notes on moulding

uni/mmme/1029_materials_and_manufacturing/manufacturing.md

@@ -178,3 +178,196 @@ A material being worked on hot has its deformations eliminated as fast as they a
 
 A material is said to be cold when $T < 0.35T_m$.
 
+# Powder Processes
+
+Poweders can plowflow if forces between them are low
+
+With small amounts of binder, they can form "*plastic*" materials like clay.
+
+A *slurry* can be formed with a liquid carrier (where there is enough liquid to separate particles).
+In a slurry, often you want to reduce liquid content but avoid the particles touching or attracting
+each other.
+Adding a *deflocculant*[^d_deflocculant] results in the formation of a stable *slip*.
+
+Making the powders is often quite expensive when you have a controlled size distribution.
+
+## Clay and Ceramics
+
+Clay is an abundant raw material but it needs to be milled and screen for a controlled size
+distribution.
+When mixed with water it forms a *plastic* material.
+
+Structural clay products include bricks, tiles, and pipes.
+Other proucts include whitewares such as porcelain, pottery, and tableware.
+
+Ways to form the clay include pressing, isostatic pressing, extrusion, and machining.
+
+Engineering ceramics (e.g. silicon carbide, alumina) are shaped with small amounts of binder ---
+commonly pressed or isostatically pressed.
+
+## Slip Casting
+
+1. Pour slip into a mould (e.g. plaster of Paris)
+2. The mould is extremely water absorbing. This results in the remaining part developing some
+   structural integrity.
+3. Remove the mould and place in the oven to reduce water content.
+4. Fire to harden
+5. Add glaze and fire again.
+
+Drying leads to shrinkage and potential cracking.
+It also gives strength and allows for handling and maybe machining.
+
+![](./images/vimscrot-2022-02-28T22:03:43,392791602+00:00.png)
+
+## Sintering of Metals and Ceramics
+
+![](./images/vimscrot-2022-02-28T22:17:23,587537954+00:00.png)
+
+Atoms diffuse to points of contact, creating bridges and reducing the pore size.
+Diffusion is driven by a desire to reduce the surface area as surfaces are regions of high energy.
+
+## Powdering Metallurgy
+
+- Competitive with processes like casting, forging, machining
+- Used when the melting point is too high, a chemical reaction occurs at melting point, the part is
+  too hard to machine, or a very large quantity (on the order of 100 000) of the part is needed
+- Nearly 70% of parts produced is by powder metallurgy
+- Good dimensional accuracy
+- Controlloable porosity
+- Size range from balls in ball point pens to parts weighing 50 kg
+
+Basic steps of powder metallurgy:
+
+1. Powder production (commonly atomization) --- this is often a costly process and you must minimize
+   oxidation of the metal
+2. Blending/mixing --- add binders to keep the particles together and lubricants to reduce damage to
+   dies and aid consolidation
+3. Powder consolidation
+
+   - Shaping in a die
+   - 100-900 MPa of pressure applied
+   - Fast process as no heat needs to be removed
+
+4. Sintering at $0.7T_m$ to $0.9T_m$
+
+Shaping equipment has no requirement to be able to withstand high temperatures and the sintering
+equipment does not have the need for complex designs.
+This separates problems, making them easier to design.
+
+The pressing equipment is costly but the time spent pressing is quite small, allowing for greater
+throughput.
+Additionally, the furnace can operate continuously and is simple and cost effective.
+
+![](./images/vimscrot-2022-02-28T22:50:45,735174146+00:00.png)
+
+### Green Density
+
+The *green density* is a fraction of the true density.
+A low green density will result in high shrinkage on sintering.
+
+## Moulding
+
+Moulding is a shaping process used for viscous materials (typically polymers and glasses).
+Here the material can hold a shape unsupported but not for very long or under even small stresses.
+
+In order to mould a material we must raise the temperature above the glass transition temperature,
+$T_g$.
+At this temperature, the C-C bond in the chapolymer chain are able to easily rotate around each
+other.
+
+Large side chains or molecules on the main chain make it harder to rotate these bonds, making
+$T_g$ higher.
+Polar groups (e.g. chloride, cynaide, and hydroxide) have also hinder bond rotation.
+
+More information about polymers
+[here](https://notes.alv.cx/notes/uni/mmme/1029_materials_and_manufacturing/materials.html#polymers-1).
+
+## Extrusion
+
+Extrusion produced parts of constant cross section, like pipes and rods.
+The process is used primarily with thermoplastics and 60% of polymers are prepared by extrusion.
+
+![](./images/vimscrot-2022-03-01T18:28:42,810593415+00:00.png)
+
+## Blow Moulding
+
+Blow moulding is a rapid process with low labour costs.
+It produces hollow components that do not require a constant thickness, such as
+bottles, petrol tanks, and drums.
+Common materials to blow mould are HDPE, LDPE, PP, PET, and PVC.
+
+There are three common types of blow moulding:
+
+- Extrusion blow moulding
+- Injetion blow moulding
+- Stretch-blow processes
+
+However, they involve the following stages:
+
+1. A tubular preform, called a *parison* (a word I haven't been able to remember since GCSE) is
+   produced by either extrusion of injection moulding
+2. The *parison* is transferred into a cooled split-mould
+3. The *parison* is sealed and inflated to take up the shape of the mould
+4. The moulding is let to cool and solifidies under pressure
+5. The mould is opened and moulding is ejected
+
+![](./images/vimscrot-2022-03-01T18:30:18,545745201+00:00.png)
+
+## Injection Moulding
+
+1. Powder or pellets of polymer heated to liquid state (low viscosity)
+2. Under pressure, the liquid polymer is forced into a mould through a *sprue*, a small opening
+3. The pressurized material is held in the mould until it solidifies
+4. The mould is opened and the part is removed by ejector pins
+Selection was cancelled by keystroke or right-click.
+
+![](./images/vimscrot-2022-03-01T21:30:56,215686378+00:00.png)
+
+Theromoplastics are most common in injection moulding.
+A very high level of detail is attainable through this process and it produced little waste.
+
+Similar to [Die Casting](#die-casting-high-pressure-die-casting), you must consider corners (avoid
+sharp ones), draft angles (so you can get the part out), and section thickness (using ribs instead
+is preferable).
+
+Due to the high capital cost, injection moulding is only economical at high production volumes.
+
+### Co-Injection Moulding
+
+There is *sequential moulding* (one after the other) and *co-injection moulding* (together).
+
+These processes reduce assembly costs by integrating the parts and can use low grade recycled
+material for the inside of a component.
+It also allows for a part have to have multiple colours.
+
+This process requires special attention to be payed to shrinking/cooling.
+
+## Rotational Moulding
+
+Rotational moulding involves coating the insides of a heated mould with a thermoplastic.
+It is a low pressure alternative to blow moulding for making hollow components and is used
+for large components such as storage tanks, boat hulls, kayaks, and cones.
+
+## Moulding for Thermosetting Polymers
+
+There are two types:
+
+a. Compression moulding
+b. Transfer moulding
+
+![](./images/vimscrot-2022-03-01T22:15:05,965638775+00:00.png)
+
+### Compression Moulding
+
+For thermoplastics, the mould is cooled before removoal so the part will not lose its shape.
+Thermosets, however, may be ejected while they are hot so long as curing is complete.
+
+The process is slow but the material only moves a short distance and has lower mould pressures.
+It also does minimal damage to reinforcing fibres in composites and it is possible to make large
+parts.
+
+More manual labour is required and has longer cycle times than injection moulding.
+
+# Glossary
+
+[^d_deflocculant]: a substance which, when added to scattered particles in suspension, causes a reduction in apparent viscosity. Deflocculants are substances which prevent flocculation by increasing zeta potential and therefore the repulsive forces between particles. (<https://digitalfire.com/article/deflocculants%3A+a+detailed+overview>)

uni/mmme/1029_materials_and_manufacturing/materials.md

@@ -318,6 +318,19 @@ They are made of long carbon-carbon chains.
 
 ![](./images/vimscrot-2021-11-01T11:13:39,370133338+00:00.png)
 
+## Industrially Important Polymers
+
+The worldwide production of polymers in 2019 was $368\times10^6$ tonnes and the majority is from
+just 5 polymers:
+
+- Polyethylene (PE) --- wire insulation, flexible tubing, squeezy bottles
+- Polypropyene (PP) --- carpet fibres, ropes, liquid containers, pipes, chairs in Shoreham Academy
+- Polyvinyl chloride (PVC) --- bottles, hoses, pipes, valves, wire insulation, toys
+- Polystyrene (PS) --- packaging foam, egg cartons, lighting panels
+- Polyethylene terephthalate (PET) --- carbonated drinks bottles
+
+All of these materials are low cost.
+
 ## Thermoplastics
 
 The simplest polymer is poly(ethene):