Heating – Frangible or fusible safety relief or shutdown means
Patent
1985-07-26
1987-03-31
Yuen, Henry C.
Heating
Frangible or fusible safety relief or shutdown means
432126, 432144, 34 66, 220 89A, F27D 2100, B65D 2500
Patent
active
046540032
DESCRIPTION:
BRIEF SUMMARY
This invention relates to process apparatus comprising an enclosed housing having at least one internal superatmospheric chamber for containing, in normal operation, gaseous matter at a pressure not more than about 0.01 atmosphere above the ambient pressure; and to explosion relief panels suitable for use as part of such apparatus.
A typical, but non-limiting, example of such process apparatus is an oven for the curing or drying of coatings of printed matter on components made in large quantities: for example, containers such as metal can bodies. Due to the presence of high temperatures and of volatile solvents in such an oven, there is always a risk of internal explosions (which term is to be understood to include any increase in the internal pressure of the oven over that under which it is designed to work in normal operation).
One type of oven for the treatment of metal can bodies in this way is a rapid-cycle pin oven, i.e. an oven which typically consists of an oven unit and a cooler unit arranged in tandem with a common chain-type conveyor, for carrying can bodies on pins projecting laterally from the conveyor chain, extending through first the oven unit and then the cooler unit. Each of the two units of the pin oven has a said housing subdivided into an air delivery chamber, a working chamber and an air recirculation chamber. The working chamber lies between the other two chambers, being separated from the former by a perforate air delivery screen, and from the latter by a perforate air recirculation screen. Each unit has means for circulating a forced draught of air through the delivery chamber and thence through the working chamber to the recirculating chamber, the air passing from one chamber to the next through the appropriate one of the screens already mentioned. The oven unit has means for heating the air, which is recirculated in a closed circuit.
Since the treatment air is heated, it will normally contain products of combustion, and the process of curing the coatings on the can bodies involves evaporation of volatile matter from the coatings. To ensure that rapid curing takes place, this volatile matter requires to be positively removed from the vicinity of the can bodies (and therefore from the working chamber of the oven unit). Since the treatment air in the oven unit is recirculated, the volatile matter and combustion products (if any) must be removed from the interior of the oven unit to prevent their concentration building up to amounts such as to affect the curing process. In addition, whilst, in the circumstances prevailing inside a high-temperature curing oven operating on modern can body coatings, there is always some danger of explosion or fire, these risks can be minimised by ensuring that the products likely to give rise to such risks are continuously removed.
Thus the oven unit includes extraction means, which continuously induces a forced draught of scavenging air through the working chamber generally perpendicular to the direction of the treatment of air flow across the working chamber. While combustion products and volatile products are thus continuously removed, so also, inevitably, is a considerable part of the treatment air. To compensate for this, it is essential that fresh air be able to be drawn continuously into the oven unit housing, but in a manner such as not to reduce significantly the temperature in the working chamber.
The oven unit housing is generally in the form of a short and quite narrow enclosure, which is furthermore subdivided into the chambers already mentioned and which, in operation, contains very hot air under forced draught, together with the volatile products and, if the heating means is a fuel burner, combustion products. Under these circumstances the risk of explsion is inevitably enhanced.
According to the invention, in a first aspect, in process apparatus comprising an enclosed housing having at least one internal superatmospheric chamber for containing, in normal operation, gaseous matter at a pressure in the approximate range 1 to 1.01 atmosphe
REFERENCES:
patent: 1227674 (1917-05-01), Rudolph
patent: 1750313 (1930-03-01), Emmert
patent: 1930138 (1933-10-01), Van Derhoef
patent: 3972442 (1976-08-01), Malcolm
patent: 4498261 (1985-02-01), Wilson et al.
Fishwick Alan J.
Jackson Robert K.
Wilson Anthony J.
Metal Box Public Limited Company
Yuen Henry C.
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