Careers
When it comes to storage, special and large products can cause serious difficulties, so it is best to be aware of their characteristics when planning a warehouse, and choosing, for example, cantilever racks.
When assessing the storage options for these goods, which can be classified as atypical, it is necessary to group them into three categories: sheet, tubular, and cylindrical. This classification is the most basic, given that shape has a direct impact on how most goods are handled and stored.
Nonetheless, the shape of the load is not the only variable to be taken into account: other factors also need to be assessed when classifying these goods, such as fragility, safety, hazard level and, above all, volume and weight. The following is an analysis of each of the three main groups and their characteristics.
Sheet type goods
This type of load has subdivisions moving from less fragile to more fragile: metal sheets, plastic sheets, and wooden boards and sheets.
To determine the best ways to handle and, in particular, store these different types of goods, it is important to take into account not only their shape and fragility but also the other factors mentioned above.
To determine the most appropriate handling method for metal sheets, one must above all take into account a fundamental characteristic of this type of goods, which is its degree of flexibility. This is determined based on the size and thickness of the sheet. The larger and thinner the sheet, the more flexible it will be.
For metal sheets cut into small pieces, the best approach is to place and strap them onto a wooden platform or pallet, creating a solid unit load that it is practically impossible to deform. This unit can be handled and even stored using the traditional systems for handling and storing materials described in previous chapters.
If the sheets being handled are large but thin in relation to their size, the problem is completely different. In that case, the damage that handling could cause to the material must be assessed. There are two types of damage. First, the sheet could be permanently bent (becoming warped, for example). Second, inappropriate handling could lead to the material becoming marked, reducing the quality of the goods, with the resulting financial losses.
To minimise the possible effects of bending, the distance between the supports of the lifting and storing elements and the cantilevers of the loads away from these must be reduced. There are three ways to do this: using more forks, adding more supports than usual and, as already mentioned, handling the sheets on a platform.
In addition to this bending, it is crucial to consider a second factor: weight. These products have a density far greater than that of goods usually handled, and, as a result, machines and racking units must be of an appropriate design. One must take into account that a cubic meter of iron weighs around 8 tonnes.
Plastic sheets
The handling of plastic sheets presents a single significant problem, which is the bending of the material. There are many types of hard plastics handled in the form of sheets, so the amount of bending will vary. However, the behavior of hard plastics is always very similar. The problem only arises in large sheets, which in fact have relatively little bend.
Small and medium-sized sheets are usually handled and stacked in exactly the same way as any other load of a similar size. Their storage does not create additional problems.
If, however, the sheets handled and stored are large, a procedure similar to that described for metal sheets is used: the standard approach is to store them on wooden trays and even pick them up directly, for which there are supports between the sheets to create a space sufficiently large for the forks of the forklift truck to enter.
In contrast to metal sheets, plastic sheets do not create any additional problems due to excessive weight or the possibility of damaging the goods.
Wooden sheets and boards
If the wood is in the form of sheets, the factor to be considered is bending. This is the same issue as discussed above for plastic sheets, and therefore their handling and storing is the same as for plastic sheets.
The rigidity of wooden boards depends on the thickness of the wood. Usually their shape is similar to that of metal sheets. However, when it comes to weight, this material is not as dense as metal and 1 cubic metre of wood weighs between 650 to 800 kg.
Medium-sized boards can be stored on pallet racking units with special cross ties or in cantilever rack units.
Tube-shaped goods
When planning the storage of this type of load, it is important to carry out an initial assessment of one of the characteristics which most affects their handling: their ability to retain their shape. Specifically, one must distinguish between rigid tubes (of steel or concrete, for example) and semi-rigid tubes (such as plastic tubes). The two types of tube are handled and stored in a completely different manner, and the system used to create their unit loads completely different.
In terms of the handling and storage of rigid tubes, this information applies to medium to large tubes, since small tubes fall under the category of large loads, already discussed in this chapter.
Very similar problems are encountered in the handling of metal and concrete rigid tubes. This type of large object is normally stored outside the facilities. They form pyramids, with the tubes strapped together into groups of three and stacked on top of each other. Some are stored with others inside vertical structures.
When stored on racking units (generally cantilever), the tubes must be prevented from rolling toward the edge. To this end, stops are fitted to the arms supporting the tubes where required. Where possible, they are stored in pyramid-shaped packs of three tubes strapped together, as this provides greater stability.
Handling and storage of semi-rigid tubes
Hard plastic tubes, which fall under the category of semi-rigid tubes, must be handled using unit loads. These consist of cages made from welded metal sections or wood (of the appropriate strength), with the tubes stored inside them. Given that the material is relatively light, the most important factor to take into account is the large volume of these cages.
These tubes are fairly simple to handle: they can be handled using side-loading or front-loading forklifts, with the difference between using one or the other of these being the space required. However, when using front-loading forklifts there is an additional problem in the transverse stability of the load, since its large volume and light weight can prove very dangerous, in particular during the storage process. Apart from this factor, the load is usually positioned using the cages themselves, which act as support for others, and therefore it is easy to stack them to considerable heights.
Generally speaking, semi-rigid tubes are stored outside. When positioned on racking units (cantilever as a rule), additional problems do not normally occur, provided that rigid cages are used. However, if the tubes are stored loose in racking units they must be prevented from rolling, as is the case with rigid tubes. Furthermore, however one must consider the potential bending of the material and more supports must be added if necessary.
Cylindrical type goods
Now that loads in the form of sheets have been analysed, we can move on to cylindrical loads. Cylindrical goods are those that are rolled up for handling, using either a mandrel or a structure (metal or wooden) or directly in the form of a reel. The three reel types analysed below are paper and cardboard reels, sheet metal rolls, and cable reels. Each type of reel is handled and stored in a completely different manner.
The handling of paper reels requires forklifts fitted with special clamps for gripping and turning. The size of machine required depends on the reel size. The machines lose some of their capacity once clamps are fitted, so their capacity must be from 1.5 to 2 times the original capacity needed to handling the weight of the reel. This margin will vary according to the diameter of the loads and how many will be stacked.
These paper and cardboard units are stored inside the warehouse. Given the high resistance of paper when wound tightly on a reel, they are stored directly on top of each other. In other words, units can be stacked on top of each other almost without limit.
Reels are manufactured horizontally but are stacked vertically (thus preventing them from rolling). They are turned from one position to another using the clamps on the handling equipment, which have this function.
There are two possible solutions for storing these goods on racking units: vertically on pallets, or horizontally on support cradles, handling them using specific forks or equipment. In any event, the size, weight, and protection applied to the goods will determine the best way of storing them.
Sheet metal rolls
These can be handled directly or on pallets. The main issue arising with these goods is their weight. Large sheet metal rolls can weigh between 20 and 30 tonnes.
When these reels are handled directly, lifting machines fitted with a shaft or spur are used, with this fitting into the space in the centre of the reel. Alternatively, an overhead crane is used. When stored on pallets, forklifts of sufficient capacity are used and fitted with conventional load forks.
Large heavy reels are usually stored outside the facilities, on the ground and in a pyramid shape. Lighter units can also be stored in this way, or inside the warehouse on special racking units created specifically for this purpose and with the appropriate sections. This unit forms a structure similar to a honeycomb, on which the reels rest (one for each cell created). In general, these warehouses are constructed for special materials, such as reels of stainless steel or other similar materials, which are more widely used in the processing industry than in primary industry.
Cable reels
In this section we address the handling and storage of reels of steel cables and multipolar electric and telecommunications cables, insulated for carrying high voltages or for transoceanic sheet reels transmissions. These two types of cables represent two different but typical handling problems, each with its own solution.
Steel cables are rolled to form a cylinder, creating a reel as a unit load. They are relatively simple to handle and can be handled by cranes, using the hook that these machines have installed in their boom. Another option for handling them is forklifts, for which forks are used as a shaft, entering the space in the centre of the reel. Alternatively, a shaft can be fitted instead of standard forks. The handling method is the same in both these cases: the shaft enters the space in the centre of the reel.
In general, cable reels are stored outside and on the ground with no additional problems, although one must remember that it is difficult to place one load on top of another. One solution for storing them might be to construct conventional racking units, since these reels are not too heavy. For heavier reels, racking units similar to those for metal reels must be used.
The solution used for handling and storing multipolar electric and telecommunications cables is quite different, since they tend to be rolled onto large wooden or metal reels (metal ones are currently most commonly used), thereby constructing a unit load which at times is very large and can be difficult to handle.
First, the metal reels onto which these long cables are wrapped do not come with a central hole of the right size to be used to help lift it (by entering a shaft, for example), which means that they have to be grasped on the outside. This poses another problem, in that the reel is completely cylindrical in shape and cannot be easily handled with the standard forks of a forklift.
The only practical way of gripping this type of reel is by using cranes or adaptors fitted to the forklifts instead of conventional forks.
Reels that are large or heavy (or both) are stored on the ground and, in some cases, stacked to form pyramids. Smaller ones can be lodged on racking units by fitting a shaft of the appropriate size and strength through the hole that this type of reel normally has, as explained previously in this article.