What is the difference between a Machine Screw Jack and a Ball Screw Jack?

The machine screw jack uses an acme thread form and is typically self-locking meaning it will hold its position without a brake. Ball Screw jacks use ball screws and nuts to convert rotary to linear movement using approximately 1/3 the horsepower required by a machine screw. Due to the efficiency of the Ball Screw jack, brakes must be used to stop and hold the load screw in position. Brakes are also recommended for all jacks if vibration is present.

Why use a machine screw vs. a ball screw jack?

Due to the differences in efficiency and horsepower requirements, running duty, cycle times, application, environmental conditions and the number of jacks used in a system, one type of jack may better suit the operating conditions. Typically, fast operating speeds, and frequent cycle times may be more suited to a ball screw jack particularly with loads close to the jack rated capacity. High loads at slower speeds, less frequent cycles, the ability to hold the load in position when the system is at rest may be better suited for a machine screw jack. 

What is the input torque requirement for a given output load?

The input torque for a specific load and jack model is calculated using the technical specifications and formulas in the catalog. The input torque (inch pounds) is listed for each jack model in the technical section as “Torque Required to Lift One Pound”.

How do I operate the jack?

Most jacks are operated by electric motor but air motors and hydraulic motors can also be used. Occasionally hand wheels are provided for hand operation. 

What size motor and horsepower is required?

The standard engineering formula: Torque times speed divided by a constant equal’s horsepower. The Horsepower requirement for Uni-Lift is calculated using the jack input torque to move the load times the input RPM to the jack divided by the constant of 63025.

Can I use a larger motor than required?

Yes but this is not recommended. The jack or system components could be damaged if an oversize motor is used. Electronic position switches should be used for each end of travel to stop the motor, if solid emergency stops are used, jack components are subject to shock load conditions and oversize motors can cause catastrophic failure of these stops and other components.

How many input turns are required for 1 inch of load screw travel?

This is called TPI (turns per inch) and is listed in the technical specifications for each jack model. This is calculated by dividing the jack ratio by the lead of the load screw.

How do I stop the jack at the travel limits?

Limit switches must be used to shut of the motor when the jack has reached its full extended or retracted position. Solid stops are not recommended. Their continued use can cause severe damage to the jack. Uni-Lift offers as and option a standard rotary limit switch for this purpose. Other electronic devises include Encoders and Linear Position Transducers can also be provided by Uni-Lift.  

Can multiple jacks be used in a system?

Yes but do not exceed 280% of the rated input torque for a given jack. Use the standard catalog formulas to determine input torque and motor size.

Can different size jacks be used in the same system?

Yes as long as the input turns for 1 inch of travel are equal. This is sometimes done to accommodate varying load conditions.

What is the System efficiency?

2 jack system 95% 3 jack system 90%, 4-jack system 86% 6 jack system 82%, Right angle gearbox efficiency is 95%, Helical gear Reducers: Single reduction 98.5%, Double reduction 97%, worm Gear Reducers = Horsepower out x 100, Horsepower in

What is the maximum input speed?

Most Uni-lit units can be run at 1800 RPM (some run up to 2587 RPM). The catalog sizing procedure accommodates the Load vs. Input RPM and Duty Limits and Cycle times.  Usually a gear motor is used to reduce the input RPM to the jack to accommodate the required travel speed of the load screw (load screw velocity). Many Uni-lifts can be driven directly by 1800, 1150 and 900 RPM motors. Motors and reducers are available mounted directly to many Uni-Lift models.

Can the standard Uni-Lift jacks be used for continuous duty?

Yes. The standard catalog sizing procedure includes the formula for determining the duty limits for each jack model. This is a unique feature allows you to determine the duty limits of each Uni-Lift model.

What is the duty cycle?

The standard Uni-Lift sizing procedure has formulas to determine the duty cycle of each jack. This is a unique feature allows you to determine the duty cycle of each Uni-Lift model.

What causes heat build up in the jack?

The jack is a mechanical gear box assembly. The friction of the gears, load screw, bearings and seals generates heat while the jack is operating. The combination of travel, loading, input speeds all effect the temperature rise and duty limits of the jack. Uni-Lift sizing calculations take these variables into account to insure that you select the right jack model for your application. 

What is the Load Screw capacity and travel?

This is based on the relationship of the screw diameter and the length. Screws in tension are rated for the full capacity of the jack regardless of length providing they do not rotate faster than the critical speed. For screws in compression, capacity is related to column buckling and screw end mounting conditions. Check the column load charts for capacity.  (Make sure you check for the full-extended screw length extending from the jack housing not just the travel.)

How do I determine the full-extended screw length?

The Extended Screw length (ESL) is normally equal to the travel. Allowances must be added for the closed height of a bellows boot and the addition of stop nuts or special closed heights. These will all increase the length of the screw. For inverted jacks the thickness of the structure the jack is mounted to must also be included. This total length (ESL) should be used when determining the column load capacity of the jack.

Can the jack withstand side loading or a bending moment?

Yes, but this is not recommended. Consult Uni-Lift if this condition will be present! These types of loads apply greater forces on the jack load screw and jack housing assembly causing premature wear. Guides are highly recommended and should be used to eliminate side and moment loads.

Should the load being positioned be guided

It is highly recommended that the load be guided however it is not necessary. A guided system will provide more column stability and allow longer load screw travel. Column length is greatly reduced on unguided systems. External load forces common with unguided systems are detrimental to the life and operation of the Uni-Lift.

Is there backlash between the Load Screw and gear nut?

Yes. This is necessary to allow for sliding or rolling action of the screw through the nut. Anti-Backlash jacks are available when the backlash needs to be minimized. See the catalog section for these models and features. Input torque requirements is typically greater for anti-backlash design jacks.

Can the jack withstand Shock loading?

This is not recommended. Use a jack rated for twice the capacity of the load. Solid thrust bearings are also available in many jack models when constant vibration and shock are present in the application.

What mounting position can the jack be mounted?

Uni-Lifts can be mounted in any position, vertical, horizontal of in-between.  Positions other than vertical should be noted on inquires and purchase orders since special accommodations may be required.

How is the Load Screw protected?

Standard translating screw jacks are provided with screw protection tubes that the screw retracts into during the closed position. Boots are available and recommended to protect the screw in the extended position. Two (2) boots may be required for rotating jacks with traveling nuts.

How do I attach the load to be positioned to the jackscrew?

For translating jacks, the load screw has a standard threaded end that can be used to attach the load. Also available is a Top Plate or a Clevis. For traveling nut designs, the traveling nut has a flange with mounting holes. The jack housing has a mounting base and is also available with a Clevis Mount for double clevis requirements.

Will the load screw rotate

Yes. You need to prevent the load screw from rotating to produce linear motion. The jackscrew will not rotate in a multi jack system with all the load screws attached to the same structure. If rotation of the screw cannot be prevented in the application design, a Keyed jack configuration is available for either the Machine or Ball Screw Uni-Lift. (Input torque will increase for keyed jacks)

What is the maximum temperature rating?

400F. Uni-lifts are designed to operate at a standard 80F ambient temperature with a 100 F-temperature rise. For higher temperatures, special grease and seals are used to reach temperature ranges to 400F. Advise Uni-Lift of these requirements.

What is the low range operating temperature?

Minus 50F with special grease.  Advise Uni-Lift of these requirements.

Can jacks be used in Food industry applications (USDA) 

Uni-Lift uses USDA approved lubrication for these applications. Advise Uni-Lift of these requirements.

How do I lubricate a screw jack?

Use the proper grease. Fill the gearbox by pumping grease into the grease fittings supplied in the jack housing. The screws should have grease applied directly to them with a rag or paintbrush. This must be done on a regularly scheduled maintenance program.

How do I select the right jack?

Determine the direction of the load (compression/tension) and the screw-mounting configuration. Determine the dynamic and static load per jack. From the catalog identify the configuration, Upright, Inverted, Translating, Rotating and attachments (top plate, clevis, boots etc). Determine the travel time in minutes (inches per min.). Follow the simple sizing calculations included in the catalog. 

Who do I call for help?

Uni-Lift, 800-323-9114, Templeton Kenly & Co. Inc., Broadview IL.