Foundry Mechanization and Use of Computers in Foundries
To improve the productivity in a foundry, a variety of equipments are used in different stages of manufacture. As, major part of capital investment goes into plant and machinery, it is essential to study the type, capacity and suitabilityof eachequipment for a particular application, before purchasing. 1. Objectives of Foundry Mechanization
1. Increased production from a given floor area and high productivity 2. Accurate castings, better surface finish and closer tolerances 3. Labor saving due to mechanized equipment
4. Better working environment 5. Reduced cost due to less labor 1. Limitations of Foundry Mechanization
1. Can’t be employed in jobbing foundry because no repetitive castings are required there 2. Can cause unemployment
3. Can reduce the skillful workers of hand molding
Mechanical Equipment in a Foundry
For a new base sand
Vibrating multi-deck screen to grade and separate sand grained to specific sizes are used. Sand dryers with fuel burners, hot air supply are required for drying wet sand. Inclined cylindrical rotary sieves are used for removing fine grains.
Motorized drive through rugged reduction gear box with blades to mix sand and other ingredients like binders, and additives, arrangement to automatically add the required amount of water and controlled mixing time cycles, mechanical loading and discharge system are some important features.
Sand Muller’s have motorized rollers I the cylindrical vessel to properly knead the molding sand ingredients for developing better strength, especially for return of baking sand.
Core sand mixers incorporate smaller size of batch with more efficient mixing system, sometimes with helical screw type blades and faster time for batch to prevent presenting of chemicals.
Vibrating out table
Vibrating shake out table consists of a large sturdy welded steel grid with openings on which poured molds are placed. The table with grid vibrates through and eccentric rotary device separating the sand, casting and mold box. The sand lumps falls through the grid with bottom chute on to a conveyor belt. The casting and mold boxes are picked up by an over head crane system and segregated for further operations, this is
essential mechanical equipment, especially for
machine molding of small and medium size
Vibrating shakeout table
Magnetic separators are used to remove metal pieces like nails, gaggers, fine after pouring, flashes of which may get mixed with backing sand after shake out of pouring molds. They have a rotating magnetic drum which picks up the metal pieces in the flowing sand and segregates them.
A wheel with revolving hammer, placed in the path of return sand stream discharge from the shake-out is used to break lumps of sand mechanically.
A device placed after lamp braking to separate and loosen the sand grains, by forcing a mild blast of air into the freely falling used sand stream. This is the final stage of used sand processing before it is sent to storage hoppers.
Sand Handling and Conveying
These are used to carry return sand from the underground shake out to overhead hoper through a system of pulley drivers in segment, specially designed roller support to prevent spillage from belt are needed. Due to hot sands handled, maintenance is critical.
Plate Band Conveyer
It is used for both horizontal and inclined travels and for short as well as long distances. The plates are joined together and mounted on a continuous chain moving on power-driven sprockets.
Ready mixed sand is placed in covered bins to prevent drying and conveyed by roller conveyor from sand mixers to molding points where hand molding is adopted.roller
conveyors are used extensively for easy handling of bins, mold boxes, molds, heavy patterns as well as poured molds. The disadvantage is that roller conveyors occupy much floor space and also are costly to maintain.
This device is exclusively used to transport underground or ground level sand to be conveyed to over head hoppers at high elevations. This is a fast and efficient system. A number of metal buckets are attached to a vertical belt loop driving from support roller at top through motor and gear box.
Bins with cover and trolley system for manual handling used for transporting ready molding and core sand mixer to molding points. They can be pushed manually or by removing wheel and handle, can be placed on roller conveyors as per the requirements.
13. Molding machines
Normally in foundries pneumatic (compressed air operated) machines are used to compact the molding sand on the pattern placed inside mold box.
In this, the table containing the pattern plate and mold box clamped with it get, jolted by means of a piston device in the machine base cylinder. The molding sand placed gets
compacted by the weight, the maximum hardness being achieved nearest to the pattern plate. Molding sand at the top does not get fully compacted.
The molding machine table containing
the pattern plate, mold box and
molding sand is lifted up and squeezed
against a metal squeeze head positioned
above it. Molding sand gets
compacted maximum at the top
nearest to the squeeze head, being
progressively softer towards the pattern.
This is a combination of the above
two operations simultaneously, which helps
to achieve uniformly high hardness
across the entire section of mold.
The other features in the molding
machines include pin lift system to accurately and vertically lift the rammed mold box half away from the pattern. In some cases mechanism is provided to draw or
mechanically separated pattern plate from the rammed mold to prevent damaging the mold.
Pneumatic jolt-squeezing molding machine
Hand molding in larger molding boxes is done using pneumatic portable rammers. Sand placed in the mold box ix compacted by the bottom ramming head of the long tubular rammer, which vibrates at high speed giving strokes to the sand below. Different shaped ramming heads as well as length of holding pipe are available for large molds or smaller cores. The pneumatic rammer is held vertically in hand by molder and moved over the surface to be compacted.
To compact very large molds and in deep pit molds, sand slingers are used for fast operation. They have a large travelling mixed sand hopper, a conveyor belt to supply sand to a swiveling head, with high force into the mold below, as directed by the overhead swiveling head, simultaneously filling and compacting the mold. Very large molds, which would take many shifts by manual ramming, can be compacted in a few hours by a sand slinger. These are costly machines needing fast supply of mixed sand in large quantities.
19. Knockout of Molds
Removal of the casting from the mold after solidification process is called as knockout. Mechanization in the area of knockout gives good quality castings. It is economical in cost and time. The sand mold is to be broken to extract the casting. But the breaking of the sand mold is to be done only when the casting is sufficiently cooled, since the metal at high temperature has very little strength. Ideally the molds should be broken at a temperature when no transformation occurs. The dry sand cores can be removed simply by knocking off with an iron bar, by means of a core vibrator, or by means of hydro-blasting. The method depends on the size, complexity and the core material used.
The incline knockout cum Feeder, Knockout and Vibratory Feeder are available in several sizes, starting from 500 kg to 10000 kg capacity as standard. Special types also can be designed and supplied to suit foundry needs; multi grid high capacity Knockout stations for extra-large molds are also available in modern mechanized foundries. In mechanized foundry, knocking out multiple-component molds can be done by mounting a pneumatic breaker.
This type of non-contact knockout machine has the following advantages: 1. The operator does not come into contact with any vibratory parts. 2. The knockout time of a mold is reduced from 20 minutes to 5 minutes 3. Reduced risk of back problems as less lifting is required.
4. To reduce noise from the machine, the machine can be partially or fully enclosed.
After casting is extracted it may not be ready for immediate use. Hence, cleaning and finishing of the casting is required. This operation of removing the unwanted parts, cleaning and finishing the casting is known as ‘fettling’. It is a process of complete removal of cores, gates, risers, cleaning of casting surface and chipping off any of the unnecessary projections on the surfaces.
The gates and risers can be removed by hammering, chipping, hacksawing, abrasive cutoff or by flame or arc cutting. Removal of gates and risers can be simplified by reducing the metal section at the casting joint. For brittle materials like grey cast iron, gates can be simply removed by hammering. For ductile materials like steel, sawing with hacksaw or band saw is preferred. But for gates of large size it may be necessary to use flame or arc cutting to remove them. Similarly abrasive cut off may also be used for removal of gates with the help of portable grinding machine.
The fins and other small projections may be chipped off using hand tools or pneumatic tools. For smoothening the rough edges of the gates either a pedestal or swing frame grinder is used depending upon the size of the casting. For surface cleaning or surface smoothening the sand particles sticking on the casting surface have to be removed. This is generally done by sand blasting. In sand blasting processthe casting is kept in a closed box and a jet of compressed air with a blast of sand grains or steel grit is directed towards it, which thoroughly cleans the casting. The typical speed of these shots is of the order 80 m/s the shots used are chilled cast iron or steel grit. Chilled cast iron is less costly but is lost quickly by fragmentation. In this process the operator safety has to be ensured.
Another method of cleaning casting surface is tumbling. In this method the casting is kept in a barrel which is completely closed and is rotated slowly about a horizontal axis with a speed of about 30-40 rpm. The barrel is packed with enough room for the casting to move so that they will be able to remove sand and unwanted fins and projections. However, precaution must be taken that the casting should be rigid enough and should not have overhanging features which may get knocked off during tumbling process.
Steps involved in fettling process are: 1. Knocking out of dry sand
2. Removal of gates and risers
3. Removal of fins and unwanted projections 4. Cleaning of smoothening the surface 5. Repairing casting to fill up blow holes.
The castings to be cleaned are put into a barrel which is completely closed and also containing small pieces of white iron called ‘stars’ which rub against the barrel when it is rotated, thereby cleaning the casting.
2. Tumbling with Hydro-Blast
In this method the barrel is arranged at an angle of about 30 instead of horizontal arrangement. The castings are tumbled by high velocity steam water and sand at a velocity of 100 m/s.
3. Cleaning with Compressed Air (Sand Blasting)
A high velocity stream of compressed air along with abrasive particles is directed by means of a blast gun against the casting surface to perform cleaning process.
4. Cleaning with Mechanical Impact (Impact Blasting)
Instead of using air pressure for hurling the abrasive particles towards the casting, centrifugal force may be exerted by means of an impeller wheel in which shot moving from the impeller get accelerated and hit the casting with high velocity, thus cleaning and polishing it.
5. Arc Air Process
In this method the casting surface is heated by arc heating and blowing off the melted metal with compressed air. The projections or surface imperfections are heated by arc, so that they reach the molten state and arc simultaneously blown away by air.
Pickling is the process of cleaning the cast surface by dilute acid treatment. It is effective in removing sand, scales or tentacles of metal producing clean and bright surfaces on iron and steel castings.
Location of plant site
1. Some of the considerations for the location of a foundry site
2. Availability and proximity of high tension power supply substation, especially when electricity is need for melting.
3. Available of large area of industrial land due to need for storing large quantities of material like melting scrap, molding sand open storage for ready castings etc, in addition to the normal requirements of production, services and offices.
4. Distance from normally populated urban areas due to pollution, dust, fumes, heat and smoke generated from the foundry.
5. Availability of area for dumping waste materials like burnt sand, slag, and used refractories etc. 6. Availability of water, roads and other basic infrastructure facilities.
7. Layout of plant
Operations in metal casting relatively large handling and movement of materials compared to other production processes of same turn over value. Approximately 4 tons of molding sand and additives, 2 tons of charge materials, refractories and may other bulk items like mold boxes, patterns etc are needed for every tone of casting produced. Many auxiliary services like pattern shop, maintenance, sand and refractory preparation, scarp segregation, proof machining etc are needed along with the basic operation of molding, melting and finishing, which complicate material handling and flow. 1. Application of Computer in Foundry
Information technology has changed the way products are designed, produced and delivered today. A stream of new software products and services are enablingcontinuous improvement in product quality and cost, while compressing the lead timefor development. Today, a number of computer applications are available for the foundry industry.Computers have been playing a wide role in the foundry industry in the following areas:
2. Casting design and development for good quality products.
3. Pattern designs, calculation of allowances, and pattern preparation 4. Sand control for obtaining good characteristics of sand and mold. 5. Production planning and control, process control and optimization. 6. Material procurement and selection, lead times, inventory control. 7. Quality control, inspection and testing.
8. Cost control at every stage of production
9. Maintaining database at every stage of casting process.
Some of the most important computer applications, used in foundry industry are as follows:
• CAD/CAM: Solid modeling, tooling (pattern/mould) design and tool pathgeneration for manufacture on CNC machines.
• Casting Simulation: Feeder and gating system design and simulation of mouldfilling and casting solidification.
• Manufacturing Planning: Materials requirement planning, scheduling, costestimation, and quality control and management.
• Internet and Collaboration: E-mail (for communication with employees,customers and suppliers), company website, design data exchange over LAN andInternet, design for manufacture and concurrent engineering.
Moulding Techniques (Assignment) Name: ALI SHER Roll No. : E12-333 Semester: 3rd(Evening) Submitted To:
Sir Faraz Hussain
Department of Metallurgy & Materials Engineering, CEET, University of the Punjab.