NO821893L

NO821893L - SUPPORT FOR EDUCATION SCRAPS.

Info

Publication number: NO821893L
Application number: NO821893A
Authority: NO
Inventors: George Bernard Arthur Young
Original assignee: Acrow Eng Ltd
Priority date: 1981-06-08
Filing date: 1982-06-07
Publication date: 1982-12-09
Also published as: CA1172057A

Description

Foreliggende oppfinnelse angår én bærestøtte eller såkalt fallstøtte for oppstøtting av forskalingselementer til bruk ved konstruksjon av betonggulv og/eller tak. •En bærestøtte eller fallstøtte av den typen som normalt anvendes ved toppen av et forskalingselement brukes til å opp-støtte forskalingselementet i to hovedstillinger, nemlig en øvre stilling hvor betongen (eller annet herdbart materiale) støpes på forskalingselementene, samt en nedre - stilling hvor førskalingselemtene senkes ned for å frigjøres fra delvis herdet betong, hvoretter de fjernes fra fallstøtten for å kunne brukes andre steder. Den delvis herdete betongplaten oppstøttes deretter av med innbyrdes avstand anordnede hodeplater på fall-støttene . The present invention relates to one bearing support or so-called drop support for supporting formwork elements for use in the construction of concrete floors and/or roofs. •A bearing support or fall support of the type normally used at the top of a formwork element is used to support the formwork element in two main positions, namely an upper position where the concrete (or other hardenable material) is cast on the formwork elements, as well as a lower position where the pre-formwork elements lowered to release from partially hardened concrete, after which they are removed from the fall support to be used elsewhere. The partially hardened concrete slab is then supported by spaced head plates on the fall supports.

En fallstøtte ifølge foreliggende oppfinnelse omfatter en stolpe eller stang med et fiksert hode i den ene enden, idet den andre enden er tilpasset for forbindelse med en forskålingsbære-stolpe av i og for seg .kjent type, idet et fallhode er glidbart montert på stolpen, bevegelig mellom en bærestilling i tilstøtnihg med hodet, og en løs-stilling hvor støtten befinner seg i avstand fra hodet, og oppfinnelsen karakteriseres ved åt stolpen er anordnet med en sliss som strekker seg i lengderetningen mellom - bærestillingen til fallhodet, idet et kileorgah er bevegelig langs lengden av slissen mellom dens bærestilling hvor en kant-eller , et anslag utformet på den ene eller begge sider av kilen komnier A fall support according to the present invention comprises a post or rod with a fixed head at one end, the other end being adapted for connection with a formwork support post of a per se known type, a fall head being slidably mounted on the post, movable between a support position adjacent to the head, and a loose position where the support is located at a distance from the head, and the invention is characterized by the fact that the post is arranged with a slot that extends in the longitudinal direction between - the support position to the drop head, as a wedge organ is movable along the length of the slot between its bearing position where an edge or , a stop formed on one or both sides of the wedge comni

i inngrep med en krave (eller kraver) utformet på den ene (eller begge.) sider av slissen for å oppstøtte fallhodet i bærestillingen, og frigjøringsstillingen, idet kilebévegelsen mellom bærestillingen og f rig j øringsstillingen muliggjøres ved ' u ttirekking av anslaget eller anslagene fra kraven eller kravene, idet organer er anordnet for å holde kileorganet fastlåst i slissen og for korrekt innstilling av fallhodet .i bærestillingen i forhold til' det faste hodet. in engagement with a collar (or collars) designed on one (or both) sides of the slot to support the drop head in the carrying position, and the release position, the wedge movement between the carrying position and the release position being made possible by extending the abutment or abutments from the collar or the requirements, as means are arranged to keep the wedge member locked in the slot and for correct setting of the drop head in the carrying position in relation to the fixed head.

Ved en anvendelse av oppfinnelsen omfatter et forskalings-syst.em for oppstøtting av betong (eller annet herdbart materiale ) under størkning på en støpeflate et antall bjelker som i bruk spenner horisontalt mellom og bæres av fallstøtteenheter, idet et antall formplater bæres av bjelkene og fallstøttene, idet hver fallsføtteenhet omfatter en stolpe med et fastgjort hode i en ende, idet den andre enden er tilpasset for forbindelse med en bærestøtte eller stolpe av vanlig utførelse, idet.en fallstøtte som oppstøtter' bjelkene og/eller formpanelene er glidbart montert på stolpen og bevegelig mellom en bærestilling i.tilstøt-ning med det faste hodet og.en fristilling hvor den er atskilt fra det fastehodet, og anordningen karakteriseres ved at stolpen er .anordnet med en sliss langs sin lengdeutstrekning mellom den fikserte bærestillingen til fallstøtten, idet et kile-'organ er bevegelig langs slissen mellom bærestillingen, .hvori et anslag utformet på en eller begge, sider av kilen står i inngrep' med en krave'eller kraver utformet på den ene.eller begge sider av slissen for å oppstøtte fallhodet i bærestillingen og i fristillingen, idet kilens bevegelse mellom bærestillingen og fristillingen muliggjøres ved borttrekking av anslaget fra kraven (anslagene fra kravene), og ved at kileorganet har organer for å holde organet låst i slissen, idet slissen er anordnet med en stopper eller én sperre for korrekt innstilling av fallhodet i bærestillingen i forhold til det faste hodet, slik at bjelkene og/eller fallhodene -støtter:: formpanelene slik at disse danner en jevn, ifluktliggende støpeflate. In one application of the invention, a formwork system for supporting concrete (or other hardenable material) during solidification on a casting surface comprises a number of beams which in use span horizontally between and are supported by fall support units, a number of form plates being supported by the beams and fall supports , each fall foot unit comprising a post with a fixed head at one end, the other end being adapted for connection with a supporting support or post of ordinary design, a fall support which supports the beams and/or form panels being slidably mounted on the post and movable between a support position adjacent to the fixed head and a free position where it is separated from the fixed head, and the device is characterized by the post being arranged with a slot along its length between the fixed support position to the fall support, a wedge -'organ is movable along the slot between the bearing position, in which a stop formed on one or both sides of the wedge stands in engagement' with a collar' or collars designed on one or both sides of the slot to support the drop head in the carrying position and in the free position, the movement of the wedge between the carrying position and the free position being made possible by withdrawing the abutment from the collar (the abutments from the requirements), and by that the wedge member has means to keep the member locked in the slot, the slot being arranged with a stop or one lock for correct setting of the drop head in the bearing position in relation to the fixed head, so that the beams and/or drop heads -support:: the form panels so that these form a smooth, flush casting surface.

Kileflaten på kileorganet samvirker fortrinnsvis med en tilhørende, flate på fallhodet... The wedge surface on the wedge member preferably cooperates with an associated surface on the drop head...

Avstanden mellom bæreflaten på fallhodet når det er i sin bærestilling og det faste hodet ;er fortrinnsvis lik avstanden mellom toppen av bjelken som skal bæres av fallhodet og dets bære-anordning. The distance between the support surface of the drop head when it is in its carrying position and the fixed head is preferably equal to the distance between the top of the beam to be supported by the drop head and its support device.

Stolpen har fortrinnsvis rektangulært tverrsnitt,og fallhodet har fortrinnsvis en.plate som er rettet'nedover i rett vinkel med stolpen og som er utformet med. en nedre kileflate bestemt for kontakt med kileflåtene på kileorganet. The post preferably has a rectangular cross-section, and the drop head preferably has a plate which is directed downwards at right angles to the post and which is designed with a lower wedge surface intended for contact with the wedge rafts on the wedge member.

Når fallstøtten med fallhodet holdes av kileorganet i bærestillingen og skal beveges til sin fristilling, avsmaies kilen i retningen for å senke fallhodet litt før anslagene på kileorganet beveges klar av kravene, slik at der finner sted eh inn-ledningsvis gradvis avskaling av formpanelene før .bjelkene og panelene faller raskt ned til. f rigjøringsstillihgen. Dette bidrar til å redusere liggebelastningen på den delvis herdete betongplaten og avlaster kileorganet fra belastningen av den ut-støpte betongen. When the drop support with the drop head is held by the wedge member in the bearing position and is to be moved to its free position, the wedge is tapered in the direction to lower the drop head slightly before the stops on the wedge member are moved clear of the requirements, so that there is initially gradual stripping of the form panels before the beams and the panels quickly fall down to f the exemption permit. This helps to reduce the bearing load on the partially hardened concrete slab and relieves the wedge member from the load of the poured concrete.

■Fallhodet er fortrinnsvis anordnet med et organ som også griper inn- i slissen i stolpen. ■The drop head is preferably arranged with a device which also engages in the slot in the post.

Organene for å holde kileorganet " fast i bærestillingen omfatter fortrinnsvis en'første stopper montert 1 den ene enden av kileorganet og en andre stopper montert i den andre enden av kileorganet, slik at orga'net holdes fastlåst i slissen, når fallhodet er i sin bærestilling eller i' f rig jøringsstillingen,. og også når fallhodestøtten er i bruk eller på lager, eller, transporteres fra et byggested til et neste. Organene'på eller i slissen sørger for korrekt innstilling av fallhodet i bærestillingen, slik at bjelkene eller fallhodene som oppstøtter formpanelene tilveiebringer en jevn, fortløpende støpeflate. The means for keeping the wedge member fixed in the carrying position preferably comprise a first stopper mounted at one end of the wedge member and a second stop mounted at the other end of the wedge member, so that the member is kept locked in the slot when the drop head is in its carrying position or in the release position, and also when the fall head support is in use or in storage, or transported from one construction site to another. The bodies on or in the slot ensure the correct setting of the fall head in the carrying position, so that the beams or fall heads that supporting the mold panels provides a smooth, continuous casting surface.

■Oppfinnelsen skal nå beskrives, med henvisning til vedlagte tegninger som viser en ufførelsesform'for oppfinnelsen og hvor: ■The invention will now be described, with reference to the attached drawings which show an embodiment of the invention and where:

Fig. 1 viser et perspektivriss av en utføirelsesform for en fallstøtte ifølge oppfinnelsen, idet denne er anordnet i bærestillingen , Fig. 2 er et . tilsvarende sideriss av fallstøtten., og Fig. 3 er et sideriss av fallstøtten.i den nedre fri-g jøringsstillingen. Fig. 1 shows a perspective view of an embodiment of a fall support according to the invention, as this is arranged in the carrying position, Fig. 2 is a . corresponding side view of the fall support, and Fig. 3 is a side view of the fall support in the lower release position.

Fallstøtte._enheten 10 vist på tegningene omfatter en rek-tangulær sentrisk stolpe 12 med et fastgjort øvre hode' 14 og en nedre plate 16 for tilslutning til en, forskalingsstøtte av vanlig .type. Fall support. The unit 10 shown in the drawings comprises a rectangular centric post 12 with an attached upper head 14 and a lower plate 16 for connection to a formwork support of the usual type.

Et fallhode 18 er montert på stolpen med glidebevegelse mellom en øvre bærestilling hvori den er plassert i''tilstøtning med det faste hode 14 (se fig.- 1 og 2), og' en nedre frigjøringsstilling som vist på fig. 3 • A drop head 18 is mounted on the post with a sliding movement between an upper support position in which it is placed in abutment with the fixed head 14 (see fig. 1 and 2), and a lower release position as shown in fig. 3 •

Stolpen er anordnet med en sliss 20 søm strekker seg langs stolpens lengde mellom det faste hodet og en stilling ved siden av den nedre platen 16.. Et kileorgan generelt angitt méd: tal-let 22 holdes låst i slissen,samtidig som det kan bevege seg fritt'opp og ned i slissen mellom en bærestilling som vist på figurene 1 og 2, og en frigjøringsstilling som vist på fig. 3. The post is provided with a slot 20 seam extending along the length of the post between the fixed head and a position next to the lower plate 16. A wedge member generally indicated by: the number 22 is kept locked in the slot, while being able to move freely up and down in the slot between a carrying position as shown in figures 1 and 2, and a release position as shown in fig. 3.

I bærestillingen griper en kant eller et anslag 24. som er anordnet på hver side av kileorganet, mot en krave 26 skåret ut. på hver side av. slissen slik som vist på fig. 1. Når i denne stillingen, er kileorganet hindret fra å gli nedover, i spissen, og kileorganets øvre kileflate 28 ligger an mot en tilsvarende og tilhørende skrå flate 30 utformet langs den nedre kanten av en plate 32 som strekker seg gjennom slissen på tvers av stolpen og utgjør en del av fallhodet 18. Det vil således forstås at fallhodet holdes fiksert på denne måten, i sin øvre bærestilling. In the carrying position, an edge or abutment 24. which is arranged on each side of the wedge member, grips against a collar 26 cut out. on either side of. the slot as shown in fig. 1. When in this position, the wedge member is prevented from sliding downwards, at the tip, and the upper wedge surface 28 of the wedge member abuts a corresponding and associated inclined surface 30 formed along the lower edge of a plate 32 which extends through the slot across the post and forms part of the drop head 18. It will thus be understood that the drop head is kept fixed in this way, in its upper support position.

Når fallhodet er i den .øvre bærestillingen v.il bjelker, såsom vist . ved 33 ftilkobles, på oppover rettede tapper 34 på fallhodet for å bæres av dette, slik at bjelkene spenner mellom tilstøtende enheter med toppoverflåtene 35' av bjelkene liggende i flukt med toppflaten på de faste hodene 14 på.fall-st.øtteenhetene. Forskalingspanelet 36 bæres enten av over-sidene 56 på bjelkene 37, av kanter 52 på bjelkene 33 eller av fallstøttene 18. Ulike alternative.løsninger for bjelkene 33, 37 og panelene 36 beskrives i britisk patentsøknad nr. 8117524. When the drop head is in the upper support position with beams, as shown. at 33 are connected, on upwardly directed pins 34 on the fall head to be supported by it, so that the beams span between adjacent units with the top surfaces 35' of the beams lying flush with the top surface of the fixed heads 14 of the fall support units. The formwork panel 36 is supported either by the upper sides 56 of the beams 37, by the edges 52 of the beams 33 or by the fall supports 18. Various alternative solutions for the beams 33, 37 and the panels 36 are described in British patent application no. 8117524.

En utsparing 54 er anordnet i toppflaten av kilen for an-ordning av en tapp, tunge eller lignende for å låse kilen i bærestillingen under støpingen. A recess 54 is arranged in the top surface of the wedge for the arrangement of a pin, tongue or the like to lock the wedge in the bearing position during casting.

En betongplate 38. (se figurene 2 og 3) støpes • deretter langsover panelene, toppflatene som er i flukt med toppflatene av bjelkene 33 og- de faste hodene, slik at det fremstilles en enhetlig plate. A concrete slab 38. (see figures 2 and 3) is • then cast along the panels, the top surfaces of which are flush with the top surfaces of the beams 33 and the fixed heads, so that a uniform slab is produced.

Når betongplaten er delvis herdet, senkes fallhodene med den virkning .at bjelkene 33 , 37. og panelene 36 senkes, slik at. der etterlates en delvis herdet betongplate (som vist på When the concrete slab has partially hardened, the drop heads are lowered with the effect that the beams 33, 37. and the panels 36 are lowered, so that. where a partially hardened concrete slab is left behind (as shown in

fig. 3) som bæres av.de faste hodene 14 på fallstøtteenhetene. Bjelkene, og panelene kan deretter brukes om igjen, på annet sted:' fig. 3) which is carried by the fixed heads 14 of the fall support units. The beams and panels can then be used again, elsewhere:'

For at fallhodene kan senkes langs stolpene, beveges kile-elementene 22 til høyre (som vist på tegningene) .- Under denne bevegelsen vil fallhodene.beveges gradvis nedover på- grunn av avskråningen av de samvirkende overflatene 28 og 30 på kile^' elementene 22 og platen 32. Dette innebærer.at'den innledende frigjøringen av forskalingsp.anelene og bjelkene fra betongen skjer' gradvis', noe' som bidrar til å unngå- at det oppstår sjckk-belastninger, og kileorganene avlastes for belastningen fra betongen . In order for the drop heads to be lowered along the posts, the wedge elements 22 are moved to the right (as shown in the drawings). and the plate 32. This means that the initial release of the formwork panels and beams from the concrete happens gradually, which helps to avoid the occurrence of shock loads, and the wedge members are relieved of the load from the concrete.

Når kileeiementet er blitt beveget til .stillingen vist på fig. 3 i hvilken anslagene 24, som bare strekker seg delvis på begge sider langs, kilens lengdeutstrekning, kommer klar av kravene 26 i slissen, vil kileelementet være fritt til å falle-ned langs slissen hvorved samtidig muliggjøres at fallhodene og bjelkene og panelene som bæres av disse, også faller ned langs slissen til f rig jøringsstillingen vist p.å fig. 3. When the wedge element has been moved to the position shown in fig. 3 in which the abutments 24, which only partially extend on both sides along the longitudinal extent of the wedge, come clear of the requirements 26 in the slot, the wedge element will be free to fall down along the slot thereby enabling at the same time that the drop heads and the beams and panels carried by these, also fall down along the slot to the release position shown in fig. 3.

Kilen 22 er videre anordnet med organer for å holde kilen fastlåst' i slissen 20. Disse organer omfatter en første stopper 40 ved den smalere enden av kilen 22 og en annen stopper 50 ved den større enden. Disse to stoppere 40 og 50 hih-. drer enhver mulighet for kilen til å komme løs og eventuelt .mistes når f.eks. fallhodet 18 er i sin bærestilling eller sin f rig j øringsstilling, eller når -f allstøtteenheten .10 er i bruk, lagres, eller transporteres fra et brukssted til et annet. The wedge 22 is further provided with means to keep the wedge locked in the slot 20. These means comprise a first stop 40 at the narrower end of the wedge 22 and a second stop 50 at the larger end. These two stoppers 40 and 50 hih-. removes any opportunity for the wedge to come loose and possibly be lost when e.g. the drop head 18 is in its carrying position or its release position, or when the support unit .10 is in use, stored, or transported from one place of use to another.

En,stopper.51 er plassert på stolpen 12 i slissen 20, slik at når fallhodet er.i bærestillingen vil stopperen 51 gripe inn. på oversiden av hodet 18 (se fig. 2), slik at overflaten 35 på bjelken 33 og toppflaten av panelet 36 automatisk kommer i flukt med oversiden av hodet 14. Følgelig fås.en ubrutt jevn støpeflate på enkel måte ved å banke kilen 22 langs anslagene A stopper 51 is placed on the post 12 in the slot 20, so that when the drop head is in the carrying position, the stopper 51 will engage. on the upper side of the head 18 (see fig. 2), so that the surface 35 of the beam 33 and the top surface of the panel 36 automatically come flush with the upper side of the head 14. Consequently, an unbroken smooth casting surface is obtained in a simple way by tapping the wedge 22 along the estimates

.24 inntil stopperen 51 berører hodet 18. .24 until the stopper 51 touches the head 18.

Platen 30 anordnet på fallhodet er, forsynt med to utstik-kende tapper 42 på hver side som ligger an mot sidene av stolpen'for å øke konstruksjonens stivhet og for å hindre at fallhodet vrir seg i forhold til stolpen. Fallhodet er .videre anordnet med to nedoverrettede flenser 43 festet langs to av" kantene på platen 30 for .å øke stivheten av platen 30. The plate 30 arranged on the drop head is provided with two protruding studs 42 on each side which rest against the sides of the post in order to increase the rigidity of the structure and to prevent the drop head from twisting in relation to the post. The drop head is also provided with two downward-facing flanges 43 attached along two of the edges of the plate 30 to increase the rigidity of the plate 30.

Ifølge vanlig praksis kan f allstøtteenheten 1.0 enten bæres According to common practice, the support unit 1.0 can either be worn

■ på topp-platen av en vanlig bærestolpe som f.eks. kan boltes .fast til platen 16 på fallstøtten, eller alternativt kan én gjenget boltstamme 44 som strekker seg nedover fra platen 16 forsynes med et mutterorgan,tildannet'med et ringformet nav 46 som passer over toppen av en standard forskalingsbærestolpe 48. Dette- muliggjør at topp-platen 14 på fallstøtten kaii reguleres i forhold til bærestolpen, slik at delene kommer i flukt, og videre for å sikre at toppflatene- av topp-platene 14 og bjelkene 33 og panelene 36 kommer på riktig høydenivå. ■ on the top plate of a normal supporting post such as can be bolted to the plate 16 on the fall support, or alternatively one threaded bolt stem 44 extending downwards from the plate 16 can be provided with a nut member formed with an annular hub 46 which fits over the top of a standard formwork support post 48. This enables the top plate 14 on the fall support kaii is regulated in relation to the support post, so that the parts come into alignment, and further to ensure that the top surfaces of the top plates 14 and the beams 33 and the panels 36 are at the correct height level.

Claims

1... Fall support unit comprising a post with a fixed head at one end, the other end being adapted to be connected to a formwork support post or the like, a fall head being slidable. mounted on the post and movable between a', bearing position adjacent to the attached head, and. a release position where the drop head is located at a distance from the attached head (14), characterized in that the post is arranged with a slot (20) which extends in the longitudinal direction of the post between the carrying position and the release position of the drop head (18), and by that a wedge (22) is movable along the slot between its bearing position, wherein a stop (24) formed on one or both sides of the wedge engages a shoulder (or shoulders) (26) formed thereon. one or both sides of the slot (20) to carry the drop head in the carrying position, and the releasing position, wedge movement between the carrying position and the releasing position being made possible by pulling the stops away from the shoulders, and by the means being arranged to keep the wedge locked or close the slot and for correct setting of the drop head in the carrying position in relation to the attached head.

2. Fall support unit as specified in claim 1, characterized by the distance between the bearing surface of the fall head (18) in the bearing position and the attached head (14) being equal to the depth of the beam (33) which is supported by the fall head. -3. 'Fall support unit as stated in claim .1 or 2, - characterized by. the drop head (18) has a plate (.

3 2) which is directed downwards at a right angle, in relation to the post (12) and it is designed with a lower wedge surface (30) intended for. to grip the counter-wedge blade (2.8) on the wedge (22). •

4. Fall support unit as-specified in any of the pre- . ongoing claim, characterized in that the wedge (22) is bevelled so that when the wedge moves from the carrying position to the release position, the drop head will be lowered a little before the stops are pulled away from the shoulders (26).

5. Fall support unit as specified in any of the preceding claims, characterized by means for keeping the wedge trapped or locked, as well as for correct setting of the fall head in the carrying position and comprising two stops. on the wedge, in that a first stop (40) grips against the post when the drop head is in the release position, and another stop (50) grips against the post when the drop head is in the carrying position.

6. Formwork system for supporting concrete or other curable material during curing on a casting surface, characterized by a number of beams (33) which in use span horizontally between and are supported by fall support units (10), a number of formwork panels (36 ) which is carried by the beams (33) and/or the fall support units, each fall support unit comprising a post (12)' with a fixed head (14) at one end, the other end being adapted for connection with a formwork support or the like, a fall head (18) carrying the beams. and/or for the scaling panels are slidably mounted on the post and movable between, a bearing position adjacent to it. fixed the head and a release position where it is located at a distance from the attached head, characterized in that the post (12) is arranged with a slot (20) which extends in the longitudinal direction between the support position and the release position of the drop head and in that a wedge (22) is movable .along the length of the slot between the bearing position in which a stop (24) formed on one or both sides of the wedge engages-against a shoulder (26) (or shoulders) formed at one (or both.) sides of the slot-for supporting the drop head in the carrying position and in the release position, as wedge movement between the carrying position ■ the reset and release position is made possible by pulling the stops away from the shoulders, as the wedge has means (40,50) to keep the wedge -caught or locked in the slot, as well as means for correct adjustment of the drop head in the carrying position in relation to to the attached head, so that beams and/or drop heads can support the formwork panel head, so that a smooth, flush casting surface is provided..

7. Formwork system. as stated in claim 6, characterized by means that cooperate with the posts (12) for the fall support units■for correct setting of the beams (33) and the fall heads (18) that carry the formwork panels so that a smooth, flush casting surface is provided,

8. Formwork system as specified either in claim 6 or 7, characterized in that the distance between the bearing surface to. the drop head in the bearing position and the attached head is equal to the distance between the top of a beam that is supported by the drop heads, and the head's support organs..

9. Formwork system as set forth in any one of claims 6 to 8, characterized in that the drop heads have a plate (32) directed downwards from the plate at right angles to the post and which is designed with a lower wedge surface (3G) intended for contact with the wedge surface (28). on the wedge.

10. Formwork system as specified in any one of claims 6 to 9, characterized in that the wedge (22) is beveled as such. that with wedge movement from the carrying position to the release position, the drop head will be lowered somewhat before the stops (24) are pulled away from the shoulders (26).

11.. - Formwork system as specified in any of the preceding claims 6 to 10, characterized by. that the means for keeping the wedge locked or trapped comprise two stoppers (40,50) mounted on the wedge.

12. Formwork system as stated in any one of the preceding claims, characterized in that the means for setting the drop heads in the support position comprise a stop (51) on the post (12) and which grips the top of the drop head when it is in the support position.