Showing posts from May, 2015

Lathe Operations: Facing

Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

What are the Advantages and Limitations of Broaching Machine?

Advantages of Broaching Machine
Broaching has been adopted for mass production work. It has following features and advantages:

Rate of production is very high with properly applied broaches, fixtures and machines, more pieces can be turned out per hour by broaching than by any other means.
Little skill is required to perform a broaching operation, in most cases the operator merely loads and unloads the work piece.
High accuracy and high class of surface finish is possible. A tolerance of ±0.0075 mm and surface finish of about 0.8 microns can be easily obtained in broaching.
Both roughing and finishing cuts are completed in one pass of the tool.
The process can be used for either internal or external surface operation.
Any form that can be reproduced on a broaching can be machined.
Cutting fluid may be readily applied where it is most effective because a broach tends to draw the fluid into the cut.

Limitations of Broaching Machine
Following are the limitations of the broaching machine:

High tool …

What are the Broach Elements?

Ordinary cut broaches for machining previously drilled holes consist of the following elements:

Pull End - This is designed to permit engagement of the broach with the broaching machine through the use of puller head.
Front Pilot - This centres the broach in the hole before the teeth begin to cut.
Roughing and Semi Finishing Teeth - These remove most of the stock in the hole.
Finishing Teeth - These are for sizing the hole and must have the shape required for the finished hole.
Rear Pilot and Follower Rest - These support the broach after the last tooth leaves the hole.

Land - The top portion of a tooth is called land and in most cases it is ground to provide a slight clearance.
Back Off or Clearance Angle - This corresponds to the relief angle of a single point tool. This is 1.50 to 20 for cast iron and steel. Finishing teeth have a smaller angle ranging from 0 to 1.5O.
Rake or Hook Angle or Face Angle - This corresponds to the rake angle of a lathe tool. The rake angle varies according to t…

How Many Types of Broaching Machine are there?

There are four types of broaching machine:

Horizontal broaching machine
Vertical Broaching machine
Surface broaching machine
Continuous broaching machine

Horizontal Broaching Machine
All horizontal machines are of pull type. These may be used for either internal or external broaching. The horizontal broaching machine consists of a bed more than twice the length of broaching stroke. The broach pilot gives drive for pulling the broach.
Horizontal broaching machines are primarily used for broaching key ways, splines, slots, round holes and other internal shapes or contours. These machines have the disadvantage of taking more floor space than the vertical machine. However, long broaches and heavy work pieces are easily handled.

Vertical Broaching Machine       
The vertical broaching machines are available in either pull or push type. The push type is the most common. A vertical broaching machine is employed in multiple operations, and these are more likely to be found doing surface operations. …

What are the Main Parts of a Broaching Machine?

Ram - It is actuated by the piston in the cylinder of the hydraulic drive. It moves to and fro during the operation. In case of pulling type of broaching machine the ram pulls the broach with the required pressure for cutting stroke and goes inside the ram head.

Hydraulic Drive - It is housed in the base and powered by electric motor. This provides the required pressure for pulling or pushing the broach.

Bed - Bed is the robust casting on which the main units are mounted. The construction of bed is such so that it can bear the load/pressure exerted during the operation.

Pulling Slide - It supports the front end of ram.

Puller Head - It secures the pull end of the broach.

Platen - It supports the work piece against the cutting force while broaching operation is carried out.

Broach - A broach is a multiple-edged tool that has successively higher cutting edges along the length of the tool.

Follower Rest - It supports the rear end of the broach

What is a Broaching Machine?

The term broaching may have been derived from an ancient roman word braccus, which meant an object having projecting teeth. The operation started in the year 1850 when broaching tools were called “drifts”. These drifts were being hammered in blacksmith shop through the work or pushed through with an arbor press.
Broaching is a method of removing metal by pushing or pulling a cutting tool called a broach. The tool may be pulled or pushed through the surface to be finished. Surface is finished by broaching flat or contoured and may be either internal or external. Broaching is generally limited to the removal of about 6 mm of stock or less.  Different types of broaches are used for different types of work.
Broaching machines are probably the simplest of all machine tools. These consist of a work holding fixture, a broaching tool, a drive mechanism and a suitable supporting frame. Although the component is a few, several variations in design are possible. There are two principal types of ma…

How Testing of Rubber Compound is Carried Out?

This can be sub-divided into two distinct categories:

Testing of unvulcanized compound.
Testing of vulcanized compound.

Testing of Unvulcanized Compound
Testing of Unvulcanized Compound

Measuring Instrument

Moony viscometer
It gives idea about processing performance of the rubber compound in moulding.

Scorch time
Moony viscometer
Optimum cure time can be obtained.

Testing of Vulcanized Rubber Compound
No tests should be performed until at least 16 hours after vulcanizing as significant post vulcanization changes in structure of the material may occur during this period.
Tensile Test - These tests are most widely used test in the rubber industry. They are used to determine rate of cure and optimum cure, quality check on the compound, effect of immersion in liquids etc.
Hardness - Hardness, as applied to rubber, may be defined as the resistance to indentation under conditions that the rubber is not punctured. Hardness is one of the most useful and often quoted properties of r…

What is Cryogenic Tumbler?

After the rubber parts are removed from the moulds, they contain thin flash, a result of the elastomer flowing in multisection mould. This flash is typically removed by exposing the parts to a cryogenic tumbling process. This process is carried out in a machine known as cryogenic tumbler. In this machine liquid Nitogen is used to bring the temperature down upto -1960 C. Rubber components are put in the machine and the machine is then switched on. Due to the cooling effect, these components become brittle. The flash being the thinner section brakes easily and the cleaned items come out without damaging/affecting the profile of the seals.
Flash should not be removed by grinding or knifing operation due to the reasons given here. When the rubber is heated, pressed and cured in a mould, the surface contact between the metal mould and the outermost layer of the rubber seal, where the temperature is maximum when compared to the core of the seal, ensures that a case hardened, smooth, compact …

What is Vulcanization of Rubber?

The process transforms elastomers with weak thermoplastic properties into a strong, elastic and tough substance with useful properties and introduces a network of cross links into the elastomers. Tensile strength is maximum at optimum cure. Beyond this point, the stock is said to be over cured. It gets stiffer and harder but weaker and less extensible.

Techniques of Vulcanization
Vulcanisation can be carried out using several techniques.

Compression Moulding - This is the most common method used in the industry. Here the blank is placed in a two piece mould, one part of which is movable and the other stationary. The mould is closed, then heat and pressure are applied so that the material flows to fill the mould. A little excess of the material is used to ensure that the mould is completely filled.
Transfer Moulding - This technique is a variation of compression moulding. The blank is placed in a separate chamber called as pot, preheated to a temperature below cure temperature and transfer…

What are the various types of resistant rubbers?

Weather Resistant Rubber
Ethylene Propylene Rubber - These are the fastest growing elastomers because of its outstanding properties such as good weather resistant in ozone environment. It is used in tyre side walls, tank linings, wire and cables, mechanical goods, agricultural equipment and automotive applications.
Modified Polyethylene or Chlorosulphonated Polyethylene - It is unique among elastomers as it is derived from a plastic. It is prepared by dissolving polyethylene in a suitable solvent and passing simultaneously Sulphur dioxide and Chlorine in the presence of a free radical catalyst to bring about chlorination and chlorosulphonation. The rubber is completely saturated and so has excellent resistance to chemicals, weather and ozone. It has flame resistance as well due to the presence of chlorine. It is used for making white tyre side walls after blending with neoprene and neutral rubber and gives a beautiful white colour and a surface free from cracking and ozone attack. It is…

What are the General Purpose Rubbers available?

There are four types of rubbers under general purpose rubbers. They are:
Styrene-Butadiene Rubber - Styrene-Butadiene Rubber (SBR) constitutes more than half of the world production of synthetic rubber and exceeds natural rubber supply. In fact, tyre industry depends more on SBR than a natural rubber because it is available in plenty and serves the purpose better after the incorporation of fillers.
Butyl Rubber - Butyl rubber is produced by copolymerising small amount of isoprene (1-3%) with isobutylene catalysed by aluminium chloride (AlCl3) dissolved in methyl chloride. The extremely rapid reaction is complete in less than a second. Methyl chloride diluent and monomer should be carefully dried. They possess unique age-resistant properties. This type of rubber is used for inner tubes of tyres. Other uses are in the field of mechanical goods.
Synthetic Polyisoprene Rubber - Isoprene is derived from petroleum. It is mixed with hydrocarbon solvent. Two types of catalysts can be used. One i…

How many types of rubber are there?

During the initial period of rubber manufacturing, the raw material was procured almost entirely from South America. Rubber occurs in the ‘Hevea Brasilienses’ tree as latex, a milky liquid exuded when the tree is wounded or cut. As early as 1834, Hancock from Brazil, suggested the possibility of growing rubber tree under more controlled conditions in the similar tropical climate of the Far East. In 1876, an alternate was made by Sir Henry Wikham. Some 70,000 seeds brought by himself from Brazil were planted at Kew and about 2,000 young plants were obtained. Most of these were sent to Sri Lanka where they were successfully established. It was principally from Sri Lanka that the Hevea tree was established in other parts of the Far East like Malaysia, Indonesia, Thailand, India and other places.

Types of Rubber
There are two types of rubber which are described in the following paragraphs:
Natural Rubber - It is obtained from the rubber tree by tapping process when it exudes out in the form …

Why Sands are used in Moulding?

The principal material used in moulding is the moulding sand' which is also referred as "Green Sand". This sand must possess the following qualities.

Cohesiveness - The ability to retain its shape when the pattern has been removed during the pouring and solidification, of the metal.
Refractivity - The ability to withstand the heat of the molten, metal without fusing.
Porosity - his enables the free escape of gases which form as the hot metal contacts the moisture in the mould.
Re-Tempering Qualities - The quality that enables it to be re tempered for use in many successive moulds.

Cohesiveness or bonding properties are imparted to moulding sands chiefly by the presence of 2 to 6 percent of clay, The clay in moulding sand must be ideally distributed in the form of a thin layer on the individual grains, and this distribution and complete mixing of the water and coal dust is done by milling the sand mixture in various mills. The sand is finally riddled by pressing it. Bentonite …

What are Various Types of Moulding Furnaces?

A metal must be heated to the correct pouring temperature which is slightly higher than its melting point before it can be cast. There are several ways in which a metal can be reduced to the liquid state.
Cupola Furnace - The first and usually the cheapest method of melting iron is in a cupola furnace. The cupola is a melting furnace which is fired with coke to produce the high temperature required for melting iron. In addition to the charge of pig iron, other materials such as lime stone and prepared fluxes are added to each lot of metal. The lime stone and flux aid in separating the impurities from the pig iron.
Gas Fired Crucible Furnace - A second method of melting metals in a foundry is a gas fired crucible furnace. In this type of furnace, the burning gas does not come into direct contact with the metal charge, but heats a crucible in which the metal, in turn is melted.
Electric Arc Furnace - In some foundries the electric furnace is found to be the best equipment for melting metal…

What are the various types of moulding tools?

Moulding work is a basic need to almost every manufacturing process. It is a highly skilled profession. To carry out his craft the moulder has to apply his skill to the vision of the designer and draftsman, the art of the sculptor, the preciseness of the machinist and the exactness of the mathematician. As a result, the moulder has an unchallenged position in the industrial progress in the world.
Foundry work deals with the making of moulds, melting the metal and pouring of these metals into moulds to form castings. Industrial foundries are often identified according to the type of metal used in the pouring. Foundries which specialize in casting brass, bronze, aluminium and white metal are classified as nonferrous foundries. A foundry which cast principally grey cast iron, steel and malleable cast iron is classified as ferrous or iron foundry.

Types of Moulding Tools
Moulders Flask - The box like container in which the sand mould is made, is called a flask. Flasks are made entirely of wo…