Sand blasting is a metal surface mechanical treatment technology widely used in rubber production. The basic principle of sand blasting is to use sand, steel balls, glass beads, etc., with compressed air of 0.5~0.6MPa, and spray it onto the surface of the workpiece to be treated, and use high-speed jets of sand, steel balls or glass beads to remove the surface of the workpiece. Rust, oxide and other contaminants make the bond between the rubber grommets and the metal stronger.

The purpose of sand blasting is as follows:

1. remove rust spots, welding slag, carbon deposits and other contaminants on the surface of the skeleton;
2. Make the surface of the skeleton rougher and increase the bonding area with the rubber grommets.
3. removing the oxide layer on the surface of the skeleton;
4. to remove the burrs and directional marks (such as tensile marks, scratch marks, etc.) formed during the processing of the skeleton;
5. Commercially decorated the surface of the outer skeleton by sandblasting.

Sandblasting requirements: After the sandblasted metal skeleton, there shall be no rust marks or burrs on the surface; the treated skeleton shall not be deformed; the surface roughness shall conform to the process requirements; after sandblasting, the skeleton shall be The diameter dimensions, especially the aluminum alloy casing of the shock absorber, shall not exceed the tolerances required by the drawings.

Sand blasting is divided into dry blasting and wet blasting. Sandblasting the skeleton is mainly done by dry blasting. The methods of sand blasting include injection type, pressure feed type, projectile type (also called centrifugal sand blasting method), and dust-free blasting type.

The metal skeleton after sandblasting should be bonded to the rubber product as soon as possible to avoid secondary oxidation and contamination of the surface.

Metal oxide vulcanization is of great importance to chloroprene rubber, chlorobutyl rubber, chlorosulfonated polyethylene, chlorohydrin and polysulfide rubber, especially chloroprene rubber, which is commonly vulcanized with metal oxides. When chloroprene rubber is vulcanized, the allyl chloride structure produced by 1,2-polymerization is used, and there are two kinds of vulcanization mechanisms.

It should be noted that both zinc oxide and magnesium oxide can be separately cured of neoprene. When zinc oxide is used alone, the vulcanization rate is fast and scorch is likely to occur; when magnesium oxide is used alone, the vulcanization rate is slow. The best combination of the two is ZnO: MgO=5: 4. At this time, the main role of zinc oxide is vulcanization, and the rubber has good heat resistance and ensures the flatness of vulcanization. Magnesium oxide is mainly Improve the anti-coke performance of the rubber compound, increase the storage safety and plasticity of the rubber compound, and absorb the HC1 and CL₂ released during the vulcanization process.

In order to improve the heat resistance of the rubber, the amount of zinc oxide can be increased (15 to 20 parts). To prepare a water-resistant compound, Pb₃O₄ can be used instead of zinc oxide and magnesium oxide in an amount of up to 20 parts.

The sulfur-adjusted neoprene also uses the accelerator ethylene sulfur vein (NA-22 or ETU), which improves the production safety of GN-type chloroprene rubber and improves the physical properties and heat resistance of the vulcanized rubber. The general dosage is about 1 part.

When a peroxide-saturated rubber such as PE is used, the reaction mechanism is mainly to take hydrogen to form a radical, and the radical coupling to form a crosslink. When the peroxide is sulfided with PP, EPM or EPDM, there is a possibility of β-cleavage in the EPM due to the presence of a pendant methyl group in the propylene structural unit.

Therefore, a vulcanizing agent is often added to the formulation, which can shorten the vulcanization time and improve the tensile strength of the compound. Commonly used vulcanizing agents are sulfur TAIC and the like.

Peroxide-vulcanized hetero-chain rubbers such as methyl silicone rubber are similar to vulcanized polyethylene.

In addition to vulcanizing rubber, peroxide can also crosslink plastics, polyurethanes, and the like.

Peroxide vulcanization coordination points

The amount of peroxide varies with the gum grade. For the cross-linking efficiency of rubber SBR (2.5). BR (10. 5), the amount of DCP is 1.5-2.0 parts; for NR (1.0), the amount of DCP is 2-3 parts.

Acidic substances such as stearic acid and acidic fillers (such as silica, hard clay, and channel black) and substances that easily generate hydrogen ions can cause ion decomposition of peroxides and affect cross-linking, so it should be used less. Or not. Adding a small amount of alkaline substances such as triethanolamine can adjust the acidity and alkalinity and improve the crosslinking efficiency.

When peroxide is vulcanized, the role of ZnO is to improve the heat resistance of the rubber compound, rather than the activator. The role of stearic acid is to increase the solubility and dispersibility of ZnO in rubber.

The most commonly used vulcanizing agent is sulfur, about 0-3 parts, as well as TAIC, TAC, HVA-2 and the like. The amount of HVA-2 is generally from 0.5 to 0 parts.

Determination of vulcanization conditions

The peroxide vulcanization temperature of the rubber should be determined by reference to the peroxide decomposition temperature of 1 min. During the vulcanization process, the rate of decomposition of the peroxide depends on the vulcanization temperature. Generally, 6-10 times of the half-life time is passed, and the peroxide is basically consumed. Therefore, the vulcanization time is selected to set the peroxide half-life time of 6-10 times at the vulcanization temperature.

In addition to the sulfur vulcanization system, most rubber manufacturers also have some non-sulfur vulcanization systems for both vulcanization of unsaturated rubber and vulcanization of saturated rubber, such as peroxides, metal oxides, phenolic resins, and terpenoids. Derivatives, maleimide derivatives, and the like. The vulcanization of unsaturated rubber with a non-sulfur vulcanization system can further improve the heat resistance of the rubber compound, while the fully saturated rubber must use a non-sulfur yellow vulcanization system.

Peroxide curing system

• Application range

The peroxide can not only vulcanize saturated carbon chain rubber such as EPM, miscellaneous chain rubber such as Q, but also vulcanize unsaturated rubber, female mouth NR, BR, NBR, CR, SBR and the like. Compared with sulfur vulcanized vulcanizate, the crosslinked bond in the network structure of peroxide vulcanizate is CC bond, high bond energy, high heat, chemical stability, excellent resistance to thermal aging, and no vulcanization. Originally, vulcanizates have low compression set but poor dynamic properties. Static sealing rubber in static sealing or high temperature has a wide range of applications; some peroxides have odor, such as DCP, should be used when using.

• Commonly used peroxide vulcanizing agents and vulcanizing agents

Commonly used peroxide vulcanizing agents are dialkyl peroxides, diacyl peroxides and peroxyesters, which can vulcanize most rubbers. The choice of peroxide generally requires consideration from the half-life of the peroxide, the volatility, the odor, the influence of the acid-base substance on it, the safety of the process, the physical and mechanical properties of the vulcanizate, and the like. Among them, dialkyl peroxides have been widely used, such as dicumyl peroxide (DCP), which is suitable for vulcanization at 160 ° C. It is cheap and is currently the most used vulcanizing agent; 1,1 – di-tert-butyl Oxy-3,3,5-trimethylcyclohexane (3M) suitable for lower temperature vulcanization.

• Peroxide vulcanization mechanism

The crosslinking efficiency of a peroxide means the amount (mol) of a substance in which 1 mol of an organic peroxide causes chemical crosslinking of a rubber molecule. If 1 mol of peroxide can produce 1 mol of rubber crosslinks, the crosslinking efficiency is 1.

Peroxide vulcanization is the simultaneous generation of free radicals by peroxide under heat or radiation, such as alkyl peroxides to produce dialkoxy radicals, diacyl peroxides to produce two acyloxy radicals, and peroxyesters. An alkoxy radical and an acyloxy radical are produced. During thermal crosslinking, the tertiary alkyl and tertiary oxy radicals may be further cleaved to produce alkyl radicals.

In order to overcome the shortcomings of unsaturated diene rubber, especially natural rubber CV vulcanization system in rubber production, in 1977, S. Woff used the ratio of Si69 tetrasulfide in the amount of substances such as accelerators. Under the condition, the cross-linking density of the vulcanized rubber is in a dynamic constant state, the reversion of the vulcanization is minimized or the reversion of the vulcanization is eliminated, and the vulcanization system is called an equilibrium vulcanization system. The system has better flatness of vulcanization, stable crosslink density, excellent heat aging resistance and fatigue resistance in a long vulcanization cycle, and is particularly suitable for vulcanization of large and thick products.

Si69 is a vulcanizing agent with coupling. At high temperature, it is unevenly cracked into bis(triethoxysilylpropyl) disulfide and bis(triethoxysilylpropyl) polysulfide. The mixture is as shown.

Si69 acts as a sulfur donor in the vulcanization reaction of rubber to form a rubber/rubber bridge. The chemical structure of the crosslinks formed is related to the type of accelerator. In the NR/S169/CZ (DM) vulcanization system, it is mainly formed. Disulfide and polysulfide crosslinks; in the NR/Si69/TMTD system, a network structure dominated by monosulfide crosslinks is formed.

Since the crosslinking rate constant of the sulfurized system of Si69 is lower than that of the corresponding sulfur vulcanization system, the rate of positive vulcanization of Si69 is slower than that of sulfur vulcanization, so in the vulcanization system of the S/Si69/accelerator equimolar ratio combination, because The reduction of the crosslink density caused by the reversion of sulfur can be compensated by the new polysulfide or disulfide crosslinks formed by Si69, so that the crosslink density remains unchanged during the vulcanization process, and the physical properties of the vulcanizate are stabilized. status.

In the silica-filled compound, Si69 is coupled with silica in addition to the cross-linking reaction. The filler-rubber bond is produced to further improve the physical properties and process properties of the compound.

The order of anti-reversion ability of various accelerators in natural rubber is

DM>N()BS>TMTD>DZ>CZ>D

In order to improve the disadvantages of NR reversion, in addition to Si69, the rubber industry also uses other anti-reversion agents, such as cyclohexane-1,6-dithiosulfate dihydrate (Duralink HTS), 1,3- Bis(Limonimidomethyl)benzene (Perkalink-900) and the like.