Abrasive slurry supply system for use in metallographic sample preparation

An alumina slurry supply system for use in conjunction with a polisher or grinder apparatus or the like for preparing the surfaces of metallurgical specimens, the system comprising an alumina slurry reservoir, a recirculation pump disposed in the reservoir, an applicator arm for dispensing the abrasive slurry to a platen or lapping wheel of the polisher or grinder apparatus, a first conduit for receiving slurry pumped from the reservoir, a second conduit connected to the first conduit for recirculating the slurry to the reservoir, a third conduit leading from the first conduit to the applicator arm, a valve in the third conduit movable between an open position to supply abrasive slurry to the applicator arm and a closed position in which all abrasive slurry pumped from the reservoir is recirculated thereto, and a timer for controlling the operation of the valve.

BRIEF SUMMARY OF THE INVENTION 
The present invention relates to a system for supplying alumina or other 
abrasive slurry from a reservoir to an applicator arm for dispensing on a 
rotatable platen or lapping wheel or the like of apparatus used in the 
surface preparation of metallurgical samples. It is known in the art to 
use alumina or other abrasive slurry in the preparation of metallurgical 
samples, as in the polishing, grinding or lapping of the surfaces of such 
samples. However, such slurry is difficult to circulate, and if any 
settling out of the abrasive particles occurs they have a tendency to 
cause clogging of the system. It is desirable where possible to maintain 
such slurry in an agitated state continuously to prevent settling of the 
alumina particles, even though it is normally desirable to operate such a 
system intermittently by supplying abrasive slurry to the lapping 
apparatus only at timed intervals. 
It is therefore an object of our invention to provide an alumina or other 
slurry supply system designed to continuously pump slurry from a reservoir 
to a conduit for recirculation to the reservoir, while utilizing timed 
valve means to determine when a selected portion of the slurry is to be 
conducted to an applicator arm for use in the preparation of metallurgical 
specimens. 
Another object of the invention is to provide a slurry supply system as 
last above-mentioned including an applicator arm disposed at a higher 
elevation then the reservoir and conduit, and used in conjunction with a 
normally-open valve in the conduit which supplies the applicator arm, 
thereby permitting the applicator arm and conduit to drain back to the 
reservoir whenever the system is turned off. 
Still another object of our invention is to provide improved means for 
controlling the volume and pressure of alumina slurry supplied to the 
applicator arm for use in the preparation of metallurgical specimens. 
The foregoing and other objects and advantages of our invention will be 
apparent from the following description of a preferred embodiment, taken 
in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawing, there is shown a reservoir 10 for containing 
a supply of alumina or other abrasive slurry for use in the surface 
preparation of metallurgical specimens. It will be understood such alumina 
slurry is known in the art for use in the preparation of metallurgical 
specimens, and that the slurry supply system of the present invention is 
also well adapted for use with other types of slurry utilized for such 
specimen preparation. 
A recirculation pump 12 includes a pump motor 14 and an outlet tube 16 for 
pumping the abrasive slurry from reservoir 10 through a first conduit 18 
to a tee fitting 20. The tee fitting 20 communicates both with a valve 22 
and also with a second conduit 24. The conduit 24 leads back to the 
reservoir 10 through a globe valve 26. On the other hand, the valve 22 
leads to a third conduit 28 of an applicator arm 30 having a nozzle 32 for 
spraying abrasive slurry to a rotatable lapping wheel or the like (not 
shown) of apparatus for the surface preparation of metallurgical 
specimens. The electric pump motor 14 is connected to a source of power 
through lines 34 and 36, and a switch 38 is provided for starting and 
stopping the pump. 
When the slurry supply system of the present invention is on, pump 12 is 
operated continuously to pump the alumina slurry from the reservoir 10 
through conduit 18. If valve 22 is closed, the entire amount of such 
slurry will be recirculated back through conduit 24 and valve 26 to the 
reservoir. The position of valve 26 may be varied, as will be described 
later herein, but it must of course be partly open to permit the 
recirculation of the slurry by pump 12 as described. When valve 22 is 
open, a portion of the slurry from conduit 18 will pass through valve 22 
and third conduit 28 to the applicator arm nozzle 32 from which it will be 
dispensed to the sample preparation apparatus. 
Valve 22 is a normally-open solenoid operated valve controlled by a timer 
40. When timer 40 is "off", valve 22 is open, and alumina slurry is 
dispensed from applicator arm 30. When timer 40 goes "on", valve 22 closes 
and the supply of slurry to the arm 30 is cut off. The timer 40 is 
preferably set to be "off" for a predetermined fixed time, such as 0.5 
seconds, whereas the ontime may be varied between 0.8 to 18 seconds. Thus, 
valve 22 is controlled to permit applicator arm 30 to produce intermittent 
dispenses of slurry, each spray lasting for a duration of 0.5 second, and 
the interval between such intermittent sprays may be varied from 0.8 to 18 
seconds. 
The solenoid operated valve 22 is controlled from an electrical power 
source through leads 42 and 44, and the foregoing circuit includes switch 
38a which operates in conjunction with switch 38. Timer 40 and manual 
override switch 46 are also connected in the foregoing circuit. The timer 
40 is of known type and is set for the desired interval which as indicated 
above is preferably in the range of 0.8 to 18 seconds, for example, 8 
seconds. Thus, in the foregoing example, every 8 seconds the timer will go 
"off" to permit valve 22 to open, thereby causing slurry to be dispensed 
from applicator arm 30 for a duration of 0.5 second, the switches 38 and 
38a being closed during operation of the slurry supply system. 
Whenever it is desired to supply additional slurry to the associated 
apparatus for surface preparation of metallurgical specimens, an operator 
need only manually open switch 46 to override the system and turn "off" 
the timer, thereby causing additional spray of slurry. Such an override of 
the timer may be desirable to load-up a lapping wheel with abrasive slurry 
at the beginning of a lapping operation. 
One of the advantages of the slurry supply system of the present invention 
is that the slurry is continuously recirculated when the system is "on", 
thereby keeping the alumina particles in suspension and preventing 
settling out which tends to cause clogging of the system. By setting valve 
26 in a selected position, it is possible to control the amount of slurry 
conducted to the applicator arm 30 and the amount of slurry which is 
recirculated, as well as the pressure of the slurry supplied to applicator 
arm 30. Thus, by opening valve 26, the amount of slurry conducted to arm 
30 is reduced, as is the pressure of that slurry. On the other hand, by 
closing down valve 26, more slurry is conducted to applicator arm 30, and 
at a higher pressure. 
It is also an advantage of the present system that applicator arm 30 is 
located at the highest point in the system, reservoir 10 is at the lowest 
point, and valve 22 is normally open. The result is that whenever the 
system is turned "off" by opening switches 38 and 38a, the alumina slurry 
is permitted to drain from the arm 30 and associated tubing back to 
reservoir 10, thereby minimizing settling and the creating of blockages in 
the passages. 
It is also a feature of the present invention to provide timer 40 in 
conjunction with normally-open valve 22, so the timer's contactor opens 
periodically to permit valve 22 to open and cause a portion of abrasive 
slurry to be emitted from applicator arm nozzle 32. It will be noted that 
after the timer is set, it is activated at the same time that 
recirculation pump 14 is turned "on", through closing of switches 38 and 
38a.