Construction Technique

As a group, the Walthers steel mill kits are relatively easy to assemble. In the case of the blast furnace and coking ovens, they are larger kits with more assemblies to produce, so more time is required, but the same skills apply.  There are two techniques which will make your work look better and that will make your resulting work stronger.


All of the Walthers steel mill kits have “H” shaped girders which are attached to flat surfaces.  In the case of the rolling mill and the electric furnace, almost the entire assembly is devoted to girders. Here, the rolling mill, which has been built as a backdrop structure.

In the above example, the rolling mill has been built as a “false-front” structure, designed to act as a backdrop to the model railroad scene. During construction, the various girders and panels are joined together to produce a support frame for the walls and roof of this structure. By themselves, these girders are flimsy and flexible.  Once the girders are mounted to wall and roof panels, the resulting structure becomes considerably stronger because both the girders and the walls form a strong box structure.  The problem is that the girders need to be “dressed” before assembly.

This issue is the result of the manufacturing of the girders themselves. The injected plastic molds used are meant to keep production costs low, keeping these kits at an affordable price. The girders are cast in a two-part injection mold, which produces a girder with a slight “hump” on the flat surfaces which are to be glued to the structure walls; this slight hump being a result of the draft angle of the mold.  Consider this rough sketch:

On the left girder, the excess plastic of the girder edge caused by the draft angle is shown. If you are using a tube glue, which has plastic solids in solution, you can simply “butter” the edge with glue and place it into the receiving slot of the walls and roof.  This will not be as strong as if the girder surface is flat. If you are using a solvent glue such as Micro-weld, Tenax or such, the resulting joint will be very weak because the glued surfaces are very small.

Leveling the surface of the H-Beams will create a stronger joint because there will be more surface area for the two parts to be joined together. With two flat surfaces for joinery, the liquid adhesive will flow into the joint by capillary action, melting the two pieces and producing a strong joint.

There are several ways that you can clean up the girders.  Certainly sandpaper will do it, but using a rigid tool such as a mill file (a big one, not a tiny modeler’s file) or the back edge (not the cutting edge) of a modeling knife will work faster and better.  Because these are rigid tools, you get a more level outcome than from sandpaper held in the hand.  A sanding block will also help.

Mill file (middle)

Modeling knife (orange handle)

Personally, I use a cabinet scrape, which is a flat piece of metal with a slight hooked edge. Whether with a mill file, knife edge back or scrape, the process is the same.  You draw the tool over the raised area of the girder, clearing away just enough material to create a flat surface for the adhesive to join the parts. It will be a messy process, with the knife blade back or the scrape producing tiny shavings of scrap plastic. The mill file creates plastic dust.  Although this might seem to be unnecessary extra work, you will find that the results will be better and more satisfying, producing a stronger structure.

The classic Xacto® knife blade can also be used as a scraper. The back edge of the blade tip can also be used to scribe light lines in plastic. The cutting edge of the blade can also be sharpened with sandpaper or a sharpening stone so you get longer use out of each blade.

Cylinders & Tubes

The blast furnace, in particular, has a large number of cylindrical shaped parts.  These parts are comprised of two half sections which must be glued together and then assembled into the final structure. Consider this photo of a section of the Walthers blast furnace:

Note the different cylinders of the dust scrubbers, the stoves and the furnace itself.  All were made by joining two half cylinder parts together to form one completed part.

In most cases, joining the two parts together leaves a visible seam that must be cleaned up for a proper appearance. Any gaps or sunken sections are filled with green putty, sanded smooth and then primed.

It is helpful to put masking tape on each side of the various joints being filled and sanded. Doing so helps avoid damage to the surrounding details (such as rivet details and the like). Prior to applying the filler, the masking tape protects the final piece by limiting how much filler putty is applied to the assembly. Once the putty has dried, the tape protects the balance of the assembly while the putty is sanded and smoothed down.  If necessary, you can also scribe lines that were accidentally filled with the putty. Once the work is complete, the tape is removed.

Once the glue had dried, I would look for any further obvious gaps or rough edges and clean them up. I then applied a coat of gray primer (above). After this primer coat had dried, I inspected the seams for any further problems, cleaned them up and primed again.  Once the time for final assembly came, I cleaned the paint off of the areas to be joined so that the adhesive would work properly, assembled and then let things dry thoroughly.  After that, the final paint colors were applied and the kit completed.

Plastruct Friendly

In the instructions with the blast furnace and the coking ovens, it is mentioned that these kits are “Plastruct friendly”, which is to say that you can expand these kits with additional pieces of Plastruct shapes, tubes, valves and such.  In these cases, many dimensions in the injected plastic Walthers kits are the same as the dimensions of Plastruct parts. There are several examples:

Blast Furnace High Line

The Walthers kit includes a short length of “high line”, a girder support for tracks where hopper car loads of coal, coke and limestone can be unloaded and fed into the blast furnace. In general practice, the high line is much larger than what is included in the kit, and this section of the kit can be expanded by using Plastruct girders. Further, the bottoms of the support columns can be improved by adding a Plastruct item called a column base mount, which makes the columns look more realistic.

To the left is the kit-built high line.  The base mounts were added to the support girders and the final high line was expanded in each direction by a total of 48”€¯ using girders, mounts and handrails.

The Outside World

The Walthers blast furnace kit and the coking oven kits have points where additional piping can be added to connect the facility to other steel mill structures.  In the case of the coking ovens, the manifold pipe from the coking batteries can be extended to a coal tar processing facility. Each individual battery prepares the coke from coal; one of the byproducts from this process is coal tar gas, which is collected and then turned into ammonium sulfate fertilizer and other chemicals. In the as-built kit, this pipe merely opens up to the atmosphere, but you can use Plastruct  tubing and fittings to connect it to a collection tank. Plastruct girders can also be made into pipe supports and such.

In the case of the blast furnace, there also are two open connections that could use the help of Plastruct parts and your imagination.  Here is the area around the scrubber of the blast furnace:

The blast furnace requires waste gas, combined with the coke fuel, to provide the heat necessary to make pig iron. The waste gas input is shown in the diagram. Also necessary is the pressurized air necessary for the “blast” in blast furnace. Since these notes were originally written, Walthers has introduced a Blower Engine House (No. 933-2957) and a piping kit (No. 933-2958) to complete this connection for the blast furnace.

Even if you don’t model the blower building necessary for the air blast because of space limitations, you can extend the piping away from the Walthers kit to an imaginary blower building which is off-scene.