Structural defects of seam

Introduction

The main structural defects that can be detected due to visual and tactile examinations are presented below.

Brand damaged mandrel (Projection)

This is a poorly crimped tight in some areas, manifested by a projection on its inner surface due to a depression in the lip of the chuck (Figure 21). This defect is considered serious because of the lack of tightening at the location of the defect.

Footprint (décuvetage)

The presence of such a mark on the inside of the seam (Figure 22) is the index of following anomalies:

1. Chuck diameter excessive relative to the bottom, to the point of not fully embedded into the bowl of it, even when the compression is sufficient.
2. Low compression, not allowing the mandrel to remain fully embedded in the basin bottom during crimping, even when the value of the diameter of the mandrel is normal.

The severity of this defect can not be judged after hulling crimped and determination of the Overlap. Indeed, this fault affects the size of the seam, including the seam thickness and body hook, and may therefore affect the hermetic seal by reducing the Overlap.

Imprint excessive streaking of the lip of the chuck

Of such marks (Figure 22) generally lead to damage of the coating, that is to say if the varnish is one, and possibly the tin layer.

We can then at those locations in addition to the default appearance, observed metal corrosion (rust, detinning, perforation). The tightness of the closure is generally not affected by this defect.

Possible causes of this failure are:

1. Streaks too deep lip of the chuck;
2. Overtightening 2nd pass.

Seam cutting with or without fracture

A cutting is set with a sharp edge of metal that forms during crimping the seam where the crown is pushed out of the groove of the wheel lip coat the mandrel. A slightly sharp edge does not indicate that the seam is defective. However, the worsening of the defect can cause a fracture in the laminate area (seam cutting fractured), which may compromise the seal. That is why we must address the presence of sharp edges when they appear (Figure 23).

Cutting the seam may be present all around the seam, but it occurs mostly at the junction box assembly and the seam (thickness) and where there are inclusions in the weld. The best way to detect it is to slide your finger along the inside seam. This defect is also known by the following expressions: barb, beak, sharp edge bead.

Possible causes are:

1. Excess solder assembly.
2. Wear on the shaft.
3. Wear of wheels.
4. Chuck too low compared to dials first pass.
5. Tightening the wheels first or second pass.
6. Excessive compression.
7. Vertical play in the crimping head.
8. Body hook too long.
9. Produced in the seam.
10. Excess elastic seal.

Crimped incomplete (slipping, skidding or slipping)

The crimped incomplete (unfinished or crimped) occurs when the mandrel slides over the closure of the box. It is found that the seam is a normal part of the periphery and is loose (thick) on the other party due to insufficient torque (Figure 24). This defect may be accompanied by a scratch on the curvature of the bowl wall caused by the sliding of the mandrel.

The seam may be incomplete as designated by the terms "slip", "Derailed" and "Skate."

Possible causes are:

1. Insufficient compression.
2. Mandrel (diameter, taper or tension) at the bottom inappropriate.
3. Chuck spent.
4. Incorrect height adjustment of the mandrel relative to the compression plate.
5. Binding of wheels.
6. Oil or grease on the core, or compression plate.
7. Vertical clearance of the mandrel stem.
8. Incorrect setting of the timing.

False seam (folded edge)

Unstapled crimped over a portion of the perimeter, with the hook body folded and pressed against the body of the box. It can be detected visually by the presence of a folded edge (folded body hook above the base of the seam (Figure 25). But sometimes the folded body hook does not exceed the base of the seam, in which case the false seam can be detected only by careful consideration and even a cup, then to highlight it.

This defect is serious and must be corrected immediately because it results in the absence of Overlap in the defective area and may cause leaks.

Possible causes are:

1. Crimp edge damaged during shipping, handling, filling, feeding screws, attachment, crimping or because of the presence of product or foreign material on the edge crimped.
2. Crimp edge mushrooms (lowered).
3. Hem too damaged or bent.
4. Improper installation of the box during assembly.

Cracked seam at the base

The "seam cracked at the base" is in the form of fracture of the curvature of the end hook (Figure 26). It can be difficult to detect without the aid of a magnifying glass: carefully monitor the seams which have footprints by the gorge of the wheel a second time, including the location of the clip or if a sag is observed .

This defect is serious and must be corrected immediately. It is also known as "seam fractured" or "projection cracked at the base of the seam."

Possible causes are:

1. Tightening the seam.
2. Excess solder at the pad.
3. Defective background.
4. Excess elastic seal.
5. Product or foreign material in the seam.
6. Body hook too long.

Sag

When the seam has a slight bulge below its normal level, it is called "sagging" (Figure 27). This situation may occur at any point along the perimeter, but there is commonly a slight sag at the assembly (the case of three-piece cans) that is considered normal. But if it is pronounced, the Overlap at this level is reduced and one can then expect a lack of tightness.

The accurate assessment of a slump is only after hulling crimped and determining the degree of real and Overlap rate tightening following the manufacturer's recommendations boxes: Any sagging examined that has a degree of real Overlap less or equal to 25 % is considered a serious defect crimping which must be addressed.

When visual inspection is performed, a sag is considered a serious defect if crimping spans more than 20% of the height of the seam, or more than 1 cm along the seam, or if the This crimped over a slump.

Possible causes are:

1. Product or foreign material in the seam.
2. Excessive or poor distribution of the elastic seal.
3. First-pass rolled too loose or too tight.
4. Wear in the groove of the wheel first pass.
5. Body hook too long.

Picot V

A "V" or "spike" V "is an irregularity of the seam due to the inadequacy or the absence of overlapping hooks (Overlap) in certain points of the seam. The metal hook cover projects into its curvature in the seam and form one or more "V" (Figure 28). This defect is also designated by the terms "project", "indentation" and "lip". The causes are the same as for the collapse.

The pins are in V considered as a serious defect crimping due to lack of Overlap to place the pin.

Output seal (creep)

One can observe in the crimp seal fragments expelled at the base of the seam in one or more points (Figure 29).

This may, as the case may be minor or compromise the seal. Anyway, this situation should lead to ensure that the output of joint does not worsen during sterilization.

Possible causes are:

1. Excessive or poor distribution of the joint.
2. Use of a joint non-nested for the product.
3. Further tightening in the second pass.

Jumping Wheel (jump to thicknesses)

A "wheel hopping," also called "jumping the protrusions, is a portion of the seam that is not rolled tight enough around the clip body. Examined from the inside, like failing a couple of wrinkles on one side of the clip (Figure 30). This defect occurs when the wheel of ^the 2nd pass has a tendency to jump after the passage of the fastener and results in a rate insufficient tightening of the seam zone at the "assembly".

A jump of wheels is considered a serious crimp failure due to insufficient tightness.

Possible causes are:

• Excessive speed of the seamer.
• Slow action of the spring damper wheel second pass.
• Absorber spring break.
• Pellet too thick to mount.
• Excess solder from outside the patch.
• Insufficient tightening the knob second pass.