GB1594209A - Foundry processes and compositions - Google Patents

Description

(54) FOUNDRY PROCESSES AND COMPOSITIONS (71) We, THE WHITE SEA & BALTIC COMPANY LIMITED, a British Company, of Patman House, George Lane, South Woodford, London E18 2SA do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The normal way of making a foundry mould or core comprises shaping a mixture of foundry sand and of binder in a mould or core box and allowing the mixture to set, preferably at room temperature. It is often preferred to use an organic resin condensate as the binder in which event the mixture has to include also an acid catalyst to promote setting.

The normal way of making such a mixture is to disperse the catalyst uniformly through the sand and then to add binder. If the mix is formed the other way round, with the acid catalyst being added to a preformed mix of binder and sand, localised curing of the binder starts immediately the acid contacts the mixture and so non-uniform curing occurs.

Conventional mixtures of sand and binder that are to be shaped behave substantially as solids and have to be rammed or otherwise mechanically forced into the core or mould box.

In British Patent Specification No. 1,085,651 and U.S. Patent Specification No. 3,424,600 Liass disclosed the concept of making a fluid sand composition in which the aqueous phase was foamed, as a result of which the composition could be shaped merely by pouring it into the box. Unfortunately the specific compositions described by Liass are not entirely satisfactory, even when the mould is vibrated. In the process of Liass and subsequent proposals of making fluid mixtures of foundry sand and a foamed aqueous phase it seems generally to have been considered desirable or necessary that the materials used and the conditions of mixing should be such that the foam collapses soon after its formation and usually quickly, e.g. a few seconds or minutes, after being poured into the mould or core box.Thus the foam collapses before setting and as a result a permeable set structure is obtained that is substantially denser and stronger than would be obtainable if the foam had not collapsed before setting. Also in these processes the usual order of mixing the sand, binder and catalyst (i.e. catalyst first) seems to have been generally accepted as being necessary and indeed the only disclosures of which we are aware of processes in which the acid is added to a preformed fluid mix of sand and foamed aqueous phase containing binder are Examples 12 and 13 of British Patent Specification No. 1,430,841 and it is stated in that specification that the compressive strength of the products of these Examples is inferior to the compressive strength of the products of the other Examples in that specification (in which acid is mixed with the sand before the binder was added) even though more acid was used.

In British Patent Specification No. 1,373,647 we have described how improved results can jbe achieved if the composition contains a silane and in the described process the foam is stable, that is to say it does not break until the composition sets, the foam bubbles breaking during setting. Such processes are very advantageous because the stability of the foam means that the composition will conform accurately to the mould during setting and will not shrink away from complex shapes before setting. and the preferred compositions described in that specification, using a silane and, preferably, a sodium lauryl ether sulphate foaming agent, are capable of giving good overall strength and in particular good surface smoothness and strength.The conventional method of forming foundry mixtures was described in that specification, the acid being mixed with the sand before addition of the binder.

We have now surprisingly found that the amount of water in the total mixture can be reduced far below the 2.0CHc figure suggested in our British Patent Specification No.

1,373,647. When the binder is free of urea and is a condensate of two or more of phenol, formaldehyde and furfuryl alcohol best results are obtained when the amount is 0.9 to 1.5% by weight. A method according to the invention of making a foundry mould or core thus comprises forming a fluid mixture that is stable against collapse before setting and that comprises a foundry sand and a foamed aqueous phase comprising resin condensate, foaming agent and an acid curing agent. pouring the fluid mixture into a mould or core box and allowing the mixture to set, and in which method the total amount of water in the fluid mixture is 0.9 to 1.5% by weight and the resin condensate is free of urea and is a condensate of two or more of phenol, furfuryl alcohol and formaldehyde.

The minimum amount of water is controlled by the need to form a fluid mixture having an appropriate foamed aqueous phase and for this reason the amount must be at least 0.9% by weight. Water is usually introduced both with the resin condensate and the curing agent and so preferably no additional water is added.

The fluid mixture may be made by conventional methods, i.e. mixing the acid with the sand and then adding the binder. However preferably the fluid mixture is made by forming a fluid mix of the sand and a foamed aqueous phase comprising the resin condensate and foaming agent and then mixing the acid curing agent into this. This method is described and claimed in our application No. 51811/76 (Serial No. 1594208) from which the present application is divided.

The fluid mixture obtained in the invention can easily be made having fluidity such that it will readily flow into the mould or core and conform accurately to its shape without the need for mechanical assistance, e.g. ramming or vibration of the mould or core box.

Accordingly in the preferred process no consolidation techniques are applied and the mould or core box remains immobile throughout.

A number of foaming agents are capable of giving fluid mixtures that are stable against collapse before setting, including certain fatty amido alkyl betaines, such as that sold under the trade name "Lorapon AMB13" which is a cocoamide alkyl betaine, and certain substituted imidazolines such as those sold under the trade names "Crodateric C" and 'Crodateric L" but the strength of the cured product with these may not be as high as is desirable even when used in the composition of British Patent Specification No. 1,373,647, and best results are obtainable when using a lauryl ether sulphate, generally sodium lauryl ether sulphate.

Suitable sodium lauryl ether sulphates are those obtained by ethoxylating lauryl alcohol with, for instance, a chain of three ethoxy groups, and sulphating the product. Examples of such materials are those sold by Lankro Chemicals under the trade name "Perlankrol ESD" and those sold by Albright & Wilson Limited under the names "Empimin KSN 27" and "Empimin KSN 60" "Empimin" is a trade mark. They are all an industrial grade of sodium lauryl ether sulphate based on a narrow cut lauryl alcohol, "Perlankrol ESD" and "Empimin KSN 27" being 27% aqueous solutions and "Empimin 6P" being a 60% aqueous solution containing about 10% ethanol.

The amount of foaming agent will be chosen having regard to the stability that is desired upon pouring and having regard to the choice of foaming agent and other components in the mix. Generally the amount is from 0.05 to 0.5%, preferably 0.1 to 0.5%, dry weight based on the weight of foundry sand. In general rather more foaming agent is needed when the resin is a phenolic resin than when it is for instance a furfuryl alcohol resin.

The resin condensates used are preferably furfuryl alcohol/formaldehyde or phenol formaldhyde resin condensates but it can be advantageous for the binder composition also to contain free furfuryl alcohol. The resin condensates are usually water-soluble and are normally available and used in the form of aqueous compositions, e.g. solutions, containing from 1 to 30% by weight of water. The aqueous resin condensate composition is usually used in an amount of 1 to 5% based on the weight of the foundry sand e.g. 0.75 to 4.5% resin solids. Preferably we use 0.8 to 2%, preferably 1 to 1.75%, of aqueous resin condensate, the condensate usually containing 10% water if the resin comprises phenol formaldehyde.

In order to obtain products of good strength, and especially good surface strength, it is preferred to include a silane in the fluid mixture, for instance as described in British Patent Specification No. 1,373,647. The silane is best mixed with the resin before, and preferably just before, the resin is mixed with the sand.

The silane must be one that will improve the strength of a composition containing the binder, some silanes being more suitable for use with some binders than others. In general the silane will be preferably of general formula R'Si(OR) in which R' is a C-C" alkylene group bonded to an amino. epoxy, mercapto, hydroxy, hydroxy-C1-C6 alkylamino, amino-C,-C" alkylamino, C7-C, alkenyl or C-C6 alkenylcarboxy group and the groups R may be the same or different and are selected from CI-C, alkyl and C,-C" alkoxy substituted-C1-C6 alkyl.The amount of silane used is usually from 0.05 to 0.5%, preferably from 0.1 to 0.2%, based on the total weight of aqueous resin condensate composition and silane.

Any acid that will serve as a curing agent for the resin condensate may be used in the invention and many such acid curing agents are known. Preferred curing agents comprise one or more of phosphoric acid, p-toluene sulphonic acid and sulphuric acid, mixtures of the last two being particularly preferred. The amount of curing agent, on a non-aqueous basis, is generally from 10 to 150%, preferably 50 to 75% by weight based on the amount of resin solids or 0.3 to 2% based on the weight of foundry sand. However the curing agents are preferably introduced as aqueous solutions generally containing 15 to 40% water. The amount of aqueous curing agent is generally 10 to 150%, preferably 50 to 75%, based on aqueous resin condensate or 0.5 to 2.5% based on the weight of foundry sand.

Any particulate inorganic material suitable for use as the sand of a foundry mould or core may be used in the invention, conventional sand being preferred.

The advantages and particular details of the preferred method of mixing the ingredients are described in Application No. 51811/76 (Serial No. 1594208).

To make a foundry mould or core in the invention preferably the sand, binder, silane and foaming agent are mixed together under conditions and for a duration sufficient to obtain adequate distribution of the components and a foamed aqueous phase, the acid catalyst is then added and further mixing is conducted, and the mixture is then poured. The duration of each mixing steps depends inter alia upon the type of mixer being used. Conventional mixers are satisfactory. The first mixing stage often lasts from 1 second to 3 minutes, e.g. 1 to 30 seconds in a continuous mixer or 1 to 3 minutes in a batch mixer, while the second mixing stage, after or during adding the acid, often lasts 1 to 90 seconds, e.g. 1 to 30 seconds in a continuous mixer or 30 to 90 seconds in a batch mixer.

In the preferred processes of the invention the mixture has a very high stability against collapse before curing, and as a result it is not necessary to select the quantity of each component as critically as has to be done with many conventional processes, where the foam is designed to collapse, or at least does collapse, very quickly. Whether or not foam has collapsed can be determined by measuring the permeability of the cured mould, since if curing occurs before there is any subtantial collapse the permeability and density of the mould will be low whilst if there has been substantial collapse of the foam before the mix starts setting the density (and strength) and permeability would be higher.

The following are Examples of the invention. In these the viscosity figure is the time in seconds during which 2 kg sand drops from the mixer in the test described below. It is desirable for the figure to be as low as possible since low figures indicate low viscosity and therefore a mixture which will pour easily and conform accurately to an intricately shaped mould. The viscosity test uses a viscometer which consists of mild steel vessel with an opening at the bottom. The shape of the vessel is a cylinder of 170 mm diameter 180 mm high finishing at the bottom with a cone 65 mm high and cut for the outlet. The diameter of the outlet is 45 mm and it is closed by a shutter connected electrically with a stop watch.

Inside the cylinder there is a stirrer with 8 blades round the vertical shaft and which rotates at 85 revs per minute.

The mixer serves to prepare a mix of 4000 grammes of fluid sand. When ready (after 41/2 mins of mixing) the shutter is opened manually and sets the stop watch in motion. The sand drops into a tared container. Its bottom is placed 350 mm below the opening of the mixer.

The container is placed on a scale having a dish which, when it receives a weight of 2 kg of sand, tilts and electrically stops the stop watch to record the viscosity figure that is quoted.

Examples 1 to 4 4 kg sand, binder (b), foaming agent (F) and 60 g (1.5%) curing agent (C) were mixed in the amounts and order given below in Table 1 in the vessel described above the viscosity of the mix was measured as described above. The binder was a phenol formaldehyde furfuryl alcohol binder containing 10% water and 0.2% silane (the product sold as A1100), the foaming agent was the 27% solution of sodium lauryl ether sulphate sold under the trade name "Perlankrol ESD" and the curing agent was a composition having 33.13% water content and formed from 83.34% paratoluene sulphonic acid, 13.32% of 77% sulphuric acid and 2.34% water. The total amount of water in each mix was about 1.4% based on the weight of sand.

In Examples 2 and 4 the foaming agent and catalyst were first mixed with the sand thoroughly by a paddle mixer for 21/2 minutes, by which time the aqueous phase has foamed and the mixture fluid, and the binder and silane were then added and mixed with the paddle mixer for another minute, whereupon the viscosity was measured and the mixture was poured into a mould or core and left to set. Examples 1 and 3 were carried out in the same manner except that the binder, silane and foaming agent were mixed with the sand in the initial 21/2 minute mixing period and the curing agent was added afterwards, for the final minute mixing. The results obtained are shown in Table I.

TABLE I Example Binder (B) Foam Agent (F) Order of Viscosity g % g Wo Addition 1 71.5 1.7875 38.5 0.9625 B+F;C 13l/2 2 71.5 1.7875 38.5 0.9625 F+C;B 26 3 70 1.75 36 0.9 B+F;C 15 4 70 1.75 36 0.9 F+C;B 28 In each of Examples 1 to 4 the composition was poured into a mould and upon curing in the mould a product having good compression strength and having very high surface finish but having low density was obtained.

Examples 5 to 8 In these Examples the binder and foaming agent and apparatus used were broadly as described in Example 1, the catalyst was p-toluene sulphonic acid and the compressive strength after 24 hours was recorded in pounds per square inch. In Example 5 the binder was added last while in Examples 6 to 8 the curing agent was added last, and the amount of foaming agent and curing agent was reduced in Examples 6 and 7 and in Example 8 the amount of binder was also reduced. The results are given in Table IV. In Example 5 the amount of water in the mixture is about 1.4% but in the other Examples it is from about 0.9 to about 1.2%.

TABLE IV Example 5 6 7 8 Binder 1.75% 1.75 1.75 1.5 Foaming Agent 1.0 0.6 0.7 0.8 Acid 1.5 1.0 1.0 1.0 PTSA C+F:B B+F:C BtF;C B+F;C Viscosity 213/4 23 181/2 17 Compressive Strength 320 370 350 320 Example 6 shows that by mixing in the invention it is possible to have a very large reduction in the amount of foaming agent and curing agent, with a very small increase in viscosity and a significant increase in compressive strength, while Examples 7 and 8 show that by having a slightly smaller decrease in the amount of foaming agent one can obtain a desirable decrease in viscosity and improved compressive strength or, with less binder, an equivalent compressive strength and even greater reduction in viscosity.

All of these Examples show that satisfactory results are obtainable with the very low water contents in accordance with the invention but that best results are obtained when the acid catalyst is added last. Better results are obtainable in the invention using the specified low water contents than when the water content is about 2% and, especially, than when the water content is much higher than this, for instance as proposed in British patent Specification No. 1,085,651.

WHAT WE CLAIM IS: 1. A method of making a foundry mould or core comprising forming a fluid mixture that is stable against collapse before setting and that comprises a foundry sand and a foamed aqueous phase comprising resin condensate, foaming agent and an acid curing agent, pouring the fluid mixture into a mould or core box and allowing the mixture to set, and in which method the total amount of water in the fluid mixture is 0.9 to 1.5% by weight and the resin condensate is free of urea and is a condensate of two or more of phenol, furfuryl alcohol and formaldehyde.

2. A method according to claim l in which the total amount of water is 0.9 to 1.25% by

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. initial 21/2 minute mixing period and the curing agent was added afterwards, for the final minute mixing. The results obtained are shown in Table I. TABLE I Example Binder (B) Foam Agent (F) Order of Viscosity g % g Wo Addition

1 71.5 1.7875 38.5 0.9625 B+F;C 13l/2

2 71.5 1.7875 38.5 0.9625 F+C;B 26

3 70 1.75 36 0.9 B+F;C 15

4 70 1.75 36 0.9 F+C;B 28 In each of Examples 1 to 4 the composition was poured into a mould and upon curing in the mould a product having good compression strength and having very high surface finish but having low density was obtained.

Examples 5 to 8 In these Examples the binder and foaming agent and apparatus used were broadly as described in Example 1, the catalyst was p-toluene sulphonic acid and the compressive strength after 24 hours was recorded in pounds per square inch. In Example 5 the binder was added last while in Examples 6 to 8 the curing agent was added last, and the amount of foaming agent and curing agent was reduced in Examples 6 and 7 and in Example 8 the amount of binder was also reduced. The results are given in Table IV. In Example 5 the amount of water in the mixture is about 1.4% but in the other Examples it is from about 0.9 to about 1.2%.

TABLE IV Example 5 6 7 8 Binder 1.75% 1.75 1.75 1.5 Foaming Agent 1.0 0.6 0.7 0.8 Acid 1.5 1.0 1.0 1.0 PTSA C+F:B B+F:C BtF;C B+F;C Viscosity 213/4 23 181/2 17 Compressive Strength 320 370 350 320 Example 6 shows that by mixing in the invention it is possible to have a very large reduction in the amount of foaming agent and curing agent, with a very small increase in viscosity and a significant increase in compressive strength, while Examples 7 and 8 show that by having a slightly smaller decrease in the amount of foaming agent one can obtain a desirable decrease in viscosity and improved compressive strength or, with less binder, an equivalent compressive strength and even greater reduction in viscosity.

All of these Examples show that satisfactory results are obtainable with the very low water contents in accordance with the invention but that best results are obtained when the acid catalyst is added last. Better results are obtainable in the invention using the specified low water contents than when the water content is about 2% and, especially, than when the water content is much higher than this, for instance as proposed in British patent Specification No. 1,085,651.

WHAT WE CLAIM IS: 1. A method of making a foundry mould or core comprising forming a fluid mixture that is stable against collapse before setting and that comprises a foundry sand and a foamed aqueous phase comprising resin condensate, foaming agent and an acid curing agent, pouring the fluid mixture into a mould or core box and allowing the mixture to set, and in which method the total amount of water in the fluid mixture is 0.9 to 1.5% by weight and the resin condensate is free of urea and is a condensate of two or more of phenol, furfuryl alcohol and formaldehyde.

2. A method according to claim l in which the total amount of water is 0.9 to 1.25% by

weight.

3. A method according to claim 1 or claim 2 in which silane is included in the mixture.

4. A method according to claim 1 substantially as herein described with reference to any one of Examples 2, 4 or 5.

5. A foundry mould or core made by a method according to any preceding claim.