Key points of aluminum alloy coated silicone technology

Aluminum alloy coated with silicone is a more challenging technology than plastic coated with silicone, as it involves the combination of metal and elastomer. The key to its success is very clear, and the core lies in solving the century old problem of strong adhesion between metal and silicone.

Here are several key points of this technology, ranked in order of importance:

Core Key Points: Pre treatment and Activation of Aluminum Alloy Surface

This is the cornerstone of the entire process, directly determining the success or failure of adhesive strength. Due to the smooth and inert surface of aluminum alloy, as well as the significant polarity difference with silicone, it is necessary to create an active surface that can "lock" silicone through physical or chemical methods.

The main methods are as follows:

Micro porous mechanical interlocking (the most commonly used and reliable method)

Principle: Create microscopic, high-density pits or holes on the bonding surface between aluminum alloy and silicone. In the mold, liquid silicone is injected and infiltrated into these micropores under high pressure, and after vulcanization molding, countless tiny "mechanical anchor points" are formed, thereby achieving physical and secure locking.

Implementation technology:

Micro arc oxidation: This is currently the most mainstream and effective process. A hard and porous ceramic oxide layer is grown in situ on the surface of aluminum alloy through electrochemical methods. This oxide layer is extremely firmly bonded to the aluminum substrate, and its porous structure provides a perfect anchoring site for the silicone gel.

Anodizing: It can also form porous structures, but its bonding effect and stability are usually not as good as micro arc oxidation.

Laser texturing/etching: using laser to carve fine rough structures on metal surfaces. High precision, but also high cost, and requires optimizing the pattern to maximize anchoring effect.

Sandblasting: forming a rough surface through physical bombardment. This is a more traditional and economical method, but the resulting roughness uniformity and anchoring effect are usually not as good as the chemical methods mentioned above, and are often used in situations with lower requirements.

Chemical bonding (auxiliary and enhanced)

Principle: Apply a layer of specialized primer on the treated aluminum alloy surface. This layer of primer contains functional groups on one end that can react with the hydroxyl groups (- OH) on the metal surface, and on the other end that can undergo condensation reactions with the silicon hydroxyl groups (Si OH) on the silica gel, thus acting as a "molecular bridge".

Key:

The selection of primer must be perfectly matched with the type of silicone used (such as platinum sulfide or peroxide sulfide).

Before applying the primer, the surface of the aluminum alloy must be absolutely clean, free of oil stains, dust, and oxides. Usually requires strict cleaning (such as ultrasonic cleaning) and activation steps.

The coating thickness and uniformity of the primer are crucial and usually require automated operations to ensure consistency.

The best practice is a combination of "micro porous mechanical interlocking+specialized primer" to achieve the highest and most stable adhesive strength.

Other key technical points

In addition to the core surface treatment, the following steps are also indispensable:

1. Mold design and injection molding process

Mold considerations:

Positioning and clamping: The mold must be able to accurately fix the aluminum alloy inserts to prevent displacement during high-pressure silicone injection.

Thermal balance design: Aluminum alloy is an excellent thermal conductor that quickly absorbs the heat required for silicone vulcanization. The mold must be designed with a good heating system (usually using hot oil or electric heating tubes) to ensure that the temperature in the bonding area can REACH the optimal vulcanization temperature of the silicone gel (usually 165 ° C-200 ° C).

Exhaust system: Silicone has low viscosity and excellent fluidity. The mold must have precise exhaust grooves to prevent trapped gas from causing missing glue or burning.

Injection parameters:

Injection pressure and speed: Sufficient pressure is required to ensure that the silicone can fully fill the micropores, but the speed should not be too fast to cause air entrapment or flash.

Sulfurization time and temperature: Due to the "endothermic" effect of aluminum alloys, it may be necessary to extend the vulcanization time or increase the temperature appropriately to ensure complete curing of the silicone gel.

2. Material selection

Aluminum alloy: The appropriate grade for surface treatment should be selected. For example, aluminum magnesium alloys with lower silicon content (such as 5 series and 6 series) are usually more suitable for micro arc oxidation or anodizing than high silicon content die cast aluminum alloys (such as ADC12) to obtain a more uniform and dense oxide layer.

Silicone: High tear strength and high tensile strength varieties should be selected to ensure that stress is not easily concentrated at the bonding interface during product use, resulting in silicone tearing. Specialized adhesive grade silicone is the preferred choice.

3. Production process control

Cleanliness: This is the lifeline. Aluminum alloy inserts that have undergone surface treatment must be injection molded in a clean environment (such as a Class 1000/Class 10000 dust-free workshop) within a short period of time, as any contamination can lead to bonding failure.

Process automation: In order to improve yield and consistency, it is best to use automated equipment to complete the picking and placing of inserts, gluing (if used), and injection molding.