Renovating of Shafts for Folio Extrusionusing new Type Coating with Nano Components

D. Karastoyanov1, T. Penchev2, G. Gavrilov2

1Institute of Information and Communication Technologies-BAS, Sofia, Bulgaria 2Techical University – Sofia, Bulgaria

dkarast@iinf.bas.bg

Abstract - The main goal of the project described in the paper is the creation of industrially applicable technology and the design of a relevant technological line for laying of coatings with high mechanical wear-resistance and surface-smoothness for renovation of the working area of shafts for extruding sheet material (PVC, Plexiglas, other plastics) by laying and polishing of new types of highly wear-resistant coatings based on ultra disperse nickel coatings with nano-dispersoids and/or nano-particles included.

Keywords - extrusion shafts, nickel layer, nano-elements, mechatronics, robotics

І. INTRODUCTION

Extruding (pressing by pushing) of sheet material from non-metal materials (Plexiglas, PVC, other plastics) is widely used in households. Gifts, flowers, sugar and chocolate packing is made from thin aluminum sheets. Thin Plexiglas sheets are used to make pack-boxes, and thick nylon sheets are used to make bags, raincoats, etc.

The vast amount of production of smooth sheets of various sizes from these materials has brought to the development of technologies in which the material is pressed and pushed out (extruded) between shafts of various diameters (100 – 500 mm) and various lengths (1 – 3 m). The shafts are chromed, have very narrow tolerances of diameter size and very high degree of smoothness by polishing.

With the time and at high production rate shafts age, their surface wears out, and sometimes scratches appear in incidents. All this makes the shaft surface not precisely circular and even. Because of a new shaft’s very high price, renovation of the defected shaft is applied in such cases by applying a new coating and polishing it to mirror shine.

Although there are many companies in Bulgaria and Europe which produce smooth folia by extruding, renovation of such shafts is done mainly in Italy and Germany. The operation is a company secret and is very expensive – between 25 and 35 thousand EU; one has to wait in queue; transportation is also expensive for remote destinations. Scientific research on the subject exists in Bulgaria (Sofia TU, Space Research Institute - BAS) but there is no working technological line for renovation.

ІІ. IMPORTANCE OF THE SUBJECT

The creation of an industrially applicable technology and the design of the respective technological line are of great economical importance for the technical

support of all kind of extruding and rolling mills producing sheets of various plastics and aluminum alloys.

The renovation of working surfaces of extruding shafts for various types of folio – plastics, PVC, Plexiglas, household or packing folio is done outside Bulgaria by the producers of the corresponding equipment or by a small number of specialized companies using their own classified technologies. This creates great difficulties to Bulgarian and South-east Europe companies in the case of prophylactics or minor repair of their equipment due to:

- High transportation expenses because of distant locations of renovating companies’ sites and the necessity of special measures during transportation of those oversize precise machine details;

- Additional investment is needed to procure spare shafts to minimize idle time losses of those high-productivity machines, working 24/7/365;

- Limited production capacities of the renovating companies and the relatively long technological cycle of the methods used make these services rather expensive and time-consuming;

- The existence of limitations following Bulgarian EU membership connected to Directive for prohibition of coatings and activities using highly harmful substances, as chrome coatings and cyanide baths.

These exploitation and organizational problems obviously create enough motivation in Bulgarian producers and Bulgarian government, to turn to relevant scientific organizations and experts for technical support. They are also willing to co-finance the research and innovation developments needed to solve that technological problem.

ІІІ. DESCRIPTION OF THE PROJECT

ІІІ.А. General description of shaft renovation processes

A technological line for chrome based smooth shaft renovation should include at least the following technological cells and operations:

1. Grinding of the old chrome layer at a given roughness

2. Coating of a new chrome layer in a galvanic (cyanide) bath

3. Rough grinding of the coating down to a predetermined diameter and roughness

4. Fine grinding of the shaft down to a predetermined roughness

5. Polishing of the chrome to a predetermined smoothness (Ra ~ 0.02 - 0.03)

The grinding of the old chrome layer is a routine and easy operation if one has lathes with long guides, accurate screws and good bearings. Usually 120 µm to 150µm of the old chrome are taken off, where greater roughness is required to enable the new chrome layer to stick better.

The laying of the new layer of chrome can be done in a galvanic bath where part of the shaft is dipped and it is slowly rotated. Thus relatively big thickness (120-150 m) and unevenness of the coating is achieved. The evenness is improved through the next operation.

Like the previous stage, if one has lathes with long guides, accurate screws and good bearings, one can achieve enough accuracy of shaft’s diameter, a decent smoothness (unlike operation 1 where bigger roughness is required) and one can take off the excess chrome.

The operations enlisted are common, traditional and well-known. They can be done using the available machinery in the majority of machine-building plants after a certain renovation of machinery. Next a transportation method has to be developed to move the shafts between operations – conveyers, inter-operations-stations – as well as whether there is necessity of fitting details – industrial hardware and controlling software.

The following characteristics of the existing situation should be taken into account when discussing the eventual new innovative technology:

1. Currently, according to company information and own marketing research there is no place in Bulgaria to make quality chrome coating with such thickness and shaft dimensions (detail). The nearest chroming companies are in Turkey.

2. There are EU Directives (which we have to follow after 01.01. 2007 as EU members) forbidding chrome coatings as exclusively harmful. Furthermore, the waste (cyanides) from chrome baths is also highly harmful and banned.

3. As a rule the finishing and polishing of steel (from which shafts are made) is more developed, cheap and successful as well as less harmful than processing with chrome, especially for big details and smooth-finish.

The idea of polishing the steel base of the shaft to the necessary smoothness emerged on the basis of these studies and it also included laying a thin (15-25 µm) nickel coating with nano-particles in it, or a thicker one (25-40 µm) including other micro - and nano-dispersoids for increasing hardness and wearing out resistance.

Fig. 1. Hollow smooth shaft for extruding of folio.

Plastics are pushed through a pair of shafts at about 200° C working temperature– fig. 1. To maintain constant working temperature all along the shaft, channels are made inside it, where hot oil is circulated at controlled temperature. The extruded material has the same temperature as the circulating oil.

Note: The high working temperature is an advantage with the chosen renovation method, because the hardness and wear-resistance of the suggested coatings is increased through tempering, which is naturally obtained in our case during normal operation.

ІІІ.В. Chemical nickelling and disperse coatings on its base

Chemical nickelling as an applicable technology started in the 1950s. For several decades this technology was rightfully called NONELECTRIC NICKELLING, as it is carried out without the use of external electric current source. In these processes, also called AUTOCATALITIC, the role of electric driving force is played by specific reductors: sodium hypophosphite and more rarely – sodium boron hydride, [1]. Being in the solutions, these reductors inevitably bring their ‘noncleanings’ in the metal coatings. A certain percentage of PHOSPHORUS / BORON is embedded in the nickel matrix. The respective phosphides/borides are formed during low temperature processing e.g. 200 - 400° C. These are solid phases, which bring to increased hardness and wear resistance, [2].

The chemical nickel coatings are 6-8 times more expensive compared to galvanic nickel coatings. Nevertheless they are being increasingly introduced in new areas. The reason lies in their unique qualities. The most important are, [3]:

- High evenness in the layer thickness i.e. they are sized coatings, requiring minimal finish processing;

- High hardness and wear resistance. Friction coefficient with many partners is relatively low;

- Low porosity/high corrosive resistance; - Excellent polishing ability because of great

hardness and microcrystal structure;- Convenient disperse coatings matrix. They can be

MICROSCALE и NANOSCALE.The application of disperse coatings with nickel-

phosphor matrix started in the 1980s. The variety is comparatively big. It comes from the possibility of management of matrix contents as well as from the increased supply of MICROSCALE DISPERSOIDS and NANOSCALE PARTICLES in the last decade, [4]. Micro-scale insertions are mainly on the basis of carbides of titanium, tungsten and cobalt, characterized by high hardness and good bonding with the nickel matrix. Nano-scale particles are mainly nano-diamonds obtained through various technologies, [5]. The research on the project requires design and development of:

- Tribo-tester for evaluation and comparative testing of tribo-technical characteristics of technological micro- and nano-composite coatings;

- Testing device for measuring the geometrical parameters of renovated shafts and the evenness and smoothness of the coating.

The described production process includes some negative characteristics and conditions as:

- High working temperature - 200° C;- Abrasive effect of the extruded material;- Significant normal efforts on the contact surface of the shafts;- Non-interruptive working process.

The new type of coating offers improved characteristics and exploitation advantage regarding:

- Wearing resistance and micro-hardness;- Corrosion resistance;- Reduced porosity;- Rapid reduction of the friction coefficient;- Increased cohesion and adhesion.The listed improvements and physical-mechanical

features, due to the nano-structured nickel coatings, increase the exploitation time of the extruding shafts 2 to 10 times while at the same time reducing the thickness of the coatings 3 to 5 times. The reduced thickness compensates for the higher price of the operation. The increased working time is an additional advantage. Furthermore, the replacement of the chrome coating with nickel one satisfies the requirements of the EU Directives on pollution.

ІV. BASIC IDEA

The applied idea for development of combined (composition, dispersed) coatings including nano-particles for invariant metal formers is fundamental based on technologies, well known after 70 –ties. We are calling them DISPERSOID COATINGS.

Essentially these are a metal matrix, received in galvanic or chemical (reducing) method and distributed (more or less uniformly) micro- particles – second phase.

Principally, the combining of metal matrix (coating) features and the type of particles (dispersoids) improves some characteristics, such as hardness, wear-resistance, low rubbing coefficient, high rubbing coefficient, corrosion – resistance, etc. As a rule the second phase is non – metal, for example: graphite, silicon carbide, corundum, polymer dusts, diamonds and other.

ІV.А. Dispersoids. Classifications of dispersoids with tribologycal purpose

To elucidate some steps of the main task we will review some most used dispersoid groups. In this review, the accent will be under micro- area of nano- area.

Dispersoids of the micro-areaPhysical and chemical features of particles from the

second phase have a main role in the forming of dispersoids. They having an influence as well in process of building as well in coating’s operating quality. To receive dispersoids with a good physical and mechanic quality the specific features of dispersoids are used in managing control of technological process.

Dispersoids with different size and ingredients have a different conduction in electrolyte. For example, different conduction have dispersoids “conductors” and dispersoids “insulators”, large dispersoids (10-50 μm) and small dispersoids -(0,1-5 μm).

New features assume dispersion coatings, where particles have a specified orientation in relation to detail’s surface. It is a perspective trend to use dispersoids with specified physical features for orientation. Their movement and their precipitation could be controlled.

As dispersoids can be served micro-dusts of hard-fusible oxides, carbides, silicones, borides, nitrides, diamonds, ect. (Tabl. 1). Micro dusts are produced in two ranges of grains – wide and tight. The size of the grains of the basic fraction set by screening through two sieves – allowing and holding, for tight rage micro- dusts, and for wide range – through three.

Tabl. 1. Micro-area dispersoids

Dia-mond

Silicon Carbide

Electro-Corundum

Wolfram Carbide

Boron Carbide

Titan Carbide

Dispersoids of the nano-areaIt is considered, that nano- technologies are one of

the high achievement in the science for the last few years and they have found a hundreds applications in the wide range of areas – from medicine to solar panels, from ecology to coating fils with surprising new features.

Some of the companies offer different nano- elements, mainly nano- powders. These are Oxides, Carbides & Nitrides. Some of them, included in our experiments are:

C – Diamond Synthesized - 4-25 nmSiC – Silicon Carbide - 50-60 nmAl2O3 – Aluminum Oxide - alpha, 200 nm

We foresee two types of experiments:1. Investigations in small prototypes of different

types of Nickel – based coatings including micro- and nano- dispersoids in laboratory conditions.

2. Investigation in working – like conditions (t = 2000C) of hardness and weariness in prototypes of moving shafts

ІV.В. Experimental results The laboratory experiments were made for chemical nickeling with nickel – phosphorus matrix with micro/ nano scale dispersoids addition – silicon carbide, diamond synthesized. As optimal temperature is assumed 90-920 С, optimal pH – 4,7 to 4,9 and relation between cultivated area and volume of the solution (S /V) 1-2 dm2/l.

In approximately observing of the parameters above, the mass percents of phosphorus are between 8 – 10 mass %. This value is corresponding to the matrix relative weight. From here we deduced a theoretical (average) speed for coating – 24-25 µm/h.

The coating for combination of experimental models was made – fig.2. The combinations for the different models were chosen to be close to the assumed value of the relation S/V.

In this series of experiments, where silicon carbide nano-filter 700 nm was used, the concentration of the working solution was chosen to be 0,4 g/l. In the experiments the dispersoid we added on the 15-th minute from the beginning of the process.

The weight measures of the polishing plates from 0,25 dm2 proved calculated deposition speed – 23,8 to 25,2 µm/h. The coating follows the relief of the base and keeps the same smoothness, [6]. Same experiments were made also with nano-filter 150 nm Same experiments were made as well with dispersoid– nano – diamond dust. The following depositions were made:

Pure nickel – phosphorus matrix + Diamond Synthesized - 4-25 nm

The relief and smoothness of the coating are remaining.In some of the experiments the temperature was

increased (for about 40 min up to 960 С). Harmful effects (decomposition of the solution) were not observed.

Some of the models were used in preliminary experiments for chemical coloring (oxidation) of nickel – phosphorus coatings – fig.3. For a test in working conditions we designed a stand for high temperature testing (2000С) – fig.4.

The stand is consists of hollow shaft, driven by electric AC motor, and heater, blowing the shaft with hot air. A heat-resistant Teflon roller is pressed to the shaft, which serves as extruded material.

PLC Allen Bradley is used for stand control and inverter SEW Eurodrive (fig. 5) is used for driving mechanism. The personal computer is used to collect data regarding tests of wear resistance after continuous work.

ІV.С. Extruding and producing schemesHanding of material to shafts could be done from

the bottom or from the top – fig.6, but more used is from the top scheme. Fig. 7 describes the structural scheme of a producing line for sheet production.

Fig. 2. Coating of experimental models

Fig. 3. Chemical coloring - oxidation

Fig. 4. Experimental stand for testing in work conditions

Fig. 5. Control system of the stand

Fig. 6. Scheme of material handing in calendering of elastomers:а – three - shafts calender ; б – four – shafts calender;

в – four- shafts Г – shape calender with bottom material handing; г – four –shafts Г – shape calender with top handing; д – Z – shape calender

Fig.7. Producing line structural scheme for a sheet producing:1- extruder; 2 – calender; 3 – rolling for the sheet cooling;

4 – unit for longitudinal cutting; 5 – stretching shafts;6 – guillotine for crosswise cutting; 7 – packing unit

V. CONCLUSIONS AND RESULTS

As a final result in the long term (3-5 years) we are expecting:

- A successful development of a new type of nickel coating with micro- and/or nano-structures included;

- Development of a project of a technological line for renovation of smooth extruding shafts;

- Installment and testing of the technological line in a production plant;

- Market realization of the ready technological line for renovation of shafts.

ACKNOWLEDGMENTS

The paper is supported by Bulgarian NSF (National Science Fund) Grant No D02-13/2009

REFERENCES

[1]. Gavrilov  G., Chemical(electroless) Nickel Plating,  England , 1979, Monography, 307 pages[2]. Riedel W., Funktionelle Chemische Vernicklung, Springer, BRD, 1989, 176 pages[3]. Gavrilov G., Chemische nickelierung., Galvanotewchnik , vol.101., 2003, pp 17-22[4]. Gavrilov G., Nickelierung mit mikro-elements., Materialwissenschaft , vol.29, 2004, pp 56-61[5]. Gavrilov G., Nano – powders by nickeling., G.,J.Electrochem.Soc,   vol.152, 2005, pp 132-137

[6]. Gavrilov G., Karastoyanov D., Method for renovating of coating over steel surfaces., Bulgarian Patent No 110745, announced 2.9.2010

HIGH SPEED ROCKET PROPELLED INDUSTRIAL HAMMER:CONSTRUCTION AND AREAS OF APPLICATION

T. Penchev1 D. Karastoyanov2

1Tech. Univ. – Sofia, tzpenchevi@abv.bg 2IICT-BAS, dkarast@iinf.bas.bg

Abstract: This paper discusses the characteristics of an Industrial Rocket Engine (IRE) and the constructive features of the machines, propelled by it. The conditions were defined to produce hits of various duration, according to the peculiarities of the technological processes, requiring the use of such machines: a hammer for die forging; a hammer for pile driving, and a high-speed metal scrap briquetting. An experimental stand for “combined hit effect” research is described.

Key words: high-speed hammer, forging, pile driving, briquetting.

1. INTRODUCTIONHammers are used for 3D die forging and pile

driving. In the first case the hammer is propelled by a pneumatic cylinder, and in the second – by a modified diesel engine. The speed of the falling parts of these machines is 5-7 m/s. For forging of special alloy forgings and forgings of complex shape, high-speed gas forging hammers are used with speed of the falling parts of 16 – 20 m/s.

In the 70-ties of the 20th century Dr. Petar Bodurov patented a high speed forging hammer, propelled by the Industrial Rocket Engine (IRE) [1]. In the early 90-ties the first licensed IRE – Fig.1 [2], and a hammer propelled by that engine were produced. Several hundred conical gears were produced by it. IRE has a maximum thrust of 2 t.

Technical characteristics of IREThrust 5KN to 20KN;Combustion chamber pressure max 6 MPa;Fuel kerosene;Oxidizer air;Fuel consumption max. 0,62 kg/s;Oxidizer consumption max. 8,90 kg/sCoefficient of performance 0,92Engine mass 25 kg

In 2008 The Pile Driving Hammer was patented [3], propelled by IRE and 1 years later the first prototype was produced.

The use of the new type IRE expands the technological capabilities of the respective machines and allows for the development of new processes. These possibilities will be discussed below.

2. BASIC DESCRIPTIONConstruction and scope of application of a die

forging hammer propelled by IREFig. 2 [2] shows the photograph of a die

forging hammer with IRE attached to the ram.. It is seen that the construction of the hammer is significantly simpler compared to currently used pneumatic and gas high speed hammers. The element connecting the propeller and the hammering part was removed. One-way acting hydraulic cylinder is used to return the ram

up. The retrieval of the forging from the shape is done by a hydraulic pusher.

Fig. 1. A photograph of IRE

Technical parameters of the IRE propelled die forging hammer:

Maximum blow energy 36 KJ;Ram speed 10 to 18 m/s;Ram stroke max. 1659 mm;Height above floor level 3350 mm;

Width x depth 1250 x 800 mm;

Total mass (with a 22000 kg anvil) 28 000 kg;

Time of one working cycle 2 s.

Fig. 2. Photographs of IRE propelled die forging hammer

The value of the IRE thrust ‘R’ can be continuously adjusted in the limits 0 ≤ R ≤ Rmax. The reaction time is 0,001 s. Since the time of contact in die forging is 0,030 – 0,050 s [5] it is seen that the time of reaction is completely sufficient to perform the change of the IRE thrust ‘R’. This makes it possible to achieve a new quality level of the technological process in the following direction:

- When the ram is thrusted downwards by IRE and it is switched off just before the moment of impact, a high speed deformation is performed at 16-18 m/s. As mentioned in a great number of publications during the 70-ties and 80-ties of the last century [4], [5], forging at such speeds (called high-speed forging) allows us to produce complex shape forgings or forgings from hard -to - deform or special alloys;

- If IRE works during deformation conditions are created to decrease (combined blow) or completely eliminate the ram rebound (sticking blow). In that case the time of outflow of the metal in the die is increased. That improves the quality of complex shape forgings, which cannot be obtained by current technologies and decrease of forging stages. In order to have a combined or sticking blow it is necessary to define the force generated at rebound. That force is denoted as P1. The following formula to calculate P1 has been empirically obtained [6]: к m2+[k2m2

2-m2(m1+m2)(ηi+k2–1)]1/2

Р1=g(R+m2)(---------------------------------------- - k), (1) 2(m1+m2)

where g – earth’s gravity, m/s2 ; R – thrust of IRE, kg; m1 – anvil mass, kg; m2 – mass of ram, kg; η – coefficient of performance; k – coefficient of recovery.

Figure 3. shows a diagram of the change of the force Р1(R,к) for the existing hammer where m1 = 22000 кg; m2 = 220 кg; R = 500 – 2000 кg.

R=500

R=1000

R=1500

R=2000

0.00

1000.00

2000.00

3000.00

4000.00

5000.00

6000.00

7000.00

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

k

P1,kg

Fig. 3. A diagram of the change of the force Р1(R,к) for the hammer shown on Fig. 2.

After defining the rebound force Р1 we can tune IRE so that R ≥ Р1 and thus get a a blow with the necessary characteristics - combined or sticking blow.

The features of an IRE propelled forging hammer mean that a guided blow can be obtained by using IRE.

A similar IRE propelled construction can be used to produce briquettes out of metal or non-metal waste. The currently used briquette production technology is based on hydraulic presses. The quality of the briquettes is relatively good, but density is too small. For example, metal briquettes is 0.55 – 0.60 of the density of monolithic metal.

In the 70-ties of the 20th century high-speed briquetting machines were produced in the then USSR. The force to lute the waste was obtained from the explosion of a substance – Fig. 4 [7]. Those technologies did not become popular because of low reliability due to the use of

Fig. 4. Drawing of a high speed press for briquetting: 1 – waste; 2 – container; 3 – piston; 4 – explosion chamber.

explosives. The density of aluminum and titan shavings is increased to 0.7.

Experiments conducted by us via an IRE propelled laboratory device showed that the density of briquettes made of steel and cast iron shavings is 0.65 – 0.75. The production of briquettes from small size steel metallurgic waste is of particular interest. Briquettes are usually made of steel metallurgic scrap with particles

size bigger than 5 mm and about 10% connecting organic substances. The waste of smaller size, which is about 10 – 15% of the total quantity, is not utilized. When stuffing metallurgic waste with particles size ≤ 5 mm in an IRE propelled device, briquettes were obtained with density 0.55 without the use of connecting substance.

The existence of a pusher in the construction of an IRE propelled hammer allows to achieve full automation of the briquetting process.

3. IRE WITH PILE DRIVING HAMMERThe current technologies for pile driving use

diesel hammers with ram mass 500 – 2500 kg. An important feature of those machines is that they can drive vertically or at angles of up to 200 off the vertical direction. In a number of cases, such as pile driving in quake areas or installing of drain tubes in landslides, they have to be put at greater angle off the vertical direction. Because they cannot be driven, they are made by effusions which are expensive and slow.

Installing IRE on the ram significantly increases the technological capabilities of diesel hammers. Fig.5. [8] shows a drawing of a diesel hammer before and after installing an IRE. Fig. 6. [5] shows the driving capabilities of such a hammer. It is seen that an IRE propelled hammer does not have any limitations of the angle of driving – it can even drive vertically upwards.

a b Fig. 5. A drawing of diesel pile driving hammer; b – IRE propelled hammer.

Fig. 6. A drawing of the possible directions for pile driving.

4. EXPERIMENTAL STAND WITH IREThe stand (fig. 7) will be used for investigations

the hit processes of sphere over massive fixed plate, hit velocity up to 20 m/s. The diameter of the sphere is 50

mm; the brightness of the plate is up to 100 mm and thickness 80 mm. These dimensions are chosen due to constructive design and to avoid energy lost regarding to waves diffusions.

Fig.7. Structure of the stand: 1-base; 2-massive plate; 3- pneumatic sensor; 4- plate; 5-vertical guide columns; 6-upper position key; 7-upper plate; 8-control unit; 9, 12 – path sensor; 10- IRE; 11-

sphera; 13-air hose for the IRE; 14- el. magnetic valves; 15- manometer ; 16-tank, 17- tense sensor

A laser sensor for path measuring is used. The sensor consist of emitter of parallel beams 1 and receiver 2 – fig. 8. The brightness of the beams field is 70 mm. The beams are under angle α toward the sphere

movement and the rock of the plate 4 intersects them. The accuracy of the measuring of the vertical movement S is 0.0175 mm.

Fig. 8. Scheme of the path sensor

5. CONCLUSIONSThe construction details of an IRE propelled

hot die 3D forging hammer are described.Based on a formula to determine the force of

rebound of forging hammers a diagram has been drawn Р1(R,к), out of which one can determine the necessary thrust R of the rocket engine to produce combined or sticking blow.

The capacities and scope of application of an IRE propelled blow-hammer for briquetting of waste and pile driving are also described.

ACKNOWLEDGMENTSThis research was sponsored by The National

Scientific Research Fund, Grants ID 02-262/2008

REFERENCES [1]. P.Bodurov, High speed hammer, BG Patent No 24567/1978, [2]. P.Bodurov, T.Penchev, Industrial Rocket Engine

and its Application for Propelling of Forging Hammers,

J. of Mater. Processing Technology, 2005, vol. 161,

pp.504-508.

[3]. P.Bodurov, Device for pile driving, BG Patent No 65331/2008. [4]. Sogrishin J.P., Grishin L.P., Vorobjev V.M.,

High speed die forging, Мoskva., Mashinostroenie,

1978, 166 pages, (in russian).

[5]. Glanvill-Jones, Progress in high –energy -rate –

forgig, J. Inst. of Metals, 1970, IX, vol.97, pp.257-270.

[6]. T.Penchev, P.Bodurov, D.Karastoyanov.,

Rebound Force Calculation in the Case of Hot Forging

by Rocket Engine Proppeled Hammer., John Atanasoff

Celebration Days, International Conference Automatics

and Informatics ’09, Symposium Robotics and

Automation, Sofia, Bulgaria, sept. 29 – oct. 4, 2009, pp

II– 41 – II – 44

[7]. V.G.Stepanov, I.A.Shavrov, High energy impuls

methods for metal procedimg, Leningrad,

Mashinostroenie, 1975, 204 pages, (in russian).

[8]. Jet Technologies for ground protection and other building works, “B+K” Ltd Prospect, Sofia, 2006, pp 4-22.

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