Blowing nozzle for silent outflow of gas

A blowing device for compressed air or the like comprising at least one supply channel (15) which is connectable to a source of compressed air and outlet (19) which is shaped to impart to the compressed air a jet in the form of a ring or part of a ring, and at least one communication channel (20) adapted to connect the inside of the jet with the atmosphere. The object of the invention is to provide a blow nozzle with a large contact surface between outflowing pressurized air and the ambient air in order to provide an airflow with a low sound level, a large momentum, high efficiency and reduce striking velocity against the object intended to be cooled, dried or blown clean. This has been attained in that the product of the ratio between the outer plus the inner circumference (O.sub.2 and O.sub.1) of the outlet (19) and its area (A.sub.out) and, on the other hand the inner diameter (D) of the outlet and its width (S), is at least 4 mm/mm.sup.2, preferably considerably larger than 4 mm/mm.sup.2.

The invention of this application is disclosed in International Application 
PCT/SE No. 82/00388, filed Nov. 17, 1982, in which applicant claims 
priority under 35 USC 119. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a blowing device for compressed air or the 
like having at least one feed channel which is connectable to a source of 
compressed air and an outlet which is shaped to impart to the compressed 
air a jet in the form of a ring, or part of a ring, under adiabatic 
expansion, and at least one communication channel adapted to connect the 
inside of the jet with the atmosphere. 
2. Description of the Prior Art 
The most common way to use compressed air for blowing purposes is by 
supplying the compressed air to a nozzle with one or several substantially 
circular outlet channels. The velocity of the discharge of the air is 
dependent upon the pressure upstream of the outlet channels and the 
pressure situation downstream of the same. If this pressure relation 
corresponds with the so-called critical pressure relation, the velocity of 
the discharge will be equal to the sound velocity. In most industries 
utilizing compressed air, the pressure normally present in the air supply 
network will be such, that the velocity of discharge, for example for 
cleaning purposes, using nozzles of the kind mentioned will be essentially 
equal to the sound velocity. Thus in most cases, the pressure relation 
will be equal to the critical pressure relation, i.e. 0.528. 
When air is flowing out from an outlet in this manner under substantially 
adiabatic expansion there will occur a conically shaped core jet and 
outside of this a mixing zone where the air jet, due to transmission of 
movement to the ambient air in the form of expansion, will diverge and 
bring ambient air along with it in its movement. Thus, the air jet will 
increase in mass but will loose velocity. The loss of velocity entails 
that the dynamic pressure of the air jet will be partly transformed into 
static pressure. This pressure, added to the atmospheric pressure, 
comprises the counter pressure to which the pressure ratio is related. 
The supply pressure at which critical flow occurs will thus be determined 
by the degree of co-ejection. From the point of view of co-ejection, among 
other things, it is an advantage to divide a given mass flow into several 
smaller part flows, so called multi-channel nozzles. This will provide, 
related to the mass flow amount, a considerably larger contact surface 
between outflowing air and ambient air, since the contact surface "KA" 
between outgoing flow and ambient air is directly proportional to the 
total circumference, O.sub.out, i.e. KA.dbd.O.sub.out .times.K. K is a 
constant which is determined, among other things, by the angle at which 
the air jet diverges, i.e. by the conditions of turbulance, and by the 
distance between the nozzle outlet and the work piece to which the air jet 
is directed. 
For instance, in the case of 10 outlet channels with a diameter of 1 mm, 
O.sub.out =31.4 mm, whereas, for the same outlet area A.sub.out using 1 
outlet channel, O.sub.out is less than 10 mm. Thus, the contact number KT, 
which may be expressed as O.sub.out /A.sub.out, will be 4 mm/mm.sup.2 and 
about 1.24 mm/mm.sup.2, respectively. One drawback of multi-channel 
nozzles is the manufacturing of the long and narrow channel. An increased 
O.sub.out, while maintaining the same A.sub.out, to for instance 2 times 
31.4 mm, i.e. to an increased KT of 8 mm/mm.sup.2, will necessitate 40 
channels with a diameter of 0.5 mm. Such a nozzle outlet, which gives a 
lower noise level, is difficult to implement in view of the manufacturing. 
At the normal supply pressures of 6-8 bar there is obtained at larger 
nozzle outlets, preferably larger than 40 mm.sup.2, a counter pressure 
which is lower than 0.528 times the supply pressure. 
Within an outgoing air jet there will occur downstreams of the outlet local 
differences in velocity, pressure and density. The locally and 
periodically varying pressure differences will be reduced at a reduced 
outlet cross section. From the point of view of noise it is for instance 
known, that it is an advantage to divide a larger flow into several 
smaller and well distributed flows. 
However, if the outlet channels in a multi-channel nozzle are placed too 
close to one another--for instance when there is a demand for larger mass 
flows--the atmospheric air will be prevented from communicating with the 
central portions within the generated jet bundle in a satisfying manner. 
Such communication is a prerequisite for, among other things, a low noise 
level in these nozzle embodiments. 
Another common type of nozzle is the so called ejector nozzles which are 
commonly used for cooling, drying, and above all to blow away smoke or 
exhaust gases. The ejector nozzles, for instance in accordance with the 
Swedish patent specification SE.A. No. 8000567-1, operate by co-ejection 
via the central portions of the nozzle and remove smoke or exhaust gases 
from for instance a welding work place. The outgoing flow has a low power 
concentration and is strongly turbulent. This is caused by the fact that 
the trough-flow area of the common central outlet is much larger and by 
the fact that the friction losses within the outlet channel are extremely 
high. The frequencies spectrum of the resultant noize differs markedly 
from conventional blow nozzles. 
For instance, it is known that pressurized outflowing gas gives a dominant 
noise generation at the so called Strouhal frequency, fs, which is 
determined by the relation SN.times.u/d, where 
SN=The Strouhal number which at a Reynold's number of &gt;500 is equal to 0.2 
(dim. less) 
u=outflow velocity, m/s 
d=cross-sectional dimension (s), m 
For instance, in a circular outlet with an outlet diameter of 10 mm, there 
will be obtained, at normal critical outflow of air, a dominant noise 
generation within the frequency range of 6-7 kHz. At lower outlet 
velocities, for instance in ejector nozzles, a dominant noise generation 
will occur at substantially lower frequencies. With the outlet dimensions 
normally present in ejector nozzles, 10-75 mm, the dominant noise 
generation is at frequencies which are especially damaging to the human 
ear, or from about 4 kHz at the smaller outlet dimensions to about 1 kHz 
at the larger outlet dimension. 
If, in an annularly shaped slit orifice, the ratio between the velocity of 
flow and the slit width is sufficiently large, dominant noise generation 
occurring at the outlet may be displaced to higher frequencies which are 
outside the range of frequency audible to humans. However, the vacuum 
generated in the central portions of the air jet will give rise to such a 
turbulent flow, that minimizing of the slit will not result in any 
substantial noise reduction in the surrounding area of these types of 
nozzles. Filling up a vacuum space with a solid body, for instance in 
accordance with the U.S. Pat. No. 3,984,054 does not result in any 
substantial improvements with regard to the noise. 
The commerically available blow nozzles differ widely as concerns the 
blowing power. Since furthermore the need of blowing power varies 
considerably from one work place to another, and also within one and the 
same work place, and since neither the conventional nozzles and complete 
blowing tools are possible to regulate, nor are provided with information 
about the blowing power, the purchase and installation of such blowing 
devices involves many problems. The consequence is that the blowing 
devices will mostly have a too large capacity. Thus in most cases the air 
consumption, the noise and the risk of injury will be unnecessarily high. 
A blowing tool of conventional type has a valve or regulation arrangement 
the blow-through area of which is substantially directly proportional to 
the displacement of the valve or regulator element. Since the blow-through 
amount at the outlet is a function of the area ratio between the 
blow-through areas at the valve and at the outlet, and since this function 
is very unlinear, the possibility of a control regulation of the amount of 
flow will be limited. 
Displacement of the valve body from the closed position only a few tenths 
of a millimeter results in multiple changes of the amount of flow through 
the blowing device. On the other hand, a corresponding valve displacement 
at a position of larger opening will only result in percent changes of the 
amount of flow. 
In the often reccuring work of blowing away dirt form machines, 
manufactured parts etc., additional noise is caused when the flowing gas 
hits the object to be cleaned. When cleaning so called bottom holes, a 
noise situation occurs which is completely dominated by the generation of 
sound at the hole. This type of work, which is mostly performed manually, 
gives rize to sound levels which at a distance of one meter generally 
exeeds 100 dB(A). The work also causes chips and cutting fluid to be 
squirted around. Such squirting of chips and cutting fluid causes a lot of 
eye injuries to the user as well as to persons in the vicinity. 
The noise as well as the risk of squirting around chips may be reduced a 
certain amount by the aid of previously known technics, for example 
according to the German Pat. No. 2,908,004. However, this type of design 
has the considerable drawback that the gas fluid exiting from the 
centrally located exhaust tube will often obtain a hit zone which is 
outside of the hole to be blown clean. The operator therefore has to move 
the nozzle, by means of sweeping movements, to a position where the 
outflow of gas from the exhaust tube is located directly above the hole. 
The smaller the hole is, the longer time is needed for finding the correct 
position. Furthermore, such sweeping movements also entails that the 
operator will momentarily raise the plane of the nozzle from the object to 
be cleaned in order to reduce the friction between the end of the nozzle 
which mostly is made of rubber, and the object. The flow of gas through 
the slot thereby formed results in very high noise levels and, in certain 
cases, severe squirting of cutting fluid. 
The drawbacks mentioned may be reduced if the exhaust tube is placed 
outside of the nozzle plane. However, this placement causes the exhaust 
tube as well as the object to be cleaned to be subjected to mechanical 
abrasion. The abrasion of the exhaust tube is especially high in 
connection with threaded hole configurations. In most manufacturing 
processes no mechanical abrasion, i.e. scratches, on the manufactured part 
are acceptable. Another drawback with an exhaust tube projecting from the 
nozzle is that this design is not usable at smaller hole diameters. In a 
threaded bottom hole, as an example, the diameter of the hole generally 
has to be larger than 6 mm. 
A very important inconvenience in the cleaning of bottom holes according to 
the technic mentioned is the absence of an extensive regulation of the 
amount of stream. Different hole depths, hole configurations, cutting 
fluids etc. give rise to greatly different requirements as concerns the 
blowing power. 
BRIEF SUMMARY OF THE INVENTION 
The object of the invention is to provide a blowing nozzle which, related 
to the outlet area has a large contact surface between outflowing 
pressurized air and surrounding air for the purpose of obtaining an 
airflow with a low sound level, a large momentum, high efficiency and 
reduced striking velocity against the object to be cooled, dried or blown 
clean. In the latter case, it is of special importance to obtain a low 
sound level. In the basic concept the nozzle should be simple and 
inexpensive to manufacture and should be capable of forming the base of a 
manually portable blowing tool. Independently of whether the nozzle is 
used as a stationary or portable tool, the nozzle should be capable of 
being provided with a simple device for a well defined, substantially 
linear regulation of the mass flow amount through the nozzle. When the 
nozzle is used as a hand tool it should be capable of being converted, by 
simple hand movements, to a blowing tool which when used for cleaning 
holes, grooves etc., gives a low sound level and also the necessary 
protection against squirting around of chips and fluid. The basic concept 
should be capable of being modified to a nozzle at which there is present 
at least one further outflow substantially in the shape of a ring, or a 
part of a ring, to which outflow the surrounding air may be admixed to a 
substantial degree, externally peripherally as well as internally 
peripherally. These objects have been solved in that the product of, on 
the one hand, the ratio between the outer plus the inner circumference of 
the outlet and its outlet area, and on the other hand the ratio between 
the inner diameter of the outlet and its transverse dimension (i.e. the 
slot width S), is at least 4 mm/mm.sup.2, preferably considerably larger 
than 4 mm/mm.sup.2.

DETAILED DESCRIPTION 
The simplest embodiment of a "silent" nozzle for a blowing device 10 
according to the invention consists of an inner sleeve 11 and an outer 
sleeve 12, according to FIGS. 1 and 2. The two sleeves may by themselves 
together constitute a complete nozzle 13, preferably intended to be used 
in stationary installations. By means of a permanent connection, i.e. a 
screw connection 14, the sleeves are interconnected, at their rear ends, 
to form a unit in such a manner, that there is formed, between the sleeves 
11, 12, an annular space 15 which serves as a supply channel for the 
compressed air. At the front end of the unit there is provided an outlet 
channel in the form of a substantially annular slot 16. 
The blowing device 10 further comprises a connection 17 for the compressed 
air to the supply channel 15 and an outlet opening 18 in the inner sleeve 
11. The outlet opening does not necessarily have to be conical as shown in 
the drawing. 
When compressed air is supplied to the nozzle 13 through the connection 17, 
an annular jet C will be obtained at the outlet opening 19 of the slot 16. 
At the outlet opening, bound heat is transformed into kinetic energy under 
simultaneous expansion of the gas. A nozzle according to the invention is 
intended to be used for such types of work where the air pressure 
connected to the nozzle preferably is larger than 4 bar, i.e. the outflow 
from the outflow opening 19 is mainly in the form of critical flow. 
The object of the invention is attained with the nozzle embodiments 
according to the following descriptions. 
If in FIG. 1 the outer and inner diameters, respectively, of the sleeves 
11, 12 at the outlet opening 19 is designated by D1 and D2, respectively, 
then D2-D1=twice the slot width S. In order to obtain a large contact 
surface between the outflowing gas or air and the surrounding air the 
nozzle according to the invention is provided with at least one 
communicating channel 20, i.e. in this way co-ejection is made possible 
outwardly peripherally as well as inwardly peripherally of the 
substantially annular flow. 
In order to, in accordance with among other things one of the objects of 
the invention, delay the occurrence of the outgoing, substantially annular 
flow downstream of the outlet being integrated into a common flow with a 
large cross-sectional area with high velocity, the nozzle according to the 
invention has a cross-sectional ratio TF=D1/S which is larger than 3, 
preferably larger than 6. This is in order that the ratio between the 
total outlet circumference O.sub.out and the total outlet area A.sub.out, 
comprising the contact number KT, multiplied with the cross-sectional 
ratio TF, together comprising a capacity number ET, will be substantially 
larger than 4 mm/mm.sup.2, preferably substantially larger than 10 
mm/mm.sup.2. Thus, referring to FIG. 1, the relation 4 (D2+D1)/D2.sup.2 
-D1.sup.2) times the relation D1/S should be considerably larger than 4 
mm/mm.sup.2 but preferably substantially larger than 10 mm/mm. 
The indicated lower limit for the capacity number ET if "substantially 
larger than 4 mm/mm.sup.2 " is based upon the fact that dominant sound 
generation will thereby be displaced to higher frequencies which, in 
comparison with a conventional cylindrical tube outlet with the same 
blowing power, corresponds to a frequency displacement of about one 
octave. 
Hereby is obtained a sound pressure reduction which at the standardized 
middle frequency with a frequency width of one octave at 4 kHz will be 
about 2 dB and at the standardized middle frequencies 8 and 16 kHz, 
respectively, will be about 3 dB. 
This will cause a reduction of the dB(A)-filtered sound level of about 3 
dB(A), i.e. at a capacity number of about 4 mm/mm.sup.2 will be obtained a 
lowering of the sound level which largely corresponds to the lowering 
which is necessary for a human being to subjectively notice the lowering 
of the sound level. 
Thus, the purpose of designing a blowing device with a capacity number of 
about 4 mm/mm.sup.2 is that when a working blowing device is put up beside 
a working tubular nozzle, the blowing device according to the invention 
should be noticed as the decidedly more silent of the two. 
In blowing devices with a plurality of substantially part ring shaped slot 
outlets where the individual outlet may have different slot diameters 
corresponding to the diameter D1, FIG. 1 the diameter D1 according to the 
above will be defined as a mean value of the inner slot diameters of all 
the partial outlets. 
The slot S according to the above is defined as the mean value of the slot 
S computed over the actual number of slot outlets. 
At the normally occuring mass flow amounts for the most common forms of 
cleaning, the mean value computed slot S should be smaller than 3 mm, 
preferably smaller than 1.5 mm. This is in order that dominant sound 
generation from the outlet will be found at frequencies higher than 20 
kHz. 
The acoustical advantages of the nozzle described obtained, among other 
things, is achieved by the unavoidable turbulency whereas in the stream 
flow C being limited to their largeness. 
High co-ejection due to a large contact surface between outflowing air and 
surrounding air entails a rapidly decreasing velocity of flow but an 
increase in momentum. 
Thus the increased co-ejection means that the airstream will reach the work 
object in question with a lower velocity and a higher mass flow. This 
means that a nozzle according to the invention, in contrast to the so 
called noise absorptive blow nozzles, has a substantially lower noise even 
when it is used as a working blowing tool. 
Tests performed with nozzles substantially corresponding to the description 
herein above have been compared to most of the blow nozzles according to 
known embodiments. In all cases, a lower sound level and mostly markedly 
higher efficiency where noted while maintaining high blowing power. 
Compared to the more usual tube nozzles there is obtained, already at such 
a low value of the capacity number ET as about 4 mm/mm.sup.2, a sound 
generation which is more than halved. The reduction of sound level will 
thereby be at least 3 DB(A). With a capacity number ET of about 10 
mm/mm.sup.2, the sound generation may be reduced to at least one third. At 
considerably higher values of the capacity number, very noticable 
reductions in sound level have been noted. With a capacity number ET of 
about 500 mm/mm.sup.2 the sound generation may for instance be reduced to 
less than one tenth, and with a capacity number of about 5.900 mm/mm.sup.2 
up to one hundredth of the sound generation in traditional tube nozzles 
with the same amount of mass flow and/or blowing power. 
Thus, the comprehensive tests have shown that, compared to a tubural nozzle 
with the same outlet area, a noise reduction in dB(A) is obtained which, 
at critical flow, is substantially proportional to 5 times the 
10-logarithm for the capacity number ET. 
Since, from the point of view of sound, it is of importance that the inner 
diameter D2 of the outer sleeve 12 is substantially concentric with the 
mantle surface of the inner sleeve 11, spacing elements 22 centering the 
sleeves relative to one another are provided on one or both of the 
sleeves. 
When the nozzle lacks the regulation possibility, according to FIGS. 3 and 
5, while maintaining the advantages of the nozzle the corresponding 
spacing elements may be disposed in the annular slot 16 which may then be 
made with axial grooves, where the upper edges of the grooves abut against 
the inner side of the outer sleeve 12, or vice versa, the grooves may be 
provided at the inner side of the outer sleeve 12 and abut against the 
inner sleeve 11. 
Thus, the annular outflow may not be completely cylindrical, but the flow 
may be divided in a number of flows shaped as a part of a ring. Also, 
these need not necessarily be situated along a common division diameter. 
In order to reduce the possibility of the pressure variations occurring 
within the supply channel 15 from affecting the pressure situation at the 
outlet 19, the annular slot 16 should be longer than 4 times the slot 
width. 
When creating extremely high blowing powers per surface unit, for instance 
when blowing away parts from automatic machines, it may be of advantage, 
from the point of view of noise, to provide a number of substantially 
circular flow-through channels 23, according to FIG. 4 within the nozzle 
portion of the inner sleeve 11, instead of increasing the slot width S. 
The circular outlet channels 23 should be smaller than 2 mm, preferably 
smaller than 1.7 mm, and should be placed at a distance relative to each 
other which is larger than 2 times their diameter. 
If a blowing device 10 is desired which is to allow a regulation of the 
amount of flow of air, the nozzle and the blowing device 10 are made 
according to the embodiment of FIGS. 3 and 5. By the aid of a regulated 
nut 31 which cooperates with threads 32 at the rear end of the outer 
sleeve 12 the inner sleeve 11 may be axially displaced against the action 
of a spring 33. 
When the two sleeves 11 and 12, respectively, are displaced in relation to 
each other the slot width S will be increased or alternatively decreased. 
A precondition for making this possible is that the substantially circular 
surfaces 24 and 25 which delimit the annular slot 16 are angled in 
relation to the longitudinal axes 27 of the nozzle, see FIG. 3. The angles 
.alpha.1 or .alpha.2 should be less than 10.degree., preferably less than 
2.degree.. The angles need not necessarily be of the same size. 
Furthermore, the angles may be negative, i.e. the surfaces 23 and 24 may, 
relative to the direction of flow, be converging relative to the 
longitudinal axes 27 of the nozzle. The amount of air through one and the 
same may in this way be regulated within very wide limits. Furthermore, 
the regulation is substantially linear. The outer and the inner sleeve, 
respectively may advantageously be provided with markings 39 indicating 
the size of the blowing power (see FIG. 8). 
In the embodiment according to FIG. 5, the outer sleeve of the blowing 
device 10 consitutes a portion of the base 30 of the device. The regulator 
nut 31 is screwed onto the rear portion of the base, and in order to 
reduce the friction of movement between the inner sleeve 11 and the 
regulator nut 31, one or several roller or ball elements 34 are provided 
within the rear end plane of the inner sleeve. 
In the drawing position shown the inner sleeve has its front position 
within the base 30, i.e. the shoulder 35 of the inner sleeve bears against 
the shoulder 36 on the base. 
For preferably higher needs of blowing power it is of advantage to 
subdivide a ring shaped, or part-ring shaped, flow into one or several 
further substantially ring and/or part-ring shaped flows where the inner 
and outer limiting surfaces of the respective flows have the possibility 
of co-ejection--for instance as in the nozzle according to FIG. 6. Wherein 
the co-ejection routes are indicated with arrows. 
Thereby, the increase in the capacity number ET may be multiplied while 
maintaining the total outlet areas A.sub.ut because the slot width S for 
the respective part flows will then be more than halved. Dominant sound 
generation will be displaced to still higher frequencies because the 
frequency with which dominant sound generation occurs is inversely 
proportional to the slot width S of the air flow. 
Furthermore, with correctly controlled outflows as regards pressure, 
density and velocity, the embodiment with an increased number of outlets 
will give the possibility of further sound reductions relative to the 
amount of mass flow present. Further, by the aid of at least one 
substantial annular additional flow in the surrounding area around a 
mainflow, the latter may be imparted with over-critical flow the radiated 
higher sound effect of which will interfere to substantially with pressure 
pulses present within surrounding additional flows. 
The embodiment according to FIG. 6 may be an addition to the blowing device 
10 according to FIG. 1. In a first step the blowing device 10 may be 
provided with an outer nozzle part 50a which consists of two cylindral 
sleeves 51a and 52a. The inner sleeve 51a is connected, by means of a 
pressfit, a groove or screw connection, via the spacer elements 53, with 
the outer sleeve 12 of the blowing device 10. 
The spacer elements 53 are shaped in accordance with the same principle as 
the spacers 22 in FIG. 1. Within at least one spacer element 53 there is a 
flow-through passage 54a which is supplied with pressurized air from the 
supply channel 15 and conducts it to the chamber 55a. 
The space 56a between the two nozzle outlets 19 and 57a, respectively, 
communicate with the surrounding area via a substantially annular 
communication channel 58a. 
As a second step, the blowing tool 10 may advantageously be provided with 
an inner nozzle part 50b. As shown in FIG. 6, this made be shaped 
substantially at the outer nozzle part 50a. 
With a nozzle embodiment having at least two annularly shaped partial 
flows, the surrounded flow-through nozzle 13 will obtain, with adjustment 
of the amount of mass flow for the surrounding flows from the outlets 57a 
and/or 57b, a counter pressure downstream of the outlet which is 
substantially lower than the critical pressure. That is, the counter 
pressure downstream of the outlet 19 may be made less than 0.528 times the 
supply pressure connected to the blowing device 10. 
The annular nozzle outlet 19 (FIG. 7) is adjusted to give over-critical 
outflow at the outlet 19 of the blowing device 10. In order to reach an 
over-critical flow at the outlet 19, the capacity number ET in this 
embodiment should be at least 20 mm/mm.sup.2, preferably larger than 100 
mm/mm.sup.2. Further, the relation between D12.sup.2 -D11.sup.2 =G and 
D2.sup.2 -D1.sup.2 =H should be less than 1.7 at an available supply 
pressure of 8 bar. At an available supply pressure of 6 bar, G/H should be 
less than 1.45. The latter entails a velocity increase by a factor of 
1.55. The angle V should be 3.degree.-6.degree.. 
Available velocity increases for the outlet 19 will allow savings of air by 
20-30% while maintaining blowing power. 
Acoustically achieved advantages with the over-critical flow mentioned is 
that for a given mass flow and/or blowing power the outlet velocity will 
increase when the slot width S is reduced. Dominant sound generation may 
thereby be displaced to even higher frequencies, because the frequency at 
which dominant sound generation occurs is directly proportional to the 
velocity of the airflow and inversely proportional to the slot width S of 
the airflow. 
The blowing device according to FIG. 5 may be converted into a blowing tool 
for cleaning so called bottom holes as shown in FIG. 8. 
To the nozzle end 13 of the blowing device there is connectable a 
protective collar 41 consisting of a thin-walled tube of plastic or sheet 
metal and provided with a brush element 44 intended to be placed against 
an object to be blown clean, for instance a hole. Since the resistance 
against flow in the brush element is considerably larger than the 
resistance against flow in the communicating channel 20, the cleaning air 
will be evacuated through said channel. The brush element 44 may of course 
be replaced with some other flexible material such as foamed plastic or 
foulded rubber. By connecting the communicating channel 20 to a collecting 
device 45, i.e. to a central service suction conduit, alternatively to a 
collecting bag, (not shown) which, for instance by means of an insertion 
tube 47 is connected to a conical seat 48 in the inner sleeve 11, large 
reductions in sound level are obtained. 
Tests that have been made have shown that a blowing tool substantially 
corresponding to FIG. 8 will reduce the momentarily occuring sound peaks 
with more than 20 dB(A), whereby, the amount of noise during a typical 
working day may be reduced by 7-10 dB(A). The nozzle gives an airflow with 
an impact surface substantially corresponding to the diameter of the brush 
element 44. Thus, the blowing operation may be started directly after the 
brush element has been placed above the hole to be blown clean, whereby 
uncontrolled squirting of chips and cutting fluid will be eliminated. 
Furthermore, there will be no risk for mechanical abrasion on the blowing 
tool or the object to be blown clean. 
Tests which have been made have shown that when the overhang E is well 
adapted in relation to the diameter D1 of the outlet channel 16, a flow 
picture is obtained which is illustrated diagrammatically in FIG. 9. 
Within the zone P10 there will be formed a turbulent air cushion which is 
at rest in relation to the air stream and which has a higher static 
pressure and guides the flow to the hole 15 to be blown clean. 
When the overhang is too small, as diagrammatically illustrated in FIG. 10, 
a flow picture is obtained which does not have the ability of cleaning the 
hole 50. That is, a small measure E and the small air cushion P11 will 
cause a direction of movement which very much diverges from the optimum 
direction of movement for cleaning. It should also be pointed out that a 
too large overhang E gives a deteriorated blowing clean function. However, 
in this case, the divergence from the optimum working function may be 
compensated to a certain extent by an increased mass flow through the 
blowing device. 
Tests which have been made have shown that the clean blowing function is 
dependent upon the diameter D1 of the ring- or part-ring shaped outlet, 
the overhang E and the cross sectional and longitudinal dimensions of the 
hole 50. 
Variations in hole dimensions may be compensated to a large degree by 
varying the mass flow through the blowing device. 
FIG. 11 illustrates how, in a test with one and the same amount of mass 
flow, the lifting height of a test body varies depending upon the ratio 
E/D1. Lifting height here means the distance between the plane 51 of the 
work object and a reference plane which is placed behind which is 
positioned in the vertical plane. The test body which was placed in the 
bottom of a hole standing in the vertical plane (here with the diameter 10 
mm and the depth of the hole about 30 mm) was thus distributed via the 
communication channel 20 of the blowing device and thereafter via the 
atmosphere to the reference plane. The distance of the reference plane to 
the plane 51 was adjusted so that the test body could hit the same with a 
slight margin. 
In order to obtain a sufficiently good work function for most different 
hole dimensions at the hole 50, the relation between the overhang E of the 
protective collar and the mean value inner diameter D1 for the ring or 
part-ring shaped outlet (S) should be greater than 0.6 and smaller than 
12.7. However, preferably the relation should be greater than 1.2 and less 
than 8. 
The communication channel 20 need not necessarily, as shown in FIG. 8, be 
consituted by a single channel. Further, the ring or part-ring shaped 
outlets 19 need not be constituted by slot-shaped channels 16, but the 
substantially ring or part-ring shaped flow within the protective collar 
41 may be formed by an outlet consisting of a series of cylindrical 
channels, as the channels 23 in FIG. 4. 
When the blowing tool is used in the manner described for the clean-blowing 
of holes, grooves etc. the essential of being able to continually regulate 
the blowing power will be more clearly apparent since the total pressure 
drop through the collecting bag (not shown) will vary with respect to the 
degree of filling, but above all, with respect to the fact that different 
hole shapes, types of cutting fluid, etc. demand different blowing power. 
A regulation may easily be provided by means of the fitting of the 
regulating means 31. 
The invention is not limited to the embodiments shown and described but may 
be implemented in many other ways within the scope of the claims.