US2492904A - Tube forming apparatus - Google Patents

Description

Dec. 27, 1949 Filed Dec. 30, 1947 R. B. THOMAS ETAL 2,492,904

TUBE FORMING APPARATUS 2 Sheets-Sheet l GERALD QUINN A'rroe NEY R. B, THOMAS ET AL Dec, 27, 1949 2 Sheets-Sheet 2 Filed Dec. 30, 1947 ATTORNEY Patented Dec. 27, 1949 UNITED STATES PATENT OFFICE TUBE FORMING APPARATUS Ralph B. Thomas, Beverly, and Gerald S. Quinn, Salem, Mass, assignors to Sylvania Electric Products Inc., Salem, Mass., a corporation of Massachusetts Application December 30, 1947, Serial No. 794,618 4 Claims. (01. 49-7) This invention relates to electric gaseous discharge devices and more particularly to fiuorescent lamps of the curved or circular type.

An object of this invention is to provide apparatus for accurately forming a substantially circular glass tube.

Another object of this invention is to provide apparatus for accurately forming a substantially circular glass tube from a helically formed section of glass tubing.

A further object is to provide apparatus for accurately forming a substantially circular fluorescent lamp from a helically formed section of glass tubing which has had its inner wall coated with a luminescent material and electrodes sealed in the endsthereof.

Other objects advantages and features will be apparent from the following description when read in conjunction with the accompanying drawings in which:

Figure 1 is a top plan view of one modification of the apparatus of my invention;

Figure 2 is a front elevational view of the apparatus shown in Figure 1;

Figure 3 is a side elevational view of the apparatus shown in Figure 1;

Figure 4 is a fragmentary detail plan view showing the manner in which one of the lamp lead Wires is secured to the base of the apparatus;

Figure 5 is a front perspective view of another modification of the apparatus of my invention;

Figure 6 is an enlarged perspective view of that portion of the apparatus of Figure 5 which accomplishes the formation of a circular glass tube from a length of helically formed glass tubing; and

Figure 7 is a front elevational view of the apparatus of Figure 5.

This invention embodies the idea of providing a flattening jig whereby a length of helically formed glass tubing, which has had its inner wall coated with a luminescent material and electrodes sealed at each end thereof, may be formed into a circular lamp.

The manufacturing of a circular fluorescent lamp presents many problems which are not confronted in the manufacturing of conventional linear type lamps. It is quite difiicultto start with a curved tube of the exact dimension and configuration finally desired because of the difiiculties which would be encountered incoating the inner wall of the tube with luminescent material and sealing electrodes in the ends thereof. This would be so because the ends of the tube would be quite close to each other and in the same horizontal plane. Thus, far too little working area about the ends of the tube would be available for accomplishing these operations.

Basically there are, in general, two sequences of manufacturing operations possible. One may start with a conventional linear tube, coat it with luminescent material, seal electrodes in the ends thereof, and then bend the tube to the desired form, or one may start with a helix of several turns of tubing, cut it into several units of about one turn each, coat each unit with a luminescent material, seal the electrodes in the ends thereof and then form the tube into the finally desired shape. In both cases the lamp is evacuated, a filling of inert gas is introduced therein, and the exhaust tube sealed, after the tube has been fashioned to the finally desired form.

The apparatus of this invention provides means whereby a helically formed unit of glass tubing which has had its inner wall coated with lu- .minescent material and electrodes sealed at each end thereof may be shaped into its final circular form prior to evacuation.

The unit on which this operation is performed is formed from single turn sections cut from a helix of glass tubing, with a space between the ends thereof preferably slightly less than the finally required spacing. The pitch of the helix is predetermined so that the ends of each unit cut therefrom will be offset from each other the desired amount. Although this helically formed unit of glass tubing may be obtained by making a simple radial cut at the desired point on the helix, we have found it more desirable to cut the tubing so that the end faces of the unit of tubing out are substantially parallel to a plane containing the axis of the helix and passing through the center of the space between the ends so cut. The inner wall of each unit is coated with luminescent material and electrode mounts are sealed in each end thereof, at least one of said mounts being provided with an exhaust tube through which the sealed .device may be evacuated. This. exhaust-tube is then bent at right angles and perpendicular to the axis of the helix at a point along'its longitudinal axis where it is disposed outside-the .re-entrant stem of the electrode mount. This is done to permit the positioning of the lamp in. the flattening jig.

We have found it desirable to position this helically formed unit of glass tubing on the fiattening jig with reference to a line running through the center of the circle defined by the unit and through the center of the space between the ends of the unit as finally formed.

Referring now to the drawings, and more particularly to the embodiment illustrated in Figures 1, 2, 3 and 4, the flattening jig comprises a base plate I on which a lamp (the unit or section of tubing referred to above) 2, is positioned, an adjustable yoke 3, a fixed stop 4, and an adjustable eccentric stop 5,, all of which are mounted on the base plate and which serve as guides in positioning the lamp 2 on the base plate, a clamping arm 6 pivotally mounted on the eccentric stop movement thereof, the purpose .for which 'will be described later.

In operation, the :lamp :2 is placed on the'base plate I with the end I;I thereof:abutting-the-stop 4, andthe exhaust tubulati'on 3-I resting'on 'or .slightly above the :upper surface of .the stop 4. Oneof the lead-wires 33 maythenbewoundfabout a stud 32 on the base .plate 2 (Figure 4).. Although this is not necessary, it has been found desirable because itaids in securing .this end. of thelamp =in position. The other lead wire should be bent outwardly substantially as shown in Figure "4 so that it will not inteffere with the operation of the jig.

The-arm "I is then moved into position by causing the V-blockB to engage "the lamp 2 adjacent the-end II thereof. The V-block 9"is provided with a cam 20, the outer surface-of which engages the end I I of the lamp.

'The adjustable yoke 3 which is mounted on the base plate I servesasan internal centeringgauge and is a means for centering the lamp '2 on the base plate so that the center of the circle defined "by the lamp is on-a linepassing through the 'center of the space between the ends of the lamp,

The position of the lamp *2 on the'base plate "I is adjusted so that both ofthe arms -I3 of the yoke 3 touch the lamp. These two points of contact, in conjunction'with the disposition of the end II of the lamp in contact with the 'stop 4, provide a three-point contact for positioning the lamp. Although we have found the use of the adjustable yoke to be of assistance in accurately positioning the lamp "'2 .for the flattening operation we have also foundthat its use may .be dispensed with and the lamp lined up .visually if .desired.

The eccentric stop 5 is then rotated until it touches the lamp 2. The clamping arm "6 is then moved into positionto lock the lamp 2 tothe base plate I (Figure .1). The "adjustable yoke 3, .if ,used, may then'be removed from the jig.- The lamp '2 is now held in positron'on'the jig by the stop 4, the :V-block 9, the eccentric stop *5 and the clamping arm '6.

As mentioned above each of .thearms1 and .8 have a weightedV-block 9 hand Illtrespectively disposed on itsfree end. 'The 'v-block 9 is providedwith a cam 29 and the vblock II] is 'proit touches the base plate I.

As mentioned above, the arm 8 is pivotally mounted in the plate I5 in a manner which will permit a small amount of horizontal angular movement. This is done to afford freedom of movement of the cam follower 2| and to permit adjustments to be made for small variations in the initial distance between the :ends !I I and I2 of the lamp. The V-blocks 9 and I0 are properly positioned on the lamp 2 when the outer faces of 'cam 29 and cam follower 2I respectively abut :the-ends II and I2 respectively of the lamp.

In order to prevent distortion of the cross sec- "tion of the lamp .2 during the heating and fiattening operation the arm I is provided with a support I6 'which'comprises a block II attached to the arml, a pin 'I'8 extending through the block \III anda locking screw I9. After the arm I has beenpositioned the screw I9 is loosened to permit the pin I8 to drop down in the block I! until The pin I3 is then "locked in this position by the locking screw I9. Tn this 'way,the =V-block 9 still'engages the lamp 2 but its weight and the weight of the arm I 'is now carried by the'pin I8.

The lamp 2 is now ready for the flattening operation. This assembly is then placed in a heating chamber where it is exposed to heat of a degree calculated to cause the glass, of which the lamp '2 is made, to soften and become plastic. When the glass softens the weighted V-block IE! will slowly, by force of gravity, push the raised and I2 of the lamp "2 downwardly until the en- .tire lamp rests 'on'the'base plate 'I and the ends .II and I2 thereof are 'in proper circular alignment andspaced the predetermined distance.

In placing this assembly in a heating chamber it has beenzfound desirable to elevate the side of the base plate which supports the raised end of the lamp about '8 degrees. This is done to insure a positive contact between the cam 20 and its 'follower'ZI as the 'end' I2 of the lamp moves into position and to make sure that when the fiattening operation is completed the ends II and I2 of the lamp will be spaced the desiredpredetermined distance. This cantin'g is particularly desirable in-cases where the distance between the ends of the lamp initially is greater than the finally desired distance because, when .the heated glass becomes plastic, gravity will cause the end of the lamp .I2 and the cam follower 2I to move until .the cam follower 2'I is .in contact with the cam '20. 'Thus the flattening operation may be satisfactorily performed on the apparatus of our invention .in cases where the ends of the tube are initially spaced a greater distance from each other than the finally desired distance as well as in cases where the ends are initially closer to each other than is finally desired.

A. ,plate .22 is mounted on top of cam follower -2I.. This plate :serves .as means for limiting the downward movement of the weighted vblock I0 .and the cam follower .2.I durin the fiattening operation. After the end I2 of the lamp '2 hasheen caused to move downwardly so that the entire lamp .isin contact with the base plate I .it .is extremely undesirable to have the weighted .V-block .IIl continued to exertpressure on the lamp. When the flattening operation has been accomplished the plate '22 will strike the top of the cam '29 on the V-block 9, thus limiting the V-block I5 from any further downward movement. Thus if the apparatus were Dermitted to remain *in theheating chamber after the flattening of the lamp had been accomplished the plate 22 would serve "as asafety device to prevent the weighted V-block from continuing to exert pressure on the lamp and deformin the end thereof.

Referring now to the modification shown in Figures 5, 6 and '7, many of the principles embodied in the structure shown in Figures 1, 2, 3 and 4 and described above are applicable to this structure. Similar reference numerals have been used in Figures 5, 6 and 7 to designate elements which are the same as elements in Figures 1, 2, 3 and 4. The adjustable yoke 3 shown in Figure 1 has been omitted in this modification.

A lamp 2 is positioned on the instant structure in substantially the same manner in which it was positioned on the Jig just described. The end I I of the lamp is positioned so that its end surface abuts the stop 4; the lamp is centered with reference to a line running through the center of the circle which it defines and the center of the space between the ends of the lamp as finally formed; the eccentric stop is adjusted to cause it to engage the lamp; and the clamping arm is swung in to lock the lamp in position. The exhaust tube 3I is disposed on or above the stop 4.

In the present structure the V-blocks 9 and I0 are mounted on posts 23 and 24 respectively instead of on arms 1 and 8 as is done in the abovedescribed structure. The posts 23 and 24 are mounted on the base plate I. The V block Ill is provided with channels 21 out in the sides thereof, through which posts 24 extend. The weight of the V-block 9 which was removed from the lamp by the arm support I6 in the previously described apparatus is removed in the present structure by means of screw 25 which extends through the V-block 9 and a wing nut 26. After the end I I of the lamp 2 has been positioned the V-block 9 is mounted on the posts 23 and dropped down to engage the lamp. The screw 25 is turned down until it makes a positive contact with the top of post 23. Thus the weight of the V-block 9 is carried by the posts 23 instead of the lamp 2.

In the description of the first embodiment of this invention it was pointed out that the arm 8 which carried the V-block II! was pivotally mounted in a manner which permitted a small amount of angular movement in a horizontal plane to afford freedom of movement of the cam follower and to compensate for small variances in the initial distance between the ends of the lamp and thereby permitted the V-block ID, in all cases, to be positioned on the lamp with the outer face of the cam follower 2! abutting the end I2 thereof. In the present structure the use of cam 28 and cam follower 2| is dispensed with. Their function is now performed by the posts 24 which are not mounted perpendicular to the base plate I but rather at a pre-determined angle. This angular disposition of the posts 24 is calculated so that when the flatmning operation is completed the stop 28, on the V-block I9, which abuts the end I2 of the lamp 2 will have caused the lamp in its plastic condition to assume a position in which the ends I I and E2 of the lamp will be in proper circular alignment and spaced the desired distance apart.

The adjustable screw 29 mounted in the bracket 30 which is attached to the V-block Iii performs the same function as the plate 22 does in the structure illustrated in Figures 1, 2, 3 and 4, i. e., when the flattening operation has been accomplished, the screw 29 engages the top of the V- block 9 and thus shifts the weight of the V-block Hi from the end I2 of the lamp to the V-block 9. This prevents distortion of the contour of the lamp while it is plastic.

Thus the apparatus of our invention provides a means whereby one may form a substantially circular fluorescent lamp from a unit cut from a helix of glass tubing. We have found it desirable to start with a unit of tubing in which the ends are substantially parallel to a reference plane containing the axis of the helix and passing through the center of the space between the ends. We

.have also found it desirable to form this unit of tubing so that when the operation has been completed the ends will be in circular alignment with no point on the principal plane of either end of the tube less than a pre-determined distance from a reference plane through the center of the circle defined by the tube and perpendicular to the plane of the circle and passing through the center of the space between the ends.

However, it is to be understood that the principles herein enunciated provide the basis for the manufacturing of substantially circular electric gaseous discharge devices in which the ends are not disposed in the specific manner mentioned above without departing from the spirit of this invention, For example, it is not absolutely necessary that one start with a unit of tubing in which the ends thereof are substantially parallel to a reference plane containing the axis of the helix and passing through the center of the space between the ends. For example, one may well start with a unit of tubing in which the ends are formed from radial cuts. Similarly, it is not absolutely necessary that the ends of the tubing as finally formed be in circular alignment.

This is a division of our abandoned application Serial Number 676,193, filed June 12, 1946.

What we claim is:

1. Apparatus for forming a substantially circular glass tube in which all points on the axis of the tube are in the same plane, from a segment of a helix of glass tubing, said apparatus comprising; a base member, means for positioning said tube on said base member, means for securing said tube on said base member, a pair of weighted members supported from said base member, each being disposed in a position to engage the tube adjacent a free end thereof, a cam mounted on one of said weighted members, and a cam follower mounted on the other weighted member and engageable with said cam.

2. Apparatus for forming a substantially circular glass tube in which all points on the axis of the tube are in the same plane, from a segment of a helix of glass tubing, said apparatus comprising: a base member, means for positioning said tube on said base member, means for securing said tube on said base member, a pair of weighted members supported from said base member, each being disposed in a position to engage the tube adjacent a free end thereof, a cam mounted on one of said weighted members, and a cam follower mounted on the other weighted member and engageable with said cam.

3. Apparatus for forming a substantially circular glass tube in which all points on the axis of the tube are in the same plane, from a segment of a helix of glass tubing, the ends of which are initially substantially parallel to a reference plane containing the axis of the helix and passing through the center of the space between the ends, said apparatus comprising: a base member, means for positioning said tube on said base member, means for securing said tube on said base member, a pair of weighted members supported from said base member, each being disposed in a position to engage the tube adjacent a free end there- 01,2. oammounted'on oneofsaid weighted memcular glass tube in which all points on the aXis of the tube are in the same plane, from a segment of a helix of glass tubing, said apparatus comprising: a base member, means for positioning :said tube on said base member, means for securing said tube on said base member, a pair of weighted members supported from said base member, each being disposed in a position to engage the tube adjacent a free end thereof, a cam 8 mounted on one of said weighted members, and a cam follower mounted on the other weighted member and. engageable with said cam.

RALPH B. THOMAS. GERALD S. QUINN.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 539,291 Germany Nov. 24, 1931

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