US2348291A - Manufacture of plywood tubing and the like - Google Patents

Description

May 9, 1944. P. R. GOLDMAN MANUFACTURE OF PLYWOOD TUBING AND THE LIKE 'Filed Jan. 22. 1945 Patented May9, 1944 MANUFACTURE F PLYWQOD TUBING AND THE LIKE Paul R. Goldman, Andover, Mass., assignor to Plymold Corporation, Lawrence, Mass., a body corporate Application January 22, 1943, Serial No. 473,212

7 Claims.

My present invention relates to the production of hollow tubular articles such as pipes, tubing and the like of plural-ply material, especially wood veneer or plywood, either alone or in combination with other sheet or strip elements. In a prior copending application Serial No. 453,931 I disclose and claim lamillar veneer tubing illustrative of the product suchv as here concerned, together with methods of making the same. The present invention aims to improve in certain respects over that of said earlier application.

AIn the accompanying drawing illustrating diagrammatically the several steps or operative phases according to the method of the present invention, together with the associated means and product; N

Fig. 1 shows the series of operative stations and apparatus thereat;

Fig. 2 shows in cross-section an initial or core element of the tubing; and

Figs. 3 and 4, on -a somewhat smaller scale, are cross-sections representing the tubing as at a second or intermediate stage and a, succeeding or third stage, respectively.

The present method or process as awhole comprises a plurality of successive operative phases or stages of which three are indicated in the Fig. l diagram of A, B and C, each including certain steps and stations to be described.

At the iirst station A1 of phase A the inner or core elements 1, see also Fig. 2, are formed by spirally winding about a mandrel M thin wood stripping or veneer tape 8, 8a, etc., in successive layers or laminae, each with its edges abutting and with each succeeding spiral wrap having the opposite hand or direction of wind from the one preceding. In these veneer strips or tapes, usually about three to seven, and of which ve are here represented at 8 to 8d, Fig. 2, as average, the grain or prominent libre direction desirably is lengthwise of the strips, as in my above identied application.

The mandrel M at this lrst winding station A1 has a diameter the same as or substantially that desired for the inside diameter of the core and of the resulting .tube or pipe as a whole, such mandrel being of an adjustable-size type or otherwise, as preferred. The several plies or laminae of the cores l as formed at station A1 have applied to them a bonding or uniting agent,

Apreferably of the polymerizing `or plastic type,

such as a urea formaldehyde, a phenolic resin or 'other composition the polymerizing or setting of which may be facilitated and expedited by the the addition of heat. The procedure as described to this point, that is, through station A1 of phase A of Fig. 1, may be the same as or substantially that of my mst-mentioned application Serial No. 453,931 to the corresponding intermediate product status. s

On completion of the winding and the application of the bonding agent each resulting core l is transferred from a station A1 to a polymerizing or curing station A, Fig. 1. While in Fig. l I have represented but one station A1 feeding to the station A2, it should be understood that a number of such stations A1 with their corresponding spiral winding and bonding applying apparatus may be and preferably are employed simultaneouslyy so that a corresponding number of cores 'l may be under preparation at any given time.

Following the wrapping of the outermost layers such as 8d, Fig. 2, each core 1 is removed from its mandrel M. Each core isthen hermetically capped, plugged or otherwise sealed at its two ends, including the end faces of the pluralply walls themselves and also their central openings, making each core in eiect a closed cylindrical chamber. This sealing may be done either at station A1 or Az or intermediately. The sever-al cores l as represented at station A2 have received such capping or end sealing means, as indicated at la and lb. Further, the cap, plug or like sealing device at one end of each core, herein that at 1b, is equipped with a exible or other tubing 'lc 'communicating with the closed interior of the core and adapted for introducing thereto a gaseous medium, such as air, under pressure and desirably in a heated condition. l

At the core treating station A2 of phase A of the process one or any convenient plurality of the cores l are vertically or otherwise supported as upon an appropriate rack or frame or by sus'- pending them, as from an overhead track or endless conveyer, either by the gas in let V,tubing lc itself or other suspension means. This tubing 'lc for each core is in communication with a source of supply 0f the air or other gaseous medium under pressure, such as an air compressor of appropriate capacity, desirably adapted to afford pressures up to about lbs. as the approximate maximum. Where the medium is air, and also in the-case of other adequately stable gaseous media, these may be heated to temperatures ranging from room temperature up to as high as 300 F. or more, in some instances, depending on the particular bonding agent employed. The core elements l from the station or staapplication of pressure, either with or without Il tions A1 in their initial gre'en or non-polymen'zed condition are` to an appreciable extent permeable or penetrable by the compressed air or other gaseous medium at the positive pressure differentials contemplated. The resistance to permeative passage of the pressure medium through the cylindrical wall of a core varies somewhat with the gauge of the veneer, the kind of wood, the number of veneer plies contained and the nature of the bonding agent. In some instances it is found desirable to retard the through passage of the gasby applying to the cores a temporary outside sheath such as a paper wrap or a light coating of removable quick-drying lacquer or other sealing agent. In the great majority of cases, 'however,'such external treatment is found unnecessary, the permeation of the air or other gas under pressure through the cylindrical walls of the cores usually being at such a slow rate that the desired positive pressure differential as between the inside and outside of the core and internally of and throughout the core walls is of itself is concerned, it may be substantially the same as fully described in connection with Figs. 4 and 5 of my said copending case. As there explained, the straight-wound veneer sheeting element l0 may comprise one or a plurality of full turns or wraps, with the leading and the terminal longitudinal edges in close radial proximity to each other, so that the entire resulting core-surrounding element I0 is of uniform thickness free of excess overlap or part turns, and regardless of the gauge of the veneer which generally is of the ordei of V54 to 1/100 in. for tubing of from about 1/4 in. up to 3 or 4 in. internal diameter.

Before or during winding of the core-surrounding readily maintained for the necessary pOlymerizing period at the station A2.

The gaseous pressure differential thus supplied internally of the cores, and also the temperature, where heat above room temperature is employed, are proportioned-as appropriate to the particular urea formaldehyde, phenolic or other bonding agent and to the character and total thickness of the cylindrical wall of the given core. Largely by reason of the permeative action and penetration of the gas pressure medium into and through the core walls, whereby such medium and its positive pressure differential is more or less directly effective upon the bonding agent within the walls, the curing and polymerizing period is materially shortened. Thus the duration of the internal pressure and heat treatment as at station A2 may in many cases be as brief as 10 minutes or even less, and for the least readily pressurepermeable cores seldom requires more than one or a few hours. In general, the greater the positive pressure differential applied, the less is the time required. Also the time period in general may be shortened by heat, whatever the internal positive pressure differential utilized.

At. the end of this permeative gas pressure period'the first main phase or step A of the process is completed, the various cores 1 then being in readiness for transfer from station A2 for storage or further processing. These polymerized hard dry cores 1 may proceed from station A2 by endless conveyor or other transfer, to a second main operative phase B, which also comprises two steps and stations as indicated at B1 and B.

At a station such as B1 the base tubes or cores 1 are themselves manipulated in the manner of mandrels, each to have wrapped about it a longitudinally rigidifying element represented as a whole by the numeral Ill.` The resultant intermediate tubular structure comprising the base 1 and the surrounding element l0 will be referred to as the tubing body.

Similarly as in my preceding application Serial No. 453,931, the core-surrounding element I0 comprises one or more wraps of wood veneer in sheet form wound straight onto the-given core 1, that is, with the side edges of the single or plural ply veneer sheets perpendicular to the core axis. These veneer sheets are selected and a1"- ranged to have the grain or fibre extend predominantly crosswise the'sheet and hence in or approximately in parallelism with the axis of the core as the veneer is wo d onto th'e latter.

element l0 of station B1, it is coated at one or both faces, except at the externally exposed surface of the ilnal wrap, with a similar impregnating and bonding agent as in connection with the formation of the core 1.

As in the case of phase A, there may be a plurality of stations B1 simultaneously operating upon a like number of cores 1 to apply to them the straight-wound veneer elements ill. On completing said winding at the one or more stations Bl the resulting tube bodies, each comprising a core 1 plus an intermediate straight-on veneer winding I0, are transferred by conveyor or otherwise to station B2.

At or before reaching station B2 the tube bodies 1-l0 are capped, plugged or otherwise endsealed, similarly as in preparation for the previous core treatment at station A2, it being understood that if any portion of such prior sealing means overlapped the end portion of. the outer cylindrical wall of the core, in the manner of a flanged cap, at least such portion is removed prior to the winding on of the intermediate element I0. Otherwise the same sealing means may be retained from station A2 through the succeeding phases B and C, save for any appreciable projecting length of the pressure and heating tubing such as 1b.

l At station B2 one-'or more of the tube bodies 1-l0 are suspended or otherwise supported or conveyed in a generally similar manner as in connection with station A2. Here, however, the tube bodies are placed in or caused to travel through a closed pressure-tight chamber, as designated by the full line enclosureb. And in this case the exible tubing or the like 1b, instead of receiving a positive pressure medium is maintained in open communication with atmosphere or is connected to a source of negative pressure (vacuum), thereby to facilitate the creating of a positive pressure differential externally of, upon and into or through the body walls, as contrasted with the previous inside-out pressure as at station A2.

The tube bodies 1-I0 in the pressure-tight chamber b are externally subjected to a gaseous medium, generally air, under substantial pressure. This may be accomplished by pumping the air or other gas medium into, or admitting it under the selected pressure, to the chamber b. as at the pressure entrance port bx. By keeping the sealed hollow interiors of the tube bodies in communication with atmosphere through the described tubing connections or similarly creating a negative or less-than-atmospheric pressure In so far as the proce ure at station B1 in and 75 within them, the desired positive external pressure differential is attained. The procedure at station B2 may be expedited, with economy in supplying of the pressure medium, by the' provision of air-locks in connection with the chamber b, the tube bodies entering and leaving the lthe presence of the supporting chamber through such pressure-conserving locks..

Since the tubebodies 1I 0 to be compressively treated at station B2 have the composite strength of both the spiral-wound core element 'I and the straight-on applied veneer winding I0, a higher range of pressure differentials generally may be employed than at the core treatingstation A2. Thus for example the positive pressuredifferentials employed internally of the cores 'las at station A2 generally is within a range of about 15 to 50 lbs., while at station B2, by reason of radially rigid cores, external pressure differentials of a substantially higher range usually are practicable. This is also in part due to .the fact that the permeation of the pressure-supplying gas into or through the body walls is in general at a lower rate than for the cores alone.

Here again the polymerizing action may be further accelerated by the simultaneous application of heat. 'I'his may beaccomplished by supplying the gas pressure medium in a heated condition or by providing heat within the chamber b in any convenient manner, electrically or otherwise, as by installing lights, coils or other heating or heat-supplying sourceh in or effective upon the chamber b, including diathermal or radiant heating means under automatic or other control. The temperature range may be generally similar as in connection with station A2, from room temperature or thereabouts up to 300 F. or more, depending on the materials and bonding agents employed.

At the end of the treating period at station B2, which in general may be of a similar range of duration as at the station A2, the resulting intermediate products, consisting of the tube bodies 1 -Ill, having their total bonding and impregnating agent polymerized so as to present the outer elements l in a hard dry and substantially smooth clean condition at theirouter surfaces. are ready for' any following operation, such as phase C of the three-stage process. However for some purposes the tubular products resulting at the end of operative phase B may be utilized without further treatment, particularly where in the nature of the use they are to be directly enclosed permanently within some othier means. Preferably, however, the tube bodies resulting from the treatment at station B2 are transferred by conveyor means or otherwise to a further Winding station such as indicated at C1. Here again, as in the case of stations A1 and B1, a plurality of winding units or stations may be employed, so that a corresponding number of the tube bodies may be handled simultaneously.

At each such station C1 the tube bodies are again mounted or manipulated in the manner of a mandrel and have applied over their straight-laid veener winding I0 an outer covering or protective finishing jacket as indicated at I3 in Figs. 1 and 4. 'I'his may be similar to that of Figs. 6 and 7 of my earlier application Serial No. 453,931, comprising one or more spiral wraps of thin wood stripping, lengthwise the strips and with alternate strips wound of opposite hand. Bonding and impregnating means is applied, similarly as in connection with the procedure'at stations A1 and B1. Following the application of the one or more spiral veneer layers as atstation C1, two such layers being illustrated in Fig. 4, the resulting tubing products from the one or more stations'C1 ,latter after application of an outer are cured and set. under a polymerization expediting treatment at a station C2. This latter may be the same in all respects as at station B2, including a pressure-tight compartment c. Further detailed description in connection with station C2 accordingly is unnecessary.

The end product following completion of the treating period at station C2 of the third phase or stage C of the plural-phase process is a substantially homogeneous tubing unit of substantial rigidity both radially and axially and with hard and wear-resistant surfaces. improved method of my present invention, including particularly the 'subjection ofthe cores, the intermediate elements or tube bodies, or the spiral cover, to the compressive and permeative action of a gaseous pressure medium such as air, while maintaining a substantial positive pressure differential, internally as to the cores and externally as to the other product stages, an extremely uniform end product results. Its outer surface is relatively smooth and clean, being free of adhering foreign material such as frequently experienced under earlier practices. By reason of the maintained air or other gas pressure differential, and especially where the pressure medium is in a heated condition, the substantially direct contact thereof with the bonding and impregnating agents materially facilitates their polymerization.

While I have illustrated and described provision for a positive pressure differential through a gaseous medium applied internally of the core elements as at station A1, in certain instances, particularly with the larger or thicker-walled cores the pressure may be applied externally, similarly as for stations B2 and C2. Conversely the pressure at the latter stations may be utilized internally of the tubular structures. In still other instances differential counter-acting positive pressures may be applied simultaneously both inside and outside the hollow tubular structures, such as thosey with comparatively thick walls.

My invention is not limited to the particular steps or means as herein illustrated or described.

with the grain preferably y its scope being pointed I claim: 1. In the manufacture of wood tubing and the like, the process which includes the steps of spirally winding wood veneer stripping to form out in the following claims.

a hollow tubular core element, applying a polymerizable bonding agent to such winding, sealing the ends of said core element pressure-tight to present its hollow interior as a closed chamber, supplying a gas medium at above-atmospheric pressure to the sealed chamber of said core element thereby creating a substantial positive pressure differential therein, maintaining such pressure differential during. medium at least partially through the wall for a substantial portion of the polymerizing period for the particular bonding agent, thereafter winding one vor more veneer layers onto the core element to provide a composite tubing body, applying a polymerizable bonding agent to and between the windings, venting the end-sealed interior chamber of the tubing body to not greater ment and there subjecting it to a gaseous medium under pressure adequate to create a substantial positive pressure differential externally upon and into the body wall, and maintaining such pres'- sure differential through at least an initial por- Under the permeation of the gas' non o: the pqlymerizing periodio'r the selected bonding agent.A 2.; In the manufacture of wood tubing andthe like, the process which comprises spirally winding in alternating directions a plurality of superposed wood strips and. applying a polymerizable bonding agent between each such winding, thereby to form a hollow tubular core, sealing the ends of the core pressure-tight to present its hollow interior as a closed chamber, supplying gas under pressure' to said core chamber and maintaining the pressure therein until the bonding agent is polymerized, wrapping upon the resulting hard dry core a surrounding layer of wood veneer and interposing a similar bonding agent therefor, end sealing the resultant tubular body while affording communication with its hollow interior for atmospheric or negative pressure, placing said body in a closed pressure-tight chamber, and subjecting it to the positive pressure of a gas medium uniformly'over its entire outer cylindrical surface.

3. The process according to claim 2 including the further steps of spirally winding a wood covering strip upon the resultant tubular body with an associated like bonding agent, and similarly end-sealing and creating a positive pressure differential externally of and uponthe resultant sealed hollow tubular body by a gas medium applied uniformly externally thereof.

4. The process of claim 1 including in combination therewith the application of heat while maintaining the positive internal pressure differential.

5. The. process of claim 1 including in combinationtberewith the heating of the pressuresupplying gas medium.

6. The process of claim 1 including in combination therewith the application of heat while maintaining the external pressure differential.

1. In the manufacture ofwood tubing and the like, the process which comprises spirallywinding in alternating directions a plurality of superposed wood strips and. applying a polymerizable bonding agent between each such winding, thereby to form a hollow tubular core, sealing the ends of lthe core pressure-'tight to present its hollow interior as a closed chamber, supplying gas under pressure to said core chamber and maintaining the pressure therein untilthe bonding agent is polymerized, wrapping upon the resulting hard dry core a surrounding layer of wood'veneer and interposing a similar bonding agent therefor, end

f sealing the resultant tubular body while aording mospheric or negative pressure,

communication with its hollow interior for atplacing said body in a closed pressure-tight chamber, and subjecting it to the positive pressure of a gas medium uniformly over its entire outer, cylindrical surface, spirally winding a wood covering strip upon tneresultant tubular body with an associated like bonding agent. similarly end-sealing and creating a positive pressure differential externally of and upon the resultant sealed hollow tubular body by a gas medium applied uniformly externally thereof, and simultaneously subjecting the tubular structure to heat during any or each of the-periods of pressure application thereto.

PAUL R. GOLDMAN.

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