NSK has developed a new type of ball screw that exhibits reduced motion errors to deliver higher surface finish quality for machine tools used in mould and die machining and other surface-critical applications. By eliminating or reducing the time needed for secondary burnishing or polishing applications, the new ball screw also contributes to higher productivity, while simultaneously reducing the amount of drive torque to save energy.
In recent years, builders of machine tools such as five-axis milling machines have been demanding increased accuracy to produce higher quality mould and die surfaces, where the ball screws used in these machines must further improve motion accuracy.
When a ball screw reverses direction, sudden fluctuations in friction cause ‘quadrant glitch’ motion errors with two peaks, leaving streak marks on the machined surface and reducing surface quality. Numerous studies conducted on quadrant glitches show that it is possible to correct the first peak through numerical control (software-based servo controller compensation). Although it is more difficult to fully compensate for the second peak due to the combined effects of more factors (compared with the first peak), NSK can now present the machining industry with a solution to this problem.
Using real digital-twin simulation and friction analysis, NSK has developed a new ball screw with an optimised internal design. Key to this outcome was the company’s understanding of the underlying mechanism of friction fluctuations in ball screws.
Among its many features, the new ball screw stabilises drive torque and reduces friction fluctuations when reversing its direction of motion, thereby improving motion accuracy and reducing quadrant glitch motion errors. The result is a near elimination of the second peak. Indeed, up to 20% less friction fluctuations also contributes to reducing the height of the first peak.
Through a combination of NSK's new ball screw and software servo controller compensation, machine tool manufacturers can assure their customers of significant improvements in machined surface quality. Furthermore, the enhanced surface quality eliminates or reduces the need for any previously required burnishing or polishing processes, reducing lead times, while lower drive torque contributes to energy savings. All of these benefits provide machine tool builders with the opportunity to pitch unique selling points to potential customers.
PR Ref. L062022-N | 1/3
To maximise convenience for machine tool manufacturers, the mountings of NSK ball screws with quadrant glitch control are fully interchangeable with those of conventional products, allowing adoption without costly equipment changes. The ball screw will be available in shaft diameters from 25 to 63mm, with leads from 5 to 30mm. Preload types will include: offset preload (Z preload), double nut preload (D preload) and spring-type double nut preload (J preload).
1) Motion error during circular interpolation machining (with servo controller compensation)
2) Enlarged view of machined surface (simulated image)
This article also featured in the December/Jan issue below
What if we could lubricate our bearings remotely, from any device, making sure that the right amount and right lubricant are always used – and even better, based on bearing condition? Then we would address the 3 main lubrication issues which cause most of early bearing failures. Today this is already possible. Using ultrasonic sensors and single point lubrication devices, all connected to a central system, we can now bring lubrication practices to a whole new level!
Prevention in place of monitoring
We have a serious problem with bearing condition monitoring! Technology is making it easier and more cost-effective to monitor our bearings in real-time and as a result, we are seeing sensors and systems being installed on equipment at an exponential rate.
There is a race from these monitoring systems to detect the onset of failure (Point P on the P-F curve) at the earliest possible point. And this race to detect a failure is a serious problem. We are spending more money and extra TIME to detect a failure when we should be preventing that failure in the first place.
Addressing lubrication issues – the root of most bearing failures
It is no secret that over 80% of premature bearings failures can be traced back to lubrication related issues. These issues can be put into three general categories: inadequate lubrication (over or under lubricated), wrong lubricant, and contamination. When it comes to addressing premature bearing failure, reducing the impact on just one of these issues can have a large impact on the bearing life. But when we start to address all three, then we canreach excellence in our lubrication programs.
It’s all about the friction levels
A lot of expertise needs to be designed into the bearing selection and lubrication requirements, no technology will likely ever replace the need for trained and experienced lubrication experts.But when it boils down to it, it is all about friction - that’s why they are called anti-friction bearings.
Once the correct bearing is installed properly and the right lubricant is chosen, it comes down to managing that friction in the bearing by using the correct regreasing volume and frequency. Simple to understand but often difficult to put intopractice.
Time based lubrication vs condition-based: using ultrasound to avoid under and over-lubrication
One technique is to use time-based lubrication. In this case, regreasing is done based on time, with a predetermined amount of grease. This method is often based on an ideal calculation that is not reflective of the real-life condition that influences the friction in the bearing. This often leads to under greasing or over greasing the bearing.
A step-change in lubrication practices came with condition-based lubrication. Using ultrasound to measure the friction in real-time to determine exactly when lubrication (and how much)is required to bring the friction back to or near the ideal level. Moving to ultrasound-assisted lubrication will ensure we do not over or under lubricate but has still not addressed the two other lubrication related issues: using the correct lubricant, and contamination.
What about automatic lubricators?
To address these two other lubrication issues many have turned to automatic lubrication devices or auto lubers. Automatic lubrication provides a safer and more convenient method of supplying the precise amount of lubricant into the bearings on a more frequent basis.
These devices ensure we always use the correct grease stored in the device but also reduce or eliminate the possibility of contamination caused by the operational environment. These devices are time-based and set to dispense lubricant on a set frequency or run time.
The auto lubricant devices have evolved to become smarter. Many of them not only dispense the lubricant but can also set alarms based on excessive feedback and low lubricant.
The best of two worlds: SmartLube – single point lubricator, remotely operated, based on friction levels
We have two solutions addressing the different aspects of the common lubrication issues. On one side we have ultrasound-assisted lubrication, using friction to determine when and how much lubrication is required. Combined with good lubrication practices, it will provide benefits but still requires an investment in time and training to ensure the proper lubricant is used to reduce the potential of contamination.
On the other side, we have automatic lubrication devices ensuring the correct, contaminant-free lubricant but still based on time or running hours versus the condition or friction in the bearing, often still leading to not optimizing lubrication frequency.
What if we were able to combine the proven precision and best practice of condition-based lubrication using ultrasound with the convenience, safety, and accuracy of automatic lubrication devices? We would then have a solution that allows us to lubricate our bearings only when required by measuring friction and ensuring we always use the correct, contaminant-free lubricant every time. That’s exactly what the SmartLube from UE Systems does.
Lubricate based on friction, from any device, anywhere
When we use technology to make all this remotely operated, we can now monitor the real-time friction of our bearings and, when needed, remotely dispense the correct lubricant. All this with theconfidence that the lubricant is getting to the bearing with real-time alerts and notifications from any internet-connected device, anywhere in the world!
The OnTrak SmartLube by UE Systems has the power of real-time bearing friction monitoring and the convenience, safety, and accuracy of single-point bearing lubricators. Lubrication experts can now lubricate remotely with confidence from anywhere, anytime, on any device.
How does it work?
This disruptive device works with a simple concept: ultrasonic sensors are permanently mounted on the bearings to monitor friction levels. All this data is sent to a central processing unit – the OnTrak – and can be viewed in dashboards using any internet-connected device. The OnTrak then is also connected to single point lubrication devices. Based on the friction levels and on setup alarms, we now have the possibility to tell the OnTrakthat a certain bearing needs lubricant. The OnTrak will then instruct the SmartLube – single point lubricator – to dispense lubricant, just the right amount. And the best part: all can be done remotely, anywhere, anytime.
SKF has unveiled a trio of new seal profiles for its SNL plummer block housings. For distributors and end-users an efficient and cost-effective means for their production has also been introduced.
The latest SKF seals have been developed for applications where better sealing performance is required than that provided by a labyrinth seal, but where space does not allow for a taconite seal. The new seal profiles are: TX, a single acting design with a lip seal facing outwards that prevents the ingress of contaminants while enabling grease flushing; TY, a double acting design with a lip facing outwards and a lip facing inwards; TZ, a double acting solution that features two single-lip seals in a back-to-back configuration.
The reliability of most rotating equipment is almost inevitably linked directly to bearing life, and it is estimated bearing failure is responsible for almost 21% of these equipment failures (Bloch, 2011).
Research into bearing failures shows that just over half of these are a result of contamination of the bearing oil (Fig 1). Clearly it is therefore essential to ensure that contamination of the bearing lubricant is minimised and if possible eliminated if optimum bearing life is to be achieved thereby improving the equipment reliability (MTBF).
Save your bearings with LabTecta®66, which can reduce bearing oil contamination from 83% to 0.0003%.
Research shows that 52% of bearing failures are due to contamination of the bearing oil, which represent 20.8% of all rotating equipment failures.
LabTecta®66 is a labyrinth design bearing protection seal, which is proven to increase equipment reliability in pumps, electric motors, fans, pillow blocks, steam turbines and gearboxes.
By offering a wide choice of materials and heat treatments for rolling bearings, performance and operating life can be optimised, even for the most demanding industrial applications, says Dr Steve Lacey, Engineering Manager at Schaeffler UK.
In recent years, there has been a significant increase in the demand for rolling bearings that, even under extreme operating conditions – including lubricant starvation, highly corrosive or high temperature environments – still provide a long operating life and optimum performance.
But selecting a suitable material or heat treatment process for rolling bearings often requires expert advice and guidance, normally from the manufacturer of the bearings. Selection depends on the application itself and the specific environment in which the bearings will operate. This means a number of factors require careful consideration, such as the mechanical, chemical and thermal requirements placed on the bearings, as well as lubrication conditions, particularly if the application requires dry running bearings.