What are the Commonly Used Vacuum Process Auxiliary Materials?

 

The vacuum infusion process appeared in 1950, but was not introduced to China until around 2000. With its environmental protection, light weight and high strength, it has attracted the attention of many composite material people in recent years.

 

Vacuum infusion process, referred to as VIP.

 

Pre-lay the reinforcing material on the mold, lay the demoulding cloth and other auxiliary materials, and then seal it with a vacuum bag. Use a vacuum pump to extract the air, form a negative pressure in the mold cavity, and use the negative pressure to press the prepared resin into the cavity to allow the resin to infiltrate the reinforcing material. After the product is cured, remove the vacuum auxiliary material and demould to obtain the product.

 

 

On this basis, there are other vacuum-related processes, such as vacuum bagging, prepreg autoclave… The common point of these processes is that they all require some vacuum auxiliary materials to a greater or lesser extent.

 

Today, Longbow Man will introduce some commonly used vacuum auxiliary materials to you, hoping that you will have a deeper understanding of vacuum technology.

 

Vacuum Bag Film

 

The vacuum bag film mainly plays a sealing role, forming a closed space between the bag film and the mold, and forming negative pressure after the air inside is extracted. On the one hand, it can provide pressure to allow the resin to infiltrate the reinforcing material, and on the other hand, it can also make the product more compact.

 

 

No leakage, this is the basic quality of vacuum bag film.

 

Material, thickness, width, shape, we need to consider these factors when making a choice.

 

Different resin systems, product shapes and process conditions will also result in different materials for vacuum bag film. Common materials include polyester, polyester/nylon, nylon 6, nylon 66, and polyimide. The main influencing factors are temperature resistance, tensile strength, elongation at break, etc.

 

The thickness is generally 50μm, 60μm, and 75μm. Thin ones have low costs, and thick ones are not easy to leak. How to choose? It mainly depends on the complexity of the product. In the absence of the risk of rupture, the thinner the vacuum bag film, the higher the cost performance.

 

The width and shape are mainly determined by the shape of the product. Since it is to be sealed, of course it can cover the entire product. The depth area must also be taken into account, and there must be a certain margin around it. Generally speaking, sheet membranes are more commonly used, but when making some small products, in order to improve efficiency and reduce the risk of air leakage, some companies will choose barrel membranes, directly put the entire product in, and seal both ends.

 

Why are there so many choices? Isn’t it to strike a balance between cost and performance, and do the best with the least money.

 

Release Cloth

Release cloth, you can tell what it does as soon as you look at the name. Just like what rank is Uncle San…

 

 

The release cloth is usually placed between the product and the other vacuum auxiliary materials. Its main purpose is to make it easy to tear other vacuum auxiliary materials off the product after the product is cured. The key point is the word “easy”.

 

If you don’t have it, you will doubt your life after the product is cured.

 

The standard for judging whether the release cloth is easy to use is whether it is easy to tear.

 

Material and width are two more important factors for release cloth. The material mainly affects the temperature resistance and the degree of tearing. Common materials are polyester, nylon 6, nylon 66, polyimide, glass fiber/PTFE coating.

 

Release cloth is generally applied to the back of the product. Some companies also have requirements for the texture on the back of the product, so they will require the texture of the release cloth. It is a special requirement and not common. The most important thing is that it is cheap and easy to tear.

 

Isolation Film

When it comes to isolation, some friends will be scared, so calm down first.

The main function of the isolation film is isolation and demoulding. Sometimes it is directly used instead of release cloth.

 

 

Although they are all films, the difference between the isolation film and the vacuum bag film is that the isolation film is divided into non-porous and perforated. Why do they have holes? To facilitate exhaust and glue removal.

When choosing an isolation film, the main considerations are material, non-porous/perforated (opening method), thickness, and width.

 

Common materials include polyolefin, ETFE, FEP, and polyimide. Different materials have different effects on data such as temperature resistance, tensile strength, and elongation at break.

 

In general, isolation films are mostly used in prepreg autoclave processes. Some vacuum induction products will also use isolation films with holes to improve the uniformity of resin flow.

 

Breathable Veil

Breathable Veil, also called glue-absorbing felt by many people. The fluffy structure provides an air guide channel for easy air extraction, and can also absorb excess resin.

 

 

Material and weight are two factors we care about when choosing breathable felt.

 

Common materials include polyester, nylon 66, and glass fiber. Different weights have an impact on compressive strength. The better the compressive strength, the better the air permeability.

 

Adhesive felt is mainly selected based on the requirements of temperature resistance, compressive strength (air permeability). Generally, breathable felt is also used in the prepreg autoclave process.

 

Breathable Veil can also be laid in some sharp places to prevent puncturing the vacuum bag film.

 

Guide Net

As the name suggests, the guide net is used to guide air and resin. Establish a channel so that the resin can flow quickly and infiltrate the reinforcing material, thereby improving production efficiency.

 

 

Common guide net materials include PP and PE. According to different molding processes, it is divided into extrusion type and woven type.

 

Gram weight mainly affects the guide speed. The larger the gram weight, the faster the guide speed.

 

Under the same gram weight, the guide speed of the extruded guide net is faster than that of the woven type. However, the extruded guide net is relatively hard and has poor conformability. It is not suitable for some products with more complex structures and is mainly used for products with large flat surfaces.

 

Guide nets are generally only used in vacuum introduction processes.

 

Sealing Tape

 

If the vacuum bag film wants to seal the mold, it also needs a capable partner, that is, sealing tape.

 

The material of the sealing tape is generally synthetic rubber, and there are corresponding products according to different temperature resistance requirements. For easy distinction, manufacturers generally make different heat-resistant sealing tapes in different colors. The most common colors are black and yellow.

 

 

The dimensions of common sealing tapes are generally 3mm thick, 12mm wide, and 7.5 meters or 15 meters long. The dimensions do not have much impact on the use, but some merchants will reduce the thickness or width to save costs. If there is no risk of leakage, it is a good way to reduce costs.

 

A good sealing tape should be moderately soft and hard, have good sealing performance, be able to withstand process temperatures, and leave no residue on the mold when removed.

 

Of course, price is another important consideration.

 

In addition, sealing tapes are also commonly used to seal the joints of resin pipes.

 

Pressure-Sensitive Tape

 

Pressure-sensitive tape is a special adhesive (pressure-sensitive adhesive) applied to a strip substrate. Fix the laid layers of vacuum auxiliary materials, such as release cloth, isolation film, breathable felt, or bond the auxiliary materials to the mold to play a temporary fixing role. Mainly used in the prepreg autoclave process.

 

 

Common substrates include PET, PTFE, PTFE/glass fiber, nylon, polyimide, etc. Adhesives include rubber, silicone, acrylic, etc.

 

Different materials are mainly aimed at different temperature resistance requirements.

 

PTFE membrane or glass fiber with PTFE coating can also be used to cover the mold surface, which can be demolded multiple times instead of semi-permanent release agent. This method can avoid the transfer of release agent and is suitable for some products that need post-painting or post-bonding.

 

One-Way Breathable Membrane

One-way breathable membrane is generally composed of nylon cloth plus a special coating.

 

 

Its characteristic is that it is breathable but not resin-permeable.

Because the resin cannot pass through, it can be used to wrap the suction port to prevent excessive suction from causing resin deficiency. This characteristic can also be used to add suction ports on the edge of larger products to increase the suction force.

 

09 Auxiliary Tools

The auxiliary tools mainly include: vacuum pump, resin collector, resin tube, winding tube, tee, injection seat, quick connector, vacuum valve, reinforced hose, vacuum gauge, leak detector…

 

 

Basically, you can understand what these materials are by looking at their names or physical objects, so I will not go into details here. If you don’t understand, you can leave a message and Longbow Man will explain it again.

 

With the continuous development of technology, materials are also constantly improving. Many new materials have been added to the vacuum auxiliary material system. No matter how they change, the ultimate goal is to assist the process so that the performance of the product can meet our expectations and meet the performance requirements of the product.

 

The selection of vacuum auxiliary materials often determines the success or failure of the product. Although it looks like a supporting role, it is actually the protagonist. Find time to write another article to teach everyone how to choose vacuum auxiliary materials.

 

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