Large shoe factories often have problems with molding bottoms
The bottom molding of the shoe factory is an important part of shoe production. Whether a pair of shoes is durable or not is not important, and the adhesion of the sole is very critical in the shipment inspection. I believe that the personnel in the shoe factory are very careful about this, but There will always be more or less problems. The following is the ultimate summary of a series of frequently occurring problems based on the actual production conditions of several large domestic brand shoe factories:
1. The purpose of adding a hardener to an adhesive is to strengthen (harden) the adhesive (glue) itself and prevent the subsequent adhesive from producing "glue" that would cause the adherend to shift and slip away. Therefore, adding a hardener should be done separately. (Adhesion) function has nothing to do with it.
2. When using shoe adhesive, it must be properly dried before it can be glued. The drying time is related to the amount of glue. If you apply too much glue, it dries slowly. If you apply too little, it dries faster. If the same adhesive is applied, the glue will not dry. The drying time varies depending on the amount of glue, so the adhesive must be applied "thinly and evenly".
3． The adhesive is prone to chemical changes when heated. When exposed to the air, the solvent is easy to volatilize and the concentration increases. Therefore, the adhesive should be stored in a cool, dry and ventilated place.
4. Then, the greater the difference in the curvature of the two surfaces with the same bonding area (such as a flat surface joining a spherical surface), the greater the peeling force. Otherwise, it will be small or even non-existent (such as a flat surface joining a flat surface, or each other). Fitting curved surface), the peeling force is called peeling tension or tensile force; when making shoes, the fitting surface of the molded upper and sole must be shaped as closely as possible to achieve a good adhesion effect.
5. When using adhesives, you should understand two things, one is the adhesive force, and the other is the adhesion force (the glue factory calls it the initial adhesion force); the adhesion force is the force that makes the adhesive on both sides join each other. Only with the adhesion force can there be Adhesion force (adhesive molecules fuse and solidify with each other in the later stage), when the peeling tension of the local bonding surface is greater than the adhesive force, even if the adhesion force of the two partially bonded surfaces cannot be fused and solidified, resulting in failure of the bonding, the bonding position will appear Glue-like peeling or complete peeling; generally, appropriate hardener is added to the adhesive to avoid glue-like peeling at the joint.
6． The hardener is added to the adhesive, and its function is to harden the colloid of the adhesive itself; usually the addition amount is 3%--5%.
7. The subsequent treatment agent is designed for the lamination of chemical materials, such as PU leather, PVC leather, nylon cloth, nylon (plastic) tape, rubber, etc.; such as natural leather with rough surface (smooth surface roughened or suede), cotton cloth (Canvas) and then no surface treatment is required.
8. The chemical agent that is added to the strong glue to change the glue from gel to solidification, and to solidify and adhere the stickers (strengthening the adhesion effect), is called a hardener (liquid); in order to harden or stiffen the leather, The chemical agent added to the leather is called mortuary hardening paste, such as the glue paste (pure, transparent and gel-like) applied to the front and rear hard linings.
9. When using adhesive, you must pay attention to the following matters:
one. Complete treatment of the bonding surface: Regardless of any material, such as natural leather and rubber, that needs to be roughened or treated with a treatment agent, it must be completely roughened and then treated or completely treated.
two. Complete adhesive coating on the bonding surface: The bonding surface that has been roughened or treated with a treatment agent must be completely coated with adhesive, and there must be no leakage.
three. Uniform application of adhesive on the laminating surface: Uneven application of adhesive will affect the consistency of the drying time. For example, if too much adhesive is applied to a local location, then when other locations have reached the drying time for lamination, the local area will be dry. If the parts are not dry yet, if you rashly stick them together, the parts that are not dry (before the appropriate time) will not be glued together.
Four. The drying time of each laminating surface is the same: the laminating surface refers to the two sides that are laminated together. Coating defects on any side (including roughening that should be done, or treatment that should be done but not done) will result in inaccurate (bad) adhesion. .
10． In the production of footwear, heating molding is very important. Generally, the natural method can be set to about 150 degrees; PU leather and PVC leather can be set to about 110 degrees, but not exceed 120 degrees. To check whether the setting temperature is too high, you can check the surface of the fabric. (Bead surface layer) condition, if there is local bubbling, it means the temperature is too high, if it is locally shiny (embossing changes and digestion), it means the temperature is slightly high, and the oven temperature must be adjusted and lowered before production.
11. We often hear that natural leather has better "breathability", so shoes made of natural leather can more easily discharge foot sweat and keep feet dry. In fact, good "breathability" is a characteristic of natural leather, but it can keep feet dry. Dryness does not come from the "breathability" of natural leather; those who are familiar with shoemaking should know that shoes are not composed of a single layer of natural leather. In the made upper, any layer (including the inner lining and hard lining, reinforcement etc.) and fitting glue can block the "breathability" of natural leather, so in fact it should be derived from the "temperature absorption" of the lining; when using shoes, foot sweat (moisture) is absorbed through the lining, When not in use, moisture naturally evaporates from the natural leather, thus keeping the interior of the shoe dry.
12. White glue (LATEX) is a temporary adhesive glue (can be peeled off again). It has strong water penetration. It is suitable to use foam as a coating tool. It dries quickly after heating. Because of the addition of "ammonia", it has Odor: Ammonia is added to white glue in order to preserve it for a longer period of time, making the white glue less likely to deteriorate. It will have an odor when used, but after the odor evaporates, it means it is dry.
13. The fitting surface of the molded base is generally provided with grooves (commonly known as windows) to firstly reduce the weight of the outsole, secondly to save materials, and thirdly to increase flexibility.
14. After aluminum is hot-melted in the mold, it will definitely shrink after cooling (the principle of thermal expansion and contraction of metal), commonly known as shrinkage. The master mold for casting aluminum last needs to add the shrinkage rate in advance, so the master mold must be slightly larger than the original last (fat, Width), the master mold that has been shrunk, we call it (shrink last).
15. The method of distinguishing PVC base materials can be identified by the appearance of the base. If there is a small flower concave and convex pattern on the surface, you can check whether the small flower pattern is intact. If it is complete, it can be judged as a PU base; the reason is that PVC material is thermoplastic The material needs to be extruded into the mold using high temperature and high pressure. Because of the high pressure squeezed into the mold, the PVC material can fill every corner of the small flower pattern, and a more complete base can be obtained after demoulding.
16． The method of separating PU substrates is that PU material is a material in a normal temperature fluid state. It does not need to be squeezed into a mold using high temperature and high pressure. It only needs to be made in a similar way to casting a plaster image. Since high pressure is not required, the accuracy of the mold can be improved. It is lower and the mold cost is less, but small bubbles will naturally remain in the base making process, and more or less bubble-shaped gaps can be found in the corners of the small flower case.
17． There are many factors that cause the error in last curvature. For example, if the last curvature of a shoe is selected to be 8m/m, and it becomes 10m/m after the shoe is completed, the following errors may occur: 1. The heel is too low (The skin is too thin), 2. The sole is too thick, 3. The sole is too long, 4. The midsole is too soft, 5. The planting does not touch the ground, 6. The core is not strong, 7. The filling is too thick, 8. Knot The heel pull force is too large (the upper is too small or the pattern is too warped), 9. The heel throat is too deep (deformation occurs after turning back the nail), 10. The heel is knotted (including skew).
18. The importance of the midsole is often overlooked for shoes that are formed by a knot; for shoes that are knotted, the upper is made into a top shape, and the midsole is used as the bottom, which is connected to form a container. The upper and midsole constitute each other and are suitable for use. The volume space for the foot, so any defective or poor connection between the upper and the midsole will not only cause the shoes to be easily damaged (short service life), but also cause changes in the volume space (wearing too loose or too tight will not reach the required level). standard last shape), and hazard-proof clothing.
19. The midsole is the "bottom" that constitutes the shoe container. In order to meet the molding operation and shoe volume standards, the midsole has its appropriate "bottom shape" which is of course based on the "last", so it is originally a flat material. The midsole is processed into a proper "bottom shape", which is called midsole shaping. It must be done accurately, that is to say, the midsole needs to be shaped, and the shaped midsole must fit the last, otherwise it will definitely Making it difficult to form a gang.
20． There are two molding methods: one is to form the upper, and the other is to insert the last into the last. In the first form, the upper part of the shoe is left to be clamped into the last, and the upper part of the shoe to be clamped into the last is covered by the sole. As long as it is not Affecting durability, the width error of the upper position can be larger, so it is easier to make upper samples of upper-formed shoes; last-formed shoes are made by preforming the upper into a bag shape and then squeezing the last into the shape. In addition to the volume space of the bag-shaped shoe upper needing to match the volume of the shoe last, there must also be a bag opening (shoe opening) (not counter-intrusive) to squeeze the shoe into the shoe smoothly, so the last molding method is used. The sample of the shoe (the upper and the midsole are connected, so there is no distinction between the upper sample or the sole sample) must have a relatively precise accuracy, which is much more difficult to make.
twenty one. There are two types of shoes made by the last molding method, one is the bag shoe style, and the other is the California style. The so-called bag shoe style is to wrap a piece of leather from the bottom of the last to the last surface, and sew it to the back cover. Named after a bun, there are no seams on all or part of the last edge; the California-style last making method has two types of shoe upper structures. One is the California shoemaking method, where only the seams are left on the edges. The upper of the upper and the midsole with the remaining joint position are sewn together to form a bag-shaped upper connected to the midsole, which is formed by the above-mentioned lasting. The first method is to connect the midsole part in an (S) shape to form a bag-shaped upper. , the plate making principle is the same as that of California shoes where the midsole is connected (sewn to the upper), except that after the midsole is disassembled ([S] shape), the plate is placed on the upper and then the partial toe and toe are stitched It has the same characteristics as bag shoes, and is made of the same machine material extended into a bag-shaped upper.
twenty two. The method of stretching the finished upper into a shoe shape is called the forming method. There are two main forming methods, one is the upper forming method and the other is the last forming method; the other is the forming method where the upper is matched with the last , such as bag shoes with the front section inserted into the last and the upper section knotted, or shoes with the back section inserted into the last and the front section knotted; shoes formed by the adhesive method are knotted, using a mesh method (the upper is sewn with a thread after the upper is knotted) Located in the midsole) are also lasted; California shoes are lasted, and sports shoes with an S "shaped midsole structure are also lasted.
twenty three. When joining chemical leather materials such as rubber, plastic, EVA, PU, etc., the joining surface needs to be treated with a treatment agent (wipe test) first; when joining natural leather, the decorative coating (paint, paint, etc.) on the surface needs to be scraped off (roughened) first. Leather paddle or wax oil, etc.), so that the adhesive can penetrate into the "leather body" (fibrous walnut layer), so as not to peel off with the surface paint, resulting in poor adhesion effect; the joining of natural leather and cotton does not require the use of treatment agent.
twenty four. Adhesive is used to distribute the adhesive for the base and the adhesive for making noodles; the adhesive for the base is a permanent adhesive that is firmly attached once and is not allowed to be torn apart, such as yellow glue, syrup paste, PU glue, etc. ; Temporary adhesives are used for making noodles, such as white glue (LATEX), gasoline glue (rubber paste), etc. The reason why temporary glues are used for making noodles is that they are mostly used for folding, lining, etc. After being folded and attached, it must be sewn back through sewing, so strong adhesion is not required, and it is also easy to correct misfolding or misattachment.
25． The skew of the shoe upper after molding (knotting or lasting) is caused by the following reasons:
1. Shoe last part:
1) Because the angle between the center line and the length line of the last base (midsole) is too large (usually less than 5 degrees), the last body is skewed, resulting in a large difference in volume between the inside and outside of the last, making it difficult to make the knot correct. .
2) The difference between the left and right middle lasts.
2. Sample part:
1) The sample itself is obviously skewed (or the joint lines are not coordinated with the shoe last).
2) Wrong sample curvature can easily cause the front section and shoe wall to become skewed.
3) The angle and arc of the center line of the heel of the model are wrong, causing the center line of the heel to be skewed.
4) The inner lining pattern and the upper pattern match incorrectly, making it difficult to attach the lining.
5) Inner and outer joint line errors.
6) The model is not generalizable (manual cutting, line drawing, bending, etc.)...
3. Face making part:
1) The main leather flap is poorly cut and/or folded.
2) Poor joint sewing.
3) The inside of the sticker is twisted or skewed.
4) The leather material is cut in the wrong direction.
5) No matching selection is made (the elongation rates of the inner and outer skin grafts are different).
6) The decorative lines are not sewn correctly and the decorative pieces (flowers) are not correct.
4. Forming part (knotting or lasting):
1) The "three-point fixation" error or the "clamping point" error before the machine is connected.
2) The left and right shoe uppers and shoe lasts are wrong (the left shoe upper matches the right shoe last or the right shoe upper matches the left shoe last).
3) The upper shoe size (SIZE) does not match the shoe last.
4) Poor placement of back lining and heel shaping.
5) The skew can be easily corrected, but no attention is paid to correction.
6) The posture of the clamp is wrong.
26. When forming, it is best to soften the upper first to facilitate the formation of the upper;
There are approximately three methods for softening shoe uppers:
(1) Heating method: Mostly suitable for uppers made of artificial leather (PVC and PU) and uppers lined with artificial materials;
(2) Steaming and softening method: only applicable to shoe uppers made of natural leather (referring to mammalian skin). It is obtained by heating and softening the leather by steaming it;
(3) Solvent coating: Each steam softening method is only applicable to shoe uppers made of natural leather. It is the earliest method of hand-made shoes to soften shoe uppers. Natural leather will have softening properties when it is humidified, but it is generally softened with water. The production of stains and watermarks is also due to the slow evaporation of water, which is likely to hinder the subsequent work of preparing soles. Therefore, although water can also achieve the softening effect, most of them use "alcohol" that evaporates quickly to soften the uppers. Solvent.
27. During molding, in addition to softening the upper first to facilitate the formation of the upper, the front lining should also be softened. There are generally three methods of softening the front lining.
(1) Water immersion softening method; the softening object of this method is the material with cowhide midsole leather as the front lining, which was also the front lining softening method used in the past when leather shoes were made by hand;
(2) Soaking solvent (toluene) softening method; this method is used to soften "Gangbao" as the front lining material. The method of softening "Gangbao" by soaking it in solvent has become a revolutionary shoe material in the shoemaking industry in recent years. one. Its characteristic is that it can be very soft by soaking it in solvent, which is most conducive to the molding of shoes. It does not need to add or strengthen any processing. It can achieve a stiff effect after drying. It is a softening method commonly used in the shoe industry.
(3) Thermal softening method: Use heating (about 100 degrees to 120 degrees) to soften the "hot melt glue" pre-pressed on the front lining of the shoe to facilitate the formation of the upper. If the toe head is not too stiff, If required, this method is the simplest, cleanest, and most conducive to softening the front lining of the toe.
