11/7/13 Introduction to Vacuum Infusion

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By Todd Johnson

Introduction to Vacuum InfusionThe Advantages of Resin Infusion

Definition of Vacuum Infusion

The vacuum infusion process (VIP) is a production process used to

make parts out of fiber-reinforced polymers (FRP). Vacuum infusion

uses negative pressure to pull-out air, while impregnating the

reinforcement with resin.

How VIP Works

First, dry materials are place on either a male or female mold

surface. Often, stitched or woven fabrics used, and many of which

are specially designed to promote resin flow.

On the part perimeter of the material, a semi rigid counter mold or a thin plastic vacuum bag is sealed. Using a vacuum pump, air is evacuated and

atmospheric pressure is applied to consolidate the dry materials. Once this occurs a vacuum cavity is created. Through resin feeder lines, resin is

introduced into the cavity.

Because the higher atmospheric pressure pushes on the lower pressure inside the vacuum cavity, resin is pushed through porous materials to a point

where it is 100 percent saturated. The vacuum persists until the part cures. This ensures consolidation.

Determining Factors for Filling Time of a VIP Part:

In summary, for the best infusion process results:

When comparing cycle time of a VIP part to hand lay-up or spray-up open molding, it is usually slower. This is dependent upon how big the part is and

how quickly the resin can enter the mold. The longer the infusion time the longer the gel time. Ultimately resulting in a long cure cycle.

Benefits of Using Vacuum Infusion

Composite parts made using the Vacuum Infusion Process (VIP) are superior to traditional open molding because they are:

Additionally, quality control and assurance is much easier to facilitate using this process rather than open mold manufacturing. Inspections can be

done prior to resin being introduced into the part. If clear gel coat is used, the part can be studied for imperfections after infusion.

VIP is also earth friendly. Both Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) are greatly diminished. This is because there is

little to no resin that is being exposed to the air. All the styrene in the resin cures into the part instead of being released into the air. This results in a

safer working environment as well.

VIP is gaining popularity because of relatively low capital investment and an easily manageable learning curve.

Other Advantages of VIP Include:

Porosity/permeability of the reinforcements: Permeability of the materials is directly proportional to the flow of the resin. Proper infusion requires

flow medias unless a scored or grooved core is used. Simply put, pathways need to be created to allow the resin to flow.

Viscosity of the resin: The higher the viscosity of the resin, the lower the flow speed (inversely proportional). Therefore, a more viscous resin will

result in more part saturation. The ideal viscosity falls in the range of 100 and 300 cps. Stated another way, runny water-like resins are ideal for

infusion, while thick syrupy resins do not work well.

Applied pressure difference: The bigger the gradient between pressures, the faster the resin will flow. For best results, full vacuum must exist.

Flow and distance: Not to exceed 54 inches. Adequate flow requires a resin temperature of 72 degrees F or higher.

Use a very thin resin

Use very permeable materials

Create the highest pressure differential possible

Stronger (better consolidation)

Lighter (Higher glass ratio, less excess resin)

Cheaper to manufacture (Many debate this, but history shows a cost savings)

Ability to conform to simple and complex shapes (even atmospheric pressure is applied by the vacuum bag).

Control of part thickness (the vacuum compresses the laminate during cure).

A stronger laminate (vacuum removes air, excess resin and volatiles, and a stronger bond between layers).

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Gel Coating a Mold Prior to

Resin Infusion

Todd Johnson

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