GB2310816A

GB2310816A - A feed mechanism for use in powder spraying utilising a porous member

Info

Publication number: GB2310816A
Application number: GB9704204A
Authority: GB
Inventors: Philip Anthony Evans; Paul Harrison
Original assignee: CERADENT Ltd
Current assignee: CERADENT Ltd
Priority date: 1996-03-05
Filing date: 1997-02-28
Publication date: 1997-09-10
Also published as: GB9704204D0

Description

FEED MECHANISM FOR FREE FLOWING POWDERS This invention relates to a feed mechanism for feeding free flowing powders in spraying applications, including thermal spraying, and the invention also relates to the choice of location of such feed mechanism.

Conventionally, the powder feed mechanism in spraying applications is an integral part of the powder feed unit, the powder being bought in containers and subsequently introduced into a powder hopper, or alternatively the container located into a powder feed block to counter face with the powder feed mechanism.

The present invention permits the powder feed mechanism to be located in the conventional position, or alternatively to be located as an integral part of the original powder container. such that the container becomes the powder feeder and hopper in combination, thus minimising crosscontamination effects for critical applications.

According to the present invention there is provided a feed mechanism for free flowing powders in spraying applications, said mechanism including a member of porous material above which is created a fluidised bed of powder and through which the passage of fluidised powder is promoted Said powder feed mechanism may form an integral part of a powder container or alternatively it may be an integral part of a powder feed unit.

In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example only, reference being made to the accompanying drawings, wherein: Figurs 1 to 3 illustrate conventional arrangements of powder feed mechanisms; Figure 4 illustrates a general arrangement of a powder feed mechanism in accrodance with the invention; Figure 5 is a detailed view of part of Figure 4; and Figures 6 and 7 are detailed views of an alternative arrangement to that shown in Figure 4.

Referring to the drawings and firstly to Figure 1, there is shown a powder hopper 2, which may be pressurised or non-pressurised, containing free flowing powder 4, the hopper being supported on a mounting block 6 incorporating a vibrating mechanism 8. Located in the mounting block 6 and counterfacing with the base (in the drawing) of the hopper 2 is a solid disc or plate 10 having an orifice 12 which may be variable in size. Tubing 14 incorporating an on/off valve 16 connects the hopper 2 to an injector 18 into which a carrier gas is introduced in the direction of arrow 20. From the injector 18, the mixture of powder and gas goes to the spraying process in the direction of arrow 22.

A fluidised bed is created in the hopper 2 due to the vibrating mechanism 8. Powder is drawn through the orifice 12 in the solid disc or plate 0 by the injector 18 which operates via a venturi effect with the flow of carrier gas. The powder is subsequently delivered through a nozzle piece (not shown) to facilitate the spraying process.

It should be noted that the hopper 2 can be supplied as a disposable item, but such a hopper does not contain its own powder feed mechanism. Thus cross-contamination can still occur due to the powder feed mechanism being part of the actual block into which the container/hopper is located. The present invention overcomes this problem.

Figure 2 illustrates an arrangement similar to that shown in Figure 1, such that like parts are given like reference numerals. Beneath the mounting block 6 and vibrating mechanism 8 is a distribution chamber 30 and instead of the rate of flow of the powder being controlled by the venturi effect of the injector 18, it is controlled by a needle valve 32 and the negative pressure created in the chamber 30. The provision of the needle valve 32, having an adjustment head 34, more accurately controls the flow of powder.

In Figure 3, where again like parts to those illustrated in Figure 1 are given like reference numerals, a fluidised bed is created at 40 by the passage of an inert gas usually nitrogen or argon - through a porous material member 42, a vibrating mechanism 44 being located adjacent said member 42. Powder port orifices 46 are provided and the powder is removed from the fluidised bed in the traditional manner using the venturi effect via the passage of carrier gas through the powder port orifices 46, whose number and size may be variable.

Referring now to Figure 4 - which illustrates generally a powder feed mechanism in accordance with the invention there is shown a powder hopper 50, which may or may not be pressurised. With a pressurised hopper, a pressure relief valve/orifice 52 is provided. The hopper 50 contains a free flowing powder 54 and is secured to a mounting block 56 having a vibrating mechanism 58 (which is optional), a seal 60 being provided between the block 56 and the hopper 50.

In the mounting block 56 is a plate or disc 62 of porous material having an orifice 64 (which may be variable both in size and number), the plate or disc 62 being either an integral part of the powder feed unit, i.e. the mounting block 56, or alternatively an integral part of the powder container (powder hopper 50) as will be later explained.

The powder passes through the orifice 64 in the plate or disc 62 of porous material to deliver powder to an injector 66 and thence to the spraying process in the direction of arrow 68, a carrier gas entering the injector 66 in the direction of arrow 70. A fluidising gas is directed to the plate or disc 62 in the direction of arrow 72.

The alternative locations for the porous powder feed mechanism will now be described firstly with reference to Figure 5 and then with reference to Figures 6 and 7.

Figure 5 shows the powder feed mechanism as an integral part of the powder feed unit. The aforementioned mounting block 56 houses at its lowerend (in the drawing) the porous plate or disc 62, the front face 62A of the porous plate or disc being sealed. The orifice or powder port 64 of plate or disc 62 has fluidising gas directed thereto through the porous material of the plate or disc 62 in the direction of arrow 74 so as to create the fluidised bed, the fluidised powder then being drawn downwardly through the orifice or port 64 to the injector 66.

Figures 6 and 7 illustrate a powder feed mechanism as an integral part of the powder container. The powder container 76 - forming the hopper - has a closure 78 formed of porous material, the-closure being fixed to the container at 80. An access point for the fluidising gas is indicated at 82. The closure 78 has a powder port or orifice 78A and a sealed front face 84. The container is supplied with a screw-on top or cover, not shown.

The container 76 is secured to an injector or mounting block 86, referring now to Figure 7, by means of its externally screw-threaded portion 90 engaging an internally screw-threaded portion 88 of the mounting block 86, a seal 92 being provided between the container 76 and the injector or mounting block 86 to prevent the escape of fluidising gas. A second O-ring seal 93 is provided between the sealed face of the porous closure 78 and the block 86 in order to ensure that fluidising gas is channelled through the porous sides of the closure 78 to create a fluidised bed in the container 76. The block 86 has a mechanical groove 94 therein which communicates with a fluidising gas inlet 96.

Although the access point or inlet 96 for the fluidising gas is shown in two dimensions, the fluidising gas may be supplied circumferentially all around the porous material closure 78 by means of the mechanical groove 94 in the injector or mounting block 86.

The sealing of the front faces 62A and 84 of the plate or disc 62 and the closure 78 is important so as to ensure that all the fluidising gas is directed upwardly to fluidise the powder bed or alternatively into the powder port(s) or orifice(s) 64 and 78A to promote the passage of powder to the injector, and the provision of the O-ring seal 93 - as previously mentioned - ensures that the fluidising gas is channelled through the porous sides of the closure 78.

The provision of the previously referred to pressure relief valve/orifice 52 is necessary since the flow of fluidising gas into the powder container or hopper 50 is used to create a positive pressure in the container or hopper and thereby promote the flow of powder through the powder port. The pressure relief valve/orifice also acts as a safety mechanism to relieve any excessive pressure build-up.

A feed mechanism in accordance with the invention ensures that a uniform rate of powder delivery can be achieved in the spraying process, thus negating problems of blockages and pulsing of the powder.

The choice of the location of the powder feed mechanism as an integral part of the original powder container has several advantages: it acts to maintain constant environmental conditions surrounding the powder so as to ensure flowability; it decreases cross-contamination problems and facilitates ease of cleaning of the powder feed unit; the powder feed mechanism becomes returnable/ disposable; and it is economic to produce.

Claims

CLAIMS:

1. A feed mechanism for free flowing powders in spraying applications, said mechanism including a member of porous material above which is created a fluidised bed of powder and through which the passage of fluidised powder is promoted.

2. A feed mechanism in accordance with Claim 1, wherein the fluidised bed of powder is created in a powder container.

3. A feed mechanism in accordance with Claim 1 or Claim 2, wherein said porous material member has at least one orifice therein for the passage of fluidised powder through said member.

4. A feed mechanism in accordance with Claim 2 or Claim 3, wherein said porous material member is a disc or plate which is carried by a mounting block to which said container is secured, sealing means being provided between said mounting block and said container.

5. A feed mechanism in accordance with Claim 2 or Claim 3, wherein said porous material member is a disc or plate which is carried by said container such that said disc or plate is an integral part of said container.

6. A feed mechanism in accordance with Claim 5, wherein said disc or plate forms a closure of said container.

7. A feed mechanism in accordance with Claim 5 or Claim 6, wherein said container is securable to a mounting block, seals being provided between said container and said mounting block and between said disc or plate and said mounting block.

8. A feed mechanism in accordance with any of Claims 3 to 7, wherein said fluidised bed of powder is delivered through the orifice(s) in the disc or plate to an injector and thence to spraying apparatus.

9. A feed mechanism in accordance with Claim 8, wherein said injector is carried by said mounting block.

10. A feed mechanism in accordance with any of Claims 4 to 8, wherein said mounting block is provided with a vibrating mechanism.

11. A feed mechanism in accordance with any of Claims 2 to 9, wherein said powder container has a pressure relief valve therein.

12. A feed mechanism for free flowing powders in spraying applications substantially as herein described with reference to and as illustrated in Figures 4 and 5 or Figure 4 as modified by Figures 6 and 7 of the accompanying drawings.

13. A container for housing free flowing powder for use in spraying applications, said container having a closure which is of porous material and which forms part of a powder feed mechanism for feeding powder from said container to powder spraying apparatus.