Fasteners

Metal fasteners, metallographic

Due to the complexity of geometric shape, even for the most experienced metallographic analysis personnel, metal fasteners (such as bolts, screws, pin and rivet) may also be a challenge.In the introduction to this application, you can find the metallographic test samples used for the preparation of metal fasteners (including bolt test) mature methods and techniques.

Download the complete application instructions

Tighten - an important part of many industrial components

Metal fasteners for fixed parts and components in many applications.Usually these fasteners is important for structure safety.Metal fasteners, therefore, is a very common in process and quality control of metallographic test objectives.

Metallographic can be used for sampling of raw materials, production process control and validation or bolt testing and failure analysis.Metallographic test of metal fasteners, including size, structure inspection and quantitative analysis.

Fastener technology

Fastener technology including all kinds of fasteners.Metal fasteners, such as bolts, screws, pin and rivet, can be divided into two categories.
  • Threaded fasteners, such as bolt, nut and screw.
  • No thread fasteners, such as rivets and pin.

Fastening solutions and the choice of material depends on the application requirements, including strength, torque and environmental conditions.Fastener materials and application of commonly used:

Fastening material Common application
Carbon steel and low carbon steel Fastening solutions for general applications
High strength steel Construction and mechanical engineering
Stainless steel Highly resistant to corrosive fastening solutions
Nickel and cobalt Fastening solutions for high temperature applications
titanium Aircraft, medical and food industry
Brass and copper Decorative rail and accessories

Decorative rail and accessories

In the preparation of metal fasteners samples for metallographic analysis, metallographic analysis personnel faces two major challenges.

cutting: in the clip tight firmware for cutting, the size and shape of the metal fasteners may affect cutting.

Fasteners,
Figure 1: screw head cut off before the sample with spare parts

Set: metal fasteners, the contraction of the threads and screw head clearance may affect edge protection, make it difficult to clean sample.

Fasteners,
Figure 2: thread, caused by shrinkage clearance

A complete description to learn about how to deal with these challenges,Please download the complete application instructions.

Fastener production and technology of fasteners

Simple unthreaded metal fasteners (such as pin and connecting rod) is one of the most ancient of fastening technology.Threaded rivets, screws and bolts are succeeding, the original is made of precious metals production.

Fastener technology development is one of the biggest can run under pressure the ductility of the metal.At this point, the use of cold forming of metal fasteners for mass production.Today, the widespread adoption of no cutting forming (rolling), by cold or hot press molding.

Cold forming of metal fasteners
Cold is the most commonly used method so far in the production of metal fasteners.Be incorporated into continuous wire extrusion machine.Then, use the mold compression wire and reducing its diameter, until to form the correct shape.Threaded through cold rolling forming.In some cases, the induction hardening can be used to increase the surface hardness of metal fasteners.

  • In order to obtain high quality steel fasteners, can adopt different methods of heat treatment to obtain specific material properties.
  • Low carbon steel after carburizing treatment, can form hard surface and the center of the flexible structure.
  • Carbon steel after quenching and tempering treatment.
  • High quality of screws can be processed after the initial forming structure, to achieve a specific shape, tolerance, and surface.

Hot forming of metal fasteners
Thermoforming can still be used for very large or complex shape metal bolt.

Metal fasteners, anti-corrosion protection
In order to improve the anti-corrosion performance, can be coated on fasteners manganese phosphate, zinc phosphate, or iron phosphate, and then coated with grease.If you need more strong anticorrosion performance, can be in metal fasteners, zinc and cadmium and chromium, or by cadmium and aluminum vapor deposition.

To learn more
Understanding the production of various metal fasteners, process and technical details,Please download the complete application instructions.

Fasteners,
Figure 3: cold heading is a kind of basic processing methods, can be in the "cold" state will round wire into the shape of the necessary.Must maintain the continuity of grain processing, in order to ensure the integrity of the metal fasteners.

Fasteners,
Figure 4: in the process of screw thread rolling, billet has accurate in two parallel groove rolling between flat die.Cold or hot working, rolling thread strong and smooth, do not waste material.

Metal fasteners, cutting and kind advice

Test for metallographic sample preparation of metal fasteners, bolts (including test) are the main challenges for geometric shapes.Because of the head, so it is difficult to when making the section cutting firmly grip the fasteners.In addition, the head and bend thread may also lead to shrinkage clearance when set samples.Is particularly important for the coating of metal, because if the edge protection is not good, cannot check right fasteners of the coating.

Below, we how to deal with these challenges Suggestions are presented.To more fully understand how the preparation of metal fasteners, metallographic analysis and bolt test samples,Please download the complete application instructions.

Cutting: how to securely clamped metal fasteners
  • For medium or thin screws and bolts, can create a special thread holder, in the process of cutting the fixed screw or bolt.
  • For smaller screws, rivets and bolts, can be in a side trimming head, so that you can flat fasteners.Set sample, after grinding fasteners to the center.

Set: how to avoid metal fasteners sample a contraction gap
  • forHot Mosaic, the use of hot pressing Mosaic or resin containing hard packing, such asDuroFast,PolyFastorLevoFast.
  • forCold inlaidWith epoxy resin, such asEpofixBecause its minimum shrinkage rate.
  • Set sample before, the use of degreasing agent thoroughly clean samples.
  • Very small screws and bolts should be used a piece of metal or plastic as a gasket set.Then the grinding fasteners to the center.

Learn more about cutting and sample information
 Fasteners,
Figure 5: a special holder for screws and bolts.

Metal fasteners, grinding and polishing

Fasteners samples preparation metallographic test, may need to coarse grinding into the center of the sample.It can use the millstone done in automatic grinding machine.Specific grinding and polishing methods should be based on the materials of fasteners.

Over the years, Struers into a variety of fastening solutions, materials and applications (including bolt test) developed a specific method of sample preparation.In the complete application instructions, you can find a mature detailed sample preparation method, is used for grinding and polishing and copper alloy steel bolt screw.

For more information about grinding and polishing
Fasteners,
Figure 6: bolt test: on the left side is carbon steel bolt head cleft (caused by cracks), on the right side is the bolt fracture cross section (with 3% nitric acid etching for ethanol).

Fasteners,
* the value of the 6 set samples 30 mm in diameter.In the holder.

Fasteners,
* the value of the 6 set samples 30 mm in diameter.In the holder.

Etching of metal fasteners

Metallographic analysis, preparation of metal fasteners samples should choose suitable fasteners, metal etching solution and method.

The results of interpretation

Many mechanical defects such as burrs, fracture and fold, can through the visual inspection or nondestructive testing method.To determine the depth of the defect, however, may require further metallographic sample preparation.
  • Microstructure defects are usually caused by heat treatment, such as excessive heating, grain growth, or decarburization.
  • Fracture is usually the result of long-term stress, such as bending, tight and hot and cold cycle.

Fasteners,
Figure 7: due to the excessive heating and melting of the grain boundary.Nickel base alloy, the modified Kalling etching chemical etching.

Metal fastener material phase

Thread and non metal fasteners, such as pin and bolt, is one of the oldest fasteners technology.Nowadays, metal fasteners are still widely used in fixed parts and components.Therefore, fasteners and bolt testing metallographic analysis is commonly used procedures.

Metallographic test is often used to check production in the process of the subsequent heat treatment and mechanical and thermal damage.

Fasteners, metallographic test sample preparation are the main challenges caused by geometric shapes.The shape of the head may be in the process of cutting a fastener clip becomes difficult, and thread may lead to shrinkage clearance when set samples.Can be through the use of specific methods of sample preparation and/or tools to tackle these challenges.The grinding, polishing and etching method should be selected according to the material of the fasteners.

Download the application instructions, how about the preparation of fasteners, bolts and sample testing of complete specifications, including used for grinding and polishing and copper alloy steel bolt screw sample preparation method in detail.

Fasteners,
Figure 8: display the thread section of decarburization by 5% nitric acid ethanol etching.

Get the complete application instructions

Want to read about copper and copper alloy metallographic preparation of complete application instructions?Please click here to download

In-depth understanding of other materials

If you want to learn more about the material and phase property of the metal and other materials, please checkOur materials page.

Holger Schnarr

All images by Danish application specialists Birgitte Nielsen