DE3413240A1 - Method and apparatus for applying a layer of zinc to parts made of cast iron or steel - Google Patents

Abstract

According to a special feature of this method, the parts to be treated are preheated approximately to the temperature of the molten zinc under a blanketing gas prior to being dipped into the molten zinc. In contrast to the conventional methods, it is as a result possible to keep the layer of zinc applied as thin as possible, thereby making it possible to make savings of up to 50% in the consumption of zinc. Unwanted evolution of fumes during the introduction of the parts into the molten zinc and hence unnecessary pollution of the environment is furthermore avoided. In a apparatus for carrying out the method, the parts to be treated are preheated in a continuous furnace (11), from which they pass singly into the molten zinc (17), in which they are received by a perforated container (12). From this container (12), which is secured on a swivellable cantilever arm (13), the parts pass, again singly, into an adjoining tilting centrifuge (21) and from here, via a drying stage (36), into a transport container (35). Unlike conventional apparatuses, in which the parts to be treated are in circulation in containers during the entire treatment operation, in this apparatus the parts are transferred singly to the respectively following treatment station. <IMAGE>

Description

The invention relates to a method for applying a

thin zinc layer on parts made of cast iron or steel by immersion in a zinc melt, in which the metallically bright parts from a storage bunker a weighing device and then fed to the treatment. Further concerns the invention a device for performing this method.

Process and equipment for galvanizing metalli's Objects are known, e.g. from DE-PS 21 00 332. The goods to be treated is usually used in conventional processes with temperatures around 1000 C in immersed the zinc melt. As a result of the relatively large temperature difference between the good and the zinc melt is the time until temperature equilibrium and corresponding to the boiling of the flux film on the property. This inevitably leads to form an unnecessarily thick zinc layer on the property. To that extent are procedures not particularly economical of this kind. With these procedures there is the Items to be treated during the course of the process in perforated baskets that are carried along or containers.

On the one hand, these containers increase the masses to be moved and are subject to them on the other hand, a high level of wear and tear, which is due to the constant change in temperature Contact with the liquid zinc and mechanical stresses is.

The invention aims to remedy these disadvantages, i.e. it wants galvanizing of metallic parts so that the applied zinc layer is so thin can be kept as possible, but still at all points of the to be treated Parts a constant strength is guaranteed, and that also for moving of the parts to be treated can largely be dispensed with.

Based on a method of the type mentioned above, the first sub-object achieved according to the invention in that the parts to be treated before immersion in the zinc melt under protective gas to approximately the temperature of the Zinc melt can be preheated.

This has the significant advantage that the residence time of the Parts in the zinc melt exclusively to the technological requirements can be turned off. This can significantly reduce the consumption of zinc and savings of up to 50% can be achieved. The zinc layers that are at conventional processes are unnecessarily thick. For screws greater than M10, for example, they are between 70 and 100 μm, although according to DIN 267 only zinc thicknesses of 40 µm are required.

Another advantage is that the volume of the zinc bath can be smaller, because only the wall and bathroom radiation losses in the form of Energy must be supplied. With this method, in addition to a Saving raw materials also means reducing the amount of energy used.

In conventional methods, when the parts are immersed in the zinc melt usually unavoidable considerable smoke development because there are liquids on the surfaces of the parts that are in the Burn molten zinc. Such smoke development occurs when introducing below Protective gas does not apply to preheated parts. Also an unnecessary burden on the environment is therefore avoidable. An additional zinc bath suction in connection with a costly gas cleaning, as is the case with conventional methods to avoid is often used, can be omitted in the new process.

Furthermore, since the parts in the zinc melt can no longer "boil off" complex manual stirring processes or automatic upward and downward movements of the batch within the zinc bath.

According to a further feature of the invention, the parts are separated preheated and occasionally fed to the zinc melt. Get in the zinc melt them in a perforated basket, with which they are removed from the molten zinc and subsequently a tilting centrifuge, with the basket only between the receiving position Movable in the zinc melt and the emptying position above the tilting centrifuge is.

Since the parts to be treated are isolated in the zinc bath temperature When molten zinc falls, there is no risk of it sticking together. In this way the scrap is reduced to a minimum.

According to a further advantageous method step, the parts after centrifugation, placed on a conveyor belt in a cooling bath. This conveyor belt runs with its middle section in an inclined course out of the cooling bath. Here the parts are made according to a further procedural feature dried during their movement after leaving the cooling bath in a gas stream.

In contrast to the traditional procedures, in which the to be treated Parts are in circulation in individual containers during the treatment process Such a container transport is not provided for in the new method. So that will Avoid moving unnecessary masses and at the same time prevent costs being incurred, arising from the maintenance of the containers or baskets in circulation.

A device for carrying out the method is expedient designed so that the parts can be preheated to the temperature of the molten zinc a continuous furnace is used, which has a swiveling discharge sluice at its exit has, the outlet end over a in the zinc melt on a tilting device attached perforated container ends.

The tilting device advantageously consists of a horizontal one Axis swiveling about 1800 boom, at its free end the perforated container is attached.

There is a perforated receiving basket provided on a pivot lever around a horizontal Axis up to a tilted position above the cooling bath with the tank opening facing the bath is pivotable.

It is also expedient to install a control device on the zinc bath, e.g. a lifting cylinder, zinc ash scraper movable in the plane of the melting level to arrange. This is advantageously controlled so that before each immersion and each time the basket is swiveled out, the zinc bath surface is automatically removed from zinc oxide layers is cleaned. Impurities on the applied zinc layer are therefore reliable avoided.

In conjunction with other known treatment stations, the Device can be designed so that an automatic drain from the storage container until it reaches the collecting tank behind the cooling bath. Such a facility for automatic galvanizing of metallic parts can be easily done by a single Supervising person are monitored and operated.

An embodiment of a device according to the invention is shown in shown schematically in the drawing and will be explained in more detail below. Show it: Fig. 1 is a plan view of an automatically operating device for galvanizing metallic parts from the storage bunker to drying, Fig. 2 shows a cross section of the device in the plane of the line I-I of Fig. 1, Fig. 3 is a side view the device in the direction of arrow A of FIGS. 1 and 4 shows a section of the Device in the plane of the line II-II in FIG. 1.

Starting point of the parts to be treated in the case of the illustrated in FIG. 1 The device is a storage container 1.

The bare metal parts are placed in batches in this storage container in a size of approx. 400 kg fed with a crane or a forklift. From the The process runs automatically from the storage bunker. Depending on the set Weight, which depends on the shape and size of the parts, promotes one under the Storage container 1 located vibrator 2 the weighed parts to a weighing container 3 as part of an inclined elevator 4, which stands on a weighing device 5.

The inclined elevator 4 conveys the weighing container 3 vertically upwards and tipping the batch uniformly onto a discontinuous one via a feed sluice 7 running conveyor belt 8 of a continuous furnace 11 for preheating the parts. While The conveyor belt 8 precedes the allocation by one cycle. The clock speed is adjustable. The conveyor belt 8 has equidistant from each other lying transverse divisions 9, between which the allocated quantities are located.

In the case of a cyclical process, controlled via contact pins on the Cross divisions 9, parallel to the allocation is always only the one at the weighing device 5 set amount of separated parts given in a container 12, which is on a pivotable boom 13 is attached.

In the continuous furnace 11, the parts to be treated are placed under protective gas preheated to a maximum of 5500 C. In this way it is avoided that the metallic oxidize bare parts, which would lead to poor galvanizing.

l The feed sluice 7 is provided with closure flaps at its ends. The flap on the exit side remains during the filling process closed. After completion of the filling process, the on the input side existing flap closed and the feed hopper 7 via a line 14 with Inert gas flooded. Only then is the lower flap opened and the parts can then be distributed evenly on the conveyor belt 8. The conveyor belt 8 consists advantageously from an endless band made of a close-meshed wire mesh.

i The parts are heated by convection using protective gas, which is heated on heating registers 15 and circulated by fans.

After leaving the continuous furnace 11, the parts pass through a pivotable discharge sluice 16 into the container 12 inside the zinc melt 17 of a zinc bath 18 in a conventional design.

On the zinc bath 18, a zinc ash scraper 19 is arranged, which is of a Lifting cylinder 20 is movable in the plane of the melting mirror 6. Before the parts into the container 12 is directed by a back and forth subsequent movement of the scraper 19 cleaned the surface of the zinc melt.

After the specified dwell time in the zinc melt, it is swiveled of the boom 13 of the container 12 swiveled out of the zinc bath up to a position in which the filling side of the container points almost downwards (Fig. 3).

This movement is expediently made up of a first slow one Pivoting movement up to the surface 6 of the zinc melt 17 and a subsequent one faster tilting movement to the end position above one next to the zinc bath 18 located tilting centrifuge 2 together. A hinged cover flap 22 closes the container 12 after the beginning of the tilting movement and prevents it the galvanized parts falling out before reaching the end position. In the End position the flap 22 is unlocked; it opens and now serves as a Slide for the galvanized parts falling out of the container.

For the execution of the pivoting movement of the boom 13 is a lifting cylinder 23 is provided, which acts on the boom 13 via a chain drive 24. At his Pivoting movement pushes the boom 13 in the end position against end stops that consist of rubber buffers. Due to the sudden braking of the swivel movement supports the falling out of the parts from the container 12 and thus ensures that no parts remain in the container.

During the swivel movement there is a constant change in the parts in their mutual position, and there is therefore no risk of sticking together of the parts that have just been galvanized.

After filling a perforated one located in the tilting centrifuge 21 cylindrical basket 25 is this with a by a lower> eighth Axis pivotable cover 26 closed.

The cylindrical basket 25 is rotatably mounted about its cylinder axis and directly coupled to an electric motor 27 as a drive. During the fast Rotation of the cylindrical basket 25 will remove the excess amount of zinc of the galvanized Parts thrown outward through openings in the wall of the basket 25. It hits the inner wall of a hood 28 and falls from here as zinc grit at the bottom in a collecting container 29.

l After the centrifugation is complete, the lid 26 moves to the side swiveled and tilting centrifuge 21 tilted up and sideways by approx. 1350, as indicated by arrow 30 in FIG.

In the end position, the tilting centrifuge is caught by rubber buffers, with the sudden braking of the movement of the cylindrical basket 25 reliably is emptied.

The movement of the tilting centrifuge 21 is the same as for the receiving container 12 caused by lifting cylinder 31 in conjunction with chain drives 32.

Because the time between centrifuging and cooling the parts is extremely short in a subsequent cooling bath 33, there is practically none Risk of galvanized parts sticking together.

The parts falling out of the cylindrical basket 25 reach a conveyor belt 34 located in the cooling bath 33, which has an approximately horizontal starting section, a central section rising obliquely from the cooling bath 33 and an approximately horizontal one Has end portion. With the help of this conveyor belt, the galvanized parts a transport container 35 is supplied, which is below the discharge end of the conveyor belt 34 is set up.

The galvanized parts are moved during their movement after leaving of the cooling bath 33 dried in a stream of warm air.

For this purpose is above the section protruding from the cooling bath 33 of the conveyor belt 34 a hood-like drying device 36 is installed, as is from Fig. 4 can be seen. Inside the hood is a heating element 37 and the impeller 38 of a radial fan generates a flow of hot air that has a fast Drying of the galvanized parts causes so that the parts dry in the transport container 35 arrive. Intensive drying is particularly important for thin-walled parts from Significance, because with these the relatively low storage heat for self-drying is generally insufficient in a short time.

Claims (9)

Method and device for applying a zinc layer to parts Made of cast iron or steel Claims 1. A method for applying a thin zinc layer on parts made of cast iron or steel by immersion in a zinc melt, in which the metallically bare parts from a storage bunker of a weighing device and afterwards to be supplied to the treatment, d u r c h e k e n n -z e i c h n e t that the parts before immersion under protective gas to approximately the temperature of the zinc melt be preheated. 2. The method according to claim 1, characterized in that the parts individually preheated and individually fed to the zinc melt. 3. The method according to claim 1 or 2, characterized in that a Batch of isolated parts taken from the zinc melt in a perforated container and then emptied from the container into a tilting centrifuge. 4. The method according to claim 3, characterized in that the parts the batch after centrifugation singly on a conveyor belt in a cooling bath to be abandoned. 5. The method according to claim 4, characterized in that the parts dried in a stream of warm air during their movement after leaving the cooling bath will. 6. Device for performing the method according to one of the claims 1 to 5, characterized in that a continuous furnace for preheating the parts (11) is provided, which has a pivotable outlet sluice (16) at the end, the outlet end of which is attached to a tilting device in the zinc melt (17) perforated container (12) ends. 7. Device according to claim 6, characterized in that the tilting device consists of a boom (13) that can be pivoted about a horizontal axis by approx. 1800, at the free end of which the perforated container (12) is attached. i 8. Device according to claim 6, characterized in that the Tilting centrifuge (21) contains a perforated receiving basket (25) around a horizontal Axis up to a tilted position above the cooling bath (33) with the bath facing Basket opening is pivotable. 9. Device according to claim 6, characterized in that the zinc bath (18) one from an actuator, e.g. a lifting cylinder (20), in the plane of the melting level (6) movable zinc ash scraper (19) is arranged.