GB2117007A - Detonation coating - Google Patents

Abstract

The method comprises the following repeating steps: conveying a powder and an explosive mixture of gases to a barrel (2) provided with electric discharger 3, igniting the explosive mixture to produce detonation in the barrel (2), and subsequently transporting said powder in the flow of detonation products to a body (11) of consumable material so as to impinge upon the surface of the body of consumable material and knock out therefrom particles of consumable material which are directed onto the surface of the workpiece (9). The body (11) of consumable material may consist of a plurality of elements made from different materials being components of the coating to be formed, which elements are assembled into a tight stack. The powder may be abrasive e.g. sand or a component of the coating. The invention is of a particular advantage in the case of applying composite coatings and coating from reactive materials. <IMAGE>

Description

SPECIFICATION Method of, apparatus and consumable body for detonation coating The present invention relates to the practice of applying a coating using a high-temperature spraying technique, and more specifically is concerned with methods and apparatuses for detonation coating as well as to the construction of a consumable body for carrying out said method. The invention is of particular advantage in the case of applying multi-component coatings and coatings from reactive materials.

Though the detonation coating technique has been known relatively long ago and is extensively used in the USA and USSR, there still exist a number of difficulties encountered in applying coatings from reactive materials and materials containing alloying additions. In particular, deposition by detonation waves of such reactive metal as titanium and various alloyed steels still remains an urgent problem. Attempts to deposit such materials with the use of the prior art techniques (cf. for instance, US Patents Nos 3,773,259, 3,884,415) have not produced wanted results. Said methods comprise mixing a powdered consumable material together with an explosive gaseous mixture, igniting the resultant mixture to cause detonation, and subsequently transporting said powder in a flow of detonation products to effect deposition of the powdered coating material onto a workpiece.

It has been established by testing as formed coatings that the properties of a deposited material are much lower than those of consumable materials before their deposition. In the case of reactive materials this is explained by rapid oxidation thereof in the flow of detonation products. In the case of alloyed materials the degradation of quality of deposited materials is associated with the burning-out of the alloying additions. There is known a method of applying a multi-component coating (cf. US Patent No 2,714,563) wherein as a consumable material use is made of a mechanical mixture of powders.This method comprises the following repeating operations: conveying a powder and an explosive mixture of gases to a barrel, igniting the explosive mixture of gases to produce detonation within the barrel, and subsequently carrying said powder in a flow of detonation products to a workpiece to be coated. Thus, the powdered consumable material impinges upon the surface of the workpiece to form a coating thereon.

Although the above method seems to be a promising one it has not solved the problem of applying a quality coating from reactive and alloyed materials. While carrying out this method there were observed disadvantages similar to those which have been mentioned above, that is oxidation of alloying and reactive elements. It has been well known that these disadvantages are caused by that the coating consumable material remains for a too long time in a high-temperature atmosphere of detonation products but the existing technology and equipment are not capable of removing them. The only way to remedy said disadvantages was to position the workpiece close to the outlet end of the barrel.Making the barrel shorter was not practical since it would result in a sharp lowering of a kinetic and thermal energy of the powdered coating material at the moment of impinging thereof upon a base material, which would considerably affect the quality of the coating being formed.

The above method is carried out with the aid of an apparatus comprising a frame carrying a barrel provided with an electric discharger, a gas mixer, a powder batch meter, said gas mixer and said powder batch meter being communicated with the barrel, and a workpiece holder positioned before the outlet end of the barrel. However, during operation this apparatus manifested all the abovementioned disadvantages.

The principal object of the invention is to provide a method of detonation coating which would provide producing quality coatings from reactive and alloyed materials.

Another object of the invention is to provide a method which permits producing quality composite coatings by using detonation coating technique.

Still another object of the invention is to provide a method which permits applying a coating onto non-heat-resistant materials with the aid of detonation coating technique.

Yet another object of the invention is to provide an apparatus for detonation coating, capable of producing coatings from alloyed and reactive materials.

An additional object of the invention is to provide a consumable body which permits quality composite coatings to be produced with the aid of the proposed method.

These and other objects of the present invention are achieved by that a method of detonation coating carried out with the aid of an apparatus having a barrel provided with an electric discharger, which method comprises the following repeating steps: conveying a powder and an explosive mixture of gases to the barrel; igniting the explosive mixture of gases to produce detonation in the barrel; subsequently transporting said powder in a flow of detonation products to the consumable body; knocking out particles from the surface of the consumable body by the powder carried by the flow; directing said knocked out particles onto the surface of the workpiece.

The proposed method permits the period of time within which the dispersed consumable material is exposed to the detonation products in the flow thereof to be substantially decreased. The consumable material in this case is not practically subjected to an oxidative attack of the detonation products. All these favourable factors enable producing quality coatings from alloyed and reactive materials applying detonation coating technique.

It is worth noting that said powder which is used to knockout particles from the consumable material, for instance, silicon dioxide (sand).

Producing a composite coating, for instance two-component coating, is preferably done by applying a modification of the proposed method wherein as a said powder use is made of the particles of one of the coating components, and the particles knocked out from the surface of the consumable body are carried together with the particles of said powder by the flow of detonation products to the surface of the workpiece. It is quite evident that a material of said powder must be neither reactive nor alloyed one. This modification enables the components of the coating to be uniformly distributed therein, which could not be achieved with the use of the prior art methods utilizing the powder mixture.

In the case of using a dispersed abrasive material as a powder it is advisable that the particles knocked out from the surface of the consumable body be transported to the surface of the workpiece separately from the particles of said powder, which will rule out affecting the workpiece and the coating being formed by the particles of abrasive material.

Application of coating with the aid of a detonation coating technique onto substrates (workpieces) from non-heat-resistant materials (plastics materials, for instance) requires that the particles torn away from the surface of the consumable body be directed to a workpiece positioned outside the detonation product flow, and a quantity of kinetic energy imparted to said particles by knocking them out from the consumable body be sufficient for these particles to leave said flow.

It is worth noting that neither of the prior art methods of this type features such a possibility.

To obtain a quality coating it is expedient that said abrasive material have a melting point and hardness which are higher than those of the consumable material. This will allow not only effectively knocking out particles from the consumable material but also heating them up to a temperature sufficient to provide their bond with the workpiece.

To provide a higher efficiency and make possible applying a coating from hard refractory materials it is advisable to use modification of the proposed method wherein the consumable body is heated before deposition. Being heated the consumable material becomes less hard so that its particles let themselves more readily be knocked out from its surface by the impinging particles of said powder.

In carrying out this modification it is desirable that the consumable body be heated to a temperature at which its hardness is less than the hardness of the abrasive powder used.

The consumable body is preferably heated by passing an electric current therethrough.

These and other objects of the invention are also accomplished by that an apparatus to carry out the proposed method comprises a frame carrying a barrel provided with an electric discharger, a gas mixer and a powder batch meter, each being communicated with said barrel, a workpiece holder mounted on the frame opposite the outlet end of the barrel, a consumable body holder positioned before the workpiece holder. Such construction of the proposed apparatus permits a thermal and chemical effect (oxidative attack) of the detonation products on an alloyed material to be reduced to a minimum.

The simplest modification of the proposed apparatus is that wherein the outlet end of the barrel is used as a consumable body holder.

To rule out deterioration of the workpiece by abrasive powders and detonation products it is expedient that outlet end of the barrel be made V-shaped and its bore be divided into two outlets, with the consumable body holder being positioned at the place at which said bore branches into two outlets. One of the bore outlets is adapted to direct the particles knocked out from the consumable body to the workpiece, while the other one serves for deflecting abrasive powder aside from the workpiece.

It is advisable that the apparatus be also provided with a direct current source having one pole connected to the consumable body holder and the opposite pole connected to the workpiece holder. This allows producing within an ionized flow of detonation products an electric discharge to facilitate transporting the particles of the consumable material onto the workpiece.

These and other objects of the invention are also achieved in that a consumable body for carrying out the proposed method of detonation coating consists of a plurality of elements made from different materials being coating components, which components are assembled into a tight pack. The use of a consumable body of such construction enables producing high-quality composite coatings.

The consumable body may be made in the form of rods.

The consumable body may also be made in the form of plates.

The invention will now be explained in greater detail with reference to embodiments thereof which are represented in the accompanying drawings, wherein: Fig. 1 is a functional diagram of an apparatus of the invention for detonation coating; Fig. 2 is an axial section of a modification of the proposed apparatus wherein the barrel serves to support the consumable body; Fig. 3 is a functional diagram of the proposed apparatus according to the modification used for application of coating on the workpieces of non-heat-resistant materials; Fig. 4 is an axial section of a modification of the proposed apparatus having a barrel with a Vshaped outlet end; Fig. 5 is a functional diagram of a modification of the proposed apparatus provided with an additional electric current source;; Fig. 6 shows a modification of a consumable body of the invention, in the form of a pack of rods; Fig. 7 shows an alterantive modification of said consumable body of the invention, made in the form of a stack of plates.

The proposed method of detonation coating is carried out with the aid of an apparatus illustrated in the attached drawings. The apparatus comprises a frame-1 (Fig. 1) on which is mounted a barrel 2 having an electric discharger 3. Mounted on this frame 1 are also a gas mixer 4 and a powder batch meter 5. The gas mixer 4 communicates with the barrel 2 through a connection pipe 6. The powder batch meter 5 communicates with the same barrel through a connection pipe 7. Mounted on the frame 1 opposite the outlet of the barrel 2 is a workpiece holder 8 to keep a workpiece 9 in position. The proposed apparatus is provided with a holder 10 for a consumable body 11 , which holder 10 is mounted on the frame 1 before the workpiece holder 8 so that the consumable body 11 fixed therein is positioned on the path of the detonation product flow.The consumable material is used in the form of a solid body 1 1 which may be variously shaped Shown in Fig. 2 is a modification wherein the outlet end of the barrel 2 functions as the holder 10 of the body 1 1. In this particular case the body 1 1 is made in the form of an insert 12 and in the form of a streamline part 13 fixed on supports 14 coaxially to the barrel 2.

A modification of the proposed apparatus shown in Fig. 3 of the accompanying drawings is adapted to apply coating onto workpieces of non-heat-resistant materials. As can be seen in the diagram the holder 8 of the workpiece 9 is displaced relative to the axis of the barrel 2 so that the detonation products are not directed to the workpiece 9. The body 1 1 has a flat surface 15 at an angle a to the axis of the barrel. In this case 0 < a < 900, and the surface 15 area facing the barrel 2 is equal to the area of the projection of the barrel cross section on said surface.

The workpiece 9 is fixed in the holder 8 at a distance of I from the body 1 perpendicularly to the surface 15. It is expedient that in each particular case the said distance be determined from the following relationship:

where I, is a distance from the end of the barrel 2 to the midpoint of the surface 15; D is an inner diameter of the barrel 2; p is an angle of the detonation product flow.

A modification of the proposed apparatus shown in Fig. 4 allows the abrasive powder and detonation products to be prevented from affecting the workpiece. According to this modification the outlet end of the barrel 2 is made V-shaped and its bore 16 is divided into two outlets 17 and 18, in which case the holder 10 of the body 1 1 is positioned at the place whereat the bore 1 6 branches into two said outlets. The outlet 1 7 is adapted to withdraw a portion of the dispersed abrasive material which is used as a powder. Positioned opposite the barrel outlet 18 is the holder 8 of the workpiece 9.

Shown in Fig. 5 is a modification of the proposed apparatus which is similar to that shown in Fig.

1 and disclosed above, but is additionally provided with a d.c. source 1 9 having a positive pole connected to the holder 10 of the consumable body 1 , the holder 10 and the consumable body 1 1 being made from electrically conducting materials. The negative pole of the source 19 is connected to the holder 8 of the workpiece 9, which holder 8 and the workpiece 9 are also made from electrically conducting materials.

In a modification of the proposed method, wherein the body 1 1 of consumable material is heated the proposed apparatus may include a conventional electric heating device (not shown), whose terminals may serve as the holder 10 of the body 1 1.

In the case of applying composite coatings it is advisable to use the consumable body 11 composed from a plurality of elements made from different materials being coating components. The said elements are assembled in a tight pack (Figs. 6 and 7). A modification of the consumable body 11 is also possible wherein said elements are made in the form of rods 20 embraced by a clamp 21 (Fig.

6). According to an alternative modification of the proposed apparatus said elements are made in the form of plates 22 tightened with the aid of bolts and strip 23 (Fig. 7).

The method of detonation coating is carried out with the use of the described apparatus as follows. Powder from the batch meter 5 is conveyed through the connection pipe to the barrel 2 (Fig.

1). Simultaneously from the gas mixer 4 an explosive gas mixture is fed through a connection pipe 6 into the barrel wherein said explosive mixture is ignited by the electric discharger 3 to produce detonation of said explosive mixture in the barrel 2. A gas product flow produced by the detonation entrains the powder suspended therein. At least a portion of the consumable material is used in the form of a solid body 1 1 which is positioned on the path of the flow of detonation products. The flow of detonation products is directed to the body of consumable material and the powder particles moving in the flow of detonation products knock out from the surface of the body 1 1 particles of the consumable material, which particles of the consumable material are directed onto the surface of the workpiece 9 and impinging thereupon form a coating.

According to one embodiment of the proposed method, as said powder use is made of particles of the material used as one of the coating components. In this case the particles knocked out from the consumable body 1 1 are directed onto the surface of the workpiece 9 together with the particles of said powder. Transporting the knocked out particles of the consumable material onto the surface of the workpiece is effected both at the expense of a kinetic energy imparted to them as a result of the powder particles impinging upon the surface of the consumable body and a dynamic head of the detonation product flow. This modification of the proposed method allows producing composite coatings. The use of a modification of the consumable body shown in Figs. 6 and 7 allows producing multi-component composite coatings.

A modification of the proposed apparatus shown in Fig. 2 operates generally as that disclosed above except for that the consumable body 1 1 is made in the form of an insert 12 and a streamline part 13 made from the consumable material. The powder particles moving in the barrel 2 knocked out particles of consumable material from the insert 12 and the streamline part 13. This process takes place at the end of the barrel 2. The knocked out particles of the consumable material are transferred onto the surface of the workpiece 9 at the expense of the gas dynamic pressure of the flow of detonation products behind the streamline part 13.

Applying coating from very hard reactive or alloyed materials may be advantageously effected by using a modification of the proposed method which is carried out with the aid of an apparatus shown in Fig. 3. According to this modification as a powder use is made of a dispersed abrasive material. The particles knocked out from the surface of the body 1 1 are directed onto the surface of the workpiece separately from the particles of said abrasive material.To effect such separation of the particles the body t 1 (Fig. 2) may be used as a deflector, in which case the particles of said abrasive material after impinging upon the consumable body 1 1 do not move to the zone of deposition of coating material while smaller and lighter particles of the consumable material at the expense of the whirl remain in the flow of detonation products and are directed, as a result, onto the surface of the workpiece to form a coating thereon.

In the case of applying a coating onto workpieces from non-heat-resistant materials a modification is preferably used wherein the workpiece 9 is positioned outside the flow of detonation products. In this case the surface 17 of the consumable body 1 facing the barrel 2, has to be arranged relative the barrel 2 axis at an angle a (Fig. 3), in which case also is preferably used abrasive dispersed material. It is further expedient that said abrasive material have a melting point and hardness higher than the consumable material.

A higher efficiency is obtained by using a modification wherein before applying a coating the consumable body 11 is heated. In this case the conditions required in the above-said modification are not necessarily observed. The consumable body 1 1 may also be heated during the formation of coating, that is continuously. The simplest way to effect said heating is passing an electric current through the consumable body 11. The best results are obtained by that the consumable body is heated to a temperature at which the material of the consumable body 1 1 has a hardness which is substantially lower than the hardness of the abrasive material used as a powder.

A modification of the apparatus shown in Fig. 4 operates generally in a similar manner as that shown in Fig. 3, with the exception that the particles of the abrasive material after their impinging upon the consumable body 1 1 are exhausted through the outlet 1 7, while the particles knocked out from the consumable body 1 1 are directed through the outlet 18 to the workpiece 9.

Distinctive features of the operation of a modification of the proposed apparatus shown in Fig. 5 consists in that at the moment of detonation in the flow of ionized detonation products a separate electric charge is produced between the consumable body 11 and the workpiece 9 which electric charge substantially intensify the transfer of the particles of the consumable material onto the surface of the workpiece 9.

In principle, any of the above-described modifications of the proposed method may be used for applying multi-component composite coatings if as a consumable body 11 use will be made of the modifications thereof shown in Figs. 6 and 7.

The invention will now be explained in the way of examples of embodiments thereof.

Example 1 A method of detonation coating was carried out with the aid of an apparatus having a bore 21 mm in diameter and 1.3 m long. Silicon dioxide (sand) with a range of particle dimensions of from 220 to 400 m was used as a powder. The explosive mixture was composed of the following components: combustible gas (acetylene), oxidizer (oxygen) and an inert gas (nitrogen). Said explosive mixture was obtained by that the acetylene was mixed together with the oxygen and the resulting mixture was diluted in nitrogen (C2H2:O2:N2=1 :1.5:1.5).

Before igniting the explosive mixture to produce detonation, silicon dioxide powder was fed into the barrel. Feeding said powder was effected by injecting said powder with the aid of the inert gas (nitrogen). The consumption of nitrogen constituted 0.8 m3/h, and the duration of feeding was 125 ms.

Supplying powder into the barrel was ceased 70 ms before initiating the explosion.

As a body of consumable material use was made of a rectangular plate of alloyed steel having the following composition (in %): iron 86.93%, chromium 13% and carbon 0.07%.

The plate was positioned at an angle of 400 to the axis of the barrel, with the upper edge of the plate being at the level of the barrel axis and at a distance of 20 mm from the surface of the workpiece.

The workpiece was made from a structural steel with a 0.3% carbon content. The distance between the outlet end of the barrel and the surface of the workpiece was 100 mm.

After 100 shots, with the frequency of 4 shots per second, on the surface of the workpiece was deposited a layer of coating from alloyed steel 180 ,um thick. The physicomechanical properties of the coating thus obtained were as follows: adhesivness of the bond between the coating and the substrate was 4.5 kg/mm2; porosity=1 %; height of irregularities=1 5,um.

For the purpose of comparison a similar workpiece was coated applying the prior art method of detonation coating. The powder of consumable material was alloyed steel having the following composition, in percents: iron 86.93 chromium 13.00 carbon 0.07 The results of comparative analysis of the coatings produced by the proposed method and the prior art method are given in a tabulated form below.

Carbon content in Carbon content the starting con- in the coating Phase in Mlcrohardness of Method used sum able material % % the coating the coating kg/mm2 Prior art 0.07 0.01 ferrite 300 method Method of the 0.07 0.05 ferrite 500 invention +martensite As can be seen from the table the burningsut of carbon in the case of proposed method is substantially decreased.

Example 2 A composite two-component coating was deposited from tungsten and copper, using the method described above. The coating was applied with the use of an apparatus having a cylindrical barrel 1.4 m long, with the inner diameter of the bore of 21 mm. The rate of firing was 4 shots per second. The explosive mixture was composed from acetylene and oxygene taken with a ratio of 1 :1.5. Tungsten having the size range of its particles from 5 to 40 ym was used as a powder, and the body of consumable material was made of copper. The workpiece to be coated was positioned at a distance of 8 cm from the outlet end of the barrel. After 100 shots there was formed a coating 1 50#m thick.

Analysis of the resultant coating showed that the components (tungsten, copper) were uniformly distributed within the layer of coating. The height of microirregularities did not exceed 202#m. The adhesiveness of the bond between the coating and the base metal (steel) was 2.5 kg/mm2.

Attempts to produce a coating with a uniform distribution of coating components with the use of the prior art method and a mixture of tungsten and copper powders failed without yielding wanted results. The resulting coating produced in a conventional way had a laminated structure.

Example 3 A composite coating was applied in a similar way onto a steel workpiece. The coating material consisted of tungsten and copper. The conditions of formation of said coating and parameters thereof were similar to those described in the above cases for except that the consumable body of copper was heated to a temperature of 4000. The thickness of the coating being formed reached 150 #m after 50 shots. Heating the consumable body was effected by passing an electric current therethrough. Thus the efficiency this time was 2 times higher than that manifested in the previous case.

While the invention has been described herein in terms of the preferred embodiments, various modifications may be made in the invention without departing from the scope of the following claims.

Claims (18)

Claims

1. A method of detonation coating was carried out with the aid of an apparatus having a barrel provided with an electric discharger, which method comprises the following repeating steps: conveying powder and explosive mixture of gases to the barrel; igniting the explosive mixture of gases in the barrel to produce detonation therein; transporting said powder in a flow of detonation products to a body of consumable material; knocking out particles from the surface of said body of consumable material by the powder moving in the flow of detonation products; subsequently directing said knocked out particles onto the surface of the workpiece.

2. A method as claimed in claim 1, wherein said powder is particles of one of the coating components, and the particles knocked out from the surface of the body of consumable material are directed together with the particles of said powder onto the surface of the workpiece.

3. A method as claimed in claim 1, wherein said powder is dispersed abrasive material, and the particles knocked out from the surface of the body of consumable material are directed onto the surface of the workpiece separately from the particles of said powder.

4. A method as claimed in claim 3, wherein the particles knocked out from the surface of the body of consumable material are directed to a workpiece positioned outside the flow of detonation products, and kinetic energy imparted to said particles while knocking them out is sufficient for these particles to be forced out from said flow of detonation product.

5. A method as claimed in claim 3, wherein said abrasive material has a melting point and hardness which are higher than those of the consumable material.

6. A method as claimed in claim 1, wherein before applying a coating the body of consumable material is heated.

7. A method as claimed in claim 6, wherein the body of consumable material is heated to a temperature at which its hardness is lower than the hardness of the abrasive powder used.

8. A method as claimed in claim 6, wherein the body of consumable material is heated by passing an electric current therethrough.

9. An apparatus to carry out the method of claim 1, which comprises a frame; a barrel mounted on said frame; an electric discharger mounted within the barrel; a gas mixer communicated with the barrel; a powder batch meter communicated with the barrel; a holder for a workpiece mounted on the frame opposite the outlet of the barrel; a holder for a body of consumable material mounted before the workpiece holder.

10. An apparatus as claimed in claim 9, wherein as the holder of the body of consumable material use is made of the outlet end of the barrel.

1 An apparatus as claimed in claim 10, wherein the outlet end of the barrel is made V-shaped, and the bore of the barrel is divided into two outlets, with the holder of the body of consumable material being positioned at the place whereat the bore branches into two outlets.

12. An apparatus as claimed in claim 9, which is further provided with a d.c. source having one pole connected to the holder of the body of consumable material, and the other pole connected to the workpiece holder.

13. A body of consumable material for carrying out the method of claim 1, which consists of a plurality of elements made from different materials being components of the coating to be formed, which elements are assembled in a tight stack.

14. A body of consumable material as claimed in claim 13, wherein said elements are made in the form of rods.

15. A body of consumable material as claimed in claim 13, wherein said elements are made in the form of plates.

16. A method of detonation coating substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

j 7. An apparatus for detonation coating substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

18. A body of consumable material substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.