GB2398080A

GB2398080A - Powder injection apparatus

Info

Publication number: GB2398080A
Application number: GB0301530A
Authority: GB
Inventors: Michael Bernard Coupla Quigley
Original assignee: QUIGLEY ASSOCIATES
Current assignee: QUIGLEY ASSOCIATES
Priority date: 2003-01-23
Filing date: 2003-01-23
Publication date: 2004-08-11
Also published as: GB0301530D0

Abstract

Powder injection apparatus for use with thermal spraying systems where particles of mixed size 15, are injected into the curved injector channel 21 via carrier gas 22 causing the separation of the heavy and light particles in the flow stream. Baffles 23 (figure 3, 31 and 32) can also be inserted to further separate the particles. The apparatus can be machined from a solid bar.

Description

This invention relates to thermal spraying processes and is most

particularly concerned with the control of the injection of the powder particles into the plasma, flame, gas jet or shock front.

i. Thermal spraying processes typically generate a high temperature plasma, flame, gas jet or shock front, hereinafter to be call the jet, in order to heat and propel powder particles towards the substrate to be sprayed. These particles then impact on the surface and fomm a specialised coating which will protect the substrate from corrosion, erosion or both or to impart special properties such as low friction. In most spraying processes powder is injected into the plasma or flame from a side port. It is thus imperative to arrange that the powder particles are injected into the jet at a speed such that they reach the centre of the jet and are carried along axially towards the workpiece.

As the particles typically have a range of sizes of 3:1 the mass of the individual particles will vary by a factor of 27:1. As the particles are injected into the jet the lighter particles will tend to bounce off the jet whereas the heavier ones will tend to penetrate through the jet. In both cases the particles will not be propelled axially through the plasma; the lighter ones will be overheated, oxidise and tend to form a Fog" above the jet and will create oxide on the workplace and in the coating. The heavier particles will not be heated sufficiently to enable melting to take place and will result in a number of unfused (i.e. loose) particles being present in the coating. Current folder type" spray systems have this type of powder injection and are renowned for their Spray droop" problems. With this phenomenon the spray pattern tends to be below that of the aiming point. In practical terms the spray stream does not go where it is aimed resulting in a loss of efficiency and productivity and an increase in environmental issues such as powder recovery and handling. Many of the powders involved in these processes are hazardous and it is essential that both the fume and the powder residue are kept to a minimum.

ii. The principle of this invention is to separate the different sized particles into different positions for injection into the jet. In this way the heavier particles would be injected into the jet at a position close to the end of the nozzle and thus be in the jet for the longest period. They would thus be melted and accelerated to much higher velocities than normally. Conversely the smaller particles will be injected into the plasma at a position much further away from the torch nozzle and therefore receive less heating than before and oxidation will be prevented.

The particles of median size will be injected into the mid part of the jet and will be heated and accelerated nominally.

iii. To achieve this separation it is necessary to design an injector which automatically arranges the particles into the appropriate sizes. The general principle is that of a cyclone type system so that the particles are blown into the injector, the powder and gas is swirled and the powder then issues from, initially, three ports which are then sited along the sides of the jet in the appropriate positions.

In UK Patent GB 2300649B Quigley Associates disclosed a device which would achieve the above objective. The present application takes this approach further.

Instead of having tubes to carry and separate the powder, channels are machined in a solid bar and a simple baffle provides the separation. The new principle behind this application is to make it possible for the separation baffle to be positioned at various points around the radius of the channel so that adjustments can readily be made for different powders and mixes. This application also discloses the possibility of having numerous loops so as to ensure full separation before the baffles are reached.

Referring to Figure 1 as an example there is shown an electrode 11 in a plasma torch 12 and the plasma jet generated is shown as 13. The powder injector 14 injects the powder 15 into the jet 13. The lighter particles will be convected upwards as 16, the heavy particles will pass through the jet as 18 and the medium sized particles will form the useful spray 17.

Referring to Figure 2 there is shown the proposed design of a new powder injector nozzle. The particles of mixed size 15 are injected into the injector channel 21 by means of powder feed carrier gas 22. The injector channel is typically of curved shape that causes the particles to separate around the curve.

A baffle 23 is inserted to physically separate the already partially separated particles and send them into tubes 24 and 25 representing the exit tubes for the finer and heavier particles respectively.

A further embodiment might be to have 3 or more separations with two or more baffles as shown in Figure 3. Referring to Figure 3 there is shown the proposed design of a new powder injector nozzle with 3 separations. The particles of mixed size 15 are injected into the injector channel 21 by means of powder feed carrier gas 22. The injector channel is typically of curved shape that causes the particles to separate around the curve. Baffles 31 and 32 are inserted to physically separate the already partially separated particles and send them into tubes 33, 34 and 35 representing the exit tubes for the finer medium and coarser particles respectively. \

Claims

What we claim is 1.powder injection apparatus, the apparatus comprising a

casing having an inlet orifice, a number of outlet orifices and internal baffles so disposed as to separate the heavy particles from the light particles.
2. powder injection apparatus as claimed in claim 1 in which the outlet orifices are of a size such that the heavy particles will enter the jet a similar distance to the lighter particles
3. powder injection apparatus as claimed in claim 2 in which the outlet orifices are positioned such that the heavier particles will enter the jet upstream of the lighter particles
4. powder injection apparatus as claimed in claims 2 and 3 in which a number of outlet orifices are disposed along the jet.
5. powder injection apparatus as claimed in claims 14 in which a number of loops of the tube or hollow is used to separate the particles. powder injection apparatus Amendments to the claims have been filed as follows 1. Powder injection apparatus in which the powder to be sprayed is transported along a channel with baffles positioned at points along the channel to separate out the heavier and lighter particles.

2 Powder injection apparatus as in claim 1 in which a number of loops of the channel are used to ensure better separation of the particles.