Description of Plant, Processes, etc.

1. Mixing Room

The stocks of raw materials were:

There were two mixing machines (mortar mill type) and the batch from these machines falls into the boot of a short elevator which lifts the batch trucks placed underneath. The whole arrangement was connected with an exhaust system for dust removal, The batch bogies, of which there were a great number as many tints were made, were wheeled to the furnaces.

The following were the most important compositions:

to which was added: -

The above compositions were given in good faith without documents as nearly all the Company's books and records were said to have been destroyed during the seven weeks' time they were in the firing line.

2. Gas Producers

Rectangular brick type producer (Siemens). There were 16 bells arranged longitudinally down the centre line of the producer and it was stated that these could be worked four at a time. The fuel feed was by bogies run on “butcher” rails to the gas tight bells and each bogie was of the breeches type to feed two bells at a time. 18 tons of brown coal briquettes could be gasified per day. There was no water seal to the producer, and the blast at 45°C was blown through small hoods, the pipes going through the sides of the producer just above ashing level. The ashing was done by hand through small cast iron doors opposite each bell, at bottom level. There was very little (and this only fine) ash from the fuel used. Only one man per shift was needed. The gas was not washed or de-tarred and passed straight to the furnace without going through regenerators. There was no bum out, but once a year the flues were cleared of dust. There was no poking of the producer. There was an auxiliary suspended gas main which could be connected to the common gas collecting flue behind the producer but this was rarely used.

Gas control to the furnaces was effected from a “jump” box valve between producer and furnace.

3. Furnace Hall

There were two round recuperative furnaces each for 14 pots, but only one furnace was worked at a time. It was stated that the life of a furnace and recuperator could be as long as five years. All the glass for cathedral, ornamental and pressed ware was made in the one furnace and there were always different colours melting at the same time. The air only passed through the recuperator, the tubes of which measured 20 in. x 14 in. x 10 in. and were about 1 in. thick. These were supplied by the Didier Werke, and installed in horizontal fashion with socket joints.

The melting and working cycle was 24 hours, melting taking place at night and the glass being worked during the day, but there was no work on Sundays. The glass was ladled from the pots, the ladles being conveyed on a set of wheels to the casting tables. There were two Chance type machines about 1.20 m. in width and tables about 4 or 5 m. long (not measured.) Thicknesses of 2.3 mm. to 3.4 mm. were cast and on the average 6 of the 14. pots were used for cathedral and ornamental glass, the other eight being used for pressed ware. For most colours the practice was to work from darker to lighter shades by “curing” the pots with lump “arsenic”. The pot capacity was 630 litres or 1,450 to 1,500 kg. in weight and the melting temperature was l,480°C. measured with an optical pyrometer.

For pressing, the glass was also ladled from the pots to

feed 17 side-lever type presses and one Schiller machine. There were also two semi-automatic presses with 6 pressing positions each, but these were not used as they were considered to be uneconomical with pot furnaces and only suitable for tank work. The chief production lines in the pressing department were glass bricks, roof tiles and glass blocks for concrete structures. It was stated that a man could make 700 half bricks per day of eight hours of 2,400 round blocks for concrete roofs. Roofing tiles however were only made at the rate of 300 per man per day. These tiles were rather large, measuring 16" x 9" each; each were of different patterns.

Glass brick halves, were fused together, the fusing being accomplished using a mixture of 1 part of propane gas and 5 parts of air. There were six different sizes of machine. The half bricks were placed on a suitably shaped table and box burners containing many small jets about 1 mm. in diameter were pushed up into position by foot pedal round the sides of the brick. In 16 to 18 seconds the edges were soft enough to be hand pressed together. The bricks were removed from the press and sent in carts made of sheet iron to small kilns (there were 11) where they were annealed at 450° to 520°C. for nine hours, i.e., annealing and cooling time was 9 hours. It was said that a 75% vacuum was obtained within the bricks by this method. Bricks of the ribbed and also of the hammered pattern surface were inspected on the cullet dump as no stocks of any saleable glass existed.

4. “E” Cullet Marbles for Glass Fibre Production

This glass was made for Herzogenrath, but it was not certain whether the production would continue in future.

There was a small one-ton furnace like a large round pot constructed of blocks. There was only one burner, for producer gas. Melting took 28 to 32 hours and the glass was ladled from this furnace to a glass container about 1.5 m. long x 45 cm. wide which had a kind of feeder over the marble making machine which was now at Herzogenrath. This apparatus operated at the rate of 80 marbles per minute or 10 to 12 tons per month.

There were two glass compositions for “E” Cullet:

Moulds for pressed ware were made on the premises and also bought from outside. Ordinary close grained cast iron was used and no special alloy has been tried. The life of moulds was from 40,000 to 50,000 pressings. None of the work was fire-finished.

5. Pots

The firm did not make their own pots, these being produced at Herzogenrath, but they made clay work for furnaces, such as tweels, stoppers, blocks, etc. In the pot rooms there was a stone crusher for burnt clay, two horizontal mixers, and a pugging machine. They mostly use Strecksteiner clays.

General

The plant included a small 75 HP Lorenz-Mannheim boiler working at 12 Atm. pressure and a small dynamo generating 350 amps, at 230 V. when run at 350 R.P.M.

It was stated that most of the documents here were destroyed during the fighting as this Works was for seven weeks in the firing line.

Samples of cathedral and ornamental glass were taken.

Vereinigte Glaswerke

Sindorf Glaswerk

Figure 3

Anti-slip glass floor tiles in office corridor and on staircase

Description of Plant, Processes, etc.

1. Quality of Plate Glass as Received at Depot

The stock of about 10,000 sq. ft. awaiting processing consisted for the most part of a greenish glass. In selecting a plate suitable for examination as typical of silvering quality (with some preliminary re-polishing) three plates were first rejected for seed. The selected plate was good for seed and ream, but showed short finish; other plates showed polishing sleeks.

This organisation had no laboratory but had its raw materials and glass analysed by the Landesgewerbe Anstalt at Zwiesel.

2. Repolishing

This was done on a traversing table carrying two plates each about 6 sq. ft. in area and using two rotating square felts. A large repolishing shop containing several machines was completely wrecked.

3. Bevelling

There were three shops for bevelling. The first was an improvised one containing a number of rotating horizontal hollow cylindrical stones (5 ft. long, 3 ft. external diameter, 2 ft. internal diameter approximately) for edge grinding, the glass being held horizontal and stationary. A second contained small grinding wheels and further cylindrical stones working large quantities of small silvered glasses, six at a time. The third shop was not working owing to damage; the plant however was said to be undamaged and suitable for working ovals and large circles, for precision bevelling and for drilling holes 1/100th mm. bore.

4. Silvering

The warm process was used in a plant described with pride as unique in the world and continuous. It was installed in a shop approximately 50 ft. wide and 100 ft. long. A number of tables supported shallow lead troughs 9 ft. long x 4 ft. wide, and 4" deep and were capable of being rocked and run round the shop on a light oval track. Three tables were on the track but similar tables were outside; they were known as “Schaukel” tables. For cheap articles only one silvering treatment was given but for better quality (e.g. for export) two were given using 5 to 8 gm. of silver per square metre of glass. Prior to silvering the glass was washed with distilled water and stannous chloride solution. The protecting lacquer was put straight on to the silver, the use of copper being discontinued in 1936. Prior to the war, a cellulose paint was put

on by spraying but during the war they had turned to hand-brushing with a paint made from ochre and Dammar gum to which a little bitumen was added. Two coats were being put on and the preparation was in a can bearing a clean label “Fr. Megerle K.G., Friedberg, Hesse.” After lacquering the mirrors were placed on wheeled trucks 6 ft. x 3 ft. x 7 ft. high, constructed from tubes with 32 tiers of racks, the glass being supported on pyramidal cross laths; there were about 20 of these trucks in all. Normally they were pushed into one of six drying chambers, each holding one truck; these chambers were in the spraying room which was seriously damaged.

5. Other Processes, printing on glass, etc.

Small shops were working for producing metal and celluloid mirror frames, cardboard packages etc. A printing room was completely wrecked; this was said to have produced 80% of the radio scales used in Germany and much advertising work, printing in 14 colours from fine-textured lithographic stones. A glass quality intermediate between those used for glazing and silvering was said to be best for this printing process.

The glass leaving this depot was packed in solid cases using wood shavings. Sections undamaged included the case-making shop, the fitting shop and two Lancashire boilers burning brown coal, tar residues and coke breeze.

6. Samples Obtained

(1) Octagonal mirror 6Œ" x 6Œ", bearing present silvering and lacquering. (2) A small plate 6" x 4" said to be of pre-war silvering quality. No sample of pre-war silvered glass was available. (3) A small plate 5œ" x 4" (also said to be of pre-war silvering quality) showing differently worked edges.

Description of Plant, Processes, etc.

1. General

Annual coal consumption 15,500 tons.

Annual power consumption 2,000,000 K.W.H. for grinding and polishing, etc.

No electric melting was carried out. Normal output of rough cast plate glass 128,000 sq. m./annum, plus polished plate glass 100,000 sq. m./annum.

Substance range was 3 mm. - 14 mm. (occasionally 20 mm.) Prior to October 1944 only normal compositions were made, but in the last year of war a colourless glass from low iron sands and

chalk, using antimony as a decolouriser was manufactured, for producing circles for searchlight reflectors. These circles were 2.5 m. diameter, with a polished thickness about 20 mm; at first they were ground and polished before bending but later they were bent first. Some of the circles in stock were of greenish glass.

2. Gas Supply

There were three “Demag” static producers with rotating grates to facilitate ash removal. Top poking was carried out by hand. Each producer was fed through a central gas tight bell. The fuel used was raw brown lignite - not briquettes. The blast, at a temperature of 58°C. was fed through an ordinary type blower. Two producers were always in use with one on reserve. Each producer would gasify 16 tons good coal or 21 tons poor coal per 24 hours.

3. Mixing Room

This was a very old building with no attempt at modernisation. Eight per cent. of saltcake was mixed with the soda ash before delivery. Each material was stored in separate bins but all the materials were collected in the same bogie and weighed on a dial type weighing machine showing direct weight. They were then delivered along a track to an old “concrete” type mixer. The batch dropped from the mixer on to a sieve - approximately œ" mesh - into a bogie.

This batch was for colourless Plate. Ordinary Plate was made from a slightly different batch in which the Ammonium and Sodium Nitrates were replaced by 12 grams of a mixture of 1 kilo Nickel Oxide and 10 kilos Sand.

4. Tank Furnace

The tank had a waist 3 metres 20 cm. wide, and had a square ladling end provided with five ladling holes across the end wall, with a monorail to each hole. All tank blocks were of Didier Werke Chamotte. The sides were constructed in two courses - 50 cm. deep top course on a 70 cms. deep bottom course with 4" tuck stones. The tank was heated with a “horse-shoe” flame.

Stacks There were two stacks built on the front wall of the tank. The gas and air were both regenerated and reversals took place every half hour. A Dyblie type valve for gas and Porter valve for air were used. There were no midfeather arches so that the gas burned well back in the port at the top of the upcast.

Crown Sprung type, of Dinas (silica) from Didier Werke.

Regenerators Horizontal

The regenerators ran underneath the tank and the gas and air entered underneath the working end. They were stuffed with large square bricks also by Didier Werke, giving very large straight horizontal, but no vertical passages. The bricks were 8 cm. thick.

Floaters There were two sets of two piece floaters made of Grossalmerode clay. One set was fixed midway between the front wall and the waist; the second set at the entrance to the waist. They were held by lug blocks.

Springers A feature of the tank construction was the very large size of springer block used. Each block was 64 cm. long, 12 cm. wide, and 20 cm. deep. The thickness of the nose was 22 cm. and its depth 26 cm. They were keyed together by means of a flange and rebate.

Filling Arrangement There were two small filling pockets, one at each side of the tank. Filling was done by hand. No definite percentages of cullet were filled - the largest amount of cullet available was used. The cullet and batch are shovelled from the

floor. Filling occurred every half hour on alternate sides of the tank, always on the “pull” side to prevent dust from getting down to the ladling end.

Ladling There were five ladling holes across the square ladling end, each fitted with a monorail. Ladle rings were not used. The ladles held 70 to l50 litres of metal.

Tank Repairs When the side blocks become thin grillage water pipes are fixed down the inside face of the top course blocks. The top course blocks have in the past been renewed during hot repairs every 7 or 8 months. Complete side block and port repairs were carried out after 2 years running.

5. Casting Machine

The casting plant resembled a Bicheroux one but was smaller; it was designed by Rudolf Simon who was at one time engineer to Bicheroux. Oval ladles holding 70 - 150 litres molten glass were brought by an overhead monorail from the tank to the machine for casting on to the one table. The table was of Chance type with slight modification. It consisted of a pair of large diameter rollers and a water cooled flat tray. The table moved along under the machine to receive the plate of glass as it was formed through the revolving rollers.

Roller details:-

The roller surfaces were turned down only during tank repairs. All rollers were contoured - concave.
The machine rollers and the table were driven by separate motors, synchronised by resistances.
All rollers were supplied by Machinfabrik Augsburg Nürnberg (M.A.N.)

Casting Fine sand was used on the casting table. The plates were 3.4 m. long by 2.2 m. wide by 8 mm. thick and the width varied with the thickness.

6. Lehr

At present this had all the kiln bed blocks out for redressing; the blocks were supplied by Grossalmerode from Grossalmerode clay and had a veneer. The plates were moved by hand into and from the first three positions, being transferred by a single pipe system (bearing six slippers) from the fourth kiln position to the rails, on which there were sixteen positions. The kiln had a shadow wall before the second position. The rails lifted and moved and then lowered the plates on to blocks placed between the rails along the whole length of the lehr. Dirty gas was used for annealing. The lehr length was 50 metres. The drawing end cutting table could be tilted.

7. Bending Kilns

There were three bending kilns for producing 2œ m. diameter searchlight reflectors, taking large cast iron moulds, with a combined output of 20 to 24 per month, and two for bending Plate glass.

8. Grinding Shed

This contained four grinders, five polishers and fifteen tables 3.8 m. diameter, with one central transporter. The glass was laid on cloth and set with plaster. The grinding sand was obtained from Roding and the rouge from Bodenweiss. No emery was used. The average grinding time was 60 mins. and polishing time 70 mins. All the grinders and polishers were belt driven from one motor except one pair which were on a separate motor. The polishers were enclosed with wooden panelling to retain heat. There was one large repolishing machine. After polishing the glass was hand washed using water only.

9. Warehouse

There was only one examining frame (backing on a window) and one cutting table; there was said to be only this one examination before packing unless the glass was to be used for silvering. A piece of silvering glass when examined was considered to be good for ream and fair for surface but poor for seed. Packing was done in solid cases placed on a tilting table and using wood wool. The stock of rough cast glass was said to be 20,000 sq. m.

Description of Plant, Processes, etc.

1. Gas Supply

The factory had always been well supplied by coke oven gas because the Company is the owner of a coal mine and coke oven. Two “Demag” producers had been provided but were never used and both were destroyed by bombing.

2. Mixing Room

This was very antiquated. (The building is in such a dilapidated condition that Dr. Hermannsaid that he wished it had been destroyed during the air raids rather than other parts of the plant.) Drawings had been prepared for a new one but the outbreak of hostilities had prevented its erection. All the raw materials were measured by volume and not by weight and the mixer is a very old type of mortar mill.

3. Pot Process

The production of normal plate glass was discontinued in this Works in 1932. A good stock of pots (300-400) was still available. These pots were made about 15 years ago from French and Belgian clays. The pot furnace, originally for 8 small pots, was converted to take 4 larger size pots.

The casting hall contained the machines used prior to 1932: 1 machine with a stationary table and moving rollers and 3 machines with stationary rollers and moving tables. (Two of these were used for pot glasses and one more recently for glass from a tank.) In all cases the glass was ladled to the machine. Each table was approximately 20 ft. by 5 ft. The plates were stowed by hand into a lehr consisting in part of a kiln bed and in part of moving rails.

The pots were made from a mixture containing 50% burnt clay and had a wall thickness of 12 cm. at the top and 13œ cm. at the bottom; they were said to have a capacity of 700 litres and a life of 40-60 founds.

The blocks made (by hand) more recently contained 67% grog.

4. Continuous Flow Tank

The tank was of unusual construction. The filling pocket was situated at the side of the melting end and the drawing machine at the side of the working end diagonally opposite to the filling pocket. There were two stacks, one at each end of the tank so that the flame travelled along the tank and not across it.

The cullet and batch were received in bogies along a monorail system and the “lumps” pushed out by hand.

The bottom blocks and side blocks (three courses) were made on the premises from French and Belgian clays. Grossalmerode could be used but was not the other clays being preferred in general practice. The superstructure (sprung crown) was of Dinas (silica)

bricks. The tank was repaired every nine months. Soda ash and saltcake were used in the proportion of 50:50. Floaters were not used.

5. Rolling Machines

Boudin type. Width of ribbon 1 metre 20 cms. (48")

Rolling speeds

Wired: 1 metre 20 cms. per min. 6 - 8 mm. thick - 48"/min.
Rough Cast: 2 metres 20 cms. per min. 5 mm. thick - 86"/min.
Cathedral: 3 metres per min. 3.5 mm. thick - 116"/min.

Casting Rollers There were two types of top rollers; one type contained Chromium and Nickel (percentages not known), the other type was electro-cast steel. The bottom rollers were cast iron. Top and bottom rollers were driven from one motor. All were supplied either by Krupps of Essen or Ruhrstahl of Witten.

There was one flat tray and two tray rollers (water cooled)

6. Lehr

This was 90 metres long. All the rollers were cast iron and the first thirty were water cooled by means of hairpin pipes. Hand lubrication was used. The lehr rollers were gear driven.

7. Wired Glass Production

1. Square mesh (Georgian) 6 mm. square. The wires were not welded. All the glass examined from previous operations was very poor for bubble, dirt and very badly distorted wire, partly due to the strands not being welded.
2. Square mesh (Georgian) 12 mm. square. The wires were spot welded. Here again quality from previous operations was very poor for bubble, dirt and distorted wire.
3. Hexagonal. Very small quantities of hexagonal had been produced. Generally poor for bubble.

All wire was bought from either Brüne of Dorsten or Pieper of Hohenlimborg near Hagen, in 100 metre rolls.

8. Cutting

All wire was cut with selvedge edges. The centre and edge cuts were made with mounted fixed wheels. The cross cut was made by hand from the side of the lehr. The cut was “run” by raising the ribbon slightly underneath the cut. The ribbon then passed to lehr rollers fitted on a table, the front edge of which was attached to a pulley in the roof by means of wire ropes. The wire mesh was broken by lifting the table to an almost vertical position.

Both top and bottom surfaces of wired glass were clear (smooth rollers) and the machine was changed every seven days to reduce top surface defects. Pattern machines were changed every three days or earlier according to the demand for the pattern.

Some ribbed wired glass was manufactured.

All packing was carried out at the Lehr end.