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Working with Nidaplast

1 - CUTTING and MACHINING
2 - FORMING
3 - WORKING UP
4 - FINISHING of the SANDWICH PANEL

NIDAPLAST Is a polypropylene honeycomb covered on both faces with a soft polyester non-woven fabric. It is available in 2134 x1219 (4' x 7') ready for direct use: lamination or gluing. The flexible and light sheets enable an easy use in sandwich panels where most usual techniques of cutting, laminating and gluing can be applied. Since it is a thermoplastic product, other additional specific properties make its use even easier.

1 - CUTTING and MACHINING

1.1 - CUTTING

NIDAPLAST is conventionally cut by usual means: saws, knives or a hot wire OS it is thermoplastic.

  • Saws- In order not to burst or melt NIDAPLAST when cutting, the best tooth spacing is close to: 10 teeth per inch Circular saws are particularly suitable for straight parts. 1/2 to 1" wide band saws are suitable for straight cuts, 3/8" for curved cuts.
  • Knives - Cutting with a knife is possible. A "hawk bill" or "Linoleum" knife is quite suitable.
  • Hot wire - Cutting can be carried out with an approx. 2mm tensioned wire heated at about 350Cs (662'F).

1.2 - MACHINING

  • At cold temperature - Classical tools for wood (ripper, grinder...) can be used by adapting the number of cutting blades and possibly the speed (too few blades can burst NIDAPLAST; too many can melt it),
  • At hot temperature - Another way is to use the thermoplastic property: softening under heat.

1) nidaplast polypropylene cells melt at 160C (320.0"F) whereas the non-woven polyester, which covers the facings, melts at 240C (464F). Hence if nidaplast is heated at about 200C (392F), (it melts locally to the shape required (hot stamping) without damaging the non-woven facing.

Thermoform Nidaplast

2) A second way is to cut the required shape and then to re-weld the nor polyester. For example, the following edges can be achieved:

Nidaplast Edge Cutting

2 - FORMING

2.1 - COLD FORMING

The soft polyester non-woven scrim, which covers the large faces of nidaplast makes it formable by:

- In the case of standard panels (3 psi to 12 psi) should be applied during curing time of polyester or glue. This can be done on a mold with vacuum or a matched die mold and a press.

- In the case of marine panels (scored 2" x 2" = 50mm x 50mm one side), a simple mold is sufficient.

2.2 - HOT FORMING and PRE-FORMING

Again a thermoplastic product Is easily thermoformed:

In an oven, in 3d mold, at less than 100C (212F), nidaplast softens and under a very light pressure it very easily takes the required shape.

nidaplast can also be hot preformed. Two possible processes:

- Preheating in an oven between 140C (284F) and 150C (302F), then forming in a cold mold.

- Forming in a mold heated at 130C (266F) -140C (284F).

In both cases nidaplast will keep its shape at cold temperature.

In all cases, temperatures, pressures and timings should be setup according to the shape of the par and to the thickness of nidaplast.

3 - WORKING UP

Sandwich panels with a nidaplast core can be achieved either by direct laminations or by gluing a rigid skin.

3.1 - LAMINATION

The non-woven polyester applied on nidaplast is an ideal surface for direct lamination of thermo hardening resins of polyester type (or other). However, considering their huge variety, resin formulations and lay up techniques should be checked against their compatibility with nidaplast.

Most traditional techniques (hand lay up, spraying, vacuum, pressing, low pressure injection), which are function of existing tooling and depend upon the parts to be achieved, can be applied and need only slight adjustments to nidaplast specificities.

Within the NIDAPLAST range, nidaplast 8  is especially suitable for lamination. Indeed. nidaplast has, as an under face of the non-woven polyester, a plastic film which restricts resin passing trough into cells.

The operating principle of sandwich panels is to have a perfect adherence between the core and the rigid skins. Therefore when working up a panel, it is necessary to check:

-The good impregnation by resin to the core and skins.

- The good contact, e.g. through pressure, between the core and the skins.

Manufacturing process of a laminated sandwich panel with a nidaplast core:

a) Traditionally make the first skin of sandwich panel (gel coat on the mold, then required layers of glass-resin).

b) Before the first skin has hardened, apply nidaplast, interposing an extra ca 400-g/m.2 quantity of resin, either applied on the skin or on nidaplast when hand lay up laminating.

If necessary, in the manufacturing process or in case of a thin laminate and if a very high quality surface finishing is required, it is possible to let the gel coat and one of several layers of glass-resin polymerize. As soon as polymerization is over, a last of glass-resin is spread in order to glue nidaplast as explained earlier. It is also possible to glue with shrink less polyester glue.

c) On nidaplast, traditionally apply the required layers of glass-resin of the second skin, providing for and extra ca 400-g/m2 (1 1/2 fl. oz./ft.2) quantity of resin to impregnate nidaplast and to ensure gluing with the laminate.

If necessary or if a gel coat finishing is planned on both faces of the sandwich, either a mold and countermold are used, or the first layers of the  as explained before.

Pouring resin in heaps on nidaplast without spreading it immediately should be avoided in order to prevent it from going through into the cells by gravity.

As nidaplast is a heater insulator, using a resin with too much exothermic should be avoided since it could damage the laminate or cause air bubbles.

A glass mat should be preferred to a fabric for direct contact with nidaplast.

d) Once the part is achieve, it is advised to apply the most evenly distributed pressure on the whole (vacuum, press, and weight...).

Hand lay up working is possible but a good nidaplast laminate bonding (on the mould side) should be ensure by a former impregnation of nidaplast then by a hand pressure on nidaplast when fitting it. It is the same on lamination by simultaneous glass-resin spraying. Bonding of the other side is easier to check, as it is visible: additionally it is naturally made on the pressure unbubbling of the glass-resin layers.

e)Two methods may be used for bedding scored nidaplast Honeycomb. The first method uses either Chopped Strand Mat (CSM) or chopped fiberglass from a chopper gun and the second uses a core bonding putty or a sprayable compound.

  Assuming the gel coat, skin coat and any additional structural laminates of the outer skin have polymerized and returned to ambient temperature you may proceed to core bedding. To achieve a good chemical bond this should be started as soon as this "green" cure stage is reached. The fiberglass will have a "surface tack" indicating that it is still chemically active and subsequent laminates will adhere well. Also, please note that the scored core flexes freely in both axesso that it will conform to the tool.

  To properly bed the core, there should be no projections from the laminate surface that might create an air pocket underneath core. These may be sanded or ground off and any dust, particles or loose fibers removed.

  The surface should be wet out and a layer of 1.5 or 2oz CSM or the equivalent in chopped strand from a chopper gun. This bedding layer should be thoroughly saturated with catalyzed resin and rolled out to eliminate air bubbles.

  The core may be bedded scored side up or down depending on whether the mold is convex or concave. Just prior to bedding the core, a small amount of resin should be sprayed or rolled onto the side of the core to be bedded. This will prevent the scrim from potentially leaching resin from the chopped fiberglass bedding layer.

  Press the lightly wetted core firmly into the chopped strand layer. If the core does not stay fast to the contour, perhaps a few relief cuts will have to be made along the scoring lines. When all the core is observed to be firmly bedded, allow the bedding layer to polymerize without disturbing until it has returned to ambient temperature before proceeding to the next laminate. This is to prevent out-gassing or extreme exotherm from creating bubbles or blisters in the subsequent laminates.

  The process for trowelable or sprayable core bonding is identical with only the replacement of chopped strand fiberglass with a filled and thixotroped resin to adhere the core. As with the chopped strand bedding, a little extra resin must be applied to the bedding side of the core to prevent the scrim from leaching resin from the compound and potentially creating a resin starved interface. Instructions for use of Nida-Bond CBC may be found in our website or in our catalog/handbook.

RTM

RTM techniques are possible with some products of the nidaplast range. It depends on the technique used, injection pressure, temperature, and fluidity; therefore it is preferable to consult us in order to decide together upon a suitable product.

3.2 - GLUING

There again, non-woven polyester is used as a gluing surface to a lot of rigid skins such as wood, melamine laminates, marble, fibrocement or metal.

The glue to be used essentially depends upon the skin to be glued and on the physical and the mechanical strains applied to the finished sandwich panel. Numerous glues were already satisfactory tested on nidaplast: polyurethane, epoxy, neoprene, vinyl, polyester, and ureaformaldehyde.

However, in all cases using a glue, tests should ensure compatibility of the different materials and the mechanical properties of the sandwich panel made. Polyurethane or epoxy bicomponent glues are the most often used thanks to their good mechanical characteristics and their adherence on most materials.

  • Gluing process of sandwich panel with a nidaplast core:

According to the manufacture's directions, evenly apply the required quantity of glue on the rigid skin or on nidaplast or both at the same time, if so required by the glue. For polyurethane glue the quantity should be around 400 g/m2- (11/2 fl.oz/ft)

In the same way apply glue on the second skin or on the face of nidaplast.

On the panel made apply the pressure specified for the glue, minimum of 0,2 bar and maximum of 1 (15 psi 29 In Hg,) bar is enough with regard to nidaplast. Let the glue set under the indicated conditions before handling or applying efforts on the panel.

Characteristics of the sandwich panels are mainly due to the good adherence between the core and the skins, therefore a special care should be brought to gluing and the results obtained should be well checked.

Note: Cells may show through the glued skin if the latter is too thin or not rigid enough. Print through is made worse by an excessive gluing pressure and/or the glue shrinkage when drying.

3.3 - WORKING UP PREPREGS

The high melting temperature of polypropylene makes it possible to use prepregs, which polymerize at temperatures up to 125C (at 100C [212F] nidaplast still resist to 1 daN/cm compression).

Position the prepreg on nidaplast, apply pressure at the required temperature and let the whole polymerize. According to the temperature and to the polymerization time, check that there is no risk of collapse of nidaplast due to the flow. Under a press, a possible solution consists in positioning shims very slightly less thick than nidaplast in order to avoid this flow.

Unmolding should not be carried out too hot to avoid any risk of distorting the panel or of de-laminating nidaplast.

4 - FINISHING of the SANDWICH PANEL

4.1.1 - LAMINATED PANELS

Several types of finishings are possible in case of laminated panels. Molding of polyester skins makes if easier to work out edges as shown in the following examples:

Honeycomb

Most frequently, edge finishing is carried out through a frame or a finishing profile. It's material will be chosen according to the physico-chemical strains of manufacture and use. Wood is interesting by it's very wide flexibility of use but it may require trimming and is sensitive to moisture. Plastic or metal enable a direct finishing but need a very exact size.

Setting the frames or profiles can be carried out, as shown by the following examples, either before or after the panel is made:

Honeycomb

4.1.3 - GLUED PANELS

Several types of finishings are possible according to the skins, the panel use and the mechanical strains applied.

Unstrained decorative edges can be merely glued an both rigid skins. In case of a metal sheet, a mere fold can hide the edge.

Honeycomb

Honeycomb

4.2 - LOCAL STRENGTHENING PARTS, FIXING INSERTS for ELEMENTS OR OBJECTS

Fixing elements on a sandwich panel may require local strengthening parts or inserts.

Choosing the adequate solution essentially depends on the strains transmitted by fixing to the skins or to the core.

Fixings can be tranversing or not.

4.2.1 - NON TRANVERSING FIXINGS

4.2.1.1 - LIGHT LOADS

Considering the good cohesion of nidaplast and the good adherence of skins if they were bonded up properly, fastening can be carried out in a normal way: rivets, bolts and, self tapping screws, on only one skin (Fig. 1).

If the load makes it necessary or if the skin is insufficiently strong, a glued metallic strengthening part can be added and will distribute the stress (Fig. 2).

Honeycomb

4.2.1.2 - HEAVY CONCENTRATED LOADS

  • In case of non-though fastenings, the most frequent solution consists of, before gluing the skins of the sandwich panel, in placing inserts which locally build up a solid panel into which fastening is carried out in a classical way.

The most frequently used insert is wood, but metal or resin inserts are also suitable.

The insert can occupy the full or only part of the thickness of the panel.

  • For a greater flexibility of use, it is also possible to make resin Inserts on finished panels.

Considering the fixings to be made, inserts can be large or small:

a) Large inserts
The upper skin is removed from the surface concerned by the insert. A mastic resin is applied with a spatula into the cells of nidaplast. Once the resin is dry, its sandpaper leaves a clean and surface on which solid fixing is possible.

b) Small inserts
The upper skin is perforated at the spot planned for the insert. Using a cutting tool, a few cells sheared around the hole then filled up with resin. Fasteners can be inserted into the resin.

4.2.2 - THROUGH FASTENINGS

Through fastening can be carried out:
-with inserts as described above,
-with a metal or pultruded plastic compression sleeve,
-with to specially adapted fasteners.

4.3 - THERMOWELDED INSERTS

Because of its polypropylene composition, nidaplast can very easily receive polypropylene inserts by friction welding.

The 15mm thick insert, whose diameter can vary according to the resistance wished, is positioned or nidaplast at required spot.

Using to a rotating tool at 1500 revolutions a minute, a light pressure is applied on the insert.

Rotation and pressure create the heating, which enables a perfect welding between the insert and nidaplast.

The panel thus prepared can received the final skins. On the insert, solid fixing is carried out with specially adapted screws.

 

Enquiries 

Please call Boatcraft Pacific 07 3806 1944 ( +617 3806 1944) for how to contact your nearest reseller.

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