Roller Chain Sprocket Basics

 

Think of all chain drive machines. Now consider the sprocket that drives all the chains. Pinions tend to be ignored until they fail because they are often exposed to extreme temperatures, corrosive environments, rough cleaning, and / or impact loads that destroy the keyway and cutting teeth. Suddenly, you have to find and install the right replacement so that production can continue as quickly as possible. Understanding the basics of roller chain sprockets will help you do just that (and prevent unexpected breakdowns in the future).

In addition to helping you identify the type of sprocket, the following guidelines will help you identify options that may provide better performance and longer life. The right replacement at the right time reduces downtime and saves money.

Sprockets identification and technology

Step 1. Chain type and pitch. . . The sprockets are designed to be used with specific chains. All chains are manufactured to a given standard and ANSI is the most common in the United States. Each chain is identified by a "pitch" that represents the measurement from the center of one roll pin to the center of the next in a given chain. ANSI chain pitch is always measured in 1/8 ”increments.

Of course, there are roller chain standards other than ANSI, but they are not commonly used in the United States. The second most widely used is the British standard chain. Here the chain pitch is 1/16 ”between the center of the roller pin and the gap between the center of the increased roller pin.

After determining the chain pitch, record the number of chain strands used in the application: single stranded, double stranded, triple stranded, etc. The sprocket chosen for the application must match the chain. In other words, a double-stranded chain is a double-stranded sprocket.

Step 2. Sprocket hub style. . . There is an unlimited arrangement, but most roller chain sprockets fall into one of the main styles: No hub (style A); Bucket bulge from one side (style B); Or hub bumps on both sides of the pinion (style C)

Step 3. Number of sprocket teeth or sprocket diameter. . .

The easiest way to determine the number of teeth is to simply count them. However, sometimes the teeth are completely worn. In this case, the diameter of the caliper can help identify the sprocket.

 

The term "collet diameter" refers to the dimension measured from the valley of the pinion tooth to the valley of the tooth on the opposite side of the pinion. This dimension measures the diameter of the sprocket plate without the sprocket teeth. On sprockets with an odd number of teeth, the measurement is measured from the valley of one tooth to the valley about 180 ° on the opposite side of the tooth.

 

Step 4. Hub diameter for type B and type C pinions. .

The outside diameter is commonly referred to as the "hub diameter" specified by the supplier of the sprocket. The diameter of the hub is determined by the size of the sprocket bore, the keyway used, and the requirements to maintain the sprocket wall thickness to withstand the force required for the application.

Step 5. LTB (length through hole). . . "LTB" refers to the inside diameter of the hub and the length to be machined. This length must be long enough to accommodate the appropriate size keyway to withstand the shear and torsional stresses caused by the rotating shaft.

Step 6. Diameter of the sprocket. . . This term refers to the inside diameter of the sprocket and how it is attached to the shaft.

 

 

 

 

 

The term "flat hole" refers to type A, type B and type C sprockets. Here, no special processing is done to accommodate the keyway or set screw, only holes to accommodate the diameter of the shaft. Plain bore sprockets generally require more machining before installation.

The term "finished bore" refers to Type B and Type C sprockets. Here, the hub bore is machined to fit a specific shaft diameter; This configuration includes standard keyways and set screws. The finished hole hub is non-standard based on application requirements, but can also be machined to your specific requirements.

Step 7. Keyway dimensions and location of set screws. . . Typically, the sprocket is secured to the shaft using ANSI standard dimension keyways and one or more setscrews. ANSI standards provide specific length, width, and depth keyways for a given shaft diameter. Your application may not match this standard. In this case, you must measure or reference the proper size keyway and provide this information to your pinion supplier.

Set screws are used to prevent axial movement of the sprocket. When using one, the location is usually above the keyway. This position prevents the sprocket from moving along the shaft and the keys from moving. To better fix the pinion, U.S. Tsubaki includes two set screws as standard. The second set screw located 90 ° from the keyway not only provides additional clamping force, but also reduces lateral force on the key, extending its life.

Step # 8. Hardened tooth pinion. . .

When the chain comes into contact with the sprocket, it causes frictional wear of the teeth and cavities. With each turn, all the teeth of the sprocket touch the chain. Sprockets are usually stamped to plate, pressed into powder metal, or machined into stock bar. The hardness of the teeth is directly related to the life of the pinion. Sprockets with "hardened teeth" can last 3 times longer than soft sprockets. Some manufacturers charge more for this option.