US3165299A

US3165299A - Ultrasonic mixing apparatus

Info

Publication number: US3165299A
Application number: US216537A
Authority: US
Inventors: Balamuth Lewis; Kuris Arthur
Original assignee: Cavitron Ultrasonics Inc
Current assignee: Cavitron Ultrasonics Inc
Priority date: 1962-08-13
Filing date: 1962-08-13
Publication date: 1965-01-12
Anticipated expiration: 1982-01-12

Description

Jan. 12, 1965 1 BALAMUTH ETAI.

ULTRAsoNIc MIXING APPARATUS 3 Sheets-Shee l Filed Aug. 13, 1962 INVENTORS LEWIS BALAMUTH 8x ARTHUR KURIS iher ATTORNEYS Jail 12, 1965 L. BALAMUTH ETAI. 3,165,299

ULTRASONIC MIXING APPARATUS Filed Aug. 13, 1962 3 Sheets-Sheet 2 76) /72 F/GZ l FLAVORy osclLLAToR u L /6:3 l INVENToRs ELECTRIC LEWIS BALAMUTH e CONTROL ARTHUR KURIS COMPONENTS their ATTORNEYS Jan. 12, 1965 BALAMUTH ETAL ULTRASONIC MIXING APPARATUS 5' Sheets-Sheet 3 Filed Aug. 13. 1962 INVENTORS LEWIS BALAMUTH 8| ARTHUR KURIS their A7'7URNEX5 United States Patent O This invention relates to mixing of materials by means of ultrasonic energy, and more particularly, to apparatus employing ultrasonic energy to provide dispersions of solids in liquids, especially applicable to the reconstitution or rehydration of powdered foodstuffs.

Dehydration of materials has become a widely used expedient in many fields for rendering bulk materials easier to store, handle and dispense. The food industry has been a prime user of dehydration techniques and a wide variety of food products are now available to the consumer in powdered form. In many instances, the dehydration of an otherwise perishable product enables it to be kept for extended periods of time without refrigeration or special handling. For example, milk, which normally requires constant refrigeration to prevent souring, may be reduced to a powdered state in which it can be kept without refrigeration almost indefinitely. Other products, such as soups, also enjoy the same advantages when reduced to a powdered state.

- In addition to being of great convenience in restaurants, the home kitchen, etc., powedered food substances have been recognized as being potentially well suited for use in automatic vending and dispensing machines. Since they may be stored with a minimum of temperature control, and require only water yfor reconstitution, the construction of the dispensing machinery would be considerably simpliied. Furthermore, since the powder is in greatly concentrated form, a relatively large .amount of finished product could be dispensed before refilling and servicing of the machine is necessary. K

However, in spite of the apparent advantages of powder food substances for vending machine application, several drawbacks are present which until now 'have ex-k tremely limited their use. The principal objection has been the inability to properly mix the powdered substance with the water in the relatively short time allotted to provide the customer with the finished product after he has inserted his coin. ideally, the product should be reconstituted in itsnished form as a complete dispersion of the powder in the liquid. In the home, or restaurant, considerable time may be expended for the mixing process to produce a smooth, palatable mixture, but when vending machines are used, speed of service is of prime importance. Moreover, ordinary manual or mechanical mixing methods now available are inherently unable to produce the total dispersion necessary to provide a' product approaching the original in consistency and taste and, in addition, tend to produce a froth or foam which lessens the eye appeal of the reconstituted liquid.

The second obstacle presented in the use of automatic dispensing apparatus involves' sanitation. Obviously, the apparatus for dispensing the foodstuffs must be. maintained clean, but even when the greatest care is taken, small quantities of the reconstituted liquid will remain on portions of the mixing or dispensing mechanism and will be subject to the effects of harmful bacteria. At the present time, it is necessary to have the machines manually cleaned at relatively frequent intervals Vby servicemen to maintain them in sanitary condition and comply with local health requirements. The frequent attention required would seriously detract from the advantages that would be gained from the use of powdered materials.

The foregoing factors are of particular concern in the dispensing of milk or cream. Heretofore, automatic 3,ld5,29` Patented Jan. r2, rees dispensing of milk in bulk form has not been practicable because of the storage and sanitation problems presented, and milk vending machines now provide only cartons or bottles which must be kept continously refrigerated. Attempts to use powdered milk have been discarded because of the inability to produce a mixture of the milk powder and water which approaches the flavor and consistency of the original fluid milk. Even in connection with coffee dispensing machines, the use of powdered cream has been limited because of the failure to provide suitable mixing techniques. In the case of the latter, whole cream is generally used, requiring frequent replacement to avoid spoilage. i

It has been known for some time that the application of ultrasonic energy to a mixture of liquid and powder will produce a uniform dispersion. This principle has been applied to many bulk mixing problems and some success has been achieved. It is the primary object of the present invention to provide novel ultrasonic apparatus for producing complete dispersions of powders in liquids, particularly suitable for use in vending machine applications.

A further object of this inventori is to` provide a novel ultarasonically actuated vibrating device for rapidly producing an intimate mixture of a plurality of materials.

`Still another object of the present invention is to provide novel ultrasonically vibrating apparatus for producing dispersions wherein adherence of the mixed materials to the apparatus is reduced to` a negligible minimum.

Yet another object of the invention is to provide ultrasonic mixing apparatus for liquids and solids wherein the resultant dispersion is rendered free of entrapped gases.

A still further object of the invention is to provide ultrasonically actuated mixing apparatus particularly adapted to reconstitute dehydrated foodstuffs and operating at speeds suitable for use with automatic vending machines.

ln accordance with the present invention, materials to be combined, which may be a powdered food product and water, are loosely mixed in a receiving means andv then conducted through a relatively narrow opening prosuitable transducer means.

vided in an ultrasonically vibrating element, driven by The vibratory element preferably is in the form of an elongated member, longitudinally vibrated, having one or more narrow passages therethrough adjacent an areaV of maximum vibration and disposed transversely to the direction of vibration. As the powder and water mixture passes through the passage in the vibrating member, the dispersion is formed and, at the discharge end, the reconstituted product is available for Vsupplying to a suitable receptacle.

The vibrating membe'ris actuated at a frequency on the order of 20,000 cycles per second and withan amplitude which may be approximately one to two thousandths of an inch. The opening or passage in the member through which the mixture fiows is made relatively small with respect to the size of the membenvenabling the vibratory energy applied to it during its passage through the member to induce cavitational action therein. The violent stresses set up in the mixture during cavitation produces a rapid and complete dispersion of the powder in the liquid. The energy supplied to the materials by the vibratory action eliminates the requirement for heating .the liquid which heretofore has been considered necessary to properly dissolve the powder. Thus, a mixture may be'produced with the liquid at a temperature just slightly above the freezing point, enabling, for example, reconstituted cold milk to be produced directly from milkpowder and ice water.

A further beneficialv effect provided by the present in Vention is delgassing of the reconstituted liquid. In any mechanical mixing method, the agitation tends to entrap Y air in the liquid, rendering the product frothy or foamy. The ultrasonic mixing provided by the apparatus described herein not only avoids entrapment of air, but drives olf gases inherently present in the materials to beY mixed` or otherwise introduced therein prior to the mixing. The'result is a smooth mixture, free of bubbles or foam. The consumer is thus given his full measureof the product.

Sanitation problems in the ymixing apparatus of the present invention are maintainedat a minimum by providing a smooth, nonporous plastic liner for the passage through the vibrating element. action ensuing during the mixing process, in combination with the smooth inner surface thereof, Virtually eliminates any tendency of the reconstituted product to adhere to the interior walls of the passage. As a result-,- the mixing device may be kept clean by a simple water flushing of the mixing and discharge paths.

The transducer of the mixing apparatus may be of the magnetostrictive type, driven by a relatively low power electrical oscillator, and is readily adapted to be incorporated into vending machines similar in size to those presently used. Relatively simple electrical controls are necessary to operate the mixingl apparatus and presently known coin handling and Yswitch gear may be readily adapted to actuate the apparatus.

The foregoing and other objects, features .and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment thereof, when taken in conjunction with the accompanying drawings, in which:

FIGURE 1A is a side view of the vibrator'y mixing apparatus in accordance with the present invention;

FIGURE 1B is a top view of the apparatus of FIG- URE lA, showing details of the mounting assembly for the input and output conduits;

FIGURE `2 is a schematic diagram illustrating the application of the mixing apparatus of FIGURES 1A and 1B to an automatic dispensing arrangement;V

FIGURE 3 illustrates how the apparatus of FIGURE 2 may be incorporated in` a vending machine;

FIGURE 4 illustrates an alternate embodiment of the mixing apparatus of FIGURES 1A and 1B; and

FIGURE v5 illustrates a further embodiment of the apparatus wherein improved degassing of the mixture is Y obtained. Y

The details of the mixing apparatus according to the present invention are illustrated in FIGURES 1A and 1B. As shown, the apparatus 10 comprises a transducer portion, indicated generally at 12, which drives thevmixing member 14 atan ultrasonic frequency. The transducer 12 may be of anywell known type capable of inducing a vibratory mechanical movement inresponse to the application thereto of an alternating electrical current. Preferably, this apparatus includes a stack of plates 16 of magnetostrictive material, around which is wound a magnetic coil 18, in well known fashion. The coil 13 is supported on a nonmagnetie sleeve 20 and connected via leads 22 to a source of alternating electrical energy of suitable frequency.

One endof the magnetostrictive stack 16 isrigidly The cavitational fastened to an elongated connecting member 24,-which is rigidly mounted in a support block 26. The connecting member 24 is provided with a peripheral depression at its midpoint which retains a rubber O`ring 28 fitting into a corresponding depression in the support block 26. A retaining ring 30 threadedly engages the block 26 to prevent movement of the O-ring and yet permit disassembly of the structure when desired. The nonconductive sleeve 20 is threadedly received in the support block 26.

Upon application ofpalternating current to the coil 18, the magnetostrictive stack 16 expands and contracts in length at a rate equal to the frequency Yof the alternating current. The resultant mechauicalmotion isA coupled the supply means.

to the connecting member 24 which is provided at its other end with a threaded portion 32 for engaging the vibratory member to be described hereinafter. The con-- nesting member 24 is made equal in lengthto a half wave length at the frequency 'of vibration inthe material of" which it isV formed. Consequently, its midpoint, and' thus the mounting ring, is at a node of motion andmay be rigidly fixed in the support block 26 without affecting its amplitude of vibration'. Y

A blower 34, operated by a suitable Vmotor 36, is fastened at one end of the sleeve 20, providing a stream of air over the stack- 16 to dissipate the heat generated thereby duringits operation. Suitable ports 21 are provided in the sleeve 20 to permit circulation'of the air for adequate cooling effect.

As seen in FIGURE 1A, the entire structure including the transducer and mixing member can be supported by means such as lugs 35 bolted or otherwise secured to the support block 26. Since substantially no vibratory energy is imparted tothe support block 26,by'virtue of its coupling to the connecting member 24 at its nodal points this mounting arrangement imparts no vibrational energy' to the remainder of the equipment with .which'it is? used. Y

The mixing member 14 comprises principally a vibrating element 40, in they form of an acoustic impedance transformer. The `element 4th-which maybe a solid block of metalsuch as aluminum alloy or Monel, is made a half wave length 4(oranintegral number thereof)` long at the frequency of vibration. The portion 46a thereof coupledto thek connecting member 24, is of relatively greater-massthan the other or free end, 4017. The transition region between the two sections of' differing mass is located at approximately the nodal or quarter wave point along its length. TheY difference'in mass between the two halves of the element 46 effect an acoustic impedance transformation which increases the amplitude of vibration at the free end relative to the'driven end in inverse` ratio to vtheir masses. A more complete discussion of the acoustic impedance transformer may be found in patent No. Re. 25,033, of-the presentinverltors, granted August 29, 1961. For the purposes of the present invention, it is sufficient to note that the application of arelatively, small longitudinal vibration to the end 40a of the element 46 will produce an amplified longitudinal vibrationl at its outer or free end, in the directionindicated by the arrows. Thus, the vibration induced in the magnetostrictive stack 16 is coupledA through connecting member 24 and'amplied in thervibrating element 40.

Adjacent the free end ofthe element 40, there is provided an opening or passage 42 traversing the entire width of the toolj transversely to its directionV of vibration. This passage is located near the freel end of the element soas to be subjected to considerable amplitude of vibration; The passage 42 may be thinly lined with a smooth, nonpor0us'plastie44 such as'- nylon, over -its entire length through the element 4G. Y

For monitoring purposes, a vibration responsive device 41 may be'provided on the element 40, of any suitable type capableV of generating auV electricalsignal proportional `to its amplitude of vibraiton. A meter may be connected thereto to enable adjustment of thetransdueer to produce the ldesired amplitude of vibration.

To couple theconduits 'carrying the materials to be mixed into the passage 42, special coupling'means are provided to isolate, thevibration of the member 40 from the Ypassage 42 'to provide seats for pads 46.: lThe latter are made of a resilient but non-absorbent material such aspclosed cell silicone Irubberv sponge. A bushing 48,

of stainless steel -or other noncorrosive4 material includes pad 465 'in liquidtight relation. The input and output Both the upper and lower ends ofv the elementl 40 are counter-bored concentrically with conduit 52 to a suitable receptacle.

conduits

50 and 52 respectively, are tightly tted over the outer ends of the respective bushing 48, and are preferably made of a noncorrosive plastic material such as nylon.

The bushings 48 are supported in their vertical positions by means of a U-shaped bracket 5.4, provided with holes in each of its arms to accommodate the corresponding bushing. Compression springs 56, one for each coupling means, are provided around the respective bushings 48 Ibetween the depending portions thereof and the arms of the bracket 54.

The center portion of the bracket 54 is bolted to a pair of stiffening member 53, to the outer of which is fastened a support post 60'. As seen best in FIGURE 1B, a strap member 62 straddles the entire mixing device, having one end thereof fastened to the end of the transducer sleeve 20, and the other end bolted to the post 60. Additional supports 64 are provided for the strap 62 and are fastened to the support block 26.

During the mixing operation, the powder and liquid, which are either premixed in a receptacle provided therefor, or merely jointly introduced into a common channel, are supplied to the upper end of the input conduit 50. The mixture then flows downwardly through the bushing 48 and into the plastic lined passage 42 in the vibrating element 4u. As the powder and liquid flow through the passage 42, the vibratory energy imparted thereto by the vibration of the element 40, engenders cavitation in the liquid and consequent violent agitation thereof. In addition -to the mixing eiiect, any gases entrapped in the materials are liberated and removed from the mix-ture. The reconstituted and degassed mixture then exits through the lower bushing 4S and the output The entire process is continuous and the materials need not be halted while subjected to the ultrasonic vibrations.

The intense, concentrated energy imparted to the fluid during its passage through the opening 42, permits the length of the passage to be kept relatively short, while providing a suitably reconstituted product. The time for reconstitution is correspondingly brief, and enables the device to be readily adapted to automatic vending machine utilization. Furthermore, the plastic lining ft-4 on the passage 42, in conjunction with the cavitational action induced in the iiuid, prevents adherence of any significant amount of the product to the interior of the vibratory member, thereby reducing the sanitation problem.

The coupling arrangement for joining the input and output conduits to the passage 42 in lthe element 40 insures that little of the vibrational energy of the element 40 is lost or coupled into the remainder of the apparatus. The cushioning etect of the silicone rubber pads 46 and the resiliency of the members '5.4- and 62 isolate the vibratory element 40 from the remainder of the apparatus. The springs 5.6 absorb any lateral motion between the vibratory element and uthe remainder of the structure.

A typical dispensing arrangement utilizing the mixing device of FIGURES lA and 1B is illustrated in FIG- URE ,2. The apparatus may incorporate a source of cold water 7 2 at the `desired temperature (eg. 40-50 F.), l

and a supply o f milk in powdered form 74. The latter may be nonfat dry milk or whole milk, or in fact may be any powdered milk product which it is desired to reconstitute. If desired, a source of various flavors 76 and vitamins or other additives 73, 80 may also be provided to further enhance the avor and quality of the resultant product. Each of the constituents of the iinal product is coupled to a common conduit S2 via suitable metering valves 84, actuated in response to operation of a suitable selection mechanism, various types of which are well known in the automatic vending art. Thus, for example, upon insertion of a coin into the receiving slot in the machine and pressing of the various selecting buttons, measured amounts of each of the constituents 6 are delivered to and roughly premixed in the common channel 82. Insertion of the coin will also be effective to actuate the mixing apparatus 16.

The premixed constituents then flow through the ultrasonically vibrating mixing device 10 where the mixing and degassing occur in accordance with the principles discussed hereinabove. The reconstituted product is then delivered to a cup .placed in receiving position by a cup dispensing mechanism 36 of any known type. The vent stack S8 allows air removed from the liquid during the degassing operation to escape from the otherwise closed system.

`FIGURE 3 illustrates the mounting of the apparatus of y'FIGURE 2 in a cabinetcorresponding to those commonly used for automatic vending machines. The water, powdered milk and other constituents are located in suitable containers as shown and a simple waterl cooling apparatus provided to maintain the water temperature at the desired level. Refrigeration of the entire cabinet 1s not necessary. The mixing device I@ is mounted as shown in the cabinet and the output conduit 92 arranged to communicate with .the cup holder through which the consumer may remove the tilted cup. The controlv circuitry for the various conventional Vending 4machine operations as well as the oscillator provided for the alternating electrical energy driving the transducer may be located in the lower section 94 of the machine. Thecoin operated and cup dispensing mechanisms have not been shown for the sake of clarity, and 1t will be understood that any suitable form thereof may be used.

A modification of the mixing device of FIGURES 1A and 1B is shown in FIGURE 4. This embodiment is particularly suitable for applications where the transducer arrangement may be more suitably mounted in a vertical position. As shown therein, the vibratory element 4@ is disposed so that its direction of vibration 1s aligned vertically. The powder and liquid to be mixed are introduced into the upper end of the plastic tube 162 which then is passed through the upper end of the Vibratory element t0 at a slight angle below the horizontal. The tube 192 is then doubled back and again passed through the eiement 4@ at a small angle, and thence to Athe output spout.

As can be seen, the constituents to. be mixed are subjected to ultrasonic vibratory energy twice prior to being supplied to the output. By means of this arrangement, powders which are more ditiicult to dissolve may .be adequately handled or, in the alternative, lower power .transducers and smaller vibratory elements may be used.

As in the case of the apparatus of FIGURES 1A and 1B,

cavitation is induced in the liquid mixture as it passes .through the tool producing the complete dispersion and degassing, as well as maintaining the inner walls of the plastic tubmg relatively free from adhering material.

Where degassing ofthe liquid is a particular problern, such as where an additive ingredient may release large amounts of gas when put into solution, the arrangement shown in FIGURE 5 may be utilized. In this ernbodiment, the vibratory element 40 is shown as being provided with an elongated slot through its free end, rather than the circular hole as shown in the previous embodiments, although the latter may also be used. A funnel-shaped chamber N8 is brazed or otherwise rigidly -iixed to the upper surface of the element .4t-tb closely surrounding the opening or passage 106. The chamber is completely sealed except for a plurality of openings in the upper surface and a larger central duct 112 through which thepremixed powder and liquid is supplied. The passage 106 may be provided with a plastic liner as discussed in connection with FIGURES 1A and 1B, which extends below the tool to form an output spout 114.

The degassing chamber 108, being rigidly xed to the element 4t), will vibrate therewith in the direction as indicated by the arrows. As the premixed constituents tions thereof will occur to those skilled in the art.

' said powder passage 106, is effective to remove substantially all of the entrapped gases therein, which escape via the vents 11G. Freedom from foam of the nal reconstituted prod-l uct is thereby assured.

Although obviously applicable to mixing of many different substances, the mixing apparatus of the present invention has found particular utility in connection with the reconstitution of powdered milk. Its .speed of op eration renders it well suited for use in automatic vending machines and by using ultrasonic energy to perform the mixing, the process can be carried out at low temperatures. Therefore, cold milk in bulk form may be dispensed.

In addition to the obvious advantages gained by the ability to store the milk in the form of a dehydrated powder, the present invention avoids the flavor and fluidity limitations inherent in presently known methods of reconstituting powdered milk. The cavitational action induced by the ultrasonic energy permits substantially cri complete dispersion of the milk powder in the liquid,

thereby closely reproducing the avor and consistency of the original product. It has been found that the sedimentation rate of the reconstituted product produced by the present apparatus is far below maximum acceptable levels set by the dry milk industry. Thisfgure is arrived at by centrifuging the reconstituted product in graduated containers andv noting the amount of sediment obtained thereby. The lower the amount of sediment, the more complete the dispersion. The reconstituted milk produced by the present invention is uniformly a clean drinking liquid, that is, no powder particles are detectable by the consumer while drinking, and the reconstituted produce closely resembles in texture the fluid milk product from which the powder is made. Moreover, the reconstitution is effected without the generation of foam which accompanies ordinary mechanical agitation methods.

While several embodiments of suitable mixing device according to the invention have .been illustrated and described herein, it will be apparent that many other varia- Accordingly, the invention is not deemed to be limited vrexcept as set forth in the appended claims.

We claim:

1. Apparatus for producing a dispersion of a powder ina liquid comprising, transducer means adapted to convert alternating electrical energy into mechanical vibration at ultrasonic frequencies, 1a vibratory element coupled to said transducer means to be set into vibration thereby in a givendirection, at least one opening extending through said element transversely to its direction of vibration, means to continuously supply said powder and liquid to said opening whereby they are subjected to vibratory energy and ia dispersion produced as they pass through said element, and vent means in said supply means forrenabling the escape of gases liberated from and liquid by the vibratory energy applied thereto. i f i 2. Apparatus for producing a dispersion of a powder in la liquid comprising, transducer means adapted to convert alternating electrical energy -into mechanical vibration at ultrasonic frequencies, a vibratory element cou- 8 pled to said transducer means to ber set into'vibration thereby in a given direction, an opening extending through said element transversely to its direction of vibration, .a smooth, nonporous lining for said opening, means t'o continuously supply said powder and liquidto said opening Vwhereby they are subjected to'vibratory energy vand a dispersion produced as they pass throughV said element, and vent means in said supply means, for enabling the escape of gases liberated from said powdered liquid v by the vibratoryV energy appliedfthereto.

3. Apparatus according to claim l2 wherein said opening is circular and of adiameter relatively-small with respect to the length thereof through said element.

4. A mixing device comprising a member adapted to be set into vibrationin a given direction at ultrasonic frequencies, a plurality of passages of nar-row width relative to their length extending throughsaid member transversely to the direction of vibrat-ion, conduit means interconnecting said plurality of passages to form a single continuous flow path, input meansfor supplying the substances to be mixed to one end of said flow path, and output means coupled to the other end of said ow path for conducting the resultant mixture to a receptacle.

5. A mixing device comprising a memberv adapted to be set into vibration in a given direction at ultrasonic frequencies, a passage of narrow width'relative to its length extending through said member -transversely to the direction of vibration, a chamber rigidly mounted on said member to be vibrated therewith and having one end thereof in communicationV withsaid passage; at least one vent aperture in said chamber, means to supply the materials to be mixed tol said chamberV whereby the materials Vare degassed before passing into said passage for mixing,

and output means coupled to the end of said passage opposite said chamber for conducting the resultant mixture to a receptacle. I

6. Apparatus for producingV a dispersion of a powder in a liquid comprising, transducer means for providing mechanical vibration at ultrasonic frequencies, a vibratory element coupled to said transducer means tovbe set into vibration therebyk in a givensdirectiomat least one opening extending through said element transversely to its direction of vibration, means for supplying said powder and liquid together to said opening whereby they are subjected to vibratory energyand a dispersion produced as they pass through said element, and vent means coupled to said supply means for enabling' the escape of gases liberated from said powder and liquid by the vibratory energy vapplied thereto.

7. Apparatus according to claim 6 further comprising a smooth, non-porous liner Yfor said opening.

References Cited inthe le of this patent I UNITED STATES VPATENTS Re. 25,033 Balamuth et-al. Aug. 29, 1961 2,147,677 smith Feb. 21, 1939 2,460,919 Bodioo Feb. 8, 1949 y 2,478,207 Robinson Aug. 9, 1949 2,515,570 Rubinfold i-, July 1s, 1950 2,725,219 Firth Nov. 29, 1955 2,879,042,V Jones l Mar. 24, 1959 2,986,306 Cocanour -..anni May 30, 1961 3,063,683 v Westbrook Nov. 13, 1962

Claims

2. APPARATUS FOR PRODUCING A DISPERSION OF A POWDER IN A LIQUID COMPRISING, TRANSDUCER MEANS ADAPTED TO CONVERT ALTERNATING ELECTRICAL ENERGY INTO MECHANICAL VIBRATION AT ULTRASONIC FREQUENCIES, A VIBRATORY ELEMENT COUPLED TO SAID TRANSDUCER MEANS TO BE SET INTO VIBRATION THEREBY IN A GIVEN DIRECTION, AN OPENING EXTENDING THROUGH SAID ELEMENT TRANSVERSELY TO ITS DIRECTION OF VIBRATION, A SMOOTH, NONPOROUS LINING FOR SAID OPENING, MEANS