US3355533A - Method of lining internal spiral grooves of a tube with resilient material - Google Patents

Description

G. MlSTlC 3,355,533 METHOD OF LINING INTERNAL SPIRAL GROOVES OF A TUBE Nov. 28, 1967 WITH RESILIENT MATERIAL 1 Filed June 5, 1964 2 Sheets-Sheet 1 GEORGE MISTIC l'll Ill

, 3,355,533 METHOD OF LINING INTERNAL SPIRAL GROOVES OF A TUBE G. MISTIC Nov. 28, 1967 WITH RESILIENT MATERIAL I 2 Sheets-Sheet 2 Filed June 5, 1964 INVENTOR Aflys.

GEORGE MISTIC fir/f N I I\ I I h \I W I \I\ n 2 %M a y z o o o 7/ 6. mwmfimEoo m mm mm\ 7 54 III nmwmmaEoo United States Patent METHQD OF LINING INTERNAL SPIRAL GROOVES OF A TUBE WITH RESILIENT MATERIAL George Mistic, Niles, Ill., assignor to Motorola, Inc., Franklin Park, 111., a corporation of Illinois Filed June 3, 1964, Ser. No. 372,285 3 Claims. (Cl. 264-267) ABSTRACT OF THE DISQLOSURE Core movement in an inductance device is restrained by the use of a resilient torque producing material substantially evenly filling a spiral groove in a coil form which contains a movable core. A tubular injection tool having an outside diameter substantially equal to the diameter of the inside wall of the tube and radial holes in the outside surface thereof is placed within the tube. Resilient material is applied under a predetermined pressure through the radial holes to force the resilient material into the grooves. The tube may be rotated through a predetermined angle to regulate the distribution of the resilient material of the grooves.

In electronic components such as intermediate frequency transformers and coils, the inductance may be varied for tuning a circuit to a. desired characteristic such as resonance. The windings of such intermediate frequency transformers and coils are usually wound around the periphery of a tubular coil form. A core or slug of permeable material is then positioned inside the form and held therein by threads or other means. By moving the coil or slug relative to the coil it is possible to vary the inductance of the coil. In order to prevent changes in the coil parameters after postioning the core, it must remain fixed in position even though subject to shock andvibration forces. It is also desirable that the torque developed to fix the core in position remain substantially unchanged throughout repeated positionings of the core. Coil form structures presently used, which provide for sufficient torque to maintain the core in the proper position relative to the coil, are expensive to manufacture and do not make use of standard readily available components.

It is therefore an object of this invention to provide a method of making an inductance device using standard readily available coil forms and cores, in which the core will remain in fixed position in the coil form after tuning.

Another object of this invention is to provide a method of making an inductance device having a movable core which may have its position repeatedly changed without reducing the torque developed to fix the core in position.

Another object of this invention is to provide a method of making an inductance device having a movable core wherein the torque developed to fix the core in position can be established at an-optimum value.

A feature of this invention is the provision of a method of making an inductance device including a hollow cylindrical tube having a spiral groove on the inside wall thereof substantially evenly filled with a resilient material and with the wall of the tube between the groove being substantially free of the resilient material.

Another feature of this invention is the provision of a method of using an injection tool, which is inserted into a hollow cylindrical coil form having a spiral groove on the inside wall thereof, for substantially evenly filling at least a portion of the .groove with a resilient material and wherein the clearance between the surface of the tool and the inside surface of the coil form is a minimum so that the inside surface of the coil form between the grooves is substantially free of the resilient material.

3,355,533 Patented Nov. 28, 1967 The invention is illustrated in the drawings wherein:

FIG. 1 is a cross-sectional view of a coil form having a resilient material filling a spiral groove on its inside surface;

FIG. 2 illustrates the method by which the resilient material is deposited within the groove;

FIG. 3 is a cross-sectional view of a portion of the structure shown in FIG. 2;

FIG. 4 is a cross-sectional view of a nozzle and coil form;

FIG. 5 is a cross-sectional view of the structure of FIG. 4;

FIG. 6 is a cross-sectional view of a coil form having a resilient material filling portions of the groove in the form of bands; and

FIG. 7 is a cross-sectional view of a coil form having a resilient material filling spaced portions of the groove.

In practicing this invention a variable inductance device is provided consisting of a coil wound on a hollow cylindrical coil form having a spiral groove on the inside surface. Within the coil form is positioned a threaded core whose threads cooperate with the spiral groove so that the position of the core relative to the coil may be changed. In order to prevent undesired movement of the core with respect to the coil, while allowing the core to be smoothly positioned with respect to the coil when desired, the spiral groove is substantially evenly filled with a resilient material such as silicon rubber while the wall between the grooves is subtantially free from the resilient material so that the core does not make frictional contact with the resilient material outside of the grooves. The resilient material within the groove is compressed by the threads of the core to provide an even torque of suliicient strength to prevent the forces of shock and vibration from moving the core relative to the coil form. The resilient material is injected into the grooves by a tool which is inserted into the coil form. The resilient material is forced through holes in the tool and is evenly distributed in the grooves by rotating the coil form relative to the tool. By making the clearance between the surface of the tool and the inside surface of the coil form a minimium, the inside surface of the coil form between the grooves is maintained substantially free of resilient material.

By varying the pressure forcing the resilient material through the holes and/ or keeping the tube stationary relative to the tool, the resilient material can be distributed within spaced portions of the groove. Controlling the portion of the groove filled with the resilient material con trols the amount of torque developed to fix the core in position.

FIG. 1 is a cross-sectional view of a coil form 6 having a coil 7 wound on the outer periphery. A spiral groove 10 is cut on the inside surface of the coil form. A core 8 having threads 13 is positioned within coil form 6. Threads 13 cooperate with groove 14) so that the core 8 may be positioned within coil form 6. Core 8 has slots 18 on the end surfaces so that a tool such as a screwdriver may be used to position core 8 within coil form 6.

Spiral groove 10 of coil form 6 is substantially evenly filled with a resilient material 11 such as silicon rubber. The spaces 12 between grooves 10 are substantially free of resilient material. Threads 13 of core 8 compress the resilient material within groove 10 developing a frictional torque between the resilient material and the threads. The resilience of the material in groove 10 acts to maintain an even torque after repeated positioniugs of the core. Since the space between the wall 12 of the coil form 6 and Wall 15 of core 8 is substantially free of resilient material, there is no frictional force developed except where the threads compress the resilient material within the grooves.

FIG. 2 illustrates the method by which the resilient material is deposited within the groove of the coil form. Compressed air is applied to a reducing valve 21 through tube 20. Valve 21 is operated by a foot pedal 23 to apply compressed air to container 24. Container 24 is held in position by a bracket 26. An injection tool 27 is secured to a polyethylene bottle 30 containing the resilient material and located within container 24. A coil form 28 having a spiral groove on the inside surface is inserted over injection tool 27 and foot pedal 23 is depressed. The resilient material within bottle 30 is ejected through holes 19 in injection tool 27 to susbtantially evenly fill the spiral groove with the resilient material. Coil form 28 is rotated through a predetermined angle to insure an even coating of the resilient material and removed from injection tool 27.

FIG. 3 is a cross-sectional view of the container 24 and injection tool 27 of FIG. 2. Within container 24 is a polyethylene bottle 32 containing the resilient material. One end of polyethylene bottle 32 includes a piston 33 which is forced toward the neck 36 of polyethylene bottle 32 by the force of compressed air applied to inlet 38. An injection tool 39 is secured by threaded means to polyethylene bottle 32. Injection tool 39 has a central longitudinal hole 40 and radial holes 41. The resilient material is forced through holes 40 and 41 by the action of piston 33.

An enlarged view of the tool inserted within a coil form is shown in FIGS. 4 and 5. Radial holes 42 connect central longitudinal hole 43 with the outside surface 44 of tool 46. The diameter of tool 46 is substantially equal to the inside diameter of coil form 47 so that the clearance between the outside surface of the tool and the inside surface of the coil form is as small as possible. The resilient material is forced through center hole 43 and radial holes 42 to substantially evenly fill grooves 48 of coil form 47. Coil form 47 is rotated around tool 46 as shown in FIG. through an angle at least equal to the angle between the rows of radial holes, in this case 120. This insures even distribution of the resilient material throughout groove 48 of coil form 47. By making the clearance 49 between the surface of tool 46 and coil form 47 a minimum the inside surface of coil form 47 between the grooves is substantially free of resilient material. After the grooves have been filled, coil form 47 is removed from tool 46.

The amount of torque developed by the resilient material in frictional contact with the core can be established at an optimum value by distributing the resilient material within spaced portions of the groove. This is accomplished by varying the pressure used to force the resilient material through the holes and/or by keeping the tube stationary relative to the tool. By establishing the air pressure applied to force the resilient material through the holes at a predetermined value and rotating the tube, the resilient material can be distributed in the form of bands as shown at 50 in FIG. 6. If the tube is not rotated with respect to the tool while the resilient material is forced through the holes, spaced arcs of the groove are filled as shown at 52 of FIG. 7.

Thus a simple eifective structure has been shown for providing a torque to control movement of a core within 4 a coil form. The structure uses standard readily available coil forms and cores andthe position of the core can be easily and repeatedly changed without loss of the cocking properties.

I claim:

1. A method of evenly filling at least a portion of a spiral groove cut on the inside wall of a hollow cylindrical tube with a resilient material while maintaining the inside wall of the tube between said grooves substantially free of said resilient material, including the steps of, placing within said tube a tubular injection tool which has an outside diameter substantially equal to the diameter of said inside wall of said tube and radial holes in the outside surface thereof, applying said resilient material under a predetermined pressure through said radial holes whereby said resilient material is forced into at least a portion of said grooves, and withdrawing said tool from said tube.

2. A method of evenly filling a spiral groove cut on the inside wall of a hollow cylindrical tube with a resilient material while maintaining the inside wall of the tube between said grooves substantially free of said resilient material, including the steps of, placing within said tube a tubular injection tool which has an outside diameter substantially equal to the diameter of said inside wall of said tube and radial holes in the outside surface thereof at a predetermined angular position, applying said resilient material under pressure through said radial holes whereby said resilient material is forced into said grooves, rotating said tube through an angle at least equal to said predetermined angle, and Withdrawing said tool from said tube.

3. A method of evenly filling a spiral groove cut on the inside wall of a hollow cylindrical tube with a silicon rubber mixture While maintaining the inside wall of the tube between said grooves substantially free of said silicon rubber, including the steps of, placing within said tube a tubular injection tool which has an outside diameter substantially equal to the diameter of said inside wall of said tube and radial holes in the outside surface thereof at predetermined angular position, applying said silicon rubber under pressure through said radial holes whereby said silicon rubber is forced into said grooves, rotating said tube through an angle at least equal to said predetermined angle, and withdrawing said tool from said tube.

References Cited UNITED STATES PATENTS ROBERT F. WHITE, Primary Examiner.

T. J. CARVIS, Assistant Examiner,

Claims (1)

1. A METHOD OF EVENLY FILLING AT LEAST A PORTION OF A SPIRAL GROOVE CUT ON THE INSIDE WALL OF A HOLLOW CYLINDRICAL TUBE WITH A RESILIENT MATERIAL WHILE MAINTAINING THE INSIDE WALL OF THE TUBE BETWEEN SAID GROOVES SUBSTANTIALLY FREE OF SAID RESILIENT MATERIAL, INCLUDING THE STEPS OF, PLACING WITHIN SAID TUBE A TUBULAR INJECTION TOOL WHICH HAS AN OUTSIDE DIAMETER SUBSTANTIALLY EQUAL TO THE DIAMETER OF SAID INSIDE WALL OF SAID TUBE AND RADIAL HOLES IN THE OUTSIDE SURFACE THREOF, APPLYING SAID RESILIENT MATERIAL UNDER A PREDETERMINED PRESSURE THROUGH SAID RADIAL HOLES WHEREBY SAID RESILIENT MATERIAL IS FORCED INTO AT LEAST A PORTION OF SAID GROOVES, AND WITHDRAWING SAID TOOL FROM SAID TUBE.

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