MV Blog

Matilda swapped a life working as an engineer for a life curating the museum’s historical Engineering collection. She’s very curious about how stuff works, how it’s made and why. If a machine’s got a switch, she’ll definitely flick it.

Last week I visited a foundry in Melbourne that was casting a vital component for our restoration of the Great Melbourne Telescope. The original part of the telescope - the declination disc - had been modified and broken at some time in its history and was not repairable.

The Great Melbourne Telescope in its own house at the Melbourne Observatory, 1870. The red arrow points to the declination disc needing replacement.
Source: Museum Victoria  

This is the first part of the project to be made by a sand moulding or casting process very similar to that which was used in Ireland in the late 1860s. Our modern part is made from a type of cast iron invented in the 1940s which has magnesium added to give it properties that make it easier to shape. The electric induction furnace, which is used to melt the metal, was developed in the early 20th century.

A couple of weeks ago, Peter made a pattern out of wood for the casting. Tom next used the pattern to form a hollow in a sand mould. This kind of mould is a mixture of washed sand and a binder, made in two halves, and cured to retain its shape once the pattern is removed. The two halves of the mould were then closed, after a pouring spout, flow paths and risers (to allow the metal to flow to and fill all sections of the hollow) were added. Heavy weights on top ensured it remained closed when the metal was poured.

The sparks fly as Bryn takes a sample from the furnace for temperature testing.
Image: Matilda Vaughan
Source: Museum Victoria  

The pounded earth floor and the filtered light through the open doorways and skylights in the roof of the foundry transported me back in time. It was 7 AM and Bryn had already been awake for hours and the sparking pot of molten metal (spheroidal graphite iron) was his morning's labour. He tested its temperature and composition, turned the knob of the electric induction furnace's control panel, and gave the signal. After the removal of the slag crust, the metal was ready for pouring.

Bryn pours the molten metal into the next mould as Tom looks on. Our filled mould is on the floor behind them.
Image: Matilda Vaughan
Source: Museum Victoria  

Bryn added the final ingredients and carefully tipped the 1500°C molten metal into the pre-heated ladle. He then transported the ladle to the moulding area and poured it first into our waiting mould, and then onto the other smaller moulds. Being such a large casting, ours needed almost 24 hours to cool down before breaking open the mould.

The lower half of the sand mould, with the casting removed. The sand from the top half is in pieces in the background. The sand will be cleaned and reused, as will the molten scraps of metal.
Image: Matilda Vaughan
Source: Museum Victoria  

At 6 AM the following morning, Bryn was ready to break open the mould. The weights were removed and the upper part of the mould lifted away. Then the casting itself was lifted into the air and the sand and metal debris removed. It was then transported by the overhead mobile crane to the finishing room, where the hardened parts of the spout, risers and flow paths were ground and knocked off and the surfaces cleaned.

Bryn (left) with the pattern for our declination disc, and Tom (right) with the freshly removed casting. Note the four cylindrical 'risers' at the edge, the pouring pathways (almost like a running person) in the middle and the square shaped pouring spout (head of the running person). These pieces are reused for the next batch of metal.
Image: Matilda Vaughan
Source: Museum Victoria  

The next step for this part will be heat treatment to 'relax' the metal, followed by the final shaping and machining. It is a rare sight to see this process so close in our urban environment and one of the great aspects to working on restoration projects of this magnitude.

Links:

Great Melbourne Telescope website

Great Melbourne Telescope on Collections Online

Dr J. Patrick Greene is an archaeologist and the CEO of Museum Victoria.

On Saturday I attended a remarkable event in Whakatane, a town on the Bay of Plenty in New Zealand's North Island. I was a guest of the Ngāti Awa people, and the event was the opening of Mātaatua Wharenui (meeting house), a wonderful structure that was originally built in 1875 by the iwi (tribe) despite the devastating effects of colonisation and land confiscations.

Mātaatua Wharenui back home in Whakatane, New Zealand.
Image: Patrick Greene
Source: Museum Victoria  

Unfortunately, the building was soon lost to the people who built it as it was dismantled to be taken to be displayed in Sydney and then, in 1880, as part of the New Zealand display at the Melbourne International Exhibition. That was my connection with the event, as Museum Victoria is the guardian of the Royal Exhibition Building constructed for the 1880 exhibition. Charlotte Smith (Senior Curator in MV's History and Technology Department) carried out some research at the request of the Ngāti Awa which revealed that only the carved wooden panels were displayed rather than the complete structure.

  The interior walls of Mātaatua Wharenui have intricate woven panels and carvings. They were restored by Ngāti Awa craftspeople.
Image: Patrick Greene
Source: Museum Victoria  

After Melbourne, Mātaatua was taken to England where it was displayed, and remained for several decades. It then went to the Otago Museum, and in 1996, under the Treaty of Waitangi, it was returned to the Ngāti Awa. A team of craftspeople — carvers and weavers — have worked for 15 years to restore the building that had become seriously decayed on its travels.

I was present for the pohiri (general welcome), a series of speeches and songs in which the Ngāti Awa welcomed their guests, who, group by group, responded. As well as other iwi, there were delegations from Hawaii and the Cook Islands. It was a great privilege to part of the ceremony and to witness the oratory that is a treasured part of Maori (and Polynesian) culture, a world away from the sound bites that constitute so much current discourse. The restoration of the building is a triumph: it has been beautifully carried out and the building will stand as a testament to survival of a people and their culture.

Mātaatua: The House That Came Home is a short film that tells the story of the meeting house, courtesy of Te Rūnanga o Ngāti Awa.