Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND 0~ THE INVENTIQN
Field of the Invention
The invention relates to electrically heated screens,
and particularly to rail members which extend longitudinally
along~the edges of the screen for mounting and tensioning the
screen on a paiI of spaced side frame members. More particu-
larly, the invention relates to a tensioning rail having a
wedge-shaped clamping bar which securely clamps the screen edge
to the rail and which provides an improved electrical connection
between the rail and screen.
Description of the Prior Art
Screen assemblies have been used in industry for many
years for screening of materials. The screens may be oscillated
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1 mechanically to assist in screening the material, or may be sta-
tionary. In either case the screen is heated electrically to
reduce binding and clogging of the screen openings. Examples
of such electrically heated screen constructions and the means
for electrically heating the same are shown in my previously
issued U.S. Patents, Nos. 2,704,155, 2,812,062, 2,825,~61,
3,154,757, and 3,195,725.
Screen constructions of the type shown in my above-
identified U.S. patents and in other screen assemblies have
rails which extend longitudinally along the edges of the screen
or screen panels for mounting and tensioning the screen cloth
or fabric on a pair of associated side frame members. These
tensioning rails generally are formed of metal having good
electrical conducting characteristics and ar0 connected to a
source of electrical power which is transferred through the rails
to the metal screen material for heating the same. The rails,
in turn, are mounted on the side frame members and are electri-
cally insulated therefrom by various ~;nsulating means.
The screen edges are connected by various means to the
tensioning rails in order to provide an electrical connection
between the rail and screen and to provide means for tensioning
the screen between the spaced side frame members. Various types
of connections have been devised for both electrically heated
screen constructions and for mechanically oscillated screen
constructions.
One type of screen connection consists of a pair of
mutually engaged, reversely angled brackets, sùch as shown in
U.S. Patents Nos. 1,353,549 and 2,052,467. Another type of
connection consists of forming a reversely angled, stiffened
30 and reinforced edge on the screen which engages a horizontal
flange on the frame members, such as shown in U. S. Patents
Nos. 1,663,164 and 1,906,336. Other screen tensioning devices
~ 2 ~
1 use a V-bar which clamps the screen portions adjacent its edges
in a V-grooved channel, such as shown in U.S. Patents Nos.
2,213,773, 2,378,~63, and 3,776,382.
One of the most common types of screen tensioning
means which is used, particularly in electrically heated screen
assemblies, consists of angled blocks OT flanges mounted on the
frame members about which reinforced hook-shaped, stiffened
screen edges are engaged. An example of this type oE connection
is shown in my heated screen assembly of U. S. Patent
10 No. 3,195,725.
Problems have been encountered in the past with many
of these known tensioning rails, especially tensioning rails
using a hook-shaped member which is engaged by complementary
reinforced hook-shaped screen edges. It has been found that
after extended periods of heated operation of the tensioned wire
screen cloth that the heating of the screen results in some ex-
pansion and that the screen loosens from its hooked engagement
with the flange of the tensioning rail. This results in poor
tensioning contact which causes the screen to whip back and
20 forth resulting in premature failure at the point of contact
with the tensioning rail. This is a problem in both electri-
cally heated and nonheated screen assemblies. This premature
loosening of the screen rail engagement, however, is more crit-
ical in electriGally heated screens in that it results in poor
electrical contact between ~he screen and rails causing arcing,
power loss and inefficient power use.
Prior tensioning rails are formed of relatively thin
sheet metal which has a relatively short life when used in in-
stallations encountering abrasive materials such as slag, lime-
30 stone, iron ore, silica sand, etc. These prior tensioning railconstructions are mounted on their side frame me~nbers by bolts,
the heads of which projec~ outwardly beyond the outer surface
1 of the rails. These bolt heads also are subjected to the abra-
sive action o-f the materials being screened thereby.
It has been found that in many electrically heated
screen assemblies metal strip edge stiffeners which are formed
about and engaged with the edges of the s~-reen~ are required to
provide the necessary stiffness to the screen. This reinforcing
strip enables the screen to be drawn up tightly and tensioned
by the rail and provides the necessary electrical contact between
the rail and screen when initially installed. These stiffening
strips usually are formed of stainless, plain or galvanized
steel, thereby increasing both the material and installation
costs of a screen assembly. However, screening with stiffening
strip edges when heated are subject to the described expansion
loosening.
No tensioning rail construction of which I am aware
has eliminated these problems by providing a wedge shaped
clamping bar and complementary-shaped channel for firmly mounting
the screen thereon.
SUMMARY OF THE INVENTION
Objectives of the invention include providing a ten-
sioning rail construction for screen heaters having a wedge-
shaped bar which clamps the hooked edge of a screen within a
complementary wedge-shaped channel formed in the rear surfacc of
the rail which provides a relatively large and continuous contact
surface area between the ~ensioning rail and clamped screen edge
to reduce premature loosening of the screen and to maintain a
good electrical connectio~ between the screen and rail; pro-
viding such a rail construction having a relatively large metal
mass with a special cross-sectional shape to provide e~treme
rigidity so that large tensioning forces can be applied to the
rail, establishing maximum e~ficiency for the electrical
connection with the screen uniformly throughout the
length of the tensioning rail, and to provide maximum
screen life by reducing failure or wear at the clamped
connection with the tensioning raili providing such a rail
construction in which one or both of the opposed clamping
surfaces of the wedge bar and complementary channel is
serrated to provide increased gripping contact between the
wedge clamp and screen edgei providing such a rail
construction in which the heads of the rail mounting bolts
and of the wedge bar clamping.bolts are recessed in the :~
outer surface of the tensioning rail to increase the wear
life thereof by reducing the abrasive action of the material
being screened, and with which only two usual wrenches are
required for installation, one for the wedge bar clamping
bolts and the other for the nuts of the rail mounting
bolts; providing such a rail construct.ion in which a usual
screen edge stiffening strip may be eliminated due to the
broad clamping and electrical contact area between the
wedge bar, screen edge and angled surface of the wedge-
shaped channel, thereby reducing the labor and material
cost of a screen installation; and providing an improved
tensioning rail construction which eliminates difficulties .
existing in the art and which solves existing problems,
satisfies needs and obtains new results in the art. -
These objectives and advantages are obtained by the
rail construction for mounting and tensioning a screen
between a pair of spaced, longitudinally extending frame
members, including rail construction for mounting and
tensioning a screen between a pair of spaced, longitudinally
extending frame member including: a rigid metal rail
member having outer, bottom and inner surfaces; the rail
member inner surface having longitudinally extending wedge-
sam/
~:~186~Z~
shaped channel means formed therein, the channel means
having an angled surface extending acutely from the bottom
surface upwardly towards the outer surface to form with
the rail member bottom surface an acutely angled flange
hook-shaped in cross section; bar means wedge-shaped in
cross section having an angled surface generally complemen-
tary to the channel means acutely angled surface; bolt
means movably mounting the bar means on the rail member,
the bar means when so mounted being located in a position
adjacent to and extending along the channel means to
clamp a hook-shaped end formed along a longitudinal edge of a
screen in the channel means between the acutely angled ;
surface of the channel means and the complementary angled
surface of the bar means when the hook-shaped screen end
is engaged over the hook-shaped flange of the rail member;
and adjustable tensioning means extending between and
engaging one of the frame members and the rail member
operative to move the rail member toward the frame member
to tension the screen.
BRIEF DESCRIPTION OF. THE DRAWINGS
A preferred embodiment of the invention - illustrative
of the best mode in which applicant has contemplated applying
the priciple - is set forth in the following description and
shown in the accompanying drawings, and is particularly and
distinctly pointed out and set forth in the appended claims~ j
Fig. 1 is a fragmentary perspective view showing the
improved tensioning rail construction mounted on a side
frame member with a heated screen being clamped thereon;
Fig 2 is a fragmentary exploded perspective view of
the tensioning rail and side frame member of Fig. l;
Fig. 3 is an enlarged fragmentary section view taken
on line 3-3, Fig. l;
sam/ - 6 -
8~24
Fig. 4 is an enlarged fragmentary section view taken
on line 4-4, Fig. l; :
Fig. 5 is a fragmentary elevational view looking in
the direction of arrows 5-5, Fig. 4;
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sam/ - 6a -
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1 Fig. 6 is a fragmentary sectional view taken on line
6-6, Fig. 4;
Pig. 7 is an enlarged fragmentary sectional view of a
modified wedge-shaped clamping bar and channel configuration;
and
Fig. 8 is a fragmentary diagrammatic sectional view
illustrating opposite improved rail constructions tensioning a
screen panel.
Similar numerals refer to similar parts throughout
the drawings,.
DESCRIPTION OF THE PREFERRED BMBODIMENT
A section of the improved tensioning rail construction
is indicated generally at 1, and is s'hown in Fig. 1 tensioning
and mounting a section of electrically heated screen 2 on a
frame member 3. Fig. 8 illustrates a pair of the improved rail
constructions 1 mounting and tensioning screen 2 between a pair
of frame members 3 in a usual screen assembly. Tensioning rail l
includes a rail member 4 formed of a relatively large metal mass
when viewed in cross-section, preferably formed of an aluminum
extrusion. Rail member ~ has a modified channel shape defined
by an outer surface 5, inner surface 6, a horizontally extending
planar bottom surface 7, and a vertical end surface 8 ~Figs. 1
and 2).
Outer surface 5 extends vertically upwàrdly from bot-
tom surface 7 and terminates in an upper inwardly curved flange
9. A lower angled flange 10 is formed by bottom surface 7 and
an inwardly upwardly extending angled surface 12 forming an
included acute angle of approximately 45 therebetween. An
intervening, generally V-shaped projection 13 is formed on
inner surface 6 and is defined by an inwardly downwardly e~-
tending angled surface 1~ and a concave, curved upper surface 15.
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Z~L
1 Angled surfaces 12 and 14 are connected by a vertical surface 17
and together form a longitudinally extending wedge-shaped
channel 18. Inner concave surface 15 joins with upper curved
flange 9 in a rounded, horizontally extending edge 19.
In accordance with one of the main features of the in-
vention, a wedge-shaped clamping bar, indicated generally at 20,
is mounted on rail member 4 adjacent to channel 18 by a plural-
ity of bolts 21 (Figs. 1 and 3). Each bolt 21 includes a hexa-
gonal-shaped head 22, a shank 23, and a threaded end 24. Bolts
21 extend through horizontally extending holes 26 formed in
rail member 4. Circular recesses 27 are formed in outer sur-
face 5 concentric with holes 26 for receiving bolt heads 22
therein. The inner ends of bolt holes 26 communicate with
vertical wedge surface 17 of channel 18.
Clamping bar 20 has a trapezoidal-shaped cross-sec-
tional configuration ~Figs. 2, 3 and 4) formed by vertically
extending rear major surface 28, a parallel inner minor surface
29, angled side surfaces 30 and 31, and end surfaces 33. Hori-
zontally extending threaded openings 32 are formed through
clamping bar 20 for threadably receiving bolt ends 24. Angled
surfaces 30 and 31 of clamping bar 20 are formed at an angle
generally equal to the slopes o angled surfaces 12 and 14,
respectively, of wedge-shaped channel 18.
Rail member 4 is movably mounted on a respective frame
member 3 by a plurality o bolt assemblies 35 ~Figs. 2, 3 and
4). Bolt assemblies 35 each include a bolt 36 having a rec-
tangular-shaped head 37 and a shank 38 which terminates in a
threaded end 39. Bolts 36 extend through holes 40 which are
formed in rail member 4 and which extend horizontally between
outer surface 5 and V-shaped inner surface projectifcfn 13. Holes
40 have slightly tapered configurations as shown in Fig. 4 with
1 the diameter of the holes adjacent projection 13 being larger
than the opposite end of the hole. A concave notch 41 (Figs. 2
and 6) is formed in the upper portion of wedge bar 20 adjacent
each hole 40 to provide passage of bolt 35 without contacting
or interfering wi~h bar 20.
A plurality o-f rectangular-shaped slots 42 are formed
in outer surface 5 of rail member 4 ~Pigs. 1, 4 and 5) con-
centric with holes 40. Slots 42 each have a width complementary
to the width of rail mounting bolt heads 37. Bolt heads 37 are
recessed in slots 42 which fix bolts 36 against rotation when
projecting through rail member 4.
A usual screen assembly will include a pair of longi-
tudinally extending side frame members 3 which are mounted in a
spaced parallel relationship with screen 2 or a plurality o-f
individual screen panels extending therebetween as shown in
Fig. 8. Each frame member 3 includes a vertîcal wall 44 and a
horizontal ledge 45. Wall 44 and ledge 45 preferably are formed
of sheet metal possessing sufficient strength and rigidity for
the particular application in which an electrically heated screen
assembly is intended for use.
An L-shaped insulator plate 46 is mounted on -frame
ledge 45 and extends upwardly along a portion of -fTame wall 44
for electrically insula~ing screen Z and rail 4 from frame
member 3. Insulator plate 46 includes a pair of spaced L-shaped
top and bottom metal plates 47 and 48, respectively, with an
intervening thickness of an electrical insulating material 49.
Top plate 47 preferably is smaller than bottom plate 48 as
shown in Figs. 3 and 4.
The longitudinal edges o-f screen 2 are formed with a -
reversely angled generally V-shape or hooked edge 50. Screen
edge 50 may be reinforced by a usual complementary shaped hooked
1 metal sheath 51. Hooked edge 50 of screen 2 and reinforcing
metal sheath 51 have angled configurations which are comple-
mentary to lower angled flange 10 of rail member 4 and are in
hooked engagement therewith (Figs. 1, 2, 3 and 4~ for mounting
and tensioning screen 2 on rail member 4.
When installing screen 2 on rail member 4, hooked
edge 50 and metal sheath 51 are mounted on angled flange 10
with angled legs 52 and 53 of screen edge S0 and sheath 51,
respectively, being clamped between flat angled surface 12 of
rail member 4 and angled end surface 31 of clamping bar 20.
These mating angled surfaces provide a maximum gripping area
and accordingly excellent electrical contact between screen 2
and rail member 4 throughout the entire length of clamped
screen edge 50. Angled end surface 30 of clamping bar 20 will
slidably contact angled surface 14 of wedge-shaped channel 18
when bar 20 is clamping screen edge 50 to pro~ide even distri-
bution of the forces on bar 20 to prevent twisting or pivotal
movement of bar 20 on bolts 21. Clamping bar 20 is advanced
into channel 18 easily by rotation of bolts 21 by a usual
socket~ype wrench engaging bolt heads 22. This same screen
clamping procedure usually will be performed on the opposite
edge of screen 2 by a similar raii member 4 and its clamping
bar 20 ~Fig. 8).
After hooked edge 50 of screen 2 is clamped to rail
member 4 throughout its longitudinal length by a plurality of
bolts 21 screen 2 then is tensioned between a pair of frame
members 3 by outward movement of one or both rail members 4.
Bolts 36 of rail mounting bolt assemblies 35 extend through
holes 55 (Figs. 2 and 4) which are formed in vertical frame
wall 44 and which are horizontally aligned with rail holes 40,
for drawing rail member 4 outwardly toward vertical frame wall
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1 44. An electrical insulating bushing 56 ~Fig. ~) is tele-
scopically mounted on shank 38 of bolt 36 and includes a
cylindrical sleeve portion 57 and an annular radial flange
portion 60. Sleeve portion 57 is mounted concentrically within
the bore of a conical metal washer 58. A flat disc-shaped
metal washer 59 is mounted on bolt 36 and is in clamping en-
gatement with radial flange portion 60 of insulating bushing 56
by nut 61. Bushing 56 electrically insulates bolt 36 from
frame wall 44.
A third insulating zone is provided along upper flange
edge 19 o-f rail 4 by enclosing edge 19 with a U~shaped strip
of insulating material 62. Strip 62 in turn is covered by a
complementary U-shaped metal strip 63 to physically protect
insulating material 62 -from being crushed by rail 4 as it is
drawn tightly against frame wall 44.
Nuts 61 are rotated by a usual wrench which draws
rail member 4 toward frame wall 44 arld tensions screen 2 between
spaced rail members 3 since screen 2 is securely clamped to
rail member 4 by channel bar 20. Rail mounting holes 55 are
lar~er than the diameter of bolt shank 38 and the outer circum-
ference of conical washer 58 (Fig. 4) so as to permit movement
of conical washer 58 with respect to the edges of holes 55.
Enlarged holes 55 permit the continued movement of lower angled
-flange 10 toward frame wall 44 when tensioning screen 2, even
when insulator protective strip 63 is engaged with vertical
wall 44. The horizontal leg portion 65 o-f screen metal sheath
51 is slidably engaged with horizontal leg portion 66 of top
L-shaped metal plate 47 of insulator plate assembly 46. Engage-
ment of rectangular-shaped bolt heads 37 in complementary-
shaped slots 42 prevent rotation of bolts 36 upon tightening ofnuts 61. This requires only a pair of usual wrenches, one for
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1 clamping screen 2 on rail member 4 by bolts 21 and the other
for clamping rail member 4 on -frame member 3 by bolts 36.
Fig. 7 shows a slightly modified construction of the
wedge bar-screen clamping arrangemen~. Hooked edge 50 o-f screen
2 is clamped by a wedge-shaped clamping bar 67 without the use
of reinforced hook-shaped metal sheath 51 as described above.
Bar 67 is similar to bar 20 except angled end surface 68 is
serrated. Preferably, angded clamping surface 69 of lower
angled 1ange 70 also is serrated~ and together with serrated
surface 68 provide increased gripping contact between wedge clamp
67 and screen edge 50. This clamping arrangement eliminates
reinforcing sheath 51, thereby decreasing the cost of a heated
screen assembly without losing any o the advantages of the
improved tensioning rail construction.
Mounting holes 26 for wedge bar clamping bolts 21 are
positioned slightly above center of vertical surface 17 of wedge-
shaped channel 18 (Figs. 3 and 7). This positioning compensates
for the anticipated thickness of hooked screen edge 50 and/or
sheath 51 whereby angled top surface 30 of clamping bars 20 and
67 slidably engage corresponding angled surface 14 of channel 18
upon angled clamping surfaces 61 and 68 engaging the hooked end
of screen 2 to prevent any twisting forces being exerted on
clamping bars 2n and 67.
Improved tensioning rail construction 1 has a number
of advantagious features. Heads 22 and 37 of the bar and rail
clamping bolts 21 and 36 are recessed in the outer surface of
rail member 4, requiring only two wrenches for installation of
tensioning rail 1, and to reduce the abrasive action of the
material being screened. The hooked edge 5~ of screen 2, with
or without reinforcing metal sheath Sl, is clamped between a
pair of flat surfaces 31 and 12, or between serrated surfaces 68
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1 and 69 of wedge bars 20 or 67 and wedge channel 18 on ten-
sioning rail 4 to provide a broad and continuous clamping sur-
face. This broad surface provides a relatively large clamping
area, and correspondingly, a relatively large electrical contact
area between the edge of screen 2 and rail member 4 throughout
the entire length of the clamped edge of screen 2.
Another advantage of the improved tensioning rail con-
struction 1 is the ease of installing and replacing screen 2 or
screen panel sections when worn or damaged. The wire screen
cloth is usually in roll form and is cut to the necessary length
and width for a particular screen or panel size of a heated
screen installation. U-shaped metal sheath 51 is placed along
the screen edge, if such a reinforcing sheath is desired, and
then the hook-shaped screen edge 50 is formed by appropriate
forming equipment along the entire longitudinal length of the
screen edges. If reinforcing sheath Sl is not desired, the
hook-shaped configuration is :Eormed directly alo~g the screen
edges. It has been found that the wedge bar - wedge channel
configuration of improved rail construction 1 provides a uniform
clamping of the hooked screen edges with an improved uniform
electrical contact so that in many applications reinforcing
sheath 51 can be eliminated with a subsequent cost reduction
of both material and labor. ~he serrated surfaces 68 and 69
(Fig. 7) are especially desirable for direct clamping of the
hooked edges of the screen when the metal reinforcing sheath
has been eliminated.
Another advantage of improved construction 1 is that
the large mass of rail member 4 with its special cross-sectional
configuration provides extreme rigidity so that large tensioning
forces can be applied to the rail establishing maximum efficiency
for the electrical connections with screen 2 uniformly throughout
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1 the length of rail 4, and which provides for maximum screen life
by reducing wear or failure of the screen at the clamped con-
nection with ~he tensioning rail.
Also, the uniform clamping pressure and broad contact
area between the wedge-shaped clamping bar, the screen edge and
the clamping channel throughout the entire longitudinal length
of the screen edge requires less power to heat the screen due
to virtually no contact losses between the rail and screen,
resulting in considerable energy savings and providing uniform
screen heating.
Accordingly, the improved tensioning rail provides a
construction which is effective, safe~ less expensive in nstal-
lation and operation than prior devices, efficient in assembly,
operation and use, and which achieves all the enumerated objec-
tives, provides for eliminating difficulties encountered with
prior devices, and solves problems and obtains new results in
the art.
Furthermore, the improved tensioning rail construction
may be used in non-heated mechanical screen assemblies and need
no~ be limited to electrically heated screen asse~hlies as de-
scribed above. When used in mechanical screen assemblies, the
insulation used in the three insulation zones shown in the draw-
ings and described above can be eliminated.
Summarizing, the improved tensioning rail construction
minimizes energy costs~ increases productivity and reduces screen
cloth replacement. The tensioning rail is a rugged aluminum ex-
trusion that serves as a very efficient, high-capacity conductor,
which provides more efficient heating at a lower cost, more uni-
form heating efficiency and higher production rates. The screen
cloth lasts longer, reducing maintenance and downtime. The wedge-
shaped clamping bar locks the screen cloth in a vice-like grip
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1 that will not loosen even under very severe operating conditions.
By maintaining the more effective contact between the conductor
and the cloth, the ~ajor causes of premature screen cloth fail-
ure, namely, contamination and arcing, which is the result of
poor tensioning, are greatly reduced. The improved tensioning
rails may be supplied in kit form for easy do-it-yourself retro-
fitting of all existing, electrically heated vibrating screens
or may be a component for new electrically heated screens of
various manufacturers.
In the foregoing description~ certain terms have been
used for brevity, clearness and understanding; but no unnecessary
limitations are to be implied therefrom beyond the requirements
of the prior art, because such terms are used for descriptive
purposes and are intended to be broadly construed.
Moreover, the description and illustration of the in-
vention is by way of example, and the scope of the invention is
not limited to the exact details show]n or described.
Having now described the features, discoveries and
principles of the invention, the manner in which the wedge-type
tensioning rail construction for screen heaters is constructed
and used, the characteristics of the construction, and the
advantageous, new and useful results obtained; the new and use-
ful structures, devices, elements, arrangements, parts, and
combinations, are set forth in the appended claims.
