Filter apparatus and method for filtering contaminants from machine tool coolant

A filter apparatus (10) for filtering machine tool coolant is disclosed as including a filter assembly (12) including a foraminous non-reticulated metal screen (30) having minute openings and a smooth planar surface for providing improved scrape cleanability and preventing movement of machining chips, particulate and also elongate contaminants from one side of the filter (12) to the other side thereof.

TECHNICAL FIELD 
This invention relates to filters for filtering industrial liquids such as 
machine tool coolants and more particularly to filtering elongated 
contaminants onto a foraminous surface. 
BACKGROUND ART 
Conventional filter apparatus utilized in machine tool operations of the 
type described in U.S. Pat. Nos. 4,507,061 and Re. 32,135 separate machine 
tool chips and other contaminants from coolant so that clean coolant may 
be returned to the machine tools for reuse. Often times, the contaminants 
are very small and of an elongated shape. Usually one or more horizontally 
disposed filter drums are located adjacent the bottom of a settlement 
tank. A suction is provided by a pump to the interior of the filter drum 
to pull coolant through the filter element to move the coolant from one 
side of the filter to the other. Filter cake, comprised of small chips and 
other contaminants, is formed on the outside of the drum surface. The drum 
is periodically indexed to enable a doctor blade to scrape off a portion 
of the accumulated filter cake, which drops to the bottom of the tank for 
removal by a dragout conveyor. 
The conventional filter element is comprised of a continuous length of 
wedge shaped wire wrapped around a drum-shaped support. The filter element 
thereby includes elongated openings through which some elongated 
contaminants are allowed to pass if the contaminants are aligned in the 
direction of fluid movement as they strike the filter. The passage of 
these elongate contaminants allows the contaminants that pass through the 
filter to be recirculated to the machine tools. 
An alternate type filter system that has been tried is fabricated from 
rectilinear mesh, wire cloth or the like. Although the minute square 
openings formed by the woven wire cloth are effective in preventing the 
passage of elongate contaminants, the surface is not a flat planar surface 
and thus becomes clogged when scrape cleaning is attempted. 
DISCLOSURE OF INVENTION 
An object of the present invention is to provide an improved filter 
apparatus for filtering industrial liquid such as machine tool coolant. 
A further object of the invention is to provide an improved filter 
apparatus having a filter that provides improved scrape-cleanability of 
the filter surface. 
A still further object of the invention is to provide a filter element that 
prevents movement of machining chips, particulate and also elongate 
contaminants found in machine tool coolant from one side of the filter to 
the other side. 
In carrying out the above objects and other objects of the invention, the 
filter apparatus includes a horizontal rotatable cylindrical drum filter 
in a settlement tank having a dragout conveyor. The settlement tank 
contains industrial liquids such as machine tool coolant or the like 
containing machining chips. These chips are found in a wide spectrum of 
particle sizes and shapes, including elongate contaminants. A circulating 
pump creates suction on one end of the drum filter. The drum filter has a 
foraminous surface comprised of a non-reticulated metal screen having 
minute openings and having a smooth planar surface. A doctor means is 
provided for scraping the foraminous surface to remove deposited 
contaminants. The minute openings in the foraminous surface are generally 
in the range of between 50 and 250 microns and provide improved scrape 
cleanability to the surface while preventing movement of machining chips 
(particulate including elongate contaminants) from one side of the filter 
to the other side. 
In a preferred embodiment of the invention, minute openings are generally 
120 microns. In one arrangement of the preferred embodiment, the minute 
openings in the direction of movement are conical in shape tapering 
outwardly in the direction of movement. In an alternative embodiment, the 
minute openings in the direction of movement are hourglass in shape. 
A method for filtering machine tool coolant contaminants including the 
elongate contaminates from the industrial liquid includes the steps of 
interposing a foraminous filter surface perforated with a plurality of 
minute openings configured to pass the fluid while preventing passage of 
contaminant into a flow of the contaminated industrial liquid. 
The objects, features, and advantages of the present invention are readily 
apparent from the following detailed description of the best mode for 
carrying out the invention when taken in connection with the accompanying 
drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to FIG. 1 of the drawings, a filter apparatus for filtering 
machine tool coolant constructed in accordance with the present invention 
is generally indicated by reference numeral 10. As is hereinafter more 
fully described, apparatus 10 includes a filter assembly 12 which is 
easier to keep clean and that prevents machining chips, particulate as 
well as elongate contaminants in the coolant from being recirculated to 
the machine tools. 
Referring again to FIG. 1, a settling tank 14 is set into a pit disposed 
below the floor level or elevation F in an industrial environment. Tank 14 
is generally rectilinear in configuration and has a sloping end wall or 
ramp 16 for use in conjunction with a dragout conveyor 18. Tank 14 is 
comprised of two discrete compartments; a dirty or contaminated coolant 
compartment, designated 20, for receiving dirty coolant from trough T in 
communication with the machine tools, also not shown; and a clean coolant 
compartment 22 for receiving clean filtered coolant from tank 14. 
Within dirty coolant compartment 20, there is provided a horizontally 
disposed drum filter assembly 24 between two parallel sides 26,28 of tank 
14 for filtering the dirty coolant whereby clean coolant filtrate may be 
supplied machine tools as explained hereinafter. Preferably, drum filter 
24, as best seen in FIG. 3, has a foraminous surface 30 comprised of a 
non-reticulated metal screen having minute openings 32, as best seen in 
FIGS. 6-9, and a smooth planar surface. Minute openings 32 are preferably 
in the range of between 50 and 250 microns in diameter and most preferably 
120 microns. In a first configuration, shown in FIGS. 8 and 9, minute 
openings 32 in the direction of coolant movement are conical, tapering 
outwardly. In a second configuration, shown in FIGS. 6 and 7, minute 
openings 32 in the direction of coolant movement are hourglass in shape. 
During operation of the filter apparatus 10, drum filter 24 collects a 
filter cake composed of machining chips (particulate including elongate 
contaminants) from machine tool operations about its surface 30. Coolant 
is moved through the filter cake and surface 30 of the drum filter 24 into 
the interior of the drum. More particularly, a suction is drawn on the 
inside of drum 24 by pump P. Coolant in dirty filter tank compartment 20 
thus passes through the filter cake and drum, and cleaned or filtered 
coolant is supplied by the pump P to the machine tools. 
Dragout conveyor 18 is conventional in construction and serves to remove 
both the solids settled out from the coolant and the filter cake removed 
from the filter drum 24 by a doctor blade 34 shown in FIG. 3, both of 
which settle to the bottom of tank compartment 20. Doctor blade 34 
comprises a non-abrasive material, preferably a flexible plastic material, 
having a leading edge flexed to contact the surface 30 in a parallel 
relationship whereby the surface is easily cleaned. The solids removed 
from the bottom of the tank compartment 20 by conveyor 18 are deposited in 
a suitable receptacle, not shown, at the end of the conveyor. For present 
purposes, it will be appreciated that clean coolant is supplied from the 
interior of the one or more filter drums 24 to the machine tools by 
operation of the pump P hereof. Clean coolant compartment 22 includes an 
elevated or false floor 36 above the lower tank wall bottom and which 
defines a lower chamber 38 for receiving clean coolant from the suction 
side of filter drum via conduit 40. 
Disposed in clean compartment 22 is a main outlet conduit 42 for connection 
with the machine tools. Thus, clean coolant is supplied the machine tools 
from the suction side of filter 24 by way of chamber 38, pump P and outlet 
conduit 42. The purpose of clean coolant compartment 22 is to provide a 
reservoir of clean coolant which can be supplied the machine tools when 
the drum filter 24 is indexed for cleaning. Thus, a valve, not shown, is 
opened affording communication between the clean coolant in chamber 38 and 
the clean coolant in the remainder of clean coolant compartment 22 above 
floor 36. In this manner, pump P suction is applied to the clean coolant 
in compartment 22 to supply coolant to the machine tools. The suction is 
also removed with respect to the inside of the drum filter assembly 24 to 
facilitate cleaning filter cake from the outside surface of the drum. Upon 
closing this valve, pump suction to the filter drum is reestablished, as 
will become clear from the ensuing description. 
Referring now to FIGS. 2 and 3, drum filter 24 is shown to have axial 
extensions at each end, one end comprising a ball duct joint 50, the 
socket 52 of which is placed in an aperture 54 in the side wall 28 of tank 
14; and the other end of which filter 24 is provided with a spring axially 
outwardly pressed cap or pin 56 which in the position shown has an 
over-all length greater than the distance between the wall 26 and the base 
of the socket 52 as shown. Thus, when the filter assembly 24 has its ball 
duct end 50 placed into the socket 52 guided by the U-shaped bracket 58, 
the other end may have its pin 56 pressed against the wall 26 of the tank 
14 so that a resilient means, which may be a compression spring inside an 
axially aligned sleeve in the drum filter 24, will urge the whole assembly 
24 and its ball duct 50 into sealing engagement with the socket 52 
anchored in the opposite parallel wall 28 of the tank 14. Since it is not 
possible to lift the ball duct 50 vertically out of its socket 52 in order 
to remove the drum filter assembly 24, the opposite end with pin 56 must 
be lifted first as shown in FIG. 2 so that ample space above the tank 14 
is had to remove the ball duct 50 from socket duct 52. 
Similarly, in installing the drum filter assembly 24, the same procedure 
must be followed. If desired, the ends of the drum filter assembly 24 may 
be provided with lifting handles 72 as shown in FIGS. 2 and 3, in which 
event it is necessary that the connections 74 between each handle 72 and 
the non-rotatable bearing ends 76 and 76' should be inwardly directed or 
flexible plates to permit clearance from the side walls 26 and 28 as shown 
particularly at the right end of the filter 24. 
In a first arrangement of filter apparatus 10 shown in FIGS. 1-3, the 
filter assembly 12 is a drum filter assembly 24 having foraminous 
non-reticulated metal screen surface 30 providing the filtering. An end 
disc 80 is centrally apertured and may be integral through a hollow hub 
portion 82 with the ball duct 50. Another end disc 84 is also communicable 
with hollow hub portion 82 and may be peripherally serrated to form a 
ratchet wheel engageable by a drive means, not shown, for rotating the 
filter assembly 12 for cleaning. 
In a second arrangement of filter apparatus 10, the drum filter assembly 24 
shown in FIGS. 1 and 2 is replaced by disc filter assembly 24', shown 
partially in FIGS. 4 and 5. Filter assembly 24' is a disc filter assembly 
comprising a plurality of hollow disk filter elements 88 spaced along and 
in communication with hub portion 82 which can, in number, increase the 
filter surface area as compared to a drum filter of the same volume. Each 
disk filter element 88 includes the same foraminous surface 30 and an 
adapted doctor blade 34' for scraping the surface. As seen in FIG. 5, 
coolant is communicated through surface 30 of disk filter 88, whereby 
machining chips, particulate as well as elongated contaminants form a 
filter cake on the surface, and is passed through the hollow disc and into 
hub 82. 
In either construction, clean liquid which passes through the surface 30 
can flow unobstructedly out through the apertured disc 80 and hub 82, ball 
duct 50 and socket duct 52 into a suction duct 92 which may comprise a 
separate chamber on the outside of the wall 28 of the settling tank 12. 
The stationary bearing means 76 and 76' are provided with radially 
outwardly extending flanged wing portions 94 for adjustably supporting the 
flexible plastic scraping or doctor blades 34,34' against the outer filter 
surface 30. The non-abrasive doctor blades 34,34' remove the fine solid 
particles that accumulate and form a filter cake on the foraminous 
non-reticulated surface 30 when the filter 24,24' is indexed at intervals 
by the drive means. During this operation, the suction in duct 92 is 
reduced to aid in allowing the removed particles to settle and be carried 
out by flights 96 of the conveyor. 
While the best mode for carrying out the invention has been described in 
detail, those familiar with the art to which this invention relates will 
recognize various alternative embodiments for practicing the invention as 
defined by the following claims.