Cranes with hoists and suction lifters have literally taken a large part of the workload away from stonemasons. But not every crane is ideal for every company. Here you can find out what is important. The range of crane solutions for stone processing companies is enormous: it extends from lightweight cranes with a maximum load of 250 kilograms for […]
Cranes with hoists and suction lifters have literally taken a large part of the workload away from stonemasons. But not every crane is ideal for every company. Here you can find out what is important.
The range of crane solutions for stone processing companies is enormous: it extends from lightweight cranes with a maximum load of 250 kilograms for light slabs and workpieces to permanently installed or rail-mounted double-girder gantry cranes, which can have a load capacity of 500 tons and more. While the latter are mainly used outdoors for handling raw blocks weighing over 25 tons, overhead cranes are usually found in the machine halls of the somewhat larger stonemasonry companies for further transport of the stones processed into slabs (tranches and raw slabs) using saw frames or circular block saws. The cranes available in single girder or – in the upper transport area – double girder design usually run on elevated crane runways on the hall walls. One of these most common crane types is used, for example, at Heuger Fliesen & Naturstein GmbH in Glandorf. With a load capacity of two tons and a span the width of the hall, the Scheffer overhead travelling crane is ideal for lifting and lowering the large machines at the Münsterland-based natural stone and tile specialist with its own factory.
In addition, overhead traveling cranes offer solutions for special hall conditions where the crane runway cannot be attached to supports but only to the hall ceiling. And wall-mounted overhead travelling cranes (bracket-mounted overhead travelling cranes) are used on their own crane runway below other overhead travelling crane types on the second hall level – a suitable solution for serving several workstations at the same time.
An interesting special feature of overhead traveling cranes is the semi-gantry crane, in which the upper trolley girder travels on a conventional crane runway; no floor-side guide rails are required on the lower trolley girder, so that no interfering edges are created. As this type of crane only causes minor loads on the hall construction, it is suitable for retrofitting in older halls. From an economic point of view, the semi-gantry crane is characterized by comparatively low investment costs and, last but not least, simple and quick installation.
Stationary overhead monorail systems – available as single or double rail systems as well as single or double girder cranes – are specialized in on-site lifting and linear transport from point to point, unlike overhead travelling cranes that can be moved in two directions.
Pillar and wall-mounted slewing jib cranes for smaller companies
Smaller companies, usually with lower halls, usually have pillar and/or wall-mounted slewing jib cranes. They work at the touch of a button and can easily and carefully handle loads of up to several tons, but in most cases are limited to 500 kilograms or one ton. It is irrelevant whether they stand on their own column or are mounted on walls or pillars. The former simply increases the working radius from 180 to up to 270 degrees or even 360 degrees. Whether machines need to be loaded, heavy tools changed or workpieces lifted onto work tables – slewing jib cranes make lifting easier, more economical and safer.
Finally, light gantry cranes are an economical solution wherever lifting capacity is not required permanently and frequently at different locations.
The various cranes are usually equipped with an electric chain or rope hoist or with a spur gear pulley block and a crane hook as load-bearing equipment. This is where the various load handling and lifting equipment is attached, such as lifting beams, chain slings, lifting straps, vacuum lifters and plate tongs.
Plate clamps for non-positive lifting
Plate clamps, which are clamps that close under load and apply their holding forces through pressure and friction, are used both in conjunction with forklift trucks and in crane operation. They are connected to the forklift truck via a forklift gantry so that the freely suspended panel can be rotated in front of the mast.
The simultaneous transportation of several panels with the panel tongs is not permitted – for the following reasons: Even if there are sufficient friction factors between the panel and the clamping surface on the outer panels, the middle panel(s) is/are only held by friction between the panels themselves. The holding force can be significantly lower here. The lateral compressive force of the clamp halves also increases with increasing load weight. If there are slight unevennesses between the panels, e.g. due to foreign objects or saw cuts, a panel can break and fall off due to the high pressure. When transporting several panels with the panel clamp, there is therefore less safety margin than when attaching a single panel.
Variable vacuum lifters
Vacuum lifters are becoming increasingly popular for transporting oversized sheets and for intermediate transportation within the machining process. As the vacuum lifter, like the panel clamp, does not enable a positive connection between the load and the lifting gear – the load is held exclusively by suction forces – the load must never be passed over people.
In addition, the different load capacity specifications for the load perpendicular to the suction surface (tear-off force) and parallel to it (sliding force) must be observed.
In contrast to a panel clamp, a vacuum lifter with several suction pads can very probably hold both panel parts if a hairline crack is not detected in the panel. And the panel is not loaded at specific points, but over a large area, so that the material is unlikely to tear. Another advantage is that a panel can be placed directly flat on the saw table without effort; a tilting table is not required.
As the slab can tip over when lifting an inclined stone slab with the vacuum lifter, the lifter should always be positioned above the slab’s center of gravity so that the lower edge of the slab does not deflect backwards.
The golden rules of transportation
-Never use lashing equipment as lifting gear.
Slings must meet other requirements and are specially manufactured.
-Slinging with an inverted angle of inclination is prohibited.
The slings can slip out from under the load.
-There are precise regulations for extending slings.
Lifting slings and round slings must not be knotted or extended by tying them together, but only connected using suitable shackles. Special connecting elements must also be used for all other slings!
-Always use only similar slings and pay attention to the material! Chains, as well as polyester and polyamide lifting slings, stretch differently under load so that the load can slip out.
-Always maintain the “natural” lacing angle of 120 degrees when lacing.
-Never attempt to tighten the sling during lacing.
The resulting frictional heat can damage the sling.
-Always observe the special instructions for use for each sling.
-Ensure that the lifting gear cannot be damaged during lifting. Pay particular attention to adequate edge protection.
-Never let lifting slings or round slings run loosely over the crane hook.
The load could tip over.
You can find a more detailed report on transport options and occupational safety in STEIN 1/2018.
