Note: Descriptions are shown in the official language in which they were submitted.
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8AW CHAIN WITH INDENTED 8IDE LINK~
Background and Summary of the Invention
This invention relates to saw chain, and more
particularly to saw chain which typically includes left- and right-
hand cutter links distributed along the length of the chain
interspersed with and interconnected by center links which together
with other links complete the chain. Saw chain of this description
is widely used in powered equipment such as chain saws, and so-
called tree harvesters, for producing the cutting action when the
equipment is used.
The usual chain saw includes a portable frame and motor
unit, and an elongate saw bar extending outwardly from the frame
and motor unit. Saw chain in the chain saw is trained about a
power-driven sprocket in the frame and motor unit, and extends from
such sprocket along opposite margins of the bar and around the nose
of the bar. In traveling between opposite ends of the bar, the saw
chain, through its side links, slides along what are referred to
herein as guide edges in the bar extending longitudinally of the
bar. In a tree harvester, which includes a mobile vehicular frame
and an adjustably mounted saw bar, a chain is trained over the bar
and about its opposite ends, with the chain again having side links
which slide along guide edges in the bar with powered movement of
the chain.
The usual saw chain includes what are referred to herein
as center links, which are distributed along the length of the
chain, and pairs of side links interconnecting adjacent ends of
adjacent center links, with the side links of each pair disposed
on opposite sides of the center links. Certain of these side links
are so-called cutter links, and include cutter portions which
extend upwardly and laterally outwardly from body portions in the
links and thence across the top of the saw chain. These cutter
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links, which include so-called left- and right-hand cutter links,
are distributed along the length of the chain. Other side links
have no such cutter portions, and serve primarily to interconnect
center links, and such commonly are referred to as tie-strap links.
A saw bar typically has a channel or groove extending
along its length and along each of its opposite margins. With the
saw chain moun~ed in place, projections in the center links extend
downwardly to ride within these grooves. The guide edges of the
saw bar are the outer edges of the flanges which bound the grooves
described. Side links in the saw chain have lower edges which ride
along these guide edges with powered movement of the saw chain.
Problems have arisen with conventional saw chains in cold
climates where the ambient temperature is in the neighborhood of
freezing or below. Specifically, small cracks or fissures tend to
form in edges of the side links which travel, i.e., slide, over the
guide edges of the saw bar. As the cracks or fissures grow, they
extend further into the links, ultimately to join with the bores
or openings provided in the links that receive the usual rivets
securing the links in the chain together. It should be understood
that in the usual chain, the bores in the side links have a chamfer
or bevel in the ends that face outwardly on the link. The rivet
which connects a side link to other links is "spun down" when
making the chain, 80 that material at the end of the rivet fills
this bevelled region with the rivet end then being securely mounted
in place. The operation tends to internally stress the link in the
region of the bore, which explains the fact that the cracks or
fissures which initiate at the edge of the link tend to travel
inwardly to join with the bore that receives a rivet. Observations
that have been made seem to establish that the cracking which
occurs is the result of frictionally caused heat build-up in a link
in regions where it slides over the guide edges of the saw bar, and
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the fact that there is a substantial difference in the temperature
of the metal in the link in regions where the link slides on a
guide edge and portions of the link remote from these regions. The
problem is particularly severe with tree harvesters and like
equipment, where the bar over which the saw chain travels is moved
mechanically and at a rapid speed through the tree, to produce a
cut in a time period of only a few seconds. Under these
circumstances, friction (and resulting heat build-up) may be
substantial.
A general object of this invention is to provide a novel
side link construction (and a novel chain constructed from such
side links) which is better enabled to withstand destructive heat
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build-up in the link (and the chain).
More specifically, this invention contemplates the
provision of a curving indent in the base of a side link positioned
below the center of a rivet-receiving bore in the link and disposed
inwardly from an adjacent end of the link. An elongate bearing
expanse, between this indent and the link end, is adapted to bear
against the guide edge of a saw bar. Heat build-up in the bearing
expanse tends to be dissipated before producing cracking extending
toward the stressed region in the link which surrounds the rivet~
receiving bore.
In one embodiment of the invention, the side link is
provided with a notch located between the ends of the link adapted
to receive a drive sprocket tooth. On each side of this notch is
an elongate expanse adapted to bear against the guide edge of a saw
bar. Each of these expanses is interrupted between its ends by an
indent in the base of the link positioned below the center of a
rivet-receiving bore. This indent inhibits heat build-up in a
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region below the bore.
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A chain including the link of the invention may be used
advantageously where the chain is driven utilizing a spur sprocket,
or where the chain is driven with a rim sprocket. Further, the
chain may be mounted on a saw bar with such traveling about the
nose of the bar while supported either directly by the nose, or by
a nose sprocket which is rotatably journaled on the bar.
These and other objects and advantages are attained by
the invention, which is described herein below in conjunction with
the accompanying drawings, wherein;
Fig. 1 is a view illustrating a saw bar with portions
broken away, and showing a chain as contemplated mounted on the saw
bar;
Fig. 2 illustrates, on a slightly enlarged scale, a
portion of the chain illustrated in Fig. 1;
Fig. 3 is a cross-sectional view somewhat enlarged, taken
along the line 3-3 in Fig. 1;
Fig. 4 illustrates the chain traveling over what is known
as a rim sprocket;
Fig 5. is a side view of a link, drawn on a larger scale
than that in Fig. 2; and
Fig. 6 illustrates a modified form of side link.
Referring now to the drawings, and initially more
particularly to Fig. 1, an elongate saw bar 10 extends from a
mounted end, which is at the left of the figure, to a free end or
nose, which is shown at the right of the drawing. The saw bar is
mounted in place in a suitable manner, utilizing, for instance,
bores and apertures 12. A saw chain 14, which is continuous,
extends along the top of the bar, around the nose of the bar, along
the base of the bar, and thence about a spur gear 16 to continue
again along the top of the bar.
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Spur gear 16 is adapted to be suitably mounted on the
motor-driven shaft of a chain saw or tree harvester (not shown).
With operation of the motor, the driven shaft is rotated and with
rotation of the driven shaft spur gear 16 is rotated under power
to cause the saw chain to travel in the direction indicated by
arrow 17 while supported by the saw bar.
A portion of saw chain 14 is shown on an enlarged scale
in Fig. 2. Referring to this figure, the chain includes a series
of center or drive links 18 following one another along the length
of the chain. These center links include a downwardly projecting
portion 20 which is engaged by a tooth of the spur gear to be
driven thereby. Adjacent the forward end and adjacent the rear end
of the center link are rivet-receiving bores, such ac the bore
shown at 22.
The saw chain further includes side links, with the side
links organized as pairs appearing along the length of the chain
and the links of a pair being on opposite sides of the chain.
Specifically, the side links include what are known as tie-strap
links indicated at 24, and cutter links indicated at 26 and 28.
Cutter link 26 is known as a left-hand cutter link, since it is
adjacent the left side of the chain facing the direction of chain
travel, whereas cutter link 28 is known as a right-hand cutter
link, being located on the right side of the chain.
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The side links have rivet-receiving bores adjacent their
forward and rear ends, as exemplified by bore 30 in side link 24.
Pairs of side links interconnect the adjacent ends of a pair of
center or drive links. ~;
In connecting a pair of side links to a center link
(refer to Fig. 3), a rivet 34 extends through a rivet-receiving
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bore in each of these link. The bore in a side link normally has ~-
a chamfer or bevel, as shown at 36, at the end of the bore which ~ -
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meets with the outer face of the link. In securing the side links
to a center link, the rivet is passed through the various bores and
spun down, to enlarge each of the opposite ends of the rivet and
produce a flow of metal in the rivet into the chamfered regions.
This serves firmly to anchor the ends of the rivet in the side
links, with the rivet between its ends passing through the bore in
the center link with sufficient looseness to accommodate rotation
of the side links with respect to the center link. The mounting
of the end of a link in a side link tends to produce some stressing
of the side link in the region of the link surrounding a rivet-
receiving bore.
As shown in Fig. 3, saw bar 10 normally has a groove,
illustrated at 38, extending along each of its opposite margins.
This groove receives the downwardly projecting portions 20 of the
center links as the chain travels along the saw bar. Guide edges
40, 42 on opposite sides of the bar bound the groove and slidably
support the lower edges or bases of the side links in the chain as
the chain travels along the length of the bar.
Considering now in more detail the construction of a side
link, and referring to Fig. 5, the side link has a base 46. A
notch 48 appears intermediate the ends of the base, and as will be
later described, this notch is to receive the end of a tooth in a
sprocket which drives the chain. On either side of this notch is
an elongate, essentially flat expanse, shown at 52 and 54. Each
of these expanses defines an acute angle, normally of less than
about three degrees, with respect to a line joining the lowermost
regions of the two expanses, such angle being shown at 56 in the
drawing. In the specific link shown, the angle depicted is
approximately two degrees.
The base of the link further includes an indent,
indicated at 58 and 60 for the two expanses 52 and 54, which
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interrupts the expanse between its ends. More specifically, each
indent is a convexly curved surface curving about a center located
essentially directly below the center of a rivet-receiving bore.
This convexly curved surface at its ends smoothly meets with the
adjacent parts of the base of the link. The indent introduces a
region recessed upwardly from the plane of the expanse containing
the indent, and this recessed region may have a side-to-side
dimension which is fifty percent or more of the diameter of the
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bore located above the recessed region.
With the chain mounted on a saw bar, such as shown at 10, -
and because the bar has slightly convex guide edges extending along
the length of the bar, inclined expanses 52 and 54 of the various -
side links substantially engage throughout their lengths the guide
edges of the saw bar. The construction provides a substantial -
bearing surface for the chain, which adds to the life of the chain.
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However, because of the indents, there is no sliding contact of the ~ -
base of a link with the bar in regions directly below the link's ~ - ;
rivet-receiving bores. Put in another way, that part of the base
of the side link which is closest to a rivet-receiving bore -~
includes the indent, where there is no sliding contact with the ;~
bar. Regions on either side of an indent which do bear against the
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bar are regions which are relatively remote from the rivet~
receiving bore.
The result of the construction is to introduce into the
chain resistance to failure by reason of fissures or cracking being
produced in the links. This is because when there is heat build-
up in the link, it is in regions of the link which are relatively
remote from the bores, and there being present more metal in the
body of the link to dissipate heat before such travels to the
rivet-receiving bores.
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Fig. 1 illustrates the chain described as such travels
around a spur gear employed to drive the chain. Teeth 64 of the
gear fit into the spaces existing between adjacent center or drive
links, and notch 48 in each side link permits a tooth to extend
upwardly to some extent into the body of a side link.
As illustrated in Fig. 1, the bar includes a nose
sprocket 66 which is rotatably mounted adjacent the nose of the
bar. The nose sprocket supports the chain through supporting its
center links as such travels about the nose of the bar. The chain
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on running along the length of the saw bar is supported through its
side links, but on reaching the nose sprocket is lifted off the bar
to be supported by the nose sprocket.
Considering a modification of the invention, and
referring to Fig. 4, here there is illustrated a rim sprocket 68
which is sometimes utilized to support a saw chain in lieu of the
spur gear 16 illustrated. The rim sprocket has notches 70
distributed about its interior which provide a means for
establishing a drive connection between the rim sprocket and the
driven shaft in a chain saw or tree harvester. The chain is
mounted on the rim sprocket with its side links resting on rim
edges 72 of the sprocket. Pockets 74 provided within the rim
sprocket are adapted to receive, the downwardly projecting portions
20 in the drive links of the chain.
There is illustrated in Fig. 6 a modified form of side
link, which might be used in conjunction with a chain saw provided
with a saw bar which does not include a sprocket at the nose of the
bar (this type of organization being known as a hard nose bar).
The link 76 illustrated (a tie-strap link), includes a base having
central notch 78, and bearing expanses 80 and 82, one adjacent each
end. Inwardly of each bearing expanse is an indented region,
exemplified by regions 84 and 86, performing the function of the
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indents described in connection with the first embodiment of side
link described. Connecting the indent regions with the notch are
edge portions 88 and 90. These portions have a rather substantial
inclination (the angle shown at 91) with respect to a line extended
through the lower most regions of the link, for example, from seven
to nine degrees. The edge portions extend in a generally concave
course. This is to enable the bottom of the side link
approximately to conform to the curvature of the fixed nose in the
saw bar, such curvature being exemplified by the curved line 92 in
Fig. 6.
The operation of the saw chain should be obvious from the
above description. Generally speaking, the side links which
support the chain with the chain moving along the top and bottom
of the saw bar have bearing expanses providing the sliding contact
with the bar. And, as explained in connection with the first
modification of the invention described, these bearing expanses may
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be substantial in length. However, in regions of the base of a
link which are closest to a rivet-receiving bore, the side links
are indented or recessed, which has the effect of preventing
sliding contact of a side link with the bar in these regions. As
a consequence, heat build-up in a link is in regions of the link
which have a greater spacing from the rivet-receiving bore,
promoting better dissipation of heat before such travels to a
region of stress around a rivet-receiving bore.
While several modifications of the invention have been
described, it should be obvious that other modifications in
variations are possible without departing from the invention.
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