Note: Descriptions are shown in the official language in which they were submitted.
~05848S
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The invention relates to bandmills and in parti-
cular to an improved jackîng system for applying strain
to a band saw received on the bandwheels of the mill.
Strain is conventionally applied to a bandsaw
in a bandmill by a mechanical jacking system which causes
; the idler and driven wheels of the mill to be separated.
`' The jacking system normally incorporates a pair of opposed
and offset knife edges which engage in correspondin~ offset
recesses in a torque bar which is biased to rotate so
as to apply strain by a weight acting through a lever.
Such a ~ystem enables relatively constant saw tension
to be maintained on the saw blade regardless of saw length
; changes caused by load and temperature variations. A
; typical bandmill utilizing such a system is described
.. . .
~' 15 in United States Patent 3,158,184. ;-
- ~ Recently however there has been a tendency to
reduce the thickness of the saw blade in bandmills in
order to in turn reduce the thickness of the cut and minimize
sawdust loss. This however gives rise to instability in
the blade, particularly when a log first contacts
and finally le~ves the saw, resulting from the rapid
` load changes in the thinner and more flexible blade.
Thus, the sudden load applied to the blade at the
beginning of a cut tends to momentarily slow the blade
. . .
down and thus the driving band wheel. Since the wheel
is of heavy construction in order to provide flywheel
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effect and maintain speed, the shock is taken directly
by the saw blade in which the tension is increased
~- between the log and the driven wheel. This tension
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will cause the saw blade to stretch, and if the idler
wheel is rigid and not free to move upwards, a sur-
plus length of saw blade will exist between the log
: and the idler wheel thus creating a ripple or wave
in the saw blade. The resulting change in length
rippling effect and vibrations results in poor cutting
accuracy which to a large extent negates the advantages
,.~
. resulting from the use of the thinner blade. Furthermore,
the mechanical jacking systems above referred to are
~ 10 not sufficiently responsive to such rapid changes
in the load on the blade and do not provide an adequate
,; compensatory effect.
It is among the objects of the present invention
. to provide an improved system for applying strain
~ 15 to a bandsaw, whereby the desirable high strain can
be applied and maintained and which at the same time
responds sufficiently rapidly to shock loadings on
'7,"' the saw blade to overcome the instability above referred
' to.
., .
The invention therefore provides a bandmill
comprising a frame, first and second bandwheels for
receiving and guiding a band~aw, first and second
pairs of journals re~pectively journalling said first
~ and second bandwheels, means fixedly mounting said
first pair of journals in said frame, jacking means
supporting said second pair of journals from said
frame for varying the spacing of said first and second
pairs of journals, said jacking means comprising a
pair of jacks each independently supporting one each
: 30 of said second pair of journals and at least one air
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spring for generating live strain in a b2ndsaw received
on said bandwheels subsequent to the application of
primary strain by operation of said jacks.
In a preferred embodiment, the air spring
~;5 comprises a bellows which may be connected to a pres6urizedair reservoir. The air spring may however also comprise
a rolling diaphragm air cylinder unit.
The invention will now be further described
with reference to the accompanying drawings in which,
Figure 1 i8 a side elevation showing the
general arrangement of a bandsaw incorporating a strain
~`~ system according to the invention,
Figure 2 is a side elevation, partly in
section, of one embodiment of strain system according
to the invention,
.
Figure 3 is a sectional plane view on the
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line 3-3 of Figure 2,
Figure 4 iq a sectional rear elevation on
the line 4-4 of Figure 2, ~ -
Figure 5 is a side elevation, partly in
section, of a ~econd embodiment of bandmill strain
8y9 tem according to the invention,
Figure 6 is a side elevation, partly in
section, of a third embodiment of bandmill strain
~25 system according to the invention and,
,
;; Figure 7 is a plan view, partly cut away,
on the line 7-7 of Figure 6.
Refexring first to Figure 1, this shows
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a bandmill having a frame 1 including a table 2. The
table 2 carries a fixed lower band~aw guide 3 and
the frame 1 carries an adjustable upper bandsaw guide
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1058~85
4 for a bandsaw 5 extending around idler and driven
bandwheels 6 and 7 respectively. The driven bandwheel
7 is mounted for rotation between a pair of journals
8, one of which is seen ln Figure 1. The idler band-
wheel 6 is mounted for rotation between a pair of
; journals 9, one of which is seen in Figures 1 and
2. Each journal 9 is carried at ~he end of a screwed
rod 10 locked in a threaded bushing 11 by lock nuts
12. This arrangement permits easy and accurate alignment
of the idler wheel 6 with the driven wheel 7 and he
bandsaw guides 3 and 4. Accurate alignment in relation
to the saw guides and driven wheel is essential for
precision sawing.
The bushing 11 is pivoted at 13 at the upper
end of a ~wan neck 14. The swan neck 14 extends upwardly
from a ring boss 15 secured at the upper end of a
tubular post 17. The post 17 extends slidably through
guide bushings 18 provided on the frame 1 and is bolted
at the lower end to a plate 19. The plate 19 is secured
by vertical spacer plates 20 to a Yecond plate 21
mounted on a jack 22. Within the tube 17, the plate
19 carries a concave bearing plate 23 on which a convex
bearing member 24 at the lower end of a strain rod ;;
25 is received. The elements 23 and 24 constitute
a rocker bearing and the clearance between the strain
rod 25 and the tubular post 17 is sufficient to permit
limited rocking movement of the strain rod.
At the upper end of the strain rod 25, an
axial recess 26 is provided in which a cylindrical
insert 27 is received. The insert 27 is formed with
an upwardly facing knife edge 28 which engages in
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~; a downwardly facing V recess 29 formed in a torque
bar 30. The journal 9 on each side of the bandmill
is also provided with a recess 31 in which an insert
32 is received. The insert 32 has a concave surface
against which fits a convex surface of a member 33.
The member 33 has a downwardly facing knife edge 34
engaging in an upwardly facing V recess 35 formed
in the torque bar 30.
The bearings 23/24 and 32/33 ensure that
the load bearing knife edges self-align, provide for
even distribution of load along the knife edges, and
,~ minimize friction.
Each torque bar 30 has a rocker arm 36 keyed
thereto, the free end oî the rocker arm 36 having
one end of a link rod 37 pivoted thereto at 38, by
means of self-aligning ball bushings and needle roller
t bearings.
As best seen in Figures 3 and 4, the link
rods 37 on each side of the bandmill extend downwardly
and are pivoted at their lower ends 39 to short levers
40, also by means of self-aligning ball bushings and
needle roller bearings. Each of the levers 40 is
connected to a position adjacent to one end of a cross
.~ shaft 41 which is journalled for rotation at each
end in bearings 42 carried on bracket plates 43. The
i
bracket plates 43 are secured to the vertical plates
20 carrying the plates 19 on each jack. In order
to permit the independent raising or lowering o~ the
jacks 22 for producing the correct tilt in the idler
wheel 6, the bearings 42 incorporate self-aligning
rol~er~ to permit li mited independent movement relatlve
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1058~85
to the cross shaft 41.
The bracket plates 43 have portion 44 extending
upwardly and rearwardly at an angle as best seen in
Figure 2. The portions 44 are upwardly slotted from their
~5 undersides and receive in loosely interlocking engagement
herewith the stepped ends 45 of a bridge member 46, as
best seen in Figure 4. The loose engagement of the ends
,~ 45 in the slots also facilitates independent operation
of the jacks 22.
A lever 47 extends rearwardly from the cross
shaft 41 to a position beneath the transverse beam
or bridge member 46. The end of of the lever 47 has a
dependent pin 48 pivoted thereto at 49 and carrying a
weight 50.
Between the transverse beam member 46 and
the lever 47, a bellows unit 51 is secured, the unit
having an inlet connector 52 connected by a pipe connection
53 to a reservoir 54 of air under pressure. The bellows
unit 51 may he of any suitable kind, preferably having
;;20- no static friction. The unit manufactured by the
Firestone Tire and Rubber Company of Canada Limited under
the trade descxiption "Airstroke" has been found suitable
for this duty.
The lever 47 has a mercury tilt switch 55
mounted thereon suitably connected into two warning light
circuits (not shown) in a conventional manner for indicat-
ing respectively excessively high or low positions of the
lever.
In order to prevent uncontrolled upward
movement of the link rod 37 which would allow the
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torque bar 30 to rotate anticlockwise and slacken
the bandsaw, a stop 56 is provided on each swan neck
14 so as to engage the upper surface of the rocker
; arm 36. Damage due to over extension of the bellows
, 5 unit 51 is prevented by a crossbar 57 extending beneath
the lever 47 and connected at its ends by chains 58
to the transverse beam member 46.
'~:
In operation, the bellows 51 is first pressurized
to a predetermined pressure calculated subsequently
, 10 to provide the required live strain in the band saw
blade. The two jacks 22 are next raised simultaneously
until the load on the knife edges 28 and 34 act~through
, the rocker arm 36, link rod 37 and cross shaft 41
to compress the air in the bellows 51. This jacking
continues until the lever 47 is lifted from the crossbar
57 into a balanced sensitive state. This state can
be determined by means of the two indicator lights
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(not shown) opsrated by the mercury tilt switch 55.
The saw is then mentarily started to check that the
saw is running correctly on the wheels, one or other
of the jacks 22 being ind~pe~dently adjusted to provide
correct running and the correct tooth projection. The
; saw i9 then ready for full operation.
With an arrangement generally as above described,
a total strain of 24,000 pounds on a 5 foot bandmill
or 65,000 pounds on a 9 foot bandmill can be developed
with an air pressure not exceeding 50 pounds per s~uare
inch. By slightly increasing the air pressure, the
weight 50 can be dispensed with, although it may be
preferred to retain it.
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1058485
Referring now to Figure 5, this shows a
bandwheel strain system generally similar to that
of Figures 2 to 4 but modified in respect of the means
of supplying air pressure. Similar features however,
are accorded the same reference numerals and will
not be further described.
The embodiment of Figure 5 omits the bellows
unit 51, the portions 44 of the bracket plates 43
and the transverse beam member 46. The lever 47 however
is further provided with an upstanding lever portion
60 to which is pivoted one end 61 of a piston rod
~:
~ 62 extending from an air cylinder unit 63. The other
; end of the air cylinder unit 63 is pivoted at 64 in
a bracket 65 secured to the frame 1. The air cylinder
unit 63 is preferably a rolling diaphragm air cylinder,
for example of the kind manufactured and sold under
the registered trade mark "Bellofram". The air cylinder
;, .
unit 63 is connected by means of the connection 53
to the air reservoir 54.
, 20 The operation of the embodiment shown in
Figure 5 will be apparent. The rotation o the cross
shaft 41 i8 in thiq case caused through the lever
portion 60 by pressurization of the air cylinder unit
63.
Reerring now to Figures 6 and 7, these
show a third embodiment according to the invention.
The basic construction is generally similar to the
assembly described with reference to Figures 2 to
4. The same features have been assigned the ~ame
reference numerals and will not be further described.
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~058485
In this embodiment, the bellows unit 51,
B portions 44 of the bracket plates ~ and the transverse
beam member 46 are omitted, the remaining portions
i of the linkage previously described then serving only
to ensure wheel stability and prevent sideways tilting.
Weight 50 may or may not be included.
On each side of the wheel 6, the bosses
15 are provided with forwardly extendlng support platforms
70, the journals 9 being provided with forwardly extending
reaction plates 71 immediately above the platforms
70. A bellows unit 72 is secured between each platform
70 and the reaction plate 71 immediately above it,
and has a connector 73 connected by means of an air
connection 74 to an air reservoir (not shown) similar
to the reservoir 54 of Figures 2 to 4.
In this embodiment, the strain on the bandsaw
is effected simultaneously by means of the deadweight
50, when provided, acting through the linkage 47,
36 and by pressurization of the bellows units 72 to
cause separation of the plates 71 from the platforms
70.
The bellows may contain an inert gas instead
of air.
