US2402040A - Wood tubing and the like - Google Patents

Description

June 11, 1946.

P. GOLDMAN WOOD TUBING AND THE LIKE Original Filed Nov. 28. 1943 Invw/Zor: 0 PauZB.G;0Zdman 02 W AIM 0 022%;

Patented June 11, I v x wool) TUBING AND THE LIKE Paul R. Goldman, Andover, Mass., assignor to Plymold Corporation, Lawrence, Mara, a corporate body Original application November 28, 1942, Serial- No. 467,243, now Patent No. 2,352,533, dated June 27, 1944. Divided and this application March 14, 1944, Serial No. 526,462

Claims. (01. 13879) 1 v 2 My present invention relates to tubes, pipes where a plurality of spiral wraps are provided, and other hollow cylindrical structures having each succeeding wrap is wound oppositely to the thin wood strips and sheets as a component maone preceding, so that the resulting plural layer terial. It aims to provide for such structures core element 1, such as that of Fig. 2, has its novel constructions, arrangements and combina- 5 layers or plies individually alternated as to the tions of component means and elements presentdirection of wind. ing in the resulting articles and products dis- Thus the side-edge juncture line in any given tinctive strength and rigidity, both axially and layer crosses such line of any next adjacent layer, radially, for a given mass and weight of the wood whether inside or outside it. Desirably also the material, and wherein the relation as between plies having the same direction or wind, such for flexure resistance as characterized by axial example as 8, 8b, 8d, etc., are slightly advanced strength and rigidity, on the one hand, and or set back relative to each other, with resultant crushing resistance as characterized by radial staggering or offsetting of their spiral joint lines. strength and rigidity, on the other hand, may The number of windings, plies or layers for such be predeterminedly selected and calculated as core element 1 may be varied within a consideraappropriate to different use conditions and reble range, from a single layer upward, depending quirements. on the wall thickness desired or permissible in This application is a division of my copending any particular instance. in the majority of cases application Serial No. 467,243, filed November 28, about three to seven plies are employed, with four 1942, now Patent 2,352,533, dated June 27, 1944, or five representing an average construction, it containing claims directed to certain novel procbeing understood that the veneer strips such as esses and methods whereby tubular wood veneer 6 and 6a of Fig. 1 are representative and usually products such as here concerned may be manuare followed by'others such as 81:, 8c, 811, Fig. 2, Iactured. these being similarly applied under alternated In the accompanying drawing, representing spiraling starting at either end of the plural ply somewhat diagrammatically a typical embodicore I. Desirably the individual wood strips or ment of the invention: tapes 8, 8a, etc., which may themselves be plural Fig. 1 shows an initial stage of the process, ply in some instances, have the grain or prewherein a tubing core is formed; dominant fibre direction disposed lengthwise of Fig. 2 illustrates in cross section a typical rethe strips, as indicated at 8g. Fig. 1, so that in suiting core element; the formed core 1 they extend angularly and out Fig. 3, also relating to the core-forming stage, of parallel to the core axis.

illustrates an example oi a pressure treatment Each such thin wood layer or wound strip 8,

01' the core; 8a, etc., as spiraliy laid on the mandrel is coated,

Figs. 4 and 5 represent an intermediate phase, either before or' in conjunction with the wrapbeing respectively an elevation of a short length ping. with a bonding or plastic agent, such as of the tubing under construction and a crosscertain glues, cements or like adhesive or uniting section of the resultant intermediate structure: agents, preferably one of the polymerizableor Fig. 6 illustrates a step in a further or third plastic type either of the cold setting or the heat phase of development of the product; and 40 setting varieties, depending on the particular Fig. 7 is a cross-sectional view of the finished field of use for the tubing product in the given tubing product. instance. 4

Referring first more particularly to Figs. 1 and On completion of the winding of the core ele- 2, the initial phase or operation in accordance ment 1, pressure is applied uniformly to the enwith the invention comprises the formation of tire core, either before or after it is removed an inner element or core I. For this purpose a from the mandrel M. Such pressure application removable mandrel M is'employed, of a diameter may be variously accomplished. One effective the same as the inside diameter desired for the and convenient procedure is that of temporarilycore and for the resulting tube or pipe as a whole. wrapping the core I with a strip or web or resil- On this mandrel there is wrapped spirally one 1 ient material 9, Fig. 3, such as a rubber or rubberor a successive plurality of layers or laminae of like composition, wound onto the core under tenthin wood stripping or veneer 6, la, etc. Each sion proportioned to the degree of pressure desuch layer is individually wound spirally with a sired, removabiy held at its ends as by suitable selected pitch such that the leading and trailing ties or clamps, not shown.

edges of succeeding turns are abutted. Further, The cores, such as the element l,'with the pres- 3 sure-applying means such as 9 in position upon them are then subjected to a drying and setting or polymerizing treatment. In the case of coldsetting binding agents this may be accomplished by hanging or otherwise placing the tubing cores so as to. subject them to ordinary room temperatures for a period of usually 24 to 48 hours, more or less. With heat-setting bonding agents the cores with the pressure-applying means upon them may be suspended in or passed through a drying compartment or oven at controlled temperatures generally of the range of about 180 to 240 depending on the particular agent and on the time available. In general also the polymeri-- zation, curing, drying or setting of the cores where relatively coolor cold-setting agents are employed may be considerably accelerated by a heat treatment such as referred to.

Following the drying and setting operation, wherein the compressive pressure such as afforded by the resilient means 9 is maintained, with or without the application of heat, such means is removed'from the core element 1, leaving the core in individually finished condition as a compact and substantially homogeneous unit in readiness for the surrounding outer elements to be described.

It is particularly noted that by reason of the wholly spiral disposition of any component veneer strips 8, 8a, etc., of the inner base or core elements l, maximum advantage is taken of the compression resisting capacity of such spirally formed structure. Resultantly these bases or cores l are of high rigidity and strength in the radial direction, that is, against stresses acting radially and tending to crush or deform them. It is a demonstratable fact that for a given total wall thickness the radial strength factor of a cylindrical structure varies with the diameter, being relatively high for the smaller diameters, and decreasing proportionately with any increase in diameter. Hence by utilizing the inherently radially rigid spiral formation for the innermost 01 base element Lthe one having the least internal diameter, the total resulting radial rigidity for the final tubing product of given overall 'or external diameter, is proportionately increased. Otherwise stated, due to its innermost location and consequent relatively small diameter, adequate radial rigidity is obtained with a less wall thickness and weight of component material. The result is a core or base I which is highly resistant to radial stresses but which is of relatively less rigidity in the axial direction, against forces tending to bend or deflect it or cause it to sag out of straight alignment, such as a weight or pressure intermediately applied to the element while it is supported only at or near its ends. 1

Turning now to Figs. 4 and 5,.these represent diagrammatically a further and intermediate phase in the manufacture of the product, under ,the process of my said application Serial No.

467,243. A finished base tube or core I is itself manipulated in-the manner of a mandrel to receive upon it a longitudinally rigidiiying element represented as a whole by the numeral Ill. The resultant intermediate structure comprising the base i and the surrounding element It) will be referred to as the tubing body.

As shown in Fig. 4 byway of example, this core-surrounding element iii comprises one or more wrappings or layers of wood veneer in sheet form wound straight onto the core I, that is, with the side edges of the veneer sheets permitdicular to the core axis. The veneer for this core-surrounding element l0 may be of single thickness, or it may comprise a plurality of plies,

, two or more, three of which plies ii, Ho and lib are shown in Fig. 4 by way of example, such veneer plies being bonded together either before or in association with their application to the core. Further, the wood material for these sheets is selected and arranged so as to have the grain or fibre extend predominately crosswise of the sheet, as indicated at i2 in Fig. 1, that is, in or approximately in parallelism with the axis of the core as the veneer is wound onto the latter.

Thetubing base or core I has one or more full turns or wraps of the veneer sheeting it] applied to it straightwise, that is, with a straight-on wind as above explained. As indicated diagrammatically and in an exaggerated manner at the left in Fig. 5, wherein two turns or layers of the veneer iii are illustrated by way of example, the leading and the terminal longitudinal edges of this veneer are disposed in close radial proximity to each other, so that the entire resulting coresurrounding element i0 is of uniform thickness, with no excess overlap or part turns. The individual plies such as H, Ila, lib, Fig. 4, as also the spirally applied veneer strips 8, 8a, etc., of the tubing base, generally have a thickness of the order of about ya to ,5 0 of an inch in the smaller sizes of tubing; that is, tubing of internal diameters of from say A inch up to 3 or 4 inches. Hence the outward deflection 0r shouldering of the material of the straight-wound veneer ill where it passes from one convolution to the next, as at the left in Fig. 5, is but a similar small fraction of an inch in radial dimension. But by using a length of the veneer i0 precalculated to afford exactly the desired number of winds, or by cutting it of! directly opposite the position of its leading longitudinal edge as applied upon the core, the terminal longitudinal edge is abutted against and merged with the adjacent shallow shoulder in smooth non-thickening juncture with it. After the following pressure and setting operations the resulting joint is scarcely discernible. Prior to or during the operation of winding the core-surrounding element Hi, it is coated at one or both faces, except at any externally exposed surface of the final wrap, with'a similar impregnating and bonding agent as in connection with the formation of the core 1. The resulting composite tubing body composed of both the base 1 and the surrounding element ill is then subjected to external pressure uniformly over its outer cylindrical surface. This again may be variously accomplished, as by temporarily winding onto it under determined tension a resilient pressure strip or web such as that indicated at 9, Fig. 3, in connection with forming the core. While maintaining this pressure the core-surrounding element ll of the tubing body is cured, dried or set, with or without the application of heat, also as previously described in connection with Figs. 1 to 3. On completion of the drying and setting the pressure strip or other compressive means is removed, leaving a composite tubing body such as that of Fig. 5 as an intermediate product.

Such composite body i-tii has a high radial. rigidity derived primarily from the base i. This is eflectively augmented by the surrounding ele ment iii. The latter, however, serves mainly to afford an axial rigidity or fiexure resistance in the resulting product of maximum efiiciency with the given thickness and weight of the-component wood material. This is largely due to the do termined fact that for a given character and thickness of the wood material substantially greater longitudinal or axial rigidity is obtained from the straight-on or convolute wound formation as illustrated in Figs. 4 and and wherein the natural graining or fibre direction of the veneer is disposed in general parallelism with the tubing axis. Further, such axial or fiexure-resistant strength for a laminate wood cylinder of given wall thickness increases with the diameter of the cylinder; for exampla'such tube or cylinder of say 1 in. diameter and having a wall thickness of say a in. has a higher longitudinal rigidity, against axial fiexure, than a similarly formed tube or cylinder of say /2 in. diameter with the same wall thickness and material.

Hence, in accordance with the invention, by locating the straight-grained straight-wound veneer element in an outer position, outside the core or base 1, and thereby affording it a relatively larger diameter, the inherent high axial rigidity factor of such element In is made to contribute to a maximum extent toward a total axial rigidity for the resultant wood tubing product of a given material and given inside and overall diameter, wall thickness and weight. In the resulting tubing body such as 1-40 its two main elements thus cooperatively complement each other to produce a structure of remarkabl high rigidity both radially and axially, and in which each such factor is present to a greater extent than in either of the elements alone. By relatively varying the thickness of the respective elements 1 and ill the radial and the axial rigidity factors may be proportionately adjusted as any particular use circumstances may require. If desired, one or more further elements corresponding either tothe core I or the intermediate element It may be-applied.

With a straight-on application of straightgrained veneer as illustrated and described in connection with Figs. 4 and 5 there is in some instances a tendency at its outer surface for it to check or crack lengthwise of the tubing. To overcome this I complete the tubing by applying to any external straight-laid element such as ill of the drawing an outer covering or protective and finishing jacket such as indicated as a whole by the numeral 13 in Figs. 6 and '7. This may be composed of one or more spiral wraps of thin wood stripping. two of which are here indicated at M, Ma. The procedure for the application of these spirally disposed cover strips, in which the grain a preferably but not necessarily extends mainly lengthwise the strips, may be substantially the same as already fully described in is a. finished substantially homogeneous tubing unit having hard, wear-resistant surfaces anda high total radial and axial rigidity as above explained.

Other and continuous processes for fabricating products such as those hereof are disclosed and claimed in the copending application of Goldman et al., Ser. No. 488,854, filed May 28. 1943. Other tubing products to the manufacture of which the processes of said Goldman et a1. application and 3 6 of my previously mentioned copendent Patent 2,352,533 are applicable. are disclosed and claimed in my copending application Ser. No. 476,690, filed February 22, 1943.

My invention is not limited to the particular embodiment as herein described or illustrated, its scope being pointed out in the appended claims.

I claim:

1. Lamillar wood veneer tubing comprising a radially rigid core of length-grained tape-like wood veneer strip material spirally wound in edge-abutted relation and bonded into a unitary hollow tubular element, a core-surrounding amally rigid element consisting of straight-on wrapping of veneer having its fibre direction paralleling the tube axis and being compressively bonded with itself and to the core to provide with the latter a composite tubing body, and a spirally wrapped veneer strip covering and compressively bonded to said tubing body.

2. An integrated plywood tubing product comprising in combination a length-grained tape-like wood-veneer strip spirally wound in closed edgeabutted formation both as to wind direction and grain extent presenting a unitary radially rigid hollow tubular core, a concentric core-surround ing axially rigid element consisting of a straighton wrapping of wood veneer formed and positioned to present its graining predominantly parallel to the core axis and having both longitudinal side edges closely proximateto a given radial plane-lengthwise of said element, said core-surrounding element having incorporated with it a synthetic resinous agent interbonding it to said core to provide with the latter a composite tubular body, and a further spirally-wrapped tapelike wood-veneer strip covering and-bonded to' said body to present therewith the integrated tubing product.

3. Rigid hollow tubing having concentric continuous smooth-walled inner and outer surfaces.

said tubing formed of wood veneer stripping and comprising a spirally disposed edge-abutted winding of said stripping defining'a core, an intermediate wood veneer layer of circumferentially uniform thickness convolutely surrounding said core with the grain paralleling its axis, and an outer spiralled edge-abutted winding of said veneer stripping covering said intermediate layer, each winding and layer being resin-bonded to that next adjacent and together presenting an integrated substantially homogeneous unitary product of predetermined radial and axial strength and rigidity for the given total wall thickness.

4. A substantially rigid hollow tubing structure comprising a series of tape-like length-grained veneer strips wound spirally one on another alternately in opposite directions each in edge-abutted relation and bearing between winds a polymerized plastic bonding agent consolidating them into a dense-walled radially rigid hollow base unit, a predominantly transversely grained veneer web wound straight onto said base unit convolutely with the graining lengthwise the latter, said web applied to a uniform thickness of wind about the entire circumference of the base unit with its leading and trailing longitudinal side edges edges terminated closely proximate to the same radial plane lengthwise of the unit and beingsimsaid tubing body.

5. An integrated plywood tubing product comprising in combination a series 01 length-grained tape-like wood-veneer strips respectively wound in alternately opposite directions in closed edgeabutted spiral formation both as to wind direction and grain extent and having between successive strips a synthetic resinous agent bonding them into a unitary radially rigid hollow tubular core, a concentric core-surrounding axially rigid element consisting of a straight-on wrapping oi. wood veneer formed and positioned to present its graining predominantly parallel to the core veriang and similarly bonded to said body to

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