Hitachi

Drive Chain Selection Step 1: Determine the Design Horsepower (DHP) DHP = Motor HP x SF SF (Service Factor) is based on the type of input power and classification of the expected shock loading in the application. Use the table below to determine an appropriate SF. Class of Driven Load Type Internal Combustion Engine with Hydraulic Drive of Input Power Internal Combustion Electric Motor or Engine with Mechanical Turbine Drive Uniform 1.0 1.0 1.2 Moderate 1.2 1.3 1.4 Heavy 1.4 1.5 1.7 Example: In the example we have been using the required average tensile strength would be 24,514 / .15 = 163,426 lbs. Step 5: Confirm and/or Reselect Chain Size Now we must verify our preliminary selection is correct. If it was not sufficient we need to modify our chain selection so that the combination of Chain Pitch and Average Tensile Strength (ATS) meet the requirements of the equation as shown in Step 4. Example: Returning to our example we note that our 3.5" pitch chain is H238 which has an average tensile strength of 140,000 lbs. Since this strength is less than required ATS of 163,426 lbs. we must make another selection. We note that increasing pitch will increase linear speed and therefore reduce calculated chain tension, however, we might be limited by the diameter of the sprocket. We therefore will consider two larger pitch chains, H1242 and H1245. First, we check H1243 (P = 4.063"...ATS = 140,000 lbs.) Example: A 25HP electric motor which will operate with moderate shock loading has a DHP = 25 x 1.3 = 32.5 thus DHP = 32.5 Step 2: Calculate Expected Chain Linear Speed Begin by assuming the recommended 12 tooth small sprocket and make a preliminary selection of chain pitch from the Drive Chain dimensional data shown in the preceding pages. It is not important that the selection be correct at this point. Use the following formula to determine linear chain speed (S): S = (P x r x n) / 12 Example: Choose a 12 tooth sprocket (n) with an input speed of 15 rpm (r) and estimate a chain pitch of 3.5" (P) we get: S = (3.5 x 15 x 12) / 12 = 52.5 fpm Step 3: Determine the Calculated Chain Tension (T) T = [DHP x 33,000) / S] x F F (Speed Factor) can be determined from the table below: Linear Chain Speed (fpm) 0 - 50 51 - 100 101 - 160 Factor 1.0 1.2 1.4 Example: From the example we have been using since the linear chain speed is 52.5 fpm we would specify a speed factor of 1.2. Calculated Chain tension (T) = [(32.5 x 33,000) / 52.5] x 1.2 = 24,514 lbs. Step 4: Determine the Required Chain Tensile Strength For chain speeds less than 100 fpm, after applying the appropriate speed and service factors as shown above, we may operate a chain with the calculated chain tension (T) at 15% of the Average Tensile Strength. Required Average Tensile Strength = T / 0.15 S = (4.063 x 15 x 12) / 12 = 60.9 fpm T = [(32.5 x 33,000) / 60.9] x 1.2 = 21,133 lbs. Required ATS = 21,133 / .15 = 140,866 lbs. H1242 is close, but does not satisfy the requirement. Next, we try H1245 (P = 4.073" . . . ATS = 170,000 lbs.) We don't need to calculate this based on a 12 tooth sprocket since it will obviously be satisfactory, however, can we use a smaller sprocket? Let's try 9 teeth: S = (4.073 x 15 x 9) / 12 = 45.8 fpm T = [(32.5 x 33,000) / 45.8] x 1.0 = 23,417 lbs. (note the speed factor changes). Required ATS = 23,417 / .15 = 156,113 H1245 with a 9 tooth sprocket does satisfy the requirements of Step 4 and may be selected. We would recommend that the largest number of teeth up to 12, which can be accommodated by available space, be specified. Note that it was possible to make H1242 or perhaps H238 work as well by increasing the number of teeth on the small sprocket. Sometimes much trial and error is required to get the best possible combination of chain pitch and number of teeth in the small sprocket to satisfy space limitations. Final Notes: The above method selects a chain based on chain strength. If the user desires less replacement over a more economical selection rather than comparing the calculated chain tension (T) to the ATS, the user may compare the calculated chain tension (T) to the rated working load given in the dimensional tables. This will select a chain with a larger pin diameter and will require less frequent replacement due to wear 9 out (i.e. elongation).

• Cover