Heat Treatment: Annealing

Annealing is made to increase machining abilities and to soften the metal. Generally the purpose of annealing is as follows.

To refine the grain size.

To increase mechanical properties such as strength and ductility.

During casting, to remove those holes that are trapped in metal.

To make changes to the magnetic and electrical properties.

Annealing are processed in two types

Full Annealing

To soften the metal, Full annealing to refine the grain structure and relieve the strain.

In this process hypoeutectoid steel heated over 32 to 50 degree above than the upper critical temperature and for hypereutectoid steel heated over the 32 to 50 degree above than the lower critical temperature.

Hold this temperature until internal structure is not change, this maturation period is 1 mm per thickness square area 3 to 4 minutes.

And in the furnace it slowly cools down.

Process Annealing

Process annealing is used to remove internal stress due to previous setup.

In this process, the steel is heated to a lower temperature than the lower critical temperature.  Keeping it cool for a while at a temperature, it is cooled gradually.

This process increases in machinability.

It happens a recrystallization in steel.

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Normalizing of Steel

The finished product of casting is processed to get good properties by heat treatment. Certain properties or desirable condition is obtained by heating or cooling of the metal by without any changing of chemical composition in solid state. 

The metal consists of micro structure of grain particals. It is a mechanical and metallurgical process in which, By the changing of grain size or micro structure we can obtain some challenging properties of metal.

Following properties to be obtained by the heat treatment process.

• To Soften metal.
• To increase the hardness and strength of metal.
• To change the magnetic properties.
• To Increase the resistance of wear.
• To change grain size.
• To change the electric properties.
• To Improve machinability and quality of casting.

Considering its different properties in way of engineering, its 1st topic is normalizing 

Normalizing

Normalizing process is used to soften the metal. By the normalizing we can achieve highest machinability and improve tensile strength. By this improvement in electric and magnetic properties of metal.

The cold working process like hammering, knockout, bending causes strain on metal, its remove by normalizing.

It used to refine grain structure and uniformity of grain size and composition. It makes the material brittle and unreliable. This process less expensive than annealing.

For Hypo eutectoid steels the heating temperature is 45 to 50 degree above to its upper critical temperature and for Hyper eutectoid steels, the temp. is 45 to 50  above to its lower critical temp. The metal is kept for a while at this temperature and then cooled down by air.

The upper and lower critical temp of steed depends upon the total percentage of carbon consists in steel.

For best quality and machinability it performed after forging and casting.

In Hypo-eutectoid steel less than 0.8% of C in its composition. It is composed by pearlite and α-ferrite and Hyper-eutectoid steel has between 0.8% and 2% of C, composed by pearlite and cementite. It is very important to understand Iron-Carbon phase diagram to understand the Hypo-eutectoid and Hyper-eutectoid.

This process provides a uniform structure consisting of ferrite and pearlite for hypoeutectoid

steels, and for hypereutectoid steels pearlite and cementite.

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Investment Casting Defects

In the every manufacturing process defects is mandatory. Defect is condition of the casting when its finalized. And that must be removed by several process otherwise it will categorized to the rejection. There are many types of casting defect which resulted from many cause. It can be removed by proper die design. proper pouring method proper gate and riser design and proper coating cycle. Defect is lost casting quality.

Dependencies of casting defects and discontinuity

1) Mould Design.

2) Pattern Gate Design.

3) Pattern Assembly Design.

4) Coating Cycle and Precoat  Viscosity.

5) Melting speed and its temperature.

6) Yield Method

There are many types of casting defect as we discussed below.

1) Hole of Gas

It exists on the casting surface in inside area also. Its shape is irregular like oval, round like this. If it is appear on the casting surface than it can be solves by welding process, but when  gas hole is in side the material than it is inspected by the various test. However it appear only  after  machining. It cause s due to low temperature of metal and pouring speed is very slow. 

Gas hole also happen when ceramic mould is not preheated perfectly. It can be solved by increasing temperature of pouring metal, proper preheating of Ceramic Mould. and remove slog from surface.

Gas Hole

. 

2) Shrinkage

This is a most common defect in many manufacturing are. In this field there are two types of shrinkage is a) wax shrinakge 2) Metal shrinake. Wax shrinkage gets solved from the mould. But metal shrinkage is very crucial problem. When the gating system is not proper than its happen. The gate of pattern should be proper draft angle.  Below fig shows a draft of gate.

Draft Angle

Shrinkae defect occure when metal feed is very slow. In this there are two types of shrinakeg open shrinkage in which when freezed cast contract its size in atmoshphere and close shrinkage is porosity in metal. Especially shrinake is occure where the casting is enter from gate.

Shrinkage

3) Mismatch

This defect cause due to improper assembly of wax mould and parting line gets mismatch.

Mismatch

4) Sandwash

Sandwash defect cause to sharp corner of wax pattern. In coating cycle precoat is first layer. Due to very small size of sand particles sand is trapped on wax edge and its exists on casting edge. To resolve this remove sharp edge of pattern make a radius on it.

Sandwash

5) Penetration

When the sand size grains is larges, the molten fuses into the sand  These casting defects appear as an uneven and rough surface of the casting. and solidifies giving us metal penetration defect. It is caused due to  large grain size, low strength and high permeability. Because of this the molten metal penetrates in the molding sand and we get rough or uneven casting surface.

Penetration

6) Bulge

Bulge is cause due to shell is very thin, deform in dewaxing, Molten metal pressure is very high. In this defect some of surface area is blooming. Tor resolve this decrees the pressure of metal and height poring height. 

Bulge

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Metal Preparation

As we have seen earlier, the casting is done using investment casting as it is used in different places.Different metals are used in different places depending on usage. There is a ferrous or non ferrous metal. 

So today I will show you some formulas related to how to prepare some standard metal in investment casting. Although this topic is a metallurgical, but I also know a little about this subject.

In investment casting, the ferrous and non-ferrous metals and their alloy metal are made of their row material. If foundry works with a standard company, it is a working pad as per the standard of the metal standard. 

Different countries have their own standards. But the analogy is found in the chemical composition of the metal's grade. The most common is the ASTM standard. Because the ASTM standard has covered all grades of steel. 

ASTM standard is also provided in the pet type, such as 

1)Analytical Chemistry Standards: cover the chemical analysis of various metals, alloys, and ores and it describe and specify certain instruments and equipment that must be used for chemical analysis. 

2)Fastener Standards: it use for some general physical properties like mechanical, and metallurgical properties 

3)  Fatigue and Fracture Standards: provide procedures for carrying out fracture, fatigue,  and other  tests. 

4)Nonferrous Metal and Alloy Standards provide other evaluation procedures to assess and identify compositions,  dimensions,  nomenclature, properties, analysis, classification 

5)Metallic Coating Standards: it help to identify characteristics of material such as compressibility , tensile, density, stength, etc.

So now come to the topic that how to prepare the metal. The erosion of metal in investment castings is melted at 1500 to 1800 degrees in furnace. At the same time, dewaxing ceramic cells are preheated. 

The preheating temperature of the cell is approximately 900 to 1100 degrees. Generally speaking, for preheating, Generally speaking, for preheating, when the molten metal is at high temperatures, it does not come from the speed to low temperatures, so that does not hit the speed. And if this is not done then normal ceramic cell can not bear the temperature of molten metal and it breaks. When the metals are melting and ready, samples of their chemical elements are analyzed. 

The machine used for this is called a spectrometer. there are mainly 8 elements are analyzed such as Carbon, Silicon, Manganese, Phosphorus, Sulfur, Nickle, Chromium, Molybdenum. The test shows that the Q element is in the ratio. 

The metal is made proportionally by adding elements of the elements according to the given excel sheet.

1) In this sheet you have to first decide the size of ferns in kg 

set value in cell E2

2) Determine what metal should be cast

set value in cell F2 from D35 to D41

it automatically detect chemical composition of given material according to ASTM standard  in RED portion 

If you write WCB in F2, something will come in such a way

3)Now, input your spectro analysis result in raw in raw 9

it gives total kilogram of composition of your total kg in raw 10

4)Add some composition in raw 13

Now when you add a composition into metal preparation, there will be a lot of impact on the remaining composition.

5)you can see a result of metal in raw 16 to 25 in form of percentage in kg also.

To download Please click here...

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Wax Preparation

As we previously discussed, wax play an important role in investment casting.So today I will tell you the type of wax and how it happens. The company that uses the green wax is generally get readymate  from the market.Generally making a green wax is expensive for the company. So the company uses Brown wax in the company. Different types of materials are used to make a Brown Wax.

The company uses three different methods to make a Brown wax. Brown wax is made by mixing of Paraffin, Montan, Rosin, LDP plastic, Microsoft, Microhard and Sticky wax.

1)In the first method Paraffin, Rosin, Montan and LDP Plastics are heated at 200 degrees temperature by mixing of 42.5%, 20%, 35% and 2.5% respectively. As before, paraffin is melted, then another material is added.

2)The second method is a mixture of Paraffin, Montan, Rosin, Microsoft and Microhard 40%, 20%, 30%, 5% and 5% respectively. Also in this method first paraffin is melted, then another material is added.

3) Paraffin, Montan, Rossin, Sticky wax and LDP Plastics are mixed on 40%, 35%, 20%, 2.5% and 2.5% respectively in the third method. And it is also heated at 200 degree temperature.The photos in the material used in this wax are as follows.

1. Rosin

Rosin

2. Montan

Montan

3. LDP Plastic

LDP Plastic

4. Paraffin

Paraffin

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Investment Casting Cycle

Hello friends,

This is my first blog post. Today I am giving you information about the investment casting cycle. Many of the products produced from this process are used in many industrial place like in Aeronautical and Aircraft Components, medical implants, Automotive-Diesel-Engine-&-Generator-Parts, defense, Engineering, Marine Hardware, pumps and valves, automobile sector, turbine blades, in fabricated items etc. Investment casting is lost wax cycle or wax preparation cycle. In short, the wax is melted and casting is done. Toady i will cover all points, There are mainly 5 division in investment casting foundry.

1) Die Shop Department

2) Press Dept. (Cleaning, Repairing and Assembly included)

3) Coating Dept.

4) Dewaxing Dept.

5) Melting Dept.

6) Hammering and Knockout Dept.

7) Fetteling and Finishing Dept.

8) Dispatch Dept.

1) Die Shop Dept.

This is first division if this cycle. generally this division is covered in CAD/CAM branches.

Some foundries are make die inhouse, first of all,  all dimensions are check according to the final product and very crucial is shrinkage allowence, generally for the ferrous and non ferrous casting has 2.5% shrinkage calculated , it means 0.7 to 0.8 % is wax shrinkage and 1.5 to 1.8% is casting shrinkage.

For example, If your product dimension is 100mm

Than die dimension is 102.5mm. we will discuss in brief that how to make dies and mould in future.

2) Wax or Press Dept.

In this dept wax is injected in die by press machine. This division is fully covered by the air conditioning system because of to maintain wax dimensions.At the normal temp wax pattern loose its shape and destroy its dimensions. When the Wax pattern emits from the die, it shows the some parting line effect of the Die. 

It is removed from a special knife. And it is being repaired from the repairing wax. The wax pattern is combined with a solid wax bar in the assembly room. you can understand by this image.

Wax Tree Assembly

3) Coating Dept.

In this department, from the small sand to the wax tree, the level of large sand is adorned. And it's called a shell(Mold). This mold is kept in temperature of 17 to 18 degrees. This process is about 2.5 to 3 days.

Coating

4) Dewaxing Dept.

The wax is removed from the mold in this department. Hanging the mold in a tank, it is heated from 190 to 200 degrees and the wax flips out of the liquid form. 

The liquid form of the vacuum was then re-sent to the wax department and reused.That's why this process is also called Lost wax method Casting.

5) Melting Dept.

The ferros or non ferrous metal is heated  from 1700 to 1800 degree temp. at this temp the metal is comes from solid form to liquid form. 

When the liquid is sown in metal and powdered in the mold, it is usually kept for a while until it becomes again in solid form.

Melting(Pouring)

6) Hammering and Knockout Dept.

After melting this mold is broken by the hammering and knockout process. So the sand is removed and the casting tree is ready.

7) Fetteling and Finishing Dept.

The main casting product is separate from the casting tree and it will be finish by different type of finishing operation

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