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The low cost tribology laboratory
wear, 66 (1981) 1 - 7 0 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
THE LOW COST TRIBOLOGY
1
LABORATORY*
J. SCHOFIELD Faculty
of Engineering,
Liverpool
Polytechnic,
Liverpool
(Gt. Britain)
(Received December 24,1979)
Summary In further and higher education, finance for capital items in laboratory development is extremely difficult even in times of national prosperity. In times of financial constraint it is virtually impossible to equip a new laboratory. The following paper outlines low cost laboratory experiments developed on a consumable item budget using a maintenance workshop for simple woodwork~g and machining operations to fabricate the apparatus.
1. Introduction In the multidisciplinary subject of tribology there are many areas such as chemistry, physics, mathematics, metallurgy, metrology and engineering which interact and overlap in tribological areas. Standard laboratory equipment can be used or readily modified to illustrate basic tribological principles. The experiments fall naturally into the following groups: metallurgy, chemistry, fluid mechanics, tribophysics, wear, microbiology and metal forming.
(1) One experiment is the in situ casting of a journal bearing in Babbett metal. A bearing metal is preferred although a low melting point metal such as Woods metal melting at 90 “C can be used. For ambitious experimenters brass or phosphor bronze can be cast using a self-igniting crucible ($1.50 (1978)) to melt the metal, thus eliminating the need for a furnace. (2) Small samples of the casting metal can be taken for metallurgical examinations. This gives an experiment in polishing, etching and microexamination using standard metallurgical equipment. *Presented at the 4th International 10 - 15,1979.
Conference on Tribology, Paisley, September
2
(3) A standard metallurgical polishing machine can be adapted as a wear rig to measure weight loss for a given load at a fixed speed over a given time. An interesting variation of this test can be applied to show the effect of a Tartan running track on different types of rubber-soled running shoes. The polishing disc holds the Tartan track material and rubber discs of various grades are substituted for the metallurgical discs (Fig. 1). (4) Hardness testers can be fabricated from designs outlined in ref. 1.
P
a ‘..
Fig. 1. Metallurgical
polishing machine.
Fig. 2. Solvent distillation
rig.
3. Chemistry (1) Vegetable oil can be extracted by standard solvent distillation techniques from crushed ground nuts, palm nut kernels, castor seeds etc. (Fig. 2). (2) The vegetable oil can be reduced to a fat by using a standard chemical technique. (3) The vegetable fat can be converted to a grease; a comparison can also be made with other greases manufactured at the same time from other bases such as clay, lime, soda etc. (4) Hardness and drop point tests can be carried out on the various manufactured greases (Fig. 3). (5) The oxidation effects of heat and agitation can be compared on oil samples containing varying percentages of oxidation inhibitors such as Ionol (Fig. 4).
3
Fig. 3. Hardness and drop point testing machines (grease).
Fig. 4. Oxidation rig.
Fig. 5. Soluble oil apparatus.
(6) Blotting paper tests of acidity, dispersency, contamination etc. can be used to show the progressive deterioration of used oil. (7) The “crackle test” can be carried out using aluminium foil (cooking foil) twisted to form a spoon shape. If a few drops of water-contaminated oil are placed in the bowl of the spoon and heat is applied the presence of water will be indicated by crackling or boiling of the oil. (8) Soluble oils can be checked for correct ratios by splitting them back into the original amounts of oil and water (Fig. 5).
4
4. Fluid mechanics (1) Simple viscosity comparison tests can be carried out using drops of an unknown oil rolling on an inclined plane in comparison with two liquids of known viscosity. (2) A viscosity comparison test similar to that of (1) but using ball bearings in glass tubes can be carried out. Other possible experiments involve the following: (3) the modified Redwood apparatus (see ref. 2, p. 3 7) ; (4) the suspended level test (commercially available); (5) the rotating paddle test (Brookfield viscometer; commercially available) (Fig. 6) ; (6) the hydrodynamic lubrication model [ 2, 31 (Fig. 7).
Fig. 6. Brookfield
viscometer.
Fig. 7. Hydrodynamic
lubrication
model.
5. Tribophysics (1) Contact areas between loaded surfaces measured by using ball and roller bearings coated
can be shown and with copper sulphate.
5
(2) Heat loss or gain in bearings with different colours and/or surface roughnesses can be demonstrated by small heating elements inserted in each type simulated by aluminium cylinders machined to about 50 mm in diameter by 100 mm long. The two holes are drilled in the face of each cylinder. One hole 12 mm in diameter and 75 mm deep holds the 12 V heating element which represents the heat generated from a rotating shaft. The second hole 3 mm in diameter which is offset from the 12 mm centre hole holds a mercury-in-glass thermometer (Fig. 8). (3) Sliding friction tests can be carried out on various types of adjustable inclined planes. (4) Rolling friction tests can be carried out on inclined planes with grooved tracks to accommodate rubber balls of various grades of hardness (squash balls). A further refinement can be made in the methods of measuring ball speeds, e.g. microswitches and microsecond timers. (5) Photoelectric techniques can be used to demonstrate the stress distribution in roller bearing assemblies. Inner and outer rings, rollers etc. can be cast in an epoxy resin and machined to close limits. Loads can be applied through a simple lever mechanism and when viewed through Polaroid sheets against a light source (daylight) photoelastic fringes can be observed (Fig. 9).
- --____ Fig. 8. Heat loss apparatus.
Fig. 9. Photoelastic
rig.
6. Wear (1) Simple wear tests (volume or weight) can be carried out using the headstock, bed and tailstock of a small lathe. A revolving mandrel with various weighted bushes can establish wear rates or wear constants K. (2) Four-ball tests can be carried out using a modified pistol drill, stand, oil cup and torque spanner. (3) If the facilities of a radiochemistry laboratory are available a range of wear tests can be carried out using the loss of radioactivity as a wear measurement parameter.
6
(4) Drilling tests can be carried out on the number of holes drilled in mild steel plate using a carbon steel drill (high speed steel drills last too long). Various soluble oil ratios or additives in soluble oil can be used to establish the maximum drilling life condition. A more sophisticated test is to establish a tape programme to drill a series of holes along a given path on fixed centres until drill failure occurs; a geometric average of holes drilled per three drills per test can be taken.
7. Microbiology (1) Bacterial counts using dip-slides can be carried out on soluble oil emulsions in machine tool sumps. If the facilities of a microbiology laboratory are available then staining, culturing and sterilization experiments can be carried out. (2) Corrosion effects from anaerobic activity can be determined using a modified Herbert corrosion test. A more sophisticated test involves the use of a surface texture measuring instrument such as the Talysurf before and after the tests. A simple type of surface measuring instrument is described in ref. 1, p. 15.
8. Metal forming (1) A modified Erichsen sheet metal test can be carried out to study the effect of friction between deforming metal and a punch surface with different lubricants (ref. 1, p. 24, Figs. 19 and 20). (Details of this test can be obtained from Pearson Panke, 1 - 3 Hale Grove Gardens, London, Gt. Britain.)
9. Conclusion The 30 experiments outlined give some indication of what can be achieved on a low budget and with much ingenuity. The educational advantages that accrue are due to the lack of sophistication and complication in the equipment so that the student readily understands what is taking place. The experiments are all practically biased so that the student also benefits educationally in an area which all too often lacks practical application. In the Department of Mechanical Marine and Production Engineering at the Liverpool Polytechnic there are seven tribology streams involving students in Higher Diploma, Higher Certificate, full time, part-time and sandwich degree schemes as well as postgraduate students. These students have all benefitted from the low cost laboratory experiments that have been developed over a 10 year period.
7
References 1 T. Kelly (ed.), School Science and Technology, Schools Council Project Technology, London, 1969. 2 Tribology Projects for Schools, Committee for Industrial Technologies, Department of Industry Committee on Tribology, London, 1972. 3 D. Dowson, Laboratory experiments and demonstrations in tribology, Tribology, 1 (2)(1968)104-108.
THE LOW COST TRIBOLOGY
1
LABORATORY*
J. SCHOFIELD Faculty
of Engineering,
Liverpool
Polytechnic,
Liverpool
(Gt. Britain)
(Received December 24,1979)
Summary In further and higher education, finance for capital items in laboratory development is extremely difficult even in times of national prosperity. In times of financial constraint it is virtually impossible to equip a new laboratory. The following paper outlines low cost laboratory experiments developed on a consumable item budget using a maintenance workshop for simple woodwork~g and machining operations to fabricate the apparatus.
1. Introduction In the multidisciplinary subject of tribology there are many areas such as chemistry, physics, mathematics, metallurgy, metrology and engineering which interact and overlap in tribological areas. Standard laboratory equipment can be used or readily modified to illustrate basic tribological principles. The experiments fall naturally into the following groups: metallurgy, chemistry, fluid mechanics, tribophysics, wear, microbiology and metal forming.
(1) One experiment is the in situ casting of a journal bearing in Babbett metal. A bearing metal is preferred although a low melting point metal such as Woods metal melting at 90 “C can be used. For ambitious experimenters brass or phosphor bronze can be cast using a self-igniting crucible ($1.50 (1978)) to melt the metal, thus eliminating the need for a furnace. (2) Small samples of the casting metal can be taken for metallurgical examinations. This gives an experiment in polishing, etching and microexamination using standard metallurgical equipment. *Presented at the 4th International 10 - 15,1979.
Conference on Tribology, Paisley, September
2
(3) A standard metallurgical polishing machine can be adapted as a wear rig to measure weight loss for a given load at a fixed speed over a given time. An interesting variation of this test can be applied to show the effect of a Tartan running track on different types of rubber-soled running shoes. The polishing disc holds the Tartan track material and rubber discs of various grades are substituted for the metallurgical discs (Fig. 1). (4) Hardness testers can be fabricated from designs outlined in ref. 1.
P
a ‘..
Fig. 1. Metallurgical
polishing machine.
Fig. 2. Solvent distillation
rig.
3. Chemistry (1) Vegetable oil can be extracted by standard solvent distillation techniques from crushed ground nuts, palm nut kernels, castor seeds etc. (Fig. 2). (2) The vegetable oil can be reduced to a fat by using a standard chemical technique. (3) The vegetable fat can be converted to a grease; a comparison can also be made with other greases manufactured at the same time from other bases such as clay, lime, soda etc. (4) Hardness and drop point tests can be carried out on the various manufactured greases (Fig. 3). (5) The oxidation effects of heat and agitation can be compared on oil samples containing varying percentages of oxidation inhibitors such as Ionol (Fig. 4).
3
Fig. 3. Hardness and drop point testing machines (grease).
Fig. 4. Oxidation rig.
Fig. 5. Soluble oil apparatus.
(6) Blotting paper tests of acidity, dispersency, contamination etc. can be used to show the progressive deterioration of used oil. (7) The “crackle test” can be carried out using aluminium foil (cooking foil) twisted to form a spoon shape. If a few drops of water-contaminated oil are placed in the bowl of the spoon and heat is applied the presence of water will be indicated by crackling or boiling of the oil. (8) Soluble oils can be checked for correct ratios by splitting them back into the original amounts of oil and water (Fig. 5).
4
4. Fluid mechanics (1) Simple viscosity comparison tests can be carried out using drops of an unknown oil rolling on an inclined plane in comparison with two liquids of known viscosity. (2) A viscosity comparison test similar to that of (1) but using ball bearings in glass tubes can be carried out. Other possible experiments involve the following: (3) the modified Redwood apparatus (see ref. 2, p. 3 7) ; (4) the suspended level test (commercially available); (5) the rotating paddle test (Brookfield viscometer; commercially available) (Fig. 6) ; (6) the hydrodynamic lubrication model [ 2, 31 (Fig. 7).
Fig. 6. Brookfield
viscometer.
Fig. 7. Hydrodynamic
lubrication
model.
5. Tribophysics (1) Contact areas between loaded surfaces measured by using ball and roller bearings coated
can be shown and with copper sulphate.
5
(2) Heat loss or gain in bearings with different colours and/or surface roughnesses can be demonstrated by small heating elements inserted in each type simulated by aluminium cylinders machined to about 50 mm in diameter by 100 mm long. The two holes are drilled in the face of each cylinder. One hole 12 mm in diameter and 75 mm deep holds the 12 V heating element which represents the heat generated from a rotating shaft. The second hole 3 mm in diameter which is offset from the 12 mm centre hole holds a mercury-in-glass thermometer (Fig. 8). (3) Sliding friction tests can be carried out on various types of adjustable inclined planes. (4) Rolling friction tests can be carried out on inclined planes with grooved tracks to accommodate rubber balls of various grades of hardness (squash balls). A further refinement can be made in the methods of measuring ball speeds, e.g. microswitches and microsecond timers. (5) Photoelectric techniques can be used to demonstrate the stress distribution in roller bearing assemblies. Inner and outer rings, rollers etc. can be cast in an epoxy resin and machined to close limits. Loads can be applied through a simple lever mechanism and when viewed through Polaroid sheets against a light source (daylight) photoelastic fringes can be observed (Fig. 9).
- --____ Fig. 8. Heat loss apparatus.
Fig. 9. Photoelastic
rig.
6. Wear (1) Simple wear tests (volume or weight) can be carried out using the headstock, bed and tailstock of a small lathe. A revolving mandrel with various weighted bushes can establish wear rates or wear constants K. (2) Four-ball tests can be carried out using a modified pistol drill, stand, oil cup and torque spanner. (3) If the facilities of a radiochemistry laboratory are available a range of wear tests can be carried out using the loss of radioactivity as a wear measurement parameter.
6
(4) Drilling tests can be carried out on the number of holes drilled in mild steel plate using a carbon steel drill (high speed steel drills last too long). Various soluble oil ratios or additives in soluble oil can be used to establish the maximum drilling life condition. A more sophisticated test is to establish a tape programme to drill a series of holes along a given path on fixed centres until drill failure occurs; a geometric average of holes drilled per three drills per test can be taken.
7. Microbiology (1) Bacterial counts using dip-slides can be carried out on soluble oil emulsions in machine tool sumps. If the facilities of a microbiology laboratory are available then staining, culturing and sterilization experiments can be carried out. (2) Corrosion effects from anaerobic activity can be determined using a modified Herbert corrosion test. A more sophisticated test involves the use of a surface texture measuring instrument such as the Talysurf before and after the tests. A simple type of surface measuring instrument is described in ref. 1, p. 15.
8. Metal forming (1) A modified Erichsen sheet metal test can be carried out to study the effect of friction between deforming metal and a punch surface with different lubricants (ref. 1, p. 24, Figs. 19 and 20). (Details of this test can be obtained from Pearson Panke, 1 - 3 Hale Grove Gardens, London, Gt. Britain.)
9. Conclusion The 30 experiments outlined give some indication of what can be achieved on a low budget and with much ingenuity. The educational advantages that accrue are due to the lack of sophistication and complication in the equipment so that the student readily understands what is taking place. The experiments are all practically biased so that the student also benefits educationally in an area which all too often lacks practical application. In the Department of Mechanical Marine and Production Engineering at the Liverpool Polytechnic there are seven tribology streams involving students in Higher Diploma, Higher Certificate, full time, part-time and sandwich degree schemes as well as postgraduate students. These students have all benefitted from the low cost laboratory experiments that have been developed over a 10 year period.
7
References 1 T. Kelly (ed.), School Science and Technology, Schools Council Project Technology, London, 1969. 2 Tribology Projects for Schools, Committee for Industrial Technologies, Department of Industry Committee on Tribology, London, 1972. 3 D. Dowson, Laboratory experiments and demonstrations in tribology, Tribology, 1 (2)(1968)104-108.