IMTEK External Circulating Ball Screws
An external circulating ball screw is a type of ball screw in which the recirculating balls move outside the ball screw nut body through an external return tube (or pipe) before re-entering the ball track.
IMTEK ball screws can provide high positioning accuracy and repeatability, and it can move smoothly and stable together with a long service life. Highly efficient ball screws are absolutely a good solution for kinds of different applications.
Typical Applications of External Circulating Ball Screws：
- CNC machine tools (large travel axes)
- Industrial lifting systems
- Injection molding machines
- Heavy-duty automation equipment
How Does External Circulating Ball Screws Work?
External circulating ball nut has holes connecting to a return tube fixed on the nut’s outer surface. Balls roll along the helical groove between the screw shaft and nut. When reaching the return hole, they exit into the external return tube. The tube leads the balls back to the starting point of the ball track. The circulation repeats continuously, enabling smooth, low-friction linear motion.
Key Features of External Circulating Ball Screws:
1.High Load Capacity – Supports more balls in contact, making it suitable for heavy-duty applications.
2.Efficient Recirculation – Allows long lead (large pitch) designs since the return path is external.
3.Easy Customization – Return tubes can be designed for different lead angles and nut sizes.
4.Durable – Since the balls travel in a larger loop, the design reduces stress concentration.
IMTEK Ball Screws Technical Data
- Nut Design
- Lubrication
- SFVR
- OFVR
| Type | Nut Model | Features | |
| Single | Double | ||
| External circulation | SFV; | OFV | 1-Economy; 2-Suitable for larger lead and diameter; 3-For high loading purpose. |
Adequate lubrication is absolutely needed when using ball screws because insufficient lubricating will result in increasing friction and detrition, then cause failure or a shorten service life.
There are two main lubricant types: consistent grease and lubricating oil.
Consistent grease will increase the dynamic friction torque linearly together with increasing rotated speed. Generally, oil lubrication is a better way than consistent grease when speed exceeds 3-5m/min.
| Model | SFVR |
| Nominal Model | S(Single Nut) |
| Flange or not | F(Flange) |
| Nut Type | V type nut |
| Thread Direction | R(right)/L(left) |
| Length of Shaft | 100~6000mm |
| Diameter(φd) | 12; 15; 16; 20; 25; 32; 40; 50; 63; 80; |
| Lead(l) | 5/10; 10; 4/5/10; 4/5/10/20; 5/6/8/10/25; 4/5/6/8/10/20; 5/10/20; 5/10/20; 10/20; 10/20/20 |
| Diameter of Ball(Da) | 2.5/2.5; 3.175; 2.381/3.175/3.175; 2.381/3.175/3.969/3.175; 3.175/3.969/4.762/6.35/3.175; 2.381/3.175/3.969/4.762/6.35/6.35; 3.175/6.35/6.35; 3.175/6.35/9.525; 6.35/9.525; 6.35/9.525/9.525 |
| Accuracy of Grade | C3/C5/C7 |
| Preload | P1/P2/P3/P4 |
| Load Rating Ca (kgf) | 661/623; 972; 931/1614/1008; 1247/1814/1518/764; 2017/2711/3466/3040/843; 1517/2249/3079/3962/5620/3509; 2468/6316/3935; 2698/7023/7336; 7860/8162; 8593/15103/22423 |
| Load Rating C0a (kgf) | 1316/1241; 2020; 2285/3662/2161; 3584/4650/3398/1758; 5884/7268/8776/6547/2199; 5806/7612/9575/11547/14649/8644; 9586/18600/10893; 12053/23537/19700; 30430/24741; 38344/57296/90719 |
| Nut Material | 20CrMo |
| Shaft Material | S55c Alloy Steel |
| Model | OFVR |
| Nominal Model | O(off set double nut) |
| Flange or not | F(Flange) |
| Nut Type | V type nut |
| Thread Direction | R(right)/L(left) |
| Length of Shaft | 100~6000mm |
| Diameter(φd) | 16; 20; 25; 32; 40; 50; 63; 80 |
| Lead(l) | 5; 5; 5; 5/10; 5/10; 10; 10; 10 |
| Diameter of Ball(Da) | 3.175; 3.175; 3.175; 3.175/6.35; 3.175/6.35; 6.35; 6.35; 6.35 |
| Accuracy of Grade | C3/C5/C7 |
| Preload | P1/P2/P3/P4 |
| Load Rating Ca (kgf) | 1614; 1814; 2017; 2249/5620; 2468/6316; 7023; 7860; 8593 |
| Load Rating C0a (kgf) | 3662; 4650; 5884; 7612/14649; 9586/18600; 23537; 30430; 38344 |
| Nut Material | 20CrMo |
| Shaft Material | S55c Alloy Steel |
IMTEK Ball Screws Specifications
Selection Procedure
When choosing the right ball screws for your application, kinds of details are needed to take into consideration. This Procedure show you clearly about the main specifications needed, such as the load capacity, the maximum walking length, critical speed, etc.
Summary Selection Checklist：
1.Define load & travel conditions of ball screws
2.Choose precision grade.
3.Select lead (pitch) of ball nut based on speed vs accuracy.
4.Calculate life expectancy (L10).
5.Verify critical speed.
6.Check buckling load safety.
7.Decide ball nut style & preload.
8.Apply proper lubrication and sealing method of ball screws.
Nominal Model Structure
Please check and confirm the nominal model code of IMTEK Ball screws with us if you have specific requirements but you can tell what you really want. Your demand for the efficiency of ball nut’s mounting space, longer service life and a good performance should possibly be considered when selecting number of turns.
Professional Selection Procedure
- Focusing on Practical Engineering and Application Needs
1.Define Application Requirements:
load type and load capacity; Duty Circle of ball nut; Installation place and other environment requirement.
2.Determine Precision Grade
C0 – C3: Ultra-high precision (CNC, semiconductor)
C5 – C7: General machine tools, industrial automation
C10: Low precision, positioning not critical
External circulating types are usually chosen for C5–C7, suitable for heavy-duty and long-travel applications.
3.Select Lead (Pitch)
·Small lead (fine pitch): High positioning accuracy, low speed
·Large lead (coarse pitch): High speed, fast travel, heavy load handling
External circulation allows large lead ball screws, which internal systems cannot easily handle.
4.Calculate Load Capacity
Use basic dynamic load rating (Ca) and life equation:
Ensure safety factor is applied depending on shock load and duty cycle.
5.Check Critical Speed of Ballscrews
Must ensure operating speed < 80% of critical speed.
6.Ball Nut Type & Return Tube Design
Standard external return tube: for general heavy-duty use
Custom return path: for large-lead applications
Consider preload level to minimize backlash:
- Light preload: smooth, low torque
- Medium preload: improved rigidity
- Heavy preload: high stiffness, reduced vibration