In the production of rubber products, compression molding trapping is one of the key factors affecting product quality. Trapped gas can lead to defects such as bubbles, pores, and looseness. In severe cases, it can also reduce the physical properties of the product, shorten its service life, and weaken its market competitiveness. To solve this problem, every step from mold design to vacuum gluing needs to be carefully optimized. This article will explore nine effective measures to crack the trapped gas in rubber molding, providing practical technical references for practitioners.

1、 Mold design optimization: control gas trouble from the source

Mold design is the primary step in avoiding trapped gas during molding. Reasonable mold design can not only improve production efficiency, but also minimize gas troubles to the greatest extent possible. The following are the key elements in mold design:

1.1 Reasonable exhaust system design

The exhaust system is the core of mold design, and poor exhaust is one of the main reasons for trapped air. Gas must be quickly expelled through effective exhaust channels, otherwise it will accumulate in the mold cavity and form bubbles. When designing, the following points should be noted:

Layout of exhaust slots and exhaust holes: The mold should be equipped with evenly distributed exhaust slots or exhaust holes. The diameter of the exhaust hole is generally not less than 1mm and should be close to the lowest point of the mold cavity or where gas is prone to gather.

Optimization of the number and location of exhaust holes: The number of exhaust holes needs to be determined according to the volume and complexity of the mold, usually using porous discharge to avoid local gas accumulation.

1.2 Optimization of Mold Heating System

Rubber compression molding needs to be carried out within a specific temperature range, and uneven heating can cause uneven gas expansion, affecting product quality. The heating temperature of the mold is generally controlled between 160-180 ℃, which varies for different types of rubber. For example, natural rubber has a vulcanization temperature of 160 ℃, while fluororubber requires a higher temperature. To ensure uniform temperature, multiple heating tubes or electric heating film heating technology can be used to reduce trapped gas.

1.3 Design of mold closing force

Inadequate closure of the mold can cause gas to enter the mold cavity. To prevent this issue, it is necessary to ensure that the mold closing force meets the design requirements and to avoid gas leakage through reasonable sealing design.

2、 Optimization of rubber formula: reducing gas generation

Rubber formula is crucial for gas trapping, as certain components can increase gas generation. Optimizing the formula can effectively reduce the phenomenon of trapped gas.

2.1 Optimizing the ratio of additives

Some rubber additives, such as accelerators and vulcanizing agents, are prone to gas generation during the mixing process. Controlling the amount of additives added and selecting an appropriate vulcanization system (such as sulfur crosslinking or sulfur free crosslinking) can effectively reduce gas production. For example, in the production of chloroprene rubber, excessive vulcanization accelerators can lead to over crosslinking and the generation of gases. Reasonable ratio of additives and selection of vulcanization system are crucial for reducing trapped gas.

2.2 Use of fillers

Fillers are an important component of rubber formulations, but improper use can exacerbate gas generation, especially for fillers with smaller particle sizes that are more likely to capture air. The use of larger particle size fillers or surface treated fillers can reduce the probability of gas generation.

3、 Rubber mixing process: sufficient exhaust

The process of mixing rubber is the core link of rubber production. Insufficient mixing or incomplete air discharge can cause gas to be trapped inside the rubber material and form bubbles. Therefore, it is necessary to start from every step of the rubber mixing process.

3.1 Optimizing mixing equipment

Advanced mixing equipment can effectively prevent air from being trapped. It is recommended to use an efficient sealed internal mixer to reduce the entry of air during the mixing process and ensure the uniformity of the mixed rubber. Increasing the speed and mixing time can better eliminate gases from the rubber material.

3.2 Reasonable selection of mixing process

Different types of rubber have different mixing requirements. For example, natural rubber usually adopts a two-stage mixing process, with the first stage mixing the base material and the second stage refining. This segmented mixing process can better remove air from the rubber material and improve its compactness.

4、 Suppression process: reduce the chance of trapped gas

The coordination of temperature, pressure, and time is crucial during the molding process. Reasonable process conditions not only contribute to the flowability and molding effect of the rubber material, but also reduce gas retention.

4.1 Appropriate molding time

Excessive or insufficient molding time can affect the molding effect. Usually, the molding time should be controlled between 5-20 minutes, depending on the type of rubber and the complexity of the product. Excessive time can lead to gas retention, while insufficient time may result in incomplete molding of the rubber material.

4.2 Appropriate molding pressure

During the molding process, the pressure is too low to completely fill the mold with the rubber material, resulting in gas retention. Usually, the molding pressure should be set between 10-30MPa, and the specific pressure needs to be adjusted according to the rubber flowability and product requirements.

5、 Vacuum glue injection: completely remove gas

If the above measures still cannot completely solve the problem of trapped gas in molding, vacuum injection molding technology is an effective supplementary method. By performing vacuum treatment before filling the mold with rubber material, the air in the rubber material can be maximally removed to prevent trapped air.

5.1 Vacuum glue injection process

The basic step of vacuum gluing is to evacuate the air inside the mold before gluing. The specific operation is to first place the mold in a vacuum environment for preliminary vacuuming, and then proceed with gluing. In this way, the rubber material has removed most of the air when injected into the mold, reducing the generation of trapped air.

5.2 Optimizing Vacuum Degree

Vacuum degree is an important factor affecting the effectiveness of vacuum glue injection. In general, the vacuum degree should be controlled below 0.01 MPa. Excessive vacuum can cause bubbles in the adhesive material, while insufficient vacuum cannot completely remove air. Adjusting the vacuum degree to the optimal state can significantly improve the quality of glue injection.

6、 Optimization of Production Environment: Control of Air Humidity and Temperature

The production environment also has an impact on the phenomenon of trapped gas. Excessive air humidity can cause the rubber material to absorb moisture, affecting its fluidity and increasing the risk of trapped air. Controlling the workshop temperature between 20-30 ℃ and relative humidity between 50% -70% can effectively reduce the problem of trapped gas.

7、 Regular equipment maintenance and inspection

Regular inspection and maintenance of molds and mixing equipment are the foundation for preventing trapped gas problems. Regularly check whether the exhaust holes of the mold are unobstructed and whether the sealing of the mixing machine is good, to ensure that the equipment is always in the best working condition, which can effectively avoid trapped gas.