Below we have explained how you can determine the number of cycles your equipment has undergone, so that you can prepare to replace your equipment, because running expired equipment could lead to user safety concerns and loss of productivity.
Life Cycle Counts (Max. Cycles)
All metal parts such as rotors and buckets are subject to stress, which ultimately makes the lifespan of the part finite. The faster the speed and the heavier the load the greater this stress is.
The stress on a centrifuge rotor and its carriers (buckets) occurs when the system accelerates, reaches max load and then decelerates (one cycle).
We use the maximum allowed speed and maximum allowed load (for the rotor/ bucket combination) to physically test max cycle counts. Through better CAD desing and an improvement in materials the cycle count of rotors and buckets has dramatically increased over the years.
The choice of materials used balances on the physical strength characteristics. The choice is to find the best materials for the application, understand their life cycle limits and to replace them when they reach their limit. Exactly the same principle is applied to aircraft components (turbines, etc.). which are also subject to similar stresses.
Since 2009, Hettich has provided information about the useful life of rotors and buckets used in its centrifuges (this information is etched or engraved on each rotor and bucket.) The term "cycles" refers to the number of times a rotor and its buckets can be spun. This in line with requirements of continuous improvement and awareness of safety and reliability. One cycle is one centrifugation run.
(Example of etched life cycle counts)
It is important to know (or be able to calculate) the number of cycles a rotor and its buckets have experienced. Appropriate replacements steps can be planned for, when the max cycle counts has been reached. Using a simple calculation, the cycle count can be determined or estimated.
Note: Current centrifuges will provide a count via the control panel, however older centrifuges, prior to 2009, require the user to calculate the cycles themselves).
Example: A centrifuge is set to run for 5 minutes at 5000 RPM. It has 7,950 control hours.
7,950 (hrs) = 477,000 minutes
477,000 (mins) / 5 (mins) = 95,400 cycles
Note: speed has no relevance in the calculation.
The accuracy of this cycle count calculation depends on the centrifuge settings staying the same for its entire use. If there are multiple programs and multiple settings, the accuracy diminishes.
Click here to download the Life Cycle Counts PDF.