Mechinopedia For Mechanical Engineers

Cold Chisels are used for cutting and chipping away pieces of metal and are made of carbon steel usually rectangular , hexagonal or octagonal cross-section. They are forged to shape, roughly ground, and then hardened and tempered. Afterwards the edge is ground sharp to the correct cutting angle, care being taken not to overheat the steel and draw the temper. The cutting angle given to the chisel is determined mainly by the nature of the metal to be chipped. It varies between 35* to 70* , the less acute angles being for the harder and tougher metals.  The Chisel is subdivided into cutting edge, shank and head, and this is generally specified by the length. and width of the cut ting edge ; and particularly by the width of the cutting edge. A 25 mm cold chisel means a chisel with a 25 mm wide cutting edge. The shape of its cutting edge is also required to completely specify the chisel. The five most common types are the flat, the cross-cut, the diamond pointed, the half round and the ...

 Hammers are used to strike a job or a tool. They are made of forged steel of  various sizes  ( weights ) and shapes to suit various purposes. A suitable range would be from 0.11 to 0.33 kg for light work such as clinching small rivets and dot punching, 0.45 kg of chiseling, 0.91 kg of heavier work such as chipping, the popular sizes of  bench work being 0.33 to 0.45 kg. A Hammer consists of four parts namely peen, head, eye and face. The eye is normally made oval or elliptical in shape and it accommodates the handle or shaft. The end of the handle which fits into the eye is spread or split by forcing a metal wedge into to prevent the hammer head from flying of the handle during striking. The handle is made of elastic wood or bamboo and is so shaped and sized that when gripped it gives an easy feel to the hand. This "feel" is known as the "balance of the hammer. A well balanced hammer "feels" just right when the handle is grasped at the correct point. The face ...

 The vice is the most common tool for holding work. Various types of  vices are used for various purposes. They include bench vice, leg vice , pipe vice, hand vice, pin vice and  tool maker's vice.  Bench Vice : The most commonly used is the engineer's parallel-jaw bench vice, sometimes called fitter's vice. It must be firmly fixed to the bench with coach screws , or with nuts and bolts. The vice essentially consists of cast iron body, a fixed jaw, a moveable jaw - both made of cast steel , a handle, a square-threaded screw, and a nut- all made of mild steel. Separate cast steel plates known as jaw plates are fixed to the jaws by means of set screws and they can be replaced when worn. The holding faces of the jaw plates have teeth for holding the work firmly but this has some disadvantage for soft metal which may be damaged when firmly held between the faces. Protective grips or "clamps" which can be made of lead , fiber, tin-plate , etc. are, therefore,  usual...

Casting, that is, pouring a liquid into a mold without pressure, can be done with several plastics. When there is not sufficient justification for making expensive dies, the casting process is generally used.  Open molds into which the liquid resin , mixed with a catalyst or hardener , is poured can be used for most plastics.  Centrifugal casting , using the same methods can be used with several plastics to such as polyesters.  Shell molding is some what similar to casting in that no pressure is used. In this process, powdered resin is placed in a heated mold until a layer fuses to the desired thickness. The unfused resin inside is taken out of the mold and the hollow molding removed. Sometimes the mold is rotated in what is called rotational molding.  Slush molding is similar to shell molding. It employs a thermoplastic-resin  slurry or "slush" which is poured into a preheated mold. The heat causes slurry to set in a viscous layer of the desired wall thickn...

Blow molding is a process of placing a softened thermoplastic closed-end tube (Parison) and applying air pressure to inflate it. In operation, the heated Parison is continuously extruded , cut to the proper length and sealed at one end, gripped in the two-piece mold and then air is injected to force the plastic against the walls of the water-cooled mold. The parts cools and then the mold is opened and the part is removed.  Production methods range from simple manual operations to relatively complicated automatic ones. Blow molded products include ducts and similar articles. 

Injection molding is the most widely used method of producing parts of  thermoplastic and more recently, thermosetting resins as well. The process resembles the hot chamber die casting of metals : the die, split to allow removal of the solidified product, is kept shut with an appropriate press force and ejectors are provided for removing the molded component. The difference between metals and plastics lies in the supply of the polymer, which is usually fed in a solid form, pellets or powder, through a hopper to a injector screw, a die-end of which is surrounded with heaters that gradually brings the polymer to the required temperature. There the material is softened. The process starts with feeding plastic pellets into the hopper above the heating cylinder of the machine. The resin falls into and is pushed along the heated tube by reciprocating screw (feeder) until a sufficient volume of melted plastic is available at the injection nozzle end. This may take from 10 sec to 5 or 6...

  Thermoforming sometimes called vacuum forming, is the shaping of hot sheets or strips of thermoplastic materials into a desired shape either by mechanical or pneumatic methods. The sheets of  plastic used in the thermoforming process are produced by either extrusion , calendaring or pressing . Thickness of the sheets that are processed range from 0.125 to 3.2 mm or even greater.  The basic process is quite simple. A piece of plastic sheet is clamed into a frame. The plastic is heated, usually with electric heaters, until it begins to sag. Vacuum , air or mechanical pressure is then applied through small holes in the mold and the plastic is rapidly pulled tightly against the mold creating close profile conformity. The frame is raised, the part is removed and then trimmed in a punch press. The mold may have several shapes, for the same part or for different parts.  In vacuum forming, the sheet is clamped in a stationary frame and the heated sheet is vacuum-drawn ...

 A important method of making film and sheet is known as calendaring . In this process the plastic compound (composed of resin, filler, plasticizer and color pigment) is passed between a series of heated rollers. It comes out from the rolls  squeezed into film or sheet. Thickness is controlled by a combination of squeezing and altering the speed of  the finishing rolls. The finished product is cooled by passing through water-cooled rolls. The finished product is cooled by passing through water-cooled rolls. Vinyl floor tile, cellulose acetate sheeting and films are some of the applications. 

Transfer molding, also called extrusion or gate molding , is the process of  forming articles in a closed mold, where the fluid plastic material is conveyed into the mold cavity under pressure from outside of the mold.  The material, often a preheated preform, is placed in a heated transfer pot. As soon as the material is sufficiently softened, the plunger forces the almost fluid plastic through the orifice (sprue) into the closed mold where final cure takes place. Pressures used are 50 to 100% higher than those used for compression molding ; thus better details and higher strengths are possible .  Extrusion Molding :  Extrusion means the continuous flow of material through a die. Extrusion molding is used mostly for production of sheet, tube bar and typical applications in thermoplastic materials. Granulated powder made of such materials as vinyl resins, cellulose derivatives, nylon, polyethylene and polypropylene make up the materials used in the process.  Pl...

Compression molding is essentially a forging process, performed in a heated die that forms a premeasured quality of the polymer. The process is most widely used for the forming of the thermosetting plastics.  The basic procedure for compression molding , consists of  placing a measured amount of powder or a compressed perform (called the charge), into the open mold cavity, closing the mold and then applying heat and pressure through a downward moving die (called the force, plug or core) to the material until it softens and is forced fill the mold cavity. In the closed mold, a chemical reaction or polymerization , that cross-links the polymer chains takes place and the material hardens into the required shape. Heat for polymerization or curing is supplied through the walls of the cavity by steam or electricity.  Molding pressures (hydraulic) may be a low as 0.35 kgf / mm2 (3.5 Mpa) for polyester and epoxy but most thermosets require 1.4 to 4.2 kgf/mm2 (13.8 to 41.4 Mpa)...

Most plastic resins have to be combined, compounded or otherwise chemically treated with processing materials before they are ready for processing. Thorough mixing of ingredients is vital for all classes of  polymers and special equipment has been developed for the purpose. One of the following additions are usually employed.  1. Plasticizers :   Organic Solvents, resin and even water are used as plasticizers . These substances act as  internal lubricants improving flow of  and giving toughness and flexibility to the material. Plasticizers  are also used to prevent crystallization by keeping the chains separated from one another. For example vinyl are generally hard and brittle materials. By adding a plasticizers they can be made soft and flexible. 2. Fillers : Typical fillers which include wood flour, asbestos fiber, glass fiber, cloth fiber, mica, slate powders, may be added in high proportions to many plastics essentially to improve strength, dimen...

Thermosetting plastics are made from chains which have been linked together, referred to as cross-linked. These have a three dimensional network of molecules and will not soften when heated. They are practically insoluble, fireproof and usually hard and brittle. These plastics cannot be  reused. EPOXY RESINS : EPOXY RESIN is one of the new comers to the plastic field. It is cured or cross-linked by the addition of a hardener. Epoxies have excellent chemical resistance and electrical insulating properties. Their working temperature is from 150*C to 260*C with fillers additives. Coatings made from these resins combine the properties of  toughness; flexibility, adhesion and chemical resistance to a degree not found in other coating materials. Epoxy adhesives are now finding applications in aircraft, automobiles and in the home. While epoxy adhesive are well known, these plastics are also used as casting for pipe fittings , electrical and other equipment. These are also used in ...

This is the general name of a large group of plastics usually polyvinyl-chloride (PVC) is the most frequently used of this group. This is a very clear, transparent plastics, easily colored, resistant to most chemicals and very water repellant. It can stand outdoor exposure and is quite abrasion resistant, but it has low tensile strength.  PVC can be extruded as wire insulation, chemical tubing and refrigerator door gaskets. Coating of fabrics of  all kinds for industrial uses (such as tents and tarpaulin-type cover) is a major use of PVC.  Other Thermoplastic types  >>>  click here

This is one of the newer plastics perhaps better known by its trade name of  Derlin . I has been developed as a material for mechanical parts including sprinkler nozzles , handles , gears, housings etc., At present this is widely used for stereo tape catridges, toys , furniture casters and cigarette lighter cases. It has good tensile strength , resistance to temperature (115*C) , low friction characteristics, resistance to most solvent and low moisture absorption.  Other Thermoplastic types  >>>  click here

 The full name of  Acrylic resin is polymethyl methacrylate and it is better known as Acrylic Plexiglass or Lucite. This Beautifully clear, easily shapes plastic is most widely used in sheet form for signs of all kinds. Rods and tubes are cast in glass or metal cylinders or extruded. Acrylics can also be injection molded.  Acrylics will "pipe" light and are used in fiber optics and edge - lighted dials. It is tough but easily scratched. It is now widely used for outdoor signs, contact lenses, brush backs, transparent bowls, drink dispenses, etc.  Other Thermoplastic types  >>>  click here