PRODUCTION METHODS:
HOT PRODUCTION
COLD PRODUCTION
TURNING
THERMAL TREATMENTS:
BONIFICA
TEMPRA A INDUZIONE
CEMENTAZIONE
TRATTAMENTI SUPERIFICIALI:
GEOMET
ZINCATURA
DELTA PROTEKT
TRATTAMENTI PRE APPLICATI
HOT PRODUCTION
The material (usually steel) is heated to temperatures of around 900–1250 °C, making it malleable, and then molded or forged into the desired shape.
Cutting the raw material
The process starts with steel bars or wire rod.
The bars are cut to size to obtain the “raw pieces” (called billets or preformed pieces), based on the length of the screw or bolt.
Heating
The pieces are heated in gas or induction furnaces to approximately 1000–1250 °C.
At this temperature, the steel is malleable but not liquid: it can be easily forged without breaking.
Hot stamping/forging
The red-hot piece is placed in a stamping machine or press.
Using hardened steel dies, the piece is shaped into the head (e.g., hexagonal, cylindrical, round) and part of the shank.
This process can be:
Closed-die forging (the most common), progressive stamping (with several successive strokes)
Trimming and deburring
After forging, any excess material (burrs) is removed using special tools.
This results in a “finished blank” that is still unthreaded.
Heat treatments (e.g., tempering)
The piece undergoes:
Tempering (hardening + tempering) to increase its strength and hardness, or annealing or normalizing, depending on the specifications.
Final mechanical processing
Threads are made (by rolling or turning), as well as any holes, chamfers, notches, etc.
Checks and finishing
The parts undergo:
Dimensional checks, hardness and mechanical characteristics checks, non-destructive tests (e.g., magnetoscopy, ultrasound) if required.
Surface finishing
Zinc plating, burnishing, phosphating, painting, etc.
COLD FORMING
Cold forming is the most common and widespread method used in the production of small and medium-sized screws, bolts, pins, and studs, especially for large series. It consists of the plastic deformation of steel at room temperature, without heating, using the pressure of high-powered machinery.
This means that the material (usually steel wire rod) is mechanically deformed at room temperature using multi-station machines (also known as transfer or cold heading machines) that perform various steps in sequence to obtain the finished piece.
STAGES OF COLD HEADING PRODUCTION
Preparation of the raw material
Starting with wire rod (steel wire in coils), the wire is pickled (removal of oxides), lubricated (to facilitate deformation), and drawn (brought to the required diameter).
Cutting
The wire is cut to length (the “preformed”) by an automatic machine within the same production line.
Cold forming
The piece is inserted into a multi-station press:
Each station performs a part of the process: Head formation (hexagonal, cylindrical, torx, etc.), shank elongation (if necessary), thread preforming.
Plastic deformation occurs by compression in hardened steel dies, with very high pressures (up to 1,000 tons). The material hardens as a result of cold working.
Threading
This is done by rolling (not chip removal):
The piece passes between two threaded rollers that imprint the thread profile by deformation.
The result is a very resistant thread with continuous metal fibers, which is more robust than turning.
Heat treatments (optional)
Surface finishes
Zinc plating (white, yellow, black)
Phosphating
Burnishing
Special anti-corrosion coatings (e.g., Geomet, Delta Protekt)
TURNING
In the fastener industry, turning is a precision machining process carried out using machine tools called lathes, with the aim of shaping and finishing threaded elements such as screws, bolts, studs, and pins.
During the process:
The workpiece (usually made of steel or metal alloys) rotates at high speed on its axis, while a cutting tool removes excess material, giving the component the desired shape and dimensional tolerances.
What is turning used for in the fastener industry?
In the field of fasteners, turning is used to:
• Shape the shank of bolts and studs
• Finish cylindrical or conical surfaces
• Create special threads (as an alternative to thread rolling)
• Perform custom machining on small batches or non-standard parts
HEAT TREATMENT
BONIFICA
This is a thermal treatment that aims to improve the mechanical characteristics of the material (screws, bolts, pins, etc.), such as:
Mechanical strength (breaking load)
Hardness
Toughness (ability to withstand impact)
Resilience (resistance to crack propagation)
Tempering involves two main phases:
1. Hardening
The piece (screw, bolt, etc.) is heated to a high temperature (usually between 800–900°C) and then cooled rapidly (usually in oil or water).
This induces a martensitic structure, which is very hard but brittle.
2. Tempering
After hardening, the piece is reheated to a lower temperature (between 500–700 °C) and cooled slowly.
This serves to reduce internal stresses and increase toughness, while maintaining high mechanical strength.
Result of tempering
• The “tempered” component has excellent mechanical properties and is suitable for structural or high-stress applications, such as:
– Bolts for industrial machinery
– Screws for automotive or aerospace applications
– High-strength pins and studs
HEAT TREATMENT
INDUCTION HARDENING
Induction hardening is a localized heat treatment used to increase the surface hardness of a metal part (such as shafts, gears, screws, etc.) by rapid heating generated by high-frequency induced currents.
What is induction hardening?
It is a form of surface hardening that exploits the principle of electromagnetic induction:
• A coil (inductor) generates a high-frequency electromagnetic field.
• The metal part, placed inside the coil, is traversed by induced currents (eddy currents).
• These currents rapidly heat only the surface of the piece to a temperature above the critical point of the steel (approximately 850–900 °C).
• This is followed by rapid cooling (hardening), usually with water or oil spray, to obtain a martensitic structure on the surface.
Objectives of induction hardening
• Hardening only the surface of the workpiece, leaving the interior more ductile.
o Increasing wear resistance, surface hardness, and fatigue resistance.
• Maintaining:
o Internal toughness (less brittleness than total hardening)
CARBURIZING
Carburizing is a process in which a low-carbon steel part is:
Heated in a carbon-rich environment (between 850–950°C), then held at temperature for a certain amount of time (even several hours)
During this time, carbon penetrates the surface of the metal (by diffusion), followed by quenching (rapid cooling) to harden the surface area, which now has a high carbon content.
Purpose of carburizing
• To obtain a very hard and wear-resistant surface
• To leave the inside of the piece softer and more ductile, so that it can absorb shocks or deformations without breaking
SURFACE TREATMENTS
GEOMET
Geomet is a protective coating based on zinc, phosphates, and resins that guarantees excellent corrosion resistance without altering the mechanical characteristics of the fasteners. It is environmentally friendly, free of hexavalent chromium, and ideal for industrial applications that require durable protection and low environmental impact.
ELECTROLYTIC GALVANIZING
Galvanizing is a corrosion protection treatment that consists of applying a layer of zinc to metal. This coating protects fasteners from oxidation and rust, extending their life even in aggressive environments.
DELTA PROTEKT is an advanced zinc and resin-based anti-corrosion coating that offers long-lasting protection to bolts, ensuring excellent wear resistance and low environmental impact thanks to the absence of hexavalent chromium.
DEHYDROGENATION
Thermal dehydrogenation is a treatment used in the metallurgical industry which, through the high temperature of a special furnace, allows the hydrogen accumulated during the galvanizing process to be removed from the metal surfaces of the treated parts.
PRE-APPLIED TREATMENTS
Pre-applied treatments such as Loctite and Tecnologic 3 offer a practical and safe solution for locking screws and bolts. Applied directly in the factory, they guarantee excellent sealing, prevent loosening due to vibration, and improve the reliability of joints, reducing assembly time and costs.