Chain Drives & Types of Chains
Chaindrives are most commonly used to transmit power between two components that are
at a greater distance, but they may also be used for short distances. They are
one of the five most frequently used mechanical power transmission methods
alongside shaft couplings, gear drives, belt drives and lead screws.
Each method has several advantages and disadvantages over others, which means
engineers must be careful before making the final selection.
In
this article, we’ll take a look at chain drives and their various types. They
are a crucial part of many machines and they can also be used in applications
other than just transmitting power, but more on that later. Let’s start from
the beginning.
What Is
a Chain Drive?
Chain
drive is a type of mechanical power transmission system that uses
chains to transfer power from one place to another. A conventional chain drive
consists of two or more sprockets and the chain itself. The holes in the chain
links fit over the sprocket teeth.
When
the prime mover rotates, the chain wrapped on the shaft’s sprocket rotates with
it. This applies mechanical force onto the driven shaft, transmitting
mechanical power in the process.
One
of the main advantages over a belt drive is that a chain drive maintains
a constant speed ratio, thanks to its zero slip feature. There
is no lag in power transfer and hence, it serves as a timing chain in
applications such as internal combustion engines. Having no slippage also
ensures high mechanical efficiency. The only losses in a chain drive are due to
friction between the chain links and the sprocket.
Compared
to gears, chain drives are way more versatile when it comes to operating
distances. They come into play when shafts are separated at distances greater
than that for which gears are practical. Chain drives are efficient at varying
distances while still keeping the setup rather compact. They’re found in
short-distance applications such as bicycles and long-distance applications
such as 5-storey high marine engines. A single chain can power multiple shafts
at a time.
Types
of Chain Drives
There’s
a wide variety of different chain drive designs developed due to finding use in many different
mechanical applications. They can be classified into various categories
depending on what we choose as a yardstick. When classifying based on their
function, chain drives can be divided into three main types.
· Power transmission chain drive
· Conveyor chain drive
· Hoisting and hauling chain drive
Power
transmission chain drive
This
type of chain drive is specifically used for transmitting power between two
shafts. Most machines that produce power cannot consume it at the same place,
e.g. pumps with attached motors. Transmission systems convey power to the
consumer through different methods. When chains are used for this process, they
are known as power transmission chains.
Common
examples are bikes, agricultural machinery, compressors, engine camshafts, etc.
All these applications use chain drives for power transmission.
Conveyor
chain drive
Another
common application for chain drives is conveyor chains. Conveyors use chain
drives that are crafted especially for material transportation. They come in
hundreds of different designs and sport features such as low friction, high
temperature- and chemical resistance. They can also be anti-static and magnetic.
Conveyor
chain drives find use in industries such as packaging, automotive, food and
beverage production, pharmaceuticals and textiles. Attachments can be fitted to
conveyor chains to adapt them for various uses.
Hoisting and hauling chain drive
Chain
hoists are probably the most common piece of machinery used to lift and lower
equipment. They can lift massive weights with very little effort using pulleys.
Hand
chain hoists or chain blocks are a common sight in garages, workshops,
construction sites, ship engine rooms and in many factories. They can
lift/lower heavy loads going up to 20 tonnes. Hoisting chains can be pneumatic,
electrical or manual.
We
will be focusing on the different types of chains in the next section but since
hoisting chains are rather straightforward in their design and field of
application, we’ll be covering them here. Hoist chains can be divided into two
categories:
·
Oval link chains
·
Stud link chains
Oval link
chains
Oval
link chains are also known as coil chains. They are commonly used as hoisting
chains for low to medium loads and
are generally meant to be used in low-speed
lifting applications. The chain link is oval-shaped and each
one is welded after interlocking.
Sometimes,
square link types of chains may be used but they are generally avoided due to
poor stress distribution and kinking issues.
Stud link
chains
Stud
link chains are a better alternative for high-load
applications. Each chain link is fitted with a stud across its
inner width. The studs prevent kinking and increase strength and durability.
Stud link chains find use in ship anchors and in other heavy-duty lifting
machines.
Types
of Chains in Use
There
are many types of chains used in chain drives, each with its own advantages and
disadvantages. The five most common types in use are as follows:
1. Roller chain (bush roller chain)
2. Silent chain or inverted tooth chain
3. Leaf chain
4. Flat-top chain
5. Engineering steel chain
Roller chain
When
talking about chains, roller chain is probably the one that comes into most
people’s minds. Roller or bush roller chains are widely used for power
transmission in bicycles, motorcycles and other applications in the
transportation industry. They are usually made from plain carbon steel or from
steel alloys.
A
roller chain is made up of an inner plate (roller link plate), outer plate (pin
link plate), bushes, pins and rollers. The rollers are placed equidistantly
between chain links. These rollers engage with the sprocket teeth and transfer
power through the chain. An important advantage of roller chains is that they
rotate as needed when they come into contact with the sprocket teeth, thus
reducing power losses.
In
transmission chains, the height of the roller chain link plates (on each side
of the roller) is greater than the rollers. This prevents the side plates from
making contact with the sprocket during operation. In addition to that, they
also act as guides and prevent the roller chain from slipping off.
For
roller chains in conveyors, the roller diameter is relatively larger than the
height of the sidebars. This prevents contact between the sidebars and the
conveyor track and improves efficiency by eliminating translational friction.
Larger rollers also reduce rotational friction.
For
greater power requirements, designers can opt for multi-strand roller chains.
Having multiple strands permits the use of low speeds and small chain pitches
for the same load requirements.
Silent
chain (inverted tooth chain)
.jpg "meptools")
Most
chain drives are infamous for their high operational noise. In noise-sensitive
environments such as enclosed spaces, mines and residential areas, a quieter
chain is more suitable. This keeps the disturbance to the surrounding
environment under control and promotes worker well-being.
Enter
silent chains, also known as inverted tooth chains. A silent chain can transmit
large amounts of power at high speeds while maintaining a quiet operation. The
chain consists of flat plates stacked in rows and connected through one or more
pins. Each link has the contour of sprocket gear teeth on the underside where
it engages with the sprocket teeth.
The
load capacity for a silent chain increases with the number of flat plates in
each link, and so does the tensile strength and the chain width.
Leaf chain
These
are the simplest types of chains in use. They consist only of pins and link
plates. The link plates are alternated as a pin link and an articulated link.
They don’t mesh with sprocket teeth as leaf chains are designed to run over
sheaves for guidance.
Leaf
chains find use in lifting and counterbalancing applications. Some common
examples of applications using leaf chains are lifts, lift trucks, forklifts,
straddle carriers and lift masts. In all of these low-speed machines, the
lift’s chain endures high static loads and a small amount of working load. Leaf
chains can handle shock and inertia better than other chain designs.
All
lift chains must be capable of handling high tensile stresses without
elongating or breaking. They must have sufficient ductility to endure fatigue.
As always, lubrication and service environment must be given their due thought
already in the design process.
Flat-top chain
Flat-top
chains are intended only for conveying. They can replace conveyor belts and
belt drives as the material can be carried directly on its links. An individual
link is usually made out of a steel plate with barrel-shaped hollow protrusions
on its bottom side. The links are connected to preceding and succeeding links
by passing a pin through these protrusions underneath the links. The nature of
these joints allows movement only in one direction.
There
are special types of flat-top chains that can flex sideways. The pin
construction permits sideways movement in both directions to enable the
conveyor chain to go around curves.
Flat-top
chains are used in low-speed conveyor machines for material transportation in
assembly lines.
Engineering
steel chain
The
engineering steel chain has been around since the 1880s. This chain was
designed to handle the toughest environments and the most demanding applications.
They were made of hot-rolled steel and sometimes heat-treated for extra
strength.
Engineering
steel chains are just as relevant today. However, their strength, wear rate,
loading capacity and pitch have increased to match present-day industrial
needs.
These
chains consist of links and pin joints. The clearance between this chain’s
components is larger than other chains as it has to handle dust, dirt and
abrasives under normal operating conditions.
Most
engineering steel chains function as conveyor chains for material handling but
some are also used in drives. They can be seen in applications such as
conveyors, forklifts, bucket elevators and oil drilling machines.
How to Select the
Right Chain Drive for Your Application?
With
the amount of variety in the form and function of various chain designs,
selecting the right chain drive for an application can become a bit
overwhelming. The right way to go about this selection is to eliminate
unsuitable options by evaluating the chain’s application and features. This
will help to narrow down viable options before the final selection. The most
important factors in chain drive selection are as follows:
1. Loading
2. Chain speed
3. Shaft layout
4. Distance between the shafts
5. Service environment
6. Lubrication
Loading
When
selecting the right chain drive for your application, the most important
question to focus on is how much power needs to be transferred. The chain must
be able to handle the power produced by the prime mover.
The
safety of the crew and the chain drive system depends upon the correctness of
the calculations at this stage. It is recommended to work with an adequate
factor of safety.
Chain speed
Not
all chain drives can handle high-speed applications. Some chain drives are
specifically designed for low speeds. The specifications can be obtained by
carrying out calculations and ensuring that the speed is within the recommended
range. This evaluation will considerably narrow down the number of designs that
can be used for the application.
Shaft layout
Most
chain drives cannot work with non-parallel shafts. If the shafts aren’t exactly
aligned, the designers may have to look towards gear drives as an
alternative.
Distance
between the shafts
It
is recommended that the center distance between shafts be in the range of 30-50
times the chain pitch. The designer must also ensure that a
minimum arc of contact of 120 degrees is
obtained on the smaller sprocket. If the number of sprocket teeth is small, at
least five teeth must be in contact with the chain at any
given moment.
Service
environment
The
service environment will dictate the expected resistance of the chain drive to
moisture, dirt, abrasives, corrosion and high temperature. It will
also affect other parameters such as vibration, noise levels and fatigue
strength. For instance, in areas where noise is a concern, the designers can
opt for the use of an inverted tooth chain.
Lubrication
Most
chain drives require lubrication for a satisfactory wear life. Chain type,
size, loads and operating speed will dictate the need and extent of
lubrication. Depending on the application, designers may prefer manual, drip
feed, oil bath or forced feed lubrication.
Some
chains are self-lubricated and do not require any external lubrication
throughout their service life. Such chains use bushings made from
oil-infused sintered plastics or metals that provide uninterrupted
lubrication during operation.
Advantages
of Chain Drives
· Able to transfer torque over long distances
· Contrary to a belt drive, a chain drive does not slip
· A chain drive is more compact than a belt drive and can fit into relatively tight spaces
· Multiple shafts can be powered by one chain drive
· Versatile drive that can work at high temperatures and in all kinds of service environments (dry, wet, abrasive, corrosive, etc.)
· It is a low-friction system that guarantees high mechanical efficiency
Disadvantages
of Chain Drives
· Cannot work with non-parallel shafts
· Chain drives are known to be noisy and they can also cause vibrations
· Misalignment may cause the chain to slip off
· Some designs require constant lubrication
· An enclosure is usually needed
· They require chain tensioning from time to time in the form of a tightening idler sprocket
0 Comments