Voice Coil 2007 1

The Audio TechnologyAuthority

Article prepared for www.audioXpress.com

Introducing CURV® Composites By Mike Klasco

An innovative and superior-performance cone is now available globally with performance comparable to

woven composites, yet its pricing is just above extruded PP sheet cones. The material, CURV®, manufactured by Propex, is light, stiff, with a high Young’s modulus and high damping, not hydroscopic, and provides high temperature tolerance. CURV is relatively inexpensive, at least when compared to carbon fiber or Kevlar.

What is it made of? In a nutshell, pure polypropylene (PP) is extruded, drawn into tapes, woven, and heat-treated to pro-duce a self-reinforced PP composite. In this unique patented process, the surface of the tapes is selectively melted to bond the fabric together, providing a single polymer composite.

The drawing process provides higher stiffness by orient-ing the polymer and, as the surface facings are melted and re-crystallized to form the matrix, an ultra-stiff and smooth skin sheet is produced. The resulting sheet material proper-ties are enhanced through this molecular orientation rather than mineral loading. Typical polypropylenes for speaker cones have talc, mica, or glass compounded into the PP that increases the material density about 10%. CURV is pure PP without mineral loading, and while the stiffness is 30% higher than conventional glass-filled PP, CURV’s density is .92, about 10% lower than glass-loaded PP.

The processing not only results in a stiffer and lighter cone, but also increases temperature tolerance. The autosound industry has always valued PP being impervious to moisture and its high UV resistance, but PP needed a bit higher tem-perature tolerance for the automotive industry’s nightmare of a parking lot in Phoenix in the summer. CURV’s heat deflec-tion temperature is 160° C (320° F) that more than meets autosound OEM targets. CURV also provides tremendous low temperature performance at levels of –40° C/F and below, and even maintains its performance at cryogenic levels.

Highly oriented polymerization is one of the secrets the Japanese brands, such as Sony, have used to achieve superior sound in their headsets by biaxial stretching and heat anneal-ing (crystallization) of the polyester diaphragms such as PET and PEN films. The Japanese material suppliers have not

offered this processing outside of their Keretsu group(s). Now this sophisticated molecular processing is readily avail-

able in PP sheet material for speaker cones. Steak at hamburger pricing. The high Young’s modulus, high damping (identical to conventional PP cones), light but strong cone, and relatively low cost make CURV ideal for autosound OEM and after-market, outdoor speakers, home theater woofers, and satellite mid-bass woofers, as well as prosound. CURV should have an enormous impact on the speaker industry.

PHOTO 1: CURV cone.

PHOTO 2: CURV sheet after forming but before trimming.

2 Voice Coil 2007 www.audioXpress .com

This technology advancement was originally developed at the University of Leeds in the UK before BP Amoco acquired the technology and spun off Propex Fabrics in 2005 to com-mercialize the process. CURV had never been utilized en masse to the US or Asian speaker industries, so most of the usual cone vendors a speaker engineer would source from were not familiar with this material. Propex, along with Jimmy Ying of Sea Galleon, the local agent for CURV, has been working aggressively with Chinese cone vendors and sampled the material with tremendous success. Many vendors have recently mastered the forming process.

Menlo Scientific has been involved with PP for speaker cones for over 20 years. In the early 1980s we supported our Korean clients in sourcing extruded PP sheet materials from Transilwrap. In the 1990s we worked for Transilwrap, which for years was the key converter for extruded PP sheet world-wide. More recently we worked with Nike on their extruded PP sheet material applications.

PP IN THE SPEAKER INDUSTRYHigh-power subwoofers, whether for home theater or

autosound, often use PP cones if they are to be crammed into tight enclosures because PP resists creasing and tearing. Often heavy-gauge PP is used, as thick as .040-.050˝.

PP also stands up to outdoor duty speakers, due to its low moisture absorption and loading with carbon black, the ultimate UV block. Of course, PP is available clear, as well as in some colors, but the black PP (carbon black as a UV stabilizer) will weather the sun the best. On the downside, polypropylene is soft, and while it is quite light (specific gravity .92, but most PP is mineral loaded and closer to 1), the typi-cal PP cone replaces paper cones with a weight and sensitivity penalty. Midrange speakers use much thinner PP sheet stock, as narrow as 0.20˝.

But today Transilwrap, Sherwood, and Nike IHM have left the extruded PP sheet speaker cone business. Running soft PP resin through an extrusion machine seems to be a no-brainer, but product consistency has been elusive for all these quality extruders, eventually causing each of them to drop extruded PP sheet for the speaker industry from their product lines. Since the 1990s Japan and Taiwan have entered the supply chain, and now even local Chinese extruders can provide at least marginally adequate product.

Regardless of the vendor, endless grief with PP sheet cus-tomers has resulted from:

- Inconsistent thickness gauge (±5% is desired but ±10% is typical)

- Pits and gels - Poor surface finish and keeping finish consistent- Regrind issues- Sloppy resin vendors

The target ideal characteristics include:- Lightweight and stiffness- Scruff resistant surface- Consistent thickness

Beyond the weight and temperature value enhancements

described previously, CURV provides solutions for each of these characteristics.

BACKGROUNDThermoformed plastic cones produced quite a stir when the

famous British speaker firm B&W introduced speaker systems with Bendextrene woofers over 35 years ago. Bendextrene extruded sheet was thermoformed into a cone. While distor-tion was reduced over paper pulp cones, this polymer packag-ing material was too inconsistent for the precision thickness required of speaker cones.

Polypropylene was soon found to be the preferred resin sheet material for thermoforming speaker cones and “PP” has been with us ever since. Polypropylene cones are popular for home theater audio, whole house audio (inwalls, onwalls, ceil-ing speakers, and autosound) because PP cones do not absorb moisture and can have low distortion. Avoiding moisture absorption is more important than you might think, because the cone mass and other critical parameters all can significantly shift with humidity. PP has remained at the edge of main-stream audio, but had never achieved the share of the cone business that paper has owned since day one. PP has its allur-ing attributes: consistency, stability, and strength (regardless of humidity) and smooth and well-damped sound quality. PP is a terrific value, with price varying by quantities and reinforcing fibers, but PP sheet is typically well under $2.25 lb.

Many speaker companies have been using injection-mold-ed PP cones for years. Injection-molding has some benefits, but requires a large investment in tooling. Material flow and “grain” are different than thermoforming, but every cone body profile requires a separate tool.

While injection-molded PP cones were considered the future a few years back, they have turned out to be relatively rare due to the speed of thermoforming multiple PP cones. Cycle time of injection-molding and cost of multi-cavity tools in injection-molding have made thermoforming look attractive. Injection-molded PP has a slightly higher Young’s modulus than most extruded PP, but CURV has a higher Young’s modulus than injection-molded PP as well as a lower density (over 700,000psi). WOVEN COMPOSITE CONES

There are many techniques for fabrication of woven com-posite cones. Some cone vendors buy resin-treated woven sheets of glass, aramid (Kevlar, Technora, and so on), and carbon fiber. Woven sheets containing no resin are also com-monly available, and then a few coats of epoxy seal lock-in the shape. There are other proprietary processes to bind the woven fibers, lock-in the shape, and seal the cone. While the fibers can be light and stiff, the thermoset epoxy binder coat-ings are heavy and the resulting cones tend to be heavier than paper cones.

Some cones are composed of woven fiber with the epoxy coating. But multi-layer cones using a core of Rohacell or hon-eycomb are popular with woven fiber skins. In this case, the skins are of the thinnest weave possible, as the weight of the skins and core add up! A more recent issue is availability and price of the woven fibers; carbon fiber pricing has especially

Voice Coil 2007 3

gone crazy, not to mention it is on allocation with not enough to go around.

Joe Fians, business manager of CURV—N. America, lists the benefits of CURV versus extruded PP and woven com-posites:

“CURV allows speaker manufacturers to avoid the key problems that extruded PP has presented in the mainstream speaker market.

1. Softness and marring: PP is soft and easily scuffed during handling and production, while the self-rein-forcing construction of CURV provides strength and a tough abrasion-resistant surface.

2. Weight savings: While conventional PP has low specific gravity, thermoformed PP must be used in a thick gauge to achieve adequate wall stiffness. CURV is strong, light, and stiff (tensile strength, ASTM D638: 26,400 psi). CURV has a lower specific gravity than mica, talc, or glass-filled PP, yet CURV has a higher Young’s modulus.

3. Uniform quality: The CURV process provides uni-form thickness across the entire sheet versus extruded PP sheet (±3%). The CURV process is free of gels and aggregates (uneven dispersion of carbon black, and so on).

4. Stiffness/strength vs. weight performance: At 30% higher stiffness, thinner gauge CURV cones meet the strength requirements of speakers with cone weights comparable to paper and much lighter than PP cones.

5. Durability: CURV has superior tear resistance quali-

ties, utilizing its 0-90° reinforcing core.

“Furthermore CURV also avoids the key issues of woven composite cones that have kept this premium approach at the edge of the speaker market.

1. CURV is a thermoplastic, while treated woven com-posite cones are often B-staged. While CURV does not have shelf life limitations, B-staged woven cones must be stored in a cool warehouse and have a limited shelf life.

2. CURV is complete and does not require resins, coat-ings, or curing. CURV combines woven PP with a PP matrix, thus the entire composite cone consists of PP material without other binders or material loading. Most woven composite cones require 4-6 resin coatings to seal and bind the cone into shape.

3. CURV is light and available in very thin gauges so its high stiffness-to-weight-ratio can be taken full advan-tage of. Woven carbon fiber and Kevlar cones are light and stiff, but when the epoxy coating is applied, much of this weight advantage is lost.

4. CURV has high internal damping (tan delta). While Kevlar has a terrific combination of high Young’s modulus and high internal damping, the epoxy resin often used to seal and bind the cone into shape has poor damping and degrades an otherwise superior cone.”

I also discussed the potential speaker applications of CURV with Propex market development manager Derek Riley. He

4 Voice Coil 2007 www.audioXpress .com

points out the following:“Speaker engineers know that three important physical

properties determine the suitability of a material for use in loudspeaker diaphragms—stiffness, density, and internal damping. Stiffness, in particular, determines the bending wave velocity and hence for any given design the frequencies at which resonance will occur. The upper resonance in a dia-phragm determines the transition point at which the response becomes rough. The high Young modulus (and the steepness of the cone body angle and the diameter) determines at what point things become nasty. The degree of internal damping, or loss factor, determines the effectiveness of the material in suppressing such resonances, especially important near and above the upper resonance.

The graph in Fig. 1 simply plots sound velocity against loss factor (damping). The best materials will have high velocity and high damping, but you can see that in many cases these properties are mutually exclusive, whereas CURV offers a good combination of the two.

Figure 2 takes material density into account and plots relative bending velocity against loss factor. This is important because materials with low density can be made thicker for the same weight, and because stiffness increases with the cube of thickness the effective bending velocity. This puts all the materials into a practical perspective and shows that paper, due to its low density, offers the highest properties. However, it is difficult to produce a consistent paper product, which inevitably deteriorates over time, along with moisture absorp-tion, issues with tear resistance, and additional issues industry experts know all too well.”

FORMING CURV CONESDuring my trips to cone forming facilities in Asia in April

and August, I received some first-hand experience in form-ing CURV. Conventional fabrication of PP cones often uses thermoforming, in which the cone is heated until it is soft and then it is pressed (often by vacuum pressure) into shape. The surround is then glued onto the cone, or more at more sophisticated operations, the surround may be a TPE (such as

Santoprene) injection-molded onto the cone periphery.The textbook solution for forming CURV is compression

molding. Using a positive and negative mold and a hydraulic press, the sheet is clamped at its periphery and slowly formed. In Asia all of the cone vendors I visited had years of experience in forming PP cones, woven composite cones, and PPester (Mylar, Teonex, and other films for tweeters, microphones, headsets, and mike diaphragms). During the week of forming trials, all were successfully able to form CURV cones, typi-cally using preheating to bring up the CURV sheet to a tem-perature at which the material viscosity was low and the cycle time in the mold was short. Dai-Ichi in the Philippines has mastered the CURV process, at least for the thinnest gauges, using vacuum-forming techniques, which is a faster and more cost-effective process than compression molding.

CURV THICKNESSTypically CURV cones will be about 30% thinner than

extruded PP cones. Keep in mind that even for the same gauge, CURV cones are over 5% lighter than mineral-loaded PP. CURV is available from 0.25mm to 3.0mm, with thinner gauges in the works.

COMPOSITE CONES In many industries CURV is used with sandwich construc-

tion. While CURV works well with Rohacell and similar foam cores, even more appealing is foam PP with CURV skins. No adhesive is used as the CURV skins are heated and then pressed to the foam PP core, fusing the composite together. Extremely stiff and light cones can be formed for the larger size cones.

Yet another application of CURV composite sandwich panels is speaker enclosures, but that is a topic for another article.

INJECTION-MOLDED SANTOPRENE SURROUNDS (IMSS)

Propex and Advanced Elastomer Systems (AES/ExxonMobil) have confirmed that CURV is compatible with the IMSS process. In Asia, Sea Galleon is the agent for both materials and is supporting IMSS for CURV cones using approved vendors for this process.

With over a half-dozen speaker cone factories offering CURV with high production yields, pricing is competitive and quality is high. Speaker engineers feeling a price pinch on

TALE OF THE TAPE

Speaker sizeextruded PP sheet thickness

CURV sheet thickness

4˝ diameter 0.3 and 0.4m thick.25 - 3.5 (.325 available now)

5.25 to 6.5, 5 × 7 oval, 6 × 9 oval

0.4mm thick .35

8˝ diameter 0.5mm to 0.7mm thick .4 to 4.5mm

10˝, 12˝, 15˝ diameter

0.7mm and 1.0mm thick .6mm to .8mm

18˝ diameter 1.2mm or 1.4mm 1mm to 1.2mm

FIGURE 2: Relative bending velocity vs. loss factor.

FIGURE 1: Sound velocity vs. loss factor.

Voice Coil 2007 5

their carbon fiber cones can switch to CURV at a huge cost advantage (30-40% on average), and extruded PP users who want to increase sensitivity while achieving the benefits of a 30% increase in Young’s modulus for a tolerable price increase can upgrade to CURV. In China all the usual suspects who offer woven carbon fiber now offer CURV—one more option for the speaker designer’s pallet.

WHAT’S NEXT?Propex has announced it is developing CURV in colored

weaves, such as black/red weave (Photo 3), yellow weave, and blue weave. All these sheet materials appear visually similar to the woven carbon fiber and Kevlar cones. The CURV cones match the appearance and performance of their more-expen-sive cousins, but at pricing more comparable with PP sheets.

The flexibility customization of CURV provides a high-performance, visually appealing, and economical solution for the industry across most of the spectrum of materials, from low-end extruded PP to premium Kevlar and carbon fibers. VC

www.curvonline.com

Michael Klasco is the president of Menlo Scientific Ltd. in Richmond, CA, a consulting firm to the loudspeaker industry. He is the organizer of the Loudspeaker University seminars for speaker engineers. Mike contributes frequently to Voice Coil. He specializes in materials and fabrication techniques to enhance speaker performance.

PHOTO 4: CURV can be used as the skins for composite woofer cones, flat disc passive radiators, and speaker enclosures.

PHOTO 3: Carbon fiber red-black weave.

Verso Filler Page♦ ♦

Curv® Self-Reinforced Polypropylene Composite

Processing Guide

Curv® Composites Propex Fabrics GmbH

Düppelstr. 16 Gronau 48599

Germany info@curvonline.com

www.curvonline.com

1

Processing Overview Curv is a 100% polypropylene (PP), ‘self-reinforced’ composite. In a unique and patented process, highly drawn polypropylene tapes are heat treated to selectively melt every surface. The melted material bonds the tapes together to produce a single polymer composite. In short, the material properties are enhanced through molecular orientation resulting in ‘self reinforcement’. This unique structure creates a bridge between the performance of isotropic PP and continuous glass-reinforced PP composites. The material can be used in a variety of forms, depending upon end-use requirements. For example:

Flat sheet Thickness from 0.3 – 3.0 mm, in 0.3 mm increments Width up to 1.36 m (53.5 inches) Sheet lengths cut to customer requirements Rolls available for 0.3 – 1.2 mm thicknesses

Moulded parts, using matched tool or bladder thermoforming

Laminate skin for core materials such as:

Expanded PP (EPP) foam Honeycomb core (paper, PP, aluminum) “FML” fibre-metal laminates produced from thin sheets of aluminium alloy

interleaved with Curv

Localized reinforcement in compression/injection moulded parts. Curv’s outstanding impact performance at low temperatures makes it ideal as a localized reinforcement with glass-reinforced composites.

In addition, a number of post processing techniques can be used with Curv composites:

Decoration Methods Painting Carpeting

Attachment Methods

Adhesives Vibration welding Ultrasonic welding Mechanical fasteners

Trimming Methods

Water jet cutting Die cutting CNC routing Circular saw

2

Making Parts by “Thermoforming”

Curv, like all thermoplastics, is processed by heating to a point where the material becomes soft. However, unlike most conventional thermoplastics, even at moulding temperatures Curv has a relatively high stiffness and it requires a few bars of pressure to shape the material. Curv cannot be vacuum formed. Matched tooling with pressures up to around 30 bars or bladder (diaphragm) forming at pressures of 5 – 10 bars are required for best results. Depending on the degree of deformation and complexity of part required there are two possible thermoforming strategies. For reasonably simple shapes and low degrees of deformation (10% tensile extension, 30% shear deformation) then the best temperature for the sheet at the point of forming is 150°C. At this temperature the shrinkage of the sheet is low so it can be heated unclamped in an oven if required. It must be noted that in order to have a temperature of 150°C at the point of forming the sheet has to be heated to a higher temperature to allow for cooling during the time taken to transfer the sheet to the press and for the press to close. A temperature of 165°C is the highest that should be used before the onset of shrinkage: depending on sheet thickness this gives around 20 seconds for transfer of the sheet and mould closure. This thermoforming strategy is the most commonly used commercially. For more complicated shapes better results can often be seen if the sheet is moulded at a temperature of 170°C at the point of forming. Matched tooling is required. At this higher temperature, the tools must be closely matched to the final dimensions of the finished part taking into account the respective degrees of thinning in areas of higher deformation. This can make tool design challenging, but one solution is to have at least one half of the mould “flexible” which is then able to conform to the thickness changes of the sheet, while maintaining forming pressure and consolidation after forming. At the higher forming temperature the material must be clamped to restrain shrinkage, although it is an advantage to allow it to flow into the mould during forming as this reduces the forming force and reduces inter-ply shear and delamination. For both approaches, only modest thermoforming pressures are required. Appropriate pre-heating is a critical step in moulding Curv. Either of two methods can be used successfully, depending on the amount of draw and geometry required.

Preheating Pre-heating Curv without a frame:

1. Heat sheet material to 165°C +/-5 (320 – 340°F) using infrared heaters, convection oven, contact plate heaters, etc. Extreme care should be taken not to overheat the surface of the material, particularly when using IR heating. Medium wavelength IR is recommended

2. Heating time varies with the method used but for best results allow approximately 2 minutes of heating time per 1.0 mm thickness. For example, a 2.1 mm thick sheet should be heated approximately 4 minutes to allow the heat to soak through the sheet. Quicker heating can result in high shrinkage.

3

Pre-heating Curv with a frame: 1. Clamp sheet in a frame to securely hold the sheet and enable higher pre-heat

temperatures. A “spring clamp” frame works particularly well (see photograph), although a standard fixed frame typically can be used.

2. The sheet may be heated to 180 – 185°C (355 – 365°F) while clamped in the frame, as the frame will restrict shrinking.

3. Allow approximately 2 minutes of heating time per 1.0 mm thickness. For example, a 2.1 mm thick sheet should be heated approximately 4 minutes to allow the heat to soak through the sheet. Quicker heating can result in shrinkage, seen by the sheet pulling out of the clamp.

Curv sheet held in sprung frame during heating and moulding cycles

Moulding Curv Curv composites are processed by ‘low pressure compression moulding’ or by bladder forming. These processes provide high definition with even fiber distribution and minimal thinning in high draw areas. The material’s high stiffness makes it unsuitable for vacuum forming. Tool design:

Tool substrate: Process Curv with matched (e.g. male/female) tooling. For production purposes aluminium is recommended, however tools may be of wood or resin for prototype work. Alternatively, a bladder forming system may be used.

Note: Steel tools will not harm the material, but they are not necessary due to the low pressures required to process Curv.

Tool geometry: The tool gap should be matched to the thickness of the Curv sheet being moulded. In areas of extended draw, the material is likely to thin slightly and this effect should be taken into account in tool design. In addition, areas of the tool which

4

may trap air during moulding should be vented. Maximum draw: Depends greatly on part design and if a “slip clamp” frame is used

during moulding. Minimum radius: Depends on sheet thickness but typically 2 x sheet thicknesses. Mould shrinkage: ~1%

The overall tool design depends to a great extent on the complexity of the part to be moulded. Parts with relatively little depth of draw can be successfully moulded using simple matched tool where the sheet is positioned, by hand or by robot, between the tools immediately prior to closure. Parts with deeper draw usually require some type of clamping frame which restricts the material as it is drawn into the mould to prevent creasing. The example shown below, a soccer shin guard insert, has many ribs and a high degree of curvature, but the overall depth of draw is small. No clamping frame is used.

Simple male / female matched tool Tool mounted in Moulded part hydraulic press Parts with deeper draw, and certainly those parts with complex details around the edges, require some mechanism to prevent the material from being pulled into the tool too quickly. In such cases creasing will likely be seen around the edges of the drawn area. This can be prevented by the use of a frame to either completely clamp the material to prevent any movement into the tool – in such cases all the draw is obtained by stretching the material – or to restrict the movement of the material into the tool such that deeper parts are formed by a mix of ‘slip moulding’ and stretching. In the example shown below, the loud speaker cones are produced by tightly clamping the sheet during forming such that all the depth is created by stretching.

5

. The maximum depth of draw attainable during moulding depends greatly on the geometry of the part. However, a typical maximum strain to failure of the material, at moulding temperatures, is around 50%. For parts where a deeper draw is required it is important to allow the material to move or slide into the tool. By restricting the movement of the material, through back tension, creasing can normally be eliminated. Deeply drawn parts, such as suitcase shells, need a sprung mounted clamp frame similar to that shown below. In this example, as the tool closes the sheet is automatically held by a clamp frame which is spring loaded. The sheet is able to slip under the frame but the back tension is high enough to prevent creasing in the corners.

Matched aluminium tool for the production of loud speaker cones. The material is clamped during forming such that all the draw is achieved through stretching the material. Note the small holes at the points of deepest draw which allow trapped air to escape.

The moulded part is trimmed from the sheet by die stamping

Top tool (female)

Bottom tool (male)

Clamp frame

Springs

Spring tension adjustment

Tight radius and deep draw achieved without creasing

6

Moulding conditions:

Pressure: Modest pressure is needed at the tool face, in the range of 15 - 30 bars (150 - 300 N/mm2, 217 - 435 psi)

Tool temperature: Curv forms best with a tool temperature of ~70°C (158ºF). If heated tools are not available, the tool may be run at ambient temperature, as the tools will be somewhat heated during processing.

Clamping: Sheets may either be clamped or allowed restricted flow into the mould cavity (depending on the complexity of the part being produced). Best results are seen where a sprung clamping frame is used to restrict the movement of the sheet into the mould.

Tool closing speed: Approximately 30 - 50mm / second Cycle times: Cycle times are dependent on tool design and material thickness.

However, most parts can be produced in <60 seconds. The overall limit to cycle time is the time required to heat the sheet, which may be overcome by preheating multiple sheets in a convection oven or multi-stage IR oven.

Removal from the mould: The formed part should be removed from the tool after the temperature has decreased to <100°C (212ºF) to prevent warping. Depending on geometry, parts may benefit from cooling on a clamped frame.

An alternative to matched tool compression moulding is to use a single-sided tool with a rubber diaphragm and compressed air to produce the required pressure. Air pressure in the range 5 - 10 bars (70-140 psi) is recommended. One advantage of using a diaphragm with compressed air is that equal pressure is applied over the entire mould regardless of orientation.

7

Laminating Curv to Core Materials Curv can be used with a variety of core materials to achieve specific properties. For example: Curv/Expanded Polypropylene (EPP) Foam Curv can be combined with EPP foam by thermoforming with matched tooling without the use of an adhesive. We suggest the following starting conditions:

Pre-heat the skins and core together to the required processing temperature of 160 – 170°C (320 – or 340°F). These conditions result in a temperature of 140 - 150° between the foam and Curv sheet, which melts the surface of the foam and gives good adhesion between the core and skins.

Sheets should be clamped in a frame, and the tool temperature should be adjusted to ~30°C (~85°F).

For parts with simple geometry, a flat sheet of foam can be used as the core material. The tool will create minimal geometry in the final part.

For complex parts, it is better to use pre-formed foam.

Curv/EPP foam laminate with ‘simple’ rib, moulded in one-shot process

Curv/EPP foam laminate with more complex form – note tools used to close edges

8

Curv/Honeycomb (PP, Paper, or Aluminum) Curv/honeycomb laminates offer high stiffness and light weight. Laminates made with PP honeycomb are also easily recycled. Curv skins can be bonded to honeycomb cores with hot-melt film adhesives either by continuous lamination or a static press. Curv / PP honeycomb laminates possess high stiffness but are not easy to form into shapes. Such laminates are best reserved for light weight, high stiffness panels.

Curv / PP honeycomb panel bonded with hot melt adhesive

Curv / paper honeycomb laminates may be moulded in a single shot process by heating both sheets and Curv and placing in a matched tool along with hot melt adhesive. As an alternative to using a hot melt film, Curv may be specified with a suitable heat activated adhesive already applied.

Curv / paper honeycomb moulded in a single shot process. Note honeycomb compresses to meet tool geometry and can be closed completely at the edges.

9

Decorating Curv

Paint Curv is 100% polypropylene and as such has very low surface activity (typically 30 dynes/cm as produced). However, standard flame treatment or plasma treatment methods are sufficient to raise the surface activity to enable Curv to be painted using conventional painting systems. Flame treatment will raise the surface activity to around 40 dynes/cm whereas two passes from a hand held gun can raise the surface activity to around 70 dynes/cm - a level which is maintained for more than 7 days. Painting trials following such surface preparation have been shown to provide a Class A automotive finish which meets industry standards for temperature and humidity cycling, stone chip and adhesion. Carpeting Automotive carpet may be attached to Curv using a heat activated adhesive suitable for polypropylene. In many cases carpet may be bonded as part of a one shot moulding process.

Attachment Methods

Adhesives Hot-melt adhesives are available from a wide number of suppliers. The exact type depends on the substrate to which Curv is to be attached. Remember, Curv is polypropylene so any adhesive choice must take this into account. For specific recommendations contact the Curv team or email info@curvonline.com Vibration Welding and Ultrasonic Welding Curv may be bonded to itself and polypropylene compatible materials by vibration welding and/or ultrasonic welding. Careful selection of conditions will result in high quality bonding without witness marks on the “A” surface. Additional Methods Laser welding may be used. The carbon black used as a pigment in “standard” Curv is an excellent absorber of laser light but successful welding by this method requires that one substrate must be laser transparent. Non-pigmented Curv can be supplied on request. Mechanical fasteners can be used provided they are designed for use in plastic materials.

10

Trimming Methods Water Jet Cutting Starting parameters: orifice size: 0.15-0.2 mm diameter water pressure: 3300-3800 bars cutting speed: depends on thickness, but suggest starting at 200 mm/sec Die Cutting The blade should be cut to an angle of 22º with the cutting edge ground at 24º to a depth of 3 – 4 mm. For best results a high performance cutting steel should be used (such as “Duritan” from Messrs Klingenberg in Germany). Alternatively use HSS, high speed cutting steel.

11

Sawing Curv may be successfully trimmed using a circular saw but to give a clean cut a special saw type is required. From our experience we find the following details give the best results: Blade diameter: 220 mm Number of teeth: 42 Cutting speed: 3000 revolutions / minute Tooth angle: 5 - 8° Metal type: high speed circular saw with DH teeth (special description of tooth form) See next page for information regarding supplier.

�

�

����������� ��� � �������������

���������������������������������������������� ��������������

�

��� �������������� ��������� ����� � ��

� �������� ������ !� �"#$� %��&�

�' ��������������� ��(�)!�*#)� +�"�� ,�

�� ��

� ��������-�.����� ��(�/(�����)$0� *$��� *$��� (���1�

� �������������%�� ��(�/(�����)$0� �$�� �$�� (���1�

� ����������� ������2 ������ ��(�/(�����)$0� $�� $�� ,�

�2��3�� ��-�.�����4�� ��5���6� ��(�/(������0 � !)��� !)��� (���1�

������������������%��4�� ��5���6� /(�����7�*� !��� -� �

� � � � �

�

� ������� ���

4$�������)$�8���/����6�/(������0#�$� 9�$)����� :8��1�

�

� ������� ��

4$�������)$�8���/����(���.������;6�/(������0#�$� �$�� :8��1�

�

�<������ ��

4(���.������;���$�������)$�8���/�6�/(������ ��$� *��� :8��1�

�

�<������ ���

4�*�������)$�8���/����(���.�������6�/(������ ��$� 7��� :8��1�

�

����������� ��;� �������

4$���"�)$�8"�$"����6�����77�!�

7�

*��

:(�

8�

������������ �������%��4$��������)�8���$"����6� /(����� $)7� ����� ����� :8��1�

� � � � �

/(�����0)�$�;� ��$� =��

�>� ������������������ �������.���?� .�4�� ��5���6�

/(�����0)�$��� �7�� =��

�

��������������?��� ������ ��/3� �������

4$������ ���6�

��(�)!0)$� 7" � 3����)�@���

�2����;� ��������;���.��%�- ���� ��� ��(�*��$� ;�$� � ���

� �

•� ��A������� :��

� �

��������� �������� ���������� ���

�������A� �� �. �.��� :�B�����������������C����D� ��:����A� �E!����!E����� �

�� �. �.�?��%��A� ������%��������!�������"��

�������� ���� �� � �� �������������� �� ����'�.�A� �������!7����� �

�

������������� �

������������������������

������ �������� � �!!�� ��

"#� �������� � �!!�� !��

$��%�&������'�(�)*�+���%��,-���

.�/�%��&���000,-�+���%��,-�����

$#-���%����(�1%/%�%����

'�(���%���-���%��2�%����%����/�%-�%���%��--�����������/�����(�����3��0��24���(��56�$7�"895'*:,�8���%�(���%��� �� 2+%-�� �/�%��2� (��� �56�$7� "895'*:� ����0%��� ���� /�� ����� �(� ��%�� ��/�%-�%��� �2�0������ ���%�4� ����56�$7�"895'*:����%����� ��������%��;� %�� ����4%+��� %��4��2� (%��,�<�0�+�;� %����%���������%���;�����������%/%�%����(�����-���������������������56�$7�"895'*:����%�������%�/���(��������%-����������%����2�2,�'���(������%����������(-���2��������%�2�/���56�$7�"895'*:������2�%��-��=��-�%���0%�����%����2��(��56�$7�"895'*:����%��;�����-������������2����������������� �-�%+�2� (��� �������(-���� �� �����%�� ��� ���� ��-��%-�� 2�� �2������ %�(���%��� ���%�4� ��� ��-�����%��,��56�$7�"895'*:�--���������%/%�%���0�����+����#-����������0%����#���������+%2�2�/���0��%�%�4������(����������(� %�(���%��������%�2;��������%-�%�������-���%�4��(�������2�-���2��-%/�2����%�;����������(���������%���%���%����(��56�$7�"895'*:����%���%��-��=��-�%���0%�����-����������%��,��

������������� � �� ��

�

�