GB2320761A - Frost proof testing a ceramic article - Google Patents

Abstract

A method of frost proof testing a ceramic article comprising the steps of covering at least part of the body with a liquid comprising water to attempt to at least partially impregnate the article with the liquid, to ascertain whether the article is porous, reducing the temperature of the article to below the freezing point of water; and then allowing the article to thaw. A pot which has any degree of porosity cannot be completely frost proof, as the porosity will make it susceptible to frost damage.

Description

TESTING FROST PROOF CERAMICS The present invention relates to a method of testing a ceramic or other earthenware article for its ability to withstand frost, in order to determine a "frost proof" status, as opposed to a "frost resistant" status; and/or to ensure that an article is correctly designated as "frost proof".

This invention relates particularly, but not exclusively, to a method of testing articles in the form of ceramic garden or patio pots, however other applications include hanging pots, wall hangers, house bricks and ceramic roof tiles, or any other ceramic, fired clay or earthenware article.

One particular problem associated with ceramic pots and containers intended for use outdoors e.g. in gardens, patios and on walls, is the tendency towards damage due to the action of frost. It is a well-known fact that when water is absorbed into the walls of porous earthenware pots, freezing temperatures will cause that water to expand and the pots will often crack, laminate, effloresce or simply fracture.

The action of frost can break all types of "frost resistant" natural ceramics, including low fired and high fired earthenware and stoneware, and even natural stone or rock. In general, it is not the general weather conditions which causes damage to ceramic or earthenware pots, but rather the damage is caused naturally by hydrolic expansion activity i.e. the expansion of gases, liquids and solids, such as water, when trapped within a confined space or area.

This is why some pots of a porous nature can survive frost damage for many years, because the porosity provides an escape route, and therefore hydrolic action is avoided. If the pores of the pot, or other article, become partially or completely sealed, for example by ice, hydrolic action would then occur, resulting in the breaking of the pot.

Attempts have been made in the past to obviate this problem by making surfaces of the pot water repellent or waterproof, eg by glazing. If the glaze is applied while there is still some moisture in the earthenware then freezing temperatures will nevertheless have the same detrimental effect on the ware. Further, it has been found that because of the environment in which garden or patio pots are used and located, damage is often suffered by the glaze, allowing ingress of water or moisture which is acted upon by the freezing temperature so that expensive and attractive pots are damaged and often destroyed.

At the Ceramic Research Centre in Stoke-on-Trent, UK, a test has been developed for ceramics which attempts to mimic the weather conditions which might cause damage to the pots. First a pot being tested is made wet and filled with wet peat. It is then placed within a freezer so that the pot is frozen. The pot is removed from the freezer and water is poured over the body to mimic the thawing out process during rain conditions. The freeze and thaw process is then continued over a period of time. If the pot survives this expensive and time consuming process, it is labelled as "frost proof".

However, by its very nature, this method of testing can only achieve a "frost resistant" ceramic. This method of testing might actually reduce hydrolic expansion activity by providing an escape route for the gases, liquids and solids.

Siliconed pots and other impregnated ceramics such as tiles and bricks are not frost proof, but rather are water repellent, since they retain moisture, particularly in inclement weather conditions, or under hydrostatic pressure. With reduced porosity, moisture build up over longer retention periods tends to provide a catalyst for hydrolic expansion activity. Moisture trapped within sealed bodies will also provide a means for hydrolic expansion activity.

Many of these treated pots are designated as "frost proof" when a designation of "frost resistant" would be more appropriate, as they still might be damaged in frosty conditions, when in use.

A need therefore exists for a more complete testing procedure which incorporates and allows for hydrolic expansion activity, and which more accurately determines whether a body is "frost proof".

It is therefore an object of the present invention to provide a method of testing whether a ceramic item is frost proof, and/or to more accurately mimic frost action within a ceramic article; and or to provide improvements in relation to one or more matters discussed above, or generally.

It is intended that one use of the method of the present invention is for testing ceramic pots which have been designated as "frost proof", to check that this designation has been correctly assigned.

According to the present invention there is provided a method of frost proof testing as claimed in the accompanying claims.

In an embodiment, the testing process comprises a first step of cleaning and drying the article to be tested, so that the pot is returned to its natural state. In an embodiment this comprises heating the article to be tested, for example by firing in a kiln, and then allowing the article to cool. The heating of the article may correspond to the firing of the article as part of the manufacture process. This stage of the process removes any foreign or waste matter, such as an existing coating, and excess moisture content in the body of the ceramic. Even at this stage, the ceramic body may break if the catalyst for hydrolic expansion activity is present.

Alternatively removal of the moisture content may be effected by subjecting the article to a vacuum, eg by sealing the ware in a tank and then connecting to a vacuum source or the article may be exposed to a carbon dioxide atmosphere.

Once the body has cooled, the next stage in the process is to attempt to impregnate the ceramic with water or a silicone containing liquid or solution comprising water.

This process may be done at an increase pressure if necessary, to increase the efficiency of the process and/or to reduce the treatment time. It is not necessary to completely impregnate the pot, as long as at least the surface of the pot is impregnated.

If the ceramic is porous, then it will take in the solution. A pot which has any degree of porosity cannot be completely frost proof, as the porosity will make it susceptible to frost damage. However, it may be difficult to ascertain whether the pot has become taken in the liquid, without continuing further with the test.

Therefore, in order to ensure retention of any fluid absorbed during the impregnation stage, the surface of the pot may be sealed or semi-sealed with a suitable surface treatment medium, which may be a silicone solution, a varnish, a lacquer, a paint or a rubber solution. The sealing of the pot ensures that hydrolic expansion activity will take place, if it is going to, during the next stage of the process.

The next stage in the process is to reduce the temperature of the article to below at least the freezing point of water, until the required degree of freezing takes place.

After freezing the body, the next stage in the process is to allow the article to thaw. This may be done naturally, or it may be achieved by raising the temperature of the article in a drying cabinet, kiln or fire, until the pot is either fully thawed, or until a result is achieved, namely the cracking or breaking of the article to be tested.

If the article is able to survive the process then it may more accurately be described as frost proof. Otherwise, if the article is susceptible to hydrolic expansion activity, then it will not survive the testing process, which closely mimics frost action within the body.

This process may be used on the whole of a ceramic article, or only part of it, and may be repeated if necessary.

An embodiment of the invention will now be described by way of example only, with reference to the following illustrative drawings in which: Figure 1 is a view of a ceramic pot to be frost proof tested; Figure 2 is a section view the pot of Figure 1 as it is dried in a kiln; Figure 3 is a section view through the pot which has been impregnated with a silicone solution; Figure 4 is a section view through the pot during the next stage in the process, in which the silicone solution is drained; Figure 5 is a section view through the pot which has been frozen as part of the testing process; and Figure 6 is a section view through the ceramic pot which has been heated as part of the testing process to thaw the pot.

Figure 1 illustrates a ceramic pot P, having side walls W, which is to be tested to see if it is frost proof. As seen in Figure 2, the pot P is first fired in a drying oven 2, such that any moisture within the pot P is caused to evacuate. The firing process also removes foreign matter from the pores of the pot, such an earlier surface treatment. The pot P may crack or break at this stage due to hydrolic action as the pot P is dried.

Alternatively removal of the moisture content may be effected by subjecting the article to a vacuum, eg by sealing the ware in a tank and then connecting to a vacuum source or the article may be exposed to a carbon dioxide atmosphere (not shown).

After cooling, the dried pot P is then placed within a tank 4 containing a silicone water solution Ss which will impregnate the pot hydrostatically, if the pot P is porous, and therefore susceptible to frost damage. To expedite the impregnation process a lid 6 is sealingly fitted over the top of the tank and compressed air is fed through a port 8 to pressurize the tank, as seen in Figure 3. The tank remains in this condition for a pre-determined period of time according to the size and thickness of the pot or pots placed therein.

If desired, the silicone solution may include any other vehicle besides water, eg a solvent. In this specification, unless otherwise stated, references to a "silicone solution" in water are intended to refer to a solution or dispersion or emulsion of a silicone compound in water, for example an aqueous solution of potassium methyl siliconate.

The tank is then depressurized and the solution is drained away via a drain cock 10 as seen in Figure 4. The silicone impregnated walls of the pot P are then sealed to maintain any moisture absorbed within the pot P.

Figure 5 illustrates the next stage in the test process.

The pot P is placed in a freezer 16, or otherwise frozen.

Once fully frozen, the pot P is thawed by kiln firing in a kiln 14, as shown in Figure 6. However, the pot P could be left to thaw naturally.

At the end of this process, a ceramic pot P will either be damaged by the thawing process, which indicates that the pot would not have withstood frost action in use, and therefore should not have been designated as frost proof.

Alternatively, if the pot P remains in tact and undamaged, it indicates that the pot P is likely to withstand frost action, and may be designated as "frost proof".

Although the process of the invention has been described with reference to a ceramic pot, it should be understood that it can be used in the frost proof testing of other fired clay products, eg house bricks, roof tiles, and unglazed floor tiles.

Claims (11)

1. A method of frost proof testing a ceramic article comprising the steps of: a) covering at least part of the body with a liquid comprising water to attempt to at least partially impregnate the article with the liquid; and b) reducing the temperature of the article to below the freezing point of water; and c) allowing the article to thaw.

2. A method according to claim 1 further comprising the initial step of heating the article to render it clean and dry.

3. A method according to claim 2 wherein the article is heated within a drying kiln.

4. A method according to claim 2 or claim 3 wherein the heating of the article corresponds to the firing of the article as part of the manufacture process.

5. A method according to any one of the preceding claims wherein the article is initially prepared by subjecting the article to a vacuum, and optionally exposing the article to a carbon dioxide atmosphere.

6. A method according to any one of the preceding claims wherein the article is immersed in a water/silicone solution.

7. A method according to any one of the preceding claims wherein the liquid is caused to impregnate the article under super-atmospheric pressure.

8. A method according to any one of the preceding claims wherein the article is placed within a sealed tank containing water/silicone solution and the tank is pressurized to cause the solution to impregnate the article.

9. A method according to any one of the preceding claims wherein the surface of the pot is sealed or semi-sealed with a surface treatment medium, after the impregnation stage.

10. A method of frost proof testing a ceramic by attempting to at least partially impregnate the article with a liquid to ascertain whether the article is porous, freezing the liquid within the article, and then thawing the article to see whether it is damaged.

11. A method of frost proof testing a ceramic article substantially as herein described with reference to the accompanying drawings.