Find the crosshead slide clearance value
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One 4M125 reciprocating compressor in our unit got its piston rod stuck in the slide during the installation and commissioning phase; it is suspected that the clearance value provided by the manufacturer is inaccurate. We are seeking the formula for calculating the clearance between the piston rod and the slide, as well as the thickness of the oil film on the slide. The diameter of the piston rod is 700, and the manufacturer’s recommended clearance range is 0.45–0.65; we have set the clearance at 0.52
Whenever a problem arises, my first reaction is to look for faults within myself; only after confirming that there are no issues with me do I consider the faults of others. 1. One should trust the clearance values provided by the manufacturer; they are given after careful consideration, so there is generally no issue of these values being too large or too small. 2. Before the trial operation phase, what is the degree of parallelism between your crosshead slider and the slideway? When the slider is fixed, is there any imbalance in the adjustment shims, and is the locking oil pressure for the crosshead at the proper level? 3. The most important point is: before the trial run, was the piston rod’s runout measured using a electric winch, and what were the results?
The statement that the crosshead is engaged with the slide is itself incorrect. It should be said that it is the engagement between the bushing and the slideway’s babbitt, and the wording needs to be accurate. Why does babbitt alloy experience seizure, vibration, or an inappropriate oil film (it may be due to too small a gap or an inappropriate choice of oil)?
The clearance value provided by the manufacturer should be fine; first, look for the problem within your own setup, and only then turn to the manufacturer.
Check whether babbitt has fallen off and blocked the oil holes, and also verify whether the oil circuit is functioning properly
1. Is there a problem with the lubrication? 2. What is the contact area between the crosshead and the slideway? 3. Is the crosshead subjected to abnormal forces? There are many doubts
It’s not necessarily the case that the gap is too small; another possibility is that the foot bolts were not tightened properly when adjusting the level of the machine, and there aren’t enough shims near the foot bolts, resulting in the machine becoming deformed. Clamping will occur in the crosshead.
The gap value given is correct; check whether the oil path is unobstructed and whether the oil pressure is within the acceptable range
The play of the piston rod is detected by a thermocouple; there is interlock in place, and it is around 0.07 mm. :P
The runout value of the piston rod should be measured using an eddy current proximity probe, in order to check the trends in settlement and runout. Check whether the lubricant parameters meet the requirements, and whether the oil pressure and flow rate are normal; it is necessary to analyze the causes from various aspects, taking into account the actual wear conditions on site
Based on your clearance value, it seems to be a machine made by Shenmu; the clearance value is fine. It is still recommended to check the oiling system and alignment, as well as whether there are any impurities in the oil holes.