Capping glass jars
Introduction
The capping operation is mechanical seal is a container with a capsule. The container-cap system is so-called "packaging".
Found in trade, several types of packages whose closure is ensured by capping "glass container-metal cap," "glass container, plastic cap," "plastic container, plastic cap, etc.. But in this paper, we restrict ourselves mainly to the system package consisting of a glass jar and a metal cap.
In food processing, is used as capping closure technique for preserving food: after filling the container with the product, it is closed with a cap, then the assembly is subjected to adequate heat treatment. The safety of the food product thus produced can not be guaranteed by controlling the capping operation via software controls.
Different components of a glass jar
A glass jar is made of three basic elements: the ring, body and substance. Each of these elements is manufactured by a mold which is specific to. Besides these three elements, it can be seen on certain types of jars, the presence of a neck. The latter, when present, is in the form of a cylindrical portion located between the body and the ring.
Figure 1 shows the various components of a glass jar.
Ring
The ring is the top of the jar. It is manufactured to the interior of a mold as a ring and serves to retain the cap (the cap) through the glass thread.
The examination of a jar ring revealed the existence of the following: surface sealing, threading, the cons-transfer ring and two joint planes one of which is vertical and one horizontal.
Sealing surface
The sealing surface is the part that is at the top of the ring, sometimes it can also cover the sides of the ring. It is this surface that comes into contact with the seal of the capsule and thereby ensuring the sealing of the closure.
Thread
The thread is a glass bead located on the side of the ring and serves to retain the cap on the jar. It may be continuous or discontinuous (Figure 2), and therefore adapted to a very specific type of capsule.
The continuous thread consists of a single bead in a spiral shape that guides the continuous thread of a screw cap.
The thread is composed of several discontinuous sharp ridges arranged around the circumference of the ring. It allows, in the case of the capsule type ¼ turn (twist-off), to guide the legs and secure it to the jar in less than a lap. The number of beads making up the thread and their configuration is determined by the manufacturer of the capsules. Figure 2 shows some types of threads.
Cons-transfer ring
The cons-ring is a horizontal glass bead located near the base of the ring, just before the vertical plane of ring (Figure 1). This item has no role in capping and is used only for handling the jars and can not be found on some types of jars.
Parting ring
The parting of ring is a vertical or horizontal line appearing on the ring.
The parting vertical ring is caused by assembling the two halves of the ring, while the horizontal split (parting ring / body) is caused by the assembly of the ring with the body. In the case of rings formed in one piece, the vertical joint plane can not be present.
Background
The bottom is the bottom of the jar on which it rests (Figure 1). It is characterized by the presence of "parting the bottom" which is in the form of a horizontal line caused by assembling the bottom with the body and the bearing surface. The latter may have a special surface, suitable for stacking jars on each other.
Body
The body is the part of the jar that sits between the bottom and the ring or collar when it exists. The different body parts of a jar are: shoulder, heel, side wall and the parting of body (Figure 1).
- Shoulders: The shoulder is the body part where the diameter decreases to match the neck or in his absence, the ring.
- Heel: The heel is the part of the body where the diameter decreases to match the background.
- Sidewall: The side wall is part of the body between the heel and shoulder.
- Parting of body: Vertical line appearing on the surface of the body caused by assembling the two halves of the body.
Capsule
The capsule is a jar lid, and may be metal or plastic. In this paper we are particularly interested in metal capsules.
Several types of caps are available on the market. The choice of one or the other is conditioned by the product to be packaged, the method used, the type of jar and also by the price of the capsule.
Characteristics of capsules
The main components of a metal cap are shown in Figure 3.
The flat part of the dish is called "Macaroon" in the center of which is possibly the 'diaphragm security. " The latter, when it exists, is used to detect products in vacuum-packed jars with vacuum is imperfect or nonexistent. For consumers, this diaphragm is proof seal: the opening of the jar, the diaphragm moves up and emits a characteristic sound ("pop"). This indicates that the jar was tightly closed and is opened for the first time.
On the inside of the capsule, we note the presence of a plastic seal that covers the portion to be in contact with the sealing surface of the jar, seal it. This is really the glue that keeps the seal of the jar. The seals are made of one material, and this, according to the food product and process used. There are two kinds: joint cast (case of capsules quarter-turn) and molded joint (case of capsules Press-on, twist-off). In the case of capsules quarter-turn, the seal is applied to the inner face of the button, whereas in the case of capsules PT (Press-on, twist-off), it is applied to the inner face of the button and that of the side.
The lateral part of the capsule is called "ferrule" is that it takes to aim or unscrew the cap. This part, in front view, cover two important elements: the hem and tabs.
The hem is curved part at the bottom of the ring. It improves the rigidity of the capsule.
The legs are in the form of tubercle in the hem. Their role is to keep the capsule sealed in the interlocking threads of the ring of the jar. The number of legs is 4, 6 or 8 depending on the diameter of the capsule. It should be noted that the presence of legs is a feature of Twist-off caps, other types of capsules are equipped with tabs.
Types of capsules
One generally distinguishes five groups of capsules: Capsules Eurocap, pressure caps, capsules quarter-turn caps PT and screw cap.
Capsules Eurocap
Capsules Eurocap type (Figure 4) are generally used for closing glass bottles containing soft drinks (lemonade, beer, etc..).
The tightness of the closure is horizontal and ensured through a joint plastic cast, which matches the ring under pressure from the bottle.
The capsules have a flared shape before crimping, the implementation principle is to bend the hooks of the cap under the ring of glass that puts pressure on the joint. Thus, the capsules Eurocap resist some internal pressure.
Retains a bite can be opened with a tool for prying, and is therefore inviolable on the point of sale. After opening the package, the capsule can be reused to close the bottle.
Capsule pressure (Pry-off)
The pressure capsule (English: Pry-off cap) are for jars with rings without thread (Figure 2). In the case of capsules, sealing is ensured by a lateral rubber coated on the inside edge of the capsule (Figure 5).
Capping is performed simply by pushing the cap onto the ring of glass jar, but it must be done under vacuum. For the opening, we need to lever under the cap by taking the shoulder of the pot as a fulcrum. Hence, these capsules can not be used after opening.
Capsule quarter-turn (twist-off cap)
This is the capsule of a jar that opens and closes in less than a revolution (¼ turn), in English it is referred to as "twist-off cap" (Figure 3). This is called a capsule functional as it is opened by hand without tool and can be closed easily and repeatedly.
After opening the jar, the consumer can reseal. Thus, the twist-off cap is best suited for products that are not intended to be consumed at one time (jam, pate, honey, etc.).. To compensate for the inviolability of such conditioning, the presence of the diaphragm security may be required by some distributors.
Capsule PT (Press-on, twist-off cap)
PT capsules are commonly used on the jars of baby food as well as other food products (Figure 6). It combines ease of sealing, with pressure, Pry-off caps and feature twist-off caps.
The sealing of the closure capsule PT is ensured by a gasket molded plastisol that covers both the flat surface (horizontal joint) and the lateral surface (side seal) of the capsule (Figure 7). This seal must have been heated properly beforehand.
The sealing is done by simply pressing the cap onto the ring. She (the capsule) remains in place on the ring through mostly empty and with the help of engraving created by the thread of the ring in the seal side, once the capsule is cooled (Figure 7).
Screw cap (TC)
The abbreviation CT (Continuous Thread) is used to describe the type of caps that screw to close a menu from a jar ring continuous thread (Figure 8).
The thread of the cap engages CT below that of the ring to keep the inside of the button pressed against the sealing surface of the jar. The tightness of the closure is provided either by a seal, either with a lid. This maintains the seal of the jar even after removal of the capsule so it is necessary to destroy permanently open the jar.
CT capsule can be reused by the consumer to close the jar after opening. However, the tightness of the closure remains to be desired, unless the capsule is a tiny seal.
Closing jars by the capsules CT can be performed in different ways: manually, automatically or semi-automatically. In the latter case, the capping is done using machines that can be incorporated into production lines and working at high speed.
Capping glass jars
Capping jars can sometimes be done manually as is the case of twist-off caps (quarter-turn) and screw cap. But when the presence of vacuum in the jar and heating prior seal is needed, especially when one wants to work at a high rate, we then use the mechanical seal.
The vacuum inside the jar plays an important role in the formation and permanence of a good seal. It is obtained by two types of machines: (1) the machine capper vacuum and (2) the steam machine capper.
The capper vacuum is used primarily for sealing dry products. Capping is performed in a vacuum chamber, it will be created mechanically.
The capper steam is used primarily for sealing of jars containing food hydrated. The jar is subjected to a controlled atmosphere of steam, which flows by his hunting gases in free space. The steam is trapped in the headspace lorsqu'est raised the cap, then condenses into creating a vacuum that helps keep the lid in place. The steam also serves to soften the seal and further improves the sealing of the closure.
Another way to create a vacuum is filling hot jars, followed by immediate capping. After cooling, the product volume decreases and creates a vacuum inside the jar. This approach is practical manual for sealing jars.
Vacuum formation depends on four main factors: the free space, the product temperature, the air present in the product and the effectiveness of vacuum formation of the capsule used.
(1) The space is vacant part of the jar, which is located between the product surface and the top of the jar. It plays an important role in capping, especially with cappers steam. The space must be sufficient to store enough steam. After cooling, the vapor condenses and creates a vacuum inside the jar. The volume of free space depends on the food, the method and type of container, but we can say roughly that it must be at least 6% of the volume of container taken from the temperature of the capping.
(2) The temperature of the capping has an important role in the formation of a vacuum, and this in two ways:
- (3) The air in the product has an adverse effect on the formation of a vacuum; it is therefore advantageous to reduce its volume to maximum. Heating the product at a suitable temperature is the simplest method that achieves this goal by driving the gas present in the product.
- Hot product, when it cools, takes up less volume and is used to create a vacuum in addition to that created by the condensation of the vapor stored in free space. More product temperature, the higher the vacuum is important.
(4) The effectiveness of vacuum formation of the capsule used is its ability to create the empty breasts of hermetically closed. In the case of capsules, steam efficiency is verified using the method called "checking the vacuum in cold water."
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Method Principle "checking the vacuum in cold water": |
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This method involves filling a series of jars (4 to 6 jars) with tap water while leaving the same space. They are sealed in the capsule after letting it warm to normal operating temperature. We open the jars, then the board is the second time in the capper. Finally, we measure the vacuum using a vacuum gauge. The first pass in the capper is used to expel the air in the water and thereby provide a more accurate measurement of the vacuum. We judge the effectiveness of the capper to create sufficient vacuum is obtained when the measurement is 0.75 bar minimum. |
Capping Control
There are two types of controls: (1) non-destructive testing based on external visual observation and does not affect the hermetic jars controlled and (2) the destructive testing which involves opening jars, or simply a violation of the tightness of the closure, to make the necessary observations and measurements.
The verifications will vary depending on the type of capsule, "twist-off cap," "Pry-on course", "PT Cap (Press-on, twist-off cap), etc.. In this document we will limit ourselves to the various checks on the capsules' Twist-off caps and "Press-on, twist-off".
Nondestructive testing
Capsule inclined: On systems "Press-on, twist off the cap should be level, or skipped, or inclined (tilted), and must be fully seated around the ring. This feature is judged by the level of the cap from the transfer ring-cons and did not exceed 2.38 mm.
Jumping Paw: This defect relates to the capsules legs (capsules quarter-turn). It appears when a leg has not installed properly on the thread. This can be seen easily, because the capsule is tilted abnormally (Capsule inclined).
Leg crushed: This defect also affects capsules legs. It appears when a tab is forced through the capsule to be positioned above the thread; leg bends inward, and is said to be crushed. This defect can be detected by external examination, but sometimes you have to uncap to realize it.
Trivia aside: One capsule is a capsule ruled quarter-turn which was tightened to the point where the legs are open to the passage of the thread. A visual inspection, one can see that the legs are apart.
Destructive
Vacuum: For a diaphragm capsules conducted security, we can note the presence of a vacuum when the diaphragm has a concave position (hollow form). In other cases, and for the accurate measurement of the vacuum, we shake a vacuum gauge, the vacuum should be within the normal range for the product in question. This is a destructive test which results in loss of package integrity.
Temperature: The temperature of the product should be within the normal range of product manufactured. It should be noted along with the degree of vacuum.
Free space: In most cases, the clearance should not be less than 6% of the container volume at the sealing temperature. Once established the ratio of the volume of free space for a given product and container, the headspace may be measured using a depth gauge or space rather than by volume.
Seal nicked: After removing the capsule, it must be seen in the normal case, a circular trace visible and consistent in the joint, created by a tight contact with the top of the ring (sealing surface). Failure of joint nicked "occurs when the top of the ring was too deep in the joint, until it touches the metal of the capsule. This causes a leak at the seal and must be corrected immediately to the situation.
Security: Security measures (voltage of the paw of a sealed cover) are the measures most reliable sealing. The ranges of security specified by the manufacturer of the capsules, roughly speaking, they are between 3 and 8 mm. If the values are higher than the acceptable values, this indicates a well-sealed packaging but with a certain degree of closure excessive and should be reduced to acceptable levels to ensure the best performance of the cover. If values are consistently below the required minimum, this usually indicates that the closure is not far enough and must be corrected immediately to the situation.
The safety test on a package consisting of a glass jar and a capsule quarter-round is played as follows:
- Using a marker, draw a vertical line on the cap and a corresponding line on the container (Figure 10-a). (This line has nothing to do with the plane of the ring seal or the parting of the body).
- Turn the cap clockwise to counterclockwise until the opening of the jar (Figure 10-b).
- Put lid on jar and close it lightly with the fingertips (Figure 10-c).
- Measure, using a double-decimetre, the distance between the two vertical lines drawn before opening (Figure 10-d). Security is positive if the line on the cover is right from that of the jar and it is negative if it is left of it. Negative values require them to troubleshoot the problem and remedy.
Safety is measured after sterilization (or pasteurization) and cooling in the same manner as at the closure apparatus, but the range of normal measurements are shifted to lower values because the O s 'flattens during the heat treatment. The heat and pressure pound the lid on the ring, which changes tightening the lugs on the glass thread.
Inspection Frequency
The frequency of inspection varies from one production line to another depending on the rate, type of capsule used and its state of repair. The historic anomalies detected capping is an essential element for determining inspection frequency. Anomalies occur more often, the higher the frequency of inspection should be high.
In general, non-destructive testing are more frequent than destructive testing.