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An article to understand the material selection, structure and performance requirements of automotive rubber sealing strips​


The main function of automobile sealing strip: waterproof, dustproof, shock absorption, sound insulation and sealing.  With the development of technology and people's awareness of environmental protection, people's requirements for sealing strips are not only excellent sealing and environmental sound insulation, but also comfortable and decorative, and beautiful, safe, and environmentally friendly.

1 Introduction to the development of rubber sealing strip materials:
Natural rubber neoprene is the preferred rubber for automotive sealing strips.  With the rapid development of the automotive industry, the appearance quality and internal performance of this type of sealing strip can no longer meet the requirements of automotive sealing strips.  Especially in terms of weather resistance and service life.

Due to the difference in structure between neoprene and natural rubber and EPDM, there are big differences in heat resistance, light resistance, crack resistance and ozone resistance, and thus the service life is also very different.  The excellent performance of EPDM rubber is mainly due to the fact that EPDM rubber is a saturated rubber.  The main chain is composed of chemically stable saturated hydrocarbons, and only has unsaturated double bonds on the side chains, and the molecules are tender and unlimited.  Intermolecular cohesive energy is low, and the molecular chain maintains flexibility in a wide temperature range.  These structural characteristics determine its extremely high chemical stability, good resistance to ozone aging, weather aging, heat aging and Low temperature performance (EPDM can still maintain good elasticity and small compression deformation at low temperatures, and its ultimate use temperature can reach -50 ℃)

In recent years, the application technology of automobile sealing strips has developed rapidly in the world.  EPDM has been industrialized with controllable long-chain branched EPDM, which can provide good mixing processing and excellent extrusion performance, and has good physical and mechanical properties.  Thermoplastic elastomers have been continuously developed and applied in automobile sealing strips.

At present, some countries have used different types of thermoplastic elastomers to mass produce automotive sealing strips.  Moreover, there is a great tendency to replace the currently commonly used EPDM rubber.  Compared with EPDM rubber, these materials have the outstanding characteristics of not only the inherent excellent properties of elastomer materials, but also the excellent processing properties of plastics and can be recycled and reused.  , It also solves the problem of low tear strength of EPDM rubber.

2 Common types and structures of sealing strips:

2.1 Types: Mainly used in car doors, windows, hatch covers and other parts with gaps and activities.

Play sealing, shock absorption, sound insulation, decoration (covering defects).  Prevent the intrusion of harmful substances such as wind, sand, rain and dust from the outside, and improve the working life and ride comfort of auto parts.
①Classified by composite components: compact glue (single hardness is compact glue, and different hardness is composite glue);  sponge glue and compact glue double compound;  sponge glue, compact glue and skeleton three compound;  four compound;  multiple compound, etc.
②Classification according to the parts of the assembled car: door frame strips;  luggage compartment strips;  engine cover strips;  guide grooves;  inner and outer strips (cutting water inside and outside);  windshields and others.

2.2 The fixing form of the sealing strip and the car body:
①Fixed by the clamping part: the clamping part of the sealing strip itself is clamped and fixed at the car body installation part.  The clamping part can be composed of a skeleton and rubber, or can be composed of rubber.
②Embedded fixing: the hook teeth of the sealing strip structure are embedded in the car body and fixed.
③Fix with foam nails: drill nail holes on the sealing strip to install the foam nails.  When installing the whole vehicle, install the sealing strip with foam nails in the nail holes of the body.

④Fix with adhesive or tape: Paste double-sided tape or apply adhesive on the joint part of the sealing strip and the car body, tear off the release paper when installing the whole vehicle, and install the sealing strip on the designated part of the car body.

2.3 Characteristics of various structures
The specifications and structure of the sealing strip are directly determined by the vehicle model. The basic principles and structures are usually as follows:
1. Door frame strip, luggage compartment, engine cover strip.
This type of sealing strip usually consists of a sealing part and a tight part. The common form of the sealing part is a foam tube (single tube, double tube), which is a variable sealing strip. The fixed part is the clamping part (with or without skeleton)

2. Guide groove, inner and outer strips.
Because this kind of sealing strip is located in the glass lifting part, it is usually flocked or sprayed on the surface of the part that contacts the glass. This can not only reduce frictional resistance, reduce noise and surface cleaning, but also use the sealing lip to seal (a sliding seal).
Flocking: single-sided flocking or double-sided flocking and can be embedded in the skeleton. The flocking process is relatively complicated and the processing cost is high. At present, many car models use coatings, and such sealing strips are usually embedded and fixed.

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