German Glass Industry Report 04 on

German Glass Industry 28 After September 1945

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  Target No.
Map Ref.
Name of Target Rheinische Ziehglasfabrik A.G. (REZAG)
Address Porz-Urbach, Cologne.
Date of Visit 13th August, 1945
Products Sheet window glass.
Present Position Although shut down in March 1945 owing to interrupted fuel supplies, this Works had suffered no serious damage and was ready-to start up production units. Fuel was now being obtained but the raw material position, although stocks were at least 3 weeks for one of the larger tanks, was not settled; the smallest tank was being heated up and would start producing glass in 2 weeks' time. A second tank could be started up 1 month later but this would be determined by the raw materials supply position.
Key Personnel General Manager - Herr E. Schmit (Luxembourger)
Assistant Manager - Herr Andorfer
Accountant - Herr N. Zieger
Engineer - Herr Bruck
Furnaces, Plant, etc. 3 tanks including one with 9 Fourcault machines, a second with 6 Fourcault machines (it previously had 4 Pittsburgh machines), and a third with 1 Pittsburgh machine.
Employees Pre-war

Description of Plant, Processes, etc.

1. General

The Rheinische Ziehglas plant is the only factory in Germany at which the manufacture of sheet glass by the P.P.G. process is attempted. There were three tanks in the works as follows:-

German Glass Industry 29 After September 1945
No. 1 Tank - Large tank with 9 Fourcault machines
No. 2 Tank - Smaller tank with 6 Fourcault machines
No. 3 Tank - Small tank with 1 P.P.G. machine

The main point of interest here lay in the fact that, formerly, No. 2 Tank was equipped with 4 P.P.G. machines but owing to manufacturing difficulties which made the manufacture of glass by this method practically impossible, it was decided to convert the working end of the tank to 6 Fourcault machines.

Herr Schmidt was very open regarding the Works, past and present, and pointed out that while a much superior product should be expected from the P.P.G. method, the demand for glass in Germany was such that any experimental work is out of the question for a very long time.

At the time of the visit, shortage of fuel was preventing the operation of No. 1 Tank. No. 2 Tank was under complete reconstruction, while No. 3 Tank was being warmed up and would be in operation in 14 days' time.

This Works was not entirely self-supporting when in operation. Washed gas was bought from the neighbouring factory of Germania Spiegelglas A.G. and transferred by pipe line. When this arrangement was made it was thought that washed gas would be efficient for melting. Results very quickly proved otherwise and it was necessary to mix the washed gas with producer gas made on the premises. Cullet was also bought to specification from the same factory where it is produced from a special very small tank by means of a Chance type rolling machine.

2. Gas Supply

Apart from the above mentioned supply, there was a battery of five producers by “Demag” situated just outside the melting ends of the tanks. The producers were of automatic type inasmuch as the grates rotated and thereby helped the removal of the ash. The producers were hand fed with lignite briquettes from a hopper conveyed along an overhead rail. This type of producer was fitted with a chamber which prevented loss of gas during charging. The blast was worked at 50°C.

Gas Composition:- CO2 6.0%
  CO 30.0%
  CH4 2.0%
  H2 14.0%
  N2 48.0%

Each producer was capable of gasifying 20 tons of fuel per day.

German Glass Industry 30 After September 1945

3. Mixing Room

The stocks of raw materials were sound:- 2,000 tons of sand and sufficient soda ash for the small tank for 7 months.

The mixing room was built on the silo system, each material being housed in its own silo. All the materials were collected in one hopper fixed on an automatic scale and then transferred to an Eirich Mixer.

The batch was conveyed to the tanks on a monorail system. Cullet was also weighed.

  Fourcault P.P.G.
Sand 600 kilos 600 kilos
Soda ash 195 " 186 "
Saltcake 17 " 14 "
Limestone 95 " 60 "
Dolomite 85 " 130 "
Felspar nil 16 "
Anthracite 1œ " l "

Fill:- Batch 70%, Cullet 30%

4. Tanks

General All Corhart sides were preferred with Chamotte bottom blocks, with the exception of No. 3 Tank, which was equipped with Corhart side blocks, ordinary clay blocks were being used, made by Didier Werke, because of the impossibility of obtaining Corhart. The tank sides were air cooled from the start of the tank and at a later life, when the blocks were worse for wear, square section water pipes about 3 metres long were placed along the tops of the blocks from the front wall to the 2nd stacks underneath the springer blocks.

All the superstructure was of Dina3 (Silica) Brick.

Didier Werke regenerator bricks were used with straight passages and normal spacing. Two-piece floaters, made on the premises from French and Belgian clays, were used, one set to each tank. There were no skimming pockets but cleaning was carried out behind the floaters.

The melting end crowns were high and were dropped to a -lower height over the working ends.

German Glass Industry 31 After September 1945
Dyblie valves were used for the Gas and Forter valves for the Air. Reversal was carried out at 30 minute intervals.

No. 1 Tank

Capacity 1,000 tons Length: 28 metres
  Width: 6 metres 50 cm.
  Depth: 1 metre 20 cm.
Regenerators Length: 11 metres
  Height: 2 metres 80 cm.
  Width: Gas 1 m. 30 cm
Air 1 m. 75 cm.
Load 100 tons per day
Temperature by Optical pyrometer: Melting end 1,450°C
  Middle l,360°C
  Behind shut-off l,070°C
There were 5 stacks on this tank    

No. 2 Tank

Will be exactly as No. 1 Tank but comparatively smaller.

No. 3 Tank

Capacity 200 tons Length: 18 metres
  Width: 4 metres 50 cm.
  Depth: 1 metre 30 cm.
Load 17œ tons per day
Temperature by Optical pyrometer: Melting end 1,500°C
  Middle l,400°C
  Working end l,220°C
There were 5 stacks on this tank    

Under normal conditions with Corhart sides repairs occurred on Nos. 1 and 2 Tanks every three years (Fourcault manufacture) and on No. 3 Tank every two years.

The three tanks were built parallel to and adjacent to each other so that the top floor was common to all three tanks.

Drawing Kiln Claywork The tweel and shut-off are combined. These pieces together with L-blocks, L-shaped skimbars, drawbars and debiteuses were hand made, on the premises, from either French, Belgian or Grossalmerode clays, there being no preference for any of the three types. No experimental clay-work had been even thought of because of normal manufacturing difficulties. All the claywork was flat with the exception of drawbars, which were made concave to avoid seam lines.

German Glass Industry 32 After September 1945

Water Coolers These were 10" deep, grill type with pipes welded longitudinally. The front cooler was placed 1" from the glass, the back cooler œ" from it. Baffle plates from L blocks to tower were water cooled. Compression arches were not used. The curtain, rear and front “arches” were all rectangular one-piece blocks supported by an iron bar through the centre. They are not arched, but have a flat underside.

Towers These were gear driven by a vertical shaft from a motor on the 2nd balcony. The motor was not cooled, neither were the rollers nor the bearings. Asbestos for the rollers was bought outside in disc form, usually Canadian, but Russian asbestos had been tried. The Russian asbestos consisted of short fibres and was not therefore as good as Canadian. The bottom sections of the towers were very occasionally lubricated with paraffin and the top sections of the towers were with special oil for hot bearings.

The glass was cut off by the old “cut-off iron” method and after the edges had been removed on the cutting tables, the sheets were transferred to the warehouse on loose racks on automatic trucks, to be squared.

The warehouse cutting tables were very neat. They had rulers set in in two directions to measure both Metric and English systems. They were manufactured by F. Michanse at Lodelinsart in Belgium.

Machine Widths

Fourcault 6 m/cs. 1 m. 50 cms.
  2 m/cs. 1 m. 80 cms.
  1 m/c 2 m. 20 cms.
P.P.G.   2 m.

Speeds of Drawing

Fourcault 1.1 mm. at 90 metres per hour
  2.9 mm. at 42 " " "
  7.0 mm. at 9 " " "
P.P.G. 2.9 mm. at 48 metres per hour

7.0 mm. at 12 " " "

It was found impossible to manufacture any glass thinner than 2.9 mm. by the P.P.G. process. Herr Schmidt stated without reserve that the best Fourcault glass in Germany was manufactured at Witten.

The labour position at this factory was liable to be very difficult, insofar as skilled labour is concerned, for some considerable time. During the war Herr Schmidt, being a Luxembourger,

German Glass Industry 33 After September 1945

had as overseer to his management an ardent Nazi who, at the time of the Allied advance, ordered all the workmen into the Volkstürm irrespective of nationality. Since then nothing had been heard of a large percentage of the men thus directed. (A similar situation existed in other Works situated on the lines of Allied advances.)

German Glass Industry 34 After September 1945


  Target No.
Map Ref.
Name of Target Deutsche Libbey-Owens Gesellschaft für Machinelle Glasherstelling A.G. (DELOG)
Address Gelsenkirchen - Rotthausen
Date of Visit 10th August, 1945
Products Sheet glass
Plate glass (up to 1940 only, by grinding and polishing sheet glass.)
Present Position This Works could start production when it receives a supply of coke oven gas; it had three months' stock of raw materials. One tank was ready for heating up and its output would be 400,000 sq. metres/month; one month after starting this output could be doubled by bringing a second tank into production.

This factory is said to be a replica of the Libbey-Owens Ohio factory. It operated throughout the war producing sheet glass only from three tanks until March l945, when during an air raid, two tanks were damaged and one received a direct hit in the centre, causing a complete shut down of the factory. War damage elsewhere had been mainly to buildings, particularly to the brick shed and grinding and polishing department.

Key Personnel Directors - Maurice Hulin (Brussels)
Baron E. Jannsen "
Bank Director - Herr Atz (Berlin)
General Manager - Wilhelm Kesten (at present away)
Acting Manager - Dr. Lütgen
Production - Herr Krügerke
Maintenance - Herr Muhlert

We were shown round by the three last named.

K. Schmettau died in l943, L. Wenzel and G. Despret have left the Company.

Furnaces, Plant, etc. Three tanks with a total of six machines for

producing sheet glass by L.O.F. process. Disc grinding and polishing department with 16 tables and 20 polishers.

German Glass Industry 35 After September 1945
Employees Pre-war

Description of Plant, Processes, etc.

1. Gas Supply

The factory was situated in the grounds of the Dahlbusch Colliery and was supplied with gas from the Coke ovens of this Company. The gas was led in through the usual overhead main. It first of all entered a Wedekind centrifuge plant where the tar was removed by centrifuging and counter current washing with water. The gas then passed through a series of three towers. In the first, in which fresh water trickled through coke, hydrogen cyanide was removed. The second and third towers contained a 3% solution of sodium carbonate for the removal of hydrogen sulphide. (The sodium carbonate solution was later regenerated.) Before reaching the melting chambers the gas was diluted with air and boosted.

Composition:- CO2 2.0%  
  O2 2.0  
  CO 5.7 91.5% combustible
  CH4 25.4 (4,400 Cals. per cu. m.
  H2 60.4 ( 495 B.T.U's per cu. ft.)
  N2 4.l  

2. Raw Materials

Stock House The raw materials were stored in separate bins in an old building adjoining the mixing room. Present stocks were:-

Soda Ash (from Millingen) 600 tons  
Saltcake (from Duisberg) 300 tons  
Dolomite (from Bergisch-Gladbach) 700 tons (0 - 2 mm. grade)
Limestone (from Beckum) 900 tons (0 - 2 mm. grade)
Sand (from Haltern) 5,000 tons  

The materials were picked up by grab cranes and transferred to overhead bunkers in the mixing room.

3. Mixing Room

The materials were transferred from the overhead bunkers into separate bogies and weighed. The weighing machines gave direct weight as dial readings. The materials were then collected into one hopper and transferred to an Eirich mixer. The batch travelled along two chutes and up a lift to bunkers situated at the filling ends of the tanks.

German Glass Industry 36 After September 1945
Composition of Batch: Sand 58.6%
  Limestone 9.9%
  Dolomite 10.5%
  Soda Ash 17.5%
  Saltcake 3.5%
1 Batch = 850kg.    






The batch was calculated from dry material weights and made up to 5% moisture. Cullet of known composition only was used.

4. Tank Furnace

General All three tanks were of similar design., construction and dimensions.



Capacity: 1,250 tons Length: 38 metres
    Width: M.E. 10.5 metres widening at 6th stack to 14 metres
    Depth: 1.5 metres

Side blocks were in three courses - two bottom courses of blocks from Rheinischer Schamotte Werke and top course of Corhart. The Corhart blocks used were large - 80 cm. x 40 cm. x 40 cm. The tank bottom was Schamotte. Air cooling of blocks was only used towards the end of the life of the tank.

Stacks Six each side, air only regenerated. The gas was led by pipe line from the main through the stack necks and met the hot air at the port mouths. The ports were constructed with Dinas (Silica) brick. The first four stacks were worked fully open, the fifth restricted and the sixth was rarely used.

Crown Suspended crowns have been used but became very unpopular. Much trouble was caused changing bricks and eventually the crowns were converted to the ordinary sprung type except for ten feet at the working end. This section was left suspended so that its adjustability could be used for temperature control.

Regenerators Air only, of normal dimensions. Straight passages. Checkerwork constructed with Koppers brick.

Floaters One three-piece set at the last stack, 45 cm. deep.

Repairs Side blocks every two years. The regenerators gave much trouble during the latter months of the life.

Temperature Melting end 1,450°C by recording optical pyrometer. Drawing end 900°C.

German Glass Industry 37 After September 1945

Filling Arrangement The batch and cullet were dropped down from the large overhead bunkers into hoppers, weighed, and dropped to the pocket. The filling consisted of 80% batch and 20% cullet. Filling time - every 15 mins.

Machines Edge holding devices were not seen. The ribbon was drawn from glass four cm. deep. Each tank had two machines - a total of six in all. 10" coolers were used. After the ribbon had been formed it was bent over a series of 2 nickel rollers, the first of which was water cooled. The nickel bending rollers were changed every three days. These rollers were supplied by Krupps of Essen. The machine cycles continued from 6 to 12 months of uninterrupted life. Normally 8 mm. glass was manufactured, but thickness could be varied from 1 mm. to 32 mm. Width of sheet was 10' 6".

Speed of Draw
1.0 mm.
8.0 mm.
32.0 mm.
      180 inches per minute
16/17 inches per minute
1.5 inches per minute

production 7,200 sq. m. (77,300 sq. ft.)
per 24 hours on a 2 mm. basis

Lehrs These were 63 metres long, directly heated by gas.

The rollers, which consisted of asbestos discs mounted on a hollow iron shaft, were not cooled. They measured 3 m. 90 cm. in length x 14.2 cm. in diameter and were chain driven in pairs. They were hand lubricated. The first section of lehr rollers (40 rollers) was fitted with dry bearings on which graphite was used as a lubricant. The tops of the lehrs were insulated with Kieselguhr.

The lehr rollers were made up on the premises from asbestos supplied by Frowein of Berlin. Normally Canadian asbestos was used but the last consignment came from Finland.

Glass Cutting - Lehr End All cutting was done by hand. The cross cut was performed from the side of the lehr by means of a wheel cutter mounted on the end of a stick. The edges were cut off by hand at the lehr end, and the glass put into racks and transferred to the Warehouse by monorail.

5. Warehouse

There was only one cutting machine in the Warehouse. The Warehouse was fitted with natural lighting along one side only. The cutters' tables were situated on this side and each table was fitted with a cullet chute. The packing was done on the opposite side of the building.

German Glass Industry 38 After September 1945

6. Grinding and Polishing

The building was damaged but not the plant. There were 16 single grinders and 20 polishers arranged in two rows each of eight grinders and 10 polishers along the shop. Each table was a round disc with a square recess taking a plate about 2 m. x 2 m. Some of the tables were said to take plate 1.86 m. square and others 2.06 m. square. The retaining ridges on the tables were 8 mm. high. The glass was laid on linoleum or rubber, no plaster being used, and it was relaid for polishing. The grinding operation took 35 mins. per side and only three grades of sand were used (the glass was drawn sheet.) Sand was ground in a ball mill with flint stones before being graded. The grading plant consisted of six compartments, two for each grade, three funnel shaped divisions forming the under part of a larger container where the flow from division to division was 15 cm. in depth. Emery was not used. The consumption of sand was 10 tons daily. The “nogs” were 5" or 6" high and they lasted one month. They were supplied by Krupp from Essen and the Brinell hardness was given as 140.

Each polisher had 22 felts of various sizes arranged in 4. groups. The rouge was obtained from Bodenweise in Bavaria. Polishing one side was said to take 42 mins. The washing machine was described as of Libbey-Owens design. Its overall length was less than 20 ft. The design was simple and no acid was used.

7. Wages

At Gelsenkirchen teasers were paid 90 pfennig per hour, and these worked 4 sets, i.e. 42 hours weekly average. The machine operators received RM 1.50 per hour and all could earn in addition up to 10% of the base rate as bonus.

German Glass Industry 39 After September 1945


  Target No.
Map Ref.
Name of Target Deutsche Spiegelglas A.G. Werk Grünenplan
Address Grünenplan, Alfeld a/d Leine, Hannover
Products Sheet Glass (now)
Spectacle Glass (pot and Fourcault drawn)
Special coloured Plate Glasses
Lenses, watch glasses
Date of Visit 4th August, 1945
Present Position Re-starting part production 6/8/45 with renewed fuel supply. Will make sheet window glass by Fourcault and hand-blown processes. This is a new undertaking since previous production was of sheet spectacle glass. No production of pot glasses but good stock of pots. Stocks of lenses and watch glasses partly processed.
Key Personnel General Manager - Dr. Gerhardt Schott
(since September, 1943) Works Manager - A. Stahl Office - F. Albrecht Watch glasses - W. Krippendorf Sales - F. Schade (Dr. J. Hochhut, the pre-war General Manager, died in September, 1943)
Furnaces, Plant, etc. 1 one-machine (Fourcault) Tank
1 small experimental (Fourcault) Tank
1 ten-pot furnace
2 four-pot "
1 two-pot "
12 one-pot "
Other Plant Disc Grinding Shed
Moulding (lens) furnaces and presses
Watch glass sinking furnace and mould holders.
Bevelling (hand and machine) shop
Pot Rooms
Mixing Room
Power Station (A.C., not visited)
German Glass Industry 40 After September 1945
Employees Pre-war
  April - Aug., 1945 Production stopped, fuel etc. shortage
  August, 1945 200  

Description of Plant, Processes, etc.

1. Gas Supply

There are six gas producers of the revolving base automatic ashing type, but no automatic charging or agitating. The fuel feeding arrangement for each producer is the old “George” gas-tight bell with cover over the bell. There was very little gas leakage. The fuel, lignite briquettes (oval 4” x 3” x 1”) is brought to the bells in small bogies which run on butcher rails fed from overhead bunkers. The ash removal is a simple arrangement of a chute from each producer which feeds into small wagons running on rails the whole length of the battery at a level about 4 ft. lower than that of the water seal.

Steam and air were injected at about 55°C. saturation. Thermometers were fixed but no recorders. The gas was passed through a de-tarring (water scrubbing) plant (see Drawing l) before entering the main flue, the object of de-tarring being to prevent the flues from getting dirty. Dr. Schott said they never bum out the flues.

These producers are about the same size as Morgan or Chapman producers and it was said they can gasify 15 to 20 tons of lignite fuel per day. A gas analysis given to us as typical was:

CO2 5%
CO 20 to 25%
H2 10 to 14%
CH4 1 to 2%

2. Pot Furnaces and Casting Hall

The pot furnaces are regenerative with horse-shoe type flame, the ports and pull being on the same end. During melting a large horse-shoe flame between ports at either side of the backwall was used whilst during working the gases entered through both these ports and were exhausted through a third located in the centre of the backwall, giving a double horse-shoe flame. The gas and air meet just before entering the furnaces, the mid-feather being vertical. The combustion chamber was a simple square construction in silica bricks with a low crown of about 9” thickness with no insulation. Two pot furnaces were being warmed up at the time of our visit. There was no sign of any fire pockets and they had evidently been brought up with gas (de-tarred). The pot setting

German Glass Industry 41 After September 1945

machine was of the spade type pushed by hand but there was a set of tongs on a monorail for lifting the full pots from the furnaces and teeming. They can teem 4 to 6 pots per hour. There was one large casting table and rollers, the table being about 6 metres long by 4 metres wide. This was not water cooled, nor was the roller. The thick plates from this larger table were annealed in one or other of several single-plate kilns. Plates were pushed into kilns or the lehr by hand. It was stated that they could cast up to 30 mm substance on this table.

There were also two small Chance type rolling machines with narrow tables about 4 ft. wide which could be pushed in front of a roller lehr about 80 yds. long, wide enough to take the plates with the table length as the width of the lehr. It was stated that the rollers in this lehr were asbestos covered, but at the cold end they were wooden. This lehr needs repairing.

Founding cycles were stated to vary from 24 to 36 hours. With the plant being out of action, no personnel were available to give reliable details of cycles for particular glasses.

Pots average 30 founds when used for casting and sometimes 50 founds for blowing work. Pots are stored in a heated chamber near the arches before arching. Pot arches are top-fired, the flames passing over the pots (2 small pots or 1 large in an arch) and down the far side, the products of combustion returning across the arch beneath the bottom tiles.

At all furnaces and pot arche3 (which were gas fired) the gas, air and draught controls were neatly arranged in panels near their respective furnaces, with height measuring arrows, and warning bell pushes to the producers for gas quality and quantity variations; there was no automatic regulating device for gas pressure. The gas valves were of the old revolving drum type and the air valves were the butterfly kind.

3. Glasshouse Pots

The pots were made from a Grossalmerode clay mixture by the traditional German beating method.

Two clays from Grossalmerode were used and were said to be of the same composition, namely 22 per cent alumina content. They were mixed dry with 25 per cent of Steinberg-Bocksgraber grog and 25 per cent of potsherds. The grading of the grog was as follows:-

German Glass Industry 42 After September 1945
On 12 mesh sieve nil
" 12 - 17 mesh sieve 9.0
" 17 - 30 " " 32.6
" 30 - 60 " " 22.2
through 60 " " 36.0

The clay was wet mixed in a pug mill and “soured” for 6 months before use. The pots were built on very coarse grog and production was about 1 pot per day from each of 3 pot makers with 7 assistants. Total production was thus 18 per week and it was stated that 900 per year was a maximum. They were lifted from the boards after 4 weeks and tilted to enable the bottoms to dry. Temperature in one room was 75°F. and in a second containing dry pots it was only 60°F. Temperature was controlled but not humidity. In spite of the use of a clay mixture containing less water than is used for hand moulding and the fact that pots were lifted 4 weeks after manufacture, they were not used under 8 months. Both round (36” and 60” external diameter) and oval pots (of 1 ton capacity) were made. The wall thickness was rather less than in British practice, side walls being 3”. The casting pots had a slot for lifting moulded in the side walls all round. This slot was formed by moulding two projecting bulges so that the wall was strengthened rather than weakened. All pots were of this one mixture and no other clays were used, nor was quartzite added,

There was nothing novel about the German pot making. The pot rooms were clean, spacious and well laid out, and the pots were well finished.

It was stated that the average life of the pots was 30 founds with 50 as a maximum.

4. Other Claywork

Three sizes of debiteuses (25 cm. 64 cm. and 104 cm. slot length), gathering rings, flattening stones and large L shaped-blocks (for experimental tank) were also being made, all from the same Grossalmerode mixture. A core was used in moulding debiteuses.

5. Fourcault Glass Tanks

There are two tanks (1) Production Unit
  (2) Experimental Unit
German Glass Industry 43 After September 1945

Production Unit Fourcault Process. (For manufacture of Spectacle Glasses). This was a full width Doghole type tank with a capacity of 70 tons. The tank sides and bottom were built with Didier blocks, the sides being approximately 4. feet deep (full depth blocks) with 4” tuck stones of Didier material. The bridge wall was built with L shaped blocks manufactured on the premises - a rather novel construction giving a large cooling area between the sides of the bridge wall, and the glass flowing underneath. There were four ports each side - two each side at the Melting End side of the dog-hole and two each side at the Working End side of the dog-hole. These latter two were fed from one upcast.

The Melting End ports were of unusual construction consisting of 3 ways - air on top and underneath with gas in the centre; provision was made for air cooling the mid-feather arches. A drawing of these ports is attached (see Drawing 2) Small Dyblie type valves were used for reversing the gas and Butterfly valves for the air.

The Fourcault machine is 1 metre wide with no unusual characteristics. Provision was made at either side of the working end for hand blowing, there being one gathering hole at each side used in the production of blown watch and clock glasses (c.f. Mitterteich Report.) The machine cycle was 14 days between reheats. Tank life between repairs was 8-9 months.

Tank Temperatures: Melting End l,450°C.) Spectacle
  Working End 1,100°C.) Manufacture
  (Radiation pyrometer)
Production: 2œ mm. - 800 metres per day
  10 mm. - l50 metres per day

Experimental Unit This was an exact replica of the production unit on a small scale, except the crown which was suspended. The capacity was 22 tons. A miniature Fourcault machine giving 60 cms. wide sheet was installed and provision was made for blowing as in the bigger tank.

Debiteuses Two sizes of debiteuses were manufactured on the premises from Grossalmerode clay, a normal size 1 m. 20 cm. x l4 3/8” and a smaller size 80 cms. x 14Ÿ”. The slots are 1Ÿ” wide at the centre tapering to 1” at the ends. These are burnt to 900°C. -1,000°C. before use.

Unusual Features (i) Tank Side Cooling:- Full depth fish tail jets at all vertical joints between blocks.
  (ii) Melting End Ports:- Three way ducts.
  (iii) Working End Ports:- Divided at top of upcast angular.
  (iv) Dog-Hole:- Bridge Wall Construction.
German Glass Industry 44 After September 1945

6. Batch Mixing

The batch mixing house was well laid out and the arrangement for handling a large number of the different chemicals was good.

Dorentrup O.P. and O.P.B. sands were used with Sorne-Duingen for less particular purposes and all chemicals were kept in hoppers. A multibeam scale weighing machine was used for the batch used in large quantities. This batch was mixed in a horizontal rotating drum concrete type of mixing machine.

The most interesting feature of the mixing house was the method of handling the chemicals used for making coloured and special glasses. They were contained in a large wooden partitioned hopper which had wooden slides and a shelf with vertical partitions to prevent spill over. Each chemical thus fell on to a small counter from which it could be scooped up and it was noticeable that each chemical had its own scoop. Further, weighing was presumably accurate for there was a scale capable of weighing 30 Kgm. to an accuracy of 20 g. and other balances weighing to 1 g. or less. There was a small Eirich type of mixer and a very small hand mixing machine. Cullet for special glasses was stored in narrow vertical hoppers, there being a labelled hopper for each glass. As far as could be seen the unit system was not employed.

The following glasses were made:-
  Sheet glassSpectacle glass
Special coloured plate glasses used
as filter glasses, e.g. sun and
welding glasses.

The following list was taken from the 40 bunkers used for storing cullet and some of the compositions are given later.

Neophan 75 neutral sun spectacle
Fieuzal N3 yellow green
Neophan yellow  
R51. X-ray protecting  
Rosalin 4 )
Rosalin 963 )
pink glasses
Sinuval UV protecting
Pinkotit B light red
Ophtase 120 UV absorbing
Azurin Substitute 12 UV absorbing
Azurin Substitute 24 UV absorbing
Azurin Substitute 16 UV absorbing
German Glass Industry 45 After September 1945
Rosal 50 sun glasses
IMS 37)
" 300 )
" 301 )
NW 13 )
Colourless spectacle glasses
XCO UV absorbing screen
Green 206  
Flint-glass Fl 274
" Fl 273
Canary yellow  
Lemon yellow  
Brephos black glass  
USp 35  
RES 135  
Lead glass R51  
Dichromatik A, B, C and D yellow
Tintasan Al, A2 )
Bl B2 )
UV protective
Ultrasin 3  
Daylight blue 3  

No substitute for lead oxide or boric oxide had been employed neither was heat resisting sheet glass made.

7. Production of Watch Glasses and Pressed Lens Blanks

Watch Glasses were produced at the rate of 700,000 per month by a device with a rotating table which carried 25 - 30 moulds made of fine textured plaster material. The cut circles of flat glass were laid on these and rotation of the table brought them in turn within the firing zone causing the glass to sink to conform to the contour of the mould. Further rotation brought them out of the furnace when the glasses were removed from the mould supports and placed in a simple pan cooler. In another department they were edged by rotating a driven shaft (friction grip) against a revolving abrasive wheel, adjustable to control the extent of the bevel produced. Some 100 such machines were installed.

Pressed Opthalmic Lens Blanks The flat glass circle, preheated in a furnace through which it was moved step by step, was placed on a cast iron mould located below a pneumatically operated plunger having a suitably profiled nose to co-operate with the mould. Flames were directed on the glass and by operation of a handle the plunger was brought down. The pressed blank was then removed and pushed through a hole in the side of the work table to be delivered into a circular annealing pan forming the top component of a tower of such pans within a heated casing. When the top pan was filled, the bottom pan of the tower was removed through an opening in the

German Glass Industry 46 After September 1945

base of the casing whilst the weight of the other pans was held by suitable support fingers. The column was then dropped by handwheel and screw arrangement thus making room for the insertion of an empty pan at the top. No external heating was used. Production was stated to be at the rate of 2,000 blanks per shift per press and there were 19 such presses. A 4-head rotary press was also used.

8. Grinding and Polishing

This department comprised 6 normal grinding tables, about 8 ft. diameter each with two grinding runners and 4 polishing tables each with 1 runner fitted with a number of 15 in. diameter polishing felts. Sand was used for roughing and emery for smoothing. A transporter was provided for tables and mechanical gear for lifting tables off mushrooms. The layout was entirely conventional though small and old fashioned.

9. Glass Compositions

Since no-one was available during the visit to give reliable information on compositions, founding cycles, etc., Dr. Schott was asked to send, amongst other things, information on certain batch compositions by post. The following glass analyses were forwarded, however, instead of batches.

(i) Colourless Spectacle Glass SiO2 71.7
    Na2O 11.3
    K2O 4.5
    CaO 12.1
    Fe2O3 0.05 - 0.1
  The Fe2O3 content had been given earlier verbally as 0.03%
This glass was used during the war for searchlights and spectacles.
(ii) U.V. Transmitting Glass SiO2 68.6
    B2O3 2.1
    Na2O 5.0
    K2O 15.7
    BaO 5.8
    ZnO 3.6
    Fe2O3 0.01 - 0.02
  The Fe2O3 content had been given earlier verbally as 0.002%
German Glass Industry 47 After September 1945
(iii) U.V. Absorbing Glass SiO2 70.0
    Na2O 11.7
    B2O3 0.3
    K2O 5.2
    CaO 5.3
    Cr2O3 7.4
(iv) Lead Glass SiO2 30.7
    Na2O 2.1
    K2O 1.1
    PbO 65.3
    Ce2O3 0.3
    As2O3 0.5
(v) Welders' Glass SiO2 64.0
    Na2O 16.5
    CaO 9.5
    Sb2O3 0.4
    MnO 3.5
    FeO 1.8
    NiO 0.4
    Co2O3 2.4
    Cu2O3 0.8
    Cr2O3 0.4