What is a Handbuilt Rubber Expansion Joint?

We have a great publication called "Expansion Joint Production. A Step By Step Guide". Should you never need an expansion joint, you might want to write for it anyway because the process is so interesting, but let's do what we can here. The illustration shows a typical cross section. The ends are normally rubber flanges that will mate with the piping system. The arch is the flexible element that allows for expansion, contraction transverse motion and misalignment. The sealing element is the rubber tube on the inside, and this is backed by multiple layers of fabric reinforcement. The straight portion is reinforced with steel wire and then fabric placed over that under the cover. While it is not absolutely mandatory, we find that the expansion joint holds up better if there are steel rings at the base of the arch to hold the arch shape. Since flange bolts would pull through the rubber flanges, we furnish steel back up rings. Ends can be built in weld nipples, slip on or any other mating arrangement. Regardless of whether the final shape is going to be round with a single arch, a rectangular ducting transition piece, elbow, tee or cross, eccentric or concentric reducer, or any other unusual shape, we start with a steel form that matches the inside steel contours of the finished product. This form or mandrel is mounted in a slow turning foot controlled lathe, and the builder proceeds as follows:

1. Place a solid rubber arch form in the correct position on the mandrel. (After the joint is finished and cured, this rubber piece is pulled out to leave the arch opening.)
2. Cover the mandrel and the arch form with the rubber tube.
3. Add multiple plies of rubber impregnated tire cord, which forms the backing behind the tube.
4. Slide the arch reinforcing rings on from the ends and complete the wrapping of the reinforcement materials around these steel rings and up over the arch.
5. Add the helical wire reinforcement.
6. Add the rubber filler between the wire rings.
7. Add the fabric reinforcement over the wire.
8. Bring the end fabric and rubber construction up vertically at the ends, and clamp these flanges between steel mold plates.
9. Wrap the assembly securely with Nylon tape to force the many layers together and maintain the shape during the curing process.
10. Place the wrapped product in a steam pressure vessel (autoclave) and cure it for about 3 hours until completely vulcanized.
11. Remove the steel flange rings, nylon tape, etc. Drill the holes precisely, in the rubber flanges. Add the steel or ductile iron split back up rings. Pack properly and ship to the jobsite. Handbuilt expansion joints are also referred to as handwrapped, because Nylon wrapping rather than a steel mold maintains the outer shape during the curing process.

Picture 1 – Pulling back cover, tire cord reinforcement and tube prior to building the flanges on an eccentric reducer.
Picture 2 – Checking steel wire reinforcement spacing. This guarantees consistently high safety factors.
Picture 3 – A range of products in the open autoclave before closing the door and steam curing for approximately 3 hours at 305° F.