screw jack questionnaire and selection guide

Screw jack questionnaire

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Screw Jack Selection Guide

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Screw Jack Calculation Formulas

Input Torque: T=(F*p / 2*π*i*η) + To
Input Power: P=F*V / 60*η, P=T*n/9550, V=n*p / 1000*i
Worm Gear Ratio: I=(n / 1000*V)*p
* Travel Speed: V=n*p / i

* Travel Per Turn Of Input Shaft: L=p/i
* Hand Turnning Force: HF=T/R, HF=F*p / i*R*1000
T = Input torque (Nm)
F = Given load (N)
p = Screw pitch (m)
i = Gear ratio (ex. 24:1, i = 24)
η = Jack efficiency
To = Idling torque (Nm)
P = Input power (kW)
V = Screw axial speed (m/min)
n = Jack input speed (rpm)
S = Stroke (mm)
L = Travels (mm) per turn of jack input shaft
HF = Hand turning force (kg)
R = Radius of hand wheels (m)
 Total Equivalent Load Ws (N): Ws=Wmax*f1 (N)
Wmax: maximum dynamic load (N)

f1: factor for driven machine

Load CharacteristicExampleFactor for driven machine (f1)
Uniform load, small inertiaShifting device for switches, valves and conveyors1.0 < f1 ≤ 1.3
Moderate shock load, medium inertiaMoving devices and elevators1.3 < f1 ≤ 1.5
Heavy shock load, large inertiaHeavy trolleys and railway lifts1.5 < f1 ≤ 3.0
Equivalent Load Of Single Jack W(N): W=Ws / (Arrangement Factor*Number Of Jacks In Arrangement)

Ws: Total Equivalent Load Ws (N)

Number Of Jacks In Arrangement       1          2         3            4        5~8
Arrangement Factor1   0.95 0.9  0.850.8

Verification The Stability Of Screw: Pcr=fm*d4/L2    ensure    Pcr>W*SF (SF=4)
Pcr = Critical load (N)

d = Thread root diameter (mm)
fm = Support factor
L = Distance between load supporting point and mounting point as drawing (mm)
W = Equivalent load of single jack (N)
SF = Safety factor (generally SF=4)

Verify the screw stability when the axial compression load exists. If the load is greater than the critical load, increase the sizes before calculation.
A = 2.5*104, B = 1*105, C = 2*105

Duty Circle %ED: ED=work time in one load circle / (work time in one load circle+rest time in one load circle).
Trapezoidal screw: the unit of %ED for a single screw jack is 1 minute duty circle max. 40%ED; 10 minutes duty circle max. 30%ED; 60 minutes duty circle max. 20%ED.
Ball screw: the unit of %ED for a single screw jack is 10 minutes duty circle max. 50%ED; 30 minutes duty circle max. 30%ED; 60 minutes duty circle max. 20%ED.
What is efficiency of screw jack?

Two screw jacks lift system, transmission efficiency 95%
Three screw jacks lift system, transmission efficiency 90%
Four screw jacks lift system,  transmission efficiency 85%
Six screw jacks lift system,  transmission efficiency 80%
Eight screw jacks lift system,  transmission efficiency 80%

Notes: don’t ignore the bevel gearbox efficiency 98%.

What’s the difference between oil lubricant and grease?

Oil lubricant is better than grease. Less resistance at the start and high efficiency. Possible in high-speed operation Etc.

What’s the working temperatures of our screw jack actuator?

Normal operating conditions are -20ºC to 80ºC. Please consult for applications that require temperatures outside this range.

What’s the tolerances and backlash of our screw jack lift?
  • Machining precision level eight
  • Radial play is 0.2mm
  • Trapezoidal screw end play is 0.15mm
  • 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
What’s stop nut and how are they used?

Stop nut are offered as options for screw jacks, and are not to be used as operating limits. Engaging the stop may prevent damage to your structure but will most likely damage the jack. To control jack or actuator travel, include limit switches in the system design. Including stops may increase the closed height of the jack and the length of the protection tube.

What do you need to consider when adding a protective boots?

Closed height dimensions may increase when boots are added. Standard material is Neoprene coated nylon. Special boot material is available. Horizontal screw applications may require boot guides.

What grease does our worm gear jacks lubricated?

Our worm gear jacks are lubricated with 0# or 1# lithium grease prior to shipment. You can find more specific information from our Operation & Maintenance Manuals.

Can your screw jack operate at high speeds?

The travel Speeds of the screw actuators mainly depend on the input RPM, load, internal ratio and lead of the screw. Maximum allowable travel speeds for machine screw jacks are typically slower than ball screw jacks. Worm gear jacks have slower travel speeds than bevel gear jacks.

For our model NDLB high-speed screw actuator, it uses both ball screw and bevel gear, which make the speed quite fast. Pay attention that the input horsepower to these screw jacks should not exceed the hp rating shown in the specifications tables. Maximum RPM should not exceed 1500.

What is the allowable duty cycle of a worm gear screw jack?

The worm gear actuators efficiency is low, so the duty cycle is also low at the rated load. If you reduce the load or increase model NO, the duty cycle can be increased. Talk to our engineering sales for more information.

What is the maximum input RPM for our Screw Jack?

Maximum input RPM may be slower than 1500 RPM depending on the dynamic load and other factors specific to the application. You can contact and talk with an application engineer.

Can screw jack withstand the side load?

The load must be positioned axially. The standard screw jack is not designed for dynamic side loads. Static side loads are limited. Where side thrusts are present, the loads should be guided and let the guides take the side thrust especially when long travel length is involved. Even a small side load can exert great force on the housings and bearings and increase the operating torque. Contact for technical assistance.

What is screw jack duty cycle?

The duty cycle is the relationship between operation time and rest time. The allowable duty cycle for screw jack actuator is based upon several application variables such as load, speed, and temperature. Contact and talk with an application engineer about your requirements.

What is the life of the worm gear actuator and how is our wanrranty?

The life of a machine screw actuator varies considerably due to extent of lubrication, or improper maintenance, eccentric loading, abrasive, chemical, overloading, excessive heat, , etc.

We warrant that its screw jack sold will be free of defects in material and workmanship in a period of 13month from the original date of receipt.  During this period, Nuodun will repair or replace defective parts free of charge.

This warranty covers only normal use of the products. We will not repair or replace any parts that become unusable and show clear evidence of improper maintenance, eccentric loading, overloading, excessive heat, chemical or abrasive wear, tampering or abuse. Equipment and accessories not manufactured by Nuodun are warranted only to the extent the manufacturer warrants them, and only if the claimed defect arose during normal use, application and service. Equipment that has been altered or modified by anyone without our authorization is not warranted. Except as stated herein, Nuodun makes no other warranties, express or implied including warranties of merchantability and fitness for a particular purpose.

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