GB2177026A

GB2177026A - Rotary atomiser

Info

Publication number: GB2177026A
Application number: GB08614856A
Authority: GB
Inventors: Kui-Chiu Kwok
Original assignee: Graco Inc
Current assignee: Graco Inc
Priority date: 1985-07-01
Filing date: 1986-06-18
Publication date: 1987-01-14
Also published as: GB8614856D0; DE3621899A1; JPS6219270A; FR2583994A1

Abstract

A rotary atomiser is provided with a cup 114 having a radially outwardly directed discharge edge (128) formed by upper and lower surfaces (130, 132) Figure 3. By forming the angles between the upper and lower surfaces and the plane in which the discharge edge (128) lies to beat least 20 DEG , improved results are obtained by preventing roll-over and air entrapment. A pipe 118 can supply paint to the base of the atomiser cup. <IMAGE>

Description

SPECIFICATION A rotary atomiser The present invention relates to a rotary atomiser, and particularly to an atomiser of a type in which a liquid such as paint is fed in use into the interior of a rotating cup-shape member in which it is caused, by the rotation of the member, to travel over the upper surface towards the periphery which acts as a discharge edge. As the liquid passes over the discharge edge it is atomised and sprayed outwardly. In the case of paint the atomised spray is used to coat a workpiece. Prior art such devices, however, suffer from several problems. The first such problem is known as roll-over which occurs when a liquid such as paint adheres to the discharge edge as it passes instead of being thrown off so that, in effect, it rolls over the discharge edge on to the outer surface of the cupshape member where it dries.The dried paint later flakes off, and the flakes are thrown with the freshly atomised paint to contaminate this. This causes imperfections in the finished coat.

Another problem commonly encountered in the use of known atomisers is air entrapment, wherein bubbles form in the fluid as it atomises at the edge of the atomiser; this also causes imperfections in the finish on the part to be coated when the atomiser is used to spray paint.

It has been found that by careful selection of the shpae of a rotary atomiser of the type described above, particularly as regards the discharge edge and the angles leading to the discharge edge, problems such as that of roll over and air entrapment can be reduced or eliminated.

According to the present invention, therefore, there is provided a rotary atomiser having a radially outwardly facing discharge edge at the junction between opposite faces of the atomiser, the said faces comprising a first surface lying at a first angle in relation to the plane in which the said discharge edge lies and a second surface lying at a second angle in relation to the plane in which the said edge lies, the said first and second angles being at least approximately twenty degrees.

In a preferred embodiment of the invention the first angle is approximately thirty degrees and equal to the second angle. In this preferred embodiment the discharge edge is formed at the rim of a cup-shape member. Preferably the cup-shape member has a frusto-conical wall defined by an inner surface and an outer surface of generally frusto-conical form.

In embodiments having a cup-shape member it is preferred that there is a rounded transition between one of the said surfaces defining the discharge edge and an adjacent face of the cup-shape member.

One embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial sectional view of a prior art rotary atomiser; Figure 2 is a similar axial sectional view showing a rotary atomiser formed as an embodiment of the present invention; and Figure 3 is a partial sectional view, on an enlarged scale, taken on the line 3-3 of Figure 2 and showing the discharge edge in more detail.

Referring now to the drawings, a typical prior art rotary atomiser, generally designated with the reference numeral 10, is shown in Figure 1. The atomiser 10 comprises a cup-shaped body 14 mounted so as to be rotatable about a shaft 12. Attached to the cup-shape member 14 is a feed baffle 16 located in the interior thereof and fixed to the cup-shape member 14 by means of a plurality of posts 22 which, at the same time as securing the cup-shape member firmly to the feed baffle 16, space the feed baffle above the bottom of the cupshape member and transmit the rotary motion thereto from the shaft 12 which is secured to it.

The bottom of the cup-shape member 14 has an aperture 25 to allow the introduction of a liquid such as paint through a feed tube 18. The space beneath the baffle 16 serves as a reservoir of liquid which then passes out radially to spread over the inner surface 24 of the cup shape 14. The outer surface 26 of the cup 14 meets the inner surface 24 at a discharge edge 28 which is merely a sharp edge in the prior art device shown in Figure 1.

Referring now to Figures 2 and 3 the rotary atomiser 110 of the present invention has a rotatably centre shaft 112 which, like the prior art device shown in Figure 1, carries a baffle 116 to which is attached a cup-shape member 114 by means of posts 122. A feed tube 118 feeds paint or other liquid through an aperture 125 into a central reservoir 120 from where the liquid passes between the posts 122 on to the inner surface 124 of the cupshape member 114. As so far described the embodiment of Figures 2 and 3 is similar to the prior art structure shown in Figure 1. The present invention differs, however, primarily in the nature of the discharge edge, and also the side wall of the cupshape member.

As can be seen in Figure 2, the side wall of the cup-shape member is generally conical (or more precisely, frusto-conical) such that the inner surface 124 diverges outwardly and upwardly to a rounded transition zone 134 which joins an upper discharge surface 132 which meets a lower discharge surface 130 at a sharp discharge edge 128.

The lower discharge surface is formed at the upper part of the outer surface 126 defining the frustoconical wall of the cup-shape member 114, the upper discharge surface 132 forms a first angle A with the horizontal plane at the discharge edge, as shown in Figure 3, whilst the lower discharge surface 130 forms a second angle B with this horizontal plane.

In the preferred embodiment, angles A and B are both approximately thirty degrees, although it has been found that these should be at least twenty degrees of thereabouts. This configuration has in tests produced excellent results using a cup-shape member of approximately 6.3 cm (2.5 inch) and speed of rotation of at least about 10,000 RPM. For best results it has been found that the speed of the discharge edge should be at least as great as in the above-mentioned example. For comparison, the product of the cup diameter (in centimetres) and cup rotational speed (in RPM) should be at least about 63,000 (the same product with the diameter in inches is 25,000). The minimum value of angles A and B should be not less than about twenty degrees. These values are important in providing the improved results by minimising roll-over and air entrapment.

Claims

1. A rotary atomiser having a radially outwardly facing discharge edge at the junction between opposite faces of the atomiser, the said faces comprising a first surface lying at a first angle in relation to the plane in which the said discharge edge lies and a second surface lying at a second angle in relation to the plane in which the said edge lies, the said first and second angles being at least approximately twenty degrees.

2. A rotary atomiser as claimed in Claim 1, in which the first angle is thirty degrees.

3. A rotary atomiser as claimed in Claim 1 or Claim 2, in which the second angle is thirty degrees.

4. A rotary atomiser as claimed in any preceding Claim, in which the discharge edge is formed at the rim of a cup-shape member.

5. A rotary atomiser as claimed in Claim 4, in which the cup-shape member has frusto-conical wall defined by an inner surface and an outer surface of genrally frusto-conical form.

6. A rotary atomiser as claimed in any preceding claim in which the first surface lies on one side of the plane defined by the discharge edge and the second surface lies on the other side of this plane.

7. A rotary atomiser as claimed in Claim 4, Claim 5, or Claim 6, in which there is a rounded transisiton between one of the said surfaces defining the discharge edge and an adjacent face of the cup-shape member.

8. A rotary atomiser as claimed in any preceding Claim further comprising means for feeding a fluid onto one of the said faces defining the discharge edge.

9. A rotary atomiser as claimed in Claim 1 and substantially as hereinbefore described with reference to, and as shown, in the accompanying drawings.

10. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or shown in the accompanying drawings irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.

11. A rotary atomiser having a radially outwardly facing discharge edge, said edge being formed by: an upper surface having a first angle relative to the plane defined by said edge and a lower surface having a second angle reiative to the plane defined by said edge, wherein said first angle is at least approximately twenty degrees and said second angle is at least approximately twenty degrees.