While there are many ways to ensure that your roll forming system or tube mill is as efficient in production as possible, it's a universal truth that when your machines aren't running, you are not making money. And the longer the changeover, the more production time (and profit) lost. One of the most notorious threats to achieve short changeovers, as you may know, is exchanging the rolls to produce a different profile or product. A different method of changeover known as rafting can significantly decrease changeover time and keep your machines up and running for more hours a day. In this post, we'll explain the basics of rafting for roll forming or tube mill efficiency and the benefits of using a spare raft set during changeover.
What is Rafting?
The concept of rafting in roll forming machines and tube mills involves adding mechanical components to your machines so that your team is able to change a group of roll stands at once, instead of switching out rolls, one at a time. Effectively, when you use a rafting changeover method, you can change your tooling offline — without shutting your machine (i.e. your money maker) down.
By mounting the new tooling on a spare, removable subplate, called a "raft," you can prep for changeovers in advance while the current product on the line is still running. When your machines are set up to handle these removable spare rafts, you'll only need to shut down production once the spare roll stands have been prepped on the raft.
The Benefits of Rafting
The biggest benefit of rafting, as opposed to not using a rafting method during changeovers, is the possibility of offline assembly. While your current product is still running online, your team can prepare the next raft in advance. This can cut down your changeover time by a large percentage. As an example, if changing 16 rolls individually takes four hours of downtime, changing four raft sets of four roll stands each could theoretically take only one hour or less. On a traditional driven stand design, where the outboard housing must be removed first in order to remove the roll tooling, this process is incredibly time consuming, especially in large mills with multiple stands to change.
Rafted changeover represents a huge gain for your mill in terms of productivity, especially when you realize that you can still be producing products while the rafts are being setup (offline). For many roll forming machine and tube mills, these steps toward a quicker tooling change are invaluable when it comes to increasing daily efficiency and throughput.