Curing Time Of Silicone Rubber O-rings

Usually in the rubber industry, we are used to use the same purpose or related additives collectively known as the system. For example: Curing Agent, curing accelerator, activator and anti-coke agent collectively referred to as curing system, because they are related to curing. Sulfides include sulfur, selenium, tellurium, sulfur compounds, organic peroxide, quinones, amine, resins, metal oxides, and other sulfides.

In fact, the so-called rubber vulcanization, is a plastic rubber into a flexible vulcanizate process, that is, the rubber molecular chain under the chemical or physical factors under the action of chemical cross-linking, into a spatial network structure. Any chemical which can cause the cross-linking effect of rubber can be called a vulcanizing agent.

1. Define

1.1 Vulcanization time of silicone rubber O-rings

Standing at a certain temperature, molding, in order to make the rubber from plastic to elastic, and to achieve the maximum cross-linking density, the physical and mechanical properties of the optimum time is called silicone rubber O-rings vulcanization time. This usually does not include auxiliary time for the Operation Process.

Curing time and curing temperature is closely related, in the curing process, the physical and mechanical properties of vulcanizate reached or near the best point, the degree of vulcanization or the most appropriate curing. The curing time needed to reach positive cure at a certain temperature is called positive cure time, and a certain curing temperature corresponds to a certain positive cure time. The vulcanization degree is determined by vulcanization time when the formula of rubber compound and vulcanization temperature are fixed, and the vulcanization degree is controlled by the vulcanization time of silicone rubber O-ringss with different sizes and wall thicknesses, the longer it takes to cure.

2. Setting of curing time

2.1 Test of positive curing time

The test methods for curing time of rubber compound are as follows:

2.1.1 Physical-chemical methods (including determination of Free Sulphur and swelling) ;

2.1.2 Physical-mechanical properties determination methods (including constant tensile stress method, tensile strength method, constant tensile strength method, tensile product method, compression permanent deformation method, comprehensive value method) ;

2.1.3 Special instrument method (including Mooney viscosity method, vulcanizer method) , etc. .

At present, the most commonly used method is vulcanization instrument. The positive vulcanization time of the compound can be obtained by the test of vulcanizer.

Determination of curing time of 2.2 silicone rubber O-rings

2.2.1 If the thickness of the product is 6 mm or less and the forming process condition of the rubber compound can be considered as a uniform heating state, then, the curing time of the product is the same as the curing time measured in the curing curve (if the temperature is the same, that is, the curing temperature measured by the curing apparatus) ;

2.2.2 If the wall thickness of the product is more than 6 mm, the positive curing time is increased by 1 min for each additional 1 mm thickness. This is an empirical data. For example, a silicone rubber O-rings with a thickness of 22 mm and a positive curing time of 6 min for the test piece at a temperature of 150°C would have a curing time of 6 + (22-6)1 = 22 Min at 150 °C. This time does not include auxiliary time for the Operation Process.

3. Two-stage sulfur dosing time setting

3.1 To achieve a reasonable manufacturing process and reasonable costs, the rubber vulcanization process is divided into two stages, the second stage of the process is the so-called two-stage vulcanization. The first stage vulcanization is mainly to shape the products, and then concentrate the products which are not 100% vulcanized to shape for the second stage vulcanization. As a result, the efficiency of the first vulcanization and the centralized treatment of the second vulcanization are improved, and energy is saved.

3.2 Setting of secondary curing time

In addition to reasonable cost considerations, for special rubber such as Silicone rubber, FKM rubber, its positive vulcanization process is longer, the normal process using two-stage vulcanization.