Ex. 15. Render the text B using the plan of rendering on page 67.

Supplementary reading.

Texts for written translation with a dictionary

Read the texts and translate them in writing. Use a dictionary

Bearing (mechanical)

A bearing is a device to permit constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.

Bearing friction

Low friction bearings are often important for efficiency, to reduce wear and to facilitate high speeds. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces.

• By shape, gains advantage usually by using spheres or rollers.
• By material, exploits the nature of the bearing material used. (An example would be using plastics that have low surface friction.)
• By fluid, exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurized medium to keep the two solid parts from touching.
• By fields, exploits electromagnetic fields, such as magnetic fields, to keep solid parts from touching.

Combinations of these can even be employed with the same bearing. An example of this is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.

An example of a four-point contact ball bearing

 

Principles of operation

Animation of ball bearing

 

There are at least six common principles of operation:

• sliding bearings, usually called "bushes", "bushings", "journal bearings", "sleeve bearings", "rifle bearings", or "plain bearings"
• rolling-element bearings such as ball bearings and roller bearings
• jewel bearings, in which the load is carried by rolling the axle slightly off-center
• fluid bearings, in which the load is carried by a gas or liquid
• magnetic bearings, in which the load is carried by a magnetic field
• flexure bearings, in which the motion is supported by a load element which bends.

Motions

Common motions permitted by bearings are:

• Axial rotation e.g. shaft rotation
• Linear motion e.g. drawer
• spherical rotation e.g. ball and socket joint
• hinge motion e.g. door

Loads

Bearings vary greatly over the size and directions of forces that they can support.

Forces can be predominately radial, axial (thrust bearings) or moments perpendicular to the main axis.

Speeds

Bearings vary typically involving some degree of relative movement between surfaces, and different types have limits as to the maximum relative surface speeds they can handle, and this can be specified as a speed in ft/s or m/s.

For rotational bearings generally performance is defined in terms of the product 'DN' where D is the diameter (often in mm) of the bearing and N is the rotation rate in revolutions per minute.

Generally in terms of relative speed of the moving parts there is considerable overlap between capabilities, but plain bearings can generally handle the lowest speeds while rolling element bearings are faster, followed by fluid bearings and finally magnetic bearings which have no known upper speed limit.

Life

Fluid and magnetic bearings can potentially give indefinite life.

Rolling element bearing life is statistical, but is determined by load, temperature, maintenance, vibration, lubrication and other factors.

For plain bearings some materials give much longer life than others. Some of the John Harrison clocks still operate after hundreds of years because of the lignum vitae wood employed in their construction, whereas his metal clocks are seldom run due to potential wear.

Maintenance

Many bearings require periodic maintenance to prevent premature failure, although some such as fluid or magnetic bearings may require little maintenance.

Most bearings in high cycle operations need periodic lubrication and cleaning, and may require adjustment to minimise the effects of wear.

How to measure a bearing

Sometimes you may need to identify a bearing due to general wear and tear. Most bearing references now are laser stamped but these wear and rub off more quickly than the previous method, which was engraved deep in the bearing's metal.

Bearing Sizes

Each bearing has an inside diameter, outside diameter and width diameter in that order. Most bearings are metric in size, but can also be imperial. On our site, each bearing shows its principal dimensions.

d = Inside diameter
D = Outside diameter
B/T = Width diameter

You can search for a bearing entering this information on the home page in the boxes provided.

Once you have identified the bearing's code some bearings come complete with seals or shields. This is known as the suffix in the bearings reference.

Bearing Example

RS1C3

The bearing type design that you need is a single row deep groove ball bearing with the following dimensions and suffix.

d = 25mm
D = 52mm
B/T = 15mm

Result = 6205

The bearing also has a seal either side of the bearing.

2RS1 = 2 Rubber seals
2RSR = 2 Rubber seals
DDU = 2 Rubber seals
2Z = 2 Metal shields
ZZ = 2 Metal Shields

Result = 6205 2RS1

And the internal clearance being C3 means that the bearing has room for expansion if needed between the races of the bearing, whilst holding the outer ring and moving the inner ring in a radial movement you will detect a little amount of play between the 2 rings. All standard clearance bearings have this movement, it may only be a small amount of movement but is controlled by international standards. C3 means the bearing has more clearance than standard.

For example we may use C3 clearance on bearings where a cold start up application my cause the balls to heat up quickly, the heat needs to go somewhere. Some of the heat gets passed through the outer race to the housing and the inner race to the shaft, this causes expansion which closes up the clearance in the bearing. If you did not allow for this clearance the bearing would not have room for expansion and lead to bearing failure.

C2 = Clearance less than normal
C3 = Clearance greater than normal
C4 = Clearance greater than C3

Result = 6205 2RS1C3

UNIT 9

Clutches

І. Language

Ex.1. Remember the following words and word combinations:

clutch   device   pulley coupling ensure rigid disengaging clutch coaxial solid bushing key   friction clutch jaw clutch breakage transmission train   axial clutch rim clutch rim cone clutch disk clutch engage clamp spring band clutch block clutch   fixed clutch safety device

зчеплення   прилад   шків муфта зціплення забезпечувати жорстка муфта позчіплювана муфта сувісний нерухома втулка шпонка, заклинювати, закріплювати фрикційна втулка кулачкова муфта поломка система зубчатих передач осьова муфта обгінна муфта обід, край конусна муфта дискова муфта зачіплювати затискач пружина дискова муфта муфта з розсунутими колодками нерухома муфта запобігаючий прилад

сцепление, муфта сцепления устройство, приспособление шкив муфта сцепления обеспечить жесткая муфта расцепная муфта соосный неразъемная втулка шпонка, заклинивать, закреплять фрикционная втулка кулачковая муфта поломка, разрыв система зубчатых передач осевая муфта обгонная муфта обод, край конусная муфта дисковая муфта зацеплять, включать зажим пружина дисковая муфта муфта с раздвижными колодками постоянная муфта предохранительное устройство