new development in shot blasting machine. - Metalworld.co.in

New Development in ShotBlasting Machinehot Blast Cleaning Equipments are used for surface preparation inFoundry, Forging, Shot Peening, Strip Descaling, Plate, Billet, Wire CoilSCleaning, Stainless Steel Strip Cleaning and have many moreapplications. It has now become more efficient and sophisticated. Shotblasting minimizes operation cost, maintenance cost. Therefore there is needfor better understanding of the basic factors which controls the process andsub assemblies, which makes up a whole Shot Blast MachineTechnology- P. A. Patel, Patel Furnace & Forging Pvt. Ltd..Two Systems of BlastingFig - 1 “Pressure Blast System”:In pressure blastingsystem the blast media is stored in pressurized vessel,which is mixed with compressed air. The air flowaccelerates the media, through a blast gun on to thesurface.10mm Nozzle 5 Bar Pressure.Blast Media Flow : 22 Kgs./Min.Air Consumption 275 M/Hr.Energy Consumption 25 KW.Specified Energy Consumed 1.14 KW/KGThis comparison of different blasting systems, clearlyshows that the blast wheel blasting system (fig - 2) has thelowest specified energy consumption. Blast wheels aredriven by electric motors, whereas the air required by theair blasting system (fig - 2) has to be generated by acompressor which is to be purchased and maintained inaddition to blast machine itself and the additional powercost.The MachineFor efficient shot blasting operation we should understandthe basic concept of the process and the machine (Fig 3)Fig - 3Fig - 1Blast Wheel Blasting SystemFig - 2 In blast wheel system the blast media is fed to thecenter of the blast wheel, which is rotating at high speed.The media is rapidly accelerated by centrifugal force and isdirected on the surface to be blasted.Blast Media Flow 150 Kgs./Min.Air Consumption NegligibalEnergy Consumption 7.5 KW/Kg.Specified Energy Consumption0.05 KW/Kg.Fig - 2The shot blasting machine consists of six basic parts:1. Blast Wheel 2. Cabinet3. Work Handling Mechanism 4. Elevator5. Separator 6. Dust Collector.June 200921

TechnologyLet's take a close look at these six parts and see whatroleeach plays in the shot blasting process.1. Blast Wheel :Abrasive particles are projected by centrifugal force fromvarious kinds of turbine wheels. The number of wheelsinstalled in the machine depends on the type of jobs to beshot blasted and the rate of work. The wheel is the heart ofevery centrifugal shot-blasting machine. Efficiency andcleaning effect depend to a great extent on the quality ofthe wheel and its components.2. Cabinet :As high speed of abrasive particles (50-100 m/s) isinvolved the articles to be shot-blasted have to be treatedin closed, vibration free booth or cabinet made of strongsteel, lined with wear resistant alloy liners. Formaintenance purpose proper inspection door andventilation are essential.3. Abrasive Recovery System and Elevator :The abrasives are recovered at the bottom of the cabinetby means of a screw conveyor and delivered to the base ofthe elevator, which then carries these to the separator.4. Separator :Before abrasives enters into the blast wheel for reuse,these have to be cleaned of all contaminants. This is therole of the air separator.5. Dust Collector :The last essential feature is the filtration, which retrievesdust laden air from the separator and cabinet ventilationsystem and discharges clean air into atmosphere forpollution free environment.6. Work Handling :Various systems exist for conveying the parts dependingon the type, size and quality of the items to be treated.Tumblast Type Machine(Fig. A) :This design employs endless conveyor beltmade of steel link and flats or rubber belt,which does not damage the job duringtumbling.Table Type Machine(Fig. B) :In this type of machine parts beingcleaned must be positioned orrepositioned on the table to assurecomplete cleaning of the full surface.Blade Lock TypeControl Cage Small.Impeller Small.Monorail Hanger Type Machine(Fig. C) :In this type of machine, parts aresuspended on trees hung onhanger or special fixtures and arecarried into the abrasive stream.Roller & Belt Conveyor Machine(Fig. D) :This picture shows plate, sheetor structural shape de-scalingat high speed. Both upper andlower surfaces are shot blastedsimultaneously.Door Hanger Machine(Fig. E) :In this machine jobs arehung on the door. The partsare carried into abrasivestream after closing thedoor. The parts aremounted in front of thewheel. On completion ofshot blasting, door isopened and second doorwith job hung enters thecabinet. In this type ofmachine, one may get 30 to40% more production.Compare Old M Type Wheel (Fig-4)New High Power Wheels :With the need for increased output it has become apparentthat 'Shot Blast Cycle' on the machine must be reduced ineffort to give increased output. We have introduced NewRLM (Radialok) wheel, which throws more abrasive andconsume less power. In this way one machine being able todo the work formerly required by two machines. The newwheel has large control cage and impeller making itpossible to throw more abrasive and better and fastercleaning.Old M Wheel(Fig-4)22June 2009

New RLM WheelBlade Self Locking.Control Cage Big.Impeller Big.New Abrasive Resistant Lining (Fig-8)Again due to the fact that moreabrasive is being thrown, it hasbecome necessary to completelylined machines with abrasiveresistant material.This has been made possible by theuse of special high chrome alloymaterial. These are made invarious sizes to provide completeinterlocking lining for most types ofshot blasting machines.TechnologyWheel Unit (Fig - 6) :With this increased amount of abrasive being thrown it hasbecome necessary to have wheel, which are capable oflasting a great deal, longer thantheir predecessor. This has beenmade possible by introduction ofnew Hard Alloy Wheels.In addition it has been necessary toincrease the life of Blades, Impeller,Control Cage, Liners and otherparts by using High Chrome Alloymaterial. This has been possibledue establishment of our newFoundry with Induction Furnace,Shell Moulding Machine and HeatTreatment Facility. Very few equipment manufacturersunderstand importance of wheel and its parts.Wheel Unit Liners (Fig - 7)The blast wheel is usually enclosed within a housingserving as a safety guard and abrasive seal around rapidlyrotating wheel to minimize wear on the housing, a series ofspecial alloy cast liners are installed inside the housing.Older wheel Fig-7 consisted of 21 liners where abrasivebounces in uncontrolled manner. In our new RLM Fig-8)wheel only nine liners are installed inside the housing.High chrome liners are approx. 25mm thick with labyrinthtype joints providing and abrasive tight seal between theliners and very Long life.Alloy Perforated Plates :One of the biggest problem in the foundry industry has beenthat wire, chaplets and other material used for givingsupport to the mould gets in the elevator and separator, asthe perforated plates are not proper. We manufacture andsupply in High Chrome Alloy Steel with the result there isno wear or holes for wire to pass.Moulding TechniqueMost popular moulding technique used in India is greensand moulding and About 80% of foundries use thistechnique. The drawback of this technology is that largeamount of sand, sticks on surface of the castings, which areto be cleaned by shot blasting.Foundry, using cupola has more sand compared toautomated foundries. Other technology like CO2 process,has 5 % to 10 % sand sticking to casting because of badshaking operation, poor property of mould and coretherefore shot blasting is quite essential.There are number of items produced by Indian foundries.Some of them are impeller castings. pump castings, valvebodies & automobile or tractor components like breakdrum, cylinder head, housings, fly wheel, manifold covers,weighing from 5 kgs to 60 Kgs. or more. To clean thesecastings it takes 7 to 10 minutes using S-550 (1.4mm) shot.Some other types of castings when hanged on monorailtake 15-20 minutes for a lot of 500 Kgs. or more.Most of the foreign foundries use No bake Process, WaxProcess and Foam Process. There is very little sand oncastings so most of the foreign shot blasting machinemanufacturers do not understand requirement of Indianfoundries . The costs of foreign machines are 3 to 4 timesmore than Indian machines. Many imported machines havecartridge filters instead of bag filter. The disadvantage ofcartridge filter is that in humid atmosphere sand sticks tothe paper. It can not handle heavy sand load with the resultit chockes frequently. The imported machines do not giveany production advantage and spare parts cost is very highJune 200923

TechnologyProperly designed shot blasting machine will not only cleanthe castings efficiently, but it will also satisfy the usersquality needs and also assure optimum productivity and thelowest possible operating cost.Abrasive Flow Control Valve (Fig-11)(soundabrator):The abrasive flow to each wheel isregulated to match the mechanicalcapacity of the abrasive reclaimingsystem and must stay within theAmperage capacity of Electric Motor.Enclosed air operated Soundabratorreduces noise level, which is below 85(Fig-11) dB and prevents leaking of shots and itis easy to maintain.Shot Peening : (Fig-12)Shot peening is one of the application for increasing thefatigue life of various components like Coil Springs, LeafSprings, Gears, Rack & Pinion, Torsion Bar, ConnectingRod, Crank Shaft widely used in auto industries. We SeeMany trucks broken down on the Road due to Fatiguefailure of axle Shaft or Spring, Sometime it results inSerious accidents. This Fatigue can be reduced byadoption of Shot Peening Process.Shot & Abrasive : (Fig-13).070”.0110”Effect of Shot Size on Impact & CoverageSHOT SIZEInches in (mm)0.18mm0.30mm.0170” 0.40mm.0230” 0.60mm.0280” 0.70mm.0330” 0.80mm.0390” 1.00mm.0460” 1.20mm.0550” 1.40mm.0660” 1.70mmApprox. ImpactValue14920335590150260440Approx. Nos. ofShots / ID82,00,00021,00,0007,45,0003,24,0001,92,0001,14,00068,00040,00024,00014,000Equiv. Size ofin GritG-80G-50G-40G-25G-18G-16G-14G-12Shot Impact Value varies as the cube of the diameter (2:1 Size = 8.1Impact Value and 1:8 number of Shots / Ib). Considering Impact valueof 70 size shot as 1.Fig. 13(Fig-12)The impact Power and coverage of steel abrasive isgoverned by its mass and velocity in accordance withequation of kinetic energy.Ke = ½ MV2 (Where Ke = Kinetic Energy M=MassV=Velocity).The impact force delivered to the work piece will changeonly if the mass factor (i.e. the abrasive size) is altered.The relationship of abrasive size to both impact power andcoverage is shown in figureThe economy and performance of blast cleaning dependsupon the abrasives used. The proper size and type ofabrasives is most important. The following three factorsshould be considered while selecting the abrasivesa. Area of job surface these can cleanb. Quality of work producedc. Cost of the shotsChilled Iron ShotsThe shots are manufactured by quenching the stream ofmolten gray iron over high pressure water jet. Its hardnessis about 60 Rockwell C.Due to this hardness and quenchedstructure it fractures and disintegrates very quickly onimpact with the work surface. Due to greater amount ofdust produced in fracturing process, the part cleaned bychilled iron shot does not have very good finish. Also themaintenance cost is very high. This led to the introductionof malleable iron-, cast steel-, cut wire-shots and heattreated steel shots.Heat-Treated Steel ShotsThe heat treated steel shots are having hardness of 45Rockwell C (424 Brinell hardness). These are the mostsuitable for the shot blasting machine.Stainless Steel Shot & Cut Wire Shots (Fig. 13)Die casted components manufactured from Aluminium,Zink & Magnesium Alloys required to be blasted forremoving burr and also give asthetic value with aim toobtain even, shiny finish on all sides. Many users preferstainless steel shot as the consumption is one sixth of steelshot, carbon steel shot give dull grey finish, while stainlesssteel imparts matt silver finish pleasing to eye. Many autounits like Honda, Bajaj, Endurance are uses stainless steelshots.Concluding RemarksShot blasting is no more an optional process in a foundry. Itprovides faster and better cleaning. It saves power, labour,space and also saves on cutting tools and permits betterinspection, thus minimizing the rejection of castings. Apartfrom foundry it is also widely used in many otherindustries.Proper understanding about the machine, itsconstruction and use enables us to improve its efficiencyand utility. Before Selecting the equipment it is necessary,to consider above points, spare parts, availability, salesservices offered, and many other points.24June 2009