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With the rapid advancement of the automotive industry’s “New Four Modernizations” (Lightweighting, Electrification, Intelligence), engineering plastics are undergoing unprecedented performance innovation. Among the many alternatives to metal, **PP long glass fiber reinforced material (PP-LGF)** has become the preferred choice for automotive structural parts and interior functional components, thanks to its excellent specific strength, fatigue resistance, and unique potential for “plastic metallization.”

As a company deeply engaged in this field, Jurong Best Composite Materials Co., Ltd. produces the PP-GF30, PP-GF40, and PP-GF50 series, which precisely cover the full range of needs from secondary load-bearing structures to high-rigidity skeleton parts. Below, we delve into the specific application logic and value of these materials in three key components: the shift lever base, engine cover, and sunroof rail.

 I. Shift Lever Base (Gearshift Mechanism Bracket): The Balance Between High Stiffness and Creep Resistance

Application Scenario Description:

The shift lever base is located in the vehicle’s center console area. It not only bears the driver’s shifting force but also secures the complex electronic shift mechanism. Traditional metal bases are heavy and prone to NVH (Noise, Vibration, Harshness) issues.

Material Solution: PP-GF40 (The Golden Ratio) For this application, PP-LGF with 40% glass fiber content is a cost-effective choice.

Mechanical Performance Match: Compared to PP-GF30, PP-GF40 typically achieves a flexural modulus above 6000 MPa, providing higher deformation resistance. This ensures that during frequent pushing and pulling by the driver, the base does not creep or shift, maintaining a precise mechanical shift feel.

Case Study & Results:A major joint venture automaker switched the base to PP-GF40 in a model upgrade. Results showed that in thermal cycling tests from -35°C to 85°C, PP-GF40 not only maintained stiffness comparable to nylon but also reduced costs by approximately 20-25%. Additionally, leveraging the low density of PP, it achieved a single-part weight reduction of over 15%.

Production Considerations:

Warpage Control: The shift lever base has a complex geometry with multiple mounting and locating holes. Although PP-GF40 has better flowability than PA, proper gate design (preferably valve gate hot runners) is required to control glass fiber orientation and avoid warpage caused by anisotropic shrinkage.

Connection Strength: Due to the inherently low polarity of PP, if the base requires load-bearing screws, it is advisable to design metal inserts or use ultrasonic welding to avoid stress cracking caused by direct self-tapping screw threading.

II. Engine Cover (Intake Manifold Cover / Cylinder Head Cover): A Battle of Endurance in the High-Temperature “Steamer”

Application Scenario Description:

The engine cover is located in the core area of the engine compartment, in long-term contact with hot air, oil vapor, and high temperatures (long-term 120-140°C). The core requirements are long-term heat aging resistance and dimensional stability.

Material Solution: PP-GF30 (Heat-Stabilized Upgrade)

Although PP-GF30 is a general-purpose reinforced grade, applications around the engine require special heat-aging stabilization (Heat Aging Stabilized) modification.

High-Temperature Fatigue Strength: In conventional short-glass-fiber PP, molecular chain mobility increases at high temperatures, causing a sharp drop in rigidity. However, the three-dimensional network structure formed by long-glass-fiber PP-GF30 gives it a high-temperature fatigue strength at 120°C that is twice that of ordinary short-glass-fiber reinforced PP, and even 10% higher than glass-fiber reinforced nylon, which is known for its heat resistance.

Case Study & Results: A European automaker replaced aluminum with PP-LGF30 for an engine decorative cover. The results were significant: besides a weight reduction of over 40%, the LGF material notably reduced the transmission of high-frequency engine vibrations to the cabin. It passed 150°C / 1000-hour hot air aging tests without cracking or deformation.

Production Considerations:

Low Odor & Low VOC: The engine cover faces the passenger compartment, and high temperatures accelerate VOC emission. During compounding and injection molding, shear heat must be strictly controlled to avoid PP degradation and the generation of aldehydes and ketones, ensuring an odor level ≤ 3.0.

Glass Fiber Retention Length: This is the core secret of LGF materials. Low-shear screws must be used during injection molding to ensure that the glass fiber length in the finished part remains between 3 mm and 6 mm (as opposed to 0.2-0.4 mm for ordinary short fibers). Otherwise, the benefit of “long glass fiber” reinforcement is lost.

III. Sunroof Rail (Drain Channel / Frame): The Ultimate Pursuit of Lightweighting and Dimensional Precision

Application Scenario Description:

Panoramic sunroof rails typically span the vehicle roof, demanding extremely high rigidity and a low coefficient of linear thermal expansion (CLTE). Traditional metal rails are not only heavy but also require complex, costly processing steps.

Material Solution: PP-GF50 (High-Rigidity Flagship Grade)

With 50% glass fiber content, this is the “ceiling” level for PP reinforcement, designed for extreme rigidity requirements.

Rigidity Comparable to Metal: PP-GF50 typically achieves a flexural modulus above 10,000 MPa. This allows slender, thin-walled sunroof rails to maintain straightness under temperature cycling, ensuring smooth glass sliding and no abnormal noise.

Low CLTE: The network structure of long glass fibers effectively restricts the thermal expansion/contraction of the PP matrix, reducing its CLTE from 10-15×10⁻⁵/K for ordinary PP to 2-3×10⁻⁵/K (close to aluminum alloy levels), effectively solving rail binding issues caused by thermal expansion/contraction.

Case Study & Results: A leading Chinese automaker used PP-LGF50 to replace aluminum extrusions for the sunroof rails of its flagship SUV. This achieved a 30% weight reduction per part and integrated multiple metal brackets into the molded part, reducing assembly steps by five and significantly lowering total manufacturing costs.

Production Considerations:

Glass Fiber Blooming: With GF50′s high fiber content, “glass fiber blooming” on the part surface is common, affecting appearance. High mold temperatures (80-100°C) with rapid heat/cool cycling technology and fine textured mold surfaces are recommended to cover or absorb the fibers.

Weather Resistance: Sunroofs are exposed to water and UV radiation. Carbon black and UV stabilizers must be added to the formulation to prevent material degradation and chalking under UV exposure.—

IV. Summary and Industry Outlook

PP long glass fiber materials are no longer simply “plastics,” but rather complex “composite material solutions.”

PP-GF30 is a universal grade, suitable for components around the engine (such as covers) that require a balanced combination of heat resistance and overall performance. It is also the first choice for interior structural parts, balancing toughness and rigidity, and can be adapted for shift lever bases and sunroof rails.

PP-GF40 is the best choice for replacing nylon. As a medium-to-high strength universal grade, it covers all three major components, balancing performance and cost. It delivers both performance and cost efficiency in structural parts such as shift lever bases.

PP-GF50 is a powerful tool for “replacing metal with plastic,” specializing in large structural parts with extremely high rigidity requirements, such as sunroof rails and front-end modules. Designed for high-load engine compartment applications, it offers ultra-high rigidity, heat resistance, and creep resistance, with a primary focus on engine covers.

As the demand for automotive lightweighting transitions from “recommended” to “mandatory,” the application boundaries of long-glass-fiber PP materials in automotive structural parts are continuously expanding.

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