FiberglassBlog.com » composites

Making Your Own Prepregs

Sun, 25 Mar 2012 20:06:32 +0000

Composite materials that are used as reinforcements can be impregnated with resin ahead of time, are called prepregs. You use a prepreg in manufacturing different composite parts by cutting it out and laying it onto your mold, shaping as required. Since it has already been impregnated with resin, there are not any concerns with spreading the resin and curing agents on the dry materials while they are in the mold.

Pre-impregnated materials can be purchased from a composites supplier, or they can be made yourself. Woodward Aerospace shows us how.

Carbon Fiber Pipe Wrap Carbon Fiber can be used to wrap the outside or...

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Carbon Fiber Pipe Wrap

Sun, 26 Feb 2012 03:07:54 +0000

Carbon Fiber can be used to wrap the outside or the inside of pipelines as a way to reinforce and strengthen them. Carbon Fiber is lightweight yet extremely strong. It can be field-installed on pipelines that are clean and non-pressurized.

Repairs to pipelines can be extremely expensive if they need to be dug out of the ground, cut out, and replaced with new sections. This is time-consuming work requiring long shutdowns. Composites repairs can be accomplished by professionals that can access the work area and have a line that is non-pressurized and clean.

These carbon fiber reinforcements help to restore structural integrity that has been lost through age, damage, or other new design requirements. There are many advantages to repairing existing pipelines and other structures rather than replacement.

Interior repair from ABC 10 News in California demonstrates an interior pipeline repair:

An external pipeline repair is shown here in an instructional video. I do have a few concerns about the use of all of the unreinforced resin that is used to cover the carbon fiber wrap. I am not sure what the purpose there is, other than maybe to protect the carbon fiber from future damage.

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Machining Composites

Sat, 30 Apr 2011 16:53:42 +0000

Much like other materials can be machined, so can composites. Everything from basic fiberglass fabrications to advanced composites materials can be machined to add details and features.

This can be accomplished using hand-held tools guided by fixtures and measurements. Hand tools such as air routers, drills, and saws. A disadvantage is that the operator can commit errors and must be protected from safety hazards. These hazards include airborne dust, bending strain, lifting strain, and physical cuts.

For high volume or high precision applications, there are CNC routers that can be employed. These are fast, efficient, and safe. They may be expensive though.

Several manufacturers make CNC routers, and Thermwood is one as shown below.

This video shows several different applications and parts that can be routed with this large machine.

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1992 GM Ultralite Concept Car

AKeson — Fri, 14 Jan 2011 02:14:18 +0000

I found a very interesting video demonstrating the 1992 GM Ultralite Concept Car. What a blast from the past!

This project, like all concept cars, was well before its time. They had some cutting-edge engineering that went into this vehicle to work towards several goals.

Reducing vehicle weight was important, so carbon fiber materials were utilized to decrease the weight of the body/chassis. Efficient drive-train options were also developed, including the use of two-cycle engines and battery power. Designing for great aerodynamics was also considered.

Many years have passed by, and some things were right on, some were not. Aerodynamics have been improved. Lighter weight materials have been used as composites have been working their way into vehicles, though it has been SMC/BMC reinforced with Fiberglass rather than Carbon Fiber.

Gull-wing doors have not been adopted for family cars, and I am not sure if I am disappointed or not.

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Composite Guitar Cases

AKeson — Sun, 31 Oct 2010 01:13:42 +0000

Not being a musician, I had not been familiar with instrument cases, specifically for guitars. Many of them are made of composite materials, both fiberglass and carbon fiber.
The advantages of composites align well with requirements for handling musical instruments. Composites are strong and lightweight, as well as impact resistant. Composites are also not affected by moisture.
I came across an interesting video by WallyUpdabungenstein who does a comparison of a Calton deluxe fiberglass guitar case as compared to a Hoffee carbon fiber guitar case.
He does a great job comparing the actual fit and handling of the guitar in the case. He does not discuss the construction materials of the cases, but does look at the important aspects of them. Any item that is intended for a primary purpose such as protecting musical instruments needs to do a good job at this primary purpose.

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Making a Small Mold

AKeson — Sat, 21 Aug 2010 19:42:37 +0000

There are many methods and materials that can be used for making a fiberglass composite mold.

I found a video from Eastbay Composites that demonstrates a method for making small molds in a very quick an inexpensive fashion.

As you see from watching this, the basic construction materials are tooling gelcoat and inexpensive bondo for the support structure.

This mold construction technique certainly has drawbacks, but also has several advantages. None of the materials required spray equipment, which is messy. Brushes are inexpensive and easily disposed. A disadvantage of this method is that surface finish might suffer from a lack of consistency on the coating thicknesses for the gelcoat and the release agents.

Using bondo as the support structure is quick and easy compared to glass and resin, but can cause problems as well. It is more likely to crack, and can warpage issues as it cures and may be hotter in some areas than others. Bondo may have some difficulty maintaining dimensional tolerance as it shrinks during cure. Industrial resins used to create molds have minimal shrinkage in their chemistry and are placed on slower to minimize heat from the chemical reaction.

For quick, inexpensive and easy parts, this method from Eastbay Composites may work well for you. What has not been discussed yet is that the mold model can be the most difficult part. Off the shelf items are easy, but custom ones may be difficult. Creating a shape or surface is time consuming and tenuous. After that is complete, you can make your mold and final production parts!

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Cutting Epoxy/Fiberglass with Ring Saw

AKeson — Sun, 20 Jun 2010 15:25:15 +0000

Cutting and machining of cured composites parts can be challenging. Cured composites can wear cutting blades out very quickly. They are also very dusty when cut without using some sort of cutting fluid.

Many of these problems can be eliminated with the proper equipment. I found a very interesting video of a fiberglass-reinforced epoxy resin block being cut using a water-cooled ring saw. This saw is called the Revolution XT and it uses some neat technology to get a relatively quick and clean cut without making dust. It looks like it would also allow some good freehand movement to cut curves and angles in composites parts.

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Cirrus Composite Airframes

AKeson — Tue, 23 Mar 2010 15:44:17 +0000

I found a very interesting Youtube peek inside of the Cirrus airplane assembly factory in Minnesota. While it would be cool to learn more about the actual composites fabrication of the individual parts, there is some great information about part bonding, inspection, and final assembly of the Cirrus aircraft. They use fiberglass and carbon fiber reinforcements to create a very strong and durable fuselage, and it is great to see in action.

Personal jets made of composite materials offer many advantages and unique properties. Design of complex shapes and anti corrosion of aluminum are two advantages. Disadvantages include repeatability and upgrading/modification.

Composites that are properly designed and fabricated can be used in many applications where safety is a big concern. Proper design and inspection during production can create an airplane that can be easily maintained and have a very long life.

Great factory tour courtesy of Aero-TV:

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Panel Stiffness

AKeson — Wed, 03 Feb 2010 13:40:13 +0000

Composites structures have requirements for stiffness to provide support and stability. Tests can be completed to identify the stiffness of a given area on a composites structure, i.e. how much it will bend for a given force.

The required stiffness of a section of a composites part depends upon the overall design and service expectations. Several factors, including the life expectancy of the object, the load rating of the composites surface, the inter-laminar bond strength, will help determine the threshold requirements. Testing is very important to determine the life expectancy of the part and whether it meets the requirements of its’ job.

Panel stiffness can be modified to meet these requirements using two basic methods. One way to increase the stiffness of an unsupported composites panel is to reduce the size of the panel through additional support structures. The other way is to increase the panel thickness across the same area. Choosing which method to use depends upon the engineering of the part and determining which method is acceptable with the surrounding part layout. If there is room to add supports, this is likely a quick and easy option. If there is room to increase the thickness, adding new or additional coring materials may be a simple solution.

Building a strong and stiff composites structure can be accomplished with the extremes of building a robust “skeleton” with small open areas and a thin skin, or having a basic, limited “skeleton” with a heavy duty cored laminate that supports itself.

A combination of the two usually works out best.

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Making Holes

AKeson — Tue, 12 Jan 2010 16:17:22 +0000

If you are working with fiberglass parts, you may need to attach other parts, pieces, and features mechanically with fasteners. Bolts and rivets are the most common mechanical fasteners used to accomplish this.

Composites with a nice, decorative gelcoat finish such as boats and RV’s require special care to make holes in them for placing bolts and rivets. Disturbing the area around your hole in a gelcoated surface can lead to very expensive repairs by a fiberglass expert.

You can make holes yourself, but it requires extra care and attention. I found a great Youtube video that demonstrates this from user CenturionCrew.

Of course the biggest mistake that can be made is improper placement of the hole.

Following the instructions in the video and drilling a nice slow speed hole is the best way to be successful. He also mentions the caution that must be noted to stop the drill chuck from contacting the gelcoated surface. One tip that I have is to place a small piece of rubber hose over the drill bit to contact the gelcoat before the drill chuck.

One other note with holes (all shapes and sizes) in cored composites fiberglass pieces. If there is a layer of balsa or foam core in the cross section, extra precautions should be exercised. One is to coat the inside surface of the hole with gelcoat, resin, or silicone to keep moisture and UV out of the core.

Another concern is compression of the core with mechanical fasteners. Balsa and foam cores typically are low in density, and are not meant to be highly compressed. If you are going to bolt something on, and it is going to be really tight, it is best to use a metal sleeve in the hole that is the same thickness of the fiberglass part. Large washers or backer plates should also be used to distribute the load across a larger surface.

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