Text 20

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Machine elements screw fastenings

Machine parts are held together by parts: (a) working in tension, (b) working in shear, (c) creating friction, and (d) using both shear and friction forces.

Types of Fastenings. — All fastenings can be divided into two classes — disconnectable fastenings and permanent joints.

Disconnectable fastenings, in turn, are effected by: (a) bolts (Fig. 4 a, b) and screws, (b) wedges, (c) dowel pins (Fig. 4 c, d; Fig. 5 a), (d) keys.

Permanent joints are obtained by means of: (a) press fits, (b) shrink fits, (c) rivets, (d) welding, brazing, and soldering and (e) casting.

Forms of Threads. — Screw fastenings are used for holding two or more machine parts together or for adjusting one part with relation to another. In screw fastenings the threads are made in several forms but are always of triangular-type single thread.

Screw threads are made right-hand and left-hand.

Answer the questions:

1. How are the machine parts held together?

2. What are the types of fastenings?

3. How are permanent joints obtained?

Для спеціальності вцр text 16

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The science of chemistry

Chemistry is an experimental and theoretical study of the composi­tion of matter and the changes that take place in matter. A chemical change involves changes in composition and in properties. A physical change involves only changes in properties with no change in composi­tion.

Chemical changes are usually accompanied by the liberation or the absorption of energy in the form of light, heat or electricity.

All forms of matter consist of either pure substances or mixtures of two or more pure substances. Elements are the building blocks of matter. Compounds are combinations of elements. Most of the elements are metals and most of them will unite with other elements and form compounds. The formation of a compound from simpler substances is known as synthesis. Analysis is the process of breaking down a compound into simpler substances or its elements and thus is the determination of its composition. The composition of a pure substance never changes.

Every substance has physical and chemical properties. Physical properties include colour, smell, solubility, density, hardness and boiling and melting points. Chemical properties include the behavior with other materials.

Answer the questions:

1. What is chemistry?

2. What does chemistry study?

3. What does a chemical change involve?

4. What does a physical change involve?

5. What does all forms of matter consist of?

Text 17

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Sorbitol powder with -crystallinity

General process description

The production of Y-crystalline Sorbitol powder is based on a melt crystalliza­tion process. The first step serves to remove the water almost completely. The resulting melt is then gradually cooled in a specially designed crystallizer whereby small Sorbitol agglomer­ates are formed. The coarse Sorbitol agglomerates are milled in a dry air atmosphere and finally screened to obtain the desired product fractions.

Evaporation

The Sorbitol solution (70 % w/w, assay  68 %) from the storage tanks is pumped via a feed tank to a thin film evaporator. It enters at the top of the evaporator through a distribution device from which the solution flows into the heated tube and runs down­wards as a thin liquid film. To achieve a very low water content in the resul­ting melt, the whole process is carried out under vacuum.

Melt Crystallization

Sorbitol melt is continuously pumped via a pre-cooler, equipped with rotating scrubbers, to the crystallizer the Sorbitol melt is cooled by chilled water, which is circulating in the mixer and jacket. Cristal formation and growth start at a temperature of about 100⁰C. The transformation from the liquid to the solid form is an exothermic process which requires permanent removal of the crystallization enthalpy.

Answer the questions:

1. What is the production of -crystalline Sorbitol powder based on?

2. What does the first step serve to?

3. How is the whole process carried out, to achieve a very low water content?