Why did the Advertising Standards Authority have to rule on what should be common knowledge? What is HAVS monitoring best practice, what do insurers say and could zero monitoring be the best option? You would have thought that the issues surrounding wrist-mounted vibration monitors had already been thoroughly settled. Apparently not so in the minds of some. The following is an outline of some of the very costly myths associated with
Automated HAVS Tool Condition Vibration Testing
HAV-Test is used to cut the scheduled tool maintenance programme costs by 40% – 60% and to minimise Hand-Arm Vibration risk.
The unique vibration analysis technique used by HAV-Test is currently the only practical way to determine the mechanical condition of rotating tools. The HAV meter measurements commonly used in tool maintenance contracts do not assess tool condition and cannot be used to prove that refurbished tool vibration is within the manufacturers’ declared value specification.
The system provides rapid (in seconds), automated rotating tool vibration workshop testing to determine the mechanical condition of tools. It not only detects the high percentage of tools that do not require maintenance (a huge cost saving), but it also improves tool availability (more cost saving) and ensures that the overhauled tools are mechanically “as new”, generating the lowest levels of Hand-Arm Vibration possible (less risk).
Tool Maintenance Contracts
Vibration Maintenance Measurements – Beware HAV Meter Tests!
Increasingly, post-maintenance vibration checks are included in tool maintenance contracts, either at the behest of the user or as an additional service from the provider. Currently, these checks are usually carried out using a HAV meter. Unfortunately, this provides no useful information about tool condition or vibration levels.
“Theory”: HAV meter measurements prove that the refurbished tool vibration is within the manufacturers’ declared value specification – and this will show that the tool has been has been returned to “as new” mechanical condition.
Reality: HAV meter measurements cannot be compared with manufacturers’ (ISO 28927) declared values – the test conditions are completely different – nor do they provide any useful information about the mechanical condition of the tool (except obvious gross defects). They could provide risk assessment values, but only if the tool is tested under simulated conditions that accurately reflect those in the workplace.
Time v Condition Based Maintenance Regimes v HAV Risk
The levels of Hand-Arm Vibration produced by many tools are strongly influenced by their mechanical condition. Field (HAV) vibration from tools can increase by an order of magnitude as the tool condition deteriorates – and risk assessments are based on the typical worst (poorly maintained) case.
Time based maintenance schedules reduce the range of vibration levels. However, some high use tools will not be picked-up before they become very worn, whilst many other tools will be needlessly overhauled. A condition based maintenance schedule uses automated vibration signature testing in the workshop (over a few seconds) to provide an instant evaluation of the mechanical condition of the tool. If the tool is mechanically “as new”, then it is returned without overhaul, increasing availability. If a fault is found (even in the early stages – the tool might otherwise be used for months with steadily increasing vibration), then it is stripped for maintenance. This not only reduces maintenance costs (often by 40% – 60% or more), but over a period it also substantially reduces the vibration exposure of operators. As they only use tools that are in good condition, the range of vibration values during normal use is substantially reduced (see graphic).
As the condition based approach will also detect any maintenance induced faults (e.g. a bearing with a manufacturing defect), it ensures that all operators use equipment that is mechanically “as new”. This corresponds to the lowest vibration – and lowest HAV risk – possible for each model of tool.
Pre-maintenance: conventionally, all tools due for maintenance are refurbished, despite the fact that 40% – 60% of them may be in perfect condition. HAV-Test identifies these tools, drastically reducing maintenance costs and increasing tool availability.
Post-maintenance: HAV-Test will confirm that the refurbished tool vibration is within the manufacturers’ specification and will identify any that do not comply.
HAV-Test in Operation
Pre-Maintenance Tool Condition Diagnosis: Fit the simple, robust transducer and operate the tool briefly. HAV-Test generates and compares the vibration signature with pre-configured criteria for the tool type in “as new” condition. This identifies tools that do not require maintenance – they can be returned to the user, saving the cost of overhaul and down-time caused by the unavailability of a tool. HAV-Test can also provide a detailed diagnosis of any component faults in a tool which can be used to guide maintenance.
Post-Maintenance Tool Condition Check: Once a tool has been overhauled, the tool condition diagnosis is repeated to confirm that the vibration signature has been returned to the manufacturers’ “as new” condition and that there are no component (e.g. damaged bearing) or assembly faults that will reduce the life of the tool and cause high levels of operator HAV exposure.
Traceable Documentation: HAV-Test stores the vibration data in a simple, time stamped database format to provide a permanent record of the maintenance process.
HAV-Test Hardware and Software
The HAV-Test software is a customised version of the ProTest noise and vibration production test system. It converts any PC into an automated vibration test system, applying tool specific stored expertise to identify component faults that could cause an increase in Hand-Arm Vibration when the tool is in normal use.
Tool Condition Vibration Testing
Comparing the vibration signatures for a simple new tool running at a nominal 18000rpm with that of a similar tool with a damaged bearing gives similar overall vibration levels. However, the bearing fault shows up only in the high frequency peaks which are filtered-out by HAV meters – the overall filtered / unfiltered vibration levels are similar, but all the diagnostic fault data has been removed by the HAV filter.
The only reliable way to assess tool condition is to compare the vibration signature of the tool under test with the average typical signature for the model acquired from tools in perfect condition. This is the technique used in HAV-Test.
The averaged signature is then used to generate a fail criterion for the whole signal. If a tool signature falls outside this criterion, then the mechanical condition
is not within the manufacturers’ tolerance and the tool requires maintenance. If necessary, additional tests can be applied to pinpoint the cause of the fault as an aid to maintenance e.g. excessive run-out, bearing fault, balance …