Tinplate

Tinplateconsists ofsheetsofsteelcoated with a thin layer oftinto impederusting.Before the advent of cheapmild steel,the backing metal (known as "backplate" ) waswrought iron.While once more widely used, the primary use of tinplate now is the manufacture oftin cans.

In thetinningprocess, tinplate is made by rolling the steel (or formerly iron) in arolling mill,removing any mill scale by pickling it in acid and then coating it with a thin layer oftin.Plates were once produced individually (or in small groups) in what became known as apack mill.In the late 1920s pack mills began to be replaced bystrip millswhich produced larger quantities more economically.

Formerly, tinplate was used fortin ceiling,andholloware(cheap pots and pans), also known as tinware. The people who made tinware (metal spinning) were tinplate workers.

For many purposes, tinplate has been replaced bygalvanisedmetal, the base being treated with azinccoating. It is suitable in many applications where tinplate was formerly used, although not for cooking vessels, or in other high temperature situations—when heated, fumes from zinc oxide are given off; exposure to such gases can produce toxicity syndromes such asmetal fume fever.^[1]The zinc layer prevents the iron fromrustingthroughsacrificial protectionwith the zinc oxidizing instead of the iron, whereas tin will only protect the iron if the tin-surface remains unbroken.

History of production processes and markets

The practice oftin mininglikely began circa 3000 B.C. in Western Asia, British Isles and Europe. Tin was an essential ingredient of bronze production during the Bronze Age.^[2]^[3]^[4] The practice of tinning ironware to protect it against rust is an ancient one. This may have been the work of thewhitesmith.This was done after the article was fabricated, whereas tinplate was tinned before fabrication. Tinplate was apparently produced in the 1620s at a mill of (or under the patronage of) the Earl of Southampton, but it is not clear how long this continued.

The first production of tinplate was probably inBohemia,from where the trade spread toSaxony,and was well-established there by the 1660s.Andrew Yarrantonand Ambrose Crowley (a Stourbridge blacksmith and father of the more famousSir Ambrose) visited Dresden in 1667 and learned how it was made. In doing so, they were sponsored by various localironmastersand people connected with the project to make theriver Stournavigable. In Saxony, the plates were forged, but when they conducted experiments on their return to England, they tried rolling the iron. This led to the ironmastersPhilip Foleyand Joshua Newborough (two of the sponsors) in 1670 erecting a new mill,WolverleyLower Mill (or forge) inWorcestershire.This contained three shops, one being aslitting mill(which would serve as arolling mill), and the others were forges. In 1678 one of these was makingfrying pansand the other drawing outbloomsmade infinery forgeselsewhere. It is likely that the intention was to roll the plates and then finish them under a hammer, but the plan was frustrated by William Chamberlaine renewing apatentgranted to him andDud Dudleyin 1662.^[5]^[6]

The slitter atWolverleywas Thomas Cooke. Another Thomas Cooke, perhaps his son, moved toPontypooland worked there forJohn Hanbury.^[7]He had a slitting mill there and was also producing iron plates called 'Pontpoole plates'.^[8]Edward Lhuydreported the existence of this mill in 1697.^[9]This has been claimed as a tinplate works, but it was almost certainly only producing (untinned) backplate.

Tinplate first begins to appear in the Gloucester Port Books (which record trade passing throughGloucester), mostly from ports in theBristol Channelin 1725. The tinplate was shipped fromNewport, Monmouthshire.^[a]This immediately follows the first appearance (inFrench) ofReamur'sPrincipes de l'art de fer-blanc,and prior to a report of it being published in England.

Further mills followed a few years later, initially in many iron-making regions in England and Wales, but later mainly in south Wales, most notably theMelingriffith Tin Plate Works,Whitchurch, Cardiff,which was founded some time before 1750. In 1805, 80,000 boxes were made and 50,000 exported. The industry continued to grow until 1891. One of the greatest markets was the United States, but that market was cut off in 1891 when theMcKinley tariffwas enacted. This caused a great retrenchment in the British industry and the emigration to America of many of those were no longer employed in the surviving tinplate works.

Despite this blow, the industry continued, but on a smaller scale. There were 518 mills in operation in 1937, including 224 belonging to Richard Thomas & Co. The traditional 'pack mill' had been overtaken by the improved 'strip mill', of which the first inGreat Britainwas built by Richard Thomas & Co. in the late 1930s. Strip mills rendered the old pack mills obsolete and the last of them closed circa the 1960s.

Pack mill process

The raw material wasbar iron,or (from the introduction ofmild steelin the late 19th century), a bar of steel. This was drawn into a flat bar (known as a tin bar) at theironworksorsteel workswhere it was made. The cross-section of the bar needed to be accurate in size as this would be the cross-section of the pack of plates made from it. The bar was cut to the correct length (being the width of the plates) and heated. It was then passed four or five times through the rolls of the rolling mill, to produce a thick plate about 30 inches long. Between each pass the plate is passed over (or round) the rolls, and the gap between the rolls is narrowed by means of a screw.

This was then rolled until it had doubled in length. The plate was then folded in half ('doubled') using a doubling shear, which was like a table where one half of the surface folds over on top of the other. It is then put into a furnace to be heated until it is well 'soaked'. This is repeated until there is a pack of 8 or 16 plates. The pack is then allowed to cool. When cool, the pack was sheared (using powered shears) and the plates separated by 'openers' (usually women).^[11]Defective plates were discarded, and the rest passed to the pickling department.

In the pickling department, the plates were immersed in baths of acid (to remove scale, i.e., oxide), then in water (washing them). After inspection they were placed in an annealing furnace, where they were heated for 10–14 hours. This was known as 'black pickling' and 'black annealing'. After being removed they were allowed to cool for up to 48 hours. The plates were then rolled cold through highly polished rolls to remove any unevenness and give them a polished surface. They were then annealed again at a lower temperature and pickled again, this being known as 'white annealing' and 'white pickling'. They were then washed and stored in slightly acid water (where they would not rust) awaiting tinning.

The tinning set consisted of two pots with molten tin (with flux on top) and a grease pot. The flux dries the plate and prepares it for the tin to adhere. The second tin pot (called the wash pot) had tin at a lower temperature. This is followed by the grease pot (containing an oil), removing the excess tin. Then follow cleaning and polishing processes. Finally, the tinplates were packed in boxes of 112 sheets ready for sale. Single plates were 20 by 14 inches (51 cm × 36 cm); doubles twice that. A box weighed approximately ahundredweight(cwt; 112 pounds or 51 kilograms).^[12]^[b]

Strip mill process

The strip mill was a major innovation, with the first being erected atAshland, Kentuckyin 1923. This provided a continuous process, eliminating the need to pass the plates over the rolls and to double them. At the end the strip was cut with a guillotine shear or rolled into a coil. Early –hot rolling– strip mills did not produce strip suitable for tinplate, but in 1929cold rollingbegan to be used to reduce the gauge further. The first strip mill inGreat Britainwas opened atEbbw Valein 1938 with an annual output of 200,000 imperial tons (203,210 tonnes or 224,000 short tons).

The strip mill had several advantages over pack mills:

It was cheaper due to having all parts of the process, starting withblast furnaces,on the same site.
Softer steel could be used.
Larger sheets could be produced at lower cost; this reduced cost and enabled tinplate and steel sheet to be used for more purposes.
It was capital-intensive, rather thanlabour-intensive.^[15]

Notes

^Data extracted from Wanklynet al.(1996).^[10]
^
What is described here is the process as employed during the 20th century. The process grew somewhat in complexity with the passage of time, as gradually it was found that the inclusion of additional procedures improved quality. The practice ofhot rollingand thencold rollingevidently goes back to the early days, as the Knight family's tinplate works had (from its foundation in about 1740) two rolling mills, one at Bringewood (west of Ludlow) which made backplate, and the other the tin mill at Mitton (now part ofStourport), evidently for the later stages.^[13]
- For more on the Knight tinplate works, see Ince (1991).^[14]

Citations

^Bradberry, S. M.; Vale, J. A. (28 January 1998)."Zinc oxide (UK PID)".INCHEM.International Programme on Chemical Safety (IPCS); World Health Orgnization.
^Cierny & Weisgerber (2003).
^Valera & Valera (2003).
^Dayton (2003).
^Brown (1988).
^King (1988).
^King (1988),p. 109.
^Schubert (1955),p. 429.
^Minchinton (1957),p. 10.
^Wanklyn et al. (1996).
^
- Davies, Graham (1 February 2022)."The Tinplate Industry".The Llanelli Standard.
- "Ashburnham Tinplate Works".Pembrey and Burry Port Heritage | Threftadaeth Penbre a Phorth Tywyn.Retrieved4 September2024.
^Minchinton (1957),pp. 250–253.
^Greene (2015).
^Ince (1991).
^Reutter (1988),pp. 155–170, 265–280.

Sources

Brown, P. J. (1988). "Andrew Yarranton and the British tinplate industry".Historical Metallurgy.22(1): 42–48.
Giumlia-Mair, Alessandra; Lo Schiavo, Fulvia, eds. (2003).Le problème de l'étain á l'origine de la métallurgie – The problem of early tin.Actes du XIVème Congrès UISPP, Université de Liège, Belgique, 2–8 Septembre 2001; section 11, âge du Bronze en Europe et en Méditerranée; colloque 11.2 [Acts of the XIVth UISPP Congress, University of Liège, Belgium, 2–8 September 2001; Section 11. Bronze Age in Europe and the Mediterranean, Symposium 11.2] (in French and English). Oxford: Archaeopress.ISBN 9781841715643.16 papers (13 in English, 3 in French):
- Cierny, J.; Weisgerber, G. (2003). "Bronze Age tin mines in Central Asia". In Alessandra Giumlia-Mair; Fulvia Lo Schiavo (eds.).The Problem of Early Tin.pp. 23–31(in English).
- Dayton, J. E. (2003). "The problem of tin in the ancient world (part 2)". In Alessandra Giumlia-Mair; Fulvia Lo Schiavo (eds.).The Problem of Early Tin.pp. 165–170(in English).
- Valera, R. G.; Valera, P. G. (2003). "Tin in the Mediterranean area: History and geology". In Alessandra Giumlia-Mair; Fulvia Lo Schiavo (eds.).The Problem of Early Tin.pp. 3–14(in English).
Greene, Miranda (March 2015) [First published 2005],"The Knight family and the British iron industry",in Herefordshire Archaeology (ed.),Herefordshire Through Time,Herefordshire Council,archivedfrom the original on 19 April 2024
King, P. W. (1988). "Wolverley Lower Mill and the beginnings of the tinplate industry".Historical Metallurgy.22(2): 104–113.
Minchinton, W. W. (1957).The British tinplate industry: A history.Oxford: Clarendon Press.
Reutter, Mark (1988).Sparrows Point: Making Steel—the Rise and Ruin of American Industrial Might.University of Illinois Press.ISBN 9780671553357.
Schubert, H. R. (1955).History of the British Iron and Steel Industry from c. 450 B.C. to A.D. 1775.London: Routledge & Kegan Paul.
Wanklyn, M. D. G; Wakelin, P.; Hussey, D.; Milne, G. (March 1996),Database: Gloucester Port Books, 1575–1765,Colchester, UK: University of Essex; UK Data Archive; University of Wolverhampton,doi:10.5255/UKDA-SN-3218-1,Catalogue record: [computer file on CD-ROM].Gloucestershire Heritage catalogue record