It’s time now to examine the overall pros and cons of climbing on board rafting as a tube mill quick-change design compared with the still-popular conventional method for producing brand new tube shapes and sizes.
For a tube mill, quick-change means adjusting or exchanging the necessary tooling, i.e. rolls, to make a new tube with a different wall thickness and/or outside diameter (OD). The conventional method takes about 60 minutes. As noted in Part 2, with automated universal shaft disconnects and raft handling systems, changeover times of 15 minutes or less are possible.
This much speedier rafting time is very attractive, but there are pluses and minuses, and they should be weighed based on each individual situation. A most important factor is changeover frequency, which can range all the way from just once a month to as much as once a shift. Three shifts per day means fifteen changeovers per week, a good recommendation for rafting by any stretch of the imagination!
But three shifts per day is not everybody’s changeover experience, by any means, and buying a spare raft set is definitely not always a necessary investment for a less active quick-change group.
However, if you are purchasing a new mill and have expansion motives, you should certainly adopt rafting. The upfront cost to supply raft plates is small compared to the cost of the entire mill itself and, furthermore, the cost to upgrade later is going to be considerably higher. In other words, the sooner the better. Timing is everything.
Stefan Emunds
“Time is an illusion, timing is an art”
