US2293670A - Means for the localization, control, or prevention of fires - Google Patents

Description

1942- D. v. SlCKMAN 2,293,670

MEANS FOR THE LOCALIZATION, CONTROL, 0R PREVENTION OF FIRES Filed July 3, 1940 440 Von-s luvs i- 50mm flag? U ciz'cznzzazu Patented Aug. 18, 1942 2,293,670 MEANS ron THE LOCALIZATION, CONTROL,

OB PREVENTION OF FIRES Davy V. Sickman, Los Angeles, Calif., assignor to Agicide Laboratories, Inc., Milwaukee, Wis., a corporation of Delaware Application July 3, 1940, Serial No. 343,743 12 Claims. (01. 83-94) This invention relates to methods and means for the prevention, control, or localization of fires in machinery and equipment in which inflammable or combustile material, such, for instance, as dust or gas, is present.

There are many types of machinery for grinding, crushing, mixing, and the like, which operate with high relative speeds between moving surfaces, and, when such machinery is used with finely divided materials, any hard, metallic or non-metallic material getting in the feed of the machine, coming into contact with the rapidly moving surfaces can cause a shower of sparks, which forms an almost perfect ignition device, resulting in disastrous fires and explosions of he substance being ground, mixed, or crushed. Many types of grinding or crushing mills employ an air stream, running through a conduit, to carry oil the material being treated, and the presence of such finely divided particles in an air stream makes the operation of the machinery very dangerous, if there is any chance of sparking at any point in the system. It is the combatting of the above hazard to which the present invention is directed.

It is an object of the present invention to prevent fires and explosions incidental to the operation of machinery operating on inflammable substances.

It is a further object of this invention to provide means for the detection of the presence between the working faces-of a mill-of hard particles which are apt to cause fires.

A still further object of the invention is the provision of means for the detection of electrically conducting objects in the material being treated.

It is another object of this invention to provide means for confining fires and explosions to the mill in which they originate.

It is a further object of this invention to provide means for automatically shutting down the mill upon entrance of spark producing objects between the working faces.

It is a further object of this invention to accomplish the prevention of sparking without the introduction of static producing conditions.

one embodiment of the invention. For this purpose there is shown a form in the drawing accompanying and forming part of the present specification. This form will now be described in detail, illustrating the general principle of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

The drawing is directed to that type of grinding mill which is termed an attrition mill. It is to be understood that the invention is applicable to spatular mills, hammer mills in which there is no contact between the hammers and the shell under normal conditions, and even to roll mills, which possess spaced rollers running at different peripheral speeds. A description of the invention as applied to an attrition mill should make amply clear to one skilled in the art the application of the instant invention to these other types of mills, as the principles are the same, and the necessary modifications evident.

The drawing illustrates one form of attrition mill ill in which two motors II and I! are mounted with their shafts Ila and l2a in alignment, said shafts carrying the generally discshaped members I 3 and M, respectively. Grinding plates l6 and I l are mounted on these discshaped members and are formed with cooperative grinding faces Ilia and Ila. One of the discs is provided with openings l8 through which the material to be ground is fed to the space S between the discs I3 and M, a hopper I9 serving to deliver the material to said openings. The entire disc assembly is enclosed by .a suitable housing 20 connected with a discharge conduit line C leading to separators, classifiers, and other equipment, (not shown). maintained under suction by a blower or fan (not shown). In operation, the two motors ll and I2 operate to drive the discs l3 and I4 in opposite directions and the material passesfrom the space S outwardly between the cooperative grinding faces "5a and Ila and is ground therebetween.

The shaft of one of the motors, here illustrated holding the adjustable shaft in its adjusted positionto permit spreading apart of the discs in case of overload, caused by too rapid a feeding This conduit C is of material into the hopper I9 and between the discs. The above construction is common to atlrition mills of this type and need not be shown or described in detail.

For the detection of conducting foreign bodies which may bridge the gap between the grinding faces. it is proposed to electrically insulate one of the grinding discs from the other and provide electrical control means responsive to the establishment of a conducting path between the discs. Thisis done in the present instance by mounting motor I2 upon insulating plates 2|. Contact between the casing 20 and the frame and shaft of motor I2 is avoided by the provision of insulated plate 2I' on the side of casing 20. This is sufllcient to insulate the disc I4 from the rest of the structure as the insulation of the armature of motor I2 is in this condition. Y

To detect the presence of metallic particles bridging the space between the grinding faces Mia and I'Ia, there is provided the electrical circuit consisting of a sensitive relay 22 and a battery 23 connected in series, one side being grounded and the other side being connected to a brush 24 riding on the insulated shaft of motor I2. A bridging of the gap between I6 and I1 will obviously actuate the relay 22. A battery energized direct current detecting circuit is utilized to prevent stray magnetic fields from the motors from setting the detecting mechanism in the friction of material between the discs and grinding faces will cause the motors to stop almost immediately. In actual practice, this has been found to result in shutting down of motors and closing of valve 28 before metallic bridging bodies have had an opportunity to pass completely across the grinding faces Ilia and Ho. It has also been found that there is very little danger of fire or explosion while the bridging body remains between the grinding faces, which is due, perhaps, to the lack of sufficient oxygen to promote combustion in the tightly packed material in this space. It is only when the bridging element is near the peripheries of I61: and He that motion. In order that grounds be readily de-' tected, a voltmeter V may be applied across the terminals of the battery 23. bridging of the gap between th grinding faces will immediately lower the terminal voltage of the direct current source, which diminution will be indicated on the voltmeter.

In order that the bridging of the space between the grinding faces I6a and H11 performa useful function in preventing fires, the relay 22 has been shown as energizing the independently tripped circuit breaker 23 in the line which supplies energy to motors II and, I2. A suitable transformer 24' provides the energizing current for the circuit breaker.

At the same time, as it is desirable to confine any fire which may start in the mill to the particular mill involved and not have it spread through the conduit system leading from a series of mills or to the dust separator customarily employed, there has been provided an explosion stack 25 in the conduit C leading from the mill. This explosion stack 25 has'a light diaphragm 21 secured in place by any suitable holding means. This diaphragm is'so light that it readily gives vent to any explosion or burning in the line C. At the same time, a shutoff valve 28 is provided in conduit C at a point beyond the explosion stack 25. This valve 28 may be operated by the solenoid 29 which is in turn energized by the same circuit which operates the circuit breaker 23. In the form shown, energizing the solenoid 29 results in the armature 30 being withdrawn from under the arm 3 I, which permits the weight 32 to cause the arm to drop, thus automatically closing the valve 28. To reset the shut-off valve in open position, it is merely necessary to lift the arm 3| by means of the rope 33 or some other common device.

From what has been so far described, it may be seen that operation of the relay 22 caused by bridging of the space between the grinding faces IGa and He will immediately open the main line circuit at 23' and close the shut-off valve 28. As these mills operate under extremely heavy loads,

Any ground ormaterial in the casing 20, will ignite the same,

often with destructive explosive violence.

The above structure is, of course, operative only when the foreign bodies getting between the mill faces is of an electrically conducting character. Hard particles of rock will also lead to the production of dangerous quantities of sparks. In order to provide 'for the detection of rocks and other hard particles, the equipment shown to the extreme right of motor I2 has been supplied. Two contacts 34 and 35 are mounted upon relatively moving parts of the adjustment means in such a manner that abnormal axial displacement of the shaft of motor I2 to the right, caused by entrance of rock or non metallic objects, will cause them to complete a circuit. As shown, contact 35 is fastened to the stationary portion of motor I2 and insulated therefrom. The contact 34 is connected to the adjusting means of the shaft of motor I2 and also insulated therefrom. Axial movement of the shaft relative to the frame closes the contacts 34 and 35. Contact 35 is connected to the general ground of the machine, and contact 34 is connected to the line leading between the brush 24 and the relay 22. Upon closing of contacts 34 and 35, the relay 22 will operate exactly as when the space between the grinding faces I So and I1a is bridged by a conducting particle. It will be noted that the grinding faces are slightly bevelled on their inner edges so that a hard particle, which has found its way into the machine, will, in its travel towards the periphery, wedge the grinding faces apart, thus moving the shaft of motor I2 and close the circuit involving the relay 22.

As static electricity causes sparks of sufficient intensity to ignite the material being ground, some provision must be made whereby all parts of the machine can be grounded without interfering with the operation of relay 22. This means that the disc I4 and motor I 2 must be grounded. This is accomplished by providing condenser 36 for the mercury discharge lamp 31 in parallel connection from the insulated motor I2 to the ground. As the discharge lamp 31 does not act as a conductor until the voltage. between the motor I2 and the ground has reached quite a high value, the voltage of battery 23 will not cause discharge through the lamp 31. Of course, it is essential that the relay 22 be so adjusted that it will not operate on lamp current. This condition is easily attainable as the current through the lamp is very small, while that necessary to operate the relay can be much larger.

Although the contacts 34 and 35 will operate no matter whether the particle of foreign material passing through the mill is metallic or nonmetallic, provision is made for the detection of metallic particles which does not depend upon relative; movement of the grinding faces, as metal, because of its strength and softness, can often be reduced in thickness sufliciently to pass through the mill without becoming small enough to become harmless. Rocks and other non-metallic bodies, however, if subject to the action of the mill, either are so hard as to force the faces of the discs apart, or else when subject to the grinding action are reduced to small particles which are harmless as a sourc of sparks. It is, therefore, necessary to provide both forms of protection.

I claim:

1. In a mill of the type including cooperative working surfaces moving with respect to each other and a discharge conduit for conducting the treated material from said surfaces by air movement, an explosion stack in communication with said conduit, a diaphragm closing said stack but readily displaced by an explosion in the conduit, means for detecting the presence of spark producing foreign bodies in the material between the working faces, and valve means responsive to said detecting means shutting the conduit upon actuation of said detecting means by entry of foreign bodies into the space between the working faces, said valve means being located in said conduit downstream of said explosion stack, whereby upon detection of said foreign bodies the conduit leading from the mill is isolated from all parts of the system except the explosion stack.

2. An apparatus for confining fire or explosions caused by sparks in a mill and its adjoining connections, including a mill having cooperable working faces, a material discharge line leading from said mill, means for shutting off said discharge line from said mill, and means for producing closing operation of said shut-off means comprising electrically operable instrumentalities in an electric circuit controlled by spark forming foreign bodies in the material between the working faces of said mill.

3. An apparatus for confining fire or explosions caused by sparks in a mill and its adjoining connections, including a mill having cooperable working faces, a material discharge line leading from said mill, means for shutting off said discharge line from said mill, means for stopping operation of said mill, and means for producing closing operation of said shut-01f means and causing operation of said mill stopping means comprising electrically operable instrumentalities in an electric circuit controlled by spark forming foreign bodies in the material between the working faces of said mill.

4. An apparatus for confining fire or explosions caused by sparks in a mill and its adjoining connections, including a mill having cooperable working faces, a material discharge line leading from said mill, an explosion stack in communication with said line, a diaphragm closing said stack but readily displaced by an explosion in said line, means for shutting off said discharge line at a point therein downstream from said stack,

and means for producing closing operation of said shut-off means comprising electrically operable instrumentalities in an electric circuit controlled by spark forming foreign bodies in the ing one working surface from the other, and an electrical control circuit including said pair of working surfaces for discontinuing operation of said mill, said control circuit being completed upon bridging of the space between said working surfaces by a conducting particle,

6. An apparatus for confining fire or explosions in a mill caused by sparks, including a mill having a pair of cooperative electrically conductive working surfaces, a material discharge line leading from said mill, means for shutting off said discharge line from said mill, and an electrical control circuit includ 'ng said pair of working surfaces for producing closing operation of said shut-off means, said control circuit being completed upon bridging of the space between said working surfaces by a conducting particle.

7. An apparatus for indicating the presence of electrically conducting particles in a mill, including a mill having a pair of cooperative electrically conductive working surfaces, means electrically insulating one working surface from the other, indicating means, and an electrical circuit including said pair of working surfaces for producing operation of said indicating means, said circuit being completed upon bridging of the space between said working surfaces by a conducting particle.

8. In an apparatus for preventing or isolating fires or explosions in a, mill caused by sparks, a mill including a pair of grinding elements having extended electrically conductive grinding surfaces whereby the mass of material between said surfaces excludes sufllcient oxygen to promote combustion induced by a spark, means electrically insulating one grinding surface from the other, and an electrical circuit including said pair of grinding surfaces for controlling operation of said apparatus, said circuit being completed uponbridging of the space between said grinding surfaces by a conducting particle.

9. Apparatus for denoting the presence of electrically conductive particles in the material being fed to a mill, including a mill having a pair of cooperative electrically conductive working surfaces, means electrically insulating one working surface from the other, and an electrical control circuit including said pair of working surfaces for producing operation of means forming part of said apparatus, said control circuit being completed upon bridging of the space between said working surfaces by a conducting particle.

10. An apparatus for confining fire or explosions caused by sparks in a mill and its adjoining connections including a mill having cooperable working faces at least one of which is mounted for movement with respect to the other, a material discharge line leading from said mill, means I said mill, means shutting off said discharge line from said mill, and means for producing closing operation of said shut-off means and stopping of the operation of said mill comprising instrumentalities controlled by the movement of one of said working faces with respect to the other.

12. An apparatus for confining fire or explosions caused by sparks in a mill and its adjoining connections, including a mill having cooperable working faces at least one of which. is mounted for movement with respect to the other, a material discharge line leading from said mill, an explosion stack in communication with said line, a diaphragm closing said stack but readily displaced by an explosion in said line, means for shutting off said discharge lineat a point therein downstream from said stack, and means for producing closing operation of said shut-oi! means comprising instrumentalitles controlled by movement-Tot one of said working faces with respect to the other.

- DAVY .V. SICKMAN.

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