Advantages and Features
Roton’s rolled thread Hi – Lead® screws and high performance Hi – Lead® nuts provide faster linear travel than Acme screws and nuts. Hi – Lead® screws use multiple start threads to increase the thread lead, thereby increasing the linear movement output for each revolution of rotary input.
The highly burnished surface finish of the screw and low friction bronze and plastic nuts yield a smoother, less abrasive action than conventional milled or cut multiple start screws. Improved wear and surface properties insure users a longer service life and quieter operation, requiring less power in a wide variety of applications.
Materials and Processes
All Hi – Lead® screws 1 1/2 inches in diameter and smaller are made from special quality low carbon steel. Screws greater than 1 1/2 inches are made of special quality medium carbon steel. These materials provide an ideal combination of machinability, weldability, and strength. Sizes designated SS on page 19 are made from 304 type stainless steel. Alternate screw materials are aluminum alloys, other stainless grades and high machining grades of carbon steel. (For more information on materials see Table 30)
Hi – Lead® screws are cold formed using a unique, highly accurate, thread rolling process which guarantees a smooth, high quality thread. Our thread rolling process eliminates the interrupted grain flow of conventional cut threads, thereby increasing yield, ultimate, and fatigue strengths.
With over 25 sizes and many left hand versions, Roton offers the most complete line of multiple start screw products in the industry. Standard nuts are offered in several styles and materials.
All screws are furnished with a plain, oil dip finish. Screws may be electroplated, but use of stainless steel is encouraged for corrosive environments because electroplated surfaces are the first to wear off in use. Also, electroplating requires very close process control to avoid fit-up problems with mating nuts. Without extremely accurate control, the thickness of plating can vary greatly over the length of the screw shaft. Users intending to electroplate are encouraged to review Roton Engineering Bulletin No. 963 which discusses the plating process in detail. Black oxide finish is also available.
Most applications can be satisfied by selecting from the stock sizes listed; however, OEMs may find an optimum design solution requires a special size or special features such as stub series threads, special diameter and lead combinations, metric diameters and leads, etc. For these applications, Roton is uniquely qualified with over 25 years experience serving the OEM market.
Tooling and software resources can be utilized to assist the OEM designer in finding the very best solution for any application. An extensive tooling inventory exists for many special sizes, not listed in Table 10. This allows OEMs to purchase many “specials” quickly without the expense and delay of new tooling. Consult Roton Application Engineering for more details.
Bronze nuts provide superior service at high working loads. They should be well lubricated with a good quality, Extreme Pressure (EP) grease compatible with the operating environment. Plastic nuts can be used without lubrication and are popular with stainless steel screws for wash-down applications.
Bronze and plastic sleeve style nuts provide generous wall thickness and overall nut length for ease of machining and modification to existing installations. Threaded nose (T-nose) style nuts are available for use with mounting flanges. See Tables 10, 11, 12, and 13 for screw and nut part numbers and other detailed information.
Application engineering information is available from Table 10. Additional engineering information is available in the Application Engineering Section. Those designers not familiar with power screw applications are encouraged to review this section as well.
All Hi – lead® screws have lead angles greater than 5° making them non self-locking. These screws can backdrive, especially under vibration conditions (see discussion on backdriving in Application Engineering). Brakes or other holding devices will be needed with Hi-lead® screws to sustain loads after they have been positioned, unless the drive train itself provides enough holding torque. For applications demanding self-locking screws, refer to the Acme screw section.
All sizes of Acme lead screws are made in large volume and their widespread popularity makes them the least costly of all power screws.
Mechanical efficiencies for Hi – lead® screws are higher than Acme screws. Efficiencies range from 30% – 60% depending upon the lead angle, coefficient of friction, and nut material. Plastic nuts offer approximately 10% – 20% better efficiency than bronze because of their lower coefficient of friction when running against steel power screws.
The higher lead angles of Hi – lead® screws demand more torque for a given load than Acme screws. For maximum mechanical advantage users should consider Acme power screws.
Roton’s Hi – lead® screws and nuts are widely used and well suited for both manual and power drive applications including:
- Conveyor drives
- Factory automation drives
- Pick and place mechanisms
- Fast machinery slide drives
- Garage door openers
- Adjustable work tables & lifts
- Quick acting valve stems
- Medical device drives
- Farm machinery
- Robotic drives
- Web press drives
- Survey equipment adjusters
- Quick change jig & fixture screws