Material Properties, Applications, and Quality Control

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Material Properties, Applications, and Quality Control

EPDM rubber sealing strips are widely used in construction, automotive, electrical and other industries due to their excellent comprehensive performance. Mastering their material characteristics, application scenarios and quality control points is crucial for ensuring product sealing, durability and safety.

1. Basic Material Properties of EPDM Rubber

EPDM (Ethylene Propylene Diene Monomer) is a copolymer of ethylene, propylene and a small amount of non-conjugated diene monomers. Its unique molecular structure endows it with outstanding performance advantages:

Weather resistance: Excellent resistance to ozone, ultraviolet radiation and temperature changes, maintaining stability in the range of -40℃ to 120℃. It is not easy to age, crack or harden when used outdoors for a long time.
Chemical resistance: Resists erosion by most acids, alkalis, salts and polar solvents, and is compatible with common lubricants and coolants.
Sealing performance: Good elasticity and compression set resistance, can maintain effective sealing under long-term compression, and has low water absorption (less than 1%).
Electrical insulation: Excellent dielectric properties, suitable for electrical equipment sealing and insulation protection.
Environmental friendliness: Does not contain heavy metals or harmful plasticizers, meets international environmental standards such as RoHS, and is non-toxic and odorless.

2. Typical Application Scenarios

EPDM sealing strips are favored in multiple industries for their versatile performance, with core application areas including:

Industry Field	Specific Application Parts	Core Functions
Construction Industry	Door and window gaps, curtain wall joints, building expansion joints, glass mounting seams	Waterproof, dustproof, sound insulation, thermal insulation, energy saving
Automotive Industry	Door and window seals, trunk seals, engine compartment seals, sunroof seals	Waterproof, dustproof, sound insulation, shock absorption, wind noise reduction
Electrical Industry	Electrical cabinet doors, instrument enclosures, battery pack seals	Dustproof, waterproof (IP rating protection), moistureproof, electrical insulation
Mechanical Equipment	Mechanical equipment covers, pipeline connections, valve seals	Sealing, shock absorption, corrosion resistance to working media
Household Appliances	Refrigerator door seals, air conditioner enclosures, washing machine door gaps	Sealing, thermal insulation, noise reduction, moistureproof

3. Key Production Process Control

The quality of EPDM sealing strips is closely related to the production process, and the core control links include:

Formula design: According to the use environment, adjust the ratio of ethylene-propylene monomers, vulcanizing agents, reinforcing agents and plasticizers. For example, increase the ethylene content to improve weather resistance, or add carbon black to enhance wear resistance.
Extrusion molding: Control the temperature of the extruder barrel (generally 80-120℃) and the extrusion speed to ensure uniform cross-section, smooth surface and no bubbles or cracks of the product.
Vulcanization process: Adopt continuous vulcanization (steam or hot air vulcanization) with temperature controlled at 150-180℃ and time adjusted according to product thickness. Full vulcanization ensures the elasticity and durability of the sealing strip.
Post-processing: Carry out trimming, deburring and surface treatment (such as flocking or coating) to meet the assembly requirements and improve the friction resistance or adhesion of the product surface.

4. Quality Inspection Standards and Methods

To ensure the performance of EPDM sealing strips meets the application requirements, the following key indicators need to be inspected:

Inspection Indicator	Standard Requirement	Test Method
Hardness	50-70 Shore A (adjustable according to application)	Use a Shore hardness tester to measure at 3 different points on the product surface and take the average value
Tensile strength	≥10 MPa	Cut standard dumbbell-shaped samples and test with a tensile testing machine at a speed of 500 mm/min
Elongation at break	≥300%	Same as tensile strength test, record the elongation when the sample breaks
Compression set	≤30% (after 22 hours at 70℃)	Compress the sample to 25% of its original thickness, keep it at constant temperature, and measure the recovery rate after releasing the pressure
Weather resistance	No obvious cracking, hardening or discoloration after 1000 hours of UV aging	Use a UV aging test chamber to simulate outdoor environment and observe the appearance and performance changes
Waterproof performance	No water leakage under specified pressure	Install the sealing strip on the test fixture and conduct a water pressure test (pressure ≥0.3 MPa)

5. Common Quality Problems and Solutions

In actual use, EPDM sealing strips may encounter various quality problems, and targeted solutions are as follows:

Problem 1: Poor sealing performance
- Causes: Improper cross-sectional design, insufficient compression ratio, uneven product thickness.
- Solutions: Optimize the cross-sectional structure to match the assembly gap, ensure the compression ratio is 20%-30%, and strengthen the control of extrusion and vulcanization processes to ensure uniform thickness.
Problem 2: Easy aging and cracking
- Causes: Inferior raw materials, incomplete vulcanization, lack of anti-aging additives.
- Solutions: Use high-purity EPDM raw rubber, add anti-aging agents (such as carbon black, UV absorbers) to the formula, and strictly control the vulcanization temperature and time.
Problem 3: Poor adhesion to the substrate
- Causes: Contaminated product surface, improper surface treatment, mismatched adhesive.
- Solutions: Clean the surface of the sealing strip before assembly, carry out surface activation treatment (such as plasma treatment), and select a dedicated adhesive compatible with EPDM.
Problem 4: Compression set exceeding the standard
- Causes: Excessive plasticizer content, insufficient vulcanization degree, unreasonable filler ratio.
- Solutions: Adjust the formula to reduce plasticizer dosage, optimize vulcanization parameters to improve vulcanization degree, and select high-quality reinforcing fillers.