Part i - spindle facts

More documents

Recommendations

Info

Bearing Lubrication Methods Angular contact ball bearings require some form of lubrication to operate properly. The function of lubrication is to provide a microscopic film between the rolling elements to prevent abrasion and skidding. In addition, lubrication protects the surface from corrosion, and protects the working area from particle contamination. Grease Lubrication The most common and simplest method of lubricant is grease. The grease is injected into the space between the balls and the races. It is permanent and therefore requires minimal maintenance. Grease lubrication, however, does have limitations. Grease packed spindles generally are not run above dN values of approx. 850,000 for continuous operation. As speeds increase, operating temperatures increase, and begin to break down the grease. Most grease is rated to operate at temperatures under 300° F. The grease type that can tolerate high speeds generally has an ester oil base. With regard to the quantity of grease, more is not better. Excessive grease can cause overheating due to churning, causing the grease to deteriorate. Approximately 20% to 30% of the open area between the races should be filled. Following the grease fill, a careful run-in period is required to distribute the grease within the bearing. In general, high speed spindles that utilize grease lubrication do not allow for replacement of the grease between bearing replacements. During a bearing replacement, clean grease is carefully injected into the bearing. Positive air overpressure is typically used to prevent contamination from entering the bearing, which could lead to rapid bearing failure. Oil Lubrication Techniques In many cases, particularly when high rotational speed is required, lubrication of the bearings with grease is not sufficient. Oil is then used as a lubricant, and delivered in a variety of ways. As previously mentioned, grease can support bearing speed up to a dN value of approx. 850, 000. Oil lubrication can support speeds at much higher speed than grease Figure 13. AIR/OIL MIST LUBRICATION SYSTEM One common method of oil lubrication is oil mist. An oil storage tank is used, and compressed air is mixed with the oil. This creates oil droplets that are carried by the airflow to the bearing area. The major benefits of oil mist are: it is a good supply of lubricant, oil mist is simple to use, and it also cleans and cools the bearings. This system is best applied to spindles having high speeds and relatively light loads. Oil mist is somewhat difficult to measure and control, so if the quantity of oil delivered to the bearings must be very accurate, oil mist may not be the best system to use. - 13 -
Figure 14. OIL JET LUBRICATION SYSTEM Figure 15. PULSED AIR/OIL LUBRICATION SYSTEM filter) and dry (40° dew point). The oil must be of high quality with a viscosity of 150 SUS at 38°C. Direct oil injection through the outer bearing ring This type of lubrication is a newly developed system, typical for high speed applications. The holes allow the lubricant to directly reach the ball raceway contact and ensure the presence of an oil film even at high speed. Another common method of oil lubrication is an oil jet. The oil jet utilizes a high pressure pump that delivers oil directly into the bearing race. This system is suitable for spindles that must tolerate high loads, high speeds, and high temperatures. Care must be taken to insure that the oil can be quickly routed through the bearing, or oil churning will develop. This system requires a complex pump, storage tank and temperature control system. Sometimes, though, it is necessary to support very high performance spindles. Another system, pulsed oil-air, injects oil in very small quantities with compressed air, into the bearing cavity. The frequency of injection may be related to the spindle operation, or simply on a timed basis. Experience has shown that this is the lubrication system that gives the most precise oil quantity control. An additional benefit from this system is that the airflow helps to exclude contaminants from the spindle. Optimum flow may need to be established experimentally. A guide value for the delivery rate can be estimated from the expression: The air used must be clean (5micron V=0,15 x b x w -in cubic mm/hour where b= bearing bore in mm w= bearing width in mm Figure 16. DIRECT OIL INJECTION - 14 -
Page 2 and 3: PART I - SPINDLE FACTS 1. Introduct
Page 4 and 5: 2. Precision Spindle Design 2.1 Lis
Page 6 and 7: otate up to the maximum speed, and
Page 8 and 9: Bearing Contact Angle Angular conta
Page 10 and 11: Back to Back Configuration The most
Page 12 and 13: Motor-Spindle with Tandem Bearing P
Page 16 and 17: There are many oils available on th
Page 18 and 19: 2.5 Spindles with Integral Motors S
Page 20 and 21: Synchronous Spindle Motor : AC asyn
Page 22 and 23: The synchronous motor built in spin
Page 24 and 25: Torque: This is the most critical a
Page 26 and 27: 2.7 Spindle Cooling Systems Heat is
Page 28 and 29: 2.8 Seal Types High precision beari
Page 30 and 31: The values are valid for spring-loa
Page 32 and 33: and the influence of higher tempera
Page 34 and 35: 2.9 Tool Retention System A high sp
Page 36 and 37: Assuming that equivalent force is a
Page 38 and 39: of tooling. This means that users m
Page 40 and 41: HSK-Clamping Unit / Design B • A
Page 42: 3. Conclusion and Future trends A h
Page 45 and 46: Dynomax’s dedication to new spind

Part i - spindle facts

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?