BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a method for drying and baking of covered arc welding electrodes such as coated arc welding electrodes and an apparatus for carrying out the method. Particularly, the invention relates to a method and an apparatus for quickly drying and baking of covered arc welding electrodes by using far infrared such that the moisture content is lower than a predetermined value.

Description of the Prior Art

Conventionally, covered arc welding electrodes are manufactured by preparing the core wire with predetermined length by drawing and cutting a wire rod, forming coating flux to have a proper shape by dry mixing and wet mixing, inserting the coating flux into a extruder and then extruding it out of the extruder together with the core wire, applying the coating flux onto the surface of the core wire, and drying and baking of covered arc welding electrodes. Generally, the moisture content of the coating applied within the extruder exceeds about 9%. If the coating is dried artificially by using a heat source or a hot blow, etc., the coating may be cracked easily and/or weakened. Thus, the coating must be dried under in natural conditions before artificial drying so that the moisture content is lower than the predetermined value. Therefore, in conventional art, the moisture content of the coating is kept under 3% by drying the welding electrodes applied with coating flux under indoors natural condition for 24 to 48 hours, and the welding electrodes are dried and baked within a drying and baking oven.

The process of artificial drying and baking is performed by supplying the heat generated in a main combustion chamber which use light oil, natural gas or liquified propane gas as a fuel to the drying and baking oven in convection heating manner.

The process of such drying and baking operation consists several steps: pre-drying at about 70 to 90°C, main drying at about 150°C and baking at about 400°C for one hour. The coating flux of the finished product has moisture content lower than 0.5 % .

In the conventional method as discussed above, there is a long time, about 27 to 51 hours, to produce the finished product from the pre-drying, main drying and baking and to completion thereof, and the length of the equipment required for drying and baking about 24 meter which leads to problems with installation. Also, a bulky warehouse is needed to dry the products in a natural condition for 24 to 48 hours, natural drying causes a delay in production of the product, and the conveying operations from the warehouse to the natural drying and baking oven and from the oven to the packaging place of the finished product are performed over long distance and by manual operation, thus time and labor are lost and the operation is unsafe.

Particularly, in order to perform the natural drying operation and the drying and baking operation within the oven, the welding electrodes to be dried must be placed with a certain distance from each other, thereby the operations occurring in the oven are not performed successively and then, the loss of work and heat will be significant, and especially air pollution occurs due to the use of the fossil fuel. Also, another drawback of using such a drying and baking oven is that to process a number of the products requires bulky equipment.

SUMMARY OF THE INVENTION

To solve the above problems, the object of the present invention is to provide a method and an apparatus for drying and baking of covered arc welding electrodes, which can perform the drying and baking process within a short time without a separate natural drying operation.

Another object of the invention is to provide a method and an apparatus for drying and baking of covered arc welding electrodes, which can reduce the loss of work and heat by performing the drying and baking operation automatically and successively.

Still another object of the invention is to provide a method and an apparatus for drying and baking of covered arc welding electrodes, wherein the air pollution can be avoided and the heat efficiency will be higher by using far infrared as a heat source.

The above objects are accomplished by providing a method for drying and baking of covered arc welding electrodes which are cut to a predetermined length and to which the coating flux is applied, said method comprises the steps of arranging the plural welding electrodes applied with the coating flux within a certain distance of each other, and passing the arranged welding electrodes through the beneath the far infrared source.

Further, the objects of the invention are accomplished by providing an apparatus for drying and baking of covered arc welding electrodes, which comprises a drying means having a far infrared source as heat source.

In the present invention, by directly radiating far infrared, which is a kind of electric wave with a wave length of 3 x 10 ^'5 micron to 1000 x IO' ⁵ micron, the covered arc welding electrodes with the coating flux and then the electric wave which penetrates into the deep portion of the coating will be quickly converted to heat so that the covered arc welding electrodes with the coating flux can be dried and baked within a short time without any crack occurring in the welding electrodes. Particularly, by using far infrared as a heat source, the temperamre control, which is a difficult operation in the prior art, is easily achieved and the stability will be high, thereby the reliability is obtained.

Hereinafter, the preferable embodiments of the present invention will be described in detail with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic side elevation view of an apparams for drying and backing of covered arc welding electrodes according to one embodiment of the present invention;

Fig. 2 is a schematic front elevation view of the apparatus shown in Fig. 1;

Fig. 3 A is a partial perspective view of a device for automatic arrangement and pitch division to be used in the apparatus shown in Fig. 1;

Fig. 3B is an enlarged side elevation view of A portion in Fig. 3 A; Fig. 4 A is a partial perspective view of a stage connection conveyor to be used in the apparams shown in Fig. 1;

Fig. 4B is a partial side elevation view of the stage connection conveyor; and

Fig. 5 is a partial perspective view of a welding electrode conveyor to be used in the apparams shown in Fig. 1.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring to Figs. 1 and 2, there is shown an embodiment of the drying and baking apparams 1 for performing the method of drying and baking of covered arc welding electrodes (hereinafter, so called as "welding electrodes") according to the invention.

The drying and baking apparams 1 comprises the first stage 2 for pre-drying the covered arc welding electrodes, the second stage 3 for main drying of the coating, the third and the fourth stages 4 and 5 for baking of the coating, and the fifth stage

6 for cooling of the welding electrodes. In this embodiment, although each of the first to the fourth stages consist of four sections, each stage may comprise one or more sections as desired. At the inlet of the first stage, a slanted supply conveyor 12 for supplying the welding electrodes to be dried from the inspection conveyor 11 is mounted, and at the outlet portion of the fifth stage, a slanted discharge conveyor

13 for discharging the welding electrodes which have completed the drying and baking process from the apparams is mounted, and then the slanted conveyor 13 is connected to the final inspection conveyor 14. A stage connection conveyor 15 is mounted between each of the stages, such that the welding electrodes can be flowed successively.

As shown in Fig. 2, each stage 2 - 6 is divided into an upper portion and a lower portion by the partitions 16, and for the purpose of minimizing the loss of heat, all of the stages except for the fifth stage 6 are enclosed by an insulation portion. If

desired, each stage is provided with a side door (not shown) on one side. Far infrared heat sources 21 - 24 are provided in the upper portion of the first and the fourth stages. It is preferable that the height from the far infrared heat source to the upper side of the conveyor can be adjusted as desired, and in such case it is preferable to mount the far infrared heat sources 21 -24 to be movable in upward and downward. This is easily constructed by a known technique, and thus the detailed description to the strucmre will be omitted.

If the distance between the far infrared heat source and the welding electrodes is too small, the moismre within the coating moves quickly, which causes cracks in the coating. Also, if the distance is too great, cracks will not occur in initial stage, but the crack will be occur due to the latent heat generated in the baking process.

Therefore, from many experiments it has been found that the far infrared heat sources

21 - 24 are preferably placed on the portion above 50 to 150 mm from the upper side of the conveyor 25 to which the welding electrodes are conveyed. On one side of each of the first stage 2 and the second stage 3, a discharge device 26 is provided to discharge the moismre and the like generated in the drying process, and the discharge device may be mounted on the third stage 4 and the fourth stage 5. In the fifth stage, a showered cooling device 27 is mounted above the conveyor 25 and on its side a blowing fan 28 is mounted to supply cooling air to the showered cooling device 27.

In the apparams 1 for drying and baking in accordance with the invention having a construction mentioned above, since the apparams utilizes far infrared heat sources 21 - 24 other than convection heating using fossil fuel, air pollution can be avoided. Further, since the entire process including an inspection operation for inspecting the welding electrodes coated with the coating flux, supplying operation, drying and baking operation, cooling operation, the welding electrodes discharge operation and the final inspection operation are performed automatically and successively, the loss of work can be minimized. Particularly, the entire apparams is constituted to be stacked in five layers, thereby the space occupied by the apparatus can be minimized, and the drying and baking operation can be obtained successively without having to shut down the entire apparams, thereby the loss of the heat in each stages can be minimized.

The constitutional elements of the apparams for drying and baking the welding

electrodes will be described in more detail below.

In Figs. 3 A and 3B, there is shown an automatic arrangement and pitch dividing device 40 for arranging the welding electrodes successively. The welding electrodes to be dried are conveyed by means of conveyor chains 43 which are driven by a main shaft 41. Each of the conveyor chains 43 locates in identical height on the main shaft 41 , and cylindrical grooves 43b are provided in the chain block 43a of the conveyor chain 43, as shown in Fig. 3B. Since the welding electrodes W are placed within an opposed pair of cylindrical grooves 43b of each of the conveyor chains 43 mounted on the main shaft 41 in opposed manner, the welding electrodes W do not adhere to each other and are divided one by one and can be conveyed with more stability. An arrangement and pitch adjusting roller 45 is rotatably mounted on the center of the main shaft. Further, the sprocket shaft 46 is mounted in parallel with the main shaft 41. A sprocket 41a is provided in one end of the main shaft 41 and a sprocket 46a is provided in one end of the sprocket shaft 46, and the sprockets are connected to each other to be driven by a chain 47a.

Further, a sprocket 46b is provided in the center portion of the sprocket shaft 46 and a sprocket is provided in the center portion of the arrangement and pitch adjusting roller 45, and the two sprockets are connected to each other to be driven by a chain 47b. Thus, the rotation driving force of the main shaft 41 is transmitted to the arrangement and pitch adjusting roller 45 via the sprocket 41a, the chain 47a, the sprocket shaft 46, the sprocket 46a, the chain 47b, and a sprocket (not shown) of the arrangement and pitch adjusting roller 45, then drive the roller 45. By constructing the arrangement and pitch adjusting roller 45 to be the same pitch as the conveyor chain 43 at its peripheral portion and the outer diameter of the roller to be larger than that of the conveyor chain 43, the welding electrodes W are adapted to be conveyed one by one on the main shaft by the arrangement and adjusting roller 45. Thereby, it is permitted to correct and divide automatically the welding electrodes W being supplied in offset of their pitch to the conveyor chain 43 by the arrangement and pitch adjusting roller 45.

Such arrangement and pitch dividing device 40 is commonly mounted between the inspection conveyor 11 and the slanted supplying conveyor 12, however it may be mounted on the inlet portion of the first stage 2 and the connection part between

the stages as desired.

In Figs. 4A and 4B, there is shown a stage connection conveyor device 50. The stage connection conveyor device 50 is provided between each stage and makes the welding electrodes W flow successively between the upstream in the upper portion and the downstream in the lower portion. Each of the conveyors comprising two conveyor chains 43 respectively are disposed to be spaced in upward and downward in parallel with each other and the lower conveyor is projected toward the front side of the upper conveyor. The stage connection conveyor device 50 comprises a stage connection conveyor chain 54 which is mounted between the two conveyor chains 43 and has a caterpillar 53 in the form of , being attached to the upper portion of the conveyor chain block.

As shown in Fig. 4B, the stage connection conveyor chain 54 is mounted on the upper conveyor chain 43 in a slanted manner so that in the initial connection portion against the upper conveyor chain 43, the end of the caterpillar 53 of the stage connection conveyor chain 54 is positioned beneath the chain block of the upper conveyor chain 43 and the end of caterpillar will be mounted to be positioned above the conveyor chain 43 in downstream. That is, when the conveyor chain 43 on which the welding electrodes are conveyed, the caterpillar 53 of the stage connection conveyor chain 54 enters into the gap between the welding electrodes so that in the position where the conveyor chain 43 and the stage connection conveyor chain 54 are converted from a horizontal direction to a vertical direction, the welding electrodes positioned in the cylindrical groove 43b (Fig. 3) of the conveyor chain 43 are adapted to be moved to the caterpillar 53 of the stage connection conveyor chain 54.

Further, a guiding member 55, having a guiding face corresponding to the moving line of the caterpillar 53, is mounted in the position where the stage connection conveyor chain 54 converts from a vertical direction to a horizontal direction. The guiding member 55 prevents the welding electrodes W being moved by the caterpillar 53 from dropping out of the apparams, as well as maintains the welding electrodes W in the space defined by the cateφillar 53 and the guiding member 55, and thus in the discharge end of the guiding member 55, the welding electrodes W are positioned one by one in each cylindrical groove of the lower conveyor chain 43. Therefore, the welding electrodes W is moved in successively

from the upper conveyor chain 43 to the lower conveyor chain 43.

In Fig. 5, there is shown a welding electrodes turning conveyor device 60 for turning the welding electrodes in succession. If the welding electrodes W are passed through the beneath of the far infrared heat source without being turned, the far infrared radiates a certain portion of the welding electrodes, thereby the coating applied to the welding electrodes will dry unevenly and cracks will occur on that portion. Therefore, in the invention a welding rod turning conveyor device 60 acting as a means for turning the welding electrodes W in succession is provided. The welding rod turning conveyor device 60 is comprised of a planar conveyor chain 61 which is mounted on the opposing sides or inner side of the conveyor chain 43 in each stage and parallel with it.

The upper side of the planar conveyor chain 61 is flat and the planar conveyor chain is mounted so that the height of the upper side being higher than the bottom of the cylindrical groove 43b of the chain block 43a of the conveyor chain 43 in each stage. Further, the conveying speed of the conveyor chain 43 is faster than that of the planar conveyor chain 61. Thus, since the welding electrodes W positioned on the cylindrical groove of the conveyor chain 43 must be moved faster than the planar conveyor chain 61, there is relative movement between the welding electrodes W and the planar conveyor chain 61 and the welding electrodes W will be turned by the friction existing therebetween. Therefore, the welding electrodes are moved and at the same time will be turned about their axis by the conveyor chain 43 and the planar conveyor chain 61. Then, the far infrared heat source mounted on the upper portion of the welding electrodes radiates uniformly the surface of the coating applied to the welding electrodes, drying the coating uniformly and avoiding cracks due to drying shrinkage.

Hereinafter, the method of drying and baking the welding electrodes coated with coating flux by the drying and baking apparams 1 according to the invention will be described.

Firstly, an experiment for drying and baking the welding electrodes coated with coating flux is performed such that the temperature of the far infrared heat source is raised slowly as in that of the drying and baking oven. In performing the

experiment, cracks occurred in the coating applied to the welding electrodes. Generally, the cracks occur during drying on the portion of the rod which is more dry as compared to the other portion, due to the unevenness of the moismre content within the surface or the interior of the coating of the welding electrodes. In order to eliminate the cause of the cracks, in the present invention the welding electrodes are constructed to be dried while turning about the axial direction. However, the cracks in the coating cannot be prevented sufficiently by merely turning the welding electrodes. Therefore, it has been found by inspecting the crack condition with raising the temperamre of the heat source that when the temperamre of the heat source is lower than 100°C cracks in the welding electrodes do not occur, but cracks do occur at temperamres above 100°C. Also, further cracking does not occur in the welding electrodes in which a crack does not occur until the temperamre of the heat source reaches to about 300°C. Further, in order to quickly decrease the moismre contained in the binder of the coating and to prevent the occurrence of cracks resulting from the expansion of the moismre vapor, it is preferable to lower slowly the temperamre of the heat source to 400 - 500°C during the pre-drying operation.

Therefore, the method according to the present invention comprises the steps of pre-drying, main drying, and the first and the second baking. Also, during the pre-drying step, the initial temperamre of the heat source is lowered slowly from 400 - 500°C to 300 - 350°C, during the main drying to the baking the temperamre of the heat source is raised gradually from 300 - 400°C to 600 - 700°C, and during the end of the baking the temperamre is further lowered to 300°C, whereby the welding electrodes are dried and fired.

The finished welding electrodes manufacmred by the present invention were compared to the welding electrodes obtained by the conventional convection heating method.

The dimensions of the welding electrodes used in the experiment was 5.0 mm x 700 mm (K-7028LF) and the length of the welding electrodes is 12.5 meters, and the conveying speed of the welding electrodes within the apparams was about 3 m/min. The processing time in each stage was about 4 minutes and the time required for the entire process was about 16 minutes. The result of the experiment is shown in Table 1.

Table 1

Test Item Prior Present Welding Condition Remark Art Invention

Arc Continuity A A Flat Stability

Concentration A A Welding Horizontal f Jet A Position Fillet

Arc Power o A

Restrikability D D Welding 220-230 A Current

Quantity B B

Spatter Size of Particle A A Evaluation Criteria

Removability B B ® Good

Fluidity A A O Medium

Removability A A X Bad

Slag Covering A A

Quantity A A Scoring Criteria

Melting Homogeneity of Nail A A A 5

Appearance of Bead A A B 4

Blow Hole / Pit Occurrence A A C 3

Quantity C C D 2

Gas

Smell C C E 1

Heat Resistance of End Part A A

Easiness of Using A A Moisture Content ( <0.5%)

Range of Welding Current A A 1 Stage 3.10%

Efficiency A A 2 Stage 1.15%

Total 91 91 3 Stage 0.88%

Final Evaluation ® ® 4 Stage 0.48%

As can be seen from Table 1, the weldability and the moismre content in the welding according to the invention are the same as those of the conventional convection heating method.

In accordance with the invention, the time required in drying and baking the

coating applied to the welding electrodes is significantly reduced. That is, in the conventional method the processing time, excluding the cooling step, requires from 27 hours to 51 hours because each step including the namral drying step requires at least 1 hour. However, in the method of the present invention the processing time, including the cooling step, for obtaining a finished product requires about 20 minutes.

Specifically, since the method of the present invention does not require the natural drying, the products flow smoothly and productivity is improved significantly, as well as the loss of labor and work can be minimized. Further, in the method of the present invention the length of the entire line and the cost for equipment may be reduced compared to those of the prior art. Also, the energy efficiency is high, the temperamre control is easy and the stability is high, thereby the reliability will be further improved.

While particular embodiments of the invention have been shown and described in detail, it will be obvious to those skilled in the art that changes and modifications of the present invention may be made without departing from the invention. For example, the drying and baking apparams may be constructed by using other forms such as a horizontal type or a helical type apparams and the like. In conveying of the welding electrodes, it is possible to convey the welding electrodes by gripping of a part thereof and positioning it in vertically.

As such, the scope of the invention should not be limited by the particular embodiment and specific construction described herein but should be defined by the appended claims and equivalents thereof. Accordingly, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.