The durability and safety of footwear products largely depend on the reliability of the adhesive structure between the sole and upper. As one of the common quality problems in footwear, the root cause of "glue opening" is the adhesive surfacepeel strengthdeficiency Therefore, usingElectronic tensile testing machineScientific and quantitative peel strength testing of finished shoes or samples is a crucial quality control method in the manufacturing, quality inspection, and research and development processes of footwear. This article will systematically analyze the core purpose of peel testing and delve into several typical testing methods and their applications.

The core value of peel strength testing

The peel test aims to simulate the peel stress experienced by the adhesive between the sole and upper during repeated bending and twisting in actual use. By quantifyingpeel forceorpeel strengthThis test can:

• Objective evaluation of adhesive performance and process levelAccurately determine whether the bonding process (such as adhesive amount, pressing pressure, processing time) meets the standards.

• Prevent quality defectsEffectively screen out products with poor adhesion, avoid early adhesive problems such as "worship shoes" and "street shoes", and maintain brand reputation.

• Support research and quality controlProvide reliable performance comparison data for the application of new materials (new shoe soles, uppers, or adhesives) and establish internal quality acceptance standards for the enterprise.

Comparison of mainstream testing methods and key operational points

At present, the industry mainly adopts the following methods, each with its own applicable scenarios and characteristics.

Method 1: Whole shoe peeling test (simulating actual damage)
This is the most intuitive method to simulate the real glue opening process.

1. Sample preparationInstall the corresponding shoe last on the finished shoe to provide stable support.

2. test processUsing an electronic tensile testing machine, equipped with specialized wide jaw fixtures or customized fixtures, clamp on both sides of the shoe sole edge and upper that have been pre peeled with a small opening (about 10-20mm). Peel off at a constant speed (usually 100 ± 20 mm/min).

3. Result AnalysisThe testing machine records the changes in force values throughout the entire peeling process, which can be obtainedpeel forceandaverage peel forceThe advantage of this method is its intuitiveness, but its results are greatly affected by shoe type and structure, and the data repeatability is relatively low, making it more suitable for finished product sampling or simulation verification.

Method 2: Multi point sampling test (evaluating adhesive uniformity)
This method focuses on evaluating the uniformity of the adhesive quality around the entire shoe and is commonly used for quality control in the production process.

1. Sampling and MarkingSelect several testing points evenly along the joint between the sole and upper of the shoe (such as 22 points for adult shoes and 12 points for children's shoes). Remove the stitching at this point (if any).

2. inching testUsing an electronic tensile testing machine, cut a fixed width (e.g. 1cm) sample of the adhesive layer between the sole and upper at each marked point, and clamp them separately. Measure the force required to peel off the point.

3. Calculate intensityDivide the measured peel force values of each point by the width of the sample to obtain the peel strength of each pointPeel strength (unit: N/cm or kN/m)This method can effectively detect weak adhesive points, but the operation is cumbersome and causes significant damage to the sample.

Method 3: Standard Sample Method (with accurate data and high comparability)
This is the most recommended method in laboratory and standard research, which can obtain data with good reproducibility and strong comparability.

1. Standard sample preparationCut standard strip specimens of specified width (such as 10mm, 25mm) and length from the most critical areas of shoe bonding (such as curved areas) or simulated bonding parts made using the same materials and processes as the finished product.

2. Standardized testingSeparate the unattached ends of the sample and clamp them separately in the upper and lower fixtures of the testing machine to form a stable peeling angle (usually 90 ° or 180 °). Peel off at a constant speed.

3. data analysis: Software automatic drawingPeel force displacement curveCalculate the average peel strength. This method eliminates the interference of shoe structure and produces accurate results, making it an ideal method for evaluating the performance of adhesive bodies and comparing suppliers.

Key factors to ensure testing accuracy

Regardless of the method used, the following are common keys to ensuring the validity of test results:

• Equipment RequirementsHigh precision force values (such as ± 0.5%) and stable speed control must be usedElectronic tensile testing machineThe selection of fixtures is crucial, ensuring a firm grip to prevent the specimen from slipping or being pinched.

• Sample statusBefore testing, the sample needs to be fully conditioned in a standard temperature and humidity environment (such as 23 ± 2 ° C, 65 ± 5% RH), as temperature and humidity have a significant impact on the performance of most adhesives.

• Operational consistencyThe parameters such as peeling angle, peeling speed, and sample width must be strictly consistent throughout the entire testing process and clearly recorded in the report.

Frequently Asked Questions about Shoe Peel Testing

Q: How should companies choose these three testing methods in quality control?
Answer: The choice depends on the testing purpose.

• Final quality control sampling inspection: OptionalMethod 1 (Whole Shoe Test)Directly simulate the usage scenario.

• Process technology monitoring: RecommendedMethod 2 (Multi point Testing)To facilitate the identification of weak links in the bonding process on the production line.

• Material evaluation, incoming inspection or arbitration experiment: Must be usedMethod 3 (Standard Sample Method)Because of its precise data and high comparability, it is the foundation for quantitative analysis and responsibility determination.

Q: In testing, the sample often slips or gets pinched off from the fixture. How should it be handled?
Answer: This is a common problem, usually caused by improper fixtures.

• Regarding slippageChoose a clamp with fine tooth patterns, rubber pads, or pneumatic driveSpecialized peeling fixtureTo increase friction and evenly distribute clamping force.

• Regarding pinch breakage: RequiredReduce the clamping pressure appropriatelyAnd check if the edges of the fixture are smooth and free of sharp angles. For very thin or soft upper materials, customized specialized clamping pads may be required.

Q: How to test the bonding strength of shoes that use both sewing techniques (such as marking thread) and adhesive techniques?
Answer: This is a composite structure test. There are usually two approaches:

1. Test overall adhesionDirectly conducting a peel test on the joint of the suture and adhesive, the result obtained is the total strength of the combined action of the suture and adhesive.

2. Evaluate separatelyFirst, test the pure adhesive peel strength of the unstitched sample, and then test the total strength of the complete sample. The difference between the two can approximately reflect the contribution of sutures. This requires careful sample preparation and testing design, sometimes requiringNon standard fixtures or testing plans.

Q: The test data has a large dispersion. How to determine whether it is an adhesive problem or a testing method problem?
Answer: Firstly, ensure that the testing methods (such as method three) and operations are strictly standardized. If the data dispersion is still significant, it is likely to reveal the real process problem:

• Uneven application of adhesiveUnclean bottom treatment can lead to significant differences in strength at various points.

• Different batches of materialsProcess fluctuations during production periods can also lead to data dispersion.
  At this point, the data discreteness of the stripping test itself is an important quality warning signal, indicating the need to check the stability of the production process. Professional testing instrument suppliers usually provideData analysis supportHelp distinguish between equipment issues and material and process issues.

DisclaimersThe purpose of this article is to introduce the general principles and methods of shoe peel strength testing. The content is based on common industry practices and is for reference only. The specific testing operations and qualification judgments should follow the applicable product standards, customer agreements, or internal specifications. If there are any updates or discussions in the information in the article, please feel free to exchange and correct them.