Fastener processing technology flow, inspection standards industry solutions

Fastener processing technology flow, inspection standards industry solutions

Fasteners are a class of mechanical parts widely used for fastening and connecting. Fasteners are used in a wide range of industries, including energy, electronics, electrical appliances, machinery, chemical industry, metallurgy, molds, hydraulics, and other sectors, in a variety of machinery, equipment, vehicles, ships, railroads, bridges, buildings, structures, tools, instruments, chemical, instrumentation, and supplies, etc., can be seen on the top of the various types of fasteners, is the most widely used mechanical foundation parts. It is characterized by a wide variety of specifications, performance, and use of different, and standardization, serialization, and generalization of the degree are also very high. Usually include bolts, studs, screws, self-tapping screws, wood screws, nuts, pins and keys, washers, gear rings, rivets, combinations, and connecting sub-fasteners.

1. What are the types of fasteners?

Bolt: by the head and screw (with external threads of the cylinder) composed of two parts of a class of fasteners, need to cooperate with the nut, used to fasten the connection of two parts with a through hole. This form of connection is called bolt connection. For example, the nut from the bolt spins down, which can make the two parts separate, so the bolt connection is removable.

Stud: no head, only the two ends of a class of fasteners with external threads. Connection, it must be screwed into one end with internally threaded holes in the parts, the other end through the parts with through holes, and then screwed on the nut, even if the two parts are tightly connected into a whole. This form of connection, called stud connection, also belongs to the detachable connection. Mainly used for one of the connected parts of greater thickness, requires a compact structure, or, due to frequent disassembly, should not be used in bolt connection occasions.

Screws: also consists of the head and screw, two parts of a class of fasteners, according to the use, can be divided into three categories: machine screws, fastening screws, and special purpose screws. Machine screws are mainly used for fastening threaded holes in the parts. A through-hole part with a fastening connection between the parts does not need to be a nut (this form of connection is called a screw connection and also belongs to the removable connection; it can also be used with the nut with the two through-hole parts with a fastening connection between the parts.) Set screws are mainly used to fix the relative position between two parts. Special-purpose screws, such as ring screws for lifting parts.

Nut: with internal threaded holes, the shape is generally shown as a flat hexagonal column; there are flat square or flat cylindrical, with bolts, studs, or machine screws used to fasten the connection between the two parts, so that it becomes a whole piece.

Self-tapping screws: similar to machine screws, but the threads on the screw for the special self-tapping screws with threads. Used to fasten the connection of two thin metal components so that it becomes a whole, the components need to be made beforehand on the small hole; due to the high hardness of this screw can be screwed directly into the holes in the components, so that the formation of responses in the components of the internal threads.

Wood screws: also similar to machine screws, but the threads on the screws are specialized for wood screws, which can be screwed directly into a wooden component (or part), and are used to connect a metal (or non-metallic) part with a through-hole to a wooden component in a fastening connection. This connection is also removable.

Washers: a class of fasteners shaped like a flat circular ring. Placed on the bolt, screw, or nut support surface and connection between the surface of the parts play a role in increasing the contact surface area of the connected parts, reducing the pressure per unit area, and protecting the surface of the connected part is not damaged; another type of elastic washers, but also play a role in preventing the nut back to the role of loose.

Retaining ring: For installation in the machine, equipment, shaft groove, or shaft hole groove, it plays a role in preventing the shaft or hole on the parts of the left and right movement.

Pins are mainly used for positioning parts left and right; some can also be used for connecting parts, fixing parts, transmitting power, or locking period fasteners.

Rivets: The head and nail rod are two of a class of fasteners that connect two parts with holes (or components) to become a whole piece. This form of connection is called a riveted connection or riveting. Rivets belong to the non-removable links because if the two connected parts are separated, the rivets on the parts must be destroyed.

Components and connecting vice: a combination of parts is a combination of a class of fasteners, such as some machine screws (or bolts, self-supplied screws) and flat washers (or spring washers, lock washers) combination of supply; connecting vice refers to some special bolts, nuts, and washers combination of supply of a class of fasteners, such as steel structure with high-strength hexagonal bolts connecting vice.

Welding screws: the screw and nail head (or no nail head) constitute a different type of fasteners, with welding method to other fixed connection in a part (or component) above, to then connect with other parts.

Locking or biting often occurs in stainless steel, aluminum alloys, and titanium alloy material fasteners; these metal alloys have anti-corrosion properties and will cause surface damage in the metal surface to produce a thin layer of oxidation to prevent further corrosion. When the stainless steel fasteners are locked, the pressure and heat generated between the threads will destroy this oxide layer so that the metal between the threads blocks or shears, and then the adhesion phenomenon. When this phenomenon continues to occur, the stainless steel fasteners will be completely locked and can no longer be removed or continue to lock. Usually, this series of blocking, shearing, adhesion, and locking of a series of actions occur in just a few seconds, so the correct understanding of using such fasteners is necessary for this phenomenon. Please get in touch with our team if you need high-quality, high-strength screws& fasteners with more detailed specifications and related information.

Email:adelajonly@gmail.com,www.juxinfasteners.com.

2. What are fastener threads?

A thread is a solid outer surface or inner surface of the cross-section shape of a uniform helical line raised. Thread classification can be divided into three categories according to its structural characteristics and use.

Ordinary thread: This thread's shape is triangular and is used for connecting or fastening parts. Common threads are divided according to the pitch into coarse and fine threads, and the connection strength of fine threads is higher.

Transmission Threads: Thread shapes are trapezoidal, rectangular, saw-shaped, and triangular.

Sealing threads: These are used for sealing connections, mainly pipe threads, conical threads, and conical pipe threads.

3. What are the standards for threaded fasteners?

Hexagon head bolts, double-headed studs, hexagon nuts, hexagon slotted nuts, hexagon socket cylindrical head screws, slotted cylindrical head screws, slotted countersunk head screws, set screws, flat washers, spring washers, round nuts with stop washers, round nuts and so on. Pins, keys, and keys of many kinds are commonly used in the form of ordinary keys, half-round keys, hook-head wedge keys, etc., of which ordinary keys are the most common. Keys are also standardized: flat, half-round, and hook wedge keys. Fastener standards, DIN German standard, GB national standard, ASME/IFI/ANSI American standard, Q steam standard, PEM standard, JB standard mechanical department, EN European standard, ISO international standard, JIS Japanese standard, HG chemical standard, NFE French standard, UNI Italian standard, BS British standard, and other common standards. American fastener thread series:

UNC/UNRC: Unified Coarse Threads / Coarse Threads with Arc on the Bottom of the External Threads

UNF/UNRF: Unified fine/ fine thread with rounded outer thread base.

UNEF/UNREF: Unified ultrafine thread/Ultrafine thread with rounded outer thread base

UN/UNR: Fixed pitch series threads/ Fixed pitch threads with rounded outer thread base, e.g., 4UN, 6UN, 8UN, 12UN/4UNR, 6UNR, 8UNR, 12UNR, etc.

UNS: Uniform threads for special series

In addition, the product marking and standards of American fasteners also follow specific regulations; for example, the performance level marking is generally expressed in numbers, symbols, or letters, and the manufacturer identification mark is usually expressed in letters and symbols to indicate the standard number Classification according to different product types, such as bolts, screws, studs, and other external threaded fasteners are all bundled in the same standard as the ASME B18.2.1, and square nuts, hexagonal nuts, heavy-duty nuts, and heavy-duty nuts, and so on, are all bundled in the same standard. Hexagonal nuts, heavy nuts, thick nuts, and other internally threaded fasteners are bundled in the ASME B18.2.2 the same standard in the U.S. fastener product marking and standards are the U.S. SAE, ASTM, IFI, ASME Association standards, and ANSI American National Standards developed by the American Association of Standards and these standards provide for the fastener's mechanical properties of the grade and the manufacturer's identification mark to ensure that the fastener's quality traceability and manufacturer's identification mark: quality traceability and producer responsibility.

3.1 Fastener product size standards: specify the primary size of the product content; products with threads, including the primary size of the thread, thread closing, shoulder distance, backing groove and chamfer, the end of the threaded parts of the end of the size and other aspects.

3.2 Fastener product technical conditions of the standard: mainly including product tolerances, mechanical properties, surface defects, surface treatment, product testing standards, and the corresponding specific provisions of the content of the standard.

3.3 Screw product acceptance inspection, marking, and packaging standards: specify the product factory acceptance of the qualified quality level of sampling items and sampling program, as well as product marking methods and packaging requirements aspects of the content.

3.4 Standard parts, fasteners, screws, screws marking method standard: specify the complete product marking method and simplify the content of the marking method.

3.5 Fasteners in other areas of standards, such as fastener terminology standards and fastener product weight standards.

4. Solutions for marking of bolts

4.1 Performance level marking of bolts and nuts: hexagon head bolts and screws (thread diameter ≥5mm). It is necessary to mark the top surface of the head with raised or concave characters or on the side of the head with concave characters, including the performance level and factory label. For the steel strength grade, the marking code consists of two parts of numbers separated by "-." It was marking code in the "-" before the meaning of the digital part of the nominal tensile strength, such as 4.8 grade "4," that the nominal tensile strength of 400MPa 1/100. Marking code in the "-" and the meaning of the numerical part of the point after the yield ratio is the nominal yield point or nominal yield strength and the ratio of nominal tensile strength, such as a 4.8-grade product yield point of 320MPa and a flexural strength ratio of 0.8.

4.2 bolt nut grade: For ten performance levels, metric bolt mechanical properties can be divided into 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, and 12.9.

5. Metric bolt's mechanical properties level and material selection solutions

Bolt production process 1.Process (cold heading) - disc element - annealing pickling - drawing (annealing) - cold heading - packaging - surface treatment - heat treatment - rolling (rolling) teeth

The purpose of annealing is to heat the wire to the appropriate temperature, keep it for a certain period, and then slowly cool it down to adjust the crystalline organization, reduce the hardness, and improve the machinability of the wire at room temperature.

Manufacturing process and feeding: The products to be processed hang in the furnace. Pay attention to the furnace cover, which should be covered tightly. Generally, a furnace can handle several rolls at the same time.

Heating: The furnace temperature is set slowly (about 3-4 hours) to the specified temperature.

Holding: material 1018 wire at 680 ℃ -715 ℃ to keep 4-6h, material 10B21 wire at 740 ℃ -760 ℃ to keep 5.5-7.5h.

Cooling: the furnace temperature slowly (about 3-4 hours) down to below 550 ℃, and then cooled with the furnace to room temperature

Quality control hardness: material 1018 and 1022 wire annealed hardness of HV120-170, and material for the medium carbon wire annealed hardness of HV120-180.

Appearance: There shall be no oxide film and decarburization on the surface.

Pickling removes the oxide film on the wire's surface and forms a layer of phosphate film on the metal surface, reducing the wire drawing, cold piercing, molding, and other processing and abrasion of the mold.

Workflow: pickling: The whole disk Yuan was immersed in room temperature, 20-25% of the three hydrochloric acid tanks, for several minutes to remove the oxide film on the surface of the wire.

Cleaning: Remove the hydrochloric acid corrosion products on the surface of the wire.

Oxalic acid: to increase the activity of the metal so that the following process generates a denser film.

Phosphate treatment: The raw material wire is immersed in phosphate, the steel surface and chemical treatment solution contact, and the steel dissolves to generate insoluble compounds (such as Zn2Fe (Po42-4H2o)), which are attached to the steel surface to form a film. Shimizu: Remove the film surface residues.

Lubricant: As the coefficient of friction of the phosphate film is not very low, it can not give the processing of adequate lubrication, but with the reaction of the metal soap (such as sodium soap) to form a hard layer of metal soap, it can increase its lubricating properties.

Drawing purpose: The raw material wire is cold drawn to the required wire diameter. This is practical for some products and can be divided into rough drawing (shelling) and OK stretching, which have two stages.

(Hot & Cold Heading) Head Forming Purpose: Cold heading (or hot forging) of the wire to form the head of the bolt or nut to achieve the semi-finished product's shape and length (or thickness).

Purpose of screw forming: to roll or tap the shaped semi-finished product to achieve the required thread. General bolts (screws) are called rolling threads, large-diameter bolts or fully threaded posts are called rolling threads, and nuts are called tapping threads.

Threads of several processing methods: rolling, tapping, and rolling threads.

Heat treatment normalizing: Normalizing refines the grain, reduces the degree of banding in the organization, and adjusts the hardness. Steel with fine-grain pearlitic organization is easy to machine.

Quenching: The steel body is heated to about 850 ℃ for quenching. The quenching medium can be selected according to the size of the steel parts and the steel's hardenability. Generally, water, oil, or even air can be used for quenching. Steel in the quenched state has high hardness but low plasticity and internal stress.

Tempering: to make the steel have high plasticity, toughness, and appropriate strength, steel at 400-500 ℃ or so for high-temperature tempering, tempering brittleness sensitivity of the steel, tempering must be rapidly cooled to inhibit the occurrence of tempering embrittlement; if the parts are required to have an exceptionally high strength, tempered at 200 ℃ or so to get tempered martensite organization.

Tempering: high temperature tempering after quenching (500-650 ℃). General high-strength bolts are primarily used in this process.

Spring steel: medium temperature tempering after quenching (420-520 ℃)

Quenching: oil quenching at 830-870 ℃.

Tempering: tempering at about 420-520 ℃ to obtain tempered quartzite organization.

Carburized steel: quenching and then low-temperature tempering after carburizing (150-250 ℃)

Carburizing: A chemical heat treatment refers to the infiltration of element C into the surface of steel parts in an active medium containing certain chemical elements at a certain temperature. Sub-preheating (850 ℃) carburizing (890 ℃) diffusion (840 ℃) process

Quenching: Carbon and low alloy carburizing steel are used directly or through quenching.

Tempering: Low-temperature tempering to eliminate internal stresses and improve the strength and toughness of the carburized layer.Juxin Fasteners production, tapping screws tempering temperature of 360 ℃ or so, self-drilling screws (wallboard nails) tempering temperature of 200 ℃ or so, after cooling to 34-35 ℃ and 39-40 ℃, respectively.

Definition: surface treatment that involves specific methods on the workpiece surface to form a covering layer of the process. Its purpose is to endow the product surface with a beautiful, corrosion-resistant effect.

Methods: Electroplating: The parts to be plated are immersed in a water solution containing the deposited metal compounds, and the current is passed through the plating solution so that the plated metal is precipitated and deposited. Generally, electroplating uses zinc-plated copper, nickel, chromium, copper-nickel alloys, etc.; sometimes, blackening (bluing) and phosphating are included.

Blackening (blue): In the chemical drug solution, heated to the appropriate temperature so that the steel parts surface forms a layer of the blue or black oxide film to improve its corrosion resistance and appearance of the surface treatment process

Hot Dip Galvanizing: This is accomplished by submerging carbon steel parts in a bath of dissolved zinc at approximately 510 degrees Celsius. The result is gradually transforming the iron-zinc alloy on the steel part's surface into passivated zinc on the product's exterior surface.

Quality Control Appearance: The product's surface is not allowed to have local plating, burning, roughness, gray, peeling, crusting condition, noticeable streaks, pinholes, pockmarks, black slag, passivation film laxity, cracking, peeling, and severe passivation traces.

Plating thickness: The operating life of fasteners in a corrosive atmosphere is directly proportional to their plating thickness. The generally recommended economical plating thickness is 4 to 12 um. The standard average thickness for hot-dip galvanizing is 54 um, with a minimum thickness of 43 um.

Distribution of Plating: Different deposition methods are used, and how the plating accumulates on the surface of the fastener varies. In electroplating, the plated metal is not uniformly deposited on the peripheral edges, and thicker layers are obtained at corners. In the threaded portion of the fastener, the thickest plating is located at the top of the threaded tooth, tapering along the side of the thread, with the thinnest deposited at the bottom. In contrast, the opposite is true with hot-dip galvanizing, with thicker plating deposited at the inside corners and the bottom of the threads.

Adhesion: Cut or pry off with a firm tip and considerable pressure. If, in front of the tip, the coating flakes or peels off in such a way as to expose the base metal, adhesion should be considered insufficient.

6. Fastener Inspection Solutions

Plating quality inspection and salt spray test: the quality of plating to its corrosion resistance as the primary measure. Corrosion resistance is to mimic the working environment of the product, set up for the test conditions, to the corrosion test. A salt spray testing machine is usually used for testing.

Plating thickness measurement: Generally, the thickness can be detected using a thickness gauge.

Guaranteed load test: The tensile testing machine test, the specimen combination in the test bolt or stud, tightened in a particular fixture, the specimen specified guaranteed load must be axially applied to the nut. The movement rate of the fixture during the test shall not exceed 3mm/min and last for 15 sec. ASTM F606M stipulates that the movement rate of the fixture during the test shall not exceed 25mm/min, and the duration of the load shall be 10 sec.

6.1 The nut shall withstand the load during the test without buckling or breaking. When the load is removed, the nut shall be loosened by hand or with the aid of a wrench, but not by more than half a buckle.

HARDNESS TEST: The hardness test shall be conducted by hitting at least three points. The average of at least two hardness test values at 180° opposite angles shall be taken as the nut's hardness value. Surface cleaning during the test shall remove any oxides, decarburization layer plating, and other surface debris.

6.2 Chisel load test: hammer blow several times so that the head of the bolt is bent into 90 ° - β angle in the head, supporting surface, and transition circle shall not find any cracks.

6.3 Key dimensions: according to international standards and drawings. For testing, use vernier calipers, a spiral micrometer (micrometer), a height gauge, or a depth gauge.

6.4 Decarburization layer test: (metallographic method test)

6.5 Thread inspection: using the screw gauge, test the internal thread through the gauge, test the internal thread stop gauge, and check the external thread ring gauge.

6.6 Thread limit gauge through gauge: inspection role in the diameter so it does not exceed his maximum entity size. The indicator is made into a complete thread type. And through the length of the indicator is equal to the design of the thread length of the screw (usually 80%, and the current international 8-12 threads). Since the through gauge is a complete thread, it can comprehensively inspect several thread parameters and control the internal diameter of the external thread.

6.7 Thread Limit Gauge Stop Gauge: Inspection of a single center diameter so that it does not exceed the minimum solid size. To avoid the influence of thread half-angle, which will be made into a truncated tooth, generally only take 2.5-3 threads.

Raw material procurement process control: mainly through the steel warranty verification method to control; only some have laboratory spectrometer equipment and laboratory testing. Pay attention to whether there are inspection procedures and acceptance criteria and whether the steel warranty collection and acceptance records align with the inspection procedures' provisions. Because the production process is mainly automated (especially the cold heading process), the process inspection records are mostly simple, and process cards even replace some of them; b. Still, the first inspection should be carried out to confirm the replacement specifications (mold change).

Unique processes: finished product heat treatment, tempering, and surface treatment. Spheroidal annealing after drawing, hot forging head, and beam rod can generally not be used as unique processes.