The processing of silicone insoles needs to control details from multiple dimensions such as materials, molds, molding, post-processing and safe production. The following is a specific analysis:
1. Material selection and storage: Laying the foundation for quality
Matching purity with purpose
Choose the purity of silicone according to the purpose of the insole. For example, medical-grade silicone needs to pass FDA certification, and the purity requirement is much higher than that of ordinary household insoles to ensure non-toxicity; industrial-grade silicone needs to have wear-resistant and aging-resistant properties to adapt to high-intensity use scenarios.
Storage environment control
Silicone materials should be stored in a dry, cool, and well-ventilated environment, avoiding direct sunlight and high temperatures. If the humidity in the storage environment is too high, the silicone may absorb moisture and affect the curing effect; if the temperature is too high, it may accelerate the aging of the material and shorten the shelf life.
2. Mold design and production: dual guarantee of precision and life
Mold design details
Demolding slope: Design a reasonable demolding slope (usually 1°-3°) according to the shape of the insole to avoid product jamming or damage.
Vent layout: Vents with a diameter of 0.1-0.3mm are set at the edge of the mold cavity to prevent bubbles from being generated due to air entrapment during silicone injection, resulting in uneven insole surfaces.
Parting surface selection: Planes or simple curved surfaces are preferred as parting surfaces to reduce flash and reduce the difficulty of post-processing.
Mold manufacturing process
Material selection: Select mold materials according to production batches. Aluminum molds can be used for small batch production, which are low in cost but easy to wear; steel molds are required for large batch production, which have a long life but high cost.
Surface treatment: The surface of the mold cavity needs to be polished to a mirror effect (roughness Ra≤0.4μm) to ensure a smooth surface of the insole; if a matte effect is required, sandblasting can be performed.
Cooling system design: Heat-conducting copper pipes or cooling water channels are embedded in the mold to accelerate the curing of silicone by circulating coolant and shorten the production cycle (such as from 30 minutes to 10 minutes).
3. Molding process control: Accurate balance of temperature, pressure and time
Temperature management
Curing temperature: Set the curing temperature according to the type of silicone. Addition type silicone usually needs to be cured at 80-120℃. Excessive temperature (such as 150℃) may cause material decomposition, produce odor or performance degradation; low temperature (such as 60℃) will not completely cure and the insole is easy to deform.
Mold temperature uniformity: Use a mold temperature controller to control the mold temperature, and the temperature difference is controlled within ±2℃ to avoid the insole from generating internal stress due to local temperature difference, resulting in cracking or warping.
Pressure and injection control
Injection pressure: Adjust the injection pressure (usually 50-150bar) according to the thickness of the insole. Too low pressure will lead to insufficient silicone filling and glue shortage; too high pressure may cause silicone to penetrate into the mold gap, increasing the difficulty of cleaning the flash.
Injection speed: Use a segmented injection process to first fill the mold cavity at a low speed (10-20cm³/s), and then complete the final filling at a high speed (30-50cm³/s) to reduce the generation of bubbles.
Time control
Curing time: Set the curing time according to the size of the insole and the type of silicone. For example, a 5mm thick insole needs to be cured for 10 minutes at 100°C; if the curing time is insufficient, the hardness of the insole will not meet the standard and it will be easily deformed; if the curing time is too long, energy will be wasted and costs will increase.
Demolding time: After curing, it needs to be cooled to below 50°C before demolding to avoid high-temperature demolding causing deformation of the insole or adhesion to the mold.
4. Post-processing and inspection: Details determine quality
Deburring and trimming
Use a laser cutting machine or a manual knife to trim the edge of the insole. The accuracy must be controlled within ±0.1mm to avoid dimensional deviation caused by excessive trimming.
Surface treatment
Anti-slip treatment: Spray an anti-slip coating (such as silicone particles or TPU film) on the surface of the insole to increase friction and prevent sliding.
Antibacterial treatment: Add silver ions or nano-titanium dioxide antibacterial agents to inhibit bacterial growth, suitable for sports insoles or medical purposes.
Quality inspection
Dimension detection: Use a three-coordinate measuring instrument to detect the length, width, and thickness of the insole, and the tolerance must be controlled within ±0.5mm.
Performance test: compression rebound test (such as rebound rate ≥80% after compression of 50%), aging test (such as no cracking after 70℃×72h) and wear test (such as weight loss ≤0.1g after 500 turns of Taber abrasion test).
5. Production safety and environmental protection: responsibility and efficiency are equally important
Safety operation procedures
Operators need to wear protective glasses, gloves and gas masks to avoid contact of silicone with skin or inhalation of volatile gases.
Mold heating equipment needs to be equipped with overheating protection devices to prevent fire caused by temperature runaway.
Environmental treatment
Waste gas treatment: Install activated carbon adsorption device or catalytic combustion equipment to purify organic waste gas (VOCs) generated during silicone curing to ensure that the emission concentration is less than 50mg/m³.
Wastewater treatment: Sedimentation and filtration of wastewater from mold cleaning to recover silicone particles and reduce environmental pollution.
6. Continuous improvement and innovation: adapt to market changes
Process optimization
Introduce 3D printing technology to make molds, shorten the development cycle (from the traditional 2 weeks to 3 days), and reduce the cost of trial and error; adopt liquid silicone injection molding (LSR) technology to achieve automated production and improve efficiency by more than 30%.
Material innovation
Develop high-elasticity, low-density silicone materials (such as foamed silicone with a density of 0.6g/cm³), reduce the weight of insoles (40% lighter than traditional silicone), and improve wearing comfort.
Function expansion
Integrate smart sensors (such as pressure sensors, temperature sensors), and develop smart insoles that can monitor gait and foot pressure distribution to meet the needs of high-end markets such as sports health and medical rehabilitation.