There are a bunch of belt mechanisms available for the construction of mechanisms. Chain drive mechanisms are also very good alternatives to belt drive mechanisms that have very specific features, advantages, and disadvantages. Here, we explain;
- Advantages and uses of chain drive mechanisms,
- The design procedure and guide of chain drive mechanisms with calculators,
- Maintenance and lubrication of chain drive mechanisms.
What Is Chain Drive Mechanism?
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Chain drive mechanisms are very important to power transmission mechanisms used in such types of machinery. Typical chain drive includes link plates that are linked with rollers. These rollers are attached to link plated on both sides with pins. With the respective alignment of this assembly, long chains are obtained.
These long chains are assembled with toothed around pulleys called sprockets. So, very high powers and loads can be carried with chain drives which is their most important advantage.
There are lots of kinds of chain types available for various kinds of applications. The most common type of chain drive is the ‘roller chain’. Other types of chain drives are also included 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 types of machinery.
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 have standards that are provided by chain drive manufacturers.
In roller chain drive catalogs, maximum tensile strength information is also provided. In the design of the chain drive, it will be safe that the mechanism has stressed that 1/10 of this tensile strength value.
Standards of roller chain drives are numbered starting from 40 to 240 in general manufacturer catalogs. This number indicates the pitch of a chain drive. You must divide this number by 180 to find out the pitch length of this chain in inches. To indicate the heavy-duty roller chain drives, there can be ‘H’ before the number of chain drives such as 40H. For heavy-duty roller chain drives, the thickness of link plates is higher.
How To Design Chain Drive Mechanism?
If you need to obtain a chain drive mechanism inside machinery, you need to define the input information to start design. Your chain drive design must ensure that;
- There will no galling of links because of the loads applied to chains.
- To obtain the required number of lifecycles for fatigue which is generally resulted from the stress applied to the chain at the tighter side of chain drive.
- Life of rollers that are worn in the engagement of sprocket teeth during service.
All the design parameters of chain drives are related to these situations.
Because of the moment increment, when the number of teeth increases in a constant velocity, the power that is transmitted is increased. In terms of the quietness of chain systems, smaller teeth of chains must be used on a larger diameter of sprockets.
Like in v-belt and synchronous belt drive mechanisms, several chain strands can be used in one mechanism. But this does not mean 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;
- 1.7x for two strands of chains,
- 2.5x for three strands of chains,
- 3.3x for four strands of chains.
You need to select a proper service factor for your mechanism according to different parameters;
- Working conditions,
- Working environment,
- Sensitivity of your application etc.
In general, given data in standard catalogs are provided with a safety or service factor of 1.
The optimization of chain velocity and sprocket velocity is very important. There is an optimum speed for a specific chain drive mechanism. At lower speeds, fatigue because of the fluctuating stress at the tight side on-chain is important to effect. At higher speeds, the galling of rollers is a 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 with much 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 is because the power transmission is very hard in terms of strength at high rpm’s greater than 100. The big sprocket must not be 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 the slag side is preferred also.
Horizontal alignment of sprocket and chain drives is more proper. And it is recommended that the tight side of the chain must be at the upper side of the chain drive system.
Determine the length of the chain by using this calculator;
Chain Drive Length Calculator
This calculator provides you to calculate the required chain length for your application. What you need to do is, just enter the center distance C(meters, millimeters, inches…) and the number of teeth of the small sprocket(N1), and the number of teeth of the big sprocket(N2). Click on the ‘Calculate!’ button to see the required chain length. To make another calculation, click on the ‘Reset’ button. Then re-enter the values.
This calculator uses the formula below. You can check your calculation with this formula;
If the pitch of the chain is known, say ‘up for it, the required diameter of sprocket can be calculated with this calculator also;
Sprocket Diameter Calculator
Enter the pitch of the selected chain for the chain drive mechanism in terms of millimeters or inches. Enter the number of teeth of your sprocket then click on the ‘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;
Angle Of Contact Calculator For Sprockets And Chain
θ1 is the contact angle between the smaller sprocket and the chain. θ2 is the contact angle between the big sprocket and the chain. You need to just enter the center distance(C), the small sprocket diameter(D1), and the big sprocket diameter(D2).
The formulae for the angle of contacts between small and big sprockets and chain;
Once you calculated the required diameter and number of teeth of sprockets and the length of chains, you need to select the closest standard parts of them from standard catalogs provided by sprocket and chain manufacturers.
The units of entered values must be consistent with each other to obtain correct results from calculators and calculations.
If you want to convert your units into consistent values, you can use the MB-Unit Converter tool.
Lubrication Of Chain Drives
In chain drive mechanisms, there is great interaction between metal parts dynamically which leads to very high frictions and wearing of metals that constitute chain system. Sprockets and pins are open to wearing 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 between them.
In general, there are three types of lubrication systems are applied to chain drive systems;
- Oil pump lubrication: Like in modern car engines, lubricant is jetted via a pump on a chain drive system to supply enough lubrication to the chain system.
- Manual lubrication: The operator of certain machinery which has a manual lubrication system, lubricates the chain system between specific periods. Lubrication is done with special brushes generally.
- Bath lubrication: In this system of lubrication, a part of the chain is dipped inside a sump of lubricant which is generally beneath the chain drive system. This dipped part of the chain takes the required lubricant to the different parts of the chain drive system.
This article can be a very good guide to designing 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