Can a glass-filled PP case replace ABS?

Answer: On stiffness and strength yes: 4.6 GPa against 2.3 GPa, 58 against 42 MPa. On impact no: 4.5 kJ/m² against 14, so drop-critical work stays with ABS.

Is read-through a tool problem or a compound problem?

Answer: Mostly mould temperature and injection speed: below 70 °C or above 80 mm/s the streaks are worst, and 80–90 °C at 40–60 mm/s brings depth from 0.15 mm to 0.05 mm.

Should I specify 20% or 30% glass?

Answer: By where the weld line lands. Within 30 mm of a latch seat, take 20% at 60% retention and 29 MPa; routed to a low-stress zone, take 30% for 4.6 GPa and 0.85 mm sag.

Does every glass job need different tool steel?

Answer: At 30%, yes: P20 flashes at 80,000 shots, while HRC 48–52 or 0.02 mm chrome lasts 200,000. At 20% glass P20 survives if the gate is a replaceable insert, at 0.4 CNY per case.

Glass-Filled PP Protective Case: Strength and Finish

Quick answer: A glass-filled PP case trades impact for stiffness: 20% glass lifts tensile strength from 28 to 48 MPa and flexural modulus from 1.4 to 3.2 GPa. At 30% glass the figures reach 58 MPa and 4.6 GPa, while notched impact falls from 8 to 4.5 kJ/m² and a gloss surface stops being possible.

How glass-filled PP steps up in strength
Modulus and heat deflection
Cost one: impact and weld lines
Cost two: read-through and finish
Tool wear and mould life
Screening: when to go glass-filled
FAQ

1. How glass-filled PP steps up in strength

Glass-filled PP gains strength in steps, not on a straight line: 28 MPa unfilled, 48 MPa at 20% short glass, 58 MPa at 30%, gains of 71% and 107%. Values follow GB/T 1040.2 on 1A bars at 50 mm/min.

Stiffness climbs faster in glass-filled PP: flexural modulus runs 1.4, 3.2 and 4.6 GPa, so the 30% grade is 3.3 times unfilled, because short fibres above 20:1 build the skeleton that carries bending load.

Heat deflection at 1.82 MPa tracks the same steps: 100 °C unfilled, 122 °C at 20% glass, 135 °C at 30%. At the 75 °C a closed vehicle reaches in summer, the unfilled grade softens while 30% glass keeps 60 K of margin.

Property	Unfilled	20% glass	30% glass
Tensile MPa	28	48	58
Flexural modulus GPa	1.4	3.2	4.6
Heat deflection °C	100	122	135
Notched impact kJ/m²	8	5.5	4.5
Density g/cm³	0.91	1.04	1.12
Shrinkage %	1.5	0.6	0.4

Shrinkage must be read with direction: 0.4% along flow and 0.8% across it, which turns into warp on long parts.

2. Modulus and heat deflection

Lid sag makes modulus visible. A 600 mm × 400 mm cover, 3 mm walls, 60 kg spread evenly at 25 °C, sags 2.6 mm unfilled, 1.2 mm at 20% glass and 0.85 mm at 30%.

Glass-filled PP case open on a scarred steel bench, lid upright with corner gussets, slotted foam tray, deep gasket groove

Creep converges the same way. At 40 °C with 20 kg for 24 h the unfilled cover deflects 3.0 mm against 1.4 and 1.1 mm for the glass grades, and recovery after 2 h runs 78%, 85% and 88%. Four cases stacked for 30 days leave 5.5 mm of permanent set unfilled and 1.8 mm at 30% glass.

Only the 135 °C grade can sit within 300 mm of an exhaust; compound steps by 1.7 and 3.1 CNY/kg, or 7 and 14 CNY on a 4.5 kg case. Growing unfilled walls 3 to 4 mm raises stiffness 2.4 times and mass 33%, while 30% glass gives 4.6 GPa at 3 mm for 23% more mass.

3. Cost one: impact and weld lines

In glass-filled PP, notched impact falls from 8 to 5.5 and 4.5 kJ/m², losses of 31% and 44%; at -20 °C it drops from 6.2 to 3.4 and 2.6. Fibre ends are stress raisers, so a crack joins the next within tens of microns.

Weld lines are the bill most often missed. Where two melt fronts meet, fibres align along the interface and strength keeps 40%–60% of bulk: 29 MPa at 20% glass, 23 MPa at 30%.

Position	Bulk MPa	Weld line MPa	Retention
20% glass	48	29	60%
30% glass	58	23	40%

Weld lines must stay 30 mm clear of latch seats, hinge bosses and handle roots; otherwise move the gate to the base centre, which on a 48 L case cuts weld length from 380 mm to 210 mm. A 5 kg/1 m drop dents the 20% grade 4 mm with no crack and the 30% grade 3 mm with a 6 mm hairline; chilled to -10 °C, the same drop opens 11 mm and 22 mm.

4. Cost two: read-through and finish

Read-through is built into glass-filled PP: fibres float to the surface at the flow front and leave pale streaks 0.05–0.15 mm deep, and sanding drags more up. Running the mould at 80–90 °C, melt at 230–245 °C and medium speed keeps depth under 0.05 mm.

Glass-filled PP case from above: cream lid, even corner radii, shallow front recess, flush bosses, matte finish, no flow marks

A gloss route does not exist: unfilled PP polishes to Ra 0.4 μm, but every fibre cross-section then shows. Texture at Ra 1.6–3.2 μm, deeper than the 13 μm fibre diameter, is the workable route.

Colour suffers as well. Glass carries a beige cast, so light shades land at ΔE 1.5–2.5 and dark shades stay inside ΔE 1.0; holding ΔE ≤1.0 on a light part needs 8 CNY of paint and one more day.

5. Tool wear and mould life

Glass-filled PP wears the tool in proportion to loading. Against P20, 20% glass abrades about 6 times faster than unfilled compound and 30% glass about 9 times; gates and vent slots groove first, and 0.02 mm already prints on the part. Inserts run at HRC 48–52 or carry 0.02 mm of hard chrome, which holds life past 200,000 shots, while untreated P20 flashes at 80,000. The press changes too: bimetal screw and non-return valve, barrel 2 flights longer, 15% cushion. Without them shot weight scatters from ±1.5% to ±4%. Tooling runs 80,000 CNY unfilled against 120,000 at 30% glass, or 2 CNY per case over 20,000 shots plus 0.8 CNY upkeep.

6. Screening: when to go glass-filled

The question is whether the case carries load, not whether it should be harder.

Duty	System	Wall mm	Surface
Structural, stacked 4 high	30% glass	3.0	texture Ra 2.4 μm
Load-bearing, drop critical	20% glass	3.0–3.5	texture Ra 3.0 μm
Visible face, light gloss	unfilled copolymer	3.5–4.0	polished
Handled below -20 °C	unfilled or 20% glass	3.5	texture Ra 3.2 μm

Compound runs 10.8 CNY/kg unfilled, 12.5 at 20% glass and 13.9 at 30%, so a 4.5 kg case carries 49, 56 or 63 CNY; running 0.5 mm thinner saves 0.6 kg and pulls 7 CNY back. After 1000 h of xenon to GB/T 16422.3, modulus retains 92% on glass and 85% unfilled, but with impact at 2.6 kJ/m² the drop height must fall from 1.2 m to 0.9 m.

Conclusion

The value of a glass-filled PP case is not that it is stronger; it is that stiffness, heat deflection and dimensional stability arrive together: 4.6 GPa and 135 °C at 3 mm walls, paid for with 4.5 kJ/m² of impact, 40% weld-line retention and a surface that can only be textured. Screen in this order: can the weld line clear the latch and hinge, what is the lowest service temperature, then how much strength is needed. JUNZHIJIA fixes gate position, glass loading and texture roughness on one drawing.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.