A New Type of Screw Conveyor for Metallic Chips

F. Soavi, 0. Zurla - Submitted by Prof. R. Levi (1) Received on January 25,1990

SUMMARY

At present then is no type of chip handling equi ment which can satisfactorily transport all the kinds of metal swarf that are produced in industrial metal cutting. For the basic activity of swdremoval from the cutting ZOM and transfer to the machine tool perifery. an original screw conveyor is proposed.

The new screw type conveyor is suitable for handling all types of swarf (from fine dust to long helical ribbon) and can give a high axial thrust to the handling material. Experimental apparatus was used to find the effects of different types of swarfon screw performance at 100 % fill level. Experiments are described in which the dependance of capacity, torque and axial force vs rotational screw sped is tested.

KEY WORDS: Chip screw conveyor, screw conveyor performance, mechanical conveyor, handling metallic swarf, machine tool, manufacturing technology.

1. INTRODUCTION

The development of modern machine tools and the advances in tooling techniques demanded by the continuous improvements in productivity, have made it possible to produce large quantities of metal workpieces in less time and, consequently, to create great volumes of metal swarf at a faster rate.

The increased quantity of material removed from workpieces in the form of swarf is the waste-material produced by thecutting operation which has always created a problem in terms of collection, removal, handling and disposal.

Amongst themany factors connected with theeconomical production of workpieces, we should take into account the fact that associate production of swarf is an expensive business and therefore analysis must be carried out in order to reduce the volume of swarf generated to a minimum and to produce the swarf in the most easily handled form.

The volume occupied by the swarf produced is related to: - the quantity of metal removed as swarf, which depends on the

method by which the raw material is processed and on the efficiency of the design of the component to be produced; - the form and size of the swarf, as it leaves the cutting tool, which depends on: workpiece material, machining operations, machining conditions (feed, depth of cut, ty of cuttin? tool,

‘Karf can vary widely between very fine particles (dust in the dry condition and sludge when wet) and long spiral strands or ribbons. Machining operations and tooling that produce swarf as dust or broken chips may be considered as satisfactory because both these swarf forms can be readily and efficiently handled.

By far the largest proportion of handling problems are caused by long ribbons of swarf forming unmanageable bundles. These are impossible to move by hand and tend to get caught on machine projections or on the conveying mechanism itself. The main sources of this kind of swarf are usually machining operations such as drilling, turning and boring on ductile materials (i.e. steel, soft brass and aluminium).

The machine tool user can often simplify the swarf-removal problem by employing correctly designed cutting tools and chip breakers. When machining is economical the machine tools are maintained at peak production rates and swarf is continuously produced. The main objective of swarf-handling equipment is to achieve non-stop swarf removal from the cutting area in order to allow for continuous operation.

The problem of dealing with large quantities of swarf is aggravated by the fact that high-production-rate machine tools require the use of copious supplies of cutting fluid. The swarf and the cutting fluid must be separated and removed from the machine so that the cutting fluid may return to the machine tool with an acceptable standard of cleanliness.

The handling of swarfalways presents problems that requirecareful analysis in order to ensure effective and economic solutions.

The four methods of removing swarf from the cutting area of the machine tool to the machine periphery are: 1) gravity removal, 2) mechanical removal, 3) hydraulic removal, 4) pneumatic removal.

Wide variations in the characteristics and size of swarf materials handled mean that thedesigner ofequipment for conveying and handling these materials must have a thorough knowledge of chip handling.

Due to these wide variations not all conveyors are suitable for transporting all ty s of swarf, and selection of the most appropriate equipment calls close consideration.

General rules to follow, when selecting the type of conveyor best suited to a particular type of swarf, are as follows: - Mechanical conveying means, such as drag-link, continuous slat,

Drag-link is suitable for dealing with swarf in the form of broken chips or dust, whether the swarf is wet or dry.

Continuous-slat is used for handling the swarf in broken form and a limited proportions of bushy swarf.

Magnetic means are employed for the removal of ferrous swarf

of chip breaker, type and flow rate oKutting fluid).

magnetic and screw.

from the cutting fluid. Screw means are effective when dealing with broken or dust-

type swarf in either wet or dry conditions. - Pneumatic chip handling systems. The dry product must be in

a fine enough state for handling in the pneumatic conveying system, that ensures maximum collection of swarf chips and dust at the point of creation.

- Gravity removal. The critical features for swarf removal from the machine tool are the positioning of the discharge the machine and the effective design of slideways and toof%!:d:: in order to ensure that all swarf forms can freely reach this point from the cutting tool.

- Hydraulic conveying. Swarf is washed away from the cutting zone into a storage bed in the base of the machine by mean of the cutting fluid. In order for swarf to be dealt with at the point nearest its creation,

it is necessary to build the conveying equipment into the machine tool.

In general, machine tools are equipped with a storage bed in the base of the machine where the chips drop as they are cut from the workpiece and the cutting fluid is usually held in the same areah most machine tools, removal from this area is manual and the chips are raked up from the machine base into some form of container.

In many automatic machine tools (such as C.N.C. lathes, M.C. and F.M.S.) self contained mechanical chip removal conveyors are built into the machine for the continuous discharge of swarf into a cross conveyor serving a number of machines, or into a suitably sized container that

It is standard practice to remove swarf from the cutting zone of the machine tool by mechanical conveyors (such as drag-link, continuous-slat and screw) because of the advantages that favour their use for transporting swarf. - They are generally quite reasonably priced, robust in construction

and the materials used assure a long and useful life. - They will operate effectively in the presence of large quantities

of cutting fluid without allowing the liquid to leak and can be fully integrated with the machine’s hydraulic system.

- They can be used effectively on horizontal and inclined levels for discharge.

- They can be positioned in the machine structure so that the entire unit may be removed easily for maintenance purposes. Mechanical conveyors used are not without mechanical troubles

and need to be regularly serviced in view of the difficult conditions in which they operate.

In general, bulk conveying of steel swarf by mechanical conveyors is very difficult unless the material is first broken down to a suitable size.

Where mechanical chain conveyors are used, fine chips find a way of working into all the pins of the chain links and into all wearing parts of the system. The numerous moving parts in this type of equipment are attacked by these fine particles which ultimately break them down. Maintenance and replacement are extremely difficult and often the entire length of the chain must be replaced.

In recent years there has bcen a trend towards simplifyin the mechanisation of swarf conveyors and lowering the cost of haofling, through a reduction in maintenance. Consequently, traditional or modified screw machines have been set up on many modem machine tools. The adoption of this type of mechanical conveyor is actually limited because it is not suitable for the transportation of bushy swarf.

The aim of this work project is to present a new type of screw conveyor that is more effective in dealing with all forms of swarf (from the fine dust obtained working brittle materials to the long helical ribbons formed by turning ductile materials) and that can give high axial thrust to the handling material.

The proposed equipment is considered in terms of its basic activity of swarf removal from the cutting zone and transfer outside of the machine.

In order to allow for effective design of the equipment, expe- rimental apparatus was used to study the effects of different types of swarf on screw performances when equipment operates in steady,

may be handled by a forklift.

Annals of the ClRP Vol. 3/1/1%@ 399

near clogging, conditions. The depedence of capacity, torque and axial force vs rotational

speed was tested on two types of experimental screws actually built into two types of commercial machine tool.

2. NOTATION

D d p pitch of the screw t thickness of flight w width of the duct h height of the duct c clearance between screw and casing a angle of the mouth of the duct s length of the mouth of the duct L length of the screw a, b sides dimensions of the rectangular cross section bar I length of the chip feeding area n rotational speed of the screw T maximum steady state torque near clogging Fa maximum steady state axial force near clogging Q maximum steady state capacity near clogging Va apparent specific volume of swarf

3. THE CONVENTIONAL MACHINE AND MODIFICATIONS

Standard conventional screw conveyors are transporting devices which can handle a great variety of materials that have relatively good flowability, but they cannot handle long chips which inevitably wind round the shaft of the equipment.

These devices include a helical flight, mounted on a central shaft, which revolves in a stationary tubular casing or in U-shaped cross- section trough (Fig. 1).

The casing (or the trough) not only confines and guides the flow of material, but also serves as the housing in which all operating components (i.e. bearings, etc.) are supported and held together in their proper functional relationship.

A high (about 3 or more) D/d diameter ratio of the screw, a p/D=0.6+1,ahigh(50+120mm) of(D-d)R ratioand alow (0.014.08) 2t/(D-d) ratio are very common in this type of equipment.

Another device, which is now in use. is a revolving coil spring which rotates in a U-shaped guide. This equipment is easy and cheap to produce, but cannot handle long chips or give high axial thrust to the material.

outside diameter of the screw shaft diameter of the screw

Sez.C-C

I I

Fig. 1 The standard conventional screw conveyor.

4. THE NEW MACHINE CONCEPT

The new type of screw conveyor proposed (fig.2) has the following

i)the trough, in which the screw runs, has the walls at right angles (Section AA, Fig.2);

ii)a rectangular cross-section duct is inserted after the chip feeding area (Section BB, Fig.2);

iii)the screw operates with a low (1.6+2.1) D/d diameter ratio of the screw, a p/D = 0.9+1.1, a low (12+25 mm) difference (D-d)/2 and a high (0.6+1) 2t/(D-d) ratio;

iv)the screw shaft is driven by motor and reduction gear via a gimbal and rotates freely at the screw end dischar e. A chamfered rectangular cross-section bar (wiich is substantially

the same length as the device) is inserted into the bottom comer of the trough (see sections AA, BB). The screw is in contact, or almost in contact, with the rectangular cross-section bar and with the walls of the duct and can therefore rotate with imposed eccentricity.

The above mentioned features enable the new screw-ty conveyor to handle all chip forms and to give high axial thrust to t E material.

The tendency of long chips to wind round the shaft is avoided: - . by the trough walls set at right angles (i) and by a low value

of (D-d)R (iii) which prevents rotational velocity of the material; - by a low D/d diameter ratio of the screw (iii) since the helix

angle increases towards the centre of the screw, the rotational material velocity also increases in this direction with an accom- panying reduction in axial velocity;

features:

Se2.A-A A-l

I

I Sez. B-B I

I l l

Iwl Fig. 2 The new type of screw conveyor.

-by achamfered rectangular cross-section bar (iv) that stops rotational velocity of material allowing effective feed of the swarfs at the same. time.

A high axial thrust is iven to the material: -by inserting a rectangufar cross-section duct (ii) into which material,

which is prevented from rotating and pressed between the container v y walls and the screw, is forced to run, following the equipment axis;

-by a low D/d diameter ratio of the screw and by a high 2t/@- d) ratio (iii) which enable the helical flight to give and to bear high axial thrust.

A high axial thrust allows for notable reduction in the apparent specific swarf volume when the machine is working suitable materials. Another advantage in using the proposed new screw conve or, lies in the reduction in overall dimensions of the swarf handing devices outside the machine tool and of the collecting equipment (i.e. standard conventional conveyor in Fig.3a). New machine versions can force material into a swarf skip from the bottom, Fig.3b. or discarge swarf from the top, Fig.3~.

The cutting fluid can be separated from the swarf through the overflow apparatus in Fig. 2. The particular design of the unloading point prevents the cutting fluid from overflowing in the swarfdischarge point.

b rn I

Fig. 3 The overall dimensions reduction. a) standard mechanical conveyor. The new type of screw conveyor forcing material b) into the swarf skip from the bottom c) to discarge swarf from the top.

5. EXPERIMENTAL APPARATUS AND PROCEDURE

Figure 4 shows the general arrangement of experimental apparatus which was specially made to investigate the characteristics of the new screw-type conveyor.

Fig. 4 The general arrangement of experimental apparatus. (1) Tested screw conveyor . (2) Feeding belt conveyor. (3) T and Fa gau- ging equipment. (4) Interconnected measuring instruments.

5.1. Gauging equipment

A schematic illustration of the equipment is shown in Fig. 5. The plate (l), of a modified four guidepost die set, is supported

by bearings (3) held on a frame (4) and its rotation is stopped, via a suitable torque arm (5). by a load cell (6) (DSEurope Mod. 5464220 daN range) that allows for torque determination. A motor (7). with variable-speed drive (S), actuates the screw (9) by means of a gimbal (10). Torque reaction acts on the plate (1) through the connection between drive casing, plate (2) and the four guideposts (11)-(14) of the dieset. Moreover, the plate (2) can slide smoothly along the guideposts in the horizontal direction; this motion is stopped b four load cells (15). (16). (17). (18) (DS Europe Mod. 5464 228 daN range) which gauge (via a summing network: DS Europe Mod. AN371) the axial thurst that operates on the screw. f i o digital display units with hold circuit (DS Europe mod. AN332-H) allow torque and thurst determination.

Fig. 5 The equipment that allows torque and axial force determination.

5.2. Screw conveyors

conveyors whose dimensions are listed below: - Type 1: D=

The experimental apparatus was used to test two types of screw

12 mm, w= 112 mm, h= 74 mm, a= 4O, s= 165 mm, L= 2425 mm, a= 20 mm, b= 35 mm, 1= 1445 mm.

95 mm, d= 45 mm, p= 85 mm, t= 15 mm. w= 145 mm, h=100 mm, a= 26", s= 155 mm, L= 1300 mm, a= 30 mm, b= 55 mm, I= 810 mm.

70 mm, d= 45 mm, p= 75 mm, t=

- Type 2: D=

When the level of duct loading is 100%. the working cross section is 0.56 dmz for screw Type 1 and 1.02 dmz for screw Qpe 2.

Screw conveyors are made with sectional helical flights that are cold bent from a square or rectangular draft bar. A continuous helix is made by joining a number of sectional flights together on a round draft bar and by butt welding them together.

A commercial mild steel (Fe360) was used to build the screws which were then surface hardened by carbonitriding up to 62 HRC.

The casing is built by welding combined channel iron parts. Both screws have' right hand helical flights and rotate into the

trough in an anti-clockwise direction. The screws turn into the trough with a clearance (between screw

and bottom side of casing) that decreases from a maximum (at the connection with gimbal) to zero (at screw end discharge).

The points of the casing which come into contact with the screw are shielded by steel plates that are of the same material and are surface hardened like the screw.

The advantage to be gained by evaluating the performances of these two machines concerns the close relationship existing between shape, dimensions and capacity of the screw conveyors, and the type and size of swarf forms.

1 is used on a Mandelli M5 machining center - Type 2 is u sye i the r on a Maho Graziano GR 400 CNC lathe or on a Mandelli M8 machining center.

For this reason, the first one was tested with three types of swarf (dust, broken and long conical helices) that are commonly produced by machining centers while the second was also tested with long, tubular and helical swarf that is typically formed in turning operations.

5.3 Types of swarf

- Type A:dust and short comma (Pi 6) swarf produced by turning nodular cast iron (GS &:3) with particle size less then 2mm and a specific apparent volume Va = 0.66 dm3/

- Type B:broken and short helices (Fig.7) generated by face milling of special alloyed steel (39 NiCrMo 3) which had been quenched and tempered (ultimate tensile strength of 90 daN/mm2) with an average diameter of 9.3 mm, average length of 16.7 mm and Va = 2.51 dm3/kg.

- Type C:long conical helices (Fig. 8) created by drillin ordinary steel (Fe 360, ultimate tensile strength of 3gO N/mmz and 27% elongation) with an average diameter of 8 mm, an average length of 312 mm and Va = 9.54 dm3/kg.

- Type D:long tubularand helical (Fig9)produced by turnin stainless steel (AISI 304) with an average diameter of 7.5 mm, an average length of 800 mm (for tubular form). and an average diameter of 15 mm, and average length of 420 mm (for helical form), with Va = 4.16 dm /kg.

Average dimension values are the arithmetic mean of twenty measurements.

5.4 Test description.

The equipment was tested with the screw axis horizontal, and feedine dry swarf. Dry swarf was used in order to impose harsher operating conditions on the equipment. It should be noted that the experimental apparatus is designed to allow for testing with cutting fluid.

The standard experimental procedure consisted of operating the screw conveyor with an increasin amount of swarf which loaded up to form a steady condition, cfose to clogging of the duct. In these steady conditions the screw flight is submerged in the swarf as it operates in the feeding area because the duct is completly full. The conveyor capacity was determined by weighing the discharged material in a measured time interval. The torque and the axial force acting on the screw were measured by means of the above-said load cells. Each ex rimental result is the average value of ten tests.

Feeding ot%e experimental apparatus, for swarf materials A and B, was carried out using a belt conveyor device (2) Fie. 4, 260 mm width, equipped with an adjustable opening gate, and vanable speed drive. In view of the well known difficulties involved in feeding swarf material C and D, as stated above, loading of the screw conveyor with these materials was performed manually.

We tested the new type of screw conveyor by varying its rotation speed from 15 to 50 rpm. This is an advantageous range which is offered as a compromise between reasonable capacity and reduced maintenance. A significant point to note is that the equipment will usually operate at a constant revolution speed in industrial use. An exception may be offend by the use of a hydraulic power system.

The two types of screw tested have different uses -

The types of swarf used are described below:

kg.

6. EXPERIMENTAL RESULTS AND DISCUSSION

Tests were carried out to determine design data for equi ment and the results are plotted in Figs. 10, 13, 16 for screw $pe 1 and in Figs. 1 1 , 12. 14. 15, 17 for screw Type 2.

6.1 Screw performance data

The measured maximum capacities Q (Kg/min) versus rotational speed n (rpm) are plotted in Fig. 10 for screw Type 1 and in Figs.

401

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 6 Dust and short comma swarf (TLpc A). Fig. 7 Broken and short helices swarf (Qpe B). Fig. 8 Long conical helices swarf (Qpe C). Fig. 9 Long tubular and helical swarf (Type D).

11, 12 for Type 2. From the experiments it results that the maximum capacities vary

considerably according to the type of swarf. In the speed range tested, the capacity is roportional to the rotational speed. For the same speed and s w a d screw Type 1 gives a lower capacity then Type 2, according to the increase in Dld ratio, and no substantial difference in p/D ratio.

Therefore, by careful investigation of the experimental results, it can see that screw 'Qpe 2 gives a greater capacities than expected because of the significant increase in the slope of Qpe 2's fitting curves in comparison to Type 1's curves.

B from 0.G to 0.193; Type C from 0.071 to 0.136. These res% are influenced by the complicated relationship between certain factors such as: form, size, apparent s cific volume and flowability of swarf material. With constant swart%orm and size the capacity raises from screw 5 p e 1 to Type 2 as working cross scction of the duct increases. Both screws'capacity decreases when apparent specific volume increases. Good flowability is a positive factor for the effective handling of swarf.

In steady working conditions dust tends to accumulate in the bottom comers of the trough and duct so that build-ups are formed.

The slo increase for swarf 'Qpe A from 0.397 to 0.912; T

402

10 20 30 40 50 60 n rpm

Fig. 10 Screw 'Qpe 1. Experimental distribution of maximum capacity Q versus rotational speed n for the Types A, B and C swarf.

10 20 30 50 60 n rpm

Fig. 11 Screw 'Qpe 2. Experimental dishibution of maximum capacity Q versus rotational speed n for the Type A swarf.

12

1 . 0 swarfType6 - swarfTypeC .1 l o - swarfTypeD Y U '

8 -

-

10 20 30 40 50 60 n rpm

Fig. 12 Screw ?)rpe 2. Experimental distribution of maximum capacity Q versus rotational speed n for the Types B, C and D swarf.

Bushy swarf, resulting from long tangled ribbons or helices, are discharged through almost the whole cross section of the conveyor because there are only negligible build-up zones. This behaviour is justified by the easy connections that occur with these swarf forms.

Broken and short helix swarf, depending on their forms, behave in a way which comes between the two.

In order to handle dust swarf, the new screw conveyors have wider buil-up areas than those in conventional standard screws. This causes no detectable effect on the performance capacity of the screw operating either in the U-shaped trough (Fig. 1) or the proposed trough (sections AA. BB, Fig. 2). Therefore the design of the proposed cross section (ruogh is justified by the need for the new equipment to operate with either broken chips or the bushy type of swarf with equal efficiency.

6.2 Torque requirements

The measured maximum torque T (daNm) versus rotational speed n (rpm) are plotted in Fig. 13 for screw Type 1 and in Figs. 14,

I c

c

30 -

20 -r

140 I 1

/ ’ , , , . I . ,

0 swarf TypeA swarf Type6 swarfTypeC

1

o ! . , . I . I . I ’ I 10 20 30 40 50 60

n rpm

Fig. 13 Screw ?Lpe 1. Experimental distribution of maximum torque T versus rotational s p e d n for the Types A, B and C swarf.

40 / I

10 20 30 40 50 60 n rpm

Fig. 14 Screw w 2. Experimental distribution of maximum torque T versus rotational speed n for the Types D swarf.

6 , I

I

- . . - I I - , - ,

10 20 30 40 50 60 n r p n

Fig. 15 Screw Qpe 2. Experimental distribution of maximum torque T versus rotational speed n for the ms A, B and C swarf.

15 for screw Type 2. From experimental results it was found that the maximum torque

required to transport swarf was dependent on the rotational speed. In the rotational speed range tested, maximum torque varied considerably according to type of swarf. Through comparison of the experimental results, it becomes clear that only small differences are found between torque values for screw Type 1 and Type 2, although screw Type 1 has a lower capacity.

Among the many factors connected with swarf handling there are two which should be given special consideration due to their influence on the torque: - the apparent specific volume Va (dm’/kg) of swarf i s extremely

important, and the torque increases as Va decreases as shown by the results of swarf Type A in comparison to swarf Type B; - the form and size of swarf are also very important and the torque increases in spite of Va increases as is shown by comparing the results of swarf Type C with swarf Types A and B. The higher torque values required for handling swarf Type D

(mi 60

0 swarf Type A swarf Type6 swarf TypeC

60> 40

L ” , . I . I - . 10 20 30 40 50 60

n r p n

Fig. 16 Screw Type 1. Experimental distribution of maximum axial force Fa versus rotational speed n for the Types A, B and C swarf.

9 200

0 swarfTypeA swarf Types

rn swarf TypeC

200 0 swarfTypeA

10 20 30 40 50 60 n rpm

Fig. 17 Screw Type 2. Experimental distribution of maximum axial force Fa versus rotational speed n for the Qp e s A, B and C swarf.

are due to a more marked effect of form and size. It can be Seen that swarf Type D results, agree with Va variation of swarf Type C.

6.3 Screw axial force

The measured maximum axial force Fa (daN) versus rotational speed n (rpm) are plotted in Fig.16 for screw Type 1 and in Fig.17 for screw Type 2.

The experimental results show the dependence of maximum axial force on rotational speed. In the rotational s ed range tested, axial force is influenced by the type of swarf. E o m companson of the results it can be noted that axial force is practically the same for screws Type 1 and Ty 2 when Type A and Type B swarf are handled. For swarf Type the axial force required by screw Type 1 i s greater than that of screw 5 p e 2.The results for swarf Type D are greater than for the others because of the bushy swarf form.

7. CONCLUSIONS

- An original screw swarf-handling device has been proposed to carry out the basic activity of removing swarf from the cutting zone and transferring it to the machine tool periphery. - The new type of screw conveyor is well suited to dealing with wide swarf variations in form and size. This means that the device can overcome the general rule stating that no conveyor is capable of transporting all types of swarf. - There are many design features which enable the new screw conveyor to efficiently fulfil its function and to which distinguish it from standard conventional screw conveyors. - The performance of the screw conveyor was tested using ex- perimental a paratus which was specially made in order to investigate the effect oProtational speed, form and size of swarf, on capacity, torque and axial force i n steady, near-clogging flow conditions. The experimental results confirm the special operating advantages offered by this type of conveyor, it is able to give satisfactory capacity values for handling the swarf which is produced by modem machine tools with high metal removal rates. The overall dimensions of the conveyor casing make it easy to overcome the problem of building the conveying equipment into the machine tool. - In the experimental conditions, very low torque requirements were observed depending on the type of swarf material handled and

403

on the dimensions of the duct. - Axial force is not generally a critical factor, but it was investigated for design urposes because relatively high values can result when bushy swarris forced into the rectangular cross section of the duct, and a considerable reduction in the apparent specific volume can occur. - High axial thrust values can force material into the swarf skip from the bottom (Fig.3b) or discharge swarf from the top (F'ig.3~). Both solutions reduce the overall dimensions of the chip handling device outside the machine tool as shown in Figs.3a, b, c. - From comparison of experimental results, it appears clear

that screw conveyor 2 has better operating features than Type 1. The capacity of screw 'Qpe 2 is really greater than expected, on the basis of cross sectioii ducts ratio, for screw Type 1, while values of torque and axial force are practically the same. - The experiments were carried out with dry swarf in order

to impose more difficult operating conditions on theequipment. Industrial use has shown that the conveyor can operate effectively in the presence of large quantities of cutting fluid without allowing the liquid to leak. - The compactness, economy and reliability of the equipment are advantages that favour its use for swarf handling.

ACKNOWLEDGMENTS

The authors are grateful to Prof. R.Levi of the Dipartimento di Tecnologia e Sistemi di Produzione Politecnico di Torino for his interest in this study. The authors also wish to acknowledge financial support from contract No. 84.1 193, received from the C.N.R. (Comitato Nazionale per la Ricerca Tecnologica) which has enabled them to carry out this research.

REFERENCES

[ l ] Rolz, H.A.. (4.). 1958. Materials Handling Handbook, Ronald, New York

[2] Gough, P.J.C., (ed.), 1970, Swarf and Machine Tools, Hutchinson, London

[3] PCT/IT89/00035 - on the basis of italian application No. 40072- A/88 - on date 10 May 1989 by Trasportatori Govoni S.r.1. - Via Bologna, 21 - 44042 Cento (FE) Italy; inventor Prof. Ing. F. Soavi.