Synchronous Belt Drive Mechanisms And Designing
There are bunch of belt mechanisms avaliable for the construction of mechanisms. Chain drive mechanisms are also very good alternatives of belt drive mechanisms that has very specific features, advantages and disadvantages over them. In here, we explain;
Chain drive mechanisms are very important power transmission mechanisms used in such machineries. Typical chain drive includes link plates which are linked with rollers. These rollers are attached to link plated in both sides with pins. With the respective alignment of this assembly, long chains are obtained.
These long chains are assembled with toothed round pulleys called sprockets. So, very high powers and loads can be carried with chain drives which is the most important advantage of them.
There are lots of kinds of chain types avaliable for various kinds of applications. The most common type of chain drive is the ‘roller chain’. Other types of chain drives are also includes different designs of link plates and linkings.
Roller chains are generally used in load carrying applications such as conveyors, part support chains or conveyor slats etc. Chains are linked to each other with different attachments to obtain these machineries.
For roller chains, the distinctive information is the ‘pitch length’ which defines the distance between adjacent pins in a chain drive. Like other machine elements, roller chains also has standards which are provided by chain drive manufacturers.
In roller chain drive catalogues, maximum tensile strength information is also provided. In the design of chain drive, it will be safe that mechanism has stress that 1/10 of this tensile strength value.
Standards of roller chain drives are numbered starting from 40 to 240 in general manufacturer catalogues. This number indicates the pitch of a chain drive. You must divide this number with 180 to find out pitch length of this chain in inches. To indicate the heavy duty roller chain drives, there can be ‘H’ before the number of chain drive such as 40H. For heavy duty roller chain drives, the thichness of link plates are higher.
If you need to obtain a chain drive mechanism inside a machinery, you need to define the input informations to start design. Your chain drive design must ensure that;
All the design parameters of chain drives related to these situations.
Becuase of the moment increment, when the number of teeth increases in constant velocity, the power that is transmitted is increases. In terms of quietness of chain systems, smaller teeth of chains must be used on larger diameter of sprockets.
Like in v-belt and synchoronous belt drive mechanisms, several number of chain strands can be used in one mechanism. But this is not means that the transmitted power capacity will increase proportionally. In general, the transmitted power capacity of a chain drive system with the increasing strands of chains increases with this ratio;
You need to select a proper service factor for your mechanism according to different parameters;
In general, given data in standard catalogues are provided with safety or service factor of 1.
The optimization of chain velocity and sprocket velocity is very important. There is a optimum speed for a specific chain drive mechanism. At lower speeds, fatigue because of the fluctuating stress at tight side on chain is important effect. At higher speeds, the galling of rollers is very important factor. So, an optimum speed for chain drive must be obtained.
The speed ratio between small and big sprockets must be lower than 7. You can also design it much more higher speed ratio numbers. But, in the application, it will be safe to design two or more steps of chain drives for bigger speed ratios.
In most applications, the minimum sprocket teeth number must be higher than 17. This because the power transmission is very hard in terms of strength at high rpm’s greater than 100. The big sprocket must not bigger than 120 teeth.
The center distance between sprockets must have between the 30-50 pitch lengths of chains. The adjustable center distance to adjust the sag of slag side is preffered also.
Horizontal alignment of sprocket and chain drives is more proper. And it is recommended that the tight side of chain must be at upper side of chain drive system.
Determine the length of chain by using this calculator;
This calculator provides you to calculate required chain length for your application. What you need to do is, just enter the center distance C(meters, milimeters, inches…) and number of teeth of small sprocket(N1) and number of teeth of big sprocker(N2). Click on ‘Calculate!’ button to see required chain length. To make an another calculation, click on ‘Reset’ button. Then re-enter the values.
This calculator use the formula below. You can check your calculation with this formula;
If the pitch of chain is known, say ‘p’ for it, the required diameter of sprocket can be calculated with this calculator also;
Enter the pitch of selected chain for chain drive mechanism in terms of milimeters or inches. Enter the number of teeth of your sprocket then click on ‘Calculate!’ button.
The angle of contact between smaller sprocket and chain must be bigger than 120 degrees. You can calculate the angle of contact between smaller sprocket and bigger sprocket by using this calculator again;
θ1 is the contact angle between smaller sprocket and the chain. θ2 is the contact angle between big sprocket and chain. You need to just enter the center distance(C), the small sprocket diameter(D1) and big sprocket diameter(D2).
The formulae for angle of contacts between small and big sprockets and chain;
Once you calculated the required diameter and number teeth of sprockets and the length of chains, you need to select the closest standard parts of them from standard catalogues provided by sprocket and chain manufacturers.
The units of entered values must be consistent to each other to obtain correct results from calculators and calculations.
If you want to convert your units into consistent values, you can use MB-Unit Converter tool.
In chain drive mechanisms, there are great interaction between metal parts dynamically which leads very high frictions and wearing of metals that constitutes chain system. Sprockets and pins are open to wear without enough lubrication.
Chain lubricants are generally petroleum based, which has optimized viscosity to cover all the required chain and sprocket parts to prevent wearing and decrease the friction betweeen them.
In general, there are three types of lubrication systems are applied to chain drive systems;
This article can be very good guide to design your chain drive systems. All the aspects of chain drive systems can be explained like above.
Do not forget to leave your comments and questions about the chain drive systems below.
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Source Of Formulas: https://www.pearson.com/store/p/machine-elements-in-mechanical-design/P100001430091