6MD(2)110——2 How to troubleshoot faults in hydrogen and nitrogen compressors
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6MD(2)110——2 Hydrogen and nitrogen compressor failure: Our factory installed a 6MD(2)110——2 type hydrogen and nitrogen compressor last year. Recently, a failure occurred where the small end bearing of the connecting rod broke apart. After replacing it with a copper sleeve, the compressor operated normally for an hour, but then the same problem arose again; the small end bearing seized with the crosshead pin, and the crosshead hole became worn beyond use. The connecting rod, crosshead, pin, and small end bearing were replaced once more. At that time, all oil circuits functioned properly, and the compressor ran for an hour without any issues, with a temperature of 12 degrees. When pressure was increased to 15 MPa for 30 minutes, everything was normal as well (system pressure at 23 MPa). However, after 20 minutes of operation, the temperature became abnormally high, prompting an emergency stop. It was found that the babbitt material of the crosshead had worn out, the entire crosshead was extremely hot, and the small end bearing had seized again with the pin, although the connecting rod bearings were fine (oil flows from the crosshead through the small end bearing to the large end bearing of the connecting rod). We’re very frustrated now – how can we separate the crosshead pin from the small end bearing? What exactly caused this accident? Please, everyone, help me!!!
The compressor mentioned by the original poster has seven stages of compression, while ours have six stages; the structure is the same. In my opinion, the high temperatures are caused, first, by problems with the oil system, second, by issues with the gaps, and third, by poor quality of the spare parts. If the large-end tile is normal, low oil pressure and blocked oil circuits can be ruled out as causes. The quality of equipment spare parts generally doesn’t vary much within a single batch. I think the issue is mainly due to the assembly clearances. First, there is a small clearance between the copper sleeve (the small end bearing) and the pin shaft; second, there is a small clearance between the small end bearing and the crosshead. The equipment operates normally when it starts up, but as temperature rises after it has been running for some time, the available expansion clearance becomes insufficient, leading to the phenomenon described by the original poster. This is just my opinion – it’s better to listen to those who are more experienced
Personally, I think the gap between the copper sleeve and the pin, or between the copper sleeve and the crosshead, is small.
I think the issue raised by the poster might be related to the material of the small tiles; it is recommended to analyze the material of the copper tiles
1. If low oil flow is suspected, check the oil passage. 2. If a small clearance in the bearing shells is suspected, this clearance disappears due to thermal expansion, resulting in seizure
If, as the people above mentioned, failures should occur during the running-in period, then consider the process-related factors: could it be that the diameter of the outlet pipe is too small, resulting in excessive pressure and thus excessive stress on the crosshead?
6MD20(2)-110/320 is an improved version of the 6MD20-110/320 model, with an additional balancing section added to the fourth section; in fact, the seven small bearing shells are identical to the other 5 small bearing shells and can be used interchangeably. Before replacing the crosshead block, the oil passages should be carefully inspected and cleaned. This type of compressor uses positive lubrication, not reverse lubrication. After passing through the crosshead body, the lubricating oil enters the rod via the crosshead pin and then reaches the big-end bearing. This situation is actually very simple: the assembly is incorrect! That is, after the small-end bearing is installed, its hypothetical axis is not parallel to the hypothetical axis of the large-end bearing, and in addition the clearance is too small. The material used for the small-end bushings nowadays is 10-1 phosphor bronze. There are two types of accessories: 1. The inner hole of the small-end bushing is enlarged during processing to facilitate assembly. However, after being subjected to alternating loads over time, the inner hole 140 of the rod end becomes deformed. Once the bushing is pressed into the rod, the inner hole 120 of the bushing also deforms. Although the clearance can be adjusted after lapping, the geometric tolerances are already **out of spec**, which results in the burnout of the babbitt material in the crosshead sliding surface. For the second type of bushing, 1 millimeter of machining allowance is left in the inner hole; after it is pressed into the connecting rod, the larger-bore bushing is aligned on a boring machine, and the smaller-bore bushing is bored to the appropriate fit size. This is the correct method of assembly. Note: The small-end bearing must be pressed in, rather than being assembled after heating the connecting rod small end.
When both the large-end and small-end bearings are burned out: 1. First, check the parallelism of the centers of the holes in the large and small ends of the connecting rod, as well as the parallelism after the bearings have been lapped. It should be kept within 0.03 mm. 2. Check the perpendicularity between the center line of the slide and the crankshaft; it should be within 0.03 mm. 3. Check whether the oil pipelines connecting the slide rails and the internal oil circuits of the crosshead are unobstructed; turn on the oil pump during disassembly for inspection to ensure there is sufficient oil. 4. The gap in the slide rail should not be too large, as this can lead to a loss of oil pressure, resulting in insufficient oil supply and an increased risk of bearing burnout. 5. The bearing contact surface should be even, and the clearance should be appropriate
The poster said, “The machine operated normally for an hour of grinding; the temperature was 12 degrees. Pressuring it to 15 megapascals for 30 minutes also showed no issues (the system pressure was 23 megapascals), but after 20 minutes of operation the temperature became abnormally high.” There are several possibilities: First, could the process pressure be fluctuating too much? II. The hypothetical axis of the small-end tile is not parallel to that of the large-end tile; under low pressures, no obvious abnormalities are observed, but once operation begins and higher pressures are applied, such abnormalities become evident. III. The possibility of a large gap in the slideway is zero; if such a gap exists, the oil pressure will be lost during testing, resulting in insufficient oil supply and bearing burnout. It’s possible that the gap is small; once production begins and the temperature rises, the gap becomes even smaller, eventually leading to seizure. IV. Check the filter screen or oil pipeline for rags that may be causing the oil flow to slow down.
This post was last edited by jyszyx on 2009-6-1 at 12:45. All the possibilities mentioned by the above individuals are possible; during actual verification, each one must be checked carefully. First check the oil circuit, then the assembly clearance and parallelism, and finally the material and operating conditions
Thank you all for your detailed analysis; upon further inspection, it was indeed found that the thermal expansion clearance of the small-end bearing was insufficient, and the scuffing on the crosshead body during the second attempt was also caused by an inadequate thermal expansion clearance. Thank you all for your help!