Onehunga Ironworks

Vast deposits of iron-sand exist over 480 kilometres of the North Island's coast from Kaipara Harbour down to Whanganui.

Currents, wind, and wave action then move the minerals along the coastline, concentrating them in dark-coloured sands on the sea floor, on beaches and in dunes.

[5] The most notable of these earlier ventures was the New Zealand Titanic Steel and Iron Company, which was led by Edward Smith[6] and had erected a blast furnace at Te Henui near New Plymouth.

[7][8][9] Attempts to smelt iron-sands in blast furnaces—the conventional means used for other iron ores—failed for two main reasons; the fine sand grains blocked the flow of hot air through the furnace—something that could be overcome, to an extent, by binding the sand into 'bricks' as mentioned above—and carbon from the coke combined with titanium in the iron-sand to produce a thick pasty layer of compounds that blocked up the tap holes used to draw off the molten iron and slag.

[9] It was the potential to exploit deposits of iron-sand near the heads of Manukau Harbour, which led to the establishment of the Onehunga Ironworks.

[10][11] Wilson provided the services of William Henry Jones to come out to New Zealand to supervise the work.

[10] The site on which the experimental furnace had been erected, 5 acres on the south-eastern side of Onehunga railway station, was purchased.

[10] The puddled-iron ball was then removed from the furnace, and its processing thereafter was by conventional 19th-century iron-making techniques—shingling to create wrought iron, and hot-rolling to manufacture wrought-iron bars.

The works' reliance on the skill and knowledge of its American manager, William Henry Jones, became a serious problem, when in December 1883, he was charged with attempted murder.

Gas quality was initially good but, by the time the furnace was up to temperature, either the heat fell away or explosions occurred, bringing work to a stop.

[16] The plant managed to continue to operate but, by November 1886, the company had liabilities of £20,000 and all its paid-up capital had been expended.

[23] At the end of June 1889, skilled workers from Pennsylvania were coming, to operate the sheet mill and commence production of corrugated iron.

[31] Hughes position on the technology of iron-sand smelting seems to have been that direct reduction would not work at a commercially viable scale, and only a blast furnace —making pig-iron— could be successful.

[18][29] Hughes saw the solution as being to mix the iron-sand with other material such as hematite or clay-band ore.[32] In July 1889, a blast furnace, with a nominal capacity of 120 tons of iron per week, was under construction at Onehunga.

[36][37] However, in early September 1890, the furnace was 'allowed to cool', reportedly as a result of insufficient coal, due to industrial trouble at the mines.

[34] Hughes should have been aware of the previous failure of the lengthy, earlier attempt at New Plymouth, but may have drawn the wrong conclusions from its partial success in making pig-iron;[32] the outcome was predictable.

[9] In late October 1890, Hughes was advocating the erection of another blast furnace at Kamo near Whangārei, where there was a hematite iron ore deposit with coal and limestone nearby.

In 1891, the Onehunga Works was a much larger plant than it had been before Enoch Hughes's management—even before the blast furnace was erected, it was claimed to be the largest ironworks in the southern hemisphere[33]—but it was no longer smelting iron ore, let alone iron-sand.

Other operations continued during 1891, but were subject to industrial trouble as the key 'puddling' workers went on strike for higher wages.

[41][42] Thomas J. Heskett became manager and conducted a trial smelting of 300 tons of limonite iron ore from Onekaka on Golden Bay, in the South Island.

[6] By August 1893, a bonus had been paid, but critics claimed that little if any of the marketable iron involved was smelted from local ores; one describing the efforts as "a tin-pot experiment".

[48] The workers, from the Eskbank Ironworks at Lithgow, had left that works in 1894 with the blessing of their employer, William Sandford, because it was short of orders.