What are self-locking lead screws?
This blog is to try and give people a greater understanding of what a self-locking lead screws are. This hopefully will help you decide if this is something you need in your application.
Read how to identify the right lead screw for your application here: blog.igus.co.uk/identifying-the-right-leadscrew-nut-for-your-application/
Let’s start at the beginning; what does the term self-locking mean?
What does “self-locking” mean in conjunction with lead screw technology? And what are the differences between high helix threads and trapezoidal threads? Let’s see if we can explain it as simply as possible.
Self-locking means that the lead screw nut and lead screw cannot be moved without external force. It has to do with the pitch and coefficient of friction. The self-locking ability allows the user to eliminate a costly brake in many applications, predominantly when the application is in a vertical orientation.
Single-start trapezoidal lead screw drives are self-locking. This means that the flank angle and the sliding friction prevent the nut or lead screw from moving without outside forces being applied. As soon as the static friction is exceeded, the components are no longer self-locking. Multi-start trapezoidal lead screw drives have a “residual self-locking” feature; high helix lead screw drives do not.
This GIF clearly shows that the pitch of the single-pitch trapezoidal lead screw is less than that of the high helix lead screw. The coefficient of friction of the two lead screw nuts is identical to those of the stainless-steel lead screws. As described above, the lower pitch means that the lead screw nut cannot move without external help.
Influences affecting self-locking lead screws
We need to look at whether or not the effect of self-locking lead screws can be externally influenced. For example, the coefficient of friction depends on correct combination of material, surface finish, lubrication and self-lubricating substances. Axial load and external influences also play a role in the efficiency and effectiveness of the lead screw and therefore need to be a consideration.
Using the correct lead screw drive is vital and it will always depends on the individual application. Here are some other examples of leadscrew applications https://www.igus.co.uk/info/lead-screw-units-applications-screw-drives
If you are unsure, please contact one of our experts!