Better way found to produce compact hinges

Cosmetic powder compacts have been usually hinged using solid pins or even metal wire cropped to length, but manufacturers saught a better way to produce the compact hinges.

Cosmetic powder compacts have been usually hinged using solid pins or even metal wire cropped to length.

In an industry where margins are small and volumes high, the compact with the cheapest price has traditionally been the driving factor.

However, with increasing quality demands, the need to eliminate scrap, and product failures, the moulder and cosmetic manufacturers are seeking a better way to produce the compact hinges.

Spirol Industries were called upon to provide the solution with their coil pins which have been specified for a new line of cosmetic compacts.

Previously the practice of the moulder was to design misalignment into the holes to create a friction hinge.

This was in response to the demand from cosmetic companies for the lid of the compact to be able to be held open for display purposes and create a smooth hinge action.

The pins were normally assembled at the moulding machine whilst the plastic was hot.

This made assembly easier, but as the component cooled and shrunk, the unyielding pin generated stress on the plastic.

This result was hinges cracking and failure of the compact resulting in considerable scrap levels.

Allied to this was a problem with production throughput.

It was easy to mould the compacts, but assembling such a small pin was problematic, especially with cropped wire that had ends with burrs and would not enter easily into the holes.

Spirol Industries' coil pins have now become the fastener of choice for plastics, because they fit readily into holes and also because they distribute stress uniformly.

They were the ideal solution for the cosmetic compact.

As the pin is a helical spring throughout its length and has smooth swaged chamfers, it accommodates small misalignments and minor diameter variances between mating parts as it is being inserted.

Due to the radial pressure of the pin in the hole, it is no longer necessary to design and mould in misalignment to create the friction hinge.

This significantly reduces scrap and rejects.

Another cost reduction improvement using the coil pin is through reduced assembly time.

Typically, the pins used in this application are less than 1.5mm in diameter and this in itself was a problem.

However, when the Spirol coil pin is coupled with the automatic HC pin insertion machine, specifically developed by Spirol for this application, productivity has also been increased significantly.

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