Clearly any new product, whether a one off or a series produced item, must be commercially viable and that can lead to pressure to cut costs wherever possible. However it is surprising how often the problems which arise are due to poor design and a lack of forethought rather than cost cutting. For little or no extra cost, the problem could be eliminated or minimised.
Historically there have been widely varying practices throughout the world, ranging from virtually no controls at one extreme to formal approval by an officially appointed body at the other. In the UK, prior to the current European based legislation, it was common practice to rely heavily on the item withstanding a proof load test. This was particularly so for lifting structures such as runways, slewing jib cranes, lifting beams and fabricated lifting accessories. Indeed it was not uncommon for a user to fabricate their own equipment and send it to a test house for testing and certification.
Relying so heavily on load testing alone ignored many of the other aspects of performance which are necessary for the item to be considered safe. Some of these relate to the load bearing capability of the item whereas others relate to functionality and the way in which the item can be used or misused. For example, in the former category, the item must have adequate resistance to fatigue, must not be prone to low temperature brittleness and must have wear and corrosion resistance commensurate with the intended application.
To a large extent, these are matters which must be addressed at the design stage, particularly in the specification of the materials for each component. However they also require quality control during the manufacturing processes. Some processes can produce a variation in quality from one component to the next whereas others produce a more consistent result which can only vary gradually or from batch to batch. Ensuring that every finished item meets the specification can therefore involve checking components at certain stages of manufacture, a process known as verification. The verification regime should be chosen to take account of the variations which can result from the particular process. For example if the variation in quality is gradual, a sampling regime can adequately monitor it. However, if the quality can vary from component to component, a sampling regime is inappropriate and every one must be checked.
Heat treatment is an example of a process which can produce surprisingly variable results. Factors such as tolerances on furnace controls, the temperature of the quench medium, and the position of the component within the furnace all have an effect and can produce a scatter of results. Different batches of component material can respond differently, despite being to the same specification, making it necessary to trial a sample in the laboratory before processing the batch. Verifying that the result obtained is what was expected requires a sampling regime which takes account of all these variables.
Machining tolerances are another quality control area where we sometimes see poor results, particularly in some products from low wage economies. The product manufacturer often only assembles components bought in from numerous suppliers and, to ensure they can be easily assembled, the tolerances are wider than desirable. The result is a ‘rattling fit’ rather than a good one. In extreme cases this significantly affects the performance of the individual item, despite it still being to specification.
On-site installations also present problems. One question which frequently arises concerns the fixing of lifting points and runway beams into concrete and masonry structures such as lift shafts. In most cases it is impossible to verify the fixing embedded into the structure after it has been installed. Similarly the foundation for a free standing slewing jib is impossible to verify. What is required is a proper record of the fixing specification together with documented confirmation from someone competent, who was present at the installation, that it was done to specification. This record should be available to anyone subsequently called upon to periodically inspect it. Without such information, those who inspect it have to rely solely on indications of movement and, choosing to err on the safe side, may well fail any installation showing the slightest indication.
The functional and ergonomic aspects of any product are also very important and it is in this area that manufacturers often fail to adequately consider how it will be used. One of the principles of good product design is that it should be as ‘idiot proof’ as possible. By our nature, human beings make mistakes and also tend to push the boundaries. We are also not very good at reading instructions let alone following them. Clearly it is impossible to address every situation by design alone but there is a lot the good designer can do.
The European Machinery Directive embodies the approach of identifying the potential hazards, assessing the risk associated with the hazard, then eliminating the hazard or reducing the risk to an acceptable level in a hierarchical manner: designing out the hazard wherever possible, then guarding out wherever possible etc. The last resort is the instructions for use. Throughout this process, the manufacturer is expected to exercise a degree of foresight about the way his product might be used including during any storage, transport, installation, use in service, maintenance and ultimate decommissioning. Whether the product concerned is for the European market or elsewhere, this approach can be regarded as good practice.
In the context of hand operated blocks and lever hoists, I have often commented on the inadequacy of the slack end chain anchor or chain stop. Regrettably, I still see poor design. Although the operative should be wary, it is entirely foreseeable that he or she may inadvertently run the chain fully out. If that happens the brake will be open and the full weight on the hook will be transmitted to the chain anchor or stop. However the operative may continue trying to lower and thereby transmit a torque to the load wheel. This will further increase the load on the anchorage. A total of twice the working load is easily possible and, if the anchorage fails, the chain will run through and the load will drop.
To be considered safe, the chain anchor or stop should be capable of withstanding 2.5 times the working load. It is no less important than end stops on a runway or gantry, or the hoist limit switches on a crane.
Another area of concern is the stability of heavy lifting accessories when set down and detached from the crane hook. Lifting beams, grabs, crane forks and similar items may not be inherently stable when set down, particularly if the surface is not level and even. However it is surely foreseeable that products intended to handle materials on a construction site may be set down on ground that is not perfectly level. It is a question of reasonable tolerances. If operational requirements prevent an inherently stable design, then another solution such as a support stand can be employed.
The same type of equipment often has to be steered or orientated manually onto the load and whilst landing the load. If there are no natural handholds then handles should be provided. Equally there may be potentially dangerous parts the operative might foreseeably take hold of, such as the arms of a scissor grab which have a shearing motion. The risk of such areas can be minimised by good design, for example by providing adequate clearance between the arms, but guarding or other measures such as warning signs and colour coding may be necessary.
These are just a few examples of what is required to illustrate the principle. Having designed a product exercising the necessary foresight and putting in place the necessary manufacturing quality controls and verification procedures, the manufacturer also needs to provide adequate information for all aspects of use including installation, commissioning, environmental conditions, maintenance, storage and decommissioning as appropriate. Having seen many such attempts at user information over the years, I can say with authority that they range from the excellent to the truly dire. Even the quality of reproduction of some will discourage the reader, let alone the confusing translation from the original language.
Finally, the manufacturer needs to keep overall control of production through a record system which tracks design and specification changes, materials, components and finished product. There should be full traceability so that should any problems arise, the extent of the problem can be easily established and addressed. By such means are safe quality products conceived and good reputations built.
