WHY DOES THE SPRING NEED STRESS RELIEF ANNEALING?

The spring stress is generated during the rolling spring process. The original straight steel wire is wound into a spring shape, so the spring will generate stress at each point, and the residual stress after heat treatment. For these stresses, heat treatment should be performed again. Remove the internal stress, otherwise the spring will break easily during work.

The coil spring rolled by the cold coil process generally uses a lead bath austempered cold drawn steel wire (carbon spring steel wire, piano wire) and oil quenched and tempered spring steel wire. Springs made from these steel wire cold rolls do not require quenching, but must be subjected to stress relief annealing. Stress relief annealing is often referred to simply as tempering, sometimes referred to as stress relief tempering or stress relief tempering.

The purpose of stress relief annealing is to:

1) Eliminate the internal stress of wire cold drawing and spring cold roll forming;

2) Stabilizing the size of the spring, the spring that has not been subjected to the stress relief annealing will have an increase in the outer diameter and dimensional instability during the subsequent processing and during use;

3) increase the tensile strength and elastic limit of the wire;

4) Use stress relief annealing to control the spring size. For example, the spring is sometimes placed on the fixture for stress relief annealing to adjust the height of the spring.


Our company is dedicated to the sales and communication of springs and spring machines. If you have any intention, please contact us.
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A Brief Summary of Spring Surface Treatment

The corrosion of springs can be divided into chemical corrosion and electrochemical corrosion according to the type of reaction. They are all the result of changes in metal atoms or electron gains and losses on the surface of the spring. Spring anti-corrosion methods generally use a protective layer, which can be divided into: metal protective layer, chemical protective layer, non-metal protective layer, and temporary protective layer according to the nature of the protective layer. The first three methods are emphasized here.

 

Stainless steel springs and copper wire springs have a certain anti-corrosion ability, so they are generally not treated with anti-corrosion.

1.Metal protective layer of spring

There are many types of metal protective layers. In the case of springs, electroplated gold is generally used to obtain metal protective layers. The plating protection layer can not only protect from corrosion, but also improve the appearance of the spring. Some electroplated metals can also improve the working performance of springs, such as increasing surface hardness, increasing anti-wear, improving thermal stability, and preventing radiation corrosion. However, if it is purely for the corrosion of the spring, electroplated zinc layer and electroplated cadmium layer should be generally used.

 

2.Chemical protection layer of spring

A chemical reaction method is used to form a dense protective film on the surface of the spring to prevent the spring from corrosion. Oxidation treatment and phosphating treatment are usually used. Oxidation treatment and phosphating treatment have low cost and high production efficiency. Generally, spring manufacturers use oxidation treatment as anticorrosive treatment.

 

3.Non-metal protective layer of spring

The non-metallic protective layer is a dip or spray coating of an organic substance on the surface of the spring, such as paint, asphalt, plastic, etc. to protect the spring from corrosion.

The non-metallic protective layer has a thicker film layer, good chemical stability, and better mechanical anti-corrosion effect, but has lower hardness and is easy to be scratched and damaged, and at the same time the film layer has aging phenomenon.

Our company is dedicated to the sales and communication of springs and spring machines. If you have any intention, please contact us.
Name:Luoyang Xian Heng Spring Machinery Co., Ltd.
Email: marketing@springcoiling.com
Tel: 0086-379-62265677
Fax: 0086-379-67878852
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Common Problems and Causes of Oil Quenched-tempered Spring Steel Wire

In our daily steel wire production, oil-quenched steel wires occupy a large part. Mastering the method of judging the quality of steel wires is very important for us to make a good spring.

The use of spring steel wire to judge the problem of oil quenching currently only stops on the surface of the wire and the entire shape. It is not easy to judge the deep interior. Today we will gradually analyze the surface and internal problems of the wire.

First, the surface quality defect

1. Surface crack: The linear cracks on the steel surface should generally be consistent with the forging or rolling direction.

Reasons for formation:Mainly because of wrinkles and thermal cracks during processing (forging, rolling, heat treatment and tempering) due to surface over-burning, decarburization, loosening, deformation and excessive internal stress, as well as high levels of sulfur and phosphorus impurities on the surface And cold cracks.

Surface cracks can be detected by visual inspection, pickling, magnetic particle inspection, color inspection and gold equivalent methods. When confirming cracks, we must pay attention to distinguish the cracks on the surface of the steel itself that are brittle and loose, and cracks that appear after slight bending, but the steel itself does not have cracks.

2. Heavy skin and folds: "Tongue" or "scaly" metal flakes adhered to the surface of the steel, forming overlaps on local surfaces with obvious folds.

Reason for formation: During the hot working process, due to burrs, depressions, inclusions, subcutaneous pores, and surface looseness on the billet, the metal rheologically changes during thermal deformation, and heavy skin and folds are formed on the surface.

3, Ear: The surface of the steel material extends along the rolling direction.

Reasons for formation: The gap between the rolling holes of the rolling mill is too large, which causes the surface of the steel to form protrusions along the pores.

4. Scratch: The surface of the steel is a linear or arc-shaped groove mark under the action of external force (the groove bottom can be seen). 

Second, internal defects

1. Segregation: In fact, it is a general term for the uneven distribution of chemical components in steel. On the acid leaching sample, when the segregation is an erodible substance or gas inclusions, it is dark and dark in color, irregular in shape, slightly concave, flat at the bottom, and there are many dense microporous spots. If it is a resist element, it is light in color, irregular in shape, and relatively smooth, slightly concave spots. According to the location and shape of segregation, they are generally classified into the following categories:

① Center segregation: dark and dark spots with irregular shapes appearing in the center.

② Ingot-type segregation: Dark-spotted spots concentrated on a closed band with different widths， which have the cross-sectional shape of the original steel ingot (usually square), so ingot-type segregation is also called box segregation.

③Spotted segregation: The spots are generally large, showing darker, slightly concave shapes, oval or melon seeds. Generally distributed, called general point segregation: those distributed on the edge of the steel are called edge point segregation.

Reason for formation: Segregation is the aggregation of certain elements caused by selective crystallization and diffusion during the ingot casting and solidification process. Segregation is unavoidable under normal production conditions. 

2. Looseness: The pores in the steel are generally irregular polygons on low magnification samples, and the sharp pits at the bottom usually appear in the segregated spots. In severe cases, there is a tendency to become spongy. According to the situation of loose distribution, they are divided into two categories: central loose and general loose:

① Loose center: there are concentrated voids and dark spots in the center of the low magnification sample. There is a slight interlayer on the longitudinal fracture. Under the microscope, you can see that pearlite increases in the center looseness, indicating that the carbon content in the center looseness increases.

②Generally loose: The tissue is dense on the low magnification sample, showing scattered small pores and small black spots. The pores are mostly irregular polygons or graphics, which are distributed on the entire cross section except the edge part.

Central loosening generally occurs at the head and middle of the steel ingot. The difference from ordinary loosening is that it is distributed on the steel section and the central part instead of the entire section. Generally, the higher the carbon content of the steel, the more severe the center porosity.

Reason for formation: During the solidification process of the steel ingot, due to the solidification and contraction of the low-melting-point material in the intergranular part and the release of gas, voids were generated, and the welded pipe was not equipped during the hot processing.

In steel, slight segregation and higher levels of porosity are allowed.

3. Inclusions: Inclusions include metal inclusions and non-metallic inclusions.

①Metal inclusions: Mainly due to defects caused by metal bars, sheets, and blocks falling into the ingot mold or iron alloy blocks added at the end of the smelting process during the casting process, which are not melted, and the edges are mostly clear. The color is significantly different from the surrounding geometry.

② Non-metallic inclusions: During the pouring process, there is no time to float out of the slag or the furnace lining peeled into the molten steel and refractory materials on the inner wall of the pouring system. After peeling off, leaving small round holes.

4. Shrinkage: On the low magnification sample, the shrinkage hole is located in the center, and there are often segregation, inclusions, or dense places around it. Sometimes, you can see caves or cracks before corrosion. After the corrosion, the pores became dark and irregularly wrinkled.

Reason for formation: When the ingot is poured, the last solidified part (heart) of the molten steel cannot be filled after the solidification and shrinkage, and the macroscopic holes left behind are not filled. The shrinkage holes are mainly formed at the ingot head (cap end).

5. Bubbles: On the low magnification sample, there are cracks that are approximately perpendicular to the surface, and there is a slight oxidation and decarburization phenomenon nearby. Below the surface, there are called subcutaneous bubbles, and deeper subcutaneous bubbles are called pinholes.

Causes: Defects caused by the gas produced during the ingot casting process and the gas released.

6. Crack: On the low magnification sample, the axis position cracks along the intergranular, forming a spider web, and when severe, it cracks radially.

Reasons for formation: There are mainly two types. One is internal tearing of the ingot due to some reason during solidification and cooling, which fails to weld during forging and rolling; the other is internal cracking due to improper forging. .

7. White point: On the low magnification sample, there are short cracks, which are generally concentrated in the steel, and there is almost no surface layer with a thickness of 20-30mm. Because cracks are not easy to distinguish, a fracture test should be added to verify. White dots appear as coarse silvery white dots on the fracture.

Reason for formation: It is generally believed that the effect of hydrogen and tissue stress is the small cracks caused by the combination of local pressure and the internal stress generated by the steel when the hydrogen is released and concentrated in the loose micropores to generate huge pressure.

Third, the external size defects

1, dimensional difference: including the length, diameter, thickness, positive and negative tolerances, grinding depth, width and other dimensions of the steel does not meet the requirements of the order standard.

2. Curvature: The steel is not straight in the length and width directions. The curvature of different materials has different names. Profiles are expressed by curvature; plates and strips are expressed by sickle, wave, and flutter.

3. Twisting: The steel bar is twisted into a spiral in the axial direction.

Common defects of steel wire

1. Scratching: Generally, the quality of phosphating is poor during the drawing process, and the wire drawing die is damaged and scratches the surface of the wire.

2. Local cracking: Generally belongs to local non-metallic inclusions or localized hardened phase structure in raw wire rods, subsequent drawing is not conducive to extension.

3. Crack: Generally belongs to the inheritance of raw material wire rods or the compression ratio of fine gauge steel wire is too large, which causes the internal stress of the steel wire to be too large.

4. Bending: Generally belongs to artificial handling and hanging bending

5. Ellipse: caused by drawing die ellipse

6. Decarbonization: caused by serious oxidation during genetic or heat treatment of raw materials

Common problems in spring production

1. Winding fracture:

① Local defects

② The spring winding ratio is small, and the hardness of the wire is too large

③ The hardened structure appears locally, and the material has poor ductility, which is generally related to the local segregation of the material

2. There is a sound of winding: the surface of the steel wire is not sufficiently lubricated, the surface oxide film is uneven or the material hardness is high

3. The spring diameter is unstable and the height is different: the performance of the wire rod is not good, or the setting of the winding machine is abnormal.

4. The fatigue life cannot meet the requirements:

① There are pits, scratches, abrasions, cracks, micro-cracks (improper shot peening) on the surface of the material, non-metallic inclusions on the surface, folding, decarburization, or severe segregation

② Improper spring design, uneven ends, stress concentration should at a certain point during fatigue test .

③ coarse material structure

④ Insufficient shot peening on the surface.

⑤ Insufficient tempering after spring winding, stress is not completely removed

This product is strictly forbidden from contact with acid and is easy to be brittle （hydrogen embrittlement）.

Our company is dedicated to the sales and communication of springs and spring machines. If you have any intention, please contact us.
Name:Luoyang Xian Heng Spring Machinery Co., Ltd.
Email: marketing@springcoiling.com
Tel: 0086-379-62265677
Fax: 0086-379-67878852
Whatsapp: 0086-1833 8852 671
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What are the maintenance and repair of the spring machine hydraulic system?

The hydraulic spring machine uses a spring as an energy storage component and a hydraulic oil as a transmission carrier. It has the advantages of small size, high reliability, low noise, convenient installation and flexible operation in the work. For the hydraulic system, maintenance is required from the following aspects:

1. Select the right hydraulic oil.

Hydraulic oil plays the role of transmitting pressure, lubricating, cooling and sealing in the hydraulic system. Improper selection of hydraulic oil is the main reason for the early failure and the decrease of durability of the hydraulic system. The hydraulic oil should be selected in accordance with the brand specified in the instruction manual; when special circumstances require the use of alternative oil, it should try to choose an alternative oil with the same performance as the original brand.

2. Prevent solid impurities from entering the hydraulic system.

Clean hydraulic oil is the life of the hydraulic system. If solid impurities invade, it will cause problems such as oil passage clogging of precision instruments. General solid impurities invade the hydraulic system through the following methods: the hydraulic system is unclean; the refueling tools are unclean; the refueling and repair and maintenance are not careful; the hydraulic components are chipped. You can prevent solid impurities from entering the system in the following ways:

（1） When refueling

The hydraulic oil must be filtered and filled, and the refueling tools should be cleaned reliably. In order to increase the refueling speed, the filter at the fuel filler of the fuel tank cannot be removed. Staff members should use clean gloves and work clothes to prevent solid and fiber impurities from falling into the oil.

（2）During maintenance

Remove the fuel tank fuel filler cap, filter cover, detection hole, hydraulic oil pipe and other parts, so as to avoid the dust when the system oil duct is exposed, the disassembled parts must be cleaned thoroughly before opening. For example, when removing the fuel filler cap of the hydraulic oil tank, first remove the dust around the fuel tank cap. After loosening the fuel tank cap, remove the debris remaining at the joints (do not rinse with water to prevent water from penetrating into the fuel tank), and confirm the cleaning before opening the fuel tank cap. If you need to use a wiping material and a hammer, you should choose a wiping material that does not lose fiber impurities and a special hammer with rubber on the hitting surface. The hydraulic components and hydraulic hoses should be carefully cleaned and blown dry with high pressure air for assembly. Use a well-packed genuine filter element (the inner packaging is damaged, although the filter element is intact, it may not be clean). Clean the filter at the same time when changing the oil. Before installing the filter element, carefully clean the dirt on the bottom of the filter case with a wiping material.

3. Cleaning of hydraulic system.

The cleaning oil must use the same hydraulic oil as the system used. The oil temperature is between 45 and 80 ° C. Use a large flow to remove impurities from the system as much as possible. The hydraulic system should be repeatedly cleaned more than three times. After each cleaning, release all of the system while the oil is hot. After cleaning, clean the filter and replace the new filter element with new oil.

4. Prevent air from entering the hydraulic system.

At normal pressure and temperature, the hydraulic oil contains a certain amount of air. When the pressure is reduced, the air will escape from the hydraulic oil, and bubbles will rupture and erode the hydraulic components to generate noise, which will reduce the working efficiency of the hydraulic system. The following points should be noticed to prevent air intrusion:

（1） After maintenance and oil change, the air in the system must be purged according to the provisions of the “Instruction Manual” for normal operation.

（2） The suction pipe opening of the hydraulic oil pump must not expose the oil surface, and the suction pipe must be well sealed.

（3） The seal of the oil pump drive shaft should be good. Pay attention to the use of genuine "double-lip" oil seals when replacing the oil seals there. Do not use "single-lip" oil seals, because "single-lip" oil seals can only seal oil in one direction , does not have the function of sealing gas.

5. Prevent water from entering the hydraulic system.

Excessive moisture in the oil will rust the hydraulic components, emulsify the oil, deteriorate the strength of the lubricant film, and accelerate mechanical wear. In addition to preventing water intrusion during maintenance, it is also necessary to pay attention to the cap when the oil storage tank is not in use, and it is best to place it upside down; oil with large water content must be filtered several times, and the filter paper to be dried should be replaced every time. When there is no special instrument for testing, the oil can be dripped on the hot iron plate, and there is no steam coming out and burning immediately before filling.

6. Precautions during operation.

The mechanical operation should be gentle and smooth, and rough operation of machinery should be avoided. Otherwise, shock loads will inevitably occur, causing frequent mechanical failures and greatly shortening the service life.  The impact load generated during operation, on the one hand, causes early wear, fracture, and fragmentation of mechanical structural parts, on the one hand, it generates impact pressure in the hydraulic system, and the impact pressure can cause damage to hydraulic components, oil seals, and high-pressure tubing joints and hoses. Premature failure Oil leakage or burst pipe, overflow valve frequent action Oil temperature rises.

7. The key to preventive maintenance is to strengthen daily maintenance. 
The main maintenance tasks are as follows:

(1) Daily inspection

Its main items include hydraulic systems, sliding lubrication systems, cooling systems, and pneumatic systems. Daily inspection is based on the normal conditions of each system.

(2) Weekly inspection

Its main items include machine tool parts and sliding lubrication systems. They should be properly inspected weekly, especially the machine tool parts must be cleaned of iron debris and external debris.

(3) Monthly inspection

Mainly check the power supply and air dryer. The power supply voltage is rated at 180V-220V and frequency 50Hz under normal conditions. If there is any abnormality, measure and adjust it. The air dryer should be disassembled once a month, and then cleaned and assembled.

(4) Quarterly inspection

The quarterly inspection should mainly be performed from three aspects: the machine bed, the hydraulic system, and the sliding lubrication system. For example, when inspecting the machine tool bed, it mainly depends on whether the accuracy of the machine tool and the level of the machine tool meet the requirements in the manual. If there is a problem, you should contact the mechanical engineer immediately. When inspecting the hydraulic system and the spindle lubrication system, if there is a problem, the new oil 60L and 20L should be replaced and cleaned.

(5) After half a year's inspection, the hydraulic system and sliding lubrication system of the machine tool should be inspected. If something goes wrong, you should replace with new oil and then clean it.

After comprehensively familiarizing and mastering the knowledge of preventive maintenance, it is necessary to have a deeper understanding and necessary grasp of the causes and treatment of abnormal phenomena in the oil pressure system. For example, when the fuel pump does not inject fuel, the pressure is abnormal, and noise occurs, you should know what the main reasons are and what the corresponding solutions are. The causes and treatment of abnormal phenomena in the oil pressure system should be understood from three aspects:

① Oil pump does not inject fuel

The main reasons may be the low liquid level in the fuel tank, the reverse rotation of the oil pump, the speed is too low, the oil viscosity is too high, the oil temperature is low, the filter is clogged, the volume of the suction pipe is too large, the intake air is drawn in at the oil inlet. For the damaged part, there are corresponding solutions to the main reasons, such as filling up with oil, confirming the label, and changing it when the oil pump is reversed.

② Stress is abnormal

That is, the pressure is too high or too low. The main reasons are also various, such as improper pressure setting, poor operation of the pressure regulating valve coil, abnormal pressure gauges, and leaks in the hydraulic system. The corresponding solutions include dismantling and cleaning according to the prescribed pressure settings, changing a normal pressure gauge, and checking each system in turn.

③ Noisy

Noise is mainly caused by oil pumps and valves. When the valve is noisy, the reason is that the flow rate exceeds the rated standard, and the flow rate should be adjusted appropriately; when the oil pump is noisy, the reason and the corresponding solutions are also multifaceted, such as high oil viscosity and low oil temperature to raise the oil temperature; when there are air bubbles in the oil, the air in the system should be released.

8. Troubleshooting for possible problems in the maintenance of the hydraulic system:

It is more economical to perform regular maintenance and maintenance inspections of the hydraulic system than to perform repairs after a failure. It is recommended that after a certain period of work, the system is subjected to periodic preventive maintenance and regular replacement of important sealing materials. To prevent omissions, maintenance procedures are recommended in accordance with the direction of oil flow:

Fuel tank: The oil level must be correct, the oil must be of the specified type and have a corresponding viscosity. For large systems, regular oil sample analysis can be performed to confirm whether the oil can continue to be used.

Suction pipe: Damage and severe bending must be checked. It will reduce the diameter of the oil pipe and become a noise source. Oil pump: Check the shaft seal and other oil leakage. Pressure oil pipe: Different oil circuits at the pressure end should be checked one by one along the direction of oil flow, and there should be no leakage. Control part: mainly check the leakage situation at the valve interface. Oil return pipe and oil filter: They should be checked for leaks. The filters must be checked. If there is no pollution indication, the filters must be taken out and checked for cleaning or replacement. Actuator: Check for leaks. Accessories: check the work. Electrical section: Periodically check the connection of the motor wiring section. The hydraulic oil should be replaced once after three months of initial use, and then every six months to ensure the normal operation of the system. During the operation of the hydraulic system, the oil filter blockage should be checked at any time and the filter element should be cleaned or replaced in time. The hydraulic system should always be provided with wearing parts and spare parts in order to deal with the failure in time. When the indoor oil temperature does not reach 25 ° C in winter, it is not allowed to start the sequential operation. When the oil temperature in summer is higher than 60 ° C, pay attention to the working condition of the system and notify the maintenance person to handle it. For equipment that has been stopped for more than four hours, the pump should be run for five minutes at no load before starting the actuator. The interlocking device of the electronic control system cannot be arbitrarily adjusted, the position of each limit stop is damaged or arbitrarily moved. When the hydraulic system fails, unauthorized movement is not allowed, and the maintenance department should be immediately notified to analyze the cause and eliminate it. Check the components and accessories of the hydraulic system regularly.

Our company is dedicated to the sales and communication of springs and spring machines. If you have any intention, please contact us.
Name:Luoyang Xian Heng Spring Machinery Co., Ltd.
Email: marketing@springcoiling.com

Tel: 0086-379-62265677

Fax: 0086-379-67878852

Whatsapp: 0086-1833 8852 671

Wechat: 0086-1833 8852 671