Leather drumming paddle assembly (drum shelves, pegs and paddles)

01

Choose shelves, pegs or paddles for the mechanical action

The Leather Working Group's Making Leather Overview (Part 2) says drums are the leading vessel for all wet operations; on rotation hides and floats are mixed, and the forces applied, governed by rotation speed, load weight, float volume, time and internal construction, help determine how chemicals penetrate while the hide is flattened. Its simplest drum has 6 shelves set horizontally across the body, giving a moderate drop but a rolling motion that can tangle the goods; pegs give a gentler, continuous teasing action that helps avoid tangling, and the two can be combined. Deep shelves, at 25–40% of the drum radius, fitted 3 or 4 per drum according to shelf length, give a high lift and drop and good mechanical action while helping avoid tangling. [1]

It adds that tri-compartmental (Y-section) vessels, divided into 3 sections by perforated divisions, are used for more delicate leathers and are fitted with small pegs; that drums are traditionally wooden, with polypropylene and stainless steel also used; and that paddle arrangements are used occasionally, with paddles made of wood and polypropylene. [1]

Editorial calculation: in a drum of 3.0 m diameter (1.5 m radius), deep shelves at 25–40% of the radius would project about 0.38 to 0.60 m from the shell; check the actual depth on the supplier's drawing for your drum. [1]

US patent 6,151,932 (Drum for treating leather, fur and similar products) replaces radial bats or rods with scoop-shaped bats set slightly off the radius at the vertices of an imaginary polygon with an even number of corners, each opposite pair parallel; its example drum has four scoops, each pair perpendicular to the other, with transverse heels at the scoop tips. It gives scoop heights of 600–1,500 mm fitted to the drum heads and rotation in one or both directions at 0.25–8 rpm. The inventors estimate about 60% lower energy use and about 50% less water in soaking, unhairing and tanning than with conventional drums fitted with bats or rods; these are the patent's own estimates. [3]

Editorial calculation: a 3.0 m drum at the patent's top speed of 8 rpm moves its shell at about 75 m/min (π × 3.0 × 8); at 0.25 rpm, about 2.4 m/min. The drum size is an assumed example. [3]

Give the supplier the vessel type (drum, Y-section, paddle vat) and its internal diameter and length, shell material, the processes and leathers run (soaking, liming, tanning, retanning, dyeing), load weight and float volume, rotation speed, the fitting type and layout wanted (shelves, pegs, deep shelves, paddle blades), fitting material and fixing method, chemical and temperature exposure, and drainage or perforation details.

02

Check hide damage, capacity and drive limits

US patent 6,935,144 B2 (Council of Scientific and Industrial Research, Device for leather processing) states that wet processing is conventionally done in pits, vats, paddles and wooden drums; paddles impart agitation by rotating blades driven by a motor and gearbox, while drums lift hides with shelves or pegs and let them fall into the liquor. It lists drumming limitations: possible damage by scraping, scuffing, knotting, distortion, wrinkling, grain pebbling, loosening of fibre structure or loss of area; difficult cleaning; float limited to below the axle so capacity use is only about 35% of drum volume; turbulence that increases friction between hides; and starting torque about 3 times running torque, so the patent says drum motors are oversized. [2]

Editorial note: when replacing or changing fittings, ask the supplier how the new layout changes lift height, drop and load on the drive, and agree a trial batch to check tangling and grain damage on your leather.

03

Size drum, drive and paddle speed against a reference tannery

The UNIDO/ILO technical memorandum Tanning of Hides and Skins (Technical Memorandum No. 1; ILO 1981, UNIDO edition 1982) specifies, for deliming, bating, pickling and chrome tanning in its model hide tannery, four wooden drums each 2.5 m long by 2 m in diameter, each handling 100 hides (200 sides) per 2-day cycle and rotated by a 7.5 kW (10 HP) electric motor at approximately 5 rpm. Retanning, dyeing and fatliquoring use three smaller drums of 2.5 m by 1.2 m diameter. [4]

For the paddle pits in its skin line, it sets paddle speed between 5 and 10 rpm, enough to keep the skins moving without entangling them in the blades. Paddle axles and mountings should be wood, plastic or stainless steel, not iron, which may stain the liquors and skins, and the nails or pegs in the paddles should preferably be of non-corrosive material. [4]

Editorial calculation: at 5 rpm the shell of a 2 m drum travels π × 2 m × 5 ≈ 31 m per minute, and deep shelves at 25–40% of its 1 m radius would project 0.25 to 0.40 m. [4] [1] Editorial note: give the fittings supplier your drum diameter, speed range and motor rating.

04

Horizontal and deep shelves, pegs, Y-section dividers, scoop bats and paddle blades

Shelves and pegs act differently on the hide: shelves lift and drop hides but can roll and tangle them, pegs tease more gently, and the LWG overview notes that shelves and pegs can be combined in one drum. [1]

05

Shelf or blade size, speed range, weight, material and fixing for a drum-fittings order

The speed row has three published references to work from: 0.25–8 rpm for the scoop-bat drum patent, 5–10 rpm for UNIDO/ILO paddle pits, and the drum speed of your own vessel, which sets the drop the new fittings will give. [3] [4]

06

Send the vessel, process and fitting data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Vessel: [drum; Y-section; paddle vat; size; material]
Processes: [soak; lime; tan; retan; dye]
Load: [hide weight; float volume; speed]
Fittings: [shelves; pegs; deep shelves; paddle blades; layout]
Material: [wood; polypropylene; stainless]
Fixing: [method; access]
Trial: [batch to check tangling and grain]

See manufacturer records Send an enquiry through CNFX