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Wednesday, December 28, 2011

Type of FRC Moulds : Matched-Mould

    Where matching moulds are required for processes such as resin injection, foam reservoir moulding or cold press moulding, a full size pattern of the final moulding is generally required. If this is a vaila ble the two halves of the mould can be made in a similar way to making a split mould but incorporating appropriate injection and vent tubes along the join between the two halves. The dictates of the process will govern which attachments are necessary. Locating dowels must also be accurately positioned.

    With thin mouldings an alternative procedure is to make a pattern of the outside of the moulding and then make the negative mould. This negative mould, after full cure, is then used as a base on which to construct a model of the moulding using sheets of pattern maker's wax. When the required thickness of wax has been applied the positive mould is constructed on top. During construction of the wax pattern due consideration must be given to the provision of drainage channels and vent/injection points. The positive mould must be accurately made, allowing for resin shrinkage, so that the mould cavity is of the correct size. An oversize mould will only waste expensive materials each time a moulding is made.

    For cold press moulding the back of the mould should be filled with a material capable of withstanding continuous loading in a press. One such material is concrete, although a filled resin system may also be used. Here, after the final layer of glass reinforcement has been applied to the mould, a further layer of resin is applied at a rate of about 400 gjm2, into which is sprinkled a layer of broken stone chips. After the resin has been fully cured the back of the mould is filled with the concrete or resin mix which bonds around these stone chips. Both halves of the mould should be similarly treated.

    Where fibre reinforced plastic (FRP) moulds are used for cold press moulding the moulding cannot be trimmed as part of the moulding cycle. To maintain pressure on the resin and prevent it from being squeezed out leaving air bubbles in the moulding, the mould should be constructed with a pinching area. During final closure of the mould this allows air to escape but retains the resin. For mouldings up to about 5 mm in thickness, the pinching area should be sufficient to compress two layers of glass mat in a gap of 0-4-0· 5 mm. For thicker mouldings the pinching area should accommodate three or four mat thicknesses. In addition, it is useful to incorporate a drainage channel into which surplus resin can drain. An example of such a design is shown in the image.

    When not in use, moulds should be stored flat to prevent distortion and protected from dust and moisture. In use, continuous scrutiny is necessary so that any imperfections which occur can be immediately rectified.

Sharp instruments must always be kept away from mould surfaces.

Properly treated, FRP moulds can give excellent service. 

Pinch Area for Cold Press Moulding



Wednesday, December 21, 2011

Type of FRC Moulds : Split Mould

     Where deep draw mouldings or ones with undercuts are to be produced which would be difficult or impossible to remove from a one-piece mould, split moulds can be used. Here a temporary barrier should be fitted to the pattern so that the first half of the mould can be made with a flange (image below). 

      The flange area should be about 50% thicker than the mould shell to ensure adequate life. The first half of the mould is left in place, the temporary barrier removed and the second half of the mould manufactured using the suitably released flange as former. A metal plate can then be laminated onto either side of the flange to assist in supporting the bolts used to clamp the flange halves together. Once the resin has cured, holes can be drilled to take fixing bolts. These should be spaced at about 150 mm intervals.

     The mould should not be removed from the pattern until all necessary work has been carried out. Mould release can be assisted by using compressed air carefully applied between the mould and the pattern. Release can also be assisted by filling the gap between the mould and the pattern with water to soften and dissolve the polyvinyl alcohol release agent. If the mould has to be struck in any way, extreme care should be taken to ensure that this does not result in star patterns forming in the gelcoat.

     Any imperfections in the mould surface can be removed by rubbing with fine abrasive such as grade 600 wet emery paper followed by a fine cutting paste or by using a metal polish. Before use, the mould surface must be thoroughly polished to a high gloss finish using a silicone-free wax polish applied in several thin coats.

Method of  Constructing a Split Mould
PVA Release Agent

Wednesday, December 14, 2011

Type of FRC Moulds : Opened Mould

In this type of mould, only one mould surface is used in open mould process. This single mould represents either the positive (male plug) or negative (female cavity) surface as shown in image below.

Types of open mould: (a) Positive and (b) Negative 
In order to produce large fibre reinforced plastic and composite components and structures, (for instance swimming pools, boat hulls, etc.) very large moulds are usually used. The main matrix materials used are thermosetting resins of epoxy and polyester, while E-glass fibres are the most widely used reinforcement material. Depending on the desired thickness, matrix resins and reinforcement fibres are applied to the mould surface layer by layer. The fibre reinforcement can be used in the form of mats, woven roving or yarns. The use of prepregs may simplify the laying process. After the lay-up process, curing treatment will be necessary for rigid thermoset matrices. Depending on the type of resin used, little or no pressure will be necessary during curing.

Open mould processes have several advantages over closed mould composite manufacturing processes. Since a single mould is used in open mould processes, mould costs will be much less than using two moulds in the closed mould processes.

Another advantage is that very large and complex structures of fibre reinforced plastic and composite, may be produced in open mould processes, which is difficult in closed mould processes. Depending on the component to be produced, a variety of materials (e.g., metals, plaster, woods, fibre reinforced composites) are available for cheaper open moulds, whereas expensive metallic moulds should be designed for closed mould processes. Therefore, it may be concluded that open mould processes have better design flexibility compared with closed mould processes. However, open mould processes have some disadvantages as well. Firstly, only one surface of the product will be finished and smooth. This is because the other surface will be not in contact with the open mould surface. Moreover, to achieve a good surface finish on at least one surface of the component, the surface of the open mould must also be very smooth.

The second disadvantage of open mould processes is that they are very labor intensive. Therefore, for the production of components with higher quality, the personnel working in the process should be adequately skilled. There have been many advances in the automation of open mould processes, which helps to solve the skilled personnel problem. Automation in open mould processes is increasing not only the quality of the product, but also the number of the parts manufactured per unit time. Another disadvantage of open mould processes is the much longer curing periods required compared with other methods. Normally, application of heat will decrease curing time. However, it is difficult to heat treat components which are very large. Open mould processes are usually classified according to the methods of resin and reinforcement application to the mould, or according to the curing methods. If the matrix and reinforcement is applied by hand, then it is named hand lay-up, if it is by a spray gun, then it is called spray-up. Similarly, if the curing is accomplished in a bag, then it is called bag moulding, if it is performed in an autoclave, then it is termed autoclave moulding, etc. However, in order to use the advantages of each method, generally two or more of these methods are combined during manufacturing.


Wednesday, September 7, 2011

Light Weight Carbon Fibre Cases

These feather-light cases manufactured by ECS using compression moulding method. The material being used is carbon fibre and DuPont Kevlar reinforcement materials with enhanced thermoset resin.

These rack mount cases are ultra-lightweight and show exceptional structural rigidity. They can be moulded in a variety of wall thickness to meet unique performance and weight requirement for military application. Additional layers of carbon fibre and/or optional ballistic reinforcement material can provide enhanced performance characteristic for challenging application.

ESC also produce other FRP cases. For more info do visit http://www.ecscase.com
Carbon Fibre Rackmount Cases


Monday, March 14, 2011

Carbon-Carbon Composite (CCC)

One of the most advanced and promising engineering material is the carbon fiber reinforced carbon-matrix composite, often termed a carbon–carbon composite; as the name implies, both reinforcement and matrix are carbon. These materials are relatively new and expensive and, therefore, are not currently being utilized extensively. Their desirable properties include high-tensile moduli and tensile strengths that are retained to temperatures in excess of 2000oC (3630F), resistance to creep, and relatively large fracture toughness values. Furthermore, carbon–carbon composites have low coefficients of thermal expansion and relatively high thermal conductivities; these characteristics, coupled with high strengths, give rise to a relatively low susceptibility to thermal shock. Their major drawback is a propensity to high-temperature oxidation.


Application of Carbon Carbon Composites

The development of Carbon Carbon materials began in 1958 and was nurtured under the US Air Force space plane program, Dyna-Soar and NASA's Apollo projects. It was not until the Space Shuttle Program that CC material systems were intensively researched. The criteria that led to the selection of CC composites as a thermal protection system were based on the following requirements:

1. Maintenance of reproducible strength levels at 1650°C (3002°F);
2. Sufficient stiffness to resist flight loads and large thermal gradients;
3. Low coefficient of thermal expansion to minimize induced thermal stresses;
4. Oxidation resistance sufficient to limit strength reduction;
5. Tolerance to impact damage;
6. Manufacturing processes within the state of the art

An example of CC composite applications is a one-piece, bladed turbine rotor that, in service, is coated to prevent oxidation. The rotor offers higher temperature performance without cooling; low weight and use of low-cost, non-strategic materials. Other gas turbine engine applications using CC composites include exhaust nozzle flaps and seals, augmenters, combustors and acoustic panels. CC material systems using coatings, TEOS and additions to the basic CC recipe have improved the oxidation resistance of products made of CC composites by an order of magnitude.

These composites are being used in products such as the nozzle in the F-100 jet engine afterburner, turbine wheels operating at >40 000 rpm, non-wetting crucibles for molten metals, nose caps and leading edges for missiles and for the Space Shuttle, wind-tunnel models and racing car and commercial disk brakes.

Carbon Carbon Composite Plate from SINOTEK MATERIALS

Sunday, March 6, 2011

Gelcoat and Gelcoating - Method, Procedure and Tips

Gel coating is usually polyester resin that formulated to give a protective layer of waterproof color coat. Its main function is to protect the subsequent layer from defects. Some gelcoating resin is colored while it also available in original clear form, and pigment can be added according to users need.

Gelcoating method and procedures

The composite work is started with the preparation of the mould . The mould shall first be cleaned, followed by polishing that normally end up with shiny surface. The suitable wax is then applied to the mold surface that will help to release the finished component when cured. The wax usually applied between two to three times before the application of gel coat. When the release agent is completely dry, the gelcoat is applied by brush or spray. When choosing brush, a wide brush with long soft hairs is preferred. Two coats are generally necessary to prevent brush marks from showing. The second coat being applied once the first has sufficiently cured .

Gel coat is applied to about 0.3-0.5mm (Thickness vary manufacturer to manufacturer and from user to user) one to two layers. The operator must ensure the coat in total contact with the contour before starting the lay-up. Gel time of the gelcoat in bulk should preferably be about 15 minutes.

The condition of the gelcoat can be determined by touching it, once it feel tacky and not easily removed by finger, the next coat resin system is ready. In some cases, surfacing tissue may be used to reinforce the gelcoat.

After the tackiness has been achieved, the first layer of reinforcement (fibre) and impregnation of resin can be start.

Tips on Gelcoating :

1. To avoid uneven colour of the finish product, pigment can also be added to the resin – same pigment colour that being used in the gelcoat. (If you are using it)

2. Please refer to the Materal Data Sheet to determined the ratio of catalyst that will be mix with gelcoat / resin.
That shiny surface is a layer of gelcoat. The person in the image is repairing the gelcoat surface. (Image from http://continuouswave.com/ )

Thursday, February 24, 2011

Hand Lay Up / Wet Lay Up Procedure and Tips

Hand lay-up is the simplest process in the low end composite products, require low investment, higher operating skill, and versatile shapes of product that need single high quality surface finish.

Hand lay-up is the process that starts with the application of gel coating onto a completely polished and waxed mould. (gelcoating is an optional step. We will discuss about gelcoating next time)


A coat of laminating resin (resin that being mixed with catalyst / hardener, or else your part will not cure) is then being applied by brush or roller. Follow by the first layer of chopped strand mat (preferably 300 gs/m2 or less), or if desire a surface tissue.

The laminating resin is then applied to the reinforcement (the fiberglass) so that all trap air can be force out using roller.


Continue doing this for your next layer of fiberglass, until desired thickness is achieved.


Once finished, allow the resin to cure. You can feel the reaction taken place when your product is producing heat.

Finally, remove your product from the mould (demould) and next step is trimming the fiberglass product.

Hand Lay Up Tips

1. Make sure the mould is properly waxed. 5-6 layer of paste wax should be apply to the newly use mould. This is to make sure the product can be easily be demould.

2. Refer to Material Data Sheet on ration for resin-catalyst. Make sure laminating process can be finish before the resin start gelling. This is called the resin gel time.

3. Use compress air to help you demould the product.

4. Quickly wash the brush and roller with acetone if you wish to reuse it.

Brushes for resin impregnation process and metal rollers to force the air buble out.

Paint rollers can be use as alternative to brushes depending on mould size and profile

Monday, February 7, 2011

Reinforced Plastic System Composite Beam

RPS composite beams are solving corrosion problems in the Flue Gas Desulphurization Industry. The environment inside SO2 absorber towers is very corrosive and can be problematic for metals. Due to the abrasive and corrosive atmosphere and chloride concentrations, these environments often require very expensive alloy materials for a variety of components including support beams. Composites beams developed by RPS are now being installed in FGD absorber towers.

RPS is currently supplying 120 composite beams to be installed in 4 FGD absorber towers. The beams are being shipped in lots of 30 to be assembled in a 35 ft x 135 ft rectangular scrubber in two layers of 15 beams each.

The beams will support the mist eliminators and associated ME wash pipe. The beams were designed to a customer defined envelope and were modeled by structural and composite engineers using RISA structural engineering software to meet the end-users performance criteria. The beams are of 3 specific designs: 8"W x 19"D x 26'L, 8"W x 19"D x 38'L with 1" camber, and 12"W x 25"D x 36'L with 1" camber. These beams are manufactured using RPS Flow Core infusion technology with vinyl ester resins and proprietary multi 3 dimensional fabrics that produce a laminate with a modulus of elasticity of > than 6 million psi. These laminates are incorporated in the top and bottom flanges of the beam. This high stiffness fabric is complimented with interlaced 45 degree bi directional fabrics that optimize load distribution between the compression and tension side of the beams in bending.

RPS vacuum infusion technology ensures consistently high quality parts with repeatable and predictable properties.

Once the vacuum infused beam is removed from the mold the beam is de burred of any resin flashing, visually inspected, and is moved to a test fixture.
Each beam is performance tested using a 4 point bending test fixture that deflects the beams to full operational limits and from this the bending stiffness (EI) is determined and checked against specified stiffness.
 
For this application the inherent corrosion resistance of RPS Composite beams was enhanced by the addition of an exterior proprietary erosion resistant liner which is applied after visual inspection and testing are complete. Attachments for pipe supports, guides, etc., are manufactured with traditional vacuum infusion laminates and are attached to the beams by contact molded secondary bonds. The overall assembly of 15 beams for each layer is shop trial fit as a system prior to beam shipment.

RPS Composite Beams

For more information on RPS Composite Beam or other FRC product, please visit : http://www.reinforcedplasticsystems.com/

Wednesday, February 2, 2011

RTM Variant : Light RTM

LRTM process for composites is best described as a complimentary process to RTM (Resin Transfer Moulding). LRTM mould costs are basically half the price of equivalent RTM moulds but they produce, at best, at half the rate of RTM however the process provides molders an attractive introductory route into closed mould production.


In LRTM, resin flow rates cannot be speeded up above an optimum level in order to fill the mould more quickly as the recommended LRTM mould construction and the atmospheric mould clamping pressures limit overall in-mould pressures to less than 0.5 bar (8 psi).

As with any composite closed mould production technique LRTM is no exception to the rule in demanding high quality accurate composite moulds in order to provide good mould life and consistent production of good parts.

LRTM is now well established as an alternative FRP/GRP moulding technique and we encourage any traditional hand lay moulder starting up in LRTM to ensure their mould build technology, equipment and parts for LRTM are acquired from professional sources.

The advantages of closed molding for either true RTM or RTM Light, offers working environments for the molding operators that are far more comfortable and healthy. They then are willing to apply their skills of quality and productivity at a consistently higher level each day. Even though it is true that RTM Light will not yet meet the production rates that are enjoyed in traditional RTM, RTM Light will provide a 300 to 400% increase in per square foot productivity over open mold, with significant improvement of bill of material compliance and lower operator employment turnover.

Process Flow of Light Resin Transfer Moulding (LRTM)

Source : Magnum Venus Plastech (MVP), their website is http://www.plastech.co.uk/

Ps: I have attended training organized by MVP on building a RTM mould. It was very helpful and informative. Their trainer, Mr Charles is a very friendly and skillfull person. I also met him at JEC composite Asia Show in Singapore while he at MVP booth.

Monday, January 31, 2011

RTM Moulding Prosess / Procedure for FRP

For simplicity in understanding the complete Resin Tranfer Moulding (RTM) process, the basic steps for the fabrication of a composite component are describe as below.

1. A thermoset resin and catalyst are placed in tanks A and B of the dispensing equipment.

2. A release agent is applied to the mold for easy removal of the part. Sometimes, a gel coat is applied for good surface finish.

3. The preform is placed inside the mold and the mold is clamped.

4. The mold is heated to a specified temperature.

5. Mixed resin is injected through inlet ports at selected temperature and pressure. Sometimes, a vacuum is created inside the mold to assist in resin flow as well as to remove air bubbles.

6. Resin is injected until the mold is completely filled. The vacuum is turned off and the outlet port is closed. The pressure inside the mold is increased to ensure that the remaining porosity is collapsed.

7. After curing for a certain time (6 to 20 min, depending on resin chemistry), the composite / FRP part is removed from the mold.

Saturday, January 1, 2011

Honeycombs Produced By Laser Welding

A customized honeycomb can now be made out of any thermoplastic material supplied in the form of a thin sheet reinforced or not with fibres or webs. The sheet can be watertight, porous or even perforated. It is first folded into a semi hexagonal shape and then welded with an array of very homogenous laser lines onto another sheet along the adjacent nodes.


The welding speed is very high and the weld is as resistant as the constituting material itself, demonstrating the same properties. A honeycomb block is thus assembled automatically on a compact machine with impressive production rates. The length of the honeycomb block can also be chosen with the accuracy of half a cell width.

The honeycomb is mainly used as a core for sandwich panels. Which achieve a construction with unique resistance/weight ratio. A lot of application are to be found in automotive, aerospace, boating, building, energy, furnishing, construction, packaging, trains, etc.

PVC Honeycomb

PEEK Honycomb
Source : http://www.plasticell-honeycomb.com/