Rate of Travel
Travel is determined by the ratio of the worm gear screw jack, the standard ratio, N, produces 1mm of travel per one revolution of the input shaft, or worm. An input speed of 1,500 rpm equals 1,500mm of travel per minute. Maximum input shaft speed is 1,800 RPM.
The alternative ratio, L, produces 0.25mm of travel for each revolution of the input shaft. Based on an input shaft speed of 1,500 rpm, this ratio produces a linear speed of 375mm per minute.
Tolerances and Backlash
- Trapezoidal screw end play is 0.15mm
- Radial play is 0.2mm
- Lifting screw outer diameter and sleeve diameter free tolerance is 0.2mm
- Worm shaft and gear play is ± 3 degrees for ratio N, and ± 5 degrees for ratio L
Lateral force will reduce the working life of the screw jack and can lead to product failure. The screw jack(s) should be isolated from lateral forces via the use of guide rails. A Rotating or Traveling Nut-Type worm gear screw jack must be used in single jack applications with no external guiding.
Trapezoidal type screws are typically self locking. This function, however, depends on a variety of parameters, including, but not limited to screw pitch, screw jack ratio, lubrication, vibration, mounting position, etc. A brake or brake-motor may be required to guarantee holding position, please consult Candy Controls during the design process. A brake is recommended for all applications involving vibration.
Following a customer’s requirement, screw jacks may be fitted with a stop collar to prevent the screw from being removed from the gearbox. A stop collar is not to be used as a fixed stop.
Normal operating conditions are -20ºC to 80ºC. Please consult Candy Controls for applications that require temperatures outside this range.
Worm gear screw jacks are shipped from the factory with our standard NLGI Grade 2 grease. Recommended lubrication maintenance is recommended after the first 300 hours of use, and then every 1,000 hours of use thereafter.
Q: What is the difference between a trapezoidal worm gear screw jack and a ball screw jack?
A: The trapezoidal screw jack uses a threaded acme screw that is typically self-locking, meaning it will hold its position without a brake. Ball screw jacks incorporate ball screws to convert rotary motion to linear movement. Ball screw jacks are inherently more efficient, requiring 1/3 the horsepower compared to trapezoidal worm gear jacks. Due to the efficiency of a ball screw jack, a brake must be used to stop and hold a load in position.
Q: What is a Translating or Keyed-Type Screw Jack?
A: This type of jack has a key fixed to the jack housing and inserted into a keyway milled into the lifting screw which forces the screw to translate through the gearbox housing without rotating.
Q: What is a Rotating or Traveling Nut-Type Screw Jack?
A: This design incorporates a lifting screw keyed to the worm gear as a single unit, forcing the lifting screw to rotate in the gearbox, but not translate. A traveling nut, running onthe rotating screw generates linear motion for the attached load. This type of jack is ideal for applications that cannot accommodate a screw protection tube.
Q: Which type of screw jack is best for a single jack system?
A: In a single jack application, with no guide rails to isolate lateral load, a Rotating or Keyed screw jack must be used. Multiple jack applications, or single jack applications that are fully guided may use Translating or Keyed-Type screw jacks.
Q: Can a screw jack be operated in multiple unit systems:
A: Yes, screw jacks may be easily configured in systems, motorized and manual, to raise and lower a load in unison.
Q: Can a worm gear screw jack be operated at high speed?
A: Input power should not exceed the KW rating in specification tables. Maximum gearbox speed should not exceed 1,800 rpm.