How to Guide

 

Fibreglass Mould Construction

Moulds are the most important equipment in F.R.P production, upon which depend surface finish and reproducibility of parts, as well as the efficiency of the shop. They represent a considerable investment in money and time and all methods of prolonging their life should be considered essential before, during and after construction.

Refer to FGI Data Sheets – Pattern (Plug) Design & construction and T.R. Mould Release System for information on pattern preparation.

1. MOULD DESIGN

A Basic guide is that the mould should be 2 to 2.5 times the thickness of the component part it will product. This must be modified to incorporate increased thickness for bolted flanges, lifting and cradle fixing points. If sandwich construction is employed, the outer laminate is additional.

It is essential that where a mould has external loads applied to it due to moving around a shop or swinging for accessibility, an external frame must be incorporated so that these loads are not transferred directly to the mould. Sandwich construction is desirable on flat or moderately curved areas to ensure rigidity.

Request FGI advice when using balsa or termanto to ensure print-through of blocks is avoided. Avoid the use of woven reinforcements as they tend to “print-through” and the weave pattern can be seen in every subsequent moulding. The extra strength of woven products is not needed in a well-constructed mould, but if sandwich construction is not employed, it will improve stiffness.

Where the mould is to be split, an upstand is temporarily fitted to the pattern. This is made from plasticine, shaped to the desired contour, or from strip plywood held in position using plasticine or modelling clay. An aid to location of split moulds is to place on the upstand large dome-head upholstery tacks spaced at a suitable distance. These will form recesses in the mould flange. When the upstand is removed and the mating part moulded, a protrusion is formed. thus on future assembly, the parts will locate together.

2. GELCOAT

To obtain a minimum recommended cure gelcoat thickness of 0.5mm, you will require 0.8kg of FGI Tooling Gelcoat per square metre of mould surface. Select a colour which will provide a good contrast with the most common colours to be produced.

Brushing viscosity may be used on small moulds but spraying is much superior and less prone to error. Do not make any additions to the gelcoat, particularly of styrene, as this will reduce the moulds’ durability and crazing resistance. Do not apply spraying viscosity gelcoat by brush. General purpose gelcoats should not be used as they do have the resilience, chemical resistance and heat distortion level required to resist and hot gaseous styrene which is present during exotherm of parts. This is the main cause of mould surface deterioration.

3. GELCOAT APPLICATION

Important – Thoroughly stir the pail of gelcoat before commencing spray-up as settling of pigments and promoters will occur in a very short space of time. Stir the pail and decant the gelcoat quantity required.

Before application of the gelcoat a geltime check should be made. The ideal is to use gelcoat with a relatively short pot gel time to obtain maximum cure. For smaller parts, 10-12 minutes with 1.5% catalyst @ 25˚C will give a 25 minute gel time on the part. For larger mouldings, such as swimming pool moulds, the pot gel time needs to be approximately 15 minutes @ 25˚C to obtain a working time of 30 minutes.

The gel time check should be made at ambient temperature. Into 100 gm of the gelcoat add and mix 1.5 gm of M.E.K.P Catalyst (1.5%). The gel time should be 12-15 minutes.

It is pointless to try to make a mould below 20˚C as the gelcoat must gel within 30 minutes on the pattern to achieve good thorough cure. This also applies to the back-up resin, so ensure that the minimum temperature in the mould-making area is 20˚C throughout the mould manufacturing time period. This may involve the use of heating overnight to maintain minimum temperature.

The most reliable system is to use a hand-held pressure pot type spray gun, where the catalyst can be accurately mixed at 1.5%. This may be reduced to 1% at high ambient temperatures or increased to 2% at lower ambient temperatures. Do not work outside these percentages.

LOW PRESSURE SPRAY EQUIPMENT can be used so you can achieve a slow material flow rate and excellent atomisation with the equipment specified, but remember that the gelcoat in the pot is pressurised and thus will gel quicker than in an open cup. Ensure that the plug and material temperatures have all reached 20˚C minimum and test spray a small area of cardboard, etc. to adjust the spray pattern. If a refill will be necessary to cover the area, it is essential to have a spare pot on hand and a helper to catalyse the second mix at the right moment and pass it to the sprayer. The first pot can then be refilled with gelcoat if a third batch is required and the residue mixed into the fresh material, to prevent it gelling on the wells of the pot. Spray a minimum wet film thickness of 0.6mm (25 thou.).

For large moulds, catalyst injection equipment can be used but the risk of find porosity resulting from unmixed catalyst droplets needs to be considered. Calibrate the equipment carefully to obtain the correct catalyst ratio. The only sure method is to check the gel time of material

To the extent permitted by law and subject to any implied warranties under the Trade Practices Act 1974, we make no warranties and representations, express or implied, as to the description, merchantable quality or fitness for purpose of the goods described or the care and skill of any services provided. If any implied statutory provisions apply, to the extent that is permitted by law, our liability will be limited at our option to:

(a) In the case of supply of goods:

      1. The replacement of the goods or supply of equivalent goods;
      2. The payment of the cost of replacing the goods or acquiring equivalent goods; or
      3. The payment of having the goods repaired or the repair of the goods;

(b) In the case of services:

  1.  The supply of the services again; or
  2.  The payment of the cost of having the services performed again.

To the extent permitted by law, we will not be liable for any loss, damage, expense, injury or death sustained or incurred by a customer or any

Other party resulting directly or indirectly out of:

  1. The supply,  performance or use of any goods or services;
  2. The breach of any agreement between us and a customer; or
  3. Our negligence.

Sprayed into a bucked against several small samples catalysed at varying percentages where the catalyst has been accurately measured.

Ensure that no dust is entered the work area and dust off the plug with lint-free rags. Check the air supply to make sure that no water is coming through and then apply the gelcoat with at least five fine passes. The gel coat must have time to “breath” between passes to allow entrapped air and free chemicals to escape. This is possible even with a substantial material flow, but rapid gun movement is necessary to avoid dwelling with subsequent runs. Never apply gelcoat in one pass. It is a sound principle to spray a test panel on a piece of glass, laminex, etc., which can be checked for porosity before proceeding with laminating. It is wise to strip off a suspend gelcoat and start again rather than to make a sub-standard, porous mould. Should any faults occur during gel coating, refer to FGI Data Sheet, “QUICK TROUBLE SHOOTERS’S GUIDE TO GELCOATS”.

4. MOULD LAMINATE CONSTRUCTION

Select a resin which has a high heat distortion point, excellent chemical resistance to minimise styrene attach, low shrinkage and excellent physical properties. Normally, this will result in the choice of an isophthalic resin. Vinyl Ester Resin (Derakane) is recommended where very ghigh exotherm is likely in production, but a posture before use in production will normally be required. Use a wax-free type, unless subsequent laminates are likely to be delayed longer than overnight, in which case use a waxed resin and sand between laminates.

For use ask our technical service department about special non-shrink tooling resin system. After allowing two to three hours for the tooling gelcoat to gel, apply 0.2mm of resin behind the gelcoat and allow to TACK. It is critical to have a resin rich gelcoat/resin interface. Then apply one layer of 225 gm. Chopped Strand Mat, followed by one layer of 450 gm Mat. The Split Strand 225 gm. Mat will minimise print-through of strand pattern. This thickness of laminate will develop sufficient exotherm to ensure adequate initial cure. Leave overnight. A surface tissue may be used behind the gelcoat and helps to minimise strand pattern print through. However, it may trap air and care must be taken.

Once the first layer is cured, the laminate is then further built up to designed thickness by successive layers of chopped strand mat or with a chopper gun. Ensure that laminates do not develop excess exotherm. Each 2 x 450 gm should be cured before processing to the next layer. Ensure that a minimum temperature of 20˚C is maintained throughout this back-up process, applying heat where necessary.

It is essential through the laminating process that a high glass to resin ratio is maintained, to ensure minimal shrinkage and if catalyst injection equipment is used it must be properly calibrated. Avoid the temptation to facilitate wetout by using more resin, which will increase shrinkage.

5. RELEASE FITTINGS

Where parts are difficult to release incorporate some of the following recommendations:

 

(a)        Laminate lifing lugs into the part to enable an evenly distributed load to be applied via a hoist or similar device. Use spreader bars, so the part is pulled away from the mould.

(b)        Laminate pipe nipples onto the outside of the mould, drill through nipple and mould. Cover the small hole with an adhesive tape to prevent ingress of gelcoat and resin, then apply water or air through the nipple to assist release.

(c)        Use hardwood or high density polyethylene wedges to free the edge of the mould and follow-up with compressed air.

Note:Do not strike the mould with a mallet, as this can initiate star cracking in the gelcoat, which will spread with each subsequent moulding.

6. FINISHING & BREAKING IN

The most important facet of satisfactory mould life occurs when the mould is first made. The mould must be allowed to cure for seven days at 25˚C incorporating post-curing wherever possible, additional curing time may be advantageous.

Ideally leave the new mould on the plug for one week to ensure minimum shrinkage and distortion during cure. Postcuring of 6 hours during this time at temperatures up to 65˚C is desirable if facilities are available, especially for vinyl ester moulds.

Experience will enable operators to decide whether P.V.A. is necessary in addition to waxing; if in doubt, it is prudent to apply it for the first 2-3 mouldings, after which the mould will have cured considerably reducing the possibility of stickups. Make sure to select a wax which is compatible with P.V.A.; refer to FGI Data Sheet “T.R. MOULD RELEASE SYSTEM”. Apply a coat of Paste Wax between pulls for at lease the first three parts.

7. SPLIT MOULD OPERATION

When botling split moulds together, ensure that the following points are covered:

 

(a)        The flanges are rigid enough to withstand bolt loads.

(b)        Bolt holes are close enough to effect closure of parts.

(c)        Lare washers are placed under bolt heads and nuts to prevent crushing of flange laminates.

Should gaps occur on a split mould, assemble the parts together with a bead of Silicone or Urethane Sealant (available from FGI), screen off the excess and allow to dry. This provides an excellent gap-filling membrane. Alternatively, masking tape or modelling clay may also be suitable.

To the extent permitted by law and subject to any implied warranties under the Trade Practices Act 1974, we make no warranties and representations, express or implied, as to the description,merchantable quality or fitness for purpose of the goods described or the care and skill of any services provided.If any implied statutory provisions apply, to the extent that is permitted by law, our liability will be limited at our option to:

 

(a) in the case of supply of goods:

  1. The replacement of the goods or supply of equivalent goods;
  2. The payment of the cost of replacing the goods or acquiring equivalent goods; or
  3. The payment of having the goods repaired or the repair of the goods;

(b) in the case of services:

    1. The supply of the services again; or
    2. The payment of the cost of having the services performed again.

To the extent permitted by law, we will not be liable for any loss, damage, expense, injury or death sustained or incurred by a customer or any other party resulting directly or indirectly out of:

    1. The supply,  performance or use of any goods or services;
    2. The breach of any agreement between us and a customer; or
    3. Our negligence.

Pattern (Plug)

8. DESIGN & CONSTRUCTION

In mould-making, finish is as important as dimensional accuracy in that it strongly influences the saleability or products, performance of highly tuned marine craft, etc., and particularly the life of the mould. Quality and efficiency in production cannot be achieved unless the correct pattern and mould-making techniques are observed from the beginning. A smooth well cured mould surface resists entry of styrene fumes, which are the main cause of mould breakdown, apart from physical abuse such as the use of mallets to induce release.

  1. PATTERN DESIGN
    1. It is essential that the component to be manufactured should be produced using as few moulds as possible. This must be incorporated in the pattern stage, eg. avoid undercuts at all costs.
    2. The use of large, completely flat surfaces is to be avoided wherever possible realising the limitations of F.R.P. laminates from a stiffness aspect, both in the mould and product.
    3. On edges and corners, always use the largest radius permissible. A guide is to use a minimum radius equal to twice the thickness of the component laminate and a minimum 12mm everywhere. Avoid sharp edges and corners wherever possible.
    4. Where two surfaces are at right angles, the pattern must be constructed convex (for a female mould), allowing approximately 1cm per metre length of surface, or the cured mould will have an inbuilt “bow”, due to resin shrinkage. This can be minimised by employing sandwich construction for both mould and product.
    5. Where unavoidable undercuts occur, the pattern must be modified to allow for split moulds to be manufactured. This is achieved by introducing a flange following the contour of the undercut, moulding one section to the flange, removing the flange and then moulding the mating section.
    6. Give consideration to whether the plug should be made male or female.
  2. PATTERN CONSTRUCTION

    The method and material to be used will be dependent on the complexity of the shape required. The following will provide a guide to methods available:

    1. Fabricate a rigid timber and/or metal frame conforming to the basic shape of the final component. This is achieved by conventional screw and glue for timber and weld and bolt for metal.
    2. Flat surfaces are achieved by fixing plywood or pressed timber board to the basic frame, using countersunk screws and bolts. Ensure that these surfaces are thick enough to provide adequate rigidity and an allowance to fair off into adjacent areas (eg. particle board 18mm thick).
    3. Large radii and areas of simple curvature require suitable shaped templates to be fixed to the basic frame. Screw and glue thin plywood planks or fibreglass sheet to the templates.
    4. Textured surface areas
    1. Several different methods are used for incorporating textured patterns into moulds. The choice of method is dependant upon the type of texture desired and the contour over which the textured surface must be shaped. The desired finish appearance must be incorporated in the plug surface.

      Common texturing materials include embossed sheet (aluminium or plastic) for regular patterns such as diamonds or squares on flat surfaces or simple curves and vinyl fabrics for irregular patterns on either flat surfaces, simple curves or compound curves. Consideration must be given that too deep pattern is difficult to produce and creates an area which is not self cleaning and is difficult to walk on. conversely, a very fine pattern disappears as release waxes are applied to the subsequent moulds.

      When incorporating these materials into the plug, care must be taken to ensure that they are smoothly applied and firmly adhered, especially at the edges. The surface should then be washed with acetone and sprayed with polyurethane, to prevent the tooling gelcoat from attacking the textured surface of the plug. Ensure acetone does not attach or distort by prior test.

    2. To obtain return edges for the mould, fix 25mm x 25mm timber to the pattern edges. The return edges on the mould provide extra stiffness and a trimming surface for the moulded part.
    3. Then entire surface is then sanded to remove excess

      To the extent permitted by law and subject to any implied warranties under the Trade Practices Act 1974, we make no warranties and representations, express or implied, as to the description, merchantable quality or fitness for purpose of the goods described or the care and skill of any services provided. If any implied statutory provisions apply, to the extent that is permitted by law, our liability will be limited at our option to:

      In the case of supply of goods:

      1. Tthe replacement of the goods or supply of equivalent goods;
      2. The payment of the cost of replacing the goods or acquiring equivalent goods; or
      3. The payment of having the goods repaired or the repair of the goods;


      In the case of services:

      1. The supply of the services again; or
      2. The payment of the cost of having the services performed again.

      To the extent permitted by law, we will not be liable for any loss, damage, expense, injury or death sustained or incurred by a customer or any other party resulting directly or indirectly out of:

      1. The supply,  performance or use of any goods or services;
      2. The breach of any agreement between us and a customer; or
      3. Our negligence.

      To achieve the desired shape and contour and to provide a surface for the application of BUILD UP COATS.

  3. BUILD UP COATS
    1. For large moulds requiring dimensional stability and for patterns where multiple moulds will be needed, it is advisable to stabilise the pattern with a fibreglass laminate. This could be a 2 x 225 gm. Chopped Strand Mat laminate, a light spray-up application or preferably a glass cloth laminate. The glass laminate may not be necessary for less critical applications. The surface is then rough sanded to achieve a smooth surface.
    2. Following 3.1 there are several alternative build-up systems:
    1. (a) Ramanel Primer and Finish (refer separate data sheet).

      (b) Reface Polyester spray putty.

      (c) EASY SAND Apply several small mixes rather than one large slow curing mix as   catalysing small quantities ensures that sanding is not delayed unduly.

      (d) Q-Cell Putty. Made from 61341 resin or similar and Q-Cells. Add sufficient Q-Cells to make a medium paste. Avoid making the mix too stiff as it may be too dry and have poor strength.

    2. Always carry out all levelling and surface profile finish on the plug, rather than deferring minor detailing to be done on the mould, because the top skin of the tooling gelcoat is the most durable and gloss retentive. Rubbing this away with abrasive and/or cutting compounds destroys the most valuable layer of the mould and must be avoided by ensuring that plugs are as near perfect as possible.
    3. Assuming that the plug has been soundly constructed of material which will not warp in the time span required for finishing and mould construction (or is an

      F.R.P. moulding from which a new mould is to be made), the first step is to remove all high spots. This can be done by:

      (a) Using machinery such as Random Orbital.

      (b) Fasten a strip of coarse sandpaper, such as aluminium oxide “Open coat” to a flexible board with handles attached, which is then rubbed over the plug. These are known, with good reason, as “torture boards” but do produce a more accurate profile.

    4. After fairing of the plug some low spots will remain after which it is more economical in man-hours to apply a soft, readily-sanded putty (eg Easy Sand) to the low areas, rather than reduce the entire surface to the lowest level. Before applying the putty, sand low areas lightly to ensure adhesion.
    5. It may be necessary to revert to 3.2 depending on the build-up required. It is suggested that Easy Sand be used as it will have better adhesion to the sub-surface.
    6. Apply “torture boards” to the cured putty, repeating the process until all low spots have been eliminated. Check the plug dimensionally and visually with good lighting to make certain that large errors have not developed, which is easily done when “chasing down” a low spot.
    7. Produce a maximum allowable radius on convex corners by sanding. Concave corners can be achieved by the following:

      (a) Applying microballoon putty with a ball bearing silver-soldered to a rod.

      (b) Rubbing in FGI modelling clay, which can be done last as it does not react with gelcoat and need not be coated.

      Large radii, eg 12mm and over, make the laminator’s job much easier, minimises rejects and reduces chipping of corners on moulds and products. This applies particularly to clinker hulls where it is very easy to leave bubbles in the total length of clinker.

  4. PATTERN FINISHING
    1. The pattern can be sprayed with
    1. (a) 2 pack sterling polyurethane

      (b) Ramanel finish coat Refer separate data sheet for application techniques.

  5. PATTERN SURFACE PREPARATION
    1. Apply T.R. Extra Heavy or Heavy Duty cleaner with a machine buff, taking care not to burn the surface finish.
    2. Apply T.R. Sealer Glaze Cleaner, at least two coats with a machine buff, taking care not to damage previous coats.
    3. Apply 3-4 coats T.R. Wax.

    The pattern is now ready for mould construction. Refer to FGI data sheet “Fibreglass Mould Construction”.

 

To the extent permitted by law and subject to any implied warranties under the Trade Practices Act 1974, we make no warranties and representations, express or implied, as to the description, merchantable quality or fitness for purpose of the goods described or the care and skill of any services provided. If any implied statutory provisions apply, to the extent that is permitted by law, our liability will be limited at our option to:

(a) In the case of supply of goods:

(i)         The replacement of the goods or supply of equivalent goods;

(ii)         The payment of the cost of replacing the goods or acquiring equivalent goods; or

(iii)        The payment of having the goods repaired or the repair of the goods;

(b) in the case of services:

(i) The supply of the services again; or

(ii) The payment of the cost of having the services performed again.

To the extent permitted by law, we will not be liable for any loss, damage, expense, injury or death sustained or incurred by a customer or any other party resulting directly or indirectly out of:

(i) The supply,  performance or use of any goods or services;

(ii) The breach of any agreement between us and a customer; or

(iii) Our negligence.

Please contact soli solutions for farther information