WO1981001668A1

WO1981001668A1 - High pressure blowing tool having low noise level

Info

Publication number: WO1981001668A1
Application number: PCT/SE1980/000327
Authority: WO
Inventors: H Moss
Original assignee: Ingemanssons Ingenjorsbyra Ab; H Moss
Priority date: 1979-12-12
Filing date: 1980-12-09
Publication date: 1981-06-25
Also published as: JPS56501754A; BE886598A; EP0041534B1; DK323781A; FI69256B; EP0041534A1; JPH0316182B2; SE7910235L; DE3068922D1; FI812316L; IT8026560A0; FI69256C; IT1134668B

Abstract

A blowing tool comprises a body part with a connection (8) for pressurized, gaseous fluid, an exhaust nozzle (13) and a valve (9, 10) located between said connection and said nozzle and having an adjustable fluid passage. The nozzle is provided with a plurality of exhaust channels (12) ending near or in the mantle surface of said nozzle and spaced from the central parts of said nozzle. The location of the outlet apertures brings co-ejected air to effectively reduce differences in pressure and velocity between the ambient air and the exhausted gas so that a pronounced lowering of the noise level of the working blowing tool can be obtained.

Description

High pressure blowing tool having low noise level

In Swedish patent application

78 06883-0 a blowing tool at which for a certain blowing power an essential reduction of the noise level around the working blowing tool has been attained. The present invention relates to a further development of the blowing tool described in the mentioned patent.

The most common blowing tools have in principle a design according to Fig. 1 which is a longitudinal section view. The gas is supplied to the tool through a high pressure hose 2 which is connected to the gas source and has a high pressure above atmospheric. When the blowing tool is to be used a hand grip 3 is depressed, a valve slide 4 being moved so that gas can pass through a groove in the slide and an extension tube 6 out through the mouth 7 of the extension tube.

When a gaseous medium in this way is brought to exhaust to the environment a velocity of discharge is obtained which depends on the pressure ratio between the counter pressure after, i.e. in the direction of the flow, the mouth arid the pressure before the mouth.

If the mouth is not formed as a so-called Laval nozzle maximum velocity of discharge is obtained at the so-called critical pressure ratio.

The pressure before the mouth at which critical pressure ratio can be obtained is determined by the counter pressure after the mouth which in its turn is influenced by the degree of coejection, i.e. to which extent the air jet leaving the mouth in its motion takes the ambient air with it, in such a way that the higher co-ejection which can be obtained the higher supply pressure can be applied on the high pressure hose 2 before the critical pressure ratio is reached. The resulting higher density of the gas gives larger blowing force in addition to the supplementary blowing power that co-ejected air gives. If the interior of the blowing tool is designed so as to achieve low losses, i.e. if all of the flow passages before the outlet have a substantially greater cross sectional area than that of the outlet 7, the pressure of the gaseous medium immediately before the outlet would substantially correspond to the applied supply pressure within the high pressure hose 2, i.e. at normally occurring supply pressure of 6-8 bars the pressure of the gas immediately before the outlet would be substantially equal to 6-8 bars.

Since the pressures of gases immediately after their expansion are never lower than the critical pressure, i.e. not lower than 0.528 times the pressure immediately before the outlet, the pressure of the gas would, if all the air passages before the outlet are substantially greater than the outlet passage, after expansion be greater than 3.15 bars, i.e. more than 3 times the pressure existing around the tool.

It is important to design the outlet nozzle in such, a way that co-ejection is sufficient for the counter pressure after the outlet 7 to deviate only slightly from the pressure immediately after the expansion zone. The more the pressure differs immediately after the expansion from the ambient pressure the stronger turbulence and with that generation of noise results namely outside the outlet.

For constructions known up to now it has been possible to reduce this effect to a certain extent by providing a restriction by the air passages before the outlet passage each individually or jointly, i.e. they provide a pressure depression of the supplied pressure connected to the tool. For the conventional tool according to Fig. 1 the flow area at the air passage 5 is for example only about 0.45 times the flow area at the outlet 7. In such a construction a gas pressure is obtained within the extension tube which is about 0.42 times the supply pressure connected to the tool. The pressure upstream the expansion cross section at the outlet port is thus at normal supply pressures then only about 2.5 to 3.4 bars.

As the co-ejection ii. such constructions is small, however, a counter pressure is obtained after the outlet port which is lower than 0.528 times the gas pressure existing before the outlet. The difference between the pressure of the gas after the expansion and the present counter pressure results in a strong turbulence also here in the gas flow leaving the outlet port - though to a smaller extent - in comparison with a situation with the whole supplied pressure of 6 to 8 bars prevailing within the extension tube 6.

The object of the. present invention which is based on studies is to provide a blowing tool having a low noise level, a great blowing power and a high mecanical efficiency.

A blowing tool according to the invention has the characteristic features stated in the claims.

Figs. 2 to 9 show examples of blowing tools according to the invention. The gas is supplied to the tool through a connection 8 and passes through a passage between the valve plate 9 and the valve seat 10 as the front rubber cone 11 is tilted. For a fully opened valve this passage is greater than 0.5, suitably greater than 0.65, preferably greater than 0.8 times the total outlet area of the outlet apertures 12 at the nozzle 13, i.e. preferably so that the velocity of the gas at the valve passage is lower than the velocity of the gas at the outlet passage, so that the generation of noise at the valve preferably is lower than the generation of noise at the outlet.

By having the outlet apertures spaced from each other a large distance the valve passage can advantageously also be made larger, preferably substantially larger than the total outlet passage, so that in the main the whole supply pressure connec ted to the blowing tool can be utilized, i.e. the gas pressure in the chamber 14 can advantageously be essentially equal to the supply pressure.

The front part of the tool can be formed as a cylinder, a trun cated cone or with the chamfering increasing towards the nose.

The outlet passages can advantageously end. near or in the mantle surface as appears from Figs. 2-5 and Figs. 6-7 respectively.

The outlet apertures are so positioned that co-ejection is obtained around the whole periphery of each partial jet. For the embodiments according to Figs. 2 to 5 and Figs . 8 to 9 this can in practice be realized a.o. by placing the outlet apertures 12 on a circle the diameter D of which is greater than 4 times the diameter d of the largest outlet passage, which is less than 2 mm, preferably at the most 1.5, e.g. about 1 mm, and by spacing the apertures with a large distance and substantially not within the central parts of the nozzle.

Studies which have been carried out show that even with large distances between the outlet apertures placed on a circle having the diameter D, it is extremely difficult to obtain good co-ejec- tion for those outlet apertures which are placed within the central parts of the nozzle, i.e. inside the diameter D.

The outlet apertures should be positioned with a mutual centr distance which is larger than 2 times the diameter of the aperture for outlet apertures which are less than 1 mm. For outlet apertures which are larger than 1 mm the mutual centre distance should be greater than 2 times the square of the dia meter of the aperture . In this way also a reduced mutual inte action between the outgoing gas jet is obtained. In order to obtain the object of the invention more than 10 %, suitably more than 20 % , preferably more than 40 %, of the outlet area should be positioned outside a surface A_c, which is 3 times greater than the sum A_ut of the cross sectional areas of the outlet passages, A_c being situated so that its centre of gravity coincides with the centre of gravity of a form area A_f situated in the same plane as A_c, being uniform with A_c and with the smallest possible periphery containing the outlet areas of all the exhaust passages.

Further, the largest cross sectional dimension of the outlet jet should be at the most 2 mm, preferably at the most 1-5 mm, e.g. about 1 mm, i.e. for circular outlet apertures the diameter should be at the most 2 mm, preferably at the most 1.5 mm and can e.g. be about 1 mm. for a.o. having a fast pressure equalization between the ambient pressure and the pressure in the central parts of the gas jet.

To design the area A a form area A_f is first designed by connecting the outer outlet apertures in the picture of the apertures with straight lines which in relation to the centre of the picture of the apertures are tangents to the outer side at the outer apertures.

The area A_c is so situated that its centre of gravity coincides with the centre of gravity of the form area A_c Each side of A_c is parallel to the corresponding side of the form area A_f.

At a nozzle in which the outlet apertures are positioned on a circle with equal partition, the area A is thus projected symmetrically around the centre of the circle. The mantle 15 at the termination of the nozzle can be conical or tapering as in one of the shown embodiments. Half of the cone angle, α according to Fig. 4 should then be less than 20°, however not less than 10°. For the embodiment according to Fig. 6 or 7 the outlet aper tures should be spaced with a centre distance exceeding 1.5 preferably exceeding 2 times the diameter of the aperture for the outlet passages which is less than 2 mm, preferably less than 1.5 mm, e.g. 1 mm.

To obtain the object of the invention with this embodiment more than 10 %, preferably more than 20 %,and best more than 40 %, of the sum Aut. of the cross sectional area of the exhaust passages at the outlet, transversally to the direction of the flow, should be placed outside an.area A which is 2 times larger than A_ut, A being so located that its centre of gravity coincides with the centre of gravity of a form area A_f, situated in the same plane as A_c, being uniform with A_c and completely enclosing with the smallest possible periphery the outlet areas of all the outlet passages. Half of the cone angled for the nozzle should then be between 10° and 20°, and in addition it is assumed that the direction of the flow from the outle passages does not deviate more than 10° from the axis of the cone.

To get a mechanical shield so that the outlet apertures are not deformed by hits or impacts the termination of the nozzle can advantageously be provided with means 16 projecting from the nozzle body as shown in Figs.2 and 4 to 9, which are so designed that they do not influence the co-ejection capacity of the nozzle or otherwise disturb the outflow of gas. It is important that the nozzle has this mechanical shield, because if for instance only one of the outlet apertures should be deformed, for instance by a burr or a flash arising within the flow area, this will result in an increase of. the noise leve which can be of 3to4 dB (A). Since the noise thus arising further more has the nature of a pure tone, the increase in the noise level should be placed on an equality, as regards the risk of impaired hearing, with an increase of the noise level of 13-14 dB (A) for a wide band noise. Common to the devices according to the invention is that the exhaust passages of the nozzle together give directed exhaust of the gazeous fluid from the nozzle. To obtain this the hypothetical central lines of the passages in the direction of the fluid flow can be parallel to each other, but this is not necessary, as said central linescan diverge up to about 20 or even 30° between themselves and in relation to the exhaust direction of the nozzle and yet give a directed jet of fluid from the nozzle. Annularly arranged exhaust passages of a nozzle having a conically mantle can for instance have their central lines located on a hypothetical conical surface situated inside and presenting a smaller cone angle than the conical mantle of the nozzle.

Prototypes of the device according to the invention in accordance with the embodiments illustrated in Figs. 2 to 9 have been subjected to practical testing and have been compared with most commercially available so-called silent blowing nozzles having a body of porous, sintered metal inserted into the exhaust tube. and have also been compared with the majority of conventional blowing nozzles. In all the cases for a given blowing power in addition to a higher air consumption the noise level was considerably higher for the comparison nozzles than for the blowing tool according to the invention.

The invention is not limited to the shown and described embodi ments but can be realized in any other way within the scope of the claims.

Claims

1. A blowing device comprising a body part having a connect for pressurized gaseous fluid, an exhaust nozzle comprising plurality of exhaust passages which jointly give directed exhaust of said fluid from the nozzle, and a valve located bet ween said fluid connection and said nozzle determining the rate of flow of fluid through said device, characterized in that at least 10 % of the sum Aut. of the cross sectional areas of the exhaust passages at their outlets, seen in the direction of the fluid flow .is lying outside a plane area A_c perpendi cular to the exhaust direction of the nozzle, the magnitude of which is 3. A_ut, A _c being located so that its centre of gravity coincides v/ith the centre of gravity of a uniform form area A_f which is parallel with A_c and which with the smallest possible circumference contains the cross sectional areas of all the exhaust passages at the outlet.

2. A blowing device comprising a body part having a connection for pressurized gaseous fluid, an exhaust nozzle comprising a plurality of exhaust passages which jointly give directed exhaust of said fluid from the nozzle and a valve located between said connection and said nozzle which determines the rate of flow of fluid through said device, characterized in that said nozzle has a substantially conical mantle in which said exhaust passages end, and in that at least 10 % of A_ut is lying outside a plane area A'_c perpendicular to the exhaust direction of the nozzle, the magnitude of which is 2A_ut, A'_c being located so that its centre of gravity coincides with the centre of gravity o f a form area A^ which is parallel to A'_c and which with the smallest possible circumference contains the cross sectional areas of all the exhaust passages at the outlet.

3. The blowing device according to claim 1 or 2, characterized in that the through flow area of said valve, when the latter is fully opened, is at least 0.5 A_ut, suitably at least 0.65 A_ut., and preferably at least 0.8 A_ut.

4. The blowing device according to any of the previous claims, at which device the nozzle has a substantially conical mantle, characterized in that half of the cone angle of said mantle amounts to between 10 and 20º.

5. The blowing device according to any of previous claims, and presenting one or more additional characteristic features according to the description and the drawings.