Boxes and Trays Fabricated from Fluted Plastic Using Hot Melt Rivets
Channeled or fluted sheets of extruded polypropylene/polyethylene have been used in the museum because of their chemical stability and versatility.
Commercial box companies have developed die cutting and folding machinery, and various fasteners to fabricate an array of containers from this material. Every year, a wider range of box sizes is available. Typically, however, container requirements in museums are too varied in size and number to be able to locate affordable ready-made sources.
Therefore, in-house, customized containers must be made. To do this economically requires techniques that employ a minimum number of fabrication steps and tools.
Polypropylene is not easily joined with adhesives and industry employes a wide range of mechanical systems. For in-house box making, it is not always easy to find suitable fasteners. The technique described here provides a viable option to the museum container fabricator.
Canadian Conservation Institute
1030 Innes Road
CANADA K1A 0C8
Tel (613) 998-3721
Fax (613) 998-4721
Illustrator: Carl Schlichting
Channeled or fluted, extruded polypropylene/polyethylene sheeting is cut so that it can be folded to form a lidded box or tray. The container is folded and sides and corners are joined with hot-melt rivets (Fig. 1).
Figure 1. Polypropylene/polyethylene fluted plastic box. Three hot melt rivets have been completed, and
the fourth is clamped while the adhesive sets.
Materials Tools Supplies
- Corrugated cardboard (for pattern)
- Glue gun with hot melt adhesive sticks 8in refill white resin
- Pencil, soft-leaded
- Polymethylmethacrylate squares or thick mat board
- Polypropylene/polyethylene, 4mm channeled/fluted extruded sheeting
- Silicon release paper
- Spring clamps (hand clamps)
- Steel wool, coarse
- Utility knife
- Wood rasp
- Develop the pattern for the box using corrugated cardboard (Fig. 2). Using similar thickness cardboard helps determine where fold lines should be on a complicated box pattern.
Figure 2. Develop a corrugated cardboard pattern and trace the pattern onto the plastic fluted sheet.
- Mark the pattern onto the polyethylene/polyethylene sheeting with a pencil, and cut it out using a utility knife (Figs. 2, 3).
Figure 3. The pattern is cut out of the plastic fluted sheet.
- Cut the fold lines on the reverse side of the pattern by cutting through the top flute skin. When cutting across the flutes, the cut should be about halfway through (Fig. 4).
Figure 4. The fold lines are cut both with and against the flute grain. The utility knife blade can be adjusted
to prevent cutting too deeply. Only the top skin of the plastic should be cut. The pattern is then turned
over and the sides are folded up.
- Turn over the pattern and fold the container sides up. Tape the joints together, leaving free space for the rivets.
- Prepare the glue gun by cleaning the cold nozzle with a flat wood rasp. Clean the hot nozzle with a thick wad of coarse steel wool. Use caution when wiping the nozzle if it is very hot.
- Hold the two layers of polypropylene together with one hand and place the index finger on the inside of the intended rivet location.
- Insert the hot nozzle slowly, letting it melt its way completely through one plastic layer, and only partially through the second layer by swiveling the gun back and forth. Do not force the gun through the plastic (Fig. 5). This procedure is not as dangerous as it may look. The point becomes too hot to touch, well before a burn occurs.
Figure 5. The hot nozzle is inserted until the lower channel is penetrated. Rotating the
nozzle helps to perforate the skins.
- When the index finger tip feels the heat, begin applying pressure to the trigger to let the molten adhesive flow into the channel closest to your finger.
- Lift the nozzle slowly from the hole while still holding the two layers together. Fill the hole as illustrated, taking care not to overflow onto the surrounding surface. It is not necessary to allow much resin to flow into the channel cavities (Fig. 6).
Figure 6. The flow of resin is started into the lower channel as the nozzel is slowly removed. The resin should fill
the spaces as indicated. Only a small bead of surplus resin should remain on the surface.
- Place a 1in square of silicone release paper over the molten bead of resin (Fig. 7).
Figure 7. The resin bead is covered with a scrap of silicon release paper. A small square of
polymethylmethacrylate sheeting or stiff mat board is pressed over the resin bead.
- Place a piece of polymethylmethacrylate sheeting or thick mat board over the paper and hold all the layers snugly together with a spring clamp (Figs. 8, 9). Move on to the next rivet while the clamped areas cool down.
Figure 8. Pressure is applied to hold the joint snugly. A hand spring clamp works well.
Figure 9. Additional rivets can be fabricated while other rivets cool. The finished rivet is smooth and flush.
- Allow a minimum of 15min cooling time before removing the clamps and paper.
The finished rivet is glossy and flush both inside and out. The joint strength develops as a result of the keying effect of the resin inside the channels. However, it is only as strong as the diameter of the portion that flows between the two sheets as indicated by the “x” in figure 8.
One rivet can withstand a surprising amount of stress. Insert additional rivets if a high degree of tension is anticipated. It should be noted that hot-melt glue is suspected of embrittling with age due to the loss of resin property modifying additives, although the time frame is unknown.
Eight-inch hot-melt resin sticks are the most practical for this construction. If long sticks are not available, simply glue shorter sticks together with a dab of the same hot resin. The medium strength, white sticks give the best finished look.
Schlichting, C. 1987. Coroplast box construction using hot-melt rivets. Textile Conservation Newsletter, (Fall): 7-11.