Ball Screw Applications
Every engineer whose line of study involves courses directed toward mechanical design is familiar with ball screws. A ball screw functions similarly to a traditional lead screw but has the important feature of transmitting load via ball bearings running in the helical channel. It is frequently necessary for high-precision applications to convert a motor’s rotating motion to linear motion for the payload. The use of a ball screw is one method to accomplish this.
Ball screws are mechanical linear actuators made of a screw shaft and nut, with a ball that rolls between the helical grooves on each component. The main job of a ball screw is to transform rotational motion into linear motion. Ball nuts are used to accurately, precisely, and consistently transfer forces to a load, whether stationary or moving.
The rolling balls in the helical groove, which eliminate mechanical contact within the screw assembly and switch sliding friction for rolling friction, make ball screws special. Balls screws’ efficiency is determined by how well they can convert the energy used to produce rotating force into the linear distance traveled.
Customers turn to ball screws because they offer control coupled with low friction. Some of the many industries that rely on ball screw assemblies include semiconductor, robotics, manufacturing, automotive manufacturing, aerospace, military and defense, nuclear energy and mechatronics.
Ball screws are used for a wide range of applications within these industries and others. Examples include in steppers (for semiconductor manufacturing), in robots, in precision assembly equipment, in machine tools, in automobile power steering motors, and in missiles and aircraft to move control surfaces (particularly electric fly by wire (FBW) systems). Also, quite commonly, ball screws join other linear motion parts, such as carriages, drive units, linear slides, and linear actuators, to create a smooth, precise, and complete movement system.
Ball screws find their application in:
- Machine tools
- General robotics
- Milling machines
- Food processing equipment
- High-precision assembly equipment
- Industrial robots in manufacturing
- Semiconductor manufacturing equipment
History of Ball Screws
Ball screws were born in the late 1800s. Before they were invented, people created the load movement they required using lead screws, which are screw and nut assemblies that consist of a threaded screw shaft and a nut. Ball screws, on the other, have ball bearings integrated into the nut. The nut of a ball screw, called a ball nut, reduces friction and improve efficiency.
Engineers first developed ball screws to facilitate linear motion load feeding in press machines. They worked well, but there was no standard design. Countless inventors around the world filed ball screw patents throughout the late 1800s and early 1900s. In 1874, for example, an American named C.W. Crenshaw filed a patent for his “screw-press” mechanism design. Records of patents for similar ball screw mechanisms can be found in Germany (1879) and Great Britain (1909), to name a few.
Despite the widespread interest from engineers, ball screws were not found to be useful or consistent until around World War II. During WWII, for example, manufacturers first began installing ball screws in airplanes. About a decade after the war ended, in 1955, General Motors started installing ball screws in automobiles to assist in front wheel steering. Then, during the 1960s, manufacturers began using the predecessors of computer numerically controlled (CNC) machinery, numerically controlled (NC) machinery; to make them work smoothly, they used ball screw as load feed components.
Today, since technology has advanced, ball screw designers have been able to produce increasingly precise devices. With the help of precision screw forming (PSF) processes, they have reduced the production of inferior products, such as lopsided or off-center ball screws.
With the help of automated equipment, computer programs, and special sensors, they can more easily find the center of a steel rod meant to be machined or rolled into a screw. With this same technology, they can also cut and grind material better, leading the more accurate and consistent ball screw threading. The better the threads and grooves, the smoother and faster ball bearings can work. Also, with the help of computer and/or operator supervision, an assembly’s ball nut and load carriage can be much more tightly controlled, resulting in fewer glitches, more concise movements and quieter operations. As time goes on, we can only expect ball screws to work better and better.
Ball Screw Materials
Ball screws are either made from plastic, metal or both. The shaft of the ball screw is always machined from steel or stainless steel, but the ball nuts may be made from plastic or metal, depending on the application.
Main Components of a Ball Screw
Following are the three main components of a ball screw:
- Screw Shaft: The screw shaft is the part of the ball screw that receives rotational force to revolve about its axis and transform into linear motion. A motor is located on the shaft’s end to provide the rotational power.
- Nut: The ball bearing and its recirculation system are housed in a cylinder that serves as the ball screw’s nut. The internals of the nut also include ball grooves that match the grooves on the screw shaft.
- Ball Bearing: The most prominent part of a ball screw is the ball bearings, often known as the balls. Ball bearings travel between the clearance of the nut and the shaft, and they work as components designed to reduce friction. The ball bearings are typically made of steel.
Ball Screw Considerations and Customization
When designing ball screws and ball screw assemblies, manufacturers think about factors such as load type (static load vs. dynamic load), load weight, required critical speed (the speed that triggers the screw’s natural frequency), mounting type, environment (likely exposure to dirt, dust and other contaminants), temperature, frequency of use and required accuracy.
Based on these considerations, manufacturers make choices regarding materials, ball nut shape (rounded nut, flanged nut or custom nut), protective coatings, lubrication, ball nut size (ball circle diameter), screw diameter (root diameter, pitch, lead, etc.), the screw’s load direction and the type of mounting. During design, manufacturers decide whether or not to make you a preloaded ball screw system. Preload is a style of positioning that makes the assembly more rigid. It does so by removing the clearance between the ball nut and ball screw. Preload eliminates the backlash and deflection normally associated with carrying large loads. Manufacturers typically achieve preload by loading the system with oversized balls, adjustable nuts, or by tensioning two single nuts.
In addition to standard configurations, buyers may request ball screws made with custom configurations. Custom ball screws offer the customer the assurance that they will encounter no problems in terms of productivity or compatibility. Common customizations include custom ball diameters, custom screw diameters, the conversion to the metric system (mostly for use outside of the United States), single or double ball nuts, customized screw ends and customized nut designs.
Ball Screw Features
Ball screws feature two pieces: a screw shaft and a ball screw nut. The ball screw nut runs up and down the helical grooves of a screw on ball bearings. To work, the threading of the nut and the threading of the screw must match one another. Together, the nut and threaded screw are known as a ball screw assembly; their movement powers torque and thrust. Note that the nut is a non-contact ball; it works without ever physically touching the screw shaft.
In more detail, this movement begins with ball bearings rolling in the grooves of the threads, which simultaneously provides a smooth motion and a rolling friction. Next, the ball bearings encounter a deflector, stationed inside the nut’s ball return system, which reroute them to the opposite end of the nut. Thus, the balls continuously recirculate.
Types of Ball Screws
To meet the various requirements of their applications, balls crews are available in multiple configurations, such as miniature, rolled, ground, and precision.
Miniature ball screws are popular for use in lasers, gauge measurement devices, semiconductors, medical instruments, and other small devices that require smooth and precise linear motion.
Rolled ball screws, or roll ball screws, are named as such because, beginning as blank metal workpieces, they are formed through cold screw rolling. These cold rolled ball screws offer the advantage of a positional precision of several thousandths of an inch per foot. Rolled screw threads are created through cold work deformation. The grooves are formed by passing the uncut blank shaft through rotating tool dies; the substantial plastic deformation of the blank produces a high-strength screw shaft. Compared to ground screws, rolled screws are more affordable and simpler to manufacture.
Ground ball screws, which boast extremely high levels of precision, are made in three steps: machining to gross shape, case hardening, and grinding. This grinding takes place on rapidly spinning machines that are coated with abrasive materials. This treatment bestows upon the finished ground screws the ability to withstand temperatures that would normally distort their shape and mar their efficiency. Ground ball screws are best for applications that require not only high precision, but high stiffness.
Precision ball screws are simply a wider category of ball screws that carry exceptionally high levels of accuracy, or precision.
Lead screws, while not technically ball screws, are occasionally categorized as such. This is because lead screws do convert rotational motion/rotary motion into linear motion. Lead screws are made up of a threaded screw shaft and a nut that generate friction via sliding, rather than through the rolling that is the practice of ball screws. Because they must rely on sliding action only, screw lead assemblies have a relatively low level of efficiency that sits anywhere between 25% and 75%. Commonly, lead screws are made with an acme screws design, or a trapezoidal lead screw design, both which have distinct threading patterns and shapes.
Ground screw threads are created through abrasion. A harsh abrasive cutter carves out the metal to create the grooves while the blank shaft is horizontal. The surface of the groove created is smoother than that of a rolled screw. This technology produces high-precision ball screws but is also more expensive and makes the parts more slowly.
Return-pipe type ball screws are made where the balls flow through an exterior tube that extends from the wall of the nut. The balls are directed back to their starting location by the return tube. To help the balls enter and exit the return tube, fingers are fastened to the ends of the tube. A tube retaining bracket supports the return tube’s length. It is simple to assemble and disassemble the return tube assembly.
Advantages of Ball Screws
Ball screws are highly advantageous for a number of reasons. First, they serve their applications with levels of efficiency up to approximately 90%, which are efficiency levels much higher than those of lead screws. At the same time, they maintain low levels of energy consumption. They also offer close tolerances, an ability to both withstand high thrust loads and low levels of friction. In addition, they can run at low temperatures, which helps systems last longer. Because they are so efficient and durable, they are a cost-effective investment. No matter its configuration or whether it is identified with American or metric ball standards, ball screws are a great asset to manufacturers and engineers.
Ball Screw Accessories
You may purchase a wide variety of accessories to support and complement your ball screw assemblies. Examples include screw jacks, custom or standard screw support bearings, recirculation caps, mountings, extra ball nuts, lubricant and wipes.
Proper Care of Ball Screws
A well-maintained ball screw that is properly lubricated and kept free of interferences like dust, will prove itself to be an integral component of many operations. So, you need establish a regular cleaning schedule. Usually, wiping will do the trick. To find out what type of lubricant is best for your ball screw assemblies, you need to talk to your supplier. To fortify your ball screw assembly, consider getting it preloaded. Preloaded assemblies are more rigid, which helps some systems. If you’re not sure about preload, talk to your supplier.
Another way to maintain your ball screw assembly is by testing the ball nut component to make sure it is in alignment. If it is not, your ball screw could suffer significant damage. Next, we also recommend that you leave your ball screws in their packaging until you are ready to install them, because any dust they get on them can detrimentally affect their performance. Likewise, if you plan on storing your ball screws for a long time, you need to rotate them every few months, so that the oil on them remains evenly distributed.
Ball Screw Standards
The standards to which your ball screws are beholden depend on your industry, application and machinery, the environment in which you are working and your location. Some very common standards for accuracy, ball screw dimensions and load tolerances include those put out by ISO (International Standards Organization) and by comparable national standards. Examples include DIN (Deutsches Institut für Normung, or German Institute for Standardization), BSI (British Standards Institute), JIS (Japanese Industrial Standards), ANSI (American National Standards Institute), SCC (Standards Council of Canada), and so on and so forth.
Things to Consider Regarding Ball Screws
If and when you are on the hunt for high quality ball screws, you need to know the signs of a good manufacturer. Good manufacturers will be professional (respectful, cordial, adherent to the schedules they make), up front about pricing (no hidden costs or last minutes changes), experienced and ready to take on your application. The right manufacturer for you will not only be able to provide you with quality options within your budget, but deliver you your products on time, produce your products to the standards you require, delivery to your area and provide you with all the post-delivery support you desire (ball screw repair, parts replacement, installation assistance, etc.)
To give you a leg up, we’ve listed on this page several ball screw manufacturers we trust, including Rockford Ball Screw. Scroll up to check out the various manufacturers’ contact information, website links and interactive profiles. Before doing that, though, we recommend you put together a list of your specifications that you can reference quickly. In addition to those things we mentioned above, we also recommend you put down your request quantity or volume. With your specifications in hand, take a look at the manufacturers we’ve listed, and pick out three or four to whom you’d like to speak at length. Then, reach out to each of them to discuss your application. Based on your conversations, select the one you think is right for you, and get started. Good luck!
Ball Screw Informational Video