Understanding Silicone Compression Molding As a Method of Manufacturing Silicone Products

Silicone manufacturing methods keep evolving with time. This can be said for techniques like silicone compression molding which is among the oldest methods. Since these changes affect production outcomes, it is necessary to keep up with current standards. This article delves deep into the current state of this method of manufacturing silicone.

The Definition of Silicone Compression Molding

There are many ways of making products from silicone rubber. As stated earlier, silicone compression molding is among the most effective ones. It can be used to make almost all varieties of silicone products.

Put simply, silicone compression molding is a process where silicone material is shaped using various compression techniques. Alternatively, think of it as a process where silicone is placed in a mold and then heat is applied as a curative to form a desired shape. As expected, the product will resemble the shape of the mold cavity.

LSR injection molding machineTo expand that definition, heat is the primary agent used to cure silicone material. In this case, curing refers to the turning of raw or un-vulcanized silicone material from its state to a useful product. Also, note that heat is not the only agent used to cure silicone. Let us look at what the process entails to understand this method better.

The Silicone Compression Molding Process

Although there are various compression molding techniques, there is a general process that applies to these approaches. The process is usually modified according to the specific method. The following is a breakdown of the general process. 

Step 1: Preparation of the Mold

The mold cavity used is designed to resemble the product to be manufactured. In most cases, this mold is made of metal since it has to be heated. These molds are created using processes such as machining, casting, and electroforming.

Preparing molds is an integral process since it impacts the outcome of the manufacturing process. Fine details such as dimensions and shapes need to be meticulously engraved in the mold to ensure the product comes out as designed. Inconsistencies in the mold design and design of product leads to incorrect shapes and sizes of products.

Step 2: Readying the Molding Machine

The specific molding machine used is prepped for manufacturing in the second step of the process. The preparations involve cleaning, mechanical checks, and calibration. All this is done to ensure the machine functions flawlessly when turned on.

Molding machines are classified broadly based on the mechanism by which they compress the silicone material. Based on this classification, there are exists machines that use slab side, post-type, electricity, or other types of pressing mechanisms. Each of these types of machines requires special tactics to prep them for the machining of silicone rubber.

Step 3: Getting the Silicone Ready

compression molding technique

The type of silicone used in compression molding is also referred to as a charge. Using this term implies that the material used has a specific quantity. Preparing the charge is equally a critical step in the process. 

This phase is largely manual. For the most part, qualified technicians have to perform a visual inspection when preparing the charge. Doing so has mitigates the chances of errors that can be missed by autonomous systems.

Preliminary steps in the charge preparation are meant to ensure the material is of the required quality, quantity, and specifications. As such, this step includes the selection of materials, testing, and other relevant operations. Once the correct charge specifications are selected, they are cut and placed on the molds for the compressor.

Step 4: Charging or Loading the Charge

The charge is first placed on the bottom cavity then the top part is used as a lid. This step is quite straightforward. However, it will vary depending on the particular compression method in use.

Placing the charge on the lower cavity ensures that the upper part is used as the lid and a press. It also ensures the charge is evenly distributed on the mold to avoid situations where the products are deformed. This step can be manual or automated for large-scale productions.

Step 5: The Compression Starts

After successfully accomplishing the preparatory steps, the compression machine is started and the compression begins. This happens in different ways depending on the method, type of product, and complexity of the design.

Compression methods that use solid sheets of silicone start by curing the silicone using cross-linking processes. This preps the material and gives it the required properties such as hardness, resistance, and so on. Curing is a standard step in the silicone compression molding process.

The cured silicone is usually in a liquid or flowy state. In this state, it is able to be distributed evenly on the mold cavity. Curing agents used are also responsible for the hardening of the material. If anything, the curing process is primarily what defines the molding process.

Step 6: Sampling and Quality Control

Before the compression process ends, samples of molds are ejected for quality control operations. Here, small samples are collected for analysis. Technicians will cross-check mostly the initial molds with the desired outcome. In some production processes, this can be considered the prototyping stage.

This step is significant for various reasons. One, it ensures the final products meet your expectations. Secondly, it ensures an iterative manufacturing process. In other words, the samples are tested and refined and the process is adjusted accordingly.

Step 7: Finalizing the Manufacturing Process

Since this is the last step in the silicone compression process, it entails several essential operations. To start with, the machine is stopped and the molded products are ejected after cooling. Then a series of activities follows.

Some of the mandatory exercises carried out in this step include surface finishing, cleaning, and de-flashing. They are done to ensure the product packaged is of high quality. This is why defective products are picked and pilled in a separate section. The products that meet the required standards are packaged and prepared for shipping.

Types of Silicone Used in Compression Molding

types of silicone rubber

Silicone elastomers manifest in various forms. These forms are dependent on the molecular structure of silicone and external conditions. Each method of manufacturing silicone requires specific types of silicone, for various reasons. The following are the types of compression molding processes:

High-Consistency Rubber (HCR) Silicone

HCRs have a clay-like form when they are uncured. They can undergo platinum or peroxide curing to achieve durometer and other properties. Heat curing can also be applied on top of these curing approaches. These types of silicones are mostly known for their biocompatibility which allows for the manufacture of medical products. 

Fluorosilicone

This elastomer has trifluoro-propyl and methyl groups on its polymer chain. With these molecular groups in the chain, silicone has advanced chemical resistance. Fluorosilicone is relatively costly since this is quite a desirable characteristic. Despite being costly, products made from fluoro silicone are durable hence cost-effective.

Medical-Grade Silicone

Silicone products for medical have particular requirements that they need to satisfy. In this case, medical-grade silicone is used. It is a special type of silicone that has been approved for being biocompatible and safe for internal and external body use. Medical grade can be used to manufacture implants and other medical devices.

Electrically Conductive Silicone

This type of silicone is infused with electrically charged particles. Doing so creates a product that continuously dissipates static. This is possible because the molecular composition of the silicone has electrodes. While this might seem unusual, such a property could be useful in specific situations.

Why Silicone Compression Molding? 

Compression Molding Silicone Rubber Parts

Have you wondered what circumstances make this method suitable in comparison to others? On top of having a ton of benefits, there are particular factors that make these techniques appropriate. They include the following:

  • Molding retains the mechanical and chemical properties of silicone. Due to the low-impact approach used in the process, the final product has similar properties to the silicone material.
  • This method is practical for certain products. Silicone products with inserts are manufactured using techniques such as transfer molding. The approach is used because it is accurate, effective, and reliable.
  • This method is required for particular specifications. Compression leads to products with specific properties and dimensions. For instance, certain shapes can only be achieved by molding silicone.

Essentially, silicone compression molding temperature ranges between 160°C to 232°C because it’s the only alternative applicable to certain situations. Its versatility, benefits, and features make it indisputable.

Benefits of Silicone Compression Molding

When you think about it, this method of manufacturing silicone products has several advantages. This is evident in the process and features. Let us look at some of these benefits and how they apply.

  • Compression molding is cost-effective: Since cost is a major factor considered in business, you want to use means that have value for money. This method is cost-effective in terms of low production costs and high production quality.
  • Wide range of applications: Compression molding is a versatile manufacturing process that can be used to create a wide variety of products for different purposes.
  • The process is straightforward: Since this is a non-complicated process, it is attractive to many product dealers. Straightforward processes have many benefits to you and the manufacturer.
  • Suitable for large-size products. The size of products that can be made using compression molding is adjustable because molds can be made in a variety of sizes, both large and small.

These are just a few of the many advantages of silicone compression molding. What’s more, you might come across more benefits that are specific to your industry.

Disadvantages of Silicone Compression Molding

Silicone compression molding does not come without a flaw. That means it has some drawbacks that limit its potential. These disadvantages include:

  • Not suitable for complex designs. While techniques like transfer molding can achieve some degree of complexity, molding generally is limited in terms of constructing detailed configurations.
  • Long post-production. Most molded products have to undergo visual inspection and de-flashing to refine them after curing. This makes the post-production process hectic and sometimes costly.
  • Some compression techniques are slow. Regular compression molding for instance takes a longer time to cure the mold. This lengthens the production process and slows output.

Evidently, silicone compression molding is not a perfect manufacturing method. The positive thing is that it is used for specific applications where these disadvantages are expected and can be tolerated.

Applications of Silicone Compression Molding

silicone products

We have implied that compression molding is applicable in certain cases. Let us explore these use cases and what specific technique is used.

Making Automotive Parts

The automotive industry requires silicone in the fabrication of various parts. This should not come as a surprise since silicone is resistant to multiple conditions. Silicone can tolerate stressors like heat, friction, vibration, and other extreme conditions for long durations with minimal wear and tear.

Compression molding is used to make automotive parts such as LEDs and headlamps, potting components, sealants, head gaskets, and thermal transfer materials.

Medical Equipment Fabrication 

The medical field also benefits hugely from the properties of silicone. In Particular, most surgical tools are made from silicone. On top of being soft, silicone is considered one of the most biocompatible materials—the body tolerates it with ease. Other factors such as its inertness and durability make it ideal for manufacturing medical equipment.

Some of the medical equipment molded from silicone include; digit covers, menstrual cups, radiopaque materials, medial gaskets, and nursing pads.

Personal Care Products

The personal care industry is booming and part of the reason for this growth is the variety of products made from high-end materials. Silicone is leading the charge in this revolution for its properties.

There is an increase in personal care products—specifically beauty products—that are milled or molded from silicone. These products include make-up, beauty tools, hairdressing, and cosmetic accessories. 

Manufacturing of Houseware 

Given the high thermal resistance of silicone, it makes perfect sense to use it to manufacture houseware products. Also, silicone is quite inexpensive, which allows for the mass production of many household products, especially kitchenware. These houseware products include; oven mitts, bowls, spatulas, spoons, and straws.

Conclusion

Turning silicone into useful products is a deliberate process that takes a lot into consideration. This is particularly valid for large-scale manufacturing. As demonstrated in this article methods like silicone compression molding provide a simple and cost-effective approach to making various products. To this end, you now have a better understanding of what is involved in this process. 

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