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Mechanical engineering |Машиностроение
Read the text: Grinding machines
A grinding machine is a machine which employs a grinding wheel for producing cylindrical, conical, or plane surfaces accurately and economically and to the proper shape, size, and finish. The surplus stock is removed by feeding the work against the revolving wheel or by forcing the revolving wheel against the work.
There is a great variety of grinding machines. The machines that are generally used are: cutter grinder, surface grinder, centerless grinder, external grinder, internal grinder tool grinder, and hand grinder. These machines are usually classified as to size by the largest piece of work which they can completely machine (as 6"x8" External Grinder).
To sharpen the teeth of a plain milling cutter, the cutter is generally mounted on a lathe mandrel and supported between centers or the cutter is mounted on a special stub arbor and held in a universal swivel fixture. After the cutter has been mounted in the machine, a tooth rest is mounted on the table or work head and adjusted to the tooth to be first sharpened. The table and tooth rest are adjusted so that the grinding wheel follows the surface on the back of the tooth and gives the proper clearance. The cutter is then fed to the rotating grinding wheel until sparks indicate contact between it and the wheel; the table is moved back and forth traversing the cutter until the wheel has finished cutting. Then the cutter must be resolved backward 180° against the spring tension of the tooth rest and, without changing the depth of the cut, the trial cut must be made on this opposite tooth to check the taper. If there is no taper, the cutter is to be revolved backwards and the next tooth is then engaged to be sharpened. This process is repeated until all teeth have been sharpened and ground concentric.
Tooth rests are of two kinds, plain and hook. They consist of a piece of spring steel about .030" thick, l/2" to 1 1/2" wide, and from 1" to3" long brazed or riveted in a piece of round 3/s" cold rolled, steel. They are held by means of a forged clamping fixture by bolting the fixture either to the work table or to the grinding wheel head.
External grinders are used to produce external cams, eccentrics and special forms on the outside diameter of work. External grinders are divided into three general groups. They are the Plain Cylindrical, Universal, and Special Grinders like the Centerless and Cam Grinders.
The plain cylindrical grinder is used to produce external cylinders, tapers, fillets, and may be used for form grinding by dressing the desired contour on the grinding wheel.
In any cylindrical grinder there are three movements which are very important. They are rotation of the work on its axis, movement of the work back and forth in front of the wheel (traversing past the grinding wheel), and movement of the wheel into the work.
The movement of the work back and forth in front of the wheel must be steady and smooth to 'insure a good finish and accurate sizing of the work. At the end of each traverse the table stops momentarily to give the wheel a chance to grind the work to size, to permit the wheel to clear itself on the new cut.
Holding the work in grinding
The commonest method is by means of a magnetic chuck, this is nothing more than a multipolar magnet whose surface is accurately flat to receive work and which is adapted to be clamped to the machine table. The magnet is usually an electromagnet but, with the development of improved magnet, steels, permanent-magnet magnetic chucks can now be made satisfactorily. The chucks are bolted to the tables of the machines and hold the work by magnetic attraction. In some machines the magnetic chuck is built in as an integral part of the work table. Magnetic chucks are sometimes used on cylindrical grinding machines.
Work that has been held on a magnetic chuck must be demagnetized on a demagnetizing fixture after grinding.
1. Match the left part with the right:
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1. The chuck are bolted….and tired…. |
a) there are three movements which are very important. |
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2. These machines are usually classified as |
b)to the tables of the machines … the work by magnetic attraction |
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3. An any cylindrical grinder |
c) by means of a fayed clamping fixture. |
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4. Tooth rest are held |
d) to size by the largest piece of work. |
2. Complete the sentences with the suggested words: wheel, sparks, contact, table, traversing
The cutter is then fed to the rotating grinding until indicate____ between it and the wheel; the ____ is moved back and forth ____ the cutter until the wheel has finished cutting.