Ball screws are the most preferred linear motion control solutions that offer precision and efficiency in the industrial sector. They are considered an ideal solution for applications that need smooth motion, efficiency, accuracy, precision, and high-speed movement.
According to Extrapolate’s recent report, the global ball screw market size is projected to hit $2468.63 million by 2028. Learn more about ball screws, their components, the different types available in the market, and their advantages in this blog.
What is a Ball Screw?
A mechanical linear actuator that converts rotational motion to linear motion with minimum friction is called a ball screw. It has a screw shaft and a nut with a ball that rolls through the matching helical grooves.
These screws help transfer forces to a stationary or dynamic load with top-notch accuracy, precision, and repeatability. One of their unique characteristics is the rolling balls in the helical groove that minimizes the mechanical contact within the screw assembly and transforms sliding friction with rolling friction. This mechanism reduces the friction created significantly, resulting in efficient power conversion. The efficiency of screws is evaluated by its ability to convert power used in exerting rotational force to linear distance covered.
Compared to other types of screws, ball screws have a much more complex structure. Additionally, they also appear to be bulkier and are more expensive. However, they have immense benefits and capabilities that can outweigh the high pricing.
Components of a Ball Screw
The following are the components of these screw types:
- Screw Shaft: It is the main component of the ball screw assembly. It comprises helical grooves (threads) cut along its length. Screw shafts are also called lead screws or threaded shafts.
- Ball Nut: A component placed on the screw shaft consists of recirculating ball bearings. When the screw shafts rotate, the ball bearings travel along the grooves, causing the nut to move linearly along the shaft.
- Ball Bearings: Small spheres that roll between the screw shaft and the ball nut are called ball bearings. They minimize the friction and allow smooth nut movement along the shaft.
- Return System: Ball screws typically have a return system to recirculate the ball bearings from one end of the nut to the other. This return system ensures continuous smooth motion and prevents the balls from falling out of the system.
- End Supports: These structures support and guide the ball screw drive assembly. They help maintain alignment and prevent buckling of the screw shaft under load.
- Seals and Wipers: Seals and wipers are leveraged to prevent the ball bearings and other internal components from contaminants like dust and debris. They assist in extending the lifespan of the ball screw assembly by keeping it clean and lubricated.
Major Ball Screws Types
The categorization of these screws is based on the mechanism of their ball recirculation. Internal recirculation and external recirculation systems are the two groups of recirculating ball screws. Let us have a look at some major` types:
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Internal Ball Recirculation
In this ball recirculation mechanism, the balls reside on the nut housing during their recirculation. The ball nuts in this return mechanism are compact, as they do not have any external protrusions. Compared to the external recirculation systems; this mechanism creates less noise and vibration. The major reason for this is that the recirculation happens inside the nut housing. Following are the types that fall under this recirculation system:
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Deflector-Type
Deflectors are leveraged to lift the balls over the screw shaft’s diameter to redirect the balls back to the adjacent groove that served as their starting point. For every rotation, there should be one deflector to block the ball’s pathway. Hence, the number of turns is equivalent to the number of circuits for these return systems.
Deflector-type ball screws are leveraged for applications that need fine leads. The size of these screw types is compact, which makes it perfect for small clearance assemblies.
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End Cap-Type
End caps are placed to direct the balls through a tunnel within the ball nut. This redirects them back to their initial point. This design can endure the force from fast-moving balls, which makes it a perfect solution for high lead ball screw applications.
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External Ball Recirculation
The ball travels outside the nut housing during its recirculation in an external ball recirculation system. This system can be effective in fine lead ball screw assemblies and a vast range of screw shaft diameters. It is more affordable than internal recirculation and suitable for bulk production. The overall screwball size is based on this recirculation mechanism. The return pipe is the only ball screw type that leverages an external ball recirculation system.
Following are other classifications of these screws based on the fabrication method used for producing the ball grooves:
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Ground Screw Threads
The abrasion process is used to fabricate ground screw threads. An extremely hard abrasive cutter is used to carve out the metal to form the grooves, and the blank shaft is placed horizontally. The groove surface created is much smoother compared to the rolled screw.
The screws manufactured using this technique have high precision. However, they are slower in production and are more expensive.
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Return Pipe
The balls travel through an external tube sticking out on the ball nut’s wall. The return tube guides the balls back to their initial point. Fingers are mounted on the return tube’s endings to direct the balls in entering and exiting the return tube. A tube-holding bracket supports the length of the return tube. It is easy to install and dismantle these return tubes.
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Rolled Screw
A cold work deformation process is used to fabricate the rolled screw threads. An uncut blank shaft is put through rotating tool dies to create the grooves. A high-strength screw shaft is the end result of the huge plastic deformation of the blank. Rolled screws are economical and easy to fabricate compared to ground screws. The surface manufactured is rough, which reduces the ball screw’s efficiency and wear resistance because of the higher friction it will encounter.
Notable Benefits of Ball Screws
Ball screws are immensely beneficial in motion applications. The following are a few advantages they provide:
- They are efficient and need less torque – resulting in smaller motor
- They offer better accuracy grades for effective positional accuracy
- They undergo minimal friction, which makes them capable of running at cooler temperatures
- They are available in rolled and ground types
- Ball screws can be adapted according to the increase or decrease of the preload
- The frequency of need for replacement is less
- 4mm to 80mm diameter ball head screws are available
To Summarize
The power efficiency, accuracy, precision, and load capacity of ball screws make them a valuable product. Additionally, they have better features than lead screws and find applications in various cutting-edge technology and industrial equipment. There is a tremendous amount of evolution in the design, performance, and application of ball screws based on the requirement of the industry. Since their inception, ball screws have not only played a crucial role in industrial machinery but also in the advancement of computing technology.
