Why are shoe upper tanners moving to processing full hides?
Tanners have used side leather to fulfill the needs of shoemakers for nearly a century. Prior to the use of sides, the shoemaker preferred croupons or double butts as their preferred material. It is not well documented whether shoe makers preferred sides because of the ease of work, when clicking, or whether there were other material reasons.
As shoe manufacture moved from vegetable- tanned upper leathers to chromium-tanned the industry saw a shift away from double butts that were prepared in the pits, to side leathers that were created in drums.
Full cow hides were received by tanneries, were sided after liming/unhairing so that they could be unhaired/fleshed on the beam. The croupon/double butt fleshing machines that came later could not fit full hides, but could fit sides and hides, which were sided to facilitate mechanisation. Shoe makers would have gotten used to sides, as they are similar in working size to croupons and could have used the bellies in other lower grade requirements.
Medium to light hides have generally been used in shoe upper manufacture, because of the historical fact that the hides were sided, taken to the blue and then split and shaved. Those drop splits would hopefully have yielded some additional income to the tanner, but were not too heavy facilitating extra splitting into middle and flesh splits.
Modern developments in machinery have meant that the availability and the cost of full hide machinery have allowed ease of use and service. The precision and reliability of these machines have also improved, allowing greater efficiency. One full hide machine has double the output of a side machine and approximately half the base probability of causing a machine error.
As a hide is placed into a full hide machine, it will pass through the machine faster than two sides can be placed through a side machine. Of course extra production time has to be added due to the time needed to side the hides in the first place. Backbone trimming later may also add extra production time on side leather production.
The probability of error is a tricky one, as logically if two operations are performed instead of one the chance of error is doubled, but full hide processing is more complex and can be said to increase the chance of error – but certainly not up to the level of two side machining.
When a tanner considers a machine, attention to working width has to be coupled to the machine footprint. Full hide machines are not double the working width of side machines, they are around 1.9 times larger.
Around the working width of the machine, the machine consists of core/peripheral components, including drive assemblies, service components, motors, machine frame mountings/extensions - which add to the dimension of the equipment (up to ½ of the working width). In addition to the equipment the tanner needs to add yet another ½ the working width as space at the sides of the machine to allow service/safety and machine access.
The largest space implication has to be given to the material access/exit. It is illustrated very simply, see Figure 1, where up to 3 times the machine depth for materials is to be added so that material can be placed in or taken out. Through-feed machines take even more space, especially if loading/unloading is on to horses.
Figure 1. A schematic diagram showing that hide machinery is not double the working width of side machinery, but that its working footprint would be slightly smaller than two side machines.
From Figure 1 you can see that it is 10% more space efficient to have one machine that is capable of double the output than two machines, because of the industry’s current working width portfolio’s. Of course this is a generalisation, because: some machines vary in size; the working practices of engineers and how much space they leave varies; and the machine footprints vary by design. The conclusion of this consideration is that shoe upper machinists should be considering the dimensions of their equipment and calculate to see if space savings could be made.
The other machine consideration for full hide vs. side must be that the labour cost for one machine generally stays the same. Two splitters feeding the machine are generally required, but an operator at the back of the machine can be saved or completely eliminated if the drop split and grain are lowered, to the trimming table, by gravity. Of course the elimination could be made on side splitters too.
There are machine disadvantages however, in that having one big machine could result in a catastrophic effect on production if one machine is out of commission, but I doubt that any self-respecting tannery would not have redundancy, so extra capital requirement may be required for full hide machining. You can always split sides on a full hide splitter, but you cannot split full hides on a side splitter.
Eighteen months ago, the price of splits rose so high that this allowed many shoe upper leather manufacturers to move over to lime splitting. This gave rise to many benefits: the ability to release limed material to gelatin or suede manufacturers without significant investment in the raw material; to process their grain leathers at a fraction of the weight and with significantly lower cycle times; and if desired to tailor their own deliming/bating, pickle, and tanning recipes for bespoke split tannage/retannage.
I would guess, that the one major bonus that upper tanners gained from this is the experience that lime splitting produces a larger, whole drop split that can be crusted and then laminated, finished, or processed as suede to give a surface area that has a larger area for cutting (and questionably more yield). If a percentage yield increase is not predicted by clickers, then I would challenge the clicker to try and get the same yield if a hide was cut into 16 pieces using the same logic. The centre cut from the siding process has to reduce the valuable leather obtained from the backbone and that cut should be eliminated if possible.
Low substance splits now cost tanners a significant drop in income in business models that place great emphasis on all leather by-products subsidising the grain leathers. Heavier hides will give better drop splits and less wastage.
The same yield is seen in grain leathers, but the real benefit to full hide processing of the grain leathers is the reduction in the amount of handling of the leather. One piece for toggling, setting, measuring slowly adds to the reduction in handling time compared to two pieces.
A final note in the future of shoe clicking must consider the way in which automotive clicking has gone. Full hide clicking presses, water blades, and even laser cutting have sped up the rate of clicking for footwear manufacturers and the only real resistance to the move over to full hide is a resistance to the breaking of tradition or the mental block stalwarts will have over change.