Acceptance and Pre-Production Testing
Acceptance criteria for the resins we use have been determined by performance history and production experience. These criteria are provided to resin suppliers and are certified by the supplier. If these criteria are met and the materials processed correctly, we are assured we will achieve the processability and functionality we need to meet customer and internal requirements.
When review of resin supplier certifications determines that ordering criteria have been met, the resin lot is prepared for pre-acceptance testing.
Pre-acceptance tests are not made for any particular job or company but are performed on new lots of material before they are accepted for use in making belts. When a new lot of material comes in, a certain amount is extruded and made into belts for test purposes. Test results are recorded in a custom-designed interface which not only calculates the PSI, but collects information relevant to that specific lot of resin.
These pre-acceptance tests must meet certain criteria for the material to be accepted for production use. If the tests meet our specifications, the material is accepted by upper management and further tests are scheduled to determine the optimum temperature for welding material of that lot.
Material is released for production extrusion only after being verified as meeting our tensile strength standards. Results of all pre-acceptance tests are saved in the database which contains all tensile strength tests.
During extrusion, the cross sectional size of the extrudate is continuously measured by a laser micrometer as it exits the cooling bath. Dimensional tolerances have been established that meet or exceed the performance requirements for this type of product.
Cutting: Length Checks
Cutter operators are required to check cut belt lengths against a “check board” on a required frequency to assure that the cutter is functioning properly and belts are within the standard length tolerance.
Welding: Visual Inspection of Welds
While Pyramid has developed and uses a number of welders and welder designs, they all basically do the same thing. Welders have been designed and built to consistently provide the proper amount of heat, pressure and time to create a weld in the polyurethane that is close to matching the physical properties of the base extrudate.
The shape and size of the weld flash (excess material created at the weld during the welding process) provides a visible indicator as to the quality of the welding operation. A belt from all welders is inspected at the beginning of each work period by the operator prior to going into full production. These startup belts are left for supervision to inspect, as well. During production, operators and supervisors make random checks throughout the welding process.
After welding and further processing, belts are sent to the grinding area where the flash is removed. Each belt is individually inspected to see that the flash is the correct size and shape and if so the flash is removed by grinding so that the weld area is as close to the body size as is possible.
Photographs of improper welds and flashes are posted in the grinding area to assist personnel in determining which belts are unacceptable. Unacceptable belts are placed in designated tubs for recycling.
Pyramid's Quality Inspection Procedures
There are two tests performed on every line item of every order prior to shipment. These tests are the quality assurance (Q.A.) check and the tensile strength test.
Quality Assurance (QA) Checks
Quality assurance tests are non-destructive tests of belt and extrudate dimensions and material compared to the specifications on the order. Round belts are measured for cross-section and length while flat belts are measured for thickness, width and length. For all cross-section or thickness and width readings, tests are performed at multiple locations on the belt to get an average reading for the entire belt. Length is calculated using a Diametape, a flexible ruler which is coiled inside the belt circumference and provides either the inside circumference of the belt or inside diameter, which is then converted to belt length. Belts over 62” cannot be measured by our Diametapes, but are measured using a measuring tape. These results are also fed into our database for further examination and analysis.
All of the instruments used for measuring the belts are traceable to NIST standards. The Diametape and measuring tape are listed on our normal calibration schedule and the hand calipers used to measure cross section or thickness and width are verified every morning using an NIST standard plug gage.
A result of Pass or Fail is achieved for cross-section and length on round belts and for thickness, width and length on flat belts. A visual and tactile check assures that the belt is made from the correct material and any other special requirements are met (color, texture, etc.). Any belt that falls outside of our tolerance on any of the dimensions or that is made from the wrong material fails the check. An additional belt is tested to determine if the failure was a fluke or a problem with the order. Any failure must be reported to a supervisor and logged in the Internal Issues Log if it causes a job to be remade.
Tensile Strength Tests
Tensile strength tests are performed on belts which are complete and ready for shipment. When belts for an order have been counted in the shipping area, the appropriate number of sample belts are set aside from each line item for testing. This number of samples varies by the quantity of the line item from as few as one to fifteen or more.
A tensile strength test is a destructive test performed to determine the strength of the weld or body of the finished belt. One end of the belt is looped over an apparatus that is hooked to a load cell which measures the amount of force being generated while the other end is looped over a pin on a motor shaft which is turning at a certain pre-defined speed. Because the weld is the weakest point, it is purposely made vulnerable during this procedure. (We also perform tests in the body of the belt to determine the tensile strength of the base material as necessary.) As the belt stretches, the load cell measures the tension on the belt and calculates the force being placed on the belt while a meter logs the peak tension. When the belt reaches the point of failure, the final reading is left on the meter and this number is entered into our custom-designed software to calculate the pounds of pressure per square inch (PSI) at which the belt finally broke as well as to collect other relevant information about the belt and the order to which it belongs. This information is stored in a database for further examination and analysis. Minimum tensile strength levels have been established for each Pyrathane® material based upon many years of historical performance tests and field reports.
Tensile test results will fall into one of three categories: acceptable, warning and unacceptable.
A “warning” result is one that falls below our target but is still above our minimum. This warning result requires a supervisor be notified who must then enter their password into the computer for further tests to be performed. If the tensile strength of the belt falls below the minimum tensile level, top management must be notified. This “failure” result requires that the top management representative enter their password into the computer. The quality inspector cannot enter further test results until a password has been entered into the data collection interface, thereby assuring that the appropriate level of management will be involved when belts fall below our target tensile strengths.
In either of the above cases, five more belts must be tested to determine if the warning or failure was a fluke or if there is a greater problem with the belts from this order. Based upon the information available, the appropriate person will make a determination on the status of the quality of the belts. The result of this could be anywhere from releasing the order if the warning or failure was a fluke to quarantining the belts for further testing to scrapping the order completely and remaking the entire order.
Non-Conforming Material Disposition
Non-conforming belts or extrudate will be immediately segregated from good products and the non-conforming material is brought to the attention of the supervisor or manager for further evaluation.
If you have questions or would like more information about Pyramid's quality assurance testing procedures, please contact us with your specific questions.