CA2021554A1 - Saw chain with indented side links - Google Patents

Abstract

Abstract of the Disclosure A saw chain with side links that have bases that are indented in regions located below rivet-receiving bores in the links. The indents inhibit cracking produced by heat build-up in the links.

Description

~ 2~2L~

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 fJ ~

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 ~2~

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 , ,~ :
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 ::
region below the bore.

.. ~ = . - . , , . . ~ ,. - , . -. . . . ~ , . . . .

t~ ~ 2 ~

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.
~:

.. - . .- - - ~ . .
'J< . . . ~ ~ . , ' . ` : . ' . ' ~ ', : ` .` :::: ` ' .. . . .

, ~, 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.

- . ... ~
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 .-:
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 ~ -. ~

~--.. . . ... .

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 ~Q~

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 . . ; .. ~ ; .
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.
. . ~ :: . :. ~:
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 ...... ..................................................................... ... .... ........ .- ~., ,: .
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.

. ,.. I . ~ . . . . . . . .
,, -., - . .. - :. . . . . .

~ 0 2 ~
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 .. ~ ., : ~ . . ~.
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 --` 202~

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 :.. ~ ~ .. ..
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.

..~

~.

.:
" ~ -'.- -9 .: --

Claims (7)

1. In saw chain including center drive links and side links on opposite sides of the chain, rivets interconnecting the center links and side links, a side link having a forward rivet-receiving bore adjacent its forward end and a rear rivet-receiving bore adjacent its rear end and said bores receiving said rivets, the improvement comprising:
a base for the side link which includes a notch between the ends of the link for receiving a drive sprocket tooth, the base further including an elongate expanse on each side of the notch adapted to bear against the guide edge of a saw bar, each expanse being interrupted between its ends by an indent in the base and the indent being positioned below the center of a rivet-receiving bore in the link, the indent eliminating sliding contact of the base of the link with the guide edge of a saw bar in a region below a rivet-receiving bore.

2. The saw chain of claim 1, wherein an elongate expanse in a direction extending toward an adjacent end of the link inclines at an acute angle of less than about three degrees with respect to a line joining lowermost regions of the two expanses.

3. The saw chain of claim 1, wherein the indent is a convexly curved surface curving about a center located essentially directly below the center of a rivet-receiving bore.

4. The saw chain of claim 2, in combination with a saw bar having opposite ends and slightly convex guide edges extending between the ends of the bar, the inclination of the expanses in a link enabling the expanses to substantially engage the curvature of the guide edges of the saw bar.

5. The saw chain of claim 4, in combination with a spur drive sprocket adjacent one end of the bar which moves the chain and which has teeth which fit within said notches, and a nose sprocket rotatably mounted on the opposite end of the bar having teeth which fit between the center links to train the chain about the opposite end of the bar.

6. In saw chain including center drive links and side links on opposite sides of the chain and rivets interconnecting the center links and side links extending through rivet-receiving bores adjacent the forward and rear ends, respectively, of each side link, the improvement comprising: a base for a side link which includes an elongate expanse adjacent one end of the link adapted to bear against the guide edge of a saw bar and located beyond the center of the rivet-receiving bore at said one end of the link, an elongate expanse adjacent the opposite end of the link adapted to bear against the guide edge of a saw bar and located beyond the center of the rivet-receiving bore at said opposite end of the link, a curving indent in the base of the link positioned below the center of a rivet-receiving bore in said one end of the link and joining at one end with the edge expanse at said one end, a curving indent in the base of the link positioned below the center of a rivet-receiving bore in the opposite end of the link and joining at one end with the edge expanse at said opposite end, the base further having edge portions joining opposite ends of the curving indents.

7. The saw chain of claim 6, wherein said edge portions extends generally in a concave course.