Bends and shapes.
Styrene will bend easily but not retain a permanent bend unless glued or heated, and the temperature for the latter is quite critical. Too low a temperature and there will be no change; too high and the styrene will melt and become badly distorted. There are a number of techniques available and you will need to experiment to find the one that suits you.
There are a number of internet sites which recommend clamping the styrene sheet around a former and then dipping it in boiling water. This should work if the water is actively boiling, because the temperature at which the styrene begins to soften is 95°C.
Clamping the styrene around a former and then holding it in the steam from a boiling kettle or pan with the lid removed has worked. Take proper precautions so that you are not scalded by the steam.
Holding it in a vice and running a hand-held steam cleaner over it has not been very succesful.
Another method that has been used is heated sand. If you have ever worn glasses you will probably be familiar with the opticians’ little heated sand box when he, or she, has to reshape the arms of your glasses. Take an oven roasting pan, half fill it with sand, and place it in the oven. Use a food thermometer placed in the sand to obtain a temperature of about 240ºF (115ºC). The purpose in using the sand is to heat it to an even 240ºF. For this to be effective, your oven should have temperature control. Set it initially to, say, 350ºF to speed the heating. When the temperature of the sand reaches about 200ºF, drop the oven temperature to 240ºF. When the sand temperature is within a few degrees of 240ºF it should be uniformly at that temperature. You need to fasten your styrene to a former of suitable material and shape and then plunge it into the sand for a few minutes. Allow it to cool before removing it from the former.You will probably need to experiment with how you clamp the styrene to the former. The styrene expands more than the wood typically used as a former. The difference can be enough to create a permanent kink in the styrene if the clamps are too far apart or too tight. The main advantage of this method is that the temperature is even and predictable, and the styrene cannot get hot enough to start melting.
It should be obvious that you need to wear heatproof gloves (oven gloves) when handling the hot sand pan or styrene.
Hot moulding using a butane/lighter fluid/heat gun heat source.
BEFORE STARTING, ALWAYS KEEP A FIRE EXTINGUISHER AND A SUPPLY OF WATER AT CLOSE HAND. USE SAFETY GLASSES; ENSURE ADEQUATE VENTILATION AND NO ADJACENT COMBUSTIBLE MATERIALS!
Cut a panel of styrene (usually 1/16” thick) that overlaps the area where it is to be fitted by at least ½” per edge. This is usually the location where distortion occurs, and thinner styrene also seems to distort more easily.
Cut formers that replicate the internal dimensions of the finished panel. It is assumed most shaped panels will be for the front of superstructures. On small models, to scales around 1:75 and above, often the internal deck contact edge, contoured to this size is adequate; supplemented by a former that also fits to either the top or bottom surface. On larger models more formers may be required.
Gently warm up the styrene whist fitting it around the former. It may take several operations for this process to be completed. Once the general shape is achieved concentrate on the corners. The decreased radius there can be obtained by bending this area of the sheet around a suitable object such as a screwdriver shaft. This is also easier using a vice and pliers, which avoids burning your fingers.
This technique can also be used to make a mast shroud. Hold a length of wire of mast diameter in a vice and then heat it up. Once warm, a section of styrene can be wrapped around it and it will quickly take up the bend required to surround the mast.Whilst this technique sounds fairly crude, it has been found that the edge of the styrene is where any distortion will occur. Once the correct contours are obtained, trim the overlap off the panel which will usually remove the distorted portions. A belt sander helps to keep all the edges level.
Reverse (compound) contours can be made by making up parts for each contour and gluing together.
WIth any of the above methods, if you are lucky, or extremely skilled, the bend will be in the right location, in the right plane, and of the right radius. Chances are it will be “about right” and you will need to glue it to some correctly-shaped ribs to hold the correct radius in the correct location.
An alternative to the ribs, if it works for your model, is to make the former into part of your model, by glueing the styrene sheet onto the former. In this method, you need a former of the correct diameter or shape for your model.
If there are cutouts for windows or hatches, cut only the horizontal edges i.e. the edges that go around the bend, before forming the bend. Cut the vertical edges after bending. If you remove the complete cutout, the vertical edges are likely to buckle outwards.
If you need a very sharp bend, such as a corner with a shallow angle, use the P-800 knife to cut a groove on the inside of cold styrene, and then bend along the groove. Run glue into the groove to hold the shape.
If none of the above techniques is sufficient to create what you need, then maybe you need to try vacuum moulding. This method allows you to form some quite complicated shapes. It is probably of most value if you need to make several identical fittings, say of lifeboats on a passenger ship. It is outside the scope of this article to provide instruction on how to do this, but there is lots of information available in print and on the internet. It is possible to create moulded parts with some basic equipment. With a heat lamp as a means of softening the styrene, a shop-vac as a way of pulling a vacuum, and a homemade moulding box, Doug was able to replicate a cast part, as shown in Figure 6 on the next page.
As a general rule, 0.060” thick is good for decks, and 0.030” thick for everywhere else. Thinner or thicker material can be used for details, and structural sections as needed.
The best adhesives for glueing styrene to styrene are the Humbrol, Modelmaster and Tamiya liquid cements, the types that come in a plastic bottle with long metal nozzle. One of the advantages of this plastic cement can also be a disadvantage. The cement creates a weld by first melting the two pieces of styrene, and then allowing the weld to solidify. If used on styrene thinner than 1/32” (0.75mm) the welded portion will often show through as a shallow dimple in the thin material.
For glueing styrene to other materials, CA or epoxy work well. Other glues also state that they are suitable, such as Lepage’s “No More Nails” and polyurethane (such as “Gorilla Glue”). All have their advantages and disadvantages. These adhesives can also be used for styrene to styrene, avoiding the dimpling effect noted above, but the joints are generally not as strong. Beware of the “starved dog” effect, where the skin is sunken between any internal ribs. Lightly sand the styrene surface to provide the glue with something to grip onto better.
The basic structure for deckhouses and superstructures is a rectangular box. You glue four pieces of styrene together at the corners and you have a four-walled deckhouse. Even if the corner walls are perfectly formed at right angles, you will discover that the walls develop a slightly hollowed-out, concave shape as the adhesive hardens. This effect can be prevented by using thicker styrene, or internal bracing.
Almost all glues can form strings when you are applying the glues, and leave glue marks where you don’t want them. The best method for countering them is to remove your applicator (whether it’s a pin, a toothpick, or something else) vertically so when the string breaks it drops into the spot where you just applied glue.
Bondo Glazing and Spot putty for autobodies is good for filling small gaps and imperfections. It contains a solvent which will melt the styrene, and in most cases it will not be a problem, but care is needed if you plan to use a lot of putty on very thin styrene.
Some words of warning
Styrene has a high coefficient of expansion, meaning it expands more when it gets warm, than most of the other building materials we use. For example, let’s assume that you have a model which is 30” long, with a deck made from styrene glued to wood, and you build indoors where the average temperature is 20°C. If you take it outdoors where it is in direct sunlight and the model heats up to 50°C; then over the 30” length the styrene will expand 5mm more than the wood. Even if the model is in the shade, say on a hot day when it’s 30°C, the expansion is still 1.5mm. This might not seem like a lot, but if the wood and styrene are not firmly bonded together, then the styrene is likely to buckle in places. The expansion is directly related to the temperature change and the length. If the styrene parts are separate from the wood, and free to expand and contract independently of the wood, no problem. Also, if the wood and styrene are firmly bonded together, no problem. You must make sure they are firmly bonded, if you glue styrene to a different material.
CA glue and brittleness.
At least one modeller has reported problems when using CA glue:
“In most cases I use Medium CA for all my styrene glue joints. Never use Thin CA as it will make the styrene brittle as glass and will destroy thin 10mil sheeting on contact. I have no problems at all with Medium or Thick CA, or the use of a CA kicker.”
Effects of UV in sunlight.
Henkel, manufacturers of Loctite, make the following comment in their “Design Guide for Bonding Plastics”:
[Polystyrene grades] are susceptible to weathering and ultraviolet light degradation. Protective coatings or UV stabilizers are recommended for outdoor applications.” In our models, this typically means giving white styrene at least a coat of outdoor varnish.
Black styrene made by Evergreen Plastics states on the package that it is “UV resistant”, which the clear and white do not.
Lacquer paint caution.
Don’t use lacquer paints on styrene unless the surface is well sealed.
Confederation Marine Modellers