Welding Workshop 

Understanding the Diferences between Heat Treatment, Annealing, and Tempering!

Heat Treatment, Annealing, and Tempering are three well-known methods for giving treatment to metals. Depending on the treatment used, a material may become more or less brittle, harder or softer, or stronger or weaker. The method chosen depends on the desired characteristics of the material. If steel is being treated, for instance, the designer may desire an end material with a high tensile strength but a relatively low degree of brittleness. In order to achieve the desired levels, the designer may make use of several treatments, alter the temperature at…

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Lathe Machine 

What is Off Setting the Tailstock?

The tailstock offset method is generally used to cut a taper when no taper attachment is available. This involves moving the tailstock centre out-of-line with the headstock centre. However, the amount that the tailstock may be offset is limited. This method will not permit steep tapers to be turned or standard tapers to be turned on the end of a long piece of work. Since the work will be essentially at an angle it will need to be machined between centres. Thus, a chuck or collet can not be used…

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Lathe Machine 

What is Compound Rest?

The compound rest is generally used for turning or boring short steep tapers, but it can also be used for longer, gradual tapers, providing the length of the taper does not exceed the distance the compound rest will move upon its slide. This method can be used with a high degree of accuracy, but is somewhat limited due to the lack of an automatic feed and the length of the taper being restricted to the movement of the slide. The compound rest base is graduated in degrees and can be…

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Lathe Machine 

Taper Turning Attachment

The taper attachment is used for turning and boring tapers. It is bolted to the back of the carriage saddle. In operation, it is connected to the cross-slide so that it moves the cross-slide laterally as the carriage moves longitudinally. This action causes the cutting tool to move at an angle to the axis of the workpiece to produce a taper. The angle of the desired taper is set on the guide bar of the attachment, and the guide bar support is clamped to the lathe bed. Since the cross-slide…

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Lathe Machine 

Methods Of Taper Turning

In ordinary straight turning, the cutting tool moves along a line parallel to the axis of the work, causing the finished job to be the same diameter throughout. However, when cutting a taper, the tool moves at an angle to the axis of the work, producing a taper. Therefore, to turn a taper, the work must either be mounted in a lathe so that the axis upon which it turns is at an angle to the axis of the lathe, or cause the cutting tool to move at an angle…

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Engineering 

What is the function of waterstops in joints of box culverts and drainage channels?

The principal function of waterstops is to prevent liquids (e.g. water), water-borne materials and solids to pass through concrete joints. In essence, it aims at providing watertightness to the drainage channel. Besides, waterstops in drainage channels or box culverts can also serve two other purposes: to avoid water contacting joints’ dowel bars and causing corrosion. (ii) to avoid water seeping in from the underside of drainage channels or box culverts, thereby washing in soil particles and causing voids underneath these structures and finally leading to their failure. To serve the…

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Engineering 

What is the difference between epoxy grout, cement grout and cement mortar?

Epoxy grout consists of epoxy resin, epoxy hardener and sand/aggregates. In fact, there are various types of resin used in construction industry like epoxy, polyester, polyurethane etc. Though epoxy grout appears to imply the presence of cement material by its name, it does not contain any cement at all. On the other hand, epoxy hardener serves to initiate the hardening process of epoxy grout. It is commonly used for repairing hairline cracks and cavities in concrete structures and can be adopted as primer or bonding agent. Cement grout is formed…

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Engineering 

What is the function of shear keys in the design of retaining walls?

In determining the external stability of retaining walls, failure modes like bearing failure, sliding and overturning are normally considered in design. In considering the criterion of sliding, the sliding resistance of retaining walls is derived from the base friction between the wall base and the foundation soils. To increase the sliding resistance of retaining walls, other than providing a large self-weight or a large retained soil mass, shear keys are to be installed at the wall base. The principle of shear keys is as follows: The main purpose of installation…

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Engineering 

If on-site slump test fails, should engineers allow the contractor to continue the concreting works?

This is a very classical question raised by many graduate engineers. In fact, there are two schools of thought regarding this issue. The first school of thought is rather straightforward: the contractor fails to comply with contractual requirements and therefore as per G. C. C. Clause 54 (2)(c) the engineer could order suspension of the Works. Under the conditions of G. C. C. Clause 54(2)(a) – (d), the contractor is not entitled to any claims of cost which is the main concern for most engineers. This is the contractual power…

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Engineering 

What are the functions of different components of a typical expansion joint?

In a typical expansion joint, it normally contains the following components: joint sealant, joint filler, dowel bar, PVC dowel sleeve, bond breaker tape and cradle bent. Joint sealant: it seals the joint width and prevents water and dirt from entering the joint and causing dowel bar corrosion and unexpected joint stress resulting from restrained movement. Joint filler: it is compressible so that the joint can expand freely without constraint. Someone may doubt that even without its presence, the joint can still expand freely. In fact, its presence is necessary because…

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