Polymer and Plastics Manufacturing. Apiwat Muttamara. Outline. Polymer Equipment and process steps Design for manufacturing, tooling and defects . Materials. Solid materials. Plastics. ceramics. metals. thermosetts. thermoplastics. elastomers.
Plastic:Greek, plastikos, means to form or mold
Thermoplastics & Thermosets
poly = many
mer = part
A polymer is a long chain molecule
that is composed of a large number
of repeating units of identical structure.
These different hydrocarbons have different boiling points, which means they can be separated by distillation
n = degree of polymerization
Fringed-micelle model of semicrystalline polymers
OF PLASTIC POLYMER
Yield stress (sy) ความเค้นที่พบการเสียรูปพลาสติก(plastic deformation)
Tensile strength (TS) (สำหรับพอลิเมอร์) ความเค้นที่ชิ้นงานแตกหัก **
(ทั่วไป) ความเค้นสูงสุดบนกราฟ engineering
STAGES OF DEFORMATION
OF A SEMI-CRYSTALLINE POLYMER
Note: พบลักษณะคอดกิ่วภายใต้การดึง เรียกว่า Necking
amorphous tie chains
Tilting of lamellar
STAGES IN DEFORMATION OF A SEMICRYSTALLINE POLYMER
(crosslinked and network polymers)
vulcanized rubbers, Polyurethane Epoxy, Polyester
Phenolics (named Bakelite by Leo Bakeland)
- Resin could be shaped and hardened with heat
- Phenol and formaldehyde reaction after heat
- Replacement for shellac, natural plastic (1907)
- W. H. Carothers of DuPont (1920’s)
- W. Semon of B.F. Goodrich (1929)
Codes for plastics
EX. Computer housings
Plastics Processing:Compression and Transfer Molding
dishes, handles for cooking pots
skis, housing for high-voltage switches
some rubber parts like shoe soles
and even composites such as fiber-reinforced parts
Plastics Processing:Compression and Transfer Molding
(more complex shapes)
The process generally makes use of polyethylene powders, other powders, and liquids. However, nylon, elastomers, fluoropolymers, and polypropylene can also be used
Rotational molding, otherwise known as rotomolding or rotational casting, is a thermoplastic processing method for producing simple to complex, leak-proof hollow parts that can be filled with foam.
Plastics Processing: Thermoforming
Sheet of plastic Heated (soft) Molded using a shaped die
* Source: R. Ogorkiewicz, “Engineering Properties of Thermoplastics.”; ** http://www.arrem.com/designguide/dgprocesscap.htm
Plastics Processing:Injection Molding
- Probably the most common, most important, most economical process
A dividing line between a cavity plate and a core plate of a
- Make a parting line on a flat or simple-curved surface so that flash cannot be generated.
- Venting gas or air.
One parting line
Two parting lines
A sprue is a channel through which to transfer molten plastics injected from the injector nozzle into the mold.
A runner is a channel that guides molten plastics into the cavity of a mold.
A gate is an entrance through which molten plastics enters the cavity.
Hot runner, runnerless mold
Molding defects are caused by related and complicated reasons asfollows:
* Malfunctions of molding machine
* Inappropriate molding conditions
* Flaws in product and mold design
* Improper Selection of molding material
This is a phenomenon where a thin line is created when different flows of molten plastics in a mold cavity meet and remain undissolved. It is a boundary between flows caused by incomplete dissolution of molten plastics. It often develops around the far edge of the gate.
Low temperature of the mold causes incomplete dissolution of the molten plastics.
Increase injection speed and raise the mold temperature. Lower the molten plastics temperature and increase the injection pressure. Change the gate position and the flow of molten plastics. Change the gate position to prevent development of weldline.
Flashes develop at the mold parting line or ejector pin installation point. It is a phenomenon where molten polymer smears out and sticks to the gap.
Poor quality of the mold.The molten polymer has too low viscosity.
Injection pressure is too high, or clamping force is too weak.
Avoiding excessive difference in thickness is most effective.
Slow down the injection speed.
Apply well-balanced pressure to the mold to get consistent clamping force, or increase the clamping force.
Enhance the surface quality of the parting lines, ejector pins and holes.
This is the phenomenon where molten plastics does not fill the mold cavity completely. and the portion of parts becomes incomplete shape.
The shot volume or injection pressure is not sufficient.
Injection speed is so slow that the molten plastics becomes solid before it flows to the end of the mold.
Apply higher injection pressure. Install air vent or degassing device. Change the shape of the mold or gate position for better flow of the plastics.
This deformation appears when the part is removed from the mold and pressure is released.
Uneven shrinkage due to the mold temperature difference (surface temperature difference at cavity and core), and the thickness difference in the part. Injection pressure was too low and insufficient packing.
Take a longer cooling time and lower the ejection speed. Adjust the ejector pin position or enlarge the draft angle. Examine the part thickness or dimension. Balance cooling lines. Increase packing pressure.
ts < t
-Equal cooling from the surface
Material data base
gate location determines weld lines
* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_design_7.htm
- If the geometry of the part has undercuts [definition ?]