NO138036B - T} RNSTILLAS. - Google Patents

Description

Procedure for molding cold-hardening, synthetic resins.

The present invention relates to a

method for casting cold-hardening, synthetic resins, i.e. processes i

which a liquid, synthetic resin

fed into a container and then brought to

curing by catalytic action without

any significant application of heat. Such

processes include not only casting

of synthetic resins in molds, but especially potting processes in which an article, usually a

electrical device or element, embedded in

the resin.

It is known that casting can be carried out

with liquid epoxy or alkyd resins with added fillers such as quartz sand. This is a common method in autoclave press molding (potting), but generally the resin must be heat-cured, and

trapped air must be removed under vacuum. The use of relatively expensive, low-viscosity epoxy resins has gained ground, since . The alkyd resins (usually styrene-based, unsaturated

alkyd resins) shrink to an undesirable degree,

even after the heat curing step is

finished.

The invention makes it possible to cast

without it being necessary to use vacuum filling, and without it being necessary to

cure at elevated temperature. Further becomes

it is possible to autoclave press-cast objects, especially transformers, underneath

achievement of improved penetration or

shape adaptation of the resins.

The method according to the invention to

molding of cold-hardening, solvent-free, synthetic resins involves that

the liquid resin is fed into a container, and that a heavy, granular filler is then added through the free resin surface, which is mixed with a catalyst for the resin and an inert liquid that is compatible with the resin, the inert liquid being present in an amount just sufficient to wet the surface of the filler so that the mixture of filler, catalyst and liquids forms a moist, crumbly mass. By the term "heavy" it is meant here that the moistened granular filler will fall through the liquid resin during a period of time which is only a fraction of the time the resin needs to harden under the action of the catalyst. The term "inert" means that the liquid does not affect the catalyst or catalysis in the polymerization process, nor is it itself drawn into the process to a significant extent by the catalyst.

The preferred resin is a styrenated alkyd resin. The preferred filler is sand, and can be used in such an amount that it mainly fills the resin, i.e. so that it reaches — or almost reaches — the surface of the resin after sinking. The mixture of filler, catalyst and liquid can be prepared by tumbling the ingredients. The liquid can be a plasticizer for the resin.

According to one example, the casting resin consists of 100 parts unsaturated alkyd resin and 25 parts styrene. The filler mixture is prepared by tumbling 100 parts of dry sand, 4 parts of a glycol ether ester that softens and 6 parts of benzoyl peroxide.

When using an alkyd resin, it is preferred to have both the amine-reactive type and the cobalt-reactive type present, together with the corresponding accelerators. This makes it possible to achieve widely different curing conditions. Another example, in which such a mixed resin is used, is as follows: 100 parts of a mixed, unsaturated, styrenated alkyd resin containing both an amine-reactive type and a cobalt-reactive type, as well as amine and cobalt accelerators (total as it is available in the trade) a container ('pot') is added in which an electrical element is placed, placed so that it will be embedded, excluding the electrical connection cables to the element. A filler mixture is then allowed to flow down into the resin, which mixture is made from 100 parts dry sand, 4 parts dimethyl phthalate, % part benzoyl peroxide and % part cyclohexanone peroxide.

The filler is most suitably added to the resin in the form of a stream, preferably through a sieve to draw up lumps, without allowing the filler to build up into a layer on the surface of the resin; in this way the release of air is facilitated. A funnel provided with a sieve and a wide outlet opening has been found to be most satisfactory.

The last example was repeated using a liquid epoxy resin and a liquid polyurethane resin instead of the styrenated polyester resin. The result was as in the previous example.

A feature of the invention is that it is unnecessary to use robust containers for the resin when such casting in containers. Electrical connections and/or equipment can be embedded satisfactorily using containers of flexible material, such as e.g. paper, cardboard mache, or thin plastic, which can be produced more cheaply than the traditional ceramic

"pots"; holes can be filled temporarily using malleable material, such as putty or modeling clay. The individual connecting joints can be cast in before the entire joint or device is submerged, or ordinary sealing drives, screw nipples or other sealing can be used.

Although the resins used according to the invention are cold-curing, this does not preclude the use of heat when faster curing is desired, or in very cold environments.

Claims (3)

1. Process for casting cold-hardening, solvent-free, synthetic resins, whereby the liquid resin is fed into a container and then a heavy, granular filler is added through the free surface of the nar-pix, characterized in that the filler is added to a catalyst for the resin and an inert liquid compatible with the resin, the inert liquid being present in an amount only sufficient to wet the surface of the filler so that the mixture of filler, catalyst and liquid forms a moist, crumbly mass. 2. Method according to claim 1, characterized in that a resin is used comprising an unsaturated alkyd resin, a catalyst comprising an organic peroxide and an inert liquid which is a plasticizer for the resin. 3. Method according to claim 1, characterized in that the filler is allowed to flow to the resin surface from a screening device.