Influence of vulcanization on structure and properties:

Vulcanization is the last process in the production of rubber products. In this process, the rubber after a series of complex chemical reactions, by linear structure into a shape structure, lost the plasticity of the gum rubber has the high elasticity of crosslinked rubber, and obtained excellent physical and mechanical properties, heat resistance, solvent resistance and corrosion resistance increase the use value of the rubber products and application scope.

Before vulcanization: linear structure, intermolecular interaction with van der Waals force;

Performance: large plasticity, high elongation, soluble;

Vulcanization: molecules are triggered, chemical cross-linking reaction;

After vulcanization: reticular structure, with chemical bonds between molecules;

Structure :(1) chemical bond; (2) the position of the crosslinked bond; (3) degree of cross-linking; (4) cross-linking;

Properties: (1) Mechanical properties (fixed elongation strength. Hardness. Tensile strength. Elasticity (2) physical properties (3) chemical stability after vulcanization;

Rubber performance changes:

Taking natural rubber as an example, with the increase of vulcanization degree;

(1) Changes in mechanical properties (elasticity. Breaking strength. Fixed elongation strength. Tear strength. Hardness) increase (elongation. Compression permanent deformation. Fatigue heat generation) decreased

(2) The change of physical properties, the permeability and water permeability can not be dissolved, but the swelling heat resistance can be improved

(3) Changes in chemical stability

Improved chemical stability, reasons:

A. Cross-linking reactions eliminate chemically active groups or atoms, making aging reactions difficult

B. The reticular structure hinders the diffusion of low molecules, making it difficult for rubber free radicals to diffuse

Selection and determination of vulcanization conditions of rubber

First, vulcanization pressure

(1) Vulcanization of rubber products need to apply pressure, its purpose is:

A. Prevent bubbles of rubber material and improve the compactness of rubber material;

B. Make the glue flow and fill the mold to produce clear pattern products

C. Improve the adhesive force between each layer (rubber layer and cloth layer or metal layer, cloth layer and cloth layer) and improve the physical properties of vulcanized rubber (such as flexure resistance).

(2) In general, the selection of curing pressure should be determined according to the product type, formula, plasticity and other factors.

(3) In principle, the following rules should be followed: the plasticity is large, and the pressure should be small; Product thickness, layers, complex structure should be more pressure; Thin products should be less pressure, and even atmospheric pressure.

There are several ways of vulcanization pressure:

(1) The hydraulic pump passes the pressure to the mold through the flat vulcanizing machine, and then the mold transfers to the glue

(2) by vulcanizing medium (such as steam) direct pressure

(3) pressurized by compressed air

(4) Injection by injection machine

Two, curing temperature and curing time