BRIQUETTING OF ALUMINUM ALLOY CHIPS WITHCONTROLLED IMPACT

Todor Penchev, Stanislav Gyoshev, Dimitar Karastoianov

In this paper is investigated the possible to produce brackets from chips of two types of aluminum alloys. Chips of different shapes and sizes are compared, some of which are free of water and oil (cleaned chips), while the rest are left without cleaning (soiled chips). It has been found that the density of the briquettes produced by the cleaned and uncleaned chips is the same, and is about 93 % of density of the solid alloy. This high density allows obtaining a workpieces by subsequent plastic deformation. Upsetting and reverse extrusion of the briquettes were studded. The results show that may be accomplished a large extent of deformation of the briquettes when using processes with predominant compressive stresses.

Keywords— briquetting, chips briquetting, impact briquetting.

1. INTRODUCTION

For briquetting of metal chips are used mechanical and hydraulic presses with nominal force of several hundred to several thousands of kN. To obtain briquettes with good density the ratio H/D for different materials vary within wide limits (H / D = 0,8-0,25), where H is the height, and D is the diameter of the briquette. The greater is the density of the briquettes, the smaller are the losses in the transport and melting. Basic data used to evaluate the effect of briquetting operation are specific density of the briquette (ρ), g/sm3, and specific contact pressure for briquetting (p), MPa.

At briquetting with hydraulic presses it is achieved 60% - 75% briquette’s density in comparison with solid material density. The specific pressure reaches values p = 200-400 MPa, in briquetting of steel chips [1, 2].

Due to the large size of briquetting presses, large power consumption, and relatively low productivity, methods are searching to improve the efficiency of this process. One such method is high velocity impact briquetting [3, 4].

In [5] are presented the results of use of high velocity explosive presses for briquetting of metal chips. The obtained briquette’s density is (g/sm3): aluminum alloy - 2.2 to 2.4 (2.7 to 2.75); carbon steel - 5.0 to 5.5 (7.85); alloyed steel - 5.0 to 5.5 (7.48 to 8.0). In parenthesis is given the density of the respective solid metal. As a major drawback of this briquetting method is the impossibility of process control.

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In [6] is described construction of die forging hammer propelled by industrial rocket engine. Whit this machine is possible to work with controlled impact and with impact velocities from 4,5 m/s up to 20 m/s. Laboratory set-up for controlled impact, and the results of experimental study of metal chips briquetting by controlled impact with impact speed of 7 m/s are presented in [7]. Before briquetting chips are cleaned from residues of water and oil, which raises the cost of the production process. In this paper the possibility of briquetting of uncleaned chips is studied. It is shown in [7] that it is possible to obtain briquettes from aluminum alloy chips with density close to density of the solid alloy. The potentiality to produce parts using such briquettes is also investigated.

2. Laboratory set-up

The laboratory set-up is shown in Fig.1. The falling part 13 is accelerated by cold rocket engine 12, working with compressed air. The trust R of the engine is R = 226 N. Maximum height of fall and impact speed with 9.12 kg falling part mass are 1.1m and 7 m/s respectively. Largest impact energy is 223 J. In Fig.2 are presented controlled impact schemes of the device. Specific scheme of work is set by the control unit 16 and is performed by sensors 4, 5, 10, 11, 15.

a) b)

Fig. 1a. A laboratory set up for studying of collision processes: 1 – base plate with a mass of 235 kg; 2 – lower fixed body for elastic impact; 3 – lower fixed tool

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for plastic impact; 4 – induction speed sensors; 5 – air on/off induction sensor; 6 – guides for the falling part; 7 – trigger mechanism; 8 electro-magnetic valve; 9 – air pressure control valve; 10 - air ‘On’ sensor; 11 – receiver of the light sensor for speed; 12 – cold rocket engine; 13 – 6,17 kg mass falling part; 14 – plate for activation of sensors 4, 5 and 11; 15 – light speed sensor emitter; 16 – electronic control board; Fig. 1b. Impact schemes of the device from Fig.1a: 1- free fall (max.Vi =4.5 m/s ); 2 – free fall with additional force R at the time of impact (controlled impact with max.Vi =4.5 m/s); 3 – fall with acceleration by a rocket engine, without additional force in the time of impact (max.V i = 8.5 m/s); 4 - fall with acceleration by rocket engine + additional force R in the time of impact (controlled impact with max.Vi = 8.5 m/s ) 3. Methods

In Fig.3 are shown the chips used in the experiments. To account for the influence of the size and type of chips used in the present work (type A) are compared with those of work [7] (type B). In order to investigate the influence of the residual water and oil on the density of the briquettes produced by the impact briquetting part of the type A chips were cleaned (type AC) while others had been left uncleaned (type AUC). Table 1 shows data on chips chemical composition.

Fig.3. a- chips used in present paper (type A); b – chips used in [7] (type B).

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Diameter of the produced briquettes is 20 mm , as it is the hole of the die for briquetting. Diameter of the punch is 19.6 mm. The gap between the die and the punch is left out to ensure exit of the air that remains between the chips in the filling into the die.

Table 1. Chemical composition of Al-alloyAlloy type

Al Mg Mn Ni Si ρs

A 91.0 2.0 - 5.0 2.0 2.78 B 97.9 1.2 0.90 - - 2.71

ρs is the density of solid Al-alloy

Briquetting is carried out using controlled impact (regime 4 in Fig.2) and with maximum impact energy of 223 J. In order to investigate their density and structure the obtained briquettes are measured, weighed on an analytical balances and pictured on 3D X-ray tomography (Nikon XTH 225 Compact Industrial CT Scаnner).

Impact process is recorded with a high-speed camera. The video is processed with the software Vicsasso 2009 which defines impact speed (Vi) and acceleration (ai). The impact force Pi and impact energy Ei are calculated by formulas

, N, (1)

, J, (2)

where m is the mass of the falling part, in kg. The specific impact energy for briquetting is calculated by the formula

, J/sm3, (3)where Θ, sm3, is the briquette volume. The use of this indicator makes it possible to compare the results obtained under different conditions of briquetting.

3. Results3.1. Briquetting

In Fig.4 are shown the diagrams for velocity and acceleration by one of the experiments. It can be seen from Fig.4c that acceleration is very high - 1610 m/s2

(164 g, were g is the acceleration of gravity). Due to the action of the thrust of the

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rocket engine during the impact, the rebound is small – 28 mm (the coefficient of restitution e = 0.158) – Fig.4a.

a) b)

Fig.4. Diagrams for: a – velocity; b –acceleration in controlled impact briquetting

Fig.5. A1-A4 - briquettes from cleaned chips (type AC); AM1-AM4 – briquettes from uncleaned chips (type AUC)

Briquettes shown in Figure 5 are further processed by removing the protrusions, weighting and scanning. In Table 2 are shown the obtained data from the experiments. The average density for the briquettes received from cleaned and uncleaned chips is the same and is approximately 2.53 gr/sm3

. The average impact acceleration is about 1600 m/s2 (164 g).

Table 2. Parameters of controlled impact briquetting process

Briquette Vi,

m/s

ai, m/s2

Hreb, mm

Нbriq, sm

Dbriq, sm

ϴ, sm3 mbriq, gr ρ, gr/sm3

Ei, J Es , J/sm3

Рi, N

A1 7.12598 1609.823 1.597 0.461 2.013 1.466419 3.7346 2.546748 231.5549 157.905 14681.59A2 7.16733 1611.719 1.862 0.474 2.013 1.507772 3.7771 2.505088 234.25 155.3617 14698.88A3 6.80936 1494.162 1.743 0.488 2.011 1.549222 3.8545 2.488023 211.4353 136.4784 13626.76A4 7.17096 1631.31 2.242 0.506 2.008 1.601576 4.1275 2.577149 234.4874 146.4104 14877.55

average 7.068408 1586.754 1.861 0.48225 2.01125 1.531247 3.8734 2.529252 227.9319 149.0389 14471.19AM1 7.1024 1654.62 1.713 0.461 2.011 1.463507 3.7687 2.575116 230.025 157.1739 15090.13AM2 7.1563 1695.654 1.795 0.482 2.012 1.531696 3.8364 2.504674 233.5296 152.4647 15464.36AM3 6.95581 1609.755 1.398 0.474 2.012 1.506274 3.8442 2.552125 220.6278 146.4726 14680.97AM4 7.19591 1640.078 1.927 0.478 2.01 1.515967 3.7891 2.499461 236.1219 155.7567 14957.51

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average7.102605 1650.027 1.70825 0.47375 2.01125 1.504361 3.8096 2.532844 230.0761 152.967 15048.24

Hreb – rebound of the punch; mbriq – mass of the briquette

In Fig.6 is shown the scanned picture of an Al-alloy briquette. It is seen from Fig.6a that the highest density is in the middle area which covers about 0.5 Dbriq. From the vertical sections (Fig.6b, Fig.6c) it can be seen that the density is the lowest in the peripheral areas of the briquette. Because of the little impact time the air cannot be forced out of the briquette and remains in these areas. When using a large thrust R of the engine and it acts for a longer time, this air can be removed to obtain a briquette having a density of solid alloy. Such a briquette may be used to prepare parts by machining or by plastic deformation. This subject will be discussed below.

In Fig.6b, Fig.6c in the middle of the briquette heights there is a line which shows the material stratification. This defect in our opinion, is caused by the distribution of tensile plastic waves and has no bearing on the quality of briquettes. In the manufacturing of parts from such briquettes it can be removed by subsequent plastic deformation.

Fig.6. Photos of X-ray tomography briquette of Al - alloy: a - cross-section in the middle of the briquette height; b, c - orthogonal vertical sections through the center of the briquette; d - 3-D image

3.2. Plastic deformation of the obtained briquettes

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Due to the high density of the obtained briquettes the possibility of plastic deformation was studied. Three of the briquettes were deformed by upsetting on Instron test machine with maximum force 100 kN. On Fig.7 is shown one of the

resulting specimens with relative deformation ε = 17 %. None significant defects are seen in the surrounding surface and in the volume of the deformed briquette.

Fig.7. X-ray tomography of vertical section of deformed by upsetting briquette

Four of the briquettes (two AC and two AUC) were deformed by reverse extrusion – Fig.8. In this case for deformation is used Hydraulic press with

maximum force 400 kN. Wall thickness of the specimen is 2 mm. It can be seen that the bottom aria, which is deformed by pressure, is realized very large

a)

b) c)

Fig.8. Photos of X-ray tomography of deformed by reverse extrusion briquette: a - cross-section in the middle of the briquette height; a - vertical section through the center of the briquette; b - cross-section in the middle of the specimen height; c - 3-D image

deformation without defects. On the walls of the specimen are noted transverse defects, which are obtained by the action of the tensile stresses. From these results

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it can be concluded that the schemes of deformation with predominantly compressive stresses can obtain parts without defects, while the schemes of

deformation with predominantly tensile stresses are obtained parts with poor quality. It is necessary to be carried further and more extensive research in this field.

4. CONCLUSIONS

The studies reveal that it is possible to obtain high-quality briquettes from aluminum alloys chips by controlled impact, regardless of the type and size of the chips. The advantages of this method are as follows:

• Allows to obtain briquettes with a high density using chips which are not cleaned from residues of water and oil. Dropping out of the cleaning operations will reduce production costs for briquetting. This technology can be used only in cases where the briquettes will be used for melting.

• The density of the obtained in this work and in [7] briquettes is 93% - 96% of the density of the respective solid materials. Applied specific impact energy is Es = 150 J/sm3 and the thrust of a rocket engine, which provides additional pressure during briquetting is R = 224 N. Using industrial hammer propelled by a rocket engine described in [6], can be achieved much larger values of Es and R, which makes it possible to produce briquettes from aluminum alloys chips with a density very close to the density of solid metal.

• Greater density of the briquettes from Al - alloys allows obtaining a workpieces by subsequent plastic deformation when using processes with predominant compressive stresses (upsetting, die forging, extrusion). In this case, for obtaining of briquettes should be used free of water and oil chips. These options require further research for each separate workpiece type.

Acknowledgments This research was performed with the support of the Bulgarian Scientific

Fund Grant ID 02- 262/2008 and by the project AComIn "Advanced Computing for Innovation", grant 316087, funded by the FP7 Capacity Programme (Research Potential of Convergence Regions).

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References [1]. Stepanskii L.V., Metal waste briquetting, Mashgis, 1975, (in Russian).[2]. http://www.johnhartinternational.com/briquetting/ [3]. Poljakov A.P., Zalazinskaja E.A., Impact extrusion of powder material billets, Zvetnaja metallurgia, 2003, 1, 30-35, (in Russian).[4]. Wang J., Yn H., Qu X., Analysis of density and mechanical properties of high velocity compacted iron powder, Acta Metallurgica Sinica (English Letters), v.22, 6, 2009, 447 – 453.[5]. Stepanov W.G., Shavrov I.A., High energy impulse methods for metal working processes, Mashinostroenie, 1975, (in Russian).[6]. P. Bodurov, T. Penchev, Industrial rocket engine and its application for propelling of forging hammers, Journal of Materials Processing Technology, 2005, 161, 504-508.[7]. T.Penchev, I.Altaparmakov, Experimental Investigations on “Controlled Impact” Effect, International Conference METAL 2013, Brno, 15-17.05.2013.

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