Silicone Compression Molding Complete Guide
This guide gives you the straight facts on silicone compression molding. Know your materials: the kinds of silicone and their effects on the mold. Learn mold design: draft angles, parting lines, venting. Understand the process: how heat, pressure, and time shape your results. Problems and solutions. Get ready: how to mix, degas, and color silicone right.
Alternatively, you can learn more about the compression molding process via Wikipedia.
About Us: Dabojin Custom Silicone Product Manufacturer specializes in silicone compression molding with a focus on quality and efficiency. Our team includes engineers with 18 years of experience and a suite of industry certifications including ISO 9001, ISO 45001, ISO 14001, and FDA approval.
For further assistance or inquiries, contact us at info@siliconedabojin.com.
Understanding the Material
Silicone: Its Forms and Uses
Silicone is a standout material, known for handling heat well. It keeps its shape and strength in both hot kitchens and flying planes. It lasts long, fighting off sun, rain, and wear.
Types of Silicone
You’ll find silicone in many forms. Some are soft or clear, used for things like watches and cookware. Others are for cars and medical gear. High-clear silicone lights up LEDs and is used in medical and food areas. Platinum silicone is pure and sets quickly, perfect for healthcare and food. Some silicones are tough, bouncing back after stress, ideal for seals and cushions. Others resist flames or extreme heat, key in cars, planes, and electronics. Some even manage oil or static, solving specific problems in cars and electronics.
Making Silicone Work
Different silicones need different making processes. Platinum types might set quicker, affecting how fast and hot you need to work. The softness or stretchiness of the silicone matters for molds and shapes. And things added to change its fire resistance or clarity also change how it’s made. Knowing all this helps makers and designers pick the right silicone and make things well, for whatever job or place they have in mind.
Know the Silicone Properties
For a deeper understanding of silicone’s properties and the tests it undergoes to ensure quality and compliance, please refer to:
- Silicone Rubber Test Report: For insights into specific silicone’s compliance with standards like RoHS, EN 71-3, and Prop 65, visit Silicone Rubber Test Report.
- 17 Types of Silicone: Applications, Features, and Tests: To explore the resilience, uses, and versatility of 17 different silicone types, along with their specific applications and the tests they undergo, visit 17 Silicone Types.
Silicone Compression Molding Process Parameters.
Optimal Temperature Range.
For silicone, the optimal molding temperature ranges between 160°C to 232°C . This range ensures proper flow and curing without degrading the material.
Too Low 160°C. If the temperature is below this range, the silicone may not flow into all parts of the mold. Incomplete filling can occur when curing is insufficient, resulting in poor mechanical properties. High adhesive materials can lead to shape and surface defects in the mold.
Defective Silicone Product due to Insufficient CompressionToo High 232°C. If the temperature exceeds this range, the silicone can burn or discolor parts. Overheating can result in premature cross linking or vulcanization. This can lead to distorted shapes, weaker parts, or material degradation.
Overheated Silicone Product with Burn and Distortion DamageThe specific temperature within this range can vary and it depends on:
- The type of silicone,
- The intended application,
- And the desired properties for the final product.
Product Manufacturers often need to conduct tests. These tests help determine the optimal temperature for a new material or mold design.
In summary: Silicone molds well between 160°C and 232°C. Too cold, it won’t fill the mold; too hot, it burns. The right temperature varies with the silicone type, use, and desired product quality.
Silicone Compression Molding Pressure Application.
In our case: Plasticity in the context of silicone materials refers to the material’s ability to deform under pressure.
Therefore when considering a silicone material with a plasticity of 160 for compression molding. The amount of pressure applied is critical. Ensuring that the material flows and the final product meets the specifications.
Key Considerations for Pressure Application:
Material Flow Properties.
With a plasticity of 160, the silicone is likely to have a certain stiffness and viscosity. To get the same flow in intricate mold areas, you need higher pressure than with softer silicones like 330.
Mold Design and Complexity:
The specific design of the mold, including its complexity, size, and the fineness of details, will impact how much pressure is needed. It’s important to use enough pressure for stiffer materials to fill the mold without causing damage or excess material.
Part Thickness and Geometry:
Thicker parts need extra pressure to fill before the silicone starts to harden. Yet, too much pressure on thinner or delicate parts can cause material distortion. The overall geometry of the part will guide the necessary adjustments in pressure.
Impact of Pressure Variation:
Too Low Pressure.
Silicone doesn’t fill the mold, leaving parts incomplete. Stiffer silicone worsens it, missing fine details and shaping wrong.
Incomplete Silicone Keyboard due to Low Pressure in MoldingToo High Pressure.
Silicone squeezes out, creating flash. Needs trimming, affects precision. Stresses the mold, causing wear or damage.
Excess Flash on Silicone Product Due to High PressureOverall Quality:
Right pressure is key.
It fills the mold, cures evenly, giving consistent parts. Wrong pressure causes defects: incomplete filling, air, uneven surfaces. Balance is crucial, especially for silicone with 160 plasticity, to fill properly without problems.
In practice, finding the right pressure needs testing and tweaking. Consider silicone’s plasticity, mold design, and the final product’s needs. Start with standard pressure for the silicone type, then adjust from trial results. Aim for consistent, quality output meeting all requirements.
Curing time.
Consider this example:
Understanding platinum cured silicone with 0.5% A and 1% B, at 135°C for 2 minutes, under 15 MPa pressure. This scenario serves as a guide to illustrate the specific conditions and implications of working with a particular type of silicone.
- Platinum Agent: High purity, cures fast, especially with set concentrations.
- 135°C Temperature: Speeds up curing. Must control precisely.
- 2-Minute Time: Indicates a quick cure, typical for this system at this temperature.
- 15 MPa Pressure: Ensures mold fill and affects curing rate.
To determine curing time:
- Likely based on tests and recommendations. Fast reaction needs exact ratios and conditions for full cure.
Consequences and Mitigation:
- Under Curing: Silicone might be weak. Mitigate by ensuring correct temperature and maintaining time and pressure.
- Over Curing: Silicone might become brittle. Mitigate with precise timers and temperature controls. Check quality regularly.
Test parts for hardness, tensile strength, and elongation. Adhere to specified parameters and quality controls due to the sensitivity of the process to variations. For details and further guidance, refer to the material dataset. You can read our silicone datasheet here: 17 types of silicone: applications, features, and tests.
Operating the Press in 5 steps.
Setting up the mold right is key for good production in compression molding. This is vital when using materials like silicone. Here are the main steps to get the mold ready, aligned, and secure:
1. Clean the mold:
Clean the mold well. Remove all old residue and dirt. This includes the mold surfaces, vents, and any hidden parts. Some molds might need special cleaners.
Clean mold for silicone compression molding
2. Apply Mold Release:
Use the right mold release so the silicone doesn’t stick. The choice depends on the silicone and mold type. Be careful with release agents, as some may not work well with silicone. Ensure the agent chosen is compatible with silicone’s properties.
Applying mold release to prevent silicone adhesion.
3. Check for Damage:
Look over the mold for any damage or wear that might ruin the final product. Make sure everything fits tight and right.
4. Assemble the Mold:
Put all parts of the mold together. This includes any slides, inserts, or cores.
5. Heat the Mold:
Warm up the mold to the right temperature for the silicone. This helps cure faster and evenly.
Ensuring Correct Alignment and Security in 5 steps.
1. Alignment Checks:
Check the mold halves align precisely. Wrong alignment can lead to defects like flash or poor filling.
2. Clamping and Securing:
Clamp the mold tightly in the press. The force should be enough to keep it shut during compression but not damage it.
3. Double-checking Tightness and Positioning:
Check bolts and clamps after setting up and during production.
4. Safety Measures:
Keep all safety guards in place and follow safety standards to protect workers and equipment from the high pressures and temperatures.
5. Test Run:
Do a test run to find any issues before starting production. Adjust as needed for quality production.
Follow these steps and maintain the mold well to cut down on defects, boost safety, and make quality silicone parts. Each step is vital for good molding, especially with the precision silicone needs.
Material Placement and Mold Closure.
Guidelines for Material Placement and Mold Closure:
Pre-forming the Material:
Measure and cut the silicone precisely for less waste and complete filling. Shape it for easy placement and distribution in the mold.
Silicone measurement for efficient mold placement.
Placement:
Put the silicone evenly in the mold cavity. Make sure it’s centered for uniform filling. Lay it carefully to prevent air pockets.
Silicone placement for uniform filling, avoiding air pockets.
Mold Closure:
Shut the mold gently and securely. Check that everything lines up and that the silicone spreads evenly if there are multiple sections.
Heat and Pressure Application.
- Understand Material Specifications: Check the datasheet for the silicone you’re using for temperature and pressure ranges. Understand its viscosity, curing, and reaction to heat and pressure.
- Consider Product Specifications: Factor in part design like size and complexity for the right settings. Different designs need different conditions.
- Start with Baseline Settings: Begin with manufacturer’s recommended settings. Adjust from these baselines based on your mold and material.
- Adjust Based on Experience and Testing: Refine settings after testing initial parts. Look for signs of improper curing or defects to guide adjustments. Keep track of changes.
- Check and Control Temperature and Pressure: Use precise instruments for temperature and pressure control. Ensure the whole mold is uniformly at the right temperature.
Optimizing cooling and ejection in compression molding:
- Cooling Time: Varies with part thickness, shape, and silicone type. Ensure part is solidified and safe to handle.
- Cooling Method: Natural or active cooling. Uniform cooling prevents warping.
- Ejection Mechanism: Align and maintain ejection system for gentle part removal.
- Air Pressure Pistol: Use evenly distributed, gentle air pressure for ejection.
- Handling: Use proper tools or gloves. Ensure parts are cool and retain shape. Inspect Post-Ejection: Check for defects immediately. Adjust procedures if damage occurs.
- Prevent Sticking: Apply release agent to avoid part sticking to mold.
- Training: Train personnel for proper ejection and handling techniques.
Maintain part quality through careful management of cooling and ejection, considering silicone properties and part design. Continuously optimize based on experience.
Quick check problems and solutions.
| Problem | Causes | Countermeasures |
|---|---|---|
| Blowholes | 1. Low mold temperature 2. Insufficient vulcanization time 3. Poor exhaust 4. Material issues 5. Material discharge issues 6. Insufficient pressure | 1. Adjust temperature 2. Extend vulcanization time 3. Ensure vacuum requirements are met 4. Confirm material requirements 5. Improve material discharge position 6. Adjust pressure |
| Material Shortage | 1. Insufficient material weight 2. Improper material discharge position 3. Uneven distribution of rubber fabric 4. Insufficient pressure 5. Excessive temperature 6. Expired or poor-flowing material 7. Damage to mold padding 8. Inappropriate material thickness | 1. Weigh materials properly 2. Accurately discharge materials 3. Distribute rubber evenly 4. Increase pressure 5. Lower temperature 6. Return to compounding 7. Replace mold padding 8. For deeper keying, adjust material thickness |
| Translucent Appearance | 1. Excessive weight of material 2. Improper material discharge position | 1. Reduce and adjust material weight 2. Adjust discharge position and method |
| Rough Surface | 1. Excessive temperature 2. Prolonged external operation time 3. Excessive exhaust frequency 4. Excessive curing agent usage | 1. Lower mold temperature 2. Shorten external operation time 3. Adjust exhaust methods 4. Reduce curing agent amount |
| Cracking | 1. High temperature 2. Improper use of demolding water 3. Incorrect blowing method 4. Mold issues 5. Excessive material thickness or poor stretch resistance | 1. Lower mold temperature 2. Follow demolding guidelines, sandblast if necessary 3. Improve blowing method 4. Repair mold 5. Careful with material handling |
| Color Spots | 1. Dirty hands during material handling 2. Poor workplace cleanliness 3. Inadequate material protection | 1. Ensure cleanliness in material handling 2. Implement proper workplace cleanliness 3. Ensure material is well protected |
| Difficult Clearing of Flash | 1. High temperature 2. Heavy material weight 3. Worn mold edges 4. Low pressure 5. Slow material discharge | 1. Lower temperature 2. Lighten material weight 3. Repair mold 4. Increase pressure 5. Adjust exhaust and speed up discharge |
| Poor Load Capacity | 1. Varying mold temperature 2. Material hardness variation 3. Material weight variation 4. Pressure variation | 1. Adjust mold temperature 2. Adjust material hardness 3. Adjust material weight 4. Adjust pressure |
Silicone compression molding mold design.
Draft Angles:
- Basics:
- Choosing Angles: Choose angles for easy removal. Often, a 2-degree angle for each mm of height is good, but adjust for material and shape.
- Too Small Angles: Small angles cause removal problems. Fix by designing better or using tapered sections.
Parting Lines:
- Layout:
- Placing Lines: Place lines carefully to keep the final product clean and functional. Simple, straight lines are best.
- Flash Control: Cut down flash with precise mold halves and thicker inserts for durability.
Venting:
- Air Flow:
- Making Vents: Design vents to stop air traps and incomplete fills. Put vents right and design helpful inserts.
- Checking Vents: Test with mold flow analysis to make sure vents work well for the material and design.
Precision and Quality:
- Standards:
- Precision Steps: Control everything from choosing materials to final checks. Fine machining is key.
- Mold Care: Keep molds in good condition for consistent quality. Heat-treated materials last longer.
Heating and Cooling Systems:
- Temperature:
- Systems Integration: Combine heating and cooling systems smartly, based on material needs.
- Uniform Heat: Solve uneven heating with hot runner systems and multiple injection points.
Ejection Systems:
- Removing Parts:
- Ejection Types: Choose standard pins or special methods based on the product and mold.
- Better Ejection: For important finishes, use stripper plates or robots to keep surfaces clean.
In summary, mold design for compression molding is complex. Understand materials and mechanics. Design each part of the mold with care for efficiency, durability, and product quality. Keep molds maintained and precision high for success.