Lubricants (VMPAUTO eng) / Industry / Choice of a coating for piston trunks

In accordance with the request of the Voronezh TРЗ (Diesel Locomotive Repair Plant) set forth in letter № 300/169 of 5.06.02 on replacing the AСП3-1 coating for piston trunks of D49 diesels GUP VNIIZhT has carried out a search for enterprises producing molybdenum disulfide coatings similar to AСП3-1. It has been found out that similar molybdenum disulfide coatings are produced by: the Moscow Petroleum-Oil Plant, VNII (All-Russian Research Institute) of the petroleum-oil industry (Moscow), VMPAUTO (St. Petersburg), NPO Saturn (Rybinsk). Below you will find brands of the suspensions produced by these enterprises, their properties and recommendations for use.

Laboratory Test Methods

1. The tests were performed on a serial СМЦ-2 friction machine according to the "roller-chock" scheme. The material for the chocks was an aluminum alloy. The friction area was 1.2 m2. The brands of the coating being tested were applied to the working surfaces of the chocks having a 20 mm radius of curvature. Before applying the coatings the working surface of a chock was treated in a 20% alkaline solution to ensure a durable cohesion of the coating with aluminum. The rollers were made of gray cast iron. The roller diameter was 40 mm, the width 10 mm; the cylindrical (working) surface of the rollers was subjected to grinding and then it was polished to Ra = 3.2-5.0 ?.
2. The coatings applied to chock friction surfaces were run in a pair with the rollers before the main tests according to clauses 3.1 and 3.2. The running-in process was conducted at a stepped load of 28 and 40 kgf before obtaining a 100% contact of the chock's friction surface.
3. All the tests were conducted at a speed of 1.05 m/sec of the roller travel with respect to the chock using drip-feed lubrication (3-4 drops per minute). Diesel oil of the M14B2 brand was used as a lubricant.

3.1 To evaluate the antifriction properties of the coatings and the critical pressure, which leads to intensive coating wear, tests were performed at a stepped increase in the load (P). At each load value the tests continued for 5 minutes. The interval between the loads was 10 kgf (28,40,50,60…). In the process of the test a recording of the friction torque (frt.) was made which was used to calculate the friction coefficient (f). The dependence of the friction coefficient (f) on the load (P) was constructed in accordance with the test results.
3.2 To evaluate the wear resistance of the coatings tests were carried out at a constant load equal to 90 kgf (p=75 kgf/cm2) for 3 hours. The coating wear was evaluated by the chock weight loss on an analytical balance. A histogram showing the wear of the three coatings under equal test conditions was constructed according to the test results.
4. Each coating was tested on three pairs of specimens.

Fig.1 shows the experimental dependences of the friction coefficient on the load for ВАП-2, AСП3-1, MС 2000 coatings in a pair with gray alloyed cast iron.

At a load from 28 to 80 kgf the friction coefficients of MС 2000 and AСП-3-1 coatings are practically equal and are within a range of 0.005-0.015. The ВАП-2 showed f=0.01-0.02.

At an average load value of 90 kgf an intensive wear of the ВАП-2 coating sets in, that is testified by an increase in the friction coefficient and the appearance of wear products in the oil.

The AСП3-1 coating has a stable friction coefficient of 0.015 up to a load of 130 kgf. However, at a load of 140 kgf the friction coefficient begins to grow and intensive coating wear sets in.

The MС 2000 coating retains a low friction coefficient of 0.015 up to a load of 150 kgf. At a load of 160 kgf the friction coefficient rises sharply in consequence of intensive wear.

Fig. 2 shows the magnitude of the weight wear of the three coatings in three hours of testing according to the test methods of clause 3.2. The MS 2000 coating has the least wear of 0.004 g, while the ВАП-2 coating wears the most (0.042 g). The AСП3-1 coating has an intermediate wear value

Conclusions
1. The MС 2000 and AСП3-1 coatings have a low friction coefficient (0.005-0.015) within a wide range of loads (28-130 kgf).
ВАП-2 has a somewhat higher friction coefficient (0.01-0.02) and within a narrower load range (28-90 kgf).
2. The maximum load value leading to intensive wear is shown by the MС 2000 coating (160 kgf). AСП3-1 has a value close to the above (140 kgf), while the load value of ВАП-2 (90 kgf) is 1.75 times lower than that of MС 2000.
3. The MС 2000 coating wears 2 times less than AСП3-1 and almost 10 times less than ВАП-2.
Recommendation
The MС 2000 suspension produced according to TU (specifications) 0254-003-45540231-99 by the VMPAUTO Company (St. Petersburg) is recommended for coating Д49 diesel piston trunks; it possesses higher tribotechnical properties than the AСП 3-1 and ВАП-2 coatings.

Languages

Partners