Powder feed for underwater welding

An apparatus and method feeds weld material to an underwater plasma transferred arc welding torch. The weld material comprises a powder, which can be entrained in a fluidizing gas flow. The weld material is fed by the apparatus from a first supply through at least one conduit to a supply container. The apparatus comprises a first powder supply pressurized with a powder carrier gas positioned above the surface of the body of water; a second powder supply container positioned below the surface of the body of water and the second powder supply container comprising at least one powder outlet port and a gas vent open to the above surface atmosphere; at least one powder conduit connecting the first container with the second container; an underwater welding torch positioned near the second container and having at least one powder inlet; and at least one powder conduit connecting the second powder supply container to the at least one powder inlet of the torch. The method of underwater welding includes transferring of weld filler powder from the underwater supply container to the torch at a reduced flow rate by venting at least a portion of the carrier gas to the atmosphere above the surface of the body of water.

FIELD OF THE INVENTION 
The present invention relates to plasma transferred arc welding and to a 
welding system which includes a powder delivery system for supplying 
powdered metal from a remote powder feed hopper for welding or cladding 
metal articles and more particularly to underwater welding and cladding 
using a metal powder supplied from a remote source located above the water 
surface. 
BACKGROUND OF THE INVENTION 
The manufacture and repair of many types of devices and structures requires 
the joining of metal parts. Soldering, brazing, and welding are familiar 
generic techniques for attaching metal parts to each other. Of these, 
welding is unique in raising localized regions of the parts to 
temperatures above the melting point of the constituent metals, with or 
without the addition of filler metal, allowing the metals to flow together 
so as to form a unitary body. 
For example, it is often necessary to perform welding under water or other 
fluid for repair of hulls of ships or in heat transfer systems using a 
liquid as a medium of heat exchange. Underwater welding generally uses an 
arc induced plasma with or without a pressurized gas flow to exclude the 
liquid from the immediate vicinity of the weld. However, an exclusion 
region which is necessary to protect an arc or a flame of the welding 
torch providing the welding heat, and the resultant weld pool, is 
difficult to maintain by gas against hydrostatic pressures which occur at 
substantial depths. 
Use of a remote powder source for delivering powdered filler metal welding 
and cladding materials for underwater welding requires use of a long 
conduit relative to standard welding and cladding operations in which the 
powder hopper is close to the welding torch. The friction association with 
distance of travel in the conduit and the back pressure associated with 
the head of water makes it difficult to supply metal powder to the torch. 
To overcome the frictional force and the water head back pressure it is 
necessary to increase the carrier gas flow rate and pressure. Increased 
pressure and flow rate disrupt the plasma arc and result in poor welds. 
SUMMARY OF THE INVENTION 
In one aspect, this invention provides an apparatus for underwater welding 
comprising a first powder supply container pressurized with a powder 
carrier gas positioned above the surface of a body of water; a second 
powder supply container positioned below the surface of the body of water 
and having at least one powder outlet port and a gas vent open to the 
above surface atmosphere; at least one powder conduit connecting the first 
container with the second container; an underwater welding torch 
positioned near the second container and having at least one powder inlet; 
and at least one powder conduit connecting the second powder supply 
container to the powder inlet of the torch. 
More particularly the underwater welding apparatus comprises a plasma 
transferred arc welding torch adapted for operation underwater and having 
at least one powder inlet port; a first powder supply container positioned 
above the surface of a body of water and being connected to a high flow 
rate source of carrier gas and at least one powder outlet port; a second 
powder supply container positioned below the surface of the body of water, 
having a carrier gas vent open to the atmosphere above the surface of the 
body of water and having at least one powder inlet port and at least one 
powder outlet port; and powder supply conduits connecting the first 
container with the second container and the second container to the 
welding torch. 
In another aspect, the invention provides an underwater welding powder 
supply container for receiving powder and carrier gas at a high flow rate 
from a carrier gas pressurized remote source and transferring the powder 
to a nearby underwater welding torch at a reduced flow rate comprising a 
powder chamber, a powder receiving inlet communicating with the powder 
chamber, at least one powder outlet communicating with the powder chamber 
and the nearby underwater welding torch, and atmospheric vent means 
communicating with the powder chamber and the atmosphere. 
In another aspect, the invention provides a method of underwater welding 
which comprises the steps of delivering welding powder entrained in a 
carrier gas at a high flow rate from a remote source located above the 
surface of a body of water to an underwater powder supply container 
located in proximity to the welding torch and then transporting welding 
powder from the underwater supply container to the torch at a reduced flow 
rate by venting at least a portion of the carrier gas to the atmosphere 
above the surface of the body of water. 
An object of the present invention is to provide a technique for welding 
and cladding metals and alloys by plasma transferred arc using a remote 
powder feed hopper and increased carrier gas flow rates and pressure 
needed to bring the powder from the remote hopper to the weld without 
disrupting the plasma arc. 
The invention provides an apparatus and method for making welds under water 
or other fluid without distortion of the weld bead and with reliable and 
uniform delivery of welding material to the weld in a powdered form. 
In accordance with a further aspect of the invention, a method and 
apparatus for welding is provided comprising the steps of or arrangements 
for transporting powdered welding filler material from a remote feed 
hopper at the weld site with a flow of transport gas, venting a portion of 
transport gas, venting a portion of the transport gas from the hopper, and 
feeding the powdered material from the hopper to the welding torch. 
To serve its purpose, the underwater cladding process has to operate 
remotely up to about 100 feet away from the surface to be clad, and under 
about 80 feet of water. The distance of travel, and the back pressure 
associated with the water head presents a problem in the ability to feed 
filler metal powder to the torch. To overcome the water head back pressure 
and the frictional forces associated with powder feed line lengths, we 
must increase powder carrier flows and pressures. The result of the 
increased carrier gas flow rates and pressure is disruption of the plasma 
arc, as evidenced by the formation of poor weld beads. As the flow rate is 
increased, the gas flow from the two powder ports, integral to the torch 
nozzle and adjacent to the plasma orifice in the center of the nozzle, 
impinge on the plasma plume and distort its shape. The result is that the 
powder will reach the work plate, but the weld is distorted. If the flow 
rate is increased further, the weld divides into two separate parallel 
beads. It is believed that the shape of the plasma arc is being distorted 
and ultimately split by the higher flow rates. 
This invention overcomes these problems by delivering powder from a remote 
powder hopper located above the surface of the water pool using a gas flow 
rate sufficient to transport the powder to a gravity feed powder 
distribution hopper located close above the torch and venting the excess 
gas flow from the torch feed hopper so that powder is fed to the torch. 
The invention overcomes this problem by providing a second powder feed 
hopper in close proximity to the underwater welding torch in which the 
high flow rate and pressure of the carrier gas is reduced to the level of 
the gas flow rate and pressure at the site of the weld. This is 
accomplished by venting the second powder feed hopper to the atmosphere 
and controlling the extent of venting to maintain pressure in the second 
hopper at about the level of pressure at the weld site within the 
exclusion device. The second powder feed hopper is referred to hereafter 
as the torch feed hopper.

DESCRIPTION OF THE INVENTION 
The underwater welding system of this invention includes a high pressure 
remote powder feed hopper from which the weld material is delivered to the 
torch feed hopper located beneath the surface of the body of water. It 
also includes a plasma transferred arc welding torch fitted with a water 
exclusion device which protects the arc from the ambient water. The torch 
feed hopper is provided with flow and pressure relief means for venting at 
least a portion of the carrier gas pressure to the atmosphere without 
interrupting the flow of powder to the torch. 
In general, a plasma torch usually includes a central electrode of a 
high-temperature resistant material such as tungsten surrounded by an 
electrode, of generally annular form. The remainder of the torch is 
arranged to direct a high-pressure flow of inert gas at substantial volume 
through the gap between the central electrode and the annular electrode 
which will ionize forming a plasma when an arc is struck between them. A 
gas flow around the outer periphery of the annular electrode also provides 
for protection of the work piece. The plasma flow to the work piece is 
enhanced by the use of a gas lens which focuses the gas flow. The inert 
gas flow causes the plasma to extend outwardly from between the electrode 
to transfer heat to a surface to be heated for welding or cladding. 
A plasma transferred arc torch operates in much the same manner but 
utilizes the surface to be heated as an electrode instead of the annular 
electrode of the plasma torch as described above. The arc is struck 
between the central electrode and the surface to be heated. The plasma is 
transferred to the surface. The inert gas flow serves the same function of 
supplying ionizable gas to the arc for formation of the plasma and to 
protect the arc as well as the molten material of the weld and the 
tungsten electrode. In underwater welding, the inert gas assists in 
formation and maintenance of the exclusion region. 
The overall powder transport system is shown in FIG. 1. Powder weld filler 
material is transported to torch feed hopper 30 entrained in inert gas at 
high pressure and flow rate through hose 35. The vented carrier gas, which 
may contain some amount of powder is carried by pressure relief line 33a 
to a powder collector 36. Separation of residual powder from the gas may 
be enhanced by inclusion of a baffle. For safety, an over pressure relief 
valve may also be provided and will achieve the additional function of 
preventing excessive gas pressure build-up in torch feed hopper 30. 
Separated gas is allowed to flow from the upper portion of powder 
separator and collector 36 through a water vapor filter 37 and a flow 
meter 38. This difference between transport flow and exhaust gas flow can 
be delivered to the torch to assist in powder delivery and maintenance of 
the exclusion region. 
FIG. 2 illustrates the making of an underwater weld using the system of the 
invention. The submerged welding is schematically depicted by a 
fluid-containing tank 40. The torch 10 with inert gas supply line 11, gas 
lens 14, and exclusion fitting 16 are shown assembled and located adjacent 
the surface of substrate 41 at which the weld is to be made. The plasma 42 
extends to that surface. Weld material is supplied through hose 35 to 
torch feed hopper 30. Powdered weld material is transported from the torch 
feed hopper 30 to torch 10 through hoses 39. A plasma transferred arc 
torch being assumed, electrical power is supplied to the torch 10 and 
workpiece 41 through electrical connections 44. Excess gas pressure and 
flow rate is vented by hose 33. 
To make a weld, inert gas such as argon, is supplied through hose 11 to 
develop an exclusion region within exclusion fitting 16. An arc is struck 
in torch 10 which supplies heat to surface 41 and develops a pool of 
molten metal 45 to which powdered weld filler material is added through 
hoses 39. The torch is then moved in the direction indicated by arrow 47 
with the weld bead 45 trailing behind the plasma 42. The size of the 
exclusion region is chosen to be slightly more than the length of the weld 
pool 45 so that the weld will be quenched almost immediately after the 
onset of solidification. 
FIG. 3, shows one embodiment of a torch feed hopper 30. The structure of 
the hopper 30 is similar to fittings such as would normally be mounted at 
the bottom of a gravity fed powder hopper which would be located about 
three feet or less above the torch during welding. Such a fitting can be 
modified by enlarging the inner cavity 31 and providing a hole 32 in the 
supply side of the fitting to which a tube or hose 33 is attached. Both of 
these modifications are facilitated by making the hopper 30 in two 
sections 30a, 30b preferably threaded to each other and sealed with an 
0-ring seal 34, as shown. This torch feed hopper is mounted close above 
the torch and powder is fed to the torch through hoses 39 attached to 
barbed fittings on the lower end of the hopper 30. Two such hoses are 
preferred as a matter of convenience in adapting this feature of the 
invention to existing torches which utilize the surface welding gas 
transport technique described above. More or fewer such outlets could be 
provided, as desired or may be found convenient by those skilled in the 
art. 
By the use of the torch feed hopper 30, a controlled amount of the powder 
transport gas flow can be released through hole 32 and tube or hose 33, 
allowing a much higher gas flow rate to be used to carry the powder from a 
remote above surface powder supply to the torch feed hopper transport. It 
is desirable for a relatively small volume of carrier gas to pass from the 
torch feed hopper to the torch to facilitate powder delivery to the torch. 
In any case, the volume and velocity of gas forced into the nozzle may be 
readily reduced to levels which do not significantly distort the heat 
source and allow a single bead weld to be formed. It should also be 
understood that the principle of bleeding off of additional gas flow used 
to facilitate powder transport can be applied to a hopper of any size. 
However, a small size hopper mounted near or on the torch is preferred 
since it has the advantages of accommodating close clearances to the weld 
location, greater potential reduction of gas flow to the torch consistent 
with good powder feed, and capability of being constructed to withstand 
high internal and external pressures without requiring large amounts of 
material or special structures. The small size is particularly convenient 
since existing hardware can be modified as described above to provide the 
function of improved powder feed without significant distortion of the 
heat source. 
FIG. 4 shows a plasma transferred arc torch 10 is provided with power, 
water and gas inlet connections. The gas is generally divided into a 
so-called plasma center gas flow around a central electrode 11 for 
supplying gas to the plasma and a so-called shielding gas flow which is 
intended to displace ambient gases or liquids and to refine the perimeter 
of the plasma. These gas flows are modified and directed in the immediate 
vicinity of the arc plasma by a gas lens 16. Welding filler material in 
the form of a powder is introduced into the torch at inlets 28. Exclusion 
fitting 12 is located below the gas lens, or can be attached directly to a 
torch without a gas lens. The body of the water exclusion fitting 12 is 
shown as cylindrical but can be any other convenient shape. The diameter 
of the water exclusion device is sufficient to provide an exclusion region 
having a diameter slightly larger than about twice the length of the weld 
pool. Water exclusion device 12 is provided with a surface compliant skirt 
27 which may be formed metal mesh or fibers welded to body 12. 
The escape of gases though the spaces between wires or fibers displaces 
liquids which would otherwise be forced into the exclusion zone by 
hydrostatic pressure. The confinement of the gas by exclusion fitting 12 
allows an exclusion zone to be maintained with reduced gas flow volume by 
maintaining a pressure in excess of the ambient hydrostatic pressure. 
It should also be understood that while the exclusion zone can be 
maintained by a combination of the plasma center gas and the shielding 
gas, possibly supplemented to some degree by the powder transport gas, a 
separate gas supply can be provided for the exclusion fitting itself. 
Therefore, the use of an exclusion fitting as described above need not 
impose any particular limitations of the gas supplies provided for 
operation of the welding torch in the preferred manner. While use of a low 
pressure torch feed hopper with a plasma transferred arc welding torch is 
preferred, use of such a feed hopper in accordance with the invention can 
be used with any heat source including oxy-acetylene and carbon arc 
torches and gas tungsten arc welding torches, gas metal arc welding 
torches, as well as plasma torches described above. 
Increased gas pressure, however, would compromise the delivery of powdered 
weld material to the torch and the weld by conventional arrangements. 
Efforts to improve material delivery by increasing transport gas flow to 
overcome hydrostatic pressure and frictional forces associated with powder 
feed line lengths have been found to distort the shape of the weld 
produced. The known technique of providing powder ports integral with the 
torch nozzle on opposite sides of the plasma orifice at the center of the 
nozzle causes the increased gas flow to impinge on the plasma and distort 
its shape; resulting in the distorted bead described above and in severe 
cases developing two separated weld beads on either side of the intended 
weld location.