2013年8月27日星期二

Installation of high-speed bearings fit and adjustment

A high speed bearings with clearance and according to both the high-speed precision bearings bearing requirements, but also according to temperature bearing requirements, so consider the coordination and clearance to take account of the following points:

(1) when the temperature rose to high temperature dimensional change and hardness; (2) caused by high speed centrifugal force system change and shape change.

In short, high-speed, high-temperature conditions, coordination and clearance from the choice of the bearing should strive to maintain the accuracy and performance, it is difficult.

In order to ensure the bearing raceway after installation of small deformation, interference fit amount of interference can not get too big, and high speed centrifugal force and high temperature thermal expansion, or offset with the surface normal pressure. Or so with the surface relaxation, so the amount of interference must be considered under the premise of these two factors be carefully calculated, at room temperature constant speed and effective amount of interference for high-speed bearings may be invalid.

If the calculation results of this contradiction is too large (usually only in the ultra high speed only in this case), only by taking the lubrication ring lubrication and hydrostatic lubrication with a double measure, and this solution has the potential to break the bearing dmn value 3 million mark.

In considering the high speed bearing clearance is not only to consider the above factors, but also to consider the thermal elongation axis of the impact on the clearance required bearing in working condition, that there is at operating temperature optimum clearance, which kind of clearance is taken into account, the outer ring ball groove center precise alignment of state formation. As high-speed bearings for lower relative sliding and internal friction, it is best not to use the inner and outer rings relative axial displacement method to adjust the ball bearing clearance.

In considering the amount of interference with the bearing and clearance, to note that materials at high temperatures becomes soft and easily deformed features, as well as many from the room temperature to high temperature changes cause some permanent deformation possibilities.

(2) the requirement for host-related parts

Where the rotational speed bearing system requires precision bearing dynamic balancing shaft and the bearing seat hole installation site should have higher than normal required size and shape precision accuracy, especially for concentricity and retaining shoulder seat hole or journal vertical, and in consideration of these issues, it must also be noted that the high-speed operation of the bearing element and the temperature factor.

Shaft support systems require both high rigidity, and quality requirements as light as possible, in order to overcome this contradiction can be taken, such as reducing the surface roughness and improve surface hardening measures to improve the supporting stiffness, the use of hollow shaft to reduce system quality.

3 high-speed bearings examples of the development hereby HA type with ultra high-speed development of tapered roller bearings for example.

(1) of the problem

In the gas turbine and certain machine tools and construction machinery, high speed and axial load, using the ball bearing is life is too short, use a short cylindrical roller bearing axial load capacity is insufficient, the axial clearance is difficult to adjust, hoping to use cone roller bearings break this problem.

(2) must be solved key technology

Increase speed limit tapered roller bearing technology lies in improving inner ring large rib and roller end lubrication between the state, this area most likely to occur at high speeds severe wear and burns, is the main reason for limiting its high speed.

(3) solution

The general structure of tapered roller bearings, the oil circulation routes in the inner wall with a large roller end contact area is difficult to get oil, and this part of the relative sliding big, precisely needed most lubricants.

Therefore, Japan and other countries have developed HA-type tapered roller bearings, this bearing wall in the outer ring, so that the flow of oil can lubricate the outer ring ribs and roller end contact part, but here even when at rest can also save some oil, to avoid the starting lean burn accidents, but click on the outer wall of the need to create several drain hole to prevent oil discharge passage without, retention caused by certain parts of the oil agitation loss of power and temperature l too high. Since no inner wall, the temperature decreased, thus reducing the mating surface between the inner ring and the shaft occurs between peristaltic possibilities. This structure of the bearing outer ring on the cage used to guide the way, so that the cage can be more smoothly guide roller without askew functioning to avoid vibrations and excessive wear and tear, which will also help speed.

(4) can be achieved

This bearing type HA dmn value up to 200 million, more than triple the normal structure, for example a gas turbine this bearing spindle gear (Model I-IA30205), the axial load 1000N conditions, guarantee There 2L/min the implementation of the bearing to the oil supply of the 4th cycle turbine oil, its working speed of up to 60,000 will not appear in turn burns.

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