The Etched Stainless Steel is immersing the metal parts in an etching solution composed of various chemical components. After a certain period of reaction at room temperature or under heating, the metal to be etched slowly dissolves and eventually reaches the required etching depth, so that the surface of the metal parts reveals decorative text or patterns with a concave and convex three-dimensional sense.
The etching process is the self-dissolution of metal in a chemical solution, the corrosion process. This dissolution process can be carried out according to chemical mechanisms or electrochemical mechanisms, but since the metal solutions, and etching are all general acid, alkali, and electrolyte solutions. Therefore, chemical etching of metals should be carried out according to the electrochemical dissolution mechanism.
Etching Technology
A processing technology that uses the erosion of the metal surface to remove metal from the metal surface.
(1) Electrolytic Etching
Using the master mold as a conductive cathode and the electrolyte as a medium, the etching is concentrated on the processing part.
(2) Chemical Etching
A method that uses a chemical-resistant film to remove the etching erosion and concentrate the action on the desired part.
Photo-etching process
A processing technology that forms a layer of photosensitive chemical-resistant film (photoresist) evenly on the metal surface, and then exposes the original image to ultraviolet light, etc., and then performs imaging treatment to form a coating layer of chemical-resistant film of the desired shape. Then, the exposed part is chemically or electrochemically corroded by the acid or alkali solution in the etching bath to dissolve the metal.
(3) Characteristics of Chemical Etching Technology
• No tools such as electrodes and masters are required, so there is no need for maintenance costs for these tools.
• The time required from planning to production is short, and short-term processing is possible.
• The physical and mechanical properties of the material are not affected by processing.
• Processing is not limited by shape, area, or weight.
• Processing is not limited by hardness or brittleness.
• All metals (iron, stainless steel, aluminum alloy, copper alloy, nickel alloy, titanium, and Steller alloy) can be processed.
• High-precision processing is possible.
• Complex, irregular, and discontinuous design processing can be applied.
• The processing efficiency is good for a large area, but its efficiency is worse than that of mechanical processing for a small area.
• Horizontal cutting is easy to obtain high precision, but it is not easy to obtain the same precision of mechanical processing in-depth and vertical direction.
• The composition of the processed object should be uniform. It is not easy to process uneven materials smoothly.
Thickness Range of Etching Processing
Generally speaking, the range of metal etching processing is between 0.02-1.5mm. For materials with a thickness greater than 1.5, the etching processing time is very long and the cost is very high. It is not recommended to use etching processing technology. Stamping, wire cutting, or laser can be selected. But if there is a requirement for half-engraving, etching processing technology is needed!
Advantages and Characteristics of Etching Processing
Etched stainless steel processing has a larger production capacity than stamping processing, higher efficiency, short R&D cycle, and fast adjustment speed. The biggest feature is: that it can be half-engraved, and different height effects can be made on the same material. The most common uses are LOGO and various exquisite patterns, which are effects that stamping technology cannot achieve!
Selection and Use of Several Stainless Steel Etching Processing Materials
Stainless Steel Material Selection
Many variable factors represent the characteristics of the corrosive medium, namely chemicals and their concentrations, atmospheric conditions, temperature, and time, so if the exact properties of the medium are not understood, it is difficult to use and select materials. However, the following can be used as a guide for selection:
Type 304 is a widely used material. It can withstand general rust in construction, can withstand corrosion from food processing media (but high-temperature conditions containing concentrated acids and chloride components may cause corrosion), and can withstand organic compounds, dyes, and a wide variety of inorganic compounds.
Type 304L (low carbon) has good resistance to nitric acid and is durable to sulfuric acid at moderate temperatures and concentrations. It is widely used as liquid gas storage tanks, low-temperature equipment (304N), utensils and other consumer products, kitchen equipment, hospital equipment, vehicles, and wastewater treatment equipment.
Type 316 contains slightly more nickel than Type 304 and 2%-3% molybdenum. It has better corrosion resistance than Type 304, especially in chloride media that tend to cause primary corrosion. Type 316 has been developed for use in sulfite pulpers because of its resistance to sulfuric acid compounds. Moreover, its use has been extended to handle many chemicals in the process industry.
Type 317 contains 3%-4% molybdenum (also the highest level obtained in this series) and contains more chromium than Type 316, which has higher resistance to pitting and crevice corrosion.
Type 430 has a lower alloy content than Type 304 is used for high-polish decorative applications in mild atmospheres, and can also be used in nitric acid and food processing equipment.
Type 410 has the lowest alloy content of the three general-purpose stainless steels and is selected for high-load-bearing parts that require a combination of strength and corrosion resistance, such as fasteners. Type 410 resists corrosion in mild atmospheres, moisture, and many mild chemical media.
Type 2205 is superior to Types 304 and 316 because it has high resistance to chloride stress corrosion cracking and has about twice the strength. 316 stainless steel plate, 316 stainless steel pipe, 316 stainless steel strip
304 Etched Stainless Steel Material H-TA Means
It refers to the flatness requirements of etched stainless steel. H represents hardness, and the minimum hardness of Japanese imports is 370 or above. TA represents stress relief treatment, which means that an annealing treatment is added during the production process. TA = TENSION ANNEALED FINISH, which is made by Nichikin itself and has flatness requirements.
For example: SUS304-CSP-H has no relevant flatness requirements, SUS304CSP-H -TA has flatness requirements, and TA materials are widely used in precision accessories such as automobiles, mobile phones, optics, and machinery!
Metal Etching Processing Method
(1) Masking Operation
Most molds have complex shapes, and the surface that needs to be etched is rarely just a flat surface. Instead, there are three-dimensional planes, two-dimensional curved surfaces, three-dimensional curved surfaces, and deep flat curved surfaces. During processing, the processing surface and the non-processing surface must be separated, and the non-processing surface must be completely protected from corrosion.
To separate the processing and non-processing areas, the non-processing area is covered with chemical-resistant coatings or tapes, which is called masking.
Because the chemical used for etching is an aqueous solution, any small gaps or holes that are exposed will invade, so masking must be perfect, so it must be repeated several times, and the required operation time accounts for 30%~40% of the total operation time.
(2) Pattern Forming Operation
In the range to be processed, the coating operation is carried out according to the processing pattern, and the parts to be etched are separated from those not to be etched. This operation includes photography, the China method, meat adding method, the pear skin method, etc. Due to the different processing objects or processing procedures, the operation method should be appropriately selected.
(3) Etching Operation
The chemical is poured or immersed in the exposed mold to be processed, and only the exposed part is dissolved and removed. The solution used is an acidic aqueous solution, and the concentration is diluted to a controllable range.
The higher the concentration, the higher the temperature, the faster the etching speed, and the longer the contact time between the etching solution and the processing surface, the more etching is done. After etching, the chemical attached to the entire mold is washed with water, neutralized with an alkaline aqueous solution, and finally fully dried.
(4) Post-Processing
After etching, the mold cannot be shipped yet. The paint or tape used for masking must be removed. It is also necessary to confirm whether the etching is uniform. For example, if the etching is uneven due to poor welding or mold material, it must be trimmed.
If necessary, remove the pattern coating on the etched surface, leaving only the masking of the non-processed surface, and then perform a lightly etched pickling operation or sandblasting to make the etched surface uniform and shiny.
• Sandblasting
Sandblasting is a method of using the power of air or water and air to spray sand-like hard particles onto the metal surface to form a frosted glass-like fine rough state on the surface.
Etching is a chemical surface treatment method, which sometimes affects the appearance of the finished product. Sandblasting is a physical method to solve problems that are difficult to solve with chemical methods.
Can be divided into
- (1) Full gloss (100%): glass beads
- (2) Semi-gloss (50%): 50% glass + 50% corundum
- (3) Matte (0%): corundum (aluminum oxide sand)
Due to the different resin materials used and the differences in injection molding conditions, it is difficult to completely adjust the gloss with a single sandblasting process, so it must be repeated many times.
What you should know about mold etching operations
• Etching
Leather products have various touches. During the manufacturing process, the wrinkles formed will show a soft appearance. This wrinkle is the prototype of the so-called “etching”. The method developed to reproduce this texture in plastic products is etching processing. There are also:
- ◎ Line etching: points or lines are continuously gathered
- ◎ Fabric etching: fabric is used as the prototype
- ◎ Wood etching: the tube presented by wood
- ◎ Pattern etching: geometric patterns are gathered
- ◎ Pear skin etching: such as frosted glass, with a matte surface
- ◎ Letters and numbers are used to indicate the scale of mass or containers
Things with a flat shape and can be represented by a black and white manuscript can be processed by etching.
Pear skin etching is more commonly used on plastic molds, that is, pear ground pattern (fine pattern) and leather pattern (coarse pattern).
Most metals and alloys are unreactive to molecular nitrogen at high temperatures, but atomic nitrogen can react with many steels. And penetrate the steel to form a brittle nitride surface layer. Iron, aluminum, titanium, chromium, and other alloying elements may participate in these reactions. The main source of atomic nitrogen is the decomposition of ammonia.
Ammonia decomposition occurs in ammonia converters, heaters for ammonia production plants, and nitriding furnaces operating at 371°C~593°C and one atmosphere ~10.5Kg/mm2. In these atmospheres, chromium carbide appears in low-chromium steel. It may be corroded by atomic nitrogen to produce chromium nitride and release carbon to react with hydrogen to produce methane.
As mentioned above, white spots and cracks may be generated at this time or one of them. However, if the chromium content exceeds 12%, the carbides in these steels are more stable than chromium nitride, so the previous reaction will not occur, so stainless steel is now used in high-temperature environments of hot ammonia.
The state of stainless steel in ammonia depends on temperature, pressure, gas concentration, and chromium and nickel content. Field experimental results show that the corrosion rate (altered metal depth or carburization depth) of ferritic or martensitic stainless steel is higher than that of austenitic stainless steel, and the higher the nickel content of the latter, the better the corrosion resistance.
The corrosion rate increases with the increase in content. Austenitic stainless steel is severely corroded in high-temperature brine vapor, and fluorine has a greater corrosive effect than chlorine. For high Ni-Cr stainless steel, the upper-temperature limit in dry gas is 249°C for fluorine and 316°C for chlorine.
Problems to be Paid Attention to During Etching Processing
Processing Area:
The processing area of stainless steel parts should be relatively fixed. The platform of the stainless steel etching processing area should take isolation measures, such as laying rubber pads, etc. The stainless steel etching processing area should avoid damage and contamination to stainless steel parts.
Cutting:
The cutting of stainless steel parts adopts shearing, plasma cutting, sawing, etc. Mechanical processing:
Stainless steel parts should also be protected during machining such as turning and milling. When the work is completed, the oil, iron filings, and other debris on the surface of the workpiece should be cleaned.
Forming Processing:
During the process of rolling and bending, effective measures should be taken to avoid scratches and creases on the surface of stainless steel parts.
Reduce side erosion and protrusions, and improve the etching processing coefficient
Side erosion produces protrusions. Usually, the longer the printed board is in the etching solution (or using an old-fashioned left-right swing etching machine), the more serious the side erosion. Side erosion seriously affects the accuracy of printed conductors, and severe side erosion will make it impossible to make fine conductors.
When side erosion and protrusions are reduced, the etching coefficient increases. A high etching coefficient indicates the ability to maintain fine conductors, making the etched conductors close to the original size.
Whether the electroplating etching resist is tin-lead alloy, tin, tin-nickel alloy, or nickel, excessive protrusions will cause the conductors to short-circuit. Because the protrusions are easy to break, an electrical bridge is formed between the two points of the conductor.
Improve the consistency of the etching processing rate between boards
In continuous board etching, the more consistent the etching processing rate, the more uniformly etched the board can be obtained. To achieve this requirement, it is necessary to ensure that the etching solution is always kept in the best etching state throughout the etching process. This requires the selection of etching solutions that are easy to regenerate and compensate for, and the etching rate is easy to control.
Select processes and equipment that can provide constant operating conditions and automatic control of various solution parameters. This is achieved by controlling the amount of dissolved copper, pH value, solution concentration, temperature, uniformity of solution flow (spray system or nozzle and nozzle swing), etc.
Improve the uniformity of the etching processing rate on the entire board surface
The etching uniformity of the upper and lower surfaces of the board and various parts on the board surface is determined by the uniformity of the etchant flow rate on the board surface. During the etching process, the etching rates of the upper and lower board surfaces are often inconsistent.
Generally speaking, the etching rate of the lower board surface is higher than that of the upper board surface. Because there is solution accumulation on the upper board surface, the etching reaction is weakened.
The uneven etching of the upper and lower board surfaces can be solved by adjusting the spray pressure of the upper and lower nozzles. A common problem with etching printed circuit boards is that it is difficult to etch the entire board surface cleanly at the same time. The edge of the board etches faster than the center of the board.
Using a spray system and swinging the nozzle is an effective measure. Further improvement can be achieved by making the spray pressure at the center and edge of the board different and intermittently etching the front and back ends of the board to achieve uniform etching of the entire board surface.
Hazards of Stainless Steel Etching and Chemical Fumes to Operators
The corrosive materials used in this special processing method of chemical etching will have a great impact on the health of operators. Two important aspects of metal etching will harm human health.
1. The Impact of Etching Solution
Metal etching is carried out in strong acid or strong alkaline corrosive solutions. There will also be fluorides in the corrosive solution for titanium and high alloy steel, especially a large amount of fluorides will be used in the etching of titanium, which has a greater impact on human health.
These corrosive solutions can easily etch away metal materials, and obviously will also corrode or destroy human tissue cells. Therefore, it is extremely important to control the composition and concentration of corrosive agents in production.
All staff engaged in chemical etching or related work must be fully trained and wear necessary work clothes according to the nature of the work and job requirements to prevent splashing strong acids and alkalis from causing harm to the staff. Such accidents are caused by splashing of corrosive liquid or accidentally splashing or overturning when preparing corrosive liquid or carrying acid,
which means that a large amount of strong acids such as sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid are out of control and pose a threat to operators and other personnel.
As long as we take precautions seriously in production, serious accidents rarely occur. But this does not mean that we can relax our vigilance. Many accidents often happen when we think they will not happen, and once such accidents happen, the consequences are often very serious.
2. The Impact and Treatment of Various Etching Gases and Fumes
A large amount of acid mist or alkaline mist will be produced during the metal etching process. These fumes will not cause any damage to the surface of the human body but will cause damage to the human respiratory system, even very serious damage. Therefore, when carrying out etching processing, special attention should be paid to the reliability of the exhaust facilities in the etching room.
The reliability of the exhaust facilities mentioned here does not simply discharge these acid mists and alkaline mists directly to the surrounding environment but must be discharged after neutralization treatment.
Otherwise, the untreated acid mist and alkaline mist are directly discharged, which will also cause harm to the surrounding personnel, seriously pollute the atmosphere, and damage the environment. For those etching processes that are prone to strong corrosive gas escape, a closed etching room can be used for remote-control corrosion.
The following are common corrosive agents that are harmful to human health. Nitrogen oxide gases produced in metal etching, polishing, and other processes not only cause serious harm to the staff but also have serious effects on the environment and atmosphere.
Corrosive hazards of aluminum alloys: splashing onto skin, face, eyes, etc.
There are two types of mist hazards:
(1) Hydrogen generated during etching. Although hydrogen is harmless to the human body and the environment, high concentrations of hydrogen are prone to explosion;
(2) Alkaline mist generated during etching: Since the concentration of NaOH in the alkaline corrosive solution of aluminum is high and the etching process is carried out under high temperatures, a large amount of alkaline mist will be generated. The alkaline mist will form aerosols in the air and stay for a long time.
Inhalation of the human body will seriously damage the respiratory system. At the same time, these alkaline mists discharged into the environment will also cause secondary pollution to the ecology of the surrounding environment.
Corrosive hazards of steel/nickel alloys: Strong corrosive liquid splashes onto the skin, face, eyes, etc. At the same time, hydrofluoric acid is particularly dangerous to the human body.
Hazards of mist: Corrosive and suffocating mists will cause harm to both producers and the environment. The nitrogen oxides and HCl mist produced by etching are very destructive to the atmosphere and also endanger the human respiratory system and nervous system
Corrosive agent hazards of copper alloys: corrosive liquid splashes on the skin, face, eyes, etc. The emission of high-valent iron and inhalation by the human body will cause great harm
Hazards of mist: corrosive and suffocating mist will cause harm to producers and the environment
The various corrosive agents used in chemical etching and the various corrosive and toxic gases produced during the etching process are far more harmful to the human body than those listed above, and these corrosive and toxic gases are even more harmful to the environment and atmosphere after being discharged into the air.
So when we are still designing a chemical etching plant, we must consider the harm of these negative factors to the human body and the environment. We are engaged in this work not only for profit, but more importantly to protect the health of personnel and a good ecological environment.
3. Hazards and treatment of hydrochloric acid to staff
High concentrations of hydrochloric acid have an irritating effect on the nasal mucosa and conjunctiva, which will cause corneal turbidity, hoarseness, suffocation, chest pain, rhinitis, coughing, and sometimes blood in sputum.
Hydrochloric acid mist can cause severe pain in the eyelids and skin. If an accident occurs, the injured should be immediately moved to fresh air for oxygen, eyes and nose should be cleaned, and mouthwash should be rinsed with 2% soda water.
If concentrated hydrochloric acid splashes on the skin, it should be immediately rinsed with plenty of water for 5-10 minutes, and soda slurry should be applied to the burned surface. Severe cases should be sent to the hospital for treatment immediately. The maximum allowable concentration of hydrochloric acid in the air is 5mg/m3
4. Hazards and treatment of H3PO4 to workers
H3PO4 vapor can cause atrophy of the nasal mucosa, has a strong corrosive effect on the skin, can cause skin inflammation and muscle damage, and even cause systemic poisoning. The maximum allowable amount of H3PO4 in the air is 1mg/m3. If the skin is accidentally touched during work, it should be immediately rinsed with plenty of water.
After washing out the H3PO4, it can generally be applied to the affected area with red mercury or gentian violet solution. In severe cases, it should be sent to the hospital for treatment.
5. Commonly Used Metal Etching Materials
SUS304 SUS301 Mechanical properties introduction: For etching process, SUS304 material performance is more suitable for etching processing. SUS301 is harder and will have defects such as burrs and rough hole walls during etching.