35.1 Maintenance and maintenance Scheduling.
35.1.01 Most maintenance seen to date at older mills is either on a : "repair when breakdown" basis or on a scheduled time preventative basis. Both systems have considerable failings; the first one needs no explanation, it is always too late, the second one depends on scheduled inspections of the installed equipment in order to discover (and remedy) the condition that leads to the breakdown, damage etc.
With the knowledge acquired over many years of mill operation in many different mills and under equally as many different circumstances various systems have evolved to control and "manage" maintenance. 35.1.02 One of the more successful ones can be termed:"break down fore
cast" or a predictive system.
Such a system requires the proper recording of machine/ equipment utilization (i.e. running hours, operating loads, through put rates etc.) and the proper recording of repairs effected in terms of time, parts etc. Once the above recording system is established, usually the cost of maintenance and the total spare part inventory cost decrease, resulting in a lower overall total cost of production.
35.1.03 More efficient maintenance control by management will reduce the stock holding levels of the three major areas :
- consumables (which is about 15% of total)
- materials, pipes, valves, fittings etc. (which is about 25 % of total) and - machinery spare parts (which represent about 60 % of total stock
holding).
Usually maintenance cost operate in cycles,i.e. a very heavy cost this
year is followed by fairly moderate costs the following one or two years. 35.1.04 The main area for (initial) attention is good and consistent recording, so
that trouble areas can be identified and analyzed to attempt to predict (the cause of) failure of the machine.
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made:
a) Establish priorities b) Plan, Schedule work
c) Prepare time schedules d) Prepare work orders
e) Make cost estimates
f) Keep track of costs
g) Control of both material and spares holding h) Scheduling for preventative maintenance i) Record historical data of repairs etc.
j) Train personnel
35.1.05 All above have a specific function and apart from the actual physical repair work most of the above administrative tasks can be assisted to a high degree with the introduction of the computer in the workshop/store environment, for the recording, sorting and linking the gathered data.
Suitable interpretation of the data as noted above allows the following: a) better control by the engineering staff
b) identification / reduction of excessive R&M costs c) early indication of equipment problems / failure d) improved planning / scheduling options
e) repetitive failures can be identified / analyzed, leading to f) improvements in re design, lay out, replacements etc. g) less emergencies, more reliability
h) less paper work (computerized records)
i) better inventory control through instant access to updated data
j) lower overall stock holding, lower costs
Computer utilization to assist in the record keeping and the data bases should be on at least the following:
35.1.06 Individual machine records.
Ideally if a machine has a nameplate, all data on that should be transferred to a data base that contains all equipment information, including equipment number (a code cross reference number to the stock inventory), original cost, replacement cost, (updated), warranty data, service agent information, service location, engineering drawings and specifications, parts descriptions and technical performance data.
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Spare parts must be cross referenced to interact with an inventory control data base.
35.1.07 Machine history.
This should consist of a complete history of all equipment, assembled in accordance with machine and station.
It should interact with work orders (job cards), inventory control, maintenance data base and generate reports of corrective actions taken.
35.1.08 Work orders (job cards).
These should interact with the inventory control, equipment history and the maintenance data base, to produce on line reports of status of all equipment in total cost, including labour and parts in accordance with the allocated code numbers.
It should be capable of producing up to date station status reports on demand.
35.1.09 Maintenance data base.
These are basically activity schedules to be produced and to interact with work orders.
(This data can also be interfaced to accept data from a condition monitoring device).
35.1.10 Inventory control.
A coding system to accept inter changeability within a group of mills (general standardization, if planned for can thus be achieved).
Stock holding to be categorized and to have the ability of "purchase order tracking", order printing (on a specified time basis) and maintain necessary lowest stock levels.
35.1.11 The concept of what is termed "condition monitoring" should be introduced in all mills, old or new, and regular monthly full inspections should be done and the results recorded.
This however requires a high level of skill and competence for the carrying out of the inspection and the necessity to shut down and dismantle machinery for inspection.
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Although this type of monitoring is often the only one available,(virtually all larger companies have their own "visiting" engineers or employ consultants to monitor monthly, there are ways to mechanize this monitoring and reduce the reliance on individual levels of skill and competence.
Condition monitoring by recording the machine inherent vibration levels, for instance, can give a very clear indication of a machine condition and whether it is heading for a breakdown or not.
Such measuring/recording devices are not cheap but will, if used consistently, achieve the major aim, which remains:
- reduce costs - improve reliability.
Meanwhile it is strongly recommended that a regular full mill inspection is carried out, mill questionnaires are completed and an accurate record is kept of all the data gathered to build up an "historical data bank" for the existing mills.
A central engineering division to control this and associated mill technical problems should be created, if not already in existence.
A check list for mill visits and a questionnaire for completion by the mill staff before the inspection visit are the essential beginnings of a maintenance orientated recording system.
35.1.12 Monitoring machines / equipment.
An effective preventative system leads to an equally effective predictive system, where action can be taken in time to prevent complete breakdown.
As noted above, the major draw back is the high level of skill and competence required by the staff which carry out the routine inspections and the necessity to shut down and dismantle machinery for proper inspection.
The personal relationship between the engineer or plant attendant and the machines under their care is no longer economically feasible.
The modern integral machinery, totally enclosed and running at high speeds are designed to run automatically with only occasional, minimum attention from attendants.