About Engineering & Plastic Technology

  INTRODUCTION Multicavity injection molds can be built to make over 100  parts per cycle. Each part cavity is filled with melt through sprue and runners. As the attached sprue and runner cools down with cooling of plastic part, the sprue and runner comes out along with the plastic product when the product is ejected from the injection mould . The runners has to be seperated from the moulded plastic part which involves handling and regrinding of the sprue and runners. HOT RUNNER SYSTEM Unlike cold runners they are heated channels that keep the plastic molten during the entire cycle. HEATING MECHANISM Runners are kept hot by two ways  a) External heating By surrounding the melt channel with an appropriate electric heating element. b) Internal heating In the internal heating system their is an electric heating element which is kept inside the melt channel. DEMERITS OF HOT RUNNER SYSTEM Hot runner system is more complicate and expensive. Hot runner mould is more difficult to...

 POWDER METALLURGY Definition:- What does Powder Metallurgy (PM) mean? Powder metallurgy (PM) is a process for forming metal parts by heating compacted metal powders to just below their melting points. In other words PM is metal shaping process that creates near-net parts from powdered metal. Powder metallurgy is the process of blending fine powdered materials pressing them into desired shape or form (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). The powder metallurgy process consists of four basic steps. Powder manufacture Powder blending  Compacting Sintering Advantages The PM process provides a host of advantages over competing metalworking technologies moluding. Cost effectiveness Shape and material versatility Application versatility Part-to-part uniformity Virtually unlimited choice of alloys and non metallics with associated properties A variety of metal or non metal powders can be used. Refractory mat...

 INTRODUCTION Position indicating device is used to provide remote indication of position, such as indication of the open or shut condition of a valves. THERE ARE FOUR TYPES OF POSITION INDICATORS Limit switches Reed switches Potentiometer LVDT Limit and Reed switches act as ON/OFF indications to provide open and closed indication and control function. Reed switches can aslo be used to provide an incremental-position indication. Potentiometer and LVDT position indicators provide an accurate indications, such as the position of a rod throughout its travel. LIMIT SWITCHES Limit switch is a mechanical device, which can be used to determine the physical position of any part to provide full  open or full shunt indication. Many limit switch are the push button variety which gives ON/OFF corresponding to the valve position. Example : An extension of a valve shaft mechanically trips a limit switch as it moves from open to shunt or shunt to open. When the valve extension comes in cont...

  THERMOCOUPLE WORKING PRINCIPLE OF THERMOCOUPLE Thermocouple is a temperature measuring device constructed of two dissimilar metal wires joined at one end. When one end of each wire is connected to a measuring instrument the thermocouple becomes a sensitive and highly accurate measuring device. Thermocouple may be constructed of several different combinations of materials. The performance of a thermocouple material is generally determined by using that material with platinum, The measuring junction is normally formed at the bottom of the thermocouple housing. In a typical thermocouple, the leads are encased in a rigid metal sheath. CONSTRUCTION OF THERMOCOUPLE The most important factor to be considered when selecting a pair of materials is the thermoelectric difference between the two materials. A significant difference between the two materials will result in better thermocouple performance. Constantan is excellent for temperature up to 2000℉. Nickel/Nickel-Molybdenum sometimes r...

 INTRODUCTION An orifice is a small opening of any cross-section (such as circular, triangular, rectangular etc.) on the side or at the bottom of a tank through which a fluid is flowing. It is used to measure rate of flow of fluid  Thickness of orifice in direction of flow is very small in comparison to its other dimensions. i.e Orifice has a sharp edge so that there is an contact with fluid and consequently minimum friction resistance at its sides. If sharp edge is not provided the flow will depend on thickness of orifice and roughness of its boundary too. The rate of flow of fluid through orifice depend on shape, size and form of orifice. CLASSIFICATION OF ORIFICE A) On the basis of cross sectional area Circular orifice  Triangular orifice Rectangular orifice Square orifice B) According to size  Small orifice - If head of liquid (H) >5 Times depth of orifice Large orifice - H< 5d C) According to shape of edge Sharp edge orifice  Bell mounted D) According...

  EXTRUDER DIES Extruder Sheet and Cast Film The convention between cast film and sheet is that film is less than 0.01 inch thick and sheet is more than 0.01 inch thick. The key components in a sheet/film extrusion line are: die, three-roll stack or cooling rolls, puller or nip rolls, and windup or sheet stacking system. The sheet die should uniformly distribute the polymer melt across the  entire die width. This is to provide a uniform melt thickness and polymer flow to the three-roll stack. Die width typically range from approximately 24-120 inches (0.6-3 meters. Cast film/sheet is produced using a multiple roll stack. Depending on the thickness, film is wound in continuous rolls and sheet is cut to length and stacked. The die is designed to fit between the rolls in a three-roll stack and lay the sheet down on the roll. Roll diameters generally range between 8 and 16 inches. Roll stack designs are simple 'up' or 'down' stacks to control the entry and exit angle and th...