Custom Made Stainless Steel Bolts

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What are bolts?

Metal bolts are a high strength fastener for fastening two or more work parts together. It has a thread with ridges that wrap around the outside of their shaft in a helical pattern. They use nuts to secure them to surfaces.

There is another threaded fastener named screw, the construction similar to bolts. The similarity makes confusion, and people use both names.

What are bolts used for?

The bolt is to hold two or more parts together with many applications. There are these bolts below: automotive bolts, military bolts, aerospace bolts, civil engineering bolts, petrochemical bolts. Custom bolts are a kind of non-standard bolts and design and make according to the unique applications.

How to make a bolt?

The manufacturing process to custom made bolts is below:

The pre-treating method: 

The custom bolt manufacturers heat the wire rod into the furnace, bathe it in sulfuric acid remove any rust particles. The surface rust particles will remove after putting the wire rod into sulfuric acid. Then coated phosphate to surface for rust resistance and lubrication.

Die-shapes bolts heads: 

Bolts suppliers form the rods by cold forming. High pressure and dies to shape the bolts head.

Bolts threading: 

The cold-rolled blank threaded out. And the thread formed by the interaction between the movable and the fixed dental plate.

Custom bolts material:

The materials used to manufacture custom bolts include steel, stainless steel, aluminum, brass, copper alloys, plastics, and titanium.

A stainless steel fastener is for chemical and corrosion-resistant.

Aluminum is for making light industrial bolts that are electrically conductive and resistant to corrosion and thermal energy. 

Brass bolts have low magnetic permeability and oxidation resistance.

Copper bolts have excellent wear resistance.

Plastic offers excellent water resistance with light loads.

Custom bolts model:

Custom bolts have different sizes, shapes, grades, and materials below:

Custom Stainless Steel U bolts

U bolts are bent bolts with threads at two ends. It used for suspended items to be attached to the surface of something.  They may be round, square, or semi-round. U bolts used for the construction and automotive.

Custom made U bolts type and dimension:

Square, Round, Semi-Round, J and L type with 3/8″, 7/16″, 1/2″, 9/16″, 5/8″,3/4″, 7/8″, 1″ or customized and U-bolt nut plates

Custom Stainless Steel shoulder bolts

Shoulder bolts also named shoulder screws or stripper bolts, and it has an integral shoulder or journal between the head and thread.

Shoulder screws have a head, shoulder, and thread. The head has the largest diameter, its diameter and length describe the shoulder, and the thread has a significant diameter slightly smaller than the shoulder diameter.

Shoulder bolts size: Dia 8 x M6, Dia 10 x M8, Dia 12 x M10, Dia 16 x M12, Dia 20 x M16
Shoulder screws length: 15, 20, 25, 30, 35, 40, 50, 55, 60, 65, 70, 80, 90, 100, 120mm
Stripper bolts material: Alloy Steel, MS, SS, Brass

 Custom Stainless Steel hex Bolts

The hex bolt is very common. Made of metal with a six sides hexagon head, a shank threaded throughout the length and a washer. It needs a nut to fasten the hex bolt.

Custom Stainless Steel anchor bolts

Anchor bolts embedded in concrete and anchoring posts with supports to the foundation. It used in building and construction.

Custom Stainless Steel eye bolts

Eyebolts have threaded at one end and a round eye at the head. The eye hole fixes a cable, rope, or chain for lifting. Eyebolts are common in ships, airplanes, and buildings.

Custom Stainless Steel flange bolts

The flange bolts have an integral washer. It helps distribute bearing weight and eliminate the disfigurement of material being bolted.

Custom Stainless Steel metric bolts

Metric bolts use the metric dimension for measuring the system. They are used worldwide.

Custom Stainless Steel machining bolts

The machining bolt is made by CNC machining because they are not standard.

Custom Bolts Type by country:

According to the country, the custom bolts can be divided into metric, American, and British types.

Metric Bolts

Mark the screw model directly with the outer diameter of the screw. For example, m3 means the outer diameter of screw is 3.00mm; M4 means the outer diameter of screw is 4.00mm.

Metric ex: m3x6 – ppb: is m3 machine screw, 6mm long, cross, round flat head, black plated.

Metric thread size pitch: metric screw is located at the back of screw model; sometimes, screw pitch is indicated. For example, m3x0.5, m4x0.70, m5x0.8, M6X1.

American Standard Bolts 

It is usually marked with serial number, such as # 2-56, # 4-40, # 6-32, # 8-32, # 10-24 etc.

Or in British outer diameter. Such as 0: 0.86-56, 0.112-40, 0.138-32, 0.164-32, 0.190-24 etc.

The length of the American screw is converted to metric mm. Conversion formula: x25.40 = metric length mm

British Bolts:

Mark with denominator as 8, and then directly call the numerator number.

Ex: 1 / 8×0.50 – ppb: 1 split screw x 0.50 “long, ppb

Ex: 5 / 16×0.50 – ppb = 2.5 / 8×0.50-ppb: 2 split screw x 0.50 “long, ppb

Ex: 5 / 32×0.50 – ppb = 1.25/8×0.50-ppb: 1 minute 2.5% screw x 0.50 “long, ppb

Ex: 1 / 4×0.50-ppb = 2 / 8×0.50-ppb: 2 split screw x 0.50 “long, ppb

British screw is marked with coarse or fine teeth.

UNF: thin-tooth: commonly used in electronic industry.

UNC: coarse teeth: For heavy machinery structure.

Ex: 3 / 8×0.50, UNF – ppb: 3-minute fine thread screw × 0.50 “long, ppb.

The length of British Bolts is indicated in inch, which shall be converted into mm by multiplying 25.40.

Custom Bolts Type by HeadCode：

There are Flat, Oval, Round, Pan, Truss, Hex head bolts.

Customized Bolts Type by DriveCode：

Slotted, Phillips, Phil-Slot, Hex Scoket, OneWay

Customize Bolts Type by LengthCode:

Directly mark the screw length in mm. Mark the total length of screw, only calculate the length below the head, excluding the head height. Except for the flat head screw, the total length of the screw indicates the head height.

Custom Made Bolts Type by FinishCode:

Zine plated: Galvanized

Ni: Ni plated.

Tin Coating: Tin plated treatment.

Zinc Plated / Green Iridite: Galvanized green film treatment.

Radiant Plated: Multicolored

Passivate: Antioxidant treatment.

Alodialfinish: no appearance processing

The Hardness of the Custom Bolt

Hardness indicates the ability of a material to resist the pressure of a hard object into its surface. It is one of the important performance indicators of custom bolt. Generally the higher the hardness, the better the wear resistance.

Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.

Brinell hardness (HB) of custom fasteners

With a certain load (generally 3000kg) to a certain size (diameter is generally 10mm) of hardened steel ball pressed into the surface of the material, maintain a period of time, after the load, the ratio of the load and its indentation area, that is, the Brinell hardness value (HB), the unit of kilogram force / mm2 (N/mm2).

Rockwell hardness (HR) of custom bolts

When HB>450 or specimen is too small, can not use Brinell hardness test and use Rockwell hardness measurement instead. It is with a top angle of 120 ° diamond cone or diameter of 1.59, 3.18mm steel ball, under a certain load pressed into the surface of the material under test, by the depth of the indentation to find out the hardness of the material. Depending on the hardness of the test material, it is expressed in three different scales.

HRA: is the hardness obtained by using 60kg load and diamond cone indenter, used for materials with very high hardness (such as cemented carbide, etc.).
HRB: is the hardness obtained using a 100kg load and a 1.58mm diameter hardened steel ball, and is used for materials with lower hardness (e.g. annealed steel, cast iron, etc.).
HRC: is the hardness obtained by using 150kg load and diamond cone indenter, used for materials with very high hardness (such as hardened steel, etc.).

Vickers hardness (HV) of custom bolts and nuts

With a load of up to 120kg and a diamond square cone indenter with a top angle of 136° pressed into the material’s surface, the Vickers hardness value (HV) is obtained by dividing the surface area indentation crater of the material by the load value.

From the above introduction can be seen, Vickers hardness is one of the surface hardness. There is a conversion relationship between it and other hardness units.

Hardness refers to the surface hardness; there is no hardness requirement inside the material. Only mechanical properties are required (tensile strength, yield strength and impact toughness).

Surface hardness should not be higher than the core hardness of 30 Vickers hardness (about 3 HRC). 10.9 grade surface hardness should not be greater than 390HV0.3. As for no surface hardness requirements that are low performance grade, such as 3.6 4.6 4.8 5.6 5.8 6.8, because there is no heat treatment, so there is no requirement, because his surface hardness is mainly cold upsetting or baking hit / turning after the stress The hardness is produced by the stress of cold heading or baking and turning.

When testing the hardness of the bolt, there is no heat treatment of the bolt, only need to do the surface hardness in the qualified range on the line. If the bolt is heat-treated, the hardness should be cut on the face of the diameter of a large hardness, hardness test on the face of the 1/2R, the hardness meets the standard.

The custom bolts has a surface a core, the surface refers to the surface after removing the surface rust and so on with Vickers or surface Rockwell hardness, the core to remove the part of the 1/2 diameter of the long part in the surface and the core of the 1/2 place to play hardness, the difference between the two hardness can not exceed 30 HV, the surface higher than 30 HV means that the surface carburized, is not allowed, if the surface is lower than 30 HV means that the surface decarburized, is also not allowed. Look at this 3098 carefully.

Introduction of stainless steel bolts

1). Stainless steel main components: generally contains chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and other high-quality metal elements.

2) common stainless steel: chromium stainless steel, containing Cr ≥ 12% or more; nickel-chromium stainless steel, containing Cr ≥ 18%, containing Ni ≥ 12%.

3)Classification from stainless steel metallographic organization: there are austenitic stainless steel, for example 1Cr18Ni9Ti, 1Cr18Ni11Nb, Cr18Mn8Ni5. Martensitic stainless steel, for example Cr17, Cr28, etc.. Generally known as non-magnetic stainless steel and stainless steel with magnetism.

Common stainless steel fastener surface treatment methods

Stainless steel surface natural color treatment.

Stainless steel in the processing process, after the rolled plate, tied edge, welding or after artificial surface fire baking heating treatment, resulting in black oxide skin. This hard gray-black oxide skin is mainly NiCr2O4 and NiF two EO4 components, the previous general use of ** and nitric acid for strong corrosion method to remove. But the cost of this method is large, polluted environment, harmful to human body, corrosive, gradually eliminated. At present, there are two main treatment methods for oxide skin.

(1) sandblasting (pill) method: mainly using the method of spraying micro-glass beads to remove the surface of the black oxide skin.

(2) chemical method: the use of a non-polluting pickling passivation paste and room temperature non-toxic cleaning solution with inorganic additives for dipping. Thus achieving the purpose of whitening treatment of stainless steel natural color. After the treatment basically looks like nothing light color. This method is more applicable to large, complex products.

Stainless steel surface mirror manufacturing method

According to the complexity of stainless steel products and the user requirements of different situations can be used mechanical polishing, chemical polishing, electrochemical polishing and other methods to achieve a mirror luster. The advantages and disadvantages of these three methods are as follows.

Stainless steel surface coloring treatment.

Stainless steel coloring not only gives stainless steel products a variety of colors, increasing the color of the product color variety, but also to improve the wear resistance and corrosion resistance of the product.

Stainless steel coloring methods are as follows.

(1) chemical oxidation coloring method: is in a specific solution, through chemical oxidation to form a film color, dichromate method, mixed sodium salt method, sulfide method, acidic oxidation method and alkaline oxidation method. Generally “INCO method” (INCO) is used more often, but to ensure a batch of products with the same color, you must use reference electrodes to control.

(2) Electrochemical coloring method: The color of the film is formed by electrochemical oxidation in a specific solution.

(3) ion deposition oxide coloring method chemical method: is the stainless steel workpiece in the vacuum coating machine for vacuum evaporation plating. For example: titanium-plated watch cases, watch bands, generally golden yellow. This method is suitable for high-volume product processing. Because of the large investment, high cost, small batch products are not cost-effective.

(4) high-temperature oxidation coloring method: is in a specific molten salt, immersed in the workpiece to maintain certain process parameters, so that the workpiece to form a certain thickness of oxide film, while showing a variety of different colors.

(5) gas phase cracking coloring method: more complex, less used in industry.

Stainless steel fasteners surface treatment selection of which method, according to the product structure, material, and different requirements for the surface, the choice of suitable methods for processing.

Stainless steel bolts and nuts rust causes

1. Chemical corrosion

1) surface pollution: attached to the surface of the workpiece oil, dust and acid, alkali, salt, etc. in certain conditions into a corrosive medium, and some components of the stainless steel parts in a chemical reaction, resulting in chemical corrosion and rust.

2) Surface scratches: various scratches on the damage of the passivation film, so that the stainless steel protection capacity is reduced, easy to react with chemical media, chemical corrosion and rust.

3) cleaning: pickling passivation after cleaning is not clean resulting in residual liquid remains, direct corrosion of stainless steel parts (chemical corrosion).

2. Electrochemical corrosion

1) carbon steel pollution: contact with carbon steel parts caused by scratches and corrosion media to form primary cells and electrochemical corrosion.

2) cutting: cutting slag, splash and other rust-prone material adherence and corrosion media to form primary cells and electrochemical corrosion.

3) baking school: flame heating area composition and metallurgical organization changes and uneven, and corrosion media to form a primary cell and electrochemical corrosion.

4) welding: physical defects in the welding area (edge biting, porosity, cracks, not fused, not welded through, etc.) and chemical defects (coarse grain, grain boundary poor chromium, segregation, etc.) and corrosion media to form primary cells and electrochemical corrosion.

5) material: stainless steel material chemical defects (uneven composition, S, P impurities, etc.) and surface physical defects (loose, sand eyes, cracks, etc.) is conducive to the formation of primary cells with the corrosive medium and electrochemical corrosion.

6) passivation: pickling passivation effect is not good cause stainless steel surface passivation film is not uniform or thin, easy to form electrochemical corrosion.

7) Cleaning: the residue of the surviving pickling passivation and stainless steel chemical corrosion occurs with the formation of electrochemical corrosion of stainless steel parts.

How to remove rust from stainless steel fasteners?

1. Cleaning and polishing: If there is damage should be polished, especially with carbon steel parts contact caused by scratches and splashes, damage caused by cutting slag must be carefully and thoroughly cleaned and polished clean.
2. Mechanical polishing: appropriate polishing tools should be used for polishing, requiring uniform and consistent treatment and avoiding over-throwing and re-scratching.
3. Oil and dust removal: stainless steel parts in the pickling passivation before, must be removed according to the process of oil, oxide, dust and other debris.
4. Water blasting treatment: according to different treatment requirements, choose different micro glass beads, different process parameters, and avoid overblasting, etc.
5. Pickling passivation: pickling passivation of stainless steel parts must be passivated in strict accordance with the process requirements.
6. Cleaning and drying: After pickling and passivation, neutralization, rinsing and drying should be carried out strictly in accordance with the process to thoroughly remove the residual acid.
7. Protection: After the surface treatment of stainless steel parts, should be well protected to avoid secondary pollution by personnel touching and debris such as oil and dust.
8. Avoid reprocessing: After the surface treatment of stainless steel parts, the reprocessing of the parts or products should be avoided.

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