Apparatus for the application of blast media onto articles

Abstract

 The current invention relates to apparatus for applying blast media to an accelerated speed onto a surface to abrade the same and treat the same for cleaning or prepare the same for keying of coatings thereon. The apparatus includes an application head (20) including a channel (26) from which the blast media are emitted, a pressurised fluid supply means (22) and a blast media supply means (24) which are connected to the channel (26). The pressurised fluid is introduced through an annular channel (34) around the blast media supply means (24) and the channel is radiussed to improve the velocity of the media and reduce turbulence. The application head (20) can, in a further aspect, be adjustable in terms of the position of the outlet (33) of the blast media supply means (112) in the channel (108) and the application head (102) is provided with a series of ribs (130) which allow the blast media supply means (112) to be maintained in a concentric position relative to the channel (108) in whichever adjusted position.

Description

[0001] The present invention relates to apparatus for emitting blast media onto an article in such a manner that the surface of the article is cleaned or coatings on the article are removed due to the abrasive effect of the blast media. The apparatus can also be used to emit blast media to allow a surface to be prepared for subsequent application of coatings such as paint or plastics or cosmetic finishes.

[0002] At the present time there are two methods for applying blast media to effect impact blasting on an article. The first method is by the impacting of a slurry of blast material on the article and the second is by impacting dry blast media onto the article. This invention is primarily concerned with the second of the two methods, namely the dry blasting method.

[0003] In areas of application and specifically when blasting is used for the preparation of a surface prior to the application of a coating of material thereto, it is often required that the surface be blasted with blast media to roughen the surface and hence provide an improved keying surface which allows the coating applied to key into the surface and hence prevent the coating from flaking off the surface through time due to lack of adhesion between the materials. In general terms the deeper the key produced in the surface the better the adhesion of the coating to the surface. A further problem is that a "striping" effect can be created due to blast media emitted from one area of the nozzle of the apparatus having a greater impact velocity than the media emitted from the rest of the nozzle at any one instant and, as the apparatus is moved across the surface being treated, stripes are created.

[0004] The most common method of applying the blast media in a dry blasting process is to use a pressurised fluid such as a supply of compressed air to pick up the blast media and accelerate the same in the compressed air supply onto the surface through an application head. There are two conventional types of apparatus for applying the blast media using compressed air and these are by suction feeding of the blast media or secondly by providing the blast media in a pressurised chamber.

[0005] In the first method the application head through which the blast media is accelerated onto the surface includes a compressed air supply which enters the application head substantially along the longitudinal axis of the head. There is also provided a supply of blast media which enters the application head downstream of the air supply and at a tangent to the path of the air supply. The compressed air in the application head passes through a small diameter orifice into a larger diameter nozzle and this creates a vacuum within the head which is used to draw up the blast media, so that blast media is ejected from the nozzle.

[0006] The second method is a more complex method and involves a larger number of parts including a pressure vessel in which the blast media is held under pressure. When required the blast media is released into a flow of compressed air and, as the media is held under pressure, the acceleration of the media is substantially greater than that in the first method and typically the acceleration obtained is four times greater. While this method provides improved results over the suction feed method the system is much more expensive due to the cost of manufacture of the parts to meet the relevant safety standards and the high maintenance costs of the apparatus. However, as the acceleration achieved is significantly higher the application of blast media onto the surface by this method produces an improved keyed surface such that, for some surfaces, only the second method can currently be used to produce the required quality of coating on the surface.

[0007] The expense of the apparatus for the second method of application is such that many potential users cannot justify the purchase of the same and due to this they are placed at a disadvantage in that the results achieved using the conventional suction feed apparatus are inferior.

[0008] A further known problem with application heads which are the subject of previous patent applications is that problems occur when the same are provided to be adjustable in that the space between the blast media supply means outlet and the channel walls, which is typically annular and through which the pressurised fluid is supplied, is adjustable to allow the velocity of the pressurised fluid to be adjusted. Typically the adjustment is achieved by the provision of a screw thread arrangement between the blast media supply means and a holder which allows the position of the outlet of the blast media supply means to be adjusted by a screwing or unscrewing action relative to the channel to allow the adjustment of the annular space between the outlet and the channel wall. The problem with this adjustment method and all other known methods is that the position of the blast media outlet relative to the channel is not maintained in a concentric position with the channel in each of the various positions. This lack of concentricity has been found to cause the creation of turbulence at the point of introduction of the pressurised fluid with the blast media which, in turn, leads to uneven impact velocity of the blast media emitted from the application head and uneven treatment of the surface which can cause the striping effect discussed above with the abrasive effect of the blast media stronger at the centre of the area of emission and weaker towards the edge of the area of emission.

[0009] The aim of the present invention is to provide an improved application head for the application of blast media using a suction feed method which achieves levels of acceleration and evenness of treatment and hence surface keying means approaching those achieved by using the pressurised media feed method.

[0010] In a first aspect of the invention there is provided apparatus for applying blast media to a surface, said apparatus including a pressurised fluid supply, a blast media supply and an application head, said application head comprising a channel with an outlet through which the blast media is applied and a first inlet for the supply of blast media and the blast media enters the head substantially in line with said channel and the pressurised fluid passes into a substantially annular passage defined between the channel and the blast media supply means and characterised in that at least a portion of the channel wall is radiussed inwardly to reduce the cross sectional size of the channel.

[0011] In a preferred embodiment the radiussed portion is positioned adjacent the outlet of the blast media supply means.

[0012] Typically the channel cross sectional area is reduced at a point intermediate the outlet of the blast media supply means and the outlet of the channel. Typically the radius is convex.

[0013] In a second aspect the present invention provides apparatus for applying blast media to a surface, said apparatus including a pressurised fluid supply, a blast media supply and an application head, said application head comprising a channel with an outlet through which the blast media is applied and a first inlet for the supply of pressurised fluid and a second inlet for the supply of blast media and the blast media enters the head substantially in-line with said channel and characterised in that there is provided on the interior of the channel a series of protrusions with which the blast media supply means contacts and is maintained in a substantially concentric position within the channel.

[0014] The channel preferably passes along the longitudinal axis of the application head and the blast media is introduced into the channel along the longitudinal axis.

[0015] Preferably the pressurised fluid is compressed air and is introduced into the application head also in line with the channel such that the compressed air passes around the periphery of the outlet of the blast media supply means. Typically the compressed air passes through an annular passage, and the blast media supply means defines the inner body of the same. Preferably the area of the annular compressed air supply is reduced as it approaches the introduction point for the blast media.

[0016] In one embodiment the cross section of the media supply means is reduced in cross sectional area prior to the introduction of the media into the application head to produce a throttling effect on the supply.

[0017] Typically the linear protrusions on the channel wall are ribs which are disposed in parallel with the longitudinal axis of the channel and the ribs are spaced around the channel wall.

[0018] In one embodiment of the invention the position of the outlet of the blast media media supply means relative to the channel is adjustable to allow the annular space between the blast media outlet and the channel wall between which the pressurised fluid passes to be adjusted. Typically the adjustment of the annular space alters the speed of the pressurised fluid into the channel and hence the velocity of the blast media when leaving the application head.

[0019] Preferably the length of the linear protrusions is such as to ensure that the blast media supply means contacts the same in whichever position the same is adjusted thereby maintaining the same in a concentric position with the channel walls.

[0020] In a further embodiment at least a portion of the wall of the channel is radiussed inwardly adjacent the outlet of the blast media supply means to reduce the diameter of the same at a point between the introduction of the blast media and the channel outlet. Preferably the radii are convex.

[0021] In one embodiment the application head comprises two assemblies, a first assembly which includes the outlet and part of the channel and a removable second assembly which includes connections to both the compressed air supply and blast media supply and the remainder of the channel. Preferably the first assembly is provided with the channel in the form of a nozzle shaped to provide optimum discharge of the blast media.

[0022] In one embodiment the application head is provided with a removable handle and/or clamp means to enable ease of holding the same and preferably the application head has the external shape of a conventional suction feed application head.

[0023] Typically the application head is formed from aluminium, polyurethane or a metal alloy to allow the same to be relatively light with the channel of the gun, and, if necessary the blast media and/or compressed air supply means, lined or coated with a hard wearing material such as tungsten, boron, carbide or ceramics to improve the life of the components against wear from the blast media as it is accelerated therethrough.

[0024] Typically the blast media used will be any suitable media but preferably one of grains of aluminium oxide, carbon steel, brass or glass.

[0025] In a further aspect of the invention there is providsed an application head through which blast media can be applied to treat a surface, said application head comprising a longitudinal channel with an outlet through which the blast media are emitted, blast media supply means having an outlet mounted within the channel and defining between the blast media supply means and the channel wall a substantially annular passage through which a pressurised fluid enters the channel to induce the media through the channel toward the outlet and characterised in that at a position removed from the blast media supply means outlet a locating ring is provided and the position of said blast media supply means is adjustable relative to the channel by the selective positioning of a plurality of movable positioning means relative to the locating ring.

[0026] In one embodiment the channel wall is provided with a location means in the form of a stepped portion against which abuts the locating ring and, if so positioned, at least one of the positioning means. In one preferred embodiment the stepped portion is provided as part of an indented portion around the channel wall and which is of a width to accomodate the locating ring and the positioning means.

[0027] Hence the position of the outlet of the blast media supply means relative to the channel is determined by the position of the locating ring in the channel location means. in one embodiment several positioning means are provided and the outlet is in front position hence providing the closest annular space between the channel wall and the outlet when the positioning means are at the rear of the locating ring, the outlet is then moved back to intermediate positions by the placing of one and two positioning means respectively in front of the locating ring in the channel location means and finally can be moved to a position where the space is at a maximum size when positioning means are moved to the front of the locating ring.

[0028] Typically the movable positioning means are washers mounted on the blast media supply means and which can be moved to lie on either side of the locating ring which is provided in a permanently fixed position.

[0029] Typically the channel wall is provided with a plurality of ribs therearound to maintain the outlet of the blast media supply means in a concentric position in the channel in each adjusted position.

[0030] Specific embodiments of the invention are now described with reference to the accompanying drawings characterised in that:-

Fig. 1 illustrates the surface finishes obtained on an article using the two known methods for dry impact blasting;

Fig. 2 illustrates an elevation of a conventional application head for use in the suction feed method of application of blast media;

Fig. 3 illustrates a sectional elevation of a first embodiment of an application head of the apparatus of the invention;

Fig. 4 illustrates a sectional elevation of a second application head of the invention;

Figure 5 illustrates a plan view from the base of the application head of Figure 4;

Figure 6 illustrates an end elevation of the front assembly of the application head of Figure 4 with the handle removed;

Figures 7A- 7D illustrate sectional perspective views in an exploded fashion of the components of the application head of Figure 4.

[0031] Referring firstly to Fig. 1 there is illustrated the contrast between a typical surface finish 2 provided by a suction feed apparatus for applying blast media and the surface finish 4 obtained by applying the blast media using a pressurised system. As is clearly shown, the surface finish obtained by using the pressurised system includes substantially deeper keying recesses 6 than the recesses 8 achieved by using the suction feed method. The ability to provide deeper keying recesses on the surface allows the subsequent coating applied thereto to adhere more firmly by filling in the deeper recesses 6 and thereby allowing substantially stronger coating to surface bonds to be achieved than by using the suction feed apparatus.

[0032] Fig. 2 illustrates a cross section through a conventional application head 10 for use in applying blast media 12 to the surface 2. Also shown is the method of supply and mixing of the blast media and compressed air which carries the media through the application head. The blast media 12 is introduced into the application head 10 via pipe 14 and the compressed air is introduced via pipe 16. The compressed air is introduced in line with channel 18 such that the compressed air flows through the application head relatively undisturbed. As the compressed air passes through the head the blast media 12 are drawn into the flow of the compressed air from the supply pipe 14 which is arranged to enter the channel 18 at a tangent to the flow of the compressed air. As the blast media is drawn into the compressed air flow so the speed of the same is accelerated to a speed to cause an impact effect on the surface 2. However as shown in Fig. 1 the surface effect obtained is not as good as the pressurised feed system and this is largely due to the fact that the appliction head of Fig. 2 does not allow the blast media to be accelerated to a sufficient velocity to have any greater impact on the surface 2.

[0033] Fig. 3 illustrates a cross sectional elevation of an application head according to one aspect of the invention which allows the blast media therein to be accelerated to a greater extent than in the conventional application head of Fig. 2. The application head 20 comprises a compressed air supply 22 and a blast media supply 24 and both the supplies 22 and 24 are positioned to introduce material into the channel 26. The channel has at one end an outlet 28 through which the accelerated blast media leaves the application head 20 and at the other end 30 has a chamber 32 which defines the point at which the blast media comes under the influence of the compressed air.

[0034] The blast media supply 24 is arranged to introduce the blast media into the chamber in line with the channel 26. The compressed air supply is arranged to introduce compressed air into the chamber 32 at a point to the rear of the outlet 33 of the blast media supply 24 such that the compressed air is forced toward the channel 26 through the chamber 32. The chamber includes an annular passage 34 the cross sectional area of which is reduced to the smallest area where the blast media is supplied into the chamber 32. As shown the blast media supply pipe 24 is arranged in the chamber such that it forms the inner body of the annular passage 34.

[0035] As the compressed air passes the outlet 33 of the blast media supply 24 the blast media is induced into the compressed air stream which continues into the channel 26 to the outlet 28. As the compressed air and blast media pass from the chamber 32 into the channel 26 they pass through a reducer 36 which is provided with radiussed walls which are convexly shaped, one such convex shape is to have the walls radiussed to 50mm, but this is only one example. The effect of radiussing these walls is to cause the desired annular air flow and hence reduce the turbulence which is created and hence increase the velocity of the blast media in comparison with the conventional application head such as that shown in Figure 2. The improvement in velocity and reduction in turbulence results in an improved average velocity across the spread of the blast media emitting from the application head which results in better coverage, better impact and a more consistent finish.

[0036] Figures 4,5 and 6 illustrate a second aspect of an application head of the invention which includes the feature of the radiussed channel wall portion 101 as in Figure 3 but illustrates an application head with further inventive features. In this embodiment the application head 102 comprises a body 104 which is provided with a handle 106 by which the same can be held. Passing along the longitudunal axis of the body 104 there is provided a channel 108 into which protrudes the outlet 110 of a blast media supply means 112 which in turn is connected to a blast media supply pipe 114 which enters the application head from the rear 116. At one end 118 of the channel 108 the blast media is emitted from the application head to impact upon the surface to be treated and at the other end 120, a pressurised fluid in the form of compressed air is supplied from compressed air supply means 122 which also is connected into the rear of the application head. The pressurised fluid is introduced into the channel upstream from the outlet 110 of the blast media supply means and passes through an annular passage 124 defined between the channel wall and the blast media supply means 112. As the pressurised fluid passes through the space 124 it acts to pick up the blast media from the outlet 110 and accelerate the same to be emitted from the channel outlet 118. In order to reduce the turbulence at the point of pick up and to improve the ability to have uniform speed of media through the channel 108, the radiussed channel wall portion 101 is provided as discussed and also a series of linear protrusions in the form of ribs 130 are provided at spaced intervals around the channel 108 in a position such that the blast media supply means 112 contacts the same and is thus held in a position which is concentric with the channel 108. This ability to position the blast media supply means 112 in a concentric position relative to the channel 108 has been found to improve the flow of blast media through the channel 108.

[0037] The ability to maintain the blast media supply means in a concentric position is also required when, as in the embodiment shown in Figures 4,5 and 6, the position of the outlet 110 of the blast media supply means 112 is adjustable to alter the size of the annular space 124 and hence adjust the speed of the pressurised fluid and subsequently the blast media from the application head. The provision of the ribs 130 ensure that the concentric position of the blast media supply means is maintained. Also shown are the coatings 133 on the channel 108 of hard wearing material to reduce erosion of the same due to the blast media.

[0038] To allow adjustment of the blast media supply means 112 the same is provided with a fixed locating ring 132 and a plurality of movable positioning means 134 which, in combination, are locatable in a locating indent 136 formed in the channel 108.

[0039] The components of the application head of Figures 4, 5 and 6 are illustrated in more detail in Figures 7A-7D and the same reference numerals are used to indicate the various component parts. The number of positioning means 134 which are placed on either side of the locating ring 132 determine the position of the same relative to the locating indent 136 in the channel and hence the position of the outlet 110 of the blast media supply means 112 can be determined and adjusted to allow alteration of the blast media characteristics while the provision of the ribs 130 with which th blast media supply means 112 contacts, in whichever position, allows the same to be maintained in a concentric position relationship with the channel 108.

[0040] Figures 7C and 7D illustrate a handle 106 which can be fitted to the application head to allow the same to be hand held and a clamping means 140 which can be fitted in substitution for the handle 106 to allow the application head to be maintained in a fixed position.

[0041] Thus the application head incorporating any one, or any combination of, the features described herein represents significant improvements in the quality of control of the blast media emitted from the same and allows a uniform pattern of blast media emission to be achieved and at the same time allows improved large area finishing quality to be improved with the substantial elimination of the striping effect achieved which is of particular advantage with regards to the tratment of surfaces for cosmetic purposes such as glass bottles, perfume botles and also when treating surfaces for keying a coating thereto the keying effect which can be achieved is improved. The ability to adjust the position of the blast media supply means in the channel of the application head in the manner described allows adjustment of the blast media emission characteristics to be achieved whilst maintaining the quality of the same.

Claims

1. Apparatus for applying blast media to a surface, said apparatus including a pressurised fluid supply (22;112), a blast media supply (24;114) and an application head (13;102), said application head comprising a channel (26;108) with an outlet (28;118) through which the blast media is applied and a first inlet (32;124) for the supply of blast media and the blast media enters the head substantially in line with said channel and the pressurised fluid passes into a substantially annular passage (34;124) defined between the channel (26;108) and the blast media supply means (24;112) and characterised in that at least a portion (36;101) of the channel wall (26,108) is radiussed inwardly to reduce the cross sectional size of the channel.

2. Apparatus according to claim 1 characterised in that the portion is positioned adjacent the outlet of the blast media supply means.

3. Apparatus according to claim 1 characterised in that the channel cross sectional area is reduced at a point intermediate the outlet of the blast media supply means and the outlet of the channel.

4. Apparatus according to claim 1 characterised in that the radius is convex.

5. Apparatus according to claim 1 characterised in that the channel passes along the longitudinal axis of the application head and the blast media is introduced into the channel along the longitudinal axis.

6. Apparatus according to claim 1 characterised in that the presurised is introduced into the application head substantially in line with the channel such that the fluid passes through a substantially annular passage defined between the channel wall and the blast media supply means.

7. Apparatus according to claim 6 characterised in that the area of the annular passage reduces toward the outlet of the blast media supply means.

8. Apparatus according to claim 6 characterised in that the cross section of the media supply means is reduces prior to the outlet of the same to form a nozzle.

9. Apparatus for applying blast media to a surface, said apparatus comprising a pressurised fluid supply (122), a blast media supply (114) and an application head (102), said application head comprising a channel (108) with an outlet (118) through which the blast media is applied and a first inlet (124) for the supply of pressurised fluid and a second inlet (110) for the supply of blast media and the blast media enters the head via a blast media supply means (112) substantially in-line with said channel and characterised in that there is provided on the interior of the channel a series of protrusions (130) with which the blast media supply means contacts (112) and is maintained in a concentric relationship relative to the channel (108).

10. Apparatus according to claim 9 characterised in that the linear protrusions on the channel wall are ribs which are disposed in parallel with the longitudinal axis of the channel and spaced around the channel wall.

11. Apparatus according to claim 10 characterised in that the position of the outlet of the blast media supply means relative to the channel is adjustable.

12. Apparatus according to claim 11 characterised in that the position of the outlet is adjustable to allow the size of the annular passage between the blast media outlet and the channel wall to be altered.

13. Apparatus according to claim 12 characterised in that the adjustment of the annular gap alters the speed of the pressurised fluid into the channel and hence the velocity of the blast media when leaving the application head.

14. Apparatus according to claim 9 characterised in that the protrusions are of a length to ensure that the blast media supply means contacts the same in whichever position the same is adjusted to thereby maintain the same in a concentric position with the channel wall.

15. Apparatus according to any of the preceding claims characterised in that at least a portion of the channel wall is radiussed inwardly adjacent the outlet of the blast media supply means.

16. Apparatus according to claim 15 characterised in that the radii are convex.

17. Apparatus for applying a blast media onto a surface including an application head (102) through which said blast media passes, said application head including a longitudinal channel (108) with an outlet (118) through which the blast media is emitted, blast media supply means (112) having an outlet (110) mounted within the channel and defining between the blast media supply means (112) and the channel wall (108) a substantially annular passage (124) through which a pressurised fluid passes into the channel to induce the blast media through the channel (108) toward the outlet (118) and characterised in that at a position removed from the blast media supply means outlet (110) a locating ring (132) is provided and the position of said blast media supply means is adjustable relative to the channel (108) by the selective positioning of a plurality of movable positioning means (134) relative to the locating ring (132).

18. Apparatus according to claim 17 characterised in that the channel wall is provided with a location means in the form of a stepped portion against which abuts the locating ring and, if so positioned, at least one of the positioning means.

19. Apparatus according to claims 17 characterised in that the location means is an indented portion formed around the channel wall and which is of a width to accomodate at least the locating ring and the positioning means.

20. Apparatus according to claim 17 characterised in that the position of the outlet of the blast media supply means relative to the channel is determined by the position of the locating ring in the channel location means.

21. Apparatus according to claim 20 characterised in that three positioning means are provided and the position of the outlet is adjustable between a front position forming the closest annular space between the channel wall and the blast media supply means when the positioning means are at the rear of the locating ring, through two intermediate positions by the placing of one and two positioning means respectively in front of the locating ring in the channel location means to a rear position where the annular space is at a maximum size when the three positioning means are moved to the front of the locating ring.

22. Apparatus according to claim 17 characterised in that the positioning means are washers mounted on the blast media supply means.

23. Apparatus according to claim 17 characterised in that the locating ring is formed as an integral part of the blast media supply means.

24. Apparatus according to any of the preceding claims characterised in that the blast media is any of grains of aluminium oxide, carbon steel, brass or glass.

25. Apparatus according to any of the preceding claims characterised in that the application head comprises at least two assemblies, a first assembly which includes the outlet and part of the channel and a removable second assembly including connections to both the compressed air supply and blast media supply, the blast media supply means and part of the channel.

26. Apparatus according to any of the preceding claims characterised in that the the application head is provided with a removalble handle and/or clamp means.

27. Apparatus according to any of the preceding claims characterised in that the application head is formed from aluminium, polyeurethane or a metal alloy.

28. Apparatus according to any of the preceding claims characterised in that the channel of the gun, and/or the blast media and/or compressed air supply means, are coated with a hard wearing material such as tungsten, boron, carbide or ceramics.

Drawing