From ec195bbe6639f7fc49bb1545fbdf5ec2a44953fe Mon Sep 17 00:00:00 2001 From: Alvie Rahman Date: Tue, 14 Mar 2023 10:26:16 +0000 Subject: [PATCH] mmme2044 add incomplete notes on pneumatics, bearings --- .../bearings.md | 155 +++++++++++ .../pneumatics_and_hydraulics.md | 243 ++++++++++++++++++ 2 files changed, 398 insertions(+) create mode 100755 uni/mmme/2044_design_manufacture_and_project/bearings.md create mode 100755 uni/mmme/2044_design_manufacture_and_project/pneumatics_and_hydraulics.md diff --git a/uni/mmme/2044_design_manufacture_and_project/bearings.md b/uni/mmme/2044_design_manufacture_and_project/bearings.md new file mode 100755 index 0000000..682e40b --- /dev/null +++ b/uni/mmme/2044_design_manufacture_and_project/bearings.md @@ -0,0 +1,155 @@ +--- +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 + +
+ + +## Plain Journal Bearings + + + +- 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 + +
+ +
+ + +## Ball and Roller Bearings (Rolling Element Bearings) + + + +- 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) + +
+ +
+ + +## Plain Rubbing Bearings (Dry Sliding) + + + +- does not use liquid lubrication +- usually polymeric +- dry lubricants added (e.g. PTFE) +- reinforcements added (e.g. glass fibre) + +
+ +
+ + +## Oil Lubricated Porous Bearings + + + +- 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 + +
+ +
+ + +# Hydrodynamic Bearings + + + +- 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) + diff --git a/uni/mmme/2044_design_manufacture_and_project/pneumatics_and_hydraulics.md b/uni/mmme/2044_design_manufacture_and_project/pneumatics_and_hydraulics.md new file mode 100755 index 0000000..6be64ad --- /dev/null +++ b/uni/mmme/2044_design_manufacture_and_project/pneumatics_and_hydraulics.md @@ -0,0 +1,243 @@ +--- +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 → gas bladder contracts → more volume for oil to occupy → pressure reduces +- oil pressure reduces → gas bladder expands → less volume for oil to occupy → 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