Pipe scriber "test method" - Huaqiang Electronic Network

I. Overview

The longitudinal retraction rate is a key performance indicator for plastic pipes, reflecting their stability under thermal conditions. It helps assess the pipe's ability to withstand temperature fluctuations and environmental heat sources, ultimately extending its service life. However, due to variations in testing methods, improper handling or oversight during testing can affect accuracy.

There are two primary methods for determining longitudinal retraction: one using liquid (Method A) and the other using air (Method B). A sample of specified length is placed in a heating medium at a set temperature for a certain time. The change in distance between pre-marked lines before and after heating is measured, and the retraction rate is expressed as a percentage of the original length.

To conduct the test, two circumferential marks are drawn on the sample with a 100mm spacing, ensuring that one mark is at least 10mm from either end. This follows the national standard GB/T 6671-2001 for thermoplastic pipes, applicable to samples with diameters up to 400mm. For larger samples, slicing tests may be used instead.

II. Technical Parameters

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

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

3. Sample diameter: Up to 400mm

4. External dimensions: 550 × 420 × 250mm

5. Weight: 15KG

III. Testing Method

1. Place the scriber in a stable location and adjust the anchor screw so it remains steady without shaking.

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

3. Position the marking pen (e.g., pencil, marker, or paint pen) on the frame above the scriber. Adjust the pen’s position so that the two tips are exactly 100mm apart, ensuring accurate markings.

4. Gently turn the handwheel. As the sample rotates, the pen will draw two parallel marks. If the marks are unclear, adjust the pen height. Return the handwheel to the starting position in the opposite direction to ensure alignment.

5. Remove the sample and proceed with the test according to Method A or B outlined in GB/T 6671-2001.

IV. Data Processing

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

After marking the sample, measure the distance between the two marks again to determine the original gauge length. Set the oven to 150°C and wait for it to reach the desired temperature. Once achieved, place the sample inside. Ensure the oven returns to 150°C within 15 minutes; avoid overloading it to maintain consistent temperature.

Two methods are available for placing the sample: one involves suspending it in the oven, with the suspension point at the farthest end of the marked line, ensuring it doesn’t touch the oven walls or bottom. The second method uses a flat plate coated with talc for the sample to rest on.

When the oven reaches 150°C, start the timer and let the sample remain for 60 minutes. Afterward, remove the samples and place the suspended ones on a smooth wooden surface, while the flat samples go on a granite countertop. Allow them to cool completely to (23 ± 2)°C. Measure the maximum or minimum distance between the marks multiple times, select the largest value relative to the original gauge length, and calculate the retraction rate accordingly.