Guide to mechanical power transmission
Machines or machine parts can move through the drive, also called transporters or transmissions. A drive is the collective name for different techniques that transmit circular or back and forth motions and the power/capacity of the machine.
One of the most common examples would be a car where the wheels are propelled by the engine. In the industry we come across drives in all machines requiring movement such as pumps, ventilators, pick & place units, conveyer belts, etc. Several drive systems exist:
- Hydraulic drives
- Pneumatic drives
- Electric drives
- Mechanical drives
In this guide we will delve into the mechanical drives. This guide is meant to inform you on how these drives work, which mechanical drives exist and the different parts that belong to these drives.
1. How do mechanical power transmissions work?
Mechanical drives, one of the oldest existing drives, are consistent within the technology sector. Power and movement are transmitted through a driving engine such as belts, chains or gears. Sometimes a tool requires the same speed and power as the driving engine, but these can also differ. In the latter case, we speak of a variable transmission.
Power is usually transmitted from a rotational movement to another turning movement,
though occasionally the rotational movement will also be converted to a linear movement.
There are different ways to transmit power and speed within mechanical power transmission technology:
2. Belt drives
The main purpose of belt drives is to transfer power between two parallel axles by means of a belt.
Pulleys (also called belt pulleys) are installed on these axles so the belt may move freely over them.
A closed belt is used and therefore has no beginning or end.
When two pulleys have the same diameter, they will rotate at the same speed.
But when one of the axles uses a different diameter than the other axle, the speed will either increase or slow down. The pulleys of a belt drive usually rotate in the same direction.
There are three different belt drives: a V-belt drive, a toothed belt drive and a flat belt drive. Most drives are equipped with a V-belt or a toothed belt, these will be further described below.
Types of belt drives
V-belts have existed since the beginning of the 20th century.
This drive consists of two or more pulleys with one or several V-shaped grooves on the outside.
is then tightened over these grooves and when the driver pulley moves, the V-belt ensures that the driven pulley moves along.
If the V-belt has not been tightened sufficiently or when the V-grooves have been worn out, the belt may slip. Slippage also occurs when a system is blocked. It is possible for several V-belts to run alongside each other in one pulley to transmit more power.
Toothed belt drive
Toothed belt drives consist of two or more pulleys with teeth moulded on the outside, a toothed belt is then looped between the pulleys. The teeth of the belt engage with the teeth of the pulley and transmit movement from one drive to the other. Unlike the V-belt drives, toothed belt drives usually produce very little backlash which eliminates the risk of slippage. In turn the cost-efficiency of the toothed belt drive is higher than its counterparts.
Calculating the velocity ratio
It’s simple to calculate the speed of the driven pulley. You can use the following formula:
d1 x n1 = d2 x n2
d1 = diameter of pulley 1
n1 = rounds per minute of pulley 1 (driver speed)
d2 = diameter pulley 2
n2 = rounds per minute of pulley 2 (driven speed)
It is possible that the pulley of a V-belt drive turns somewhat slower than the formula indicates. This is possibly a result of the slippage that may occur in V-belts but will not occur in a toothed belt drive.
Uses of a belt drive
Belt drives are typically used in pumps, industrial ventilators as well as in roller tables or transportation belts, compressors, etc.
Advantages of using a belt drive
In the first place, belt drives offer a smooth transmission of power from one component to another over a longer distance. Other advantages include:
- Cost-effective; belt drives are highly efficient (95-98%)
- Easy to use and lightweight
- Low maintenance costs
- Long lifespan
Disadvantages of a belt drive
One possible reason to not use a V-belt drive could be the risk of slippage.
Though this slippage can also be desired to serve as a safety measure for a blocked drive.
You will not find the possibility of slippage in a toothed belt drive.
Other disadvantages of a belt drive are:
- The drive is not compact when paired with applications using a high-power force.
- The velocity ratio may vary due to slippage and stretching of the belt.
3. Chain drives
Similar to a belt drive, a chain drive makes use of two ‘sprockets’ that are connected through a chain. This chain consists of a series of chain links which then line up with toothed sprockets. The axles run in parallel and the sprockets all rotate in the same direction. Just like the toothed belt drive, the chain drive does not slip and is able to transmit movement over a larger distance.
Use of a chain drive
When thinking of a chain drive, we usually think of the bike and motorcycle,
but a chain drive is also often used within the agrarian sector and industrial machines.
A chain drive is known for three main purposes:
- Power transmission: A chain drive can transmit power (speed and torque) from one part to the next, even in a compact space.
- Transport: A chain drive can be used to transport materials (moving, pushing, pulling or carrying) by attaching so-called pins to the chain. Common examples include: boxes, wood, glass, etc.
- Timing: A chain drive can also be used to keep track of time or to synchronise.
Much like a toothed belt drive, a chain drive cannot slip. Other advantages include:
- Capable of a high-speed ratio
- Cost-effective, low energy loss
- Capable of withstanding high temperatures, fluids and dirt
- Easy to install
A chain drive requires more frequent maintenance and is noisier than a belt drive. Other disadvantages may include:
- The chain must be frequently lubricated
- May show signs of speed fluctuation when using a long chain, particularly when paired with smaller sprockets
- May cause frequent vibrations
4. Shaft couplings
Shaft couplings are used for different purposes. The primary purpose of a shaft coupling is to transfer power from a driving shaft to a driven shaft. These shafts are in line with one another, unlike the parallel pulleys or sprockets found in belt and chain drives. When the distance between two shafts is larger, it is possible to make use of so-called spacer couplings.
Use of shaft coupling
Shaft couplings are used as a connection between two diving components that are in line with one another.
We see this in different industries, most notably drives in machinery, the paper- and graphic industry and the synthetic materials industry.
Additionally, there are also shaft couplings available which are suitable for explosive atmospheres.
In addition to transferring power shaft couplings also have other purposes, namely:
- High torsional stiffness
- Accommodates misalignment and mechanical flexibility
- Absorbs shock and vibrations
Different shaft couplings
Couplings know different implementations, namely:
Flexible (claw) coupling
Bush pin coupling
Hydraulic coupling (or fluid coupling)
Universal joint or Hooke’s joint
The coupling you need will depend on the power, the application and the surroundings of your application.
Shaft couplings are typically used for very precise work, but they do know other advantages:
- Low maintenance
- High precision throughout the duration of its shelf life
- Most couplings can accommodate radial and axial misalignment
- Couplings come in vibration-cancelling types
- Will function in dirty and corrosive environments
- They cannot be used when using a power transmission between parallel axles.
In the industry glossary, we will discuss the most common terms and abbreviations that are used in the industries that ERIKS serves
such as the primary industry, the pharmaceutical and food industry and the energy and transport sector.
Read the glossary
5. Gear drives
Though a gear drive is used to transmit torque or power from one shaft to another, just like other drives, they are also often used to change the rotation direction or the movement angle. Additionally, gear drives are used to increase or decrease the torque and range of speed. The drive has an input gear and an output gear, also known as the driving gear and a driven gear. As we have seen before with belt- and chain drives, no slip can occur in gear drives.
Calculating the velocity ratio
It is possible to calculate the velocity ratio, also known as gear ratio, of a drive. Count the number of teeth on the input gear and the follow gear, the ratio is then determined by the number of teeth on each gear. If the input gear has 20 teeth and the output gear has 10, then your division will be 2:1. You will easily be able to determine the velocity ratio through the following formula:
z1 x n1 = z2 x n2
z1 = number of teeth of the input gear
n1 = number of turns of the input gear per second
z2 = number of teeth of the output gear
n2 = number of turns of the output gear per second
Use of a gear drive
Gear drives are often used when needing a large transmission of power to be delivered on a short distance. When a small gear moves a large gear, this creates an increase in power. Likewise, a large gear moving a small gear will cause an increase in speed though it also decreases the power.
Gear drives are compact and yet provide a large range of speed, making them ideal for small spaces. Other advantages include:
- There is no slippage
- A consistent velocity ratio
- Powerful transmission able to transfer considerable power
- Long gear life
A gear drive is not qualified for axles with long distances. It is also known for these disadvantages:
Not the best solution for high speeds
Maintenance must be done regularly; the gears have to be lubricated often
Noisy at higher speeds
Less economical than belt- or chain drives
More gears attribute to the overall weight
Static; little flexibility
The gears will damage easily under impact load