|
Precision Maintenance Explained
Precision Maintenance is the strict adherence to exacting machinery health standards for the entire equipment life cycle
Here a list of the key requirements for a precision maintenance program:
- Accurate fits and tolerance at operating temperature
- Impeccably clean, contaminant-free lubricant life-long
- Distortion-free equipment for its entire life
- Forces and loads into rigid mounts and supports
- Laser accurate alignment of shafts at operating temperature
- High quality balancing of rotating parts
- Low total machine vibration
- Correct torques and tensions in all components
- Correct tools in the condition to do the task precisely
- Only in-specification parts installed
- Failure cause removal to increase reliability
- A system to apply the standards in a successful way
You can see that there is nothing in that list that should not already be standard practice in every industrial operation. But it hardly ever seems to happen.
The reason is that no one sets the exact equipment condition standards to be met, and so everyone works to their own standards. This leads to variation, confusion and inaccuracy that, in time, causes you the operating problems and equipment failures you live with. It is as predictable as night following day. But it does not need to be that way.
Here is a list of standards that you must determine and set for every piece of equipment, every nut and bolt, every electrical connection, every motor base plate, every gearbox,... everything... in your plant and equipment.
- Distortion
- Looseness
- Lubrication
- Cleanliness
- Shaft alignment
- Balancing
- Temperature
- Vibration
|
- Assembly
- Installation
- Tools & condition
- Skills & their competency
- Job Records
- ??? What ever else your equipment
- ??? requires to have a lifetime
- ??? of health and wellness
|
What you will have in your standards are 'the numbers' that are to be measured and recorded as proof of compliance to standard.
- Like the exact turn from snug to tighten a nut so the torque is correct (you could state newton-meters of torque, but the up-to 25% error in using a tension wrench may not be accurate enough for you);
- the maximum size and amounts of contamination you will accept in your lubricant;
- the exact gap between parts that you can test with feeler gauges;
- the size and dimensional tolerance you will accept for a shaft at a bearing location before you replace the shaft
- the amount of distortion you will accept on a part before you replace it with new
- the exact distance along a shaft from a datum to mount a disc;
- the exact alignment accuracy between drive shafts that you can measure with a laser or by twin reverse dial indicators,
and so on for everything on every machine and piece of equipment in your operation.
Once you have 'numbers' to work to, you can prove if a thing is right or not. Once you measure and prove 'the numbers' (which are your minimum standards) then you know (almost without question) you are within requirements. You are virtually certain that the job is done right and the equipment is running precisely and operating under precision conditions! You could have had out-of-calibration test equipment that give you a false reading. But your quality management system should have stopped that happening. (You do have a quality management system controlling the quality of your maintenance... don't you!?)
Starting a Precision Maintenance program
When you start a precision maintenance program your intention is to introduce the twelve precision requirements (listed at the start of this article) into your everyday practices.
Everything that everyone does that is related to your plant and equipment will need to meet the standards you set for those requirements. That includes the original equipment manufacturers, operations and maintenance managers, project and design engineers, procurement people, plant and equipment operators and the maintenance crews (yes... including all subcontract work you send out).
Item twelve is the glue that keeps all the rest together. Item twelve says that you will need to install a business process that ensures all the other eleven requirements are actually met for every machine in your operation. That includes recording the dates that the precision standards were met and, if necessary, later checked. You will have records for every piece of equipment, for its entire operating life, of the exact conditions it was built to and it was operated under.
Nothing is left to chance - nothing! And if you do leave things to chance to decide, you can be sure that most times it will go badly for you.
Setting Precision Quality Standards for Your Equipment
The solution starts when management set standards, then promote them, train to them and enforce them.
Where do the standards come from? The list below is an example. They already exist, and have existed for decades. Your challenge is to bring them alive in your operation.
- Accurate Fits and Tolerance – ISO/ANSI Shaft/Hole Tolerance Tables
- Clean, Contaminant-Free Lubricant – ISO 4406
- Distortion-Free Equipment – Shaft Alignment Handbook - Piotrowski
- Forces and Loads into Supports - Shaft Alignment Handbook
- Accurate Alignment of Shafts – Shaft Alignment Handbook
- High Quality Balancing of Rotating Parts – ISO 1940
- Machine Vibration – ISO 10816
- Correct Torques and Tensions – ISO/ASME Bolt, Stud and Nut Standards
- Correct Tools in Condition – ‘As-New specification’
- Only In-specification Parts – OEM specifications, Machinery Handbook
- Failure Cause Removal – ‘5 Why’ ; RCFA
- A system to use the standards successfully – ACE 3T Standard Operating Procedures
You will have to look for additional standards to those listed above. The list is incomplete, but it is a start. Note that there are not always international standards for every standard you will have to set. In that case use the recommendations of experts in their field.
When it comes to equipment distortion and shaft alignment you can start by using the advice in John Piotrowski's 'Shaft Alignment Handbook' (the 3rd Edition is very comprehensive) until you need to set a higher standard. At that point you maybe the world-leader in a field of expertise and you will be setting your own standards to work to, which one day we will all follow.
You will only have done the job of introducing precision maintenance well when:
- you have written and published the specific details company-wide;
- you have held seminars to explain and discuss them with all the people that need to know and use them;
- you have purchased the measuring and testing equipment you need to prove compliance;
- you have written ACE 3T procedures for all activities, and
- you have trained people to the standards and they can achieve them competently;
- you have a document management system that records all important equipment information over its life and allows everyone fast access to the information they need to make good decisions.
Too few companies are that good. But it does not need to be that way.
|