Drying

1.0 Key Elements

1.1 Speed
1.2 Economy of Labour
1.3 Control of Conditions

2.0 Methodology

2.1 The taking up of the moisture from the leather by the air
2.2 Ventilation is important to prevent the air becoming saturated
2.3 Relative humidity (R.H.). The % of the moisture in the air is compared with the amount which would saturate the air under silmilar conditions
2.4 Requirements

a. Quick drying
b. Great outflow for floor space

2.5 Steam is now a direct cost, no longer a bi-product
2.6 Labour is now expensive, so automation is necessary
2.7 Louvre method is based on slats in windows, and addition of steam
2.8 Improvements: ducts and vents at intervals, quantity, quality (used and fresh), temperature, humidityof this air controlled
2.9 Use of counter current system

a. driest leather mmeest driest air
b. wet leather meets partially saturated air, therefore dries slowly
c. prevents solubles migating to surface
d. conserves labour
e. use depends on amount of space available

2.10 In a conveyor or any hanging system distance between hides and skins important, as effects ventilation
2.11 Square poles can mark leather (result of over drying at edges). A rounded pole of two inch diameter best
2.12 Before drying moisture in hides or skins is reduced by piling, horsing, or sammying
2.13 All leathers improve by being allowed to lie about in cool conditions
2.14 To prevent shrinkage during drying various techniques are used

a. Nails
b. Toggling
c. Paste
d. Vacuum
e. Framing

3.0 Nailing

3.1 The leather is nailed or tacked onto wooden boards
3.2 Wooden headed hide nails are used to save operative hands
3.3 The leather is strained with nails in legs, butts, and neck
3.4 Leather belts are sometimes used to pull leather out to give greater area
3.5 Used especially on patent leather
3.6 Primarily to get leather to lie flat, rather than increase area
3.7 Increase in area normally gives decrease in quality, therefore not economic. Gives hard handle, occasionally loose grain, loose and thin flanks, Especially obvious if leather nailed too wet and dried too fast, when it is inclined to shrink greatly
3.8 Slow dryong gives better leather
3.9 Before nailing iron on the grain side
3.10 Iron in the direction of the hair
3.11 Iron temp (425degF) (200degC) very high
3.12 Ironing smooths the grain and lowers porosity
3.13 Machine plating is poorer as solely from above
3.14 Common on vegetable tanned light leathers

4.0 Toggling

4.1 Does not put holes in leather lke nailing
4.2 Toggling can either be bookcase stove type or a through feed tunnel
4.3 Similar to nailing but board replaced by perforated metal and nails by toggles
4.4 Gives good air circulation on both sides of leather speeding drying compared to nailing
4.5 Toggle frames have longer life than boards
4.6 Easier to keep clean
4.7 Lighter to move and mechanise
4.8 Less fire risk
4.9 Invariably used in stoves or drying tunnels

5.0 Paste Drying

5.1 Wet skin slicked onto galss plate, grain on plate, held by paste
5.2 Alumninium, enamel, stainless steel are all used occasionally but glass most common by far
5.3 Area again aproximately 4 to 8%
5.4 Rough parts of the skin, especially the neck area, are made flatter, giving better quality
5.5 As thin a paste as possible is used
5.6 Paste is usually purchased made up. Otherwise make a starch solution, thicken with Me cellulose, and a little glucose and Irish Moss
5.7 The object is to leave as much paste as possible on the plates and as little on the leather after dring
5.8 Pure chrome leather can give shrinkage or with strong pastes tear
5.9 To prevent this sectional control of the tunnel was introduced e.g. tunnel a. 50degC/50%RH b. 50-55DegC/40%RH c. 60degC/40%RH most large paste units have five or six sections