Superheated steam boilers

A superheated boiler on a steam locomotive

     
          Most boilers produce steam to be used at saturation temperature ; that is , saturated steam. Superheated steam boilers vaporize the water and then further heat the steam in a superheater. This provides steam at much higher temperature , bur can decrease the overall thermal efficiency of the steam generating plant because the higher steam temperature requires a higher flue gas exhaust temperature. There are several ways to circumvent this problem , typically by providing an economizer that heats the feed water , a combustion air heater in the hot flue gas exhaust path or both. There are advantages to superheated steam that may and often will , increase overall efficiency of both steam generation and its utilisation: gains in input temperature to a turbine should outweigh any cost in additional boiler complication and expense. There may also be practical limitations in using wet steam , as entrained condensation droplets will damage turbine blades.
      Superheated steam presents unique safety concerns because , if any system component fails and allows steam to escape , the high pressure and temperature can cause serious , instantaneous harm to anyone in its path. Since the escaping steam will initially be completely superheated vapor , detection can be difficult , although the intense heat and sound from such a leak clearly indicates its presense.
      Superheater operation is similar to that of the coils on an air conditioning unit , although for a different purpose. The steam piping is directed through the flue gas path in the boiler furnace. The temperature in this area is typically between 1,300-1,600 degree Celsius (2,372-2,912°F). Some superheaters are radiant type ; that is , they absorb heat by radiation. Others are convection type , absorbing heat from a fluid such as a gas. Some are a combination of the two types. Through either method , the extreme heat in the flue gas path will also heat the superheater steam piping and the steam within. While the temperature of the steam in the superheater rises , the pressure of the steam does not : the turbine or moving pistons offer a continuously expanding space and the pressure remains the same as that of the boiler. Almost all steam superheater system designs remove droplets entrained in the steam to prevent damage to the turbine blading and associated piping.

Hydronic Boilers

Hydronic Boilers

      Hydronic boilers are used in generating heat for residential and industrial purposes. They are the typical power plant for central heating systems fitted to houses in northern Europe (where they are commonly combined with domestic water heating) , as apposed to the forced-air furnaces or wood burning stoves more common in North America. The hydronic boiler operates by way of heating water/fluid to a preset temperature (or sometimes in the case of single pipe systems , until it boils and turns to steam) and circulating that fluid throughout the home typically by way of radiators , baseboard heaters or through the floors. The fluid can be heated by any means...gas , wood , fuel oil etc.. , but in built-up areas where piped gas is available , natural gas is currently the most economical and therefore the usual choice. The fluid is in an enclosed system and circulated throughout by means of a motorized pump. The name "boiler" can be a misnomer in that , except for systems using steam radiators , the water in a properly functioning hydronic boiler never actually boils. Most new systems are fitted with condensing boilers for greater efficiency. These boilers are referred to as  condensing boilers because they condense the water vapor in the flue gases to capture the latent heat of vaporization of the water produced during combustion.
   
    Hydronic systems are being used more and more in new construction in North America for several reasons. Among the reasons are :

* They are more efficient and more economical than forced-air systems (although initial installation can be
   more expensive , because of the cost of the copper and aluminium).
* The baseboard copper pipes and aluminium fins take up less room and use less metal than the bulky steel
  ductwork required for forced-air systems.
* They provide more even , less fluctuating temperatures than forced-air systems. The copper baseboard pipe
   hold and release heat over a longer period of time than air does , so the furnace does not have to switch off
   and on as much.(Copper heats mostly through conduction and radiation , whereas forced-air heats mostly
   through forced convection. Air has much lower thermal conductivity and volumetric heat capacity than
   copper , so the conditioned space warms up and cools down more quickly than with hydronic)
* They tend to not dry out the interior air as much as forced air systems , but this is not always true. When
   forced air duct systems are air-sealed properly and have return-air paths back to the furnace (thus reducing
   pressure differentials and therefore air movement between inside and outside the house) this is not an issue.
* They do not introduce any dust , allergens , mold or (in the case of a faulty heat exchanger) combustion by
   products into the living space.

Forced-air heating does have some advantages , however.            

Boiler Accessories

Boiler fittings and accessories

    * Safety valve :
         It is used to relieve pressure and prevent possible explosion of a boiler.

    * Water level indicators :
          They show the operator the level of fluid in the boiler , also known as a sight glass , water gauge orwater column is provided.

    * Bottom blowdown valves :
          They provide a means for removing solid particulates that condense and lie on the bottom of a boiler. As the name implies , this valve is usually located directly on the bottom of the boiler and is occasionally opened to use the pressure in the boiler to push these particulates out.

    * Continuous blowdown valve :
          This allows a small quantity of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - a condition known as priming. Blowdown is also often used to monitor the chemistry of the boiler water.

    * Flash tank :
          High pressure blowdown enters this vessel where the steam can 'flash' safely and be used in a  low-pressure system or be vented to atmosphere while the  ambient pressure blowdown flows to drain.

    * Automatic blowdown/continuous Heat Recovery system :
          This system allows the boiler to blowdown only when makeup water is flowing to the boiler , thereby transferring the maximum amount of heat possible from the blowdown to the makeup water. No flash tank is generally needed as the blowdown discharged is close to the temperature of the makeup water.

    * Hand holes :
          They are steel plates installed in openings in "header" to allow foe inspections & installation of tubes and inspection of internal surfaces.

    * Steam drum internals :
          A series of screen , scrubber & cans(cyclone separators).

    * Low-water cutoof :
          It is a mechanical means (usually a float switch) that is used to turn off the burner of shut off fuel to the boiler to prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure.

    * Surface blowdown line :
          It provides a means for removing form or other lightweight non-condensible substance that tend to float on top of the water inside the boiler.

    * Circulating pump :
          It is designed to circulate water back to the boiler after it has expelled some of its heat.

    * Feedwater check valve or clack valve :
          A non-return stop valve in the feedwater line. This may be fitted to the side of the boiler , just below the water level or to the top of the boiler.

    * Top feed :
          A check valve (clack valve) in the feedwater line , mounted on top of the boiler. It is intended to reduce the nuisance of limescale. It does not prevent limescale formation but causes the limescale to be precipitaed in a powdery form which is easily washed out of the boiler.

    * Desuperheater tubes or bundles :
          A series of tubes or bundles of tubes in the water drum or the steam drum design to cool superheated steam. Thus is to supply auxiliary equipment that doesn't need  or may be damaged by or dry system.

    * Chemical injection line:
          A connection to add chemicals for controlling feedwater pH.

Safty

What Caused the Boiler Explosion at the Ford Rouge Plant

      Historically , boilers were a source of many serious injuries and property destruction due to poorly understood engineering principles. Thin and brittle metal shells can rupture , while poorly welded or riveted seams could open up , leading to a violent eruption of the pressurized steam. Collapsed or dislodged boiler tubes could also spray scalding-hot steam and smoke out of the air intake and firing chute , injuring the firemen who loaded coal into the fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.

Boiler Explosion At York Rolling MIlls Kills 9 Men; 20 injured

      A boiler that has a loss of feed water and is permitted to boil dry can be extremely dangerous. If feed water is then  sent into the empty boiler , the small cascade of incoming water instantly boils on contact with the superheated metal shell and leads to a violent explosion that cannot be controlled even by safety steam valves. Draining of the boiler could also occur if a leak occurred in the steam supply lines that was larger than the make-up water supply could replace. The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and insurance company as a method to help prevent this condition from occurring and thereby  reduce their insurance claims.

A boiler explosion would not have caused the forward decks to collapse

Configurations

Configurations

      Boilers can be classified into the following configurations :

* "Port boilers" or "Haycock boilers" : a primitive "kettle" where a fire heats a partially-filled water container
   from below. 18th century Haycock boilers generally produced and stored large volumes of very
   low-pressure
   steam , often hardly above that of the atmosphere. These could burn wood of most often , coal. Efficiency
   was very low.
* Fire-tube boilers. Here , water partially fills a boiler barrel with a small volume left above to accommodate
   the steam (steam space). This is the type of   boilers used in nearly all steam locomotives. The heat source is
   inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the
   temperature of the heating surface just below boiling point. The furnace can be situated at one end of
   fire-tube which lengthens the path of the hot gases , thus  augmenting the heating surface which can be
   further increased by making the gases reverse direction through a second parallel tube or a bundle of
   multiple tubes (two-pass or return flue boiler) ; alternatively the gases may be taken along the sides and then
   beneath the boiler through flues (3-pass boiler). In the case of a locomotive-type boiler , a boiler barrel
   extends from the firebox and the hot gases  pass through a bundle of fire tubes inside the barrel which
   greatly increase the heating surface compared to a single tube and further improve heat transfer. Fire-tube
   boilers usually have a comparatively low rate of steam production , but high steam storage capacity.
   Fire-tube boilers mostly burn solid fuels, but are readily adaptable to those of the liquid or gas variety.
* Water-tube boiler. In this type , the water tubes are arranged inside a furnace in a number of possible
   configurations : often the water tubes connect large drums , the lower ones containing water and the upper
   ones , steam and water ; in other cases , such as a monotube boiler , water is circulated by a pump through
   a succession of coils. This type generally gives high steam production rates , but less storage capacity than
   the above. Water tube boilers can be designed to exploit any heat source and are generally preferred in high
   pressure applications since the high pressure water/steam is contained within small diameter pipes which can
   withstand the pressure with a thinner wall.
* Flash boiler. A specialized type of water-tube boiler.

1950s design steam locomotive boiler , from a victorian Railways J class
      * Fire-tube boiler with water-tube firebox. Sometimes the two above types have been combined in the
         following manner : the firebox contains an assembly of water tubes , called thermic syphons. The gases
         then pass through a conventional firetube boilers. Water-tube firebox were installed in many Hungarian
         locomotives , but have met with little success in other countries.
      * Sectional boiler. In a cast iron sectional boiler , sometimes called a "pork chop boiler" the water is
         contained inside cast iron sections. These sections are assembled on site to create the finished boiler.

Fuel

Fuel

The source of heat for a boiler is combustion of any of  sevaral fuels , such as wood , coal , oil or natural gas. Electric steam boilers use resistance or immersion-type heating elements. Nuclear fission is also used as a heat source for generating steam. Heat recovery steam generators  (HRSGS) use the heat rejected from other processes such as gas turbines.

Boiler

Materials

1950s design steam locomotive boiler , from a Victorian Railways J class

     The pressure vessel in a boiler is usually made of steel (or alloy steel) , or historically of wrought iron. Stainless steel is virtually prohibited (by the ASME Boiler Code) for use in wetted parts of modern boilers , but is used often in superheater sections that will not be exposed to liquid boiler water. In live steam models , copper or brass is often used because it is more easily fabricated in smaller size boilers. Historically , copper was often used for fireboxes (particularly for steam locomotives) , because of its better formability and higher thermal conductivity ; however , in more recent times , the high price of copper often makes this an uneconomic and cheaper substitutes (such as steel) are used instead.
      For much of the victorian "age of steam" , the only material used for boilermaking was the highest grade of wrought iron , with asembly by rivetting . This iron was often obtained from specialist ironworks , such as at cleartor Moor (UK) , noted for the high quality of their rolled plate and its suitability for high-reliability use in critical applications , such as high-pressure boilers. In the 20th century , design practice instead moved towards the use of  steel , which is stronger and cheaper , with welded construction , which is quicker and requires less labour.

Diagram of a water-tube boiler

      Cast Iron may be used for the heating vessel of domestic water heaters. Although such heaters are usually termed "boilers" in some countries , their purpose is usually to produce hot water , not steam and so they run at low pressure and try to avoid actual boiling. The brittleness of cast iron makes it impractical for high pressure steam boilers.

Diagram of a fire-tube boiler

EARTH DIGGING MACHINES

Tunnel boring machine

A tunnel boring machine (TBM) also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through hard rock, sand, and almost anything in between. Tunnel diameters can range from a metre (done with micro-TBMs) to almost 16 metres to date. Tunnels of less than a metre or so in diameter are typically done using trenchless construction methods or horizontal directional drilling rather than TBMs.
Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional 'hand mining' in soil. A TBM has the advantages of limiting the disturbance to the surrounding ground and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in heavily urbanized areas. The major disadvantage is the upfront cost. TBMs are expensive to construct, and can be difficult to transport. However, as modern tunnels become longer, the cost of tunnel boring machines versus drill and blast is actually less--this is because tunneling with TBMs is much more efficient and results in a shorter project.
The largest diameter TBM, at 15.43 m, was built by Herrenknecht AG for a recent project in Shanghai, China. The machine was built to bore through soft ground including sand and clay. The largest diameter hard rock TBM, at 14.4 m, was manufactured by The Robbins Company for Canada's Niagara Tunnel Project. The machine is currently boring a hydroelectric tunnel beneath Niagara Falls.

History

The first successful tunnelling shield was developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel in 1825. However, this was only the invention of the shield concept and did not involve the construction of a complete tunnel boring machine, the digging still having to be accomplished by the then standard excavation methods.
The very first boring machine ever reported to have been built was Henri-Joseph Maus' Mountain Slicer. Commissioned by the King of Sardinia in 1845 to dig the Fréjus Rail Tunnel between France and Italy through the Alps, Maus had it built in 1846 in an arms factory near Turin. It basically consisted of more than 100 percussion drills mounted in the front of a locomotive-sized machine, mechanically power-driven from the entrance of the tunnel. Unfortunately, the Revolutions of 1848 irremediably affected the funding of the project and the tunnel was not completed until 10 years later, by using also innovative but rather less expensive methods such as pneumatic drills.[1].
In the United States, the first boring machine to have been built was used in 1853 during the construction of the Hoosac Tunnel. Made of cast iron, it was known as Wilson's Patented Stone-Cutting Machine, after its inventor Charles Wilson. It drilled 10 feet into the rock before breaking down. The tunnel was eventually completed more than 20 years later, and as with the Fréjus Rail Tunnel, by using less ambitious methods.
In the early 1950s, F.K. Mitry won a dam diversion contract for the Oahe Dam in Pierre, South Dakota, and consulted with James S. Robbins, founder of The Robbins Company, to dig through what was the most difficult shale to excavate at that time, the Pierre Shale. Robbins built a machine that was able to cut 160 feet in 24 hours in the shale, which was ten times faster than any other digging speed at that time.
The breakthrough that made tunnel boring machines efficient and reliable was the invention of the rotating head mounted with disc cutters. Initially, Robbins' tunnel boring machine used steel picks rotating in a circular motion to dig out of the excavation front, but he quickly discovered that these picks, no matter how strong they were, had to be changed frequently as they broke or tore off. By replacing the picks with longer lasting circular disc cutters, this problem was significantly reduced. The design was first utilized successfully at the Humber River Sewer Tunnel in 1956. Since then, all successful hard rock tunnel boring machines have utilized rotating cutting wheels mounted with circular disc cutters.


Description

Modern TBMs typically consist of the rotating cutting wheel,called a cutterhead, followed by a main bearing, a thrust system, and trailing support mechanisms. The type of machine used depends on the particular geology of the project, the amount of ground water present, and other factors.

RIG PLANT

Oil platform

An offshore platform, often referred to as an oil platform or an oil rig, is a lаrge structure used to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore. Depending on the circumstances, the platform may be fixed to the ocean floor, may consist of an artificial island, or may float.
Most offshore platforms are located on the continental shelf, though with advances in technology and increasing crude oil prices, drilling and production in deeper waters has become both feasible and economically viable. A typical platform may have around thirty wellheads located on the platform and directional drilling allows reservoirs to be accessed at both different depths and at remote positions up to 5 miles (8 kilometers) from the platform.
Remote subsea wells may also be connected to a platform by flow lines and by umbilical connections; these subsea solutions may consist of single wells or of a manifold centre for multiple wells.

History

Around 1891 the first submerged oil wells were drilled from platforms built on piles in the fresh waters of the Grand Lake St. Marys (a.k.a. Mercer County Reservoir) in Ohio. The wide but shallow reservoir was built from 1837 to 1845 to provide water to the Miami and Erie Canal.
Around 1896 the first submerged oil wells in salt water were drilled in the portion of the Summerland field extending under the Santa Barbara Channel in California. The wells were drilled from piers extending from land out into the channel.
Other notable early submerged drilling activities occurred on the Canadian side of Lake Erie in the 1900s and Caddo Lake in Louisiana in the 1910s. Shortly thereafter, wells were drilled in tidal zones along the Gulf Coast of Texas and Louisiana. The Goose Creek field near Baytown, Texas is one such example. In the 1920s drilling was done from concrete platforms in Lake Maracaibo, Venezuela.
The oldest subsea well recorded in Infield's offshore database is the Bibi Eibat well which came on stream in 1923 in Azerbaijan. Landfill was used to raise shallow portions of the Caspian Sea.
In the early 1930s the Texas Company developed the first mobile steel barges for drilling in the brackish coastal areas of the gulf.
In 1937 Pure Oil Company (now Chevron Corporation) and its partner Superior Oil Company (now ExxonMobil Corporation) used a fixed platform to develop a field in 14 feet of water, one mile offshore of Calcasieu Parish, Louisiana.
In 1946, Magnolia Petroleum Company (now ExxonMobil) erected a drilling platform in 18 ft of water, 18 miles[vague] off the coast of St. Mary Parish, Louisiana.
In early 1947 Superior Oil erected a drilling/production platform in 20 ft of water some 18 miles[vague] off Vermilion Parish, Louisiana. But it was Kerr-McGee Oil Industries (now Anadarko Petroleum Corporation), as operator for partners Phillips Petroleum (ConocoPhillips) and Stanolind Oil & Gas (BP), that completed its historic Ship Shoal Block 32 well in October 1947, months before Superior actually drilled a discovery from their Vermilion platform farther offshore. In any case, that made Kerr-McGee's well the first oil discovery drilled out of sight of land.
The Thames Sea Forts of World War II are considered the direct predecessors of modern offshore platforms. Having been pre-constructed in a very short time, they were then floated to their location and placed on the shallow bottom of the Thames estuary.[1][2]

Types

Larger lake- and sea-based offshore platforms and drilling rigs are some of the largest moveable man-made structures in the world. There are several distinct types[3] of platforms and rigs:

CATAPILLEAS

Caterpillar Selection Process Information Guide

Caterpillar is the world’s leading manufacturer of construction and mining equipment, diesel and natural gas engines and industrial gas turbines. We are a technology leader in construction, transportation, mining, forestry, energy, logistics, electronics, financing and electric power generation. But, as you are about to discover, Caterpillar is more than big, yellow machines. Caterpillar is people – thousands of us working as a team to help ensure our customers’ success.
By taking part in the Caterpillar Selection Process, this is an opportunity for you to become part of a dynamic team, a team that produces quality products and services.
This guide explains the basic process we use to help determine if applicants will be successful as employees of Caterpillar. You’ll learn about our employment process and receive information on how to take tests and prepare for interviews. We will provide you with sample test questions. Our goal is to provide the information you’ll need to understand and do your best in this process.


Caterpillar’s Selection Process

Caterpillar’s selection process is designed to assess the skills and talents you have compared to the jobs available. The chances for mutual success are much greater if we can obtain an accurate picture of your skills, abilities, and work preferences compared to the jobs we have available. During the selection process you will have the opportunity to learn more about Caterpillar and tell us about your unique background.
Prior to beginning the selection process, you have the right, under federal and/or state law, to self-identify as an individual with a disability. If you choose to self-identify, you must submit the appropriate documentation from a certified professional to Caterpillar to determine if an accommodation is needed and can be made. If you choose not to self-identify at this time, this does not preclude you from exercising this right at a later date, but prior to the completion of the process.
You should bring your social security number and a photo ID with you to begin the selection process.

The selection process consists of four phases:

1. Completion of an application and forms. During this phase of the process, we will answer any questions you may have regarding employment at Caterpillar. Release of information on former employment and background information forms are completed at this time.

2. Tests. These tests will help us assess your job-related abilities and skills.

3. Invitation for an interview. Upon successful completion of the tests, you may be eligible for comprehensive interviews that assess your achievements and qualifications. During this phase, your work reference may be contacted to verify information regarding past employment.

4. Job offer. Based on the results of the interview, you may be extended a job offer. Following any job offer, you will be required to provide medical information and may have to undergo a physical examination to determine your proper job placement.

Note - You will also be required to successfully pass a drug screening and background check during the selection process.

MILLING MACHINES

Milling machine

A milling machine is a machine tool used to machine solid materials. Milling machines exist in two basic forms: horizontal and vertical, which terms refer to the orientation of the cutting tool spindle. Unlike a drill press, in which the workpiece is held stationary and the drill is moved vertically to penetrate the material, milling also involves movement of the workpiece against the rotating cutter, the latter of which is able to cut on its flanks as well as its tip. Workpiece and cutter movement are precisely controlled to less than 0.001 in (0.025 mm), usually by means of precision ground slides and leadscrews or analogous technology. Milling machines may be manually operated, mechanically automated, or digitally automated via computer numerical control (CNC).
Milling machines can perform a vast number of operations, some very complex, such as slot and keyway cutting, planing, drilling, diesinking, rebating, routing, etc. Cutting fluid is often pumped to the cutting site to cool and lubricate the cut, and to sluice away the resulting swarf.


Comparing vertical with horizontal

Vertical milling machine. 1: milling cutter 2: spindle 3: top slide or overarm 4: column 5: table 6: Y-axis slide 7: knee 8: base
In the vertical mill the spindle axis is vertically oriented. Milling cutters are held in the spindle and rotate on its axis. The spindle can generally be extended (or the table can be raised/lowered, giving the same effect), allowing plunge cuts and drilling. There are two subcategories of vertical mills: the bedmill and the turret mill. Turret mills, like the ubiquitous Bridgeport, are generally smaller than bedmills, and are considered by some to be more versatile. In a turret mill the spindle remains stationary during cutting operations and the table is moved both perpendicular to and parallel to the spindle axis to accomplish cutting. In the bedmill, however, the table moves only perpendicular to the spindle's axis, while the spindle itself moves parallel to its own axis. Also of note is a lighter machine, called a mill-drill. It is quite popular with hobbyists, due to its small size and lower price. These are frequently of lower quality than other types of machines, however.

A horizontal mill has the same sort of x–y table, but the cutters are mounted on a horizontal arbor (see Arbor milling) across the table. A majority of horizontal mills also feature a +15/-15 degree rotary table that allows milling at shallow angles. While endmills and the other types of tools available to a vertical mill may be used in a horizontal mill, their real advantage lies in arbor-mounted cutters, called side and face mills, which have a cross section rather like a circular saw, but are generally wider and smaller in diameter. Because the cutters have good support from the arbor, quite heavy cuts can be taken, enabling rapid material removal rates. These are used to mill grooves and slots. Plain mills are used to shape flat surfaces. Several cutters may be ganged together on the arbor to mill a complex shape of slots and planes. Special cutters can also cut grooves, bevels, radii, or indeed any section desired. These specialty cutters tend to be expensive. Simplex mills have one spindle, and duplex mills have two. It is also easier to cut gears on a horizontal mill.


Other milling machine variants and terminology


Box or column mills are very basic hobbyist bench-mounted milling machines that feature a head riding up and down on a column or box way.
Turret or vertical ram mills are more commonly referred to as Bridgeport-type milling machines. The spindle can be aligned in many different positions for a very versatile, if somewhat less rigid machine.
Knee mill or knee-and-column mill refers to any milling machine whose x-y table rides up and down the column on a vertically adjustable knee. This includes Bridgeports.
C-Frame mills are larger, industrial production mills. They feature a knee and fixed spindle head that is only mobile vertically. They are typically much more powerful than a turret mill, featuring a separate hydraulic motor for integral hydraulic power feeds in all directions, and a twenty to fifty horsepower motor. Backlash eliminators are almost always standard equipment. They use large NMTB 40 or 50 tooling. The tables on C-frame mills are usually 18" by 68" or larger, to allow multiple parts to be machined at the same time.
Planer-style mills are large mills built in the same configuration as planers except with a milling spindle instead of a planing head. This term is growing dated as planers themselves are largely a thing of the past.
Bed mill refers to any milling machine where the spindle is on a pendant that moves up and down to move the cutter into the work. These are generally more rigid than a knee mill.
Ram type mill refers to a mill that has a swiveling cutting head mounted on a sliding ram. The spindle can be oriented either vertically or horizontally, or anywhere in between. Van Norman specialized in ram type mills through most of the 20th century, but since the advent of CNC machines ram type mills are no longer made.
Jig borers are vertical mills that are built to bore holes, and very light slot or face milling. They are typically bed mills with a long spindle throw. The beds are more accurate, and the handwheels are graduated down to .0001" for precise hole placement.
Horizontal boring mills are large, accurate bed horizontal mills that incorporate many features from various machine tools. They are predominantly used to create large manufacturing jigs, or to modify large, high precision parts. They have a spindle stroke of several (usually between four and six) feet, and many are equipped with a tailstock to perform very long boring operations without losing accuracy as the bore increases in depth. A typical bed would have X and Y travel, and be between three and four feet square with a rotary table or a larger rectangle without said table. The pendant usually has between four and eight feet in vertical movement. Some mills have a large (30" or more) integral facing head. Right angle rotary tables and vertical milling attachments are available to further increase productivity.
Floor mills have a row of rotary tables, and a horizontal pendant spindle mounted on a set of tracks that runs parallel to the table row. These mills have predominantly been converted to CNC, but some can still be found (if one can even find a used machine available) under manual control. The spindle carriage moves to each individual table, performs the machining operations, and moves to the next table while the previous table is being set up for the next operation. Unlike any other kind of mill, floor mills have floor units that are entirely movable. A crane will drop massive rotary tables, X-Y tables, and the like into position for machining, allowing the largest and most complex custom milling operations to take place.

LATHE MACHINES

Basic Operation of a Lathe

A lathe is a machine tool which turns cylindrical material, touches a cutting tool to it, and cuts the material. The lathe is one of the machine tools most well used by machining (Figure 1). As shown in Figure 2, a material is firmly fixed to the chuck of a lathe. The lathe is switched on and the chuck is rotated. And since the table which fixed the byte can be moved in the vertical direction, and the right-and-left direction by operating some handles shown in Fig. 3. It touches a byte's tip into the material by the operation, and make a mechanical part.


CAUTIONS

When we use a lathe, the following things must take great care.(1) Don't keep a chuck handle attached by the chuck. Next, it flies at the moment of turning a lathe. (2) Don't touch the byte table into the rotating chuck. Not only a byte but the table or the lathe are damaged.


Three Important Elements

In orger to get an efficient propcess and beautiful surface at the lathe machining, it is important to adjust a rotating speed, a cutting depth and a sending speed. Please note that the important elements can not decide easily, because these suitable values are quiet different by materials, size and shapes of the part.


Rotating Speed

It expresses with the number of rotations (rpm) of the chuck of a lathe. When the rotating speed is high, processing speed becomes quick, and a processing surface is finely finished. However, since a little operation mistakes may lead to the serious accident, it is better to set low rotating speed at the first stage.

Cutting Depth

The cutting depth of the tool affects to the processing speed and the roughness of surface. When the cutting depth is big, the processing speed becomes quick, but the surface temperature becomes high, and it has rough surface. Moreover, a life of byte also becomes short. If you do not know a suitable cutting depth, it is better to set to small value.

Sending Speed (Feed)

The sending speed of the tool also affects to the processing speed and the roughness of surface. When the sending speed is high, the processing speed becomes quick. When the sending speed is low, the surface is finished beautiful. There are 'manual sending' which turns and operates a handle, and 'automatic sending' which advances a byte automatically. A beginner must use the manual sending. Because serious accidents may be caused, such as touching the rotating chuck around the byte in automatic sending,.