ABSTRACT: In view of the welding difficulty and defects of thick copper plate, the method of Tig welding with flux is put forward to solve the welding defects. Keywords: Copper Plate; Argon Arc welding

1. Preface

The conductive copper bar is made of red copper (T2) with a size of 120 * 10 about 10m each. Due to the strong thermal conductivity of copper, low temperature in winter, welding is more difficult. Our company in the past production has never used Argon arc welding copper plate, there is no ready-made process for production use. And because the quality of the conductive copper plate is required to be high inside the weld, it is necessary to ensure that the copper plate still has good conductivity after welding, which requires us to do the welding test under the condition of simulating the spot, in order to obtain a qualified welding process for practical production.、

2. Experiment

(1) test equipment: AX-500 Rotary DC welding machine; Qs-500a water-cooled Welding handle set; (2) welding materials: HS-201 welding wire, gas flux 301 anhydrous alcohol, Argon Gas, oxygen, acetylene heating tools set; (3) Auxiliary Materials: Channel 10, one refractory tile pad.

 3. The problems in welding are affected by the physical properties of red copper. 

In the course of trial welding, we find that the following problems seriously affect the quality of welding seam, which need to be solved: (1) the welding seam is difficult to fuse and easy to deform; (2) The hot crack; (2) The gas hole.

4. Cause Analysis 

4.1 the weld is difficult to fuse and easy to deform. This is the first problem that we meet in welding copper plate. After the First Test Weld was welded, it was found that the weld surface was badly formed and the fusion of both sides was bad. An analysis of the causes of this phenomenon can be found by comparing the physical properties of copper and iron. As can be seen from Table 1, the thermal conductivity of copper is 7 times greater than that of iron at 20 °C and 11 times greater than that of iron at 1,000 °C

Type bad, therefore, in the welding must use greater line energy, but also must take pre-heating and thermal insulation measures. The selection of preheating temperature can refer to Fig. 1, from which we can find that the preheating temperature of 10mm copper plate is about 350 °C. In addition, as can be seen from Table 1, the linear expansion coefficient of copper is 15% larger than that of iron, and the shrinkage ratio is more than twice as large as that of iron. Therefore, in the actual work, we have taken the anti-deformation fixture see figure. 4.2 hot-cracked oxygen is a common impurity in copper. Copper easily reacts with oxygen in the Molten state to produce CU2O oxide. Copper can form low-melting-point EUTECTIC CU + CU2O with CU2O at a eutectic temperature of 1065 °C, 1,083 degrees below the melting point of copper. When copper is cooled from high temperature and the weld temperature reaches between 1083 °C and 1065 °c, the copper itself becomes solid state and forms hot crack under the action of welding stress. Because of the strong thermal conductivity of Red Copper, the weld is easy to grow into coarse grains, which also aggravates the hot crack. The high temperature oxidation color inside the weld can be seen from the weld section. In view of the occurrence of hot cracks we adopt

The following precautions have been taken. Carefully clean up the oil on both sides of the base material, oxide scale, so that it exposed metal luster, preheating part from groove more than 500 mm, in order to prevent the groove too fast oxidation. According to the technology of adding flux in gas welding, we mixed gas agent 301 with anhydrous alcohol and coated it on both sides of groove to remove copper oxide before Argon arc welding. The mechanism is as follows: the main components of gas agent 301 are Borax (Na2B4O7) and boric acid (H3BO3) . When welding, borax is quickly mixed with Cu2o in the molten pool. The reaction formula is as follows: NAB407 + Cu2ocu (BO2)2 * 2NaBO2 boric acid reacts with CU20 in the Molten Pool to form complex salt. The reaction formula is as follows: 4H3BO3 + CU2O3 -- 5h2o + 2HB02 + Cuo * B2O3 forms complex salt floating on the metal surface, the liquid metal also has a certain protective effect. Do not control the bath is too large, too large bath resulting in coarse grain, easy to produce hot cracks. By adopting the above-mentioned technology, the hot crack is basically eliminated.

4.3 a small number of pores were found during the test. In order to ensure that the conductive cross-section is large enough, the argon flow rate should be increased, the source of oxygen and hydrogen should be strictly controlled, and the water, oil and oxide on the surface of the welding wire should be carefully cleaned up, slow down the cooling rate as much as possible to create conditions for timely gas precipitation. 5. After the test results have solved the above-mentioned problems which affect the copper welding, we have conducted several tests repeatedly and concluded a set of complete and applicable welding procedure specifications as shown in Table 2(1) . (2) direct current connection is adopted in welding, arc starting and arc closing must be carried out on arc starting plate and arc closing plate. (3) when welding, reduce the welding layer as far as possible, keep the molten pool not too big. (4) during the welding process, clean up the layers strictly and confirm that there are no defects before the lower part of the welding. 6. Standard use of the above process in the construction site welding out of Qualified Weld, weld front molding and back molding are very beautiful. The internal defects of the weld were not found after radiographic inspection. The tensile test also showed that the strength of the weld was close to that of the base metal. 

Source: Chinanews.com, author: Fan Jinyou, Editor: Zhong Tian