查看完整版本: 超声波清洗的原理

超声波清洗的原理

[review=nanost-admin][b][color=red][size=3]S}Qv,[|'G
:lol
?}fw#k
g6h 话题不错，虽然大家经常用到这个技术，但我认为仔细了解的人不很多。欢迎楼主和大家完善这个帖子！[/size][/color][/b][/review]
,b0XZOD
,_ Xw!PK Rs'd Qu
t;q\+~M
[size=3][font=Arial]超声波清洗的原理，在理论要加以阐述是比较复杂的，里面牵涉许多因素和作用，可以体现超声波清洗作用的主要有以下三点。
xTmoSHz~
]!b?1pVO"M~    [b] (1)空穴作用H.o;n8DJ8Zc8G
UyMUt
[/b]    当强力的超声波辐射到液体中，清洗液以静压(一个标准气压)为中心进行变化，在压力到零气压以下时，溶解在液体中的氧会形成微小气泡核，进而产生无数近似真空的微小空洞(空穴)。超声波的正压力时的微小空洞，在绝热压缩状态被挤碎，这个发生在挤碎瞬间的强力冲击波，可直接破坏污染物并使之分散在液中，形成清洗机理。试验中这种强力的清洗作用，能在数十秒内对铝箔侵蚀成无数的小孔。v|9kQ%C
    利用空穴作用的清洗，对去油污的效果比较好，通常在28KHZ~50KHZ的频率内进行机械另部件的清洗，清洗机的超声波强度大多设定在0．5~1w／cm2。
h3f
t6g3^ C0_^S_Mx
x[Y.pB8@oT I [b]   (2)加速度Ek2c/f1CZo

;oy5xRg8M$DW [/b]    清洗液体经超声波辐射，液体分子发生振动，这种振动加速度在28KHZ时是重力加速度的103倍，在950KHZ时将达到105倍，由这个强力加速度可以对受污物的表面实行剥离清洗。然而，950KHZ的超声波不产生空穴，不适应去油污的清洗，只能在电子工业的半导体制造中，对亚微米粒子的污染进行清洗。q%[etV6g u
'z/p!Ut}
H:{9s6mYpz
[b]    (3)物理化学反应的促进作用
c9lq"E0mu(w%s$Nx %Ip/il5B&{
[/b]    由空穴作用使液体局部发生高温高压(1000气压，5500℃)，再经振动产生的搅拌，促使化学或物理作用的相乘，液体不断地乳化分散，进一步促进化学反应的速率。0~lTq,q+r
Z$z

P#gU&\(m M.l)y [b]清洗液深度的确定[/b]
-@9?"}g*N5Gl2[9Z~
!Zj&r7kb/|     液体中的超声波会因行波、回波的相互干扰及强合结果，将形成“驻波”现象，(见图1)。确定产生驻波的液体深度，能得到最好的超声波辐射效果。产生驻波的液体深度，可用下面公式计算。
P!M4NY'r IXv"^h9A
M [zU#U
~Bd

~5M~-eT*?^ 'F I5I]}%EuP
    液深(λ/2)＝声速/频率÷2 r1U)|+EtYbM^(Y

1k:U;K8?2[dMAkY e]     这个液体深度的正倍数数值，也是最适合的深度，例在20℃水温，28K1c时液深为27mm、54mm、81mm等等，38KHZ时液深为21mm、42mm、63mm等，但是，不同的液体、液温及超声振荡器，其驻波发生情况是不同的。3Fr@A-H@?

Q/_,?k?9au8J L B0a8R?P0B
n3Tm}1rO?O0I

J-V NMUH ;i~;Yy Z:} C

4sK3o2i XfruD*p ~(Dn0o%WLm-}9e
T{.S*O@n
想必大家都用过超声吧，不知道有多少人知道它的原理。。。
'}:W%{vCH&U-J
^)Ww_
SO 希望有用！～:)[/font][/size]

Introduction to Ultrasonic Cleaning

[font=Arial, Arial, Helvetica][font=Arial][size=10pt]Ultrasonic cleaning is based on the phenomenon known as cavitation.  In an ultrasonic tank, cavities (or bubbles) are formed by piezoelectric transducers attached to the bottom or sides of a cleaning tank.  The piezoelectric effect occurs in a certain group of crystalline solid materials, which have no center of symmetry.  When these materials are mechanically stressed, they produce an electric charge, and when an electric field is applied across two poles, the dimensions change.  By applying high frequency (20-80Khz) and high voltage, these elements expand and contract rapidly at a rate proportional to the frequency of the applied voltage.  As a result of the contraction and expansion, the pressure inside the liquid changes from negative to positive with respect to atmospheric pressure.  During the contraction, the pressure in the liquid is negative, allowing the cavities inside the liquid to grow in size, subsequently at the next phase of expansion the pressure in the liquid becomes positive, which causes the cavities to explode internally.  The creation and the implosion of cavities causes an intense scrubbing action upon a submerged object.  The size of the bubbles are microscopic, and can therefore penetrate the smallest cracks and holes to loosen the contaminants and remove them.#sVb*ob

-B2G4k$U-? All ultrasonic cleaners have three main components:[/size][/font]
7t-r x|4p [/font][table=98%][tr][td=1,1,42][img=10,10]http://www.sonicwise.com/_themes/virtualoutlines/bullet.gif[/img][/td][td][font=Arial, Arial, Helvetica][font=Arial][size=10pt]Ultrasonic generator or power supply that converts electrical energy from the wall (115VAC/60Hz) to high voltage and high frequency, which is then applied to ultrasonic transducers.[/size][/font] [/font][/td][/tr][tr][td=1,1,42][img=10,10]http://www.sonicwise.com/_themes/virtualoutlines/bullet.gif[/img][/td][td][font=Arial, Arial, Helvetica][font=Arial][size=10pt]Ultrasonic transducers convert high voltage and frequency to mechanical vibration.[/size][/font] [/font][/td][/tr][tr][td=1,1,42][img=10,10]http://www.sonicwise.com/_themes/virtualoutlines/bullet.gif[/img][/td][td][font=Arial, Arial, Helvetica][font=Arial][size=10pt]A c[/size][/font][font=Arial][size=10pt]leaning tank that receives the mechanical energy and causes the cleaning media pressure to rise above and bellow the atmospheric pressure, thereby causing the formation and collapse of bubbles in the liquid.  This process produces an intense scrubbing action that removes sediments from the submerged parts. [/size][/font][/font][/td][/tr][/table][font=Arial, Arial, Helvetica][font=Arial][size=10pt]Ultrasonic cleaning equipment ranges from small bench-top units to larger capacity machines up to several thousand-gallon models.  The smaller units are self-contained with a built-in power supply, and with the tank, heater and controls all within a single enclosure.  The larger systems require the power supply to be a separate console, and the very large units may utilize immersible transducers which could then be mounted on the bottom or  the side of the cleaning tank.[/size][/font]
4yG+N aGfm [font=Arial][size=10pt]Effective application of the ultrasonic cleaning process requires a number of parameters, such as operating frequency, watts per gallon of liquid, transducer efficiency, cleaning tank design, and liquid temperature. [/size][/font]Z p5p)u,?Y#E@
[font=Arial][size=10pt]SonicWise has the experience and knowledge to design and manufacture the most efficient, rugged, and cost-effective ultrasonic cleaners for each application. [/size][/font][/font]

The Ultrasonic Cleaning Process

[size=3][i]A condensed version of an article by Maurice O'Donoghue[/i]
G7OSjW&^:N
{6`C0Cj Ultrasonic cleaning has found its most successful application in the removal of insoluble particulate contamination from hard substrate surfaces. Contamination that is soluble or emulsifiable can usually be removed with facility by means of conventional methods in conjunction with suitable solvents or detergent solutions.X-QzjliM|@
:NZP0[#a`;G
Such techniques, however, cannot adequately remove particulate matter in the micron and sub-micron size range to the extent that is necessary, for example, for the critical cleaning required in the microelectronics and optical industries or for the preparation of surfaces prior to the application of thin films or coatings.
6a/|rB/Q"u&c
&o/P;L^7t\i:M A number of methods have been used for the purpose of removing microparticulates from hard surfaces. These include pressure spraying or manual and mechanical scrubbing with solvents or detergent solutions; vapor degreasing; ion bombardment; plasma, chemical, or ultrasonic cleaning; and ultraviolet/ozone cleaning. The intent of this discussion, however, is not to evaluate the relative merits of these methods but rather to describe ultrasonic technology......
g6d%K^-s [b]
d3no.Nwq~RK#q Principles Of Ultrasonic Cleaning[/b]s/U0|%Pj#y8qq
#I)V0YP3MG+B*y5q:G
In general, ultrasonic cleaning consists of immersing a part in a suitable liquid medium, agitating or sonicating that medium with high-frequency (18 to 120 kHz) sound for a brief interval of time (usually a few minutes), rinsing with clean solvent or water, and drying. The mechanism underlying this process is one in which microscopic bubbles in the liquid medium implode or collapse under the pressure of agitation to produce shock waves, which impinge on the surface of the part and, through a scrubbing action, displace or loosen particulate matter from that surface. The process by which these bubbles collapse or implode is known as cavitation.OZi0f
~
c
#g2BNHc6m@'R
High intensity ultrasonic fields are known to exert powerful forces that are capable of eroding even the hardest surfaces. Quartz, silicon, and alumina, for example, can be etched by prolonged exposure to ultrasonic cavitation, and "cavitation burn" has been encountered following repeated cleaning of glass surfaces. The severity of this erosive effect has, in fact, been known to preclude the use of ultrasonics in the cleaning of some sensitive, delicate components.
@9Vo'~d)P [_
[5mL`}(w Ultrasonic cleaning has, however, been used to great advantage for extremely tenacious deposits, such as corrosion deposits on metals. In any case, cavitation forces can be controlled; thus, given proper selection of critical parameters, ultrasonics can be used successfully in virtually any cleaning application that requires removal of small particulates.
&U^#xV%JS `o$S(B iL,fnN'\Lg$z
y
Although the ultrasonic cleaning process has been used for over half a century, no reliable means of quantifying its cavitation activity has ever been developed. Indirect methods of measurement, such as erosion tests on metal surfaces, soil removal from weighted samples, acceleration of chemical reactions, thermodynamic studies, and white noise measurement, have been employed to a limited extent, but none of these methods has proved to be effective.,c4f0\)GE+T}-o(\

'U3v,YfN {
p X Thus, operators who seek to assess the performance of an ultrasonic cleaning system must rely almost exclusively on the evaluation of actual cleanliness levels achieved. Surface patterns produced on cavitating liquids can also be observed, as can the overall degree of agitation of the cleaning medium. Operators have also observed erosion patterns produced on aluminum foil following exposure to ultrasonic cavitation. This "aluminum foil erosion test," as it is called, has come to be recognized as a fairly dependable, albeit subjective, means of demonstrating the existence of cavitation in ultrasonically agitated media. The measure has been used not only to provide an indication of the distribution of the sonic field throughout the bath, but also to locate the sites of the nodes and antinodes of the standing sonic waves. It can also generate fairly reliable side-by-side comparisons of different ultrasonic cleaning systems. In no way, however, can it be used to obtain quantitative measurements of cavitation activity.
/{OWqk8dkL)e x?4dMbN/}
y5r
The cavitation intensity in a sonic field is largely determined by three factors:8Z9@N!T4rz(P
Z&N4?/W|4w/p
   1. The frequency and amplitude of the radiating wave
O L&x(y%C@6C!aG    2. The colligative properties of the medium, including vapor pressure, surface tension, density, and viscosityv%[RvBN v#q
   3. The rheological properties of the liquid, including static condition, turbulent flow, and laminar flow.r]
ce8{9^/u5sm

"dH4?p.t,h}J/b Let us now examine each of these three factors in greater detail.
/a
b?9@Qy8\$O/R9G M5A}/~:j6?+r~T^
Frequency and Amplitude.
&C"Fd$C(e8` R[3{1iF ,LpqC5EdnG
The radiating-wave frequencies most commonly used in ultrasonic cleaning, 18-120 kHz, lie just above the audible frequency range. In any cleaning system, however, the harmonics of the fundamental frequency, together with vibrations originating at the tank walls and liquid surface, produce audible sound. Thus, an operating system that is fundamentally ultrasonic will nonetheless be audible, and low frequency (20-kHz) systems will generally be noisier than higher-frequency (40-kHz) systems.
3ts1d ~,F 3`#k:c`:RLi0m e-M$^\
Moreover, ultrasonic intensity is an integral function of the frequency and amplitude of a radiating wave; therefore, a 20-kHz radiating wave will be approximately twice the intensity of a 40-kHz wave for any given average power output, and consequently the cavitation intensity resulting from a 20-kHz wave will be proportionately greater than that resulting from a 40-kHz wave.(JmC
fonUI1|

$K,h(aT(e'S[ The cavitation phenomenon will, of course, occur less frequently at 20 kHz, but this is not thought to have a significant bearing on cleaning effectiveness. However, the longer wavelengths of low-frequency ultrasonic systems result in substantially different standing-wave patterns throughout the liquid medium.8mt!N7i6Y9Dow
8s:zROJ(S'K'S"b'U8W
The standing or stationary waves produced by ultrasonics in liquid media result from the simultaneous transmission of the surface-reflected wave motion and the wave motion originating at the transducer radiating surface. The fixed points of minimum amplitude are called nodes, and the points of maximum amplitude are called antinodes.K#\ p zdAPkx

h Gpid6Zf(fQ Obviously, the distance between the nodes and antinodes of the 20-kHz standing wave (2 in.) will be approximately twice that of the 40-kHz wave. Because cavitation takes place primarily at the antinodes, the distance between cavitation sites will thus be larger with 20-kHz than with 40-kHz radiation, and the 20-kHz waves will also have larger dead zones (i.e., zones with little or no cavitation activity)
N5uV-G.P/C R"wQZF8o
It is for this reason that cleaning resulting from 20-kHz radiation is likely to be less homogeneous and less consistent, even though this frequency produces more intense cavitation. Much of the inhomogeneity in ultrasonic fields can, however, be reduced or wholly eliminated through the use of sweep frequencies, or radiating waves with a multitude of different frequencies. By this means, several overlapping standing waves can be generated at the same time, thereby eliminating much of the dead zone.
+s H${-dq$S1_
{+n xA7{5U o,g The amplitude of the radiating wave is directly proportional to the electrical energy that is applied to the transducer. In order for cavitation to be produced in a liquid medium, the amplitude of the radiating wave must have a certain minimum value, which is usually rated in terms of electrical input power to the transducer. No cavitation can occur below this threshold value, and the use of electrical power over and above the minimum level results not in more intense cavitation activity but rather in an increase in the overall quantity of cavitation bubbles. The minimum power requirement for the production of cavitation varies greatly with the colligative properties and temperature of the liquid and with the nature and concentration of dissolved substances.6qTtiOJ?H8JJ,~"K'f:?

*Psd{S)I The Colligative Properties of the Liquid.HD)h_9~-MXZ

4b]QVs$v Q kP*P The intensity with which cavitation takes place in a liquid medium varies greatly with the colligative properties of that medium, which include vapor pressure, surface tension, viscosity, and density, as well as any other property that is related to the number of atoms, ions, or molecules in the medium. In ultrasonic cleaning applications, the surface tension and the vapor pressure characteristics of the cleaning fluid play the most significant roles in determining cavitation intensity and, hence, cleaning effectiveness.7h MN v1y v
$XBg5Y0l,T\y I6U!nc
The energy required to form a cavitation bubble in a liquid is proportional to both surface tension and vapor pressure. Thus, the higher the surface tension of a liquid, the greater will be the energy that is required to produce a cavitation bubble, and, consequently, the greater will be the shock-wave energy that is produced when the bubble collapses. In pure water, for example, whose surface tension is about 72 dyne/cm, cavitation is produced only with great difficulty at ambient temperatures.
"\WJz:|E`
ed,q*Gg7|N:q It is, however, produced with facility when a surface-active agent is added to the liquid, thus reducing the surface tension to about 30 dyne/cm. In the same manner, when the vapor pressure of a liquid is low, as is the case with cold water, cavitation is difficult to produce but becomes less and less so as temperature is increased. Every liquid, in fact, has a characteristic/temperature relationship in which cavitation exhibits maximum activity within a fairly narrow temperature range..f|$p
en^rY(k

rro LP)f4v The Rheological Properties of the Liquid.A V+usx1oT D
#?a#P` q[GN+d
The flow characteristics, or rheological properties, of the cleaning fluid play a highly significant role in ultrasonic cleaning applications.
~S1^`8d~
k |(^ Yi]E*?(X Static fluid conditions, for example, are highly conducive to the formation of the standing wave patterns that characterize intense ultrasonic fields, and hence it would seem likely that cavitation intensity would be maximized under such conditions.
'}E s.oh}-rT ;XhHs"y-@Q9h
In fact, however, optimum performance is seldom achieved in static fields, since continuous purification of the cleaning fluid either by overflow or by recycle filtration‹a process that necessitates fluid change of up to 50% of the total bath volume per minute‹is often a prerequisite to effective cleaning. And, contrary to what one might anticipate under such conditions, little or no cavitation activity is lost to this fluid flow when it is properly introduced into the bath. In fact, improvement in overall surface impingement and homogeneity of cleaning can be realized with this method."i|*RWQ+v$i
W4b^&F0?\,MBR5M~
In designing a cleaning process, one must give primary consideration to the size, configuration, and capacity of the ultrasonic tank so that this structure will be able to accommodate the parts to be cleaned in sufficient quantity to fulfill production requirements.8A+m'Una5Z;gy
"J S&e,|P+eP
Of course, every individual cleaning application has its own set of variables, such as the number of parts per load, the orientation and spacing of these parts, and the fixturing arrangements. There are, however, certain basic rules that can be used as guidelines in making design-related determinations. These are as follows:
`TR&Q/Rk;r %U4Y:g zLS \s
Tank Loading.
5rI t6o2WD The total surface area of the substrates, measured in square inches, should not be much greater than the tank volume, measured in cubic inches. In other words, the total surface area should not be greater than 230 sq. in. per gallon of tank capacity.
G+VMm)[.\m#`
.b6XR s"k f9M.C Work Baskets and Fixtures.
-` L I]&s-ecw.g3pM8~t Work baskets or fixtures should have as little mass as possible, should be made of metal (preferably stainless steel or some other hard, sound reflecting material), and should be of open construction so that there will be minimal interference with the free passage of both sound waves and cleaning fluids.I])M8E[
3Ww9yu/}-h
Work Orientation. G,X]etP3Op
The parts in the cleaning system should be arranged in such a way that they are evenly spaced throughout the tank volume, and they should be positioned so that their narrowest dimensions are oriented toward the transducer radiating surfaces. Large, flat surfaces that face transducers tend to screen sonic radiation from the bulk of the cleaning fluid.6G,IJY)w!r#IM7mB

#uA8L_ @2y;k0v3rx Location of Transducers.
0i9oZ%lJ Whenever possible, sonic transducers should be placed on the largest sides or on the bottom of the tank to allow for maximum distribution of the sonic energy throughout the cleaning solution.4I:A*jL k;F/K%K4P
5MG!L w*g;Z
Power Requirements.ew'i6M_ _t
The ultrasonic power requirements of almost all cleaning applications, expressed in terms of electrical-input wattage to the transducers, lie in the range of 50-100 W per gallon of cleaning fluid, or 2.8-3.6 W per square inch of transducer radiating surface. These values apply only to piezoelectric transducers, which are the most commonly used transducers in ultrasonic cleaning systems today.
1D*E/mj_x`%^2`n
IV+}DVF,A[ mq r1J{ Cleaning Fluid.

e\+[4jU8N9ODuK It is essential that cleaning fluids be selected on the basis of5GW r[q?
@*P#bbp)wT(@
   1. The chemical and physical nature of the contaminants to be removed; and9V zG9F+Hz` ^
   2. The identity of the substrate material.
~?N"F;R
t&j+sW)_C Insoluble particulate contaminants can, for example, be divided into two groups:~kuj~+}-QB
v5y1f-Pjyc,r
   1. Water-wettable or hydrophilic particles, including metal particles, metal oxides, minerals, and inorganic dustsM%ni(p[
   2. Non-water-wettable or hydrophobic substances, including plastic particles, smoke and carbon particles, graphite dust, and organic chemical dusts.
/pR@:q$lwN1e6~
F_4ny| u0j8n Substrate surfaces, too, can be divided into hydrophilic and hydrophobic groups. Rarely are hydrophobic contaminants found on hydrophilic substrates or vice versa, but when this is the case, cleaning is best accomplished simply through rinsing with a suitable solvent. Hydrophilic particles on hydrophilic substrates, on the other hand, are best removed with aqueous detergent solutions, while hydrophobic particles on hydrophobic substrates are most effectively removed by the use of organic solvents.oXyR,?kT
K)sar^5? U5ap
[b]Conclusion[/b]
e!F {tuk J6F8Wb`FB
In this article, efforts have been made to describe the unique cleaning capabilities of the ultrasonic process. When they are properly employed, ultrasonic cleaning methods can provide a highly effective means of removing insoluble particulates from hard substrate surfaces.[/size]

[size=5][color=green][b]The principles of ultrasonic cleaning[/b][/color][/size]
|U8_0Xt n9Vm.W^^ [size=3][color=green]V eueij
[b][size=4]Ultrasonic cavitation[/size][/b]]8n Q8\/FCfD"d%y
c2b9S"f.nj~f
Ultrasonic cavitation is the phenomenon whereby the principle of ultrasonic cleaning can be understood. In a liquid medium the ultrasonic waves, generated by an apposite electronic ultrasounds generator and a special transducer suitably mounted under the bottom of a stainless steel tank, produce compression and vacuum waves at a very high speed, the speed depending on the working frequency of the ultrasounds generator. They normally work at a frequency between 28 and 50 kHz. The pressure and vacuum waves in the liquid cause the phenomenon known as "ultrasonic cavitation".zJN EiKg'O0F

hb w!aI;y*T6|"u/z{0p [b][size=4]Surface tension, viscosity and vapour pressure[/size][/b]"wm4Ov
a(fPk|b#A
AZ2P)x!i"fiP
In order to gain a better understanding of the phenomenon, we have to refer to some basic concepts such as "surface tension", "viscosity" and "vapour pressure or tension". Liquids are in fact characterised by the fact that the particles have much greater potential for movement than in solids, albeit subject to much higher forces of attraction than those in gases. More particularly water is a molecular liquid, evaporates at all temperatures but boils at a well-defined one, i.e. at the "boiling point" which for distilled water is 100 degrees centigrade, at which the vapour pressure reaches the value of 1 atmosphere.9y4b(G/ZZ#Y:K

Sq$@*J,M(l5y6x [b]The formation of cavities and the implosion phenomenon[/b]5j~2d'xMf_Hk)V
[img]http://img263.imageshack.us/img263/8194/cavitationsq7.jpg[/img]iVe'w$Oq-~s?
Fig. 1
-C2_xVJ3m q9zIR0V
What happens when we subject a certain quantity of water at room temperature to an intense ultrasonic field? During the vacuum phase (see Fig. 1 phase A) numerous bubbles of gas are formed in the liquid and which enlarge for the duration of the acoustic vacuum phase (negative pressure). This formation of microscopic bubbles of gas is the start of cavitation (i.e. the formation of gaseous cavities in the liquid). During the second phase of ultrasonic compression (see Fig. 1 phase B), the enormous pressure exerted on the newly expanded bubble compresses the same, hugely increasing the temperature of the gas contained in it (see Fig. 1 phase C) until the bubble collapses on itself, imploding with a consequent vast release of impact energy (see Fig. 1 phase D). The impact energy caused by implosion of the gas bubble hits the surface of the object to be cleaned, interacting both physically and chemically. In physical terms a "micro brushing" effect is achieved at very high frequency (around 50,000 times per second for a machine operating at 50 kHz) with, in chemical terms, the cleansing effect of the chemical substance present in the detergent of the ultrasonic bath.
y;R(k \:a2Vc W6c8W
;@8[&E FS E [b]Choosing the type of detergent and the working temperature[/b]0x-viAw8N4B
z
y*N2}`Vg
As we will see, consideration also of the chemical and physical aspect of the type of detergent used in an ultrasonic cleaner is of fundamental importance, and account has to be taken of many parameters when choosing an ultrasonic cleaner and detergent. The first is the type of substance to be removed from the soiled object and consequently the choice of the type of chemical substance which can attack the contaminant. Clearly the chemical substance (detergent), used in order to cavitate efficiently, must be an aqueous solution, possibly with high vapour pressure and low surface tension, and must be used at a working temperature of around 50-60°C. The temperature of the aqueous solution in an ultrasonic cleaning bath is very important, as the cavitation intensity varies as the temperature varies. It also increases as the temperature increases up to around 70°C and then decreases and stops completely at the temperature of boiling of the liquid. Another important parameter to be considered is the vapour pressure of the detergent solution used. Vapour tension or pressure refers to the following concept: if we consider a liquid in a closed and temperature-controlled recipient, the surface molecules which have sufficient energy change to the vapour state and occupy the available space above the liquid. Occasionally some vapour molecules return to the liquid state until, when the state of equilibrium of the system is reached, at a constant temperature, the speed of evaporation equals that of condensation. The pressure exerted by the vapour molecules, in these conditions, is defined as vapour tension. Its value does not depend on the quantity of liquid present but only on the temperature. Therefore, if a liquid is heated, the vapour tension increases with the temperature and when the vapour tension equals the external pressure the phenomenon of boiling takes place. Each liquid therefore has its own vapour pressure and a different boiling point. Ethyl alcohol for example will have a much higher vapour pressure than that of water at the same temperature: it boils at 78°C and at the boiling point will have a vapour pressure of 1 atm, while water boils at 100°C with a vapour pressure of 1 atm. Normal boiling point defines the temperature at which the vapour tension of the liquid equals the pressure of 1 atm. A proper understanding of the concept of vapour pressure is important in that it plays a major role in the cavitation process. The energy required for forming a cavitation bubble is proportional both to the vapour pressure of the liquid and the surface tension value. Cavitation is difficult when the vapour pressure of the liquid is low (cold water). Contrarily the cavitation bubbles implode with greater energy, although the power applied has to be increased considerably in order to reach the minimum cavitation threshold. Therefore the result is generally a smaller formation of bubbles and a smaller number of implosions. For example an increase in the temperature of the liquid raises the vapour pressure of the same, making vapour cavitation easier. Therefore a high vapour pressure lowers the minimum cavitation threshold, creating many more bubbles which collapse, imploding with a lower energy in that the difference between internal and external pressure is smaller. The viscosity of the liquid should also be taken into consideration. High viscosity values prevent cavitation, while low viscosity values allow diffusion of the ultrasonic waves and therefore the formation of cavitation bubbles. Similarly liquids with high and low surface tension values behave in the same way as those with high or low viscosity value as described above.V$`Pbcr,^)@
U:^(flE(DP
m
[b]Sweep system: technology and benefits[/b]J0~2DE5h0@5xZ
Px ufW8nZ#oT
Other important parameters for achieving good levels of cavitation in a liquid are the frequency of the ultrasounds generator, the power, the use of the SWEEP SYSTEM generator and finally the type of transducer used. The frequency of the ultrasounds generator is important in that it determines the size of the gas bubble in the liquid subjected to ultrasonification. The higher the frequency of the generator, the smaller the size of the cavitation bubble generated; contrarily the lower the frequency, the greater the size of the bubble. Clearly a larger bubble will require greater energy to implode and consequently will also have greater impact energy, while a smaller bubble will need less energy to implode and consequently has lower impact energy. What is then the benefit of using ultrasonic cleaning systems with high frequencies? High frequencies allow many more bubbles to be generated in the unit of time, enabling better cavitation distribution per surface unit. For example, in a 40 kHz system, the distance between the nodes and antinodes (or loops) of the acoustic wave is practically double that generated by 20 kHz systems. Therefore 40 kHz systems generate in the unit of time many more bubbles, above all smaller in size, allowing even very small points to be reached per surface unit. To give a practical example, we can compare fine cavitation at high frequency to very fine-grained sandpaper, while low frequency cavitation can be compared to very coarse-grained sandpaper. The purpose of the sandpaper is that of abrading, however very different results can be obtained according to whether a fine-grained or coarse-grained type is used. The type of generator used can be piezoelectric or magnetostrictive. Piezoelectric transducers are normally used in that they can be designed with much higher frequencies compared to the magnetostrictive type. High-power magnetostrictive transducers do not exceed 22 kHz. Finally the use of a SWEEP SYSTEM generator allows a further improvement in distribution of ultrasonic cavitation. The frequency of the generator is modulated around a central frequency with 1 kHz increases or decreases. For example a transducer piloted at 40 kHz will oscillate at a frequency between 39 and 41 kHz. This frequency variation prevents formation in the liquid of the so-called "stationary waves" which can generate acoustic interference when two (or more) wave trains intersect in a given region of the space. The SWEEP SYSTEM therefore reduces cleaning times, prevents damage to delicate parts, considerably increases the distribution of ultrasonic cavitation and facilitates its process in liquids which cavitate with difficulty. The SWEEP SYSTEM is normally used in industrial and highly professional cleaning systems, however nowadays some producers are starting to supply it on small ultrasonic cleaning units too.[/color][/size]

[review=nanost-admin][b][color=red][size=3]非常好的一篇技术文章，有一定的深度。谢谢！[/size][/color][/b][/review]

kjg
|z+?-Uj7Y)X)D;E
qc*QdX:BG%L'm [align=left][size=3][color=green][size=5][b]Ultrasonic Cleaning: Fundamental Theory and Application[/b][/size]
1^ K {3ufx y,T6W@V
[b]Abstract[/b][/color][/size][/align][align=left][size=3][color=green][/color][/size] [/align][align=left][size=3][color=green]A presentation describing the theory of ultrasonics and how ultrasonic technology is applied to precision cleaning. This presentation will explore the importance and application of ultrasonics in precision cleaning along with explanations of ultrasonic cleaning equipment and its application. Process parameters for ultrasonic cleaning will be discussed along with procedures for proper operation of ultrasonic cleaning equipment to achieve maximum results.[/color][/size][/align][size=3][color=green][/color][/size][align=left][size=3][color=green]
m]6f'x6Q.M [b]Introduction[/b][/color][/size][/align][size=3][color=green]
7R;a`\*UN,x*N'gC [/color][/size][align=left][size=3][color=green]Cleaning technology is in a state of change. Vapor degreasing using chlorinated and fluorinated solvents, long the standard for most of industry, is being phased out in the interest of the ecology of our planet. At the same time, cleaning requirements are continually increasing. Cleanliness has become an important issue in many industries where it never was in the past. In industries such as electronics where cleanliness was always important, it has become more critical in support of growing technology. It seems that each advance in technology demands greater and greater attention to cleanliness for its success. As a result, the cleaning industry has been challenged to deliver the needed cleanliness and has done so through rapid innovation over the past several years. Many of these advances have involved the use of ultrasonic technology.[/color][/size][/align][align=left][size=3][color=green]
e;vqT2_m5}inA The cleaning industry is currently in a struggle to replace solvent degreasing with alternative "environmentally friendly" means of cleaning. Although substitute water-based, semi-aqueous and petroleum based chemistries are available, they are often somewhat less effective as cleaners than the solvents and may not perform adequately in some applications unless a mechanical energy boost is added to assure the required levels of cleanliness. Ultrasonic energy is now used extensively in critical cleaning applications to both speed and enhance the cleaning effect of the alternative chemistries. This paper is intended to familiarize the reader with the basic theory of ultrasonics and how ultrasonic energy can be most effectively applied to enhance a variety of cleaning processes.[/color][/size][/align][align=left][size=3][color=green]
O(ZF
jo [b]What is "Ultrasonics?"[/b][/color][/size][/align][size=3][color=green]
EC:K{*Y5F [/color][/size][align=left][size=3][color=green]Ultrasonics is the science of sound waves above the limits of human audibility. The frequency of a sound wave determines its tone or pitch. Low frequencies produce low or bass tones. High frequencies produce high or treble tones. Ultrasound is a sound with a pitch so high that it can not be heard by the human ear. Frequencies above 18 Kilohertz are usually considered to be ultrasonic. The frequencies used for ultrasonic cleaning range from 20,000 cycles per second or kilohertz (KHz) to over 100,000 KHz. The most commonly used frequencies for industrial cleaning are those between 20 KHz and 50KHz. Frequencies above 50KHz are more commonly used in small tabletop ultrasonic cleaners such as those found in jewelry stores and dental offices.TR@tr?H
[/color][/size][/align][align=left][size=3][color=green][b]The Theory of Sound Waves[/b] [/color][/size][/align][align=left][size=3][color=green]s)gE5G6O6^2OSOs
In order to understand the mechanics of ultrasonics, it is necessary to first have a basic understanding of sound waves, how they are generated and how they travel through a conducting medium. The dictionary defines sound as the transmission of vibration through an elastic medium which may be a solid, liquid, or a gas. Sound Wave Generation - A sound wave is produced when a solitary or repeating displacement is generated in a sound conducting medium, such as by a "shock" event or "vibratory" movement. The displacement of air by the cone of a radio speaker is a good example of "vibratory" sound waves generated by mechanical movement. As the speaker cone moves back and forth, the air in front of the cone is alternately compressed and rarefied to produce sound waves, which travel through the air until they are finally dissipated. We are probably most familiar with sound waves generated by alternating mechanical motion. There are also sound waves which are created by a single "shock" event. An example is thunder which is generated as air instantaneously changes volume as a result of an electrical discharge (lightning). Another example of a shock event might be the sound created as a wooden board falls with its face against a cement floor. Shock events are sources of a single compression wave which radiates from the source.
5R1w `,e3Rw_:i5Z&\ [/color][/size][/align][size=3][color=green]
NU+x6J7H%C2L#^ [/color][/size][align=left][size=3][color=green][b]The Nature of Sound Waves[/b][/color][/size][/align][align=left][size=3][color=green] [img]http://www.blackstone-ney.com/images/fu-fig02.gif[/img]
Yv:E$C JoJ The diagram above uses the coils of a spring similar to a Slinky toy to represent individual molecules of a sound conducting medium. The molecules in the medium are influenced by adjacent molecules in much the same way that the coils of the spring influence one another. The source of the sound in the model is at the left. The compression generated by the sound source as it moves propagates down the length of the spring as each adjacent coil of the spring pushes against its neighbor. It is important to note that, although the wave travels from one end of the spring to the other, the individual coils remain in their same relative positions, being displaced first one way and then the other as the sound wave passes. As a result, each coil is first part of a compression as it is pushed toward the next coil and then part of a rarefaction as it recedes from the adjacent coil. In much the same way, any point in a sound conducting medium is alternately subjected to compression and then rarefaction. At a point in the area of a compression, the pressure in the medium is positive. At a point in the area of a rarefaction, the pressure in the medium is negative.
#llrgch
Rs5mr7@(? [/color][/size][/align][align=left][size=3][color=green][b]Cavitation and Implosion[/b][/color][/size][/align][align=left][size=3][color=green][img]http://www.blackstone-ney.com/images/fu-fig03.gif[/img] 8gS6@l(UX/|
In elastic media such as air and most solids, there is a continuous transition as a sound wave is transmitted. In non-elastic media such as water and most liquids, there is continuous transition as long as the amplitude or "loudness" of the sound is relatively low. As amplitude is increased, however, the magnitude of the negative pressure in the areas of rarefaction eventually becomes sufficient to cause the liquid to fracture because of the negative pressure, causing a phenomenon known as cavitation. Cavitation "bubbles" are created at sites of rarefaction as the liquid fractures or tears because of the negative pressure of the sound wave in the liquid. As the wave fronts pass, the cavitation "bubbles" oscillate under the influence of positive pressure, eventually growing to an unstable size. Finally, the violent collapse of the cavitation "bubbles" results in implosions, which cause shock waves to be radiated from the sites of the collapse. The collapse and implosion of myriad cavitation "bubbles" throughout an ultrasonically activated liquid result in the effect commonly associated with ultrasonics. It has been calculated that temperatures in excess of 10,000°F and pressures in excess of 10,000 PSI are generated at the implosion sites of cavitation bubbles.[/color][/size][/align][align=left][size=3][color=green]%]1aT/Y4t?
Benefits of Ultrasonics in the Cleaning and Rinsing ProcessesCleaning in most instances requires that a contaminant be dissolved (as in the case of a soluble soil), displaced (as in the case of a non-soluble soil) or both dissolved and displaced (as in the case of insoluble particles being held by a soluble binder such as oil or grease). The mechanical effect of ultrasonic energy can be helpful in both speeding dissolution and displacing particles. Just as it is beneficial in cleaning, ultrasonics is also beneficial in the rinsing process. Residual cleaning chemicals are removed quickly and completely by ultrasonic rinsing.[/color][/size][/align][align=left][size=3][color=green]*y7Y,I QK6^Q
In removing a contaminant by dissolution, it is necessary for the solvent to come into contact with and dissolve the contaminant. The cleaning activity takes place only at the interface between the cleaning chemistry and the contaminant. (Figure 1):Z eF'^X4L-v)dMa-d
[img]http://www.blackstone-ney.com/images/fu-fig04.gif[/img]
2qa!kk%[_.] Figure 1[,J{\lM5[3N0h
[/color][/size][/align][align=left][size=3][color=green]As the cleaning chemistry dissolves the contaminant, a saturated layer develops at the interface between the fresh cleaning chemistry and the contaminant. Once this has happened, cleaning action stops as the saturated chemistry can no longer attack the contaminant. Fresh chemistry cannot reach the contaminant. [/color][/size][/align][size=3][color=green]
N{ gGY6N K;R i [/color][/size][align=left][size=3][color=green](Figure 2)
)EH(i}lA7D X{ [img]http://www.blackstone-ney.com/images/fu-fig05.gif[/img]
A"D*?&y'G6zc6q0[
Figure 2K!X9k,iQ
Ultrasonic cavitation and implosion effectively displace the saturated layer to allow fresh chemistry to come into contact with the contaminant remaining to be removed. This is especially beneficial when irregular surfaces or internal passageways are to be cleaned. (Figure 3)
;_2odar Y5d;sN [img]http://www.blackstone-ney.com/images/fu-fig06.gif[/img]
}N n;N)BOlj Figure 3d0o4k4l/@*bo
Ultrasonics Speeds Cleaning by DissolutionSome contaminants are comprised of insoluble particles loosely attached and held in place by ionic or cohesive forces. These particles need only be displaced sufficiently to break the attractive forces to be removed. (Figure 4)m'Ed+v9e(^&?G
[img]http://www.blackstone-ney.com/images/fu-fig07.gif[/img]
'L-j2kZ*WJ4i Figure 4
6a*w ?@/TIg ["b"X Cavitation and implosion as a result of ultrasonic activity displace and remove loosely held contaminants such as dust from surfaces. For this to be effective, it is necessary that the coupling medium be capable of wetting the particles to be removed. (Figure 5)G.zDY
~N%^
[img]http://www.blackstone-ney.com/images/fu-fig08.gif[/img]Q2})_Pj?
Figure 5
y"a]\
_-cg
Complex ContaminantsContaminations can also, of course, be more complex in nature, consisting of combination soils made up of both soluble and insoluble components. The effect of ultrasonics is substantially the same in these cases, as the mechanical micro-agitation helps speed both the dissolution of soluble contaminants and the displacement of insoluble particles. Ultrasonic activity has also been demonstrated to speed or enhance the effect of many chemical reactions. This is probably caused mostly by the high energy levels created as high pressures and temperatures are created at the implosion sites. It is likely that the superior results achieved in many ultrasonic cleaning operations may be at least partially attributed to the sonochemistry effect.mK.A0~5eT
A Superior ProcessIn the above illustrations, the surface of the part being cleaned has been represented as a flat. In reality, surfaces are seldom flat, instead being comprised of hills, valleys and convolutions of all description. Figure 6 shows why ultrasonic energy has been proven to be more effective at enhancing cleaning than other alternatives, including spray washing, brushing, turbulation, air agitation, and even electro-cleaning in many applications. The ability of ultrasonic activity to penetrate and assist the cleaning of interior surfaces of complex parts is also especially noteworthy.
/Qga z\6P%@g,} [img]http://www.blackstone-ney.com/images/fu-fig09.gif[/img]u2rxA7|6f1R,h.~L1B|
Figure 6[/color][/size][/align][align=left][size=3][color=green] Bs1c5QauU#c0O
[b]Ultrasonic Equipment[/b][/color][/size][/align][size=3][color=green]X,T3d:A"VTa
[/color][/size][align=left][size=3][color=green]To introduce ultrasonic energy into a cleaning system requires an ultrasonic transducer and an ultrasonic power supply or "generator." The generator supplies electrical energy at the desired ultrasonic frequency. The ultrasonic transducer converts the electrical energy from the ultrasonic generator into mechanical vibrations.[/color][/size][/align][align=left][size=3][color=green]axKXG
[b]Ultrasonic Generator[/b][/color][/size][/align][size=3][color=green]
(M)C+i+p}LqF [/color][/size][align=left][size=3][color=green]The ultrasonic generator converts electrical energy from the line which is typically alternating current at 50 or 60Hz to electrical energy at the ultrasonic frequency. This is accomplished in a number of ways by various equipment manufacturers. Current ultrasonic generators nearly all use solid state technology.X(g8h)OL2\+jf
[img]http://www.blackstone-ney.com/images/fu-fig10.gif[/img]
d-@mN|Q)B There have been several relatively recent innovations in ultrasonic generator technology which may enhance the effectiveness of ultrasonic cleaning equipment. These include square wave outputs, slowly or rapidly pulsing the ultrasonic energy on and off and modulating or "sweeping" the frequency of the generator output around the central operating frequency. The most advanced ultrasonic generators have provisions for adjusting a variety of output parameters to customize the ultrasonic energy output for the task.[/color][/size][/align][align=left][size=3][color=green]
G2}2m]\:tis;D0_ [b]Square Wave Output[/b][/color][/size][/align][size=3][color=green]4q\ `+j |8k
[/color][/size][align=left][size=3][color=green]Applying a square wave signal to an ultrasonic transducer results in an acoustic output rich in harmonics. The result is a multi-frequency cleaning system which vibrates simultaneously at several frequencies which are harmonics of the fundamental frequency. Multi-frequency operation offers the benefits of all frequencies combined in a single ultrasonic cleaning tank.[/color][/size][/align][align=left][size=3][color=green]
/NZ#PchDA PulseIn pulse operation, the ultrasonic energy is turned on and off at a rate which may vary from once every several seconds to several hundred times per second.9?R3cEA'Q~
[img]http://www.blackstone-ney.com/images/fu-fig11.gif[/img]KF"p@2{8u8F
The percentage of time that the ultrasonic energy is on may also be changed to produce varied results. At slower pulse rates, more rapid degassing of liquids occurs as coalescing bubbles of air are given an opportunity to rise to the surface of the liquid during the time the ultrasonic energy is off. At more rapid pulse rates the cleaning process may be enhanced as repeated high energy "bursts" of ultrasonic energy occur each time the energy source is turned on.IrE2WC+Q5W
Frequency SweepIn sweep operation, the frequency of the output of the ultrasonic generator is modulated around a central frequency which may itself be adjustable.
(kH^7`4h%bS!I^ [img]http://www.blackstone-ney.com/images/fu-fig12.gif[/img])[Vez2v v
Various effects are produced by changing the speed and magnitude of the frequency modulation. The frequency may be modulated from once every several seconds to several hundred times per second with the magnitude of variation ranging from several hertz to several kilohertz. Sweep may be used to prevent damage to extremely delicate parts or to reduce the effects of standing waves in cleaning tanks. Sweep operation may also be found especially useful in facilitating the cavitation of terpenes and petroleum based chemistries. A combination of Pulse and sweep operation may provide even better results when the cavitation of terpenes and petroleum based chemistries is required.[/color][/size][/align][align=left][size=3][color=green]
.~ZGCIe?KfY Frequency and AmplitudeFrequency and amplitude are properties of sound waves. The illustrations below demonstrate frequency and amplitude using the spring model introduced earlier. In the diagram, if A is the base sound wave, B with less displacement of the media (less intense compression and rarefaction) as the wave front passes, represents a sound wave of less amplitude or "loudness." C represents a sound wave of higher frequency indicated by more wave fronts passing a given point within a given period of time.:_S4xZ6T~@
[img]http://www.blackstone-ney.com/images/fu-fig13.gif[/img] [img]http://www.blackstone-ney.com/images/fu-fig14.gif[/img] [img]http://www.blackstone-ney.com/images/fu-fig15.gif[/img]
9[CAV&V Ultrasonic TransducersThere are two general types of ultrasonic transducers in use today: Magnetostrictive and piezoelectric. Both accomplish the same task of converting alternating electrical energy to vibratory mechanical energy but do it through the use of different means.[/color][/size][/align][align=left][size=3][color=green]I h4Y2d#g/F
MagnetostrictiveMagnetostrictive transducers utilize the principle of magnetostriction in which certain materials expand and contract when placed in an alternating magnetic field.0b hK~9QG_.A
[img]http://www.blackstone-ney.com/images/fu-fig16.jpg[/img]
't u(Br2M"v"TEO#b Alternating electrical energy from the ultrasonic generator is first converted into an alternating magnetic field through the use of a coil of wire. The alternating magnetic field is then used to induce mechanical vibrations at the ultrasonic frequency in resonant strips of nickel or other magnetostrictive material which are attached to the surface to be vibrated. Because magnetostrictive materials behave identically to a magnetic field of either polarity, the frequency of the electrical energy applied to the transducer is 1/2 of the desired output frequency. Magnetostrictive transducers were first to supply a robust source of ultrasonic vibrations for high power applications such as ultrasonic cleaning.[/color][/size][/align][align=left][size=3][color=green]$["m(c)s6_&V_*e m
Because of inherent mechanical constraints on the physical size of the hardware as well as electrical and magnetic complications, high power magnetostrictive transducers seldom operate at frequencies much above 20 kilohertz. Piezoelectric transducers, on the other hand, can easily operate well into the megahertz range.[/color][/size][/align][align=left][size=3][color=green]+C8U]wJbuKQ
Magnetostrictive transducers are generally less efficient than their piezoelectric counterparts. This is due primarily to the fact that the magnetostrictive transducer requires a dual energy conversion from electrical to magnetic and then from magnetic to mechanical. Some efficiency is lost in each conversion. Magnetic hysteresis effects also detract from the efficiency of the magnetostrictive transducer.[/color][/size][/align][align=left][size=3][color=green]
Ld@4z/aF2p PiezoelectricPiezoelectric transducers convert alternating electrical energy directly to mechanical energy through use of the piezoelectric effect in which certain materials change dimension when an electrical charge is applied to them.U!D(r ro'S+Y7UA
[img]http://www.blackstone-ney.com/images/fu-fig17.gif[/img]
sqE"\ZwL?P Electrical energy at the ultrasonic frequency is supplied to the transducer by the ultrasonic generator. This electrical energy is applied to piezoelectric element(s) in the transducer which vibrate. These vibrations are amplified by the resonant masses of the transducer and directed into the liquid through the radiating plate. Early piezoelectric transducers utilized such piezoelectric materials as naturally occurring quartz crystals and barium titanate which were fragile and unstable. Early piezoelectric transducers were, therefore, unreliable. Today's transducers incorporate stronger, more efficient and highly stable ceramic piezoelectric materials which were develops as a result of the efforts of the US Navy and its research to develop advanced sonar transponders in the 1940's. The vast majority of transducers used today for ultrasonic cleaning utilize the piezoelectric effect.[/color][/size][/align][align=left][size=3][color=green]
-tG$x m#?D9s-gf[ Ultrasonic Cleaning EquipmentUltrasonic cleaning equipment ranges from the small tabletop units often found in dental offices or jewelry stores to huge systems with capacities of several thousand gallons used in a variety of industrial applications. Selection or design of the proper equipment is paramount in the success of any ultrasonic cleaning application.[/color][/size][/align][align=left][size=3][color=green]#a0jnP-D3K
The simplest application may require only a simple heated tank cleaner with rinsing to be done in a sink or in a separate container. More sophisticated cleaning systems include one or more rinses, added process tanks and hot air dryers. Automation is often added to reduce labor and guarantee process consistency.
'mm
z GX3nV0c${ The largest installations utilize immersible ultrasonic transducers which can be mounted on the sides or bottom of cleaning tanks of nearly any size. Immersible ultrasonic transducers offer maximum flexibility and ease of installation and service.[/color][/size][/align][align=left][size=3][color=green]eQ`7YkQ*A!{
Heated tank cleaning systems (figure 7) are used in laboratories and for small batch cleaning needs.R0~B+n O WV
[img]http://www.blackstone-ney.com/images/fu-fig18.gif[/img]
Fe,ca4mz3U_/W Figure 7]+V8eV[${5Au`
Small, self-contained cleaners (figure 8) are used in doctors' offices and jewelry stores.
`@9v\.kk [img]http://www.blackstone-ney.com/images/fu-fig19.gif[/img]RI&YW$[8^'PAU5g
Figure 8#bKn0VCa*a
Console cleaning systems (figure 9) integrate ultrasonic cleaning tank(s), rinse tank(s) and a dryer for batch cleaning. Systems can be automated through the use of a PLC controlled material handling system.2WY5CEtd
[img]http://www.blackstone-ney.com/images/fu-fig20.gif[/img])C+m$M7[[-Nc ZAM
Figure 9c5z3mk Tq;tj
A wide range of options may be offered in custom designed systems, as pictured in figure 10. Large scale installations or retrofitting of existing tanks in plating lines, etc., can be achieved through the use of modular immersible ultrasonic transducers. Ultrasonic generators are often housed in climate-controlled enclosures.}/y5j|S
[img]http://www.blackstone-ney.com/images/fu-fig21.gif[/img]
ts6A.A*wy'bzi Figure 10L8{&u r7E]2{
Maximizing the Ultrasonic Cleaning ProcessProcess ParametersEffective application of the ultrasonic cleaning process requires consideration of a number of parameters. While time, temperature and chemical remain important in ultrasonic cleaning as they are in other cleaning technologies, there are other factors which must be considered to maximize the effectiveness of the process. Especially important are those variables which affect the intensity of ultrasonic cavitation in the liquid.[/color][/size][/align][align=left][size=3][color=green]
iJb|-H+{L [b]Maximizing Cavitation[/b][/color][/size][/align][size=3][color=green]e5r;U$W,l ]
[/color][/size][align=left][size=3][color=green]Maximizing cavitation of the cleaning liquid is obviously very important to the success of the ultrasonic cleaning process. Several variables affect cavitation intensity.[/color][/size][/align][align=left][size=3][color=green]
P)G`~:Zo/I Temperature is the most important single parameter to be considered in maximizing cavitation intensity. This is because so many liquid properties affecting cavitation intensity are related to temperature. Changes in temperature result in changes in viscosity, the solubility of gas in the liquid, the diffusion rate of dissolved gasses in the liquid, and vapor pressure, all of which affect cavitation intensity. In pure water, the cavitation effect is maximized at approximately 160°F.f3n3\s9W_Z5qU
The viscosity of a liquid must be minimized for maximum cavitation effect. Viscous liquids are sluggish and cannot respond quickly enough to form cavitation bubbles and violent implosion. The viscosity of most liquids is reduced as temperature is increased.[/color][/size][/align][align=left][size=3][color=green]
'I^)i@i'Hj For most effective cavitation, the cleaning liquid must contain as little dissolved gas as possible. Gas dissolved in the liquid is released during the bubble growth phase of cavitation and prevents its violent implosion which is required for the desired ultrasonic effect. The amount of dissolved gas in a liquid is reduced as the liquid temperature is increased.[/color][/size][/align][align=left][size=3][color=green][,z8E6gu3kW:t.S
The diffusion rate of dissolved gasses in a liquid is increased at higher temperatures. This means that liquids at higher temperatures give up dissolved gasses more readily than those at lower temperatures, which aids in minimizing the amount of dissolved gas in the liquid.[/color][/size][/align][align=left][size=3][color=green]V U5ug8`ybe
A moderate increase in the temperature of a liquid brings it closer to its vapor pressure, meaning that vaporous cavitation is more easily achieved. Vaporous cavitation, in which the cavitation bubbles are filled with the vapor of the cavitating liquid, is the most effective form of cavitation. As the boiling temperature is approached, however, the cavitation intensity is reduced as the liquid starts to boil at the cavitation sites.[/color][/size][/align][align=left][size=3][color=green]rqs\LV o]
Cavitation intensity is directly related to Ultrasonic Power at the power levels generally used in ultrasonic cleaning systems. As power is increased substantially above the cavitation threshold, cavitation intensity levels off and can only be further increased through the use of focusing techniques.[/color][/size][/align][align=left][size=3][color=green]
1^O7zT9Iq1k e Cavitation intensity is inversely related to Ultrasonic Frequency. As the ultrasonic frequency is increased, cavitation intensity is reduced because of the smaller size of the cavitation bubbles and their resultant less violent implosion. The reduction in cavitation effect at higher frequencies may be overcome by increasing the ultrasonic power.[/color][/size][/align][align=left][size=3][color=green]
L^&^ ?~&Ei [b]Importance of Minimizing Dissolved Gas[/b][/color][/size][/align][align=left][size=3][color=green][img]http://www.blackstone-ney.com/images/fu-fig22.gif[/img] ;X#gtD9O~\;A#CG
During the negative pressure portion of the sound wave, the liquid is torn apart and cavitation bubbles start to form. As a negative pressure develops within the bubble, gasses dissolved in the cavitating liquid start to diffuse across the boundary into the bubble. As negative pressure is reduced due to the passing of the rarefaction portion of the sound wave and atmospheric pressure is reached, the cavitation bubble starts to collapse due to its own surface tension. During the compression portion of the sound wave, any gas which diffused into the bubble is compressed and finally starts to diffuse across the boundary again to re-enter the liquid. This process, however, is never complete as long as the bubble contains gas since the diffusion out of the bubble does not start until the bubble is compressed. And once the bubble is compressed, the boundary surface available for diffusion is reduced. As a result, cavitation bubbles formed in liquids containing gas do not collapse all the way to implosion but rather result in a small pocket of compressed gas in the liquid. This phenomenon can be useful in degassing liquids. The small gas bubbles group together until they finally become sufficiently buoyant to come to the surface of the liquid.[/color][/size][/align][align=left][size=3][color=green]
9f:qbb%q Maximizing Overall Cleaning EffectCleaning Chemical selection is extremely important to the overall success of the ultrasonic cleaning process. The selected chemical must be compatible with the base metal being cleaned and have the capability to remove the soils which are present. It must also cavitate well. Most cleaning chemicals can be used satisfactorily with ultrasonics. Some are formulated especially for use with ultrasonics. However, avoid the non-foaming formulations normally used in spray washing applications. Highly wetted formulations are preferred. Many of the new petroleum cleaners, as well as petroleum and terpene based semi-aqueous cleaners, are compatible with ultrasonics. Use of these formulations may require some special equipment considerations, including increased ultrasonic power, to be effective.
R\RQ|3o [img]http://www.blackstone-ney.com/images/fu-fig23.gif[/img].C1_ a)OHA,e
Figure 11
f{#[5mTiA Temperature was mentioned earlier as being important to achieving maximum cavitation. The effectiveness of the cleaning chemical is also related to temperature. Although the cavitation effect is maximized in pure water at a temperature of approximately 160°F, optimum cleaning is often seen at higher or lower temperatures because of the effect that temperature has on the cleaning chemical. As a general rule, each chemical will perform best at its recommended process temperature regardless of the temperature effect on the ultrasonics. For example, although the maximum ultrasonic effect is achieved at 160°F, most highly caustic cleaners are used at a temperatures of 180°F to 190°F because the chemical effect is greatly enhanced by the added temperature. Other cleaners may be found to break down and lose their effectiveness if used at temperatures in excess of as low as 140°F. The best practice is to use a chemical at its maximum recommended temperature not exceeding 190°F[/color][/size][/align][align=left][size=3][color=green]
-f2R
P}y Degassing of cleaning solutions is extremely important in achieving satisfactory cleaning results. Fresh solutions or solutions which have cooled must be degassed before proceeding with cleaning. Degassing is done after the chemical is added and is accomplished by operating the ultrasonic energy and raising the solution temperature. The time required for degassing varies considerably, based on tank capacity and solution temperature, and may range from several minutes for a small tank to an hour or more for a large tank. An unheated tank may require several hours to degas. Degassing is complete when small bubbles of gas cannot be seen rising to the surface of the liquid and a pattern of ripples can be seen.
9eBr ^dja)| [img]http://www.blackstone-ney.com/images/fu-fig24.gif[/img]
enS`*V8X[+G Figure 12O0E+Z@3hl9[
The Ultrasonic Power delivered to the cleaning tank must be adequate to cavitate the entire volume of liquid with the workload in place. Watts per gallon is a unit of measure often used to measure the level of ultrasonic power in a cleaning tank. As tank volume is increased, the number of watts per gallon required to achieve the required performance is reduced. Cleaning parts that are very massive or that have a high ratio of surface to mass may require additional ultrasonic power. Excessive power may cause cavitation erosion or "burning" on soft metal parts. If a wide variety of parts is to be cleaned in a single cleaning system, an ultrasonic power control is recommended to allow the power to be adjusted as required for various cleaning needs. Part Exposure to both the cleaning chemical and ultrasonic energy is important for effective cleaning. Care must be taken to ensure that all areas of the parts being cleaned are flooded with the cleaning liquid. Parts baskets and fixtures must be designed to allow penetration of ultrasonic energy and to position the parts to assure that they are exposed to the ultrasonic energy. It is often necessary to individually rack parts in a specific orientation or rotate them during the cleaning process to thoroughly clean internal passages and blind holes.[/color][/size][/align][align=left][size=3][color=green]\/F
uznx7pl)b
n
[b]Conclusion[/b][/color][/size][/align][size=3][color=green]
5Jlu lh [/color][/size][align=left][size=3][color=green]Properly utilized, ultrasonic energy can contribute significantly to the speed and effectiveness of many immersion cleaning and rinsing processes. It is especially beneficial in increasing the effectiveness of today's preferred aqueous cleaning chemistries and, in fact, is necessary in many applications to achieve the desired level of cleanliness. With ultrasonics, aqueous chemistries can often give results surpassing those previously achieved using solvents. Ultrasonics is not a technology of the future -- it is very much a technology of today.[/color][/size][/align]

[size=3][color=green][b]The following is a list of books that our engineers and R&D staff have found useful. Most of the material is highly technical in nature.[/b]C!Z;m$fKq

Z0k
KP3H "[b]Cavitation"[/b] F. Ronald Young; Imperial College Press; 1999 (ISBN: 1860941982)
)C6P:U!s?T U0G/nn
\g ]2y;i*j g/D.i
[b]"Vibrations of Discrete and Continuous Systems, 2nd Edition"[/b] A.A. Shabana; Springer-Verlag; 1997 (ISBN: 0387947442)
%L&bG9~hHo jm*]$OX-x7P
[b]"Cavitation and Bubble Dynamics"[/b] Christopher Earls Brennen; Oxford Engineering Science Series 44; 1995 (ISBN: 0195094093)
&r~0n|8Pb
Q*hip\$W:FM [b]"The Acoustic Bubble"[/b] T.G. Leighton; Academic Press; 1994
!K#{[~5Dq
vG
KB4iM*~q#U _:M [b]"Theoretical Acoustics"[/b] Phillip Morse, K. Uno Ingard; Princeton University Press; 1986 (ISBN: 0691024014)
a!Lm,p)X9\"O
T1D TKG [b]"Fundamentals of Acoustics, 3rd Edition"[/b] Lawrence E. Kinsler, Austin R. Frey, Alan B. Coppens, James V. Sanders; John Wiley & Sons; 1982 (ISBN: 0471847895)

BAzn8f
g{w

ctQ0}2z*C;d;O9h [b]"Ultrasonics Theory and Application"[/b] G.L. Gooberman; Hart Publishing Company, Inc.; 1969
s@a6M4J"Y-_tLl LVm"r,Ra&Na
[b]"Physical Acoustics"[/b] Volumes I-IV Edited by Warren P. Mason; Academic Press; 1964w9v"}$A#C^ `
)|ay4L9m6e|
[b]"Sonics"[/b] Theodor F. Hueter, Richard H. Bolt; John Wiley & Sons; 1955
*F^u,lp{ 0Z uE/F a&h
[b]"Ultrasonics"[/b] Benson Carlin; McGraw Hill Book Co.; 1949[/color][/size]

学习了，谢谢 ！

:D :) 好文 谢谢啦

看到了好多有用的东西
:K_K*f#fc/`1_1P 多谢了

:D 赞，很到位！都看了1

谢谢 我的论文应该能用到

先顶再读

谢谢Lz和nano的补充。真的不错。。

好文，具体的原理搞清楚是很有必要的！

学习了。。。。。:victory: :victory: :victory:

很到位！都看了

好贴，:victory: :victory:

帖子我收藏了，谢谢:lol

谢谢,不错的文献:victory:

:handshake