EP0781863A1

EP0781863A1 - Method and apparatus for pickling aluminium disks

Info

Publication number: EP0781863A1
Application number: EP96830627A
Authority: EP
Inventors: Giorgio Tomassini
Original assignee: Alluflon SpA
Current assignee: Alluflon SpA
Priority date: 1995-12-22
Filing date: 1996-12-17
Publication date: 1997-07-02
Also published as: ITMC950135A1; IT1281925B1; ITMC950135A0; BR9606049A; TR199601044A2

Abstract

This invention concerns an industrial method for pickling aluminium disks according to which the disks are positioned above a series of combs fixed to an overhead chain conveyor which transports the same into a tunnel provided with a transverse set of nozzles which spray the substances for the pickling treatment.

Description

This patent application concerns an industrial method and relevant plant for pickling aluminium disks, in particular those used for the production of pots and pans which are treated with a coat of polytetrafluoroethylene commonly known as P.T.F.E.
P.T.F.E. is an organic compound resistant to a temperature of 250°C continuously but which also resists temperatures of up to 400°C for short periods of time.
Thanks to this characteristic together with its excellent non-sticking properties, P.T.F.E. is commonly used for kitchen pots, pans and tableware for the home as well as for all those items requiring easy cleaning and resistance to high temperatures.
Although the non-sticking properties of this organic compound ensure easy cleaning of the items with which they are coated, the same characteristic raises the problem of how to make P.T.F.E. adhere to the treated surface in that P.T.F.E. very rarely forms chemical bonds with other materials, in particular aluminium, which is the metal prevalently used for kitchen pots, pans and tableware.
Despite this it has proved to be possible to make P.T.F.E. adhere to an aluminium surface if it is roughened so that it provides a mechanical attachment for the P.T.F.E. coating.
One of the most common ways to roughen the aluminium surface is to attack the same with NaOH (sodium hydroxide commonly known as caustic soda) and HCL (chloride acid).
In the specific case of pots and pans, the aluminium disks used to produce the pots and pans, are first immersed in a caustic soda bath to degrease the same and then in a chloride acid bath which attacks the surface making it rough enough for the P.T.F.E. coating to adhere to the disk.
To immerse the aluminium disks, the same are placed and supported in baskets, generally in plastic, into which the disks are loaded and unloaded by hand.
This method, which is commonly used for pickling aluminium disks, presents numerous problems, the first of which involves the high cost of labour for the manual loading and unloading of the above baskets, added to the water purification costs which are also very high considering the large quantities of water and sludge to treat.
In order to resolve these cost-related problems, an alternative solution was proposed, which did not however prove to be very successful, consisting in placing the disks on a conveyor belt following a line flanked with nozzles spraying jets of water and caustic soda to degrease the disks and with chloride acid for the pickling process.
This method was not however very successful in that it was penalised firstly by the large spaces required for the conveyor belt on which the disks are placed flat rather than sideways as in the baskets.
It follows that on the conveyor belt the centre to centre distance between two adjacent disks can not be inferior to the diameter of each disk so that the belt becomes very long and consequently the factory in which the same is installed must be very large.
In addition to this problem, the use of a conveyor belt also presents another problem which is perhaps even more serious, namely that of properly spraying the bottom face of the disk, i.e. that facing the belt, where the pickling treatment is always less efficient with respect to the upper face. The purpose of this invention is to design a new method for pickling aluminium disks which does not present any of the above problems and that, in particular may be performed with a plant requiring a minimum of man power, having small overall sizes and low purification costs.
The method according to the invention provides that the aluminium disk are placed in sub-vertical position above a series of close-fitting combs fitted on an overhead chain conveyor positioned in a tunnel having spray nozzles placed at a suitable distance to ensure that both faces of all the disks transported on the combs are uniformly covered by the jets sprayed by the nozzles.
It is obvious that the use of a series of closely-fitting combs to support one or more disks ensures, on one hand, efficient and homogenous spraying of both faces of each disk, and on the other, the possibility of pickling a large number of disks simultaneously, in a relatively small area.
Moreover, this method makes it possible to reduce purification costs considerably since the quantity of water sprayed by the nozzles is far less than that used in the pickling plants with tanks containing the various baths in which the disks are immersed.
It should also be mentioned that the use of an overhead comb conveyor makes it possible to automatize, at a low cost, the loading and unloading of the disks; the question of automatizing pickling plants is of particular interest to sector operators considering that the disk painting and kiln drying lines have for years been automatized and connected in line.
This means that the automatization of the pickling plant would make it possible to perform the entire processing cycle without man power, other than a single control operator.
For major clarity the description of the invention continues with reference to the enclosed drawings which are intended for purposes of illustration and not in a limiting sense where:

fig. 1 is a schematic drawing of the plant according to the method in question, showing a view parallel to the forward feed of the disk-holder combs inside the pickling tunnel.
fig. 2 shows a schematic and axonometric drawing of each disk-holder comb.

With reference to Fig. 1 the plant for carrying out the method according to the invention includes a rectilinear tunnel (1) in which an overhead conveyor is installed to support and convey disk-holder disks (2).
Said conveyor includes a pair of opposing identical closed-circuit chains (3), each placed vertically against the internal walls of tunnel (1).
The disk-holder combs (2) which support the aluminium disks (5) are fixed astride the pair of chains (3) so that said disks (5) are positioned in a sub-vertical plane positioned transversally with respect to the feed direction of the two conveyor chains (3).
The interior of the tunnel being provided with a transverse series of spray nozzles, some above (6a) and some below (6b) the horizontal feed surface of the disk-holder combs (2), which move forward, loaded with disks (5), above a series of tanks (7) into which the product sprayed by nozzles collects.
The disk-holder combs (2) return, obviously without the disks (5) under said tanks (7) which are closed at the top by respective vault shaped lids (7a) forming a gallery closed on all its sides, through which the disk-holder combs (2) pass.
The spray nozzles (6a) placed above the disk-holder combs (2) are positioned along headers (8a) fixed transversally inside said lids (7a), while the spray nozzles (6b) placed under the disk-holder combs (2) are positioned along headers (8b) fixed transversally inside said tanks (7).
When the aluminium disks (5) pass through the tunnel - or more precisely through the gallery delimited at the bottom by the tanks (7) and at the top by the vault shaped lids (7a), the same (5) are invested by fine spray both from the top and from the bottom by the series of the above nozzles; said disks undergo a sequence consisting in degreasing with caustic soda, a first wash with water, pickling with chloride acid, a second wash with water and a third wash with demineralised water.
The tunnel is constructed in sectors following the length of the succession of tanks (7).
Tanks (9) containing the chemical products and wash water used for the pickling treatment being installed outside the longitudinal walls of tunnel (1).

Claims

An industrial method for pickling aluminium disks characterised in that the aluminium disks (5) are placed above a series of disk-holder combs (2) fixed to an overhead chain conveyor, which feeds the same into a tunnel (1) provided with a series of transverse nozzles (6a and 6b) operating in sequence which spray, from the top and from the bottom, the products required for the pickling treatment against the disks (5); said disks being (5) being supported on the combs (2) on a sub-vertical pane positioned transversally with respect to the feed direction of the combs (2).
A pickling plant for aluminium disks operating according to the method described in the previous claim and characterised by a rectilinear tunnel (1) having an overhead conveyor consisting of a pair of opposing identical closed-circuit chains (3), astride which the disk-holder combs (2) supporting the aluminium disks (5), are fixed transversally, so that said disks are arranged on a sub-vertical plane positioned transversally with respect to the feed direction of the combs (2) in the tunnel (1) which is provided with a series of spray nozzles, some above (6a) and some below (6b) the horizontal feed plant of the disk-holder combs (2) which move above a series of tanks (7) closed at the top by vault shaped lids (7a) thereby forming a gallery closed on all its sides, also providing that outside the longitudinal walls of tunnel (1) tanks (9) are installed containing the chemical products and water used for the pickling treatment.
A plant for pickling aluminium disks according to claim 2 characterised in that the spray nozzles (6a) above the disk-holder combs (2) are placed along headers (8a) fixed transversally in lids (7a) while the spray nozzles (6b) placed under the disk-holder combs (2) are positioned along headers (8b) fixed transversally in tanks (7).