Method for precise control of manufacture of non-rigid thin-walled tube products

Patent metadata

Field	Value
Publication number	US-11033997-B1
Application number	US-201916602376-A
Country	US
Kind code	B1
Filing date	Sep 26, 2019
Priority date	Sep 26, 2019
Publication date	Jun 15, 2021
Grant date	Jun 15, 2021

Abstract

A method for correcting non-rigid thin-walled tubular elements having geometric deficiencies, wherein, following correction, the tubular elements may perform over a wide range of pressure and temperatures, for example as a rocket motor beaker, from about −70 C to about 1000 C. Correction is required to remove asperities, maximize cylindricity, squaring a forward end wall and a rearward end wall, so that the forward end wall of the tube product may be fitted, bonded and sealed to a circular planar element using a labyrinth-joint closure. The method provides uniformity so that both the tubular elements and the circular planar elements are interchangeably uniform in size, shape and performance, and may be readily assembled into non-rigid thin-walled tube products.

First claim

What is claimed is:

1. A method for correcting a non-rigid thin-walled tubular element (tube) of a polymeric material, where said tube has a diameter and a length, where said tube has finite geometric deficiencies and asperities, comprising:
heat-treating said tube within a close-fitting cylindrical steel rounding-fixture, wherein the heat-treating is provided at several degrees above the glass transition temperature of the principle material of said tube and over a period of several days to minimize cross-sectional ellipticity, followed by cooling said tube to several degrees below the glass transition temperature, which freezes-in cylindricity;
affixing a conformal lathe steady-rest, the conformal lathe steady-rest includes a steady-rest with a counter bored center hole and a plurality of radial struts extending inward and radially through radially-oriented slots in a body proper of the steady-rest, wherein each radial strut can move radially inward or outward, a conformal scroll plate positioned coaxially aligned to the counter bored center hole of the steady-rest, wherein said conformal scroll plate has a center opening for the tube and a plurality of circumferentially spaced cam-slots, wherein each of the cam-slots have an intersecting slidable pin that is perpendicularly affixed to a radial strut;
rotating the scroll plate, causing all rollers to move radially inward as determine by the intersecting slidable pins in the plurality of circumferentially spaced cam-slots, wherein the rollers are positioned circumferentially about equidistantly around the conformal scroll plate, and there are enough rollers to support the tube therein maintaining cylindricity and providing equal and opposing support for the thin-wall of the tube as it is machined;
equipping an end of said tube with a stiffening outer sleeve as needed, wherein the stiffening outer sleeve is a close-fitting cylindrical steel axial cup to prevent damage to said tube when fastened in the jaws of the lathe chuck;
mounting said tube in the close-fitting cylindrical steel axial cup and through the conformal lathe steady-rest;
commencing lathe headstock rotation of said tube and gradually increasing speed, therein ultimately causing each of the rollers to come into contact with an outer surface of said tube, therein causing all the rollers to roll, wherein the contact imparts force against the thin-wall of said tube resulting in cylindricity of said tube while it is being turned in the conformal lathe steady-rest;
positioning a cutting tool on an inside edge of a forward end wall of said tube at a point fully supported by at least one of the rollers in contact with an opposing position on the outer surface of said tube,
using the cutting tool to cut, incrementally, as needed, a fractional thickness of the forward end wall of said tube, so that the wall has a uniform thickness, and therefore a uniform inside diameter; therein creating a mating interface surface for forming a labyrinth-joint when said tube is adhesively joined to a machined circular planar closure element, wherein the machined circular planar closure element is a disk having an outer diameter that is about equal to the outside diameter of said tube, and having an inner concentric smaller diameter that is only slightly smaller than the uniform inside diameter of said tube; and
reversing said tube in the lathe and trimming an aft end wall, squaring it off so that the aft end wall of said tube is cylindrical and planar, wherein it has an aft O-ring sealing surface.

2. The method according to claim 1 , wherein said tube initially is elliptical, and wherein said tube is about 20 inches long and has a nominal diameter of about 9.73 inches±about 0.218 inches.

3. The method according to claim 1 , wherein said tube initially has a variable wall thickness ranging from about 0.178 inches to about 0.218 inches.

4. The method according to claim 1 , wherein the cutting tool is carbide tipped.

5. The method according to claim 1 , wherein the principle material of said tube is polyphenylene oxide, and wherein the glass transition temperature is 215° C.

6. The method according to claim 1 , further comprising the step checking the inside diameter of the fractional thickness of the forward end wall of said tube for acceptability using precisely-dimensioned rigid “Go” and “No-Go” plug-gauges.

7. The method according to claim 1 , further comprising checking that the outer diameter of the circular planar closure using is about equal to the outside diameter of said tube, and that the inner concentric smaller diameter is only slightly smaller than the uniform inside diameter of said tube for acceptability using precisely-dimensioned rigid “Go” and “No-Go” plug-gauges.

8. The method according to claim 1 , further comprising interchanging a plurality of circular planar closures for fit with the inside diameter of the fractional thickness of the forward end wall of with at least one said tube.

9. The method according to claim 1 , further comprising interchanging a plurality of forward end walls of said tubes for fit with at least one circular planar closure.

10. The method according to claim 1 , further comprising adhering a checked circular planar closure to a checked forward end wall of said tube, therein forming a beaker;
filling the beaker with propellant while the beaker is in the close-fitting cylindrical steel rounding-fixture, therein forming a filled cartridge; and
confirming that the filled cartridge fits into a desired rocket motor, and is seated against the O-ring, therein forming a flush O-ring seal.

11. The method according to claim 1 , further comprising loading the filled cartridge in a rocket motor chamber; and
testing the rocket motor.

Assignees

• Us Navy

Inventors

• Jones Tina
• Kelley John

Classifications

• B29C67/0014

  for shaping tubes or blown tubular films · CPC title

• B29C57/00

  Shaping of tube ends, e.g. flanging, belling or closing; Apparatus therefor {, e.g. collapsible mandrels} · CPC title

• F02K9/24 Primary

  Charging rocket engines with solid propellants; Methods or apparatus specially adapted for working solid propellant charges · CPC title

• B24B5/04

  for grinding cylindrical surfaces externally (grinding combined cylindrical and conical surfaces B24B5/14) · CPC title

• B23Q1/763

  Rotating steadies or rests · CPC title