GB1598348A - Method of pressure die casting or injection moulding articles - Google Patents

Description

(54) METHOD OF PRESSURE DIE CASTING OR INJECTION MOULDING ARTICLES (71) We, MARLEY EXTRUSIONS LIMITED, a British Company, of Lenham, Maidstone, Kent, 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 present invention relates to a method for pressure die casting metals and metal alloys and injection moulding plastics.

In the past, it has only been possible to cast or mould articles having undercuts by the use of collapsible cores and/or by using a large number of mould parts which, when the moulding or casting process has been completed, are withdrawn in different directions. Both these methods suffer from the disadvantage that they require complex apparatus and are consequently expensive.

In order to avoid using such complex methods, objects having undercuts are sometimes produced by the use of one or more machining steps subsequent to the moulding step. However, it will be appreciated that such a procedure will again involve undesirable expense as compared with a simple moulding or casting process.

Another expedient which has been used is to make the undercut with faces which are oblique to the direction of mould separation. The moulded article can then be stripped off one of the mould halves after the mould halves have been separated. By this method, pipes, gutters, and other articles can be manufactured with V-shaped grooves and projections. However, for positive interlocking of parts to be joined and for retaining seals, such as O-rings, in place, abutting surfaces substantially normal to the axis of the pipes or gutters are required.

Such surfaces however, lock the moulded article to the mould, and thus prevent the manufacture of the article in a conventional two part mould.

It is an object of this invention to provide a method of pressure die casting or injection moulding of articles as herein defined which overcomes or greatly reduces the abovementioned disadvantages and permits such articles to be readily produced in two part moulds.

By "articles as herein defined" we mean articles having on an interior surface undercuts, grooves or reentrant portions extending in a direction generally normal to the axis of the article and to the line of withdrawal of the cooperating mould parts.

According to one aspect of the present invention we provide a method of pressure die casting or injection moulding an article as herein defined comprising forming a two part mould which defines the shape of the article, providing at least one tongue extending from the face of one of the mould parts in a direction substantially parallel to the line of withdrawal of the mould parts, the or each tongue having a face on the end thereof substantially normal to the line of withdrawal of the mould parts, said face serving to form a surface of an undercut groove or reentrant portion of the article, closing the mould parts together along said line of withdrawal, so that the or each tongue comes into contact with the other of the mould parts, feeding the material for making the article between the two mould parts and around the or each tongue, and separating the mould parts so that the or each tongue is withdrawn from the article through a slot formed therein by said tongues and removing the article from the mould.

According to another aspect of the invention we provide a moulded or pressure die cast article as herein defined made by a method as set forth in the immediately preceding paragraph.

Such an article will have a slot through one face thereof corresponding to the shape and position of the or each undercut face produced by the end surface of a tongue.

One article as above set forth within the scope of the invention is a generally circular cap for closing the end of a pipe or access chamber to a drain for example, such cap having a continuous peripheral flange extending generally normal to what in use will be its outer end surface, and having extending generally parallel to said end surface two or more dogs arranged in use to lock the cap to mating flanges on a pipe or access chamber, said end surface having slots therethrough at the location of said dogs.

The invention will be further described as applied to one particular article as herein defined by way of example only and with reference to the accompanying drawings: Figure I is a top plan view of a drain access cap produced by the method of the present invention, and Figure 2 shows a cross-section on line II-II through the drain access cap shown in Figure 1; and Figure 3 is a cross-section through a mould for producing the article shown in Figures 1 and 2 by injection moulding.

As shown in Figures 1 and 2, the cap 1 has a depending flange 2 which extends around the entire circumference of the cap. On the flange 2, there are arranged four inwardly projecting dogs 3. These dogs are arranged to engage corresponding outwardly extending dogs or a flange around the end of a cylindrical pipe, whereby the cap may be placed on the end of the cylindrical pipe and twisted by means of lugs 8 so that the two sets of dogs interengage to lock the cap onto the end of the pipe. The leading edge of each dog is tapered so that when the cap is applied and twisted initial engagement between the respective dogs is simplified and a full twist of the cap into locking or pressure engagement can be easily achieved.

It would not be possible to produce such a cap by a conventional injection moulding process in a two part mould without using costly collapsible cores, since the dogs 3 would lock the cap to the upper mould part 9 as shown in Figure 3. However, by using a method according to the invention, the cap is produced in a two part mould, the lower part 10 of which, referring to Figure 3, has four tongues 11 extending from the face thereof. Each tongue 11 forms a slot 4 in the circular portion 5 of the cap and has an end face which is perpendicular to the line of draw of the mould parts and which defines the surface 7 of the dog 3. Each tongue contacts the mould part 9 along a surface 6.

The tongue is tapered along its inner face by about 5 to assist mould release.

It will be seen that by simple moulding or die casting in a two part mould, caps for access chambers can be made economically and without the various disadvantages above mentioned. It will be understood that as outlined above the invention is not restricted specifically to such access caps.

WHAT WE CLAIM IS: 1. A method of pressure die casting or injection moulding an article as herein defined, comprising forming a two part mould which defines the shape of the article, providing at least one tongue extending from the face of one of the mould parts in a direction substantially parallel to the line of withdrawal of the mould parts, the or each tongue having a face on the end thereof substantially normal to the line of withdrawal of the mould parts, said face serving to form a surface of an undercut groove or reentrant portion of the article, closing the mould parts together along said line of withdrawal, so that the or each tongue comes into contact with the other of the mould parts, feeding the material for making the article between the two mould parts and around the or each tongue, and separating the mould parts so that the or each tongue is withdrawn from the article through a slot formed therein by said tongues and removing the article from the mould.

2. A method as claimed in claim 1, wherein the or each tongue comes into contact with said other mould part along a surface at a slight angle to the line of withdrawal of the mould parts.

3. A moulded or die cast article made by a method as claimed in claim 1 or 2.

4. A generally circular cap for closing the end of a pipe or access chamber to a drain, the cap having been made by a method as claimed in claim 1 or 2, the cap having a continuous peripheral flange extending generally normal to what in use is its outer end surface and having extending generally parallel to said end surface a plurality of dogs arranged in use to lock the cap to mating flanges on said pipe or access chamber, said end surface having slots therethrough at the locations of said dogs.

5. A method of injection moulding a cap substantially as herein described with reference to the accompanying drawings.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. and position of the or each undercut face produced by the end surface of a tongue. One article as above set forth within the scope of the invention is a generally circular cap for closing the end of a pipe or access chamber to a drain for example, such cap having a continuous peripheral flange extending generally normal to what in use will be its outer end surface, and having extending generally parallel to said end surface two or more dogs arranged in use to lock the cap to mating flanges on a pipe or access chamber, said end surface having slots therethrough at the location of said dogs. The invention will be further described as applied to one particular article as herein defined by way of example only and with reference to the accompanying drawings: Figure I is a top plan view of a drain access cap produced by the method of the present invention, and Figure 2 shows a cross-section on line II-II through the drain access cap shown in Figure 1; and Figure 3 is a cross-section through a mould for producing the article shown in Figures 1 and 2 by injection moulding. As shown in Figures 1 and 2, the cap 1 has a depending flange 2 which extends around the entire circumference of the cap. On the flange 2, there are arranged four inwardly projecting dogs 3. These dogs are arranged to engage corresponding outwardly extending dogs or a flange around the end of a cylindrical pipe, whereby the cap may be placed on the end of the cylindrical pipe and twisted by means of lugs 8 so that the two sets of dogs interengage to lock the cap onto the end of the pipe. The leading edge of each dog is tapered so that when the cap is applied and twisted initial engagement between the respective dogs is simplified and a full twist of the cap into locking or pressure engagement can be easily achieved. It would not be possible to produce such a cap by a conventional injection moulding process in a two part mould without using costly collapsible cores, since the dogs 3 would lock the cap to the upper mould part 9 as shown in Figure 3. However, by using a method according to the invention, the cap is produced in a two part mould, the lower part 10 of which, referring to Figure 3, has four tongues 11 extending from the face thereof. Each tongue 11 forms a slot 4 in the circular portion 5 of the cap and has an end face which is perpendicular to the line of draw of the mould parts and which defines the surface 7 of the dog 3. Each tongue contacts the mould part 9 along a surface 6. The tongue is tapered along its inner face by about 5 to assist mould release. It will be seen that by simple moulding or die casting in a two part mould, caps for access chambers can be made economically and without the various disadvantages above mentioned. It will be understood that as outlined above the invention is not restricted specifically to such access caps. WHAT WE CLAIM IS:

1. A method of pressure die casting or injection moulding an article as herein defined, comprising forming a two part mould which defines the shape of the article, providing at least one tongue extending from the face of one of the mould parts in a direction substantially parallel to the line of withdrawal of the mould parts, the or each tongue having a face on the end thereof substantially normal to the line of withdrawal of the mould parts, said face serving to form a surface of an undercut groove or reentrant portion of the article, closing the mould parts together along said line of withdrawal, so that the or each tongue comes into contact with the other of the mould parts, feeding the material for making the article between the two mould parts and around the or each tongue, and separating the mould parts so that the or each tongue is withdrawn from the article through a slot formed therein by said tongues and removing the article from the mould.

2. A method as claimed in claim 1, wherein the or each tongue comes into contact with said other mould part along a surface at a slight angle to the line of withdrawal of the mould parts.

3. A moulded or die cast article made by a method as claimed in claim 1 or 2.

4. A generally circular cap for closing the end of a pipe or access chamber to a drain, the cap having been made by a method as claimed in claim 1 or 2, the cap having a continuous peripheral flange extending generally normal to what in use is its outer end surface and having extending generally parallel to said end surface a plurality of dogs arranged in use to lock the cap to mating flanges on said pipe or access chamber, said end surface having slots therethrough at the locations of said dogs.

5. A method of injection moulding a cap substantially as herein described with reference to the accompanying drawings.