Vacuum Infusion: Part Two
Step One: The Mold
Prepare Your Mold
Like any lamination process, a good quality mold is required for vacuum infusion. The mold should be rigid and have a high-gloss finish. Ideally, this mold will have flange of at least six inches to be used for the placement of sealant tape and spiral tubing. After the mold is properly cleaned, apply your ordinary, preferred mold release agent. Unique mold releases are not required for resin infusion.
Select Your Reinforcement
Choosing reinforcement is an important decision for any laminate, but there are additional considerations when choosing one for infusion. While all fabrics will potentially infuse, different materials and weave styles can severely alter resin flow rates. The following offers some general guidelines for choosing materials, though individual experiences may vary.
When working with molds of a more complex shape, dry reinforcement may not readily sit flat. Super 77 Spray Adhesive (#1404) is recommended to remedy this problem. Spray a light layer of adhesive on the mold surface and lay down the reinforcement. This should provide enough adhesion to hold the materials in place. When used moderately, Super 77 will not interfere with the resin infusion or curing process.
Select Your flow media and/or core material
A concept unique to vacuum infusion is the idea of flow media. In VIP, resin enters the laminate at a fixed point (or points) and must be directed. Resin will always travel in the path of least resistance. Unfortunately, many reinforcements can provide a great deal of resistance that can prevent resin flow. Aiding the flow of resin is the job of flow media.
Although it is possible to infuse resin into a reinforcement without the addition of flow media, it is rarely successful. The flow media is typically laid as a single layer between reinforcement layers to provide an easy flow conduit for resin. This material ultimately becomes part of the laminate.
Flow Media Products
Step Two: Resin and Vacuum Lines
Before the vacuum bag is closed, careful consideration must be taken in order to set up resin and vacuum lines
Select and Install Your Resin Feed Lines
Resin will be fed from a standing source (usually a bucket.) The line for getting the resin into the laminate will have to be installed before closing the bag. Although the same tubing that is used for applying vacuum is fine for getting the resin to the bag, after the resin is being directed through the laminate there are some materials unique to VIP which can help direct the resin flow.
Resin Flow Products
EnkaFusion Filter Jacket (#1400) is used in nearly all VIP projects. This material will be used on top of the laminate and removed from the laminate when pulling the part from the mold. It will also provide the removable material which can be used for anchoring your T-fittings which will connect your resin and vacuum lines.
EnkaFusion Filter Jacket is a 4" wide resin flow channel which is typically laid out over the length of the laminate. It is similar to the nylon matting except that it's narrower and is contained within a fabric "sock." The design of this "sock" holds resin until the entire length is filled. At that point, resin begins to flow outward through the sock and into the laminate, providing consistent flow rates across a long span. This style of EnkaFusion is particularly useful for resin feed lines. When used as a surface media, be sure to place peel ply beneath the Filter Jacket. Otherwise, it will permanently attach itself to the laminate.
Spiral tubing (#1403) sometimes called spiral wrap, is a plastic ribbon that is coiled into a tube shape. Due to its construction, air or resin can enter or leave the walls of the tube throughout its entire length. This property makes spiral tubing ideal for in-bag vacuum lines or resin feed lines. When used as a feed line, resin will quickly travel through the tube, but simultaneously seep out along the way. This allows quick wet-out of a long stretch within the laminate. Be sure to wrap spiral tubing in peel ply for easy removal.
This diagram shows the addition of EnkaFusion Filter Jacket, which will be used as a resin feed line.
In addition to the feed line, a smaller piece of EnkaFusion Filter Jacket is placed on top as an anchor for the T-Fitting, which will be the connector for the resin feed line. It is necessary to lock the T-Fitting into place to prevent shifting and ensure a steady flow rate. Cut a slit into the top layer for the fitting to poke through. Figure 1 illustrates the three pieces involved, while figure 2 shows the finished sandwich.
Select and Install Your Vacuum Lines
In traditional vacuum bagging, a Breather/Bleeder material is typically used to both absorb excess resin and drive vacuum throughout the laminate. Breather/bleeder is typically not used in resin infusion.
Instead, in VIP, the vacuum lines are extended with the sealed bag. Spiral tubing is ideal for this purpose, in order to achieve complete infusion, resin must be pulled to all corners of the laminate. Because the standard set-up infuses into the center of the laminate, spiral tubing would usually be placed around the flange. Once again, spiral tubing should always be wrapped in peel ply.
When using spiral tubing, it may have a tendency to straight out or not stay where you want it. The simplest way to counteract this is to use small pieces of sealant tape. Just ball it up, stick it to the tubing, and then stick it to the mold.
Step Three: Vacuum Bag and Attach Your Resin Line
Build Your Vacuum Bag
Once the dry materials are in place, it is time to build the vacuum bag. The bag should be tight, but still allow plenty of room for all the materials, including networks of tubing. Too much or too little bag can result in resin pooling or improper infusion.
One the bag itself is built, attach tubing for the resin and vacuum lines. Be very careful when making cuts through the bag for these tubes. It is frequently these connections that spring leaks.
Before the pump is switched on, it is important to clamp off the resin line. Because the vacuum is drawn before the introduction of resin, the resin tube will act as a temporary "leak" that must be sealed off. Simply clamp off this line by creasing the tube and attaching a #1605A Flow Regulator to hold it in place.
Allow for Prohibiting Resin From Entering the Vacuum
One key piece of equipment that is important to understand is the #1500 Resin Trap. A Resin Trap is a airtight container placed within the vacuum tubing circuit, between the laminate and the pump, to catch any excess resin before it can enter and destroy the vacuum pump. When set up properly, the vacuum tubing will flow out of the laminate and connect directly to the resin trap. A separate tube will then leave the resin trap and connect to the vacuum pump.
During VIP, vacuum pressure is being used to draw resin into the laminate. In many cases, resin will flow completely through portions of the laminate while still filling dry spots in another. This is normal and is no cause for alarm, except that the resin will frequently enter the vacuum line while continuing to infuse resin.
With the Resin trap, all excess resin will be collected into the trap, while air is still allowed to flow back to the pump. If the part is large and significant resin flow into the vacuum line is expected, any number of resin traps may be placed in sequence. As soon as one is filled, the resin will overflow into the next one.
Step Four: Vacuum Pump
Attach the Pump
Once all the components are in place, it is time to attach the vacuum pump itself. Because resin is infused through vacuum pressure, it is quite beneficial to have a stronger pump. In general, a stronger pump will help expedite infusion.
Ensure Proper Vacuum
Once attached, switch the vacuum on. As in any vacuum bagging application, leaks pose the biggest problem. Even the smallest leak can greatly hinder performance or even completely ruin a part. Because VIP offers unlimted time to seek out these leaks, considerable effort should be made to find them all.
Even so, there are frequently small leaks that are seemingly impossible to discover. There are some tools that can greatly aid this process. A #1503-A Ultrasonic Leak detector, a small handheld tool designed to detect ultrasonic frequencies, can help detect any leaks in your vacuum.
For those on a tighter budget, a simple stethoscope can be used to detect leaks. Though it won't provide the precision of a ultrasonic detector, a #1504-A Stethoscope will amplify leaks and provide a helpful aid at minimal cost.