GB2075579A

GB2075579A - Road man-hole cover

Info

Publication number: GB2075579A
Application number: GB8110416A
Authority: GB
Original assignee: Pont a Mousson SA
Current assignee: Pont a Mousson SA
Priority date: 1980-04-04
Filing date: 1981-04-02
Publication date: 1981-11-18
Also published as: IT1143487B; ES264930Y; GB2075579B; DE3112641C2; IT8167469A0; ES264930U; DE3112641A1

Abstract

A man-hole frame 1 and cover 2 are rough-cast from cast iron without using cores. On its outer periphery the cover 2 has three equi-angularly spaced ribs 5 of substantially helical disposition which fit into recesses between corresponding pairs of projections 20, 21 on the interior of the frame when the cover drops and turns under gravity into the frame to locate face 13 of each rib 5 under face 24 of the corresponding projection 20. The cover is thus locked to the frame and at the same time the cover is prevented from rocking by faces 14 on the ribs 5 resting on faces 23 on projections 21. The cover can be unscrewed by blows to vertical faces 9 of recesses 8 in the cover top. <IMAGE>

Description

SPECIFICATION Man-hole for a road The present invention relates to a man-hole for a road of the type comprising a frame intended to be bedded in the road surface and a removable lid or cover cooperating with this frame.

Man-holes for roads whereof the frame is incorporated in the road surface have a cover which is subject to stress applied by vehicles, which may be an acceleration, braking or more simply the suction effect of the tyre on the cover when the vehicle travels at a constant speed. For obvious reasons of safety, it is thus indispensable that the cover is not able to rise inside its frame, nor even to be extracted from this frame. This is why a locking device is generally provided, which can be actuated solely by persons empowered to do this, which is beyond any accidental mechanical intervention.

The locked cover must also fulfil another requirement, namely that it does not rock in its housing, since any oscillation about an axis of rotation passing through two of the support points of the cover causes a knocking noise between the constituent parts of the manhole, which noise is particularly unpleasant for people residing along the road.

The object of the invention is to provide a man-hole provided with means for locking the cover which are both very effective and easy to produce and use and which eliminate any risk of rocking of the cover.

To this end, the invention relates to a manhole for a road, comprising a frame and a removable cover, the frame and cover respectively comprise on their periphery three helical ribs in the form of screw-threads and three recesses each of which respectively cooperates with at least one part of a corresponding said rib.

These ribs ensure self-locking of the cover if, in cross-section, each rib has a surface area varying over its length in order to ensure a wedging effect with the associated recess.

Automatic compensation of the radial clearances between the cover and the frame is also obtained when each horizontal section of the ribs has a non-radial upper side and/or lower side directed radially outwards at wisely chosen angles.

In order to facilitate casting without a core of the member provided with recesses, each recess preferably comprises a lower ramp and an upper ramp which are offset one with respect to the other in the circumferential direction and belonging to two internal projections of the frame, in the form of points.

If desired each cross-section of the ribs can have two rounded lateral parts and the corresponding sections of the recesses can have, in their parts intended to cooperate with these lateral parts, a concave shape with a radius of curvature greater than that of the latter.

Preferably the said parts of the recesses and of the ribs are in the form of a quadrant of a circle, with a larger radius for the recesses.

Further features and advantages of the invention will become apparent from the ensuing description, given as a non-limiting example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of a man-hole for a road according to the invention; Figure 2 is a detailed view of the cover taken in horizontal section on line 2-2 of Fig.

1; Figure 3 shows a detail of the frame in elevation; Figure 4 is a diagrammatic underneath view of part of the periphery of the cover of a manhole acording to a variation of the invention; Figure 5 is a diagrammatic plan view of part of the periphery of the frame of this manhole; Figure 6 is a diagram which illustrates the contact between a rib and its recess.

The man-hole for a road illustrated in Figs.

1 to 3 is constituted by two members of rough-cast ductile cast-iron, namely a frame 1 intended to be bedded in a road surface and a removable lid or cover 2. Each of these members 1 and 2 has ternary symmetry about a common vertical axis X-X, that is to say that each of their points is repeated after a rotation of 120 about the axis X-X.

The cover 2 is constituted by an upper disc 3 and a skirt 4 provided with three external reliefs 5.

The disc 5 is flat, relatively thin and of approximately circular shape. However, it comprises three projections 6 whereof the radius increases progressively beyond this circular shape. Each projection 6 terminates in an approximately radial side 7 which connects it to the root of the following projection 6.

Ciose to its periphery, the upper side of the disc 3 comprises three recesses 8 arranged around the circumference. Each recess 8 has a triangular shape and a depth increasing from the point of the triangle to a vertical and radial face 9 located approximately midway, in the circumferential direction, between two adjacent sides 7. The upper side of the disc 3 also comprises a non-skid relief (not shown).

The skirt 4 is directed downwards from the lower side of the disc 3. It is cylindrical and externally tangential to the circle beyond which the projections 6 protrude.

Each relief 5 is the general form of a rib approximately constituting a portion of a screw thread. More precisely, it has a roughly helical general orientation and comprises a cross-section (Fig. 2) in the form of an isosceles trapezium whereof the surface area decreases progressively downwards in a substan tially homothetic manner. This section comprises a major base corresponding to the outer wall of the skirt 4, a minor base 10, an upper cblique side 11 and a lower oblique side 1 2.

Thus, the relief 5 comprises a non-radial upper face 1 3 and lower face 14, both directed radially outwards and an approximately cylindrical peripheral face 1 5.

The face 1 3 terminates slightly below the lower face of the disc 3 and is extended upwards by an approximately rectangular small vertical and radial face 16, the upper side of which is constituted by the side 7 of a projection 6. The face 14 extends upwards as far as the lower face of this projection 6 and the face 1 5 coincides at its upper end with the outer face of the latter. The faces 1 3 and 14 are left-handed and helical like those of a screw thread.

The reliefs 5 extend downwards as far as the lower face of the flat skirt. Between the base of the face 1 3 and the beginning of the projection 6 which overhangs it, the skirt has an excess thickness 1 7 with vertical generatrices, which follows the outer contour of this projection. This makes it possible to cast without a core the arrangement of the cover 2, including the reinforcing ribs (not shown) located inside the skirt 4.

Naturally, the surfaces described as vertical in the preceding description are in reality slightly inclined by an angle of clearance facilitating easy removal from the mould.

The frame 1 comprises a lower, flat supporting base plate 1 8 of annular shape, from the inner periphery of which a cylindrical body 1 9 projects upwards. In plan view, this body has the same shape as the disc 3 of the cover, i.e. circular with three projections, its inner radius at each point being slightly greater than the outer radius of a corresponding point of the disc 3.

The body 1 9 has a uniform thickness over its entire periphery, apart from at the root of each projection of the frame, where this body is extended internally at a point 20 with excess thickness in the cavity defined by the next projection. In addition, a block 21 projects into this cavity, which block defines a second point 22 located approximately opposite the point 20 but offset in the circumferential direction and downwards with respect to the latter.

More precisely (Fig. 3), adjacent the point 20, the block 21 has an upper face 23 forming a ramp cooperating with the upper part of a face 14, whereas the lower face 24 of the point 20 forms a ramp cooperating with the lower part of a face 1 3. The two other faces 25, 26 of the two points 20 and 22 belong to the same diametral plane P inclined with respect to the horizontal. The block 21 also comprises a flat and horizontal upper surface 27 located at a distance dfrom the upper edge of the body 1 9 greater than the total thickness of the disc 3 with its antiskid relief.

Finally, a horizontal inner rib 28 is provided half-way up the body 1 9, which rib 28 starts from the end of each block 21 remote from its point 22.

On account of the general structure of the frame 1 and in particular of the points 20 and 22, the frame can be cast without a core like the cover 2, so that the entire man-hole 1-2 is very economical to produce on an industrial scale.

When in use, the frame 1 is bedded in the roadway and is flush with the surface of the latter. In order to position the cover 2, the base of the faces 1 4 is placed on the ramps 23. A slight impulse in the screwing direction is thus sufficient to cause the cover to drop in a helical manner along the axis X-X under its own weight.

During this movement, the faces 14 slide on the ramps 23 and the reliefs 5 penetrate below the points 20, until the faces 1 3 come into contact with the faces 24. There is thus a double contact 14-23 and 13-24, theoretically over the entire surface of the faces 23 and 24. The inclination of the faces 24 causes a descending centri-petal reaction on the faces 1 3 and this results in a self-centering effect of the cover, even if the initial position of the latter is imperfect.

When the cover has completed its descending movement, it is perfectly locked and can neither rise nor rock, on account of the structure of the reliefs 5. The ribs 28 prevent foreign bodies from penetrating the man-hole and also prevent the cover 2 from falling when the latter is placed in an incorrect angular position.

For removing the cover, a pickaxe blow is applied to the face 9 of a recess 8 in the disc 3, which ensures unlocking. The cover is then raised by an unscrewing movement either by acting on an overhanging part of the disc 3, in the vicinity of a relief 5, or by pressing the pickaxe against the face 1 6 of one relief and against the face 25 of the frame located opposite thereto. As a variation, for lifting the cover, two diametrically opposed slots may also be provided in the disc 3, which slots facilitate the engagement of a lifting instrument such as a winch.

The automatic absorption of the radial clearances between the cover and the frame at the time of positioning the cover requires that, in the horizontal section of each rib 5 (Fig. 2), the sides 11 and 1 2 form angles at least equal to 28 and at the most equal to 45 respectively with the radial direction. In fact, these angular values ensure six effective regions of contact 13-24 and 14-23 in at least one horizontal section of the man-hole.

Consequently, when the trapezium (or, as a variation, the triangle) formed by the horizontal section of the ribs is isosceles, its angle at the apex should be comprised between 56* and 90 .

The inclination of the ramps 23 should be greater than the coefficient of friction of cast iron on cast iron, in order to ensure the descent of the cover under its own weight.

Since this coefficient is 0.3, the inclination will be chosen to be at least equal to 18 and preferably greater than this value in order to take into account the possible presence of foreign bodies.

The helical shape of the surfaces 1 3 and 14 (or 23 and 24) ensures coincidence of the surfaces 1 3 and 1 4 of the cover with the respective corresponding bearing surface 24 and 23 of the frame, whatever the penetration of the cover, which varies according to manufacturing tolerances, which is particularly advantageous for rough-cast parts. This contact between identical surfaces produced in a reliable manner, considerably limits the danger of bruising of metal parts which, when it occurs, may hinder the extraction of the cover from its frame.

According to the variation illustrated in Figs. 4 to 6, where the references designating parts described previously also bear the suffix "A", when these members have been modified, the horizontal sectional shape of the ribs 5A of the cover 2A and of the ramps 23A and 24A of the frame 1A have been modified.

In fact, as can be seen from Fig. 4, the lower section 29 of the ribs 5A is in the shape of a convex semicircle centered on the outer face of the skirt 4 of the cover. The two quadrants of a circle 11 A, 1 2A which constitute this semicircle diverge progressively along the rib 5A, without changing radius and whilst remaining centered on the outer face of the skirt 4, up to a maximum separation d in the vicinity of the lower face of the disc 3.

The upper side of the ribs extends as far as the level of the upper face of this disc. In each section located above the lower section 29, the two quadrants of a circle are joined by a rounded portion 30, the shape of which corresponds to that of the part of the projection 6 which overhangs this section. Fig. 4 also shows a radial rib 31 for strengthening the cover.

Similarly, in horizontal section, the ramps 23A and 24A are each in the shape of a concave quadrant of a circle of radius R greater than radius rof the quadrants of a circle of the ribs 5A, the centre being offset towards the interior of the man-hoie. In each ramp, the line of the centres of the quadrants of a circle is parallel to that of the associated part of the corresponding rib 5A.

The cover is positioned automatically in the frame in the same way as previously. In each section, the three contacts 13A-24A or 14A-23A occur at the points of contact 32 of the associated quadrants of a circle (Fig. 6).

The angle a formed by the line perpendicular to two quadrants of a circle in contact at the point 32 and the radial direction D of the cover passing through the centre of the quadrant of a circle 11 A or 1 2A in question is at the maximum equal to 60 and preferably, as shown, equal to 45 . When this angle decreases, the forces exerted on the cover become very considerable and require a corresponding reinforcement.

The cover is thus in contact with the frame along six curved helical lines and experience shows that these lines are relatively well defined and move only slightly, for example on the arc 33-34 of Fig. 6 centered on the point 32, at the time of recentering of the cover which takes place during operation, under the action of moving loads.

As a variation, in horizontal section, the shape of the lateral parts of the ribs 5A could be a curve other than a quadrant of a circle and the radius of curvature of the sections of the ramps 23A and 24A could be increased to infinity, in which case these sections would be segments of a straight line as in the embodiment in Figs. 1 to 3.

Claims

1. A man-hole for a road, comprising a frame and a removable cover, the frame and cover respectively comprise on their periphery three helical ribs in the form of screwthreads and three recesses each of which respectively cooperates with at least one part of a corresponding said rib.

2. A man-hole according to claim 1, in which in cross-section, each rib has a surface area varying over its length in order to ensure a wedging effect with the corresponding recess.

3. A man-hole according to claim 1 or claim 2, in which each horizontal section of the ribs has a non-radial upper side directed radially outwards.

4. A man-hole according to claim 3, in which said upper side forms an angle at least equal to 28 with the radial direction.

5. A man-hole according to any one of claims 1 to 4, in which each horizontal section of the ribs has a non-radial lower side directed radially outwards.

6. A man-hole according to claim 5, in which said lower side forms an angle at the most equal to 45 with the radial direction.

7. A man-hole according to any one of claims 3 to 6, in which each horizontal section of the ribs is in the form of an isosceles trapezium.

8. A man-hole according to any one of claims 1 to 7, in which each recess comprises a lower ramp and an upper ramp offset one with respect to the other in the circumferential direction and belonging to two, pointed internal projections of the frame.

9. A man-hole according to claim 8, in which an oblique diametral plane defines the lirnits of the two ramps of each recess.

10. A man-hole according to any one of claims 1 to 9, in which the ribs belong to the cover and the upper side of each rib terminates at its upper end in a vertical and radial ace.

11. A man-hole according to one of claims 1 to 10, in which the upper face of the cover is provided with at least one recess of circumferential orientation, which comprises a vertical and radial wall intended for unlocking the cover.

12. A man-hoe according to claim 1 or claim 2, in which each cross-section of the ribs comprises two rounded lateral parts, and th' corresponding sections of the recesses have, in their parts intended to cooperate with said rounded lateral parts, a concave shape with a radius of curvature greater than that of the first mentioned rounded lateral parts.

13. A man-hole according to claim 12, in which the rounded lateral parts of the sections of the ribs are in the form of a quadrant of a circle.

14. A man-hole according to claim 13, in which the said parts of the sections of the recesses are in the form of a quadrant of a circle.

15. A man-hole according to any one of claims 1 2 to 14, in which the surface area of the cross-sections of the ribs increases in an upwards direction.

1 6. A man-hole according to claim 15, in which the rounded lateral parts of the sections of the ribs all have the same profile.

1 7. A man-hole according to any one of claims 1 2 to 16, in which in each section, an angle a formed by a line perpendicular to each rib at its point of contact with the corresponding recess and the radial direction of the cover does not exceed 60 .

1 8. A man-hole according to claim 17, in which said angle CL is of the order of 45 .

19. A man-hole substantially as hereinbefore described with reference to Figs. 1 to 3 or Figs. 4 to 6 of the accompanying drawings.