Magnetic separator

A separator with a continuously rotating magnetic drum which is partially disposed in a liquid flow path to attract and thereby separate magnetic particles from liquid delivered to the flow path. The separator includes an inclined scraper blade which removes the magnetic particles from the drum. The magnetic field of the drum penetrates the inclined scraper blade causing particles to build up on the blade, thereby allowing coolant which was carried with the particles on the drum to drain back to the flow path. A pushing force caused by particles subsequently delivered to the scraper blade by the rotating drum shoves the buildup of particles past the magnetic field acting on the scraper blade and down a discharge chute into a waste container. A magnetic shunt bar which is located in the rotating drum periodically interrupts the magnetic field acting on the scraper blade so that under conditions where the pushing force of the particles is diminished, the diminished pushing force is sufficient to shove the buildup of particles past the magnetic field and towards the discharge chute.

BACKGROUND OF THE INVENTION 
This invention relates generally to apparatus for separating particles from 
dirty liquid and more particularly to a magnetic separator of the type 
commonly used to clean machine tool coolant by magnetically removing 
entrained metal particles from the coolant. 
In such a separator, dirty liquid is delivered to a flow path defined in 
part by a curved apron extending around the lower side of a rotatable 
drum, the drum having a generally magnetic outer shell. As the liquid 
flows to and around the drum, the particles are magnetically attracted to 
the drum and thus are removed from the liquid. The drum is slowly rotated 
to raise the collected particles out of the flow path and to enable the 
particles to be scraped from the drum and subsequently disposed of in a 
waste container. 
The scraper has an inclined blade which is located in the magnetic field of 
the drum and which is disposed in contact with the outer shell of the drum 
at a position tending to create a dam causing coolant in the collected 
particles to drain back into the flow path and reduce the quantity of 
coolant carried to the waste container. A pushing force caused by 
particles subsequently delivered to the scraper by the rotating drum 
squeezes additional coolant from the buildup of particles at the inclined 
blade. Under most conditions, the pushing force from the subsequently 
delivered particles is sufficient to force the buildup of particles up the 
inclined scraper blade, through the magnetic field and toward a discharge 
chute. However, when the coolant is, for example, a heavy bodied oil, when 
the intrinsic magnetic attraction of the parties to the drum is low, or 
when the collected particles contain a large percentage of non-magnetic 
material, the pushing force is diminished and is insufficient to move the 
buildup of particles through the magnetic field which acts on the scraper 
blade. Under these conditions, some of the collected particles fall back 
into the flow path thereby reducing the efficiency of the separator. 
SUMMARY OF THE INVENTION 
The general aim of the present invention is to provide a new and improved 
magnetic separator by periodically relaxing the magnetic field acting on 
an inclined scraper blade which is removing magnetic particles from a 
rotating magnetic drum thereby enhancing efficiency of the separator under 
some operating conditions. 
A more detailed objective is to achieve the foregoing by providing a low 
reluctance magnetic shunt bar in the rotating drum in order to effect 
relaxation of the magnetic field each time the shunt bar rotates past the 
scraper blade. 
These and other objects and advantages of the invention will become more 
apparent from the following detailed description when taken in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings for purposes of illustration, the invention is 
embodied in an apparatus for removing magnetic metal chips and particles 
from a flow of dirty liquid such as machine tool coolant circulated by a 
machine tool system. The particular apparatus which has been illustrated 
is a magnetic separator 10 (FIG. 1) having a generally cylindrical drum 11 
adapted to be rotated in a counterclockwise direction about a horizontal 
axis, the interior of the drum carrying permanent magnets 12 which create 
a magnetic field around a major area of the outer shell 13 of the drum. 
Located below the drum 11 is an apron 14 which coacts with the drum to 
define an arcuate flow path 15 for the coolant. The apron is in the form 
of a curved metal plate having a concavely curved upper surface concentric 
with and spaced outwardly from the drum. Dirty coolant from the machine 
tool system is delivered to the entry 16 of the arcuate flow path by way 
of a generally horizontal trough 17 and flows downwardly and clockwise 
around the drum. During such flow, the magnetic area of the outer shell 13 
of the drum attracts magnetic chips and particles to separate them from 
the coolant and to form a cake of swarf 18 (i.e., a buildup of particles) 
on the drum. Non-magnetic particles may be also trapped in the swarf as 
the drum rotates. The drum is rotated continuously and at a relatively 
slow rate by means (not shown) connected to a center shaft 19 of the drum. 
As the drum rotates, the swarf is lifted out of the dirty coolant. Cleaned 
coolant spills over the discharge end 20 of the apron and into a clean 
coolant tank 21 for return to the machine tool system by means of a pump 
(not shown). 
The permanent magnet sections 12 are generally cubic and are spaced axially 
along and circumferentially around the internal surface 22 of the shell 13 
of the drum 11. Alternately, the magnetic sections could be longitudinally 
spaced rings or circumferentially spaced bars on the internal surface of 
the shell. The magnet sections are positioned so that like poles of 
adjacent magnets are facing each other. 
The permanent magnet sections 12 (FIG. 2) are separated longitudinally by 
disc-shaped pole plates 23 each having a center opening 24 to receive the 
center shaft 19. The pole plates function to create a uniform magnetic 
field in the longitudinal direction along the drum 11. Spacers 25 are 
slidably located on the center shaft in order to separate and retain the 
pole plates in spaced relation near the axis of the drum. 
The drum 11 is enclosed on its ends by covers 26 each having a center 
opening 27 which slidably receives an end of the center shaft 19. The 
covers are generally dish-shaped and Bach includes an annular rim 28, each 
cover being positioned on the center shaft so that the annular rim faces 
outwardly. Collars 29 are secured to the ends of the center shaft thereby 
retaining the covers on the shaft. The shell 13 of the drum is made of 
material having relatively high magnetic reluctance (e.g., stainless 
steel) and is suitably secured to the annular rims of the covers. 
To remove the collected swarf 18 (FIG. 1) from the drum 11, a substantially 
horizontal scraper 30, located above the drum, has an inclined scraper 
blade 31 which is in contact with the drum. As the drum rotates, swarf is 
peeled away from the drum by the scraper blade. A pushing force caused by 
the supply of particles subsequently delivered to the scraper blade by the 
rotating drum shoves the swarf up the inclined blade and across the 
scraper. The discharge chute 32 is made from a low magnetic reluctance 
material which acts as a magnetic barrier. This barrier permits the 
pushing force to advance the swarf along the horizontal portion of the 
scraper and the discharge chute. The swarf then gravitates down an 
inclined portion 33 of the discharge chute and is collected in a waste 
container 34. 
The inclined scraper blade 31 tends to create a dam causing coolant in the 
swarf 18 to drain back to the flow path 15, thereby reducing the amount of 
coolant that is carried to the waste container 34. To this end, the 
scraper blade is inclined downwardly and towards the direction of the 
oncoming swarf on the rotating drum 11 and is in contact with the outer 
shell 13 of the drum near the twelve o'clock position. The scraper 30 is 
formed from a high magnetic reluctance material (e.g., stainless steel) 
which permits the magnetic field generated by the permanent magnets 12 to 
penetrate the scraper blade. The magnetic field acting on the inclined 
scraper blade tends to retain the swarf on the blade, thereby permitting 
coolant to drain back into the flow path. The pushing force caused by the 
subsequently delivered particles further squeezes fluid from the buildup 
of swarf on the scraper blade. 
Under most conditions, the pushing force from the subsequently delivered 
particles is sufficient to force the buildup of swarf 18 up the inclined 
scraper blade 31 and on toward the discharge chute 32. However, when the 
magnetic attraction or the coefficient of friction between the drum and 
the particles advancing on the drum is low, the pushing force is 
diminished and is insufficient to move the buildup of swarf through the 
magnetic field acting on the scraper blade. This reduced pushing force may 
occur, for example, when the coolant is a heavy bodied oil or when the 
swarf contains a large percentage of non-magnetic material. Under these 
conditions, excess particles fall back into the flow path thereby reducing 
the efficiency of the separator. 
In accordance with the present invention, the magnetic separator 10 is 
uniquely constructed so that the rotating drum 11 periodically interrupts 
the magnetic field penetrating the scraper 30, thereby permitting the 
buildup of swarf 18 on the inclined scraper blade 31 to advance when the 
separator is operating in conditions that result in a diminished pushing 
force. 
More specifically, a shunt bar 35 is located within the rotating drum 11 to 
reduce the magnetic field around a minor area of the drum. The shunt bar 
is made from a low magnetic reluctance material, preferably a low carbon 
steel, to effectively short circuit the magnetic field in that area. The 
shunt bar extends axially along the length of the drum (FIG. 2) and 
creates an arc of reduced magnetic flux around the shell 13 of the drum. 
The space occupied by the shunt bar is unoccupied by magnets 12 and, in 
the present instance, subtends an angle of approximately 20 degrees 
between circumferentially adjacent magnets. 
Each time the shunt bar 35 (FIG. 1) rotates under the scraper 30, the 
magnetic field penetrating the scraper is temporarily interrupted. As this 
happens, the buildup of swarf 18 on the inclined scraper blade 31 is 
temporarily released from the magnetic field, thereby allowing a 
diminished pushing force to advance the swarf forwardly and toward the 
discharge chute 32 to a point at which the low magnetic reluctance of the 
discharge chute will shield the swarf from the attraction of the magnetic 
drum and allow it to migrate to the inclined portion of the discharge 
chute. 
From the foregoing, it will be apparent that the present invention brings 
to the art a new and improved magnetic separator in which the collection 
of magnetic particles is enhanced over prior magnetic separators of the 
same general type by virtue of the provision of the shunt bar 35. The 
shunt bar is relatively inexpensive and enables periodic relaxation of the 
magnetic field in a comparatively economical manner.