Putting Plastics to the Test

It’s hard to be a resin processor without doing some form of testing. Whether it’s a simple dimensional check of a molded part, or a laboratory analysis of resin composition, testing is an ongoing part of any quality-driver operation. Most quality assurance (QA) departments can make dimensional checks of finished parts, but few can determine the chemical composition of a custom-compounded resin, or the UV stability of a new additive package, for example. Testing services can get a processor out of trouble, or prevent it in the first place.

WHY TEST?

There are several reasons to consider testing. The most obvious is to comply with the terms of a supply contract or to meet an agreed quality standard. Even shops with relatively sophisticated statistical process control (SPC) regimes may need to submit standardized tests like those outlined by ASTM International. ASTM is a standards development organization for the development of standards around materials, products, systems and services, with equipment calibrations traceable to national standards. If it’s all about providing your customer with independent results, the task can be as easy as finding a lab with appropriate approvals (ISO 17025 for example), and keeping the paperwork in order.

There are also good reasons to use testing services in-house, according to Jacob Kleiman, president and director of R&D for Markham, ON-based Integrity Testing Laboratory.

“Often the customer requires that the molder submit (test) results with the products for acceptance,” Kleiman explains. “The other reason is when something doesn’t work internally they have to find out whether the process or the material is the problem.”

However, the variety and sophistication of available testing methods is considerable. But, if properly applied, the testing arsenal can separate the raw material/processing conditions conundrum quickly, says Dr. Andrew Sinclair, vice president of the Material Technology Group at Bodycote Materials Testing Canada Inc. (Mississauga, ON).

“There are a whole class of tests that can determine whether the resin is different between two lots, or the processing history is different giving rise to the failure,” he says. “There are rheological tests that can be performed like melt index or melt viscosity, thermal analysis measurements through DSC (differential scanning calorimetry), melting points, glass transition temperatures or stress relaxation, and there are optical microscopic techniques for failure or crystal morphology.”

FAILURE ANALYSIS

“For example, for a resin that’s filled with 10% calcium carbonate, one lot might have a coarse grade and another fine. If the drawing specified only the percentage of calcium carbonate, both lots may pass, but parts may have widely varying properties,” he adds.

There are lots of tools available to find the answers, but waiting for disaster isn’t the best time to use them, declares Joe DeRose, president of Axis Polymer Services Inc. (Toronto, ON). “Usually, the problem has already occurred and the processor is looking for an answer as to why it,” he explains. “In terms of preventative testing to determine the characteristics of materials coming in, it’s relatively rare. It’s more reactive. There’s room for more preventative testing.”

Brian Evans, marketing/business development manager for the Midland, ON-based Industrial Research and Development Institute, describes how processors can use testing to get ahead of potential problems.

“Fingerprinting is a proactive test that molders should use,” he says. “Many use it to be at least aware of batch-to-batch variations in their resin. If they get a new batch and mold thousands, or possibly hundreds of thousands of parts and have a problem, they’ve wasted lots of money.”

Used judiciously, failure analysis can also save valuable time, he notes.

“If they send us a damaged part, we can tell how the part was processed, if the materials contain the right filler, among others. It saves a tremendous amount of troubleshooting time,” he says. “Most companies put together teams to find out what’s going wrong, but with testing they can save a great deal of time and money.”

COST EVALUATION

But not everyone is convinced that testing will save them money.

According to Integrity Testing’s Kleiman, “I think they can, but it’s hard to convince them. People don’t want to spend money.”

Joe DeRose agrees: “If it’s used wisely, it doesn’t have to be expensive. For example, to confirm that a resin is the same as a previous batch, a “ballpark” figure would be under $500,” he says. “To confirm a filler type and quantity could be $300. To test additives like light stabilizers or antioxidants is more work; for a single straightforward additive it could be in the area of $500. The amount of money is not hard to deal with.”

Evans also concurs. “Fingerprinting isn’t expensive; molders send us about 100g of pellets and we identify any difference, allowing them to go back to their resin supplier, or shift their molding parameters to suit the new batch,” he says.

Like the old “pay me now or pay me later” TV ads, spending a little money early in the process can save big dollars by avoiding expensive remedial testing. If a part fails in service, it’s often a crisis situation.

MISCONCEPTIONS

“One of the problems of failure analysis is that people watch too much “CSI” and “Star Trek,”” he adds. “There’s a perception that for a hundred bucks you should be able to determine the cause for sure. Failure analysis is much like hiring a “private eye;” you pay by the hour or pay by the test, but you’re taking a risk. You may or may not discover the reason.

“Sometimes the good and bad parts have the same composition but different mechanical properties. Given infinite resources, you can get to the bottom of it, but one of the key factors is close communication back and forth with the lab about what techniques will have the best probability of success,” he explains. “Sometimes it’s better to cut your losses, and at other times it makes sense to invest to go farther. You can shop for the best price, but in failure analysis, price is not necessarily value.”

There is far more to testing in resin processing than can be described in a single article, but fortunately, knowing when to test and why, is more important than the sophisticated technology on the laboratory bench.

Ultimately, testing for success is a simple concept. As Kleiman states simply: “The general rules still apply: If you put garbage in, you’ll get garbage out.” And a sensible testing program can keep the garbage out of your feed throat, and profits in the bank.

TIPS FOR COST EFFECTIVE TESTING

Dr. Andrew Sinclair, vice-president of the Material Technology Group at Bodycote Materials Testing Canada Inc. (Mississauga, ON) has some tips on selecting and dealing with independent testing services.

1. Establish the capability of the lab

One way to establish the capability of the third-party — and to ensure customer acceptance of the data — is to use an ISO 17025 registered lab. In Canada, these labs would normally be accredited by Standard Council of Canada (www.scc.ca) and in the U.S. by the American Association for Laboratory Accreditation (www.A2LA.org). The two organizations have reciprocal recognition agreements so testing from a Canadian lab will be accepted in the U.S. and vice versa.

2. Test to Specification

The molder is often called upon to show that the raw materials and/or finished part meet the customer’s specifications. Ideally, the test, sample preparation, conditioning etc. is clearly defined. In this case, the molder has the option to do the testing internally or to use a third party laboratory. For automotive molders, the term Production Part Approval Process (PPAP) describes the process of defining the acceptance criter
ia for a part and the testing required to demonstrate it. Sometimes the customer will have a drawing which inadequately describes the part or process. For example, a drawing might specify “Polypropylene, 10% talc,” but there are lots of ways to do that. If the customer says the part is too brittle and is cracking, it’s better to redefine what mechanical or dimensional properties are needed or what resin should be used.

3. Failure Analysis

Molders often end up requiring testing when a raw material won’t process properly or the final part won’t meet specifications. The situation often relates to good lot vs. bad lot. Other variations can relate to contaminants or deformulation. In these cases, selection of an appropriate laboratory is critical as the process is that of an investigation, as opposed to a clearly defined test. To maximize the chance of success:

* Pick a good lab and establish a relationship before there is a problem

* Collect as much background information as possible to help the lab understand the situation

* Supply as many good, bad and reference samples as possible (keep retains of old lots)

* Communicate with the lab

The more information and samples that you have, the better the chance of identifying the origin of the problem quickly and minimizing the expense. A good lab will identify a series of tests and then will move through them in a sequential process giving you regular progress reports so you can make decision about additional testing.

4. Know the Real Cost

Since many failure analysis investigations relate to production being halted, the molder has to decide between “money is no object, do everything you can think of now” and “let’s do one test and discuss the results and decide on a second test (keep costs down).”

It is always a balance of cost and time. The third leg of the cost-time matrix is quality. You need to maximize cost-time-quality. Don’t take the lowest price-failure analysis that can be delivered the same day, if the lab cannot properly interpret the results and support you. It is like buying any product or service; if they can deliver it at half the price immediately, you need to understand what quality corners are being cut.