Tag Archives: worm gear screw jacks

Industries

Key Considerations for Choosing Worm Gear Screw Jacks

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MachineScrewJackWorm gear screw jacks can be found in a great number of industries, including military, automotive, manufacturing and many more. When choosing the right kind of worm gear screw jack for your product, here are just a few crucial industry considerations and specifications to keep in mind.

→ Worm gear screw jacks built up to leading industry standards are rated for up to 3,000 rpm input speed, provided horsepower and temperature ratings are not exceeding.

→ Top worm gear jack models are ruggedly designed and produced in standard styles with load-handling capabilities from 1/4- to 100-ton and can be used individually or in multiple arrangements.

→ For duty cycles, the cycle is limited by the ability of the worm gear screw jack to dissipate heat. An increase in temperature can affect the properties of some components resulting in accelerated wear damage and possible unexpected failure. The approximate allowable duty cycles are 35 percent for ball screw jacks and 25 percent for machine screw jacks. The rolling action of these screw jacks reduces friction for smooth and efficient load movement, providing higher speed operation and increased duty cycle.

→ Leading worm gear screw jacks are made to be suitable for temperatures no lower than 20 degree below Fahrenheit and no higher than 200 degrees Fahrenheit. Continuous or heavy duty operation is possible by operating the jack capacity, external cooling of the unit or through the use of a recirculating lubrication system.

→ Leading machine screw jacks incorporate an Acme screw with a 2C thread form. With a 20:1 or greater gear ratio, the jacks are considered self-locking. A drive sleeve including the Acme thread form makes an anti-backlash option possible.

Industries, Linear Motion Design Considerations, Uncategorized, Worm Gear Machine Screw Jacks

Advantages of a U-Shaped Worm Gear Jack Screw Arrangement

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In worm gear screw jacks, the “U” arrangement’s configuration is often preferred for manufacturers in the food industry.

U ArrangementFor example, a leading cookie manufacturer could be adding a new product that requires a greater distance to the top heating element of the conveyor oven. The oven originally only had a static-top heating element and with this new order, it needs to be adjustable up to 14 inches. The top heating element weighs 5,000 pounds. The manufacturer anticipates only making adjustments to the height once or twice a month.

Our specifications for the U arrangement include a single 5-Horsepower 1750 AC Motor that allows full travel in 36 seconds, food-grade grease, compression load and a double safety factor. The actuators and power train must be located outside of the oven frame. Travel rate is negligible as long as the total travel can be reached in less than 60 seconds. The application’s infrequent cycles makes the use of a machine screw jack the best fit.

Upright rotating jacks allow the jacks to be easily retrofitted to the existing oven with minimal modifications. The jacks will be fully loaded in both the retracted and extended position, but because of the retrofit condition, having a support bearing on the lift shaft will not be possible. A 10-ton jack was selected for the mounting condition to fulfill safety requirement.

For calculating column strength, check out Nook’s calculator, as well as other useful engineering calculators here.

Industries, Linear Motion Design Considerations, Worm Gear Machine Screw Jacks

H Arrangement of Worm Gear Screw Jacks

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One of the most common arrangements used for worm gear screw jacks is the “H” arrangement. The name comes from the arrangement’s shape, which is made up of four jacks, three gearboxes and a 3 HP AC Motor capable of a dual-speed 1750/800.

H ArrangmentAn example of this arrangement could be a manufacturer of steel frames for the commercial dairy industry is building a material lift which contains a stack of prefabricated frames. The material lift will index up as each frame is removed by an automated grip from the top of the stack. The jack will index up 1 inch in 2 seconds every 30 seconds. After the last frame is removed, the jacks will fully retract to the collapsed position in 6 seconds waiting for the next load of frames. Complete cycle time is 10 minutes running 6 hours per day, 5 days a week. The design calls for a four-jack arrangement lifting from underneath the lifting stage, driven by a single motor.

The frequency of these cycles and suggested design life makes the use of a ball screw jack the best option for this application. Using upright translating jacks allows the jacks to be located under the material lift without creating obstruction.

When fully loaded, the frames hold a total weight of 16,800 pounds, but when the load is fully extended, the weight is less than 5,000 pounds. The compression load travels 6 inches. The desired design life for the arrangement is one year, as the application is expected to go through 3,120 cycles a year.

 

Ball Screw Jacks, Linear Motion Design Considerations, Screw Jacks, Worm Gear Ball Screw Jacks, Worm Gear Machine Screw Jacks

8 Design Considerations for Worm Gear Jacks

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8 Factors You Need to Consider
No matter the type of worm gear jack, machine or ball, there are 8 factors that need to be known and addressed in the design of a solution. In this post, we’ll start looking at these design constraints and how they can determine the sizing, placement and configuration of your worm gear jack screw.

Stainless machine upright1. Load Capacity
The load capacity of the jack is limited by the physical constraints of the components (drive sleeve, lift shaft, bearings, etc.). All types of anticipated loads must be calculated, and be within the rated capacity of the jack. These loads can include: static, dynamic, moving, acceleration/deceleration loads as well as cutting and other reaction forces.

Appropriate design should also be made for shock loads, and should not exceed the rated capacity of the jack.

To accommodate accidental overloads, jacks can sustain the following overload conditions without damage – 10% for dynamic loads, 30% for static.

2. Duty Cycle
Duty cycle is the percentage of time on as opposed to total time. Recommended duty cycles for the two styles of jacks at max horsepower are:
• Ball screw jacks 35% (65% off)
• Machine screw jacks 25% (75% off)

The largest determining factor in calculating duty cycle is the ability of the jack to dissipate heat that builds up during operation. Anything that reduces or increases the generated heat increases or decreases duty cycle accordingly. Additionally, jacks may be limited by their maximum operating temperature (200°F) and not duty cycle.

metric inverted3. Horsepower Ratings
Horsepower values are influenced by many application-specific variables including mounting, environment, duty cycle and lubrication. The best way to determine whether performance is within horsepower limits is to measure the jack temperature. The temperature of the housing near the worm must not exceed 200°F.

The horsepower limit of a jack is a result of the ability to dissipate the heat generated from the inefficiencies of its components, based on intermittent operation. Special consideration should be given for multiple jack arrangements, as total horsepower required depends on horsepower per jack, number of jacks, the efficiency of the gear box or boxes and the efficiency of the arrangement.

If needed horsepower exceeds the maximum for the jack selected, several solutions are possible:
• Use a larger jack
• If it is a Machine Screw Jack, look at a comparable Ball Screw Jack
• Operate at a lower input speed
• Use a right angle reducer

inch inverted machine4. Column Strength
Column Strength is the ability of the lift shaft to hold compressive loads without buckling. With longer screw lengths, column strength can be substantially lower than nominal jack capacity.

If the lift shaft is in tension only, the screw jack travel is limited by the available screw material or by the critical speed of the screw. If there is any possibility for the lift shaft to go into compression, the application should be sized for sufficient column strength. Designers should also be aware of effects of side loading. Jacks operating horizontally with long lift shafts can experience bending from the weight of the screw.

If column strength is exceeded, there are several options:
• Change the jack configuration in order to put the shaft in tension
• Increase jack size
• Add a bearing mount for rotating jacks
• Change the lift shaft mounting condition, for example, from clevis to top plate

5. Critical Speed
The speed that excites the natural frequency of the screw is referred to as the critical speed. The critical speed will vary with the diameter, unsupported length, end fixity and rpm of the screw.

Because of the nature of most screw jack applications, critical speed is often overlooked. However, with longer travels, critical speed should be a major factor in determining the appropriate size jack. Since critical speed can also be affected by the shaft straightness and assembly alignment, it is recommended that the maximum speed be limited to 80% of the calculated critical speed.

inch ball6. Type of Guidance
All linear motion systems require both thrust & guidance. Worm gear jacks are designed to provide thrust only and a guidance system should be designed to absorb all loads other than thrust. Preferred systems include hardened ground round shafting or square profile rail.

7. Brakemotor Sizing
To ensure safety, a brakemotor is recommended for worm gear jack screws where there is the possibility of injury. Horsepower requirements will determine the size of the motor, and once selected, verify that the standard brake has sufficient torque to both stop and hold the load.

Lastly, high lead ball screws may require larger, nonstandard brakes to stop the load, to ensure against excessive “drift” when stopping.

8. Ball Screw Life
A major benefit of the use of ball screw jacks is the ability to predict the theoretical life of the ball screw, and all major manufacturers will provide life charts for their products.

Once these factors are understood and accounted for, and paired with the features and benefits of Machine and Ball Screw Jacks, selecting the right one for your application should be considerably easier.

Industries, Linear Motion Design Considerations, Uncategorized, Worm Gear Ball Screw Jacks

Why Use Worm Gear Screw Jacks with In-Line Arrangement

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For worm gear screw jacks in the steel tube industry, in-line proves to be the best choice for arrangement in getting the job done quickly and efficiently.

in line arrangementTo give you an idea of how an in-line arrangement works in a company’s favor, here’s a real-life scenario to observe: A steel tube manufacturer is developing a new OD polisher that will increase production by 22 percent. Because of the increased production time, the set-up crew is unable to set the feed table manually and is looking to automate the feed table height using screw jack actuators.

The feed table length is 24 feet and weighs 5,600 pounds with the largest diameter steel pipe. The table height will need to change approximately once every 15 minutes, but no more than 10 times a day. Maximum height change is nine inches. The rate is .4 inches per second.

By our specifications, the in-line arrangement comes with a single three-HP AC Motor with 1750 RPM and drive, and it comes with the possibility to be removed and driven by hand. With hand-driven possibilities, a machine screw jack with a 24-to-1 gear ratio is needed to prevent back driving.

The mounting constraints call for an upright translating jack with a clevis rod end. Due to the length of the feed table, four jacks will be used in line with a center mounted motor through a single gearbox.

Other specifications for the in-line arrangement include a compression load, a total travel of 14 inches and the ability to move .25 inches in one second.