|
|
Process description and process selection information for Fiber Reinforced Plastics
Introduction
Fiber-reinforced plastics (FRP Composite) can be fabricated using several processes – hand layup and spray-up lamination, continuous lamination, spin casting, resin transfer molding and its variations, injection molding, etc. However, let’s now focus not on individual processes, but on 3 important categories to which these processes belong
• Open molding
• Low volume closed molding
• Compression molding
Process Descriptions
A. Open Molding – Open molding is the simplest and most widely used process to produce FRP parts. It is done in ambient shop conditions. The mold is generally fabricated from FRP. The cosmetic surface of the part is fabricated next to the mold. The back of the mold is open. While most fabrication processes involve the application of the exterior coating after the main structure of the part has been built, open mold parts are built from the exterior to the interior. The first step in open molding is to apply the gel coat (the exterior coating of the part) to the mold. The remaining layers of the laminate design, which will include some but not all of the following, back the gel coat :
1. Barrier Coat – this is applied behind the gel coat. A barrier coat improves part cosmetics, reduces cracking, and improves osmotic blister resistance in marine parts.
2. Skin Laminate – a relatively thin glass fiber reinforced laminate fabricated behind the gel coat. Skin laminates improve cosmetics and osmotic blister resistance.
3. Print Blocker – a sprayable syntactic foam material used behind a skin coat to improve laminate cosmetics.
4. Coring Materials – lightweight materials used to build part thickness and stiffness without adding weight.
5. Bulk Laminate – the main portion of the laminate that provides most of the structural properties.
Glass fiber reinforcement used in skin and bulk laminates can be applied by hand layup or spray-up techniques. Emissions from open mold processes are significant and are regulated by Federal NESHAP standards and, in some cases, State and Local regulations.
B. Low volume closed Molding –
The category of low-volume closed molding processes includes processes in which liquid resin is transferred into a closed cavity mold containing reinforcing materials. Over time, many variations of low-volume closed molding processes have evolved such as
• Vacuum infusion
• Seamann Composites Resin Infusion Manufacturing Process (SCRIMP®)
• Conventional RTM
• Light RTM (shell laminate RTM)
• Silicone bag RTM
• Closed Cavity Bag Molding (CCBM®)
• Multiple Insert Tooling (MIT®) RTM
• Zero Injection Pressure (ZIP®) RTM.
Parts fabricated using these processes may or may not have a gel coat on the exterior surface. The part size for these processes is limited by mold and part handling considerations. Part-to-part consistency is better than with open molding due to less dependence on operator skill. Also, two-sided cosmetic parts can be produced. Emissions from these processes are still regulated; however, they are much lower than with open molding due to the closed portion of the process. Emissions from the gel coat application, if used, are the same as for open molding.
C. Compression molding
Compression molding is another closed molding process. It uses clamping force during mold closure to flow a pre-manufactured compound through a mold cavity. A hydraulic press generally provides the clamping force. Compression molds are generally made from chrome-plated tool steel. Sheet molding compound, bulk molding compound, and wet molding compound are examples of pre-manufactured compounds.
If an external coating is needed on a compression molded part, it is generally post-applied; however, in-mold coatings are available. Part size is limited by press platen size. Part-to-part consistency is excellent. Emissions from compression molding are still regulated; however, they are much lower than with open molding due to the closed nature of the process.
The following table gives you the gist of the differences between the processes we just discussed
PROCESS COMPARISON | |||
Part Characteristic | Open Molding | Low Volume Closed Molding | Compression Molding |
Maximum Part Size | Any Size | Any Size | Up to 100 Square Feet |
Factors Limiting Part Size | Mold and Part Handling | Mold and Part Handling | Press Size |
Part Surface | One Side | Two-Sided, Smooth or Textured | Two-Sided, Smooth or Textured |
Part to Part Consistency | Fair | Good to Excellent | Excellent |
Cross Section | Completely Variable | Better if Uniform | Easily Varied |
Number of Parts Per Year | <1000 | <10,000 | >5,000 |
Parts Per 8-Hour Shift Per Mold | 1-2 | 16-90 | 100-500 |
Mold Construction | Composite | Aluminum Nickel Shell, or Composite | Chrome Plated Tool Steel |
Mold Lead Time | 2-4 Weeks | 4-8 Weeks | 16 Weeks or More |
Tons of Composite Per Tons of Emissions | 371 | 135-16302 | 135-16302 |
1. Numbers taken from unified emissions factors; 35 percent styrene content resin; mechanical non-atomized application; and 30 percent fiberglass.
2. Numbers are taken from EPA AP-42 emission factor; 35 percent styrene content resin; compound paste (25 to 100 percent resin); and 30 percent fiberglass.
Process Selection
When the best process to use for the fabrication of a specific part is not obvious, process selection should be accomplished through a process trade study. A process trade study involves comparing the part fabrication costs and part performance factors for a specific part fabricated by various processes. Part fabrication costs include but are not limited to equipment costs, tooling costs, material costs, and labor costs. Part performance factors are dependent on the specific part being studied but can include, weight, strength requirements, and appearance requirements. Emissions of Hazardous Air Pollutants (HAP) or other regulated materials vary by process and may also factor into process selection. An example trade study follows.
The subject part is from the deck of a run-about boat. It is a hinged hatch cover that provides access to an under-deck storage compartment or cooler. The step face features a non-skid profile on the external surface. The step face comprises glass skins over a foam-filled honeycomb core. The part measures 11 inches by 25 inches with a 1.5-inch tall perimeter flange. The design criteria include an impact of 300 pounds from a three-foot elevation.
The part is shown in Figure 1 alongside.
Processes considered in the trade study were open molding and several low-volume closed
molding processes including vacuum infusion, silicone bag RTM, light RTM, and conventional RTM. Equipment costs, tooling costs, material costs, and labor costs were calculated for each process on a per-part basis.
Costs are based on typical values in the year 2005 and are presented as relative costs with open molding at 100 parts produced as the baseline. The number of parts to be produced varied from 10 to 9,000. Parts were to be produced over a three-year time frame with an equal number of parts per year. Process trade study cost results are shown in Table 1 below. The cost per part decreases as the number of parts produced increases. However, the amount of decrease depends on the process, meaning that Figure 1 Trade Study Hatch Cover different processes are the most cost-effective at different production rates.
Table 1- Process Trade Study Cost Results
Property | Open Molding | Vacuum Infusion | Light RTM | Silicone Bag RTM | Conventional RTM |
Part Appearance | The part back side is rough | The part back side is matte | The part back side is smooth | The part back side is matte | The part back side is smooth |
Strength | Acceptable | Comparable to open molding | Comparable to open molding | Comparable to open molding | Comparable to open molding |
Cost Effective Production Run Size | <100 parts | <200 parts | 100 to 9,000 parts | 100 to 9,000 parts | >1000 parts |
Emissions | 0.126 lbs/part | 0.064 lbs/part | 0.064 lbs/part | 0.064 lbs/part | 0.064 lbs/part |
Conventional RTM is not a cost-effective option for hatch cover production at production run sizes of less than 1000 parts. For production run sizes greater than 1,000 parts this process becomes competitive with light RTM, but does not become cheaper than light RTM even at production run sizes of 9,000 parts due to the need for a gel-coated surface.
The cost comparison could be different for large production runs of a non-gel
coated part. While competitive with light RTM, silicone bag RTM is never the cost-effective process for hatch cover production. This is due to the cost of the materials needed to fabricate the silicone bags. However, silicone bag RTM can be an excellent process selection for parts with closed contours that are not easily fabricated by other processes.
Light RTM is the low-cost process for hatch cover production at production run sizes greater than 100 parts.
Vacuum infusion is competitive with open molding as the low-cost process for hatch cover production runs of less than 100 parts. At higher production rates vacuum infusion is not cost-effective due to the cost of the consumable materials (vacuum bag film, sealant tape, etc.) needed for each part. Overall process trade study results including part appearance, strength, cost, and emissions, for the hatch cover, are shown in Table 2.
The use of closed a closed molding process reduces emissions by 50 percent in comparison to open molding with low VOC materials. The emissions differences as well differences in part appearance could influence process selection for hatch cover production.
This trade study is provided as an example of the type of evaluation that can be done to make an informed decision on process selection. The conclusions reached are not valid for all part types, sizes, complexity, and specific combinations of labor, material, and capital costs
Table 2. COMPARISON OF RTM PROCESSES | |||||
Property | Open Molding | Vacuum Infusion | Light RTM | Silicone Bag RTM | Conventional RTM |
Part Appearance | Part back side is rough | Part back side is matte | Part back side is smooth | Part back side is matte | Part back side is smooth |
Strength | Acceptable | Comparable to open molding | Comparable to open molding | Comparable to open molding | Comparable to open molding |
Cost Effective Production Run Size | <100 parts | <200 parts | 100 to 9,000 parts | 100 to 9,000 parts | >1000 parts |
Emissions | 0.126 lbs/part | 0.064 lbs/part | 0.064 lbs/part | 0.064 lbs/part | 0.064 lbs/part |
Open molding is the low-cost process for hatch cover production runs of less than 100 parts. But it is not cost-effective for production runs greater than 100 parts.
More information
This information on FRP composites is an extract from a book titled ‘Composites Application Guide’.
We hope you found this informative. Please feel free to share your articles in our future newsletters.
|
|
|
|
|
|
|
|
|
|
|
|
by D. Selwyn Jebadurai and A. Suresh Babu
Glass fibre reinforced polyester composites have been utilized in many applications including automotive, transportation, structural, piping, chemical storage tanks and windmill components. Unsaturated polyesters are commonly used as matrix for GFRP composite parts as they have the advantages of low viscosity, fast cure time and low cost. Glass fibre is the most widely used reinforcement because of its features like high strength, corrosion resistance, easy availability and low cost.
In general, fibre reinforced polymers are known to have high in-plane tensile strength and stiffness properties and are much weaker in through thickness properties, such as the resistance to inter-laminar fibre-matrix cracking and delamination. The inter-laminar region is devoid of fibre reinforcement and fails via various modes, primarily delamination and matrix cracking which may develop through the service life of the structure. In recent years micro and nano-scaled particles have been considered as filler material for matrix resin to produce high performance composites with enhanced mechanical properties. Carbon Nanotubes (CNTs) have been the focus of research since their discovery by Sumio Iijima in 1991. CNTs have a combination of outstanding mechanical, electrical and thermal properties that make them suitable for numerous applications. The unique mechanical properties of CNTs as well as their low density and high aspect ratio make them ideal candidates to act as reinforcement for polymer composites. Functionalized MWCNTs lead to a more homogeneous distribution in the matrix and a reduced risk of agglomerates when compared to non-functionalized MWCNTs.
A study was conducted to analyse the influence of Carboxyl functionalized Multi-Walled Carbon Nanotubes (COOH – MWCNTs) on glass fibre reinforced polyester composites. CNTs were obtained from Quantum Materials Corporation, Bangalore. The average outer and inner diameters of nanotubes were 12 nm and 8 nm respectively.
The length of nanotubes were between 4 and 5 microns and their specific surface area were between 250 m2/g and 290 m2/g. Tensile strength of CNTs was found to be > 55 GPa. The Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images of MWCNTs are shown in Figures 1 and 2 respectively.
Figure 1 SEM image of MWCNTs
Figure 2 TEM image of MWCNTs
Glass fibre reinforced unsaturated isophthalic polyester laminates were made without MWCNTs and with varying MWCNTs content (containing 0.2 and 0.5 wt% MWCNTs) by Vacuum Resin Infusion process. The composite laminates consisted of five layers of glass fibre mats. These five layers comprised of alternate layers of chopped strand mat (450 gsm) and woven roving mat (600 gsm). The MWCNTs were dispersed in the resin by ultrasonication for 1 hour and then the resin infusion process was carried out as shown in Figure 3. Specimens were characterized to determine tensile strength, tensile modulus, flexural strength, flexural modulus and inter-laminar shear strength (ILSS). The test results are shown in figures 4-8.
Figure 3 Fabrication of Composite
Figure 4 Comparison of Tensile Strength
Strength of Laminates
Composite laminate with 0.2 wt% MWCNT exhibited better mechanical properties than composite with 0.5 wt% MWCNT. It could be due to the homogenous dispersion of CNTs in the matrix at lower concentration. These homogeneously dispersed CNTs in the matrix act as interfaces for stress transfer and hence serve as additional nano-reinforcement to the matrix. Laminate with 0.2 wt% exhibited 58% increase in tensile strength and 235% increase in tensile modulus. There was a 23% increase in flexural strength and 13% increase in flexural modulus of the laminates with 0.2 wt% MWCNTs compared to laminates without MWCNTs. The inter-laminar shear strength was found to increase by 12% with 0.2 wt% MWCNTs. This study also shows that higher concentration of CNTs (0.5 wt%) leads to drop in mechanical properties which could be due to agglomeration of CNTs.
Further improvements in laminate properties can be achieved by optimizing the carbon nanotube content in the matrix. Thus there is huge potential to use carbon nanotubes in conventional fibre reinforced polymer composites for many structural applications. The safety aspects of handling virgin CNTs need to be understood clearly, although it is safe once they are incorporated in the matrix.
Figure 5 Comparison of Tensile Modulus
of Laminates
Figure 6 Comparison of Flexural Strength
of Laminates
Figure 7 Comparison of Flexural Modulus
of Laminates
Figure 8 Comparison of Flexural Modulus
of Laminates
We at Link Composites were enthused by your response to our first newsletter. We are encouraged by your support, and look forward to being in regular touch with you from now on. If you would like us to cover a particular topic or vendor, please write in. We value your suggestions, and look forward to a better interaction with you through these newsletters.
|
|
|
The global Leader in flexible core solution
will now distribute it’s range of non-woven fabric through
Link composites pvt. Ltd.
Lantor Composites offers a comprehensive range of innovative nonwoven solutions for the composites (fibre reinforced plastics) industry. Since our introduction of nonwoven core materials as a time and cost saving solution for the composites industry Lantor has built a solid reputation in the industry. In close cooperation with the world’s leading end-users and institutes, the company has developed successive generations of Lantor mat products for specific applications in the marine, transportation, construction, leisure, sanitary, aerospace and wind industry. Let’s have a look at the products for some of these industries
MARINE
Lantor core materials can be applied to all composite parts, including decks, hulls, hatch covers, steering consoles, shower cabinets and chairs. Lantor Coremat® is used as a core material in decks and hulls or as a print barrier in hull sides. Lantor Soric® is used in closed mould processes as a flexible core, interlaminar infusion medium and print barrier.
Typical key benefits from using Coremat or Soric :
• Saves labor
• Saves weight
• Excellent print blocker
• Saves resin and glass
• Soric as an interlaminar infusion medium
Lantor Finishmat® D7760 is used in closed mould processes to prevent print through effect and provide the laminate with a class-A finish. For additional information on print through blocking and osmosis prevention with Lantor Soric TF and Lantor Finishmat D7760, please contact us.
CONSTRUCTION
Lantor core materials can be applied to all composite parts, including decks, hulls, hatch covers, steering consoles, shower cabinets and chairs.
Lantor Coremat® is used as a core material in decks and hulls or as a print barrier in hull sides. Lantor Soric® is used in closed mould processes as a flexible core, interlaminar infusion medium and print barrier.
Typical key benefits from using Coremat or Soric :
• Saves labor
• Saves weight
• Excellent print blocker
• Saves resin and glass
• Soric as an interlaminar infusion medium
Lantor Finishmat® D7760 is used in closed mould processes to prevent print through effect and provide the laminate with a class-A finish. For additional information on print through blocking and osmosis prevention with Lantor Soric TF and Lantor Finishmat D7760, please contact us.
TRANSPORTATION
Soric® Flexible Core is a core material (bulker), infusion medium and print blocker (liner) and is suitable for VI, RTM light, RTM Heavy and Pultrusion.
Unique to Soric® Flexible Core is the combination of the following qualities:
• Drapeability
• Weight saving properties
• Thin
• Flow medium
All aspects of importance in composite applications of approximately 3 – 6 mm occur in the transportation market and its segments, namely:
Automotive :
Cars, Sport cars, Niche Cars, Panelling, Spoilers
Transport :
Truck, Commercial vehicles, Bus, RV panelling, Spoilers, Skirts, Floor, Doors
Mass Transit :
Trains, trams, light rail – panelling, seating, ceiling, floor, doors
Specialty :
Agricultural, Sport & leisure, Industrial – hoods, Roofs, Bonnets
WIND ENERGY : Lantor products in FRP Parts of Wind Turbines:
Business Development Wind Energy
Lantor has set up dedicated Business development specifically for the Wind industry.With Lantor flexible core products for both open and closed mould manufacturing there is an excellent fit in the production of the FRP parts of a wind turbine. In Nacelle and Spinner parts Lantor Flexibel cores can be used as core material to get economical viable laminate solutions and for blade manufacturing it can enhance the quality of the infusion process.
Lantor Composites Calculation Service
Because of years of expertise in the wind energy market, Lantor can assist in laminate build-up solutions and do calculations for an optimal use of the different composite materials and to optimise the production cycle times of the specific products.
Lantor Coremat®
In open mould manufacturing Lantor Coremat® can help you shorten the cycle time of the production of a Nacelle or Spinner by building up thickness in one layer instead of using multiple reinforcement layers. The quick bulking of the laminate in combination with reinforcements will meet the mechanical properties required by Germanische Lloyd’s standards. It increases the flexural properties of the laminate without adding weight. Lantor Coremat can therefore save materials and will help you to reduce the production times of the specific parts.
Lantor Soric®
When using closed mould processes Lantor Soric® will help the production of the FRP parts in multiple ways. The thickness loss that the Vacuum infusion or RTML process introduces compared to the open mould process can be compensated by using Lantor Soric as a core material. Lantor Soric is a compression stable core that enables you to use an optimal amount of reinforcements. The mechanical properties can therefore be optimized without making compromises to the total weight of the end product.
The channels between the Hexagonal cells of the Lantor Soric core also helps to distribute the resin thru out the total laminate build up. The controlled way that the Soric core distributes the resin will give you an optimal control of the infusion process. This will lower the risk for dry spots and therefore enhances the quality of the product and the amount of the total production cycle time. Important aspects for both nacelle and blade manufacturing.
INDUSTRIAL
A world leading producer of high-precision measurement equipment for the automotive industry, produces equipment covers made of glass fiber composite. The primary requirements of these composite covers are adequate stiffness and an excellent surface finish as befits a quality piece of equipment.
The use of Coremat Xi3 achieves both these requirements. Coremat, acting as a thin core, builds up thickness quickly. This saves labour, glass and resin. Coremat also acts as a print blocker, greatly improving the cosmetics of the finished part. The use of Coremat also reduces the weight of the panel as compared to the all glass version, making the panels much easier to install.
Why Coremat Xi 3 mm?
The 3 mm Coremat Xi proved to be the optimum thickness to achieve the required stiffness needed for the covers. Coremat Xi also adapts easily to the complex shape of the parts. Coremat Xi3 achieves both the required stiffness and the improved appearance of these laminated parts.
Laminate build up
• Gel coat blue or white
• Glass layers
• Coremat Xi 3 mm
• Glass layers
BUILDING, CONSTRUCTOR & INFRASTRUCTURE
A large producer of glass-reinforced-epoxy and phenolic pipe systems produces GRE-pipe products for industry, oil & gas, offshore, marine and fuel handling systems, Lantor Finishmat 6691 SL is used in the manufacturing of oil pipes. Finishmat 6691 SL is used on the inside of the pipes to improve the chemical resistance of the pipes.
Why Finishmat 6691 SL?
The material creates a resin-rich layer in the pipe, which has the following advantages :
• creates a chemical barrier
• the smooth finish of the pipe has a positive effect on the flow properties
• 6691 SL prevents glass fibres protruding from the surface, thus improving the durability of the pipe
• synthetic fibers have greater resistance to water than glass fibres, as they do not contain silane.
Have any questions?
If you would like to know more about Lantor’s range of products that are available with us, please get in touch with us. Our contact details are at mentioned below.
We are growing
The addition of Lantor to our product repertoire is a good way to capitalize on our strong distribution network. Link Composites’ has six branches in India. It makes us the only composites industry distributor in India with six locations in three states, truly making us a multi-state, mufti-location company. This makes us preferred resellers as our products are accessible to a bigger customer base.
How to get in touch with us
You could call us, email us or drop in.
For more information, kindly email us at response@elink.co.in
The monsoons are here, and they are notorious for creating gelling problems and gel-time issues. It is natural to blame the supplier, but the truth is a little knowledge can help you get to the root of the problem yourself. If you are aware of the curing mechanism and approach the gel-time problem equipped with the correct knowledge you won’t have any of these seasonal problems at all. So read on.
Did you know that the rate of cure of a resin is based on several factors? It depends on the amount of the resin, the type and amount of peroxide catalyst & accelerators based on the resin & curing conditions.
Peroxide catalysts: The catalysts used with polyesters and vinyl ester resins are called peroxides. Their function is to crosslink the resin, at first causing a gel and then a complete cure.
Precautions with Peroxide Catalysts
• Because peroxides and accelerators react explosively, they should never be mixed together directly. Hence resins for use at room temperature are generally preferred pre-accelerated.
• If additional accelerator is needed, it should be mixed thoroughly into the resin before adding the catalyst.
• Strictly observe safety instructions that come in the data sheets.
Let’s focus on MEKP and accelerators.
Methyl ethyl ketone peroxide (MEKP); is made from methyl ethyl ketone and hydrogen peroxide. Some of the factors governing peroxide catalyst usage are:
• Amount—Resins and peroxide catalysts are formulated so that from 0.75 to three percent catalyst solution is enough to generate the free radicals needed. If too much catalyst is used, too many polymer chains start growing; resulting in a weak cured resin with poor physical properties. If too little peroxide catalyst is used, the gel time will be very long. The resin may never cure properly even if post cured and tend to be physically weak and possibly rubbery.
• Heat—Enough heat must be supplied to properly cure the resin. It can come from an external source or from the exotherm of the resin itself. Exotherm is the heat given off as the resin cures. If the exotherm is more concentrated the part will get hotter and cure faster. If the part is a thin laminate it will cure slowly.
• Shop conditions are very important. If temperatures are below 25ºC, cure will be greatly extended. However, if the temperature is in the 40’s, gel and cure will be faster.
• Cutting back on the peroxide catalyst may result in enough working time, but there may not be enough free radicals to properly cure the resin.
Accelerators: Resins formulated for cure at room temperature contain accelerators or promoters. They increase the rate at which peroxide catalysts breakdown into free radicals. The amount of both the accelerator and peroxide catalyst should be such that the fabricator has enough working time to form the part, and at the same time, enough speed of cure to make the process economically viable.
Accelerators used in most products are generally metal salts (metal soaps) and amines. They include cobalt, calcium, copper and potassium salts and amines such as dimethyl aniline and diethyl aniline. Some of these accelerators are described as follows:
• Cobalt—Solutions of cobalt impart a pink to red color to the resin. Cobalt acts on most peroxide catalysts to form free radicals.
• Amines—Amines generally color polyester resins yellow to brown depending on the amount present. They also can cause accelerated yellowing of cured parts.
• DMA and DEA act directly with benzoyl peroxide so that this catalyst can be used at room temperature. Without an amine present, BPO is too slow in generating free radicals at ambient temperatures for use in polyester or vinyl ester resins.
Source: From the Composites Applications Guide of CCP
YouSpeak: Introducing a brand-new column for you, the reader
This newsletter is yours. Based on feedback from you, we are happy to introduce a brand-new column for you. Yes, we will share the achievements of our suppliers and customers. We will feature cases studies, successful project completions, memorable achievements and milestones. We therefore welcome articles and write-ups from our readers – our customers & suppliers !
Recent Comments