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• Chemical Analysis for carbon steel
• Brinell Hardness Test
• Rockwell Hardness
• investment casting process

Standard Chemical Analysis
Specifications 

For Carbon
Steels

The Brinell hardness test method consists of indenting the test material with a 10 mm diameter hardened steel or carbide ball subjected to a load of 3000 kg. For softer materials the load can be reduced to 1500 kg or 500 kg to avoid excessive indentation. The full load is normally applied for 10 to 15 seconds in the case of iron and steel and for at least 30 seconds in the case of other metals. The diameter of the indentation left in the test material is measured with a low powered microscope. The Brinell harness number is calculated by dividing the load applied by the surface area of the indentation.

The diameter of the impression is the average of two readings at right angles and the use of a Brinell hardness number table can simplify the determination of the Brinell hardness. A well structured Brinell hardness number reveals the test conditions, and looks like this, “75 HB 10/500/30″ which means that a Brinell Hardness of 75 was obtained using a 10mm diameter hardened steel with a 500 kilogram load applied for a period of 30 seconds. On tests of extremely hard metals a tungsten carbide ball is substituted for the steel ball. Compared to the other hardness test methods, the Brinell ball makes the deepest and widest indentation, so the test averages the hardness over a wider amount of material, which will more accurately account for multiple grain structures and any irregularities in the uniformity of the material. This method is the best for achieving the bulk or macro-hardness of a material, particularly those materials with heterogeneous structures.

Rockwell Hardness

The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load F0 (Fig. 1A) usually 10 kgf. When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration (Fig. 1B). When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration (Fig. 1C). The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell hardness number.

HR = E – e

F0 = preliminary minor load in kgf

F1 = additional major load in kgf

F = total load in kgf

e = permanent increase in depth of penetration due to major load F1 measured in units of 0.002 mm

E = a constant depending on form of indenter: 100 units for diamond indenter, 130 units for steel ball indenter

HR = Rockwell hardness number

D = diameter of steel ball

Fig. 1.Rockwell Principle

Rockwell Hardness Scales

Typical Application of Rockwell Hardness Scales

HRA . . . . Cemented carbides, thin steel and shallow case hardened steel

HRB . . . . Copper alloys, soft steels, aluminium alloys, malleable irons, etc.

HRC . . . . Steel, hard cast irons, case hardened steel and other materials harder than 100 HRB

HRD . . . . Thin steel and medium case hardened steel and pearlitic malleable iron

HRE . . . . Cast iron, aluminium and magnesium alloys, bearing metals

HRF . . . . Annealed copper alloys, thin soft sheet metals

HRG . . . . Phosphor bronze, beryllium copper, malleable irons HRH . . . . Aluminium, zinc, lead

HRK . . . . }

HRL . . . . }

HRM . . . .} . . . . Soft bearing metals, plastics and other very soft materials

HRP . . . . }

HRR . . . . }

HRS . . . . }

HRV . . . . }

Advantages of the Rockwell hardness method include the direct Rockwell hardness number readout and rapid testing time. Disadvantages include many arbitrary non-related scales and possible effects from the specimen support anvil (try putting a cigarette paper under a test block and take note of the effect on the hardness reading! Vickers and Brinell methods don’t suffer from this effect).

WAX INJECTION
Replicas of the desired investment casting are produced by injection molding or for smaller volumes using rapid prototyping (SLA or SLS). These replicas are referred to as patterns.
 

ASSEMBLY OF WAX TREE 

Wax Trees

Patterns are then attached to a central wax stick, called a sprue, to form a casting. This is called a wax tree. 
 

CERAMIC SHELL BUILDING 
The shell is built by immersing the wax tree assembly in liquid ceramic slurry and then into a bed of fluidized fine sands. Up to eight layers may be applied in this manner depending on the shape and weight of the part. 

DEWAX
Once the ceramic is dry, the wax is then melted out, creating a negative impression of the assembly within the ceramic and sand shell. This process uses autoclaves to maintain shell integrity.
 

CASTING 

Transfer Ladel

In the conventional lost wax casting process, the preheated shell is filled with molten metal by gravity pouring the metal into the ceramic shell. As the metal cools, the parts, gates, sprue and pouring cup become one solid casting. Shell temperature and melt temperature will vary depending on the alloy. 
 

KNOCKOUT 
Once the metal is cooled and solid, the ceramic shell is broken off by vibration or water blasting. 

CUT OFF OF PARTS
The parts are then cut away from the central sprue using a high speed saw.
 

FINISHED METAL INVESTMENT CASTINGS
After minor finishing operations, or possible required machining operations, the metal investment castings–identical to the original wax patterns–are ready for shipment to the customer from our metal