Actuators – specific method and content for PM
A key part of applying best practice Preventive Maintenance principles to CD actuators requires careful examination of all elements of an actuator system, determining likely ways each element can fail and establishing what systematic procedures can be performed proactively to prevent or diminish chances of failure. Virtually any machine or system including CD actuators can be categorically broken down into functional and material elements. Then each element can be scrutinized to determine likely failure modes based on available information, experience and expert opinion.
Similarities between systems
A review of each element making up different types of CD actuators used to control paper machine sheet basis weight, coating weight, moisture, caliper and gloss reveals a striking though not unexpected similarity in the maintenance aspects of each different system’s elements. Looking across all different types of old or new CD actuators there are similar and in many cases identical PM tasks and task content.
A good example is Smart Weight Profiler and Slice xP; SWP has hundreds of installations some over 15 years old compared to SxP with only dozens of installations so far, all less than four years old. Establishing best practice and content for SxP is simplified by having well developed task lists and content available in SWP which can be easily transferred, in principle at least, to SxP using engineering judgment.
To see how best practice principles can be transferred across actuator types and product generations the following simplified diagrams show material and functional elements of four different CD actuators used to control paper sheet basis weight, coating weight, caliper and moisture profiles. Element categories are color coded in List 1 and correspondingly in Figures 1 and 2. Similar considerations of likely failures and preventive tasks exist for each different element regardless of actuator type.
1. Inputs
2. Intelligence
3. Sources
4. Source distribution and conditioning
5. Active elements
6. Feedback
7. Connections, including source, process and interconnections
List 1. Seven elements or categories of components making up a CD actuator system
Smart Weight Profiler (SWP) system
Figure 1 shows a simplified line diagram of elements making up a Smart Weight Profiler CD actuator system used to control basis weight on a paper machine headbox. The two sources it uses are ambient air and electric power, source distribution and conditioning components are an air compressor, circuit breaker panel and power supplies, inputs are coming from the QCS and a PC based service workstation as well as manual adjustments of the active element actuators by humans.
Figure 1. Elements of a Smart Weight Profiler CD actuator system
Intelligence resides in the main interface cabinet and in remote SIO modules at the wireway interconnecting the active elements which are linear stepping actuators controlling a number of zones across the machine direction. Feedback of the active elements are LVDT position sensors attached to each actuator and process connections are mechanical spindles attaching each actuator across the headbox output slice opening.
An additional input is the machine environment at the headbox active and feedback elements which can be very hot, wet, corrosive and capable of affecting failure rate. Environment at all the components is capable of affecting their performance or reliability depending on its level of intensity.
Slice xP (SxP) system
Figure 2 shows elements comprising the newest ABB generation of weight CD actuator or profiler Slice xP. In this case the only source is electric power; the intelligence is located centrally at the interface cabinet off the machine as well as on machine inside each active element actuator. There is no service workstation as an input however a new input capability comes though the xP actuator assistant which connects individual actuators to a portable PC (laptop) for zone addressing and diagnostics. SxP process connections to the headbox slice are identical to SWP.
Figure 2. Elements of a Slice xP CD actuator system
Nearly identical versions of SWP and SxP called Smart Coat Weight Profiler and Coat Weight xP respectively are CD actuators used to control the sheet profiles of coating being applied at blade coaters.
Preventing failure modes
Failure modes and systematic preventive means of failure for each of the seven elements or categories are similar. For example all sources should be checked at regular designated intervals to be sure they are within specifications. All active elements are subject to wear and will require condition checking and/or parts or whole replacements at certain intervals. All connections whether they are source, process or interconnections such as cables, wires, ducts or pipes should be monitored at least visually and in some cases mechanically or electrically for condition.
Likely failure modes and systematic preventive measures are determined by reviewing product documentation available, interviewing experienced actuator system installation, field service and product development engineers, by comparing failure modes in other actuators, by reviewing historical service and parts replacement data and by using engineering judgment.
This information can be used to compile a draft list of ServicePRO PM tasks. As mentioned previously there are already proven actuator systems with good Preventive Maintenance models to use for models and comparison. Once a draft list of Preventive Maintenance tasks is prepared it should be reviewed by the aforementioned experts and improved accordingly.
The content of each task is extremely important. In this case the risk of too little or too much information becomes very apparent. This is further complicated by the many differences found from one actuator to another even in the case of same actuator types, by the difference in paper machines where no two are exactly identical, by differences in local customs, corporate policies, health and safety requirements and managements requirements and styles.
For this reason two rules used successfully by ABB service in the past are “anything is better than nothing” and “the procedures are not set in stone”. Although ServicePRO provides the necessary steps, information and record keeping required for best practice Preventive Maintenance and continual improvement its software also recognizes each individual site must have the permission and capability within limits to customize local tasks to meet local needs and requirements.
ServicePRO requires local change of any procedure or task to be documented. Typically change occurs to increase MTBF or reduce MTTR. Thus the procedure or task existing before the change should have been used long enough to get a reasonable evaluation of change effectiveness .
Typical ServicePRO PM task requirements for technical content are based on extensive ABB field service experience and shown in
List 2.
1. Type / Purpose
Diagnostic, Repair, Test, Preventive Maintenance
2. Tools / Test Equipment
Other than normal hand tools
3. Materials
Parts
Consumables – lubricants, sealant, etc.
4. Skill level required
User, maintenance tech., Field engineer, specialist, etc.
5. Estimated time to perform
By recommended skill level
6. Estimated frequency procedure will be required
Note conditions that effect frequency
7. Detail
Go-no go limits
8. Safety / health issues
Electrical, mechanical, chemical, radiological, property, Process, etc.
9. Related procedures
Prerequisite procedures, procedures performed in concert or in order.
10. Equipment Operational status required to perform this procedure.
Equipment downtime, process downtime, requirements.
List 2. Preventive maintenance task’s technical requirements
Creating and improving tasks and their content
ServicePRO procedures in order to qualify as best practice not only need local customization capability but also must be considered as living procedures subject to improvement over time based on experience. The ServicePRO tool being soft in nature and possessing central data gathering capability from hundreds of users affords this capability for improvement based on real data.
In summary for any CD actuator the method for determining best practices Preventive Maintenance tasks requires obtaining and reviewing all the available information relevant to maintenance of the particular actuator in question. Preventive Maintenance tasks used by actuator installation and service engineers as well as any Preventive Maintenance recommended by the product developers may also be available. These engineers should be interviewed and any written information available from them should be obtained.
Best practice ServicePRO PM tasks for Smart Weight Profiler and Slice xP
This third and last section applies the new method to determine best practice ServicePRO Preventive Maintenance tasks for Smart Weight Profiler and Slice xP. All product data, expert interviews and advice available is sought and obtained as best possible. The best available and applicable models are selected as a starting point; as the method is worked out each element and all its components as detailed in
List 1 and
Table 1 must be given consideration. “Cast in concrete” micro steps are not appropriate as each situation is different. However the main steps of the method are:
1. Review all product information including service manuals
2. Contact and interview experienced installation, field service and product engineers
3. As possible obtain any local or individual’s custom Preventive Maintenance task lists or content
4. Create Preventive Maintenance tasks using any applicable or transferrable models
5. Make sure likely failures and preventive means for all seven elements are considered
6. Improve the Preventive Maintenance tasks to best practice by getting reviews from experts cited in step #2.