US3011190A

US3011190A - Floor machine for hazardous atmospheres

Info

Publication number: US3011190A
Application number: US660812A
Authority: US
Inventors: Bernard J Wilke
Original assignee: HILD FLOOR MACHINE CO
Current assignee: HILD FLOOR MACHINE CO
Priority date: 1957-05-22
Filing date: 1957-05-22
Publication date: 1961-12-05
Anticipated expiration: 1978-12-05

Description

Dec. 5, 1961 i B. J. WILKE 3,011,190

I FLOOR MACHINE FOR HAZARDOUS ATMOSPHERES Filed May 22, 1957 4 Sheets-Sheet 1 202 J4 F E50 156 ya I w 90 254 V INVJENTOR.

flrmra KM 41% Dec. 5, 1961 I B. J. WlLKE 3,011,190

FLOOR MACHINE FOR HAZARDOUS ATMOSPHERES Dec. 5, 1961 B. J. WlLKE 3,011,190

FLOOR MACHINE FOR HAZARDOUS ATMOSPHERES Filed May 22, 1957 4 Sheets-Sheet 5 Dec. 5, 1961 B. .J. WlLKE FLOOR MACHINE FOR HAZARDOUS ATMOSPHERES 4 Sheets-Sheet 4 Filed May 22, 1957 INVENTOR.

United States Patent 3,011,190 FLOOR MACHINE FOR HAZARDOUS ATMOSPHERES Bernard J. Wilke. Chicago, Ill., assignor to Hild Floor Machine Co., Chicago, 11]., a corporation of Illinois Filed May 22, 1957, Ser. No. 660,312

14; Claims. (Cl. 15-49) g This invention relates to floor polishing and scrubbing machines, particularly to such machines having a motor driven, rotatably mounted brush mounted upon the bottom of a frame having an upwardly and rearwardly extending post assembly carrying handle bar means at the top thereof for maneuvering the floor machine easily about the floor being scrubbed or polished.

Due to the friction developed between the brush tufts of these machines and the floor, appreciable static charges of electricity can build up upon the machine and sometimes also upon the operator thereof whichoccasionally result in generation of sparks which can be exceedingly dangerous in hazardous atmospheres so frequently found, for example, in chemical plants, paint plants, refineries, distilleries and flour mills. Moreover sparks are sometimes generated within the'floor machine itself which can create a hazard in explosive atmospheres if the sparks escape from the machine into the atmosphere or if the atmosphere seeps into the machine. Although-some efforts have heretofore been made to reduce the static charge built up on the floor machines, for the most part, they have left much to be desired.

It is, accordingly, one of the objects of the present in-. vention to provide a floor scrubbing orpolishing machine which is kept substantially free of static charge build-up upon the frame of the machine under practically all operating conditions which can be reasonably anticipated.

Another object of the invention is to provide a floor scrubbing or polishing machine wherein the machine is sealed against passage of sparks from within the machine to the surrounding atmosphere and wherein the explosive materials in the surrounding atmosphere cannot readily gain access to the parts of the machine where sparking is readily possible.

Still another object of the invention is to provide a floor polishing or scrubbing machine having the aforementioned upstanding post assembly which is constructed in a novel and improved manner to increase the strength and rigidity thereof. A further object of .theinvention is to provide an upstanding post assembly fora floor machine which is so related to the handle bar means at the top thereof and the rest of the frame of the machine thatv a low resistance path for flow of static charges of electricity are provided between and including'the handle bar means and the floor brush.

With the conventional type ous condition exists if-the power cord plug attached to the power cord of the machine is accidentally pulled out of the electric outlet socket and the operator leaves the machine to correct the condition without first switching the conventional type on-ofi to the oil? position. Inv

such case, when the power plug is reinserted into the elecfloor machines, a danger ductive to' static electricity. Preferably the handle bar tric outlet socket the machine is turned on while unatj tended, resulting in the resumption of rotation of the brush which can drive the unguided machine against unsuspecting persons, furniture or machinery;

'Accordingly, a still further objectof the invention is to provide a floor machine which cannot be started if left unattended so as to avoid the above-mentioned situation if thepower cord plug should he accidentally pulled from the power outlet socket. 1

In accordance with one aspect of the invention, all or an appreciable number of the brush'tufts' are'rendered' conductive to static electricity and electrically connected 3,011,190 Patented Dec. 5, 1961 to the frame of the machine which is made of metal or' other good conductor of static electricity. The impor-. tant feature of this construction is that the static-chargeconducting brush tufts are well distributed over the bot-:

tom of the machine to ensure good electrical'contact with the floor even when the brush assembly is tilted into posi-' tions where the brush tufts do not all make contact with the floor or when the brush tufts wear unevenly resulting in poor' contact between some of the brush tufts and the floor. 1

In the case of wet scrubbing brushes or polishing brushes, the usual required brush tuft characteristics pre:

tributed therethrough in an amount which may com: prise at least approximately 10% by volume. of the;

strands thereof. The remainder of the strands are the usual non-metallic fibers, such as bassine, .nylon, unionfibers, etc. In the so-called dry scrubbing brushes for cleaning concrete or wood block factory floors, strands are made of fairly rigid electrically conducting, non-sparking metal wire strands. In both types of brushes referred to above, the brush tufts are preferably electrically connectedtogether by metal wires secured upon a support plate which'carries the tufts. The wires are electrically connected to a metal mounting ring at the center and :top of the plate and the ring physically and electrically connects the support plate to a rotor driven by an electric motor.

Usually, floor scrubbing and polishing machines are provided with casters for quickly and easily. moving the machine from place to place, thecasters being retract-.

made of a special rubber which is a conductor of static electricity and which prevents the accumulation of static electricity so that grounding of static charges is provided at all usual points of contact between the machine, the floor and surrounding objects.

As 'a further safety feature, the handle bar means at the top .of the hollow post assembly are rendered conmeans has a metal core surrounded by a covering of a special rubber which is treated to be conductive to static electricity. The rubber covering is 'preferab-ly'secureito,

the metal core by a static-charge conducting cement so that good electrical contact is m'adetbetween. the rubber electric motor is usually enclosed in'a' housing section covering and the core of the handle bar means. The metal core, in turn, is electrically connected to. the-hollow post assemblywhich is electrically connected to the brush tufts, casters and bumper.

In floor machines of thetype now beingdiscussed, the

above the brush assembly and an electrical connection to the motor is obtained through conductor'wires' extending down a'hollow post assembly and through anopening in the housing assembly. The conductor wires'arecon- To obtain best results, each of all of the:

nected to an on-ofl? switch usually at the top of the post assembly from which a power cord extends to a suitable power plug insertable into an electrical outlet socket. In-a'ccordance'with the invention, the various joints or couplings between the point of entry of the power cord into the top of the post assembly and the point of entry of the conductor wires into the motor housing are rendered practically impervious to the passage of sparks from within the machine to the surrounding atmosphere and 'to the passage of the explosive elements in the atmosphere, particularly dust and powder, into the machine. Most preferably, a suitable sealing compound fills the space between the inner wall surface of a conduit carrying the wires from the post assembly to the motor housing section and the conductor wires at their point of entry into the motor housing. Also, the opening at the bottom of the motor housing section through which the motor shaft passes is sealed against the passage of sparks from the motor housing section and explosive mixtures from the surrounding atmosphere.

As.an additional safety feature, to prevent the application of power to the machine when it is left unattended, an on-ofi switch controlling the flow of electric power to'the machine is provided with a control lever which is spring biased to the off position andwhich is turned on by the hand of the operator as it grips the handle bar means. Removal of the operators grip from the handle bar means requires release of the control lever which is then automatically returned to the off position by its biasing spring.

Other features of the invention reside in the details of construction of the mounting post assembly and the means for connecting the post assembly to the other parts of the machine. These features together with still other features of the invention are described in the specification to follow, the claims and the drawings wherein:

FIG. 1 is a side elevational VieW of the floor machine of the present invention;

FIG. 2 is a plan View of the machine of FIG. 1;

' FIG. 3 isan enlarged fragmentary plan view at the base and rear of the machine showing the manner in which the bumper guard assembly is secured around the base of the machine;

- FIG. 4 is an enlarged vertical section through the bumper of the floor machine, along section line 4-?% in FIG. 2';

1 FIG. 5. is an enlarged, partially vertical sectional view through the housing and post assemblies;

FIG. .6 is a horizontal sectional view through the gear assembly, taken along section line 66 in FZG.

Y FIG. 7 is a longitudinal sectional view showing a part of the conduit section extending between the post assembly and. the housing. assembly, taken along section line 7'7 of FIG. 5; Y 7

. FIG. 8 is a sectional view through the rotor assembly taken along section line 8 8, in FIG. 5, with the brush assembly appearing in a fragmentary plan form;

FIG. 9-is an exploded view showing the coupling parts which secure-the brush tuft support plate to the rotor assembly;

FIG. lO-is an enlarged vertical section through the brush tuft support plate, showing the manner in which the brush tufts are secured thereto;

FIG. 11 is an'enlarged fragmentary vertical section through a portion of a modified form of brush assembly;

FIG. 12 is a fragmentary plan, partially broken away, of the modified brush assembly of FIG. 11;

FIG. 13 is a perspective view of a cluster of brush strands making up each of the brush tufts-in the modified form of brush assembly in FIGS. Hand 12;

FIG. 14 is a partial vertical sectional view of the caster assembly, takenalong {section line 14-14 in FIG. 2; FIG-.15, se enlars d e i a e h h a par of 'ment of the floor machine.

the machine base, taken along section line l515 in FIG. 2;

FIG. 16 is an enlarged side elevational view, partly broken away, of the switch box and power cord connector at the top of the post assembly;

FIG. 17 is a longitudinal section through the switch box and handle bar assemblies, taken along section line 1717 in FIG. 16; and

FIG; 18 is a'top end view taken along line 1818 of FIG. 16.

Referring now to the drawings, the floor machine there shown includes a housing assembly 4 comprising an upper motor housing section 6 containing an electric motor, not shown, and a lower brush assembly housing section 8 containing a brush assembly 10 and other mechanism to be described which couples the motor to the brush assembly. The machine further includes a hollow post assembly 12 supported from the housing assembly and a switch control and handle bar assembly 14 by means of which the operator controls the operation and move- Electric power is delivered to the machine through a power cord connector assembly 15 attached to the switch control and handle bar assembly.

As above indicated one of the important novel aspects of the invention is the construction of the brush assembly 10 which is constructed to provide a large number of evenly distributed static charge grounding points with the floor to inhibit the buildup of static charge on'the floor machine which might produce sparks creating a dangerous condition where the, machine is used in hazardous atmospheres commonly found in chemical, plants, paint plants, refineries, distillen'es, flour mills, etc. The drawings show two generally different types of brush assemblies, one type being shown in FIGS. 5, 8 and 10 which may be used for polishing and wet scrubbing, and the other type being shown in FIGS. 11 through 13 which may be used for dry scrubbing.

In the type shown in FIGS. 5, Sand 10, each of the brush tufts, generally indicated by the reference numeral 16, is comprised predominantly of non-metallic brush strands 18 (FIG. 10), such as bassine, palmetto, union fibers or nylon, depending upon their use, which may be polishing or wet scrubbing in accordance with the invention. Conductive wire strands 20 are distributed throughout the non-metallic brush strands through practically all of the brush tufts so that they are conductive to static electricity. The strands making up each tuft are substantially of equal length and are bunched together with their ends in alignment. Then they are folded into an inverted U-shape so that all their ends are in approximately the same plane at the bottom of the brush assembly. In this way the conductive strands make contact with the floor with the other strands to effectively ground any static charges which may tend to build up on the brush tufts or other parts of the machine electrically connected thereto. Since the metal conductive brush strands form only a small proportion,

say 10 percent, of the strands in each tuft, the physical properties of the tuft are, primarily, determined by the non-metallic brush strands which are specifically adapted for the particular kind of scrubbing or polishing job to be performed by the brush assembly. In one example, .the non-metallic fibers were .bassine and the conductive fibers were 0.005 inch diameternickel plated silver wire,

constituting at least approximately 10 percent by volume of the strands in each tuft.

The tufts 16 are secured to a tuft support member, the tuft comprisedpreferably of a metal backing plate 22 preferably of a non-ferrous, non-sparking metal, such as cast aluminum, zinc, brass or the like, having a large number oftuft mounting bores 24 formed orjmolded in the bottom face thereof which are distributed alonga number of concentric circles. A Wire pass-through opening 25 connects the top of each bore v2,4 to the top sur-,

face of thetuft support plate 22. The tufts within eachbores 24 and snugly loop under the folds of the brush tufts which have been extended up into the bores 24 and then pass up through the pass-through openings to sus-- pend fixedly the brushtufts in the bores 24. The Wires 26 associated with the concentric circular rows of brush tufts may actually be part of one long piece of wire or may be interconnected by jumper wires so that all of the tufts are electrically connected together. The wire section associated with the innermost circle of brush tufts is electrically connected to a mounting ring 28 either by a direct soldered connection thereto or by soldering the wire to any suitable place on thesupport plate which in turn is electrically connected through the metal of the plate to the ring which is fixed by screws 30 to the top of an upwardly extending cylindrical neck portion 32 (FIG. at the center of the tuft support plate.

At the perimeter of the tuft support plate is an upwardly extending annular skirt 38 which forms a-liquid confining wall which adapts the brush assembly for ,use with a water supply tank, not shown, often used with floor scrubbing machines. The tank is mounted on the hollow post assembly 12 of the floor machine and has a supply tube which connects-with a fitting 37 on the top of the brush housing section 8 and directs soapy water onto the top .of the tuft support plate 22. For this purpose, a series of concentric grooves 39 are formedin the top surface of the tuft support plate 22 between the circular rows of wire pass-through openings 25. A series of downwardly diverging water supply holes 40 are formed in the bottom of the grooves 3-9 to distribute a stream of soapy water on the floor adjacent each brush tuft.

Referring now most particularly to the mountingring per wires bent into the inverted U shape down in the drawings. For example, the wires may have a generally rectangular cross section 0.150 inchwide and 0.021 inch thick. These copper wire brush tufts are mounted upon a tuft support member which may comprise a pair of correspondingly shaped, circular

wooden backing parts

22 and 22". If desired, the

backing parts

22 and 22" could also be made of a non-ferrous, non-sparking metal. The brush tufts extend through respective tuft receiving bores 24' extending completely through the lower backing part 22, which bores are preferably uniformly arranged along a number of concentric circles. The brush tufts are arranged in a random manner in the various bores 24' with the bent b-ack intermediate portions thereof protruding a small distance above the top surface of the lower backing part 22. The tufts are each securely held in place within the bores 24' by a pair of wires 26'26' passing together through the loops formed by the protruding upper portions of the brush tufts. Two wires are placed alongside one another rather than utilizing a single wire of larger diameter in order to reduce the vertical space required thereby since a single circular wire of larger diameter would occupy a greater vertical space.

In addition to their function of suspending the tufts in the bores 24, these wires electrically interconnect the various brush tufts. If separate pairs of wires are utilized to interconnect the brush tufts of adjacent concentric circles of brush tufts, then the wiresof the adjacent circular rows of brush tufts are electrically interconnected by suitable cross-connecting wires. Intheillustrated embodiment, a pair of continuous wires are used to'interconnect the brush tufts. Y j

The wires 2626 are electrically connected to the same mounting ring 28 above described by a jumper'wire 26" hooked around and soldered to one of the innermost brush tufts at thebottom of the lower backing part 22'.

28 shown most clearly in FIGS. 5 and 9, the central opening 42- thereof is provided with three equally spaced radial slots44 which are sized to receive similarly shaped radial projections 43 with beveled upper side edges 43 extending from a cylindrical neck portion 45 depending from a rotor assembly 46. .Surrounding the top of the cylindrical neckportion 45 of'the rotor assembly is a downwardly facing annular shoulder 47 which overlies the radial projections 43. y l

The mounting ring 28 has a tapered thickness formed by shaping the under surface 44' of the ring so that it progressively inclines downwardly from points adjacent each radial slot 44 proceeding in a counter-clockwise direction as viewed from above the ring, and the three resulting sloping surfaces each terminate in a depending prong 48. The top surface of the ring is flat and the thickness of the ring adjacent to the base of each prong matches the spacing between the top of the radial rotor projections 43 and the bottom of the annular rotor shoulder 47. Thus, the mounting ring 28 and the att-ached tuft support platecan be mounted upon the rotor assembly by raising the brush assembly to bring the mounting ring slots 44 over the radial projections 43 of the rotor assembly and, when the radial projections 43 are below the bottom surface 44 of the'ring, then twisting the mounting ring. clockwise as viewed from above the ring which wedges the mounting ring in the space between the radial rotor projections ,43 and the rotor shoulder 47 by camming action brought about by the shape of the undersurface 44 of the mounting ring. Sincev the rotor assembly is rotated in a counter-clockwise direction, the rotation of therotor tends to maintain the mounting ring in its locked position on the rotor.

Instead of the brush assembly 10 above described, the

embodiment shown .in FIGS. 11 through 13 may be used. when dry scrubbing concrete or wood block factory floors:

The modified brush assembly is indicatedgenerally by the reference numeral 10' and includes brush tufts 16 each 1 formed by a cluster of superimposed stiff beryllium cop The wire 26" extends through central apertures in the backing parts andterminates beneath the head of one of the screws 30, which are made of non-sparkingrnetal and anchor the mounting ring to the upper backing part. The two

backing parts

22 and 22 are secured together. by non-sparking metal bolts 31 passing through aligned holes in'theseparts, the heads of the bolts being recessed within counterbored portions of the holes in the upper backing part 22" and the ends of the bolts receiving nonsparking metal nuts v32' nestled within recesses formed in the bottom faceof the lower backing part 22'. The

connection of this brush assembly to the rotor assembly is the same as described above for the brush assembly 10.

The rotor assembly 46 upon which the brush assembly I is mounted is comprised of a pair of superimposed hollow complimentary casting parts 50 and 51 which are secured together in any suitable way along a pair of confronting edges thereof, and the lower casting part 50 has the reduced cylindrical neck portion 44 previously alluded to, from which project the radial projections 43.

The rotor assembly 46 is rotatably supported upon upper and lower ball bearings 58-58 mounted upon a stationary gear and ball bearing assembly 59.; The gear and ball bearing assembly59 includes upper and lower frame parts 60 and 61 which have confronting engagingflanged portions 62 and 63 secured together by machine screws 64. The flanged portion 62 merges with an upstanding cylindrical collar portion 65 around which is press-fitted or otherwise secured the aforementioned upper ball bearing 58. The flanged portion 63 of the lower part 61 has a reduced depending stepped collar portion 67 around which is mounted'the lower ball bearings 58'.

The .upper and lower collar portions 65 and 67 have fixedly mounted within suitably shaped internal recesses upper and lower ball bearings .69 and 70 which rotatablysupport a drive shaft 71. A drive pinion 73 is formed on" an intermediate portion of the drive shaft 71 which pinion; meshes- Withthree fidler gears 75 (see FIG. 6) mounted within respective recessesr-77 formed in the flanged porthereof.

tion 63 of the frame part 61. The gears 75 are each mounted upon ball bearings 78 mounted upon respective pins 79 secured within aligned openings in flanged portions 62 and 63 of frame parts 61 and 62. The gears 75, in turn, mesh with an internal ring gear surface 80 formed on the inner peripheral surface of the lower rotor casting part 50. Thus, rotation of the drive shaft 71 will rotate the drive pinion 73 to in turn rotate the idler gears 75 meshing with the internal gear surface 80 of the rotor assembly which rotates the brush assembly.

A splined steel coupling 31 is keyed to the top of the drive shaft 71 and meshes with the splined end 82 of the electric motor shaft. The motor shaft 82 passes into the motor housing section 6 through a sealed opening in the bottom wall of the motor housing section, the seal preventing the passage of any sparks from the motor housing section and explosive atmosphere into the motor housing section. As a further aid in preventing the intermixing of sparks and explosive atmosphere, a plug 83 is inserted into the opening at the bottom of the depending cylindrical neck portion 45 of the rotor assembly.

The upper collar portion 65 of the gear and bearing assembly 59 is secured by machine screws 84 to a hollow stationary hub portion 86 from which radially extend webs88 joining with a cylindrical, intermediate housing part 90. The intermediate housing part 90 sits upon an upwardly facing annular shoulder 92 of the brush housing section 8. The motor housing section 6 has a peripheral flange 94 at the bottom thereof which rests upon the top of the intermediate housing part 91). The

various parts

6, 90 and 8 of the housing assembly are tied together by screws 96 passing through openings in the motor housing section flange 94 and the intermediate housing part 91 and threading into the top of the brush housing section 8. A gasket ring 98 is preferably placed between the bottom of the intermediate housing part 90 and the annular shoulder 92 at the top of the brush housing section.

The brush housing section 8, which may be a metal casting as in the case of the other frame parts above described, has a depending annular skirt portion 102 which is spaced appreciably outwardly of the rotor assembly 46.

A bumper guard assembly 105 is secured around the bottom of the brush housing skirt 192 and includes a hollow rectangular body 166 (see FIGS. 4 and of flexible rubber which is rendered conductive to static electricity in any suitable way, such as by the inclusion of above normal quantities of carbon black in the latex from which the rubber is initially made. The bottom wall of Y the rubber body 106 rests upon an outwardly flared lip sembly support arms 123-123. The boss122 is provided with a post assembly mounting socket 126, the axis of which extends upwardly and rearwardly parallel to the axis of the hollow post of the assembly 12. A cylindrical nose 128 depends from the post assembly and fits within the socket 126 where it is locked securely therein by headless screws 129 respectively threading into holes drilled in the top and sides of the boss and tightly engaging the nose 12-8.

The caster mounting arms 123-123 are provided with aligned openings 130-131 in which are fixedly mounted a long metal pivot pin 131 whose ends project laterally beyond the sides ofthe arms 123-123. A pair of metal pivot arms 132-132 are fixed upon the ends of the pin 107 formed at the bottom of the brush housing skirt 102.

The rubber body is held securely upon the lip 107 by a' suitable angle bracket 108 made of flexible metal strip material secured by screws 169 to the skirt 162, the bracket having an upper outwardly extending leg which forms a channel with the housing lip 107 into which the rubber body 106 may snugly be fitted and held by its own resiliency. A conductive metal band 110 is passed through the passage 111 withinthe hollow rubber body 106 and the ends'of the band are bent and curled at 112 to form eyelets which receive a headed clamp'bolt 114 on the end of which is threaded a nut 116 which clamps the band and hence the rubber body 106 snugly around the bottom of the brush housing section 8 at the rear The brush housing section 8 is grounded in a manner to be more fully explained hereinafter and the static charge conducting rubber bumper body 106 is similarly grounded through its contact with the brush housing section so that no sparking can occur whenthe rubber bumper body contacts any similarly grounded object as the floor machine is'being moved about the floor.

The brush housing section, which maybe a metal casting, includes as an integral part thereof an upwardly and rearwardly extending boss 122 '(FIGS. 1, 5 and '14) disposed between a pair 'of'rearwardly extending, caster as- 131, and a pair of metal axles 133-133 are fixed to and project laterally outwardly from the pivot arms along aligned axes spaced from the axis of the pin 131. Casters 134-134 are mounted upon the axles 133-133, the casters being held on the axles by end caps 135-135 threaded over the ends of the axles. One of these caps 135 has an appreciable length so that it may be readily engaged by the foot of the operator which pivot the associate caster and pivot arm connected to the pivot pin 131. Since the other pivot arm and caster are fixedv to the pivot pin, they pivot with the caster and arm associated with the long end cap 135'. In this way, the casters can be swung from the position shown in FIGS. 5 and 14, where the casters engage the floor, to the retracted position shown in dotted lines in FIG. 5, where the pivot arms 132-132 rest upon pins 136-136 (FIGS. 2, 5 and 15) spaced sufiiciently forwardly of the pivot pin 131 that the center of gravity of the caster assembly is located forwardly of the pivot pin 131 so that the caster assembly is held in its retracted position by force. of gravity. The caster assembly is moved into its retracted position to place the floor machine in a scrubbing or polishing position where the entire weight of the machine is carried upon the brush assembly to increase the frictional resistance between the brush tufts and the floor for good cleaning or polishing action. When the floor machine is to be transported from place to place within a building, the caster assembly is pivoted into the lower position and the machine is titled so that most if not all of the weight of the machine is supported upon the casters to minimize the effort necessary to move the floor machine about.

The casters are so constructed that they form a staticcharge-conducting surface at their points of contact with the floor and are electrically conductively connected to the metal frame of the floor-machine. Accordingly, each of the casters comprises a central body portion 137 which may be made of a hard rubber or plastic material rendered conductive to static electricity, and-a soft, resilient rim 138 made preferably of a soft rubber rendered conductive to static electricity. As in the case of the bumper guard body, the rubber of the

caster parts

137 and 138 may be rendered conductive by the addition of above normal quantities of carbon black in the latex used in the manufacturing of the rubber. The central body portion 1-37 of each caster carries a non-sparking metal bearing 139 which rotates upon one of the axles 133.- Electrical conmotion between the rim 138 of thecaster assemblies and the brush housing section 8 is thus made via the central caster body portions,the bearings 139, axles 133;pivot arms 132 and the pivot pin 131 anchored to the arms 123-123 extending from the brush housing section. The axles 133, pivot arms 132 and pivot pin 131 are preferably made of brass to ensure good electrical contact therebetween. Y

The hollow post assembly 12 has near the bottom there- .of a cylindrical, open-top, metal junction box body 140 from which extends a pair of aligned, internally threaded,

. into which the upper end of the post A' ring ofmetal 193 is brazed or welded between the 9 and upwardly. The fitting 141 has a threadedsocket 144 which receives the upper threaded end of the cylindrical nose 128. A ring of metal 146 is brazed or welded between the nose 128 and the bottom of the fitting 141 rigidly to fix the junction box body with respect to the nose and to provide a seal to prevent the passage of explosive atmosphere into the junction box. The other fitting 142 hasa threaded socket 149 into which the bottom portion of a long metal tube 150 is threaded.- The socket 149 communicates with the inside of the junction box through a pass-through opening 152. A ring of metal 151 is brazed or welded between the tube 150 and the fitting 142 to fix the two parts and to seal the junction box body from the atmosphere.

The junction box body 140 has a metal cover 153 which is secured in place by screws 161 and which encloses the open top thereof. The cover has formed integrally therewith a forwardly and upwardly extending cylindrical fitting 154 having a threaded socket 155 into which the bottom threaded end of a short metal tube 156 is threaded, the tube 156 forming part of a conduit section or assembly 157". A pass-through opening 158 interconnects the socket 155 withthe junction box interior. A ring of metal 157 is brazed or welded between the tube 156 and the fitting-154m form 'a rigid connection therebetween and to seal 'off the junction box from explosive atmosphere. i

The upper end of the tube 156 is threaded into a socket 162 (FIG. 7) of a metal= tubular member 164 forming part of an extensible sleeve assembly 166. The tubular member 164 has a pair of axially spaced

peripheral flanges

168 and 170 which make sliding contact with the inner walls of metal sleeve member 173. A

A partition disc 10 196 or suitable wadding is located inside of the post 150 adjacent to the upper end thereof and the space above through opening 188 is filled --with a moisture-proof sealing cement 198 to isolate the switch box from the other parts of the floor machine. I Thepower conductors 183',

of course, pass through suitable openings in thedisc 196 or wadding and are embedded within the sealing cement. The switch box 186 is open at its top 200 (FIG. 16) and the opening is covered by a cover 202 which is secured to the box 186 by machine screws 204threading into the junction box. A double pole single throw on-otf switch 206 is mounted within the switch box 186 by a bracket plate 208 secured to the switch and attached to mounting lugs 210 extending inwardly from the outer walls of the switch box by machine screws 212.v The switch mechanism may be any of a number of well known varieties-30f switches including an operating shaft 214 (FIG. 18) which controls the movement of the movable contact poles of the switch. A switch operating arm 215 is connected in any suitable way to the operating shaft 214/ The arm 215 may be formed as an assembly of two vspaced arm pieces 215'-215" (FIG. 16) between the ends of which a roller 216 is pivotally mounted.

. An operating lever assembly is mounted upon the cover 202 of the switchbox and includes a rocker shaft 217 which is journaled in a suitable bearing mounted in the cover walls. An extension arm 218 is secured-to the rocker shaft 217 within the cover 202 and has a pair of bifurcated ends 219-219 which straddle the roller 216. The rocker shaft 217, which extends forwardly suitable packing 174 may be stuffed in the space between the fianges 168-170. Theoutward movement of the inner tubular member 164 relative to the sleeve member. is limited by a shoulder formed by an inturned end 175 of the outer sleeve member 173.

The outer sleeve member 173 is'provided with a :neck 178 threading into a socket 180 of a metal elbow fitting 182 projecting from the upper end of the motor housing section 6, a

In addition to the various metal rings of soldering or

welding material

146, 151 and 157, preventing the entry of explosive atmosphere into the machine andthe passage of sparks from the machine to the atmosphere, an additional seal is provided at the fitting 182 by a moisture-proof sealing cement 185 which fills the spaces within the fitting 182.

The conduit section'157, just described, acts asa conduit for a pair of insulated power conductors 183183 extending from the motor within the motor housing section 6. The power conductors 183183 extend through the sealing cement 185 embedding the same in the fitting 182 at the top of the motor housing section and pass through the extensible sleeve assembly 166, and tube 156 and the pass-through opening 158 leading to the junction I box interior. Within the junction box, the insulated power conductors 183-183 are'joined to a pair'of power conductors 183183' extending down the tube 150 and passing into the junction box throughthepass-through opening 152, The bared ends of these conductors may be spliced together in any suitable manner and covered by insulating tape 184-184 within the junction box.

The power conductors.183 183' extend up the post 150 and into a rectangular metal switch box 186 through a pass-through opening 188 in the junction box. cylindrical fitting 190 formed integrally with thejswitch box projects from the latter around the pass through opening 188, the fitting having a threaded socket 192 150 is threaded.

fitting 190 and the post 150 to fix the two parts together and to provide an explosion-proof seal which prevents the passage of sparksfrom the switch box to the atmosfrom the switch box cover along a line generally'parallel to the post 150, carries a control lever 220. The control lever 220 is urged into a position. where the switch- 2 06 is in its off position by any suitable spring means, such as by a spring 226 ciated with the operating shaft 214 and anchored at the other end to a stationary part of the switch. The position of the control lever 220 in the off position of the switch is shown in solid lines in FIG. 18 and'as shown, extends upwardly away from the switch box. The switch is operated to its on position by pulling the lever 220 against the restraining force of the spring 226 toward the switchbox into the position, shown indotted lines in FIG. 18. As the control lever is rotated, the arm 218 likewise rotates and the'bifurcated ends thereof pivot the switch operating arm 215 and hence the switch contacts into a switch closing position. If the operator re-' leases the control lever it will automatically move to its ofi position under control of the spring 226.

The control lever 220 is arranged to cooperate with b one of a pair of handle bar assemblies 228--228 so that the operator may grasp one of the handle bar assemblies and hold the control lever with the same hand in the on position, shown in dotted lines in FIG. 18, Then,

if the power cordshould pull out of the power, outlet socket when the operator leaves the machine to plug the power cord back into the outlet, the machine will remain off even when the power cord is plugged into the outlet, because, upon release. of the operators grip on the handle bar assemblies, the control lever 220 automatically snaps back into its 01f position.

The handle bar assemblies 228 each comprises a solid,

cylindrical metal core 230 whichEis threaded into asocketed fitting 232 formed'integra'lly'with and projecting from the switch box 186. The fittings 232232 associated with the respective'handle bar assemblies are in axial alignment and extend laterally of the switch box. Respective rings of metal 234-234-"are brazed or welded. between the fittings 2322 32I and ;'the rrietal cores 230"-230 to anchor these parts together and to seal theswitch box from the surrounding atmosphere. Intimately surrounding each of the cores 230-230 is a soft rubber covering 236 'which is rendered conductive to static electricity in the same manner astheirubber bumper body the disc up to and including the passsecured at one end to a lug 227 asso-- 106 previously described. The rubber covering may be cemented to the associated metal core bysuitable cement 238 which is likewise rendered conductive to static electricity. In this Way, the-handle bar assemblies are electrically conductively connected to the frame of the machine through the connection of cores 230-230 with the switch box, which in turn is secured to the hollow post assembly 12, the conduit section 156 and the housing assembly 4 through the various conductive fittings and connections above described. The ends of the handle bar assemblies are covered by suitable discs 24024ti which are secured to the core ends by recessed machine screws 242-242.

One of the handle bar cores 230 has a projecting portion 244 which projects into the switch box through a pass-opening 247. A terminal lug 248 is heldin place against the end of the projecting portion 244 by the head of a screw 246. The terminal lug 248 is connected to a ground conductor 249 associated with the power cord to be used with the floor machine.

The upper ends of the power conductors 184184 extending up through the post 150 into the switch box are secured to terminals on the switch 206. When the switch is closed, the power conductors 183 are connected through the switch to a pair of power conductors 250 also extending from the switch. The power conductors 250 together with the grounded conductor 249 extend through a pass-through opening 252 formed in the bottom wall'of a switch box into the threaded socket 253 of a cylindrical fitting 254 depending from the switch box 186. The conductors 250'-250 and 249 then pass into the connector assembly through a right-angle metal elbow 6which is threaded into and brazed in position in the socket 253 of the fitting 254. The end of the elbow 256 opposite the end secured into the socket 253 extends downwardly in a direction parallel to the post 150 and has a threaded socket 258 which'threadedly receives the end 260 of an insulating part 262 of the connector assembly 1'5,.which insulating parts 262 may be made of Bakelite or other suitable. material and which has connecting terminals 264 to which the conductors 266 of a three-conductor power cord (FIG. 1) 268 are secured by screws. 269.

The insulating part 262 receives the three power conductors 249, 250-250 in metal lined sockets (not shown) formed therein, and the terminals 264 thereof are secured in any suitable manner to the metal lining of these sockets- V The power connector'assembly 15 further includes an inner metal sleeve 271 which may have fingers which interlock with the insulating part 262 and an outer metal sleeve 272 which is threaded around the top of the insulating part 262 and has an inturned bottom end 274 which-holds the inner sleeve securely upon the insulating part 262. The inner sleeve 272 has a tapered bottom opening 273 into which a rubber sleeve 276 with a tapered head 278 complementary to the tapered opening 274 extends. The rubber sleeve 276 is held in place with respectto the outer sleeve 272 by a. suitable clamping part 286 which is screwed to a complementary clamping part 282-formed integrally with the sleeve 272. The various parts of the connector assembly 15 above described are so connected together that the interior of the connector assembly. is sealed off fro-m the outside atmosphere so-that an explosion-proof connector is provided. The Bakelite insulating part 262 is relatively fragile and to prevent the transmission of large shock forces to the insulating part, a metal ring 283 is secured around the lower end of the elbow 286 by screws 285285. The ring 283 has a larger diameter than the outer sleeve 272 so that should the floor machine fall backwards, the ring 283 will strike the floor first and it and the elbow 256 will take mostlof the shock forces instead of the sleeve 272 and theBakelite insulating part 262.

As above explained, the various fittings and connecbumper, casters and handle bars) which are electrically connected to one another provides an exceedingly safe floor machine usable practically in all explosive atmospheres for floor scrubbing and polishing operations.

It should be understood that numerous modifications may be made of the preferred forms of the invention above described without deviating from the broader aspects of the invention.

, I claim as my invention:

1. A floor machine comprising a metal housing assembly having on the bottom thereof a brush assembly mounted for rotation about a generally vertical axis and including a tuft support member and a large number of floorengaging, non-sparking, static-charge-conducting brush tufts depending from and distributed over the bottom surface of said support member, said housing assembly including a motor housing section, an electric motor supported in said motor housing section and connected in driving relationship to said brush assembly, a hollow upstanding metal support post connected to andextending upwardly from said housing assembly, handle means at the top of said post having hand-engaging portions made of a static-charge-conducting material, the various points of connection between said handle means, support post,

and motor housing section being impervious to passage of sparks from within the floor machine to the atmosphere and explosive atmosphere into the machine, and said handengaging portions of said handle means, support post, housing assembly and brush tufts 'being electrically interconnected to provide a low resistance path-of flow of static charges from the handle means to the brush tufts.

2. A floor machine comprising a metal housing assembly having on the bottom thereof a shock and mar preventing bumper projecting therefrom made of a soft, static-charge-conduoting material which is electrically connected to said metal housing assembly, a brush assembly mounted on the bottom of the housing assembly for rotation about a generally vertical axis and including a tuft support member and a large number of floor-engaging, static-charge-conducting brush tufts depending from'and distributed over the bottom surface of'said support mem her, said housing assembly including a motor housing section, an electric motor supported in said motor housing section and connected in driving relationship to said brush assembly, a hollow upstanding metal support post connected to and extending upward from said housing assembly, handle means at the top of said post having handengaging portions made of a static-charge-conducting material, the various points of connection between said handle means, support post, and motor housing section being impervious to passage of sparks from within the floor machine and explosive atmosphere from without'the machine, and said hand-engaging portions of said handle means, support post, housing assembly and brush tufts being electrically interconnected to provide a low resistance path of flow for static charges from the. handlemeans to the brush tufts.

3. A floor machine comprising a metal housing assembly having on the bottom thereof an open bot-tombrush housing section, a shock and mar preventing bumper projecting from saidbrush housing section and made of a soft, static-charge-conducting material which is electrically connected to said metal housing assembly, a brush assembly mounted in the brush housing section for rota tion about a generally vertical axis and including a tuft support member and a large number" of floor-engaging, v

static-charge-conducting brush tufts depending from and distributed over the bottom surface of said supportmeinber, casters having. a rim madev of a soft, resilient staticcharge-conducting material supported at thebottom 10f These explosion-proof features, together with the machine and electrically connected to said metal housing assembly, said housing assembly including a'motor housing section, anelectric motor supported in said motor housing section and connected in driving relationship to said brush assembly, a hollow upstanding metal support post connected to and extending upward from said housing assembly,'handle bar means at the top of said post having hand-engaging portions made of a static-chargeconducting material, the various points of connection between said handle means, support post, motor housing section and brush housing section being impervious to passage of sparks from within the floor machine and explosive atmosphere into the machine, and said hand-engaging portions of said handle means, support post, housing assembly and brush tuf-ts being electrically interconnect'ed to provide a low resistance path of flow for static charges from the handle bar means to the brush tufts.

4. A floor machine comprising a metal housing assembly having on the bottom thereof a brush assembly mounted for rotation about a generally vertical axis and including 'a tuft support member and a large number of floor-engaging, static-charge-conducting brush tufts de-. pending from and distributed over the bottom surface of said support member, said housing assembly including a motor housing section, an electric motor supported in said motor housing section and connected in driving relatioiiship to said brush assembly, a hollow upstanding metal support.- post extending upward from said housing assembly, a hollow metal conduit section extending laterally from said post and joining said motor housing section, handle means having hand-engaging portions. at the top of saidpost madeof st-atic-charge-conducting material, a power cord with a ground conductor, power leads con nected to said motor at one end and passingthrough said conduit section and up through said post to-a point near the-top thereof, connector means at the top of said post interconnecting said power leads and power cord, means for electrically connecting the ground conductor of said power cord to one of said static-charge-conduoting po-r-' tions of the machine, the various points of connection between said power cord,,connector means, handlemeans,

support post, conduit and motor housing section being impervious to passage of sparks from within the floor machine and explosive atmosphere into the machine, and said 1 hand-engaging portions of said handle means, support post, conduit, housingassembly and brush tufts being electrically .interconnected to provide a low resistance path of flow for static charges between the handle means and brush tufts. i I

e 5. 'A floor machine comprising a s'tatic-charge-conducting hon-sing assembly having on the bottom thereof a brush assembly mounted for rotation about a generally vertical axis .andincluding 'a tuft support member and a large number of floor-engaging, static-charge-conducting brush tufts'depend-ing from and distributed over the bottom surfacejof'said support member, saidhousing assembly including a ,jm'oto'r'housin'g section, an electric motor supported in; said motor housing section and connected in drijvingrclationship to said brush assembly, a hollow upstanding static-charge-conducting support postfextendi'ng' upwardfrom said housing assembly, handle means at the top. of said post, said handle means including metal core means and a hand-engaging covering thereover made of a soft, staticecharge-conducting material intimately conductively secured to said metal core means, a power cord with a ground conductor, power leads connected to said motor at one end and passing up through said post toa point near the top thereof, and connector means at the top of said post interconnectingsaid. power'leads and a 14 section being impervious to passage of sparks from within the floor machine to the atmosphere and explosive atmosphere from without the machine into the machine, and said hand-engaging portions of said handle means,

support post, housing assembly and brush tufts being electrically interconnected to provide a low resistance path of flow for static charges between the handle means and brush tufts.

6. A floor machine comprising a static-charge-conducting housing assembly having an open-bottom brush housing section, a brush assembly mounted in the brush housing section for rotation about a generally vertical axis and including a tuft support member and a large number of floor-engaging, static-charge-conducting brush tufts depending from and distributed over the bottom surface of said support member, said housing assembly including a motor housing section above; said brush housing section, an electric motor supported in said'motor housing section and connectedin driving relationship to said brush assembly, a hollow upstanding static-chargeconduoting support post extending upward from said housing assembly, a hollow conduit section extending laterally from 'saidpost and joining said motor housing section, handle means at the topfof said post, said handle means including metalcore means and a -hand-engaging covering thereover made of a soft, static-charge-conducting material intimately conductivelyf secured tosaid metal core means, a power cord with a ground conductor, power leads connected to said motor at one end and passing through said conduit section and up through said post to a point near the top thereof, and connector" means at the top of said post interconnecting said power leads and power cord, means for electrically connecting the ground conductorof said power 'cord to one of said static-chargeconducting portions of the machine, and said hand-engaging portions of said handle means, support post, con- 7 brush assembly, a static-charge conducting "bumper 'extending around and projecting outwardly from the bottom of said housing assembly, means electrically connecting said bumper to said housing assembly, pivotally mounted casters supported from said housing assembly, said casters' being pivotable intoan extended position Where they movably support thefloor machinefor movement from place to place and into a retracted position where the machine is supported completely upon the brush assembly, each of said casters having a rotatably mounted caster body made of a non-sparking material conductively connected to said housing assembly, said caster body'ha-ving a debt engaging 'rim made of a soft, "resilient non-sparking material which is a good conductor'of static electricity and is ,conductively joined to said caster body, and a post extending upwardly fromsaidhousing assembly and handle means 'at the top of said post, said handle means and post being conductively connected. together and to said housing assembly, whereby to; prevent the building up of an appreciable static chargeon said fioormachine.

8. A floor machine for usein explosive atmospheres comprising a condu'ctive housing assembly, an electric motor supported in saidhousing assembly, a brush "aspower-"cord," means for electrically connecting the ground 7 sembly at the bottom pf said housing assembly,s'aid brush assembly being mounted for rotation about a generally ver- 1 tica'l axis and haying'static-charge-conductive brush tufts depending therefrom which are electrically connected to said housing'assembly, means in said'housin g mechanically coupling said motor to said brush assembly, ametal' hollow post assembly mechanically and electrically connect-ed to its bottom to said housing assembly and extending upwardly and outwardly therefrom, a switch box at the top of said post assembly electrically connected to said post and having aligned, laterally facing,

external threaded sockets formed in the opposite sides thereof which sockets open onto the interior of the switch box, conductive handle bar means threaded into each of said aligned switch box sockets, and a covering of static-charge-conducting rubber around each of said handle bar means and electrically connected thereto, an onoff switch unit within said switch box and having a shaft extending through an opening in said switch box to the outside thereof, an operating lever secured to the end of said operating shaft, spring means biasing said operating lever to a position which operates said switch to its off position, said operating lever being movable against the restraining force of said spring means to a position which operates the switch to its on position, said operating lever in said latter position extending adjacent to said handle bar means so that the switch may be held in said position by the same hand of the operator which grasps the handle bar means, and power. conductors extending from said switch unit, down said hollow post assembly and into said housing assembly where they make electrical connection with said motor.

9. A floor machine for use in explosive atmospheres comprising a housing assembly, an electric motor supported in said housing assembly, a brush assembly being mounted for rotation about a vertical axis and having brush tufts depending therefrom, meaiis coupling said motor to said brush assembly, a hollow post assembly extending upwardly and outwardly from said housing assembly, a rigid conduit section extending laterally from said hollow post assembly and joined to said housing assembly, said conduit section including an extensible sleeve portion for adjusting the over-all length thereof, a switch box having an internally threaded socket in the vbottom thereof in which the upper end of said hollow post assembly is threaded, a ring of brazing material between said last-mentioned socket and said hollow post assembly to render the switch box and the post assembly immobile relative to one another and to prevent passage of sparks from the machine into the atmosphere and explosive atmosphere into the machine, an on-off switch in said switch box including manual operating means for the switch on the outside of said switch box which extends through an opening in the switch box, a power cord connector attached to the junction box including power terminals for respective connection to the power conductors of a power cord, and insulated conductor wires extending between said power cord connector terminals and said on-otf switch and through said hollow post assembly and conduit section into said housing assembly where they make connection with said motor.

10. A floor machine for use in explosive atmospheres comprising a metal housing assembly, an electric motor supported in saidhousing assembly, a brush assembly at. the bottom of said housing assembly, said brush assembly being mounted for rotation about a generally vertical axis and having static-charge-conducting brush tufts depending therefrom,tmeans in said housing assembly mechanically coupling said motor to said brush assparks from the switch box and explosive atmosphere into the switch box, aligned, laterally facing, external threaded sockets formed in the opposite sides of said switch box which sockets open onto the interior of the switch box, metal handle bar cores threaded into said aligned switch box sockets, respective rings of brazing material sealing off the mouth of said socket between the handle bar cores and the switch box, a covering of staticcharge-conducting rubber around each handle bar core, said covering being secured to the handle barmeans by a static-charge connecting cement, of an-oif switch unit within said switch box, and power conductors extending from said switch unit, down said hollow post assembly and into said housing assembly where they make electrical connection with said motor.

11. A floor machine for use in explosive atmospheres comprising a housing assembly, an electric motor supported in said housing assembly, a brush assembly in the bottom of said housing assembly, said brush assembly being mounted for rotation about a vertical axis and having brush tufts depending therefrom, means coupling said motor to said brush assembly, a hollow post assembly extending upwardly and outwardly from said housing assembly and including a tubular post portion, a junction box secured to the bottom end of said tubular post portion through a connection providing a pass-through opening therebetween and having a portion depending from said junction box and secured to the bottom portion of said housing assembly and an upwardlyfacing pass-through opening, said housing assembly having a downwardly facing pass-through opening near the top thereof, a rigid conduit body extending between said respective upwardly and downwardly facing pass-through openings of said junction box and housing assembly, a switch box carrying handle means secured to the top of said tubular post. portion, an on-off switch in said switch box, a power cord connector connected to said switch box and including terminals for respective connection to the power conductors of a power cord, and insulated conductor wires extending between said power cord connector terminals and switch and then through said hollow post assembly and conduit section into said housing assembly where they make connection .with said motor.

12. A floor machine for use in explosive atmospheres comprising a housing assembly, an electric motor supported in said housing assembly, a brush assembly in the bottom of said housing assembly, said brush assembly being mounted for rotation about a vertical axis and having brush tufts depending therefrom, means coupling said motor to said brush assembly, a hollow post assembly extending upwardly andoutwardly from said hous ing assembly and including a tubular post portion threaded sembly, and including means electrically connecting said brush tuftsto said housing assembly, a hollow post as sembly mechanically and electrically connected at its bottom to said housing assembly and extending upwardly and outwardly therefrom, a metal switch box mechanically and electrically connectedto the top of said post assembly, said switch box: having an external threaded socket in the bottom thereof which opens onto the box interior and into which the upper end of the post assemat the opposite ends thereof, a junction box having a threaded socket opening onto the interior thereof and into which the bottom end of said tubular post portion is threaded, a ring of material sealing off the space between the socket and said hollow post portion to render the same immobile relative to one another and'to' prevent passage of explosive atmosphere into the machinepsaid junction box having a portion depending from said junction box anchored to said housing assembly and anupwardly facing external threaded socket opening into the interior thereof, said housing assembly having a generally downwardly facing external threaded'socket, a rigid conduit section having ends respectively threaded into said upwardly facing junction box socket and said downwardly facing housing assembly socket, said conduit section ineluding an extensible sleeve portion for adjusting the bly is threaded, a ring of brazing material sealing off the mouth of said socketto render the switch box and post assembly relatively immobile and to prevent passage of,

over-all length thereof, a ring of material between one of said last two mentioned sockets and the conduit section fitting thereinto to prevent passage of explosive atmosphere into the machine, a switch ,box carrying handle means secured to the top of said hollow post portion, an on-off switch in said switch box, a power cordconnector attached to said switch box and, including terminalsfor 1? respective connection to the power conductors of a power cord, and insulated conductor wires extending between said power cord connector terminals and switch and then through said hollow post assembly and conduit section into said housing assembly where they make connection with said motor.

13. A floor machine for use in explosive atmospheres comprising a housing assembly, an electric motor supported in said housing assembly, a brush assembly in the bottom of said housing assembly, said brush assembly being mounted about a vertical axis and having brush tufts depending therefrom, means coupling said motor to said brush assembly, a hollow post assembly extending upwardly and outwardly from said housing assembly, a rigid conduit section extending laterally from said hollow post assembly and joined to said housing assembly, a switch box having a pass-through Opening in the bottom thereof, means fixing the switch box to the top of said post assembly,with said last-mentioned pass-through opening in communication with the interior of the post assembly, an on-off switch in said switch box including manual operating means for the switch on the outside of said switch box which extends through an opening in the switch box, a power cord connector attached to the junction box and including power terminals for respective connection to the power conductors of a power cord, and insulated conductors extending between said power cord connector terminals and said on-off switch and then through said hollow post assembly and conduit section into said housing assembly where they make connection with said motor, and said switch box, hollow post assembly, rigid conduit section, and housing assembly being connected by sealed joints preventing ingress of explosive atmosphere. v

14. A floor machine for use in explosive atmospheres comprising a metal housing assembly, an electric motor supported in said housing assembly, said housing assembly carrying a projecting bumper guard at the bottom thereof and retractable casters for moving the machine readily about, the external surfaces of said bumper guard and casters being made of static-charge-conducting material, a brush assembly in the bottom of said housing assembly,

said brush assembly being mounted for rotation about a vertical axis and including a tuft support member and a large number of floor-engaging static-charge-conducting brush tufts depending from and distributed over the bottom surface of said support member, means coupling said motor to said brush assembly, a hollow metal post assembly extending. upwardly and outwardly from said housing assembly, a rigid metal conduit section extending laterally from said post assembly and connected to said housing assembly, a metal switch box secured to the top of said post assembly, handle means carried by said switch box and including static-charge-conducting portions to be gripped by the operator which portions are grounded to said metal switch box, an on-off switch in said switch box which has an operating handle spring biased to a switch-opening position and positioned to be grasped and held in a switch closing position by the same hand which grasps said handle means, a power cord connector attached to said switch box and including terminals for respective connection to the power conductors of a power cord, insulated conductor wires extending between said power cord connector terminals and switch and then through said hollow post assembly and conduit section into said housing assembly where they make connection with said motor, the various points of physical connection between said power cord connector, handle means, switch box, post assembly, conduit section and housing assembly being impervious to passage of explosive atmosphere into said machine, and said switch box, post assembly, housing assembly, external surfaces of said casters and bumper, and said brush tufts being electrically interconnected to provide a low resistance path for fiow of static charges therebetween.

References Cited in the file of this patent UNITED STATES PATENTS