Criteria that can be used in making ejector sleeves, which will minimize or eliminate failures as well as improve the performance and function of ejector sleeves and minimize maintenance.
Basically, the function of an ejector sleeve in a mold is to eject either an entire finish molded piece part or apply ejection force to some portion of the molded piece part to assist with part ejection, in combination with other ejection features designed into the mold.
Custom ejector sleeves ranging from 1/2" ID to 1 1/4" made using customer specified tool steel (typically H-13) and size specifications. Photos courtesy of Performance Alloys and Services, Inc.
There are also cases where the ejector sleeve contributes to partial ejection or repositioning of the molded part, or the sleeve functions to “shut off” some feature for multi-shot molding. These later ejector sleeve applications function principally to support the multi-shot requirement and tend to be challenging as well as unique.
Sleeves can have actual molding detail on the inside and/or outside surface or function with shut off features or just have the basic “molding surface” on the very end of the sleeve, which in effect becomes the molded surface where the ejection force is applied. The mold design and piece part design determine the exact functionality, quantities and sizes of sleeves for a given mold and the relative piece part.
The following information is intended to aid in identifying common causes of failure as well as minimize maintenance with ejector sleeve assemblies, highlighting just some of the basic criteria that can be used in making ejector sleeves.
Tool steel is still the most common selected sleeve material used by mold-makers and designers, but aluminum bronze alloys are another option.
It is important to understand that adherence to specific procedures must be followed to yield predictable results when using tool steel materials for ejector sleeves. It is also important to understand that not all moldmakers, manufacturers of standard off-the-shelf sleeves or custom sleeve manufacturers neither agree with nor utilize the procedures suggested in this article.
Some sleeve manufacturers have taken the position that if they make the sleeves and the customer agrees to the manufacturer recommended material choice, running fits, clearances and coatings, a warranty for the sleeve life for an excess of three years in continuous running molds will be given (obviously this warranty would not be valid for component misuse or machine malfunction).
Tool Steel Sleeves
Custom sleeves made using aluminum bronze alloy that are TDC (thin dense chrome) coated to prevent galvanic reactions between tool steel inner core and plastic resin additives (also note “vent” or vacuum relief hole on standing sleeve on the right).
Sleeve failures can present as “going out of round,” where the component measures to be “egg shaped” without evidence of any wear or metal loss. This condition leads to a combination of tightness in the component assembly while at the same time excess clearance to the component assembly, which may present as flash on the piece part. Galling is also a common problem, which is typically the result of hardness or metallurgical incompatibility, or incorrect running fit allowances or lack of lubrication in the assembly. These failures or conditions when using tool steel sleeves can best be categorized and attributable to not following required manufacturing procedures and where the development of out of round, size of shape changes relates to a condition that is defined by metallurgists as retained Austenite.
Retained austenite is a metallurgical structure or phase that occurs in the heat treatment of tool steel and is generally most notable and problematic in tubular parts, such as ejector sleeves. To minimize the presence or the effects of the retained austenite condition on the finish machined sleeves, a combination of machining and heat treatment processing needs to be followed.
The steps are as follows:
Rotating Core Applications
Venting the Assembly
An assortment of custom made sleeves using aluminum bronze alloy ranging to fit inner cores from under .250" up to over 3", typically with wall thickness of not less than .030" per side.
Orientation or Anti Rotation Features on Sleeves
Land Length of Sleeve Bore
Nitride Treatment of Sleeve Wear Surfaces
Ejector Sleeves Made Using Aluminum Bronze in Place of Tool Steel
There also is the benefit of significantly reduced coefficients of friction between a bronze ejector sleeve and tool steel. The need for lubrication is nonexistent. Also, like hardness bronze or copper alloys can be run in combination without fear of galling. An aluminum bronze component can be run on a like hardness tool steel without fear of galling. Nitrides of any sort become unnecessary.
Moldmakers and molders using sleeves made using aluminum bronze have seen the performance improvements over the tool steel based products. That experience has led to entire plants initiating steps to switch over to aluminum bronze-based sleeves with plans to completely eliminate the use of tool steel-based ejector sleeves in any application in their facilities due to the extreme performance improvements.
Link to this article：Identifying Common Causes of Failure in Ejector Sleeves
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