Category: Materials

Machine start-up, Materials, Temperature

Thermal Stability

The first purpose of the injection unit for molding a crystalline material is to deliver to the mold the necessary amount of a homogeneous melt ( with no unmelt and no degraded material ). The rules of construction of the injection unit are then dependent on the molding material requirements in term of thermal behavior and heat needed. The first point to take into account for a crystalline material is the thermal stability at melt temperature, to avoid degradation. Then, screw, nozzle, backflow valve, adaptor should be designed to provide efficient melting of crystalline material and delivery of molten polymer to the mold.

Melting behavior is different between plastics are different. The amorphous polymer starts softening just after Tg and presents a continuous change in viscosity. This gives a very large temperature range to operate ( but a large variation of viscosity with temperature). In contrast, the crystalline polymer stays solid up to the melting point and suddenly melts to the liquid phase at a high temperature. This limits the processing range of temperature between unmelt and thermal degradation.

The second factor is the time the material stays at that temperature. For all polymers, the molecules can withstand a certain temperature before degradation can start. Obviously, the acceptable time limit becomes shorter when the temperature is higher. Degradation will result in the generation of gases which cause bubbles in the melt, splays on parts, mold deposit, yellow and brown marks on the parts.

The average residence time (or Hold-Up Time, HUT) in the injection unit is linked to the amount of polymer in the cylinder, the shot weight and the cycle time and can be calculated with the following:

HUT= (Weight of Resin in Cylinder) x Cycle Time / Shot Weight

or

HUT= (Maximum Screw Stroke x 2) x Cycle Time / Current Screw Stroke

Note: Effective screw stroke = distance the screw travels during rotation only

Materials

Common Materials

Categories

Polymer ; Thermoplastic

Physical Properties

Metric

English

Comments
Density
1.02 – 1.20 g/cc
0.0368 – 0.0434 lb/in³
Average value: 1.05 g/cc Grade Count:115
Water Absorption
0.250 – 1.00 %
0.250 – 1.00 %
Average value: 0.448 % Grade Count:24
Moisture Absorption at Equilibrium
0.000 – 0.210 %
0.000 – 0.210 %
Average value: 0.180 % Grade Count:9
Water Absorption at Saturation
0.300 – 1.03 %
0.300 – 1.03 %
Average value: 0.796 % Grade Count:5
Maximum Moisture Content
0.0100 – 0.150
0.0100 – 0.150
Average value: 0.0256 Grade Count:9
Linear Mold Shrinkage
0.00200 – 0.00800 cm/cm
0.00200 – 0.00800 in/in
Average value: 0.00533 cm/cm Grade Count:75
Linear Mold Shrinkage, Transverse
0.00300 – 0.00800 cm/cm
0.00300 – 0.00800 in/in
Average value: 0.00591 cm/cm Grade Count:6
Melt Flow
0.100 – 35.0 g/10 min
0.100 – 35.0 g/10 min
Average value: 4.94 g/10 min Grade Count:115

Mechanical Properties

Metric

English

Comments
Hardness, Rockwell R
68.0 – 113
68.0 – 113
Average value: 101 Grade Count:60
Ball Indentation Hardness
65.0 – 110 MPa
9430 – 16000 psi
Average value: 93.2 MPa Grade Count:11
Tensile Strength, Ultimate
22.1 – 49.0 MPa
3210 – 7110 psi
Average value: 36.4 MPa Grade Count:31
Tensile Strength, Yield
13.0 – 65.0 MPa
1890 – 9430 psi
Average value: 40.4 MPa Grade Count:112
22.1 – 59.3 MPa
@Temperature -18.0 – 71.0 °C
3210 – 8600 psi
@Temperature -0.400 – 160 °F
Average value: 40.7 MPa Grade Count:1
Elongation at Break
3.00 – 150 %
3.00 – 150 %
Average value: 34.2 % Grade Count:71
Elongation at Yield
0.620 – 30.0 %
0.620 – 30.0 %
Average value: 5.57 % Grade Count:49
Modulus of Elasticity
1.00 – 2.65 GPa
145 – 384 ksi
Average value: 2.07 GPa Grade Count:57
1.50 – 2.60 GPa
@Temperature -18.0 – 71.0 °C
218 – 377 ksi
@Temperature -0.400 – 160 °F
Average value: 2.05 GPa Grade Count:1
Flexural Yield Strength
0.379 – 593 MPa
55.0 – 86000 psi
Average value: 69.2 MPa Grade Count:73
49.6 – 113.8 MPa
@Temperature -40.0 – 71.0 °C
7190 – 16510 psi
@Temperature -40.0 – 160 °F
Average value: 81.7 MPa Grade Count:1
Flexural Modulus
0.200 – 5.50 GPa
29.0 – 798 ksi
Average value: 2.18 GPa Grade Count:100
1.90 – 2.80 GPa
@Temperature -40.0 – 71.0 °C
276 – 406 ksi
@Temperature -40.0 – 160 °F
Average value: 2.35 GPa Grade Count:1
Izod Impact, Notched
0.380 – 10.3 J/cm
0.712 – 19.3 ft-lb/in
Average value: 3.22 J/cm Grade Count:88
0.450 – 4.00425 J/cm
@Temperature -40.0 – 0.000 °C
0.843 – 7.50160 ft-lb/in
@Temperature -40.0 – 32.0 °F
Average value: 1.34 J/cm Grade Count:21
0.480 – 4.00 J/cm
@Temperature -40.0 – 0.000 °C
0.899 – 7.49 ft-lb/in
@Temperature -40.0 – 32.0 °F
Average value: 1.34 J/cm Grade Count:12

 

Reference : http://www.matweb.com/search/DataSheet.aspx?MatGUID=3a8afcddac864d4b8f58d40570d2e5aa&ckck=1

Materials

Injection Molding Materials

There are two types of materials(resins) which can be used in the injection molding industry; Thermoplastic and Thermoset. A thermoplastic, or thermo-softening plastic, is a plastic material, a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight[1].  A thermoset also called a thermosetting plastic, is a plastic that is irreversibly cured of a soft solid or viscous liquid, prepolymer or resin.[1]

large.png

Figure source: http://www.bbc.co.uk/guides/z9tysg8

Resin selection is a very critical step for the injection molding. There are many material suppliers offering quality materials for the injection molding.

They can formulate a plastic to meet the consumer needs properly. For example, the applications of the product play a key role in the choosing material properties. For High voltage connector, the resin has to provide chemical resistance, excellent tracking defense and heat& humidity resilience. For a Fluid Engineering Components, the resin has to have a good hydrolytic stability, excellent resistance to water and FDA approved. The formulated resin has the processability and consistent properties after molding process and in the final use.

Reference :

  1. https://www.wikipedia.org/
Materials

Injection Molding Materials

There are two types of materials (resins) which can be used in the injection molding industry; Thermoplastic and Thermoset.

A thermoplastic, or thermosoftening plastic, is a plastic material, a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight.[1]

A thermoset also called a thermosetting plastic, is a plastic that is irreversibly cured of a soft solid or viscous liquid, prepolymer or resin.[1]

large.png

Figure source: http://www.bbc.co.uk/guides/z9tysg8

Resin selection is a very critical step for the injection molding. There are many material suppliers offering quality materials for the injection molding.

They can formulate a plastic to meet the consumer needs properly. For example, the applications of the product play a key role in the choosing material properties. For High voltage connector, the resin has to provide chemical resistance, excellent tracking defense and heat& humidity resilience. For a Fluid Engineering Components, the resin has to have a good hydrolytic stability, excellent resistance to water and FDA approved. The formulated resin has the processability and consistent properties after molding process and in the final use.

 

 

Reference :

  1. https://www.wikipedia.org/
Materials

Common Materials for Injection Molding

Common Thermoplastics :

Acrylonitrile Butadiene Styrene (ABS)

Polyethylene (PE)

high-density polyethylene (HDPE) and low-density polyethylene (LDPE)

Polycarbonate(PC)

Polyamide (Nylon)

High Impact Polystyrene (HIPS)

polypropylene(PP)

Acrylic (PMMA)

Teflon

Polyvinyl chloride (PVC)

Styrene Acrylonitrile (SAN)

Polyurethane (PUR)

Polystyrene Crystal

Common Thermosets :

Melamin formaldehyde (MF)

Polyster resin (PR)

Epoxy resin (ER)

Urea formaldehyde (UF)

Bakelite or Phenol formaldehyde (PF)

Silicone Resin

Duroplast

Vinyl ester