Silicone, as a type of organic silicon product, is widely recognized for its exceptional properties, including high and low-temperature resistance, UV and radiation resistance, weather durability, electrical insulation, high permeability, physiological inertness, low compression set, and fatigue resistance. These features make silicone extensively applicable in aerospace, electronics, consumer goods, machinery, construction, healthcare, and food processing industries. Common silicone molding methods include:
1. Compression Molding (Thermal Compression Molding)
Compression molding is a widely used technique where solid silicone is cured into shape using heat and pressure from a hydraulic press. This method is commonly applied to single-color silicone products and accommodates dual-color, multi-hardness, or encapsulated items such as metal or plastic components. Encased objects must typically withstand temperatures of up to 180°C without deformation.
- Applications: Custom silicone products.
- Advantages: Versatile for single and multi-color designs, suitable for encapsulating materials.
- Process: Solid silicone mixed with curing agents is placed in a mold cavity and subjected to heat and pressure until cured.
2. Liquid Injection Molding (LIM)
Liquid injection molding uses two-component liquid silicone materials suitable for automated injection molding systems. Mixing A and B liquid silicone materials ensures precise and consistent production with minimal human intervention. The typical curing temperature for liquid silicone ranges from 110°C to 150°C, and any embedded components must withstand temperatures above 150°C.
- Applications: High-precision custom silicone products.
- Advantages: Automated, efficient, and capable of producing high-quality products.
- Process: Fully automated from material mixing to molding.
3. Extrusion Molding
Extrusion molding involves feeding silicone material through a heated extrusion machine, where it is continuously shaped and vulcanized. This method is ideal for producing linear products with various cross-sectional profiles, such as rectangular strips or circular tubes.
- Applications: Silicone hoses, seals, and other linear products.
- Advantages: Continuous production with flexible cross-sectional designs.
- Process: Material is pushed through an extrusion head, shaped, and vulcanized.
4. Drip Molding
Drip molding uses liquid silicone dispensed manually or pneumatically onto molds before heating and curing. Although labor-intensive, this method allows for multi-color designs, making it ideal for creating decorative items like colorful silicone wristbands and phone cases.
- Applications: Artistic and multi-color silicone products.
- Advantages: Customizable colors and patterns.
- Process: Silicone is dropped onto molds, cured with heat, and finished manually.
Silicone Product Manufacturing Process
The manufacturing process for silicone products involves the following steps:
1. Mold Creation
Design and manufacture the mold based on the 3D drawings of the product to be made.
2. Material Inspection
Procure silicone raw materials based on the product’s characteristics and conduct quality inspections upon receipt to ensure performance meets quality requirements.
3. Material Selection and Mixing
Select additional materials required beyond the raw silicone, such as vulcanizing agents, color masterbatches, and other additives.
4. Rubber Compounding
Silicone raw materials are typically in block form, usually milky white in color. At this stage, the material cannot be directly thermally molded; a vulcanizing agent (curing agent) must be added. If the product has specific requirements such as color, luminescence, fluorescence, phosphorescence, or conductivity, corresponding additives like color masterbatches, luminous powder, fluorescent powder, or conductive particles need to be included. The raw materials, vulcanizing agents, and other additives are mixed using a rubber compounding machine, with the process usually taking about 30 minutes (depending on the weight of the material and the gap between the rollers).
5. Cutting
Cut the compounded silicone material into specific dimensions (length × width × thickness). Place the cut material on a resting rack for a period of time. Generally, the resting time for the material is around 8 hours (both sides of the material are protected with PE film to ensure cleanliness).
6. Forming
Once the resting time is complete, shape the material using methods such as compression molding, liquid molding, extrusion, or drip molding.
- For high-temperature silicone on the market, there are two types: solid silicone and liquid silicone.
- Solid silicone forming includes thermal compression molding and extrusion molding.
- Liquid silicone forming includes injection molding, casting, and drip molding.
7. Processing/Adhesive Backing/Punching
8. Secondary Vulcanization
The silicone vulcanization process is not completed in one stage but is carried out in two phases.
- In the first stage, the silicone material undergoes heating under pressure or at atmospheric pressure to form its shape, referred to as primary vulcanization (or forming vulcanization).
- After the first stage, the crosslink density of the silicone is insufficient. The material undergoes high-temperature vulcanization in an oven during the second stage, stabilizing its physical properties such as density, tensile strength, elasticity, hardness, swelling, density, and thermal stability. This is referred to as secondary vulcanization (or post-vulcanization).
9. Printing, Spraying, Laser Engraving, and Electroplating
Conduct surface treatment on the semi-finished silicone products.
10. Full Inspection
Inspect the molded products for defects such as dirt, incomplete edges, insufficient material, under-curing, or cracking. Defective products are sorted out and discarded (they cannot be reused). Only qualified products proceed to the next process.
11. Quality Assurance
Conduct a final inspection of the products and identify any defects from the subsequent processes.
12. Packaging
Package the qualified products according to customer requirements for shipment.
13. Shipping
Deliver the products to the customer’s specified location to complete the transaction.
What Are the Silicone Molding Techniques?
1. Compression Molding for Silicone
Compression molding, also known as hot press molding, is a silicone molding technique that uses temperature and pressure from a hydraulic press to vulcanize solid silicone into a desired product shape via molds. This process is commonly used for single-color customized silicone products. It can also be applied to dual-color, dual-hardness products, or even multi-color, multi-hardness products. Additionally, it supports overmolding plastic and metal, provided the embedded materials can withstand temperatures of up to 180°C without deformation.
Compression molding is a production method for solid silicone involving two mold halves, with a mold core in the middle. Raw silicone material is evenly mixed using a mixing machine to create a compounded material, which is then placed in the mold cavity inside a vulcanizing machine. The mold is then closed and pressed, allowing the silicone to cure and take shape. Once set, the mold is opened, and the silicone product is removed. This process is well-suited for thermoset materials.
Silicone products made via compression molding typically have a hardness range of 30–70A (Shore hardness). During production, raw silicone is first placed onto a two-roll mill or into a closed mixer where fillers like silica and silicone oil are added. Different fillers and additives will alter the silicone’s properties.
Compression molding is a stable process, allowing high production efficiency and broad applications. It is widely used for single-color silicone products, as well as dual-color or multi-hardness items. It is particularly suitable for embedding materials like plastic or metal with specific temperature requirements (typically 180°C). The shape of the mold determines the final product’s shape, making compression molding one of the most widely used methods in silicone molding. Common products include industrial silicone components, buttons, silicone gifts, wristbands, watch straps, key covers, phone cases, kitchenware, mats, ice trays, and cake molds.
2. Liquid Injection Molding for Silicone
Liquid injection molding is a technique using a two-part, translucent liquid silicone material suitable for injection molding processes. This method integrates liquid silicone with precision injection molding machines to produce high-quality customized silicone products. The process is fully automated: two liquid components (A and B) are loaded into the equipment, mixed, and molded into products.
The vulcanization temperature for liquid silicone is generally between 110°C and 150°C, so embedded components must resist deformation at temperatures above 150°C. Equipment requirements for this process include silicone injection machines and pressure feeders. The raw material—a two-component liquid—is mixed in a 1:1 ratio and passed through a static mixer before injection molding. This method requires lower molding temperatures (as low as 130°C), making it advantageous for overmolding plastic components that are less heat-resistant.
Liquid silicone molding is widely used for producing medical supplies, food-grade items, pacifiers, baby products, diving equipment, electrical insulation components, and cable accessories.
3. Silicone Extrusion Molding
Extrusion-molded products, like common water pipes, are produced by heating and vulcanizing the material as it is pushed forward by a screw inside the barrel of the extruder. The material is continuously extruded through a die, forming various cross-sectional shapes or semi-finished products. The die determines the cross-sectional shape of the product, and under the effects of pressure and temperature, the product is vulcanized as it exits the die.
Extrusion molding is similar to squeezing toothpaste out of a tube. The die corresponds to the cross-sectional shape of the product, which can include rectangular strips, circular silicone tubes, or other shapes. Products made using this silicone molding process are typically strip-shaped, with a variety of cross-sectional designs such as rectangular bars or ring-shaped silicone tubes.
Extruded silicone products are typically formed by pressing silicone through an extrusion machine, a continuous molding process. This method is suitable for both dual-component peroxide-cured solid silicone and platinum-catalyzed liquid silicone. Silicone is processed in the barrel of the extruder with the interaction of a rotating screw, continuously forming semi-finished products of various shapes. It can be used to produce silicone tubes, insulation sheaths for silicone electrical wires and cables, and other silicone products. The semi-finished extruded silicone is soft and deformable, so it must be vulcanized immediately. The most common method is continuous vulcanization using hot air, while high-pressure steam vulcanization is often used in the wire and cable industry.
If continuous vulcanization is not possible after extrusion, measures must be taken to prevent deformation. The extruded product should be collected using circular disks, drums, or conveyor belts and separated to prevent sticking. If the material is too soft for extrusion, 3–5 parts of fumed silica can be added to the silicone mix to improve extrusion performance.
Silicone extrusion is widely used for silicone tubes, various sealing strips, sealing rings, automotive tires, composite silicone tubes, and multi-layer co-extruded silicone tubes. It is also applied in electrical wires and cables, such as power cords, power station wires, automotive ignition wires, building wires, mining cables, control and signal cables, etc.
In the automotive industry, applications include radiator and heater hoses, sealing strips, rubber belts, body and chassis components, weatherstrips, floor mats, and circular hoses. In the food industry, it is used for food-grade silicone tubes and reinforced silicone hoses. In the medical field, applications include urinary catheters, endotracheal tubes, feeding tubes, drainage tubes, peristaltic pump tubes, and central venous catheters.
4. Dripping Molding
Dripping molding uses liquid silicone as the raw material, which is stored in a syringe. The material is dispensed onto the mold using pneumatic force combined with manual operation and then heated and vulcanized into shape. This process is highly manual, leading to lower production capacity. However, it allows for the use of multiple colors in a single product as per the requirements, making it suitable for crafting decorative items such as multi-colored silicone wristbands and phone cases with various colored patterns.
There are two methods for dripping molding: manual dripping and machine dripping. The raw material used is liquid silicone, typically employed for making gifts, ornaments, and toys.
Products made using the dripping process have a smooth texture, a long lifespan, and features such as waterproofing, corrosion resistance, wear resistance, and aesthetic appeal. The decorative aspect is particularly notable, as the process gives products a transparent, glossy finish, enhancing their appearance while protecting their surface from damage.
The dripping process generally involves the following steps: preparing a mixture of high-purity epoxy resin and curing agent in a specific ratio, loading the mixture into a dripping syringe, and then dripping a precise amount of epoxy resin onto the silicone product surface. After the product has been coated, it is left to cure for approximately 12 hours (curing can be expedited by placing the product in an oven at 60-70°C). Once fully cured, the dripping process is complete.
5. Calendering Molding
Calendering molding involves passing raw materials through the gaps between a series of rotating rollers, where they are compressed and stretched to form uniform sheets of a specific thickness. The process can also incorporate coatings on textiles, such as fabrics or other materials, by applying adhesive layers that are simultaneously shaped by the rollers. This method is commonly used for manufacturing silicone and rubber sheets.
After mixing the silicone with additives such as fumed silica and silicone oil to form a compound, it undergoes calendering to produce sheets. Calendered sheets often exhibit distinct physical and mechanical differences between their longitudinal and transverse directions—a phenomenon known as the calendering effect. For instance, longitudinal tensile strength is higher than transverse strength, while transverse elongation at break is greater. These differences arise due to the alignment of molecular chains and fillers along the calendering direction. Factors like material composition, calendering temperature, speed, and ratio influence the degree of this effect.
Calendering is ideal for producing large products such as silicone sheets and boards. In addition to sheet production, calendering can be used for laminating textiles, steel-reinforced fabrics, and PET films, as well as processing silicone mixtures. It is an essential step in the integrated production line of silicone products.
Types of Calendering Processes:
- Pure Silicone Sheet Production: Producing silicone boards, sheets, and films through calendering, hot vulcanization, winding, and cutting.
- Laminating with Adhesives: Applying silicone adhesives to textiles, steel-reinforced fabrics, or PET films. For example, CL-26AB silicone adhesive is widely used in PET calendered films and silicone insulation fabrics.
- Solid Silicone Mixing: An essential step in processing solid or compounded silicone. Materials like raw silicone, vulcanizing agents, and colorants are mixed and processed in calendering machines for hot vulcanization.
Calendering Molding Process:
- Raw material preparation
- Extrusion (plasticizing extrusion)
- Forming with a traction machine
- Water cooling
- Traction rollers (pulling)
- Bottom grinding machine (surface grinding)
- Toothed cutting machine (cutting to shape)
- Rolling machine (final product bundling)
This process is particularly suitable for large-area sheets and rolls. It offers advantages for producing thin films, laminating fabrics, and creating products of extended lengths. While the width and thickness depend on equipment limitations, calendered products can be cut into any shape using die-cutting tools, making it highly suitable for large-scale products.
