US3520251A - Sonic dehydration of precipitate - Google Patents

Description

Juiy i4, A. G. BQDINE 3,5

SONIC DEHYDRATION OF PRECIPITATE Filed Feb. 10, 1967 4 Sheets-Sheet l ZJ T702 Me v I l (QMJQJQM I uiy M, 1976 A. G. BQDINE SONIC DEHYDRATION OF PRECIPITATE 4 Sheets-Sheet 2 Filed Feb. 10, 1967 h3g9 M, A.IG.BODINE 3,520,251

SONIC DEHYDRATION OF PRECIBITATE Filed Feb. 10. 1967 4 Sheets-Sheet 4 TIE E #mwroe. flABfET 6. BOD/IVE 0T TOEA/EY United States Patent 3,520,251 SONIC DEHYDRATION 0F PRECIPITATE Albert G. Bodiue, 7877 Woodley Ave., Van Nuys, Calif. 91406 Filed Feb. 10, 1967, Ser. No. 615,236 Int. Cl. 33Gb 9/24, 9/20 US. Cl. 1001l8 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method and apparatus for dehydrating precipiate material, and more particularly to such a method and apparatus in which the material to be dehydrated is squeezed between opposing members while sonic energy is simultaneously applied thereto to effect the migration of moisture particles from the precipitate.

In certain processing procedures it is necessary to get particulate material into a liquid by solution, colloidal suspension, dynamic stirring, or the like, certain essential reactions occurring or processing being accomplished with the material in this condition. Following this step, the liquid must then be thoroughly removed from the particulate material. While the main bulk of the water can readily be drained off, the removal of the final portions of moisture often poses a problem. This is in view of the fact that the moisture tends to become trapped in tiny spaces formed between the particles of the material, such moisture holding to the material with extremely high adhesive or capillary forces by virtue of surface tension effects. Techniques of the prior art utiiized to accomplish such moisture extraction generally involve laying the precipitate out over a surface so as to form a relatively thin layer, and then applying heat. Such drying is often accomplished under vacuum conditions to aid in the capillary migration of the moisture. Such heating and vacuum processes have the inherent shortcomings of being quite expensive and time consuming. In addition, they have a relatively low production yield due to the batch-type processing involved and often introduce other complications into the processing, such as by having deleterious effects upon the material.

The technique and apparatus of this invention obviate or reduce the necessity for heat and vacuum drying by utilizing sonic energy to cause the moisture paritcles to migrate from the interstices of the particulate material. The use of high-level sonic energy in this manner enables the thorough dehydration of particulate material in a relatively short period of time in a continuous feedthrough process having a relatively high production yield rate as compared with prior art techniques. Processing equipment involved is relatively simple and inexpensive as compared with prior art equipment and accomplishes the final drying in the same processing step that largescale removal of liquid is being accomplished by squeezing action. These two steps are thus combined with a resultant processing speed-up and more efilcient utilization of processing equipment. Further, while a certain amount of heating of the precipitate is effected by the sonic action, high-level heating such as might be involved in prior art heat drying processes is avoided, so that complications in the processing which might be caused by such heating are not presented.

The technique and apparatus of this invention involve the utilization of a pair of opposing members between which the precipitate is squeezed. While the bulk of the liquid is being removed by such squeezing action, the opposing members are elastically vibrated at a sonic fre quency as part of a resonant vibration system so as to generate high-level sonic energy. Such elastic vibration is achieved by means of orbiting-mass oscillators which are coupled to such members. Sonic energy is transferred to the particulate material, the high-level sonic activity engendered therein causing the moisture particles to readily mlgrate out from the interstices in which they are trapped to the surfaces of the opposing members. In certain ernbodiments of the invention such surfaces comprise blotter means which absorb the moisture by capillary action. In certain other embodiments, the moisture is drained off without the use of such blotter action.

It is therefore an object of this invention to provide an improved method and apparatus for extracting moisture from a precipitate by means of sonic energy.

It is a further object of this invention to provide a method and apparatus for dehydrating precipitate which has greater economy and a higher production rate than prior art techniques.

It is still another object of this invention to provide a technique for sonically dehydrating precipitate utilizing a continuous feedthrough process in which large scale drying and final drying are accomplished in the same processing operation.

It is still another object of this invention to provide an improved process and apparatus for dehydrating precipitate in which high-level sonic energy is coupled to the precipitate to cause moisture particles to migrate thererom.

Other objects of this invention will become apparent from the following description taken in connection with the accompanying drawings, of which:

FIG. 1 is an elevational view illustrating a first embodiment of the device of the invention;

FIG. 2 is a cross-sectional view taken along the plane indicated by 2-2 in FIG. 1;

FIG. 3 is a cross-sectional view in elevation illustrating the liquid drain of the embodiment of FIG. 1;

FIG. 4 is an end elevational view of a second embodiment of the device of the invention;

FIG. 5 is a partial top plan view taken along the plane indicated by 5-5 in FIG. 4;

FIG. 6 is an elevational view of a third embodiment of the device of the invention;

FIG. 7 is a cross-sectional view taken along the plane indicated by 77 in FIG. 6;

FIG. 8 is an elevational view illustrating a fourth embodiment of the device of the invention; and

FIG. 9 is a cross-sectional view illustrating an oscillator unit which may be utilized in the device of the invention.

In order to facilitate the comprehension of the operation of the devices and method of the invention, it is helpful to make an analogy between an electrical resonant circuit and a mechanical resonant circuit. This type of analogy is well known to those skilled in the art and is described, for example, in Chapter 2 of Sonics by Hueter and Bolt, published in 1956 by John Wiley and Sons. In making such an analogy, force F is equated with electrical voltage E, velocity of vibration u is equated with electrical current i, mechanical compliance C is equated with electrical capacitance C mass M is equated with electrical inductance L, mechanical resistance (such as friction) R is equated with electrical resistance R,

mechanical impedance Z is equated with electrical impedance Z Thus it can be shown that if a member is elastically vibrated by a sinusoidal force F sin wt, w being equal to 21r times the frequency of vibration, that 1 F,, sin wt Where wM is equal to l/wC a resonant condition exists, and the effective mechanical impedance Z is equal to the mechanical resistance R the reactive impedance components wM and l/wC cancelling each other out. Under such a resonant condition, velocity of vibration u is at a maximum, effective power factor is unity, and energy is most efficiently delivered to the object being vibrated. It is such a high efiiciency resonant condition in the elastic system being driven that is preferably utilized in the method and devices of this invention to achieve the desired end results.

It is to be noted by reference to Equation 1 that velocity of vibration u is highest where impedance Z is lowest, and vice versa. Therefore, a high-impedance load will tend to vibrate at relatively low velocity, and vice versa. Thus, at an interface between highand low-impedance elements, a high relative movement results by virtue of such impedance mismatch, which, as in the equivalent electrical circuit, results in a high reflected wave. In the devices of this invention, such an impedance mismatch occurs between each of the opposing members and the precipitate, such members exhibiting a relatively high impedance as compared with that of the precipitate. Where the surfaces of the opposing members comprise blotter elements, such impedance mismatch results in high sonic activity at this interface which facilitates the migration of the moisture particles into the blotter material.

Just as the sharpness of resonance of an electrical circuit is defined as the Q thereof, and is indicative of the ratio of energy stored to the energy used in each cycle, so also the Q of the mechanical resonant circuit has the same significance and is equal to the ratio between wM and R Thus high efiiciency and considerable cyclic motion can be achieved by designing the mechanical reso-- nant circuit for high Q, as, for example, by utilizing vibration members having high elasticity and mass.

Of significance in the implementation of the method and devices of this invention is the high acceleration of the components of the elastic resonant system that can be achieved at sonic frequencies. It can be shown that the acceleration of a vibrating mass is a function of the square of the frequency of the drive signal times the amplitude of vibration.

It is to be noted that in the device of this invention the mass and compliance for forming the resonantly vibrating system are furnished by the structural members of such system themselves such that the precipitate material is not dominantly incorporated in such system although there is an important impedance coupling effect. The precipitate material, under such conditions, acts as a friction load which provides no large reactive components. This results in a random vibration of the particles thereof, rather than a lumped coherent vibration as from a reactance, with a considerable relative motion between the separate particles. It is believed that each of the individual irregular grains when energized by the sonic energy in this fashion separately vibrates in a random path. Such random vibration effectively separates the particles so that they tend not to adhere to each other and are thus kept in a highly fluid condition. The moisture particles are similarly subjected to random vibration. Such moisture particles generally have a different mass than that of the particles of the precipitate and thus tend to vibrate at a different amplitude. This facilitates the separation out of the moisture by virtue of the high relative motion engendered between the moisture and precipitate particles.

In considering the significance of the parameters de- Cir scribed in connection with Equation 1, it should be kept in mind that the total effective resistance, mass and compliance in the acoustically vibrating circuit are represented in the equation and that these parameters may be distributed throughout the system rather than being lumped in any one component or portion thereof.

It is also to be noted that an orbiting-mass oscillator is utilized in the preferred embodiments of the invention that automatically adjusts its output frequency to maintain resonance with changes in the characteristics of the load. Thus, in the face of changes in the effective mass and compliance presented by the load, the system automatically is maintained in optimum resonant operation by virtue of the lock-in characteristics of applicants unique orbiting-mass oscillator. The orbiting-mass oscillator automatically changes not only its frequency but its phase angle and therefore its power factor with changes in the resistive impedance load to assure optimum efficiency of operation at all times. This is particularly significant in this invention in that the effective impedance of the load presented by the precipitate material varies with changes in the degree of wetness of such material.

Referring now to FIGS. 1-3, a first embodiment of the device of the invention is illustrated. Drum members 11 and 12 are supported for rotation in housing 15 on sleeve bearings formed between the housing and the drum members. Drum members 11 and 12 are slowly driven in opposite directions as indicated by arrows 16 and 17 by means of a motor (not shown) which is coupled to drive band 18. Drive belt 18 drives pulley wheel 19 which is integrally formed with gear wheel 20. Gear wheel 20 is attached to projecting portion 12a of drum member 12 and drives gear member 21 which is attached to projecting portion 11a of drum member 11.

Drum members 11 and 12 have rim portions 11b and 12b respectively, which are fabricated of sintered metal and form blotter surfaces. Rim portions 11b and 12b are joined to cylindrical shell portions 116 and 120, which form the structural shells of the drums, by suitable means such as, for example, silver soldering. Drainage apertures 11d and 12d are provided in drum surfaces 11c and 120 to facilitate the drainage of moisture from the blotter portions.

Press fitted into hollow central portions 11c and 12a of the drums are orbiting- mass oscillator units 22 and 23, respectively. These oscillator units are of the type described further on in the specification in connection with FIG. 9 and include eccentric rotors which are driven in orbiting paths around races formed in the inner walls of the oscillator housings. The rotors of oscillators 22 and 23 are driven by drive means (not shown), the output shafts 26 and 27 of such drive means being coupled to oscillator drive shafts 28 and 29, respectively. The central portions 11c and 122 of the drums are joined to the shell portions and thereof by spoke members 11 and 121, respectively, which radiate out from the central portions of the drums. These spoke members are integrally formed with the central portions of the drums and form radial septa which run the entire lengths of the shell portions.

The rotors of oscillators 22 and 23 are driven at a rotation speed such as to produce vibrational outputs at the resonant vibration frequency of the separate vibration systems comprising drum members 11 and 12. This provides high-level vibrational energy to rim portions 11b and 12b. At the same time as such high-level sonic energy is being transmitted to drum members 11 and 12, the drum members are slowly rotated in the directions indicated by arrows 16 and 17 by means of the drive system coupled to drive band 18, while precipitate material 30 to be dried is fed between the drum members from hopper 31. The precipitate material 30 is squeezed tighter and tigher as it moves downwardly in the increasingly more confining space between the drum members. Such squeezing action not only helps remove some of the moisture,

but also provides a bias force which enhances the coupling of sonic energy from the drum members to the precipitate material.

The rim portions 11b and 12b of the drums have relatively high acoustical impedances as compared with that of the precipitate material at the vibration frequency, which may be of the order of several hundred cycles per second. This results in high relative motion between the precipitate material and the surfaces of the rim portions. The precipitate material 30 provides an essentially resistive impedance load on the vibration system, and thus the individual particles of the precipitate and the moisture particles trapped therein tend to vibrate randomly. The moisture particles in view of their impedance difference from that of the precipitate tend to readily separate out therefrom and migrate to sintered rim portions 11b and 12b where they are drawn into these rim portions by virtue of the blotter action thereof. The moisture particles pass from sintered rim portions 11b and 12b through apertures 11d and 12d to the hollow inner portions of the drums from where the moisture is drained out through drains 33 and 34.

It is to be noted that while the sonic energy generates some heat in the precipitate which aids in the drying operation, the removal of moisture is achieved primarily by virtue of the high-level sonic vibration imparted to the precipitate material which causes the moisture trapped in the interstices of such material to readily migrate to the effective blotters formed by the drum rim portions. It is further to be noted that such heating engendered by virtue of the sonic energy is much more efficient in its drying effects than external heating in view of the fact that it is generated within the body of the precipitate it self and thus tends to produce uniform heating throughout the precipitate material. It has been found that drying can be accelerated by applying sonic energy to the precipitate material before it is squeezed through the drum members. However, such pre-drying is not essential in most instances.

Referring now to FIGS. 4 and 5, a second embodi ment of the device of the invention is illustrated. In this second embodiment, the blotter members are formed by relatively broad porous belts 40 and 41. Belt 40 is rotatably driven in the direction indicated by arrow 42 by means of drum member 44, against which it abuts the belt also being fitted over idler drums 46 and 47. Belt 41 is similarly driven in the direction indicated by arrow 43 by drum member 50 and rides on idler drums 51 and 52. Drums 44 and 50 and idlers 46, 47, 51 and 52 are rotatably supported on support frame 58. Drum members 44 and 50 are driven in opposite directions by means of a drive motor (not shown), the output drive of which is coupled through drive belt 60 to the gear train comprising gears 62 and 63. Gears 62 and 63 are attached to shafts 48 and 49, respectively, to which drums 44 and 50 are respectively attached.

Sonic energy is generated by means of orbiting- mass oscillators 22 and 23, the rotors 22a and 23a of which are rotatably driven by means of a suitable drive system (not shown). In this second embodiment, rather than resonating the drum members 44 and 50 by themselves, resonator bars 65 and 66 are utilized, such bars being attached at one end thereof to the oscillators and at the other end thereof to shafts 48 and 49 by means of coupler members 65a and 65b which form sleeve bearings for such shafts.

Bar members 65 and 66 are supported near the acoustic node thereof on mounts 67 and 68 which are attached to support frame 58 and which include vibration isolators for vibrationally isolating the bar members from the support frame. The rotors 22a and 23a of oribiting- mass oscillators 22 and 23 are driven at a speed such as to set up resonant vibration in bar members 65 and 66, producing standing vibration waves therein as indicated for bar member 66 by graph lines 70.

As for the drums in the first embodiment, drum member 44 has spokes 44a which radiate out from the center thereof to a cylindrical rim portion 44b, which has apertures 44c formed therein for passing moisture from belt 40, drum member 50 being similar in configuration to drum member 44. The precipitate material 30 is sonically activated and squeezed between the belt members 40 and 41 in the same general fashion as described in connection with the first embodiment, the moisture migrating from the precipitate material through belt members 40 and 41 to the inner portions of drum members 44 and 50, respectively, from where they are removed by drain means 44d and 50d.

In this second embodiment, the blotter action is provided by the belts rather than sintered material on the drum; however, if so desired sintered material can be added to the surfaces of the drum members to increase the blotter action.

In operation, belt members 40 and 41 are rotated in opposite directions as indicated by arrows 42 and 43 at a relatively slow speed to squeeze or bias the precipitate material 30 between the belts while high-level sonic energy is simultaneously applied to the precipitate material through the belts from each of the resonant vibration systems. In this manner, the particles of moisture are efficiently removed from the particulate material.

Referring now to FIGS. 6 and 7, a third embodiment of the device of the invention is illustrated. This embodiment, as the embodiment of FIGS. 4 and 5, also utilizes belts for the blotter elements, but the sonic energy rather than being transmitted through the belt drive rollers is coupled through a platen member which extends over a relatively large surface area. In FIGS. 6 and 7, like numerals are utilized to identify parts corresponding to those of the embodiment of FIGS. 4 and 5.

Belt members 40 and 41 are rotatably driven in opposite directions by means of drive rollers 70 and 71, respectively, in the directions indicated by arrows 72 and 73. Drive rollers 70 and 71 are driven by a suitable drive system (not shown) connected to drive shafts 74 and 77. Belts 40 and 41 are tensioned and held in the desired drive position by means of idlers 75 and 76, such idlers being rotatably supported on shafts 94 and 97 attached to support frame 78. Positioned against the backs of belt members 40 and 41 are platen members and 81, respectively. These platen members have chambers 83 and 84 formed behind them and are integrally formed with support members 85 and 86 and bar members 87 and 88, respectively. Bar members 87 and 88 are supported in resilient bushings 89 on frame 78.

Orbiting- mass oscillators 22 and 23 each comprise a pair of rotor members which are driven in opposite directions and phase with respect to each other so that transverse vibrational components cancel each other out while vibrational components along the longitudinal axes of bar members 87 and 88 are additive. The housings of oscillators 22 and 23 are integrally formed with bar members 87 and 88, respectively, so that the vibrational outputs thereof are transmitted to the associated bar members. The speed of rotation of the rotors of orbiting- mass oscillators 22 and 23 is adjusted to produce resonant standing wave vibration in bar members 87 and 88 as indicated by graph lines 90, such resonant vibration being transmitted to platen members 80 and 81. With such resonant vibration, high-level sonic energy is transmitted through belt members 40 and 41 to the precipitate material to cause the migration of moisture therefrom as described in connection with the previous embodiment. The moisture particles pass through belt members 40 and 41 and apertures 80a and 81a formed in the platens, from where the liquid is drained out of the chambers formed behind the platens by means of drains 92 and 93.

In this embodiment it is to be noted that the platens extend over a fairly large surface area of the precipitate material and thus such material experiences high-level sonic activation for somewhat longer period of time than with the previously described embodiments. The belts readily move over the platen surfaces Without difficulty due to the sonic activation at the interfaces therebetween, which minimizes frictional contact. The precipitate 30 is increasingly biased or squeezed between the belts as the sonic energy is applied thereto, to provide close coupling of sonic energy to such material especially at the final stages of the drying operation. Belts 40 and 41 are preferably made of a highly porous material. Clean-out attachments 95 and 96 are provided to facilitate the cleaning and drying of the belts, a liquid cleaner or compressed air being fed into attachment members 95 and 96 through inlets 95a and 96a and driven through the belts as indicated by arrows 98.

Referring now to FIG. 8, a fourth embodiment of the device of the invention is illustrated. The particulate material 30 is fed into hopper 101 from where it passes between the opposing surfaces of conical members 102 and 103. Attached to conical members 102 and 103 are elastic bar members 104 and 105, respectively. Bar members 104 and 105 are supported on support frame 110 on mounts 111 which have resilient bushings 112 which provide vibrational isolation of the bar members from the support frame. Conically shaped bearing surfaces are provided in supports 111 to facilitate the gyratory vibration of the bar members. Conical member 102 is driven by means of motor 115 which is coupled to elastic bar member 104 through drive belt 116. Conical member 102 is thus slowly rotated on the bearings formed by bushings 112.

Attached to the ends of elastic bar members 104 and 105 are the casings of orbiting- mass oscillators 22 and 23, respectively. The rotors of orbiting- mass oscillators 22 and 23 are orbitally driven around races formed in their respective housings by means of motors (not shown). The rotors of oscillators 22 and 23 are driven at a rotation speed such as to set up standing wave resonant vibration in elastic bar members 104 and 105 as indicated by graph lines 117 and 118, respectively, the vibrational energy having a gyratory force pattern. The particulate material 30 is squeezed between the closely spaced opposing faces of conical squeezing members 102 and 103, and while being so squeezed is subjected to the high-level sonic vibrational energy coupled to the conical members from the elastic bar members. Such simultaneous biasing and sonic activation causes the moisture particles to rapidly migrate out from the precipitate material and both drain off and evaporate.

It is to be noted that in all of the embodiments described that much of the sonic energy is delivered to the particles of the precipitate as they are dropped in between the opposing members, this by virtue of coupling through the initially fed liquid suspension as well as the air space thereabove between the vibrating members and the precipitate material. Thus, sonic actuation commences as soon as the bulk material reaches the vicinity of the sonic vibration field so that the drying action is commenced even before the more solid material is subjected to the squeezing action of the opposing members.

Referring now to FIG. 9, an orbiting-mass oscillator which may be utilized in the various embodiments of the device of the invention is illustrated. This oscillator comprises a rotor member 140 which is orbitally driven around a race 141 formed in the inner walls of housing 142. Such orbital rotation of rotor 140 sets up gyratory vibration of housing 142 which is coupled to a vibration system as described in connection with each of the embodiments. Rotor 140 is driven around race 141 by means of rotor drive members 143, these drive members having gear rings 14311, the teeth of which engage those of rotor gear rings 140a. Rotor 140 also has outer gear rings 14% which engage gear rings 145 attached to the inner walls of housing 142. Rotor drive members 143 are attached to drive shaft 146 and are rotatably supported on ball bearings 147. Thus, when drive shaft 146 is rotatably driven by a motor (not shown), rotor 140 is 8 orbitally driven around race 141 and a vibrational signal is thus generated in housing 142.

The method and apparatus of this invention thus enables the efficient drying of precipitate material without the external application of heat to such material. The drying action is greatly speeded up in a continuous flowthrough process and the cost of such processing greatly reduced.

I claim:

1. Apparatus for the dehydration of precipitate, said apparatus including a pair of opposing members between which the precipitate is squeezed, the improvement comprising means for resonantly elastically vibrating at least one of said members at a sonic frequency to sonically activate the precipitate, said elastic vibration means including:

an orbiting-mass oscillator coupled to at least one of said members; and

means for rotatably driving said oscillator at a speed such as to cause resonant vibration of said one of said members,

whereby moisture particles trapped in the precipitate are caused to migrate out from within the interstices thereof.

2. The apparatus as recited in claim 1 and additionally including a second orbiting-mass oscillator coupled to the other of said members and means for rotatably driving said second oscillator to cause resonant vibration of the other said members.

3. Apparatus for the dehydration of precipitate, said apparatus including a pair of opposing drums between which the precipitate is squeezed, the improvement comprising means for elastically vibrating at least one of said drums at a sonic frequency to sonically activate the precipitate, said elastic vibration means including:

means for drawing said drums in opposite directions,

an orbiting-mass oscillator coupled to at least one of said drums, and

means for rotatably driving said oscillator at a speed such as to cause resonant vibration of said one of said drums,

whereby moisture particles trapped in the precipitate are caused to migrate out therefrom.

4. The apparatus as recited in claim 3 wherein said oscillator is attached to only one of said drums.

5. The apparatus as recited in claim 1 wherein said members comprise belts and means for driving said belts in opposite directions.

6. The apparatus as recited in claim 1 wherein each of said members include blotter means for absorbing moisture from the precipitate, said blotter means forming the opposing surfaces of said members.

7. Apparatus for the dehydration of precipitate, said apparatus including a pair of opposing drums between which the precipitate is squeezed, each of said drums having an outer shell with apertures formed therein, said drums including blotter means for absorbing moisture from the precipitate, said blotter means being contiguous with said outer shells and forming the opposing surfaces of said drums, the improvement comprising means for elastically vibrating at least one of said members at a sonic frequency to sonically activate the precipitate, said elastic vibration means including:

an orbiting-mass oscillator coupled to at least one of said members, at least one of said drums having spoke means for coupling its outer shell to said oscillator, and

means for rotatably driving said oscillator at a speed such as to cause resonant vibration of said one of said members,

whereby moisture particles trapped in the precipitate are caused to migrate out therefrom.

8. The apparatus as recited in claim 6 wherein said blotter means is fabricated of sintered metal.

9. The apparatus as recited in claim 1 and including an elastic bar member coupling said oscillator to said one of said members.

10. In an apparatus for the dehydration of precipitate, said apparatus comprising a pair of opposing members, at least one of said members being rotatably mounted and means for rotatably driving said one of said members to squeeze the precipitate between said members, the improvement comprising means 'for resonantly elastically vibrating said members to sonically energize the precipitate, said vibration means comprising:

an orbiting-mass oscillator for each of said members,

the vibrational outputs of said orbiting-mass oscillators being coupled to said members; and

drive means for driving said orbiting-mass oscillator at speeds such as to set up resonant vibration of said members.

11. The apparatus as recited in claim 10 wherein said members are conically shaped, and further including elastic bar means for coupling said oscillators to said conically shaped members.

References Cited UNITED STATES PATENTS 2,629,244 2/1953 Rand 683 2,789,618 4/ 1957 Bennett 100158 3,131,878 5/1964 Bodine. 3,176,607 4/ 1965 Lapham 100-1 18 3,292,397 12/ 1966 Woo1iever.

FOREIGN PATENTS 393,027 3/1924 Germany.

634,191 8/1936 Germany.

921,537 3/1963 Great Britain.

PETER FELDMAN, Primary Examiner US. Cl. X.R.

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