Pipe scriber "test method" - Huaqiang Electronic Network

I. Overview

The longitudinal retraction rate is a crucial parameter that indicates the performance of plastic pipe products. It reflects the stability of the pipe material under thermal conditions, particularly in terms of its ability to maintain shape and structural integrity when exposed to heat. Accurate measurement of this property is essential for ensuring product durability and resistance to environmental factors such as temperature fluctuations and sunlight exposure. However, improper handling or lack of attention during testing can lead to inaccuracies, making it important to follow standardized procedures carefully.

There are two primary methods for determining the longitudinal shrinkage of thermoplastic pipes: Method A (in liquid) and Method B (in air). In both cases, a sample of a specified length is placed in a controlled heating medium at a given temperature for a specific duration. After heating, the distance between pre-marked lines on the sample is measured, and the percentage change from the original length is calculated as the longitudinal retraction rate.

To conduct the test, a scriber is used to mark two circumferential lines on the sample, spaced exactly 100 mm apart, with one marking at least 10 mm from either end. This procedure follows the national standard GB/T6671-2001 "Determination of the Longitudinal Shrinkage Rate of Thermoplastic Pipes." It is applicable to samples with diameters up to 400 mm, while larger samples may require slicing for testing purposes.

II. Technical Parameters

1. Straight line distance: 100 mm (adjustable via loose screws)

2. Scribing tool: Any suitable pen (e.g., pencil, marker, paint pen)

3. Sample diameter: Up to 400 mm

4. External dimensions: 550 × 420 × 250 mm

5. Weight: 15 kg

III. Testing Procedure

1. Place the scriber on a stable surface and adjust the anchor screw to ensure it remains steady without shaking.

2. Cut the sample to a length of 200 ± 20 mm and position it centrally on the four rotating wheels of the scriber.

3. Place the marking pen (such as a pencil, marker, or paint pen) on the fixed frame above the scriber. Adjust the pen’s position so that the tips are 100 mm apart, ensuring accurate marking.

4. Gently turn the handwheel, allowing the sample to rotate and the pen to draw two parallel circumferential marks. If the markings are unclear, adjust the pen height accordingly. Return the handwheel to the starting position in the opposite direction to ensure alignment.

5. Remove the sample and proceed with the retraction test according to either Method A or Method B outlined in GB/T6671-2001.

IV. Data Processing

The longitudinal retraction rate T is calculated using the formula: T = (L₀ - L) / L₀ × 100%

During the test, two circumferential markings are made 100 mm apart, with each line at least 10 mm from the ends of the sample. After marking, measure the distance again to determine the original gauge length. Set the oven to 150°C and allow it to reach the target temperature before placing the sample inside. Ensure the oven reaches the required temperature within 15 minutes; avoid overloading the oven to prevent temperature drops. Two types of samples can be tested: suspended or flat. For suspended samples, hang them so they do not touch the oven walls or bottom. For flat samples, place them on a talc-covered plate inside the oven.

Once the oven reaches 150°C, start the timer and let the samples remain for 60 minutes. Afterward, remove the samples and lay the suspended ones on a smooth wooden surface, while the flat samples should be placed on a granite countertop. Allow the samples to cool completely to (23 ± 2)°C. Measure the maximum or minimum distance between the marked lines, take multiple readings, and use the largest value relative to the original gauge length for calculation.