SAW CHAIN Background Saw chain for cutting of wood is usually made with center drive links, the purpose of which is to drive the chain along with force from a motor-powered drive sprocket and to guide the chain along a groove around the edge of a guide bar, and side links connected to the drive links with the purpose of carrying loads in the plane of the guide bar by sliding contact with the guide bar edge rails on each side of the groove. Some of the side links are cutter links.

To minimize wear of the side links a lubricant is fed to the groove by a pump, and distributed along the groove by a seoop-like cutout in the lower part of the center links.

The lubricant will spread to the inner sides of the groove to lubricate the sides of the drive links, although only small forces act between them and the groove sides. It will also spread upwards along the center links to lubricate the rivets connecting the drive links to the side links. Some lubricant will also spread to the edge rails, where it is needed because there is always sliding friction with considerable pressure between chain and rails due to the curvature and the cutting force.

Most guide bars have today a nose sprocket to carry the chain around the guide bar nose without radial load on the side links, leaving the cutting part of the chain travel as the most critical region for lubrication. Unfortunately this is also the most inaccessible, since the chain has by then already travelled the length of the guide bar as well as around the nose with extreme rotational velocity, and thrown off most of the lubricant. Various guide bar designs have been suggested with lubricant channels extending to or past the nose. such as US 2,748,810.

The present invention concerns a saw chain with side links designed to collect and concentrate the lubricant onto the edge rails and to act as hydrodynamic bearings sliding along the edge rails without metallic contact.

Description The lower contact surface of a side link is usually provided with two heels, one at each end of the link, oriented for sliding contact along the longitudinal edges of the guide bar, which are not straight but slightly convex to ensure that tension in the chain will keep it in the groove even when it is not cutting. The heels are thus flat bottomed and almost but not quite aligned. Between the heels the link may have a cutout with a large radius to fit the guide bar nose if the chain is to be used on a guide bar without nose sprocket or with a sprocket lifting the links only a small distance off the edges. In the middle there is often a deeper cutout to allow higher teeth on the nose sprocket.

If the heels of the side link are made to fit the edge rails with a fairly large contact surface but have an abrupt front end, most of the lubricant will be pushed off the edge rail with no beneficial effect on the wear. There has been a number of suggestions for heel designs where the lubricant is supposed to be retained on the edge rail to minimize wear. The patent US 3,170,497 shows in front of the front heel an extension with an inclined bottom, creating a wedge-shaped space to squeeze the lubricant under the heel. and US 3,921,490 shows that the front heel can be shortened to make room for the inclined bottom without an extension. None of these is very effective, since most of the lubricant is squeezed out to the side rather than under the heel, since the link thickness is much less than the length of the heel.

According to the invention, the heels are made to perform as hydrodynamic bearings, squeezing the lubricant under the heels with little loss to the sides. A side link according to the invention is described with reference to the figures, where figure 1 shows a lateral view of a link, figure 3 the underside of the same link with the contact surface of the heels, and figure 2 the link as seen from the front..

A side link according to the invention has one front end (11) and one rear end (12), one front heel (13) and one rear heel (14) and a cutout (15) between the heels to avoid contact with sprocket teeth. The contours of the heels (13,14) are aligned or preferably very

slightly inclined to match the curvature of a guide bar edge. At least one of the heels has a recess (16,17) in the contact surface, shaped as a hydrodynamic bearing. Each recess has one open end (18) towards the front and one closed end (19) towards the rear. The recess is tapering with a gradually decreasing depth towards the closed end (19). The length of each recess is preferably between one third and two thirds of the length of the heel, the closed end located in the middle third of the heel. The width of each recess is less than the thickness of the link, and parts of the contact surface extend on each side the full length of the recess, thereby acting as barriers keeping the lubricant from escaping to the sides.

Tapering of the recess has the effect of concentrating the lubricant towards the center of the edge rail with less leakage to the sides. The gradually decreasing depth serves to create a pressure within the recess, to lift the heel slightly off the rail and let it ride on a film of lubricant, without metal contact. It also allows wood particles trapped in the lubricant to follow the lubricant under the heel without blocking the recess. The remaining heel surface behind the recess serves as an impact bearing surface in case the cutting forces create larger forces than the lubricant film can withstand. The combined effect is to greatly reduce the wear of the chain and the guide bar. The front heel (13) and the rear heel (14) may have different size recesses. For cutter links, the rear heel (14) may be made without recess or with a very short recess, since it needs more impact bearing surface.

A preferred way to produce the recesses is to produce link blanks the traditional way by punching from a steel strip. The part of the link edge which corresponds to the heel contact surface is then coined to create the recess while the link is supported in the rivet holes. The coining tools have preferably a rounded work surface, producing a recess with negligible risk of cracking. If coining makes the link locally somewhat thicker, the spreading of material (20) should be towards the outside, leaving the inner surface flat to rotate easily against the center link.

An alternative way is to grind the recesses, which will restrict the choice of tapering and depth variation, however.

An additional advantage is that the recess will serve as an indicator of wear. Even with the improved lubrication, there will be some dry friction, when starting or when there is insufficient supply of lubricant. Wear will be noticable as shrinking of the recesses, and the chain can be exchanged before it is so worn that it is liable to break, and if this occurs too early, the lubrication system can be readjusted or overhauled.