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Screw production process and process

2021-05-02


Screw production process (1)--annealing

First, the purpose: the wire is heated to the appropriate temperature, for a certain period of time, and then slowly cooled to adjust the crystal structure, reduce the hardness, improve the wire temperature processing.

Second, the operation process:

(1) Incoming material: The product to be treated is placed in the furnace, and the furnace cover should be tightly closed. Generally, 7 rolls (about 1.2 tons/volume) can be processed simultaneously in one furnace.

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

(3) Insulation: The material 1018, 1022 wire is kept at 680 ° C -715 ° C for 4-6 h, the material is 10B21, 1039, and the CH38F wire is kept at 740 ° C - 760 ° C for 5.5-7.5 h.

(4) Cooling: The temperature in the furnace is slowly reduced (about 3-4 hours) to below 550 °C, and then cooled to room temperature with the furnace.

Third, quality control:

1. Hardness: The material is 1018, 1022. The hardness of the wire after annealing is HV120-170. The hardness of the material is HV120-180 after annealing.

2. Appearance: There must be no oxide film or decarburization on the surface.

Screw production process (2) - pickling

I. Purpose: To remove the oxide film on the surface of the wire and form a layer of phosphate film on the metal surface to reduce the scratch on the tool during the wire drawing and cold pier or forming process.

Second, the operation process:

(1) Pickling: The entire disk element is immersed in three hydrochloric acid tanks at a normal temperature and a concentration of 20-25% for several minutes, the purpose of which is to remove the oxide film on the surface of the wire.

(2) Clear water: remove the corrosion product of hydrochloric acid on the surface of the wire.

(3) Oxalic acid: increase the activity of the metal to make the film formed in the next process more dense.

(4) Film treatment: The disk element is immersed in phosphate, the surface of the steel is in contact with the chemical treatment solution, and the steel is dissolved to form an insoluble compound (such as Zn2Fe(Po4)2·4H2o), which adheres to the surface of the steel to form a film.

(5), clear water: remove the surface residue of the film.

(6) Lubricant: Since the friction coefficient of phosphate film is not very low, it can not give sufficient lubricity during processing, but it can react with metal soap (such as sodium soap) to form a hard metal soap layer, which can increase its lubricating performance. .

Screw production process (3)--drawing

First, the purpose: to pull the disk element to the required wire diameter. Practically, for some products, it can be divided into two stages: rough drawing (shelling) and fine drawing.

Second, the operation process

After the pan is pickled, it is cold drawn to the desired wire diameter by a wire drawing machine. Suitable for large screws, nuts, wire rods used in dental bars.

Screw production process (4)--forming

I. Purpose: The wire is forged (or hot forged) to achieve the shape and length (or thickness) of the semi-finished product.

Second, the operation process:

1. Hex bolts (four-mode four-stroke or three-mode three-stroke)

(1), cutting: The movable wire is unidirectionally moved, and the wire stuck in the cutting die is cut into the desired blank.

(2), a punch: the back die is pressed against the blank of the blank die to form the blank, and the die is pushed out after the die.

(3), two punches: the billet enters the second die, the second die is extruded, the billet is oblate, and then the die pushes the billet.

(4), three punches: the blank enters the third die, and is cut by the hexagonal die, and the hexagonal head of the blank is initially formed. Then, the back die pushes the blank into the third die, and the cut is cut from the hexagon. , hexagonal head formation.

2. Hex bolts (three-mode three-stroke)

3, screws (general head type one die two punch)

(1), cutting: through the movable scissors one-way movement, the wire stuck in the cutting die is cut into the desired blank.

(2) One punch: The die is fixed, and a die is initially formed to make the next stroke fully formed. When the product is a word cutting groove, a die is a concave, elliptical groove, and when the product is a cross groove, a die is a concave square groove.

(3), two punches: After a punch, the punch runs as a whole, the second die moves to the front of the die, and the second die moves forward to form the final product. The billet is then pushed out by the back punch.

Third, hot hit

1. Heating: In the heating equipment, the end of the blank to be molded is heated to a white hot state, and the heating temperature and time are set according to the product specifications. Generally, it is heated for 3-10 seconds or less for 7-10 seconds, and 7/8-1" is heated for about 15 seconds.

2. Molding: The heated billet is quickly moved to the molding machine, through the rear seat, the clamp is fixed, and the head mold impacts the billet and is molded. The distance of the rear seat can be adjusted according to the length of the blank.

3. Bundle: Use the extrusion on the beam bar to shrink the product.

Hot hits are also called red hits.

Fourth, the nut molding:

(1) Operational process:

1. Cutting: The inner die (410) is matched with the shearing knife (301) to cut the wire into the desired blank.

2. One punch: The front die (111), the stroke die (411), and the back punch (211) are combined to shape the deformed cut blank, and the blank is pushed out by the back punch (211).

3. Two punches: the running clamp (611) combines the blank from one punch to the second punch, and is matched by the front die (112), the stroke die (412), and the rear punch bar (412) to further shape the blank, and The flattening and satiety of the first punch are enhanced, and then the blank is pushed out by the back punch (212).

4. Three punches: the running clamp (612) clamps the blank from the second punch to the third punch, and is matched by the front die (113), the stroke die (413), and the rear punch bar (213), and the billet is again pressed to make The undershoot can be fully formed, after which the blank is pushed out by the back punch (213).

5. Four punches: the running clamp (613) clamps the blank from the three punches to the four punches, and is matched by the front die (114), the stroke die (414), and the rear punch bar (214), and the nut is completely formed and borrowed. The thickness of the iron is controlled to adjust the thickness of the nut, and then the blank is pushed out by the back punch (214).

6. Five punches: the running clamp (614) clamps the blank from the four punches to the five punches, and is matched by the front die (119) and the stripping plate (507) to punch the completely formed blank and make the punch. The iron filings enter the punching die and the core is finally formed. The head mark of the nut is formed during this process.

Screw production process (5) - tooth decay

I. Purpose: Twist or tap the formed semi-finished product to achieve the required thread. Practically, bolts (screws) are called fangs, teeth are called rolling teeth, and nuts are called tapping.

Second, tooth decay: fangs is to fix a piece of dental plate, another movable tooth plate drives the product to move, and the product is plastically deformed by extrusion to form the required thread.

Third, tapping: tapping is the formed nut, using the tapping and tapping to form the required thread.

4. Rolling: The rolling teeth are two corresponding screw rollers that rotate in the forward direction, and use the extrusion to plastically deform the product to form the required thread. Rolling teeth are usually used for tooth bars.

Screw production process (6) - heat treatment

First, the heat treatment method: different heat treatment methods can be selected according to the object and purpose.

Quenched and tempered steel: high temperature tempering after quenching (500-650 ° C)

Spring steel: medium temperature temper after quenching (420-520 °C)

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

After the low carbon and medium carbon (alloy) steels are quenched into martensite, the general rule is that the strength decreases and the plasticity and toughness increase as the tempering temperature increases. However, due to the different carbon content in low and medium carbon steels, the tempering temperature has different effects on them. Therefore, in order to obtain good comprehensive mechanical properties, the following approaches can be taken separately:

(1) Select low-carbon (alloy) steel, and after quenching, temper at a low temperature of 250 ° C or lower to obtain low-carbon martensite. In order to improve the surface wear resistance of such steels, only the carbon content of each surface layer is increased, that is, surface carburization is performed, which is generally called carburized structural steel.

(2) Adopt medium carbon steel with high carbon content, and temper at high temperature (500-650 °C) after quenching (so-called quenching and tempering treatment), so that it can maintain sufficient strength under high plasticity, generally called This type of steel is quenched and tempered steel. If you want to obtain high strength, but prefer to reduce plasticity and toughness, low-temperature tempering can be achieved for gold-containing tempering with lower carbon content, so-called "ultra-high-strength steel" is obtained.

(3) Steel grades with carbon content between medium carbon and high carbon (such as 60, 70 steel) and some high carbon steel (such as 80, 90 steel), if used to manufacture springs, in order to ensure high elasticity At the limit, yield limit and fatigue limit, moderate temperature tempering after quenching is used.

(4) Decarburization: refers to the loss of carbon on the surface of ferrous materials (steel). Decarburization will occur after heat treatment, slight decarburization is allowed, and the depth of the decarburization layer affects the surface hardness. The deeper the decarburization layer, the smaller the surface hardness value.

Specific testing basis GB3098.1

Second, the operation process:

Annealing (pearlitic steel)

1. Pre-heat treatment: normalizing

High temperature tempering (martensitic steel)

(1) The purpose of normalizing is to refine the grains, reduce the degree of banding in the structure, and adjust the hardness to facilitate mechanical processing. After normalizing, the steel has equiaxed fine grains.

2. Quenching: The steel body is heated to about 850 °C for quenching. The quenching medium can be selected according to the size of the steel and the hardenability of the steel. Generally, water or oil or even air quenching can be selected. The steel in the quenched state has low plasticity and large internal stress.

3. Tempering:

(1) In order to make the steel have high plasticity, toughness and appropriate strength, the steel is tempered at a high temperature of about 400-500 °C, and the steel which is sensitive to temper brittleness must be rapidly cooled after tempering to suppress tempering. Brittleness occurs.

(2) If the part is required to have a particularly high strength, it is tempered at about 200 ° C to obtain a medium carbon tempered martensite structure.

(2) Spring steel:

1. Quenching: oil quenching at 830-870 °C.

2. Tempering: tempering at about 420-520 °C to obtain tempered troostite structure.

(3) Carburizing steel:

1. Carburizing: A type of chemical heat treatment in which a C element is infiltrated into the surface of a steel member in an active medium containing a certain chemical element at a certain temperature. Preheating (850 ° C) Carburizing (890 ° C) Diffusion (840 ° C) process

2, quenching: carbon and low alloy carburizing steel, generally using direct quenching or one quenching.

3. Tempering: low temperature tempering to eliminate internal stress and improve the strength and toughness of the carburized layer.

Screw production process (7) - surface treatment

   First, the type of surface treatment:

Surface treatment is a process of forming a coating layer on the surface of a workpiece by a certain method. The purpose of the surface treatment is to impart an aesthetically pleasing and anti-corrosive effect on the surface of the workpiece. The surface treatment methods are all attributed to the following methods:

1. Electroplating: The electroplated component is immersed in an aqueous solution containing the deposited metal compound, and an electric current is passed through the plating solution to cause the electroplated metal to be deposited and deposited on the component. Generally, plating is performed by galvanizing, copper, nickel, chromium, copper-nickel alloy, etc., and boiled black (blue), phosphating, and the like are sometimes included.

2. Hot dip galvanizing: This is accomplished by immersing the carbon steel component in a plating bath of molten zinc at a temperature of about 510 °C. The result is that the iron-zinc alloy on the surface of the steel piece gradually becomes passivated zinc on the outer surface of the product. Hot dip aluminizing is a similar process.

3. Mechanical plating: The surface of the product is impacted by the particles of the coated metal, and the coating is cold welded to the surface of the product.

Second, quality control:

The quality of electroplating is based on its corrosion resistance, followed by appearance. Corrosion resistance is to imitate the working environment of the product, set as the test condition, and conduct corrosion test. The quality of electroplated products is controlled in the following ways:

1. Appearance:

The surface of the product is not allowed to be partially uncoated, charred, rough, dull, peeled, crusted and marked. It is not allowed to have pinhole pitting, black plating, loose passivation film, cracking, shedding and serious Passivation traces.

2, coating thickness:

The working life of a fastener in a corrosive atmosphere is proportional to its coating thickness. The recommended economical plating thickness is generally 0.00015 in to 0.0005 in (4 to 12 um).

Hot dip galvanizing: The standard average thickness is 54 um (the nominal diameter ≤ 3/8 is 43 um) and the minimum thickness is 43 um (the nominal diameter ≤ 3/8 is 37 um).

3. Plating distribution:

Different deposition methods use different ways of depositing the coating on the surface of the fastener. The plating metal is not uniformly deposited on the peripheral edge during plating, and a thicker coating is obtained at the corner. In the threaded portion of the fastener, the thickest coating is located on the crest of the thread, gradually thinning along the side of the thread, depositing the thinnest at the bottom of the tooth, while hot dip galvanizing is just the opposite, thicker coating is deposited inside the corner and At the bottom of the thread, the mechanical plating of the plated metal tends to be the same as that of hot dip coating, but is smoother and much more uniform over the entire surface.

   4, hydrogen embrittlement:

During processing and handling of the fasteners, particularly during pickling and caustic washing prior to plating and subsequent plating, the surface absorbs hydrogen atoms and the deposited metal coating then captures hydrogen. When the fastener is tightened, hydrogen is transferred to the most concentrated portion of the stress, causing the pressure to increase beyond the strength of the base metal and creating a slight surface crack. Hydrogen is particularly active and quickly penetrates into newly formed fissures. This pressure-fracture-infiltration cycle continues until the fastener breaks. Usually occurs within a few hours after the first stress application.

In order to eliminate the threat of hydrogen embrittlement, the fasteners are heated and baked as quickly as possible after plating to allow hydrogen to ooze out of the coating. Baking is usually carried out at 375-4000 F (176-190 ° C) for 3-24 hours.

Since mechanical galvanizing is non-electrolytic, this virtually eliminates the threat of hydrogen embrittlement. In addition, due to engineering standards, fasteners with hardness higher than HRC35 (Inch Gr8, metric 10.9 or higher) are prohibited from hot dip galvanizing. Therefore, hot dip-plated fasteners rarely suffer from hydrogen embrittlement.

5, adhesion:

Cut or squat with a solid tip and considerable pressure. If the coating is peeled off in the form of a sheet or a skin in front of the cutting edge so that the base metal is exposed, the adhesion is considered insufficient.


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