How to achieve a firm bond between rubber and inserts? ​

I. Principles and key elements of rubber-insert bonding products​
The core of Rubber To Insert Bonding is to achieve a reliable and lasting bond between rubber and inserts. From a molecular level, rubber is a highly elastic polymer material whose molecular chain exhibits soft and deformable properties. Insert materials such as metals are hard and stable in structure, while plastics have diverse physical and chemical properties. To achieve a firm bond between rubber and inserts with different properties, multiple key factors need to be considered comprehensively. ​
The first is surface treatment. The surface state of the insert plays a decisive role in the bonding effect. For metal inserts, there are usually impurities such as oxide films and oil stains on the surface, which will hinder the close contact between rubber and metal. Therefore, before bonding, it is necessary to remove surface impurities through mechanical grinding, chemical etching, etc., increase the surface roughness, thereby increasing the contact area between rubber and metal and enhancing the intermolecular force. Take the common aluminum alloy insert as an example. After sandblasting, its surface becomes uneven. Rubber can better penetrate these tiny depressions during the vulcanization process, forming a mechanical anchoring effect and significantly enhancing the bonding strength. ​
The surface treatment method of plastic inserts is different. Since some plastic surfaces are inert and not easy to react chemically with rubber, plasma treatment, flame treatment and other means can be used to change the chemical properties of the plastic surface, introduce polar groups, and increase the surface energy, so that chemical bonds can be formed between rubber and plastic to achieve strong bonding. ​
The second is the choice of adhesive. Suitable adhesives are the key to achieving good bonding between rubber and inserts. Adhesives need to have good compatibility with rubber and insert materials and can form an effective connecting bridge between the two. According to the different characteristics of rubber and insert materials, the types of adhesives are also different. For the bonding of rubber and metal, adhesives containing active groups are usually selected. These active groups can react chemically with rubber molecules and atoms on the metal surface to form chemical bonds and enhance the bonding effect. In the bonding of rubber and plastic, the adhesive needs to have good wettability, be able to fully spread on the plastic surface, penetrate with the plastic molecules, form physical entanglement and chemical bonding, and ensure the firmness of the bonding. ​
Then there is the molding process. The molding process of the rubber-insert bonding product directly affects the final bonding quality. Common molding processes include compression molding and injection molding. In compression molding, the pre-prepared rubber and insert are placed in the mold, and the rubber is vulcanized and molded by heating and pressurizing to be tightly bonded with the insert. In this process, the control of temperature, pressure and time is crucial. The appropriate temperature can promote the vulcanization reaction of the rubber to form a stable three-dimensional network structure; the appropriate pressure can ensure that the rubber fully fills the mold cavity and fits tightly with the insert; and accurate time control can ensure that the vulcanization reaction is fully carried out to avoid under-sulfurization or over-sulfurization, thereby obtaining the ideal bonding strength. ​
Injection molding is to inject the rubber into the mold cavity through an injection machine and bond it with the pre-placed insert. This process has the advantages of high production efficiency and good product precision, but it has high requirements for the fluidity of the rubber and mold design. During the injection molding process, factors such as the injection speed and temperature of the rubber and the design of the cooling system of the mold will affect the bonding effect between the rubber and the insert. ​
2. Application scenarios of rubber-insert bonding products ​
Rubber-insert bonding products have been widely used in many fields due to their excellent performance. ​
In the field of automobile manufacturing, rubber-insert bonding products can be seen everywhere. The seals of automobile engines are key components to ensure the normal operation of the engine. These seals are usually made of rubber and metal inserts. The rubber part uses its good elasticity and sealing properties to effectively prevent the leakage of liquids such as engine oil and coolant inside the engine, as well as the entry of dust and impurities from the outside; the metal insert provides sufficient strength and rigidity to enable the seal to withstand the harsh environment such as high temperature and high pressure during the operation of the engine. ​
Rubber-insert bonding products are also widely used in the suspension system of automobiles. For example, rubber bushings, which are made of rubber and metal bushings, can absorb vibrations and shocks from the road surface during vehicle driving, reduce noise, and provide the necessary movement flexibility and positioning accuracy for each component of the suspension system, thereby improving the driving comfort and handling performance of the vehicle.​
In the aerospace field, rubber-insert bonding products also play an indispensable role. In the fuel system of an aircraft, rubber-insert bonding seals that are resistant to fuel corrosion are required. These seals must not only have good sealing performance to prevent fuel leakage, but also be able to maintain stable performance under extreme temperature and pressure conditions. The rubber part uses special rubber materials with excellent fuel resistance, and the metal inserts use high-strength, corrosion-resistant alloy materials. Through a special bonding process, the two are tightly combined to ensure the safe and reliable operation of the fuel system. ​
The aircraft's landing gear shock absorber also uses rubber-insert bonding products. The elasticity of rubber can effectively absorb the huge impact force when the aircraft lands, and the metal inserts provide structural support for the shock absorber to ensure the stability and reliability of the landing gear under various complex working conditions. ​
In the field of electronics and electrical appliances, rubber-insert bonding products are often used for the protection and connection of electronic products. For example, the waterproof seals of electronic products such as mobile phones and tablets are made of rubber and plastic or metal inserts. The elasticity of rubber can achieve a tight seal, prevent moisture, dust, etc. from entering the interior of electronic products, and protect electronic components from damage; the insert provides a mounting and fixing structure for the seal to ensure its stability in electronic products. ​
The rubber foot pads, handles and other parts in household appliances also use the rubber-insert bonding process. The rubber foot pads use the anti-slip properties of rubber to make the placement of the appliance more stable, and the inserts enhance the connection strength between the foot pads and the main body of the appliance; the rubber handles are bonded with metal or plastic inserts to ensure the comfort of holding and have sufficient strength for user operation. ​
3. Challenges and solutions faced by rubber-insert bonding products ​
Although rubber-insert bonding products have broad application prospects, they also face many challenges in actual production and use. ​
Environmental factors have a great impact on the performance of rubber-insert bonding products. Long-term exposure to high temperature, high humidity, ultraviolet rays and other environments will easily cause rubber to age, resulting in a decrease in its physical properties, such as reduced elasticity and increased hardness, which in turn affects the bonding strength with the insert. To solve this problem, it is necessary to select rubber materials with excellent aging resistance, such as fluororubber, silicone rubber, etc., and add anti-aging agents, ultraviolet absorbers and other additives to the rubber formula to improve the aging resistance of rubber. At the same time, the surface of the insert is treated with anti-corrosion, such as electroplating, spraying anti-corrosion coating, etc., to prevent the insert from corroding in harsh environments, thereby ensuring the overall performance of the rubber and insert bonding products. ​
The difference in thermal expansion coefficients between different materials is also an important factor affecting the performance of rubber-insert bonding products. The thermal expansion coefficients of materials such as rubber, metal and plastic are different. When the temperature changes, due to the different degrees of thermal expansion and contraction, stress will be generated at the interface between rubber and inserts. When the stress accumulates to a certain extent, it may cause cracking of the bonding interface and reduce the service life of the product. To meet this challenge, the thermal stress can be relieved by optimizing the product design, reasonably arranging the structure and size of rubber and inserts, and reserving a certain amount of deformation space. In addition, selecting rubber and insert materials with similar thermal expansion coefficients, or using transition layer materials to reduce the difference in thermal expansion coefficients between different materials, is also an effective solution.​
The difficulty in controlling the production process is also one of the problems faced by rubber-insert bonding products. During the production process, parameter fluctuations in any link may affect the bonding quality of the product. For example, uneven application of adhesive, unstable molding temperature and pressure, etc., will lead to inconsistent bonding strength between rubber and inserts. To ensure the stability of product quality, it is necessary to establish a strict production process control system to accurately monitor and adjust various parameters in the production process. Use advanced automated production equipment to improve the accuracy and consistency of the production process; strengthen employee training, improve the skill level of operators, and ensure the accurate execution of the production process. ​