Vacuum Infusion: Part Three
Step 5 Prepare for Infusion
Select Your Resin
Resin choice is another key aspect of VIP. There is a common misconception that a special "infusion resin" is required. This is simply not the case. Any resin can actually be used for infusion, though there are some general guidelines that should be considered when making a decision. One important piece of information that should be examined is the resin viscosity. Typically, lower viscosity will aid infusion, as it allows easier permeation of the reinforcement. This is not to say that higher viscosity resins will not work, but they may require more careful planning, more resin lines, and more flow media.
Resin Bucket Set-Up
Because no brushes or rollers are used in the transfer of resin, some steps must be completed to ensure that the resin line stays in the bucket, as any air entering the line could be fatal to a project. These tools include the bucket itself, a resin line holder, zip-strips, and a spring clamp. The resin line holder is basically a length of rigid material that is attached to the resin tubing via the zip-strips. Once attached, this ensures that the resin tubing stays fixed in a straight line. This eliminates the tube's natural tendency to twist and curl. It is also helpful to cut the end of the tubing at an angle. Otherwise, the tube could potentially vacuum seal itself to the base of the bucket, preventing the flow of resin. Once attached to the holder, the line is clamped in place to the bucket. The resulting assembly should ensure that the resin line will stay exactly where it should be.
Step 6 Resin Infusion
Catalyze Resin and Allow it to Infuse
Once everything is in place and ready to go, mix up the resin. Double check that the resin bucket assembly is firmly in place so the tube will not leave the bucket. Once this is satisfactory, remove the flow regulator to unclamp the resin inlet. Resin should quickly be sucked through the tube and into the laminate.
Once resin reaches the laminate, the resin feed line will quickly fill up. Once full, the resin will begin to expand outward into the reinforcement. The rate of infusion depends upon many variables, but the resin should be visibly moving. Allow this to continue until the entire laminate is saturated.
Clamp Off Resin Line
Once the laminate is completely wet out, there is no need for further resin to enter. If the bucket were to be sucked dry, then destructive air bubbles would enter. To prevent this, the resin line should be clamped off once it's no longer needed. This is accomplished the same way it was before resin was introduced; crease the tube and attach a Flow Regulator. While performing this task, it is crucial that it be done carefully and without significant force that could potentially spring a new leak.
Once the resin line is clamped off, the infusion is complete. However, it is still not time to turn off the vacuum pump. Keep the pump running to maintain constant vacuum pressure until the resin has sufficiently gelled. Otherwise, air could be introduced prematurely.
Step Seven: Experiment and Test for Improvement
Helpful Supplies for Vacuum Infusion
Like any lamination method, there are certain supplies for VIP that are not required but offer significant advantages. These items can save time and help gather useful data for further experimentation.
A useful piece of information during infusion is the resin temperature. The temperature tells you when the resin is beginning to cure, when the laminate has achieved peak exotherm, and when the laminate has returned to room temperature.
To determine the temperature, #1502-A Thermal Gun can be used. This simple device can be pointed at an area and will instantly give a temperature reading. It is often useful to regularly check a number of areas including the resin bucket, the resin inlet, and the outer portions of the resin flow in order to keep tabs on its progress.
Stop Watch and Marker
While infusing, and especially when practicing with VIP, it is a good idea to monitor resin flow rates and resin flow paths over time. This can easily be done with a simple stop watch and a marker. Start the timer when resin is first introduced into the laminate. At regular intervals, mark the bag with the resin's current position. This piece of information can be especially helpful upon further infusion attempts, determining if small changes in set-up have any noticeable effect.
Typical Variations and Set-up
With an understanding of basic theory and supplies, it is time to discuss variations of materials within the mold. Keep in mind there is no one correct way to do this; however, the general idea is the same regardless of arrangement choices.
When choosing material arrangements, it is helpful to understand why resin travels the way it does. When a vacuum is pulled, all air is removed from the laminate, creating open spaces of complete vacuum. This causes pressure to be placed on the laminate. Naturally, this pressure will want to be relieved by refilling the open spaces. In VIP, resin will provide this relief. There is a common misconception that the vacuum pump is actually sucking resin into the part. In actuality, it is the vacuum pressure that is doing the work. Once a vacuum is achieved, the pump itself can theoretically be clamped off and removed from the equation (though this is not recommended). Infusion will still occur.
In order to create an even resin front that will wet-out the entire laminate, keep these two resin flow characteristics in mind.
Resin wants to fill open spaces created by the vacuum.
Resin wants to take the path of least resistance
Utilizing these two concepts, it is possible to manipulate resin across an entire laminate with as little as one resin inlet and one vacuum outlet. The trick is placing in-bag extensions of these lines in order to create a uniform resin front. The following figures show how this is done.
In figure 1, resin and vacuum lines are placed without the addition of any in-bag extensions. As a result, resin will basically travel from one point to the other. However, the majority of the laminate will remain untouched, and therefore ruined.
In figure 2, resin and vacuum lines are extended. Vacuum line extensions can be made with spiral tubing, while resin feed line extensions can use either spiral tubing or EnkaFusion Filter Jacket. In this example, resin will move very quickly through the gray areas. When resin is first infused, the feed line extension will fill very quickly. Once this line is full, resin will attempt to reach the nearest possible vacuum line. Because the vacuum line has been extended as well, the nearest vacuum point will be directly across the laminate. As noted by the resin path arrows, the entire lay-up will be infused.
Regardless of any particular arrangement of materials, there are a few items that are important to note.
Be sure to include a Resin trap in the vacuum line between the mold and the vacuum pump if there is any possibility that resin can enter the vacuum line while still infusing
Any material that will be later removed (such as surface flow media or spiral tubing) should be placed on peel ply. Otherwise, it will be infused into the part.
A Common Variation
In the following example, spiral tubing is used for both the resin feed and the vacuum line. Resin will enter on one side and fill the length of the tubing very quickly. At that point, resin will begin to flow across the laminate. While this approach is simpler to set up, the resin will need to travel across a longer distance. Depending on what materials and equipment are used, this distance becomes a significant factor. However, on the up-side, the inside surface texture of the finished part will be consistent.
Now that the theory of infusion is understood, it is very easy to expand on these concepts in order to apply them to larger projects. As resin travels away from the feed line, it will encounter more resistance, ultimately slowing down. To combat this, large projects will require multiple resin and vacuum lines. In general, resin lines should not be more than 30-36" apart under ideal conditions. However, when using less permeable materials or higher viscosity resins, this number may need to be reduced. It is important to experiment with the specific material set before attempting to create a large project.
Vacuum infusion can appear to be a daunting endeavor, but it doesn't have to be. Experiment with different materials and arrangements, as small changes can create significantly different Pg. 14 of 14 outcomes. Though the first few attempts may be unsuccessful, once the basics are learned, infusion will quickly become second nature.