Improvements in Ventilating Fans of that Class which is Employed in connection with Electric Motors.
Year: 1899

page_text: Date of Application, 12th Sept., 1899-Accepted, 14th Oct.,
1899
COMPLETE SPECIFICATION.
Improvements in Ventilating Fans of that Class which is Employed
in connection with Electric Motors.
--
...*
A communication from abroad by THE EMERSON ELECTRIC MANUFACTURING
COMPANY, a corporation organized under the laws of the State of Missouri,
United States of America, of the City of St. Louis, in said State.
I, PHILIP MIDDLETON JUSTICE, of 55 and 56, Chancery Lane, in the County of
Middlesex, Fellow of the Chartered Institute of Patent Agents, do hereby declare
the nature of this invention and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement:-
This invention relates to a new and useful improvement in ventilating fans
of that class which is commonly employed in connection with electric motors,
whereby a blast of air will be delivered by the fan to keep up a circulation of
the air of the room.
The objects of my present invention are to so construct the blades or flights
of the fan that less power is required to operate the same, and, also, to so con-
struct the fan blades that they will rotate freely and without noise.
The type of blades most usually employed in ventilating fans of this character
are radially disposed from the shaft, and set at a right angle or pitch, each
blade being bent longitudinally so as to shed the air with as little resistance
as possible. The construction of such a blade confines the air delivered practi-
cally at the outer end of the blade, so that, in rotation, a hollow cylinder of
air is thrown forward. In addition to this, the rapidity with which these fan
blades are driven causes the blades to vibrate, resulting in a humming noise
having a slight metallic twang, almost like that of a planing mill in operation.
This noise, as stated, is caused by the rapid rotation of the fan blades, wherein
the air is cut and forced forwardly, there being not sufficient time for the atmo-
sphere at the rear of the blades to rush in to fill the space before the next
blade in succession strikes the air. This action is somewhat like that of a
paddle-wheel of a steam-boat, of course, modified by the different conditions,
and, when the blades slap the air, they are made to vibrate and emit a metallic
whirling sound.
In the construction of the fan blades shown in the accompanying drawings,
I have so formed the blades that the cutting edges are at right angles to the
shaft, so that all the cutting edges of the different blades travel in the same path,
which is only as wide as the thickness of the blade. By doing this, the air is
not rarified or pushed back and forth, as is the case with the old style of blades.
but is gradually drawn in, the bends of the blades forcing it gradually forward
until finally impelled with force, as it is delivered from the blade.
To form a solid column of air, I, also, provide an auxiliary fin at the back of
each blade, so that almost as much air is delivered from a point near the axis
of rotation as is impelled from the periphery of the blades.

page_text: Figure 1 is a plan view of my improved ventilating fan;
Figure 2 is an edge view of the same; and
Figure 3 is a side elevational view of the motor on which my improved fan
is mounted, illustrating, in conventional form, the direction of the air blast by
the fan.
In the drawings, A indicates a spider having as many arms or flukes a as
desired. These arms, as is usual, are arranged at a slight incline or pitch, and
to which blades B are secured by suitable rivets b, or otherwise. Blades B, as
shown in Figure 1, are preferably stamped of suitable metal and, before being
attached to arms a, are slightly bent longitudinally, as shown. The cutting
edge C of the blade has an irregularly curved contour, the portion midway the
outer and inner ends of the blade being most prominent. This curvature is
preferably such that, from a point approximately the length of the blade to its
outermost extremity, the cutting edge recedes in a gradual curve, so that, in opera-
tion, this receding portion makes a shearing cut. When the blades are secured
to the arms a and given their pitch relative to the shaft, the curve at the cutting
edge C would, ordinarily, be out of a straight line relative to the shaft, so that
said blade would be unbalanced. By longitudinally bending the blade, however,
the curved cutting edge C is brought into a plane at right angles to the axis
of rotation of the shaft, as shown in Figure 2, so that, when the fan is rotating,
said cutting edge meets with little or no resistance (only its thickness), and, by
reason of the receding curved portion, the blade easily shears or cuts the air,
forcing (or wedging) the air forwardly.
D indicates the working face of the fan blade, which commences slightly back
of the cutting edge, and continues rearwardly to the rear edge of the blade.
This working face is formed with a fin E obliquely disposed to the shaft, so
that the tendency of said working face, when the fan is rotating, will be to shed
the air forwardly and outwardly, in the shape of a frustum of a cone.
F indicates a fin at the rear edge of the fan blade, which is designed to travel
in a path of less diameter than the fin E. Fin F is bent obliquely, practically
parallel with fin E, so as to form a working face G, whose function is to shed
the air adjacent to the axis of rotation to the fan, and, in this way, form a
solid column of air instead of a hollow cylinder of air as has heretofore been
done by the ordinary straight and radially arranged fan blades.
Of course, it will be understood that, in the event the fan blades are longer,
additional fins can be added to increase the capacity of the blade.
I do not wish to be understood as confining myself to the exact angle at which
these fins are bent, nor to the direction in which they tend to impel the air, as
it is obvious that they can be bent at varying angles to deliver the air in different
directions.
By arranging the arms or supports a with a slight pitch, the fan blades are
given a corresponding pitch. The longitudinal bend, extending nearly through-
out the length of each blade, strengthens said blades considerably to resist
vibration. This bend likewise accommodates the irregular curved cutting edge,
so that said cutting edge will form a straight line at right angles to the axis
of rotation. By aligning the cutting edge of each blade, said blades are not
subjected to back pressure or tortional strain. The fins at the rear portion of
the blade are, by being bent, stiffened to resist tortional strains, and, in operation,
throw large volumes of air with little or no noise. In fact, by the construction
of the blades shown in the drawings, the fan will run at high speeds and do
more work than the old style of fans with straight blades of the same diameter,
and with practically no noise. Of course, the volume of air thrown forward makes
a rushing sound, but the sound is not objectionable as the metallic ring is
entirely absent, and, moreover, this rushing sound of the air cannot be heard
at a great distance from the fan.
I am aware that minor changes in the construction, arrangement, and com-

page_text: bination of the several parts of my fan can be made and substituted for those
herein shown and described, without, in the least, departing from the nature
and principle of my invention.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, as communicated
to me by my foreign correspondents, declare that what I claim is:-
:-
1. The herein described fan blade formed with a curved forward edge, that
portion near the outer edge of the blade gradually receding in a curved line to
effect a shearing cut, and said blade being bent longitudinally to throw said
curved forward cutting edge in a plane at an angle to the axis of rotation, sub-
stantially as described.
2. The combination with a suitable support, of fan blades arranged thereon,
each of said blades being formed with curved cutting edges, that portion midway
the outer and inner ends of the blades being most prominent, from which
prominent portion the outer cutting edges gradually recede to effect a shearing
cut, and said blades being bent longitudinally to align their cutting edges in
the same plane at an angle to the axis of rotation, substantially as described.
3. The combination with a supporting spider, of fan blades B mounted thereon,
said blades being formed with cutting edges C having an irregularly curved contour
the portion midway the outer and inner ends of the blades being most prominent,
said blades being bent longitudinally to bring their cutting edges into the
same plane at right angles to the axis of rotation thereof, the working face D,
which commences slightly back of said cutting edges, and continues rearwardly
to the rear edge of the blade, terminating in a fin E obliquely disposed to the
axis of rotation, whereby the tendency of said working face is to impel the air
forwardly and outwardly in the shape of a frustum of a cone, substantially as
described.
4. The combination with a supporting spider, of fan blades B mounted thereon,
said blades being formed with cutting edges C having an irregularly curved
contour, the portion midway the outer and inner ends of the blades being most
prominent, said blades being bent longitudinally to bring their cutting edges
into the same plane at right angles to the axis of rotation thereof, the working
face D, which commences slightly back of said cutting edge and continues
rearwardly to the rear edge of the blade, terminating in a fin E obliquely dis-
posed to the axis of rotation, whereby the tendency of said working face is to
impel the air forwardly and outwardly in the shape of a frustum of a cone,
and a fin F, also, arranged at the rear edge of the blade, nearer the axis of rotation
than fin E, said fin F being bent obliquely to said axis of rotation to form the
working face G, whose function is to impel the air adjacent to the axis of rotation
of the fan, substantially as described.
Dated the 19th day of Catal
1000