What is vacuum bagging?

Vacuum bagging (or vacuum bag laminating) is a clamping method that uses atmospheric pressure to hold the adhesive or resin-coated components of a lamination in place until the adhesive cures. (When discussing composites, “resin” generally refers to the resin system— mixed or cured resin and hardener—rather than unmixed epoxy resin.)

Modern room-temperature-cure adhesives have helped to make vacuum bag laminating techniques available to the average builder by eliminating the need for much of the sophisticated and expensive equipment required for laminating in the past. The effectiveness of vacuum bagging permits the laminating of a wide range of materials from traditional wood veneers to synthetic fibers and core materials.

SILICONE FOR VACUUM BAG

Silicones for Producing Reusable Vacuum Bags

• Our silicone rubber is a brushable platinum cure silicone developed especially for making high performance, reusable vacuum bag. It is easy to mix and apply. Rubber can be applied with a brush or spatula to vertical surfaces without sagging.
• CHEMZEST offers a series of addition cure silicone elastomers for the manufacture of reusable vacuum bags for resin infusion. These silicones formulated as a sprayable material allowing for exceptionally low cost composite manufacture using resin infusion technology.
• Our silicone solutions enable composite manufacturers to decrease production times, achieve consistent part production and reduce material waste. In addition, the closed mold process enables a much safer working environment since VOC emissions are reduced.

How it works?

• Vacuum bagging uses atmospheric pressure as a clamp to hold laminate plies together. The laminate is sealed within an airtight envelope.
• The envelope may be an airtight mold on one side and an airtight bag on the other. When the bag is sealed to the mold, pressure on the outside and inside of this envelope is equal to atmospheric pressure: approximately 29 inches of mercury (Hg), or 14.7 psi.
• As a vacuum pump evacuates air from the inside of the envelope, air pressure inside of the envelope is reduced while air pressure outside of the envelope remains at 14.7 psi. Atmospheric pressure forces the sides of the envelope and everything within the envelope together, putting equal and even pressure over the surface of the envelope.
• The pressure differential between the inside and outside of the envelope determines the amount of clamping force on the laminate. Theoretically, the maximum possible pressure that can be exerted on the laminate, if it were possible to achieve a perfect vacuum and remove all of the air from the envelope, is one atmosphere, or 14.7 psi.

Vacuum bagging equipment

The vacuum bagging system consists of the airtight clamping envelope and a method for removing air from the envelope until the epoxy adhesive cures. This section discusses the components of this system , which include both specialized equipment and commonly available materials.

MAJOR APPLICATIONS

Manufacturers in aerospace and aviation have used silicones since their inception, however not everyone is familiar with all of their capabilities. Silicones seal joints, coat and encapsulate electronics and insulate and shield sensitive equipment from extreme temperatures and weather exposure. The versatility of silicone and its high temperature resistance have made it a reliable choice for decades and today it is still one of the most effective materials used in aerospace and manufacturing.

Silicone supports engines that experience high temperatures during liftoff, as well as on the exterior of a space capsule that experiences low and high temperatures and needs shock absorption when re-entering Earths atmosphere. Silicones effectiveness and versatility make them suitable for atleast 20 different areas of a launch vehicle.

RTV Silicone Rubber:

RTV Silicone rubber is short form of room temperature vulcanization silicone rubber. Once part A and part B mixed together at normal room temperature, it will create High flexible to medium flexible rubbers. RTV silicone is available in a variety of viscosities-ranging from low viscosity options that can be incorporated with additives to boost the thermal protection properties, to high viscosity formulations that can be applied to overhead surfaces.

Aviation applications

• Silicones are very effective for aircraft original equipment manufacturing(OEM) and for maintenance, repair and overhaul(MRO).
• Aircraft components are frequently replaced due to wear experienced through time. Silicone offers convenience and efficiency benefits in MRO because it comes in individual use tubes for easy delivery and in dual cartridges that deliver the materials precisely and simultaneously to save time and avoid product waste.
• Many epoxy and polyurethane adhesives can become rigid when cured and may not be able to absorb Coefficient of Thermal Expansion(CTE) mismatches between different substrates. Silicones have a low modulus that maintains flexibility even in extreme high and low temperatures, allowing silicone adhesives to more effectively cope with CTE mismatch effects.

Aircraft applications

• Black box encapsulant
• Avionic display unit adhesion
• Protective coating for critical circuits, terminals
• Radome sealant
• Sealant, encapsulant: computers, LED modules, sensors
• Engine component, thrust reverser thermal protection
• Fuel tank coating, sealant

• Epoxies and polyurethanes generally offer poor electrical properties at low or high temperatures and in damp conditions. They can also be harder to work with due to toxicity and an affinity for water absorption, and they are difficult to remove or repair when equipment needs to be serviced.
• The strongest attribute of an RTV silicone is its ability to maintain critical properties throughout a wide temperature range. That temperature range makes RTV silicones suitable to bond lenses onto telescopes and secure optics onto satellites and other structures. Since this equipment remains in orbit for a long time, it is subjected to large temperatures fluctuations due to repeated, intermittent exposure to the sun, and silicones can withstand those extreme conditions.
• A silicone coating is applied to electronic components to protect against extreme environmental conditions. RTV silicone are rubber and gel silicones that cure without heat and are used for bonding, sealing, encapsulation, coating and potting applications.

Other benefits of room temperature vulcanized(RTV) silicones

• Heat resistance, flexibility-In thermal protection systems, RTV silicones can maintain their properties in extreme heat, such as securing thermal sheilds on the exterior of aircraft and space vehicles. They can maintain adhesion during the extreme heat of re-entry and remain elastomeric in low-temperature environments. They also protect launch pads and structures during launches and landings.
• Spark, fire protection-RTV silicones resist long term smoke and fire penetration. They can be self-extinguishing, and the fumes from ignition are non-hazardous to humans. Silicones also insulates fuel lines to help keep fuel flowing in the event of an engine fire.

Electronics applications

• Advanced aviation electronics have a very high power density that generates more heat than those typically used in the past. When circuit boards that support the operation of planes and radar systems generate heat, onboard electronics are also constantly exposed to fluctuating temperature throughout their lifespan. To last longer, electronics coatings and adhesives must outlast the effects of repeated temperature changes.
• Room temperature vulcanizing(RTV) silicones are a prominent ingredient in aerospace manufacturing due primarily to their ability to withstand extreme temperatures while maintaining their physical properties. When protecting these delicate electronics and circuit board assemblies or sealing power modules and sensors, manufacturers should use compounds that provide stable dielectric, thermal and mechanical properties such as silicones. Thermally conductive silicones can also passively remove heat. There are many methods to apply liquid silicone to sensitive components, such as with pneumatic applicator guns, syringes and metered dispensive valves. The silicone is then cured into an elastomeric rubber that excels in thermal interface applications.
• Electrostatic dissipative and electromagnetic shielding silicones can electrically ground composite structures while tolerating a low electrical charge.

Step 2: Tools and Materials
Gather the tools and materials below to polish your resin part: sand paper 120, 180, 220, 400, 600, 800, 1000, 1500, 2000 grit. sanding block water.
scratch remover compound polishing compound
Lint free, scratch free polishing cloth mothers polishing ball Buffing wheel buffing compounds wax product
While there are many different buffing compounds and waxes available, I went to a regular car parts supplier box store and purchased low cost but totally effective rubbing compound made by Turtle Wax for car scratches, a Mothers Polishing Ball with a drill attachment and some Mothers Carnuba Car Wax

Step 7: Check for Scratches

We found it easiest to check for scratches by completely wiping down the resin with a clean towel and then wetting it down with water. If you rub the water in a bit with your fingers it helps to bring any potential scratches, pot marks and inconsistencies out for inspection.
If the resin passes the scratch test, keep on sanding all the way up to 2000. By 2000 it should start to look pretty clear, but not polished. That comes in the next step.