APPLIED TECHNOLOGY MECHANICAL COMPONENTS
CHAIN ENHANCES THE PERFORMANCE OF TISSUE MANUFACTURING MACHINERY
cutting was out of position. It also caused uneven wear on the chains. The result of this was that the accumulator ‘crashed’ frequently. To overcome the problem, engineers at Tsubaki recommended
replacing the existing chain with a high quality, high performance RS16B Lambda version. This has oil-impregnated sintered bushes in each link which act with a coating on the link pins to provide long-term self- lubrication for free movement and flexure, reliability, reduced wear and a long operating life. Such chains also need less frequent replacement and less maintenance. Once fitted to the log saw accumulator, the tissue company saw
immediate improvements. For a start, the self-lubrication meant the chain remained flexible and free running. In addition, the parallel drive chains benefited from Tsubaki’s ‘Match and Tag’ service, which guarantees a maximum length difference of no more than 0.5mm, no matter how long the chain. This means that the logs are always correctly aligned when entering the saw, so they are cut accurately and there are fewer rejects. With no need for additional lubrication, there are cost savings and
contamination problems are eliminated, with the chain surface always dry and clean. The accumulator is also running clean now, eliminating the quality problems associated with contaminated product and preventing the dust-related wear that was causing the machine itself to crash.
Within the often dust-laden environment of tissue manufacturing, the conventional lubricating oils used on chains will soak up some of the dust, leading to blocked lubrication paths and resulting in increased levels of wear and reduced productivity. Ultimately, premature chain failure is almost guaranteed. This was the problem being faced by a tissue paper converting company on its log saw accumulator, where large logs of wound tissue paper collect before being cut to size by high speed rotating blades. A further problem of the contaminated chain was that it lost flexibility, which meant the logs were being presented to the chain badly so that the
Tsubaki
tsubaki.eu
MINI BALLSCREW GETS TO THE HEART OF THE MATTER
The human heart is capable of flow rates of 3-4.5 l/min, adaptive control with speeds from 50 to 200 cycles per minute, and typically more than 100,000 duty cycles per day. For those whose hearts are unable to function in the correct manner, however, companies such as Berlin Heart develop heart support systems, or VADs (Ventricular Assist Devices). Berlin Heart is said to be
the only company to offer such technologies for both adults and children – in fact the youngest patient who was successfully kept alive until a heart transplant could be performed was only eight days old when he received a VAD. The company’s Excor VAD
emulates the operation of a human heart. With this, an air-operated diaphragm pump supports the heart’s function or takes over the pumping function entirely, while in the mobile version of Excor the external artificial heart is driven by a miniature ball screw that is designed and manufactured by NSK. This advanced mobile device emulates the exact way that the human
10 SEPTEMBER 2016 | DESIGN SOLUTIONS
heart functions and under no circumstances is the ball screw allowed to fail. The VAD systems can be implanted inside the body or remain external. With the latter, cannulae are implanted in the patient and connected with air-operated diaphragm pumps located outside the body (paracorporeal). The miniature ball screw used
in the Excor mobile travels 60 to 130 times per minute in a single stroke of up to 55.5mm and pushes a defined quantity of air against the diaphragm that separates it from the cannulae with the patient’s blood circulation. Commenting on why the ball
screw was selected, Nedim Arslan, engineering department manager at Berlin Heart, said “The NSK miniature ball screw achieved an impressive operating life of
approximately 120 million cycles, which was by far the highest in our benchmark tests.” Every three months, or around 10 million
cycles, the ball screw units are maintained, with the shafts cleaned and greased, among other tasks. With this in mind, NSK implemented specific ball screw geometric modifications at the design stage
that make maintenance significantly easier. A further consideration during the design
was the type of grease deployed by the driving system. According to the company, the fact that the miniature 8mm diameter shafts reach temperatures of 70 to 80˚C may seem surprising considering that the servomotors which drive the blood pumps have very low conductance, but it’s an indicator of how much the drive system is stressed. For this reason, it was very important to use grease that is able to operate and survive at these elevated temperatures. A highly finished miniature ball screw with
C3 accuracy class forms the basis of the NSK shaft system used today in the Excor mobile.
NSK T: 01636 605123
www.nskeurope.com
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