II. Retell the text «The main joints».

III. Rendering

1. Read the text and translate it into Ukrainian, using new words in their specialized meanings below.

1. key – ключ, код

2. shaft – вал, ось, стержень

3. gear – зубчатка, шестерня

4. torque – пусковий момент

5. sunked – заглиблений

6. inserted – врізаний, вкладений

7. splined – паз, силайн

8. screw – вкручений, різьблений

Key Joints

A key is a bar of a tapered or prismatic shape inserted between a shaft and the hub of a gear, pulley or coupling mounted on it, and designed to interconnect these parts and transmit the torque from the shaft to the mounted part or vice versa.

Keys are divided into two basic groups:

(a) taper keys producing strained joints

(b) prismatic (straight) keys or feathers producing un­strained joints

According to the shape of butt ends, the keys are distin­guished as plain and gib-headed ones (Fig. 163b). The head is used when the key is driven out with wedge a (Fig. 163b). To prevent accidents, the key head on the rotating shaft must be covered. The wide faces in taper keys are the work­ing faces; the side faces are installed with a clearance.

The main disadvantage of the taper key joints is the radial displacement of the axis of the mounted part with relation to the shaft axis, which leads to an additional

runout. Therefore, such joints are used comparatively seldom, in low-speed transmissions not calling for a high accuracy.

Featners (prsmatic keys) have no taper. They are inser­ted into a groove made on the shaft and are always of a sunk type. Feathers do not prevent axial dis­placement of the member on the shaft; this displacement is prevented by the use of setting or locating rings, lock screws, etc.

Feathers are employed in fixed and sliding key joints. In the latter case the key is screwed to the shaft and is referred to as a guide key.

The ends of feathers may be rounded or flat.

In addition to the above types of keys, widely used types of keys are the Woodruff keys, tangent keys, and special designs of keys.

Splined Joints

The grooves of key joints weaken the shaft. This disad­vantage can be avoided and the centering of the parts on the shaft improved by securing the parts to the shaft by a splined or toothed joint. In this way the stresses on the key are also reduced, which is vital in the case of sliding joints. This type of joint (also called spline fitting) has of late won universal recognition.

Splined joints are formed by making projections on the shaft and corresponding grooves in the mating part.

7.5. Screw joints, i.e., joints in which machine elements are connected by means of threads, are universally used in machine building and in mechanical engineering in general.

The basic element of the screw joint in the thread. (The Screw joints consist of threaded fastening parts. These are available in a wide diversity of shapes and applica­tions. These include bolts, screws, studs, tumbuckles, nuts, pipe fittings (nipples, screw couplings, Tees, etc.).

The bolt, as defined in mechanical engineering, is a thre­aded cylindrical metal bar which is usually provided with a head. The head is used to rotate the bolt or to hold it in place while joining the parts. The threaded portion of the bolt shank is screwed into a nut.

Another type of the threaded fastening part is the screw which differs from the bolt only in that it is screwed into a threaded hole in one of the parts being joined, instead of into the nut.

According to the method and accuracy of manufacture bolts are divided into black, semifinished and finished.

Black bolts are made of metal bars by hot-heading. The thread is either rolled or cut. Semifinished bolts are likewise made by the heading method, hot or cold, and then the bearing surface of the head and the end of the shank are machined. The thread is either cut or rolled with preliminary turning of the shank in the latter case.

Finished bolts are made of bright-drawn hexagonal bar (or another shape that suits the form of the head) on a turret lathe or an automatic threading machine.

2. Make up a plan in the form of questions.

3. Give the summary of the text according to your plan in a written form.

IV. Comprehensive skills.

1. Read and remember.

1. beam – промінь, ширина

2. depressurized – розгерметизований

3. indispensable – необхідний

4. project – проектувати, демонструвати

2. Listen to the text “Unusual conditions of welding” and try to understand it.

While many welding applications are done in controlled environments such as factories and repair shops, some welding processes are commonly used in a wide variety of conditions, such as open air, underwater, and vacuums (such as space). In open-air applications, such as construction and outdoors repair, shielded metal arc welding is the most common process.

Shielded metal arc welding is also often used in underwater welding in the construction and repair of ships and such as flux "cored arc" welding and gas tungsten arc welding, are also common Welding in space is also possible - it was first attempted in 1969 by Russian cosmonauts, when they performed experiments to test shielded metal arc welding, plasma arc welding, and electron beam welding in a depressurized environment. Further testing of these methods was done in the following decades, and today researchers continue to develop methods for using other welding processes in space, such as laser beam welding, resistance welding, and friction welding. Advances in these areas could prove indispensable for projects like the construction of the International Space Station, which will likely rely heavily on welding for joining in space the parts that were manufactured on Earth.