ROOT INSERT AND METHOD FOR WELDING

Abstract: The root insert (3) for welding seams between constructional parts, especially that made of highly alloyed steels has, according to the invention, a root portion (4) and melting web (5) connected to the root portion (4) as well as shoulders (6) on both sides of the web (5), which, in mounted position of the insert (3), lie on the root-sided surfaces of the constructional parts to be welded together. In the known methods for the same purpose, a weld root is produced first and than further layers of the weld seam is built up. According to the invention, before producing the weld root, a root insert is placed in between the constructional parts to be welded together, especially root insert according to any one of Claims 1 to 5, and thereafter the weld root is produced by melting the web of the insert.

Description: Root Insert and Method for Welding Field of the invention The invention relates to a root insert for welding seams to be formed between constructional parts, especial ly that made of highly al loyed steels. The invention also relates to a method for welding constructional parts to each other, especial ly that made of highly al loyed steels, wherein a weld root is produced first and than the further layers of the weld seam is bui lt up. State of the art As is known, increased difficulties have to be taken into consideration when the weld roots are formed in the course of welding constructional parts to each ' other. Great ski l l is ecessary for avoiding the burning or perishing of the constru'ctional parts to be welded together and the co I - lapse-in of the weld root and, thus, the bulge or pro¬ trusion of the root on the other side of the seam. For decreasing this danger, it has been suggested to use backing straps or underlays w ich are placed under the weld seam to be produced on the root side. If the material of the backing straps is the same as that of the base ma¬ terial , they melt more or less together with the weld root but thereafter they can not be removed. This fact decreases the qual ity and the aesthetics of the seam, and when using this method with tubes, the remainings form stream obstac¬ les for the medium to be forwarded in the tube. Moreover, the strength of the seam is often not sufficient. If the material of the backing straps differs from that of the constructional parts to be welded to each other, the straps wi l l not melt together with them. In th-is case, the role of the straps is only to support the welding melt and to avoid the col lapse of the root. However, a sincere diffi ¬ culty is in that the straps are to be removed after finish ¬ ing the weld seam. If this is not possible as it is often the case with tubes, the straps form stream obstacles and, thus, vortexes in the forwarded medium. Because of this, deposits wi l l form on both -sides of the straps which great ¬ ly increases the corrosion effects in this region of the construction parts being already overstrained and deterio- ritated by the welding. Moreover, the cleaning of the tubes with go-devi !s wi l l be impossible, too. The deff ϊ c i enc i c-s mentioned above result in greater diffi¬ culties when highly al loyed steels, austenitic steels, stainless or acid-resistant steels have to be welded to each other. As it is known, in these cases, the weld seam to be formed is to be protected against the harmful impacts of the ambient air. For this purpose, protective atmosphere is used in the course of the welding operation of such kind of constructional parts, and the protective atmosphere is provided usual ly by argone gas. In the case of tubeb " , they must be scavenged by the gas in the entire length during the whole welding operation. This makes the welding itself quite difficult since the scavenge must be control led simultaneously with the welding and constantly during tr.° whole welding. If the gas stream interrupts because e. g. the gas container gets empty or if the scavenge gets in¬ sufficient because e. g. the intensity of the gas stream decreases or if ambient air gets into the inside of the tube, the welding must be stopped, the inner space of the tube must be deaerated and the sufficient gas stream within the tube establ ished, i . e. the whole preparatory sequence must be carried out again and again. The material characteristics of constructional parts made of stainless or acid-resistant steel result in the fact that the so cal led tack welding for provisional ly fixing the parts to each other causes harmful changes in the mate ¬ rial structure itself. When the tack welds are again welded through, cracks or spi l l ies can appear at the spots of the tack welds, thus, the weld seams must be made with increas- ed care or precaution in these areas. In the case of these del icate materials as mentioned above, the danger or burning or perishing of the material is also increased. Great ski l l is necessary to form the stainless or acid-resistant welds with control led heat input, in the course of which the material wi l l be sufficiently melted through but the perishing wi l l be avoided. Moreover, the col lapse of the weld seam should also be avoided, otherwise the seam must be corrected where it is possible at al l . In the case of tubes, the portion with deffective weld seam must be cut out, the cut edges of the tube must be lathed and cal ibrated as prescribed which are not only time consuming, circumstantial and difficult work but they cause considerable material losses, too. Essence of the Invention An object of the present invention is to obviate such de¬ ficiencies and to provide a root insert for welding as we I I as a method for welding with the aid of this root insert, with which the geometrical shape of the seam can be deter¬ mined in advance, the heat transfer to the constructional parts to be welded can be regulated during the welding operation, the protective atmosphere for highly al loyed steels wi l l no more be necessary on the root side of the parts, and with which the welding operation can be simpler, easier and the seam wi I I have a better qual ity. The improvement of the root insert according to this in- vention is in that the insert has a root portion and a melting web connected to the root portion as wel l as shoul- ders on both sides of the web, which, in mounted position of the insert, l ie on the root-side surfaces of the con¬ structional parts to be welded together. In a preferred embodiment of this invention, the root portion is provided, on the outer surface of the root portion being opposite to the web, with a slag-forming coating reaching unti l the plain defined by the shoulders. For the relative measurement of the root insert, it is pre¬ ferable according to the invention that in the case of cold coating, the mass ratio of the root portion to the web is at least 2:8 and in the case of hot coating, the mass ratio of the root portion to the web is not more than 3:7. In a preferred embodiment, the root insert is made of the same material as the welding electrode used for welding the constructional parts and/or as the constructional parts themselves. The Improvement of the method for welding of .constructiona parts according to this invention is in that before pro¬ ducing the weld root, a root insert is placed in between the constructional parts to be welded together, especial¬ ly root insert according to any one of Claims I to 5, and thereafter the weld root is produced by melting the web of the i sert. In a preferred real ization, one of the shoulders of the root insert is lain on the root sided surface of one of the constructional parts to be welded together and there¬ after, the other constructional part is lain on the other shoulder of the insert. According to the invention, in the course of melting down the web of the insert, the first fi l l ing layer of the weld seam is simultaneously produced in form of a twin seam. Final ly, it is also a preferable real ization of this in-, vention when the form of the web as wel l as the mass ratio of the root portion to the web is chosen according to the material of the constructional parts to be welded together, the dissipation of heat by the constructional parts, the character of the coating and the qual ity of the weld seam to be produced. Brief Description of the Drawings The invention wi l l now be described in greater detai l on "t e basis of a preferred embodiment with reference to the accompanying drawings, in which Fig. I i l lustrates a preferred real ization of the metrod of this invention with the help of a cross section of a preferred embodiment of the root insert as in the invention, Fig. 2 shows a root weld produced with the help of this i nvent i on . Descr i pt i on of the Preferred Embod iment Referring now to the drawings, the invention wi l l be des¬ cribed with the help of an example of a tube made of hig ly al loyed austenitic steel . As it is apparent from Fig. I , the ends of tubes I and 2 to be welded to each other are finished for having the shape as usual ly necessary for the welding procedure. Between tubes I and 2, according to the invention, a root insert 3 is provided which, in this particular case, is ring shaped. Root insert 3 has a root portion 4 and, connected to this, a web 5. As it wi l l be described later in more detai l , shoulders 6 are lying on the surfaces of tubes I and 2 in their mounted position before welding. Shoulders 6 are provided on both sides of web 5 at its junction to.root portion A. In this way, root insert 3 has a stubby mushroom-shaped form turned up¬ side down. The vertical leg of the mushroom is web 5 and its pi leus formes root portion A. On the brim of the pi leus, the ends of tubes I and 2 I i e on as shown in Fig. I . In this example, the two side surfaces of web 5 are adjusted to the forms of the finished tube ends. Since, in this par- ticular case, root insert 3 is used for welding tubes I and 2 made of highly al loyed, austenitic steel, the welding seam to be formed is to be protected against the ambient air. According to the invention, this is solved by provid¬ ing a slag-producing coating 7 rather than by argon gas scavenge as usual with the previously known solutions. This coating 7 covers the outer surface of root portion being opposite to web 5 unti l the plain defined by shoulders 6. In this way, the ends of coating 7 form elongations of shoulders 6 lying on the root-sided surface of tubes I and - 2. Fol lowingly, coating 7 also contacts this root-sided surface of tubes I , 2 and in the mounted position of root insert 3 as shown in Fig. I , ambient air cannot creep in to the weld seam under production from the root side. The material of this slag-producing coating 7 on root insert 3 can be the same as that of the welding electrode with which the welding is carried out. Coating 7 is only needed where this is necessitated by the qual ity of the materials to be welded as wel l as of the welding seam to be made. Of course, root insert 3 without any coating can be provided and used, too. However, coating 7 serves, at the same time, as a support for the weld seam during the welding operation and, practical ly, it el imina¬ tes the danger of col lapse of the melt. Therefore, the use of root insert 3 having coating 7 on it can be reasonable in such cases, too, in which this would not be indispensa- ble because of the materials to be welded. In Fig. 2, a root seam 8 produced according to the invention is shown in cross section. This root seam 8 is in fact a twin seam, since not only a seam root 9 in s-trict sense of the word but also a first fi l l ing seam layer 10 is formed. A preferable real ization of the method in this invention wi l l be described hereinafter by setting forth the use of an embodiment of the root insert 3 of this invention. Before starting the welding operation, the ends of tubes I and 2 must be shaped for having the proper form for welding as usual . Thereafter , the ring-shaped root insert 3 wi I I be placed on the end of, let's say, tube I by lying shoulder 6 of root insert 3 on the root-sided surface of tube I and arranging web 5 radial ly outwards. After this, the other tube 2 wi l l be placed on root insert 3 for lying tr.e root-sided surface of tube 2 on the other shoulder 6 of root insert 3. In the course of this, the longitudinal axis of tube 2 should be brought into coaxial position with f-at of tube I , and tube 2 should be pushed in this coaxial di¬ rection onto shoulder 5. Having carried out this, sharp edges of tubes I and 2 l ie between shoulders 6 and web 5 along the whole peripheries of the tubes I , 2. But with this, the centring of tubes I and 2 is also carried out. It is guarantied that the distance between the ends of tubes I , 2 is constant along the whole periphery which hss a striking importance with regard to the welding seam to be produced. After arranging tubes I and 2 on root insert 3, the welding can be started by melting down web 5. If tubes I and 2 can be pressed towards each other and, thus, their secure position on root insert 3 can be maintained constantly, the provisional fixing of tubes I , 2 to each other by melt- ing web 5 in some places around the periphery, the so cal led stepping wi l l not be necessary. But if against al l, this fixing is carried out, conventional tack weld wi l l not come into being. In the course of melting down web 5, the root gets also melted which wi l l be supported from the inside by coating 7. Root portion A of root insert 3 formes seam root 9 whi lst the additional material for the first fi l l ing seam layer 10 is provided by web 5. The heat being necessary for melting is transferred through web 5 and the impacting tube edges to the root. The heat amount should be sufficient for total ly melting to each other the edges of tubes I and 2 and root seam 8 as we I I as for producing slag from coating 7 on the root side. Since the heat transfer occurs pre¬ dominantly through web 5 and the tube edges, the form of web 5 as wel l as the mass ratio of web 5 to root portion A have eminent importance. Dominant factor is the heat dis¬ sipation of tubes I and 2 which can be different for the two tubes I , 2. With respect to al l these factors, the form of web 5 and the mass ratio of web 5 to root portion A must be determined with great care. In the case of cold coating, for example, the mass ratio between the mass of web 5 and root portion A is preferably at least 2:8 but the root portion A in case of need can be smal ler in relation to web 5. But if hot coating is used, this mass ratio should be maximum 3:7, i.e. the difference can be smal ler between the masses of web 5 and root portion A. Nevertheless, web 5 has a heat regulating function by being formed as in this invention: it makes possible the necessary heat transfer but it counteracts to the burning of -the materials of tubes I , 2. In the course of the welding, coating 7 gets melted and forms the slag coating protecting the seam under production from the influences of the ambient air. Therefore, a prote ' c- tive atmosphere on the root side is absolutely unnecessary, even with the most sensitive materials. Of course, the root insert as in this invention can be used not only for tubes. Welding seams with optional form and tracing can be made ' ith the help of the root insert ac¬ cording to this invention but the root insert must have always the same shape as the welding seams. Experiencies and tests with this method and root insert as set forth previously have shown that the objects as mention¬ ed in the introductory part can be reached without exep- tion. Moreover, to our greatest surprise, root seam 8 wi I I be mo a beautiful and even than awaited. Seam root 9 merges with the root side surface of the constructional parts welded together to a great extent. Col laps or other deformations of the weld seam can not be observed. In the cage of' tubes, the latter has a striking importance, since for tubes, a finishing of the root seam is not possible. The root sea^ merged with the neighbouring surfaces wi l l hot cause con¬ siderable hindrances for the material flow in the tubes and, thus, the provisions in this respect can easier be fulfi l led than earl ier.

Claims: Cl a ims I . Root insert for welding seams between constructional parts, especial ly that made of highly al loyed steels, ch a r a c t e r i z e d in that the insert (3) has a root portion (A) and a melting web (5) connected to the root portion (A) as wel l as shoulders (6) on both sides of the web (5), which, in mounted position of the insert (3), l ie on the root-s ided surfaces of the constructional parts to be welded together. 2. Root insert as claimed in Claim I , wherein the root portion (A) is provided on the outer surface of the root portion (A) being opposite to the web (5) with a slag-form- ing coating (7) reaching unti l the plain defined by the shou I ders ( 6) . 3. Root insert as claimed in Claim I or 2, wherein in the case of cold coating, the mass ratio of the root portion (A) to the web (5) is at least 2:8. A. Root insert as claimed in Claim I or 2, wherein in the ,ase of hot coating, the mass ratio of the root portion (A) to the web (5) is not more than 3:7. 5. Root insert as claimed in any one of Claims I to A, wherein it is made of the same material as the welding electrode used for welding the constructional parts and/or as the constructional parts themselves. 6. Method for welding constructional parts, especial ly that made of highly al loyed steels, to each other, wherein a weld root is produced first and than further layers of the we Id seam is bui lt up, c h a r a c t e r i z e d in that before producing the weld root, a root insert is placed in between the constructional parts to be welded together, - I I especial ly root insert according to any one of Claims I to 5, and thereafter the weld root is produced by melting the web of the insert. 7. Method as claimed in Claim 6, wherein one of the shoulders of the root insert is lain on the root sided sur¬ face of one of the constructional parts to be welded together and thereafter, the other constructional part is lain on the other shoulder of the insert. 8. Method as claimed in Claim 6 or 7, wherein in the course of melting down the web of the insert, the first fi l l ing layer of the weld seam is simultaneously produced in form of a twin seam. 9. Method as claimed in any one of Claims 6 to 8, wherein the form of the web as wel l as the mass ratio of the root portion to the web is chosen according to the material of the constructional parts to be welded together, the dis¬ sipation of heat by the constructional parts, the character of the coating and the qual ity of the weld seam to be pro¬ duced .

Inventors: VEICZI CSABA, VEICZI, CSABA
Applicants: VEICZI CSABA, VEICZI, CSABA
Application year: 1986
Main classification: B23K9
IPC codes: B23K9, B23K33