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The present situation of the water heater tank welding research

Views:0     Author:Site Editor     Publish Time: 2019-05-26      Origin:Site

Abstract: For a variety of the water heater tank (commonly known as the tank) material and welding technology adopted by the method are introduced, For gas water heater tank/ The solar water heater tank/Electric water heater tank and Heat pump water heater tank The material and welding method are introduced, Which focus on the solar water heater tank and electric water heater tank welding process, I hope for you to understand the water heater tank manufacturing for reference.


Keywords: Water heater burning gas; Electric water heater; The solar water heater; Air can heat pump water heater; The water tank; The tank; welding

 

0   Foreword

       A water heater, as its name suggests, is a device that provides hot water. Water heater can be roughly divided into two types: instant water heaters and heat storage water heaters from the way of heating. In nowadays market the water heaters mainly include water heaters burning gas, solar water heaters, electric water heaters and air can heat pump water heaters. Among them, solar water heaters, electric water heaters and air can heat pump water heaters are heat storage type water heaters while gas water heaters are typical instant water heaters, and so do fast heat type electric water heaters.


The water tank ( the heat exchanger part) of the gas water heater is made of aluminum alloy and pure copper. And the water tank of the solar water heater (commonly known as the inner tank) also has two kinds of conditions. Generally, the water tank of the non-pressure-bearing solar water heater is austenitic stainless steel, while the water tank of the pressure-type solar water heater is made of low carbon steel after welding. Besides, some other parts are also austenitic. In the form of stainless steel, nano-polymer materials (nano-polypropylene modified resin) have emerged in recent years. The electric water heater water tank is mostly made of low carbon steel (cold rolled steel) post-weld enamel (Qingdao Haier electric water heater liner with hot-rolled pickled steel RST330), austenitic stainless steel and hot-dip galvanized water tank. What’s more, the crystal liner has also  emerged (the crystal liner is a kind of liner that separately designed and organically  combined the inner pressure layer and the leakage prevention layer of the inner liner. The pressure layer of the liner is made of 1.2mm ~ 2.0mm thick cold-rolled steel plate. The leak-proof layer is made of 4.0mm special synthetic polymer material. Through the steel crystal integration process, the material is integrated the entire inner surface and the opening of the inner liner without any weld seam, thus really forming the inner liner without weld seam. Since the color after the formation is generally white jade which is similar to crystal, it is called crystal “inner.”


“Crystal” is a special synthetic polymer material. "Crystal" is a special synthetic polymer material. It has a long-term comprehensive ability compared with the well-known engineering plastics such as ABC and polycarbonate. It is almost insoluble in any solvent (such as alcohol and gasoline, methanol, strong acid, strong alkali) below 100 °C, so its anti-scaling effect is particularly outstanding. However, its formation process is relatively high, and every process of the production process requires strict control.) Air energy heat pump water tank is mainly divided into pressure type and non-pressure-bearing type. Among them, there are two kinds of pressurized water tanks: stainless steel pressurized water tank and enamel pressurized water tank. At present, most of the products in the air energy heat pump water heater market are stainless steel water tanks. Various water heater water tanks (liners) are generally required welding (except for nano-polymer materials), but the welding process used is different.

 

1 Gas water heater water tank welding process

The gas water heater is composed of a casing, a heat exchanger system, a gas system, a waterway system, a smoke exhaust system and a safety automatic control system. Among them, the heat exchanger (commonly known as the water tank) is mainly composed of a combustion chamber and a heat exchanger. As the core component of the water heater, the main function of them is to provide the water heater gas burning space, and to pass the heat released by the water heater gas combustion through the heat exchange process to heat the cold water flowing in the heat exchanger to the temperature required by the user. The heat exchanger (water tank) is usually made of aluminum alloy or pure copper, and the heat exchanger (water tank) made of aluminum alloy is generally welded by continuous brazing technology; the heat exchanger (water tank) made of pure copper is generally welded by copper immersion tin-lead technology.

 

2 Solar water heater tank welding process

2.1 Introduction to solar water heater water tank

A typical solar water heater consists of a solar collector and a water storage tank. There are two main types of water storage tanks for solar water heaters: one is a non-pressure-type water tank, and the other is a water tank in a pressurized form. The non-pressure-bearing water tank is mainly made of austenitic stainless steel, and the grade is mainly SUS304. The using welding process is mainly argon arc welding and electric resistance welding. The pressure-bearing water tank is mainly made of low-carbon steel and stainless steel; among them, the mainly welding process used for low-carbon steel (brand name is Q235A) is CO2 gas shielded welding, and the interior of the water tank will be enamel-treated after welding;  Stainless steel is mainly austenitic stainless steel (main grades SUS304, SUS316, SUS304L and SUS316L, etc.) and ferritic stainless steel (main grade SUS444). The stainless steel water tank is mainly made by argon arc welding, and the low carbon steel water tank is mostly made by CO2 gas shielded welding. Among them, resistance welding adopts the form of lap joint and crimping joint; argon arc welding and CO2 gas shielded welding adopt I type groove or V type groove. In addition, the nano polymer material water tank is made by one-piece forming technology.


2.2 Solar water heater tank welding process

The welding of solar water heater water tank mainly involves two welding methods of electric resistance welding and tungsten argon arc welding. Tungsten argon arc welding is available in both automatic and manual. The automatic tungsten argon arc welding is only used for the welding of the longitudinal joint of the inner cylinder and the groove is in the form of I-shaped butt joint. At this time, the requirement of the gap is very strict and the pre-weld cleaning requirements on the groove are also very strict, and there should be no defects such as flash burrs on the edge of the weld bead (that is, it is required to have high enough precision for the cutting of the cutting process in the previous process, and it is difficult for the ordinary shearing machine to meet the requirements), otherwise, it will burn through during the welding process, causing defects in welding quality, large amount of repair, and causing quality hazards. It is not well promoted in the actual production process. and gradually replaced by better quality, lower cost and higher efficiency resistance welding later.


Manual tungsten argon arc welding is mainly used for welding the inner cylinder and the end cap and the water tank nozzle. Due to its low equipment investment and flexible operation, it have been well promoted in the initial welding process of the water tank of the solar water heater, but its disadvantages like low production efficiency, high cost, great effects by human factors, and the outstanding advantages of resistance seam welding, the inner cylinder and end cap ring weld are also gradually replaced by resistance seam welding. Finally, a manufacturing process that now completely welds the water heater liner by electric resistance welding is formed.


2.2.1 Resistance welding process

The application of resistance welding in the manufacture of water heater water tanks is mainly spot welding and seam welding. Spot welding is mainly used for spot welding of water heater tank accessories and spot welding positioning of inner liner. The seam welding is mainly the longitudinal weld welding of the inner tank of the water heater tank and the welding seam welding of the inner tank and the end cover. 


1) Resistance seam welding process parameters, see Table 1

Table 1    Resistance seam welding process parameters,

The Amount of overlap(mm)

Electrode End Face Width(mm)

Electrode Pressure

(kN)

Welding Time to Rest Time Ratio

Welding Current

(kA)

Welding Speed

(mm/min)

6.0~8.0

4.0~5.0

3.5~5.0

1.25:1~2:1

6.0~7.5

70~100

 

Resistance seam welding is mainly used for the welding of the longitudinal weld of the tank, the welding of the girth weld and the application welding of the mechanized production line of the tank liner.


2) Welding process points

a) The surface of the electrode should be kept clean, and the width of the electrode contact surface should be guaranteed, and it should be repaired frequently (turning with lathe or plate boring).

b) Forced water cooling is required in the austenitic stainless steel welding process, which is beneficial to the welding electrode and welding quality.

c) The weld overlap position and the surrounding 10mm range should be cleaned to ensure no oil, debris, etc., preferably use with acetone or alcohol.

d) Before each formal welding of the product weld, the welding specification shall be verified, that is, to test whether the welding quality of the plate meets the quality requirements or not, mainly the manual tear test.

                                            

2.2.2 Tungsten argon arc welding process

1)Manual tungsten argon arc welding process parameters, see Table 2

Figure 2 Manual tungsten argon arc welding process parameters

Welding Equipment

The Polarity of Power

Tungsten Electrode Diameter(mm)

Welding Voltage

(V)

Welding Current

(A)

Argon Gas Flow

(L/min)

Manual Pulse Tungsten Arc Welding

DC Positive Connection

2.0

9~12V

60~90

10~15

 

Manual TIG welding (TIG) is mainly used for repairing welding or fillet weld welding of faucets, generally without root protection.

2)Automatic tungsten argon arc welding process parameters, see Table 3

Welding Equipment

The Polarity of Power

Tungsten Electrode Diameter(mm)

Welding Voltage

(V)

Welding Current

(A)

Welding Speed

(mm/min)

Argon Gas Flow

(L/min)

Protective Gas Purity

Pulse Welding Straight Seam Special Equipment

DC Positive Connection

2.0

9~12V

60~90

50~70

8~12

≥99.95%Ar


Automatic tungsten argon arc welding is mainly used for longitudinal seam welding of water tanks and welding of water nozzles of pressurized water tanks. 


3 electric water heater water tank welding process

3.1 Introduction to electric water heater water tank

The electric water heater water tank is mainly made of low carbon steel (cold rolled steel), stainless steel and hot rolled pickled steel RST330, which is similar to the material of the solar pressure water heater. Low carbon steel (cold-rolled steel) and hot-rolled pickled steel RST330 generally adopt CO2 gas shielded welding process, and the longitudinal slit type is type I butt groove, the ring peak is padded type I butt groove, followed by the enamel treatment inside the tank. Stainless steel is mainly made of austenitic stainless steel (main grades SUS304, SUS316, SUS304L and SUS316L, etc.) and ferritic stainless steel (main grade SUS444). The thickness of individual austenitic stainless steel sheets is only 1.5mm, therefore the welding method generally uses argon-shielded arc welding (MIG), small batches also use manual tungsten argon arc welding to manual wire filling; the welding method of ferritic stainless steel is the same as that of austenitic stainless steel; groove type is generally V-shaped groove.


3.2 Electric water heater water tank process

The welding of the Q235A steel plate in the water tank of the electric water heater is mostly CO2 gas shielded welding. The longitudinal weld groove type is type I butt groove, and the ring weld is padded with type I butt groove.

1)CO2 gas shielded welding process parameters, see Table 4

Figure 4 CO2 gas shielded welding process parameters

Welding Equipment

The Polarity of Power

Welding Material / Specification(mm)

Welding Voltage

(V)

Welding Current

(A)

Welding Speed(mm/min)

Dry Extension

(mm)

Gas Flow

(L/min)

Protective Gas Purity

CO2 Gas Shielded Welder

DC Reverse Connection

H08MnA/Φ0.8

18~22V

80~120

19~21

8~13

8~12

≥99. 5% CO2

 

CO2 gas shielded welding is mainly used for the inner tank of the electric water tank and the  longitudinal joint, circumferential seam welding and nozzle welding of inner tank of the solar pressure carbon steel tank.


2) Tungsten argon arc welding process

The welding of stainless steel plates in the water tank of the electric water heater adopts argon-shielded arc welding (MIG), and the longitudinal weld seam and the ring weld groove type are all type I butt grooves.

Figure 5 Argon-shielded arc welding process parameters

Welding Equipment

The Polarity of Power

Welding Material / Specification(mm)

Welding Voltage

(V)

Welding Current

(A)

Welding Speed(mm/min)

Dry Extension

(mm)

Argon Flow(L/min)

Protective Gas Purity

Argon-shielded Arc welding Machine

DC Reverse Connection

ER316/Φ0.8

18~22V

80~120

19~21

8~13

8~12

≥99.95%

 

The argon-shielded arc welding is mainly used for the longitudinal seam and the circumferential seam welding of the inner tank of the electric water tank and the inner tank of the solar pressure tank. 

 

4 Welding process of air energy heat pump water heater water tank

The air energy heat pump water tank is mainly divided into pressure-bearing type and non-pressure-bearing type. The pressure-bearing water tank mainly faces the household tap water supply system and uses the pressure of tap water to provide power supply. The inner tank is a closed container. When the user closes the water valve, the water tank needs to withstand the pressure of the water pipe network, and the water heater is subjected to higher pressure when heated. The non-pressure-bearing type is mainly used in places where the required water volume is large, the tank liner is connected to the atmosphere, the liner is not a closed container, and the water supply requires additional power such as a water pump. Therefore, the pressure tank has higher requirements on the quality of the liner.


This paper mainly discusses the pressure tank. Among them, there are two kinds of pressurized water tanks: stainless steel pressurized water tank and enamel pressurized water tank. At present, most of the products in the heat pump water heater market are stainless steel water tanks. The material of the stainless steel pressurized water tank is similar to that of the electric water heater and the pressure-bearing solar water heater. Stainless steel is mainly made of austenitic stainless steel (main grades SUS304, SUS316, SUS304L and SUS316L) and ferritic stainless steel (main grade SUS444); low carbon steel grade is mainly Q235A. The welding of stainless steel water tank is mostly welded by argon arc welding. The low carbon steel water tank is mostly welded by CO2 gas shielded welding, and the groove form is mostly V-shaped groove.

 

5 Conclusion

There are many types of water heater water tanks, and the manufacturing process is different, so does the welding process. But the main welding process are brazing technology, electric resistance welding, non-molten gas shielded welding (TIG welding) and gas metal arc welding (CO2 gas shielded and MIG welding). Among them, solar water heater water tank thin plate mainly adopts electric resistance welding, thick plate mainly adopts gas metal arc welding (CO2 gas shielded welding and MIG welding); electric water heater water tank and air energy heat pump water heater water tank mostly adopt gas metal arc welding (CO2 gas shielded welding and MIG welding), individual small batch production using manual tungsten argon arc welding manual wire filling for welding, while gas water heater water tank uses brazing technology. With the development of technology, it is believable that new welding technology and new technology will soon be applied to the manufacture of water heater water tanks.


For a variety of the water heater tank (commonly known as the tank) material and welding technology adopted by the method are introduced, For gas water heater tank/ The solar water heater tank/Electric water heater tank and Heat pump water heater tank The material and welding method are introduced, Which focus on the solar water heater tank and electric water heater tank welding process, I hope for you to understand the water heater tank manufacturing for reference.


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