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mmme2044 add incomplete notes on pneumatics, bearings

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uni/mmme/2044_design_manufacture_and_project/bearings.md Executable file
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---
author: Akbar Rahman
date: \today
title: MMME2044 // Bearings
tags: [ bearings ]
uuid: 94cac3fd-c352-4fdd-833d-6129cb484b8a
lecture_slides: [ ./lecture_slides/Lecture 7 - Bearings 1 – Plain Hydrodynamic Bearings 1.pdf ]
---
> I don't think I ever finished these notes.
# Types of Bearings
<details>
<summary>
## Plain Journal Bearings
</summary>
- used to support rotating shafts loaded in radial directions
- consists of an insert fitted between the shaft and support
- the insert may be an aluminium alloy, copper alloy, or other material
- the insert provides lower friction and less wear than if just rotating in the support
- the bearing may be dry rubbing or lubricated
### Lubrication
- hydrodynamic---a shaft continuously in oil. the load is carried by pressure generated in the oil
as a result of the rotation
- hydrostatic---avoids excessive wear at start up by pumping oil into the load bearing area at a
pressure that lifts the shaft
- solid-firm---a coating of a solid material like graphite or molybdenum disulphide
- boundary layer---a thin layer of lubricant which adheres to the surface of the bearing
</details>
<details>
<summary>
## Ball and Roller Bearings (Rolling Element Bearings)
</summary>
- main load is transferred from rotating shaft to its support by rolling contact from balls
- a rolling element bearing consists of an inner race, outer race, rolling elements and a cage
![](./images/bearings_1-010.jpg)
![](./images/bearings_1-011.jpg)
</details>
<details>
<summary>
## Plain Rubbing Bearings (Dry Sliding)
</summary>
- does not use liquid lubrication
- usually polymeric
- dry lubricants added (e.g. PTFE)
- reinforcements added (e.g. glass fibre)
</details>
<details>
<summary>
## Oil Lubricated Porous Bearings
</summary>
- manufactured from sintered metal powders
- porous and oil impregnated
- more porous is weaker but allows for high speeds
- lubricant needs to replenished at regular intervals --- usually every 1000 hours of use
</details>
<details>
<summary>
# Hydrodynamic Bearings
</summary>
- pressure builds up in the lubricant as a response to the relative motion
- both journal and thrust bearings may use this principle
- surfaces touch and rub at very low speeds
![](./images/vimscrot-2022-11-15T17:56:26,739425867+00:00.png)
# fun graphs that may be useful for bearing selection
![](./images/bearings_1-035.jpg)
![](./images/vimscrot-2022-11-15T17:33:30,763609479+00:00.png)
![](./images/vimscrot-2022-11-15T17:51:56,506933942+00:00.png)
# $pV$ Factor
- a measure of the bearing's ability to cope with frictional heat generation
- rapid wear occurs at $pV_\text{max}$
- if the value is exceeded then overheating, melting, and excessive wear or seizure may follow
- general operational range should be around $0.5pV_\text{max}$
![$P_\text{max}$ is limited by strength, $V_\text{max}$ is limited by temperature rise](./images/bearings_1-036.svg)
- A - thermoplastics
- B - PTFE
- C - PTFE + fillers
- D - porous bronze + PTF + lead
- E - PTFE-glass weave + thermoset
- F - reinforced thermoset + molybdenum disulphide
- G - thermoset/carbon graphite + PTFE
## Radial Sliding Bearing
$$p = \frac{F_\text{radial}}{bD}$$
$$V = \omega\frac D2$$
![](./images/vimscrot-2022-11-15T17:48:21,486895199+00:00.png)
## Axial Sliding Bearing
$$p = \frac{4F_\text{axial}}{\pi(D^2-d^2)}$$
$$V = \omega\frac{D+d}{4}$$
![](./images/vimscrot-2022-11-15T17:48:34,860294942+00:00.png)
# Wear
$$K = \frac{W}{FVt}$$
where $K$ is wear factor (provided by manufacturer), $W$ is wear volume, $F$ is sliding velocity,
$F$ is bearing load, and $t$ is elapsed time.
# Manufacture
- nominal diametral clearance is commonly 1 $\mu$m per mm
- manufacturing tolerance
- close running fit (H8/f7)
- free running (H9/d9)

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uni/mmme/2044_design_manufacture_and_project/pneumatics_and_hydraulics.md Executable file
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---
author: Akbar Rahman
date: \today
title: MMME2044 // Pneumatics and Hydraulics
tags: [ uni, mmme2044, pneumatics, hydraulics ]
uuid: 9df953f9-13bc-40df-916a-dccaf9a338cf
lecture_slides: [ ./lecture_slides/Lecture 4 Pneumatics and Hydraulics.pdf ]
---
> I don't think I ever finished these notes.
# Actuation Systems
Actuation systems are the elements of control systems which are responsible for transforming the
output of a control system (such as a microcontroller or microprocessor) into a controlling action
on a machine or device.
![](./images/vimscrot-2022-10-24T15:48:55,638854990+01:00.png)
# Typical Hydraulic Power System
The pump pumps oil from a sump through a [non return valve](#non-return-valve) and an
[accumulator](#accumulator) to the system, from which it returns to the sump.
![](./images/vimscrot-2022-10-24T16:12:01,516571507+01:00.png)
## Advantages and Disadvantages of Hydraulic Power Systems
Advantages:
- Able to generate extremely large forces from compact actuators
- Easy to control speed
- Easy to implement linear motion
Disadvantages:
- Large infrastructure (high pressure pump, tank, distribution lines)
- Potential fluid leaks
- Noisy operation
- Vibration
- Maintenance
- Characteristics of fluids change with temperature and moisture
## Components of the System
### Hydraulic Pump
This provides the pressure and flow of the liquid in the system.
[More information about pumps](#types-of-pumps)
### Pressure Relief Valve
This is a safety system that safely let's out the fluid of a pressurised system if the pressure
exceeds a specified safe pressure.
### Non-return Valve
### Accumulator
The accumulator is a container in which the oil is held under pressure against an external force.
This smoothes out any short term fluctuations in the output oil pressure of the pump.
![](./images/vimscrot-2022-10-24T16:12:23,213636592+01:00.png)
- oil pressure rises &rarr; gas bladder contracts &rarr; more volume for oil to occupy &rarr; pressure reduces
- oil pressure reduces &rarr; gas bladder expands &rarr; less volume for oil to occupy &rarr; pressure increases
# Types of Pumps
## Gear Pump
A gear pump uses the meshing of gears to pump fluid by displacement.
They are one of the most common types of pumps for hydraulic fluid power applications.
They are also widely used in chemical installations to pump high viscosity fluids.
![](./images/vimscrot-2022-10-24T16:00:04,751432198+01:00.png)
## Vane Pump
A rotary vane pump is a positive displacement pump that consists of vanes mounted to a rotor that
rotates inside of a cavity.
In some cases these vanes have have variable length and/or be tensioned to maintain contact with
the walls as the pump rotates.
![](./images/vimscrot-2022-10-24T16:02:06,595981120+01:00.png)
## Radial Piston Pump
The working pistons extend in a radial direction symmetrically around the drive shaft to take in
fluid and output it at the outlet port.
![](./images/vimscrot-2022-10-24T16:04:18,644075219+01:00.png)
## Axial Piston Pump with Wash Plate
An axial piston pump is a positive displacement pump that has a number of pistons in a circular
array within a cylinder block.
It can be used as a stand-alone pump, a hydraulic motor or an automotive air conditioning
compressor.
![](./images/vimscrot-2022-10-24T16:08:20,920351717+01:00.png)
# Typical Pneumatic Power System
![](./images/vimscrot-2022-10-24T16:17:26,097345700+01:00.png)
1. (Filter, Silencer) The air inlet to the compressor is likely to be filtered silenced to reduce
the noise level.
2. An electric motor drives the compressor
3. The pressure relief valve protects the system against rising above a safe level
4. (Cooler, Water Trap) Since the compressor increases the temperature of the air, there may be a
cooling system and filter/water trap to cool the air and remove contaminants from the system.
5. An air receiver increases the volume of air in the system, to smooth out short term pressure
fluctuations
## Advantages and Disadvantages of a Pneumatic System
Advantages:
- Cheaper than electrical or hydraulic actuation
- Non-flammable so can use in harsh environments
- Simple to implement
- Controllable
Disadvantages:
- Does not produce a "stiff" system
- Requires a compressor, air conditioning, and control valves
- Pressurised air can be dangerous
# Actuators
Actuators generate a Force or Moment.
Both hydraulic and pneumatic actuators have the same principles, but differ in size.
Cylinders are the principal actuators for pneumatics:
![A double acting single rod cylinder](./images/vimscrot-2022-10-24T21:27:47,109056338+01:00.png)
![BS ISO 1219 Symbols of a double acting, single rod cylinder](./images/vimscrot-2022-10-24T21:28:10,876277510+01:00.png)
## Terminology
![](./images/vimscrot-2022-10-24T21:29:48,691574340+01:00.png)
Supply to compressed air to one chamber requires exhaust from the other chamber.
#### Positive Stroke
Extends and pushes to + position.
#### Negative Stroke
Retracts to - position.
## Single Acting Linear Actuator
The control pressure is applied to one side of the piston.
![](./images/vimscrot-2022-10-24T21:31:37,439073063+01:00.png)
When pressure is applied the piston moves along the cylinder.
When pressure is no long applied the piston reverts back to its initial position and the air is
vented from the cylinder.
## Double Acting Linear Actuator
Double Acting Linear Actuators are used by applying pressure to one of two sides to move a rod in
one of two directions.
![](./images/vimscrot-2022-10-24T21:35:07,023575068+01:00.png)
## Rotary Actuator
These produce a rotary motion.
A linear cylinder can be used to produce rotary motion with angles less than 360 degrees with the
correct linkages:
![](./images/vimscrot-2022-10-24T21:38:35,444846789+01:00.png)
You can also have vane type semi rotary, where the difference in pressure causes rotation:
![](./images/vimscrot-2022-10-24T21:37:41,337082140+01:00.png)
# Control Valves
Pneumatic and hydraulic systems use directional control valves to direct the flow of fluid through a
system.
They may be activated to switch the fluid flow direction by means of mechanical, electrical, or
fluid signal pressure.
## Valve Flow Symbols
![](./images/vimscrot-2022-10-24T21:41:44,043372779+01:00.png)
## Valve Actuation Symbols
![](./images/vimscrot-2022-10-24T21:42:03,065962564+01:00.png)
### Solenoid Operated Spool Valve
![](./images/vimscrot-2022-10-24T21:47:18,818669077+01:00.png)
## Spool Directional Control Valve
Move horizontally within the valve body to control flow:
![](./images/vimscrot-2022-10-24T21:40:47,390225256+01:00.png)
## Poppet Valve
This valve is normally closed.
![](./images/vimscrot-2022-10-24T21:41:21,917337342+01:00.png)
## Pressure Control Valve
![](./images/vimscrot-2022-10-24T21:48:10,147785815+01:00.png)
## Servo Valve
An electrohydraulic servo valve is an electrically operated valve that controls how hydraulic fluid
is sent to an actuator.
Servo valves are often used to control powerful hydraulic cylinders with very small electrical
signal.
Servo valves can provide precise control of position, velocity, pressure, and force with good post
movement characteristics.
![](./images/vimscrot-2022-10-24T21:50:04,086527638+01:00.png)
## Process Control Valve
Used to control the fluid flow rate.
A common form of pneuma