Method and apparatus for conveying solid particles to abrasive cutting apparatuses

A method and apparatus conveys solid particles from a supply device to a charging device for charging free-flowing cutting jets. Positive charging of the cutting jets even when located at a greater or remote distance from the supply device is ensured. To that end, the solid particles are transported in a closed circuit between the supply device and a charging or intermediate storage device and the momentarily required partial quantity of solid particles needed for charging the cutting jet is removed from the closed circuit.

CROSS REFERENCE TO RELATED APPLICATION 
This application is related to the commonly assigned, copending U.S. 
application Ser. No. 07/660,936, filed Feb. 26, 1991 and entitled "Method 
and Apparatus For Loading Free-Flowing Cutting Jets With Solid Particles". 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a new and improved method of, and 
apparatus for, conveying solid particles, typically abrasive or grinding 
particles and the like, to an apparatus, particularly a remotely situated 
apparatus for loading or charging free-flowing or fluent cutting jets with 
such solid particles, for instance, fluid jet-abrasive cutting 
apparatuses. Solid particles, preferably in a predetermined quantity, are 
removed from a container or hopper, introduced into a transport or carrier 
medium and in conjunction therewith are delivered to the cutting apparatus 
and held in readiness for charging the cutting jet with these solid 
particles. 
2. Discussion of the Background and Material Information 
Liquid jet-cutting apparatuses, using as the cutting implement a thin, 
free-flowing or fluent cutting jet possessing high kinetic energy, have 
been beneficially employed for cutting sheet- or surface-like materials. 
Abrasive cutting is usually required for this type of processing or 
machining of workpieces or materials possessing high strength, in which 
case the high velocity fluid cutting jet is charged or laden with solid 
particles, that is to say, cutting or abrasive particles or the like. When 
working with abrasive cutting equipment the cutting jet effluxing from a 
nozzle finally flows through a focusing or constricting nozzle. A negative 
or lower pressure is produced in a mixing chamber of the cutting jet 
equipment, by means of which solid particles are sucked out of a container 
or hopper which is preferably equipped with a dosing device. 
Containers or hoppers or the like, which hold in readiness the solid 
particles, are connected by transport or conveying means, such as for 
instance, a hose or a line with the cutting apparatus or cutting head, and 
the conveyance of the solid particles is undertaken by the negative or 
reduced pressure formed in the cutting head. What is disadvantageous in 
this regard is that for an adequate transport of the solid particles the 
transport line or conduit must be of short length, and thus, the distance 
between the container or hopper and the cutting head is essentially 
limited to a maximum of 5 meters. Furthermore, especially when 
interrupting the flow of the solid particles, they tend to settle in the 
carrier medium because of their greater specific weight, and hence, can 
obstruct or clog the transport or connection line or the like. Also, small 
containers or intermediate receptacles are frequently arranged above the 
cutting head in order to improve the delivery of the solid particles. 
Here, upon interrupting the flow of the cutting jet there can arise an 
undesired further feeding of the solid particles into the mixing chamber 
because of the weight of such solid particles. Furthermore, there is 
required a controlled filling of the intermediate receptacle, as a 
function of particle consumption, from a remotely situated supply 
container or hopper. When the solid particles are pneumatically 
transported, there is required an interrupted re-filling operation with 
intermediate pumping empty of the transport or conveying lines. 
In European Patent Application No. 0,152,223, published Aug. 21, 1985, 
there is disclosed a method and apparatus for producing cutting jets laden 
with abrasive particles. Transport of the abrasive or solid particles 
through a distance of 100 meters or more is contemplated. A carrier 
medium, particularly air, is delivered to a venturi, where there are 
admixed abrasive particles furnished from a supply container, the mixture 
is transported and the abrasive particles are removed in a separator and 
delivered by a pipe having a small diameter to a venturi containing a 
high-pressure cutting jet. What is here disadvantageous is that at the 
start of the operation there is required a great deal of time during which 
the abrasive or solid particles are delivered from the supply container to 
the separator. Furthermore, shutting-off of the cutting jet only can be 
feasibly undertaken when the pipe- and infeed line are extensively freed 
of abrasive particles, because otherwise there exists the danger of 
obstructing or clogging this line. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind, it is a primary object of the 
present invention to provide an improved method of, and apparatus for, 
conveying solid particles to abrasive cutting apparatuses in a manner not 
afflicted with the aforementioned shortcomings and drawbacks of the prior 
art. 
Another and more specific object of the present invention aims at the 
provision of an improved method, which while avoiding or at least 
appreciably minimizing the previously discussed drawbacks of the prior 
art, enables delivering solid particles and comparable abrasive particles 
from a supply device to a remotely situated liquid cutting head and 
retaining the delivered particles in a preparatory or ready state for 
charging a free-flowing or fluent cutting jet therewith. 
Still a further important object of the present invention is to devise an 
improved apparatus for conveying solid particles or the like to a 
particle-charging apparatus, particularly a remotely situated 
particle-charging apparatus, in order to ensure for the reliable charging 
of a free-flowing or fluent cutting jet with such solid particles. 
A further noteworthy object of the present invention is the provision of an 
improved apparatus for the efficient conveying of solid particles to fluid 
jet cutting equipment, particularly equipment which is located at a 
considerable distance, the particle conveying apparatus being relatively 
economical in construction and design, extremely reliable in operation, 
and requires a minimum of maintenance and servicing. 
Now in order to implement these and still further objects of the present 
invention, which will become more readily apparent as the description 
proceeds, the solid particle conveying method of the present development 
is manifested, among other things, by the features that solid particles 
are moved in a closed cycle or circuit between a supply device and a 
particle receiving device, in particular a charging device or intermediate 
storage device of a cutting apparatus and there is removed from the closed 
cycle or circuit a quantity of solid particles which serves for the 
charging or loading of the cutting jet. 
Certain of the more notable advantages realized by the present invention 
reside in the fact that holding in readiness or preparing the solid 
particles for charging of the cutting jet in the cutting head can be 
directly accomplished at any time and this can be undertaken independent 
of the operation of the fluid jet cutting apparatus, in other words, of 
the start of the flow of the cutting jet and the flow duration of such 
cutting jet. 
If solid particles in a certain concentration are transported in a carrier 
medium between a supply device and a charging or intermediate storage 
device, then by utilizing suitable means there can be removed at any 
desired point in time a required or desired quantity of solid particles 
from the stream of carrier medium laden with the solid particles. 
It is advantageous if the concentration of solid particles in the infeed 
line or system to the cutting head is accomplished by a dosed addition of 
solid particles to the carrier medium which is free of solid particles, 
and, if desired, recycled solid particles are separated and held in 
readiness for a renewed introduction into the supply device. It is thus 
possible, upon shutting-off the cutting jet, to interrupt or suppress the 
dosing or infeed of the solid particles and to clean the lines or conduits 
by means of the carrier or transport medium. In this respect, it is 
important that there be regulated a pressure at the removal location which 
is lower than the ambient pressure prevailing at this location. 
As alluded to above the invention is not only concerned with an improved 
solid particle-conveying method, but also is directed to an improved 
apparatus for conveying solid particles, wherein connection means between 
the supply device and the charging device for charging the free-flowing or 
fluent cutting jet or jets with solid particles comprises at,/least two 
tubular-shaped means, such as tubular-shaped conduits or lines, for 
instance, channels, hoses, and the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Describing now the drawings, it is to be understood that only enough of the 
construction of the solid particle-conveying apparatus has been depicted 
therein, in order to simplify the illustration, as needed for those 
skilled in the art to readily understand the underlying principles and 
concepts of the present invention. In the schematically depicted exemplary 
embodiments, there is shown an installation for supplying a fluid jet 
cutting device 1 with solid particles, such as pulverulent abrasive or 
grinding particles or grit or the like for charging a cutting jet 11 with 
such solid particles by means of a particle receiving device, such as a 
charging device la of such fluid jet cutting device 1. These solid 
particles are prepared in a supply and/or separator device 2 to be further 
considered hereinafter. By means of a dosing device 3, for example, a worm 
conveyor 33, the solid particles are delivered to a suitable mixing 
element 4, such as a jet nozzle. These solid particles are conveyed by a 
suitable carrier or transport medium, such as a gas, like air, or a dense 
liquid, like water, which enters by means of the infeed means or structure 
51, through a connection means defined by an infeed or delivery line 5 to 
the charging device la of the cutting device or apparatus 1. 
In the charging device la of the embodiment of FIG. 1 or at the region of a 
particle receiving device such as an intermediate storage device 7, as 
shown in the modified embodiment of FIG. 2 which otherwise generally 
corresponds to the embodiment of FIG. 1, there is removed at a hollow 
space or particle circulating passage, by the action of the cutting jet or 
by other suitable means, the momentarily required quantity of solid 
particles from the carrier medium. In the aforementioned commonly 
assigned, copending U.S. application Ser. No. 07/660,936, filed Feb. 26, 
1991, there is disclosed in detail a suitable arrangement for the removal 
of solid particles suspended in a fluid carrier medium from a hollow space 
or particle circulating passage of a fluid jet cutting apparatus and the 
infeed thereof to the fluid cutting jet, and to which reference may be 
readily had and the disclosure of which is incorporated in its entirety 
herein by reference. 
In particular, in FIG. 3, there is depicted a sectional view of the jet 
cutting device or cutting head 1 and charging device 1a in an axial 
direction, the section having been taken substantially along the section 
line 3--3 of FIG. 4. A nozzle device or nozzle 1' equipped with 
high-pressure resistant walls 12' and 13' and a nozzle body 11' for 
forming a fluid cutting jet, such as a water jet, is adjustably and 
detachably connected with an upper housing portion 2' of a housing 2', 3'. 
This upper housing portion 2' possesses a bore or duct 21' through which 
there is flow directed toward the cutting jet. A focusing or constricting 
nozzle 4' provided with a throughflow channel or duct 41' for the cutting 
jet is retained by means of any suitable fixing or securing elements 42' 
within a lower housing portion 3'. 
This lower housing portion 3' is connected by any suitable attachment or 
connecting elements 5', such as threaded bolts, with the upper housing 
portion 2'. Beneath the nozzle device 1' a hollow space or chamber 6', 
constructed as a substantially ring-shaped or annular hollow space, is 
formed by not particularly referenced coacting recesses provided in the 
housing portion 2' and 3', the hollowing space 6' being at least a part of 
the charging device 1a. An infeed means or line 61' for a fluid carrier 
medium, such as a liquid or gas, for instance water or air, entraining the 
solid particles or abrasive grit or the like is arranged neighboring the 
ring-shaped hollow space 6' as is also an outfeed means or line 62' for 
such solid particle-laden carrier medium. When using a liquid as the 
carrier medium for the solid particles there can be advantageously used a 
dense liquid with a buoyancy which essentially corresponds to the weight 
of the solid particles so as to keep them in a state of flotation or 
suspension. An essentially fluid-tight, such as gas or liquid-tight, 
closure means or element 63', like a partition wall interposed between the 
infeed line 61' and the outfeed line 62', closes or interrupts the 
ring-shaped hollow space 6' between these lines or channels 61' and 62', 
preferably at the region constituting the shortest distance between the 
entry locations of the lines or channels 61' and 62', preferably at the 
region constituting the shortest distance between the entry locations of 
the lines of channels 61' and 62' into the ring-shaped hollow space 6'. 
Instead of this arrangement, the ring-shaped hollow space 6' may be 
provided at the same region between the infeed line or channel 61' and the 
outfeed line or channel 62' with an opening or orifice of small 
cross-sectional area. 
The ring-shaped hollow space 6' is connected for flow communication with a 
mixing chamber 33' formed at the upper region of the focusing or 
constricting nozzle 4' by at least one infeed means, typically an infeed 
channel or duct 32' which possesses at least one mouth surface or orifice 
31'. In the embodiment depicted in FIGS. 3 and 4, there are provided, by 
way of example, three infeed channels 32', 32", and 32"' which may be 
arranged at the same or different angular spacing from one another and in 
a star or ray-like configuration. The three infeed channels 32', 32", and 
32"' then have three mouth surfaces or orifices 31', 31", and 31"' flow 
communicating with the ring-shaped hollow space 6'. Each such mouth 
surface or orifices 31', 31", and 31"' preferably may be smaller in size 
than the cross-sectional area of the hollow space 6' and/or the outfeed 
means or channel 62'. 
FIG. 4 depicts in top plan view the ring-shaped or annular hollow space 6' 
with the infeed line or channel 61', the outfeed line or channel 62' and 
the intermediately disposed closure means 63'. As explained previously, 
the ring-shaped hollow space 6' has flow communicating therewith three 
mouth surfaces or orifices 31', 31", and 31"' of the three infeed channels 
or ducts 32', 32", and 32"', respectively, arranged in a star-like 
configuration. 
In accordance with the invention, if the solid particles suspended in a 
carrier medium are introduced through the infeed means or line 61', then 
moved further in the ring-shaped hollow space 6' and outfeed by the 
outfeed means or line 62' and if there is adjusted in the ring-shaped 
hollow space 6' a lower or reduced pressure in relation to the ambient or 
surrounding pressure at the cutting head, in other words, the delivery is 
accomplished with under-pressure or negative pressure, then ambient gas, 
for instance, air is sucked-in through the channel or duct 41' of the 
focusing or constricting nozzle 4' and through the mouth surfaces or 
orifices 31', 31", and 31"' and there is prevented entry of the solid 
particles into the infeed channels of ducts 32', 32", and 32"'. Upon 
turning-on the high-pressure cutting jet there is formed in the mixing 
chamber 33', by virtue of the passage of the high-pressure cutting jet 
through the channel or duct 41' of the focusing nozzle 4', a lower 
pressure than the pressure prevailing in the hollow space 6'. 
Consequently, solid particles are now introduced by means of the infeed 
channels 32', 32", and 32"' into the mixing chamber 33' and the cutting 
jet is effectively charged with these infeed solid particles. An 
interruption in the flow of the cutting jet also brings about an 
interruption in the infed of the solid particles. Furthermore, it is 
possible to align the particle-laden cutting jet in three dimensions, that 
is, to cut omni-directionally, because no use of the force of gravity is 
resorted to for holding in readiness the solid particles. 
Continuing, the carrier medium, which still possibly contains some retained 
solid particles and moving in connection means defined by an outfeed or 
return line or conduit 6 or the like, is delivered to the supply and/or 
separator device 2. This supply and/or separator device 2 can be 
constructed as a cyclone, and it is advantageous if a vacuum removal pump 
21 sucks-off carrier medium essentially free of solid particles out of the 
cyclone by means of the withdrawal line or conduit 22 operatively 
connected with vacuum removal pump 21. In this way, it is possible to 
employ pumps of simpler design and/or to reduce pump wear. 
Additionally, it is advantageous if the pressure of the carrier medium at 
the point of removal of the solid particles, in particular at the region 
of the hollow space of the charging device 1a or the particle circulating 
passage of the intermediate storage device 7, is regulatable and is 
maintained at least equal to but preferably at a lower pressure than the 
surrounding or ambient pressure in order to regulate the flow of the solid 
particles in the closed circuit. Particularly when using long and/or thin 
lines or conduits, carrier medium can be forced by a not here shown but 
conventional pump into the infeed means 51, arranged proximate the supply 
and/or separator device 21, and with the aid of the further pump 21 and 
the outfeed or return line or conduit 6 can be removed by suction from, in 
particular, the supply and/or separator device 2. With such type apparatus 
it is also possible, especially for the introduction of solid particles to 
the intermediate storage device 7, to periodically regulate the pressure 
at the particle circulating passage to be greater than the ambient 
pressure, and thus, to facilitate the removal of solid particles. 
Furthermore, with the aid of a suitable sensor, such as a conventional 
level sensor, there can be determined the available amount of solid 
particles in the intermediate storage device 7 and as a function of the 
removal of solid particles therefrom by the charging apparatus 1 there can 
be augmented or increased the supply of the available amount of solid 
particles. 
Upon placement into operation of the fluid jet cutting apparatus, the 
closed circuit or cycle for the carrier medium can be activated and the 
solid particles infed, that is, delivered to the mixing element 4 in order 
to convey the solid particles. If the cutting jet is turned-off, then the 
addition of the solid particles can be terminated, so that by the action 
of the flowing carrier medium the lines or conduits 5 and 6 can be 
completely emptied and cleaned. Consequently, in a simple manner there is 
enhanced the functional reliability of the apparatus for the conveying of 
the solid particles and there is beneficially increased the degree of 
utilization of the solid particles. 
While there are shown and described present preferred embodiments of the 
invention, it is distinctly to be understood the invention is not limited 
thereto, but may be otherwise variously embodied and practiced within the 
scope of the following claims.