PRELIMINARY RESEARCH ON TRIBOLOGIC WEAR
OF MARINE PUMP SHAFT PINS
Centrifugal angular momentum pumps are utilized in the cooling system of high and medium speed engines, for supplying boilers, in bilge systems, ballast systems and in firefighting installations. Such an extensive use of angular momentum pumps on board is connected with their numerous advantages. However during operation the wear of marine hull, the rotor and shaft seals takes place. The research aimed at examining the improvement of operating durability of marine pumps in place of seals mounting. The service properties are related to contact wear tests, tribologic wear and electrochemical corrosion that are to be carried out.
The paper presents the first stage of tribologic wear tests which dealt with the selection of counter sample material and of the lubricating agent for the tribosystem.
A roller made of stainless X5CrNi18-10 steel was used for the research. The process of sample surface finish lathing was performed by a cutting tool provided with super finish plates Wiper type by Sandvik Coromant. On the basis of the results obtained the counter sample material was defined (C45 steel) for performing appropriate tribologic tests. The lubricant for the matched tribologic couple was chosen to be the machine oil enriched with an improver.
Keywords: angular momentum pump, surface layer, friction wear, stainless steel.
INTRODUCTION
Sea water pumps belong to a group of centrifugal angular momentum pumps. Their wide application on board vessels is related to their numerous advantages which comprise simple construction, good performance characteristic, easy adjustment, quiet work and the possibility of applying direct electric motor drive. Angular momentum pumps are utilized in the cooling system of high and medium speed engines, for supplying boilers, in bilge systems, ballast systems and in firefighting installations. During their service the wear of pump body, rotor, sealing and shaft takes place. One of the greatest problems of modern production techniques is the achievement of an appropriate quality at minimal costs and accompanied by the production efficiency increase. Therefore while designing the production process, the technology used should have a considerable influence on the durability and reliability of machine parts to be produced. During finish treatment the final dimensions as well as functional properties are imparted to a given element by application of proper treatment type. The process engineer has a range of production techniques to choose for the proper surface layer formation. It is crucial to find a suitable solution which will meet the requirements as well as
the work conditions of a given machine part. The traditional finish treatment methods of marine pump shafts include grinding and finish turning. Industrial requirements make it necessary to reach the surface of high precision (3–5 accuracy class) simultaneously ensuring the roughness of Ra = 0,16÷0,01 µm. Such
an effect can be obtained by proper treatment methods of high accuracy.
The traditional method of finish machining of marine pump shaft pins include finish lathing and grinding. The finish lathing that makes use of traditional plates makes it possible to reach the Ra parameter value from 0,32 to 1,25 µm. A very precise turning is usually performed by tools resistant to abrasion, on machines which are characterized by high rigidity, high machining speed and slow feed. The replaceable plates of turning cutting tools are made of diamond and regular boron nitrogen for these working conditions. The turning tools producers also offer cutting tools with replaceable super finish plates which cause machining at simultaneous super finishing of the roughness peaks.
The grinding of shaft pins on grinding machine can generate high costs which are related to the purchase of a grinding wheel. An additional drawback during grinding shafts is the necessity to ensure proper dimensions control and perform the so called honing process which aims at keeping the appropriate geometry of a grinding wheel. As a result of grinding only a suitable surface roughness is obtained without surface roughness consolidation. It is possible to achieve the value of Ra parameter in the range from 0,63÷0,32 µm while with the proper choice of method as well as traditional grinding parameters it is possible to reach Ra value of 0,16 µm. It is worth stressing that the correct choice of a machine, a tool, process parameters and the treatment fluid have a direct influence on the final result.
The above mentioned shaft machining methods do not cause the surface roughness increase which has a considerable influence of their service properties. The grinding wheels used in the production process or lathe tools can lead to contamination of the surface being machined by tool material. Within the intrusions , some areas may be created where the local corrosion can develop. That is why both mechanical and chemical surface turning is used more often as it improves alloy steel resistance to local corrosion.
The process of burnishing shafts proposed here aims at increasing the service durability of marine pump shafts of sea water installations, which should give economic benefits in comparison with traditional methods. Burnishing process enables the achievement of high smoothness of machined surface together with the surface layer hardening. This process has been performed in industrial experience on universal machine tools and on CNC machines but it is regarded as plastic tooling. Therefore the final formation of dimensions and service properties with the use of burnishing constitutes a chipless and dustless treatment, which allows for ranking burnishing among ecological tooling methods. The review of literature pointed out three fundamental purposes of the application of burnishing in the machine elements production process:
• smoothness tooling – which results in the reduction of the surface roughness after machining that precedes burnishing,
• strengthening tooling – which increases service properties (i.e. resistance to fatigue wear, abrasive wear and corrosive wear) by change of material properties in the surface layer,
• dimension-smoothness tooling – which increases the dimension accuracy with simultaneous reduction of surface roughness to its required value.
Burnishing process enables surface working at high dimensional precision (accuracy class 7 and 6), which makes it possible to achieve such advantages as [10]:
• ability to reach high surface smoothness (Ra = 0.32–0.04 µm),
• increase of the surface hardness,
• increase of resistance to surface as well as volumetric fatigue, • increase of resistance to abrasive and scuffing,
• lack of abrasive grain, chips, sharp and hard built-up edge fragments and on burnished surface,
• ability to use burnish tools on universal lathes,
• elimination or reduction of the time consuming operations such as: honing, lapping, grinding and polishing,
• ability to eliminate heat treatment in specific cases, • high process efficiency (one pass of a tool), • high durability of burnishes,
• reduction of expenses related to machine parts production.
Many scientific centres all over the world deal with burnishing treatment. Research programs usually cover issues related to burnishing of cast iron, some heat resisting alloys, stainless steel [7, 8], copper and aluminium alloys, titanium and its alloys, composite and intermetallic coatings [3, 5, 6, 9] as well as parts produced by sintering metal powders.
The analysis of the influence of particular finish treatment methods on the surface of marine pump shafts and defining their resistance to tribologic wear was preceded by the research on the choice of counter sample material and the lubricant of a tribosystem. The paper presents the first stage of research referring to the determination of conditions of the experiment performed on T-05 block-on-ring wear tester.
1. SAMPLES PREPARATION
The process of finishing turning of shaft pins φ 39 mm in diameter, made of X5CrNi 18-10 stainless steel was carried out on a universal CDS 6250 BX-1000 centre lathe. The preliminary lathing process was conducted by a cutting tool with WNMG 080408 WF removable plates by Sandvik Coromant. The super finishing Wiper plates ensure high efficiency of finishing and semi – finishing treatment. Properly designed geometry made it possible to apply two times more feed at the same surface finishing quality in comparison with traditional plates. Therefore
during the preliminary lathing (Fig. 1) the following machining parameters were used: machining speed Vc = 112 m/min, feed f = 0.27 mm/rev, machining depth ap = 0.5 mm.
Fig. 1. General view of OUPN tooling system (machine, grip, object, tool)
2. RESEARCH METHODOLOGY
The tribologic research was conducted on T-05 block-on-ring wear tester (Fig. 2) during the conditions of changeable load and various feed speed. T-05 tester is designed to examine the tribologic properties of lubricating media such as plastic oil, oil and solid oil as well as resistance to wear of the materials used during metals and plastic friction. It is also designed to examine the resistance to abrasion of coatings applied to loaded machine elements. The machine allows to conduct tests according to the following standards: ASTM D 2714, ASTM D 2981, ASTM D 3704, ASTM G 77 [1, 2, 3, 4]. The experiment consisted in holding down an immobile counter sample (block) with a given P force to a roll rotating at a given speed in one direction (Fig. 3a) which constitutes a sample made of stainless steel that underwent proper production technology. The actual tribosystem is shown in Figure 3b.
a) b)
Fig. 3. The diagram of sample load (a) and actual tribological system (b)
The research on the material selection for the counter sample was conducted at the sample rotational speed of n = 450 rev/min and at the load of G = 500 N. Machine oil type ARTEfol AN-68 was used as lubricating medium for the tribosystem.
3. RESEARCH RESULTS
During the experiment the first counter sample made of CuZn10 brass showed a stable work of a tester which was characterized by minimal vibration. During the experiment which lasted correspondingly 10 min (Fig. 4a) and 20 min (Fig. 4b) a very high wear of a counter sample material took place, which was caused by lower material hardness compared to sample material.
a) b)
c)
Fig. 4. View of counter sample surface: a) after 10 minutes, b) after 20 minutes of work, c) general view
In order to ensure the tests performance in 60 minutes it was necessary to apply other material to the counter sample, which would be characterized by a hardness higher than that of the sample material. For this purpose the counter
sample was made of tool N9 steel which was heat treated (hardened, tempered in low temperature) while the lubrication for the cooperating pair was provided by dosing machine oil. Figure 5 presents the surface of the sample and the counter sample after 5 min work. High vibrations in the T-05 machine assembly were noticed during the experiment. Intensive abrasive wear was observed on the surfaces of both the sample and the counter sample. An additional test on examining the abrasive wear was conducted for the counter sample made of C45 steel for heat improvement. Machine oil was used as lubricating medium. (Fig. 6).
The experiment that was carried out did not show the improvement during the test and a clear surface wear was observed on the sample surface as well as on the counter sample surface at an instable tester work.
a) b)
Fig. 5. Surface view of (a) sample and (b) N9 counter sample lubricated by machine oil
a) b)
Fig. 6. Sample surface view of (a) and counter sample (b) C45 lubricated by machine oil
In the next stage of selecting the counter sample the N9 tool steel was used again and the machine oil enriched with a Motor Life improver was used for lubricating the cooperating pair. Motor Life, according to its producer, is designed for machines and devices working in extreme conditions. Figure 7 presents the surface of the sample and the counter sample after 20 min work on N9 steel.
a) b)
Fig. 7. Surface view of (a) sample and (b) N9 counter sample lubricated by machine oil enriched with an improved
During the experiment the set vibrations decreased considerably and lower wear of surface layer was observed on the surface of the sample and the counter sample. Similarly for C45 steel, the application of an improver in the lubricating medium enabled to carry out the experiment for 20 min without a significant surface wear of the sample and the counter sample (Fig. 8). Moreover, when
conducting the test T-05 machine showed a stable work, without visible vibrations of the set.
a) b)
Fig. 8. The surface view of sample and C45 counter sample lubricated by machine oil enriched with an improver
CONCLUSION
Comparing the surfaces of samples and counter samples for particular materials, the most stable one with the lowest abrasive wear of the surface layer of the analyzed tribological system seems to be the C45 counter sample lubricated by machine oil enriched with an improver. The samples surface did not undergo a quick wear process of the surface layer in the form of abrasion, which could be observed on the surface of the samples where clean machine oil was used.
Therefore the counter sample made of C45 steel with the hardness of 52 HRC will be utilized during the proper research on tribologic wear, whereas the machine oil enriched with an improver will be used as the lubricating agent of a matched tribosystem.
REFERENCES
1. ASTM D2714 – 94 (2009): Test Method for Calibration and Operation of the Falex Block-on-Ring Friction and Wear Testing Machine.
2. ASTM D2981 – 94 (2009): Standard Test Method for Wear Life of Solid Film Lubricants in Oscillating Motion.
3. ASTM D3704 – 96 (2012): Standard Test Method for Wear Preventive Properties of Lubricating Greases Using the (Falex) Block-on-Ring Test Machine in Oscillating Motion.
4. ASTM G77 – 05 (2010): Standard Test Method for Ranking Resistance of Materials to Sliding Wear Using Block-on-Ring Wear Test.
5. Dyl T., Skoblik R., Starosta R., The Effect of the Ceramic Dispersion on the Nickel Matrix Composite Coating Properties after Plastic Working, Solid State Phenomena, Vol. 147–149, p. 813–818, Switzerland 2009.
6. Dyl T., Starosta R., Skoblik R., The effect of the unit pressure on the NiAl and Ni3Al intermetallic coatings selection parameters after plastic working. Solid State Phenomena, Vol. 165, p. 19–24, Switzerland 2010.
7. Labuda W., Starosta R., Estimation of the influence of burnishing parameters on X5CrNi18-10 steel, Solid State Phenomena, Trans Tech Publication, Vol. 165, p. 300–305, Switzerland 2010.
8. Labuda W., Starosta R., Dyl T., Estimation of the influence of burnishing parameters on steel X5CrNi1810 surface layers strengthening and roughness changes, Journal of KONES Powertrain and Transport, Vol. 15, No. 3, p. 259–267, Warszawa 2008.
9. Starosta, R., The influence of plastic strain on the corrosive properties of plasma sprayed intermetallic NiAl and Ni3Al coatings, Solid State Phenomena, Vol. 165, p. 165–177, Switzerland 2010.
10. Przybylski W., Współczesne problemy w technologii obróbki przez nagniatanie, Wydawnictwo Politechniki Gdańskiej, Gdańsk 2005.
11. Przybylski W., Współczesne problemy w technologii obróbki przez nagniatanie, t. 2, Wydaw-nictwo Politechniki Gdańskiej, Gdańsk 2008.
BADANIA WSTĘPNE ZUŻYCIA TRIBOLOGICZNEGO CZOPÓW WAŁÓW POMP OKRĘTOWYCH
Streszczenie
Odśrodkowe pompy krętne są stosowane w obiegach chłodzenia silników średniej i dużej mocy, do zasilania kotłów oraz w instalacjach zęzowych, balastowych i przeciwpożarowych. Powszechne stosowanie pomp krętnych na statkach wiąże się z ich licznymi korzyściami. Jednakże podczas eksploatacji występuje zużycie kadłuba, wirnika, wału oraz uszczelnień.
W pracy badawczej podjęto próbę zwiększenia trwałości eksploatacyjnej wałów pomp wody morskiej w miejscu osadzenia uszczelnień. Właściwości eksploatacyjne związane są z wykonaniem badań zmęczenia stykowego, zużycia tribologicznego oraz korozji elektrochemicznej
W artykule przedstawiono pierwszy etap badań tribologicznych, który dotyczył doboru materiału przeciwpróbki oraz środka smarującego parę tribologiczną. Do badań wykorzystano wałek wykonany ze stali odpornej na korozję X5CrNi18-10. Proces toczenia wykończeniowego powierzchni próbki wykonano nożem z wymiennymi płytkami dogładzającymi typu Wiper firmy Sandvik Coromant. Na podstawie uzyskanych wyników badań określono materiał przeciwpróbki (stal C45) do prze-prowadzenia właściwych badań tribologicznych. Środkiem smarującym skojarzonej pary tribologicz-nej będzie olej maszynowy uzupełniony dodatkiem uszlachetniającym.
