PLASTICS

Problem Solving

Plastics

The following examples illustrate some of our contributions to this business sector:

• Touchstone was asked to perform failure analysis of the thread splits used to form the threaded necks on plastic beverage containers. TRL was asked to determine the tensile strength of the material, the elemental analysis, and to evaluate the microstructure to determine the reason for the failures. It was concluded that the microstructure of the material in this part indicated that it was probably not heat-treated for a sufficient length of time to allow complete decomposition of retained austenite.
• Touchstone performed a differential scanning calorimeter analysis of photocopier toner to determine the softening range. This information allowed adjustment of the composition to meet the copier requirements for proper printing.
• Touchstone performed a failure analysis to determine the reason for breakage in 420f stainless steel plate. Evaluation of the material found that improper heat treatment allowed the growth of chromium carbides at the prior-austenite grain boundaries. This condition renders the steel brittle and prone to cracking under normal service loads. A change in the heat-treatment practice was recommended.
• A problem concerning breakage in plastic containers for the food industry was brought to Touchstone. The containers burst when filled with hot liquids in the packaging operation. Measurements including hot melt index of pellets, and tensile strength and elongation of finished products, found variability in both the raw materials and in the process used to make the containers. Quality control procedures for materials and process were implemented and the problem was solved.
• Touchstone performed a failure analysis of cracking in tool steel cavities used to form plastic parts. The problem dealt with the use of un-treated water for cooling of the cavities. The corrosion pits formed during use presented stress risers, which developed into cracks under high injection pressure. The cracks propagated under cyclic loading to failure. A sister plant that had a treated, closed-loop system did not experience any problems with the cavities.
• Several monolithic and composite polymer materials were evaluated by exposing various test coupons (tensile and compression) to a variety of media, including methane gas, hydrochloric acid, petroleum distillates, hydrogen sulfide gas, ethyl alcohol, and carbon dioxide gas at pressures up to 100 psi and temperatures up to 300 degrees Fahrenheit. The specimens were measured and weighed before and after exposure and tested in tension or compression to determine whether any change in properties had occurred. The results aided in the selection of materials for the petroleum industry.
• Brittle, delamination cracking of the stainless steel base plate for blow-mold cavities presented a problem to a beverage container manufacturer. The cracking was found to be the result of the failure to heat treat the plate after machining. This left the stainless steel plate “sensitized” and prone to cracking.
• Metallurgical analysis of a cracking problem with blow mold cavities was found to be the result of an improper tool steel grade for the application.
• Touchstone performed testing under the “Temperature Exceedance Program” wherein various materials used in the SRB (solid fuel rocket booster) were subjected to launch equivalent temperature profiles followed by immersion in seawater to simulate booster use conditions. A wide assortment of mechanical tests were then performed on materials which included paints, primers, nylon, Teflon, o-ring Nitrile rubber, and phenolic silica ablative sheet. The tests included tensile strength, short beam shear, flatwise tensile, Durometer hardness, wear resistance (Falex) and Izod impact.
• Fifteen different polymers and/or polymer/fiber composites were tested for wear resistance using the Taber abrasion test. The results aided in the selection of longer life products for the petroleum industry.
• A plastic sample was analyzed by dissolving in toluene and analyzibg using a gas chromatograph mass spectrometer. The analysis revealed the presence of styrene at approximately the 500 part per million level.
• Archimedean density determinations were performed on samples from five-gallon, plastic buckets. Because the density of plastic material was less than 1 gm/cm3, alcohol was used as the test medium.
• Production samples of 5-gallon buckets were tested to determine conformance to drawing specifications.
• A Tinius Olsen servo-hydraulic test stand and special fixturing were used to determine the load capability of tiedown straps manufactured for the military. The belt material and stitching were found to be acceptable, but the plastic buckles were not suitable for use with the gage of strapping used in the fabrication.
• Fatigue tests were performed on fiberglass reinforced plastic sheet to be used for siding on mobile homes. The goal was to compare mechanical properties of the plastic material to aluminum sheet used in the same application.
• TRL’s engineers provided information regarding the manufacture of high-pressure storage cylinders to be used for compressed methane for the automotive industry. Tests were performed on competitor’s material. Results of this investigation include typical voids, the angle of the layers relative to the long direction of the cylinder, volume determinations, fiber content, resin type, liner material, and typical resin/fiber interface photographs showing the degree of bonding achieved.
• Polymer matrix composites have been investigated for use in submarine hulls. The shock response of this material is critical if it is to be effective. A destructive technique for damage assessment in these materials was required. NDE techniques had been used, but their effectiveness had not been validated. Touchstone developed a metallographic method to quantify delaminations and transverse cracks following impact. Following method development, Touchstone was able to completely evaluate the damage to eight flyer plates impacted at various velocities. The results allowed an evaluation of various NDE techniques.
• Several polymer specimens were tested to determine thermal conductivity per ASTM C177, Mean Specific Heat per ASTM C351, Impedance and Absorption of Acoustic Materials per ASTM E1050, Resistance to Rapid Impact per ASTM D2794, and Density per ASTM C303, Density by Displacement.
• Touchstone regularly performed the qualification testing for a plastic container company for microbiological cleanliness. This allowed the company to sell their plastic containers to the dairy industry to contain milk products.
• Touchstone performs testing for potential Aids transmission in latex gloves. Touchstone has also tested numerous plastic, leather, and latex gloves to determine susceptibility to cutting, tearing, and puncturing.
• Touchstone developed the Material Data System for the U.S. Navy. That is used to collect mechanical test data on polymer composite materials under development in the Navy.
• Touchstone has developed a fire properties database for polymer matrix composites. This allows for Navy designers to screen potential polymers and polymer composites for their fire characteristics.

The above examples are only a sample of our work in this area. We would be pleased to provide any additional information you may require. We also invite you to review examples on our website of work that we have performed in support of other business sectors.