Automotive weatherstrip (door and body seal)

01

Control the sponge compression set

A patent assigned to DRB Holding, Hyundai Motor and Kia Motors describes the door weatherstrip as a soft sponge section compressed by the car body joined to a hard solid section, and states that compression set is the key characteristic of the sponge section, because sealing must be maintained after long use. [1]

Its EPDM sponge compound uses an EPDM with a Mooney (ML 1+8 at 125 °C) of 90 or more and an ENB content of 9 wt% or more with free sulphur and a BDBzTH accelerator, claiming compression set reduced to about 12% or less and better heat resistance against discoloration. Compression set was measured on discs at 70 °C for 22 h to JIS K 6301; in its table comparing three EPDM grades, compression set was 16.6–17.2% and Shore A hardness 58–59. Heat ageing ran at 70 °C for 70 h after vulcanisation at 155 °C for 20 min. [1]

Editorial note: compression set values only compare when temperature, time, specimen and recovery method match; ask suppliers to quote compression set with the full test condition, and to test the finished sponge profile as well as moulded discs.

Give the supplier the vehicle position (door, window, trunk, body), profile drawing with bulb and carrier, material (EPDM, TPE), sponge density and hardness, CLD target and test method, compression set limit and condition, colour and surface finish, length or closed-loop joining, clip or adhesive fixing, OEM material specifications, and annual volume.

02

Set blown density and compression load deflection

A Cooper Standard Automotive patent on low-gravity sponge rubber notes that weatherstrip weight reduction must be balanced against surface quality and stiffness, which suffer as blown specific gravity approaches or falls below about 0.60 g/cm³. Its formulation B reached an average blown specific gravity of 0.384 against 0.532 for a conventional formulation A, with Shore A hardness of 42 against 29 and water absorption of 8.63 against 26.81. [2]

The patent measures CLD as the force per unit area needed to compress a cured, blown rubber tube, calling it part-specific and a measure of suitability as a resilient seal; formulation B gave 0.1970 N/mm² against 0.1478 for A, and its claims cover a sponge bulb CLD of 0.1833–0.2120 N/mm² and blown specific gravity down to 0.358 g/cm³. It also cites a 2 N/mm minimum tear strength required on some parts. [2]

Editorial calculation: going from 0.532 to 0.384 g/cm³ cuts sponge mass by about 28%; for an assumed 150 mm² bulb section 4 m long, that is about 319 g down to 230 g of sponge. The section and length are assumed examples. [2]

A Toyoda Gosei patent on a door weatherstrip, US 8,353,130 B2, makes the mounting base and the hollow seal from one EPDM sponge so that only one extrusion material is needed. It claims a sponge with a specific gravity of 0.36–0.44, a low stretch stress (measured to JIS K 6254) of 200–230 kPa and an average foam cell diameter of 180–220 µm. The patent says below 0.36 the 200 kPa stress is hard to reach, a cell size of 220 µm or less gives a fine surface skin, and below 180 µm the density and stress targets are hard to meet together. [3]

It contrasts this with an earlier design in which the base used sponge below 0.45 and the seal used sponge of 0.45–1.0, and it avoids adding resin such as polyethylene to the base because that can increase permanent set. Its EPDM blend pairs a high-molecular-weight polymer with a Mooney viscosity ML 1+4 (125 °C) of 100–180 with a lower-molecular-weight one. [3]

For a general material call-out, ASTM D1056-20 covers flexible cellular rubber known as sponge rubber and expanded rubber made from synthetic, natural or reclaimed rubber, excluding latex foam and ebonite cellular rubber, and categorises it by Types 1 and 2, Classes A, B, C and D and Grades 0 to 5, each grade with specified physical properties. Its listed test methods are accelerated ageing, compression-deflection, oil immersion (open-cell sponge), fluid immersion (closed cell), water absorption, density and low-temperature flex, and it notes ISO 6916-1 as similar. ASTM adds that extruded or moulded shapes too small for cutting standard test specimens are difficult to classify or test by these methods and that such parts may need special testing procedures, and that a detailed product specification or test method takes precedence over the general specification in case of conflict. [4] Editorial note: for a weatherstrip bulb, that means a D1056 grade can describe the sponge compound, while CLD on a cured tube or on the finished profile, as in the Cooper Standard patent, and the OEM's own specification govern the part. [4] [2]

03

D, P, E and I profiles, custom extrusions and EPDM compounds

Listings include door and window weatherstripping in D, P, E and I profiles, custom EPDM extrusions and compounds, and automotive rubber seals; ask each for compression set, density and CLD on the exact profile.

04

Sponge bulb, dense carrier, insert and finish

Only the sponge bulb and dense body rows rest on the patents; reinforcement, surface finish and corner joining are drawing items to agree with the supplier. [1] [2]

05

Compression set and blown density, each with its test condition

Compression set and density are the rows that tie back to the patents above; quote compression set with its full test condition. [1] [2]

06

Send the profile, material and test data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Position: [door; window; trunk; body]
Profile: [drawing; bulb; carrier; reinforcement]
Material: [EPDM; TPE; OEM spec]
Sponge: [density; hardness; CLD]
Ageing: [compression set; condition]
Finish: [colour; coating]
Fixing: [clips; adhesive; carrier grip]
Supply: [length; joining; volume]

See manufacturer records Send an enquiry through CNFX