Evaluation of the seam

Introduction

Assessing the quality of a seam is the result of two complementary approaches: the visual and tactile examination and review dimensional. It is also important to complement these reviews by a verification test of the seal to detect some hidden defects whose cause can not be due to a movement but crimping other packaging defects.

Visual and tactile examination

Visual examination is the first check box and crimp in production. There must be frequent enough to allow observation of gross anomalies.

It is performed as follows:

1. Remove possibly the label.
2. keep the box in one hand and drag the seam between the thumb and forefinger of one hand by at least one full turn and check the presence of defects described in § crimping "7.1. Structural defects. "
3. consider the closures, the body and the clip boxes to see if the presence of some visible defects: plate defects or damage, visible leaks, etc..

The visual and tactile examination of the seam can highlight the possible presence of structural defects described in § "7.1. Structural defects. "

Dimensional examination

Dimensional examination of the seam is to be measured, well-defined points, the dimensions of various structures of the seam. Two methods are used: The method micrometer and the optical method.

The micrometer method is measuring the external and internal dimensions of the seam using a micrometer: We start by measuring the external dimensions, and then we break the seam and measure the internal dimensions. This method is also called "control of the seam by shelling."

The optical method is to measure directly on an optical image of the set with external and internal dimensions of the seam and the Overlap. This method is also called "control by spraying of the seam."

Each method requires special equipment.

Tools

For dimensional control of the seam by the micrometric method, we need primarily: Seam micrometer, micrometer-crimped and cons of the tools necessary for hulling (shears and pliers) (Figure 13). The exposure of the seam (shelling) can also be done using an automatic sheller crimped.

For dimensional control of the seam by the optical method, we need the following tools: seam saw, seam projector and / or magnifier seam (Figure 14).

1. Seam Saw: To make cuts perpendicular seam that can then view using the projector crimped or crimped magnifier.
2. Seam Projector: Used to measure directly the different structures of the seam and in particular the overlap (the Overlap).
3. Magnifier Seam: This is a magnification tool the size of a pen and having a lighting system. It is measured in millimeters (or inches) and can report directly to the ratings of the Overlap and other structures of the seam. Its scope and limitations are similar to those of the projector crimped.

Found in the trade a wide range of tools that range from simple to sophisticated. There are even automatic monitoring stations of the seam that can be integrated directly into the production line and receives boxes and instructions for testing without user intervention.

It goes without saying that to have correct measurements, these instruments must be in good condition, properly calibrated and used properly.

Measuring points set with

Measurements are performed crimped at several points. These must be marked so that the outer dimensions can be linked directly to the internal dimensions (after peeling, body hook and end hook is no longer involved). It should be noted at least the minimum and maximum values ​​observed and does not calculate the average of a dimensional crimped.

It is much more useful to identify measures seam points that indicate the possible presence of defects such as bulges or excessive thickness. Normally, it takes no position crimped assembly. When no abnormality is detected seam thickness, the measurement points suggested, based on various models of boxes, are shown in Figure 15.

In the case of round cans, measurements are made at least 3 points in the periphery located 120 ° from each other, and in all cases more than 15 mm mounting.

For non-round cans, the size of the seam must be measured in the same way as for round boxes, but because of the irregular shape of the boxes not round measures should be made to other points, as shown in Figure 15 (The manufacturer may suggest other points). Cuts can be made at other points, particularly if abnormalities are detected.

Measure the external dimensions of the seam (micrometric method)

This review focuses on the following structures (Figure 17):

1. Seam length (using a micrometer Seam);
2. Seam Thickness (using a micrometer Seam) and
3. Cup depth (using a micrometer cons crimped).

Measurement of internal dimensions of the seam (Method micrometer)

In order to examine the inside of the seam, separate the body and the lid somehow to properly expose the hooks body and lid and allow them to accurately measure and evaluate the application and rate junction. This operation is commonly called "peeling" (Figure 16).

The inside seam is subject to a minimum the following measurements and observations (Figure 17):

1. Hook body;
2. Hook cover;
3. Overlap and
4. Rate tightening.

The body hook and cover hook are measured using a micrometer crimped.

Overlap is calculated by the following formula:

Overlap = (Cc + Cv + Ev) - Hs

With:

1. Cc: hook body.
2. Cv: cover hook.
3. Ev: Thickness of cover.
4. Hs: height of the seam.

The formula for calculating the Overlap only an estimate. The optical measurement is the only accurate measurement (see §: 6.2.5. Optical Method).

The Overlap is an important element in the overall evaluation of the seam: Any part of the seam which has a optical Overlap of less than 25% of the internal length of the seam is considered a serious defect of crimping.

The rate tightening is a numerical characteristic of the relative absence of ripples on the cover hook. In a seam around the remains of ripples indicate its degree of tightness.

Tightening should not be judged by the number of undulations but from the amplitude of the largest ripple. Several measurement systems are in force, illustrated in Figure 18. The most common of these systems evaluate the tightness of 0 to 100%: 0 is a wave whose amplitude is equal to the height of the cover hook and 100% indicates no ripple.

Measurement of internal and external dimensions by projection (optical method)

Dimensional control of the seam by spraying takes place in two stages:

1. Crimped sections: Preparing cuts crimped directly to determine the dimensions of the seam and the efficiency factors such as Overlap. The cuts are made using an electric saw (single or double) or, alternatively, using a jeweler's saw (Figure 14). To improve the visibility of the image of the seam on the projector, it is recommended to polish the section using a fine-grained stone or emery paper.
2. Profile projector (Figure 14): Make sure the unit is calibrated according to manufacturer's instructions. Fix the section on the projector, the image of the section of the seam appears on the projector screen, then noted the various measures. The profile projector can be set with a magnifying glass, a projector set with integrated sliding micrometer or an image sensor coupled to a computer with software for image processing of the seam (Figure 19).

It is noteworthy that the control projection of the seam is optional and allows for rapid diagnosis of the seam, but does not replace the dimensional control by shelling. The latter remains essential to assess the rate tightening.

Check for leakage

To verify the tightness, we use the pressure test. This test is performed on the empty cans (without container), using an apparatus specially designed these boxes to submit to a standard internal air pressure (Figure 20). The bodies of cans must be completely dry and the elastic seal must be free of oil and water before and during the pressurization. The box must be completely submerged in water and the pressure must be increased slowly.

During the pressure test, the boxes must show no sign of leakage at a pressure less than 69 kPa (48 kPa for non-round cans and boxes with easy opening). If leaks are found, it is a serious defect and should be further testing to identify the cause of the defect.

The pressure test helps detect hidden flaws (leakage of shading, the incisions OF or even the lid on the body of the box), but a leak test negative (no leaks) reduces nothing in the severity of any defects that may be present. The leak check should be supplemented by other evaluation methods (visual and tactile examination, and Dimensional Examination) before deciding on the quality of a seam.

Frequency of reviews

Assessing the seams must be systematic and frequent enough to allow the maintenance of a satisfactory quality throughout the production.

The optimum frequency of inspection depends of course on many factors. The speed of the crimper is certainly the most important, and there will be examined more often crimped closed boxes at high speed as closed boxes at low speed.

Anyway, it should at least consider:

• Visually, a non-destructive, one box per head seamer every 30 minutes;
• By measures outside the seam, then cutting and peeling, a box crimper head every 2 hours of production at the start of production, after a jam or just after setting the seamer.