GB2173715A - Ceramic welding machine - Google Patents

Abstract

A ceramic welding machine has a sloping side powder hopper (1) above a feed cone (4). Below the cone is a multiple exit feed funnel (5), each exit connecting with a gas acceleration venturi (8). Transport gas is provided through line (9) and control means (10) to the venturi (8), and gas-dispersed powder is carried through line (16) to a lance (13). A remote actuator (14) is capable of initiating or terminating the supply of transport gas to each venturi. Improvements in overall powder flow rate, reliability and control are found, compared to previous machines. <IMAGE>

Description

SPECIFICATION Improved ceramic welding machine This invention concerns an improved ceramic welding machine.

Ceramic welding, also known as refractory flame spraying, is now an established method of repair for refractory lined or refractory brick built ovens, furnaces and the like. Cracks, holes, eroded or spalled areas in refractory may be filled by building up a deposit of sprayed refractory particles. We refer in particular to our UK Patent No. 2.035,524B for a description of an especially preferred method of ceramic welding. The refractory particles to form the deposit originate from a mixture of refractory particles and reactive metal or metalloid particles which combust under suitable conditions to provide heat and to themselves form refractory oxide particles.In the preferred method, in order to provide security against "flash-back", the welding powder is carried in air or another gas which does not support combustion, and the requisite oxygen for combustion is supplied to the powder/air dispersion at a point remote from the powder store or hopper.

Ceramic welding may also be carried out using the apparatus described in UK Patent Specification No 1,330,895, which, because the reactive powder is conveyed in, and stored under, oxygen, requires safety measures which respond to the detection of a "flash-back" situation. As can be seen from the two specifications referred to above, feeding powder from the hopper containing bulk powder may be achieved by a screw feeder (No. 2,035,524B) or a rotating table with a stationary paddle or plough forcing powder into a feed funnel.

We refer also to UK Published Application No 2,103,959A and 2,110,200A for variations on the known processes and methods.

We have now developed a ceramic welding machine which provides greatly improved flexibility and improved delivery rates of powder, enabling more efficient ceramic welding to be performed, compared to known machines.

According to the present invention, a ceramic welding machine comprises a sloping side powder hopper with a bottom exit aperture, a feed cone mounted underneath said aperture and presenting an annular gap therebetween, a powder receiving funnel mounted below said feed cone and having two or more powder exits, each exit connecting with a gas acceleration device having an inlet for transport gas and an outlet for gas-dispersed powder, vibration means to assist powder flow through said hopper and funnel, a powder delivery lance connected to the outlets from the gas acceleration devices, a source of oxygen for combustion of the powder and connected to the lance, a transport gas supply pipe connected through control means to each gas acceleration device inlet and a control means actuator remote from the control means and capable of initiating and terminating supply of transport gas to each gas acceleration device.

The feed cone and vibration means together provide specially reliable feeding of the type of pow der used in ceramic welding process, with greatly minimised frequency of blockage, compared to previously used equipment. For example, a rotat ing feed table and plough arrangement has been observed to give classification of the powder into a finer and a coarser fraction, and the resulting concentration of coarser material has given blockage of the arrangement for dispersing powder in transport gas. The feed cone need not be a geometric cone, but may be a dome; however, it is preferably a cone. The gap between the cone and the bottom edge of the powder hopper is suitably 1 to 30mm, preferably 2 to 25mm, especially 3 to 10mm. The minimum gap will generally be governed by the maximum particle size and the maximum gap determined by the optimum throughput.The gap is desirably adjustable.

Suitably, for simplification of the machine, a single vibration means is used, preferably this incorporates a transport gas driven motor. Most preferably, a transport gas driven motor is driven by a gas bleed downstream of the control means actuator so that a single actuation of the control means actuator is effective to stop or start the vibration means in addition to controlling the flow of transport gas. The frequency of the vibration means may be adjustable.

The powder receiving funnel has preferably two or more outlets, to each of which is attached a gas acceleration device. exit. Initial tests surprisingly indicate that the use of a gas acceleration device, preferably a venturi, having a feed bore for powder feeding to the low pressure part of the venturi, gives a greater overall flow rate of powder than a single exit powder receiving funnel with a larger venturi and that this finding still applies when the two flows of dispersed powder are combined into one using a reverse Junction. Alternatively, the use of twin powder exits and gas acceleration devices enables a twin lance to be used, if desired, or two (or more) single lances. Equipment incorporating the twin exit funnel and two venturis has been found in practical tests to give a 50-60% greater throughput of powder, compared with a single exit funnel.

Preferably, the powder hopper incorporates a detachable powder receiving container having a coarse grid bottom, so that a charge of powder emptied from a drum or bag therein is sieved by the transmitted action of the vibration means, and grossly oversize material which may contaminate the powder because of the working environment of, for example, a coke works, is not allowed into the hopper.

The remote control means actuator is suitably mounted on a handle part of the lance, and is conveniently of switch or trigger form operating a valve on a transport gas bleed from the upstream side of the control means. Accordingly, it is preferred that the remote control means actuator operates, by gas pressure, a main transport gas valve in the control means. The actuator is thus capable of more or less instantaneous shutting off of the powder transport gas supply (and preferably stop ping the vibration means), and this enables the operator to control operation of the ceramic welding to a degree never before possible. The lance preferably also carries a control valve for the oxygen supply; it will be found in the event of terminating the transport gas supply, the flow of oxygen will carry out from the lance any remaining powder.

Suitable control means are commercially available, or may be adapted from commercially available valves by a competent workshop, and a Martinair valve has been found to give satisfactory service.

Preferably, the hopper and the funnel are of circular cross-section where possible; powder flow has been found to be improved in comparison with square-section or other shapes. In the preferred apparatus according to the invention, powder flow problems are minimised, and bridging, rat-holding and other common problems are rarely met with.

Since the physical characteristics of the powder itself effect its ability to flow readily (e.g. characteristics such as size range distribution, surface area and moisture content), it will be understood that a satisfactory powder should be used.

Although the supply of transport gas may be a cylinder or tank of compressed gas, it is convenient to use the compressed air line frequently found on industrial sites. It is preferred in such a case, to incorporate a drier, to reduce the chance of damp transport air causing agglomeration of powder in the gas acceleration device or in the line to the lance, and possible blocking of these.

The invention will now be described with reference to the accompanying drawings, in which Figure 1 is a schematic end view of part of a ceramic welding machine according to the present invention, and Figure 2 is a schematic side view of the apparatus of Figure 1.

Referring to the figures, the machine has a sloping side frusto-conical powder hopper 1, with a vertical top line into which a removable powder receiving container 2, with a wire grid bottom 3, is normally fitted. Mounted below the hopper and on a threaded shaft is a feed cone 4, so that an adjustable annular gap exists between the hopper and the feed cone. In a prototype apparatus a gap of about 5 mm. was generally found to be satisfactory. Below the feed cone is a powder receiving funnel, 5, having a bifurcation into two exits, 7.

Firmly attached to the side of the funnel 7 is an air operated vibrator 6, and rigid metal straps (not shown) connect the hopper, feed cone and funnel together so that the vibrations induced in the funnel are transmitted to the hopper, feed cone and the container, 2.

Each exit from the funnel is connected, preferably by a short flexible plastic hose (not shown) which does not significantly transmit vibrations, to a venturi drilled in a metal block 8. A powder feed bore is drilled into the low pressure part of the venturi, and some air will be drawn into the venturi along with powder in the funnel. A compressed air line 9 is connected to a control block 10 which contains an internal valve actuated by compressed air. An air bleed line, 11, with regulating valve, is taken from the control block downstream of the control block valve to the air motor of the vibrator 6.Air bleed line 12, taken from upstream of the control block valve, is taken to the handle region of a lance 13, where a quick-action On/Off valve 14 controls the return flow of air through line 15, to the control block 10, where it controls the position of the valve. A regulated pressure air supply is connected to venturi block 8, where the air picks up and disperses powder which is carried through line 16 to the lance 13. The two lines carrying the powder dispersed in air may be merged by a Y-piece connector (not shown) to feed line 16.

Oxygen, conveniently supplyed from a cylinder (not shown) is fed through line 17, and preferably through a gas acceleration device (not shown) to the lance, where it mixes with the powder carried in air to create a combustible mixture which may be ignited upon leaving the lance and creates a spray of molten and/or sinterable refractory particles for repair of coke oven or furnace walls, roofs etc. The spray from the lance may be concentrated into a wedge or fan shape to more easily repair certain cracks, especially vertical cracks, by fitting a cone-shaped adaptor having a rectangular outlet, on to the end of the lance, which may be a single, twin or multiple lance. The, or each, lance may be water-cooled.

A charge of welding powder is emptied into container 2, and is sieved into hopper 1 by the vibration of vibrator 6. The powder trickles in a constant flow around the edges of cone 4, and the rate of flow is easily controlled by adjusting the speed of the vibrator 6 and adjusting the cone/hopper gap.

The powder is thus fed at a constant rate of up to about 50 kg/hr. into the two exits 7 from the funnel, and is dispersed in the air stream flowing through the venturi blocks 8.

The present invention has demonstrated several advantages over known ceramic welding machines, particularly an increase in powder delivery rate to the lance, substantially constant powder flow with a significant reduction in blockages throughout the machine and greatly increased ease of use for the operator who is thus able to concentrate his skill on making high quality repairs.

Claims (12)

1. A ceramic welding machine, comprising a sloping side powder hopper with a bottom exit aperture, a feed cone mounted underneath said aperture and presenting an annular gap there between, a powder receiving funnel mounted below said feed cone and having two or more powder exits, each exit connecting with a gas acceleration device having an inlet for transport gas and an outlet for gas-dispersed powder, vibration means to assist powder flow through said hopper and funnel, a powder delivery lance connected to the outlets from the gas acceleration devices, a source of oxygen for combustion of the powder and connected to the lance, a transport gas supply pipe connected through control means to each gas acceleration device inlet and a control means actuator remote from the control means and capable of initiating and terminating supply of transport gas to each gas acceleration device.

2. A welding machine according to Claim 1, wherein the annular gap between the powder hopper and feed cone is adjustable.

3. A welding machine according to Claim 2, wherein the gap is adjustable from 2 to 25 mm.

4. A welding machine according to any one of the preceding claims, wherein the vibration means comprises a transport gas driven motor.

5. A welding machine according to Claim 4, wherein the frequency of the vibration means is adjustable.

6. A welding machine according to any one of the preceding claims, wherein the gas acceleration devices are venturis.

7. A welding machine according to any one of the preceding claims, wherein the remote control means actuator operates a valve on a transport gas bleed from the upstream side of the control means.

8. A welding machine according to any one of the preceding claims, wherein the remote control means actuator operates a main transport gas valve in the control means.

9. A welding machine according to any one of the preceding claims, wherein a powder delivery lance is connected to each gas acceleration device outlet.

10. A welding machine according to any one of Claims 1 to 8, wherein a single powder delivery lance is connected to all the gas acceleration device outlets.

11. A welding machine according to Claim 1, substantially as hereinbefore described.

12. A method of ceramic welding comprising the use of a machine according to any one of the preceding claims.