Tin caster
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Pewter caster is a job title and an apprenticeship in the craft with a three-year apprenticeship period and the possibility of a master craftsman's training. The pewter caster uses the casting process to produce decorative and everyday objects that are created in craft workshops and whose base metal is tin . By pouring so-called pure tin (95% Sn) or fine tin (97.5% Sn) into molds made of cast iron or steel, workpieces are created that are given a highly reflective silver-metallic surface shape in further processing on woodturning lathes or by means of grinding, or work forms with a picture - and ornament motifs, which are etched with weak acid to give them an artificial patina. The pewter caster uses high-purity pewter and for the most part uses traditional craft methods and equipment.
By machining on lathes and grinding with grinding pastes, pewter dishes are given a high-quality surface finish that withstands long-term environmental influences and corrosion of the metal surface. More complex surface treatments of the inner walls of drinking vessels require the use of special turning tools. In addition, the surface is polished in more complex processes with agates. As a result, the inner walls of wine cups and beer mugs are given surfaces that are less susceptible to corrosion and which would have resulted from the grooved structure after machining with the machining process.
The pewter brand is the seal of approval for pewter foundries and dates back to the end of the Middle Ages. Every pewter foundry has its own die, which is attached to the inside of the lid, outside of the base or on the handle. The pewter foundry had its heyday from the 14th to the 16th century, when pewter dishes were common household items in the late medieval bourgeoisie. With the emergence of porcelain production, pewter dishes were gradually pushed out of use, but were mostly used for representative purposes of the bourgeoisie until the 20th century. Due to the sharply decreasing demand for pewter dishes in the last decades of the 20th century, the decline of the pewter foundry also began in former pewter casting centers. In addition to the liquidation of most of the remaining production facilities, a continuing decline in the tin foundry trade is observed due to a lack of training in the pewter founders' trade, which is also manifested in the dissolution of the pewter founding guild in Germany in 2010.
Pure and fine tin
Pure and fine tin alloys are the names used for tin workpieces. As alloys, they are produced in-house in the pewter foundry. Some foundries use particularly high-quality alloy with 97.5% Sn (fine tin), but mostly pure tin with 95% Sn is more common. The alloy is based on 100 percent commercial tin, which at best is soap tin from Southeast Asian soap deposits. This is melted in larger furnaces. Melting temperatures of approx. 500 ° C are required for alloying the higher-melting alloy metals copper and antimony . Copper is supplied with antimony through the addition of solid minerals through copper rods that are melted down in sections. During production, a homogeneous pure tin alloy is created from it by stirring with cast iron rods.
The alloyed fine or pure tin is poured into steel molds to form ingots, which are further processed in the tin foundry in smaller casting furnaces.
The craft guild places great value on maintaining the purity of the tin. In addition to the obligatory pewter brand, information about the type of alloy is often provided. Besides copper, the alloy is only attached antimony, since this as bismuth has the peculiarity of undergoing expansion upon solidification from the liquid state, which is based on the metal lattice structure of antimony, for the solid state of aggregation , there is a larger volume than the liquid state . The increase in volume in the change from the liquid to the solid aggregate state in the alloyed antimony prevents excessive shrinkage during cooling, which enables a sharper casting from the mold. In addition, alloys of copper and antimony give the tin greater hardness, a suitability that is important for machining methods that are necessary later in production.
As a well castable metal, copper is the most important component of tin alloys. In addition to good castability, copper is also easy to expand, machinable and easy to polish.
Tin alloys with a higher proportion of lead were previously more common. Such tin has a matt surface and was overall significantly softer. Because of the unfavorable physiological effect of lead, it has long been excluded as an alloy additive for common tin in handicrafts.
Another positive effect of tin alloys is that the natural conversion of β-tin into α-tin (below 13.2 ° C) slows down considerably. Tin that is affected by the " tin plague " shows gray, brittle spots on which the metal dissolves in an ugly powdery form.
In general:
- Tin - Sn - base metal with a melting point of 231.97 ° C
- Copper - Cu - alloy metal for greater hardness and strength with a very high melting point - 1083.4 ° C
- Antimony - Sb - alloy metal for greater hardness and strength, very brittle for sharp castings - 630.74 ° C
Tin alloys according to DIN 17810 for fine tin:
- 96% Sn, 2% Cu, 2% Sb
other alloy ratios:
- Imperial tin: 90% Sn, 10% Pb
- Probotin: approx. 80% Sn, 20% Pb
Common brands of pewter are: Banka, Baum, Billiton, Elektrolyth, Lamm, Pennang, Straits, Rosen and Tarsaiko.
The pure material value of 1 kg of tin is now 14 euros per kg when purchased (price on Feb. 17, 2018).
Casting process
The steps of pouring are:
- Preheating of the mold in the melt
- Overcasting and setting up the form
- to water
- Cooling the mold
In the foundry, tin is melted in melting pots that are heated by gas flames. The molds are preheated in the tin melt before they are assembled. The multi-part molds are then drawn one after the other from the tin melt, cleaned of tin residues and put together. The casting mold is fastened under a vice and slightly inclined with the inlet. The liquid metal to be poured in is removed from the melt with a pouring spoon and always poured in in one pour. Interrupting the pouring process would inevitably lead to a reduction in the quality of the cast workpiece. The saying "as if cast from a single source" therefore comes from the practice of metal foundries. The mold is cooled by means of damp cloths that are placed on the mold, moving upwards from below. It must be cooled from the back to the front and the volume must be equalized during the cooling by replenishing in order to avoid segregation of the casting. Uneven cooling and insufficiently refilled castings show casting defects which, in the worst case, prevent further processing due to voids. Also undesirable is a vein of impure oxidizing tin running through the workpiece, which must be deposited on the surface of the melt before casting.
After the casting has hardened completely due to the cooling, it is removed from the mold by striking the edge of the mold with a tin hammer. Depending on the age and condition of the mold, more or less force is required.
After cooling, is with the rough cast serging seams and sprue begun.
Fundamental casting defects of the workpiece belong to the following types:
- Foreign bodies - inclusions in the casting
- Segregation - segregation of the casting alloy
- Blowholes - cavities in the casting
Molds
The most common and most durable cast molds for hot casting are made of steel or gray cast iron. These can be used for several decades, in exceptional cases for over 100 years. Cast molds made of bronze or brass are more problematic. These can be attacked during preheating in the tin melt. Preheating ovens or heating plates are therefore more suitable. To protect the mold, briefly adhering release agents such as graphite or clay are applied to the mold before each casting. They make it easier to remove the finished casting, but they can float up during pouring. Therefore, they should only be applied thinly in order to avoid a reduction in the quality of the cast due to foreign particles.
Smaller Zinnkörper as jugs of beer mats be poured into permanent molds for Kaltgussverfahen. Today these are mostly made of silicone rubber, rarely made of wood, plaster of paris or slate. Cold cast slate molds are used in particular for pewter figures, but have the disadvantage that they are not very heat-resistant and therefore cannot be used for long production cycles.
processing
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Exciting steps
Among the processing steps, a machining process is the most common for all circular shapes.
Roughing is only appropriate for coarse pieces of tin. This results in a relatively large chip removal and is usually only used for the tin feet of ceramic mugs.
The machining on woodturning lathes is more important. This consists of a suction device and a holder, so-called sticks, attached to the rotating spindle. These are work forms that take pewter objects from glued wood. The lathe lathe is completely missing an upper slide. The tools are moving irons that are hand-held and guided along a beam along the axis of rotation. The moving iron and chisels have different cutting edge shapes with different cuts, e.g. B. with radii or in a simple wedge shape, which vary in width and thickness. Simple steel is sufficient as the tool material, since there are no great material requirements with regard to high temperature strength and hardness. Soapy water is used as a lubricant. Blades made of spring steel are used for finishing.
Moving irons are first attached to the workpiece at low speed and relatively large chip removal to remove the harder cast skin. The curved plucking iron is mostly used here.
Once the cast skin has been removed and the required dimensional and shape accuracy has been created, the surface is finally freed from deeper grooves with blades in spiral hand movements from outside to center and higher speeds and less chip evacuation.
Finally, the surface is smoothed with steel wool.
High-quality pewter goods always show the grooves left by machining, which distinguish them from those made from pewter sheets and dishes made by deep drawing.
Since tin, because of its low hardness, does not require a large feed or cutting speed when turning, the speed is also relatively low. The lathe chisels can be held in the hand as with wood turning .
Agate stone polish
Interior walls are polished with agate stone and soapy water. It is the highest quality process to get the inside of jugs and jugs free of marks and the final process of the machining steps. Agate stones can only be ground with great effort; in Germany these can only be overhauled or repaired in specialized companies in Idar-Oberstein . This means that the few agate stone tools are also the longest-handed tools in workshops.
The agate stone sits in the tool in a brass holder in a connection made by pitch at the tip of a wooden stick. As a result, when turning it should only be guided evenly to the tin body with little pressure and with enough soapy water. Agate stone polish achieves the highest surface quality on the lathe; Even the metal lattice structure can be seen with the naked eye in the fresh state. If the agate stone is guided with too much pressure, wavy unevenness will arise, which will make it necessary to cut it again with a moving iron. Since the wall thickness of the pewter body decreases when the agate stone is incorrectly polished, polishing with agate stones is one of the processes that can only be mastered by high-quality pewter foundries.
grind
Grinding is a cutting job with geometrically undefined cutting edges.
Advantages are:
- high surface quality
- good machinability of hard and difficult to machine materials
- high time stress volume
There are two grinding methods used in the pewter foundry:
- Bound abrasive grains on rotating abrasives - are used for grinding turning tools and in general for all hard metals
- Sanding with the buffing wheel, whereby the abrasive is applied to the buffing wheel - for sanding soft metals
Abrasives are natural abrasives such as oil sandstone, emery or diamond. Grinding wheels have corundum, silicon carbide, boron nitride or diamond as abrasives.
Grinding paste, polishing paste and pumice powder are used on the buffing wheel. These abrasives are characterized by their low hardness and very fine grain. This means that they have very little chip removal and guarantee a very high surface quality on pretreated surfaces. Area of application is the high-gloss polishing of tin equipment.
Ground pewter dishes can be found under the terrines and platters with irregular shapes. In particular, dishes made in the Baroque and Empire styles can only be processed with the aid of grinding on the buffing wheel. In addition, the handles and soldering points of joined larger, mostly elliptical workpiece shapes are ground. Solder seams are first smoothed with a chisel and scraper blade. Finally, the entire workpiece is polished under the buffing wheel.
Pewter ware joining process
Many pewter dishes consist of several work pieces and are put together using the following processes:
- Soldering (soldering in bottoms, handles and jugs for pewter jugs)
- Casting on (two hinge parts that connect the tin lid and the tin jar are joined by casting on)
- Pour on (beer mat and handle are joined with the hinge legs by pouring on)
soldering
Many pewter things only get their final shape when several parts are soldered together:
- Cans - snuffboxes, sugar bowls
- Pitchers
- Jugs
- Terrines
- chandelier
A distinction is made between pewter items that are already soldered in the raw casting and those that are soldered together after machining.
The procedure used is:
- Flame soldering
- Iron soldering
All pre-turned tin parts are flame-soldered: handles of jugs and jugs, buttons, feet, but also bottoms of jug bodies. Flame soldering is used for almost all small parts.
Since it is done with the material of the workpiece without lead solder, piston soldering is particularly complex. This results in bulging solder points that can only be removed with a great deal of work, but due to the same color between the solder point and the workpiece, there are no differences in color. None of the tin items that come into contact with food are made with lead solder compounds. They are therefore harmless to health.
Sprue
The sprue describes the connection between the tin lid and a hinge. Before the casting takes place, the inside of the cover is coated with clay as an insulator at the casting point. Moist clay is applied as a workpiece across the width of the hinge in parallel lines on the lid and pulled precisely to the hinge to be attached. The volume created by the two clay tracks is poured with liquid tin and, after melting, connects the hinge and lid permanently.
infusion
The infusion describes the connection between the tin lid and the handle of a ceramic jug. Clay is kneaded around the paper and leather cord that is wrapped around the handle. Liquid tin is then poured into the hollow shape created by pulling out the leather cord. The ceramic jug carries the pewter lid through the infusion. The shape of the so-called tail - the conically tapering prismatically cut extension of a short tin strip on the handle gives greater strength.
Artificial patina
Many dishes and ornaments show ornaments and semi-relief forms. Since they have no possibility of polishing, these are highlighted by means of corrosive processes and coloring. Etching is done with the help of a weak acid that is briefly applied to the motif or ornament and then washed off immediately. It is then blackened with an adhesive color emulsion, often black shoe polish is used.
Products
Pewter foundries manufacture a wide variety of traditional household items from dinnerware, cutlery, beer mugs and wine mugs, jugs, core holders, ashtrays and beer garden lids. Larger works are still counters and tin counters today, which are particularly common in Paris in various luxurious bars, restaurants, hotels, cafes and bistros. In addition, sarcophagi of the high nobility were made of tin. Thus, even Franz Maria Luitpold of Bavaria in 1957 in a Zinnsarkophag in the Wittelsbach-grave lay buried.
Pewter foundries
In 2010, a little over 20 companies were listed in the Federal Association of the German Pewter Foundry Guild. Larger companies are still Anton Schreiner & Sons in Nappurg and Röders GmbH Soltau. Smaller businesses are often only specialized in repairs or ceramics. Some companies have also remained active outside the guild, but have neither the personnel nor the operational quality that was possible a few decades ago. This also includes formerly important foundries such as the Ludwig Mory pewter foundry or Kayserzinn .
history
Tin is one of the oldest processed metals known to man. The oldest tin bronzes are known from the Balkans and the Middle East and were used for archaeological finds from the Pločnik excavation site in today's Serbia in the Balkans for the period 4500 BC. Established 1500 years before the first known tin bronzes in the Near East.
The pewter foundry as an independent craft dates back to the high and late Middle Ages, as did the widespread use of pewter tableware as objects of daily use in medieval households. The widespread use of cast pewter dishes in the late medieval bourgeoisie developed from the increase in prosperity in the trading cities of Europe. With this, the new type of tableware increasingly gained a high reputation. Pewter casting has been traceable in Germany since the 12th century, but the pewter guild only blossomed fully in the Free Cities in the late Middle Ages. Originally in use as a replacement for the very expensive silver dishes, plates and jugs made of pewter were an integral part of the household inventory of the bourgeoisie, like the nobility, in the late Middle Ages. Manufacturing centers included London, Paris and Nuremberg, where the first pewter foundry guild was founded in the late 13th century. Decisive for the flourishing were that deposits in the immediate vicinity of the medieval cities held minable tin soaps. In the Upper Palatinate area, the important tin soaps of the Ore Mountains were mined, which not only supplied local tin foundries but also those of the large trading centers of the time. Large tin deposits were still located in Cornwell, where a tin mine of national importance had developed since ancient times.
In addition to the pewter plate, pewter bowls, pewter jugs and pewter jugs (including the Hanseatic jug ) were examples of representative items made of pewter that were more common in the late Middle Ages. With different shapes of the pewter can, pewter bowls are increasingly detectable domestic utensils made of pewter from the 14th century. B. from Paris at the end of the 14th century were still expensive items for special occasions.
In late medieval depictions of the domestic bourgeois ideal, the depiction of pewter dishes and pewter jugs found their way into. Various jug shapes have been preserved in shape and images since the middle of the 14th century, and their number and variety of shapes increased sharply up to 1500. In addition to the more frequently preserved guild jugs, gender jugs, pip jugs or so-called council jugs, images also show squat, bulbous teapots in the context of baths or taverns, as well as the specifically southern German or Swiss bell jug . Especially the tall, slim, elegant so-called councilor's jugs were made as representative dishes. In particular, guild pots or gender pots decorated with the guild's coat of arms were ornamented with rich details.
For Vienna as one of the trading centers in the Middle Ages, the oldest evidence of the pewter foundry is documented for the 14th century. 1326–1342 the tin caster Dietricus is mentioned as a house owner. Up to the 15th century, 59 pewter founders can be found in Vienna. In 1395, pewter founders are mentioned on the fire site who displayed their products in simple shop windows ( arenas ). As a craft of high social standing, they sat on the city council. In 1526 there were three tin foundries in Vienna's inner council. Also three in the external council in 1460. A union within a brotherhood is documented in Vienna at the beginning of the 15th century. In 1426, the city of Vienna issued its first pewter regulation. The Viennese tin foundry trade had competition from Italian and southern German dealers. At the end of the 15th century, after four years of training, two years as a journeyman and wandering after making a masterpiece, the master's certificate was awarded. In 1527 the pewter brand was introduced as a seal of quality in the Viennese pewter foundries . In the Middle Ages, tin for Viennese master craftsmen came from Bohemia and partly from Poland.
education
Practical training in the apprenticeship as a pewter traditionally takes place within the craft businesses. As part of the dual training, apprentices attend related vocational schools, mostly those specializing in precision engineering and tool-making, as no specific curricula are offered for the profession of pewter caster. Since the end of the 1970s, vocational training as a pewter caster has increasingly proven to be economically obsolete, as the low demand for pewter dishes and the high acquisition costs of artisanal products meant that there were few career prospects in prospect. In apprenticeship training today, groups of people from the family environment are the basis for continuing the tradition.
literature
- Ludwig Mory: Nice tin. 4th edition Bruckmann, Munich 1972, ISBN 3765414166
Individual evidence
- ↑ Pewter purchase
- ↑ Etainier Tourangeau
- ↑ Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago
- ^ Felix Czeike: Historisches Lexikon Wien Zinngießer in the Vienna History Wiki of the City of Vienna