Internal Grinding Machines

Internal Grinding Machines are intended for grinding cylindrical and tapered holes. The end faces of the workpieces are usually ground in these machines as well. Surface finish attainable in an internal grinder is within the roughness values stipulated for the 6th and 7th classes after rough grinding, and the 7th and 8th classes after finish grinding.

The principal dimension specifying the capacity of an internal grinder is the maximum diameter of the hole ground. As to the arrangement of their spindle grinders are classified as horizontal and vertical; depending on whether the work rotates or remains stationary, internal grinders are classified as ordinary or chucking, and planetary machines.

In addition to the primary cutting motion – grinding wheel rotation – internal grinders of the chucking type have the following working motions:

a) work rotation;

b) traverse motion, the reciprocating motion of the work or grinding wheel;

c) infeed, the periodic crosswise motion of the wheelhead.

In the planetary-type internal grinders, designed for finishing holes in workpieces of irregular shape, or large heavy workpieces, work rotation is replaced by rotation of the axis of the grinding wheel in a circle about the axis of the hole being ground.

The following mechanisms are found in both chucking and planetary machines: wheel drive, work rotation or planetary motion drive, traverse mechanism and infeed mechanism.

Grinding wheel drive. Internal grinder spindles operate at high and super-high speeds which may reach 150, 000 rpm. As a rule, the smaller the wheel diameter, the higher the speed should be. In internal grinders the grinding wheel is driven by one of the following methods:

1. The grinding wheel may be powered from a-c motor through a flat-belt drive and in some cases, on the medium and large machines, through a V-belt drive.

2. The grinding wheel may be powered by a pneumatic drive (rotary air motor) enabling wheel speeds up to 80, 000 rpm to be obtained. One disadvantage of a pneumatic drive, however, is its lack of sufficiently flat speed characteristics. In many cases, this doesn’t allow a surface with a sufficiently high class finish to be obtained. Moreover the operation of a pneumatic drive is accompanied by a typical unpleasant noise. Because of these drawbacks, pneumatic drives have found only limited application in internal grinders.

3. Electrical grinding spindles with built-in frequency motors are widely employed in recent years. The smooth operation of these spindles and the high speeds enable surface to be ground to a high class of finish and with high precision.

4. Hydraulic drives can also be used for powering the wheel in internal grinders.

EXERCISES

1. Name the main points of the text answering the following questions:

1. What are internal grinders intended for?

2. What is the principal dimension of an internal grinder?

3. How are internal grinders classified from the point of view of spindle arrangement?

4. What other classifications of internal grinders do you know?

5. What is the primary cutting motion in internal grinders?

6. Can you name the working motions in internal grinders?

7. What mechanisms are found in both chucking and planetary machines?

8. What types of grinding wheel drive do you know? can you characterize each of them?

2. Fill in the blanks using the words below:

1. The principal... of an internal grinder is the maximum diameter of the... ground.

2. Depending on whether the work... or remains... internal grinders are classified as ordinary and planetary machines.

3. In internal grinders the... can be driven by various methods.

4. One disadvantage of a...... is its lack of flat speed characteristics.

5....... can also be used for powering the wheel in internal grinders.

6. Electrical grinding spindles are widely... in recent years.

Employed, rotates, pneumatic drive, hole, grinding wheel, stationary, dimension, hydraulic drives.

3. Find in the text English equivalents for the following words and word combinations:

Чистовая обработка поверхности, основной параметр, шлифовальная бабка, неправильная форма, приводить в действие, отсутствие, неприятный шум, встроенный, станок средних размеров, недостаток, неподвижный, рабочие движения