8/10/2019 Reducing the Cost of Autoclave Composite Repairs-HEATCON_RW_White_Paper

1/2

Reducing the Cost of Autoclave

Composite Repairs

Traditional repair technologies must

provide, often in a remote setting, cure

conditions similar to those achieved in a

manufacturing environment using an

autoclave. These conditions must also be in

accordance with the OEMs source

documents such as the structural repair

manual. The predetermined schedule of the

heat and pressure application provided in

an autoclave is critical to ensuring that

resins and composite materials are able to

meet the manufacturers required process

specifications. For example, a lack of heat

can result in under-cured resins.

Additionally, a lack of pressure may result in

not fully compacted resins and materials,

therefore compromising the properties

required for full strength.

Traditional non-autoclave vacuum bagging

methods are constrained by both theallowable vacuum level as defined in source

documents, and by the amount of pressure

that can be produced in normal atmospheric

conditions. Some of the common methods

used to apply pressure to a repair outside of

an autoclave environment include the

application of weights or pressure clamps.

Although both of these methods can provide

additional pressure to the repair area, they

do not offer the same uniformity of pressure

an autoclave is able to provide.

Applying even heating to the materials and

adhesives used in a repair is another

important consideration. Process

specifications often have tight tolerances on

allowable cure temperatures for a given

adhesive. In a manufacturing environment,

the autoclave is uniformly heated within the

interior, much like an oven, which provides

a constant temperature around the part

being repaired. In the repair environment,

however, heat is usually provided by an

alternate source, such heat blankets, aheated air source, or heating lamps. Of the

three alternatives, heat blankets are

generally accepted as providing the best

temperature uniformity for out-of-autoclave

repairs.

Drawing upon its expertise in the

development of portable composite repair

equipment for the aerospace industry,

HEATCONhas successfully combined out-

of-autoclave repair technology andadvanced heat blanket designs. This

provides both the pressure needed for

autoclave quality cure processes, and the

thermal uniformity needed to meet repair

requirements. The key to this innovation is

in the use of heat blankets in the pressure

vessel at the repair area. This even

localized heating therefore eliminates the

need to heat the whole interior of an

autoclave. This approach has significant

economic advantages: Reduced capital

costs, compared to procuring an autoclave,

due to the simplified design of the pressure

vessel system, and lower power and gas

energy requirements.

Blade repair is a practical application of the

above practices. Blade repair pressures

enable the use of standard shop-air for

pressurizing the vessel, thus removing the

requirement for expensive nitrogengeneration equipment that is often

associated with an autoclave. The pressure

vessel is constructed of single wall steel

with a simple latching door to contain

pressure while the system is in operation.

Loading and unloading of parts in the

pressure vessels facilitated by use of a

8/10/2019 Reducing the Cost of Autoclave Composite Repairs-HEATCON_RW_White_Paper

2/2

rolling cart and internal lighting, installed in

the interior of the vessel. Safety measures

include temperature and pressure alarming

capabilities, as well as a pressure relief

valve. The size of the pressure vessel can

be customized to allow the parts beingrepaired to fit in the vessel without

interference. For rotor blades, it is possible

to repair more than one blade at a time.

Connection ports in the vessel are included

for heat blanket power, vacuum, and for

thermocouples.

Standard heat blankets are constructed

using heating wire that is spaced evenly

throughout the entire heated area. Although

this even spacing provides uniform heat, itonly applies when the repair area is also

unchanging. With rotor blades, however,

there are often heat sink areas within the

blade created by complex part geometry,

material thickness variations, and a variety

of metallic and non-metallic materials. To

overcome the limitations of standard heat

blankets with evenly spaced heating wire,

HEATCON has developed advanced heat

blanket designs with altered wire spacing

which provides heat where it is actually

needed to achieve even heat distribution,

often requiring more than one individual

circuit. The additional heating circuits allow

individual control of each area to ensure

that part temperature is maintained

throughout the cure. Using proprietary

techniques for evaluating the temperature

response of a heat blanket on a blade,

HEATCON can tailor these design

parameters ensuring optimal performanceduring the cure.

Using localized heat from heat blankets to

perform the repair and pressure from the

pressure vessel results in a cure cycle that

closely matches that of an autoclave.

HEATCONs innovative approach emulates

the processes formerly achieved only be

use of an autoclave, resulting in significant

cost reductions. Repair facilities who are

serious about reducing cost of repair should

consider utilizing HEATCONs blanket and

pressure vessel approach.

HEATCONComposite Systems600 Andover Park EastSeattle, WA 98188Phone: 206-575-1333Website: www.heatcon.com