TANNING PROCESS

Table of Contents:

(click on each link to read about a certain step, or scroll down to read the whole process)

STEER: Tanners are the original recyclers- we convert cattle hides (a by-product from the meat industry) into the natural, useful and beautiful leather items the world has come to cherish. Cudahy Tanning Co. utilizes United States heavy steers and less thick heifers for our product mix. This is truly a renewable, sustainable resource. Enjoy following our process.

WEIGHT SORTING: Meat is a perishable item and, logically, so are the hides. The protective treatment given to the hides for transit to and storage at the tannery is called brine curing. A concentrated salt solution provides an environment in which protein-destroying organisms cannot function. Cudahy then takes these cured hides that arrive in truckloads of approximately 800 hides and sorts for thickness and weight with this specially developed conveyor system.

DUMPING A TAN DRUM: Large wooden drums are filled with several thousand pounds of brine cured hide material and in these vessels the hair is removed and the tanning process completed. The complex chemistry involved in dehairing and conversion of the hides into a stable, non-decaying material called leather is truly miraculous. Man, in his earliest civilizations, developed means for utilizing tree barks and vegetable extracts for tanning various skins. Modern tanners use trivalent chromium salts as their tanning agent, which shortens the process time and produces leather that combines most of the chemical and physical properties sought in the market place. There are numerous quality checks throughout the tanning cycle and laboratory test equipment is required to insure consistent results.

WRINGING/SORTING: Tan liquors and water baths for the hides in the tanning process saturate the hide with moisture. The chrome salt also turns the hide into a robin's egg blue color and the hide is often referred to as being in the "wet blue" state. A wringing machine consisting of two large rolls, which squeeze excess moisture from the hide, prepares the hide for the next several operations. By removal of moisture the hide can be evaluated for aesthetic quality and thickness. To ease handling, the cattle hide is cut from head to tail along the backbone by a circular blade to make a left and right side. Cudahy Tanning is renowned for its manufacture of "side leather". Experienced blue sorters grade each side to customer classification and place specific, computer-generated work orders on carefully selected packs of approximately 100 sides each.

SPLIT/SHAVE: Leather goods such as footwear, belts, garments and numerous others require a certain thickness for their construction. Tanneries use two machines, the splitter and the shaver, to insure proper specifications for end use. The sides are fed through the splitter with the grain side up (which means the epidermal skin layer from which the hair was removed) and pass through a band saw to create a uniform thickness. The underneath (flesh layer) that is cut off is called a split and, although the grain has been removed, it is a valuable raw material for suede products. The shaving machine has a bladed cylinder that rotates at 1500rpm and finely cuts into the flesh portion of the side to further level thickness and open the fiber structure to assist further chemical processing. Thickness is measured by a gauge in ounces or millimeters, with one ounce equal to 1/64 inch.

COLOR DRUMS: Packs of leather are weighed after shaving so that proper calculations can be made for uniform dying of the sides in smaller drums than we use for tanning. In these color drums the sides are retanned with vegetable extracts, fillers, and resins dyed to basic shade required and lubricated with various oils (called fat liquors). Our tanner, by varying the quantities and types of extracts and fat liquors, can produce from the same basic tannage, side leather that is soft and luxurious for personnel leather goods, firm with stand-up for saddlebags and shoes, or waterproofs for today's performance applications. The formulations for these retannages are quite complex and require careful monitoring.

SETOUT: "Setting out" is the term for smoothing the grain of the side and removing excess moisture so as to put the leather in proper condition for drying. All the wet end chemical operations are complete and the sides pass through rolls much like the wringing machine described earlier. Blades on the cylinder are shaped such that cutting does not take place as was the case with the shaver but, rather, a smoothing of the grain surface occurs. The leather fibers are compressed and moisture content of the side reduced to about sixty per cent.

VAC DRY: There are several methods for drying leather that have been utilized over the years but at Cudahy Tanning we use the vacuum dryer system that provides the finest quality grains for our products. In the vacuum dryer the wet side is smoothed onto a stainless steel plate, then covered by a screen which is attached to felt or cloth. While the side is enclosed, a vacuum is pulled which extracts water vapor from the leather for a few minutes with time dependent upon the heat of the plate and the thickness and retannage of the leather.

STAKING: Once the leather is dried it becomes rigid and requires a mechanical softening to increase pliability. The fat liquoring in the color drums and the staking machine pictured here determine the final firmness or softness of the leather. The tanner refers to this characteristic as temper and makes necessary adjustment to achieve the specified goal. The machine has a large number of thumb-size pins that oscillate and pound the leather as it travels along a conveyor. This mechanical pounding stretches and flexes the leather fibers in every direction providing a more pliable, relaxed piece.

FINISHING: So far we have been dealing with the operations which have converted the hides into a stable material with varying degrees of strength, flexibility and smoothness. In the finishing area the artistic nature of the tanner's creativity adds the final touches to enhance the natural beauty of the product and provides protection to the leather so as to improve serviceability. The imaginative finisher utilizes coatings of color and film to create the desired effects. Light applications are made with spray coating machines that mist the film onto the leather as it passes along a conveyor. Heavier films and oils are applied to the leather by rollcoaters in which the finish is pumped into a trough where it is picked up by a rotating knurled steel roll that comes in contact with the grain surface. The sides must then pass through a drying tunnel to evaporate the excess moisture and allow the coating materials to form into a durable, protective film on the leather.

PLATING: The plating and embossing operations are carried out in presses capable of developing extremely high pressures per square inch. Varying degrees of heat and pressure create the desired effect as the sides are passed beneath a stainless steel plate and the press is closed for one or two seconds. The press is then opened and the operation repeated until all parts of the side have received the treatment. A specially engraved plate may be used for embossing any number of fashionable textured effects upon the leather. Finishing and plating steps are often completed in conjunction with one another over the period of a week. It is common to apply a few coats of finish, plate, apply another finish coat, plate again, etc.

FINAL SORT: Cudahy Tanning's final evaluation area has bright lights and allows skilled sorters to grade the leather for our customers. It is graded for temper, uniformity of color and thickness and the extent of any defects that appear on its surface. The intense quality control systems in place at our tannery require the product to be passed along to the next operation only if it exceeds the required standards. At Final Sort the inspectors insure that those standards have been met and prepare the sides for packaging and shipment to our awaiting customers.

LAB: Testing our products for consistency and performance is very important at Cudahy Tanning. A staff of technicians utilizes laboratory test equipment for strength analysis, finish adhesion, embossability, waterproofness and many, many other specifications. Our marketing department also utilizes these lab personnel for development and testing of new leather products. The market place rapidly changes and efficient, family owned tanneries such as ours can react to the needs of the market in many ways. Color, texture and innovative technical improvements are generated in our lab. Sample sides of these developments and products can be quickly produced for our customer's approval.