US2286045A - Method of making tubes of pyroxylin material or the like - Google Patents

Description

June 9, 1942. J. N. WHITEHOUSE 2,236,045 METHOD OF MAKING TUBES OF PYROXYLIN MATERIAL OR THE LIKE Filed D60. 2, 1959 INVENTOR J'Smv M wm-renouse Y ATTO R N EYS Patented June 9, 1942 2 UNITED STATES PATENT OFFICE METHOD OF MAKING TUBES OF PYROXYLIN MATERIAL OR THE LIKE 2 Claims.

This invention relates to the manufacture of tubes, such as are used in making the barrels of fountain pens, from pyroxylin or other thermoplastic material. However such tubes are made, e. g., from a spiral wound strip, from a strip folded and with longitudinal edges buttwelded, from a cylindrical block, etc., they require a polishing operation on the exterior, in order that the finished article may present the desired attractive appearance. Heretofore the tube, prior to the polishing operation, has been so rough and irregular as to its exterior surface that an expensive and wasteful grinding operation was required.

Where the tube was made by bending the strip into tubular shape and then drawing it through a metal tube of such interior diameter that the longitudinal edges of the pyroxylin tube were in contact, softening the pyroxylin material and applying a suitable cementing agent along the abutting edges. the resulting pyroxylin tube has been irregular in general cross section, rough and irregular as to its exterior surface, and with a prominent seam-projection extending longitudinally of the exterior surface.

By my invention it is proposed to form a tube of the pyroxylin material as by the butt-welding method, softening the tube as by immersing it in hot water, then inserting a closely fitting unyielding truly cylindrical mandrel into the tube and thereafter hammer-molding the tube in such a way and under such conditions of temperature interiorly and exteriorly of the tube that the tube emerges from the operation in truly cylindrical form, with the exterior surface substantially free from irregularities and undesirable projections, and with a densification of the wall of the tube at and to an appreciable distance below the exterior surface. And as a result of this treatment the exterior of the tube requires a minimum of final polishing, and the polishing is facilitated and improved because of the densification referred to.

In the accompanying drawing, which is to be taken as a part of this specification,

Fig. 1 is a more or less diagrammatic showing of a tube in its relation to the supporting mandrel and to the hammer-molding elements involved in the carrying out of my process;

Fig. 2 illustrates a section of tubing which has been formed by the so-ca1led butt-welding method, and without being subjected to m proc ess; and

changes have occurred in the shape, etc. of the tube after it has been subjected to my process.

Referring to the numerals on the drawing, and first to Fig. 2, let it be understood that a tube indicated at 4 has been made by bendin a strip of pyroxylin material of suitable width into tubular form with the edges of the strip substantially abutting. This so-formed tube, it will be assumed, has been drawn through a metal tube with the edges thereby held in the abutting relation, and while being so drawn heat has been applied and/or a cementing material effective at the abutting edges, so that these are substantially united. All this has taken place in the absence of interior support for the pyroxylin tube. I have found that the resulting pyroxylin tube is apt to depart extensively from true circularity, that its exterior surface exhibits a marked seam-projection at the united edges, indicated at 5 in Figs. 1 and 2, and that where heat was employed as a preliminary to or during the forming operation, as is usually the case, the material of the tube is in an expanded condition so that a polishing operation performed on it does not have the maximum effectiveness. There are also apt to be irregularities, whether by way of projections or depressions, in the remaining exterior and interior surfaces other than the seam-projection, such irregularities being indicated at 6 in Figs. 1 and 2.

Starting with such a tube as I have just described, according to my invention I first insure that it is in a relatively soft condition, as by immersing it in hot water; I then insert into it a cylindrical mandrel such as is indicated at I in Fig. 1, the mandrel being of such cross sectional dimensions that the tube is snug on it and brought to approximate circularity, except for such surface irregularities as may exist, particularly the seam-projection 5 and the irregularities 6. The tube may be of any convenient length, and for ease in handling, the mandrel may project beyond both ends of the pyroxylin tube. The mandrel is heated to a degree sufficiently to keep the pyroxylin material relatively soft. The tube and the supporting mandrel are now progressively advanced between the members 8 and 9 of a hammer-molding assembly, these members 8 and 9 being at a relatively lower temperature than the temperature of. the mandrel or of the tube, so that as the members 8 and 9 operate upon the tube, as hereinafter described, they will have a chilling effect upon the exterior of the tube. The temperature of the elements 8 and 9 need not be much below atmospheric,

but at any rate it is desirable to have a considerable temperature differential between the mandrel and the elements 8 and 9, which differential can be maintained in any suitable way during the hammer-molding operation. The elements 8 and 9 are manipulated in any preferred way, preferably mechanically, so that they move intermittently towards and from each other in the hammer-molding operation, opposed faces of the elements 8 and 9 being cavitated as at H! so that when the tube and mandrel are first inserted, the cavitations closely fit around the exterior of the tube, while the opposed faces of the members 8 and 9 on either side of the cavitations H] are spaced apart somewhatas shown in Fig. l. The effect of movement of the members 8 and 9 towards each other is to mold and hammer the exterior surface of the tube, gradually densifying and reducing the wall thickness thereof until such time as the opposing faces of members 8 and 9 on either side of the cavitations H] are in contact, at which time the cavitations It! will together form a complete cylinder closely encompassing the tube, which, by reason of the hammer-molding and incidental exterior chilling, will have been densified to an appreciable depth from the exterior inwardly, and whose exterior surface will have been made smooth and uniform, with the removal of undesirable projections such as those indicated at 5 and 6. The advance of the mandrel and tube through the hammer-molding assembly is progressive, and while it is going on relative rotation between the mandrel and tube on the one hand, and the hammer-molding assembly on the other hand, properly synchronized with the movements of approach and separation of the hammer-molding elements, and with the stepby-step forward movements of the mandrel and tube, is effected, with obvious results. This relative rotation may be accomplished by intermittent partial step-by-step rotation of the mandrel and tube, while the members 8 and 9 are held against rotation relatively to the mandrel and tube; or the hammer-molding assembly :may be given a step-by-step rotation suitably synchronizedwith the movements of the elements 8 and 9 towards and from each other, the mandrel and tube being held against rotation. It will be appreciated that the full length of the tube is not operated upon simultaneously, but it is advanced progressively and with some uniformity of timing synchronized with the movements of the hammer-molding elements, so that when the operation is complete, every portion of the length will have been operated upon, that is to say, hammered and molded and densified to substantially the same extent, so that the finished tube will be uniform throughout. The mandrel will, of course, be withdrawn from the tube.

The result of the operation above described is a tube, such as is illustrated in Fig. 3 and at the right-hand end of Fig. 1, which is truly circular inside and out, whose exterior surface in particular is smooth and uniform and free from undesirable irregularities or projections, and which is desirably densified from the exterior to an appreciable depth of the wall thickness. Such a tube requires no grinding and but little polishing, and the polishing is the more effective because of the densification at the exterior of the tube.

I claim:

1. The method which consists in providinga tube of pyroxylin material with a relatively heated interior supporting mandrel, advancing the tube and mandrel progressively through the field of operation of a relatively cool hammer-molding assembly and causing relative step-by-step rotation between the mandrel and tube on the one hand and the hammer-molding assembly on the other hand.

2. The method which consists in providing a softened tube of pyroxylin material with a relatively heated interior supporting mandrel, advancing the tube and mandrel progressively through the field of operation ofa relatively cool hammer-molding assembly and causing relative step-by-step rotation between the mandrel and tube on the one hand and the hammer-molding assembly on the other hand.

JOHN N. WHITEHOUSE.

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