Vol. 1

NEW YORK, OCTOBER 28, 1911 No. 3

“Aff agin, on agin, Gon agin, Finnegan.”’

Such an oft reiterated story as the one given under the above title hardly needs repeating.

Some years ago when railroad equipment left the rails, with frequency because of—well, because there wasn’t any provision to keep it on, the rail- road authorities called for reports from the road foremen.

Some of these, being neither machinists nor engineers, and having no great skill in the writing of essays on track mismanagement, resented the liter- ary effort demanded of them, though it must be con- ceded that they knew a lot about mishandled track; in fact, it might be succinctly stated that they didn’t know about any other kind of track, for mismanage- ment ruled the day.

There was one, Patrick O’Finnegan, who firmly believed ‘“‘the divil put the cars aff and ’twas Patrick put them on agin” or incinerated them if they were beyond salvage.

Said Patrick had a derai!ment on his section; he retracked the cars, wetted the point of a pencil and proceeded to write his version of the wieck on the elaborate form provided by the company, in the exact language of the heading of this article,

And Pat. was satisfied, believing his last duty was done; he was surprised, therefore, when the “White Shirts’ in New York returned his reply for further elaboration. The cars were off, he had them back on the track, and “divii a bit was there then to be said.”

as detantlnc sis ———0—_—__—_-

Now if Pat had been working underground, not years ago, but today. it’s probable that not only

Pat, but the ‘‘White Shirts’’ in the main office would have felt all was done that should be done.

Derailment in the mine rarely takes a life, but it does destroy the track and cars and wastes valu- able time. Again and again it will occur at the self- same place, and the foreman says it can’t be helped, puts the cars back on the track with a pry, a few blocks, much grunting and a pinched finger or two. “Well, they’re on again,’”’ and when he sees the super- intendent, he explains his loss in tonnage by saying: “Another wreck. I'll do better tomorrow.”

an —QO-

There’re too many Finnegans in charge under- ground who ought to be sextons in cemeteries or jani- tors in county court houses. There’s no job in the

mines where they’re needed.

Be sure, Mr. Foreman, you inquire where, why and how that car was detracked and remedy the evil.

You say you have too many miles of track to watch. Perhaps you have; probably that’s your fault. But I doubt if you’ve got so many it wouldn’t pay to have them clean, ballasted, lined up true, free of humps, with even joints, perfect gage and no sharp curves.

Look at your equipment. Have you heavy, well spiked rails, supported by good ties, joimed by fish-

plates? Are all the unnecessary frogs and switches ripped out? :

Do they run on three wheels and Are they Have

And the cars. carry the fourth like a pointer on a hunt? prone to knuckle up or down, right or left? they straight axles, true wheels and correct gage?

Oh! by the way, hang this colliery note in your den, DERAILMENTS—A PREVENTABLE DISEASE.”



October 28, 1911

Electrical Machinery for Coal Mines

When electricity was first applied to the working of coal mines, continuous- current, or direct-current apparatus, as it is often termed, was employed, be- cause it was the only apparatus on the market. In those days, although alternat- ing currents were in use for town light- ing, it was only single-phase currents that were employed, and the single-phase motor was not then suitable for mining work. The single-phase motor has been enormously improved during the last 15 years or so, and at the present time there is a keen struggle between it and the continuous-current motor, in regard to the driving of electric locomotives for urban and inter-urban traffic.

It is claimed by the advocates of the single-phase motor that it is more economical, and possesses certain other advantages over the continuous-current motor. On the other hand, it is very much more complicated in construction than either the continuous-current motor or the three-phase ‘alternating-current motor that has come largely into use for


coal-mining work; and so far as_ the writer is aware, no attempt has yet been made to adopt it in mining work of any kind. It may be mentioned, by the way, that the single-phase alternating-current motor is merely a modification of the continuous-current motor. It is a con- tinuous-current motor, having the fami- liar commutator and also a special ar- rangement for delivering alternating cur- rents to the coils of the motor, and special windings which enable it to per- form, with single-phase alternating cur- rents, the service ordinarily required of continuous-current motors.


During the last 10 to 15 years, three- phase alternating-current apparatus has been gradually displacing continuous-cur- rent apparatus. There are several rea- sons for this, but the principal one is the absence of the commutator which forms such an important part of the contin-


By Sydney F. Walker*

The shunt-wound con- tunuous-current motor and the three-phase «induction machine are described and compared. Particular ref- erence 1s made to their government and speed reg- ulation in connection with various classes of colliery work.

*Bloomfield Crescent, Bath, England. uous-current motor and generator. The modern forms of continuous-current and three-phase alternating-current motors, are very similar in outward appearance. In each of them there is an outer con- taining cylinder, sometimes of magnetic steel, sometimes of wrought iron, some- times of cast iron as shown in Figs. 1 and 2.

In the continuous-current motor, the electro-magnets which create the mag- netic field in which the armature re- volves, project radially inward from the containing cylinder, as shown in Fig. 3. Their cores are constructed usually of laminated iron, held in various ways to the containing cylinder, sometimes cast in the cylinder, sometimes held by other mechanical means. The coils contain- ing the wires which create the magnetic field, are slipped over the cores of the field magnets, as they project inward, and crescent-shaped pole pieces are attached to the inner ends of the cores. These pole pieces more or less com- pletely inclose the cylindrical space in which the armature revolves.

In the three-phase alternating-current motor, there are a number of thin disks of either wrought iron, or mild steel, or some form of iron or steel that will readily receive and give up magnetism, built up on the inside of the containing cylinder, so as to form a drum. Slots


are made in the disks before they are placed on the inside of the cylinder, to hold the wires which carry the alternat- ing currents. The drum formed by these disks incloses the cylindrical space in which the rotor, which corresponds to the armature of the continuous-current ma- chine, revolves as shown in Fig. 4.


The armature of the continuous-cur- rent motor, and the rotor of the three- phase alternating-current motor, are also very similar up to a certain point. Each is built up of a number of thin disks of either soft iron or steel, material that will receive and give up magnetism quickly. The disks are slotted for the reception of the wires, which will cause the revolution of the armature or rotor, when the machine is working. The disks of the armature, the rotor, and the stator, as the drum inside of the containing cyl- inder of the three-phase alternating cur- rent motor is called, are all insulated


Fic. 4. SECTIONAL View A. C. Motor

from each other by being dipped in an @ insulating varnish before being strung together.

In both the continuous-current arma- ture, and the three-phase alternating- current rotor, wires are laid in the slots. In the case of the continuous-current armature, however, the wires are in cer- tain lengths and the ends of adjacent lengths, or coils, are connected to the segments of the commutator. The coils are all of the same length, are all placed in the slots and on the drum in the same way, and are insulated from each other, and from the iron in the slots of which they lie. This is shown in Fig. 5.

In the three-phase alternating-current rotor, there are two arrangements of the wires or conductors, known respectively as the squirrel cage and the wound rotor. In the squirrel-cage rotor, the conductors which lie in the slots of the iron or steel drum, are usually bars of copper, some- times laminated. The bars are insulated from the iron and from each other, and

October 28, 1911

they are connected at each end to a ring of copper; the whole arrangement of the conductors, when viewed free of the iron drum, being similar to the well known cage in which squirrels are made to perform. Fig. 6 shows a section of such a rotor.

In the wound rotor, the conductors are usually smaller, more of them are laid in the slots, and they are wound on very much the same lines as the armature coils of a continuous-current motor ex- cept that there are three sets of coils instead of one set. The special feature of the wound rotor is the arrangement that is made to insert electrical resist- ances in the circuits of the coils, during the starting period. For this purpose, rings of copper are carried on the rotor shaft; carbon brushes bear upon the rings, and the arrangement is such that during the starting period, a connection is made between the coils of the rotor and cer- tain resistances provided for the pur- pose. These resistances are cut out as the machine gets up speed, and when the speed is normal, the brushes are thrown off and the arrangement of the coils be- comes practically the same as that of the squirrel-cage rotor. Fig. 7 shows a

Laminated lron Cores =.

Commutator Copper {Segment


longitudinal section of a wound rotor with slip rings.


The working of the two machines is quite different, though the effect is the same. In the continuous-current motor, brushes bear upon the commutator. The commutator is a cylinder built up of segments of copper, insulated from each other by mica; the individual segments, as explained above, being connected to the ends of adjacent coils on the arma- ture. The coils of the armature are so arranged that there is a continuous path or, as it may be termed, a continuous loop through all the wires by way of their connections to the segments of the


When the continuous-current motor is running, current is delivered from the electrical service to the brushes,



them to the segments of the commutator, and thence to the armature coils. Cur- rent is at the same time delivered to the coils surrounding the field magnet cores. The two sets of currents, that pas- ing in the armature coils and that pass- ing around the coils of the field magnets, create magnetic fields in the cylindrical space in which the armature revolves, of such a nature that attractions and repul- sions are set up between the two and the result is that the armature turns in a certain direction, and continues to turn in that direction, as long as the current is flowing.

In the three-phase alternating-current motor, the slots in the drum formed on the inside of the containing cylinder, carry coils which receive the three-phase currents from the electrical service. There are three sets of coils, each set of coils receiving current from its own conductor, representing a particular phase. The delivery of the currents to the coils in the stator, as it is termed, is so arranged that currents are induced in the coils on the rotor, whether it be of the squirrel-cage or wound-rotor form, in such a direction that attractions and repulsions are set up between the two sets of magnetic fields, those created by the currents in the stator coils, and those


In the three-phase alternating-current motor, there are several magnetic fields created by the currents passing in the stator coils, and there are several mag- netic fields created by the currents in the

rotor coils. As mentioned above, there are three sets of coils, and three sets of currents in the stator. Each set of coils receives its currents in succession. Those connected to, say, No. 1 phase, receive their currents first; a little later those connected to No. 2 phase; and a little later again those connected to No. 3 phase receive their currents. In each set of coils, the currents are rising and fall- ing and reversing, and all of these opera- tions are taking place in succession in each set of the coils; the result is that what has been termed a revolving mag- netic field is created within the cylin- drical space in which the rotor revolves.

An eminent American electrical engi- neer has compared the action to that of a cat chasing its tail. A magnetic field of a certain strength arises at different points all round the cylindrical space in which the rotor revolves; the strength of the magnetic field so arising gradually increases, then gradually decreases, dies away and then reverses. Meanwhile the currents of the next phase commence to create another field just in front of the

IronCores., Coppers


created by the currents in the rotor coils, so that the rotor commences to revolve in a particular direction, and continues to revolve as long as currents are supplied to the stator coils.


The broad distinction between the mag- netic fields created in the cylindrical space in which the armature of the con- tinuous-current motor revolves, and those created in the cylindrical space in which the rotor of the three-phase induction motor revolves, will be noted. In the continuous-current motor, there is one magnetic field, of definite strength and of definite direction, created by the cur- rents in the field magnet coils. There is another magnetic field created by the currents in the armature coils; and the motion which is given to the armature is due to the interaction of these two fields.



first, which increases in strength to 2 maximum and dies away just as the first did; then the third set of currents takes up the running, creates another field in front uf the second, and so on. The currents which arise in the coils of the rotor are really due to the same cause as in the static transformer. It is the rise and fall and reversal of the currents in the stator coils, which induce currents in the opposite direction in the rotor coils. These currents rise and fall and reverse in exactly the same order.


It will be seen that the squirrel-cage form of the three-phase alternating-cur- rent motor, is simplicity itself. There is only the containing cylinder, the stator drum with its coils on the inside of the cylinder, and the rotor with its shaft and coils. There is nothing in the nature of

i I.

tt ee

i i L 1 I

a commutator; there is no electrical con- nection between the rotor and the stator. The question of starting squirrel-cage rotors will be dealt with separately; but when the squirrel-cage motor is running, there is, or should be, nothing to get out of order.

On the other hand, with the contin- uous-current motor, the commutator and the brushes require frequent attention, With modern machines the attendance is very much less than was required in the early days, but nevertheless, the commu. tator is a solid disadvantage, when com- pared with an apparatus of the squirrel- cage type, which has no commutator and nothing that can be compared to one.


The commutator may be said to have two disadvantages. Even the best forms of the latest construction require truing up from time to time, and brushes re- quire renewing and regulating. The more serious objection, in the case of toal mines, is the possibility that an ex- plosive mixture may be present in the neighborhood of the commutator. From experiments which have been made, it would seem that it is not easy to fire an explosive mixture at the commutator, but such a thing may happen, and at many collieries this possibility has led mining engineers to look askance at com- mutating motors for driving coal-cutting machines, etc. In the coal-cutting ma- chine, the motor is necessarily inclosed, the commuutator being out of sight, while at the same time it is difficult to prevent coal dust finding its way to the surface of the commutator and where coal dust is present, it may lead to wear of the surface of the commutator, and to sparking.

There is also another and perhaps more serious danger in this connection. The brushes are held upon brass spindles attached to some part of the framework of the machine. It is necessary that the spindles shall be insulated electrically from the framework, or whatever they may be attached to. If they were not in- sulated, a short circuit would be created from the positive to the negative brush, and no useful work could be done by the motor. The insulation consists usually of rings of various materials, micanite being a favorite. In the early days of dy- namos and motors, vulcanite and vul- canized fiber were used. Whatever the substance may be, there is always the danger of a deposit of coal dust, of car- bon dust from the brushes, and of copper dust from the commutator, forming upon the surfaces of the insulating rings. A film of dust formed in this way, may lead to a dangerous arc. Nothing usually happens until a certain quantity of dust has been deposited, and then suddenly when the current is switched off, or when


the motor, a spark may pass across the surface of the insulating ring, burning up the dust and causing a flash, which may possibly be followed by an arc.


On the other hand, the three-phase in- duction motor has certain disadvantages. In the ordinary squirrel-cage form, with heavy copper bars, the starting torque, that is, the effort which the rotor is able to exert at starting, is small, and hence it is necessary to start upon no load, or to provide special arrangements, which tend to complicate the machine. In the case of coal-cutting machines, for in- stance, it frequently happens that heavy starting torque is required. With bar and disk and chain machines alike, it is more convenient if the machine can be made to start up in the cut. The ordinary squirrel-cage motor will not do this.

In addition, it often happens when cut- ting along a coal face, that a piece of very hard strata is met with. The con- tinuous-current motor will exert practi-


cally any amount of power that may be required. It is a good natured horse, and will go on striving to deal with the load in front of it, even to the point of burn- ing itself up. With the three-phase in- duction motor, a certain amount of ad- ditional work may be got from it by slowing up, and it necessarily slows up

when faced with additional resistance, -

but there is a limit beyond which the motor will not go. It is an open ques- tion whether this is an advantage or dis- advantage. It is very annoying to have the machine stop just when it is most wanted to put forth its best work. On the other hand, it is very annoying to have the machine put forth its best work, and to be useless afterward, as the continuous-current motor may be.


There is a further drawback to the use of the three-phase induction mo- tor. In order that a high efficiency may

a large portion of the load is thrown off

October 28, 1911

be obtained, that is, in order that the largest possible proportion of the elec- trical energy delivered to the motor shal! be obtained as mechanical energy at its axle, it is necessary that the rotor shall run very closely indeed to the stator drum. With every class of motor, whether con- tinuous-current or alternating, it is an advantage for the moving parts to run very close to the stationary parts; but with continuous-current apparatus, the result of allowing greater space between the fixed pole pieces and the moving mass of the armature has not such a great effect upon the efficiency, as has a similar clearance between the stator drum and the rotor of an alternating- current machine.

With the continuous-current motor, a clearance of 1/16 in. is quite common, 3/32 in. is also often employed, and I much prefer as much as & in. With the three-phase induction motor, 1/32 in. is as much as can be allowed. This means that a very trifling wear of one bearing, or both bearings on one side, owing to a tight belt, for example, will cause the rotor to rub upon the iron of the Stator, with the result that the machine is broken down. Figs. 8 and 9 show the difference between the clearance in a continuous-current motor and a three- phase motor.

In subsequent articles, I propose to deal with other points in connection with this subject.

Immunizing Coaldust by Wa- ter and Ground Rock

A brief -report of the conclusions of the Comité Central des Houilléres de France from experiments at the Liévin gallery, printed in the Annales des Mines, September, 1910, page 227, contains among observations which are, by this time, trite reflections of mining men, a few important considerations.

A naked flame or electric arc, in the absence of firedamp, is less likely to Start an explosion than a blown-out shot of a non-permissive explosive.

The amount of water needed to render coal-dust inexplosive is a weight of the former equal to the weight of the dust which it is designed to render immune from explosion. When it is purposed to im- munize by the use of powdered rock, not less should be used than half as much rock as of coal dust, which it is desired to render inert. The dust of coal as re- ferred to in the above is defined as be- ing all fine coal, 2 mm. (0.078 in.) in diameter or finer. The dust for immuniz- ing should be of extreme fineness and in estimating it, the ash of the coal should not be considered, as its action is un- certain. To stop an explosion in a wet zone, the admixture of water should be four times the weight of the coal dust to be rendered inert.

October 28, 1911



Preparation of Anthracite Coal

In this section of the anthracite field the dominant factors in the preparation of coal are the presence of a large quan- titiy of rock, in pieces often running up to as high as 800 Ib. in weight, and comparative freedom from “bone” in the coal as it comes from the mines. The high proportion of big rock in the run of mine coal is responsible for a style of breaker construction which does not ob- tain in the northern and middle fields. The low proportion of “bone” practically reduces the problem in many instances to one of eliminating the rock.

In general, the preparation plants here consist of two distinct buildings: The head house and the breaker proper. The function of the head house is to remove all the large pieces of rock and as much small rock as possible down to and

By M. A. Walker

Methods the

Panther Creek region where

used in there 1s much large rock present in an otherwise

singurlarly pure coal.

taken as representative of the locality. It has a demonstrated capacity of 1350 mine cars per day from which it prepares about 3500 tons of coal with 118 men at a labor cost probably not exceeding 10c. per ton. From 10 to 12c, a ton is

passes off is broken down in the crushers H to steamboat size and smaller. Steam- boat size is removed by the shakers F which have a 4%-in. round mesh, and is subsequently rebroken. All of this stream goes to that one of the two conveyers which is devoted to cleaned coal.

Following next the second stream, which consists of everything passing through the 6-in. mesh of the platform screens, it is found to be led over the shakers E, having a 4'4-in. round mesh. The steamboat coal thus made is hand picked, then crushed and taken to the clean-coal conveyer. Everything pass- ing through the mesh of the shakers E is led directly to what is known as the “dirty’’ coal conveyer, to distinguish it from its partner.


including that of steamboat coal size; also to render the coal of suitable size and condition for reception into the break- er. The head-house product is carried to the breaker as a rule by conveyers of either the scraper or carrier type. These are often inclined in order to gain the necessary hight at the breaker end and frequently 250 to 300 ft. in length. All jigging, final sizing and picking of the coal is confined to the breaker.


Fig. 2 is a diagram showing the run of coal in a scheme of preparation typical of this region. Tables 1, 2 and 3 are compiled from data relating to the Lehigh Coal and Navigation Company’s breaker at Coaldale, Penn. This is a modern plant which has been in successful oper- ation for nearly two years and may be

an average labor cost for this region which compares with 6 to 8c. in the Wyoming region, where large rock is not a factor.

It will be noted from Fig. 2 that the scheme of preparation in the head house is in general as follows: A disposition of the mine rock is made, when neces- sary, at the dump by means of a by-pass gate A in the bottom of the dump chute. The coal streani from the dump is passed over the platform shakers C having 6- in. round mesh, and a consequent sep- aration made into two streams, one of Iump size, the other of mixed steamboat and smaller sizes. Following first the lump-coal stream, it is seen to descend to the picking tables D, which are about 20 ft. long and have a pitch of 2 to 2% in.in 12inches. Here all the rock is re- moved and the cleaned lump coal which


There are thus two streams of coal passing up to the head of the breaker; one cleaned, the other not cleaned, and both a mixture of broken and all smaller sizes, except when it is desired to ship steam- boat size, which is done by omitting to break down that size in the head house. The clean-coal stream is usually sized over two sets of shaking screens similar to those listed in Table 1, and is passed from them directly to the pockets with more or less examinatron in the chutes.

The dirty-coal stream is sized over four sets of shakers, or as a rule, double the number used for the clean coal, similar to those listed in Table 2. Broken size from these screens is usually cleaned by spiral pickers or some other mechanicai device, supplemented more or less by

72 COAL AGE October 28, 1911

hand picking; occasionally it is jigged. The disposition of refuse is a particu- in pieces of great size and also because Egg, stove, chestnut and pea sizes are larly important part of the subject in this the topography of the region makes it usually led directly from the screens to locality for the reason that, as already necessary to deposit all this material on the jigs. It is the practice in some break- ers, however, to spiral or otherwise me- chanically pick these sizes on their way Anita ites to the jigs, and it depends a great deal o- Sees big maindl on local conditions whether or not a = Picking Platform = Steamboat Shakers profitable percentage of pure coal can 7 yo thus be deflected to the pockets. Buck- onan ee wheat size is jigged in a number of Cleese Goal Stdhars cases, but more often it passes directly ny from the screens to the pocket, as do E | = eon nee also the rice and barley sizes. e '

Table 3 gives data relating to jigs of the “Lehigh Valley” plunger type, shown in Fig. 3, which are replacing other styles in a good many instances. The jigged

: Elevator coal is thoroughly examined and oc- Dirty Coat _(——— >. casionlly resized before passing to the

a8 ai) me { pockets. The usual provisions are, of course, made for breaking down the ma- - . fl he ra Broken L



Cean Coal Com


Clean Coal

terial rejected at the jigs and various picking places and for resizing and cleaning the same.


Rejected Coal


There is today a very marked tendency toward more rigid standards of inspec- tion at the collieries and a consequent prominence to the subject of rehandling condemned coal. Exact figures of general interest in this connection are hard to ob- tain, but it may be easily observed that rehandling condemned coal is liable to be a very expensive operation unless it is Fic. 2. DIAGRAM SHOWING RUN OF COAL

Mechanical Picking


Rejected from Picking Places

oken Coal to Pochet

sn Hand Picking

Buch wheat Coa 40 Pocket


the mountain sides, frequently at a con- TABLE NO. 1. PURE COAL SCREENS siderable hight above the breaker.

At one plant the head-house rock and

Size Coal Round Total Area, Tons per Sart. ood Revolutions the breaker refuse are brought together by

Number {Passing Over Mesh Sq.Ft. Hour —_jof Cam Shaft conveyers to a pocket which loads a skip

in. dia. 90 28 | 0.070 hoist or “gunboat.” This travels on an in-

mm ho Oo

ed ae


150 to 165

oo 4 clined plane and discharges into a pocket

in. dia. 90

in. dia. 120

ge of dump cars. The latter are then con- : - LO ; .

= dia, | =. 9 035 veyed by a steam locomotive along the

in. dia. 90

at the top from which are loaded trips in. dia. 120

summit of the rock bank and dumped.





Size Coal Round Total Area Tons per Sart et Revolutions pag sy : s ment seniiie Number Passing Over Mesh Sq.Ft. ; ( Hour of Cam Shaft ~ to omit one or more links in this series and the usual plan for handling refuse is to have two large rock chutes in the head house, each of a capacity sufficient for at least a half-day’s run, and discharging into dump cars which travel to and from the rock bank. It may or may not be necessary to elevate these cars to the summit of the rock bank; in case it is, this is usually accomplished by an in- Tons per clined plane and “barney” car. The

Hour per

Size Perforations| Total Grate | Revolutions | Tons per Sq.Ft. of break i i Number Size Coal in Grates Area Plunger Shaft eur Grate Surface pBrisigueties analy Gelivered to the

oes —— ern same dump cars that take the head-house Rt per Ze “- ;aa rock by means of a conveyer discharging } 112 ot 20 69.01 0.616 through a loading pocket. In general Bok. a So. a. 64 sq ft. 100 52 75 0 824 the disposition of refuse adds a labor charge of from 3 to 4c. to each ton of

coal shipped.

A matter which is probably receiving more attention than any other one thing

Broken. . .| 34 in. dia. 180 Egg... .| 25 in. dia. 180 Stove... 2 in. dia. 180 Nut.. : £ in. dia. 180 a ee *; in. dia. 240 Buck . : 5 in. dia. 240 Rice... : ; in. dia. 240 Barley gs in. dia. 240

150 to 165


possible to pass it through the breaker observed, there is a large quantity of rock while at the same time working on coal in the coal as it comes from the mines,

from the mines. of which a very considerable portion is in connection with the subject of coal

October 28, 1911

preparation in this district, as well as in other parts of the anthracite field, is the prevention of breakage in the chutes. Nearly all of the larger companies are continually experimenting on different forms and styles of chutes with various results and varying degrees of success.

One of the chief difficulties in connec- tion with the building of a permanent chute, is the fact that the quality of the coal is likely to vary from wet to dry and from clean to dirty, in the sense that a large proportion of fine coal constitutes dirt as well as a large proportion of im- purities. The same pitch of chute is not suited to both conditions, and in conse- quence the clean, dry coal is liable to go down with a bang, while the wet, dirty coal lags on the way.

To a limited extent, this difficulty has been overcome here, as_ elsewhere, through the use of retarding chutes,


Steel Belt Conveyers

After several years of experimenting, a Swedish steel company has succeed- ed in manufacturing a steel-belt conveyer, which has given most satisfactory service in various plants of northern Sweden.

These steel-belt conveyers are made in lengths of 100 m. (328 ft.) and are 200 to 400 mm. (8 to 16 in.) broad, and 1 to 1% mm. (0.04 to 0.06 in.) in thick-

ness. To obtain a special length or width, two or three of these standard sizes are riveted together. They are made of high-grade charcoal steel,

possess a high résistance against wear and tear and are extremely flexible.

These conveyers are used for trans- porting all kinds of material, and it is said are cheaper to manufacture and install than high-grade belts of other ma- terial.

Coal Regulating Gate |

Coal Conger y



—_ i | } ~ \ r= \ di %



which operate on the principle of allow- ing the pieces of coal to expend their ac- quired momentum at frequent intervals by sliding up a slightly adverse pitch. These chutes are constructed in zigzag fashion, with comparatively short straight- away runs, and when built with enough pitch on the straight runs to suit the slow- est coal likely to traverse them, they have here been giving excellent results within certain limits of application.

The modulus of elasticity of a hoist- ing rope varies during its working life, being small at first and afterward in- creasing to nearly the value of the modulus of the wire itself. If the rope is kept in use long enough, it will de- crease. When this decrease is observed, the rope is deteriorating.


An important item is the possibility of using relatively few supporting pulleys or idlers, in comparison with the number required for other forms of belt con- veyers. This reduction in the number of idler wheels diminishes considerably the amount of power required for oper- ation. The maintenance cost of these conveyers is low, and repairs are easily made by riveting on a new piece of the required size.

A troughing of the belt itself is im- practicable, and it is made to run in a guide channel or trough, which may be of steel, or wood covered with steel. The sides of this trough should be in- clined at a slight angle to the plane of the belt. A longitudinal elevation of these conveyers as they are in-


stalled shows the upper or carrying run to be slightly convex. This is done to keep the belt in the guide trough in the event of material piling up along the con- veyer.

Ordinary wooden pulleys, the faces of which are covered with a %-in. to %- in. layer of rubber, give excellent service as driving wheels. When cast-iron wheels are used their faces should also be covered with rubber. The bearings of the<