Custom Molded Rubber Plugs and Caps

Custom Molded Rubber Cap | Custom Molded Rubber Plug | Custom Molded Rubber Stopper

Designing a custom molded rubber plug, cap, or stopper requires three distinct considerations:  

1. Does the application require a custom molded part?
2. What is the best way to determine the interference fit?
3. Material selection

1. Does the application require a custom molded part?
   Custom Rubber Corp. always suggests trying an off-the-shelf or catalog component before making the investment in custom tooling.  In the case of plugs, caps, and stoppers, there are a number of reputable catalog companies that may have something that will work although most of the product is imported from off-shore.
   
   If you have explored what the catalog companies have to offer and have not found anything that works, call Custom Rubber Corp. for a custom solution.  Wehen we help with the design of a customer solution, the possibilities are endless.  Some examples of helpful features that may be included are; pull tabs, integrated lanyards, different colors, engraved logos or textures.  All of these features can enhance the functionality and/or the distinctiveness of your project.
    
2. What is the best way to determine the interference fit?
   Whether it's a cap, plug, or stopper, all have a certain amount of interference fit; they are pressed into place so they stay put.  The question is, how much larger or smaller should the rubber be than the thing it's plugging, stopping, or capping?  For purposes of this discussion, we'll consider the thing being plugged, capped, or stopped to be the "non-rubber component".
   
   First consider rubber plugs and rubber stoppers where the rubber part is pushed into a hole in the non-rubber component.  A traditional rubber stopper has sloped sides both to accommodate a range of openings as well as form a tighter fit the further it's pressed into place.  The same concept can be used for custom molded rubber plugs or rubber stoppers where a gradual taper is often very helpful.
   However, there are instances when the plug or stopper has to be flush with the top of the non-rubber component.  With a traditional stopper design it is difficult to consistently have the top of the stopper in the same place time after time.  Custom rubber stoppers or rubber plugs can be made with just enough interference fit to get a good seal, and then an additional shoulder that forms a hard stop on the non-rubber component. 
   In this way, the outside surface has a consistent look when the rubber plug or rubber stopper is in place.
   The specific interference design will depend on the material hardness and the overall geometry of the rubber plug or rubber stopper.
   
   In the case of rubber caps, these generally are designed to fit over some protrusion on the non-rubber component.  Here again there are some standard designs that have slight tapers and can be pressed into place.  The issue that drives people to custom rubber caps is when the protrusion is not perfectly round or square.  Custom Rubber Corp. makes rubber caps that fit all kinds of complicated geometries.
   In these cases, sometimes the best design is a slight interference fit but sometimes there is an undercut or some other feature of the non-rubber protrusion that can be used to "latch" the rubber cap into place.
   
   Custom Rubber Corp. has years of experience and practical application evidence that can be shared with customers to develop and design the most cost effective rubber cap, rubber plug, or rubber stopper.  Contact us today with your challenge.
    
3. Material Selection
   Custom Rubber Corp. works with just about every rubber or thermoset material currently on the market. The table below outlines common characteristics for the materials most used for rubber molded caps, stoppers, and plugs.  The table is a rough guide. For expert assistance with selecting the appropriate material for the rubber cap, rubber stopper, or rubber plug application, ask Custom Rubber Corp.

MATERIAL	ABBREVIATION	RECOMMENDED	RELATIVE PRICE	STRETCH / TEAR	COMPRESSION SET
Silicone	VMQ	Yes	Fair	Fair	Fair
Ethylene-Propylene	EPDM	Sometimes	Excellent	Good	Good
Natural	NR	Sometimes	Good	Excellent	Excellent
Nitrile	NBR	Sometimes	Good	Fair	Good
Neoprene / Chloroprene	CR	Yes	Excellent	Good	Good
Butyl	IIR	Yes	Fair	Excellent	Good

Custom Rubber Corp. Can Help Design
If you can't find an off-the-shelf or catalog rubber cap, rubber plug, or rubber stopper that works for your application, contact Custom Rubber Corp..  We can help with design and we will manufacture your product in the United States.