In the most basic rafted mill design, the universal drive shafts are simply disconnected manually by the mill operator prior to exchanging the rafts. When the rafts have then been physically exchanged, the operator again manually reconnects the universal shafts. Some argue that this process alone takes as long as the exchange of the roll tooling on a conventional mill; however, with the use of "quick-disconnect" universal shafts that require no tools to remove, the time is greatly reduced. In this post, we'll discuss universal shaft quick-disconnect and how it can improve changeover in tube mills.
The Concept of Quick-Disconnect
The automation of this universal disconnect procedure has successfully been done in a number of ways. The difficulty surrounding the automation centers around the fact that the top roll shafts (and in some cases the bottom roll shafts) on the driven stands are invariably set at different positions from raft to raft. This condition requires that any automated universal disconnect system must be able to account for these differences and be adjusted accordingly.
One type of automated universal shaft disconnect system utilizes an intermediate or "third" stand to support the roll stand end of the shaft while the raft is being moved. The image below shows the sequence of operation for reconnecting the universal shafts to a newly placed raft. Once the raft is positioning on the mill base, the top universal shaft must be positioned to match the incoming position of the top roll shaft. When the positions are matched, the raft can be shifted to engage the drive couplings.
This is only one method that can be employed. Other methods disconnect the universal shafts from the gear reducer side and make them part of the raft assembly. In other words, the universal shafts move with the raft. The advantage being the gear reducer side of the universal shaft never changes position because the center-to-center distance of the gear reducer shafts never changes. This fact mades the automation of the system much easier. The disadvantage here is that now each raft has the added cost of universal shafts; however, this cost could be offset by the simplified automation requirements.