Screw jacks or “jack screws” are machines that can lift moderate and heavy loads. They're commonly used in industrial equipment and complex machinery and come in many sizes, styles, and forms.
Take a closer look at the differences between machine screw jacks and ball screw jacks to decide which one performs best for your heavy lifting applications.
Types of Screw Jacks
Screw jacks can support heavy loads, safely lifting and placing them in a certain position for additional work or movement. Having the right screw jack is essential for controlling the load, converting movement, and successfully performing key industrial tasks.
Machine Screws
Machine screws can provide slow steady movement across low or moderate duty cycles. Self-locking machine screws can even suspend loads without requiring a brake motor, and they self-lock easily when there is no ongoing vibration.
Manufacturers can add anti-backlash devices to reverse loads more smoothly or adapt screws for wash-down applications. Our machine screw models are available in stainless steel, metric, and motorized options.
Ball Screws
When your applications require screw jacks that move faster and can manage high duty cycles, ball screws are likely the better fit. They are very efficient, using less horsepower to move heavier loads and offering longer continuous travel. However, they don't self-lock or respond well to manual operation. Ball screws require a brake motor for optimal performance.
Key Considerations for Selecting the Right Screw Jack: Load Handling, Duty Cycle, and Temperature
Load handling, temperature, and other factors affect which screw jack will best suit your application. Keep these eight considerations in mind as you compare different options:
Jack Sizing Considerations
Calculate the total load capacity you need for anticipated operations. This includes:
- Dynamic load
- Static load
- Moving load (accelerated and decelerated)
- Shock load
- Potential overload (calculated at 130% of static load and 110% of dynamic load)
Only consider jacks with the appropriate size for your required load capacity. If you work with heavy loads, focus on jacks that can distribute the load across multiple points.
Duty Cycle
Duty cycle is the time jacks spend moving during a single cycle. The duty cycle for a ball screw jack should be roughly 35%, and the duty cycle for a machine screw jack should be around 25%. At higher percentages, friction and movement will generate too much heat and potentially compromise the jack. A jack’s temperature generally shouldn't exceed 200 F.
Column Strength
Every jack's lift shaft has a maximum column strength. Longer screws have less strength and have a higher risk of buckling under comparable loads.
Horsepower Ratings
Horsepower measures the amount of torque needed to lift by the pound. Ensure the horsepower of your preferred product meets or exceeds the needs of your anticipated loads. Jack temperature, lubrication, duty cycle, environment, and mounting can all impact horsepower ratings.
Critical Speed
Critical speed is the point at which the screw is moving so fast that it starts to vibrate. End fixity, unsupported screw length, screw diameter, and screw RPMs all impact the critical speed point. Having a high critical speed protects loads better, especially when taking them long distances.
Guidance Support
Every screw jack will need a guide system to absorb non-thrust loads and guarantee the load's direction of movement. Systems can also add rails or guides for additional support.
Brake Motor Sizing
Brake motors stop and hold loads safely. We can help you shop for a brake motor with horsepower and torque criteria that align with the jack's capabilities and your load requirements.
Ball Screw Life
The ball screw life measures the anticipated lifespan of the product at a typical level of usage. Make sure your preferred ball screw has a long enough lifespan based on your budget and operational demands.
Comparing Machine Screw Jacks and Ball Screw Jacks: Energy Consumption and Backdrive Tolerance
Machine lifting screw jacks and ball screw jacks aren't just different mechanisms. They also have different capabilities when it comes to energy efficiency and backdrive tolerance.
Energy Consumption
Ball screw jacks are more energy-efficient than machine jacks. They need less horsepower and can operate with smaller and more efficient motors. Facility managers can easily calculate what screw jack they need for different applications by using standard horsepower calculations.
Another efficiency factor to consider is temperature. If the screw jack risks overheating, it may be better to invest in a larger machine screw jack.
Backdrive Tolerance
Backdriving can place additional axial pressure on the screw jack mechanism. Machine lifting screw jacks have a higher backdrive tolerance and are less likely to let loads slip backward. Right-sized machine jacks can even be self-locking.
Ball jacks are not self-locking and require a brake or other holding mechanism to offer the same functionality.
Find the Right Screws With Joyce/Dayton
At Joyce/Dayton Corp., we provide our clients with screw jacks that are built to last through long cycles of work. Reach out today to learn more about our selection of screw jacks, actuators, bevel gear screw jacks, and more or request a quote for pricing on your next order.