Steel wires are made by passing wire rods through conically converging dies as shown in this video. As a result of the pulling force on the wire rods through the converging section, the diameter of the wire is reduced. This reduction in diameter of the wires is a gradual process, and it takes place by passing the wires through a sequence of dies with gradually decreasing converging sections. These wire drawing dies are made of sintered tungsten carbide (WC).
For the purpose of lubrication, dry lubricants are used which forms a thin layer between the wire and die surface to prevent direct contact between wire material and die & reduce friction. Calcium and sodium stearate soap powders are mainly used as dry lubricants.
The major constituents of the dry lubricant are:
(a) Calcium Stearate – FAT (animal or vegetable) + Calcium Hydroxide.
(b) Titanium dioxide – 3 to 12%.
(c) Lime and Calcium Sulphate as fillers.
The heat generated during the wire drawing process burns the dry lubricants, which are in direct contact with the die. The used dry lubricants are collected as burnt lubricants and discarded. The wires get marginally heated up during sequential wire drawing process and this heat is carried forward to subsequent stages. While passing through the next sequence of die, this heat is transmitted to the lubricant chamber, causing partial burning of the lubricant, which generates fine burnt powders. As time passes, the burnt component in the soap powder increases, resulting in improper lubrication. Thus, this used lubricant needs to be replaced with fresh lubricant. A gradual increase in burnt components is observed from the first die box to the last die box.
Approximately 25 MT of used dry lubricant is generated per month. Since this used dry lubricant is a mixture of burnt and unburnt powders, the unburnt powder can be recycled as it has been validated as non-hazardous waste. The used lubricant was discarded by incineration. The calorific value (CV) of used powder is > 3000 and as per Waste Management Rule, any waste having CV >2500 cannot be discarded in a landfill. As the CV of burnt powder is in the range of 3300 to 3800, it can be used as an alternative fuel.
Thus, we are seeking alternate uses of this used soap powder, either as an alternative fuel or as raw material.