Production process

SPECIAL STEEL GRADE

The steel '93.SQ.13' has been developed, tested and already used worldwide during the last 15 years for the manufacturing of caster SHELLS. It is an alloy with high chromium, molybdenum and vanadium content suitable for hot working applications. Its chemical composition is accurately balanced in order to obtain the following technical properties:
- Good heat conductivity (31 W/m x °K at +20°C);
- Low heat expansion
(from +20°C to 200°C = 12,4 x 10-6 m / (m x °K)
(from +20°C to 400°C = 13,4 x 10-6 m / (m x °K)
(from +20°C to 600°C = 14,1 x 10-6 m / (m x °K)

- High resistance to thermo-mechanical fatigue
- Reduced propagation of micro-cracks


PRODUCTION OF INGOTS

The ingots used for the manufacturing of the SHELLS are produced from selected, high-quality scrap. They are melted in a 25 ton basic electric arc furnace, then refined in a ladle furnace with vacuum degassing and source bottom pouring. The ingots are of different sizes, shapes and weights, carefully chosen for each type of SHELL.


FORGING

The forging is carried out using a 6000 ton hydraulic press with the following cycle:
- Upsetting
- Hole punching
- Enlarging and stretching on the mandrel to the final rough dimensions

All the forging operations are carried out under accurate temperature control so that a fine and homogeneous microstructure is obtained, which permits the increase of the steel toughness.


ANNEALING HEAT TREATMENT

After forging, the SHELL undergoes Full Annealing heat treatment in order to get good machinability and the ideal metallographic microstructure for the subsequent quality heat treatment.


FIRST MACHINING

The annealed SHELL is cut at its ends with a saw and is then machined on all its surfaces with a suitable tolerance.


QUALITY HEAT TREATMENT

- Hardening of the SHELL in vertical position, with quenching in polymeric solution bath
- First tempering, cooling in still air
- Hardness control
- Second tempering, cooling in still air
- Final hardness control

The hardening of the SHELL in vertical position permits to obtain uniform cooling that guarantees a homogeneous microstructure and reduces the risk of deformation. The aim of the double tempering is to obtain uniform hardness on the entire volume of the SHELL and the highest toughness in the steel.


QUALITY CONTROL

As a final step, the SHELL undergoes the following Quality Control tests:
- Surface hardness HB (10/3000 kg) on three generating lines at 120°C along the whole length of the SHELL
- Ultrasonic test according to ASTM A 388 on the whole volume of the forged piece using plane and angle beam in order to guarantee the absence of internal defects
- Mechanical tests of tensile and impact are carried out using a test-piece cut from the forged SHELL after the quality heat treatment. Required values:
Rm = 1280 ÷ 1380 N/mm2
Rs0,2% = 1050 N/mm2 min.
Kv = 25 J min. at +20°C

- Micrographic examination carried out on the test-piece used for the mechanical tests. (Required: grain size according to ASTM E 112 N° 6 or finer and fine tempered Martensite microstructure)

Marking
Quality Control Certification
Packing
Shipment


FINAL MACHINING
(FOR SHELLS TO BE DELIVERED AFTER HEAT TREATMENT AND ROUGH MACHINING OF THE INTERNAL AND EXTERNAL SURFACES)

THE ROUGH MACHINING OF THE INTERNAL AND EXTERNAL SURFACES OF THE SHELLS IS CARRIED OUT AT THE BRUNO PRESEZZI FACTORY UNDER CONTINUOUS AND RIGOROUS QUALITY CONTROL, BOTH OF THE TOLERANCES AND THE ROUGHNESS.

CASTER CORES

THE BEST PERFORMANCES OF THE BRUNO PRESEZZI SHELLS CAN BE ACHIEVED IN COMBINATION WITH THE BRUNO PRESEZZI CORES WHICH ARE MANUFACTURED AT THE SAME BRUNO PRESEZZI WORKSHOP BY LONG-TERM EXPERIENCED TECHNICIANS UTILISING THE MOST ADVANCED MECHANICAL TOOLS AND THE PROVEN PRECISION FOR THE METALLURGICAL ASPECTS.


SHRINK-FITTING OPERATION
(FOR SHELLS TO BE DELIVERED ASSEMBLED WITH THEIR RELEVANT CORES)

The shrink-fitting operation is carried out at the Bruno Presezzi facility introducing the core vertically into the shell, which has been properly heated in an electrical furnace with an internal stainless steel wall.

For heating the shell, a special cycle is carried out. Such a heating cycle depends on the type of material of the shell itself and has been studied and adjusted over the years.

The interference value for the roll assemblies according to the Bruno Presezzi Patent is decided by the company's specialists whilst, for the other types of roll assemblies, the customer's indications are followed.


FORGING

The forging is carried out using a 6000 ton hydraulic press with the following cycle:
- Upsetting
- Hole punching
- Enlarging and stretching on the mandrel to the final rough dimensions

All the forging operations are carried out under accurate temperature control so that a fine and homogeneous microstructure is obtained, which permits the increase of the steel toughness.