Press and Cure, Product Takes Shape
Hello! This is the editor from Hongxiangda.
Previously, we introduced the mixing process—the first step in creating a silicone product. Today, let's move forward and talk about: How does the mixed compound actually become the product in your hand?
The answer is: It's pressed out.
What is Compression Molding?
Compression molding, also called compression vulcanization, is the most traditional and commonly used method for shaping silicone products.
Simply put, it involves placing the mixed silicone compound into a mold and using high temperature and high pressure to shape it within the mold, transforming it into the desired product form.
This process is like making baked egg tarts—you put the dough into a tart mold, press it, bake it, and when it comes out, you have a perfectly shaped tart shell.
The Three Steps of Compression Molding
At Hongxiangda, a silicone product goes through three main steps in the compression molding process:
Step 1: Material Preparation
The mixed compound can't just be thrown directly into the mold. It needs to be prepared into a shape suitable for the mold cavity.
How is it done?
Cutting: The compound is cut into small pieces or strips for easy placement into the mold.
Weighing: The amount of material needed for each product must be accurately weighed. Too much material causes溢出 (overflow) and waste; too little material results in an incomplete product (scrap).
The key here: Accurate weight and suitable shape. An experienced technician can tell at a glance how big to cut the piece and how much it should weigh.
Step 2: Loading
The prepared compound is placed into the cavity of the mold.
What needs attention?
The compound must be placed in the center of the mold cavity.
If placed off-center, the pressed product will have uneven thickness.
For products with complex shapes, the compound needs to be positioned skillfully to ensure every corner of the mold fills properly.
This step seems simple but requires experience. It's like making dumplings—if you put the filling off-center, one side of the dumpling ends up thick and the other thin after boiling.
Step 3: Compression Molding
This is the core step.
Equipment: Compression molding press (often called a vulcanizing press)
The Process:
The mold is placed between the heated platens of the press.
The press closes, applying high temperature (typically 150-200°C) and high pressure.
The silicone compound flows under heat and pressure, filling every corner of the mold cavity.
The pressure and temperature are maintained for a specific duration (the curing time), allowing the silicone to transform from a pliable state into an elastic, vulcanized state.
The press opens, and the molded silicone product is removed.
The entire process is "press and bake"—pressing gives it the shape, baking gives it the elasticity.
Three Key Parameters in Compression Molding
Compression molding isn't just "pressing it once." Three critical parameters must be carefully controlled:
1. Temperature
Temperature too low: The compound won't vulcanize (won't cure properly). It comes out soft and won't hold its shape.
Temperature too high: The compound can scorch (over-cure), making the product brittle and prone to cracking.
The right temperature: Generally between 150°C and 200°C, depending on the specific product formulation.
It's like baking bread—too low a temperature and it doesn't bake through; too high and the outside burns while the inside stays raw.
2. Pressure
Pressure too low: The compound flows slowly and may not fill the mold completely, resulting in an incomplete product.
Pressure too high: The mold can be damaged, and excessive compound溢出 (overflow) creates large flash, wasting material.
The right pressure: Enough to fill the mold completely without causing excessive overflow.
3. Time
Time too short: The product won't be fully cured, leading to poor elasticity and a tendency to deform.
Time too long: Production efficiency drops, and over-curing may occur.
The right time: Just long enough for complete curing, without wasting a second.
These three parameters are like the heat, salt amount, and cooking time in preparing a dish—a little too much or too little, and the result is completely different.
Advantages of Compression Molding
Why has compression molding remained the mainstream method for so many years?
Advantage 1: Relatively Low Cost
The mold structure is relatively simple, making mold costs lower than for injection molding. This makes it suitable for small to medium batch production.
Advantage 2: Suitable for Large Products
For items like silicone mats, large sheets, and oversized silicone parts, compression molding is easier to achieve.
Advantage 3: Dense Product Structure
Molded under high temperature and pressure, the internal structure of the product is dense and strong.
Advantage 4: High Flexibility
It allows for producing multiple different products simultaneously (using multi-cavity molds) or making large single-piece products.
The "Byproduct" of Compression Molding: Flash
Compression molding has an unavoidable "byproduct"—flash.
How does flash form?
When the mold closes, there are tiny gaps between the upper and lower halves. Under high temperature and pressure, the flowing silicone compound can seep into these tiny gaps, curing there and forming a thin layer of excess material around the product. This is flash.
How is it handled?
Flash doesn't affect the product's function, but it does affect its appearance. Therefore, after compression molding, products typically need trimming or grinding to remove the excess flash.
This is why we discussed the grinding process in a previous article—products coming out of the mold need grinding to become smooth and neat.
Compression Molding at Hongxiangda
At Hongxiangda, compression molding is one of our core production processes.
Our Equipment: Multiple compression molding presses, ranging from 30 tons to 500 tons of clamping force, capable of producing everything from small buttons weighing a few grams to large gaskets weighing several kilograms.
Our Experience:
Our technicians know intuitively how much material each product needs.
Temperature, pressure, and time are precisely set based on the formulation and product characteristics.
For complex products, there are specific operating procedures for loading the compound.
Our Quality Control:
First article inspection for every batch before mass production.
Regular in-process inspections to catch any abnormalities promptly.
Standards for flash size, product thickness, and surface quality.
Conclusion
Compression molding is the art of "press and cure."
Place the mixed compound into the mold, apply high temperature and pressure—pressing gives it shape, baking gives it elasticity—and finally, you have the silicone product in your hand. It seems simple, but every press has its purpose, and every cure has its know-how.
For 15 years, Hongxiangda has used these compression presses to create countless silicone products—from remote control buttons to automotive parts, from baby tableware to industrial sealing rings.
If you'd like to know whether your product is better suited for compression molding or injection molding, feel free to contact Hongxiangda.