Analysis Of The Vulcanization Process Of Rubber Products

Rubber product vulcanization process

One. Purpose

1. Grasp the essence of vulcanization and the factors affecting vulcanization.

2. Master the determination and implementation methods of vulcanization conditions.

3. Master the operation method of the plate vulcanizing machine.

4. Understand the structure of one of the vulcanizing equipment.

2. Vulcanization equipment and experimental principles

Figure 5-1 Flat vulcanizing machine

Vulcanization is the process of cross-linking the linear macromolecules of the rubber compound under a certain temperature, time and pressure to form a three-dimensional network structure. Vulcanization reduces the plasticity of rubber, increases its elasticity, greatly increases its ability to resist external force deformation, and improves other physical and chemical properties, making rubber a valuable engineering material.

Vulcanization is the last step in the processing of rubber products. The quality of vulcanization has a great influence on the performance of vulcanized rubber. Therefore, the vulcanization conditions should be strictly controlled.

1. The pressing surfaces of the two hot plates of the vulcanizer should be parallel to each other.

2. The hot plate adopts steam heating or electric heating.

3. During the entire vulcanization process of the plate, the pressure applied on the mold cavity area is not less than 3.5MPa.

4. No matter what type of hot plate is used, the temperature distribution over the entire mold area should be uniform. The maximum temperature difference between points in the same hot plate and between each point and the center point shall not exceed 1℃; the temperature difference between the corresponding points of adjacent two plates shall not exceed 1℃. The maximum temperature difference at the center of the hot plate does not exceed ±0.5°C.

    Technical specifications

Maximum closing pressure 200 tons

Maximum plunger stroke 250 mm

Flat area 503mm×508mm

Number of working layers Two layers

Total heating power 27 kW

3. Operation of vulcanization experiment

1. Preparation of rubber

The mixed film should be parked for 2-24 hours in accordance with GB/T 2941-2006 before it can be cut for vulcanization. The method of cutting pieces is as follows:

(1) Sheet (for tensile test) or strip sample

Use scissors to cut pieces on the rubber material. The width of the test piece should be consistent with the rolling direction of the rubber material. The volume of the rubber compound should be slightly larger than that of the mold, and its weight is weighed with a balance. The mass of the rubber blank is calculated according to the following method:

Rubber blank mass (g) = cavity volume (cm3) × rubber density (g/cm3) × (1.05~1.10)

In order to ensure sufficient amount of rubber during molding and vulcanization, the actual amount of rubber is increased by (5-10)% more than the calculated amount. After cutting, affix labels with numbers and vulcanization conditions on the side of the rubber blank.

(2) Cylindrical sample

Take a film of about 2 mm, take the height of the sample (slightly greater than) as the width, press and extend the vertical direction to cut into a strip, roll it into a cylinder, and the cylinder should be rolled tightly without gaps. The volume should be slightly smaller than the cavity and the height should be higher than the cavity. A paper label with number and curing conditions is attached to the bottom of the cylinder.

(3) Round specimen

According to the requirements, the rubber material is cut into a circular film sample. If the thickness is not enough, the film can be stacked. The volume should be slightly larger than the volume of the mold cavity. Paste the number and vulcanization condition paper on the bottom of the circular sample. label.

2. Adjust and control the plate temperature according to the required vulcanization temperature to keep it constant.

3. Place the mold on a closed plate and preheat it to the specified vulcanization temperature within ±1℃, and keep it at this temperature for 20 minutes. The preheating is not necessary during continuous vulcanization. Only one mold is allowed on each layer of hot plate during vulcanization.

4. Control and adjustment of vulcanization pressure

When the vulcanizer is working, the vulcanization pressure is provided by the pump, and the vulcanization pressure is indicated by the pressure gauge, and the pressure value can be adjusted by the pressure regulating valve.

5. Put the rubber blank for checking the number and vulcanization conditions into the preheated mold as quickly as possible, close the mold immediately, and place it in the center of the plate. After the upper and lower vulcanized models are aligned in the same direction, pressure is applied to raise the plate , When the pressure gauge indicates the required working pressure, properly release the pressure and exhaust about 3 to 4 times, then maximize the pressure, start to calculate the vulcanization time, immediately release the pressure when the vulcanization reaches the predetermined time, and take out the sample.

For the new flat vulcanizer, mold clamping, exhaust, vulcanization time and mold opening are all automatically controlled.

6. After the vulcanized sample is cut off the glue edge, it can be tested for performance after being parked at room temperature for 10 hours.

Four, factors affecting vulcanization

For a rubber compound with a determined formula, there are three factors that affect the quality of vulcanized rubber: vulcanization pressure, vulcanization temperature and vulcanization time, also known as the three elements of vulcanization.

1. Vulcanization pressure

The purpose of applying pressure to the rubber during the vulcanization process is to make the rubber flow in the mold cavity, and the Harbin office certificate is filled with grooves (or patterns) to prevent bubbles or lack of rubber; improve the compactness of the rubber; strengthen the rubber Adhesion strength to cloth layer or metal; helps to improve the physical and mechanical properties of the rubber compound (such as tensile properties, wear resistance, flex resistance, aging resistance, etc.). It is usually determined according to the plasticity of the compound and the specific conditions of the sample (product) structure. If the plasticity is large, the pressure should be lower; the pressure should be higher for the thickness, the number of layers, and the complex structure.

2. Vulcanization temperature

The vulcanization temperature directly affects the vulcanization reaction speed and vulcanization quality. According to the Van der Hoff equation:

Among them, T1—the curing time when the temperature is t1;

    T2—vulcanization time when the temperature is t2;

    K—vulcanization temperature coefficient.

It can be seen that when K=2, the vulcanization time can be reduced by half for every 10°C increase in temperature, indicating that the effect of vulcanization temperature on vulcanization speed is very obvious. That is to say, increasing the vulcanization temperature can speed up the vulcanization speed, but high temperature easily causes the rubber molecular chain to crack, thereby causing vulcanization reduction, resulting in a decline in physical and mechanical properties, so the vulcanization temperature should not be too high. The appropriate vulcanization temperature depends on the rubber formula, which mainly depends on the type of rubber and the vulcanization system.

3. Vulcanization time

The curing time is determined by the compound formula and curing temperature. For a given rubber compound, under certain vulcanization temperature and pressure conditions, there is an optimal vulcanization time. Too long or too short will affect the performance of the vulcanized rubber.

The choice of suitable curing time can be determined by a curing instrument