Fiberglass and Plastic Molding

I would recommend making a plaster of paris female mold and lay the fiberglass into it. If you make a male mold then the outside would have to be ground smooth and that is hard to do. The latest in boat layup is having a female mold and use a rubber/plastic membrane using air pressure to form the fiberglass and resin into an even thickness throughout the mold. Many years ago I made an auto body by the male mold, over a form, and had a hell of time making the exterior smooth.

You can use clay instead of P of P if you prefer. One advantage of clay is that it can be dug out if the hot tub doesn't want to release from the form. Plaster of paris would have to be chipped out.

There are several steps in the process of forming the fiberglass part. They will be easier to understand if you were able to see it done. There is a spa outlet in Florence. It is just across the bridge on 43 on the left at the first traffic light. Their manufacturing facility is about 10 miles southeast of town. The owners name is Lee and he will probably let you visit the plant if you ask nicely.

What you can do is make the model as you want it in wood and plaster.

When it has the final form you copy the mould with fiberglass, this copy can be used as your mould.

If you need to show a more state of the art design process you can start modelling in a 3D solid modelling system and make the master through CNC milling. (your school must have this possibility, or know where you can do this)

The double process makes it easier to show the final result and evaluate it before going into the fiberglass. (you can try the tub, not filled with water of course)

As you can read in other replies: design your mould carefully, don't hesitate to call in specialists. It will bring you better results and you learn to build a network. Which is one of the best things an engineer can learn (the other thing is: open your eyes, everywhere)

Gwen

Just to add a helpful tip.... If you want to make an interesting shape, make it out of polyurethane foamand then cover it with GRP and smooth and polish that to make a test prototype. If it all works well, and you can take some good sales and marketing pictures of it, before modifying as necessary and then using it as a plug to make a mould to make the production examples.

see www.explorermarine.co.uk for the boats we build in GRP

Hugh Mattos

Chartered Engineer

Foam plates are also handy as you can build your model up in slices.

The thinner the plates, the better the result, the more work you have.

You can plot sliced cuts from the solid model in real scale and use a coordinate cutter to make the plates. It looks fancy on your presentation of how you did the project. (never forget: you need to impress the jury)

Gwen

Yes it looks very smart if you can make the project up in 5mm or 10mm sheets - each profile cut to CAD drawing.

However, we use 50mm and 100 mm sheets to make our console and seat mouldings and then hack at it with wood saws and knives, before hand sanding and finishing.

This is much quicker for a pleasing result - but you will not earn so many marks on your college project.

Your choice!

Hugh Mattos

Chartered Engineer

It is a decision you have to make: the details out of thin plates and the body in thicker ones.

I am looking for a plastic mold for draining cheese. the container would have to be about 9 inches high with the container being wider at the mouth. The container would have holes to drain the chees.

#2 has the best advise. Go to a shop where they do fiberglass and get a crash course on the use of fiberglass. Next do not design your plug with any over 90 deg places as when the fiberglass is set you won't be able to pull your part. When makeing your plug, finish it to a glossy finish as any irregularities or scratches in the surface of the plug will show in the finished product. The outer shell could just as easily be made of fiberglass as well ( can the plastic idea). This will need to be a male mold (good surface to outside of part) where the inside of the tub will need to be a female plug (good surface in). Any places for nozzels and stuff like that, can be made of clay and added to the plug, that way if they don't want to pull nice they can be torn off of the plug and removed from the part when you are cleaning it up. Get help from someone that knows the business.

As a builder of fibreglass boats I would strongly recommend that you visit a production facility of any fibreglass product and ask for a day of instruction - or better still offer to take a part time job with them

Fibreglass is as much art as scince. Always have a good screw thred "pushout system" in the mould, but the most important thing is to have excellent - not just good - surface finishes on the moulds - we spell it that way in England - and then to use a set of suitable release agents to ensure that the two parts release from eachother. Expect to sand the mould with a high speed dual action sander to a 2400 grit finish and then either wet sand with a finer grit wet abrasive or we use a medium speed electric polisher - as you would find in a car repair shop - with very mild abrasive cutting compound.

We have wasted hundreds of hours, and thousands of pounds / dollars of goods when some one has missed off the correct release process - and sorry, the first molds are the best at sticking and destroying themselves. If possible, and it rarely is, wait for 30 days between finishing the mould and making the first item, or else warm the mould in a gentle oven to speed the curing process. Release is much more reliable on a cured mould. We have used 20 different release agent processes, some release well and leave a poor finish, most that leave an excellent surface are less reliable or harder to apply. We currently use a very expensive Australian release fluid ( as in 300 dollars per gallon) but it works every time.

If you have a Crownline boat dealership near you they have an excellent video showing much of the process. They may even send you a copy.

Hugh Mattos

Chartered Engineer

By the way we make our plugs in fibreglass as well since that is more successful than plaster or clay for large items.

THANK YOU FOR ALL THE INFORMATION. i WILL DEFINETELY CHECK INTO THE FIBERGLASS COMPANY. wOULD FIBERGLASS BE STRONG ENOUGH FOR THE OUTSIDE SHELL INSTEAD OF PLASTIC?

I am not entirely certain where you are expecting to support the load, but fibreglass - GRP - will support any load if you lay it thick enough - look at some "mechanical properties of solids" tables. If I can make a boat transom support 500 kg and 600 horsepower of engines and 3 tonnes of boat, at 60 miles per hour in rough seas, then I suspect you may be able to support a tonne of water.

Look at a conventional bath tub. The GRP is less than 3 mm thick - note it is often covered on the smooth inside by a 0.5 to 1.0 mm layer of clear acrylic to improve the cleaning and surface finish. The weight of the water is held up on a bonded wood board which is held up by usually five thin legs which give clearance for the plumbing pipes underneath.

Unless you have some inspiration, most good design is evolutionary rather than revolutionary, so go and look at your competitors to get some ideas.

Hugh Mattos

Chartered Engineer

reply to fiberglass and molding strength all the polyurethane will work but you need to plastic the tub . 1 lost of Polyurea ,2 wight ,3 pulse ,4 materials ) buy using a recyclable closed cell foam you can use any thing for a mold as for support it is beast to use a compress plastic low in cost polyurethane floor . to support over 800 lb go with poly wood or comprised polyurethane .if this can hold up a floor in a house it will work for you

EXspantion foam co.ltd

japan

Look in the library: Boat Building, Stage Craft, Fiber Glass, Tub and Shower, Auto body repair.

Try these websites:

ACMA, SPE, Cast Polymer Assn.

Find in your local yellow pages: Boat Builders, or, Boat Building Supply, or, Fiber Glass, or, Tub and Shower (manufacturers).

Wear old clothes, masks, goggles and rubber gloves. You will make mistakes.

Bob

I suggest you go find a used fiberglass bathtub and "chop it" to fit your requirements. This would be faster and easier than starting from scratch.

I am looking for a plastic mold for draining cheese. the container would have to be about 9 inches high with the container being wider at the mouth. The container would have holes to drain the chees.

I am looking for a plastic mold for draining cheese. the container would have to be about 9 inches high with the container being wider at the mouth. The container would have holes to drain the chees.