Ballscrews and Ballnuts
Advantages and Features back to top
Roton’s rolled thread Ball Screws and high performance Ball Nuts replace the sliding friction of Acme, Hi - lead(r), and Torqspline(r) leadscrews with the rolling friction of ball bearings placed between the screw and nut members. This construction results in very high mechanical efficiency and much less energy consumption for a given load. Thus smaller motors and other drive components can be used with Ball Screws. As Figure 1 and Figure 2 demonstrate, the same torque applied to a conventional screw moving load "x" will move 3 times the load, "3x", when applied to a Ball Screw. Duty cycles can be more severe as less heat builds up in Ball Screw drive systems when compared to conventional screw drives. Predictable wear life and smooth, quiet operation are also obtained.
Materials and Processes back to top
All Ball Screws are roll formed of quality high carbon or alloy steel. Screws are induction case hardened for maximum load and service life. Nuts are made from carburizing grades of carbon or alloy steel and case hardened for wear resistance. High grade, bearing quality chrome steel balls are utilized. Return circuitry is secured with alloy capscrews for maximum reliability.
Non Self-locking back to top
High mechanical efficiency renders all Ball Screws non self-locking. This means that Ball Screws can convert thrust loads into torque loads. If a Ball Screw is used to support a load against gravity, a rotational brake will be needed to prevent the load from rotating the screw and lowering the load.
Because they are non self-locking, Ball Screws are often used to convert thrust to torque. An input linear thrust on the nut (or screw) will produce an output torque on the screw (or nut). This action (thrust conversion) is called backdriving. Thrust conversion is not possible with Acme series screws although some Hi - lead(r) and all Torqspline(r) series screws will also backdrive. When applications require thrust conversion, the lead selected should be a minimum of 1/2 the Ball Circle Diameter (BCD) for reliable operation. Small leads have less mechanical advantage for backdriving.
Mounting Ballnuts back to top
Ball Nuts are typically mounted in mating flanges as shown in Figure 2. Many other arrangements are possible. Any method that restrains the nut from rotation and translation will suffice. Machining into the nut’s outside surfaces should be avoided as the ball circuits may be damaged.
Care should be taken to keep the loads as axial as possible. If significant side loads are present, support rails should be used in parallel with the Ball Screw so that the Ball Screw undergoes axial loading only.
Mounting for tension loads is always preferable as column loading problems are eliminated. See Figure 30 for information and limits on column loading. The longer the Ball Screw and the smaller the Ball Screw diameter, the greater the possibility of column loading limitations.
Custom nuts machined for easy mounting in OEM equipment are quite popular and favored by large volume users. Contact Roton Application Engineering for your custom nut requirements.
Typical Applications back to top
High efficiency, accurate positioning, and smooth, quiet operation at low friction make Ball Screws ideal for use in a wide variety of equipment in many industries. Predictable service life and reliability make Roton’s Ball Screws ideal for use in:
- hospital beds
- medical examination equipment
- servo drives
- log splitters
- dish antenna drives
- door actuators
- scanners and test equipment
- web tensioners
- automatic pilots
- trim tab drives
- back gage positioners
- fork lift remote accessory drives
Power Screw - FIGURE 1
Ball Screw - FIGURE 2