Forging aircraft parts at 30,000 tonnes

Joseph Bramah of London patents the hydraulic press in 1795. A small hand pump forces water, a little at a time, into a strong cylinder under a large ram. The force on the ram is the water pressure times the ram's area, so a small effort on the pump gives a very large force on the ram, which moves only slowly.

Blaise Pascal had described the principle more than a century earlier. Bramah's difficulty was keeping the water in: it leaked past the ram until his workman Henry Maudslay fitted a cupped leather collar, which the water itself pressed tight against the ram.

In 1861 John Haswell brings a hydraulic press into use for forging hot metal at the Imperial State Railway works in Vienna, and patents it. In Manchester, Joseph Whitworth's works also turn from the steam hammer to the hydraulic press for forging steel.

In 1874 the American engineer W. P. Blake describes the Vienna presses. The larger, with a ram 24 inches (61 cm) across, exerts 1,200 tons; the smaller, with an 18-inch (46 cm) ram, 600 tons. The pumps work at 600 atmospheres.

The Bethlehem Iron Company in Pennsylvania completes a 14,000-ton hydraulic forging press in 1893, built under the direction of John Fritz, to forge armour plate and heavy gun parts. It has two cylinders, each about 50 inches (1.27 m) across. The company gives up the 125-ton steam hammer it had built only a few years before.

Presses of this size stay rare. In 1948 an American engineer counted six 14,000-ton forging presses in the world, five in the United States and one in Germany, installed by Krupp about 1930.

Eduard Schloemann, an engineer from Cologne, opens a business selling fittings and steam traps in Düsseldorf in 1885, and in 1901 founds the partnership Eduard Schloemann OHG. About 1908 a fast-acting hydraulic control of the firm's own design, mainly for presses, sells in large numbers.

The engineers Paul Multhaupt, from 1909, and Ludwig Loewy, from 1914, turn the firm to designing complete hydraulic press plants: more than 100 are delivered by 1918. From 1915 Schloemann works with MAN on building presses; it adds rolling mills in 1920 and becomes a joint-stock company, Schloemann AG, in 1921. It remains a design office: other works make the parts of its presses.

By 1930 most light-metal die forgings are still made under hammers, and the largest hydraulic die-forging press, in Germany, is rated at 7,000 tons. In 1931 the Soviet Union orders a die-forging press for light metals of 16,500 short tons (15,000 tonnes) from Schloemann. It is built under the direction of Hugo Lorant, then Schloemann's chief hydraulic engineer.

In 1934 the British Air Ministry orders a press of the same size from Schloemann for James Booth Ltd in Birmingham.

Ludwig Loewy, Schloemann's chief engineer and the owner of 45 per cent of its shares, is Jewish. Facing growing discrimination, he leaves Düsseldorf for London early in 1936 with Hugo Lorant and other Schloemann staff, and on 1 April founds the Loewy Engineering Company there. On a brief return to Düsseldorf he is warned that the Gestapo is after him, and returns to London the same day. The Gestapo charges him in his absence with taking the firm's drawings and know-how.

Schloemann's other shareholders are MAN and the Gutehoffnungshütte (GHH) group, which controls MAN. In 1939 GHH obtains an order forcing the transfer of Loewy's shares for a nominal 1,287,593 Reichsmarks, paid into a blocked account. Schloemann is "Aryanised", taken out of Jewish ownership, and passes under GHH's control; its published history is rewritten without him.

I.G. Farbenindustrie's light-metal works at Bitterfeld, in central Germany, melts, extrudes and forges magnesium and aluminium alloys. Late in 1938 a Schloemann die-forging press of 15,000 tonnes (16,500 short tons) goes into service in its North Works.

In a die-forging press the hot metal is squeezed between two shaped dies until it fills them, so the part comes out close to its final shape.

Late in 1939 I.G. Farben's light-metal department plans a press of twice the force: 30,000 tonnes (33,000 short tons). Its director, Dr. Hubert Altwicker, receives permission to build it in 1940, and I.G. Farben pays for it. Schloemann designs the press, under the engineer Henry Albers, and builds it at Bitterfeld in 1942–43.

The design sets two 15,000-tonne press frames side by side under one pair of long platens. The press has eight columns and eight main cylinders, and stands 16 m (52 ft 6 in) above the floor and about 8 m (26 ft) below it. Every large part is built up from sections.

Two more Schloemann die-forging presses of 15,000 tonnes are built in Germany, designed under Henry Albers. They do not stand at Bitterfeld. One is at the Hannover-Laatzen works of the Vereinigte Leichtmetall-Werke (VLW); where the other worked is not established.

With the 30,000-tonne press they complete Germany's series of heavy die-forging presses. When the war ends a still larger press is on the drawing board.

By May 1943 the press stands in the new press building of Bitterfeld's North Works, beside the 15,000-tonne press. A German engineer who worked there later dated its first operation to July 1943; Altwicker told the Americans it went into production in 1944. The press is said to have cost 12 million Reichsmarks; Altwicker put the building, the press and its furnaces together at 15 million.

The cast-steel press beds give trouble: Alexander Zeitlin, who later worked with the press's designers, recorded that two beds failed before a third design held.

The Arolsen Archives, the international archive on Nazi persecution, hold personnel documents of Schloemann AG, Düsseldorf, for employment from 19 August 1943 to 5 March 1945. They are filed in the series on the registration of foreigners and the employment of forced labourers, and came to the archive from Schloemann's successor, SMS Schloemann-Siemag. The catalogue gives no names, numbers or nationalities, and the documents have not been read for this exhibit.

Schloemann's controlling shareholder, the Gutehoffnungshütte group, employed about 31,500 forced labourers at its peak in 1944, nearly a third of its workforce: 22,400 foreign civilian workers, 8,400 prisoners of war and almost 700 concentration-camp prisoners. Whether these figures include Schloemann is not stated. How many forced labourers worked for Schloemann, where they came from and how they were treated is not yet known.

The 30,000-tonne press first forges large parts of gun carriages for heavy artillery, to make the guns lighter. The two big presses are then used mostly for propeller blades in Duralumin, an aluminium alloy, the large press making two at a stroke. The plant's forgings include propeller blades for the Jumo 213, DB 603 and BMW 801 aero-engines, supercharger impellers, cannon frames and engine mounts.

From 1944 the shop develops tapered wing spars forged in one piece. By the end of the war it makes spars 6 metres long in series; spars of 10 metres are not mastered.

Short of workers, the I.G. Farben works at Bitterfeld and nearby Wolfen use foreign forced labourers, prisoners of war and concentration-camp prisoners. The Arolsen Archives hold the personnel cards and work books of foreigners employed by I.G. Farben at Bitterfeld-Wolfen from 1940 to 1945. Across the whole I.G. Farben concern, its camps held 70,543 foreign civilian workers and 14,156 prisoners of war in February 1943.

On 13 July 1944 the Buchenwald concentration camp tells the SS that 750 women are to be put to work not at Wolfen but at the Bitterfeld works. A subcamp of Buchenwald beside I.G. Farben's film factory at Wolfen held hundreds of women under SS guard. Of the press shop itself, the only statement found is a German engineer's:

Who these workers were, how many there were and how they were treated in the press shop is not known. Whether the 750 women came to Bitterfeld, and where they worked, is not recorded in the sources read.

On 16 January 1945 a low-level air raid on the I.G. Farben works at Bitterfeld kills 150 people. Whether the press buildings are hit is not recorded; in June an American report describes the plants as for all practical purposes unbombed. Work on the 30,000-tonne press goes on until the middle of April. On 21 April 1945 American troops reach Bitterfeld and close the works.

In June 1945 Allied intelligence teams visit the works: Lt. J. C. Wills of the US Navy for the Combined Intelligence Objectives Sub-Committee (CIOS), and a British team from 25 to 28 June. American teams take the blueprints of the 30,000- and 15,000-tonne presses, and US authorities remove the tools and finished forgings. General K. B. Wolfe, later the originator of the US Heavy Press Program, is among the Americans who inspect the German presses.

A US technical mission reaches the 30,000-tonne press with orders to move it west or blow it up. It cannot move the press at short notice and leaves it standing. Bitterfeld lies in the zone agreed for Soviet occupation; at the beginning of July 1945 the Americans withdraw.

Large magnesium forgings found in captured German aircraft show that Germany is forging parts larger than Allied methods can make. In 1944 the US War Production Board decides to build a closed-die press of 18,000 short tons (16,300 tonnes), made by the Mesta Machine Co. of Pittsburgh, for a new Wyman-Gordon plant at North Grafton, Massachusetts. The war ends before it is finished, but the work goes on: the plant is completed in 1946, built around the press, then the largest press built in the United States.

A German 7,000-tonne press later joins it as supporting equipment.

Bitterfeld is in the Soviet zone, and its presses go to the Soviet Union as reparations. Dismantling of the 15,000-tonne press begins about 20 March 1946, and of the 30,000-tonne press on 28 March. The eight cylinders cannot be drawn out of the top crosshead, so the crosshead travels in sections with two cylinders still in each, about 137 tons a load, on special railway wagons built for transformers, each hauled by its own engine at 10 km/h.

Up to 2,000 men work on the dismantling. From late June to early September 1946 the equipment of both press buildings leaves for the east. The steel frame of the building that housed the 30,000-tonne press is taken down in July and follows it. The work ends in April 1947.

The United States obtains the two other 15,000-tonne presses as reparations, arranged by General Wolfe, with smaller German presses. One comes from the VLW works at Hannover-Laatzen. They are shipped in 1948 and re-erected, one at Alcoa's works in Cleveland, Ohio, the other at an Air Force plant at Adrian, Michigan, run under contract by Bohn Aluminum. By 1953 both are in operation.

What became of them after the 1950s is not recorded in the sources read.

The Bitterfeld presses are re-erected at Plant No. 268, an aircraft-parts plant at Kamensk-Uralsky in the Urals, inside the steel frame of their old building, enlarged with two new wings. German specialists arrive in July 1949 to help with the assembly. The 15,000-tonne press is assembled from autumn 1949 to spring 1951, and the 30,000-tonne press is ready in 1951; it forges propeller blades again. The new building, for large forgings and extruded sections, opens on 14 September 1951.

The 15,000-tonne press fares badly. A guide plunger breaks within three weeks, then cylinder casings crack, cutting its force to between 5,000 and 7,500 tonnes. The casings had already given trouble at Bitterfeld.

With the 30,000-tonne press in Soviet hands, the US Air Force begins its Heavy Press Program in 1950, with General Wolfe as its originator. By 1957 it has built four forging presses, two of 50,000 short tons (45,400 tonnes) and two of 35,000 short tons (31,800 tonnes), and six extrusion presses of 8,000 to 14,000 short tons.

Two of its engineers come from Schloemann. Hugo Lorant, who built Schloemann's first giant die-forging press, is vice-president for engineering of Loewy-Hydropress, and Henry Albers, who designed the wartime German presses, is its chief engineer for the programme. The Loewy Construction Company designs and builds the two forging presses for Wyman-Gordon.

The programme's forging presses start work in 1955. At Wyman-Gordon's North Grafton plant, Loewy's 35,000-short-ton press begins in February and its 50,000-short-ton press in October. At Cleveland, Alcoa runs Air Force Plant 47 from 5 May 1955, with a 50,000-short-ton press by the Mesta Machine Co.; Alcoa and Wyman-Gordon each also receive a press of 35,000 short tons.

The Mesta press stands 26.5 m (87 ft) high, 11 m (36 ft) of it below the floor, and is driven by eight cylinders with water at 310 bar (4,500 psi): much like the Bitterfeld press in height and number of cylinders, with half as much force again.

The first part forged on Wyman-Gordon's 50,000-ton press is a landing-gear support rib for a Lockheed Super Constellation; an aluminium wing spar for a Century-series fighter follows in 1956. Magnesium, the metal that started the programme, gives way to aluminium alloys and later to titanium and steels.

For the Boeing 747, Wyman-Gordon forges a main landing-gear beam in titanium, 6 m (20 ft) long and over 1,800 kg (4,000 lb), in place of an assembly of many parts. At Cleveland the Mesta press forges titanium bulkheads for the F-15 fighter.

After the war Schloemann turns to the continuous casting of steel, working with the Concast company from 1956. In 1973 it merges with Siemag of Siegen to form Schloemann-Siemag AG, with the GHH group holding 51 per cent. The company has traded as SMS group since 2015.

A 65,000-tonne die-forging press built in the Soviet Union is inaugurated in 1977 at Interforge in Issoire, France, the largest outside the Soviet Union; by 1983 two presses of 75,000 tonnes are working in the Soviet Union itself. China National Erzhong Group's 80,000-tonne press at Deyang, 42 m tall, is ready by 2012. In 2018 SMS group, Schloemann's successor, completes a press of 540 meganewtons (about 55,000 tonnes, or 60,000 short tons) for Weber Metals in California.

Plant No. 268 is now the Kamensk-Uralsky Metallurgical Works (KUMZ). In April 2010 it signs a contract with Uralmash to modernise its 300-meganewton (about 30,600-tonne) die-forging press made by Schloemann, still the most powerful press at the plant. Uralmash has already made new frame parts and repaired the press's crown; the new hydraulic controls come from Oilgear of the United States. The modernised press is restarted in May 2012.