TECHNICAL CONSIDERATIONS
BEYOND SPROCKETS
When determining whether you need replacement sprockets, consider the following important points:
Chain Interaction: The chain-sprocket interaction is the criterion upon which most users make their judgments about replacing sprockets. If the chain engages and disengages the sprocket smoothly without hanging up or snapping into place, most people will not replace it. If a chain does start to hang up on the sprocket, damaging chain overload conditions can develop rapidly. We suggest replacing sprockets before hang-up develops. Reversible: Almost all sprockets are reversible. The key to being able to reverse sprockets is symmetry. If the sprockets are symmetrical from side to side, then they can be reversed. Reversing is not suggested in most circumstances, especially with those applications that wear the sprocket bottom diameter. New Chain: We suggest you order new sprockets when chain is replaced. New sprockets ensure proper chain interaction and also provide maximum wear performance. Relief Pocket (Mud Relief): In applications where material buildup may be a problem, the bottom of the tooth pocket can be beveled on the side to allow the material to “squeeze” out. This reduction of contact area is not critical because the pressure on the bottom of the pocket is very light in horizontal conveyors. Other relief styles may be necessary for vertical conveyors. Attachment Clearance: Any time an attachment is in the area between, above, or below the sidebars, make sure the attachment does not interfere with sprocket action.
Chordal Action: Chordal action is a very important concept in sprocket function. A sprocket is a collection of chords, or straight segments, that approximate a circle. The more teeth a sprocket has, the closer the chords are to a circle. The problem with a chordal form is that the lineal output is not consistent. Since the sprocket is not a perfect circle, the distance from the shaft center to the chain center line varies. As this distance varies, so does the lineal output (assuming a constant shaft rational speed). A hexagon inscribed by a circle represents the six-tooth sprocket shown below. You can see that the distance from the center to the corner is different than from the center to the middle of the side. The corner would be the equivalent to the chain joint center, and the side is equivalent to the chain center line at mid-pitch. Advantages of Using Larger Sprockets: Choose the largest sprocket that will fit your application. Small sprockets cause greater shock and consequently more wear on both chain and sprockets. There are several reasons for this. 1. To engage small sprockets, chain must flex more which causes increased rotation of the pin in the bushing. Since this is one of the major causes of chain wear, this flexing action should be minimized. 2. Small sprockets with fewer teeth wear out much faster than sprockets with more teeth. More teeth provide an opportunity to distribute the wearing action. 3. Larger sprockets cause smoother operation because the greater number of teeth will pick up the load more frequently.
V 1 =.2618 (PD) COS (180/T) N V max = rω Maximum Chain Speed
V min = rω Minimum Chain Speed
V 1 =.2618 (PD) COS (180/T) N
V 2 =.2618 (PD) N
Where V1 and V2 in fpm N in r.p.m. PD in pitch diameter, in inches
V 1 =.2618 (PD) COS (180/T) N
V 2 =.2618 (PD) N
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