Static molds – Including coating or adherent layer – Parting layer
Patent
1988-08-03
1989-12-19
Lindsay, Robert L.
Static molds
Including coating or adherent layer
Parting layer
65357, 6537411, 65122, 427135, B28D 736, B44D 120
Patent
active
048877913
DESCRIPTION:
BRIEF SUMMARY
Techniques for industrial production of receptacles of glass of the bottle, flask, pot or similar type, are for the most part methods known as "mould-blowing" and "blow-blowing". These methods allow production at a high rate of objects of satisfactory quality for the use envisaged.
In these methods the treated glass, enters successively into contact with two moulds, that is a blank mould and a finishing mould. These moulds are the essential elements in the process which determines not only the shape but also the surface state and the mechanical qualities of the blank moulds, are subjected to very severe conditions. They are subject especially to large mechanical and thermal shocks in large number. They are also subject to the chemical action of the surrounding atmosphere and the composition of the glass. Because of these different effects the utilised surface of the mould may degrade relatively rapidly so that the mould has to be replaced. This phenomenon of degradation is very noticeable for moulds based on cast iron, which are most commonly used because of their relatively low cost, but it is also observed with moulds made of other metals and notably moulds of steel.
It is not sufficient in order to obtain satisfactory production to maintain the surface of the mould in a good condition, it is also necessary that it can form a good contact with the parison. By good contact, is meant a good introduction of the parison and then a good distribution of the latter in the blank mould. It is necessary to prevent the glass sticking to the mould, which produces an article having striations, streaks and other irregularities on its surface. According to traditional methods in order to avoid these difficulties greases are used. Systematically and at relatively short intervals of time the mould is covered with these greases which are situated between the mould and the parison.
Independently of the restrictions on production which systematic application of these greases represents, this method does not solve the problem of degradation of the mould. In order to improve the life of the mould various techniques have been proposed such as coating of the surface with layers of metal oxides such as chromium oxide, nickel oxide or titanium oxide. These proposals also have the purpose of avoiding the need for greasing as, according to the inventors, greasing would have a bad effect on the layer of metal oxide and affect its stability and life.
However it has been found that these proposals are not entirely satisfactory and that the use of a mould which is not greased does not allow the necessary degree of regularity in sliding of the parison on the mould surface. For this reason the present invention is intended to provide a method giving glassmaking moulds an increased life and, simultaneously, satisfactory properties regarding contact with the glass. The invention is also intended to give these results under conditions, notably of cost, which are advantageous over traditional methods which require frequent changing of the moulds.
For manufacture of glass objects by the mould-blowing and blow-blowing methods, the invention proposes use of metallic moulds of cast iron, notably blank moulds, of which the parts exposed to the parison are coated with a layer of aluminium oxide of thickness less than 5 micrometers.
There is found in the literature the idea of coating moulds or other members for shaping glass with layers of refractory oxides such as alumina in order to protect them against degradation resulting from thermal shock. The aim of these layers was to form a thermal barrier on the protective surface. For this reason the coating provided had a relatively large thickness of the order of 0.15 to 0.30 mm. This type of coating is not envisaged in the present invention. One reason is that the thick layers have to be obtained by relatively expensive methods such as metallisation under plasma. Also, and this is even more important for methods according to the invention, the use of thick layers requires a very specific fixing on t
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Abriou Daniel
Dugast Alain
Tangari Celia M.
Lindsay Robert L.
Saint-Gobain Emballage
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