US3165789A

US3165789A - Mandrel for forming insulator casing

Info

Publication number: US3165789A
Application number: US300739A
Authority: US
Inventors: John T Jackson
Original assignee: Mandrels Inc
Current assignee: Mandrels Inc
Priority date: 1963-08-08
Filing date: 1963-08-08
Publication date: 1965-01-19
Anticipated expiration: 1982-01-19

Description

Jan. 19, 1965 J. T. JACKSON 3,165,789

MANDREL FOR FORMING INSULATOR CASING Filed Aug. 8, 1963 4 Sheets-Sheet 1 INVENTOR.

JOf-IN T. JACKSON BY WW A T TORNE YS Jan. 19, 1965 J." T. JACKSON 3,165,789

MANDREL FOR FORMING INSULATOR CASING Filed Aug. 8, 1963 4 Sheets-Sheet 2 J, I 1 I8 I8 I8 0 23 I5 .36.--,:'. --2.-'36.= l I?) 35 35 I6 FIG.5

INVENTOR. JOHN T. JACKSON ATTORNEYS Jan. 19, 1965 J. T. JACKSON 3,155,789

MANDREL FOR FORMING INSULATOR CASING Filed Aug. 8, 1963 4 Sheets-Sheet 5 FIG. IO

INVENTOR. JOHN T. JACKSON BY Mq ATTORNEYS Jan. 19, 1965 J. T. JACKSON MANDREL. FOR FORMING INSULATOR CASING 4 Sheets-Sheet 4 Filed Aug. 8, 1963 INVENTOR. F IG I I JOHN T. JACKSON ATTORNEYS United States Patent 3,165,739 MANDREL FOR FQRM If: INSULATGR CASING John '1'. Jackson, Louisville, Ohio, assignor to Mandrels, lnc., Louisville, Ghie, a corporation of Ohio Filed Aug. 8, 19%, filer. No. 306,739 12 Claims. (Cl. 18-45) This invention relates generally to mandrels on which hollow shells or casings are formed, and more particularly to a hollow mandrel of destructible material which can be broken up and removed after the shell has been formed thereon.

Such mandrels are frequently used to form relatively thin insulator casings for fuel in guided missiles, the casings being normally formed by winding filaments of elastomeric material, such as fiberglass, on the mandrel.

The hollow mandrels are usually cast from frangible plaster-like material which must be strong and lightweight material capable of maintaining an extremely accurate outer surface as the filaments are wound under tension thereon, producing inward pressure on the mandrel.

fter the shell has been wound and cured, the mandrel must be broken up and removed through one or more of the ports normally provided in one end of the case, and this must be done without damaging or distorting the thin outer casing.

Since the hollow mandrel must have a solid wall of substantial thickness and density in order to have adequate strength during the winding operation, the subsequent breaking up of the mandrel requires painstakingly careful chiseling throughout the entire mandrel to break it into pieces which can be removed through a port hole, and

t the same time not damage orin any way detract from the contour accuracy of the outer shell.

US. Patent No. 3,083,409, dated April 2, 1963, shows a hollow mandrel construction having a wall of plaster material supported on a cardboard core, which may be a solid laminated core .or a hollow tubular core. In either case, plaster disks mounted on a central shaft support the outer plaster wall of the mandrel. Such a mandrel is not only expensive to build, but is diflicult to break up and remove because, after the shaft, core and disks have been removed, theintact outer plaster wall of the mandrel must be carefully chiseled, broken up and removed. 7

It is an object of the present invention to provide an improved hollow destructible mandrel which provides adequate strength and accuracy of outer contour for winding an insulator casing thereon, and which is subsequently easily broken up and removed Without damaging the insulator casing.

More specifically, it is an object to provide ahollow mandrel having an inwardly removable keystone rib construction embedded in its outer wall.

Another object is to provide removable means interiorly of the outer wall of the mandrel for temporarily supporting the embedded keystone ribs.

A further object is to provide in one form of the invention an interior collapsible spoke construction for temporarily supporting the embedded'keystone ribs.

These and other objects are accomplished by the parts,

constructions and arrangements comprising the present invention, preferred embodiments of which are shown by way of example in the accompanying drawings and ,described in detail herein. Variations in details of construction and modifications are included within the scope of the appended claims.

In general terms, the improved mandrel is a hollow casting'of plaster-like material having an outer wall of extremely accurate predetermined outer contour with longitudinally extending ribs of keystone or dovetail cross section embedded in the wall and adapted for rapidly inward removal therefrom, there being removable internal supporting means in the mandrel temporarily sup- FIG. 3.

FIG. 5 is a longitudinal sectional View on line 55 of 1 FIG. 1.

FIG. 6 is a plan elevation on line 66 of FIG. 3, showing the template in position for finishing the outer contour.

FIG. 7 is a cross section of the mandrel with the shell wound thereon.

FIG. 8 is a similar view with the keystone ribs removed.

FIG; 9 is a longitudinal plan sectional view of another embodiment of the improved mandrel with the template in position for finishing the outer contour.

FIG. 10 is a similar view showing the outer shell Wound thereon.

FIG. 11 is a cross sectional view on line i11l of FIG. 19.

FIG. 12 is a view similar to FIG. inner supporting shell removed.

FIG. 13 is a cross sectional view on line l313 of FIG. 12.

The mold for casting the hollow mandrel may be of any 10, showing the suitable material and one-half of the mold is shown schematically at 15 in FIGS. 1, 2 and 5. Preferably, the mold cavity 16 is formed of any suitable material, such as a resin or reinforced fiberglass which may be coated or trade name of Ultracal has been found satisfactory.

The plaster in a semi-liquid plastic state is formed into the mold cavity by hand win any usual manner, the wall thickness being on the order of about 2 inches, but varied according to requirements. The mandrel as cast is slightly undersize with respect to the finished mandrel.

Whenthe wet plaster is being spread over the mold cavity in each half, longitudinally aligned .ribs 18 are embedded in the wall being formed, the ribs being keystone or dovetail in shape in cross section, with the inner V lateral dimension being the wider. The ribs preferably are metal, wood or plastic material but may be of any suitable rigid or substantially rigid material.

As shown in FIGS. 1 and 5, each half mandrel is substantially bathtub-like in shape and the rib portions 20 at the ends are curved to conform-to the curved ends 21 of The

ribs

18, 2% may be continuous from the mandrel. end to end, or may be interrupted as shown to form a longitudinal series.' Preferably, a plurality of circumferentially spaced longitudinal ribs or longitudinal rib.

series is provided in each half of the mandrel. For

example, two rib series are shown in each half.

Patented Jan. 19, 1965 a) through the mandrel with its ends fitting in aligned re cesses 23 in the ends of the mold, and the shaft 22 is positioned in the bottom half of the mold when the half mandrel 17 is cast therein.

The other or mating half of the mold and the cast half mandrel therein with embedded ribs are then inverted over and mated with the mold half 15, and after the half mandrels have been joined with wet plaster material, the upper mold half may be removed as shown in FIG. 2, leaving the upper half 17' of the mandrel mated with the lower half 17. Either or both of the mandrel halves may have one or more port holes formed therein, as required.

The internal supporting means for the

ribs

18, and 18', 20 are preferably metal spoke rods 26 and 26' arranged at longitudinal intervals, with the inner end of each rod abutting the shaft and the outer end abutting a portion of the ribs.

The metal spoke rods 26 are easily positioned between the shaft 22 and the ribs 18 when the half mandrel 17v has been cast, as illustrated in FIGS. 1 and 5, the rods being held in place by globs of web plaster and fibrous material such as hemp applied to the ends of the rods. The spoke rods 26' are preferably inserted after the mandrel halves have been mated and joined, access holes through the mold and mandrel permitting this to be accomplished. If necessary, these holes may be filled in with plaster or like material after the rods are positioned in the mandrel.

The internally supported ribs 18 act to reinforce the wall of the mandrel, giving it additional strength to withstand the pressures exerted when the outer shell is wound thereon.

After the joint between the two cast man-

drel halves

17 and 17 has set, the ends of the shaft are attached to a hoist and the mandrel lifted out of mold half 15 and mounted for rotation in a lathe indicated generally at 27 in FIGS. 3 and 6. The shaft 22 is journaled in bearings 28 or centered on live or dead centers and operatively connected to a motor drive 30. A side table 31 on the lathe supports a template 32 having the predetermined contour of the finished mandrel which may be about inch larger than the outer contour of the mandrel 17 as cast.

As the mandrel is rotated, additional wet plaster material is applied between the mandrel and the template 32 which acts as a screed board to apply a skin or coating 33 of the plaster uniformly over the mandrel. Preferably, the coating is built up in several stages by setting the template close to the mandrel and progressively moving it farther away thereform. By this method an accurate outer circumference is formed on the mandrel within a tolerance of .002 to .005 inch.

After the coating has set, the elastomeric material such as fiberglass may be wound on the mandrel in a usual and well-known manner to form an insulator casing or shell 34 of the required thickness. When the shell has been cured, the operation of breaking up and removing the mandrel comprises reaching into the mandrel through a port hole and knocking out the spokes 26 and 26', which is very easily done since their ends are attached only by globs of plaster. Once the spokes are removed, the snaft 22 may be pulled and the ribs or

rib portions

18 and 20 are easily dislodged due to their keystone shape, and this leaves the outer wall 17 in spaced-apart arcuate sections, as indicated in FIG. 8, which are easily dislodged and broken up. To aid in dislodging the arcuate wall sections, anchor channels 35 may be embedded therein at intervals during the casting process, the channels having pull bars 36 attached thereto ext-ending radially inward therefrom, preferably with perforate inner ends, providing projections to engage for prying or pulling the wall sections loose.

The embodiment of the invention shown in FIGS. 9 to 13, inclusive, comprises a generally conical shape of mandrel which is formed and cast around the outer surface of a substantially conical tubular metal mold. Referring to FIGS. 9 and 10, the conical inner mold has a chucking block 141 at its small end in which an arbor 142 is mounted axially of the mold. At its large end the mold has an inner mounting ring 143 to which the inner plate 144 of a dome head 145 is detachably secured by screws 146. An axial shaft 147 is secured in dome 145 and plate 144. The shaft and arbor provide means for rotatably mounting the mold in a lathe or the like.

Wet plaster material to form the mandrel is applied to the outer surface of the mold 140 and a series of longitudinally spaced, longitudinally extending, rigid ribs 148 embedded in the plaster. As shown in FIG. 11, four equally spaced ribs may be used, and the ribs are keystone or dove-tail shape in cross section. The ribs 148 may be attached at longitudinal intervals to the mold by screws 149. In this embodiment, the outer contour of the ribs may be notched at longitudinal intervals, as indicated at 159, and the notches are designed to register with circumferential grooves which are to be formed in the outer surface of the mandrel.

After the plaster has been rough formed into a mandrel 151 ha ing a girth or outer dimension slightly less than the required finished outer contour, including a plaster wall 152 over the dome 1.45, a template board 153 having projections 154 registering with the notches is mounted alongside the mandrel and used to screed on a finishing coat of plaster 155 as the mandrel is rotated, forming the required accurate outer contour within a tolerance of .002 to .005 inch.

When the coating has set, the elastomeric material may be wound on the mandrel to form the shell 156, which in this embodiment is required to be substantially thicker than the shell 34, the winding preferably being applied over both ends of the mandrel. After the shell has been cured, the dome may be severed by a rotary cutter 157, as indicated schematically in FIG. 10, and removed from the mandrel, whereupon the screws 149 are removed and the mold 140 is pulled axially out of the mandrel. Eyebolts 158 may then be screwed into the holes left by screws 149 and used as means to aid in dislodging the ribs 148 from the mandrel, leaving the outer wall in arcuate spaced-apart sections which are then dislodged and broken up.

To facilitate removing the arcuate sections of the mandrel, it may be desirable to mold anchor channel sections 160 into the wall 151 between the ribs 148 and to hinge pull bars 161 thereon. These bars 161 lie flat in the channels against the mold 140, as shown in F168. 9 and 10, and when the mold is removed they are swung radially inward as shown in FIGS. 11-13 to provide projections to be engaged for prying or pulling the arcuate mandrel sections loose.

In both embodiments, the novel mandrel provides a reinforced construction of increased strength with an accurate outer contour within the required close tolerance, and after the outer elastomeric shell is formed thereon, the mandrel is easily broken up and removed without damaging or distorting the shell in any way.

What is claimed is:

1. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall and each having a keystone cross sectional shape with the inner lateral dimension wider than the outer lateral dimension, and internal means removably supporting said ribs.

2. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, laterally spaced substantially rigid reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall, said ribs having a cross sectional shape adapted for radially inward removal of said ribs from said wall, and internal means removably supporting said ribs.

3. A hollow mandrel for forming a shell having an accurate, outer contour, said mandrel having a center axis and an outer wall of frangible material, reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall and each having a keystone cross sectional shape with the inner lateral dimension Wider than the outer lateral dimension, internal means removably supporting said ribs, and anchor means embedded in said wall between said ribs and having projections extending inwardly of said wall to aid in prying loose the wall sections between said ribs.

4. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, laterally spaced substantially rigid reinforcing ribs extending longitudinally of the mandrel axis detachably'embedded in said outer wall, said ribs having a cross sectional shape adapted for radially inward removal of said ribs from said wall, internal means removably supporting said ribs, and anchor means embedded in said wall between said ribs and having projections extending inwardly of said wall to aid in prying loose the wall sections between said ribs.

5. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall and each having a keystone cross sectional shape with the inner lateral. dimension wider than the outer lateral dimension, an axial shaft in the mandrel, and spoke rods detachably interposed between said shaft and said ribs for removably supporting said ribs.

6. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, laterally spaced substantially rigid reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall, said ribs having a cross sectional shape adapted for radially inward removal of said n'bs from said wall, an axial shaft in the mandrel, and spoke rods detachably interposed between said shaft and said ribs for removably supporting said ribs.

7. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a centeraxis and 'an outer wall of frangible material, reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall and each having a keystone cross sectional shape with the inner lateral dimension wider than the outer lateral dimension, an axial shaft in the mandrel, spoke rods detachably interposed between said shaft and said ribs for removably supporting said ribs, and anchor means embedded in said wall between said ribs and having projections extending inwardly of said wall to aid in prying loose the wall sections between said ribs.

8. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, laterally spaced substantially rigid reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall, said ribs having a cross sectional shape adapted for radially inward removal of said ribs from said wall, an axial shaft in the mandrel, spoke rods detachably inter posed between said shaft and said ribs for removably supporting said ribs, and anchor means embedded in said- Wall between said ribs and having projections extending inwardly of said wall to aid in prying loose the wall sections between said ribs.

9. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall and each having a keystone cross sectional shape with the inner lateral dimension wider than the outer lateral dimension, and a tubular internal mold within said mandrel axially removable therefrom and detachably supporting said ribs.

10. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, laterally spaced substantially rigid reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall, said ribs having a cross sectional shaped adapted for radially inward removal of said ribs from said wall, and a tubular internal mold within said mandrel axially removable therefrom and detachably supporting said ribs.

11. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer wall and each having a keystone crOSs sectional shape with the inner lateral dimension wider than the outer lateral dimension, a tubular internal mold within said mandrel axially removable therefrom and detaehably supporting said ribs, and anchor means embedded in said wall between said ribs and having projections hinged thereon for extending inwardly of said wall when said mold is removed.

12. A hollow mandrel for forming a shell having an accurate outer contour, said mandrel having a center axis and an outer wall of frangible material, laterally spaced substantially rigid reinforcing ribs extending longitudinally of the mandrel axis detachably embedded in said outer Wall, said ribs having a cross sectional shaped adapted for radially inward removal of said ribs from said wall, a tubular internal moldvwithin said mandrel axially removable therefrom and detachably supporting said ribs, and anchor means embedded in said wall between said ribs and having projections hinged thereon for extending inwardly of said wall when said mold is removed.

References Cited by the Examiner UNITED STATES PATENTS 855,174 7 5/07 Henry 25-l28 895,904 8/08 Smyth et al. 1,312,157 8/19 Buente 25128 2,303,303 11/42 Schleicher 264-66 3,030,687 4/62 Muspratt 25128 3,083,409 4/ 63 Crawford et al 18-45 WILLIAM J. STEPHENSON, Primary Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,165,789 January 19, 1965 John T Jackson It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 72, for "rapidly" read radially column 6, line 23, for "shaped" read shape Signed and sealed this 13th day of July 1965 (SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. A HOLLOW MANDREL FOR FORMING A SHELL HAVING AN ACCURATE OUTER CONTOUR, SAID MANDREL HAVING A CENTER AXIS AND AN OUTER WALL OF FRANGIBLE MATERIAL, REINFORCING RIBS EXTENDING LONGITUDINALLY OF THE MANDREL AXIS DETACHABLY EMBEDDED IN SAID OUTER WALL AND EACH HAVING A KEYSTONE CROSS SECTIONAL SHAPE WITH THE INNER LATERAL DIMENSION WIDER THAN THE OUTER LATERAL DIMENSION, AN INTERNAL MEANS REMOVABLY SUPPORTING SAID RIBS.