US2898727A - Apparatus for controlling exhaust of motor alley heat in textile work rooms - Google Patents

Description

Aug. 11, 1959 A. H BAHNSON, JR APPARATUS FOR CONTROLLING EXHAUST OF MOTOR ALLEY HEAT IN TEXTILE WORK ROOMS 4 Sheets-Sheet 1 Filed June 15, 1956 INVENTOR i I r )3, 1 m. ATTORNEYS Aug. 11, 1959 A. H. BAHNSON, JR 2,398,727

APPARATUS FOR CONTROLLING EXHAUST OF MOTOR ALLEY HEAT IN TEXTILE WORK ROOMS 4 Sheets-Sheet 2 Filed June 15, 1956 INVENTOR 5 H. awga BY/PLMIJWN%JOW ATTORNEYS Aug. 11, 1959 A. H BAHNSON, JR 2,898,727

APPARATUS FOR CONTROLLING EXHAUST OF MOTOR ALLEY HEAT IN TEXTILE WORK ROOMS Filed June 15, 1956 4 Sheets-Sheet 3 INVENTOR a 17;, 5 /fim 5% & Pm

ATTORNEYS Aug. 11, 1959 A. HL'BAHNSON, JR 2,

APPARATUS FOR CONTROLLING EXHAUST 0F MOTOR ALLEY HEAT IN TEXTILE WORK ROOMS 4 Sheets-Sheet 4 Filed June 15, 1956 INVENTOR m ATTORNEYs United States Patent APPARATUS FOR CONTROLLING EXHAUST OF ALLEY HEAT IN TEXTILE WORK Agnew H. Bahnson, Jr., Winston-Salem, N.C. Application June 15, 1956, Serial No. 591,765

15 Claims. (CI. 57-56) In textile manufacturing plants and in particular those rooms of the plant wherein continuous lengths formed from staple fibers, such as slivers, rovings and the like of cotton are drawn, straightened or twisted preparatory to weaving or knitting it is most important that proper temperature and humidity conditions be maintained. Thus in temperate zones such as in the United States where the summer temperature is too hot and, conversely, the Winter temperature too cold for processing of the fibers on the textile machines such as slubbers, drawing frames, roving frames and spinning frames it has been found necessary to install air conditioning equipment which will modify the ambient temperature and humidity as required to maintain those conditions considered optimum for the particular process being carried out. Generally speaking, additional heat is necessary in the winter period and cooling is required during the heated summer.

Also, during recent years more and more attention has been focussed on the problem of keeping the textile machines in these rooms relatively free from lint. This is a particularly important problem where the textile fibers are in a loose or only slightly twisted condition such as a rove for the reason that fibers in such condition are most likely to break and also shed loose particles which tend to grow into flutfs as they are blown about. The loose particles and fluffs can easily become entangled in the lengths of fibers being processed into strands and the like and tend to reduce quality of product. Moreover, the lint and fiuffs get into the moving parts of the machines which is also undesirable. A further reason for keeping the work rooms free from lint is that a relatively clean room promotes morale of the employees who operate the machines.

One type of apparatus that has been developed for clearing textile machines such as a spinning frame and the like of lint and broken strands is comprised of a plurality of air suction tubes positioned adjacent the strands as they come off the drawing rolls, these tubes including an intake orifice or slot in alignment with each strand. The air suction maintained at these orifices is effective for drawing in loose particles in the vicinity of the strands and also for catching and drawing in the ends of any strands which should happen to break between the drawing rolls and the spindles. The collection tubes are themselves manifolded so to speak into a larger central duct which runs for the entire length of and inside the spinning frame, and a suction fan connected to one end of this central duct serves to draw the air and collected lint and broken strand ends into a filter box Where the lint and broken strand material are caught by a filter screen, the filtered air being then discharged.

For driving the spindles of the spinning frame a motor of considerable size is required. This motor is usually located at the end of the frame and the heat given off by the motor adds considerably to the heat load of the room and thereby also to the air conditioning system especially 2,898,727 Patented Aug. 11, 1959 same is true as regards the amount of heat given off by the motor and fan unit which supplies the necessary power to operate the suction system for clearing the spinning frame of lint and broken ends.

An object of the present invention is to provide an improved arrangement for controlling the amount of heat, originating in the motors which power the spinning frame and in the motor and fan for powering the suction system for clearing the frame, that is removed from or left to circulate in the room.

In general this objective is attained by locating the suction fan and filter unit at the same end of the spinning frame as the motor which drives the frame cylinder which in turn drives the spindles, and establishing a suction pressure limited to this general area and a related exhaust duct system by which a desired amount of the heat present in such area can be removed. In the event that it is practical to establish an under-the-floor exhaust duct system for conveying away the heat from this area, an entrance to the duct system can be made through the floor in the vicinity of the frame drive motor, and the air discharged from the suction fan, i.e. the filtered air, is preferably directed downwardly in the direction of the motor and floor opening. In the event that an under-thefloor exhaust duct system is not practical, an exhaust duct system can be arranged overhead in the spinning room, in which event the air entrance to the overhead duct system would be constituted by a hood arranged above the motor and suction fan area. Consequently, by varying the suction pressure in the exhaust duct system, the amount of heat in the vicinity of the drive motor and suction fan discharge that is removed from or left to circulate in the room can be correspondingly varied. Moreover, if desired, the motor alley area and inlet to the exhaust system can be partly enclosed such as by means of upright walls between the spinning frames in order to exercise a more positive control over the air exhausted from this area.

As previously indicated, generally speaking, heat must be removed from the room during summer while it is usually necessary to supply heat during the winter season. Consequently, the suction pressure and air handling in the exhaust duct system will be higher in summer than in winter, and, during the latter season, :it may even become necessary to drop the suction pressure and air handling to zero, in which case no air will be taken out during the summer when heat must be removed. The

through the exhaust duct system. One exception to the general rule of heat removal during summer arises in regards to textile work rooms where air conditioning with refrigeration is employed. In this instance, the maximum suction pressure and air handling by the exhaust duct system will be used in very hot weather until the total heat of the outside air exceeds the total heat of the air in the room at which point the amount of air exhausted will be decreased by, for instance, an outdoor wet bulb control similar to the same conventional control that would be, at such time, closing the outside dampers of the air conditioning system in the room.

One practical method of varying the suction pressure in the exhaust duct system would be by means of a thermostat type of control, based upon the change in exterior temperatures. Another type of control possible would be to couple it with the fresh air and return dampers of the air conditioning system associated with the room so as to proportion the amount of air taken out of the room through the exhaust duct system in relation to the amount of air being brought in by the air conditioning system. The suction pressure variation itself can be obtained by changing the speed of the suction fan associated with the exhaust duct system or by the use of 3 vortex dampers in the duct, or by any other functionally equivalent means.

In spinning rooms where the drive motors of two frames are located together to form what is called a double motor alley, a suction fan and drive motor unit therefor individual to each frame can be employed but it is preferred to utilize a single suction fan and motor unit of novel construction, also claimed herein per se, which serves to operate the lint and broken end collection system of both frames. This suction fan is provided with an air intake and filter section and clean-out compartment for each spinning frame, the whole being contained within a common housing, and the discharge from the suction fan being directed in such manner as will best result in its flow into the exhaust duct system.

The foregoing as well as other objects and advantages inherent in the invention will become more evident from the following detailed description of two practical embodiments thereof and the accompanying drawings wherein:

Fig. 1 is a somewhat diagrammatic view of a portion of a spinning room containing a plurality of spinning frames, the adjacent end portions only of two such frames being illustrated in side elevation in order not to unduly complicate the drawings, this view also showing the double motor alley area between the frames, a floor outlet from such area and an under-floor exhaust duct connected to that outlet;

Fig. 2 is a vertical transverse section through one of the spinning frames taken on line 2-2 of Fig. 1;

Fig. 3 is a vertical section taken on line 3-3 of Fig. 4 of the suction and filter unit located in the motor alley area and which serves both spinning frames for removing loose particles and broken ends;

Fig. 4 is a horizontal section through the suction and filter unit taken on line 44 of Fig. 3;

Fig. 5 is a vertical section through the suction and filter unit taken on line 5-5 of Fig. 4;

Fig. 6 is a front elevation showing a modified construction for enclosing the drive motor for a textile machine; and

Fig. 7 is essentially a top plan view of the construction The air suction apparatus for collecting loose particles and broken ends from the spinning frames 11, 11' comprises central collection ducts 23, 23' which can be rectangular in cross-section extending for the full length of the frame beneath the creel boards 13. The end of the duct 23 at the end of the spinning frame 11 and the end of the duct 23' at the end of spinning frame 11 remote from the ends shown in the drawing are closed and the opposite ends of the ducts 23, 23' are connected to inlets 24, 24 of a combined suction and filter unit 25 situated in the motor alley area and above the drive motors 20, The unit functions to maintain a suction in collection ducts 23, 23', to filter the fiber laden air which flows into the same, and to discharge the cleaned air downwardly in the direction of the drive motors 20, 20', in a manner to be described later in further detail.

Connected to each of the ducts 23, 23 by means of tubings 26, 26' are a plurality of cylindrical collection tubes or flutes 27, 27 each containing a plurality of horizontally extending, spaced slots or orifices 28, 28. These slots 28, 28 are located at the places on the spinning frame where the broken ends usually occur, which is between the output side of the rolls 15 and the guides 29 through which the strands 14 pass to be wound upon the spindles 16. A separate slot 28, 28 is provided for each strand such as a roving strand or the like being processed and is located below and in line with the path which the strand follows, as clearly seen in Fig. 2, so that upon a break in any strand, the free end of the strand will be drawn by suction through its corresponding slot and will continue to be so sucked in until the operator notices the break and reties the strand so as to continue shown in Fig. 6, the view being taken at line 77 of Fig. 6.

With reference now to the drawings and in particular to Figs. 1 and 2, the floor of the spinning room is indicated at 10 upon which stands a plurality of a spin ning machines. In the particular arrangement of machines illustrated, which is quite common, the machines are arranged in rows in the room there being a plurality of machines to each row and the machines of each row being arranged generally in end-to-end relation and with suflicient space between the ends of adjacent machines in a row to accommodate the drive motors for the machine spindles of two frames. The end portions only of adjacent spinning frames in one row are indicated at 11 and 11, and all structural detail not essential to an understanding of the invention have been omitted. The spools 12 containing the roving to be processed are mounted vertically between the creel boards 13, and the roving 14 from the same is drawn by and between rolls 15 for winding upon spindles 16. The latter are driven in pairs at each side of the machine by means of endless tapes 17 which are driven off a cylinder 13 that extends for the full length of each machine in the so-called underframe portion. Each of the cylinders 13 is driven by a motor located in the motor alley area 19 between the frames, the motor for spinning frame 11 being indicated at 20 and the motor for spinning frame 11 being indicated at 20. The motor alley area can, if desired, be at least partially walled in by means of side panels 21 and 22 which extend upward from the floor at the sides of each frame to a height of a few feet, the panels being preferably removable when necessary for access to the drive motors.

the spinning thereof. The broken strand end passes through the tube 27 or 27 and tubing 26 or 26 into the central collection duct 23 or 23 and through the latter into the filter unit 25. It is preferable to make the tubes 27, 27' of such length as will service several strands, there being a slot 28 or 28 for each strand, and the several tubes being each connected by tubing 26, 26 to the central collection ducts 23, 23. The multiple number of air suction slots distributed throughout the length of each spinning frame in addition to their function of picking up broken strand ends also serve to continuously draw in a considerable quantity of loose particles along the entire length of the spinning frame and these particles also are likewise carried through the collection duct system to the filter unit 25.

The filter unit 25, the details of which are also claimed.

in this application, is featured by a single fan which serves to establish the suction in the duct systems of both spinning frames 11, 11 and a filter compartment individual to the air intake from each frame, all contained Within a common housing located in the motor alley area above the spindle drive motors for the frames. With reference now to Figs. 1 and 3-5 which show the details of construction of the filter unit 25, the suction fan 31 is seen to be of the axial intake, tangential exhaust type. The scroll of the fan in which is enclosed the impeller 33 is mounted within a housing 34,, and the tangential exhaust duct 30 from the fan scroll passes out through the bottom wall of housing 34, in a vertically downward direction and terminates just below the top ning frame. As is clearly visible from Fig. 4, air having lint particles and broken ends entrained therein coming to the filter unit 25 through duct 23 enters through intake 24 into that part 34a of the housing 34 which lies inside of three screen panels 40, 41 and 42 which are joined together at their edges and extend from the bottom to the top of housing 34. These three screen or filter panels thus form a filter compartment 34a screened ofi from the remainder of housing 34 in which is trapped all of the fibrous material incoming through the collection duct 23 from spinning frame 11. In a similar manner, air having lint particles and broken ends entrained therein coming to the filter unit 25 through duct 23' enters through intake 24 into that part 3412 of housing 34 which lies inside of three screen panels 40', 41 and 42 which are also joined together at their edges and extend from the bottom to the top of housing 34. These three screen panels thus form a second filter compartment 34b screened off from the remainder of the interior of housing 34 in which is trapped all of the fibrous material incoming through the collection duct 23 from spinning frame 11. The filtered air, after passing through the screens 4042 and 4fi42' flows into the axial intake opening 39 to the scroll 32 and is then discharged by the impeller 33 through the tangential outlet duct 30. A clean-out door 43 is preferably provided in the end wall of housing 34 leading to the filter compartment 34a to facilitate removal of the fibrous material which collects therein, and a similar cleanout door 43' is provided at the opposite end wall of housing 34 for access to filter compartment 341).

The housing 34 may be supported in the position shown in Fig. l by any suitable means, not illustrated. Such support may be by way of lateral connections to the end structure of the spinning frames l1, 11', or the housing may be carried by a suitable framework built up from the floor of the spinning room.

With reference again to Fig. 1, the opening in the floor in the double motor alley area 19 to draw a variable amount of air therefrom and discharge the same to the outside, is indicated at 44, and the duct 45 leading there from is manifolded into a larger exhaust duct 46 in which is located a suction fan 47 driven by electric motor 48 which is arranged to operate at a variable speed in order to effect a variation in the duct suction and hence also the amount of air drawn into the duct from the motor alley area 19 of the spinning room. It will be noted that the duct 46 extends to the left of the particular duct 45 illustrated and the intention is that this leads to a similar air exhaust arrangement provided for the motor alley areas of other pairs of spinning frames located in the same row. In a similar manner, like motor alley area exhaust systems will be provided for the spinning frames in the other rows of frames located in the spinning room.

In accordance with the invention, the suction in duct 46 is to be varied in accordance with a change in room temperature and climatic conditions so that during the summer months the suction is increased thereby removing most if not all of the heat given off by frame spindle drive motors 2t 21' and the exhaust from the filter unit 25 in the motor alley area 19, the heated air being drawn down through the floor opening 44 into the exhaust duets 45, 46. Conversely, in the winter, the suction in duct 46 is decreased and may even drop to zero to the end that most, if not all, of the heat given oif by the motors 2d, 21 and the exhaust from filter unit 25 will be allowed to distribute itself throughout the room area. In the seasons between mid-summer and mid-winter, the suction in the exhaust duct 46 will, of course, be suitably maintained between these two extremes of operation.

The control over the exhaust suction in duct 46 can be directed manually or the system can be made to operate automatically by some means which vary in accordance with. the change in temperature, the control being predicated either upon a change in outdoor temperature or a change in temperature within the work room. As previously indicated, an automatic control may also be predicated upon, i.e. tied to, operation of the fresh air and return dampers of a conventional air conditioning system installed to condition the air in the room, such dampers being themselves controlled as a function of the change in outside temperature. One mode of automatic control and which is illustrated schematically in Fig. 1 could comprise either a wet or dry bulb thermostat 49 responsive to the outdoor temperature, the thermostat response being used to control the action of a speed controller unit of conventional design and therefore illustrated simply by the block 50 which in turn controls the speed of motor 48 and fan 47 and thereby controls the amount of air suction in the duct 46. In the case of an air conditioning system employing refrigeration associated with the room, the air removed from the room via the exhaust duct sys tern would generally increase with an increase in outside temperature but would be decreased when the total heat in the outside air exceeded the total heat of the air in the room. in lieu of varying the speed of the fan, the fan speed could be kept substantially constant and the duct suction varied by means of controllable dampers in the duct and when the minimum. air quantity was reached, the exhaust fan could be cut off.

The arrangement which has been described in relation to room exhausts at double motor alley locations between adjacent spinning frames is, of course, equally applicable to single unit frames having the spindle drive motor for the frame and the suction and filter unit for clearing the frame of loose fibrous particles and broken ends.

Figs. 6 and 7 illustrate an embodiment of the invention suitable for single unit frames. With reference now to these views it will be seen that the drive motor 51 for the spinning frame is enclosed by a box-like structure 52 secured in place on the floor 53 at the end of the spinning frame 54. The box enclosure 52 is comprised of two sections 52a, 52b held together by any suitable type of latching means such as the trunk latches 55 shown at opposite sides of the box so that the box can be easily disassembled for maintenance of the motor. An angle iron frame 56 is fastened to the floor 53 and. the box section 525 is secured to the frame 56 with screws 57.

The bottom of the air outlet 58 from the filter unit 59, corresponding in function to the filter unit 25, fits into an opening 66 in the top wall 61 of box section 5212 and is sealed by a gasket 62 made of any suitable material such as sponge rubber to prevent any lint from entering the box 52. The box 52 is essentially open in that the top wall 61 also includes a very large screen section 63, which excludes lint but permits air to enter the box from the room and also to fiow out of the box into the room under certain circumstances. As is evident from the drawing, motor 51 is displaced laterally from the filter outlet 58, and the box section 52a which encloses the motor is fitted onto the angle frame 5'6 and held in abutment with the adjacent section 52b by means of the side trunk latches 55. The box section 52a includes a slot 67 in one side extending back from one edge to accommodate the shaft 51a of the motor 51.

That portion of the floor 53 within the box section 525 includes an opening 64 connecting with an under-floor duct 65 corresponding to duct 46 in the previously described embodiment and containing an exhaust fan, not illustrated, corresponding to fan 47. The amount of air exhausted from box 52 in relation to that exhausted from other like arranged boxes enclosing the motors of other spinning frames in the room can be equalized by means of an adjustable damper plate 66 which is slidable across the entrance to floor opening 64 to the desired position of adjustment.

In the embodiment of Figs. 6 and 7, the heat of the spinning frame motor 51 is trapped within the box 52 through the action of the exhaust fan drawing air through the floor opening 64. Almost of the makeup air comes from the air discharged through outlet 58 of the filter unit 59 as it blows into the box 52. This air coming into the box 52 provides a ventilating effect for motor 51 and hence prevents the motor from overheating. Dur- 7 ing operation in winter when the exhaust fan in duct 65 is slowed down, or stopped completely, the air discharged from outlet 58 will pass outwardly from box 52 through the screened section 63 into the room and also carry with it the heat from motor 51.

As with the previously described embodiment, the air discharge from box 52 instead of going out through the floor opening 64 may be taken out through an exhaust duct extending from the floor up to and along the ceiling of the spinning room in situations where an under-floor duct is not practical.

It will also be understood, in conclusion, that other variations in the particular construction and arrangement of parts and applications of the invention to textile machines other than spinning frames, such as slubbers, drawing frames and roving frames are possible without departing from the spirit and scope of the invention as defined in the appended claims.

This application is a continuation-in-part of my application Serial No. 502,979, filed April 21, 1955.

I claim:

1. In a textile room the combination comprising a machine such as a spinning frame on the floor of said room for simultaneously performing a textile operation upon a plurality of strands of textile material spaced along the length of said machine, said machine including a motor at one end thereof for driving the same, a suction collector system comprising a plurality of intake orifices disposed adjacent the strands respectively for collecting broken ends and loose particles, at central collection duct extending longitudinally of said machine and in communication with said orifices, a suction fan and filter unit to which said central duct is conected to establish a suction therein, said unit having a filtered air discharge outlet, an exhaust duct, said exhaust duct having an entrance opening thereto located in the vicinity of said drive motor and the filtered air discharge outlet from said filter unit, and means for establishing a suction in said exhaust duct thereby to draw off from the room the heated air in the vicinity of said drive motor and the filtered air discharged from said outlet of said filter unit.

2. The arrangement as defined in claim 1 wherein said exhaust duct is located beneath the floor of the room and the entrance opening to said duct is constituted by an opening in the floor in the vicinity of said drive motor.

3. The arrangement as defined in claim 1 and which further includes means for varying the suction in said exhaust duct.

4. The arrangement as defined in claim 1 wherein said exhaust duct includes a motor driven exhaust fan for establishing the suction therein, and means for varying the speed of said exhaust fan in accordance with the change in outside temperature.

5. The arrangement as defined in claim 1 and which further includes means for varying the suction in said exhaust duct in accordance with the heat requirements of said room.

6. The arrangement as defined in claim 1 and which further includes means for reducing the air removed from the room through said exhaust duct when the total heat of the outside air exceeds the total heat of the air in the room, and said room employs an air conditioning system with refrigeration.

7. In a textile room the combination comprising a machine such as a spinning frame on the floor of said room for simultaneously performing a textile operation upon a plurality of strands of textile material spaced along the length of said machine, said machine including a motor at one end thereof for driving said machine, a suction collector system comprising a plurality of intake orifices disposed adjacent the strands respectively for collecting broken ends and loose particles, a central colleotion duct extending longitudinally of said machine and in communication with said orifices, a suction fan and filter unit to which said central duct is connected to estab- 8 lish a suction therein, said unit having a filtered air dischareg outlet, said fan and filter unit being located above said drive motor and with said filtered air discharge outlet from said unit directed'downwardly in the vicinity of said motor, an opening in the floor of said room in the vicinity of said drive motor, an exhaust duct connected with said opening, and means for establishing a suction in said exhaust duct thereby to draw 01f from the room the air heated by said drive motor and the filtered air discharged from said outlet of said filter unit.

8. The arrangement as defined in claim 7 and which further includes means for varying the suction in said exhaust duct in accordance with the change in outside temperature to increase the suction as the outside temperature increases, and vice versa.

9. in a textile room the combination comprising a pair of elongated machines such as spinning frames on the iioor of said room for performing a textile operation upon a plurality of strands of textile material spaced along the length of each machine, said machines being arranged in line and with a space between the adjacent ends of said machines constituting a double motor alley area, a drive motor for each machine located in said alley area for driving said machine, a suction collection system for each machine comprising a plurality of intake orifices disposed adjalcent the strands respectively for collecting broken ends and loose particles, a central collection duct extending longitudinally of each machine and in communication with the intake orifices thereon, a suction fan and filter unit disposed in said motor alley area, said unit having a filtered air discharge outlet, means connecting the central collection duct on each machine with the suction intake to said fan thereby to establish a suction in said collection ducts, an exhaust duct, said exhaust duct having an entrance opening thereto located in the vicinity of said motor alley area and the air discharge outlet from said filter unit, and means for establishing a suction in said exhaust duct variable in accordance with a change in temperature to draw oif a correspondingly variable amount of air from the vicinity of said motor alley area, the amount of air drawn off generally increasing with a rise in temperature and vice versa.

10. The arrangement as defined in claim 9 wherein said exhaust duct is located beneath the floor of the room and the entrance opening to said exhaust duct is constituted by an opening in the floor of the room at said motor alley area.

11. The arrangement as defined in claim 9 wherein said exhaust duct is located beneath the floor of the room, the entrance opening to said exhaust duct is constituted by an opening in the fioor of the room at said motor alley area, said suction fan and filter unit is located above said drive motors, and the air discharge therefrom is directed generally downward towards said drive motors and fioor opening.

12. The arrangement as defined in claim 9 and which further comprises means for walling in at least a part of said motor alley area including said entrance opening to said exhaust duct.

13. In a textile room the combination comprising a machine such as a spinning frame on the floor of said room for performing a textile operation simultaneously upon a plurality of strands of textile material spaced along the length of said machine, a motor at one end of said machine secured to the floor of the room for driving said machine, a suction collector system comprising a plurality of intake orifices disposed adjacent the strands respectively for collecting broken ends and loose particles, a central collection duct extending longitudinally of said machine and in communication with said orifices, a suction fan and filter unit to which said central duct is connected to establish a suction therein, said suction and filter unit being located above the level of said drive motor and including a filtered air outlet therefrom directed downwardly, a box-like enclosure surrounding said motor,

means delivering the air discharge from said outlet of said unit into said enclosure, an outlet from said enclosure, an exhaust duct connected to said outlet of said enclosure, and means establishing a suction in said exhaust duct to draw off the motor heat and the air discharged from said suction and filter unit.

14. The arrangement as defined in claim 13 wherein one wall of said enclosure is provided with a screened opening.

15. The arrangement as defined in claim 13 wherein said enclosure is comprised of two sections, one of said sections being stationary and the other of said sections being attached to said stationary section and being located directly over said motor so as to permit access thereto for servicing when detached from said stationary section.

References Cited in the file of this patent UNITED STATES PATENTS Little Feb. 12, 1946 Thoma Aug. 12, 1947 Bechtler Dec. 2, 1947 Lang Jan. 23, 1951 Strassler June 17, 1952 Thoma May 24, 1955 FOREIGN PATENTS Australia Mar. 11, 1929 France Nov. 1, 1950

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