PP Injection Molding
Services On Aria
PP is chosen for injection molding services because it’s cost – effective, easily available, has good mechanical and chemical properties, suitable thermal characteristics, is lightweight, and is recyclable.
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What is PP lastic?
PP is made from propylene monomers through polymerization. Its chemical structure consists of long chains of carbon and hydrogen atoms.
The arrangement of the methyl groups on the polymer chain can vary. Isotactic PP, where the methyl groups are on the same side of the chain, is the most commonly used in industrial applications due to its higher crystallinity and better mechanical properties.
Description
Full Name
Polypropylene
Process
Finishing options
Mold texturing，Pad printing，Laser engraving，Electroplating, Bead Blasting
Appearance
White, Black, Gray, Blue, Green and Red
Prices
$
Features
Density
0.895~0.92 g/㎤
Strengths
Good Scratch Resistance, High Gloss, Strong toughness, Ease of processing
Tensile Strength
4800 PSI
Elongation at Break
100–600%
Hardness
Rockwell R hardness of 92
Advantages of PP Injection Molding
There are many benefits derived from plastic molding, Some of the advantages of the material include:
Cost Effectiveness
PP’s low cost cuts injection molding material expenses. Suiting mass production, makers can cheaply craft many parts for competitive market pricing.
Design Flexibility
PP injection molding enables complex forms. Molten PP fills molds of various features. Its design versatility creates wide ranging products.
Lightweight
PP’s low density makes injection molded products light, good for auto, aerospace (fuel eff.) & consumer goods (handling).
Recyclability
PP is recyclable. Injection molded PP parts can make new products. This cuts waste and virgin PP demand, an environmental plus.
Thermal Properties
PP has a relatively high melting point that allows it to be processed through injection molding without significant degradation.
Polypropylene Subtypes and Thier Properties
Subtypes
Density (g/cm3)
Tensile Strength at Yield (MPa)
Rockwell Hardness (R)
Elongation at break (%)
Melt Temperature (°C)
Mold Temperature (°C)
PPH
0.932
32.8
94.7
159
214
41.3
PPC
0.952
25.8
86.5
231
215
42.9
PP-Talc 30%
1.13
25.4
77.6
23
223
49.7
PP GF 30%
1.14
77.8
101
4.01
157
53.1
PP- Carbon Black-UV
1.04
26.7
90.1
20.3
223
49.7
Applications of PP Injection Molding
PP Injection Molding Material Properties
PP Plastic Properties
Value
Tensile Strength (Yield) （MPa）
31.0–37.2
Flexural Modulus（GPa）
0.8 - 1.2
Impact Resistance (Izod Impact, Notched)
2 to 10 ft-lb/in
Maximum Service Temperature（℃）
65-125
Chemical Formula
(C3H6)n
Glass Transition Temperature（℃）
-20°C to -0°C
Heat Deflection Temperature（℃）
100
Drying Temperature（℃）
60-80
Drying Time（hr）
2
Mold Temperature（℃）
35～65
Melt Temperature（℃）
200～250
Injection Pressure（MPa）
130～180
Injection Speed（ mm/sec）
50–100
Cooling Time（S）
20～60
Scrap Quantity（mm）
3～10
Back Pressure（MPa）
９～1７
Clamping Force（ton/in2）
2
Return Speed (rpm)
60～90
Shrinkage
1-2%
Injection Molding Design Guide
Living Hinges
Polypropylene living hinges’ thickness should be 0.2 – 0.51 mm. Good design has large radii and “shoulders” for flat recesses. See our tech article on living hinge design for more.
Wall Thickness
Injection molded PP part wall thickness: 0.635 – 3.81 mm. Ensure gradual thickness transitions to avoid sink marks. Rib thickness < half wall thickness.
Radii
Radii in injection molded parts cut stress & extend life. For PP injection molding parts, radius ≥ 25% wall thickness, 75% for optimal props.
Draft Angle
A draft angle is necessary to facilitate the ejection of the molded part from the mold. For the external surfaces of PP living – hinge – containing parts, a draft angle of 1 – 3 degrees is usually sufficient.
Part Tolerances
Tolerances are commercial or fine. Fine ones are tighter. Tighter tolerances raise tooling and part costs. Both vary with part size. E.g., a 20 mm PP part has 0.125 mm commercial tolerance and 0.075 mm fine tolerance.
Sink Marks
Sink marks can occur when there is uneven shrinkage due to variations in wall thickness or improper cooling. Solutions may include adjusting the wall thickness uniformity, optimizing the cooling system, or increasing the holding pressure and time.
Warping
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