United States Patent 3638034

Means are provided for detecting skidding of rollers. A limit switch is actuated at each rotation of a member which when no roller skidding occurs moves at the same linear speed as the rollers but which moves at a greater speed when such skidding occurs to energize an electrical circuit, which will indicate when the member is moving at a speed which indicates skidding of the rollers.

Romanowski, Chester J. (Carteret, NJ)
Guido, Paul V. (Cedar Grove, NJ)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
241/117, 340/669, 361/238
International Classes:
H01H35/10; (IPC1-7): H01H35/06; H01H35/10; H01h035/100
Field of Search:
241/117,119 307
View Patent Images:
US Patent References:
3366338Segment-type grinding ring1968-01-30Barton
3365615Speed responsive control1968-01-23Bart
3083920Grinding mill1963-04-02Schauer
3061208Crushing mill1962-10-30Schauer
2824265Electrical speed detection system1958-02-18Seeger
2812513Pulse monitor1957-11-05Breggin
2130453Speed responsive apparatus1938-09-20Bone

Primary Examiner:
Shoop Jr., William M.
What is claimed is

1. A method of indicating the skidding of a roller rolling on a surface and rotating with respect to a member which moves linearly with said roller, so that when said roller no longer rolls on said surface, said member moves through a given distance in a shorter time than when said roller is rolling on said surface, comprising the steps of:

2. The method defined in claim 1 further comprising the step of rotating said member and said roller about an axis other than the one said roller turns about because said roller is rolling on said surface and wherein said sensing step is performed, by the actuation of an electric switch each time said member moves through said distance.

3. The method defined in claim 2 wherein said predetermined distance is the distance said member moves through when it makes one rotation about said other axis.

4. A device for sensing when rollers which normally turn about their axes and roll on a surface rotating about another axis and move linearly with a member rotating with respect to and about said other axis, are no longer rolling on said surface, comprising:

5. The device defined in claim 4 wherein said switch is one which is normally closed and is actuated by being opened and which automatically closes after it is no longer being actuated.

6. A grinding mill comprising:

7. The grinding mill defined in claim 6 further comprising a channel adjacent to said switch for directing compressed air against said switch to remove from said switch any of said material which is ground in said mill.

8. The mill defined in claim 7 wherein said means to indicate when said switch is actuated more frequently than when said rollers roll on said table comprise:

9. The device defined in claim 8 wherein said indicator means is an electric light.

10. A device for sensing when rollers which normally roll on a rotating surface and move linearly with a member rotating with respect to and about the same axis as said surface, are no longer rolling on said surface, comprising:

11. The device defined in claim 10 wherein said indicator means is an electric light.


There are in industry situations when it is desirable to know when a roller is skidding on the surface on which it is rolling. An example of such a situation is found in the operation of relatively large coal-fired furnaces which are used in vapor generating systems in the utility industry for the production of electricity. In such furnaces it is necessary to supply finely powdered coal to the combustion chamber of the furnace. The raw coal feedstock is usually reduced to fine particles in a pulverizer apparatus, which generally consists of a rotating grinding table which provides a grinding surface and a number of relatively heavy rollers which are journaled within the apparatus and maintained in contact with the grinding surface by a thrust ring.

There has recently developed a major problem in connection with the pulverizing of coal feedstocks containing particles which can not be easily pulverized by the apparatus, such as iron pyrite and the like. These relatively hard constituents are commonly found in many types of coal which are being mined today. The hard particles often prevent the pulverizing apparatus from functioning efficiently when a hard particle becomes lodged between the grinding surface of a roller and the rotating grinding table to prevent the roller from rolling on the grinding surface. The rollers move with the grinding table and skid on the thrust ring.

Since the rollers must move at the same linear velocity, they will tend to rotate together or skid together. With skidding rollers the raw coal feedstock will not be pulverized between the rollers and the rotating grinding table, and there will quickly be a buildup of unpulverized coal in the pulverizing apparatus, necessitating a shutdown.

Another problem created by skidding rollers is that they will create between themselves and the thrust ring considerable heat because of the friction of the rollers skidding thereon. In an atmosphere of finely divided coal and air, excessive heating can cause combustion of the coal products which may result in an explosion.


It is the object of the present invention to overcome drawbacks found in the prior art, such as those discussed above. Accordingly, the present invention provides means to detect when the rollers in a pulverizing apparatus begin to skid so that corrective action may be taken before there is a buildup of raw material necessitating a long shutdown period or combustion caused by the creation of heat in an atmosphere of fine coal particles and air within the apparatus.


FIG. 1 is a front view, partly in section, of a portion of a pulverizing apparatus embodying features of the present invention;

FIG. 2 is an enlarged fragmentary view, partly in section, showing in greater detail the portion of FIG. 1 relating to the actuation of a limit switch by a rotating spacer means;

FIG. 3 is a diagramatic view showing the electrical circuitry used in the preferred embodiment; and

FIG. 4 is a schematic wiring diagram which when viewed with FIG. 3 illustrates the operation of the circuit set forth in FIG. 3.


Referring to FIG. 1, a pulverizing apparatus is shown which is generally designated by the reference numeral 10. The pulverizing apparatus 10 includes a steel housing 12 which is mounted at ground level for enclosing a support 14 on which there is rotatably mounted a grinding unit 16. The grinding unit 16 includes a table 20 formed with an annular groove 22 which defines a grinding surface S. A table 20 is mounted for rotation on the support 14 by means of a rotating hub 24 which is powered by an electric motor which has not been shown in the drawings for the sake of simplicity.

A plurality of spaced-apart pulverizing rollers 26, preferably three in number, which have a grinding face F roll in a groove 22. Spacer means 27, which are well known in the art, are disposed of between the rollers 26. The spacer means 27 include a plurality of arm members 28 which extend outwardly from a central column 29 to the spaces between the rollers 26. The column 29 is rotatably supported with respect to the table 20.

Each of the rollers 26 is formed with a bearing collar 30 which is formed with an annular groove 32. A thrust ring 34 is mounted in the steel housing 12 above the pulverizing rollers 26, and load is applied by means of compression springs 36. The thrust ring 34 is intricately formed with an annular lip 38 which is configurated in accordance with the outer periphery of the annular groove 32, in order to achieve smooth mating contact.

As the electric motor turns the rotating hub 24 and the table 20 above it, the rollers 30 are made to rotate because of their contact with the table 20 at the annular groove 22. Because they rotate, their linear speed is approximately one-half that of the groove 22. Material coming down the conduit 18 will be ground on the table 20 by the rotating rollers 26 which are urged downwardly by the spring thrust ring 34. The rollers 26 are maintained a given distance apart by the arms 28 of the spacer means 27 which extend between the rollers 26. The spacer means 27 and its arms 28 rotate about the longitudinal axis of the column 29 because that column is rotatably mounted with respect to the table 20.

The manner in which skidding of the rollers 26 on the thrust ring 34 is induced has already been described, as has been the undesirable and unsafe conditions which can be expected to ensue. When skidding occurs, the spacer means 27 will rotate at the same rotational speed as the table 20. This is approximately twice the speed at which the spacer means 27 rotates when the rollers 26 are rolling properly under the thrust ring 34. Thus, it is possible to detect when skidding occurs within the pulverizing apparatus 10, if the increased rotational speed of the spacer means 27 can be detected.

To this end, an elongated arm 40 is secured to the spacer means 27 for rotation therewith. The arm 40 includes a plate 42 to which is bolted a paddle 44 which extends outwardly so that it has an end adjacent to the steel housing 12. Mounted on a bracket 46 which extends outwardly from the steel housing 12 is a limit switch 48 which has an outwardly extending finger 50 which is secured to a downwardly extending pin 52 on the limit switch.

Thus, with each rotation of the spacer means 27, the paddle 44 will strike the finger 50 to rotate the pin 52 and actuate the limit switch 48. When the limit switch 48 is thus actuated, it is opened as will presently appear when the electrical aspects of the present invention are discussed. In order to permit the finger 50 to move laterally when it is struck by the paddle 44, it is mounted so that it extends through an opening 54 in the steel housing 12. Because of the presence of coal dust within the steel housing 12, caused by the grinding of coal by the rollers 26, the limit switch is preferably guarded from such dust in order to insure proper operation. In the present embodiment, the only portion of the limit switch 48 which can communicate with the interior of the pulverizing apparatus is continuously purged by compressed air, which is directed through a channel 56 which opens at a plate 58 which with the bracket 46 and sideplates 60 defines a space within which the finger 50 is secured to the portion of the limit switch 48 which is in communication with the interior of the pulverizing apparatus 10.

The electrical components of the present invention are shown in FIGS. 3 and 4. In FIG. 3, the limit switch 64 with terminals 66 and 68 is connected to a timing relay 70, which may be one of several commercially available relays and as such does not per se form a part of the present invention. The timing relay 70 has a plurality of terminals including terminals 72 and 74 between which is connected a coil 75 which is shown schematically in FIG. 4. The timing relay 70 also has terminals 76 and 78 which have a switch 79 between them in the relay 70. The switch 79 is normally closed but when a continuous rated voltage is applied across coil 75 for the predetermined delay period switch 79 opens. The relay 70 makes available switches which are normally open and close after the relay 70 is energized for the delay period. These switches are not used in the present invention. The terminal 68 of the limit switch 48 is connected to the terminal 72 by a wire 80, while the terminal 66 is connected to the terminal 76 of the relay 70 by a wire 82. The terminal 76 is also connected to a wire 84 leveling to a power source along with a wire 86 connected to the terminal 74.

A second-timing relay 90 which may be identical or similar to the relay 70, having terminals 92 and 94 between which is a coil 95, is provided. The relay 90 also has terminals 96 and 98 between which is a switch 99, which is normally open. The terminal 92 of the relay 90 is connected to the terminal 78 of the relay 70 by a wire 102. The terminal 94 is connected to the wire 86 by a wire 104. The power source which was previously mentioned is not shown. It impresses a voltage which, as shown in FIG. 3, may be 120 volts AC. A wire 106 leading from terminal 96 and a wire 108 leading from terminal 98 connect an indicator bulb 110 across the switch 99.

It has already been explained that with each rotation of the spacer means 27, the paddle 44 strikes the finger 50 to open the limit switch 48. It has also been explained that when sliding occurs between the rollers 26 and the thrust ring 34, the spacer means 27 will turn at approximately twice the speed it turns when no skidding takes place. The relays 70 and 90 have delay periods which are selected so that the delay period for the relay 70 is more than the periods between actuation of the limit switch 48 when the rollers 26 are skidding, but less than the periods between actuation when no skidding of the rollers is present. The relay 90 has a delay period which is longer than the periods between switch actuations even when the spacer means 27 is rotating at its lower speed, i.e., when no skidding of the rollers 26 is occurring.

If the spacer means 27 normally rotates at 15 r.p.m., suitable delay periods would be 3 seconds for relay 70 and 6 seconds for relay 90. With the spacer means 27 rotating at 15 r.p.m., the limit switch 48 will be opened every 4 seconds. This means that the delay period of timing relay 70 is being exceeded at each rotation of the spacer means 27 so as to open the switch 79 (FIG. 4), the switch 48 is closed within about 1 second after the switch 79 is opened to again close switch 79 but this prevents switch 79 from being closed long enough to permit a current flow through the coil 95 of the relay 90 of sufficient duration to actuate switch 99 of that relay.

When, however, skidding of rollers 26 occurs so that the spacer means 27 turns at approximately twice its normal speed, or in our example about 30 r.p.m., the limit switch 48 will be opened every 2 seconds. This means that switch 79 of the relay 70 is never opened so that current will flow continuously through the coil 95 of the relay 90. When the delay period of coil 90 (in our example 6 seconds) has expired, switch 99 will close so that a current will flow out through wires 106 and 108 to light the bulb 110 to indicate that skidding has occurred.

The foregoing describes but one preferred embodiment of the present invention. The above-described embodiment can be modified and other embodiments can be provided without exceeding the scope of the present invention, as defined in the following claims.