Open Cut » Overburden Removal
When a dragline operator purchases a new machine, the specifications relating to lubrication tend to be general rather than definitive. Current practice, therefore, in the lubrication of dragline components requires the operator to select lubricants based on the manufacturers' benchmarks, lubricant suppliers' data sheets and other dragline operators' experience.
It is argued that none of the available data is comprehensive enough to arrive at optimum lubrication, especially under circumstances where new generation lubricants are introduced.
The non-availability of effective bio-degradable lubricants may cause additional difficulties for dragline owners in the years to come.
Comparison and evaluation of lubricants is difficult because lubricant suppliers use a variety of formats in the presentation of specification sheets. A standard format for the preparation of specifications is proposed. The tendency for lubricant supply companies to alter their profile from a technical to a commercial structure has meant that operators have been subjected more to sales promotions than to receiving the type of service they require.
Objectives of the Project
The main objectives of this project were:
- to determine the lubrication modes between contacting surfaces
- to determine the means of transport of the lubricant to the lubrication zones
- to develop bench tests and field trials for evaluating lubricants for draglines
Details of the Project
In this report, dragline machine elements have been analysed, with the lubricant considered as an element of the design process, to arrive at the desired lubricant properties. This is compared with the lubricants currently being used and where anomalies occur, the theory has been challenged and alternatives proposed.
The research has concentrated on the lubrication of open gears as there is a paucity of design data for this type of machine element.
Because lubricant properties, influential to the satisfactory operation of the gears, can only be obtained by testing, significant effort has gone into evaluating standard tests and developing new ones. A range of the lubricants in current use have been subjected to these tests.
Proposed lubricant specifications for open gears are presented in two parts. The first is intended for immediate use. It proposes a standard format utilising existing standard tests and parameters. Its value lies in the adoption of a standard format which will permit comparison and evaluation of lubricants. A second standard format for open gear specifications is proposed.
This document includes some new proposals for specification parameters. It is included for future use because a certain amount of infrastructure will be needed before new parameters can be measured and utilised for specification purposes.
The other elements considered are plain journal bearings, wire ropes and enclosed gears. Although some pertinent information on the lubrication of these elements as found in draglines is given, this is not conclusive and further work on these areas is required.
A comprehensive current design method for oil lubricated plain bearings is given in detail . This is included because there is a lack of design methods for grease lubricated plain bearings which are more relevant to draglines. The design method for oil lubrication has been utilised for grease in the past but the results are likely to be inadmissible.
An investigation into the lubrication of these elements concluded that catastrophic failure of main propel shaft bushes had occurred as a result of poor lubrication. Design calculations pertinent in this case are given. However, this aspect needs further development.
Recommendations for wire rope lubricants normally consist of a wish list of desirable properties. Reference is made to a thorough investigation into mine hoist rope lubrication by Battelle Columbus Laboratories and their resultant recommendations are given. Other work on dragline wire rope lubricants is reported. Further development is required.
The main problem with enclosed gearboxes, relevant to draglines is the tendency for swing gearboxes to overheat. A method for estimating the heat balance of enclosed gearboxes is given in detail and a case history is included.