Antirust treatment in heat treatment plant

Corrosion products on metal surfaces are collectively referred to as "rust". Due to the heat treatment workshop salt, acid, alkali, harmful gas and other corrosion factors, time is potential corrosion crisis, a little careless will rust, pitting. Therefore, we pay attention to the heat treatment process before the topic, heat treatment products must be done to prevent rust.

Heat treatment products rustproof procedure

(1) all kinds of products after heat treatment must be temporarily treated with anti-rust by the heat treatment workshop. All anti-rust shall be prepared and analyzed by the workshop according to the process. The workshop shall be responsible for the cleaning, safety and adjustment of the tank liquid.

(2) for the products (except annealing and tempering parts) sent into the intermediate warehouse of the relevant workshop after the heat treatment, each intermediate warehouse shall, in addition to the acceptance specifications and quantity, also check whether the heat treatment has anti-rust treatment and what is the surface quality? If there is any problem, feedback to heat treatment workshop immediately.

(3) wip stored in the intermediate warehouse for more than a week should be re-checked and anti-rust treatment, and covered with a plastic sheet to prevent direct contact with rain, moisture and other harmful factors to cause corrosion to the product.

(4) when the interval between the two processes exceeds 5h (8h in winter), the heat treatment workshop must have anti-rust measures.

(5) anti-rust treatment must be carried out when the workpiece self-heat treatment workshop enters the intermediate warehouse. The products stored in the intermediate storehouse should be inspected once a week and re-rustproof if necessary.

(6) when the product is hot washed, rinse the product up and down several times in the cleaning solution, and then place the product in the cleaning solution for 2 ~ 3min. The temperature of the cleaning solution is ≥80℃. The bath solution is changed every three days.

(7) when the product is cleaned with kerosene at room temperature, it should also be rinsed up and down several times, or cleaned with a brush, slightly drained. Kerosene is filtered weekly and replaced monthly.

(8) when the product is immersed in anti-rust oil, the product must be moved up and down in the anti-rust tank several times to make the anti-rust oil immersed and coated evenly; Large products can be coated method, but must also cover the product surface, leaving no dead corners.

(9) before the products are sent to the finished products warehouse, they must be cleaned and rust-proof. In case of bad weather such as fog, cloudy and rainy days, they must be covered with film to prevent corrosion and rust.

Precautions against rust in heat treatment

(1) the raw materials used for rust prevention, such as NaNO2, Na2 CO3, rust prevention oil, kerosene, gasoline, etc., shall be stored safely and kept by special person, and shall not be inhaled into human body, in case of poisoning, fire and other safety accidents.

(2) in the course of operation, if the poison of sodium nitrite solution and rust prevention solution accidentally enters the eye, rinse with clean water immediately and go to the hospital for emergency treatment if necessary.

(3) the cleaning liquid tank and anti-rust liquid tank should be placed in the designated place, and the liquid tank should be covered. If the operators leave the working place for a long time, especially during the small vacation, the workshop should designate a special person to maintain the liquid tank safely.

(4) products that have been coated with antirust liquid or antirust oil shall not be touched by bare hands to prevent sweat and other erosion.

(5) wash hands with soap before work or meals.

(6) in case of fire, the usually prepared foam fire extinguisher or yellow sand shall be used to remove it, and the power shall be cut off first, it is forbidden to use water or acid and alkali fire extinguishers.

Black finish

Blackening treatment is a method of surface oxidation treatment, mainly used for carbon steel and low alloy steel, also suitable for high speed steel, generally used is low temperature alkaline blackening, not suitable for normal temperature blackening. After blackening treatment, a layer of magnetic Fe3 O4 is generated on the surface of the steel. The structure is relatively dense and the thickness is 0.6-0.8 m.

On the surface of the metal rust protection.

Increase the surface of the workpiece gloss and beautiful.

Further eliminate quenching and tempering stress.

Blackening operation specific steps:

(1) oil removal

The purpose is to prepare for pickling and oxidation, kerosene cleaning can be used, often using chemical oil removal method, formula is: 100g/L NaOH+30g/L Na2 CO3 +30g/L Na3 PO4, 85 ~ 100℃×15 ~ 30min.

(2) basket loading

Black workpiece should not be too close, to ensure that there is a certain gap between the workpiece, as far as possible to do point contact between the workpiece, the size of the pieces should be installed separately, to prevent the collision between the workpiece, especially after the alignment of the workpiece to pay more attention.

(3) wash with boiling water

New water must be changed before each blackening, center drilling, slot milling cutter and other small tools must be cleaned, boiling time is not less than 1h.

(4) pickling

Its purpose is to remove the rust and oxide skin on the workpiece, increase the surface activity, suitable for oxidation. In order to reduce the negative effect of pickling, corrosion inhibitor and fog inhibitor are often added to the acid.

Pickling time: (1) drill bit, center drill and three side milling cutter 10 ~ 15min. Middle tooth saw blade milling cutter 8 ~ 10min. After counter - attack knives shall not be pickling. The scum and sundries on the surface of pickling tank should be removed in time, and the tank liquid should be checked frequently for timely adjustment.

(5) cold water cleaning

After pickling, the workpiece is lifted up and down in the flowing clean water, turning left and right, repeatedly more than 5 times, to ensure that the acid attached to the workpiece clean.

(6) black

Alloy steel and high speed steel blackening formula: 600 ~ 620g/LNaOH+100g/L NaNO2 +20 ~ 40g/L Na3 PO4, the rest is water. Furnace temperature 142℃, blackening temperature 145 ~ 146℃. Blackening time 40 ~ 60min.

Carbon steel workpiece blackening formula: 550 ~ 600g/L NaOH+100 ~ 150g/L NaNO2 +15 ~ 20g/L Na3 PO4, the rest is water. The furnace temperature was 142℃, the blackening temperature was 145 ~ 148℃, and the blackening time was 60 ~ 70min.

(7) cold water cleaning

Lift it up and down in running tap water and turn it around several times to ensure that the blackening liquid attached to the workpiece is washed clean.

(8) saponification

Dissolve 20 bars of soap (sliced) into 200L water and saponify them at 80 ~ 90℃×2 ~ 5min.

(9) blackening quality inspection

Check items before oiling after saponification include:

Appearance: high speed steel black and brown; 9SiCr steel tan; Carbon steel and general alloy steel black. The edge of the tool that is no longer ground is not allowed to have speckle and rust.

(2) oxidation film porosity: titrate with 3% CuSO4, in 30 seconds without copper color is qualified.

(3) firmness inspection: oxide film is not allowed to fall off, is not allowed to exist hand wipe and other traces.

Rustproof code for heat treatment of products

This code is applicable to the anti-rust of the product after sandblasting. The surface of the anti-rust product should be uniform white without speckle and other macroscopic defects.

(1) rust prevention process and process conditions

1) basket: the product basket should be as few as possible, and the load of two baskets should not exceed the height of the basket.

2) hot water cleaning: the basket should be lifted up and down for several times to wash away the residual sand and dust on the surface of the workpiece and achieve the purpose of preheating.

3) anti-rust: put the product into the anti-rust tank and lift it up and down for 3 ~ 5 times, further wash the surface attachment, improve the quality of anti-rust film, and lift it again for 3 ~ 5 times when the tank is out.

Preparation method: firstly, water was poured to 2/3 of the tank capacity, and the temperature was raised to 50 ~ 70℃. Then, all the Na2 CO3 and NaNO2 to be prepared were added, mixed to dissolve them, and then water was added to the specified height of the tank solution, which was prepared strictly according to the seasonal requirements.

4) drying: after the product is taken out of the anti-rust tank, it should be timely dried by a fan or compressed air.

(2) adjustment and replacement of anti-rust liquid

1) the antirust liquid should be kept clean, and hands washing and other sundries should not be brought into the antirust liquid tank.

2) analyze the tank solution 2 to 3 times a week, and adjust accordingly.

3) the anti-rust liquid shall be replaced once a month, and all the dirty things in and around the tank shall be cleaned and cleaned up.

Antirust liquid

Some of the workpiece after quenching, tempering due to various reasons did not transfer out of the heat treatment workshop in time, or because of National Day, the Spring Festival holiday, the processed workpiece need to stay in the workshop, the workpiece at this time must be immersed in antirust liquid or spray on it, to ensure that the workpiece will not rust in a short time. Anti-rust water shall have the following characteristics:

1) it is convenient to use, store and remove, friendly to the environment, and does not cause pollution to people, equipment and the environment.

2) convenient preparation, according to the specific conditions of heat-treated parts with different concentrations.

3) it is applicable to all kinds of working conditions, including immersion, soaking, spraying and brushing. It is suitable for both hot and cold.

4) low price and high quality, save oil.

5) safe from fire.

6) relatively stable, not easy to aging.

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