GB2248203A

GB2248203A - Improvements to castings

Info

Publication number: GB2248203A
Application number: GB9117707A
Authority: GB
Inventors: James Francis Reilly
Original assignee: REILLY ROYALTIES Ltd
Current assignee: REILLY ROYALTIES Ltd
Priority date: 1990-08-14
Filing date: 1991-08-14
Publication date: 1992-04-01
Also published as: ZA916407B; GB9117707D0

Abstract

In a method for producing cast components by low pressure or gravity casting pre-manufactured tubings or profiles 15, 16 are introduced into a mould and held in place by mandrels 17, 18. Molten material is then poured in to form the main body 11, 12 of the finished cast component, which has orifices 13, 14 corresponding to the orifices of tubing or profiles 15, 16 thereby obviating the necessity for subsequent machining steps. The pre-manufactured components 15, 16 are composed of material whose melting temperature is higher than that of the material being cast. The tubings may be mild steel, stainless steel or ceramics. The casting material may comprise glass fibre, polyethylene or polypropylene when the tubing is of ceramics. <IMAGE>

Description

IMPROVEMENTS TO CASTINGS The present invention relates to improvements to castings, in particular to low pressure and gravity castings, fligh pressure die casting is used to produce many precision engineering components. However, high pressure die casting is a very expensive process requiring the use of costly moulds and equipment. Standard gravity casing and low pressure casting processes are ccnsiderably less expensive; however, the components produced by gravity casting in particular generally require finishing by machining which adds to the product:or. costs of each item.

The object of the invention is to alleviate the disadvantage assore awed with gravity casting and also to provide the d@signer wth an alternative to special machinery processes to produce internal intricate shapes in a cast component.

The present invention provides a method of producing a component by low pressure or gravity canting comprising placing a pre-manufactured component or components having the required dimensicns, feature or element in a mould, the or each coapancnt being of a material which has a higher melting temperature than that of the molten material being cast, and introducing said molten material into the mould to produce the finished item cast about the form of and including the or each pre-manufactured components.

Conveniently, the pre-manufactured component comprises a length of tubing or profile about which the molten material is cast, the internal orifice of the tube or profile forming a required internal orifice of the finished item, thereby obviating the necessity for machining that orifice.

Preferably, the molten material is molten aluminium or a molten composite material.

Advantageously, the pre-manufactured component is composed of m d steel, stainless steel or ceramics.

Conveniently, the internal orifice provides an escape path fcr gas or air trapped within the molten material.

Te invention. also provides a cast or moulded component comprising a body of a solidified molten material formed about and including one or more pre-manufactured components of a material with a higher melting temperature than that of the molten material being cast.

The cast component produced by the method described has enhanced torquo capability on its internal orifice surface over a comparable component produced by the known gravity casting process, since the orifice of the known component requires machining which leads to a somewhat roughened surface, The component produced by the method of the invention, whose internal orifice derives from the pre-:nanufact#:red item, is of high quality.

The invention will hereinafter be more particularly described with reference to the accompanying drawing which shows by way Of example only, one embodiment of component according to the invention. The drawing is a cross-sectionas view of the component in a mould.

Referring to the drawing, the component 10 comprises two sections 11, 12, the section 11 having a blind orifice 13 and the section 12 having an open orifice 14. The orifices 13, 14 each comprise a length of stainless steel tubing 15, 16 held in position by mandrels 17, 18 respectively while molten aluminium is poured into the mould to form the component.

The internal diameters of the tubing t5, 16 are chosen for the particular requirement and are finished surfaces, i.e.

they do not require any machining. The mandrels 17, 18 are centralised through closing of the mould halves and also held in position during the pouring process. The mould is a G17 grade cast iron mould.

As well as allowing the inside diameter of a cast component to be determined during the moulding process itself, the process can also be used to control the depths of finished bores by varying the length of the mandrel.

The oriontation and fixing of the mandrels in the mould can also provide for tne production of acceptable porpondicularity and parallelism tolerances on the finished items. This process and invention can thus be utilised in the development of suitable hinge mcchanisms through the application of T components for various D.1.V. assemblies.

The process lends itsolf to the production of components with improved strength characteristics in load bearing surfaces, when casting composite materials such as, for example, glass fibre or high density polyethylena or polypropylene. In such cases, the pre-manufactured component may be a ceramic or other suitable material.

Uniform wall thicknesses are attainable through strict control of the charactcristjcs of the pour and gas relieve points. The limit and fit desired between mandrel 17 and pre-manufacturod component 15, 16 can be chosen to provide a functional vent path for inherent trapped gases and air bubbles present in the molten material during the pouring process. Providing an escape path in this way reduces the tendency toward sponginess in the cast product and results in components with good wall integrity.

The intricacy of the inner profile of the finished castings is unlimited, and requires only the manufacture of suitable mandrel forms. The commercial availability of profile forms for the pre-manufactur#d components makes the process suitable for the production of interconnecting fittings in structure formation and assembly, and obviates the necessity for machining the many internal profiles which must otherwise be produced by techniques such as electrochemical (ECM), electrical discharge machining (EDM) or spark erosion.

In the operation of the invention the moulds are prepared with the necessary cavities in the form of the finished component, togethor with fixtures for accepting the mandrels. The operator assembles the pte-manufactured components on the mandrels and closes the mould ready for pouring. When the process itself is one of gravity die casting, strict control of metal temperature is required.

Through the introduction of appropriate vent pats and injector pins, sound and effective components can be produced economically. Thus, the process provides a cost effective method of producing batches of components having intricate shapes, particularly having shaped or unshaped internal orifices, for inclusion into assembly operations.

Components produced by the method described are particularly s'jitable for use as couplings, for example in scaffolding, hospital beds, stretchers and the like.

Claims

1. A method of producing a component by low pressure or gravity casting comprising placing a pre-manufactured component or Components having the required dimensions, feature or e#omont in a mould, the or each component being of a material which has a higher melting temperature than that of the molten material being cast, and introducing said molten material into the mould to produce the finished item cast about the form of and including the or each pre-manufactured compononts.

2. A method according to Claim 1, in which the pre-manufactured component comprises a length of tubing or profile about which the molten material is cast, the internal orifice of the tube or profile forming a required internal orifice of the finished item, thereby obviating the necessity for machining that orifice.

3. A method according to Claim 1 or Claim 2, in which the molten material is molten aluminium or a molten composite matorial.

4. A method according to Claim 1 or Claim 2, in which the pre-manufactured component is composed of mild steel, stainless steel or ceramics.

5. A method according to Claim 2, in which the internal orifice provides an escape path for gas or air trapped within the molten material.

6. A cast component produced by a method according to any preceding claim.

7. A method of producing a component by low pressure or gravity casting substantially as herein described with reference to the accompanying drawing.

8. A cast or moulded component comprising a body of a solidified molten material formed about and including one or more pre-manufactured components of a material with a higher melting temperature than that of the molten material being cast.

9. A component according to Claim 8, in which the pre-manufactured component comprises a length of tubing or profile about which the molten material is cast, the internal orifice of the tube or profile forming b required internal orifice of the finished item, thereby obviating the necessity for machining that orifice.

10. A cast component whenever produced by a method according to Claim 7.

11. A cast component substantially as herein described with reference to and as shown in the accompanying drawing.