AmetekHaydonKerk AmetekAMS

Leadscrews - Nuts

Is lubrication required on the leadscrews?
No. The self-lubricating polymers that we use are designed to provide adequate lubrication with no external greases. The leadscrew and nut assemblies are designed to require no maintenance. If additional lubrication is needed, we offer 2 types of TFE coatings, Kerkote® and Black Ice™. Please consult the factory for more information.

What material are the leadscrews and nuts made from?
Generally, the screws are rolled from 303 stainless and the nuts are made from self-lubricating polyacetal. Other materials are available on a custom basis. For screws, we have used 316 stainless, aluminum and steel. For nuts, we use our Kerkite® material, PEEK, Ertalyte®, and other custom materials to meet various environment and performance considerations

What are the benefits of the TFE coating?
The Kerkote® coating increases nut life 3 to 4 times, it reduces friction between the nut and screw from .15 to .09, increases efficiency by 10% to 20%, improves smoothness and can reduce or eliminate noise. 
Black Ice™ coating provides the benefits of Kerkote®, but is a hard coating suitable for harsh environments, clean room applications and wash down applications.

Are the leadscrew assemblies clean room compatible?
This depends on the class clean room the leadscrew will be used. It's acceptable to use most lead screw assemblies in a class 1000 clean room with no modifications. When using a TFE coating, Black Ice is specially designed to be used in these environments.

Can the leadscrew assemblies and slide products be used in a vacuum application?
It depends on your system requirements. Information is available for the standard acetal material used to indicate the weight reduction over time at certain temperature and vacuum. Since we have the manufacturing flexibility to make the nuts from various materials, it may be possible to use the materials that are known to be acceptable in your application and ensure compatibility. Please consult factory for more details.

What is backdriving?
Backdriving on leadscrew assemblies is the ability of a screw to be turned by a thrust load applied to the nut. Backdriving can occur when the tangent of the thread lead angle is greater than the coefficient of friction. Since this is difficult to measure, a good rule of thumb is that a screw will backdrive when the lead is greater than 1/3 the diameter on a non lubricated screw and greater than 1/4 the diameter on a lubricated screw.

Can Leadscrew Assemblies be used in harsh environments?
Since the Haydon Kerk leadscrew assemblies don't have any rolling elements, they are forgiving of many dust and dirt environments. The sliding friction allows operation in tough conditions such as paper handling, wood and metal routers, engravers and food processing. 

How much life can I expect from the assemblies?
For anti-backlash nuts, life is generally defined as the ability for the nut to compensate for wear. Otherwise, on a general-purpose nut, its defined by the amount of wear that can be tolerated before the nut cannot hold the intended load or the clearance that develops is objectionable for the accuracy of the system. Life can be improved by the different nut styles we offer. 

What is the straightness of the leadscrews?
Our standard straightness for all screw up to 4 feet long is .003" per foot. We can hold a tighter tolerance and in some cases up to .001" per foot depending on the diameter and length. 

What is the maximum speed of the leadscrews?
Maximum speed is related to standard critical speed graphs. It is based on the diameter of the screw, the bearing end supports, and the length of unsupported screw. A convenient chart can be found in our catalog and on our web-site. 

What is the design load rating of the nut?
The design load rating of the nut is the axial force applied to the nut during operation. The maximum force consisting of the mass being moved, while considering the effect of acceleration and deceleration, should not be exceeded. The design load rating relates to nut life, anti-backlash, and wear compensation

What is the standard operating temperature range of the assemblies?
Our standard temperature range is 32F to 200F (0 to 90C). For applications where your temperature will be higher and lower than this, other materials are available to meet your requirements including Kerkite which can be used in a -50C to +150C temperature range. 

How do you secure something to a threaded nut?
The best way to ensure a secure connection between the threaded nut and what it’s being mounted to is through mechanical interference. This means applying something to the nut that secures the two pieces together and prevents them from backing apart. The common method to do this is to use a pin as shown in the picture below.

Haydon_Kerk_Threaded_Nut

Once the two parts a screwed together the pin prevents them from coming apart without interfering with the motion of the nut on the lead screw.   

What type of lubricate do you recommend for uncoated screws?
This depends upon the nut that is being used with the screw. If you are using a KHD, VHD, WDG, or NTB nut it is not recommended to a grease because it can actually cause the nut to bind. If you are using a CMP, ZBX, XBA, BFW, or NTG nut, Lubriplate ES-DS has been tested to show that there is no negative impact on either the nut material or screw. There may be other lubricants out there that will work, but only the ES-DS has been tested by Haydon Kerk.   

How much does a lead screw weigh?
This depends upon the lead screw and its characteristics. Our typical lead screws are made from 303SS, which has a density of 0.289lb/in3. So if you find out the volume of the lead screw and multiply by its density it should give a very good close approximation of the weight. For the diameter of the lead screw use the average between the Outer Diameter (OD) and the Root Diameter (RD). So:

Haydon_Kerk_Weight=Volume

As an example for a ¼ inch, 0.1 lead, 8 inch screw:

Haydon_Kerk_Leadscrew_Table

 Haydon_Kerk_Leadscrew_Calc

How does the efficiency listed for the lead screws translate to my application?
The efficiency listed in the catalog is based upon a lead screw with our Kerkote® TFE coating. It can be used to calculate the minimum torque required to move in the system. 

         Torque to move                
    Haydon_Kerk_Torque_Equation          

The torque required to move the nut in the system will help with motor or drive selection for the application. 

Your catalog specifies “dynamic load” what does that mean? Dynamic load in short is the maximum load that a specific type of nut can handle and still function properly.  Depending on the orientation and acceleration of the application, it can change the maximum load that a specific application can safely handle.  Things to consider when estimating the dynamic load of the system are: vertical or horizontal orientation, motion profile, and the mass being moved.    

My application has a higher load than any of the Haydon Kerk standard nuts specify.  What are my options?
Every application is different, but we have materials that can handle up to 2x our standard load.  If you application is near these parameters, please call and speak with an applications engineer to make sure that the proper material choice is made for your specific application.  

I have a unique environmental condition for my application.  Do you have a nut material that can meet my need?
Haydon Kerk has made nuts for many different unique environmental conditions over the years.  We have materials that can handle vacuum, temperature swings, high load, high PV, chemicals, FOD, and healthcare environments.  If you have questions about which material is correct for your application please call us and ask to speak with an applications engineer about your specific application.

What is PV? 
PV is better known as Pressure Velocity.  This is a key characteristic in determining the correct material for a leadscrew application.  The PV of an application is defined by three key characteristics, Applied Force, Area force is applied to, and Linear Velocity.  Knowing these three parameters we can calculate the estimated PV of the system, and if we include the duty cycle, we can get a better idea of whether the PV will be a Peak number or an average number.  We can change decrease the PV of the system by increasing the diameter of the leadscrew, or we can change material to a higher PV threshold.  If a plastic meets or exceeds it’s PV threshold if will begin to flow and fill voids in the threadform, which will cause the nut to seize.