Resin Identification Code

If you were to flip over most everyday items made of polymer, especially those which are disposable, you would have noticed the triangular sign with a number within and maybe some alphabets below. This is the Resin Identification Code, and unless you were working with a disposable consumer item and your company is committed to label their product accordingly, you may not have given it  a second's thought.

Image taken from Flickr (by holeymoon)

In order to address the recyclers' rising need for a clear indication of polymer used, Society of Plastics Industry, Inc (SPI) developed and introduced the identification code in 1988. This code is usually found in packaging and containers since these are the main targets of municipal recycling programs, seeing that they are one of common items encountered within residential waste.

The code is used solely to identify the plastic resin in a manufactured item. In fact, the triangular label with 3 twisting arrows along with the number within are commonly misinterpreted. The number within is an arbitrarily chosen number to represent the target plastics, and has nothing to do with ease of recycling. A higher number does not mean that the plastics is harder to recycle.

IP Rating - Immersion vs Water Jet

Followers of this series of articles on IP rating will recall that a higher number on the 1st numeral will satisfy the requirements of a lower number (i.e. IP6X will mean that it passes all requirements from IP1X to IP6X, revisit here if the reader is interested). It would be prudent to note that such is not the case for the 2nd numeral.

An IPX4 test in progress. The semicircle apparatus sprays water through tiny nozzles lining the inner circumference. The apparatus is designed such that the water spray will reach the product from all directions. Notice that the spray is constrained to the top of the product, and the bottom is free from its direct effects (image taken from Qualilab).

The reason behind this is the difference in test requirement: 

• IPX1 to IPX6K, and IPX9K requires the product to be subjected to a flow of water impacting on the product 
• IPX7 and IPX8 requires the product to be immersed in a body of water.

In order to understand the test requirements, it is essential to first understand the application of the product in an environment prone to water ingress. Water ingress into the product could come in two different scenario - the product could be sprayed on by water jets, or it could be dropped into a body of water for a determinate period of time. It is possible to be subjected to both scenarios throughout the product's application lifetime as well.

IP Rating - Waterproof

Just as it would be difficult to judge the level of protection of "dustproof" products, the same applies to the term "waterproof" - it gives no indication the level of protection the product affords apart from the fact that it is protected against water ingress.

A waterproof iPod Stereo Case - how would you judge the term? Will the casing be free from water ingress if submerged for more than 1 hour? How will an engineer judge the term "waterproof" for critical engineering equipment? (image taken from Marine Audio and Stereo)

The 2nd code element of the IP rating helps shed some light on the level of protection, which is listed in the below table. The technical term usually associated to this code element is "protection against liquid ingress".

IP rating - IP5KX vs IP6KX

In the previous article, the first numeral code for an IP rating is mentioned as the protection level of a product against intrusion of foreign object, with IP5KX and IP6KX being the highest level. This article serves to elaborate on the latter requirements and how they differ from each other.

Dust test performed on a laptop within the dust chamber (photo taken from Espec website).

IP rating - Dustproof

Instead of claiming a product is 'dustproof', a better way of stating it is 'protection against foreign object intrusion', as is mentioned within IEC60529. There is a reason to it, as a product is not only in danger of being harmed by intrusion of dust or sand. One look at the grills of a table fan and it is not difficult to understand that its purpose is to prevent accidental and intentional (in the case of innocent infants) access to the dangerous rotating blades of the product. 

IP rating - Protection against Ingress

Sony Cybershot TX-5 (image taken
from Sony website).

Ever use products that failed because of water seeping into the interior? Or maybe sand jamming the moving parts? It is quite usual for products to be designed to be 'waterproof' or 'dustproof', but as an engineer, how do you know if they really are as they claimed, or what to look out for to know how 'waterproof' it is?

Engineered items are usually labeled as sealed against dust or water through a system known as IP rating. The IP code labeled on products and claimed in technical datasheet will provide users and buyers the degree of protection provided by mechanical casings and enclosures of electrical equipment against the following:

• protection against foreign objects (e.g. sand and dust)
• protection against effects due to ingress of water
• protection against access (accidental or intentional) by persons to hazardous parts inside the enclosure