Work carried out at the Depot The stock of raw glass was mainly destroyed by bomb damage, only 1,000 sq. m. remaining; the stock of silvered glass amounted to 4,000 sq. m.

There were about 20 repolishing machines consisting of traversing tables running under square rotating felts, one to each piece of glass.

Several small rooms were devoted to bevelling etc; one contained the long horizontal cylindrical stones for general work. A second contained four grinding and two polishing machines for bevelling small circles, each machine working 18 discs at a time; a small continuous machine brushed, washed and dried the finished circles.

A cold silvering process was operated using rocking tables 9 ft. x 6 ft. Using two baths of silvering solution, it was said that 6 grms per sq. m. were poured on the glass, but only 3 grms remained, the other 3 being recovered from the washings. Electro-deposition of copper after silvering was rarely carried out. Varnishing was done by a machine with rubber rollers, the varnish being obtained from various suppliers. Previously, the varnish took 24 hours to dry but during the war an inferior kind was used which required 3 days. Glasses to be bevelled after silvering had two coats of varnish applied before bevelling.

There were two Lancashire type boilers working at 10 kg. per sq. cm. pressure and a small generator for providing power.

The quality of the glass in stock was poor.

Description of Plant, Processes, etc.

1. Gas Supply

Gas was received by direct pipe line from the coke ovens at Dortmund. The pressure was boosted and the gas diluted slightly with air before being delivered to the tank furnace.

Calorific value 4,000-4,200 Calories per cubic metre (450 B.Th.U's per cubic ft.) Present consumption 60,000 - 70,000 cubic metres per 24 hours.

The gas quality at the time was very variable and rather low in quality owing to the small demand, caused by inoperable factories, from the coke ovens.

A special Orsat apparatus was used for gas analysis, and with this type the C_mH_n could be determined separately.

2. Mixing Room

Batch Materials All materials were received in wagons and stored in silos in the Mixing Room. The sand was picked up by grab and dropped on to a sieve, which is operated by means of a vibrating machine, and thence into the silo. The dolomite was shovelled into a small boot and sucked into the silo pneumatically. The limestone and sodium compounds (carbonate and sulphate) were sucked pneumatically into their respective silos direct from the wagon. The sucking device consisted of a nozzle coupled to a pipe line (flexible) which was made up of seven-foot lengths, so that any particular length of pipe line could be changed with ease. The device was operated by two men and could deal with materials at

Each of the materials was weighed on its own scale direct from the silos. The weighing machines were ordinary type "potato" scales, and the materials were transferred to the mixer along a belt running below floor level.

The batch was mixed in an Eirich Mixer and transferred to a large hopper at the melting end of the tank by means of a bogie which automatically travelled vertically then horizontally over the hopper and tipped all in one operation.

Cullet was bought externally, irrespective of composition. This was washed and transferred to a large hopper situated adjacent to the batch hopper.

All the mixing was done during the day time. Batch:-

The batch was based on dry materials, and moisture in sand and dolomite was controlled. All the materials used were fine grade and are ordered to a fixed specification; they were examined in the laboratory on receipt.

Filling Arrangement Fillings consisted of 30% cullet, 70% batch, charged every half hour by means of a large ladle rigidly fixed to a rotating tower on an overhead crane track. The ladle was filled at the cullet and batch hoppers and the materials were dropped on to the pocket without manual effort. (See Figure 1)

Glass Composition This was quoted as follows:-

All analyses are carried out at the Weiden Factory.

3. Tank Details

All tank blocks by Didier Werke. Tank sides 3 courses with 4" tuckstones. The very neat strapping arrangement for side blocks consisted of a thin iron bar fastened to brackets on buckstaves.

Stacks ("Uptakes") Eight each side. Single stacks - air only regenerated. The coke oven gas was led by pipe line from the main through the stack necks and therefore only met the air at the port mouth. The ports were constructed with Dinas (Silica) bricks. All eight stacks were opened but only Nos. 1 and 2 fully. Stack restrictions started at the 3rd and gradually increased down to the 8th. Very short non-luminous flames were obtained.

Crown Suspended type, flat arch, 1 metre 50 cm. above metal level at front wall. Constructed to a curve, longitudinally, to between 2nd and 3rd stacks then completely flat and sloping down to working end, finishing at a height of 35 cms. above metal level (See Figure 2)

Each block in the crown was suspended separately and was interchangeable. The joints were buttered with ordinary clay. The crown was covered with drippers.

Arched crowns have been used on this tank, but the flat crown has been reverted to because of the lower fuel consumption with this type of crown.

Regenerators

Regenerator bricks were by Didier Werke. They were set with wide spacing from the melting end down to 2nd and 3rd stacks then followed normal setting practice. Checkerwork not staggered. The regenerators were cleaned once each week and the dross was scraped off the top of the checkerwork. They were said to last for years.

Floaters Two sets were provided, of Grossalmerode clay 50 cms. deep. One 3-piece set at 8th stacks gave a life of 8 weeks and the other, a 2-piece set at the working end gave a life of 6-7 months. The joints were very neat - Just a small semi-circular flange and cut-out to match.

Floater lugs were not used. The floaters were set in the tank sides by means of thinner top course side blocks.

Tank Temperatures

Machines Debiteuses, Underbridgea and shut-offs all Orossalmerode clay. Machines vary in width from 2 metres 10 cm. (83") to 1 metre 35 cm. (50"). Debiteuse - 8Œ" deep, 13Œ" wide, slots 2 3/8" at centre, tapering to 1" at ends. The debiteuse life was 4 to 5 weeks. The edges were held by means of a small iron U-shaped clamp and not by Sindanyo.

The machines were stopped every 5 to 7 days for reheating.

The tower rollers were asbestos discs with solid iron core and were driven by a vertical shaft from the top floor.

Machine Speeds

One machine only was provided with an automatic cutting table. This table was set at a lower level than the cut-off platform. The breaker off rested the bottom edge of the sheets on the table and dropped the sheet on to the flat. A cutting frame with discs of wheels ranged the sheets and put cuts along the edges.

The quality of the glass being made was very poor for lines. Blisters, too, were prevalent.

Present output 6 machines - 10,000 sq. metres (107,600 sq. ft.) per 24 hours.

General The tank was not brought up from the cold by means of coal fires but was heated by gas from zero to melting temperatures. During the winter months the waste gases from the tank were passed through a waste heat boiler to generate steam for works heating.

4. Clay Rooms

Debiteuses were the chief products made. The mixture for these consisted of raw Grossalmerode (Osmosed) clay with an equal part of the burnt clay bought to a grading specification, no additional silica being added. The records gave the following gradings for the two grogs purchased, the finer being used for debiteuses and the coarse for burnt blocks, tiles, etc; the screens were those specified in DIN 1171.

The mixture was made up, wetted and tempered in the usual way and the debiteuses moulded by hand using a core which did not, however, shape the slot. This was subsequently cut out when the article was dry, using a bench which contained duct-connected bins

Debiteuses were arched in two stages. They were heated up to 1,150° C. during 7 days three at a time in a small arch, the hearth of which was the top of a moveable car. If not required immediately, the debiteuses were transferred to a second and larger arch of the normal type which could hold six and maintain a soaking temperature. These were near the tank and were fired with overhead Selas burners taking the premised gas-air mixture used in the works.

Floaters were also made from the Grossalmerode mixture but these were dried in drying chambers; they were arched in the Clay Rooms and some distance from the tank.

Burner blocks, tiles, standard size bricks were also made, all by hand. These shapes could be heated up near the tank in a moveable muffle built on a wheeled carriage.

5. Warehouse

This building was a new one erected just before the outbreak of war. At the time of the visit, the cutters were working mornings only. The glass was brought in by the overhead monorail system to the top floor and fed down to two similar lower ones. In each shop the cutting tables were set out down the two outsides, with the monorail system and racks for cut glass between them and a central packing section running the whole length of the shop. Normally, packed cases are passed down a shallow chute to the ground floor. Each cutter has a cullet truck, removed when full by service men. (At the machines cullet was thrown into a stretcher-like box easily handled by two men.) The cases used at present are merely frames with a little straw for packing. They were handled readily by small two-wheeled bogies pushed by a single long handle resembling a bent lever.

The cutting tables have wooden tops with inlaid rulers inset about 12" from each edge; they had no splitting devices. Loose loading was not carried out. Rolls for taking paper were fixed above each cut glass rack to facilitate pre-war packing.

The general cleanliness of this factory was striking; all tools were placed in suitable racks, no unnecessary materials were lying about, the caves had a concrete floor and plastered walls and roof.

Witten-Crengeldanz

Filling the suspended ladle with frit from the
frit hopper. The cullet hopper is on the right.

Witten-Crengeldanz

Figure 2

The suspended crown

Description of Plant, Processes, etc.

1. Laboratory

This was a central laboratory for all three DETAG Works. It consisted of one small room in which gas and glass analyses were carried out. Samples of all raw materials received were sieved since the materials were ordered to particle size specification. Glass analyses were determined on 1 gram samples.

2. Gas Supply

There were six. "Demag" static producers with rotating base to facilitate ash removal. They were filled from overhead bunkers through a central gas tight bell. Normally four or five producers were worked to feed the tank according to the quality of fuel received. The sixth producer was carried as a reserve. The daily coal consumption was approximately 110 tons.

The blast was introduced through ordinary type blowers; saturation temperature 57ºC. Each producer could gasify 25 tons of fuel per day.

The flues were drained into tar sumps and burnouts only occurred during tank repairs.

3. Mixing Boom

All materials were stored in silos after being unloaded either by grab or elevator.

Mixing was carried out in a "Saxonia" type machine. All the materials were collected and weighed (direct weight) in the bottom half of the mixer. This was then pushed along rails into position. The mixed batch was transferred to a bogie and transported to the tank by means of a lift.

The "Saxonia" type mixer consists of two separate parts. The bottom half acts as a receptacle for the weighed quantities of raw materials. The top half contains a series of spades which help to mix the materials and prevent the formation of lumps. The mixer is driven electrically and rotates in a vertical position.

4. Tank

The tank was constructed to the same design as the Witten tank with the following exceptions:-

The sides were built in three courses each 30 cm. (12") deep. The two bottom courses were Didier Werke Chamotte. The top course blocks were Corhart. There were 5 stacks each side, the centres of which were wide apart. Each stack was divided into four ports, giving twenty ports in all. All the ports were open during operation. Midfeather arches were flush with the tank walls.

The crown was divided into two portions. The portion from the front wall to the 5th stack was sprung. The remainder of the crown was flat and each brick was suspended individually.

One three-piece set of floaters, made of Grossalmerode clay, gave a life of 3 months between the 4th and 5th stacks at a temperature of 1,350ºC.

Dimensions of Regenerators

There was a waste heat boiler as at Witten.

Machines There were nine machines varying in width from 1 metre 20 cms. to 2 metres. The roller asbestos was supplied by Tretorn of Hamburg. Vitrea type cutters were used on the top floor. The edges were stripped and the sheets split on cutting machines on the top floor.

Claywork Debiteuses and floaters were manufactured on the premises. For floaters Didier clay was considered better than Grossalmerode clay. For debiteuses Grossalmerode clay was considered better than Didier clay. Each debiteuse gave a life of from 2 to 3 months, the machines being stopped every 6 days for reheating.

5. Warehouse

This was a continuation of the top floor, Some cutting was done here. The glass was transferred from the top floor on portable racks. Wooden laths were fixed between each two sheets.

The cutting tables were situated round the windows, and packing was carried out along the centre of the floor. The packed cases were delivered to the ground floor down a chute.

6. Glass Analysis