Recently, our company successfully delivered a customized universal testing machine designed specifically for testing the foam hardness of passenger car seats. To ensure optimal performance, Kezhun Measurement & Control tailored a comprehensive technical solution encompassing testing methodologies, fixtures, and inspection equipment.
As the automotive industry continues to evolve, there is a growing demand for enhanced in-vehicle comfort. Seats, being integral components of a vehicle's interior, directly impact the occupants' comfort and well-being. Among various factors, the hardness of seat foam is a critical parameter that influences support, resilience, and overall seating experience.
This article delves into the concept of seat foam hardness, elucidates testing principles and methodologies, and examines the implications of different hardness levels on drivers and passengers. Furthermore, it addresses the challenges faced by the automotive manufacturing sector in seat design and production, and explores how hardness testing can mitigate these challenges to elevate seat quality and comfort.
I. Test Content
1. Indentation Hardness
Indentation hardness refers to the force required to deform a foam sample under specified laboratory conditions, equipment, and test procedures, measured in Newtons (N).
2. Curing
During the production process, foam products are placed in a natural workshop environment for 24 hours after demolding to stabilize their physical properties, rendering them suitable for seat production and subsequent testing. This process is termed curing.
II. Test Principles
Passenger car seat foam hardness testing involves applying a force to the foam within a specified distance using testing equipment under defined conditions. The resultant feedback force is measured to determine the foam's hardness value.
III. Relevant Standards
Tests are conducted in accordance with the reference standard Q-JLY J7111077B-2019.
IV. Testing Instruments
1. Customized Dual-Column Tensile Testing Machine
Force measurement accuracy: ±1% or ±1N
2. Customized Platen Indenter
The platen features a smooth (non-polished) surface and is assembled using spherical joints to prevent vertical movement, or other suitable connection methods. The platen diameter is 200 ± 30 mm, with a bottom edge chamfer radius of 1.0 ± 0.50 mm.
3. Test Bracket
During foam testing, the bracket's profile must fully conform to the B-surface of the foam product, ensuring the test plane is substantially parallel to the platen surface.
Bracket Material Requirements: Resin, wood, or other rigid materials, with a perforated surface featuring 6 mm holes spaced 20 mm apart to facilitate gas venting during testing.
4. Test Conditions
- Test specimens shall be cured in a natural workshop environment for 24 hours post-production.
- Cured specimens must be conditioned in a laboratory environment for a minimum of 12 hours to prevent deformation or damage from external forces.
- Temperature: (23 ± 2)°C, Relative Humidity: (50 ± 5)%
V. Test Procedures
(A) Test Positions
1. Seat Cushion Foam Test Positions
The central test area for seat cushion foam is located at the Y-direction center of the middle section. The X-direction position is defined per product specifications. A 200 mm diameter platen is used for testing in this central area, and the 25% indentation test value is recorded.
The side wing test area is located at the highest and thickest point of the side wing, with specific positions defined per product specifications (refer to figures).
2. Backrest Foam Test Positions
The central test area for backrest foam is located at the Y-direction center of the middle section. The Z-direction position is defined per product specifications. A 200 mm diameter platen is used for testing in this central area, and the 25% indentation test value is recorded.
The side wing test area is located at the highest point of the side wing, with specific positions defined per product specifications.
3. Rear Seat Cushion Foam Test Positions
The central test area for rear seat cushion foam is located at the Y-direction center of the middle section. The X-direction position is defined per product specifications. A 200 mm diameter platen is used for testing in this central area, and the 25% indentation test value is recorded.
The side wing test area is located at the highest point of the side wing, with specific positions defined per product specifications. The hardness value variation across all tested areas should be within 10%.
4. Rear Backrest Foam Test Positions
The test area for the rear center armrest foam is located at the Y-direction center. The X-direction position is defined per product specifications. A 50 mm diameter platen is used for testing, and the 25 mm indentation test value is recorded.
(B) Test Methods
1. Central Hardness of Seat Cushion and Backrest Middle Sections
Step 1: Foam Specimen Preparation
a. Position the foam on the test fixture, ensuring the 200 mm platen is aligned with the test area.
b. Pre-apply a 4.5 N force and measure the thickness of the test area, noting the position.
c. Remove the foam and measure the thickness at the corresponding location on the fixture surface to calculate the specimen thickness.
Step 2: Compression Testing
a. Conduct three pre-compression cycles at 100 mm/min indentation speed, pausing for 10 seconds each.
b. Compress to 70-75% indentation at 100 mm/min, pause for 10 seconds, and repeat three times.
c. Compress to 25% indentation at 100 mm/min, pause for 10 seconds, and record the value.
Step 3: Data Acquisition
a. Capture data throughout the compression test, ensuring a 10-second pause at each compression stage.
b. Record the value upon reaching the specified indentation depth.
Step 4: Result Analysis
a. Analyze compression test data, including indentation depth and corresponding compression force.
b. Verify compliance with hardness standards and other specified requirements.
Step 5: Report Generation
a. Compile test results and analysis into a comprehensive report.
b. Include test conditions, procedures, results, and conclusions in the report.
2. Test Methods for Other Positions (Refer to Figures)
