rate of tube formation is very high and is therefore desirable commercially.

While in the foregoing specification and embodiment of the invention has been set forth in considerable detail for purposes of illustration, it will be apparent to those skilled in the art that considerable deviation from the details may be made without departing from the spirit of the invention.

I claim:

1. A laminated tube, comprising a plurality of strips of insulating material wound one upon another and secured together to form a tubular base, a plurality of plastic strips wound one upon another coaxial with said base and snugly enclosing the same, one edge portion of each plastic strip being in overlapping relation with the opposite edge portion of the same strip, and a plurality of strips of insulating material wound one upon another coaxial with said plastic strips and snugly enclosing the same, said last-mentioned strips of insulating material being secured together one upon another, said plastic strips being sandwiched between said base and said last-mentioned strips and being maintained in sandwiched relation therebetween solely by the frictional grip thereof.

2. A laminated tube, comprising a plurality of spirally- Wound strips of insulating material, one upon another and adhesively secured together to form a tubular base, a plurality of spirally-wound strips of thermo-setting plastic, one upon another and all being coaxial with said base and snugly enclosing the same, and a plurality of spirally-wound strips of insulating material coaxial with said plastic strips and snugly enclosing the same, said last-mentioned strips of insulating material being adhesively secured together one upon another, said strips of plastic material being sandwiched between said base and said last-mentioned strips but not secured thereto or to each other.

3. A laminated tube adapted for electrical insulating uses, comprising a plurality of spiraled strips, one upon another and all being secured to each other by adhesive to form a tubular base, a plurality of thermo-setting plastic strips spirally wound one upon another coaxial with said base and snugly enclosing-the same, one edge portion of each strip of plastic being in overlapping relation with the opposite edge portion of the same strip to provide laterally-extending lips, and a plurality of spiraled strips coaxial with said plasti strips and snugly enclosing the same, said last-mentioned strips being secured together one upon another by adhesive to form another tube portion, said plastic strips being sandwiched between said base and said outer tube portion out not secured thereto.

4. The laminated tube according to claim 3 in which said thermo-setting plastic strips are a cast polyester film having relatively high dielectric properties and are rela tively smooth and non-fibrous.

5. A laminated tube structure, comprising a plurality of spirally-wound strips one upon another and secured together to form a base, a plurality of spirally-wound strips formed of a material that is resistive to adhesives and heat sealing means as a means for securing the strips together, said second-mentioned strips being wound one upon another coaxial with said base and snugly enclosing the same, and a plurality of spirally-wound strips coaxial with said second-mentioned strips and snugly enclosing the same, said last-mentioned strips being secured together one upon another to form an outer tube portion, said secondmentioned strips being interposed between said base and outer tube portion, frictionally engaging each and being unsecured to either and to each other.

6. A spirally-wound laminated tube, comprising a plu rality of spirally-wound strips one upon another and all being secured to each other by adhesive and forming a tubular base, a plurality of thermo-setting plastic strips spirally wound one upon another coaxial with said base and snugly enclosing the same, one edge portion of each strip of plastic being in overlapping relation with the opposite edge portion of the same strip to provide laterally-extending lips, said plastic strips being resistive to adhesive, and a plurality of spiralled strips coaxial with said plastic strips and snugly enclosing the same, said last-mentioned strips being secured together one upon another by adhesive to form an outer tube portion, said plastic strips being sandwiched between said base and outer tube portion but not secured thereto or to each other.

7. A laminated tube structure comprising an elongated tubular base, at least one strip of material spirally wound upon said base and substantially covering the same with one spirally Wound edge thereof overlapping the other spirally wound edge thereof, and at least two strips of material adapted to be secured to each other, one strip being spirally wound upon said first mentioned strip and the other being spirally wound thereover and being secured thereto to form an outer, integrated sheath, said first mentioned strip being sandwiched between said base and sheath and frictionally engaging the same though otherwise unsecured thereto throughout its entire length.

8. A laminated tube structure comprising an elongated tubular base, an integral sheath coaxial with said base, and at least one spirally wound strip interposed between said sheath and said base and being spirally wound upon the latter with the longitudinal edges thereof in overlapping relation, said last mentioned strip being frictionally engaged by said sheet and base and being held in position therebetween by the frictional grip thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,390,644 Ritchie Sept. 13, 1921 1,495,823 Underhill May 27, 1924 2,054,769 Holtz Sept. 15, 1936 2,465,257 Nebesar Mar. 22, 1949 2,623,445 Robinson Dec. 30, 1952 2,640,501 Scott et a1. June 22, 1953

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