Detailed Explanation of the Resin Vacuum Infusion Process

 

 

What is Resin Infusion?

 

First, the reinforcement, i.e., the “dry” fabric (without any resin mixed in it), is laid on the mold, then the vacuum auxiliary materials (such as mold release cloth, induction mesh, vacuum bag) are laid, and finally the vacuum is evacuated using a vacuum pump.

 

Once all the air is extracted from the vacuum bag, the composite is completely flattened under atmospheric pressure, and the liquid resin (mixed with curing agent) can be drained into the reinforcement through a hose and flowed through the entire reinforcement under vacuum.

 

When the resin is completely poured into the reinforcement, the resin supply is cut off (using a hose clamp) and the rest is the resin curing (still under vacuum). If the resin infusion process is performed correctly, it can produce FRP parts with satisfactory strength and appearance quality.

 

Compared with the traditional wet hand lay-up process, resin surplus and unstable performance are avoided. At the same time, porosity (dead corners around the reinforcement when laying) and small bubbles in the part are eliminated. The quality of resin infusion, i.e. the strength of the product, is close to that of using prepreg process.

 

Preparation – Materials and Equipment you Need

 

The key factors for successful resin infusion: the need to prepare the correct vacuum equipment, auxiliary materials, etc. in advance. Although this is not part of the process, in most cases, infusion failures or problems are caused by using incorrect materials or equipment.

 

Mold

The edge of the mold should have a large enough flange to fix the vacuum auxiliary material. The surface quality of the mold determines the surface quality of your product. If you use a composite mold, the surface material of the mold is preferably epoxy mold gel coat or vinyl mold gel coat; of course, other molds such as glass, metal steel or aluminum can also be used.

 

Equipment

 

• Vacuum Pump: It can reach a vacuum degree of more than 99.99%.

 

• Silicone Nozzle: Placed in the vacuum bag to connect the resin feed line and the vacuum line.

 

• Resin Collector: If you only use the infusion process once or twice, you can also use breathable felt instead of a resin collector to collect a small amount of resin; but for long-term use, it is best to invest in a professional resin collector.

Vacuum Bag Auxiliary Materials

 

Vacuum Bagging Film

• Vacuum sealing tape (i.e. sealant or putty strips)
• Infusion mesh
• Release cloth
• Breathing felt (if you don’t have a resin collector)
• Spiral tubing
• PVC vacuum tubing
• Paper or pressure sensitive tape

 

Materials

• Release agent (wax, PVA or chemical release)
• Reinforcement such as infusion felt, chopped strand mat or fiberglass cloth
• Step-by-step guide to vacuum infusion resin

 

Prepare the Mold Surface

 The mold surface should be treated with a release agent. Semi-permanent release agent is a very reliable high-gloss release agent. If used correctly, it will produce a high-quality surface. Application: Apply the chemical release agent to the mold surface with a lint-free cloth.

 

Apply the release agent and wait for a moment for it to evaporate (1 minute, depending on the temperature and the type of release agent). Use a second lint-free cloth to gently wipe off the excess release agent in circular motions. Apply 6 layers to a new, unused mold surface, leaving at least 15 minutes between each layer. Wait at least 30 minutes after the last layer before using the mold.

 

Cut and Lay Out Reinforcements

Cut the reinforcements to the appropriate size for the molding needs. If possible, use one layer of reinforcement as a template to cut the remaining layers. Make sure you cut the fabric large enough to cover all edges of the part and account for the rough edges that will need to be cut later. Lay out the reinforcements in the mold (you can also lay out multiple layers at a time). For complex molds, especially those with uneven or multiple contours, it is sometimes necessary to use a setting glue to adhere the fabric to the mold surface and to bond each layer to the other.

 

 

Adding Release Sheet

In the resin infusion kit, the release sheet is used as the first layer of process material. It can be torn off the product after the product is completed, leaving a more consistent surface, which can also serve as an ideal bonding surface. Usually, the release sheet is laid in one layer, covering the entire surface of the reinforcement. It is not necessary to overlap the release sheet at the edge of the reinforcement, but it does need to cover the entire surface, so it is usually cut slightly larger than the reinforcement.

 

Add A Flow Grid

The flow grid (also called a “flow medium”) is used to ensure that the resin can flow freely from the resin flow tube (and spiral tube) into the laminate. The shape of the flow grid means that even under full vacuum, there are still gaps for the resin to flow. The flow grid also needs to be laid in one layer (you can overlap multiple layers if necessary, and it will not make any difference).

Fix the Spiral Tube

The spiral tube is a spirally wound plastic tube used to improve the flow of resin from the feed tube to the laminate. The resin will be dispersed along the entire spiral tube, so it is standard practice to fix the spiral tube at one end edge (that is, the end where the resin feed tube is fixed), which means that the resin is quickly and evenly distributed from one side of the mold to the other. The spiral tube must be fixed directly on the flow grid. Make sure that the resin can flow more easily from the spiral tube into the flow grid.

 

 

Secure the Silicone Nipples at the Resin Feed End

The silicone nipple is a black silicone fitting. It has a channel at the bottom that runs from one side to the other. The spiral tube can be passed through this channel to ensure that the resin can flow from the resin feed tube through the nipple and into the spiral tube. Secure the resin feed nipple in the middle of the spiral tube. Press the nipple onto the spiral tube so that the spiral tube can run under the nipple.

 

Secure the Silicone Nipples at the Vacuum End

This is also a silicone nipple. Secure the silicone nipple to the guide mesh (sometimes, to reduce the risk of excessive resin absorption, the silicone nipple is secured to the mold release cloth) at the end opposite the resin feed spiral tube.

 

Sealing Tape

Sealing tape is like a very sticky rubber tape. This tape is widely used in all vacuum bagging processes. Its soft nature can effectively provide a seal.

 

 

Lay and Stick the Vacuum Bag

Now it’s time to bag everything. Good quality vacuum bagging film is not only strong (not easily punctured) but also stretches properly. In the grand scheme of things, it’s more wasteful than a poor quality vacuum bag that causes accidental damage to the product. When using vacuum bags, it’s important to ensure that the mold’s contours and outlines are adequately bagged.

 

Improper bagging to the point where there is any “bridging” in the mold corners will result in excess resin in the final product, reducing strength and quality. Cut a piece of vacuum bagging film that is 50% larger than the mold area. Starting in the corner, peel off the paper backing of the sealing tape and press the vacuum bagging film onto the exposed sealing tape.

 

Move along the edge of the mold, peel off the paper backing of the tape and stick the vacuum bagging film, peeling and sticking as you go. As you stick the film onto the tape, be careful not to have any wrinkles or creases in the vacuum bag. Press down firmly with your fingers, kneading as you go, to stick the vacuum bagging film and sealing tape together and create a seal.

 

If you have sealed the vacuum bag but there are leaks (we will do a leak test later), it may be caused by wrinkles or folds in the vacuum bag.

 

Connect and Seal the Vacuum Tube (also called the duct) at the Resin Feed End

 

After the vacuum bag is glued on, you can make a hole in the vacuum bag to connect the resin duct. Use a pair of scissors or a knife to cut a hole in the vacuum bag just above the silicone connector for the resin feed. Cut a section of PVC vacuum tubing from where the feed tank is placed to the feed connector on the vacuum bag.

 

When you cut the PVC hose, make a bevel (about 45 degrees) so that the hose does not accidentally seal at the bottom. Press the beveled end of the hose through the small hole in the vacuum bag and into the hole in the feed connector. Make sure the hose is firmly connected to the feed connector. Seal the hose to the vacuum bag by wrapping a circle of sealing tape around the hose. Press firmly to ensure that the sealing tape creates a seal.

 

Connect and Seal the Vacuum Hose at the Vacuum End

 

Repeat the previous step, this time using another PVC hose to connect the resin collector and the vacuum nozzle. Cut the hose at an angle, cut a small hole in the vacuum bag, push the hose into the vacuum nozzle in the vacuum bag, and then seal it with sealing tape.

 

Resin Feed Tank

The resin feed tank should be firmly positioned near the mold. It is critical that the resin feed tank does not fall during infusion. The infusion tube can be connected to the bottom of the feed tank from beginning to end, and a paper clip or something else can be used to keep the hose fixed if necessary.

 

 

Connect the Vacuum Pump and Resin Collector

The other end of the vacuum tube is connected to the resin collector. Next, cut a section of PVC hose and connect the vacuum pump to the resin collector.

 

Clamp the Guide Tube at the Resin Feed End

Place a tube clamp on the feed conduit at one end of the resin feed tank to ensure a sealed environment.